Effect of Nutrient Solution EC on the Concentration and Composition of Peppermint (Mentha piperita var officinalis)

An experiment was conducted to asses the effect of nutrient solution EC on growth, essential oil concentration and composition in peppermint grown in hydroponics. Four levels of EC (., 1.4, 2.8, 5.6 dS m-1) achieved by adding all macronutrients to the Hoagland's solution were used to the plants. The experiment was arranged in randomized complete block design with three replications. The result showed that vegetative characteristics in terms of fresh and dry weight was affected by solution EC, so that the highest fresh and dry weight was observed in EC 1.4 dS m-1. Increased solution EC (5.6 dS m-1) reduced the biomass production by 40%, as compared to 1.4 dS/m. The concentration of K and P was increased as the solution EC increased, however, no changes of N concentration was observed. The maximum and minimum oil content was obtained in 1.4 and both 0.7 and 5.6 dS m-1, respectively. Oil content was decreased by 35% as the solution EC increased from 1.4 to 5.6 dS m-1. The composition of essential oil was changed in various solution EC. It consisted of 23 compounds in which Menton, Menthol and Menthophoran constituted the main composition. Increasing the EC from 1.4 to 5.6 dS m-1 reduced the concentration of Menton, however, both Menthol and Polygon concentrations was increased. In addition, the concentration of Beta-Caryophylin and Beta-Cobeben was increased as the solution EC raised. The results led to conclusion that EC manipulation can be used to change the composition of essential oil. Moreover, the EC of 1.4 dS m-1 according to Hoagland solution could be an optimum value for obtaining higher concentration of oil and proper growth of peppermint in soilless culture.