1. College of Natural Resources and EnvironmentNorthwest A&F Univ.ShaanxiYangling712100China
2. Key Lab of Plant Nutrition and the Agri–environment in Northwest ChinaMinistry of Agriculture, Northwest A&F Univ.ShaanxiYangling712100China
3. Key Lab. of Agricultural Water Resources, Center for Agricultural Resources Research, Institute of Genetic and Developmental BiologyThe Chinese Academy of SciencesHebeiShijiazhuang050021China