Determining Soil Nutrients Reference Condition in Alpine Region Grassland, China: A Case Study of Hulun Buir Grassland

Grasslands represent a source of nutrient cycling, ecosystem stabilization, and services for human use. Grassland soil quality is commonly used as an indicator of ecosystem health and sustainability due to its strong correlation with overall grassland quality and ecosystem health. Although direct and indirect effects of human activities or disturbances on soil can be taken into account, a benchmark (i.e., the reference condition (RC)) should be used and is needed to describe the baseline of an area without significant anthropogenic disturbance. Therefore, determination of the soil reference condition and suitable selection methods have become a key focal point in grassland protection and ecological assessments. In this study, several methods were selected to determine soil nutrient concentrations of Hulun Buir Grassland in northern China based on the proposed criteria. The concentrations of total organic matter, N, P, and K; 112 samples were analyzed using the population distribution method, trisection method, and regression model method. The reference concentrations of total organic matter, N, P, and K in soil were recommended to be 52.12 g/kg, 2.94 g/kg, 2.08 mg/kg, and 305.76 mg/kg, respectively. In the alpine region grassland, the major factors that impact nutrient concentration were agricultural activity and vegetation coverage. Sampling methods should be used preferentially in determining grassland soil reference condition and historical data; experts' judgment could be used in substitution.