@TECHREPORT {AMAZA:2006l, title = {Improving soil fertility management}, author = {Amaza, P. and Helsen, J. and Olayemi, J. K. * and Ellis-Jones, J. }, year = {2006}, institution = {International Institute of Tropical Agriculture (IITA)}, address = {Ibadan, Nigeria}, note = {IITA PROSAB policy briefs}, }