Effect of Different Levels of Irrigation and Nitrogen Fertilizer on Yield and Yield Components of Some Safflower Cultivars in Alborz Province

To investigate the effect of different levels of irrigation and nitrogen fertilizer on yield and yield components of some safflower cultivars, an experiment was conducted as a split-split plot in a randomized complete blocks design with three replications in the research farms of the University of Tehran, Karaj during 2018-2019. Main plots were irrigation (normal irrigation, irrigation until at middle of flowering stage and irrigation until the beginning of seed filling), sub plots were nitrogen (supply of 100 % and 50 % of nitrogen needs) and sub-sub plots were safflower cultivars (Goldasht, Golmehr, Padideh and Parnian). The effect of irrigation, nitrogen, and cultivar factors on number of heads per plant, number of seeds per head, 1000-seed weight, grain yield, and biomass were significant. According to the results, cut-off of irrigation at the beginning of seed filling and middle of flowering stages leads to a reduction of 16.2 % and 68.1 % of seed yield compared to normal irrigation, respectively. Reducing the amount of nitrogen by 50 % compared to 100 % supply decreases seed yield 8.5 % and biomass by 12 %. The triple interaction of irrigation, fertilizer and cultivar was significant in stem diameter and head diameter. The interaction of irrigation and nitrogen levels showed that with decreasing irrigation levels, nitrogen uptake also decreased and reduced the number of seed per head. However, providing 100 % of the nitrogen requirement under drought stress conditions prevents a more severe decline in the number of grains per head.