Evaluation of Growth, Yield, Oil Content, Irrigation Water Productivity and Nitrogen Use Efficiency of Sunflower (Helianthus annuus L.) at Different Levels of Plant Density and Nitrogen Content

In order to investigate the effect of planting densities and different amounts of nitrogen on leaf greenness index and leaf area index, seed yield and oil yield, irrigation water productivity and nitrogen use efficiency in sunflower, an experiment was conducted as a split plot in the form of randomized complete blocks design with three replications in the research farm of Agriculture Institute in Semnan province in the spring of 2019. Plant density in four levels (4, 6, 8 and 10 plants per m2) as a main plot and the amount of nitrogen levels (0. 50, 100, 150 and 200 kg urea ha-1) as sub plot was 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, which decreased with increasing density of the above traits. Also, the nitrogen levels significantly affected the studied traits, so that with increasing the amount of nitrogen consumption, from control (0 kg urea ha-1) to 200 kg urea ha-1, the leaf greenness index increased by 15.3%. The highest amount of plant height, 100-seed weight and grain nitrogen were obtained in the treatment of 150 kg urea ha-1 and 14.13, 9.07 and 24.3% more than no application, respectively. Mean comparing the results of water use efficiency showed that at a density of four plants per m2 and an increase in nitrogen levels, along with increasing height and leaf area index, water use efficiency also increased, but higher levels of density led to smaller plant yield, less plant biomass and water efficiency were reduced. The highest nitrogen use efficiency was obtained in the density of 8 plants per m2 and no application of nitrogen fertilizer. Finally, maximum grain yield (4016 kg.ha-1) and oil yield (1827 kg.ha-1) were obtained by consuming 150 kg urea per ha-1 and density of 8 plants per m2.