Effect of population density and spatial arrangements on the productivity of Zea mays L. and Mentha spicata L. in intercropping systems at wondo genet, rift valley of Ethiopia
In Ethiopia, intercropping of medicinal and aromatic plants, like spearmint, with cereals is not well known and undertaken as a common practice. Intercropping spearmint (Sm) with major produced cereal crops such as maize (Mz) can give a chance for farmers to diversify their incomes. Therefore, the field experiment was conducted at Wondo Genet, Rift Valley of Ethiopia under rain-fed conditions during the 2020 cropping season to investigate the effect of spearmint population density and spatial arrangements on the productivity of the maize-spearmint intercropping. The experiment was laid out in a factorial arrangement based on a randomized complete block design with three replications. Treatments were made from a factorial combination of spearmint population density (100, 75, 50, and 25%), and spatial arrangements (1Mz:1Sm, and 1Mz:2Sm) ratio. Data on phenological, growth and yield-related crop parameters were collected following their respective standard methods and procedures and further subjected to analysis of variance (ANOVA) using SAS version 9.4. Whenever the ANOVA result showed a significant difference among treatments for a parameter mean separation was further done using the least significant difference (LSD). The analysis of variance showed that the main effect, their interaction, and cropping system didn’t significant effect (P>0.05) on phenological, vegetative growth, and yield-related parameters of the main crop, maize. On the other hand, the spatial arrangement by population density interaction significantly affected the total fresh above ground-biomass, and leaf yield, and essential oil yield of spearmint where the maximum (22.70-ton, 12.72-ton, and 0.047-ton ha-1) in their respective order were recorded at 100% spearmint population density with a double row arrangement respectively. The sole spearmint was superior to other intercropped treatments in each of the two-harvesting cycles for above-ground biomass, leaf, and essential oil yield. The LER values indicated that intercropping maize with a 100% spearmint population at the double row arrangement gave a 63% intercropping advantage with a monetary advantage index (MAI) of 71108 ETB followed by a 75% spearmint population at the same density with 58% advantage and MAI of 65275 ETB. Therefore, intercropping of 75% spearmint population density at double row arrangement with maize could be recommended for the study area.