3.4. Effect of crop sequence and mineral fertiliser application on subsequent weed problems
Crop sequence and fertiliser application both influenced weed biomass associated with maize (Fig. 2). On both researcher and farmer-managed fields, higher weed biomass was associated with maize grown on plots previously under speargrass fallow than on plots previously under cassava cropping. Weed biomass after cassava in the unfertilised plots was roughly half that found after speargrass fallow and further reduced to a third of that found after speargrass when cassava was followed by maize with fertiliser. Across all crop sequences, application of mineral N fertiliser increased weed biomass by 31%. On the farmer-managed plots, weed biomass associated with maize on plots previously cropped to cassava was about 40% of that found after speargrass fallow.