Determinations of environmental factors on interactive soil properties across different land-use types on the Loess Plateau, China

Soil physical and chemical properties are prerequisites to soil functionality, which depend importantly on land use, climate, and topography. However, previous works gave little consideration to the inherent causalities between properties under environmental influences. Here, we sampled 0-20 cm soil from 82 sites across the entire Yanhe watershed, including forest, shrubland, grassland, and agriculture. We applied structural equation modelling (SEM) to explore the environmental impacts on soil properties. The results showed that clay content (Clay%) in forest and grassland was significantly higher than in the agriculture area and shrubland. Redundancy analysis indicated that the variations of soil properties were explained by environmental factors, specifically in the forest (51.3%), shrubland (71.6%), grassland (77.6%), and agriculture area (95.5%). Hierarchical partition analysis independently extracted dominant factors and found that latitude, precipitation, and elevation were critical in forest and grassland; elevation and precipitation in shrubland; elevation and latitude in agriculture area. SEM identified soil organic carbon (SOC) was directly influenced by total nitrogen (TN) and total potassium (TK) in forest; by TK in shrubland; by TK and bulk density (BD) in grassland; by total phosphorus (TP) and BD in agriculture area. Path analysis on SOC identified different paths in forest, grassland, and agriculture, and the mediators included TN, BD, pH, and TP. These findings indicate that the influence of environmental factors on soil properties should take into account the interactions within soil conditions. Grassland has a good potential regional carbon sequestration.