@ARTICLE {HENRIET:1997, title = {Quantitative assessment of traditional cropping systems in the Sudan savanna of northern Nigeria: III. Importance of trees, shrubs and secondary crops in the cropping systems}, author = {Henriet, J and van Ek, G. A. and Blade, S. and Singh, B. }, journal = {Samaru Journal of Agricultural Research}, year = {1997}, volume = {14}, pages = {61--66}, }