Corn (Zea mays L.) yield and dry matter production under different nitrogen rates and redroot pigweed (Amaranthus retroflexus L.) density condition

Field experiments were conducted at the Agricultural Faculty Research Field of the Islamic Azad University, Astara Branch (north-western Iran) during 2007 and 2008. The main goal was to examine the effects of redroot pigweed density (Amaranthus retroflexus L.) on red root pigweed dry matter (Dm(w)), leaf area index (LAI(w)) at 50%, corn (Zea mays L.) tassel time and corn grain yield (GY(c)) and dry matter (Dm(c)). The experiments were established as split plots arranged in randomized complete block design with three replications. The main plot was nitrogen (N) rate at four rates 0, 100, 160 and 220 kg/ha. The sub-plot was redroot pigweed densities, which were considered at four levels 0, 5, 10 and 20 weeds/m(2) in an extended form to the corn farm. The results indicated that nitrogen application upto 160 kg of N/ha with 5 and 10 weeds/m(2) did not have any significant effect on Dm(w) and LAI(w) of redroot pigweed. However, both characteristics increased with the weed density gain. When 220 kg of N was applied to one hectare, these two characteristics of the weed were increased, and their amounts in more densities were greater as well. The highest levels of redroot pigweed Dm(w) and LAI(w) in 20 weeds/m(2) and application of 220 kg of N/ha were calculated to be 12.4 t/ha and 1.82, respectively. Corn GY(c) was 13 t/ha under 160 kg of N/ha in sole corn condition. The highest corn Dm(c) was observed at 15.9 t/ha under the condition where 220 kg of N was applied per hectare for sole corn. Eventually, it was found that the presence of five weeds/m(2) upto 160 kg of N/ha did not have any significant effect on corn characteristics; however, they were decreased by increasing weed density. The highest decrease was observed when the researcher applied the highest amount of nitrogen and the highest weed density.