1. Institute of Soil Science, Chinese Academy of Sciences; East Beijing Road 71 Nanjing 210008 China
2. National Inst. for Agro-Environmental Sci.; Kannondai 3-1-3 Tsukuba 305-8604 Japan
3. National Agricultural Research Center; 3-1-1 Kannondai Tsukuba Ibaraki 305-8666 Japan