The effect of drought stress on yield, content and percentage of essential oil of Nepeta pogonosperma Jamzad et Assadi under different plant density

Drought stress is an important environmental factor that reduces the yield of plants. Nepeta pogonosperma Jamzad et Assadi is a perennial plant from Lamiaceae family. Iran is an arid and semiarid region and most of the agricultural lands are faced with drought stress; this is the main reason for reduced yield. In order to investigate the effect of drought stress and planting interval on Nepeta pogonosperma, an experiment was conducted under field conditions in 2012, at Alborz research station, Research Institute of Forests and Rangelands, Karaj, Iran. The experiment was conducted in factorial in the form of a randomized complete block design with three replications. Planting interval factor was in four levels (20×20, 30×30, 40×40 and 50×50 cm), and drought stress factor was in three levels (30, 60 and 90% of field capacity). Analysis of variance showed that the effect of interaction of drought stress × planting interval was significant on diameter of the main stem and the percentage of essential oil at P≤0.05. The effect of planting interval and drought stress was significant on leaf width and length, inflorescence length, yield, essential oil percentage and yield, number of flowering stems and total stems, and number of inflorescences. Mean comparison showed that the maximum leaf width (15.9 mm), leaf length (40.5 mm), and shoot yield (3391 kg/ha) were achieved in the control (90% FC), and the highest number of non-flowering stems (47), number of flowering stems (41), number of total stems (88), number of inflorescences (15), shoot yield (5185 kg/ha), essential oil percentage (3.21%) and essential oil yield (122 kg/ha) were related to 20×20 cm planting interval. The results of this study showed that in order to achieve the maximum shoot yield and essential oil yield, a planting interval of 20×20 cm at a drought level of 60%FC could be recommended.