Abstract
Weeding is one of the most labour-demanding phases of the production of maize (Zea mays L) by village farmers in Africa. Because herbicides may not be appropriate, the possibility of using the maize crop itself to control weeds was investigated. Four experiments were conducted in two years in central Malawi to determine the influence of plant arrangement, population density, maize vigour, and fertilization practices on the maize-weed competition. The effects of weeding on soil and water conservation were also studied. Weed dry matter production was negatively correlated with maize population density. Maize grain yields of 12.12 t ha-1 were produced on totally unweeded plots where 120 kg N and 22 kg P were applied and 80 000 hybrid maize plants were grown per hectare. Clean-weeded plots produced a yield of 13.66 t ha-1. With 20% as much fertilizer and an open-pollinated variety of maize, yields were much lower, both absolutely and in relation to clean-weeded control plots. The effect of plant arrangement on maize yields depended on maize density. The highest yields at 20 000 plants ha-1 occurred with equidistant spacing but at 80 000 plants ha-1 the greatest yields were associated with the widest row spacing. The weedy ground cover reduced soil erosion losses from 12.1 t ha-1 on the weeded plots to 4.5 t ha-1 on the unweeded plots.
