@INPROCEEDINGS {AKINTOYE:2001, title = {Economics of N fertilizer usage in maize production in three ecological zones of Nigeria}, author = {Akintoye, H. and Lucas, E. O. * and Kling, J. }, booktitle = {Impact challenges and prospects of maize research and development in west and central Africa: proceedings of the Regional Maize workshop, Cotonou, Benin, 4-7 may, 1999}, year = {2001}, }