@ARTICLE {VAN EK:1997,
title = {Quantitative assessment of traditional cropping systems in the Sudan savanna of northern Nigeria II. Management and productivity of major cropping systems},
author = {van Ek, G. A. and Henriet, J and Blade, S. and Singh, B. },
journal = {Samaru Journal of Agricultural Research},
year = {1997},
volume = {14},
pages = {47--60},
}