Herbage yield, essential oil content and composition of three oregano (Origanum vulgare L.) populations as affected by soil moisture regimes and nitrogen supply

To compare the response of oregano (Origanum vulgare L.) populations to soil moisture regimes and nitrogen fertilization, a greenhouse experiment with three populations of oregano cultivated in Germany (O. vulgare var. creticum, O. vulgare ssp. hirtum, O. vulgare var. samothrake) was conducted during 2006-2007 at the research station Rauischholzhausen of Justus Liebig University in Germany. A completely randomized experimental design with three soil moisture regimes (optimal, consistent water deficiency and water deficiency from the beginning of flowering) and two nitrogen fertilization levels with six replications was realized. Dry matter production of population O. vulgare var. samothrake was stable for two experiment years, whereas those of the populations O. vulgare var. creticum and O. vulgare ssp. hirtum were higher in 2007 than in 2006. Among tested populations O. vulgare var. samothrake showed the highest essential oil content in both experiment years. Consistent water deficiency caused reduction of dry matter, but not essential oil content. Water deficiency in flowering stage reduced also dry matter production, but increased essential oil content, resulting in the highest essential oil yield in 2006 and a comparable essential oil yield as control in 2007. Higher nitrogen levels caused an increase in dry matter production of oregano for both experiment years and a decrease in essential oil content in 2007, which can be explained in terms of dilution effect. Totally, 42 compounds were identified in essential oils of three populations by means of GC-MS. Carvacrol was the dominant compound (70.0-77.4%) for all essential oil samples, followed by γ-terpinene (8.1-9.5%) and p-cymene (4.5-5.3%). The composition of essential oil of oregano populations was independent of cultivation conditions. In conclusion, the population of O. vulgare var. samothrake showed a stable dry matter yield with higher essential oil content than the populations of O. vulgare var. creticum and O. vulgare ssp. hirtum. Water deficiency after beginning of blooming (folded flowers) can induce an increase in essential oil content and thus result in higher quality of oregano herbage and higher water use efficiency of oregano plants.