Influence of Leaf to Fruit Ratios and Nutrient Sprays on Fruiting, Mineral Elements, and Carbohydrates of Apple Trees

Abstract

Abstract For 5 years, the leaf to fruit ratios of mature ‘Golden Delicious’ (Malus domestica Borkh.) apple trees on M.9 rootstock with declining leaf N levels and fruit size were adjusted to low, medium, or high levels of leaves per fruit, 2 weeks after bloom, coupled with 8 weekly foliar sprays of urea, phosphorus-potassium-sulfur (PKS), or urea plus PKS beginning at pink. No interaction occurred between the leaf : fruit ratios and foliar sprays. Mean leaf N over 5 years was slightly reduced when the crop was adjusted to high numbers of leaves: fruit and increased by urea or PKS foliar sprays. The only effect of adjustment in leaf: fruit ratio or foliar nutrients on nonstructural carbohydrate (NSC) levels was an increase in leaf NSC in 1978-1980. As the number of leaves per fruit increased, the percentage of the total harvest in the larger size classes increased with corresponding decrease in the smaller size classes. Total yield per tree, fruit firmness, and russeting were not influenced by adjusting the leaf : fruit ratio, while soluble solids were increased and fruit color decreased at the high level of leaves per fruit. Foliar urea sprays increased the percentage of fruit in the largest size class, yield per tree, fruit firmness, soluble solids, color, and the amount of russet.