Chelates, primarily iron (Fe), play important roles in the production of Fe-sensitive crops when grown in alkaline soils. In addition, chelates of the element manganese (Mn) and zinc (Zn) have been of value under similar soil conditions. The form of the chelate and its method of application are important factors determining their effectiveness in providing the element to a growing crop in order to avoid deficiency. What about the use of chelates in a nutrient solution, are they necessary and effective? When a chelate is put into an acid solution, as in a nutrient solution formulation, equilibrium chemistry prevails and those divalent cations in maximum concentration will become chelated. Since both calcium (Ca2+) and magnesium (Mg2+) are usually the major divalent cations in a nutrient solution formulation, chelation will occur with these cations. Since the divalent micronutrients, Fe2+, Mn2+ and Zn2+, are at low concentrations they will not be chelated even if they were added as chelates – that bond will be broken to chelate with the Ca2+ and Mg2+ cations. Chelation does not, in an acidic solution, improve “availability,” because the chelate bond must be broken in order for the ion to be root absorbed. Therefore, actually availability is reduced with chelation in a nutrient solution. In addition, the chelate, EDTA, has been found to be toxic to some plants, so the chelate, DTPA, is that recommended. If humic acid is in a nutrient solution formulation, it will act as a chelate, but chelating those divalent cations in highest concentration that may not be a divalent micronutrient.
