Critical concentration of iron in relation to essential oil yield and quality parameters of Japanese mint

Seedlings of Japanese mint (Mentha arvensis L.) were grown in culture solutions containing 0.0, 0.56, 1.4, 2.8, 5.6, 11.2, and 22.4 μg.ml-1 Fe for 90 days under glasshouse conditions. The trials carried out indicated that the fresh weight of the herb, dry matter yield, menthol, and oil contents increased significantly with graded levels of Fe application, the optimum results being obtained at 5.6 μg.ml-1. Fe uptake was maximum at 11.2 μg.ml-1 and showed a significant quadratic trend. Oil and menthol contents were positively correlated with both fresh weight and dry matter yield of the herb indicating the influence of growth parameters on the quality and content of total oil. The critical iron concentration on a dry weight basis was calculated to be 6.72 μg.ml-1.