Comparison of Twelve Dielectric Moisture Probes for Soil Water Measurement under Saline Conditions

Recently the research on the determination of soil water content and electrical conductivity using automated technique has received tremendous attention. Selecting the type of system that should be used for soil water measurement under saline conditions depends on its precision. A laboratory study was carried out to measure the soil water content (θ) and soil solution electrical conductivity (EC_w) using eight portable dielectric moisture probes namely ML1, ML2, MP4, WET, SK8, MIN, EC2 and SM2 and four profile probes namely ES, AG, P1 and P2. Air-dried Tottori sand dune soil was converted into saline by NaCl solutions of various concentrations. The out-put results of moisture probes showed that measurement accuracy was strongly dependent on the concentration of salt in the soil. Among the sensors WET, EC2 and ES exhibited higher sensitivity to the salts and over estimated water content by 0.04-0.08 cm³ cm^-3 whereas MP4, WET, SM2, ES, AG and P1 sensors also over estimated the volumetric water content by 0.02-0.03 cm³ cm^-3 at 3.83 dS m^-1 soil salinity as compared to normal soil. Higher EC_w increased the relative error of soil water measurement across the sensors. Among the moisture meters, commercially available ML1, ML2, SK8 and P2 gave sufficient accuracy in the presence of salts.