Study on soil phosphorus nutrient and its regulatory factors during the restoration of degraded grassland in the source region of Heihe River

To explore the response of different restoration methods to changes in soil phosphorus nutrient content of degraded grassland, this research investigated unicast and mixed cultivated grassland in the source area of the Heihe River, and compared non-degraded grassland with extremely degraded grassland in terms of characteristics of grassland vegetation and soil. The results showed that established cultivated grassland significantly increased the above-ground and below-ground biomass compared with extremely degraded grassland, and the vegetation diversity of mixed grass was better than that of single grass. The amount of phosphorus nutrient (total phosphorus, organic phosphorus, available phosphorus, and microbial biomass phosphorus) in the soil of single-sown grassland was greater than that in the mixed-sown grassland. Partial methods showed that changes in soil physical properties are the main factors affecting soil phosphorus nutrient. The results of correlation analysis also showed that the soil water content, clay content, and capillary porosity of the grassland were significantly correlated with the amount of available phosphorus, and that these three characteristics were greater in grassland established by single-sowing than by mixed-sowing. Comprehensive analysis results showed that artificial restoration is an effective measure to quickly control extremely degraded grassland. Cultivated grassland from unicast establishment is relatively stable in terms of soil phosphorus nutrient restoration, but cannot been restored to the state of non-degraded grassland. The management of cultivated grassland should be continuously strengthened.