1. Department of Agricultural Sciences, School of Agriculture and Biotechnology, Karatina University, Karatina P.O. Box 1957-10101, Kenya
2. Department of Plant Nutrition, Institute of Crop Science and Resource Conservation (INRES), Karlrobert-Kreiten-Str. 13, 53115 Bonn, Germany
3. Kenya Forestry Research Institute (KEFRI), Baringo Regional Forestry Research Centre, Marigat P.O. Box 57-30400, Kenya