Improving the calibration of dielectric TDR soil moisture determination taking into account the solid soil

The influence of soil's solid phase on the dielectric constant of the soil over a range of moisture contents has been studied. Samples of soil, soil-like, and also other porous materials were analysed using Time Domain Reflectometry (TDR) to determine the contribution of bulk density and porosity to the function that relates dielectric constant to water content. The study showed that bulk density, and thus also porosity, substantially affects the relation between dielectric constant and water content. Two equivalent, empirical, normalized conversion functions were found, one accounting for bulk density and the other for porosity. Each of them reduced the root mean square error of the dielectric TDR determinations of moisture to 0.03, regardless of the material's bulk density and porosity.