The objective of this study was to document the availability of flue gas desulfurization (FGD) residue-borne boron (B), sulfur (S), and molybdenum (Mo) for alfalfa (Medicago sativa L.) uptake when applied at agronomic rates to marginally B deficient soils. The FGD residue was applied at rates of 0, 0.46 and 3.75 Mg ha(-1) on a silt loam soil immediately prior to alfalfa seeding. Alfalfa yields were unaffected by these rates of residue applications, but shoot concentrations of B and S in the second cutting, and B, S, and Mo in the third cutting were increased by residue applications. Hence, FGD residue is a readily available B source, particularly later in the growing season when native soil B availability decreased.