Carbon control of nitrogen mineralization and immobilization cycle in Forest-Steppe agrocenoses

Abstract

Goal. To determine the normative para­meters of a comprehensive model of nitrogen and carbon circulation using different types of crop rotation, the use of alternative types of organic fertilizers, and the implementation of various methods of soil cultivation. To identify the main regularities of the direction of the nitrogen-carbon cycle, the nature and mechanisms of the restoration of natural soil formation using soil-based adaptive measures in the agrocenoses of the modern climatic system of the Forest-Steppe of Ukraine. Methods. Field (soil sampling to determine organic substan­ces), laboratory (to determine the content of organic substances in the soil), mathematical, statistical, and comparative calculation (to justify the reliability of the developed models of the nitrogen-carbon cycle under various agrotechnical influences). Results. The type of organic fertilizer influences the emission of CO2 into the atmosphere depending on the mineralization of plant residues: at the use of manure, the typical interval of emissions is 25–85 tons, while for by-products their volumes increase up to 80–160 tons, which is accompanied by increased removal of nitrogen compared to its entry into agrocenoses, in the first case, and, conversely, a linearly increasing flow of total nitrogen compared to its removal in the process of mineralization of by-products, in the second case. The effect of the type of agrocenosis (crop rotation) on the nitrogen-carbon cycle is reduced to the fact that, due to the saturation of crop rotation with crops with a high yield of by-products (crop rotation with peas), a linear increase in the flow of nitrogen in the typical interval of productivity growth during mineralization of by-products and the release of nitrogen from it. Increased CO2 emissions in the latter case are accompanied by an increase in the carbon balance in the soil and the productivity of agrocenosis. The impact of the chornozem cultivation method on the nitrogen-carbon cycle is reduced to the fact that, under no-till cultivation, regardless of the type of organic fertilizer and the type of agrocenosis, in the interval of productivity growth, the carbon balance in the soil is positively increased compared to plowing, where the nature of deficit growth is subordinated to parabolicity. The interval of emission of CO2 into the atmosphere in the process of mineralization for ploughing was wider in comparison with no-till cultivation, which indicated an increase in mineralization processes in the soil with the uniformity of nitrogen-carbon cycle, which defined soil cultivation as a subordinate regulatory subsystem of the type of crop rotation and the type of organic fertilizers in general circulation. Conclusion. Use of crushed by-products of crop production as organic fertilizer with sufficient nitrogen compensation by mineral fertilizers, which are wrapped in the surface layer of chornozem during systematic no-till cultivation, models the natural nature of the nitrogen-carbon cycle in agrocenoses of short crop rotations of various types. Reproduction of the natural model of soil formation in agrocenoses, at the level with microbiological activity, is provided by the activation of photosynthetic activity of crops due to the reproduction of the stock mechanisms of carbon due to the increase in the content of CO2 in the atmosphere and the thermal resource in agroecosystems in general. This should be the basic model of extended reproduction of the fertility of typical chornozems in the Forest-Steppe of Ukraine.