Quantifying direct N2O emissions in paddy fields during rice growing season in mainland China: Dependence on water regime

Various water management regimes, such as continuous flooding (F), flooding-midseason drainage-reflooding (F-D-F), and flooding-midseason drainage-reflooding-moist intermittent irrigation, but without water logging (F-D-F-M), are currently practiced in paddy rice production in mainland China. These water regimes have incurred a sensitive change in direct N2O emission from rice paddy fields. We compiled and statistically analyzed field data on N2O emission from paddy fields during the rice growing season (71 measurements from 17 field studies) that were published in peer-reviewed Chinese and English journals. Seasonal total N2O was, on average, equivalent to 0.02% of the nitrogen applied in the continuous flooding rice paddies. Under the water regime of F-D-F or the F-D-F-M, seasonal N2O emissions increased with N fertilizer applied in rice paddies. An ordinary least square (OLS) linear regression model produced the emission factor (EF) of nitrogen for N2O averaged 0.42%, but background N2O emission was not pronounced under the water regime of F-D-F. Under the F-D-F-M water regime, N2O EF and background emission were estimated to be 0.73% and 0.79 kg N2O-N ha−1, respectively, during the paddy rice growing season. Based on results of the present study and national rice production data, subsequently, direct N2O emissions during the rice growing season amounted to 29.0 Gg N2O-N with the uncertainty of 30.1%, which accounted for 7–11% of the reported estimates of annual total emission from croplands in mainland China. The results of this study suggest that paddy rice relative to upland crop production could have contributed to mitigating N2O emissions from agriculture in mainland China.