New semi-empirical formulae for predicting soil solution conductivity from dielectric properties at 50 MHz

Abstract

Pore solution electrical conductivity ( σ w ) is an important measurement for agricultural and environmental applications. Salt concentration can be predicted from σ w and used to trace and monitor the transport of ionic solutes. Most models for predicting σ w rely also on measurements of volumetric water content ( θ v ). However, θ v dependent estimations of σ w are difficult to obtain because θ v measurements are not always available and because of the complex nature of physicochemical interactions between soil and water. Electromagnetic sensors offer an alternative approach because estimations of σ w can be obtained without direct knowledge of θ v . We developed two semi-empirical formulae for predicting σ w that are mathematically independent of θ v . The new models are dielectric equivalents of the Rhoades type two-pathway models that are based on linear and power law solutions for the transmission coefficient. The models were fitted by nonlinear regression to a data set collected from different soil textures, and disturbance treatments, to predict known electrical conductivities of ∼0, 1.23, 2.41, 2.02 and 3.96 dS m −1 . Average σ w predicted by the new models compared well to known saturating solution conductivities (average R 2 = 0.82 and average root mean square error of 0.80 dS m −1 ). The new models also compared well to models reported in the literature. The precision and accuracy of the estimates increased as σ w increased, which might be related to a reduction of the influence of soil solid phase components on the estimates as σ w becomes much higher than the solid phase conductivity.