Effect of mid-season drainage on CH4 and N2O emission and grain yield in rice ecosystem: A meta-analysis.

Highlights • Mid-season drainage decreased CH 4 emission while increased N 2 O emission. • Mid-season drainage decreased the global warming potential (GWP). • Increasing drainage times did not affect the response of GWP to mid-season drainage. • Organic matter amendment did not affect the response of GWP to mid-season drainage. • GWP decreased under mid-season drainage when N fertilizer rate increases. Abstract Paddy rice cultivation is an important source of global anthropogenic methane emissions. Drainage the flooded soils can reduce methane substantially, but N 2 O emission occur concurrently, which would offset the reduction of methane emission. It remains unclear how mid-season drainage affects the global warming potential (GWP) of CH 4 and N 2 O emissions. In this study, a meta-analysis was conducted to investigate the effect of mid-season drainage on GWP and the factors that control the response of GWP to mid-season drainage. Results showed that mid-season drainage decreased CH 4 emission by 52% while increased N 2 O emission by 242%. The GWP under mid-season drainage decreased by 47% compared to continuously flooding. The yield-scaled GWP under mid-season drainage decreased by 48%. Mid-season drainage had no effect on rice grain yield. Although soil drainage times and organic matter amendment are important factors affecting CH 4 and N 2 O emissions in rice paddy field, the study showed that neither of them had effect on the response of GWP to mid-season drainage. The reduction rate of the GWP under mid-season drainage increased when N fertilization application rate increases from 50 kg ha−1 to >200 kg ha−1. This study demonstrated that CH 4 is still a dominant greenhouse gas in rice paddies under water management with mid-season drainage. Nitrogen fertilization is an important factor that regulates the response of GWP to mid-season drainage. High nitrogen fertilization rate would decrease the overall emission of CH 4 and N 2 O under mid-season drainage. However, increasing drainage times or applying organic fertilizer under mid-season does not change the overall emission rate of CH 4 and N 2 O. [ABSTRACT FROM AUTHOR]