Test the soil pH at the foot of the tree. If the soil has a pH of less than 6.0, it is too acidic and can benefit from an application of zinc sulfate. A rate of 1/2 lb. zinc sulfate per year of age up to 10 lbs. is recommended by the University of Arkansas. Sprinkle it over the root zone of the tree, avoiding the trunk, and water it in after application. If the soil is alkaline, with a pH of more than 6.0, applications of zinc to the soil will be ineffective, so try the foliar spray instead.
Zinc Foliar Spray
Plan a schedule for spraying the pecan tree canopy with zinc foliar sprays if you want rapid growth during the first seven years of life. Zinc is more easily absorbed through leaves than roots, according to Texas A&M University. Spray the canopy once every two weeks throughout the growing season of April to late August. Mix 2 to 4 tsps. of zinc nitrate or 2 tsps. of zinc sulfate per gallon to make the spray. Apply it early in the day when humidity is high and winds are low.
Balanced NPK Fertilizer
For soils that don't need much supplemental zinc, avoid the need for foliar and soil applications of zinc by using a balanced 10-10-10 NPK (nitrogen, phosphorus and potassium) fertilizer. These all-purpose tree fertilizers contain micronutrients, including zinc. Apply at a rate of 1 lb. per tree in March and again in June. The University of Florida Institute of Food and Agricultural Sciences Extension also recommends pulling weeds in a 5-foot-diameter circle around the tree to keep weeds from absorbing all the fertilizer.
Anyhow, application of zinc sulfate is very crucial to trees.