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Effect of Temperature-dependent Hydraulic Properties on Soil Water Movement¹

ABSTRACT

Thermal effects on the soil water regime are often ignored. In addition to the effects of temperature on the driving forces for flow, there are also direct thermal effects on the soil's hydraulic properties. Accounting for this temperature dependency of the soil's hydraulic properties, the pressure head form of the general flow equation of water was solved by the predictor-corrector method for different temperature regimes and for a variety of initial and boundary conditions. Corrections of soil hydraulic properties due to temperature changes were either based on experimental data extracted from the literature or on theoretical considerations. Temperature effects were found to be much more pronounced for a pressure head than for a flux boundary condition at the soil surface. For temperature varying with both time and depth, the effect seemed to be minimal if the hydraulic properties were determined at the mean temperature of the profile. The latter suggests that soil hydraulic properties determined in the laboratory, but to be used for field conditions, should probably be determined at a temperature that approaches the mean field soil temperature. The simulations also showed that temperature effects are more pronounced as the temperature coefficient of soil-water-pressure-head increases, but that the kind of effect depends on whether the existing temperature is above or below the reference temperature (temperature at which the hydraulic properties were determined).

¹ Contribution from the Alabama Agric. Exp. Stn, Auburn Univ., AL 36849. AAES Journal no. 3-84609.

² Graduate Research Assistant and Associate Professor of Soil Physics, respectively, Dep. of Agronomy and Soils, Auburn Univ., Auburn, AL 36849.

Received for publication April 16, 1984. Accepted for publication August 29, 1984.