@INBOOK {OKIGBO:1979, title = {Soil fertility maintenance and conservation for improved agro-forestry systems in the lowland humid tropics}, author = {Okigbo, B. and Lal, R. }, year = {1979}, type = {Soils Research in Agro-Forestry edited by H.O. Mongi and P.A.Huxley}, pages = {41--78}, publisher = {ICRAF}, address = {Nairobi}, }