Effect of nitrogen and nitrate: ammonium ratio on growth indices and essential oil content of Origanum vulgare ssp. Gracile under saline conditions

In order to evaluate effects of different levels of nitrogen and different ratios of nitrate: ammonium under saline and non-saline conditions on growth indices, essential oil content and yield of Origanum Vulgare ssp. Gracile, a factorial experiment was carried out in randomized complete block design (RCBD) with third factors including nitrogen levels (5, 10, and 15 mM), nitrate: ammonium ratios (100:0, 87.5:12.5, 75:25, 50:50, 25:75, 0:100), and salinity levels (0 and 50 mM NaCl) in three replications. The results showed that under non-saline condition, the highest fresh weight (33.34 g), dry weight (8.16 g), and essential oil yield (158.9 mg/pot) were obtained by 15 mM nitrogen and 75:25 nitrate: ammonium ratio. Under saline condition, all the three above-mentioned traits were reduced in all treatments however under this condition, the highest fresh weight (33.34 g), dry weight (4.56 g) and essential oil yield (94.35 mg/pot) were observed by 15 mM nitrogen and 50:50 nitrate: ammonium ratio. The main effects of all treatments on essential oil content were significant (p ≤ 0.01); so that the highest essential oil content obtained by 15 mM nitrogen, 75:25 nitrate: ammonium ratio, and 50 mM salinity. In conclusion, 15 mM nitrogen with 75:25 and 50:50 nitrate: ammonium are recommended for non-saline and saline conditions, respectively.