Evaluation of competitive ability of canola (Brassica napus) and wild mustard (Sinapis arvensis) at different rate of nitrogen and relative density of both species

In order to evaluate competitive relationships between wild mustard (Sinapis arvensis L.) and canola (Brassica napus cv. Okapi), a replacement series interference experiment was conducted in greenhouse of Agricultural Faculty of Bu-Ali Sina University, in 2010. Experiment factors included 4 levels of nitrogen (0.75, 1, 1.25 and 1.5 g.pot-1) and 5 relative density series of canola and wild mustard (1:0, 0.75:0.25, 0.5:0.5, 0.25:0.75 and 0:1). Plant density of each species was 4 plants per pot at pure culture. At all nitrogen levels, intra-specific competitive coefficients of canola based on biological and grain yield were less than inter-specific competitive coefficients, but in wild mustard the intra-specific competition coefficients were higher than inter-specific competition coefficients. Relative competitive ability (RCA) of canola based on both mentioned traits were less than wild mustard, at all nitrogen levels. Increasing nitrogen rate to 1.25 g.pot-1 led to increment of RCA of canola. Increasing canola density increased its seed number per pod and pod number per plant, but by increasing wild mustard density per pot, contrary results for mentioned traits in weed were obtained. Nich differentiation indices (NDI) of biological and grain yield estimated less than 1 at 4 levels of nitrogen. NDI of biological yield was more than that of grain yield. Maximum NDI of both mentioned traits, obtained in 1 and 1.25 g nitrogen per pot, respectively. Generally, the results of experiment indicated that the rate of 1g pure N per pot (equivalent to 200 kg ha-1) was appropriate fertilizer treatment to increase competitive ability of canola in interference with wild mustard.