Considering the environmental problems arising from chemical fertilizers usage, many attentions has been drawn to the application of biological fertilizers in agriculture. In order to study the effects of chemical nitrogen fertilization and biofertilizer inoculation on grain yield, yield components and oil yield of sunflower (Helianthus annuus L.) under different rates of plant density, a Factorial experiment based on Randomized Complete Block design was conducted in three replications. Experimental factors were: (i). Four levels of chemical nitrogen fertilizer (0, 100, 150 and 200 kg N ha-1), (ii). Two levels of biofertilizer (with and without inoculation) containing of Azotobacter sp. and Azospirillum sp. and (iii). Three levels of plant density (8, 10 and 12 plant m-2). The highest plant height, stem and head diameter, number of grains per head, 1000-grains weight, grain yield, oil yield and biological yield were obtained from the highest level of nitrogen fertilizer (200 kg N ha-1) and biofertilizer inoculation. Application of 150 and 200 kg N ha-1 showed no significant difference in these traits. Furthermore, the highest rate of plant density (12 plant m-2) showed the maximum values of grain yield, oil yield and biological yield that was statistically in par with 10 plant m-2 density. The results pointed out that medium plant density (about 10 plant m-2) with moderate N rate (about 150 kg N ha-1) can be beneficial to improve growth, development and total yield of inoculated sunflower.
