Fe chelates from compost microorganisms improve Fe nutrition of soybean and oat

Iron availability to plants is often limited when soil pH is 7 or higher. In C rich, but Fe limiting environments, microorganisms may produce organic chelators that complex Fe and increase its availability to plants. Seedlings of soybean (Glycine max L.) and oat (Avena sativa L.) plants, with Fe-efficient or inefficient uptake mechanisms, were grown in an Fe free nutrient solution at pH 7.5. Experiments (using a complete factorial design) were conducted in which these seedlings were transferred to a fresh nutrient solution and treated with Fe sources (FeCl₃, FeEDDHA, and Fe complexed with chelators produced by compost microorganisms (CCMs) after their enrichment in an Fe free, glucose medium), Fe concentrations (0 and 6.7 µM) and antibiotic (0 and 100 mg streptomycin L⁻¹). Dry weight of soybean plants and Fe uptake were significantly (P ≤ 0.05) higher when Fe was supplied as ⁵⁹FeCCM than as ⁵⁹FeCl₃ and similar to when Fe was supplied as ⁵⁹FeEDDHA. Dry weight of the Fe-inefficient Tarn 0-312 oat cultivar was also significantly higher when Fe was supplied as FeCCM. Fe uptake by oat, when supplied as ⁵⁹FeCCM, was twice that for ⁵⁹FeEDDHA and ⁵⁹FeCl₃. Chlorophyll concentration in plants supplied with FeCCM and FeEDDHA was significantly greater (P ≤ 0.05) than in minus Fe control plants and in FeCb supplied plants. Activities of catalase and peroxidase, measured as indicators of Fe nutrition in soybean and oats, were generally increased when Fe was supplied with FeCCM as compared to the other Fe sources. The experimental conditions in which the CCMs were produced are similar to those in soil after amendment with manures or other readily available organic materials. These CCMs can bind with Fe, even under slightly alkaline conditions, and effectively improve Fe nutrition of soybean and oat.