ZINC NUTRITION OF FRUIT TREES BY FOLIAR SPRAYS

Effective methods of supplying Zn to fruit trees are needed to combat widespread deficiency of this element all over the world. Soil applications are not very effective because the roots of fruit crops occupy deep soil layers and zinc does not easily move in the soil. Although foliar sprays are more effective, foliar-absorbed Zn is not easily translocated in plants, which necessitates repeated spray applications and diminishes the ability of foliar sprays to alleviate Zn deficiency in all plant parts. Conditions under which fruit trees are most likely to respond to corrective Zn treatments in terms of growth, yield, and fruit quality are not completely understood. In citrus and apples, the occurrence of severe deficiency symptoms appears to be a prerequisite for tree responses. Zinc foliar sprays applied before anthesis may be most beneficial in terms of fruit yield in citrus and grapes. More research is needed to better define the critical periods for Zn supply to assure optimal fruit set, fruit growth, and high external and internal fruit quality.