@INPROCEEDINGS {OKIGBO:1996, title = {Intercropping systems in tropical Africa}, author = {Okigbo, B. and Greenland, D. J}, booktitle = {Multiple cropping: proceedings}, series = {ASA Special Publication}, year = {1996}, number = {27}, pages = {63--101}, publisher = {American Society of Agronomy}, location = {Madison, Wisconsin}, }