Abstract. The purpose of the study was to study the influence of biologized crop rotation with six fields by 50 %, saturated with legumes, on soil fertility and crop productivity on typical sod-podzolic light loamy soils of the Upper Volga. As a result of field experiments and laboratory studies, new data and knowledge about the effect of crop bipolarization on its productivity and the properties of sod-podzolic soil were obtained. For the first time in the region, it has been studied and established that use of legumes in the crop rotation instead of organic fertilizers partially contributes to the replenishment of the soil with organic matter and nitrogen in the form of organic residues and nodule bacteria, which leads to a decrease in the degradation of soil fertility or even to some improvement. By the end of rotation of the crop rotation when applying (NPK) 90 kg/ha compared with the control version (without NPK), in the biologized crop rotation, the humus content increased by 0.14 %, the acidity of the soil solution slightly decreased by 0.25 units, the content of nitrate nitrogen increased by 59 %, mobile phosphorus – by 72.8 % and exchange potassium – by 70.4 %. The density of soil compaction as a whole in a layer of 0–20 cm in occupied steam, under spring wheat and oats amounted to 1.22–1.24 g/cm3, in other crops (where treatment was not carried out for 2 years) – 1.35–1.39 g/cm3. Mineralization of flax tissue more actively occurred under clover 1st and 2nd years of use – 35.6–42.7 % and 31.0 and 37.3 % and in the employed (vetch-oat) – 26.5–34.4 %, less intensively under winter wheat – 20.9–27.5 and oats – 20.1–25.2 % and very weakly under spring wheat – 13.0–16.5 % at the control and the level of mineral nutrition, respectively. There were fewer weeds in winter wheat sowings – 84 pcs/m2, since it is more competitive with them, oats – 112 pcs, clover – 131 pcs, in a couple – 124 pcs and spring wheat – 138 pcs/m2. Productivity of crops to a greater extent was determined by the applied fertilizers. In fertilized plots, compared with the control, the productivity of the oatmeal mixture was 36.2 % higher, spring wheat – 24.4 %, clover 1st year of use – by 36.2 %, 2nd year of use – by 45.7 %, winter wheat – by 25.7 % and oats – by 30 %.

The article presents the results of field experiments on deepening the arable horizon of gray forest medium loamy soil to increase its fertility through applying organic fertilizer under PY-3-35 layer plow to a depth of 2527 cm. Low mineralization of organic fertilizer during layer cultivation under oxygen deficiency conditions contributed to accumulation of humus in soil by 6.6 t/ha more than during conventional plowing, and by 7.5 t/ha - than during disking. It also improved water-physical and biological properties of soil: number of water-resistant aggregates increased by 4.6 and 5.3 %, soil density lowered by 0.03 and 0.04 g/cm3, number of earthworms increased by 3...6 individuals, expanded reproduction of fertility was provided, productivity of arable land increased by 7.0 and 6.7 % and crop quality increased compared to conventional plowing and disking, respectively. Deep manure incorporation extended life of organic fertilizer up to 5 years, while after conventional plowing and disking this process lasted only 2...3 years. It is not economically and environmentally beneficial, since frequent application requires a lot of fuel, and a large amount of harmful chemical compounds contained in combustion products is dumped into the environment.

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