1. College of Natural Resources and Environment, Northwest A&F University, Yangling, China
2. Key Laboratory of Plant Nutrition and the Agri-environment in Northwest China, Ministry of Agriculture, Yangling, China
3. Suzhou Wetland Protection and Management Station, Suzhou, China
4. Agro-Environmental Protection Institute, Ministry of Agriculture of the People’s Republic of China, Tianjin, China
5. Soil Science Department, North Dakota State University, Fargo, ND, USA