This study assessed the possibility of using iodine-containing fertilizers for agronomic
biofortification of rye biomass used as fodder for cows, and establish the best application method
and form and the optimal dose of iodine (I) under field conditions. The impact of iodine fertilization
on grain iodine content was not studied. Results showed that agronomic biofortification of rye
plants with iodine, influenced by its dose, form, and method of application was highly effective in
increasing I shoot contents. Plant I-enrichment via foliar and soil application significantly affected I
concentration in plant biomass even at a low dose (2.5 kg ha−1). Soil I application as KI appeared
optimal for rye plants used as fodder for cows, especially cropped under the soil with a neutral
reaction. Iodine application improved the biological quality of rye plants by increasing concentrations
of sugar, chlorophylls, and at a low rate, protein and total antioxidant capacity.