Effect of nitrogen application and year on concentration of Cu, Zn, Ni, Cr, Pb and Cd in herbage of Galega orientalis Lam.

Eastern galega is promising forage species for Central Europe, but little is known about its forage quality in terms of elemental composition. We asked how the concentrations of Cu, Zn, Ni, Cr, Pb and Cd in its herbage are affected by application of ammonium sulphate and by year. Changes in the content and bioaccumulation of trace elements of herbage eastern galega fertilized with 15N were investigated in a field three-year experiment. The study was conducted with a legume plant, i.e. eastern galega (Galega orientalis Lam.). The experiment was completely randomized and carried out in four replications with the following mineral fertilization: control, and nitrogen fertilization (15NH4)2SO4. The second factor was years of research (1st, 2nd, 3rd). Nitrogen 15N at 10.3 at % enrichment was applied in a form of (15NH4)2SO4 at the amount of 1.66 g/m2 in early spring. The measured concentrations of the selected heavy metals (except for Pb and Cd) were within the permissible limits for trace elements in feedstuffs specified by Polish and European standards. The applied nitrogen fertilization significantly influenced a reduction in the content of Cu, Zn and Cr in soil. Calculated average values of bioaccumulation factors for heavy metals: Cd > Cu > Zn = Ni > Pb > Cr. The low dose of a nitrogen fertilizer in the form of ammonium sulphate does not significantly affect an increase of the availability of heavy metals.