@INBOOK {WALKER:1991, title = {Single site design considerations in on-farm experiments}, author = {Walker, P. }, year = {1991}, type = {On-farm research in theory and practice, edited by H.J.W. Mutsaers and P. Walker}, pages = {39--45}, publisher = {International Institute of Tropical Agriculture (IITA)}, address = {Ibadan, Nigeria}, }