EFFECT OF FERTIGATION UNDER DRIP IRRIGATION ON NPK MOBILITY AND DEPTH DISTRIBUTION IN THE SOIL OF AN INTENSIVE APPLE ORCHARD

The aim of this study was to quantitatively assess and compare the content, seasonal dynamics, and depth distribution of ammonium nitrogen (N-NH₄), nitrate nitrogen (N-NO₃), available phosphorus (P₂O₅), and exchangeable potassium (K₂O) in the soil under three different nutrient management practices in an intensive ‘Zero My Golden’ apple orchard: an unfertilized control, conventional band fertilization, and drip fertigation. The study was conducted in 2024–2025 at the“Baxmal Fruit Growing” farm in Baxmal District, Jizzakh Region, Uzbekistan, in an 11-year-old ‘Zero My Golden’ apple orchard grafted onto M26 rootstock, with a planting density of 4 × 1 m (2,500 trees/ha). The experiment was arranged according to a randomized complete block design with three treatments and three replications: (N) unfertilized control, (A) conventional band fertilization, and (F) fertigation. All fertilized treatments received the same nutrient rates of 109.85 kg N, 103 kg P₂O₅, and 158 kg K₂O per hectare. Soil samples were collected from the 0–30 cm and 30–60 cm soil layers in November, May, and September and subjected to agrochemical analysis. The results showed that, compared with conventional fertilization, fertigation increased the content of N-NH₄ in the root zone by 23–28% in the 0–30 cm layer and by 36–37% in the 30–60 cm layer. The corresponding increases in N-NO₃ were 34–44% and 54–70%, respectively. Available P₂O₅ increased by approximately 53% in the 0–30 cm layer and by 81–97% in the 30–60 cm layer, while exchangeable K₂O increased by 27–28% and 39–41%, respectively. The greatest relative increases were observed in the deeper 30–60 cm soil layer, particularly for phosphorus and potassium. Under fertigation, soil pH was 6.5–6.6, compared with 6.7–6.8 in the other treatments. Soil moisture in the 0–30 cm layer under fertigation was 28–33%, compared with 20–27% in the other treatments, while annual irrigation water consumption was reduced by 25–40%. Fruit yield was 32.0 t/ha in the control treatment, 40.0 t/ha under conventional fertilization, and 55.0 t/ha under fertigation. The study demonstrated that drip fertigation is an effective agrochemical strategy for intensive apple orchards under the dry climatic conditions of Uzbekistan, improving the mobility of nitrogen, phosphorus, and potassium in sierozem soils, enhancing their retention within the root zone, and improving their distribution throughout the soil profile while simultaneously saving irrigation water.