Abdollah Javanmard

The results demonstrated that the plant height, the number of nods per plant, number of leaves per plant, the number of lateral branches per plant, SPAD index, dry matter yield and essential oil yield decreased significantly with increasing stress levels. In contrast, the application of AMF reduced the adverse effects of water stress, so that in severe water stress conditions (irrigation after depletion of 70% available water), individual and integrative application of AMF with nitrogen fertilizer increased the mentioned traits when compared with control. In addition, the mentioned traits in the first harvest increased by 127.8, 194.6, 159.8, 147.7, 17.7, and 37.9% in comparison with the second harvest. Also, the essential oil content of peppermint is enhanced with increasing water stress to mild stress. So, the essential oil content in mild stress increased by 11.4 and 39.7%, respectively, when compared with non-stress and severe stress. The highest essential oil yield was achieved at the first harvest with the integrative application of 75% NF+ AMF. Also, the major essential oil compounds of peppermint (menthol) was recorded in mild stress integrated with 75% nitrogen fertilizer+ AMF. Generally, considering that the economic purpose of cultivating medicinal plants is extracting the maximum content of secondary metabolites, and since the productivity of peppermint essential oil increased significantly by the integrative application of 75% nitrogen fertilizer+ mycorrhiza in mild stress, it can be suggested as a superior treatment.