Allelopathic Activity of Spearmint (Mentha spicata L.) and Peppermint (Mentha x piperita L.) Reduces Yield, Growth, and Photosynthetic Rate in a Succeeding Crop of Maize (Zea mays L.)

The inclusion of species with allelopathic activity in crop rotation systems may have benefits for crop management such as weed control, but less is understood about their wider impacts on succeeding crops. The main objective of this study was to investigate the effects of two allelopathic species (spearmint and peppermint) on growth, physiological characteristics, and yield of a following maize crop. Thus, field experiments were carried out at two sites, according to a randomized complete block design, while the examined treatments were: (a) fallow-fallow-maize crop rotation system (FFM), (b) spearmint-spearmint-maize crop rotation system (SSM), and (c) peppermint-peppermint-maize crop rotation system (PPM). Our results indicated that the inclusion of spearmint or peppermint in crop rotation systems negatively affect the growth of maize plants. The highest plant height was recorded for FFM rotation system where no allelopathic species were used. At both sites and for four sampling dates, the aboveground dry biomass was also affected by the implemented crop rotation system. In particular, dry biomass was significantly lower in the PPM and SSM crop rotation systems comparing to the FFM system, whereas there were no significant differences between these two crop rotation systems. Similar to the maize biomass, the highest values of photosynthetic rate, stomatal conductance, and relative chlorophyll content were observed for the FFM rotation system. Additionally, differences in grain yield were observed among the tested crop rotation systems. Grain yield ranged from 10,200 to 13,346 kg ha(-1) and from 11,773 to 14,106 kg ha(-1) at site A and B, respectively, while it was reduced by 16.54-23.58% and 12.16-17.83% in the SSP and PPM rotation systems comparing to the FFM system. In conclusion, our results indicate that the inclusion of peppermint or spearmint in crop rotation may inhibit plant growth and reduce grain yield of maize as successive crop, an effect that could be attributed to the allelopathic activity of spearmint and peppermint.