They are useful only to determine toxicityUs from improper fertilizer application. Young nonbearing trees should make up to 24 inches of growth annually. As a general rule, young trees may require about 0.01 to 0.03 pound of actual nitrogen per year of age up to 0.3 pound actual nitrogen per tree at maturity. Adjust these general levels up or down depending upon pruning, size of crop, and cultural practices. Consideration should also be given to fruit color, maturity and quality.
Fruit trees respond to any form of nitrogen fertilizer.
Avoid use of ammonium sulfate, urea, or ammonium nitrate if pH is below 6.0. Fertilizer should be applied approximately 4-6 weeks before bloom. Soil applications are most effective when made preceding rains or sprinkler irrigation. If the rate of application is insufficient, as indicated by heavy fruit set and by tree performance, additional fertilizer may be applied. However, application of nitrogen after the middle of July is not recommended.