Influence of various electrical conductivity levels on the growth and essential oil content of peppermint (Menta piperita L.) grown in hydroponic

Peppermint plants were grown hydroponically in a greenhouse to evaluate the effects of electrical conductivity (EC) of solution on the growth and essential oil content of the plants. There were 5 nutrient solutions differing in EC (0.7, 1.4, 2.8, 5.6, 5.6(Na) dS/m). The 5(th) treatment at 5.6(Na) dS m(-1) NaCl added to the half strength of modified Hoagland solution. The plants were harvested at the flowering stage and vegetative characteristics and essential oil content were measured. The results showed that the various solutions EC levels had significant effects on the vegetative characteristics and essential oil content so that the highest and lowest fresh weight of the plants was obtained in 1.4 and 5.6 dS m I treatments, respectively. Increasing the solution EC with either NaCl or all nutrients at 5.6 dS/m reduced the fresh weight of the plants however, the extent of fresh weight reduction became more pronounced in 5.6 dS/m treatment by adding all nutrients. Both high and low EC of the solution reduced the leaf area so that the highest leaf area (1.4 m(2)/plant) was observed at 1.4 dS/m I treatment. The concentration of essential oil was significantly low in 0.7 dS m(-1) treatments however it was increased progressively when the EC of solution increased. The total content of essential oil was reduced by increasing EC of solution as the result of I the reduction in total fresh weight of the plant. The essential oil content in 1.4 dS m(-1) treatments was 63% and 47% higher than those of at both 5.6 and 5 1 6 (NaCl) dS m-1 treatments, respectively. Maintaining the EC solution in 1.4 dS m(-1) could be an optimum value of EC for achieving appropriate peppermint growth and oil production.