Chemistry and mineralogy of Fe‐containing oxides and layer silicates in relation to plant available iron

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Abstract
This paper is a review of the structures, surface properties and reactions of Fe‐containing minerals (either natural or applied materials) which influence the availability of Fe to plants. The implications of these reactions to soil testing and plant‐growth studies are also discussed. The predominant Fe‐containing minerals in calcareous soils are Fe oxides (principally goethite, hematite and ferrihydrite) and layer silicates. Dissolution of Fe‐containing minerals occurs as a surface reaction. Therefore, the rate of mobilization of Fe under Fe‐stress conditions is dependent on the particle size distribution, crystallinity and concentration of surface Fe hydroxyls of these minerals. It has been shown that availability of indigenous soil Fe to plants is related to the quantity of amorphous Fe oxides in soils. The long‐term success of solid‐phase Fe amendments to soils is dependent on the reactive surface areas (i.e., the concentration of active surface‐Fe sites), the continued exposure of new active Fe sites and the stability of the amendment in the soil environment.