1Department of Land and Water Management, University of Embu, P. O. Box 6, Embu 60100, Kenya
2Cortile Scientific Limited, PO Box 34991-00100, Nairobi, Kenya
3Department of Plant, Animal and Food Sciences (PAFS), Jaramogi Oginga Odinga University of Science and Technology (JOOUST), PO Box 210 – 40601, Bondo, Kenya
4National Agriculture Research Laboratories, Kenya Agricultural and Livestock Research Organization, PO Box 14733-00800, Nairobi, Kenya
5Department of Soil Sciences, Research Institute of Organic Agriculture FIBL, Ackerstrasse 113, Frick 5070, Switzerland