Diurnal variation of methane emission from paddy fields at different growth stages of rice cultivation in Taiwan

Paddy fields are one of the major anthropogenic sources of methane emission . Methane emission from paddy fields can vary with the growth stages of the rice (Oryza sativa L.) plant and daily environmental conditions. There are two crop seasons in Taiwan, the first crop season is from low to high temp erature (February-June), and the second crop season is reversed (August-Dec ember). The objective of this study was to investigate the effect of growth stages and daily environmental conditions on methane emission from a paddy field at the Agricultural Experimental Station of National Taiwan Universi ty in Taipei (25 degrees 1'30"N, 121 degrees 31'30"E). Methane emission rat e was high at the rice booting and the flowering stages and low at the tran splanting and the ripening stages in the first crop season; while it was hi gh at the transplanting and the active tillering stages and low from the bo oting to the ripening stages with intermittent irrigation system. Continuou s flooding treatment significantly enhanced methane emission at the floweri ng and the ripening stages in the first crop season. Methane emission rate was high from 12 a.m. to 3 p.m., and low from 2 to 5 a.m. Methane emission showed high correlation coefficient with air temperature, and low correlati on with Light intensity. Methane emission in the second crop season (13.7-2 8.9 g m(-2)) was about 2-5-fold higher than that in the first crop season ( 2.6-11.7 g m(-2)). This phenomenon was reversed in continuous flooding trea tment. Estimated total methane emission from Taiwan paddy fields in 1996 wa s between 27,352 and 69,060 Mg with intermittent irrigation system, which w as lower than 231,147 Mg calculated by the IPCC method with continuous floo ding treatment. Intermittent irrigation is a useful approach to reduce emis sions in paddy fields. (C) 1999 Elsevier Science B.V. All rights reserved.