Synthetic iron oxides as sources of Fe in a hydrophonic culture of sunflower

Abstract

Mineral structure, surface properties and reactions of Fe-oxides are of interest because of their influence on Fe availability in soil. In order to study this influence, the solubility of ferric ions from four synthetic Fe-oxides in presence of an EDDHA solution was determined at pH 6.O. Amorphous Fe(III) oxide, goethite and maghemite were prepared in the laboratory and magnetite was purchased from a commercial source. Results show that the dissolution rate decreased in the order: amorphous Fe oxide > goethite > maghemite > magnetite. Three iron oxides were evaluated for their ability to supply Fe to sunflower (Helianthus annum cv. Sirio G-100) grown under Fe-stress conditions in an aereated hydroponic culture. This was made both in the presence and absence of Fe-EDDHA (9.0 μM). The plant total Fe concentration was measured 10 and 20 days after the treatments started. The largest Fe dissolution rate from Fe-oxides, ion activity product and Fe uptake by plants was found for the Fe-amorphous oxide. The iron uptake from maghemite was higher than that from goethite in spite of the fact that goethite had a larger dissolution rate than maghemite. The lowest soluble Fe concentration was found when using amorphous Fe oxide in the absence of Fe-EDDHA.