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Determination of Sorptivity based on In-situ Soil Water Redistribution Measurements¹

ABSTRACT

A simple, physically based algebraic equation is derived for calculating sorptivity as a function of antecedent soil water content. The wetting front matric pressure head, H_f, determined from the field profile redistribution data in a previous study, is utilized in an equation which gives sorptivity, S, as a function of fillable porosity, i.e., the difference between the satiated and antecedent soil water content, (_s – _i), satiated hydraulic conductivity, K_s, and wetting front matric pressure head, H_f, namely, S² = –2(_s – _i)K_sH_f. The final equation gives S explicitly as a function of antecedent water content, _i, with _s and K_s being constants for a given soil. The calculated sorptivity is assessed by its use in the Talsma-Parlange infiltration equation and subsequent comparison of predicted and measured infiltration. The method was tested on seven different sites with 14 infiltration measurements on Oxisol soils of Hawaii. The percentage error between predicted and measured cumulative infiltration ranged from 2.1% to 51.9%, with an average error of 21.8% for the 14 comparisons.

¹ Contribution from Dep. of Forestry, Southern Illinois University, Carbondale, IL 62901.

² Assistant Professor, Dep. of Forestry, Southern Illinois University, Carbondale, IL 62901; Professor, Dep. of Agronomy and Soil Science, University of Hawaii; and Research Soil Physicist, USDA Water Quality Management Laboratory, Durant, Okla., respectively.

Received for publication February 3, 1981. Accepted for publication October 21, 1981.