Evaluation of Different Models for Estimating the Hydraulic Parameters and Thermal Conductivity of Pasture Unsaturated Soils.

A variety of empirical equations have been developed to estimate the soil hydraulic and thermal properties of unsaturated soils, which are necessary for many studies of water flow, and heat and solute transport but often are not measured because of financial as well as practical constraints associated with time- and labor-intensive methods and spatio-temporal heterogeneity of soil. This study was conducted to evaluate: (1) four closed-form unimodal analytical expressions, i.e., Brooks and Corey, van Genuchten, Kosugi, and Fredlund and Xing models to describe the soil water retention curve (SWRC) and to combine with pore-size distribution models to predict the unsaturated hydraulic conductivity function, and (2) four soil thermal conductivity (λ) predictive models, i.e., Johansen, Côté and Konrad, Balland and Arp, and Lu et al. models for pasture unsaturated soils. Soil samples (at soil depths of 0-5, 5-10, 10-15, and 15-20 cm) collected from semi-arid pastures under different drip-irrigated as well as dryland forage management systems were used to quantitatively compare the performance of models on pasture soils for selected SWRC- and λ-models. Model parameters were estimated by fitting these SWRC- and λ-models to the measured data.