effect of nitrogen rates on canola (brassica napus l.) and wild mustard (sinapis arvensis l.) competition

in order to study the effects of wild mustard density on grain yield and yield components of canola cv. hyola 401 under different rates of nitrogen fertilizer, a field experiment was conducted in 2011-2012. the layout was split-plot in a completely randomized block design and three replications. main-plots included four levels of nitrogen (0, 70, 140 and 210 kg ha-1) and sub-plots consisted of different wild mustard densities (0, 6, 12, 18 and 24 plants m-2). results showed at densities of 6, 12, 18 and 24 wild mustard.m-2, grain yield losses were 15.5%, 36.7%, 47.4% and 58.6%, respectively. grain yield loss was due to reduction in number of grains per plant and 1000-grain weight. agronomic n use efficiency (anue) of canola decreased as the weed density increased. the highest anue was obtained in 70 kgnha-1, without weed interference. the lowest anue was in 210 kgnha-1 and 24 wild mustard plant.m-2 treatment. generally, application of 140 kgnha-1 lead to higher competitiveness and lower grain yield loss in canola compared with 0 kgnha-1, whereas, in 210 kgnha-1, the negative impact of 12 wild mustard.m-2 and above on canola grain yield, was higher than other n treatments.