Effectiveness of Iron Ethylenediamine‑N,N′‑bis(hydroxyphenylacetic) Acid (o,o‑EDDHA/Fe3+) Formulations with Different Ratios of Meso and d,l‑Racemic Isomers as Iron Fertilizers

Two o,o-EDDHA/Fe3+ formulations (meso, 93.5% w/w of meso isomer; and d,l-racemic, 91.3% w/w of d,l-racemic mixture) were prepared, and their efficacy to avoid or to relieve iron deficiency in Fe-sufficient and Fe-deficient tomato plants grown on hydroponic solution was compared with that of the current o,o-EDDHA/Fe3+ formulations (50% of meso and d,l-racemic isomers). The effectiveness of the three o,o-EDDHA/Fe3+ formulations was different depending on the iron nutritional status of plants. The three o,o-EDDHA/Fe3+ formulations tested were effective in preventing iron chlorosis in healthy plants. However, the higher the meso concentration in the formulations, the higher the effectiveness in the recovery of iron chlorotic plants from iron deficiency. Accordingly, o,o-EDDHA/Fe3+ formulations rich in meso isomer are recommended in hydroponic systems.