Contribution of CH4 produced in rice paddies to the global CH4 budget

CH4 release rates from rice paddies have been measured at several paddy fields in Spain, USA and Italy. The results show strong seasonal variations of the CH4 release rates with maximum values at the end of the flowering stage. The CH4 release rates averaged over the total vegetation period range between 4 and 17 mg CH4/qm h resulting in a worldwide CH4 emission by rice paddies of 33-83x10 E12 g/yr or 10-20% of the global atmospheric CH4 budget in 1979. Because of the smaller harvest area of rice paddies, the CH4 emission in 1950 accounts for about 20-51x10 E12 g/yr indicating an increase of the CH4 emission rates by rice paddies of about 1-2% per year. The CH4 release rates from rice paddies show daily variations with maximum values in the afternoon correlating with the soil temperatures. Most of the CH4 produced in the rice paddy soil is emitted into the atmosphere due to diffusion through the rice plant. Transport by bubbles seems to be of minor importance. (IFU)