Weed communities in intensified cereal-based cropping systems of the northern Guinea savanna.
The dynamics of weed populations were analysed in intensified cereal-based cropping systems in 5 villages of the northern Guinea savanna in Nigeria in 1990 and 1991. A total of four common weed associations were identified through cluster analysis. Five factors describing soil fertility conditions and field history best differentiated the weed communities according to a discriminant model. The analysis showed that maize-based cropping systems with a high frequency of cereal cropping and a low frequency of non-cereal cropping tended to be dominated by weeds such as Commelina spp. and Kyllinga squamulata. As soil fertility declined, Vernonia spp. and Eclipta prostrata became more important. Increased frequency of non-cereal crops in mixed cropping with cereals was associated with reduced incidence of weeds such as Leucas martinicensis, Oldenlandia corymbosa, Spermacoce verticillata, Ludwigia hyssopifolia, Celosia laxa and Ipomoea spp. It is suggested that further diversification of cereal-based systems to obtain a reduced frequency of cereals is likely to increase the incidence of Dactyloctenium aegyptium in crop fields. The information provides guidance for technology development and transfer on weed control for intensifying systems in the northern Guinea savanna of Africa.