This experiment was conducted to evaluate the effects of different levels of nitrogen application on the yield and yield components of safflower at the agricultural research station of Isfahan University of Technology. Four nitrogen rates (0, 30, 60, and 90 kg/ha) and two safflower cultivars (IL 111 and Kosseh) were investigated using a factorial arrangement in a randomized complete block design with four replications. Each experimental plot was consist of five rows, spaced 45cm apart with plants 5cm apart on each row. The duration from stem elongation to button formation, button formation to flowering initiation, flowering to maturity were significantly affected by the levels of nitrogen application. The number of days from planting to emergence, emergence to stem elongation, stem elongation to button formation, button formation to flowering initiation were longer in Kosseh than in IL 111 . The number of branches per plant, leaf area index, plant dry matter, and number of buttons per plant, number of grains per button, grain weight, grain yield, and oil yield were significantly affected by the levels of nitrogen application. The grain yield of IL 111 was significantly increased as the level of nitrogen application was enhanced up to 90 kg/ha. In Kosseh, however, there was a decrease in grain yield at 90 compared to 60 kg/ha nitrogen level. The grain oil percentage was influenced by the amount of applied nitrogen in Kosseh but not in IL 111 . The greatest amount of grain and oil yield (3537 and 1012 kg/ha, respectively) were obtained from the plants of Kosseh grown at 60 kg/ha nitrogen level. This greater yield was related to producing of more buttons per plant as well as the formation of greater number of grains per button in the plants of Kosseh than in those of IL 111 . The results of this experiment shows that there are differences between safflower cultivars in response to nitrogen application and that the capability of IL 111 to use nitrogen for producing optimum yield is more when compared to Kosseh.
