1. Ministry of Agriculture Key Lab of Crop Nutrition and Fertilization Inst. of Agric. Resources and Regional Planning, Chinese Academy of Agric. Sci. Beijing 100081 China
2. Beijing Office of the International Plant Nutrition Institute Beijing 100081 China
3. Inst. of Soil and Fertilizer Shanxi Acad. of Agric. Sci. Taiyuan 030031 China
4. Inst. of Soil and Fertilizer Hebei Acad. of Agric. Sci. Shijiazhuang 050051 China
5. College of Resource and Environment Henan Agricultural Univ. Zhengzhou 450002 China
6. Inst. of Soil and Fertilizer Shandong Academy of Agric. Sci. Jinan 250100 China