Use of organic and inorganic resources to increase maize yields in some Kenyan infertile soils: a five-year experience - Okalebo, JR; Palm, Cheryl A.; Lekasi, J.K.; Nandwa, SM; Othieno, CO; Waigwa, M; Ndung'u-Magiroi, Keziah Wairimu (Academy Science Publishers, 2003)