Seasonal variations of CH4 and N2O emissions in response to water management of paddy fields located in Southeast China.

Water management is one of the most important practices that affect methane (CH(4)) and nitrous oxide (N(2)O) emissions from paddy fields. A field experiment was designed to study the effects of controlled irrigation (CI) on CH(4) and N(2)O emissions from paddy fields, with traditional irrigation (TI) as the control. The effects of CI on CH(4) and N(2)O emissions from paddy fields were very clear. The peaks of CH(4) emissions from the CI paddies were observed 1-2d after the water layer disappeared. Afterward, the emissions reduced rapidly and remained low until the soil was re-flooded. A slight increase of CH(4) emission was observed in a short period after re-flooding. N(2)O emissions peaks from CI paddies were all observed 8-10d after the fertilization at the WFPS ranging from 78.1% to 85.3%. Soil drying caused substantial N(2)O emissions, whereas no substantial N(2)O emissions were observed when the soil was re-wetted after the dry phase. Compared with TI, the cumulative CH(4) emissions from the CI fields were reduced by 81.8% on the average, whereas the cumulative N(2)O emissions were increased by 135.4% on the average. The integrative global warming potential of CH(4) and N(2)O on a 100-year horizon decreased by 27.3% in the CI paddy fields, whereas no significant difference in the rice yield was observed between the CI and TI fields. These results suggest that CI can effectively mitigate the integrative greenhouse effect caused by CH(4) and N(2)O emissions from paddy fields while ensuring the rice yield.