Grazing intensity and soil depth effects on soil properties in alpine meadow pastures of Qilian Mountain in northwest China

In the mountainous rangeland of inland arid regions of Eurasia, seasonal grazing has been important to local communities for production of food, fiber, and for income, for the past thousand years. Recent population increases and other changes have put traditional grazing systems under pressure. However, empirical data describing soil properties or the impact of traditional grazing practice on the thresholds at which increase in animal stocking rate (SR) may result in degradation are lacking. Here, we provide, for alpine "typical steppe" at Qilian Mountain on the Tibetan plateau in China, a description of variation in some soil properties with soil depth, and with variation in grazing intensity. The soils studied have a humus-rich epipedon typically exceeding our sampling depth of 40 cm. As commonly reported, increased grazing intensity has correlated with depletion in soil organic carbon (SOC). Regression of our SOC data on SR indicated no "safe" threshold for grazing intensity below which SOC depletion would not occur. Other soil changes linked to increased grazing intensity in our study included a lowering of the carbon:nitrogen ratio (indicating possibly increased risk of nitrogen loss from farming systems to the wider environment), an increase in soil bulk density, a decrease in soil moisture content, and transfer of phosphorus from less intensively grazed areas toward animal night pens. Our study site is experiencing a climate warming trend which may be contributing to loss of SOC.