1. a College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling 712100, China
2. b College of Resources and Environment, Northwest A&F University, Yangling 712100, China
3. c Key Laboratory of Plant Nutrition and the Agri-environment in Northwest China, Ministry of Agriculture, Yangling 712100, China
4. d State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Northwest A&F University, Yangling 712100, China