Semi-arid maize yield responses to conservation tillage and weeding

The major problems associated with conservation tillage approaches currently promoted to the smallholder farmer in sub-Saharan Africa are weed control and crop establishment. To date little work has been carried out to assess the interaction of different conservation tillage options with different weeding regimes on maize yield and soil water regimes. To redress this situation on-station trials were carried out on a semi-arid sandy soil in Zimbabwe. Results from three very different seasons showed that soil water regimes and crop yields were strongly influenced by both the conservation tillage option and the timing and frequency of weeding. In terms of crop water use efficiency and grain yield, a combination of weeding carried out at two and six weeks after crop emergence performed the best, whilst a single weeding four weeks after crop emergence was the worst of the weeding regimes. Where tied ridges were used, if weed control was inadequate, i.e. a single weeding four weeks after crop establishment, crop yields were significantly reduced, when compared to simple open plough furrow planting techniques that were weeded using the mouldboard plough with the body attached.