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Three-Parameter Soil-Water Transient Equations in Horizontal Water-Transport Analysis

Dep. de Fisica e Biofisica, State Univ. of São Paulo, Botucatu, Brazil

D. Swartzendruber^*

Dep. of Agronomy, Univ. of Nebraska, Lincoln, NE 68583

*Corresponding author.

ABSTRACT

For data obtained from horizontal soil column experiments, the determination of soil-water transport characteristics and functions would be aided by a single-form equation capable of objectively describing water content vs. time t at given position x_t. Our study was conducted to evaluate two such possible equations, one having the form of the Weibull frequency distribution, and the other being called a bipower form. Each equation contained three parameters, and was fitted by nonlinear least squares to the experimental data from three separate columns of a single soil. Across the range containing the measured data points obtained by gamma-ray attenuation, the two equations were in close agreement. The resulting family of (x_f,t) transients, as obtained from either equation, enabled the evaluation of exponent n in the tⁿ dependence of the positional advance of a given . Not only was n found to be <0.5 at low values, but it also increased with and tended toward 0.5 as approached its sated (near-saturated) value. Some quantitative uncertainty in n() does arise due to the reduced number of data points available at the higher water contents. Without claiming non-Boltzmann behavior (n < 0.5) as necessarily representative of all soils, we nonetheless consider n() to be worthy of further study for evaluating its significance and implications.

Contribution from the Agricultural Research Division, Univ. of Nebraska-Lincoln; Journal Series Paper no. 11628; supported also by Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, CNPq, Brazil.

Received for publication August 28, 1997.