**5. Acknowledgment**

We gratefully thank the Soil Labs in Cranfield University for the provision of spectrophotometer. Sincere thanks are given to Dr. Boyan Kuang for assisting soil sampling and laboratory reference measurement, and Dr. Robert J. A. Jones for assisting soil description. Financially supported by Natural Science Foundation of Zhejiang Province, P.R.China (Project No.Y1090885) and by the State Scholarship Fund of China (Grant No.[2009]3004).
