@BOOK {HARTLEY:1998, title = {Tractor design and operation for research stations: IITA research guide, No. 4}, author = {Hartley, P. V. }, series = {IITA research guide, No. 4}, year = {1998}, month = {October}, publisher = {International Institute of Tropical Agriculture (IITA)}, address = {Ibadan Nigeria}, isbn = {978-131-124-X}, note = {29p.}, }