Effects Of Green Manure Cover Crops On Weed Population, Pearl Millet And Maize Productivity Under Conservation Agriculture In Liselo And Mashare Namibia.

ABSTRACT

Smallholder farming communities of northern Namibia are generally cash-constrained and theyare situated in marginal areas where poor soil fertility and land degradation are predominant. They find it difficult to purchase mineral fertilizers and herbicides. There is therefore a need to identify cropping systems that are affordable and can improve their productivity. The integration of green manure cover crops (GMCCs) as rotational crops has been investigated to great lengths in Latin America and reported to improve productivity but information on their use is still scarce in Namibia. Two experiments were set up at two sites, Mashare Irrigation Training Center (MITC) and Liselo Research Station (LRS) having contrasting soil types to investigate the effects of rotating pearl millet and maize with different GMCCs on pearl millet, maize productivity and weed populations over two seasons 2016/2017-2017/2018. In the first experiment, nine different GMCCs were rotated with pearl millet, while maize was rotated with nine GMCCs in the second experiment and their effects in the succeeding season were compared with pearl millet and maize monocropping. At MITC, the highest total weed density was observed in the pearl millet-pigeon pearotation treatment with 3500 weeds ha-1 in season 1, P=0.0371 and 6400 weeds ha-1, P=0.0451 in season 2. The lowest weed density was observed in the pearl millet-lablab treatment with 1300 weeds ha-1and P=0.0371 in season 1 and 2100 weeds ha-1and P=0.0451 in season 2. At LRS, the highest total weed density was observed in the maize-pigeon pearotation treatment with 3200 weeds ha-1and P=0.0433 in season 1 and 3300 weeds ha-1and P=0.0198 in season 2. While, maize-velvet bean rotation treatment had the lowest weed densities of 900 weeds ha-1and P=0.0433 in season 1 and 1000 weeds ha-1and P=0.0198 in season 2. Lablab gave the highest biomass yields as high as 12 t ha-1 both seasons P=0.5929, P= 0.4820 at MITC and at LRS velvet bean yielded up to 10 t ha-1 and P=0.9143 in season 1. The highest plant available nitrogen was produced by jack bean (900 ppm) and P=0.0000 at LRS. Maize grain and biomass yields were significantly P=0.0172affected by different rotations at LRS in season two with maize after maize monocropping attaining the least grain yield of 2.4 t ha-1. In conclusion, rotating pearl millet and maize with cover crops has more noticeable benefits as compared to monocropping and no cover crop could offer all benefits hence this call for identification of niches and a suitable cover crop for that specific niche.,