Characteristics of CO₂ and CH₄Flux at Barley-Rice Double Cropping Field in Southern Part of Okayama

CO₂ and CH₄fluxes were measured in a barley-rice double cropping field over a one-year period. The characteristics of the fluxes in relation to field management and their seasonal variation were investigated in detail. Net ecosystem CO₂ exchange (NEE) and ecosystem respiration (RE) were estimated by the eddy covariance method. RE of the drained rice paddy was larger than that of the flooded rice paddy, because flood water restricted heterotrophic respiration and below-ground autotrophic respiration. Gross primary production showed seasonal variation corresponding to each crop growth. As a result, NEE in barley, rice and the fallow period was -255, -350 and 60 gC m^-2, respectively. CH₄flux showed diurnal variation, peaking during daytime; its value increased during the course of flood days and showed good agreement with air temperature. Finally, we obtained rough estimates of net biome production (NBP).