Effects of irrigation with different sources of water on growth, yield and essential oil compounds in oregano

Aromatic plants can benefit from the use of treated wastewater to satisfy their water requirements, but the effects on the essential oil yield and quality need an assessment. The aims of this study were to assess the effects of freshwater and treated wastewater obtained from a Sicilian (Italy) pilot-scale horizontal subsurface flow constructed wetland system on plant growth and yield, essential oil yield and composition of oregano (Origanum vulgare ssp. hirtum (Link) Ietswaart) and soil characteristics. The system had a total surface area of 100 m2 and was planted with giant reed and umbrella sedge. An experimental open field of oregano was set up close to the system. Two years and two different sources of irrigation water were tested in a split-plot design for a two-factor experiment. Treated wastewater was characterized by higher values of mineral and organic constituents than freshwater. The results highlight that short-term irrigation with freshwater and treated wastewater, in both years, led to increased plant growth, dry weight and essential oil yield of oregano plants. However, it did not significantly affect the essential oil content and composition in comparison with the control. Furthermore, the year and source of irrigation water did not significantly vary the chemical composition of the soil. Our results suggest that treated wastewater can be considered an alternative to freshwater for the cultivation of oregano due to the fact that it does not greatly influence the yield quality and quantity of this species in the short-term.