Salinity Effects on Soil Structure and Hydraulic Properties: Implications for Pedotransfer Functions in Coastal Areas

Understanding the effects of salinity on soil structure and hydraulic properties is critical for addressing environmental challenges in coastal saline and sodic areas. In this study, soil samples were collected from a coastal region in eastern China to investigate how salinity affected the soil structure and hydraulic properties based on lab experiments. A comprehensive soil dataset was also compiled from the experimental results to develop a salinity-based pedotransfer function (PTF-S) tailored to the coastal environment. The results showed that salinity significantly altered the soil aggregate size distribution and hydraulic properties. Higher salinity promoted the formation of larger aggregates (0.25–2 mm), particularly in silty clay soil. Salinity positively correlated with the saturated hydraulic conductivity (K_s) in sandy loam soil, regardless of the cation type (Na⁺ or Ca²⁺). By comparison, Na⁺ increased the K_s of silty clay soil up to a certain threshold, while Ca²⁺ enhanced the K_s regardless of the soil texture. Increased salinity also reduced the soil water retention of sandy loam soil; however, Na⁺ increased the soil water retention of silty clay soil and Ca²⁺ had different effects depending on the suction levels. The newly developed PTF-S model, which included the electrical conductivity (EC) and cation exchange capacity (CEC), showed better predictions for the volumetric water content (R = 0.886 and RMSE = 0.057 cm³/cm³) and log K_s (R = 0.991 and RMSE = 0.073 mm/h) than the traditional model that excludes the salinity variables EC and CEC (PTF-N) (R = 0.839 and RMSE = 0.066 cm³/cm³ for the volumetric water content, and R = 0.966 and RMSE = 0.140 mm/h for the log K_s). This study highlights the importance of developing salinity-based PTFs for addressing soil salinization challenges.