Zinc Fertilizers and Additives for Foliar Fertilization of Cocoa Seedlings

Foliar fertilization is an interesting strategy for nutrition with micronutrients in perennial plants; among the micronutrients, zinc (Zn) deficiency is the most frequent in cocoa trees (Theobroma cacao L.). The present study aimed to evaluate the efficiency of Zn sources through foliar application for the cocoa crop. The experiment was carried out in a randomized block design, with 10 treatments and four replicates. Treatments were: foliar fertilizations containing 1 g L-1 of Zn using two inorganic sources (chloride and sulfate), in the presence or absence of additives (urea and sucrose); two organic sources (Zn-EDTA, and from chloride and sulfate); soil fertilization with 8 mg dm-3 of Zn, and a control (without addition of Zn). Foliar fertilizations with Zn were monthly applied for five months, and the experiment was conducted for 210 days. The results were subjected to analyses of variance and contrast. Zn fertilization, regardless of the form of application, increased Zn contents and accumulations in the leaves. Zn fertilization in the soil, at planting, led to a recovery rate by the plant similar to the mean value caused by foliar fertilizations. ZnCl2 caused higher Zn contents and accumulations in the leaves and was more efficient than sulfate and EDTA; addition of urea to the ZnSO4 solution increased Zn accumulation in the leaves, whereas addition of sucrose to the ZnCl2 solution reduced Zn content in the leaves.