Field studies of nitrogen application on growth and yield of Greek oregano (Origanum vulgare ssp. hirtum (Link) Ietswaart)

The effects of four levels of nitrogen application (0, 40, 80, and 120 kg ha−1) on plant growth traits, biomass yield, oil concentration and oil yield of Greek oregano (Origanum vulgare ssp. hirtum (Link) Ietswaart) during three cultivation periods following field establishment were examined. The number of stems, branches and inflorescences per plant, LAI, dry matter and oil yield were significantly affected by nitrogen levels above 40 kg ha−1, showing an optimum mostly at 80 kg of N ha−1. No nitrogen-effect on plant height and oil concentration was observed. Nitrogen-induced biomass and oil yield variations were caused by respective variations in tillering, branching, and the number of inflorescences. Cultivation periods, involving both the age- and the weather-effects, affected all traits, except the average internode length. Root surface density in the top 25 cm of soil was positively affected by nitrogen with a peak at 80 kg ha−1, whereas leaf chlorophyll concentration (mainly chlorophyll a) was steadily increasing with nitrogen rate up to 120 kg ha−1.

Research highlights▶ Nitrogen application promotes oregano herbage yield with an optimum at 80kg N/ha. ▶ Nitrogen promotes oregano branching and secondary stems. ▶ Oil concentration is affected by cultivation period but not by nitrogen. ▶ Oil yield is promoted by nitrogen through its positive effects on herbage yield.