Fertilizing Pecan Trees
General Pecan Fertilizer
Recommendations Fruits and Nuts Soil tests should be conducted prior to planting and should be used solely as an initial guide for fertilizer Fruit Substation recommendations for pecan trees. Other considerations that provide an indication of the nutritional needs of the tree include the length and vigor of terminal growth, leaf color and size, and the amount of leaves and nut production. Nitrogen and zinc are the two nutrients most often required by pecan trees annually. Phosphorus and potassium are rarely needed in pecans. Adding additional fertilizer to pecan trees cannot overcome a poor site or soil, inadequate soil moisture or poor disease and insect control.
Young Pecan Trees
The first year’s growth on nut trees is normally very slow, and a first-year tree may not need or respond to fertilizer applications. Nonbearing trees should grow 12 to 36 inches per year. Weed and insect control and adequate water are essential for survival the first year. If the trees are growing rapidly, the recommended fertilizer should be applied in a broad band along the drip line but away from the trunk. Table 1 gives the recommended amount of fertilizer per tree based on the amounts of potassium and phosphorous in the soil. For trees two to five years old, fertilizer should be applied in a band from one foot from the trunk to beyond the drip line.
Mature Pecan Trees in Yards
Fertilizing lawns with an adequate amount of nitrogen may be sufficient for nut trees in yards, but lawn grasses will use the initial amount. The general rate for nitrogen fertilizer is 1/4 to 1/2 pound of ammonium nitrate or equivalent per 100 square feet. The fertilizer should be broadcast in a band starting 2 feet from the trunk and going beyond the drip line two or three times from bud break to early summer. Annual terminal growth of mature bearing pecan trees should be 5 to 12 inches. Poor nut production can occur from either low nitrogen, which causes weak vegetative growth, or from excessive nitrogen, which causes excessive vegetative growth. The amount of nitrogen fertilizer should be adjusted to improve nut production.
Fertilizing Native Pecan Groves
Native pecan trees use less fertilizer per acre or tree than improved varieties. However, to produce consistent crops of native pecans, an annual supply of nitrogen is needed. Nitrogen can be provided to native pecans by using fertilizer or by legumes (Table 2). Cool-season legumes such as a red clover white cover mixture can supply some or all the nitrogen a native pecan tree will need without competing with the tree for soil moisture and nutrients during the growing season. In addition, legumes attract beneficial insects and are excellent forage for livestock. If legumes are grazed, the amount of nitrogen produced for the tree will be less. Splitting the fertilizer into two applications is best. If split, fertilizer applications should be applied in mid-March and in May. Another light application in June can be used in very heavy crop years.
Ammonium sulfate is associated with lowering soil pH, thus preventing cotton root rot, to which pecans are susceptible. As a result, ammonium sulfate is often preferred for pecans. For application in irrigation water, ammonium thiosulfate would replace ammonium sulfate. In general, pecan trees are slow to respond to nitrogen fertilizer applications. By applying nitrogen in the first irrigation water before bud break, pecan trees will have an ample supply during their greatest growth period and may show a quicker response. The amount of fertilizer needed by a pecan tree depends on its size, age, production, and soil type. In general, 150–200 lb/ac of actual nitrogen is recommended in established orchards. Cultural practices also influence the amount of fertilizer needed. Nitrogen fertilizers may be applied in split amounts with irrigations from March through July. Do not apply nitrogen to young trees after June because it may delay leaf fall and result in winter injury.
Zinc For Pecan Trees
Pecans require zinc for normal stem and leaf growth. Trees not receiving zinc do not produce enough indoleacetic acid (IAA), which is a naturally occurring growth hormone responsible for shoot elongation, leaf development and other critical plant functions. In trees lacking in zinc, the internodes between the leaves and stems are shortened. This compaction of the annual growth is known as zinc rosette. Leaves are smaller, thickened and somewhat distorted. When the deficiency is severe, the affected leaves develop necrotic areas between the veins. Fungi are often associated with these necrotic lesions. Zinc sprays are essential for early-season pecan growth. The most effective applications are early and frequent. Several formulations of zinc are approved for use on pecans (Table 4). Elemental zinc is the most toxic to plants other than pecans and grapes. To protect nearby plants from poisoning, avoid drift. If drift is a possibility, use NZNTM or a similar formulation. Do not use any zinc product at a rate higher than that specified on the product label. If you are applying more than one zinc spray within 2 weeks, reduce the rate by half. Never spray young trees that are not actively growing.