1. Key Laboratory of Arable Land Conservation (North China), Ministry of Agriculture, College of Land Science and Technology China Agricultural Univ. Beijing China
2. Dep. of Agroecology Aarhus Univ. Tjele Denmark
3. State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil Sciences Chinese Academy of Sciences Nanjing China
4. Division of Agricultural and Environmental Sciences School of Biosciences Univ. of Nottingham Leicestershire UK