Hysteresis of Water Retention Curve of the Capillarimetric Diapason in Saline Soils

The hysteresis effect of water retention curve (WRC) has significant implications for comprehending soil water and salt transport, especially in areas with soil salinization. This study evaluates the hysteresis of WRC in saline soils by measuring the drying and wetting WRC of silty clay loam exposed to different salinities using a tension meter. We find that WRC is influenced by the superposition coupling effect of salinity and dry density, which results in an upward shift of WRC and increases the soil water holding capacity. In addition, soil matrix suction also rises with the increasing salt concentration, leading to a gradual upward shift in WRC. The presence of salt in pore spaces weakens the “ink-bottle” effect, disjoining pressure and air entrapment effect, results in a 30.9% reduction in hysteresis of WRC with increasing salinity. Additionally, the volumetric shrinkage of low dry density silty clay loam also weakens the WRC hysteresis. Furthermore, we utilized a WRC hysteresis model that considers the “ink-bottle” effect and entrapped air, which reasonably predicts the main wetting WRC of saline silty clay loam. The root-mean-square error and mean absolute error between predicted and measured values are 0.027–0.039 and 0.036–0.060, respectively. These findings are significant to the research and guidance of salinization in expansive soil and heavy textured soil area where salinization occurs.