Seasonal variations of CH4 flux, soil Eh and soil temperature were measured in paddy fields at Khon Kaen and Surin for the major and the second rice*. The average values of the fluxes measured for the major rice at Khon Kaen and Surin were 19.8 and 13.3 mg m-2 h-1, respectively, and for the second rice 15.1 and 15.4 mg m-2 h-1, respectively. High CH4 emission for the major rice at Khon Kaen was due to the high content of fresh organic matter, deep water depth and soil itself which has a low oxidizing capacity and low clay content. Moreover, the comparatively low CH4 flux recorded during the 67-day period after flooding in the major rice at Surin was caused by the decomposition of the easily decomposable part of fresh organic matter before flooding.
The estimated seasonal emission rates of CH4 for the major rice at Khon Kaen and Surin were 61.3 and 39.3 g m-2, respectively, and for the second rice 34.8 and 44.4 g m-2, respectively. Total CH4 emission from Thai paddy fields was estimated to be 3.7 Tg year-1 when the total paddy area was taken into consideration.