GROWTH AND PRODUCTIVITY OF APPLE TREES UNDER OPTIMIZED NITROGEN FERTILIZATION

Abstract

Optimization of mineral nitrogen nutrition is one of the key factors in the intensification of fruit growing and in increasing the productivity of orchards. Ensuring an adequate nitrogen supply to trees throughout the growing season is a decisive factor in the formation of the aboveground part of the tree, the development of the root system, and the enhancement of orchard productivity. Nitrogen nutrition significantly affects the photosynthetic activity of the leaf apparatus. A sufficient nitrogen concentration in plant tissues stimulates chlorophyll biosynthesis, which enhances metabolic processes and promotes the differentiation of generative buds. This creates a physiological basis for obtaining high and stable yields. The potential productivity of apple orchards encompasses indicators reflecting the effective interaction between the leaf canopy and the accumulation of phytomass by individual trees and by the orchard as a whole. Important indicators of tree growth include increases in trunk diameter, shoot growth, and the total accumulation of tree phytomass, which collectively determine the potential productivity of the plantation [2, 4]. The realization of the potential productivity of apple orchards results from the synergistic interaction between the structure of the assimilatory apparatus and the dynamics of organic matter accumulation, both at the level of the individual tree and of the agro-phytocenosis as a whole. The total biological biomass yield, including both vegetative organs and the marketable yield, is a comprehensive indicator of the adaptability and productivity of cultivar–rootstock combinations within specific growing zones characterized by diverse soil and climatic conditions. The results of studies on the effect of optimized nitrogen nutrition on growth parameters and yield of apple cultivars Red Topaz and Rubinola grown on podzolized chernozem in the Right-Bank Forest-Steppe zone of Ukraine are presented. The research was conducted in 2024–2025 in an experimental apple orchard of the Educational and Production Department of Uman National University. The objects of the study were different nitrogen nutrition treatments applied to apple trees of the cultivars Red Topaz and Rubinola grafted on M.26 rootstock, planted at a spacing of 4 × 1.5 m. On average over the two years of research, the increase in trunk diameter of the cultivar Rubinola was 11% greater than that of Red Topaz. Among the fertilization treatments, the highest values were recorded in the production control plots (N90). Shoot growth of the studied apple cultivars was within the optimal range (25–40 cm). Increased shoot growth was promoted by the N90 treatment and by the nitrogen nutrition model, where the increase over the control was 10.7–15.7% and 8.4–17.3%, respectively. Under calculated fertilizer application rates (based on nitrification capacity indicators and the nitrogen nutrition model), the yield of Red Topaz trees increased by 13–15% compared with the absolute control and by 6–8% compared with the production control. For the cultivar Rubinola, the yield exceeded the production control by 14%.