Evaluation of competition, essential oil quality and quantity of peppermint intercropped with soybean

Intercropping is a sustainable practice to achieve higher production per unit land area and time by maximizing the utilization of available resources. This work was aimed to study the effectiveness of peppermint/soybean intercropping patterns on the yield, quality of peppermint essential oil, competition and monetary indices in two years (2015–2016) and two harvests. The experiment was conducted in randomized complete block design keeping ratio of peppermint and soybean in 1:1, 1;2, 2:1, 2:3, 3:2, 1:3 and 3:1, respectively, along with sole plot of both crops. The results demonstrated that the highest biomass yield of peppermint in the first harvest was achieved in sole cropping pattern (317.2 g m−2) followed by 3:2, 3:1, 2:3 and 2:1 intercropping ratios. In the second harvest, the highest biomass yield of peppermint was recorded in peppermint monoculture (289.1 g m−2) and intercropping ratios of 3:2 and 3:1. In both harvests, the highest essential oil content and yield was obtained in the intercropping ratio of 3:2. Notably, the intercropping patterns gave 24.8% (first harvest) and 16.9% (second harvest) more essential oil than peppermint monoculture. Furthermore, the essential oil quality, in terms of high levels of menthol, 1,8-cineole, neo-iso-menthol, p-menth-1-en-9-ol, (E)-caryophyllene, (E)-β-farnesene and germacrene D and low content of menthofuran, improved significantly in intercropping treatments. The highest values of land equivalent ratio (LER), area time equivalent ratio (ATER), area harvest equivalent ratio (AHER), land use efficiency (LUE), monetary intercropping advantage (MAI) and system productivity index (SPI) were obtained in intercropping ratios of 2:3 and 3:2. Additionally, in all planting patterns the partial aggressivity (A) and crowding ratio (CR) values of peppermint were higher than soybean, indicating that the former was more competitive than the latter. According to our results, intercropping peppermint with soybean can improve the quality of peppermint essential oil and maintaining the crop productivity with limited external inputs; thus, this technique can be considered to be a sustainable practice for field management.