@BOOK {COUPER:1992, title = {Operations agricoles dans les fermes experimentales: Guide de recherche de l'Iita, No. 18}, author = {Couper, D. C. }, series = {Guide de recherche de l'Iita, No. 18}, year = {1992}, month = {February}, publisher = {International Institute of Tropical Agriculture (IITA)}, address = {Ibadan, Nigeria}, note = {17p.}, }