In order to study the effect of planting density and nitrogen rate on weeds biomass and some of the agronomic traits in grain maize 640, an experiment was conducted in 2013 at the research field of Khosroshahr Jahad-e-Keshavarzi in Nojedeh village based on factorial in a randomized complete block design with three replications. First factors was included crop density at three levels (8, 10 and 12 plants per square meter) and second factor was involved nitrogen fertilizer at three levels (100, 200 and 300 kg per hectare). Results demonstrated that augmentation of density caused reduction in weeds biomass (27.2%) and enhanced grain weight per square meter (28.2%) and in cob diameter. Increase of nitrogen lead to augmentation in 300-grains weight, ear diameter and cob diameter. Enhancement of maize density until 10-12 plants per unit of area simultaneous with the use of nitrogen fertilizers recommend as a technique to prevent redaction of yield due to weeds competition. According to the results, it can be stated that the appropriate density for this genotype of maize is 12 plants per square meters that, proper yield can be achieved with 300 kg nitrogen. Also, more weeds can be grown with reduction in number of maize plants per area unit and eventually will be lead to reduction in maize grain yield.
