State Key Laboratory of Nutrient Use and Management,College of Resources and Environmental Sciences,National Academy of Agriculture Green Development,China Agricultural University,Beijing 100193,China

Inner Mongolia Key Laboratory of Soil Quality and Nutrient Resources

College of Grassland,Resources and Environment,Inner Mongolia Agricultural University,Hohhot 010018,China

Key Laboratory of Grassland Management and Utilization,Ministry of Agriculture and Rural Affairs of the People's Republic of China

College of Grassland Science and Technology,China Agricultural University,Beijing 100193,China