Effects of plant density on quantitative and qualitative yield of three Thymus species in dry farming conditions of three provinces of Iran

In order to evaluate the effect of plant density on quantitative and qualitative yieldof three species of Thymus under dry farming conditions in Tehran (Damavand), Kurdistan and Kermanshah provinces, an experiment was conducted in a randomized block design based on split plot with three replications during three years (2009-2011). The treatments were included three species (T. vulgaris L., T. daenensis Celak.and T. kotschyanus Boiss. & Hohen.) and three planting densities (4, 6 and 8 plant/m2), which were considered as main and sup-plots, respectively. Shoot dry matter yield, essential oil content, yield and essential oil components were determined. Results showed that the four-interaction effect (density, species, year and province) was significant on dry matter content, calculated to be from 75 to 5172 kg/h in different treatments. The maximum dry matter yield was observed at a density of 6 plant/m2 for T. daenensis in Kermanshah in the third year of experiment. The highest essential oil yield was obtained at a density of 8 plant/m2 for T. daenensis in Kermanshah in the second year of experiment. The maximum thymol content (80.33%) was related to T. daenensis inDamavand at a density of 6 plant/m2 in the third year of experiment. Overall, high production capacity of T. daenensis in the study provinces indicates the adaptation and economic yield of this native and valuable species.