POTENTIAL FOR REGULATING THE TURNOVER OF ORGANIC CARBON AND NITROGEN IN SOILS DURING FIELD CROPS CULTIVATION ON IRRIGATED LANDS OF THE LOWER VOLGA REGION

Purpose: The quantitative assessment of the potential for regulation of soil organic carbon and nitrogen turnover during cultivation of soybeans, winter wheat and Sarepta mustard on irrigated lands of the Lower Volga region. Materials and methods. The study is based on the results of a field experiment with soybeans, Sarepta mustard and winter wheat. The possibilities of increasing the bioproductivity of irrigated soybeans were studied in a three-factor field experiment (variety, organic fertilizers and foliar treatments with a microcomplex), Sarepta mustard and winter wheat – in two-factor experiments (predecessor, aftereffect of organic fertilizers). Results. It was found that stubble and root residues of soybeans allow replacing annually no more than 0.88 t/ha of organic carbon and 12.7–12.9 kg/ha of nitrogen. The use of soybean by-products provides an increase in the regulatory potential of soybeans for organic carbon by 2.8–2.9 t/ha and for nitrogen by 93.4–101.4 kg/ha. With the by-products of the most developed mustard crops, up to 1.42 t/ha of organic carbon and 40.4–46.7 kg/ha of nitrogen enter the soil, and when plowing in green manure biomass – up to 2.57–3.39 t/ha of organic carbon and 97.5–128.8 kg/ha of nitrogen. The potential supply of organic carbon to the soil due to crop and root residues and by-products of winter wheat is 2.06 t/ha, which is comparable with the regulatory potential of soybeans. However, no more than 19.5 t/ha of nitrogen is supplied, which creates a deficient carbon-nitrogen balance, C:N = 104–116. Conclusions. Irrigated soybean crops with the use of by-products provide the formation of one of the strongest potentials for regulating the turnover of organic carbon and nitrogen in the soil. A scientifically substantiated system of soybean cultivation techniques increases the possibilities of replenishing organic carbon and nitrogen in the soil by 12.2–14.7 % due to the use of additionally formed plant biomass.