Yield of oil crops and winter wheat depending on the contents of mobile nitrogen, phosphorous, and potassium in leached black soil in a stationary field experiment of V.S. Pustovoit All-Russian Research Institute of Oil Crops

In grain-row crop rotation, sunflower - winter wheat, castor plant - winter wheat, soybean - winter wheat in stationary field experiment in 1981-1989, we studied contents of nitrate nitrogen, mobile phosphorus, and exchangeable potassium, the degree of phosphate mobility in 0-60 cm layer of leached black soil in the spring after incorporating plant residues of cultivated crops into the soil and applying mineral fertilizers. It was revealed that the application of plant residues and mineral fertilizers in the soil increased the contents of nitrate nitrogen by 0.1-9.0 mg/kg, mobile phosphorus - by 3.7-21.9 mg/100 g, in comparison with the control, depending on culture. On average, according to the experimental variants, the soil received 7.3 t/ha of above-ground plant residues of sunflower, 5.7 t/ha of castor plants, 3.7 t/ha of soybeans, 6.5 t/ha of winter wheat after sunflower, 7.9-8.0 t/ha - after castor plants and soybeans. With plant residues after their mineralization, 42-57 kg/ha of nitrogen, 13-26 kg/ha of phosphorus, and 30-208 kg/ha of potassium are returned to the soil. The dependence of the yield of sunflower, castor plant, soybean, and winter wheat after oil preceding crops on the contents of nitrate nitrogen, mobile phosphorus, and exchangeable potassium, the degree of phosphate mobility in spring in leached black soil has been established, and regression equations have been calculated. The optimal contents of nitrate nitrogen, mobile phosphorus, and exchangeable potassium, the degree of phosphate mobility in leached black soil in spring for sunflower, castor plants, soybeans, and winter wheat are shown, above which the use of fertilizers for these crops is ineffective. Sunflower, castor plants, and soybeans, as predecessors of winter wheat, have different effects on the dependence of the yield of winter wheat on the content of nitrate nitrogen, mobile phosphorus, and exchangeable potassium in the leached black soil in the spring.