N-P combined with microbial fertilizer application on vegetation characteristics and soil properties of degraded alpine meadows

Fertilization is an important technique for the prevention and restoration of degraded alpine grassland. In this study, six fertilization treatments were set up, including no fertilization (CK), nitrogen and phosphorus (N–P) compound fertilizer 600 kg∙ha⁻¹ (PM), microbial fertilizer 75 kg∙ha⁻¹ (BM), N–P compound fertilizer 600 kg∙ha⁻¹ + microbial fertilizer 75 kg∙ha⁻¹ (P₆₀₀BM), N–P compound fertilizer 450 kg∙ha⁻¹ + microbial fertilizer 75 kg∙ha⁻¹ (P₄₅₀BM), and N–P compound fertilizer 300 kg∙ha⁻¹ + microbial fertilizer 75 kg∙ha⁻¹ (P₃₀₀BM). Each treatment was replicated three times, for a total of 18 plots, to determine the restoration effect of N–P fertilizer combined with microbial fertilizer on degraded alpine meadows, and feasibility of fertilizer reduction after the application of microbial fertilizer, to screen the suitable fertilization scheme for the restoration of alpine meadows in the Qilian Mountains. The plant community characteristics and soil physicochemical properties of different fertilization treatments on the moderately degraded alpine meadows of the eastern Qilian Mountains were studied using the field community fertilization experimental method. The results showed that the fresh weight of the aboveground biomass under P₆₀₀, P₄₅₀, and P₃₀₀ treatments was significantly increased (P < 0.05) compared with the CK. After fertilization, the dominance of Legume, Cyperaceae, and Gramineous plants increased significantly. The vegetation diversity index and richness of all fertilization treatments were improved compared with the CK, but the difference between PM and three N–P fertilizers combined with microbial fertilizer treatment was not significant. The vegetation diversity index and margalef index of all fertilization treatments were improved. Soil available N content at 0 to 10 cm under P₄₅₀ was significantly higher than that in the CK and other treatments (P < 0.05). BM treatment had the highest soil organic matter content followed by P₄₅₀. BM and P₃₀₀ have minimal compactness at a 5 to 20 cm soil depth. Therefore, the application of N–P fertilizer and N–P fertilizer combined with microbial fertilizer had an obvious restoration effect on the vegetation of degraded alpine meadows, and the effect of N–P fertilizer was better than that of N–P fertilizer combined with microbial fertilizer. However, N–P fertilizer with microbial fertilizer significantly increased the main nutrient content of alpine meadow soil and improved the compactness of the soil. The effect N–P compound fertilizer 450 kg∙ha⁻¹ + microbial fertilizer 75 kg∙ha⁻¹ was the best among the treatments.