Combination of modified nitrogen fertilizers and water saving irrigation can reduce greenhouse gas emissions and increase rice yield

The combined impacts of modified nitrogen (N) fertilizers and water saving irrigation (WSI) on greenhouse gas (GHG) emissions and grain yield of rice paddies have not previously been documented. GHG emissions from rice paddies under modified N fertilizers and WSI deserve attention because water and N are being used extensively to attain higher grain yield. A field experiment was conducted to evaluate the influence of modified N fertilizers and WSI on methane (CH4) and nitrous oxide (N2O) emissions and grain yield in rice paddies. Four treatments were applied: urea with conventional irrigation (U + CI), urea with shallow water depth with alternate wetting-drying water saving irrigation (U + SWD), polymer-coated controlled release urea with SWD (CRU + SWD), and nitrapyrin-urea composition plus hydroquinone with SWD (NU + HQ + SWD). Compared to U + CI, CH4 emissions significantly decreased by 26% and 31%, and N2O emissions increased by 52% and 42% under U + SWD in the early and late rice growing seasons respectively (p < 0.05). Although SWD increased N2O emissions, total GHG emissions (TGHG) reduced by 20% and 25% in the two rice seasons under U + SWD, and GHG emission intensity (GHGI) decreased by 24% on average. Modified N fertilizer applications also affected grain yield and GHG emissions under SWD. Compared with U + SWD, CRU + SWD and NU + HQ + SWD reduced CH4, N2O emissions and TGHG by 28-49%, 12-44% and 26-45%, respectively, while grain yield increased by 6-35%. Reduction in CH4 emissions occurred because, compared to urea, CRU and NU + HQ can inhibit CH4 production and transport by controlling development of invalid tillers, while their nitrogen release patterns were more favorable for CH4 consumption. In summary, modified N fertilizers in combination with SWD are a win-win strategy to improve grain production while reducing GHG emissions in the rice cropping system.