1. Institute of Quality and Standards for Agricultural Products, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, P.R. China
2. Key Laboratory of Information Traceability for Agricultural Products, Ministry of Agriculture, Hangzhou 310021, P.R. China
3. China National Rice Research Institute, Hangzhou 310006, P.R. China
4. National Isotope Centre, GNS Science, 30 Gracefield Road, Lower Hutt 5040, New Zealand