Effects of Nutritional Factors on Regular Cropping of Apple
Any mineral nutrient deficiency or toxicity that adversely influences the normal biochemical and physiological processes in the tree can be expected to impact regularity of cropping. Deficiency of N limits growth and flowering of young trees and increases potential for biennial bearing in mature trees while excess N may stimulate excessive vegetative growth that results in shading of spurs and development of weak flowers with reduced set potential. B, Zn, and Cu shortages influence regularity of cropping through effects on flower development, pollination and/or fertilization. Effects of K, Mg, Mn, Fe, or S appear to be indirect, principally as consequences of limited carbohydrate production/availability. Crop load/vegetative growth relationships in one season can exert significant influences on nutrient status within the tree that may influence potential for cropping in the next season. Environmental stress may limit nutrient availability of various nutrient elements at critical times during the flower development and fruit setting sequence. Effects of nutritional factors on regularity of cropping must be considered in relation to their interaction with all other components of the fruit production system. Maintaining appropriate essential mineral nutrient supply and availability to avoid potential deficiencies or toxicities is critical to regular cropping of apple trees.