1. Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas, Ministry of Education, Northwest A&F University, Yangling, Shaanxi, China
2. College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi, China
3. Department of Renewable Resources, University of Alberta, Edmonton, Canada
4. Department of Soil Science, University of Saskatchewan, Saskatoon, Canada
5. Key Laboratory of Plant Nutrition and the Agri-Environment in Northwest China (Ministry of Agriculture), Northwest A&F University, Yangling, Shaanxi, China