Use of > 1:1 Chelator:Iron Ratios and Strong Iron(III) Chelators in Hydroponic Solutions for Barley

Abstract

This study examined two guidelines for preparing hydroponic solutions to ensure adequate iron (Fe) for Poaceae plants: (1) not to add chelator in excess of Fe concentrations and (2) to use only weaker forms of Fe(III) chelators. Barley was grown in low-Fe solutions for 9 d and transferred to 59Fe-spiked nutrient solutions at pH 8.1 containing ligand:Fe μ M concentrations of 30:10, 200:10, and 500:10 for 6 h assays. Shoot 59Fe increased with increasing citrate or N,N-bis(carbozymethyl)glycine (NTA). Shoot 59Fe was higher from treatment with citrate than with corresponding NTA treatments despite the ligands' similar Fe(III) binding affinity. Soluble Fe was higher from the citrate than the NTA solutions at the two highest chelator concentrations (P < 0.05). Citrate maintained higher soluble Fe levels and provided more Fe to barley than did NTA. Results of the second experiment found adequate Fe in barley when grown in equimolar HBED:Fe treatments (HBED is the strongest Fe(III) synthetic chelator). Recommendations that only weak Fe(III) chelators be used for the hydroponic culture of barley may be made because stronger chelators result in inadequate Fe for plants after solution Fe levels drop, as plants remove only Fe and little chelator from hydroponic solutions.