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This article in SSSAJ

  1. Vol. 54 No. 5, p. 1298-1304
     
    Received: Oct 13, 1989


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doi:10.2136/sssaj1990.03615995005400050016x

Phosphate Sorption-Desorption Characteristics by Magnetically Separated Soil Fractions

  1. M. Saying,
  2. A. R. Mermut  and
  3. H. Tiessen
  1. Dep. of Soil Science, Univ. of Çukurova, Adana, Turkey
    Univ. of Saskatchewan, Saskatchewan Inst. of Pedology, Dep. of Soil Science, Saskatoon, SK S7N 0W0, Canada

Abstract

Abstract

A soil sample from the surface horizon of a Paleustollic Torrert from southeastern Turkey was size fractionated, then subfractionated further by magnetic separation to study P sorption and desorption behavior of these separates. Citrate-dithionite (CD) extractable Fe constituents (Fed) were found effective P sorbers in silt-size particles, especially in the coarse-silt fraction (50–20 µm). A five-fold increase in P sorption was noted with an 8.5-times increase in Fed content, suggesting that, in this fraction, P sorption is largely controlled by Fe oxyhydroxides. Carbonates in sand and coarse-silt fractions as well as CD-extractable Al and Si, and oxalate-soluble Al and Si in all fractions had no significant effect on P sorption. In the coarse-clay fraction, besides the Fed content, clay minerals also affected P sorption. Desorption of P was, in general, lower in the highly magnetic fractions, and decreased with decreasing particle size. Fluctuations in P desorption among different concentrations of added P in each particular fraction cannot be explained clearly. This may suggest the possibility of P precipitation in a 24-hr experimental time period. Removal of about 2.9% Fed from the fine clay (<0.2 µm) resulted in a 22% decrease in sorption, and an increase in desorption, from 32 to 44% to 62 to 80%. The results suggest that Fe oxyhydroxides and other Fe-bearing constituents are important P sorbents not only in tropical soils, but also in soils of the temperate semiarid regions.

Contribution no. R654 from the Saskatchewan Inst. of Pedology, Univ. of Saskatchewan.

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