Uptake and Translocation of Fall- and Spring-applied Zinc in Bearing Apple Trees

Abstract

A zinc timing study was carried out in `Jonagold'/EM26 trees using labeled zinc chloride (98.8 atom% Zn-68). In the fall, five spurs with strong flower buds on each of five trees were labeled with a micropipet with a solution of 1000 ppm Zn at the rate of 240 μg of Zn per leaf. Almost all the Zn-68 applied was recovered in the fallen leaves. Next spring, leaves and flowers clusters sampled from the treated spurs showed that only 3% of their total Zn was fertilizer-derived. A spring application was performed on five spurs and young terminal shoots of each of five trees. The developing leaves were labeled with 500 ppm Zn-68 solution at petal fall. Two weeks later, the entire spurs and the treated shoots were sampled. Zinc remained in the treated areas and it was not transported below or above the application zone. The study supports the contention that Zn is highly immobile in the tree and, if needed, it should be applied in early spring in order to promote rapid leaf and shoot growth. Fall applications of Zn-68 were absorbed but not transported from the treated leaves to the surrounding tissues. Therefore, Zn was not recycled for the next year's growth.