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 es tablished a network of eight measuring stations in five Asian countries. Th ese stations covered different environments and encompassed varying practic es in crop management. All stations were equipped with a closed chamber sys tem designed for frequent sampling and long-term measurements of emission r ates. Even under identical treatment-e.g., continuous flooding and no organ ic fertilizers-average emission rates varied from 15 to 200 kg CH4 ha(-1) s eason(-1). Low temperatures limited CH4 emissions in temperate and subtropi cal stations such as northern China and northern India. Differences observe d under given climates, (e.g., within the tropics) indicated the importance of soil properties in regulating the CH4 emission potential. However, loca l variations in crop management superseded the impact of soil- and climate- related factors. This resulted in uniformly high emission rates of about 30 0 kg CH4 ha(-1) season(-1) for the irrigated rice stations in the Philippin es (Maligaya) and China (Beijing and Hangzhou). The station in northern Ind ia (Delhi) was characterized by exceptionally low emission rates of less th an 20 kg CH4 ha(-1) season(-1) under local practice. These findings also su ggest opportunities for reducing CH4 emission through a deliberate modifica tion of cultural practice for most irrigated rice fields.