Greenhouse gases fluxes and carbon cycle in agroecosystems under humid continental climate conditions

Abstract

Few complex studies of greenhouse gas (GHG: carbon dioxide, CO2; methane, CH4; nitrous oxide, N2O) fluxes and carbon cycle components were carried out on the geographical territory of Eastern Europe and represented in world databases. Most of the investigations had focused on particular problems of carbon and nitrogen pools and fluxes, or had covered a narrow range of ecosystems. Therefore, the idea of this research was to carry out a multi-disciplinary study of carbon fluxes and pools in the sector of agriculture and land use – one of the main sources of GHG – in regions with humid continental climate that are the most affected by current climate change. Our work was aimed at solving the problem of quantifying GHG fluxes and carbon pools in crop and livestock production, analyzing the reasons for their formation and possible absorption pathways at three locations in the European part of Russia in the cold continental climate zone. The study examined both agricultural and natural ecosystems; field measurements, laboratory analyses, and simulation modelling techniques were applied. The sites included seven types of ecosystems: croplands, pastures, hayfields, fallows, forests, stockyards, and compost piles. Livestock facilities are potent sources of three main biogenic GHG (0.42 − 9.27 g C-CO2 m-2 h-1; 2.43 − 783.51 mg C-CH4 m-2 h-1; 0.01 − 1.49 mg N-N2O m-2 h-1); whereas croplands, hayfields and forests can absorb methane (from −1.10 to −118.2 μg C-CH4 m-2 h-1), as well as pastures, hayfields, fallows and forests are weak sinks of nitrous oxide (from −0.10 to −4.57 μg N-N2O m-2 h-1). Ecosystems were ranked using a non-parametric test by increasing rate of CO2 emission from soil in the following order: croplands (0.06 − 0.24 g C-CO2 m-2 h-1) ≤ hayfields (0.06 − 0.25 g C-CO2 m-2 h-1) ≤ pastures (0.06 − 0.22 g C-CO2 m-2 h-1) = fallows (0.13 − 0.26 g C-CO2 m-2 h-1) = forests (0.16 − 0.30 g CO2 m-2 h-1) ≤ stockyards (0.42 − 1.57 g CO2 m-2 h-1) < compost piles (1.95 − 9.27 g CO2 m-2 h-1). According to the correlation analysis, the most important dynamic environmental factor on which the intensity of soil respiration depends is the soil temperature at the depth of 10 cm (r = 0.55 − 0.97, p < 0.05). As the regression analysis shows, hydrothermal and agrochemical controls explain the 46 − 89% variance of CO2 emission from soil. The content of total carbon (1.31−7.95%) as well as of total nitrogen (0.12 − 0.62%) in soil follows a latitudinal pattern and increases from north to south regardless of the type of land use and farming intensity. The amount of carbon incorporated into the arable soil layer by root residues decreases in the following sequence: barley > winter wheat > spring wheat > oats > soybean from 402 to 198 kg C ha-1 yr-1. Field crop stubble is an additional source of soil carbon at 118 − 368 kg C ha-1 yr-1 in the following sequence: spring wheat > winter wheat > oats > soybean > barley. According to simulation modelling (DeNitrification-DeComposition model, DNDC; and Rothamsted Carbon model, RothC), accumulation of soil organic carbon is possible under winter wheat (270 kg C ha-1 yr-1), while under other crops its stocks decrease (from −190 to −423 kg C ha-1 yr-1). According to DNDC modelling, agrolandscapes are net sinks of carbon to a varying degree (at least 500 kg C ha-1 yr-1), with phytomass being the main pool of carbon sink, most of which is removed with yields.