Turkish Journal of Agriculture and Forestry




Growth and essential oil content of peppermint (Menhta piperita var. officinalis) and lemon verbena (Lipia citriodora var. Verbena) were evaluated in response to salinity and nutrient solution concentrations, measured as electrical conductivity (EC 0.7, 1.4, 2.8, 5.6, and 5.6_{Na} dS m^{-1}). In peppermint, the highest fresh weight and dry weight were observed in the 1.4 dS m^{-1} treatment. The increased EC with either NaCl or all nutrients at 5.6 dS m^{-1} reduced the fresh weight of lemon verbena. The maximum fresh weight and dry weight in lemon verbena were obtained in both 1.4 and 2.8 dS m^{-1} treatments. Increasing EC level up to 2.8 dS m^{-1} increased leaf area but the leaf area was reduced by 5.6 dS m^{-1} treatment achieved by adding NaCl or all nutrients. The rate of photosynthesis (Pn) was higher in treatments with EC levels of 1.4 and 2.8 as compared to the other treatments. In both peppermint and lemon verbena, the concentrations of N, P, and K increased as the EC of the solution increased from 0.7 to 5.6 dS m^{-1} but in the 5.6_{Na} treatment their concentrations fell. The total content of essential oil was reduced by increasing the EC of the solution because of the reduction in total fresh weight of the plants. In peppermint, the essential oil content in the 1.4 dS m^{-1} treatment was 55.0% and 40.5% higher than those of both 5.6 and 5.6_{Na} treatments, respectively. The major constituents of the essential oil in peppermint were menthol and menthone and in lemon verbena they were geranial and neral in all treatments. The increased Pn and leaf area in moderate EC level led to improved plant growth. Consequently, 1.4-2.8 dS m^{-1} could be an optimum EC value in peppermint and lemon verbena production.

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