SOIL SOLUTION ELECTRICAL-CONDUCTIVITY MEASUREMENTS UNDER TRANSIENT CONDITIONS USING TIME-DOMAIN REFLECTOMETRY

Several studies have shown that time domain reflectometry (TDR) can be used to measure water content and solute concentration during steady- state experiments with constant soil water content. Few studies have b een carried out to identify the relationship between bulk electrical c onductivity (sigma(a)) and soil solution electrical conductivity (sigm a(w)) to be used for transient conditions with varying water content. In this study, a single TDR probe was calibrated and found to accurate ly measure water content and sigma(a). The sigma(a) measurements were fitted to sigma(w) using several previously published models. The accu racy of the sigma(a) and sigma(w) measurements increased with sigma(a) ; however, the error in the sigma(w) estimation was <10% for sigma(a) higher than 5.7 ms m(-1). The calibration was verified in a large sand column; sigma(a) measurements were fitted to sigma(w) measured in soi l solution extracted with suction samplers. The calibration was also u sed in a transient solute transport experiment. If not accounted for, the temperature effects of the water content measurement introduce sig nificant errors in the sigma(w) estimations.