Evaluating the linear dielectric constant-electrical conductivity model using time-domain reflectometry

Recently, Hilhorst (2000) presented a theoretical model describing a linear relationship between bulk electrical conductivity, o0, and dielectric constant, K„, in moist soil. Hilhorst (2000) found that using this linear relationship, measurements of the pore water electrical conductivity, ap, can be made in a wide range of soil types without soil-specific calibrations. If accurate measurements were to be made, only one parameter had to be optimized. In the present study, the linear model was evaluated using detailed time-domain reflectometry (TDR) measurements in coarse sand, medium sand and loamy sand. It was shown that the measured slope of the linear model was lower than expected. A reason for this might be that the Ka of the pore water is smaller than that of free water due to the presence of bound water. The results showed that the linear model was as good as other commonly used models for o,, predictions.