Micronutrient Content of Aboveground Biomass as Influenced by Different Proportions of Medicago media Pers. in Two-Component Alfalfa–Grass Mixtures

The aim of this study was to determine the effect of different proportions of hybrid alfalfa (Medicago media Pers.) in two-component mixtures with festulolium (Festulolium braunii (K. Richt.) A. Camus) and orchard grass (Dactylis glomerata L.) on the micronutrient content of aboveground biomass. The study was conducted in 2011–2013 in Poland. The experiment had a split-plot design with four replications, and the experimental variables were as follows: (i) mixtures: Dactylis glomerata (Dg) + Medicago media (Mm) and Festulolium braunii (Fb) + Medicago media (Mm), and (ii) proportion of Medicago media seeds in the mixture: 30%, 50%, and 70%. Pure-sown Dactylis glomerata and pure-sown Festulolium braunii were the control treatments. The proportion of hybrid alfalfa in the biomass yield of mixtures increased throughout the study, and this species was the dominant component of the sward already in the second year, regardless of the proportion of sown seeds. Orchard grass exerted greater competitive pressure on alfalfa than festulolium. Pure-sown Dactylis glomerata accumulated more manganese (Mn) and iron (Fe) than pure-sown Festulolium braunii; no significant differences in the copper (Cu) and zinc (Zn) content of aboveground biomass were found between species. The aboveground biomass of mixtures was characterized by higher Cu content and lower Mn content than the biomass of grass monocultures. As a component of mixtures, alfalfa had a negative influence on the Fe content of aboveground biomass (dry matter basis). No significant differences in Cu and Mn content were observed between the mixtures. The Fb50% + Mm50% mixture had the highest Zn content, and the Fb70% + Mm30% mixture had the highest Fe content. The present findings suggest that practical two-component alfalfa–grass mixtures should be composed based on species competitiveness and selection of a grass component adapted to local agroecological conditions, rather than on the proportion of alfalfa seeds in the mixture.