The climate change impact on greenhouse gas emissions (CO2 and N2O) from soils at agroecosystems

Formulation of the problem. Soils are a significant source of greenhouse gases (GHGs), the release of which into the atmosphere forms the global warming potential. Mathematical models describing greenhouse gas emissions make it possible to assess the impact of climate change on the GHG emissions on a regional scale, and study how land-use changes affect these emissions. The study is aimed at assessment of potential changes in CO2 and N2O emissions from soils at agroecosystems under the influence of temperature regime changes and increasing aridity in the context of global climate change. Materials and methods. Numerical experiments with a comprehensive model of GHG emissions from the soils at the winter wheat agroecosystem were performed by means of RCP4.5 climate change scenario. The study is based on the materials of agrometeorological observations at the hydrometeorological station of Bilovodsk (Eastern Ukraine) for the period of 1991-2020 and the climate change scenario RCP4.5 for the period of 2021-2050. Results. Classification of crop vegetation conditions allowed us to reduce the diversity of their regimes to certain weather types, characterizing the common conditions of crop formation in spring and summer, due to which the so-called 'dry' and 'humid' years were distinguished. The tendencies of change in air temperature and rainfall during vegetation of winter wheat in years different on humidity have been established. The increase in air temperature from the beginning of the growing season was gradual, while maintaining a stable correlation: a ten-day average long-term temperature was more than a temperature of the 'dry' year which was more than a temperature of the 'humid' year. The intensity of greenhouse gas emissions is defined by the type of humidification in the growing season. In the 'dry' years at the beginning of the vegetation season, CO2 emissions will make up 0.044-0.079 tons of.-CO2 ha(-1) per a ten-day period, which is higher than the average long-term values and almost twice as high as in the 'humid' years. In the spring at the beginning of the growing season, as a rule, the level of moisture content in the arable soil layer is quite high, which leads to the formation of anaerobic conditions. They, in turn, determine the level of N2O emissions. Increasing aridity reduces the level of N2O fluxes. For 'dry' years, at the expense of a fairly high level of spring moisture of the arable layer at the beginning of the growing season, the level of N2O emissions was quite high (0.061-0.089 kg of N-N2O ha(-1) per a ten-day period). Subsequently its level decreased significantly. In general, total greenhouse gas emissions in terms of CO2 equivalent will decrease by 6.2% in 'dry' years and by 32.3% in 'humid' years. Conclusions. Based on numerical experiments with the model of greenhouse gas emissions from soils at the winter wheat agroecosystem, the general patterns of vegetation-related variation of CO2 and N2O emissions are identified. The main patterns feature consists in increasing CO2 emissions during spring-summer vegetation of winter wheat from the beginning of a growing season to the wax ripeness phase and in decreasing N2O emissions from the beginning of the winter wheat growing season until its ending. Their peculiarities are defined by the years' different humid conditions.