Mechanisms of fixation and release of ammonium in paddy soils after flooding III. Effect of the oxidation state of octahedral Fe on ammonium fixation

摘要

An experiment with two typical paddy soils from China and two clay minerals was conducted to study the effect of reduction of octahedral Fe-III on fixation of NH4+ ions. Reduction of octahedral Fe-III was achieved by treating soils and clay minerals with dithionite-citrate-bicarbonate (DCB) followed by dialyzing the samples under oxygen free conditions, Reduction of Fe-III increased the negative charge of interlayers and resulted in a significantly higher ammonium fixation. Close positive correlations were found between the Fe 21 concentration or the ratio of Fe2+/Fe3+ and nonechangeable NH4+-N. Therefore, it is concluded that the reduction of octahedral Fe induced by flooding is one of the important prerequisites for the pronounced ammonium fixation in flooded soils. However, the relation between DeltaFe(2+) and Deltafix-N was not stoichiometric.