Volumetric soil water content measured by capacitance probe and its dependence on salinity

Dielectric sensors have been largely used to monitor soil water content due to their practicality and viability to automation. However, researches have been pointed out the sensitivity of those sensors under saline conditions. The aim of this paper is to analyze the influence of electrical conductivity of the solution applied on soil (EC_w) on the volumetric water content estimated by the GS3 capacitance probe, on sandy soil. The experiment was carried out in pots at the Ben Gurion University of the Negev, Israel. The soil was artificially salinized with saline solutions at increasing electrical conductivities (EC_w: 0.31, 2.5, 4.35, 8.75, 16.4 and 23.6 dS m^–1) and soil volumetric water content (VWC: 0.11, 0.16, 0.24 and 0.32 m³ m^–3). The volumetric water content of the soil estimated with the GS3 capacitance probe and the measured dielectric permittivity (Ka) was compared to gravimetric method. Solution EC_w influenced the estimated soil volumetric water content, though the variation on salinity up to 8.75 dS m^–1 did not have a significant effect on sensor calibration, which facilitates the use of GS3. However, it was found that for precise estimation of VWC in sandy soil a simple calibration should be performed. On the high salinity test, there was overestimation of soil volumetric water content, reaching values higher than saturation point. This indicates a limitation for GS3 sensor at EC_w > 16.4 dS m^–1.