Fig. 3 Calibration of the TDR-measured dielectric constant of the gypsum and the soil against matric potential for the – TDR probes. Bars indicate ± one standard deviation of measurement. For the gypsum, a calibration curve was established with r² = 0.998 using fitted parameters, _r = 3.158, _s = 21.452, = 0.0207, n = 3.150, and m = 0.228