1. Graduate School; Chinese Academy of Agricultural Sciences; Beijing 100081 P.R. China
2. Key Lab. of Plant Nutrition and Fertilizer; Ministry of Agriculture and Rural Affairs/Institute of Agricultural Resources and Regional Planning; Chinese Academy of Agricultural Sciences; Beijing 100081 P.R. China
3. Soil and Fertilizer Institute of Hunan Province; Hunan Academy of Agricultural Sciences; Changsha 410125 P.R. China
4. Scientific Observing and Experimental Station of Arable Land Conservation (Hunan); Ministry of Agriculture and Rural Affairs; Changsha 410125 P.R. China