Effect of irrigation intervals and humic acid on physiological and biochemical characteristic on medicinal plant of Thymus vulgaris

To investigate the effects of irrigation intervals and humic acid application on some phophysiological and biochemical of thyme (Thymus vulgaris), the experimental in the form of factorial in the design complete randomized block in four replications at Miandoab University Research Field. Experimental treatments were at four levels of irrigation intervals (once every three days, once every six days, once every nine days and every day as control) and three levels of humic acid solution (zero, 200 and 400 mg l-1). The results showed that increasing irrigation intervals, significantly increased total phenol, antioxidant activity, proline and soluble sugars. Irrigation interval at highest level (once every nine days) compared to control increased proline, phenolic compounds, antioxidant activity, soluble sugars, essential oil and thymol by 58.79%, 47.27%, 21.25%, 62.57%, 66.67% and 19.24%, respectively. Increasing irrigation intervals, significantly reduced plant height, fresh and dry weight of plant. Application of humic acid had a significant positive effect on all studied traits. Also, interaction of irrigation intervals and humic acid application had significant effect on all traits except essential oil percentage, phenolic compounds and thymol. According to the results of this experiment, the application of 400 mg l-1 humic acid at irrigation interval of once every nine days is considered to be the best economically treatment because with less water consumption with humic acid application, this plant can achieve the same functions as consuming more water, especially this treatment caused a significant increase in effective substance of Thymus vulgaris.