Modelling dynamics of emission of greenhouse gases (CO2, N2O) from soils in agroecosystems

Abstract

Problem formulation. One of the main factors affecting climate change is the greenhouse effect conditioned by adding greenhouse gases to the atmosphere, among which CO2, CH4 and N2O are the most dangerous heat-trapping gases. In addition to anthropogenic activities, the source of greenhouse gases is emissions from natural ecosystems and agroecosystems. Carbon dioxide (CO2) accounts for the largest share of greenhouse gas emissions, nitrous oxide (N2O) also has large global warming potential, being nearly 300 times higher than CO2 on a weight basis. The purpose of the study is to create the integrated model of greenhouse gas emissions from soils in the agroecosystems on the basis of studies concerning modelling carbon dioxide emissions from mineral soils, quantitatively describing nitrous oxide emissions and modelling agroecosystem productivity. Methods. Mathematical modelling of environmental processes, the synthesis of quantitative approaches to their description. Results. The results of modelling greenhouse gas emissions from soils in agro-ecosystems during 2017-2019 obtained by means of the integrated model developed showed that there is an interseasonal and interannual variability of CO2 and N2O fluxes. The higher CO2 flow rate was observed in 2017, in 2018 the lower CO2 emission intensity was discovered and in 2019 the CO2 flow rate was even lower. The emission of greenhouse gases varies depending on soil temperature, moisture and humus level of the soil. The equally low level of CO2 fluxes was observed at sufficiently low (from 1 to 6°C) soil temperatures. It was 0.072 – 0.401 g C-CO2/m2/day. The highest level of CO2 emission was observed in 2017 with a combination of high soil temperature (24-27°C) and sufficient soil moisture, and varies between 1,058 to 1,307 g С- CO2/m2/day. It was revealed that the most intense emission of N2O was observed during periods of high soil moisture when anaerobic conditions were established in the soil. The denitrification process was particularly intense in the spring of 2019, when the seasonal precipitation sum was 226 mm, and water-filled pore space (WFPS) reached more than 0.8 relative units. The average emission level of N2O was 15.592 g N-N2O/m2/day over this period, and the total N2O emission was the highest (1.134 kg of N-N2O/ha). The N2O emission intensity varied depending on the meteorological seasons. In the spring of 2017 and spring of 2018, the total N2O emission was 0.153–0.173 kg N-N2O/ha. The N2O emissions reached to 0.202-0.503 kg N-N2O/ha in the summer season and 0.192-0.660 kg N-N2O/ha in the autumn. The highest emission levels were observed in the spring seasons (2018 and 2019) and in the autumn months (2017 and 2018), an increase in soil moisture worsened soil aeration, which led to an intensive denitrification process. In total, for the three meteorological seasons the highest emission was in 2019 (1.567 kg N- N2O/ha). The emission level was lower in 2018 (1.323 kg N-N2O/ha) and even lower in 2017 (0.569 kg N-N2O/ha). Conclusions. Based on the synthesis of approaches to modelling CO2, N2O emissions and agroecosystem productivity, an integrated model of greenhouse gas emissions from soils in agro-ecosystems has been developed (plant-agrosoil-GHG-model). The interseasonal and interannual variability of CO2 and N2O fluxes and their dependence on weather conditions and humus level of the soil have been obtained.