USING RUNOFF HOLLOWS TO DRAIN HEAVY SOILS IN THE NOVGOROD REGION CONDITIONS

The objective of the study is to obtain new knowledge about the formation of the water-air regime by the runoff hollows in the natural and climatic conditions of the Novgorod Region. The studies were conducted in 2020–2024 on systems with runoff hollows located every 25, 40 and 55 m. The research location is the Lyapino experimental production site in the Novgorod Region, the soils of which are heavy in particle size distribution (clayey), sod-podzolic, with a low content of potassium (K2O – 13–17 mg/100 g) and phosphorus (P2O5 – 2.5–13 mg/100 g) and a humus content in the soil horizon of up to 4–6 %, acidity pHKCL = 4.8–5.5. The density of the arable layer is 1.35–1.37 g/cm3, the subarable layer is 1.52–1.54 g/cm3, the porosity coefficient is 0.46–0.48, and the total moisture capacity is 35–31 %. The runoff hollows is a shallow (less than 50 cm) triangular-shaped excavation in cross section with gentle slopes (1 : 10) 102–115 m long and a slope of 0.001, along the axis of which a cavity-free drainage system 70 cm deep and filled with sand and gravel mixture is laid. According to the degree of moisture during the study period, 1 year was wet and 4 years were dry. The study of groundwater dynamics showed that during the five-year study period, groundwater was absent in the arable horizon in the runoff hollow variant with a distance of 25 m, and groundwater was in the arable horizon in May 2020 and 2021 in the runoff hollow variants with a distance of 40 and 55 m. Heavy precipitation, which caused a rise in groundwater in August 2021 and 2024 (exceeding monthly norms by 3.6 and 1.6 times, respectively), did not cause flooding of the arable horizon in all experimental variants; drainage systems drained excess water. In the runoff valleys with a distance of 55 m in 2020, the longest waterlogging of the 0–60 cm soil horizon was noted for 55 days. In the 0–30 cm soil layer, the shortest period of waterlogging was noted on average over 5 years in the runoff hollows with a distance of 25 m. For wet years, a more favorable water-air regime is formed on runoff hollows with a distance of 25 m, and for dry years – on runoff hollows with a distance of 40 m. The highest productivity of a forage hectare was noted in the variant with runoff hollows every 25 m, where the hay harvest averaged 3.4 t/ha.