@BOOK {COUPER:1991, title = {Leves topographiques pour les stations de recherche: Guide de recherche de l'Iita, No. 1}, author = {Couper, D. C. }, series = {Guide de recherche de l'Iita, No. 1}, year = {1991}, publisher = {International Institute of Tropical Agriculture (IITA)}, address = {Ibadan, Nigeria}, note = {39p.}, }