Leonardite iron humate and synthetic iron chelate mixtures in Glycine max nutrition

The aim of this work was to study the possible synergic effect between mixtures with iron leonardite humate (L/Fe³⁺ ) and synthetic chelates iron (Ch/Fe³⁺ : o,oEDDHA /Fe³⁺ or HBED/Fe³⁺ ), and to reevaluate the classical chelate shuttle-effect model. Different molar ratios of L/Fe³⁺ :Ch/Fe³⁺ , different doses, and different sampling times were used in hydroponic and soil experiments using soybean (Glycine max) as a model Strategy I crop in calcareous conditions. Ligand competition between the humate and chelating agents was also examined.

Iron humate participates in the chelate shuttle mechanism, providing available Fe to the chelating agent and then to the plants, showing a slight synergic effect. After a few days, the contribution of the chelates to the Fe nutrition decreases substantially, but the contribution of the humates is maintained.

The most efficient ratio was two parts of iron humates and one part of iron chelate. In particular, HBED/Fe³⁺ was the most suitable iron chelate because its lasting effect fits the iron humate long-term effect better. The soluble iron in soil increased and the shoot-to-root iron translocation improved due to a synergic effect by a shuttle effect exerted by iron chelate in the mixture. © 2021 Society of Chemical Industry.