اثر سطوح مختلف کود نیتروژن و تراکم¬های علف¬هرز خردل وحشی بر عملکرد و آستانه خسارت اقتصادی کلزا

To evaluate the effect of different rates of nitrogen fertilizer on competitive ability of canola (Okapi cv.) in interference with wild mustard, a split-plot experiment based on a randomized complete block design with 3 replications was carried out at agricultural faculty of Bu-Ali Sina University, in 2008-2009. 4 levels of nitrogen fertilization (100, 150, 200 and 250 kg N ha^-1) were assigned to main-plots and plant density of wild mustard at 5 levels (0, 4, 8, 16 and 32 plants m^-2) to the sub-plots. The results showed that with increasing nitrogen application, were improved the canola vertical distribution of LAI and dry matter in pure condition and interference of wild mustard. Increasing wild mustard density led to decreased sum of canola and wild mustard yield in unit area. Nitrogen up to 150 kg ha^-1, increased grain yield of wild mustard at all levels density. Increase up to 200 kgN ha^-1, led to slight reduction of economic threshold of wild mustard on canola yield, but in 250 kg N ha^-1, economic threshold value was less than a wild mustard plant in square meter. Overall the findings suggest that nitrogen application to 200 kgN ha^-1 caused increases in competitive ability of canola against in wild mustard.