N. A. Onguene1*, L. E. M. Ngonkeu1 and T. W. Kuyper2
1Institute of Agricultural Research for Development (IRAD), Regional Center of Nkolbisson, P. O. Box 2067, Yaoundé, Cameroon.
2Department of Soil Quality, Wageningen University, P. O. Box 8005, 6700 EC Wageningen, the Netherlands.
