Temporal trajectory and determinants of permanent gully erosion in the grassland: A long-term analysis spanning 1973–2020 - Zhicai Xiao; Mingming Guo; Xin Liu; Zhuoxin Chen; Xingyi Zhang; Jinzhong Xu; Shaoliang Zhang; Jielin Liu; Xing Han; Ruifeng Xie (Soil and Tillage Research, 2026)