Water stress and manure application affect the quantity and quality of essential oil of Thymus daenensis and Thymus vulgaris

Thymes species are regarded as important medicinal plants which have extensive medical use due to the high yield of their essential oil and valuable secondary metabolites, especially thymol and carvacrol. The present study aimed to investigate the effects of different levels of water stress by applying manure on the quality and quantity of active ingredients of Thymus daenensis celak and Thymus vulgaris L. essential oils, a factorial experiment was conducted on the research field of the agriculture department University of Birjand, Iran, in the form of complete block designs with three replications in 2015 and 2016 crop year. The experiment factors included water content levels (100; 67 and 33% of Field Capacity), Thymes species (Thymus daenensis and Thymus vulgar-is), and manure (non-application and 30 tons per ha application). Based on the results, water stress has a significant effect on the essential oil content and essential oil yield, and the highest amount was obtained, from Thymus daenensis at 67% water content level of field capacity. In addition, in the first crop year, the highest amount of thymol 78.98% and 78.78% obtained from Thymus daenensis at 100% and 67% field capacity with 30 tons per ha manure application respectively while the highest amount 64.81% and 64.78% in the min year was obtained from Thymus daenensis at 67% field capacity at no manure and 30 tons per ha manure application respectively. The amount of thymol in both species increased with the decrease in the soil water content from 100% to 67% of field capacity, and decreased with the water stress increase to 33% of field capacity. The highest amount of carvacrol was obtained from Thymus vulgar-is in the first year at 33% of field capacity and under manure non-application condition while it was obtained from Thymus daenensis celak at 100% level of field capacity and under manure 30 tons per ha application condition in the min year. In this experiment, the Thymus daenensis was superior to Thymus vulgaris, in terms of essential oil content and essential oil yield and the amount of thymol available in the essential oil, and is recommended for cultivating in regions with water restriction.