BEHAVIOUR OF FEEDDHA-ISOMERS IN NUTRIENT SOLUTIONS

The chelates of iron with EDDHA and related chelating agents are stable in a wide range of pH values and have proved to be very effective to supply iron to plants. These compounds are also important in soilless and controlled cultures where iron needs may be higher than in plants grown in soil. FeEDDHA is affected by the preparation and the composition of the nutrient solutions. The characteristic of the solutions that mostly affects FeEDDHA stability is the pH. Acid values cause an intense decomposition reaction, which is not comparable to the effect caused by any other ion. However, at mild acid and neutral pH values, FeEDDHA is very stable. Despite of this high stability, FeEDDHA and related compounds show a certain lability in solutions containing ions that form less stable complexes with EDDHA. The reaction causes important losses of chelate, especially in concentrated solutions. However, mixes with a sole competing ion do not seem to cause problems meanwhile pH remains above 4. The decomposition of FeEDDHA is mainly attributable to the meso form, the less stable isomer.