Effect of timing and duration of midseason aeration on CH4 and N2O emissions from irrigated lowland rice paddies in China

Midseason aeration (MSA) of rice paddy fields functions to mitigate CH4 emission by a large margin, while simultaneously promoting N2O emission. Alternation of timing and duration of MSA would affect CH4 and N2O emissions from intermittently irrigated rice paddies. A pot trial and a field experiment were conducted to study the effect of timing and duration of MSA on CH4 and N2O emissions from irrigated lowland rice paddy soils in China. Four different water regimes, i.e., early aeration, normal aeration (the same as the local practice in timing and duration of aeration), delayed aeration, and prolonged aeration, were adopted separately and compared with respect to global warming potential (GWP) of CH4 and N2O emissions and rice yields as well. Total emission of CH4 from the rice fields ranged from 28.6 to 64.1 kg CH4 ha(-1), while that of N2O did from 1.71 to 6.30 kg N2O-N ha(-1) during the study periods. Compared with the local practice, early aeration reduced CH4 emission by 13.3-16.2% and increased N2O emission by 19.1-68.8%, while delayed aeration reduced N2O emission by 6.8-26.0% and increased CH4 emission by 22.1-47.3%. The lowest GWP of CH4 and N2O emissions occurred in prolonged aeration treatment, however, rice grain yield was reduced by 15.3% in this condition when compared with normal practice. It was found in the experiments that midseason aeration starting around D 30 after rice transplanting, just like the local practice, would optimize rice yields while simultaneously limiting GWPs of CH4 and N2O emissions from irrigated lowland rice fields in China.