Cogongrass is widespread in the moist savanna and forest zones of West Africa, where recurrent fires, tillage, weeding, and other farm activities continuously disturb land. Field experiments were conducted in the forest–savanna transition zone of Nigeria from 1996 to 2000 to evaluate the potential of two cover crops (velvetbean and tropical kudzu) for reclaiming land that had been abandoned to cogongrass. Cover crops were grown on the same plots for 3 consecutive yr (1996 to 1998). The control was natural fallow dominated by cogongrass in 1996 to 1998. Corn was planted in all treatments in 1999 and 2000. Total dry matter of cogongrass before the treatments were imposed was 9,000 kg ha−1, and rhizomes contributed 49% of this. At all subsequent sampling dates, plots with cover crops had lower cogongrass shoot and rhizome dry matter than plots without cover crops. Shoot dry matter was reduced to zero 65 wk after planting in both cover crops; rhizome dry matter was reduced to zero after 97 wk in velvetbean plots and after 105 wk in tropical kudzu plots. Corn grain yield was 60% higher in plots with tropical kudzu and 102% higher in plots with velvetbean than in control plots without any previous cover crops. Further research is required to integrate use of cover crops with other control methods for improved cogongrass management.

Weeds are a major constraint to crop production in smallholder farms in tropical Africa. The weed seedbank and annual recruitment are the main sources of weed infestation in crops. This study was carried out in Ibadan, Nigeria, to evaluate the effect on the seedbank of two types of planted fallow (alley cropping with leucaena and live mulch with tropical kudzu) and a natural bush fallow under four land-use intensities. Type of fallow was the main plot. Land-use intensities, consisting of continuous cropping of maize intercropped with cassava, 1 cropping yr of maize–cassava followed by 1, 2, and 3 yr of fallow, were the subplots. Averaged over a 3-yr period, the seedbank was 55% lower in the tropical kudzu plots and 43% lower in the leucaena plots compared with natural bush. The difference in seedbanks between plots cultivated after leucaena and natural fallow was 23%. Seed density of annual broadleaf weeds was high and dominated the seedbank of both planted and natural fallow. Overall, seeds of grasses occurred at low densities in all plots cultivated after 2 to 3 yr of fallow, whereas seeds of sedges occurred more in continuously cultivated plots and plots cultivated after 1 yr of fallow in all the fallow types. Seed density of perennial broadleaf weeds increased as land-use intensity decreased. Live mulch with tropical kudzu, especially when combined with 2 to 3 yr of fallow, lowered the seedbank more than the leucaena and traditional bush fallow systems.