Evaluation of growth, yield, oil content, irrigation water use efficiency of sunflower (Helianthus annuus L.) at different levels of plant density and nitrogen content

Iran has been facing shortage of edible oil and a rapid growing population, and the country has to supplement the needs by importing. To investigate the effect of planting densities and different amounts of some traits of sunflower, an experiment was conducted as a split plot in the form of randomized complete blocks design with three replicates in the research farm of the Agricultural and Natural Resources Research and Education Centre of Semnan province (Shahrood). Plant density in four levels (4, 6, 8 and 10 plant.m−2) as a main plot and the amount of nitrogen levels (0.50, 100, 150 and 200 kg N ha−1) as sub-plot were considered. Leaf greenness index, plant height, 100-seed weight, seed nitrogen content and seed oil content were significantly affected by the simple effect of planting density and decreased with increasing plan density. Also, the nitrogen levels significantly affected the studied traits, so that by increasing the amount of nitrogen application, from control to 200 kg N ha−1, the leaf greenness index increased by 15.3%. At a density of four plant.m−2 and an increase in nitrogen levels, water use efficiency increased along with an increase height and leaf area index, but higher levels of plant density led to smaller plant yield, less plant biomass and lower water efficiency. The highest nitrogen use efficiency was obtained at a density of 8 plant.m−2 and no application of nitrogen fertilizer. Finally, maximum seed yield (4016 kg.ha−1) and oil yield (1827 kg.ha−1) were obtained by applying 150 kg N ha−1 and density of 8 plants.m−2.