Changes in the concentrations and fluxes of CO2 were monitored to a depth of 100 cm in an Andisol, under both fallow and soybean crops for a period of 1 year. Gas flux was calculated by the diffusion equation. Diel concentrations at depths less than 40 cm followed a sinusoidal pattern similar to that of the soil temperature, with the highest value being recorded in the daytime. Heavy rainfall, which closed the air pathways to the atmosphere, resulted in a higher CO2 concentration in the shallow soil layers. The subsequent decrease in the concentration in the shallow layers was accompanied by an increase for a few days in concentrations in the deeper soil layers. CO2 concentration under fallow increased with depth throughout the year except after heavy rainfall. CO2 concentration under soybean reached maximum values at depths that increased gradually from 20 to 80 cm during the growing season, suggesting the effect of root elongation. Upward CO2 fluxes decreased with depth in both fields, and the fluxes in the soil profile were high in summer and low in winter. CO2 fluxes in the upper and middle parts of the profile under soybean were higher than those under fallow during the growing season. CO2 fluxes from the soil surface calculated by the diffusion equation and measured by the closed chamber method showed a correlation coefficient of 0.89 except after heavy rainfall. Total CO2 fluxes from the surface estimated from measurements throughout a year were 3522 g m−2 under fallow and 4975 g m−2 under soybean. The downward flux of CO2 dissolved in the soil water was found to be negligible in comparison with the CO2 flux from the soil surface.
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Osozawa et al. (1995) studied this question.