through the use of commercial chemical fertilizers and manures. Rates of application are from a quarter pound (young trees) to 1.5 –2.0 lbs. (mature trees) of actual nitrogen per tree per year. Fertilizers most commonly used are calcium ammonium nitrate, ammonium nitrate, urea or calcium nitrate. Ammonium sulfate is not used on acid soils due to their tendency to make the soil even more acid.Zinc deficiency is characterized by mottled yellowing between the veins, small leaves and more rounded fruit. Zinc sulfate (purchased from a farm supply store usually applied at the rate of 0.5 lbs. per tree per year, scattered on the soil in the wetted pattern and watered into the soil.
Alternatively, zinc sulfate can be applied at the rate of about 3 –4 lbs. per tree every five years. In some situations, other elements may be lacking. Iron deficiency (causing sharp green veins against a yellow background between the veins) is common in calcareous soils. Iron, manganese, zinc and copper can be applied as a foliar spray in the late spring to supply minor elements. Leaf analysis in the late summer/fall is done to determine which elements, if any, are lacking.Some long-term studies have indicated that yield may be improved with applications of phosphorous and potassium. A basic fertilizer schedule used for mature trees in farm advisor trials is as follows:
Early February: 6 lbs. triple 15 (15-15-15) applied per tree. (Equals 0.90 lbs. actual nitrogen); June: 3 lbs. calcium nitrate (15.5-0-0) applied per tree (equals 0.465 lbs. actualnitrogen);September: 3 lbs. calcium nitrate (15.5-0-0) (equals 0.465 lbs. actual nitrogen).
Total actual nitrogen for the year:1.83 lbs.Recent research has indicated that yield in
Hass avocado may be boosted somewhat by an extra application of nitrogen (0.25 lb. actual N/tree) in April and November.
