Effects of drought stress and nitrogen fertilizer rate on some physiological characteristics, essential oil percentage, and yield of basil (Ocimum basilicum L.)

In order to investigate the effects of drought stress and nitrogen fertilizer on some physiological and biochemical characteristics of basil (Ocimum basilicum L.), a split-plot experiment was conducted based on randomized complete block design in three replications in the research farm of Islamic Azad University, ArdabilBranch, 2015. The treatments included drought stress (70, 140 and 210 mm of class A evaporation pan) and nitrogen fertilizer at three levels (0, 50 and 100 kg/hectare) respectively. The results showed that the effect of drought stress treatment was significant on the traits investigated. The interaction of drought stress × nitrogen fertilizer had a significant effect on the traits measured, such as chlorophyll a, total chlorophyll, relative water content, dry matter yield, and essential oil yield. In addition, fertilizer treatment caused a significant increase in the physiological characteristics, dry matter yield, and essential oil yield. According to the results, the maximum content of chlorophyll a (2.65 mg/g fresh weight), total chlorophyll (3.42 mg/g fresh weight), relative water content (72.02 percent), dry matter yield (2261.25 kg/hectare), and essential oil yield (7.13 kg/hectare) were obtained for the control treatment and 100 kg of nitrogen per hectare. The maximum content of carbohydrates (3.40 μg/g glucose per fresh weight) and proline (0.681 µmol/g fresh weight) was related to the severe stress treatment. The content of chlorophyll a, b, total, relative water content, carotenoid, and essential oil percent and yield decreased by increasing the drought stress, while the content of carbohydrate and proline increased. Therefore, irrigation at 70 mm evaporation and 100 kg nitrogen fertilizer per hectare could be recommended as the best treatment to achieve the highest levels of chlorophyll a, chlorophyll total, relative water content, dry matter yield, and essential oil yield of basil.