FOR IMMEDIATE RELEASE
MONDAY, JULY 26, 2004
||Dr. Bobby Walls, Plant/Waste/Solution Section chief
What's in your compost?
RALEIGH — What comes to mind when you think of compost? Perhaps a mixture of decomposed leaves, grass clippings and table scraps? Maybe something more robust with shredded bark or animal manure? The truth is compost can be almost anything.
Unless you make your own compost, you are not likely to know what went into it. And even if you did make it, you don’t know exactly what you've got when you finish. There are many possible "recipes" for compost, and no two compost products are the same.
The characteristics of a particular compost depend on the materials used, how often it was turned, and how hot it was allowed to get. For example, compost made from deciduous leaves tends to be slightly alkaline, compost made from pine needles tends to be acidic, and compost that includes animal waste may be high in salts. Large piles of compost that are not turned regularly may become "sour" and toxic to plants.
Kevin Johnson, regional agronomist with the N.C. Department of Agriculture and Consumer Services, recommends that anyone planning to use large quantities of compost, especially in expensive landscaping projects, should have it tested first.
"As a rule, composts do improve soil texture," Johnson said. "However, they tend to vary in quality and can change soil chemical properties – but not always for the better. Low pH and high soluble salts are two of the more common problems associated with compost."
According to Johnson, waste analysis—available from the NCDA&CS Agronomic Division—is the appropriate test for composted materials. Like a soil test, it provides information on pH, plant nutrient levels, and whether additional lime or fertilizer is needed. However, waste analysis also provides valuable information that soil tests generally do not—like levels of soluble salts, types and amounts of available nitrogen, and the carbon-to-nitrogen ratio.
Waste analysis through the NCDA&CS lab is inexpensive, reliable and fast. It costs $4 per sample, and results are usually available online within two working days. Customers also receive a report in the mail.
The recommendations are the most valuable part of the report. They may include notes on whether lime or nitrogen needs to be added, salts need to be flushed out, or micronutrient problems exist, and so on. If the composted material was generated from industrial or municipal wastes, then levels of heavy metals are evaluated as well. This information is crucial to the success of any major planting project.
Johnson has collected samples from the City of Goldsboro's new composting facility over the last several months. The compost—marketed under the name Gold Dust—is made by combining the city's biosolid waste with finely shredded yard waste, mixing the two thoroughly at regular intervals, and allowing heat to build up to kill most weed seeds and pathogens. The result has been a quality product that is increasingly in demand.
Karen Brashear, Goldsboro's public utilities director, believes that the most responsible way to promote the product is to give people good information on how to use it. That is why she called on Johnson.
"There is a lot of demand from the landscaping industry for our compost so I didn't want to guess about its quality. Kevin helped me understand what to look for," Brashear said. "The testing has helped reinforce my confidence in our product."
Johnson advises anyone who purchases bulk quantities of compost to request copies of results of any tests performed from the producer. These may include a soil test, waste analysis, pesticide analysis, heavy metals test and stability test. Purchasers should look carefully for information on pH, soluble salts and nutrient levels, especially nitrogen, phosphorus, potassium, calcium and magnesium. The goals are to determine if the compost is safe for landscape planting and to ensure it will not pollute the environment with excess nutrients.
Information on collecting and submitting waste samples is available online at www.ncagr.com/agronomi/pdffiles/samwaste.pdf. For more help, contact your local NCDA&CS regional agronomist (see www.ncagr.com/agronomi/rahome.htm for contact information). Agronomist Kevin Johnson is available to provide advice for handling fertilization or nutrient management problems in Harnett, Johnston, Wake, Wayne and Wilson counties.