Effects of nutrients foliar application on quantity and quality of peppermint (Mentha piperita L.) essential oil under different irrigation levels

To evaluate the effects of different irrigation levels and foliar application of nutrients, on dry matter yield and essential oil content and composition of peppermint (Mentha piperita L.), a field experiment was conducted as a split plot based on a randomized complete block design, with 12 treatments and three replications, at the faculty of Agriculture, University of Maragheh, Iran in 2021. The factors included irrigation as the main factor at three levels (irrigation after 20 (control), 40 (moderate stress), and 60% (severe stress) of the maximum allowable moisture depletion) and fertilizer source as the sub-factor at four levels (non-application of fertilizer (control), and foliar application of Macromix gold, Ecoquel micromix, and Vitalem forte). The results demonstrated that the highest (280.5 g.m-2) and lowest (113.7 g.m-2) total dry weight were obtained under normal irrigation conditions (control) with the application of Macromix gold and severe stress without fertilizer application, respectively. Total dry weight decreased by 22.7 and 40.3% under moderate and severe drought stress conditions, respectively compared to normal irrigation. Macromix gold, Vitalem forte, and Ecoquel micromix application enhanced the amount of total dry weight by 37.7, 23.8, and 17.1% compared to no fertilizer application, respectively. The highest content (2.1%) and essential oil yield (4.5 g.m-2) and also the highest amount of menthol (40.9%), menthone (28.1%), and cineole (6.2%) in the essential oil were observerd under moderate water stress conditions fertilized with Macromix gold. Based on the obtained results, the foliar application of Macromix gold could be recommended as an effective solution to enhance the quantity and quality of the peppermint essential oil under drought stress conditions.