1. Department of Plant Nutrition, China Agricultural University, Key Laboratory of Plant−Soil
Interactions, Ministry of Education, Beijing 100094, P. R. China
2. Department of Soil Quality, Wageningen University, P.O. Box 47, 6700 AA, Wageningen,
The Netherlands
3. College of Resources and Environmental
Sciences, Agricultural University of Hebei, Baoding 071001, China
4. Alterra, Wageningen University and Research Centre, P.O. Box 47, 6700 AA,
Wageningen, The Netherlands