Weed suppression ability of upland rice under low-input conditions in West Africa

Weeds are a major constraint to upland rice production in west Africa. The objectives of this investigation were to study differences in weed suppression ability among upland rice cultivars and to determine the morphological traits involved. Twelve contrasting cultivars, including West African indigenous Oryza glaberrima (Steudel) lines and traditional and improved O. sativa L., were cultivated under natural weed competition and low-input conditions in Côte d'Ivoire in two seasons. Significant differences between cultivars were observed in weed biomass at 100 days after seeding (DAS) in 1994 and 1995, indicating differences in their competitive ability. Weed biomass was negatively correlated with rice root growth at early growth stages and with rice shoot and root growth at later growth stages. Across cultivars, grain yields with a single hand-weeding were 60% in 1994 and 49% in 1995 of those in plots that were weeded regularly. High grain yields in weedy plots were associated with low weed biomass. IG 10, an O. glaberrima cultivar, was the most competitive against weeds.