Efficiency of Solubilization of Metals by Mugineic Acid from Sodic Soil

Iron has limited solubility in alkaline soils and, consequently, alkaline soils may have insufficient available iron for optimal plant growth. Plants of the family Gramineae secrete phytosiderophores, plant-derived compounds such as mugineic acid (MA) that chelate iron, enabling them to extract iron from deficient soils. In the present study, the efficiency of MA and other chelators to solubilize iron and other metals from sodic soil, an alkaline soil, was studied. We measured the amount of solubilized metals from sodic soil, calcareous soil, and andosol. The soils were mixed with the solutions of chelators, incubated with continuous shaking, and centrifuged. The supernatant was filtered and analyzed for metals. In the calcareous soil and andosol, the chelators enhanced solubilization of iron. Although a large amount of iron was solubilized from the sodic soil, the release was independent of the presence of chelators. Similar results were obtained for solubilization of aluminum. When suspended in water, the sodic soil released a considerable amount of silicon, but this was not observed for the other soils. Subsequently, we examined the iron solubilization from salinized or alkalinized andosols by chelators. The results showed that only soil alkalinization enhanced more Fe to be released, and the chelators did not enhance Fe solubilization significantly with increasing soil pH. Because of our results and information of formerly known publications, we suggested that water extractable humic substances caused the iron solubilization from sodic soil. Therefore, we showed the significant information for plant nutrition in sodic soils. Iron, aluminum, and silicon were present in soluble forms in the soil. Further studies are required to characterize precisely the efficiency of MA on metal nutrients for plants in sodic soils. Furthermore, the risk of aluminum toxicity and the usefulness of water-soluble silicon for plant growth are strongly suggested in natural sodic soils.