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Relationship between Initial Drainage of Surface Soil and Average Profile Saturated Conductivity

USDA-ARS, Great Plains Systems Research Unit, Natural Resources Research Center, P.O. Box E, Fort Collins, CO, 80522

O. Wendroth and D. R. Nielsen

Dep. of Land, Air and Water Resources, Univ. of California, Davis, CA 95616

*Corresponding author.

ABSTRACT

The measurement of soil hydraulic conductivity, and its spatial and temporal variability, by standard techniques is time consuming and expensive. With an objective to develop a simple field technique, we investigated answers to two questions: Is the change in soil water content of the surface soil, 2 d after a thorough wetting, related to an effective average saturated hydraulic conductivity, K_s, of the soil profile? Can the water content data be used to estimate spatial distribution of this average K_s? The evaluation was based on a theoretical analysis, using finite-element numerical solutions, for a spectrum of different-textured homogeneous soils, as well as experimental data of three U.S. soils and an international data set containing various soils. In most cases, there was a highly significant correlation between log-log transformations of an effective profile-average K_s (the steady-state infiltration rate or the harmonic-mean K_s of the soil profile) and the initial 2 d drainage of the surface soil. In three of the soils, the slope of these relationships was not significantly different from the homogeneous soils theoretical value of 2.53, whereas the slope was not significantly different from an empirical value of 2.0 in all cases. Spatial distributions (fractiles) of the scaling factors of the profile-average K_s estimated from the surface water content changes in 2 d, using a slope value of 2.0 to 2.5, were fair to good approximations of the measured distributions for most of the soils.

Received for publication January 24, 1992.