Abstract
In the present research, different forms and reactions of insoluble Fe-humic substance complexes (Fe-HS) and a soluble Fe-EDDHA complex, were compared. Five Fe-HS complexes were synthesized by neutralizing Fe(II) ions and humic substances using different synthesis conditions. Analysis was centred on chemical extraction developed to study iron distribution associated with humic substance (HS). Insoluble Fe-HS showed characteristics that differ from those of poorly ordered Fe oxides, indicating the presence of Fe hydrolytic products that were co-precipitated with HS in large molecules. Fe-HS and Fe-EDDHA were tested for their ability to cure chlorosis in Fe-deficient cucumber plants; the sources were used applying 0.03, 0.3 or 3 μmol of Fe in a nutrient solution (300 mL) buffered to pH 7.5. Results indicate that both Fe sources allowed plants to recover from chlorosis, with the effectiveness depending on the Fe source applied. Data here presented suggest that insoluble Fe-HS complexes could represent an environment and friendly tool for preventing Fe deficiency in crops and for correcting Fe availability in soils.