A radium-emanation method was developed for measuring the gas diffusion coefficient D in soils of differing structure and colloidal properties. The method was quick and simple, and could be carried out under natural, undisturbed soil conditions. Diffusion coefficients varied from 200 cm2/hour in coarse-textured soil to less than 5 cm2/hour in moderately fine-textured alkaline soil. The permeability was reduced by an increase in soil moisture, clay, and alkali content in the profile. When these factors varied with depth, the diffusion coefficient was not constant and the theoretical conditions of the method were not satisfied. Useful estimates were possible, however, when the apparent D values obtained at different depths were compared with other soil properties.

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