Understanding evaporation from salinized soils in Xinjiang: Impact of sodium adsorption ratio, salt type, and concentrations

Arid regions in Northwest China were characterized by water scarcity and soil salinization problems. Understanding water evaporation behavior in salinized soils is crucial to quantify land water loss and control soil secondary salinization. This study aims to explore how specific components in irrigation water influence soil evaporation, focusing on soil pore-water composition, sodium adsorption ratio (SAR) in particular, and their concentrations. Soil columns saturated with different levels of salt concentration (C1, C2, and C3), SAR (S1, S2, and S3), and salt type (NaCl and CaCl₂) were placed in a Climate-Controlled Chamber and underwent evaporation for 20 days. The salt areal ratio, salt crust thickness, crust composition, and their mutual interactions with soil evaporation were investigated. Results show that CaCl₂ tends to precipitate as subflorescence, while NaCl as efflorescence. Subflorescence for the CaCl₂ treatment (1.192 mmol L⁻¹) inhibits evaporation, but takes no effect on evaporation for a C3 treatment (0.392 mmol L⁻¹), indicating that the evaporation rate will not be reduced if a lower salt concentration prevents internal precipitation from reaching the threshold for soil pore clogging. Under varying salt concentrations, SAR affects salt areal ratio ((Formula presented.)) differently, while increased salt concentration consistently accelerates (Formula presented.) regardless of SAR levels. Initially, the salt crust enhances evaporation (days 1–3), then suppresses it (days 3–10), and finally evaporation is primarily influenced by soil moisture content (after day 10).