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

Abstract

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 temperature (February–June), and the second crop season is reversed (August–December). 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 University in Taipei (25°1′30″N, 121°31′30″E). Methane emission rate was high at the rice booting and the flowering stages and low at the transplanting and the ripening stages in the first crop season; while it was high at the transplanting and the active tillering stages and low from the booting to the ripening stages with intermittent irrigation system. Continuous flooding treatment significantly enhanced methane emission at the flowering 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 correlation with light intensity. Methane emission in the second crop season (13.7–28.9 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 treatment. Estimated total methane emission from Taiwan paddy fields in 1996 was between 27,352 and 69,060 Mg with intermittent irrigation system, which was lower than 231,147 Mg calculated by the IPCC method with continuous flooding treatment. Intermittent irrigation is a useful approach to reduce emissions in paddy fields.