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Soil Water Diffusivity from Horizontal Infiltration¹

ABSTRACT

A method has been developed for the measurement of soil water diffusivity. The method is based on gamma ray absorption measurements of the water content as a function of time at a fixed position in a horizontal infiltration system. The calculation of diffusivity is based on the assumption that the water content is a function of position divided by the square root of time. The variability of the data led to scatter in the diffusivity function especially at high water contents. This variability in the data can be traced mainly to the inability to obtain sufficiently accurate data from the recordings of the gamma ray counting system. When the diffusivity function thus obtained was used to predict the water content time relationship in the column, even though the function had been fit statistically, the results were largely dependent upon the wet end of the relationship.

¹ Contribution from the Corn Belt Branch, Soil and Water Conservation Research Division, USDA, and the Illinois Agr. Exp. Sta. This work was supported in part by NSF grant no. G18897 and GP4981.

² Soil Scientist (Research), USDA, and Assistant Professor of Soil Physics, University of Illinois; Professor of Soil Physics, University of Illinois; and Soil Scientist (Research), USDA, and Professor of Soil Physics, University of Illinois, Urbana, respectively.

Received for publication June 29, 1967. Accepted for publication October 16, 1967.