In situ determination of electrical conductivity of potting media using time domain reflectometry

Abstract

The possibility of measuring both the volumetric water content (_{ν θ}) and bulk electrical conductivity (EC_b) of media using a single instrument makes time domain reflectometry (TDR) invaluable for greenhouse potting media _ν and EC_b determination. Laboratory experiments in three different potting media instrumented with triple‐wire TDR probes were performed to calibrate the TDR system for the determination of potting media water electrical conductivity (EC_w). The performance of the TDR for in situ determination of EC_w, using the experimentally‐determined conductivity model, was investigated using packed columns of potting media. Linear relationships between the EC_b‐EC_w data were found for all the tested media at the three water contents (0.30, 0.36, 0.45 cm³cm^‐3) for four solute concentrations ranging from 1.481 to 3.797 dS m^‐1. Linear regression coefficient of determination, r², of between 0.97 and 0.99 were achieved. Calibration accuracies ranged from 94% to 98% for EC_wpredictions. Results indicate that TDR is a useful technique for the accurate determination of potting media Ec_b. TDR allows determination of EC_w, from the measured EC_b and θ_ν, to be made quickly and simultaneously using a single and relatively inexpensive probe combined with the TDR cable tester.