EFFECTS OF BULK DENSITY AND SOIL TYPE ON THE GAS DIFFUSION COEFFICIENT IN REPACKED AND UNDISTURBED SOILS.

The gas diffusion coefficient in soil is affected by several soil physical parameters, including (1) air-filled porosity, (2) bulk density, (3) soil disturbance, (4) the kind of diffusion gases, and (5) soil texture. From the measurement of the relative gas diffusion coefficient (D/D0) of alluvial and volcanic soils, the effects of (2), (3), and (4) on D/D0 were evaluated. Gas diffusion coefficients of sieved, repacked and of undisturbed soil samples were measured in the laboratory. The gas diffusion coefficient of soil increased with bulk density at the same air-filled porosity in both soil types because the proportion of the effective pore space for gas diffusion relatively increased during the compaction procedure. In alluvial soil, the gas diffusion coefficients of undisturbed samples were higher than those of disturbed samples because of the presence of macropores and cracks in the undisturbed samples. The apparent D/D0 of CO2 gas was larger than for O2 and N2 because of differences in the solubilities of the gases.