The Distance From the Sea Determined the Distribution Pattern of Saline-Alkali Soil Quality Through Indirect Effect

Soil quality is a crucial attribute for maintaining biological productivity, human health, and ecosystem service function. However, the distribution of saline-alkali soil quality and its influencing factors in the Yellow River Delta region remain poorly understood, posing challenges to sustainable agricultural development. The study evaluated soil quality across various land-use types and depths in the southern Yellow River Delta region. A total of 134 soil samples were collected from two soil layers at 67 soil sample points, distributed across three land use types. Spatial distribution maps revealed that inland areas exhibited improved soil texture and nutrient levels compared to coastal regions. All nutrients, except soil total potassium, were higher in the 0-20 cm soil layer than in the 20-40 cm soil layer. The spatial distribution pattern of Soil Quality Index (SQI) demonstrated a pattern of higher values at the central part of the study area, gradually declining toward the edges. Furthermore, SQI in cultivated land was found to be 1.8%-8% higher than in forest land and 52.7%-84% higher than in wasteland. The Structural Equation Modeling results indicated that distance from the sea indirectly influenced soil quality through different mechanisms between the two soil layers. In the model for the 0-20 cm soil layer, SQI was indirectly affected by chemical properties, nutrients, and base ions, explaining 85% of the variation in SQI. In the model for the 20-40 cm soil layer, SQI was primarily influenced by chemical properties, accounting for 83% of the variation. These findings offer valuable insights for land use and crop selection aligned with soil properties, supporting sustainable agricultural practices in the region.