Soil Fertility Characteristics of Damaged Slopes in the Alpine Meadows of Northwest Sichuan during the Early Stages of Vegetation Restoration

To investigate the impact of different vegetation restoration modes on the soil physical and chemical properties as well as soil fertility characteristics of damaged slopes in the alpine meadows along the roads of northwest Sichuan, our study employed in-situ sampling and laboratory testing methods, focusing on the damaged slopes located on both sides of National Highway 248 within Hong yuan County. We established three vegetation restoration models: Hydro-seeding (PB), shrub-grass mixed planting (GC), and tree-shrub-grass mixed planting (QGC), using the unrestored slope from the same period as a control (CK). In the early stages of restoration, we measured soil physical and chemical properties and conducted principal component analysis. Soil fertility was comprehensively evaluated using both the Nemero index and the IFI index. The results indicated that: (1) Compared to other models, the tree-shrub-grass mixed planting model significantly increased the soil pH, organic matter, total nitrogen, calcium, magnesium, and silt-gravel content of damaged slopes during the early stages of restoration succession (P＜0.05), with increases of 23.84%, 302.37%, 105.71%, 361.66%, 118.75%, and 28.09% respectively. The Nemero fertility index ranking was QGC (1.65) ＞ GC (1.44) ＞ PB (1.12) ＞ CK (0.91). (2) Principal component analysis showed that the enhancement of soil fertility is controlled by the coupled effects of multiple factors. pH, organic matter, total nitrogen, total phosphorus, available potassium, calcium, magnesium, silt-gravel content, and available phosphorus are key limiting factors. In subsequent restoration projects in this area, efforts should be made to strengthen the overall nutrient cycling network to improve the effectiveness of ecosystem restoration for damaged slopes.Overall, during the early stages of restoration succession, the tree-shrub-grass mixed planting model can significantly improve the soil properties of damaged slopes. Its effects on enhancing soil physical and chemical properties and fertility are the most significant. Therefore, it is the preferred model for ecological restoration of damaged slopes in the alpine meadows of northwest Sichuan.