In order to investigate the effect of different levels of nitrogen and bio-fertilizers on yield of canola plants in Qazvin, Iran, a split-plot design was conducted on the base of randomized complete block design with four replications. Treatments included 3 levels of nitrogen (0, 75 and 150 kg ha-1) and bio-fertilizers on four levels (no inoculation, Azotobacter, Azospirillum and a combination ...