Effect of Different Levels of Nitrogen and Selenium on Efficiency of Nitrogen Intake and Some Morphphysiological Characteristics of Edible Onion (Allium cepa L.)

In order to investigate the effects of selenium and nitrogen on some growth and biochemical characteristics of edible onion (Cultivar Yellow Isfahan), a factorial experiment was conducted base on randomized complete block design with three replications at Razi University in year 2017. In this experiment, the first factor includes the time of split of nitrogen fertilizer (based on soil test, which includes 500 kg urea per hectare) in six levels including control, total fertilization at the time of transplantation, half fertilization at the time of transplantation, third fertilization at the time of transplantation, half fertilization at the time of transplantation+ half fertilization at the time of bulb initiation, third fertilization at the time of transplantation+ third fertilization at the time of bulb initiation+ third fertilization at the time of bulb growth and three levels of selenium (0, 10 and 50 mg.L-1 sodium selenate). The highest yield (21.44 Kg.m-2), fresh weight (251.83 g.bulb-1), the bulb length (84.19 mm), bulb diameter (78.66 mm), total phenol (19.87 mg.g-1 FW: fresh weight), total phenol (19.87 mg.g-1 FW: fresh weight), total flavonoid (9.30 mg.g-1 FW: fresh weight) and antioxidant activity (11.44 %) of the onion bulb were observed with nitrogen application of in three stages (third fertilization recommended at the time of transplantation+ third fertilization at the time of bulb initiation+ third fertilization at the time of bulb growth). Selenium had a positive effect on yield, fresh weight, length and diameter of bulb and total flavonoid in onion. Therefore, use of sodium selenate along with nitrogen plays an important role in improvement the growth and physiological characteristics of onion such as bulb dry weight (84.73 g.bulb-1) and nitrogen use efficiency (1 Kg.mg-1 DW: dry weight). In conclusion, split application of of 500 kg.ha-1 urea at the time transplantation, bulb initiation and bulb formation equally one third in each stage, and 50 mg.L-1 sodium selenate can be recommended for onion production.