Effect of monosilicate, phosphate, and carbonate on iron dissolution by mugineic acid

Abstract

Anions adsorbed specifically onto iron minerals in soil can affect the dissolution of the minerals by phytosiderophores and the occurrence of iron deficiency in graminaceous crops. Ferrihydrite was suspended in NaCl solutions (pH 4-9) containing orthophosphate, monosilicate, or carbonate at various concentrations, and then the dissolution rates of the ferrihydrite by mugineic acid (MA) were determined . The adsorption of the anion and MA were also quantified . All the tested anions inhibited both the iron dissolution by MA and the MA adsorption onto ferrihydrite . Monosilicate inhibited the iron dissolution severely (>80%) when the pH value exceeded 8 and the final concentration exceeded 0.2 mm. The inhibition of monosilicate on iron dissolution decreased significantly with decreasing pH . On the other hand, monosilicate is commonly present in soil solutions at such high concentrations as 0 .2 mm . Moreover, strict inhibition of ferrihydrite dissolution was also observed when the ferrihydrite was added to a suspension of a calcareous soil or its filtrate . These results suggest that the adsorption of monosilicate on iron minerals results in the low availability of iron to graminaceous plants which is oberved commonly in calcareous soils .

Phosphate inhibited the iron dissolution by MA at very low concentrations at all the tested pH values . However, since the application of phosphate in calcareous soils hardly affected iron dissolution by MA, it was suggested that the surface of the iron minerals in calcareous soil was already inactivated .

Key Words:

• calcareous soil
• dissolution of hydrous oxide
• iron availability
• mugineic acid
• monosilicic acid