1. Department of LARMAT, University of Nairobi. PO Box 29053-00625, Kangemi, Nairobi
2. Department of Plant Science and Crop Protection, University of Nairobi, PO Box 29053-00625, Kangemi, Nairobi
3. Department of Soil Management and Soil Care, Ghent University, Coupure links 653, B-9000 Gent, Belgium