1. College of Natural Resources and Environment, Northwest A&F University, Xianyang, 712100, China
2. Key Laboratory of Plant Nutrition and the Agri-Environment in Northwest China (Ministry of Agriculture), Northwest A&F University, Xianyang, 712100, China
3. College of Surveying and Geo-informatics, North China University of Water Resources and Electric Power, Zhengzhou, 450045, China
4. Department of Renewable Resources, University of Alberta, Edmonton, AB T6G 2H1, Canada
5. College of Computer & Information Engineering, Xiamen University of Technology, Xiamen, 361024, China
6. The State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Xianyang, China