weed nitrogen uptake as influenced by nitrogen rates at early corn (zea mays l.) growth stages

the effect of nitrogen (n) levels on n uptake by high weed densities at early growth stages of corn (zea mays l., cv. double cross 370) was investigated for two years (2008-2009) at the agricultural research station of shiraz university. the experiment was arranged in a split-plot arrangement in the randomized complete blocks design with three replications. two levels of weed control (weedy and weed free) and three levels of preplanting n (0, 50, and 90 kg ha-1) were employed as main and subplots, respectively. one month after crop sowing, total weed species were determined and shoot dry weights of both corn and weeds were measured. the highest weed biomass and n uptake by weeds were obtained from the application of 50 kg n ha-1. in the first year of the study, average n content of weed seedlings grown at any rates were not significantly different, whereas in the second year, n content of the weeds in the zero n plot was 31 and 39 % less than the weeds grown in 50 and 90 kg n ha-1 applied plots, respectively. higher uptake of n by weeds, especially redroot pigweed (amaranthus retroflexus) at the early corn growth stage is an important issue for crop-weed competition.