An analysis on agro-grassland farming systems in subtropical mountainous areas:A case study in Qinglong County, Guizhou Province Analysis of characteristics of the circular economy of grassland farming Spatial and temporal characteristics of soil water dynamics and crop yield response from a 4-year of lucerne and winter wheat rotation system in the Loess Plateau Grassland Farming Is an Important Approach for the Sustainable Development of Agriculture in Gansu Province Analysis of grassland farming systems’ economic benefit based on the short-term production model