The effects of irrigation period and humic acid on morpho-physiological and biochemical traits of thyme (Thymus vulgaris)

In order to study the effects of irrigation period and humic acid on some morpho-physiological and biochemical characteristics of Thymus vulgaris L., an experiment was conducted as split plots based on randomized complete block design with three replications at research farm of Baharan University of Gorgan, during growing season of  2016- 2017. Treatments were four levels of irrigation periods (every 3, 6, 9 days and everyday as control) and humic acid at three levels (0, 150, and 300 mg/l). Results showed that irrigation periods increased phenolic compounds, antioxidant activity, proline, and soluble carbohydrate. The effect of the longest irrigation period (every 9 days) increased 1.07, 0.016, 14.53, 1.87 and 3.82 percent of proline, phenolic compounds, antioxidant activity and soluble carbohydrate, respectively. Also the highest concentration of essential oils was observed with the every 6 days irrigation treatment showing 15% difference as compare with the control. On the other hand irrigation period decreased significantly shoot height and wet and dry weight. Moreover, humic acid had a significant effect on all characteristics under study. Also, interaction effect of humic acid and irrigation periods had significant effects on all traits except for phenolic compounds. Foliar application with 150 mg/l humic acid and every 9-day irrigation resulted in the maximum increase in thymol and antioxidant activities. The highest level of essential oils was achieved in 300 mg/l humic acid and every 6-day irrigation period. Maximum proline content was also recorded under 300 mg/l humic acid and every 9-day irrigation period. Generally, findings suggested application of 300 mg/l humic acid and every 9-day irrigation as economically the best treatment since under humic acid application and less irrigation water the same yield is achieved as under high water consumption.