Impact of Soil Salinity on the Relation Between Soil Moisture and Dielectric Permittivity

Soil complex dielectric permittivity spectrum depends mainly on soil volumetric water content and salinity, but other soil properties such as temperature, density and clay content can also significantly impact its dielectric properties. Especially, the influence of soil salinity and texture can have significant impact on the accuracy of moisture determination with the use of soil moisture-dielectric permittivity calibration curves. The paper deals with the impact of soil salinity on the real part of complex dielectric permittivity of soils of various texture. Soil samples of various moisture content and salinity were measured with the use of a coaxial transmission-line cell connected to a one-port vector-network-analyzer in the 0.01-3 GHz frequency range. The relations between soil moisture and the real part of dielectric permittivity at frequencies of 30, 70, 150, 200, 500 and 1000 MHz were examined and the frequency bands with the smallest impact of soil salinity and particle-size distribution were obtained. For the tested soils it occurred that the optimal frequency bands were located between 150 and 500 MHz.