Determining water content and bulk density: The heat-pulse method outperforms the thermo-TDR method in high-salinity soils
2022
Peng, Wei | Lu, Yili | Wang, Mengmeng | Ren, Tusheng | Horton, Robert
Heat-pulse (HP) and thermo-time domain reflectometry (thermo-TDR) methods have been used to determine soil thermal properties, water content (θ) and bulk density (ρb) 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 θ and thermal property values of packed soil columns with various textures, saturations and bulk electrical conductivities (σₐ). The thermo-TDR and HP-based methods for estimating ρb values were also evaluated. The results showed that: (1) at σₐ values lower than 1.0 dS m⁻¹, the TDR method provided reliable θ with relative errors within 5%; salt effects became apparent at σₐ values greater than 1.0 dS m⁻¹ due to the distortion of TDR waveforms; the TDR method failed to estimate θ at σₐ > 2.71 dS m⁻¹ because the 2nd reflection point on the waveform was undetectable; (2) salinity had negligible effects on soil thermal property values in the studied range (σₐ < 7.59 dS m⁻¹), and the HP-based approach was able to derive θ and ρb values from thermal property measurements, with root mean square errors within 0.02 m³ m⁻³ for θ and within 0.12 Mg m⁻³ for ρb. Thus, the HP-based approach outperformed the thermo-TDR approach for determining θ and ρb values in soils with σₐ > 1.0 dS m⁻¹.
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