A four-year record of methane emissions from irrigated rice fields in the Beijing region of China

Methane (CH4) emissions from irrigated rice fields were measured using an a utomatic sampling-measuring system with a closed chamber method in 1995-98. Average emission rates ranged from 11 to 364 mg m(-2) d(-1) depending on s eason, water regime, and fertilizer application. Crop management typical fo r this region (i.e., midseason drainage and organic/mineral fertilizer appl ication) resulted in emission of 279 and 139 mg CH4 m(-)2 d(-1) in 1995 and 1997, respectively. This roughly corresponds to emissions observed in othe r rice-growing areas of China. Emissions were very intense during the tille ring stage, which accounted for 85% of total annual emission, but these wer e suppressed by low temperature in the late stage of the season. The local irrigation practice of drying at mid-season reduced emission rates by 23%, as compared with continuous flooding. Further reduction of CH4 emissions co uld be attained by (1) alternate flooding/drying, (2) shifting the drainage period to an earlier stage, or (3) splitting drainage into two phases (of which one is in an earlier stage). Emission rates were extremely sensitive to organic amendments: seasonal emissions from fields treated with pig manu re were 15-35 times higher than those treated with ammonium sulfate in the corresponding season. On the basis of identical carbon inputs, CH4 emission potential varied among organic amendments. Rice straw had higher emissions than cattle manure but lower emissions than pig manure. Use of cultivar Zh ongzhuo (modern japonica) reduced CH4 emission by 56% and 50%, in 1995 and 1997, respectively, as compared with Jingyou (japonica hybrid) and Zhonghua (tall japonica). The results give evidence that CH4 emissions from rice fi elds in northern China can be reduced by a package of crop management optio ns without affecting yields.