Effects of reduced chemical fertilizer combined with straw retention on greenhouse gas budget and crop production in double rice fields

A two-year field investigation was conducted in a typical double rice region in South China. The treatments included conventional dose of nitrogen, phosphorus, and potassium fertilizers (NPKc); reduced chemical fertilizer combined with straw retention (NPKr+S); and no fertilizer as a control (CK). The global warming potential (GWP) was evaluated with nitrous oxide (N2O) and methane (CH4) emissions. The results showed that fertilization enhanced not only CH4 but also N2O emissions. For CK, NPKc, and NPKr+S, respectively, annual N2O emissions were 0.09, 0.47, and 0.33kgha(-1); and annual CH4 emissions were 562.4, 657.9, and 882.2kgha(-1). Consequently, the GWPs were 19,146, 22,507, and 30,094kgCO(2)-eqvha(-1)year(-1) for CK, NPKc, and NPKr+S, respectively. As rice grain yields were comparable between NPKc (9332kgha(-1)year(-1)) and NPKr+S (9261kgha(-1)year(-1)), the greenhouse gas intensity (GHGI) was significantly lower in NPKc compared with that in NPKr+S which induced more GWP. Overall, this study showed the potential of straw retention to reduce chemical fertilizer use. But it increased the GWP by 33.7% and GHGI by 34.7% in double rice systems under continuous flooding regime.