Effect of Sowing Date and Nitrogen Rate on Morphological Traits, Seed Production and Essential Oil of Pulicaria gnaphalodes (Vent.) Boiss.

Pulicaria gnaphalodes (Vent.) Boiss. is a medicinal plant perennial and herbaceous belong to Asteraceae family which grows in some parts of Iran. In order to investigate the effect of two sowing dates (May 3 and 23) and nitrogen rates (0, 80, 160, and 240 kg N/ha) on morphological traits, yield and yield components and essential oil yield of P. gnaphalodes aerial parts, a factorial experiment based on a randomized complete block design with three replications was carried out in research field of Birjand branch, Islamic Azad University, Birjand, Iran in 2018. The results of analysis of variance showed that the simple and interaction effects of sowing date and nitrogen rate significantly affected plant height, number of main branch, number of capitols per plant, seed yield, dry weight and percentage of essential oil produced by the aerial parts at 1% level. In addition, the number of secondary branches, canopy diameter, number of seed per capitols and 1000-seed weight were affected by the nitrogen content at 1% level. The effect of sowing date on the number of main branches and canopy diameter was significant at the 1% level and on 1000-seed weight was significant at 5% level. Means comparison of simple effect of sowing date showed that plant height, number of main branches per plant, number of secondary branches per plant, canopy diameter, number of capitols per plant, 1000-seed weight, seed yield, and dry weight of the aerial parts had a significant superiority in the sowing date of May 3 compared to May 23, by 15.7, 19, 12.1, 10, 51.4, 15.8, 88.3 and 33.1%, respectively. Increasing the application of nitrogen to 240 kg N/ha also significantly increased the mentioned traits by 24, 41.2, 17.6, 29.3, 82.6, 115.3, 36.2, and 187.3%, respectively compared to 0 kg N/ ha (control). Means comparison of interaction effect between sowing date and nitrogen rate showed that the maximum plant height (68.50 cm), number of main branches per plant (17 branches per plant), number of capitols per plant (170), seed yield (322.87 kg/ha) and dry weight of the aerial parts (1808.52 kg/ha) were obtained in the treatment of the sowing date of May 3 with application of 240 kg N/ha.