Determining water content and bulk density: The heat-pulse method outperforms the thermo-TDR method in high-salinity soils

Heat-pulse (HP) and thermo-time domain reflectometry (thermo-TDR) methods have been used to determine soil thermal properties, water content (theta) and bulk density (rho b) simultaneously. Their performances on salt-affected soils, however, remain unknown. This study investigated the effect of salinity on HP signals and thermo-TDR measured electromagnetic waveforms, and the derived theta and thermal property values of packed soil columns with various textures, saturations and bulk electrical conductivities (sigma a). The thermo-TDR and HP-based methods for estimating rho b values were also evaluated. The results showed that: (1) at sigma a values lower than 1.0 dS m-1, the TDR method provided reliable theta with relative errors within 5%; salt effects became apparent at sigma a values greater than 1.0 dS m- 1 due to the distortion of TDR waveforms; the TDR method failed to estimate theta at sigma a 7.59 dS m-1), and the HP-based approach was able to derive theta and rho b values from thermal property measurements, with root mean square errors within 0.02 m3 m- 3 for theta and within 0.12 Mg m- 3 for rho b. Thus, the HP-based approach outperformed the thermo-TDR approach for determining theta and rho b values in soils with sigma a 1.0 dS m-1.