Abstract
The soil water content-pressure head curve (theta(h)), described by van Genuchten, was used to predict some hydraulic characteristics of a Xeric torriorthent soil. Experimental data of volumetric soil water content (theta) and pressure head (h) were adjusted to the model, obtaining the three independent parameters used to calculate the unsaturated soil hydraulic conductivity (K) and soil water diffusivity (D). The K(theta) functions for disturbed and undisturbed soil samples were statistically different pointing to the effect of soil structure on soil water flow. For soil moisture values close to saturation, K values were >/= 0.392 and >/= 0.019 cm hE1, for undisturbed and disturbed soils, respectively. These low values would reflect the loam texture of the soil studied. In absence of roots capable of absorbing water, a supply of more than 4 L mE2 hE1 will lead to water-logging and losses through evaporation and runoff.
Highlights
The relation between pressure head and volumetric water content in a soil is termed the soil water retention curve or soil moisture characteristic curve because each curve is characteristic of a given soil
The soil water content (q) and pressure head (h) data were fitted to the van Genuchten model [Eq 1]: q qs - qr [1 + (a·h)n ]m where qs and qr are the saturated and residual volumetric water content of the soil, respectively
The Mualem model established an equation for predicting the relative hydraulic conductivity (Kr) and soil water diffusivity (D) from knowledge of the soil water retention curve (Mualem, 1976)
Summary
The relation between pressure head and volumetric water content in a soil is termed the soil water retention curve or soil moisture characteristic curve because each curve is characteristic of a given soil. Both soil water retention curve and unsaturated hydraulic conductivity data are often necessary for solving unsaturated flow problems. The unsaturated hydraulic conductivity and diffusivity of disturbed soil samples were calculated before fitting to the van Genuchten soil water retention curve model (van Genuchten, 1980).
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