Interaction of iron chelates with several soil materials and with a soil standard

Frequently the effectiveness of iron (Fe) chelates is low because they can be retained or destroyed by soil materials. The high cost of these Fe fertilizers makes it necessary to study soil material reaction with Fe chelates. Commercial Fe chelates with EDTA, EDDHA, and EDDHMA as ligands and their standards, prepared in the laboratory, were shaken for one hour with various soil materials [amorphous Fe(III) oxide, acid peat, calcium (Ca)-montmorillonite and calcium carbonate (CaCO3)] end with a soil standard made in the laboratory. After agitation, the chelate-soil mixtures were filtered and the micronutrients and chelated Fe that remained in solution were determined. Among the soil materials used, amorphous Fe(III) oxide and acid peat had the greatest affect on the amount of chelated Fe remaining in solution. The type of chelating agent was the next major factor that affected the availability of soluble Fe following reaction with the soil materials. Another factor was the commercial formulation of the Fe chelates. The chelates comprised of EDDHA or EDDHMA maintained the highest percentages of chelated Fe in solution after interaction with the solid phases, except for the acid peat. The last soil material, acid peat, retained more chelated Fe for the Fe chelates with EDDHA or EDDHMA than with EDTA as the chelating agent. The commercial Fe-EDDHA chelates had greater losses of chelated Fe than their standard after interaction with all the solid phases. The commercial Fe-EDDHA chelate (Sequestrene) and the commercial Fe-EDDHMA chelate (Hampiron) solubilized the highest amount of copper (Cu) from soil standard. This was attributed to the presence of by-products in the commercial formulations since the Fe-EDDHA standard did not have Cu in solution after the interaction. Therefore, the commercial Fe chelate by-products are able to form Cu-complexes which could affect chelated Fe and its availability to plants.