INFLUENCE OF LEAF AND RADICULAR FERTILIZATION ON APPLE GROWTH AND FRUITING PROCESSES

Fertilization is a basic condition of agriculture, as a branch of sustainable development. It is often recommended to supplement mineral nutrition with organic product administration because, through their bio-stimulating effect, it potentiates mineral nutrition. Under these conditions, between 2020 and 2022, a bifactorial study was carried out on three apple cultivars (5-7 years after planting), grown at the Research Institute for Fruit Growing Pitesti-Maracineni, in a high-density orchard. The influence of five foliar and one soil fertilizers, on the background of standard mineral fertilization, over the mineral elements and chlorophyll content of the foliar apparatus for 'Red Braeburn', 'Jonagold Boerekamp', and 'Jonagold Novajo' cvs. was studied. Indicators of growth, fruiting processes, and fruit quality were also assessed. The foliar diagnosis results indicated that the level of mineral elements (N, P, Ca, Mg, Zn, Cu, and Fe) was within the limits of normality established for apple leaves, except for manganese, which accumulated in slightly excess (108.8, compared to 100.0 ppm). On average, during the experiment, the fertilization variants significantly increased the foliar level of mineral elements such as K, Cu, and Fe, compared to the control. Regarding the growth-fruiting processes, the mean of the tree trunk cross-sectional area annual growth was 6.6 cm2. Given that the percentage of fruit set fluctuated around 66.9%, a fruit yield of 66.8 t/ha was obtained. On average, the percentage of fruit set increased significantly by 16.9-19.5% when CropMax (0.2%), M1 (0.5%), and M2 (0.5%) products were applied, and fruit yield by 19.3-21.2% for Poly-Feed (1%) and Fertisol (2 kg/tree). The fruit weight ranged from 72.3 to 443.2 g, with an average of 166.5 g. The average values recorded for firmness, juice pH and total soluble content were 76.4 units HPE-II- FFF Bareiss, 3.6, and 12.7°Brix respectively. All fertilization treatments significantly increased the average weight of the fruit, by 6.2-9.2%, compared to the untreated variant. The results of the study certify the favorable effect of supplementing the fertilization plans with the studied products, containing biostimulators that enhance and harmonize the physiological processes of the apple in a high-density system.