1. College of Natural Resources and Environ. Key Laboratory of Soil Environ. and Waste Re-use in Agriculture of Guangdong Higher Institutes South China Agricultural Univ.; Guangzhou 510642 China
2. Institute of Environmental Science Taiyuan Univ. of Science and Technol.; Taiyuan 030024 China
3. Dep. of Plant and Soil Sciences; Oklahoma State Univ.; Stillwater OK 74074