Greenhouse gas emissions from northeast China rice fields in fallow season

CH4, N2O and CO2 emissions from northeast Chinese rice fields were measured in the fallow season (November to March) to investigate the effects of freezing-thawing on the emissions. Both CH4 emission from and atmospheric CH4 oxidation by the soil occurred, but the flux was small. During the fallow season, rice fields acted as a minor source of atmospheric CH4, which accounted for about 1% of the CH4 emission during the rice growing period. The field was also a substantial source of atmospheric N2O, which ranged between 40 to 77 mg m(-2) and accounted for 40%-50% of the annual N2O emission. The largest N2O flux was observed in the thawing period during the fallow season. Laboratory incubation tests showed that the largest N2O flux came from the release of N2O trapped in frozen soil. Tillage and rice straw application (either mulched on the soil surface or incorporated in the soil) stimulated the CH4 and CO2 emissions during the fallow season, but only straw application stimulated N2O emission substantially.