Effect of weed interference and nitrogen on yields of a maize/rice intercrop

Field experiments were conducted in the Nigerian savanna during the 1994 and 1995 wet season to assess the influence of nitrogen application on weed interference, and determine the critical period of weed competition in a maize/rice intercrop. Treatments were laid out in a split-plot design with three replications. Three levels of nitrogen (0, 60 and 120 kg/ha) were assigned to the main plot, and ten periods of weed interference to the sub-plots. In both seasons, N-application resulted in significant increases in grain yields of maize and rice in the plots that were kept weed-free for 6 weeks and more. Uncontrolled weed growth resulted in 83.03% and 93.85% reductions in average grain yield of maize and rice respectively. Weed control for 9 weeks after sowing at 120 kgN/ha gave the best crop yields. However, it is recommended that for resource-poor farmers, rather than keeping plots weed-free for long periods, n-application of 60 kg/ha in combination with a weed-free regime of 6 weeks after sowing will be adequate to provide a good crop yield for the intercrop.