1. College of Resources and Environmental Sciences China Agricultural Univ. Beijing 100193 China
2. Crop and Soil Systems Research Group SRUC Craibstone Estate Aberdeen AB21 9YA UK
3. College of Atmospheric Science Chengdu Univ. of Information Technology Chengdu 610225 China
4. Sustainable Soils and Grassland Systems Dep. Rothamsted Research, North Wyke Okehampton Devon EX 20 2SB UK