Diurnal variation in methane efflux at different growth stages of tropical rice

Diurnal variation in CH4 efflux from continuously flooded fields planted to rice (Oryza sativa L. cv. IR-36) was examined at different crop growth stages using a closed chamber method during the wet season. CH4 emission showed a distinct diurnal pattern especially at tillering, panicle initiation and maturity stages of a field-grown rice crop, with maximum emission in the early afternoon (12.00 to 15.00) followed by a decline to a minimum around midnight. Among several variables (ambient temperature: flood water temperature, redox potential, soil pH, and root oxidase activity), a significant negative correlation existed between oxidase activity of the root base and diurnal fluctuations in CH4 efflux at tillering stage. Evidence also suggested that redox status in the rhizosphere region and atmospheric, soil, and water temperatures influenced CH4 emission from rice fields probably by their contrasting effects on CH4 production and oxidation.