Estimating soil water retention curves from soil thermal conductivity measurements

Abstract

The soil water retention curve represents the relationship between soil water content (θ) and matric potential (ψ). The van Genuchten (vG) model is commonly used to characterize the shape of a θ(ψ) curve. Based on the similarities between θ(ψ) curves and soil thermal conductivity (λ) versus θ curves, Lu and Dong proposed a unified conceptual λ(θ) model (LD model) for estimating λ(θ) curves from θ(ψ) curves. Their work makes it possible to relate the shapes of λ(θ) curves to θ(ψ) curves. In this study, we present an empirical approach to estimate the vG model parameter m from the LD model shape parameter p based on a model calibration with θ(ψ) and λ(θ) datasets obtained from 10 soils. The saturated water content θs and the vG model parameter α are estimated from selected soil properties (i.e., bulk density, particle density, particle size distribution and organic carbon content), and the residual water content θr is estimated from the LD model parameter θf. For model evaluation, the θ(ψ) curves of six soils were estimated from measured λ(θ) values and selected soil properties, and were compared to direct θ(ψ) measurements. The proposed method performed well with root mean square errors of estimated θ values ranging from 0.015 to 0.052 cm3 cm-3 and bias ranging from -0.009 to 0.040 cm3 cm-3. We conclude that the proposed method accurately estimates θ(ψ) curves from λ(θ) curves and selected soil properties.