Intercropping systems play an important role in achieving higher production and increasing the sustainability of agricultural ecosystems. In order to evaluate the quantity and quality of peppermint essential oil and faba bean yield in intercropping systems, a two-year (2015-2016) field experiment was conducted in Iran. The study was performed with different treatments at two harvest times (July and October). The treatments were monoculture of peppermint, monoculture of faba bean, and different ratios of peppermint to faba bean (including 50:50, 34:66, 66:34, 40:60, 60:40, 25:75 and 75:25 %). Results demonstrated that the highest peppermint biomass yield (average of two years) was obtained in peppermint monoculture and intercropping ratios of 66:34, 40:60, 60:40 and 75:25 in both harvests. However, the highest and the lowest essential oil content in both harvests were observed in 40:60 cropped pattern and peppermint monoculture, respectively. In addition, the first harvest (July) gave about 20% more essential oil content than the second one (October). The highest essential oil yield in both harvests, however, was observed in 40:60 and 60:40 intercropping patterns. Furthermore, the July harvest gave approximately 52% more essential oil yield than the October harvest. At July harvest, the menthol content was enhanced in ratios of 40:60, 34:66 and 60:40 (increase of 3.3%, 2.8% and 1.8%, respectively) compare to peppermint monoculture. In addition, all intercropping patterns in the October harvest showed a higher content of menthol than monoculture of peppermint. According to the obtained results, intercropping of peppermint with faba bean could improve the essential oil quality by increasing the content of menthol and decreasing the content of menthofuran and pulegone.
