Net global warming potential, greenhouse gas intensity and carbon footprint as affected by different tillage systems from Chinese double-cropping paddy fields

Conservation tillage may be an alternative system for rice production in China, yet differences in net global warming potential (NGWP), greenhouse gas intensity (GHGI) and carbon footprint (CF) among different tillage methods are poorly documented. Accordingly, a 3-year field experiment was conducted to simultaneously measure methane (CH4) and nitrous oxide (N2O) emissions and changes in soil organic carbon (SOC) under conventional tillage (CT), reduced tillage (RT) and no-tillage (NT) methods in Chinese double-rice cropping systems. There was no difference in SOC content among the tillage treatments, but SOC sequestration under NT reduced obviously with the increase of soil depth at 0 similar to 20 cm. CH4 emissions were conspicuously correlated with SOC content at soil depth below 5 cm. Tillage methods had no significant effect on N2O emission, except for the substantial N2O emission under NT during non-rice season. Compared with the NT plots, the annual CH4 emission and NGWP were significantly increased in the CT and RT plots over the three years. There were no significant differences among the tillage methods with respect to GHGI and CF, whereas the grain yields were greatly increased in the RT plot. We conclude that RT practice are promising in rice production for higher grain yield with similar GHGI and CF, while increasing productivity of the NT system is a high priority since the CH4 emission and NGWP can be dramatically reduced.