Characterization of methane emissions from rice fields in Asia. I. Comparison among field sites in five countries

The Interregional Research Program on Methane Emissions from Rice Fields established a network of eight measuring stations in five Asian countries. These stations covered different environments and encompassed varying practices in crop management. All stations were equipped with a closed chamber system designed for frequent sampling and long-term measurements of emission rates. Even under identical treatment-e.g., continuous flooding and no organic fertilizers-average emission rates varied from 15 to 200 kg CH4 ha(-1) season(-1). Low temperatures limited CH4 emissions in temperate and subtropical stations such as northern China and northern India. Differences observed under given climates, (e.g., within the tropics) indicated the importance of soil properties in regulating the CH4 emission potential. However, local variations in crop management superseded the impact of soil- and climate-related factors. This resulted in uniformly high emission rates of about 300 kg CH4 ha(-1) season(-1) for the irrigated rice stations in the Philippines (Maligaya) and China (Beijing and Hangzhou). The station in northern India (Delhi) was characterized by exceptionally low emission rates of less than 20 kg CH4 ha(-1) season(-1) under local practice. These findings also suggest opportunities for reducing CH4 emission through a deliberate modification of cultural practice for most irrigated rice fields.