[1] Key Laboratory of Plant Nutrition and the Agro-Environment in Northwest China, Ministry of Agriculture and Rural Affairs, College of Natural Resources and Environment, Northwest A&F University, Yangling,712100, China
[2] School of Geography and Ocean Science, Nanjing University, Nanjing,210033, China
[3] Institute of Soil Science, Chinese Academy of Sciences, Changshu National Agro-Ecosystem Observation and Research Station, Nanjing,210008, China
[4] College of Grassland Agriculture, Northwest A&F University, Yangling,712100, China
[5] Institute of Dryland Farming, Gansu Academy of Agricultural Sciences, Lanzhou,730070, China
[6] College of Resources and Environment, Shanxi Agricultural University, Taigu,030801, China