1. Professor, State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F Univ., Yangling, Shaanxi 712100, China (corresponding author).
2. Associate Professor, State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F Univ., Yangling, Shaanxi 712100, China.