effect of nitrogen and herbicide levels on wheat (triticum aestivum) competition ability against wild mustard (sinapis arvensis)

to evaluate the competition between wheat and wild mustard (sinapis arvensis) in nitrogen and herbicide levels, an experiment was conducted in ramin agriculture and natural resources university, at 2007-8. a split-plots design in rcbd (randomized complete blocks design) with three replications was used for this experiment. the nitrogen levels (0, 60, 120 and 180kg/ha) arranged in main plots. each main plot was be splitted to five sub-plots, and herbicide levels (0, 15, 20 and 25g three benoron methyl/ha) with hand-weeding as a control treatments were arranged in sub-plots. the results showed that the interaction effect between nitrogen and herbicide levels on grain yield (gy) of wheat and dry matter (dm) production of wild mustard was significant. with increase of nitrogen, while herbicide levels were low or no control was be done, gy of wheat and dm of wild mustard decreased and increased, respectively. it can be said that in high levels of nitrogen, more herbicide will be required for weed management. in low levels of nitrogen, difference between herbicide levels was little and dm of wild mustard decreased significantly. generally, increase of nitrogen caused to decrease of wheat competition ability against wild mustard and also caused to requirement more herbicide. highest dm of mustard was produced with 180kg n/ha without weed control. in the other hand, highest gy of wheat was gained by 180kg n/ha and 20g three benoron methyl/ha.