Impact of salt precipitation on evaporation resistance under different soil textures

The impact of salt precipitation on evaporation in saline soil is an important issue with adverse effects for water management and soil ecosystem services. Although much is known about this issue, there is no agreement on the mechanism by which salt precipitation affects evaporation. In this study, soil column experiments with different textures (fine sand, sandy soil and silt loam) saturated with salt solution (sodium chloride) were employed to investigate the influence of salt crust on evaporation resistance, and a mathematical equation was proposed to quantify the evaporation resistance. The results show that salt commonly precipitated as efflorescence on different soil surfaces and inhibited evaporation, but that it exhibited significant differences. Salt crusts inhibited evaporation in saline soils with varied particle sizes by 18%, 24%, and 60%, while the corresponding pore sizes of salt crusts were 19.05 μm, 5.55 μm, and 0.94 μm, respectively. The salt crust on the soil surface with smaller particle size exhibited smaller pore size and poor pore connectivity, which resulted in greater configurational resistance to vapor flow through salt crust and increased evaporation resistance. The equation based on salt crust pore characteristics can effectively explain the differential mechanism of salt precipitation resistance to evaporation (R² > 0.96). These findings provide new insights into salt precipitation and water transport in saline soils.