Effects of Nitrogen Fertilizer on Morphophysiological and Antioxidant Properties of Calendula officinalis L. under Irrigation Regimes

To study the effects of nitrogen levels on morphophysiological and antioxidants properties of calendula under deferent irrigation regimes a split plot experiment based on a randomized complete block design with three replications was conducted at the Urmia Agricultural Station of Saat Lo for two cropping seasons 2016-17. Treatments were four levels of irrigation (irrigation after 5, 10, 15 and 20 days) assigned to main plots, and application of 0, 80, 160 and 240 kg.ha^-1 nitrogen to subplots. Results showed that the effects of irrigation intervals on all studied traits waer significant. There were significant differences among nitrogen levels on all traits except proline content. Interaction of two treatments was significant on leaf area index, stomatal conduction coefficient, chlorophyll b, essential oil percentage, and essential oil yield. Resulats also indicated that, with increasing irrigation intervals from 5 to 20 days, relative water content, chlorophyll, carotenoid, and dry flower yield were reduced by 36.64, 35.27, 24.31 and 45.77 percent respectively. Proline content, catalase superoxide dismutase, and malondialdehyde activities were increased by 24.72, 33.04, 35.51 and 20.86 percent, respectively. Among the nitrogen fertilizer levels, 160 kg ha-1 increased, relative water content, chlorophyll a, carotenoid and dry flower yield by 16.18, 4.24, 23.68  and 28.26 percent, respectively, while it reduced the activity of catalase, superoxide dismutase, and malondialdehyde by 18.10, 21.23 and 29.69 percent respectively as compared to control. The highest leaf area index, stomatal conduction coefficient, chlorophyll b were increased by the use of 160 kg.ha^-1 nitrogen fertilizer and irrigation intervals of 5 days. The highest percentage of essential oil of the flower and essential oil yield were also belonged to the application of 160 kg.ha^-1 nitrogen and irrigation interval of 10 days. To obtain better quality and higher essential oil yield from calendula, irrigation interval of 10 days and application of 160 kg.ha^-1 nitrogen fertilizer is recommended.