Freshwater infiltration model and infiltration characteristics simulation in saline soil considering solute potential

Accurate prediction of freshwater infiltration into saline soils is hindered by neglect of solute‑potential feedback in conventional water–salt transport models. To address this, we developed SWSK1, a soil water–solute kinetic model extension that explicitly incorporates solute potential through an osmotic efficiency coefficient (f0) derived from semipermeable membrane theory. SWSK1 was validated in laboratory column tests on loam, loamy sand, and sandy loam at NaCl salinities of 0–5 g kg−1. Compared to the baseline model (SWSK0), SWSK1 markedly improved cumulative infiltration predictions (nRMSE reduced from 0.048 to 0.163–0.013–0.077; Pbias constrained within ± 8%) and reproduced salinity‑induced oscillatory peaks and troughs in transient volumetric water content (mean nRMSE reduced from 0.201 to 0.127; Pbias within ± 5%). Application to four USDA‑textured soils (silt loam, loam, sandy loam, clay loam) showed that inclusion of f0 shortened infiltration times by 19%–35%, increased infiltration depths by 2–5 cm and extended solute diffusion depths by up to 7 cm, with osmotic effects plateauing above 3 g kg−1 salinity. These findings underscore the critical role of solute‑potential feedback in saline‑soil infiltration modeling and provide a robust basis for enhancing water‑use efficiency and salt leaching in agricultural practice.