Iron(III) profiles of flooded paddy soil incubated in the greenhouse indicated oxidation of iron(II) in the upper 6 mm soil layer. Measurement of oxygen with a Clark‐type microelectrode showed that oxygen was only responsible for the oxidation of iron(II) in the upper 3 mm. In the soil beneath, nitrate could be used as electron acceptor instead of oxygen for the oxidation of the iron(II). Nitrate was still available 3 mm below the soil surface, and denitrifying activity was indicated by higher concentrations of nitrite between 3 and 6 mm soil depth. Nitrate was generated by nitrification from ammonium. Ammonium concentrations increased beneath 6 mm soil depth, indicating ammonium release and diffusion from deeper soil layers. High concentrations of ammonium were also found at the surface, probably resulting from N 2 fixation by cyanobacteria. Experimental adjustment of the nitrate concentration in the flooding water to 200 µM stimulated nitrate‐dependent iron(II) oxidation, which was indicated by significantly lower iron(II) concentrations in soil layers in which nitrate‐dependent iron(II) oxidation was proposed. Soil inc
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