Effects of redroot pigweed (Amaranthus retroflexus L.) competition on the yield and yield components of corn under different levels of nitrogen application

Field studies were conducted in the research field of the Agricultural Faculty of Islamic Azad University-Astara branch in 2010 and 2011 year in order to evaluate the effect of redroot pigweed (Amaranthus retroflexus L.) on yield and dry matter of corn (Zea mays L.) under different levels of nitrogen application. The experiments were established as a split plot arranged in randomized complete block design with three replications. The main plot was with nitrogen (N) at different rates (0, 100, 160 and 220 kg ha-1) and the sub plot was redroot pigweed in different densities (0, 5, 10 and 20 weeds m-2; 0, 3, 5, 7 and 14 plants m-2 in a corn row, respectively). The results showed that the highest number of seed rows per ear, grain number per ear, 1000 grain weight, grain yield per plant and harvest index of corn were, respectively, 15.6, 691.3, 247.7 g and 41.2% at 160 kg N ha-1 in a weedfree condition and the presence of 5 weeds per m-2 had no significant effect on them. The highest dry matter and grain yield of corn were 15.9 and 12.3 t ha-1 at 220 and 160 kg N ha-1 under weed-free conditions.