Effect of Different Levels of Sodium Selenate and Selenite on Morphological Characteristics and Nutrients Concentration in Peppermint

To investigate the effect of sodium selenate (Na2SeO4) and sodium selenite (Na2SeO3) on some morphological characteristics and nutrients concentration in peppermint, an experiment was conducted in a completely randomized design with four replications. Different levels of sodium selenate and sodium selenite (0, 4, 8, and 12 mg l-1) were applied in soilless cultivation in the research greenhouse of the Faculty of Agriculture, Ferdowsi University of Mashhad. Then morphological traits and the concentrations of nutrients in the leaf were measured in the flowering stage. The results showed that the application of two forms of selenium at a concentration of 4 mg l-1 increased the growth traits in peppermint. The highest concentration of both salts decreased the plant growth. The results also showed that with increasing the concentration of selenite and sodium selenate, the selenium concentration increased, but the use of sodium selenate caused higher concentration of this element in the leaf. At a concentration of 4 mg l-1 selenium, the concentrations of macronutrients including nitrogen, phosphorus, potassium, calcium, and magnesium in the leaf increased by 43.7, 11.1, 3.2, 11.6, and 9.2%, respectively, compared to the control but were not significant. The highest nitrogen concentration was observed at the concentration of 4 mg l-1 sodium selenite 43.7% greater than the control. With increasing the concentration of selenium, except for molybdenum and manganese, the concentration of zinc, iron, boron, and copper increased. The highest concentrations of iron and boron were obtained at 12 mg l-1 sodium selenate, 60.2 and 25.7% greater compared to the control, respectively. The highest concentrations of zinc and copper measured at 12 mg l-1 sodium selenite were 63.3 and 40.6% greater than the control, respectively. In general, it is concluded that 4 mg l-1 of sodium selenate can be applied to improve the growth and nutritional condition of the peppermint.