Field measurements of soil electrical conductivity and water content by time-domain reflectometry

The ability to easily and simultaneously measure temporal distributions of both soil water content and soil salinity is desirable when conducting experiments designed to evaluate management practices in irrigated agriculture where saline waters are used. Soil salinity is related to soil electrical conductivity. Soil electrical conductivity and water content in a ridge-furrow tilled loamy sand irrigated with a salt solution were measured using time-domain reflectometry (TDR). The salt solution was 0.026 mol kg-1 NaCl which has the electrical conductivity of about 0.3 S m-1. A computer controlled multiplexer was used to acquire electrical conductivity and water content data from a metallic cable tester. Information in TDR traces related to water content and electrical conductivity was not appreciably affected by impedance mismatch within a rotary switch, used as a multiplexer. Soil water content and electrical conductivity of soil solution estimated from TDR agreed well with sampled data.