Thymus daenensis Celak., also known as denaian thyme, is an endemic and endangered medicinal herb, having valuable therapeutic properties in the Iranian traditional medicine. In the present study, a two years’ field experiment was conducted to study the influence of organic and inorganic fertilizers on biomass, essential oil yield, essential oil content and compositions and antioxidant activity of denaian thyme in southwest of Iran. The treatments were: no fertilizer (control), chemical fertilizer (CF; NPK at 100-150-100 kg ha-1), cow manure, vermicompost (VC) and combined fertilizers (chemical fertilizer + cow manure + vermicompost). Application of combined fertilizers significantly increased the biomass and essential oil yield of denaian thyme as compared with control, in the first and second year, by 39.61% and 68.62%, respectively. Application of fertilizers, however, significantly affected the essential oil compositions of the plants in both growing years. The essential oil of T. daenensis was rich in the phenolic monoterpene thymol. The highest amount of thymol was obtained under application of combined fertilizers in both years. The antioxidant activity of T. daenensis methanolic extracts, evaluated by the DPPH assay, increased (10.41% compared with control) under application of combined fertilizers in the second year. In both years, the N content of the soil increased after treatment with combined fertilizers (around 43% higher over the control). Alike, soil fertility parameters such as P and K showed a marked improvement in all treatments over the control. Results of this study showed that the combined application of fertilizers enhanced biomass and essential oil yield and improved the soil characteristics, antioxidant properties and aroma profile.
