Optimization of nitrogen concentration and harvest time for obtaining maximum growth and essential oil production in summer savory (Satureja hortensis L.)

The yield of medicinal plants depends on biomass of the target organs and its essential oil content. In the present study, the effects of nitrogen concentration and harvest time on the growth, photosynthetic performance, biochemical content, and essential oil content and composition of summer savory (Satureja hortensis L.) were investigated. Seedings were grown under different nitrogen concentrations (10, 15, 20, and 25 mM) in a controlled greenhouse setting. Plants were harvested at three different times (4:00 a.m., 1:00 p.m., and 9:00 p.m.) at the flowering stage. Feeding plants with higher nitrogen concentrations significantly improved morphological and biomass parameters, chlorophyll content, and photosynthetic efficiency, with their highest levels in plants fed by 25 mM nitrogen. However, the optimal yield and quality of essential oils, were recorded in plants fed by 10 mM nitrogen at 4:00 a.m. harvests. Similarly, total phenolic and flavonoid contents peaked in plants fed by 10 mM nitrogen. Chlorophyll content elevated while carotenoids decreased with increase in nitrogen concentrations of the nutrient solution. Maximum quantum yield of photosystem II was the highest at 9:00 p.m. and reached to its lowest values at 1:00 p.m. The present study highlights the nuanced relationship between nitrogen availability, harvest timing, and the production of key secondary metabolites, providing insights for optimizing cultivation practices in summer savory. These findings emphasize the importance of harvest time and nitrogen management for enhancing both crop yield and the therapeutic properties of essential oils in agricultural systems.