UVM Apple Orchard
The UVM Apple Program:
Extension and Research for the commercial tree apple grower in Vermont and beyond...
Mineral Nutrition of Fruit Trees in Vermont
Terence Bradshaw, University of Vermont Apple Team Research Specialist
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UVM Apple Orchard
The UVM Apple Program:
Extension and Research for the commercial tree apple grower in Vermont and beyond...
Mineral Nutrition of Fruit Trees in Vermont
Terence Bradshaw, University of Vermont Apple Team Research Specialist
Unlike annual crops such as vegetables or field crops, the perennial nature of apple trees requires that their nutrient needs be maintained in a holistic and long-term manner. Practices such as fertilizer application, pruning, water management, and pruning can affect tree nutrition status for successive years. Orchard nutrition management should seek to optimize nutrients at ideal levels in the tree, that is not deficient nor excessive.
Fruit trees, like all plants, absorb most of their required nutrients from the soil solution. Therefore a grower should know the nutrient status of their soil, and apply materials to best optimize soil nutrition. Soil samples should be collected on a 3-5 year basis from uniform management units in the orchard. Sites with differing topography or tree health status should be analyzed separately. An accredited soil testing lab can provide specific sampling instructions for their tests, and perform the analysis. The University of Vermont utilizes the Maine Soil Testing Service and Analytical Laboratory to conduct soil and plant tissue analyses. Other laboratories can be found in the latest edition of the New England Tree Fruit Management Guide, available from the Cooperative Extension Service of each New England state. Most important to the fruit grower concerning soil management should be soil acidity and organic matter management. Many soils in Vermont are acidic and can best release nutrients when managed with a liming program. Apple trees prefer a slightly acid pH of 6.0-6.5. Liming instructions for various soil types can be found in the Tree Fruit Guide referenced above. Soil organic matter is a natural source of nutrients and also provides water and nutrient holding capacity to light soils and increased tilth to heavier soils. Cover crops, application of compost, and groundcover management practices can contribute to increasing or maintaining soil organic matter. Generally soil organic matter of 2-5% is considered good for fruit crops, with lighter, sandier soils benefiting more from increased organic matter.
Soil nutrients, however, make up only one part of total orchard nutrition, and their relative abundance as read on a soil report does not reflect their availability to plants nor competitive inhibition that may exist between elements. Growers should collect foliar tissue samples on an annual or at least biennial basis. Fifty to one hundred leaves are collected from the same variety and management unit between July 15 and August 15. These leaves should be from the middle growth of current season's vegetative wood. Leaves should be washed and dried according to lab requirements and submitted for analysis. The resulting report will reveal the nutritional status of the trees which may not reflect the mineral content of the soil.
Growers can reference Cornell Cooperative Extension Information Bulletin 219: Orchard Nutrition Management as an excellent source for specific tree fruit nutrient program development. Plants, including apples, utilize macro- and micro-nutrients; these categories refer only to the relative amounts utilized, and does not suggest that some nutrients are necessarily of less concern than others. For apples, the macro-nutrinets include nitrogen (N), phosphorous (P), potassium (P), calcium, (Ca), sulfur (S), and magnesium (Mg). Micronutrients include iron (Fe), boron (B), manganese (Mn), Zinc (Zn), and copper (Cu). The principle of limiting nutrients suggests that deficiency of any one of these minerals will decrease plant growth processes, such that increasing nitrogen on a copper-deficient crop, for example, will not allow the tree to 'outgrow' said deficiency. Management of these mineral nutrient levels in the tree is critical for optimal tree and crop development in both conventional and organic systems. Under organic management, the material of choice may differ from a conventional grower, but the tree still requires the same amount of each element to perform its best in the orchard. Specific organic nutrition considerations can be found in the Cornell Grower's Guide to Organic Apples.A private laboratory in Ohio, Spectrum Analytic, has produced another useful guide to Fertilizing Apples, which includes many photos of mineral deficiency symptoms.
Generally, an apple tree should receive 0.1 lbs of added nitrogen per year of age, up to a maximum of 0.5-0.8 lb. Trees grown in sod will require more fertilizer as the grass soaks up some of the nutrients. Nitrogen level should also be adjusted according to the terminal shoot growth on the tree; non-bearing trees should produce 18-24 inches of growth per year, bearing trees 12-18 inches. Trees more or less vigorous than this can have their nitrogen needs adjusted accordingly. On a per acre basis, this translates to annual applications of 25-50 lbs actual N per acre. It is always better to under fertilize a fruit tree than to over fertilize. Therefore trees in their second leaf (second growing season in the ground) with decent growth the previous year should receive 0.2 lbs of nitrogen. A common fertilizer such as calcium nitrate may have a a 15-0-0 analysis (15% N, 0%P, 0%K), so two hundred pounds per acre will provide 30 lbs of nitrogen.
Apple orchards also benefit from annual application of potassium materials to the soil. Rates of 90-150 pounds actual K2O5 are commonly applied, but actual rates used by a grower sh