Methane emissions and mitigation options in irrigated rice fields in southeast China

Methane (CH4) emissions from rice fields were monitored in Hangzhou, China, from 1995 to 1998 by an automatic measurement system based on the "closed chamber technique." The impacts of water management, organic inputs, and cu ltivars on CH4 emission were evaluated. Under the local crop management sys tem, seasonal emissions ranging from 53 to 557 kg CH4 ha(-1) were observed with an average value of 182 kg CH4 ha(-1). Methane emission patterns diffe red among rice seasons and were generally governed by temperature changes. Emissions showed an increasing trend in early rice and a decreasing trend i n late rice. In a single rice field, CH4 emissions increased during the fir st half of the growing period and decreased during the second half. Drainag e was a major modifier of seasonal CH4 emission pattern. The local practice of midseason drainage reduced CH4 emissions by 44% as compared with contin uous flooding; CH4 emissions could further be reduced by intermittent irrig ation, yielding a 30% reduction as compared with midseason drainage. The in corporation of organic amendments promoted CH4 emission, but the amount of emission varied with the type of organic material and application method. M ethane emission from fields where biogas residue was applied was 10-16% low er than those given the same quantity (based on N content) of pig manure. R ice straw applied before the winter fallow period reduced CH4 emission by 1 1% as compared with that obtained from fields to which the same amount of r ice straw was applied during field preparation. Broadcasting of straw inste ad of incorporation into the soil showed less emission (by 12%). Cultivar s election influenced CH4 emission, but the differences were smaller than tho se among organic treatments and water regimes. Modifications in water regim e and organic inputs were identified as promising mitigation options in sou theast China.