METHODS FOR INCREASING THE PRODUCTIVITY OF DIRECT-SEEDING CROP ROTATION UNITS IN THE FOREST-STEPPE ZONE OF MIDDLE VOLGA REGION

The purpose of this study was to assess the impact of mineral fertilizer application rates and intercrop cover crops on productivity of spring rapeseed - winter wheat crop rotation unit cultivated using direct seeding. Field experiments were conducted in 2023-2025 on a stationary field of Ulyanovsk State Agrarian University, on a six-field crop rotation: spring rapeseed - winter wheat - soybeans - spring wheat - buckwheat - barley. The experimental scheme included a study of mineral fertilizer rates (variants for spring rapeseed and winter wheat: control without fertilizer, N40P15K23S2, and N80P30K46S5), in addition, intermediate cover crops were sown after barley harvesting (control variant - without intermediate cover crops, spring crop mixture and winter crop mixture). The results showed that under the dry conditions of autumn 2023 (HTC = 0.51), intermediate cover crops produced biomass ranging from 0.11 to 0.28 t/ha of dry matter, with a significant advantage in the variants with mineral fertilizer application under the preceding crop. Spring rapeseed productivity increased under the influence of mineral fertilizers by 0.18-0.35 t/ha (16.5-32.1%). Ground cover crops also had a reliable positive effect, especially against an unfertilized background, providing an increase of up to 0.42 t/ha (51.0%). On average, in the experiment, the increase of spring rapeseed yield from spring mixtures was 0.22 t/ha (19.6%), from winter crops - 0.24 t/ha (21.4%). Winter wheat productivity was determined by fertilizer rates (an increase of 0.39-0.64 t/ha or 10.7-17.2%) and the aftereffect of intermediate cover crops, which was maximum against an unfertilized background (up to 0.31 t/ha or 8.8%). Crop rotation productivity increased by 0.25-0.26 thousand units (9.2-9.6%) with the direct seeding and by 0.33-0.56 thousand units (12.7-21.6%) with mineral fertilizers, reaching a maximum of 3.15 thousand units in the N80P30K46S5 variant.