Modeling Impacts of Alternative Practices on Net Global Warming Potential and Greenhouse Gas Intensity from Rice-Wheat Annual Rotation in China

Background: Evaluating the net exchange of greenhouse gas (GHG) emissions in conjunction with soil carbon sequestration may give a comprehensive insight on the role of agricultural production in global warming. Materials and Methods: Measured data of methane (CH4) and nitrous oxide (N2O) were utilized to test the applicability of the Denitrification and Decomposition (DNDC) model to a winter wheat - single rice rotation system in southern China. Six alternative scenarios were simulated against the baseline scenario to evaluate their long-term (45-year) impacts on net global warming potential (GWP) and greenhouse gas intensity (GHGI). Principal Results: The simulated cumulative CH4 emissions fell within the statistical deviation ranges of the field data, with the exception of N2O emissions during rice-growing season and both gases from the control treatment. Sensitivity tests showed that both CH4 and N2O emissions were significantly affected by changes in both environmental factors and management practices. Compared with the baseline scenario, the long-term simulation had the following results: (1) high straw return and manure amendment scenarios greatly increased CH4 emissions, while other scenarios had similar CH4 emissions, (2) high inorganic N fertilizer increased N2O emissions while manure amendment and reduced inorganic N fertilizer scenarios decreased N2O emissions, (3) the mean annual soil organic carbon sequestration rates (SOCSR) under manure amendment, high straw return, and no-tillage scenarios averaged 0.20 t C ha(-1) yr(-1), being greater than other scenarios, and (4) the reduced inorganic N fertilizer scenario produced the least N loss from the system, while all the scenarios produced comparable grain yields. Conclusions: In terms of net GWP and GHGI for the comprehensive assessment of climate change and crop production, reduced inorganic N fertilizer scenario followed by no-tillage scenario would be advocated for this specified cropping system.