@BOOK {COUPER:1991a, title = {Land survey for research stations: IITA research guide, No. 1}, author = {Couper, D. C. }, series = {IITA research guide, No. 1}, year = {1991}, month = {December}, publisher = {International Institute of Tropical Agriculture (IITA)}, address = {Ibadan, Nigeria}, note = {36p.}, }