Studies on the Gaseous Environment in Soil (4)

The Distribution of CO₂ Concentration in a Soil and Its Diurnal Change

Abstract

The relation between the distributions of the CO₂ concentration in soils and soil structures, as defined by CO₂ diffusion coefficient, was investigated. Changes in the distribution when the CO₂ concentration in a greenhouse had a diurnal variation also were investigated.
In the soil column in which the CO₂ diffusion coefficient was constant, the pattern of distribution expressing the relation between the CO₂ concentration and depth was an upward convex curve.
In the soil column in which the diffusion coefficient decreased with depth, the CO₂ concentration formed a distribution pattern that increased linearly with depth.
In the soil column in which the lower layers with a small diffusion coefficient became thicker and upper layers with a larger coefficient topped on them, the pattern was a concave in the upper and convex in the lower layer.
In the soil column which had a smaller coefficient in the upper layers and a larger coefficient in the lower ones, the pattern was an upward convex curve.
Three distinct patterns were formed in soil structures difined by the diffusion coefficient : 1) convex upward, 2) straight, 3) concave in the upper layer and convex in the lower layer.
These patterns did not vary unless the soil structures changed, even when the CO₂ concentration in a greenhouse changed diurnally.
The required ventilation hours to maintain the CO₂ concentration in a greenhouse differed depending upon whether the amounts of CO₂ generated from soil surface were constant during the whole day or were proportional to the difference between the CO₂ concentrations in the greenhouse and in the soil surface.