Relationship between thermal and electrical conductivity curves of soils with a unimodal pore size distribution: Part 2. Estimating bulk electrical conductivity from thermal conductivity

Abstract

Soil thermal conductivity (λ) and electrical conductivity (σ) influence heat conduction and electrical conduction through soils. In Part 1 of this two-part series, we demonstrated that for soils with a unimodal pore size distribution, the λ and σ curves were interrelated and could be described with a unified series–parallel resistor model. Based on the conceptual model presented in Part 1, the “mirror image” phenomenon in the λ-σ relationship was further evaluated. Starting with the Lu et al. (2007) λ model, the “mirror image” phenomenon was used to derive a new normalized σ model. The new σ model was dependent on degree of water saturation (S), and shared the same shape parameters as those in the λ model. Here, the new σ model is examined using new datasets consisting of simultaneous thermo-TDR sensor measurements of soil water content (θ), λ and σ. New model σ values interpolated between known dry and saturated σ values agreed well with measured σ values, with RMSE values within 0.102 dS m−1 and bias values between −0.083 and 0.014 dS m−1 for a variety of soil samples. Using repeated in situ λ measurements made in soils during an evaporative drying period, the new σ model estimated normalized σ values with RMSEs within 0.015 dS m−1. The new σ model offers an effective way to estimate σ of unsaturated soils.