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 been carried out to identify the relationship between bulk electrical conductivity (σa) and soil solution electrical conductivity (σw) to be used for transient conditions with varying water content. In this study, a single TDR probe was calibrated and found to accurately measure water content and σa. The σa measurements were fitted to σw using several previously published models. The accuracy of the σa and σw measurements increased with σa; however, the error in the σw estimation was <10% for σa higher than 5.7 mS m−1. The calibration was verified in a large sand column; σa measurements were fitted to σw measured in soil solution extracted with suction samplers. The calibration was also used in a transient solute transport experiment. If not accounted for, the temperature effects of the water content measurement introduce significant errors in the σw estimations.