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Effect of Soil Properties on Unsaturated Hydraulic Conductivity Pore-Interaction Factors

North Dakota State Water Commission, 900 East Boulevard, Bismarck, ND 58505

*Corresponding author.

ABSTRACT

The variability of the pore-interaction factor, , for a microscopic model proposed for predicting unsaturated hydraulic conductivity, K(), from soil water-retention, (), data was examined in relation to soil particle-size data and indices, bulk density, organic C, parameters for the van Genuchten () function, an index (W) of total energy of drainage and soil-series, toposequential, and geographic groupings. The exhibited no trend relationship to any of the soil properties tested. However, a change in the distribution of was observed in relation to the geometric-mean particle diameter (G_d) and other soil textural variables. For G_d < 0.08 mm, variability was much larger than for soils with G_d 0.08 mm. The latter consisted entirely of soils in the sand and loamy sand textural groups. A similar distributional relationship also occurred for vs. W. Examination of on three sites of the Hecla soil series and on related toposequential soils indicated that classification of on the basis of soil series or of soil-association groupings is a feasible strategy for parameter estimation on some soils. The exponential factor for a macroscopic model was also investigated. The was found to be related to W as an exponential function over the full data range. However, vs. W was nearly identical to a linear function for W data extending from 0 to 400 cm- (where is the density of water). The was also strongly related to G_d as a power function, and to other textural variables as exponential functions. The increasing slope of the power function for G_d < 0.08 mm indicated a large potential error of prediction for K() on fine-textured soils.

Contribution from the North Dakota State Water Commission.

Received for publication January 19, 1990.

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