Effect of different irrigation regimes and fertilization on essential oil yield and ‎composition of peppermint essential oil (Mentha piperita L.)‎

In order to investigate the effects of water deficit and nitrogen fertilizers on peppermint’s essential oil yield and its compounds, the current experiment was conducted in Research Field of Tarbiat Modares University in 2018, based on split with three replications. The experimental treatments consisted of three irrigation regimes (respectively after depleting 25, 40 and 55% of available water in root growth zone) as the main factor and six fertilizer treatments based on nitrogen requirement as sub-factors. The results showed that the highest essential oil yield was obtained under normal irrigation conditions with urea, while severe water deficit stress caused a reduction of 44% in dry matter and essential oil yield. In this study, 36 compounds were identified in essential oil. The most important components of essential oil were menthol, menthon, menthofuran, piperitone and menthol acetate. Water deficit increased the quality of essential oil (increased menthol and menthon and decreased menthofuran and polygon). In this regard, the use of nitrogen fertilizer increased both the quality and yield of essential oil. In general, it can be concluded that moderate water deficit accompanied with nitrogen fertilizer (urea alone or in combination with vermicompost) might increase the quality of peppermint’s essential oil. Increasing essential oil quality caused by water deficit, reduced quantitative essential oil yield.