Effect of nitrogen and zinc fertilization on zinc and iron bioavailability and chemical speciation in maize silage

Agronomic biofortification is one of the main strategies for alleviation of micronutrient deficiencies in food and feed. The objective of this study was to investigate the effect of N supply on total concentration of Zn and Fe and their chemical species in the soluble extracts of maize silage grown under field conditions. Total concentrations of Zn, Fe, Cu, Mn, S and P were measured by flow-injection inductive coupled plasma (ICP) - mass spectrometer (MS). Soluble Fe and Zn were extracted and analyzed by size exclusion - inductively coupled plasma mass spectrometry. Using the same set-up for total elemental and speciation analysis enabled direct quantitative comparison of the detected speciated molecules with the total element sample content. N or Zn treatment, except in control plots, did not significantly affect concentrations of Zn and Fe in the maize silage and grain samples. Significant positive correlation was observed between Zn and Fe maize silage (r = 0.64, p < 0.01) and maize grain (r = 0.85, p < 0.01) concentrations. N and Zn treatment did not affect solubility of Zn and Fe, while available Zn and Fe were affected by increase in Zn soil treatment. Soluble Zn was speciated in LMW complexes, while soluble Fe was speciated in MMW and LMW complexes.