Water Vapor Sorption Isotherms of Salt-affected Soils

Salt-affected soils, including saline and alkali soils, cover about 7% of the land area on earth. Their interaction with water differs from non-saline soils, thereby exhibiting distinct fundamental properties and mechanical and hydrological behaviors. The soil–water interaction is generally assessed by water vapor sorption isotherm, i.e., the relationship between soil water content and ambient relative humidity under isotherm conditions. Yet to date, there still lacks a comprehensive dataset of water vapor sorption isotherms of salt-affected soils. This study presents a water vapor isotherm dataset encompassing six distinct soil types, ranging from sandy soil to expansive clayey soils. These soils were mixed with four salt types, including NaCl, KCl, MgCl 2 , and LiCl, at varying salt content, yielding 33 combinations of salt-affected soil samples. The results reveal three intriguing features of vapor sorption behaviors of salt-affected soils: (1) the presence of soil lowers the deliquescence relative humidity (DRH) of the salt in it, suggesting a potential interaction between soil solid and salt crystals; (2) the wetting–drying isotherm hysteresis of salt-affected soils significantly increase with salt content, even for non-expansive soils, implying a crystal nucleation process of salts in soils upon drying; and (3) sodium salt abnormally lowers adsorption capacity of Ca-montmorillonite in low RH range, demonstrating the existence of cation exchange between salt and interlayer cations. A parametric study is conducted to illustrate the implications of DRH on soil hydraulic conductivity curves, revealing that the breaking points in isotherms of salt-affected soils correspond to notable shifts in hydraulic behaviors.