Characteristics of Insoluble, High Molecular Weight Iron-Humic Substances used as Plant Iron Sources

"In the present study, five insoluble Fe-humic substance (HS) complexes. (Fe–IHS) extracted from Leonardite were synthesized and characterized. by Infrared (IR) spectroscopy, scanning electron microscopy (SEM), and. dynamic light scattering (DLS). The efficiency of Fe–IHS complexes in curing. Fe chlorosis was compared with two soluble Fe sources (Fe complexed by a. water-extractable humic fraction [Fe–WEHS] and the synthetic Fe–chelate,. Fe-o,o-EDDHA]) and a poorly soluble mineral form (Ferrihydrite). The IR. spectra revealed coordination of the Fe ions with the carboxylic and phenolic. groups of the oxygen-rich humic substances. The SEM and DLS data suggest. that the Fe–IHS complexes were large aggregated particles with diameter. of about 500 to 1500 nm formed by different nanoparticles with very. small size ranging from 50 to 200 nm. Chemical extractions show that the. Fe pool is dominated by poorly ordered Fe phases strongly associated with. IHS. The efficiency of Fe–IHS complexes in curing Fe chlorosis symptoms. in Fe-deficient plants has been demonstrated, being, when used in high. concentration, comparable to those of Fe–WEHS and Fe-o,oEDDHA. The. capability of cucumber (Cucumis sativus L.) plants to acquire Fe from poorly. soluble Fe forms was also confirmed when a poorly crystalline radiolabeled. Fe-oxide (59Ferrihydrite) source, used to represent a short-range order Fe. phases associated with Fe–IHS complexes, has been used. The results of this. work point out the possible use of environmental-friendly Fe insoluble highmolecular. weight complexes (Fe–IHS) as an effective product to correct the. Fe nutritional disorder."