Significance of hydrous iron oxides in enhancing P sorption of soils with the addition of sodium hydrosulfite (Na2S2O4) |
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Authors: | Ikuko Akahane Masami Nanzyo Tadashi Takahashi |
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Affiliation: | Graduate School of Agricultural Sciences , Tohoku University , Sendai, 981-8555, Japan |
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Abstract: | Phosphorus sorption (Psor) of soils is affected by redox conditions. It has been shown that Psor of lowland soils at a pH value of about 4.3 increases when a small amount of sodium hydrosulfite (Na2S2O4) is added and decreases when an excess amount of (Na2S2O4) is added to the mixture of a soil and P solution. Hydrous Fe-Al oxides, manganese dioxide (MnO2) exchangeable Ca, models of reactive components with P in soils, were examined to identify the factors responsible for the increase of Psor in lowland soils when a small amount of Na2S2O4 was added. For clarifying the contribution of the hydrous Fe-Al oxides, goethite and 7 hydrous Fe-Al oxides (Fe/Al atomic ratio: 1/0, 5/1, 2/1, 1/1, 1/2, 1/5, and 0/1) were used. The Psor of all these materials increased when they were treated with a small amount of Na2S2O4 although the increase was the smallest for the hydrous Al oxide among the 7 oxides. Thus, the hydrous Fe oxides, and Al oxide to a smaller extent, play an important role in the increase in Psor of the lowland soils treated with a small amount of Na2S2O4 The Psor of the hydrous Fe oxides was not appreciably affected by the addition of MnO2. The increase in Psor of the Ca-saturated Hachirogata soil was almost the same as that of the Nasaturated Hachirogata soil, indicating that exchangeable Ca did not affect appreciably the increase of Psor in reduced soils at a pH value of about 4.3. |
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Keywords: | aluminum iron phosphate reduction sorption |
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