Comparative effects of long-term conventional tillage and no-till systems on greenhouse gas emissions in continuous maize monoculture soil in a semi-arid temperate climate

Agricultural tillage practices play an important role in the production and consumption of greenhouse gases (GHGs) that contribute substantially to the global warming. To explore GHG diffusion characteristic and seek for environment-friendly tillage methods, four tillage systems consisting of continuous rotary tillage (CR), continuous no tillage (CN), ploughing-rotary tillage (PR), and ploughing-no tillage (PN) were designed, and vertical variations of GHG concentrations under different tillage systems were investigated. Mean CO2 concentration in the soil profile was increased significantly with the increase of soil depth. Higher soil moisture promoted CO2 production. However, the influence of soil temperature on the content of CO2 was not obvious. The concentrations of CH4 in soil at 0–20-cm depth were greater than that of 20–40 cm, which was mainly affected by fertilization. The trend of N2O concentration variation in soil was consistent with that of CO2. The diffusion flux of CO2 in soil was all positive, and it changes greatly in the whole growth cycle of maize, which had obvious correlation with precipitation. The CH4 diffusion flux decreased with the increase of soil depth, and the change trend of 0–20-cm soil layer diffusion flux was consistent with the gas concentration. The 20–40-cm soil layer fluctuated greatly, which was mainly affected by water content, and the whole value was negative after jointing. The trend of N2O diffusion flux was similar to that of CH4. In the whole maize growth period, except for CH4 in 20–40-cm soil layer, the cumulative diffusion fluxes of greenhouse gases in each treatment were all positive, indicating that the whole farmland soil was the emission source of greenhouse gases. The effect of three greenhouse gases on greenhouse effect was CO2 > N2O > CH4, and the comprehensive warming potential of different tillage methods was CN > CR > PR> PN. So PN is the best tillage mode to reduce GHG emissions in soil profile under the test conditions.