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Abstract
Diurnal variation in CH^sub 4^ 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. CH^sub 4^ 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 CH^sub 4^ efflux at tillering stage. Evidence also suggested that redox status in the rhizosphere region and atmospheric, soil, and water temperatures influenced CH^sub 4^ emission from rice fields probably by their contrasting effects on CH^sub 4^ production and oxidation.[PUBLICATION ABSTRACT]