An experiment was conducted on clay soil at Lods Agronomy Research Center, McGill University to study the response of weeds communities and corn plants to nitrogen and herbicide application. The experiment was arranged as split plots design with 6 replications, in which application of herbicide (at 4 levels) and nitrogen (at 3 levels) were respectively the main- and sub-treatments. The herbicide Nicosulfuron (9 g ha-1) mixed with mineral oil (Agral 90, 25% v/v) was used to control grass weeds. The herbicide dicamba (590 g ha-1) was used for broadleaf control. Nicosulfuron mixed with Agral at the above mentioned rates, and dicamba at 295 g ha-1 were used to control both grass and broadleaf weeds. Weedy check also was considered as control. Nitrogen (ammonium nitrate) at 60,120, and 250 kg ha-1 was applied twice; once at planting time and again 54 days after planting. The results indicated that the density of grass weeds was higher than that of broadleaf weeds. However, broadleaf weeds could grow vigorously and by the end of the season they showed strong growth in most weedy check. Nitrogen had a pronounced effect on corn growth and yield. Reducing the nitrogen supply resulted in pale green leaves in the corn. Increasing nitrogen application increased the corn biomass mainly during the rapid vegetative growth stage.

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