The effect of foliar fertilization on the drought resistance of apple varieties in the Oryol region
Abstract
The studies were conducted in the educational garden of the Oryol State Agrarian University (Oryol, Oryol Region, Russia) on dark gray forest soil. The orchard was planted in October 2021 with one-year-old seedlings in a 3x5 m layout (rootstock 54-118). The objects of the study were apple trees of the Veteran and Orlovskoe Polosatoe varieties, as well as the organic-mineral fertilizer-biostimulant Biostim Universal, which contains 6.0% N (total), 1.3% K 2 O, 5.0% SO 3 , and 10.0% free amino acids of plant origin. Leaf fertilization was carried out 4 times per season. The experience scheme: 1 - control (without treatment); 2-4 - spraying of trees with agrochemicals with consumption rates of 3, 5 and 7 liters/ha. The repetition of the experiment is threefold, with 5 trees each. In July 2025, there was a pronounced drought due to abnormal heat, including an absolute season high of +34.3 °C. The GTC was 0.6, which is classified as an average drought. The water content of apple tree leaves directly depends on the level of moisture availability. In conditions of overwatering (June and August), this indicator was maximum (62.464.7%), whereas in the dry period (July), it decreased to 54.2–55.9%, depending on the variety. The use of organic-mineral fertilizer-biostimulant increased leaf moisture content and reduced water deficit. The most pronounced positive effect was observed at a dose of 7 l/ha: the increase in leaf water content was up to 2.7% (under drought conditions); the water deficit decreased by 2.9% compared to the control in both varieties; and the transpiration rate decreased by 3.5–3.9 mg/cm²·h, indicating a more efficient use of moisture. The Orlovskoe Polosatoe variety showed higher water content values under favorable conditions, but the difference between the varieties was insignificant during the stressful period (July). The Veteran variety initially had a lower transpiration rate, but it responded well to biostimulant treatments, especially in terms of reducing transpiration losses.