DIURNAL-VARIATION IN METHANE EFFLUX AT DIFFERENT GROWTH-STAGES OF TROPICAL RICE

Diurnal variation in CH4 efflux from continuously flooded fields plant ed 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, p anicle 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 (ambie nt temperature: flood water temperature, redox potential, soil pH, and root oxidase activity), a significant negative correlation existed be tween oxidase activity of the root base and diurnal fluctuations in CH 4 efflux at tillering stage. Evidence also suggested that redox status in the rhizosphere region and atmospheric, soil, and water temperatur es influenced CH4 emission from rice fields probably by their contrast ing effects on CH4 production and oxidation.