When soluble iron (Fe2+) was applied in two soils having similar natural pH values, Fe2+ was immediately fixed or oxidized to Fe3+ in the Wahiawa soil, which has a high level of native manganese, but not in the Paaloa soil, which is low in native Mn. It is shown that Fe2+ is being oxidized at the expense of reduction of higher valence oxides of Mn. This has serious implications in the Fe nutrition of plants grown on high-Mn soils.