Impact of Foliar Application of Copper, Manganese, Molybdenum, and Zinc on the Chemical Composition and Malting Quality of Barley Cultivars

The aim of this study was to evaluate the effect of foliar application of selected micro-nutrients on the chemical composition and malting quality of spring barley (Hordeum vulgare L.). The scientific literature lacks in-depth studies that assess the effect of foliar application of micronutrients on barley malting quality. Most studies (especially under field conditions) focus on nitrogen fertilization rather than individual micronutrients. Three brewing-type barley cultivars (Baryłka, KWS Irina, and RGT Planet) were evaluated under foliar micronutrient fertilization (Cu, Mn, Mo, Zn). Fertilizers were applied at doses of 2 L ha⁻¹ for Cu, Mn, and Zn and 1 L ha⁻¹ for Mo. The experiment examined the hectoliter mass, theoretical extractability, contents of selected micro- and macronutrients, and the protein, fat, fiber, and ash contents of the grain. Furthermore, the following characteristics of barley malt were determined, i.e., moisture, protein, extractivity, Kolbach index, and diastatic power. The results showed significant variability in grain and malt quality depending on the cultivar and year. The Baryłka cultivar was characterized by the highest grain density (66.3 kg hL⁻¹) and protein content (10.9% d.m.), while RGT Planet had the highest extractivity and the most favorable malting profile. Foliar supplementation had a slightly positive effect on the average content of trace elements in barley. Mn application increased grain Ca content by 5.6% compared with the control, while foliar Zn fertilization resulted in the highest zinc concentration (a 24.7% increase). No significant effect of fertilization on malt quality was observed, but a significant interaction of experimental factors in extractivity, Kolbach index, and diastatic power was noted. The obtained results indicate that a single foliar application of microelements affects the contents of minerals and protein in the grain, but it does not lead to a significant improvement in malting parameters. This suggests the need for further research on dosage, application date, and interactions between the cultivar and environmental conditions.