Effects of different sources of nitrogen fertilizer and applied rates on essential oil content and composition of peppermints

Peppermint known for its healing properties is a plant from the Labiatae family. Currently, different rates of nitrogenous fertilizers are used in production of peppermint while there is no precise information available about how much of nitrogen fertilizer is the optimum rate for this plant. The main purpose of this research was to evaluate the response of peppermint chemical composition to different nitrogen rates and type of nutrition strategy (with control and conventional chemical sources). Samples collected from different mint nutrition strategy [conventional: four nitrogen levels from three fertilizers source (UAN, urea and ammonium sulfate), and control (no added fertilizer) in the Khouzestan province at the southwest of Iran. Nitrogen supply led to increase of fresh and dry yield of peppermint. Maximum essential oil obtained from 210 kgN/ha of nitrogen fertilizer in UAN which showed the best results compared to urea, ammonium sulfate and control. The GC/MS data showed that the qualitative of the components appeared to be not constant in different nutrient strategy. Moreover, remarkable variations were found in the amounts of the major of essential oil constituents. A total thirty-five components, comprising 98.87, 97.62, 98.09 and 97.98% of the obtained total essential oils were characterized in control, UAN, urea and ammonium sulfate samples, respectively. Also Menthol (41.22, 33.7, 30.62 and 33.23%), menthone (16.32, 26.25, 27.33 and 26.7 %), menthofuran (4.09, 4.74, 5.81 and 5.14 %) and isomenthone (6.47, 7.48, 7.26 and 7.43%) were the main components of peppermint oil.  Since, essential oil of peppermint, particularly menthol component, has many application in pharmaceutical and perfumery industry due to antiviral, antibacterial and antispasmodic activity, UAN fertilizers is recommended to be used in addition to control in view of the increasing in quality and quantity of essential oil.