Effect of Reducing Conditions on P Sorption of Soils

概要

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The phosphate sorption (P_<sor>) capacity of soils increased when the soils were reduced (Willet and Higgins, Aust. J. Soil Res., 16, 319-326, 1978). The present study aimed at the elucidation of this mechanism using Na_2S_2O_4 and 5 different soils. The P_<sor> of the 5 soils increased with the addition of a small amount of Na_2S_2O_4. Fe(II) was released from the soils with the addition of the same small amount of Na_2S_2O_4. Furthermore, when the amount of FeCl_2 corresponding to the amount of Fe(II) released along with the small amount of Na_2S_2O_4 was added, the P_<sor> of the soil increased. However, the P_<sor> of the lowland soils, of which the hydrous Fe oxide content was lower than the others, decreased when the amount of Na_2S_2O_4 addition was increased up to 150-200 g kg^<-1>. Based on these results, the following process is inferred for the increase in the P_<sor> of the soils when they are reduced. Hydrous Fe oxide in soil takes the form of very fine, high-density particles and reacts with P mainly on their surface. When a small amount of Na_2S_2O_4 is added, the hydrous Fe oxide is partially reduced, dissolved and finally re-precipitates with P by oxidation with O_2 from the air during the experiment.
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