INFLUENCE OF MINERAL FERTILIZERS ON THE INCOME AND RESERVES OF ORGANIC CARBON IN THE GRAIN FALLOW CROP ROTATION OF THE FOREST-STEPPE ZONE OF THE TRANS-URALS

Background. Organic carbon, which is part of humic substances, is the basis for the fertility of arable soils. The intensity of agriculture has led to an increase in the use of mineral fertilizers, which have a significant impact on soil formation processes. This leads to a disruption of the natural dynamic balance of organic carbon reserves, the process of mineralization of organic matter intensifies, which leads to an increase in carbon dioxide emissions. The accepted concept of “4 ppm” calls on the world society to develop a farming system aimed at increasing the reserves of organic carbon in arable soils. Based on this, studying the influence of various elements of crop cultivation technology on the supply and fixation of organic carbon in arable soils can be considered one of the tasks of modern agricultural science. The purpose of the work is to study the effect of mineral fertilizers on the supply of plant residues and reserves of organic carbon in grain-fallow crop rotation in the conditions of the forest-steppe zone of the Trans-Urals. The novelty of the work lies in the fact that for the first time long-term stationary studies have been carried out on the effect of mineral fertilizers on the supply and reserves of organic carbon in arable soils. In the future, it will be possible to theoretically substantiate the required doses of mineral fertilizers to obtain a positive balance of organic carbon in arable soils of Western Siberia. Materials and methods. The study was carried out in grain-fallow crop rotation (full fallow, spring wheat, oats) from 1995 to 2023 on leached, thin, heavy loamy chernozem. Every year, calculated doses of mineral fertilizers were applied to spring wheat and oats for a planned yield of 3.0; 4.0; 5.0 and 6.0 t/ha of grain, taking into account the actual nutrient content in the soil. Every year, the mass of straw, stubble and root residues was determined for all crop rotation options. In which the content of organic carbon was determined annually and the mass of carbon entering the soil was determined. Before the foundation of experience in 1995, as well as in 2005; 2015 and 2023 soil samples were taken from a depth of 0-10; 10-20; 20-30; 30-40; 40-60; 60-80; 80-100 cm. In which the content of organic carbon was subsequently determined. The reserves of organic carbon in a meter layer of soil were determined using the recalculation method taking into account the equilibrium density. Statistical data processing was carried out using Microsoft Excel. Results. In the option without the use of mineral fertilizers, 117.3 t/ha of plant residues entered the soil during 28 studies. Refusal to use fertilizers led to a negative balance of organic carbon in the soil, where the decrease in reserves was 6.7% relative to the initial values. The application of mineral fertilizers for a planned yield of 3.0 and 4.0 t/ha of grain led to an increase in the flow of by-products into the soil by 25-48% relative to the natural nutrition level. This ensured a positive carbon balance, where the increase in reserves in the meter layer of soil was 4.2-5.1% relative to the initial values. The application of NP to a planned yield of 5.0 and 6.0 t/ha of grain increased the input of plant residues during the study period by 69-75% relative to the control. Despite this, there was a decrease in organic carbon reserves in the meter layer of soil by 4.7-6.4% relative to the initial value. Conclusion. Refusal to use mineral fertilizers when cultivating grain crops leads to a negative balance of organic carbon, where annual carbon losses reach 0.44-0.78 t/ha. Stable application of fertilizers to obtain 3.0 and 4.0 t/ha of grain ensures a positive carbon balance in the soil, the annual increase in reserves ranges from 0.23 to 0.58 t/ha. High doses of fertilizers to obtain a yield of 5.0 to 6.0 t/ha lead to a negative carbon balance in the soil; annual losses range from 0.30 to 0.55 t/ha.