Shifting sands to sustainable soils: Spatial dynamics of soil water and salinity in a desert oasis ecotone

Understanding the spatiotemporal patterns of soil moisture and salinity dynamics and their governing factors is essential for predicting salinization risks and developing mitigation strategies in arid agricultural landscapes. This study examined the vertical distribution (0–3 m) of soil water content (SWC), electrical conductivity (EC), and pH, and identified their dominant controls across bare sand dunes, nabkha dunes, and croplands of varying cultivation durations (2–5, 12–15, 25–30, and 40–50 years) in a desert–oasis ecotone of northwestern China. The results showed that SWC, EC, and pH generally increased with soil depth and were best described by quadratic or power functions. Bare sand dunes had the lowest values of all three parameters, while EC and pH peaked in nabkha dunes (188.20–636.83 μS·cm-¹ and 7.88–8.43, respectively), particularly those near the water area, where the early-stage cultivation may be more challenging. Conversion to cropland reduced surface (0–0.4 m) EC and pH by 7.3–34.7 % and 3.9–7.2 %, respectively, after 40–50 years of cultivation, in contrast, subsurface soil layers (0.4–3 m) exhibited stable EC and pH levels after long-term irrigation, with no significant changes between 25–30 and 40–50 years of cultivation (P > 0.05). However, subsurface salinity (0.4–1 m) in newly reclaimed croplands (2–5 years) tended to be higher than that in both nabkha dunes and older croplands, suggesting a potential risk of salinization in the new croplands, which require optimized irrigation. Soil texture was the dominant factor controlling SWC, while cultivation years primarily explained the variation in EC and pH. These findings reveal critical spatiotemporal dynamics in soil water-salt following land use change and offer guidance for optimizing irrigation practices to prevent secondary salinization in arid regions.