Significant soil acidification caused by grazing exclusion across China's grassland areas

Soil pH is strongly associated with soil biogeochemical cycles and biodiversity in terrestrial ecosystems. Grazing exclusion (GE) has been widely adopted as an effective practice to restore degraded grasslands. However, the effect of GE on soil pH is still poorly understood and remains inconclusive. We synthesized data for 63 sites from the peer-reviewed literature and 43 additional field sites and investigated the differences in soil pH following grazing exclusion across China's grasslands. The mean pH across all samples decreased by 0.13 units with grazing exclusion (mean pH 8.15 and 8.02 for the grazed and grazing exclusion groups, respectively, p < 0.001). The pH of the surface soil (0-20 cm) showed the greatest rates of decrease in grazing exclusion grasslands, whereas the pH of the deep soil layers (20-100 cm) showed a limited response to grazing exclusion. In general, the largest rate of decrease in soil pH occurred after medium-term periods (5-15 years) of grazing exclusion, whereas a smaller rate of change was found over short- (<= 5 years) and long-term periods (>= 15 years) of grazing exclusion. Of the environmental factors examined, the climatic conditions, accumulation of biomass and the soil carbon and nitrogen dynamics were important factors influencing soil pH following grazing exclusion. Our results indicate that grazing exclusion causes significant soil acidification, especially in surface soils and humid areas. Our results provide an important reference for the future management of China's grasslands.

Automated summary

Grazing exclusion results in significant soil acidification, especially in surface soils and humid areas. The changes in soil pH are most pronounced during medium-term periods, while smaller rates of change are observed over short- and long-term periods.