Spatial and Temporal Variations of Methane Flux from a Rice Paddy Field

Abstract

Methane (CH4) flux from paddy fields to the atmosphere were studied in a Japanese paddy field for three cultivation periods by using a closed-chamber method. Spatial variations of CH4 flux, having CV range from 19 to 47%, were observed within the individual plots when a chamber having a cross-sectional area of 0.09 m2 was used. CH4 fluxes showed a diurnal variation which closely correlated with soil temperature in the surface layer. The flux was doubled with the increase in the soil temperature from 25 to 35°C at the depth of 2 cm. Pronounced seasonal variations of CH4 flux were observed during cultivation periods. The variations of CH4 flux during a cultivation period were related to the change of soil Eh, at a depth of 2 cm. Annual emission rates of CH4 from the mineral (control) and the rice straw plot were in the ranges 8.2–40.6 and 27.0–43.1 g m-2, respectively, in the three cultivation periods. The soil Ehhad a significant influence on the annual variation of the CH4 flux, resulting in large interannual variations of CH4 emission. These results indicate that variation of the redox potential in surface soil layer, which results from water management, has a strong influence on CH4 emission from paddy fields.