The study aimed at evaluating of calibration models for two kinds of TDR waveguides used with Trase System and TDR 100 equipments linked to the cable tester or the multiplexer. Disturbed samples of three soils were packed in PVC columns and, after soil saturation, two TDR waveguides of three rods with capacitor and with resistor were inserted into the soil columns. The waveguides were connected to two TDR equipments (Trase System and TDR 100), directly to the cable tester or a multiplexer. Soil water content data by gravimetry were collected during the drying process from saturation to values close to the lowest limit of water availability. The readings were performed with TDR probes connected to the cable tester and the multiplexer. A mathematical model was fitted to the bulk dielectric constant (e) and water content data (q) and the performance of five models to obtain q as a function of e was evaluated. Results showed that there was no significant difference between the TDR Trase System capacitor waveguide calibration connected either directly to the water content analyzer or the multiplexer channel. In case of TDR 100 using waveguides with resistor, the calibration has to be performed according to the connection of the waveguide to the water content analyzer or the multiplexer channel. The cubic calibration model performed best, followed by the Roth model, which estimated the values of bulk dielectric constant and water content well with a closer to 0.5 for waveguides with capacitor than for waveguides with resistor.
soil water content; dielectric constant
