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Soil Science Society of America Journal Abstract -

Seasonally Precipitated Iron Oxides in a Vertisol of Southeast Texas


This article in SSSAJ

  1. Vol. 61 No. 3, p. 958-964
    Received: May 27, 1994

    * Corresponding author(s): j-dixon@tamu.edu
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  1. D. C. Golden,
  2. F. T. Turner,
  3. H. Sittertz-Bhatkar and
  4. J. B. Dixon 
  1. MailCode SN4, NASA/JSC, Houston, TX 77058
    Texas A&M Univ. Agricultural Research and Extension Center, Route 7, Box 999, Beaumont, TX 77713
    Electron Microscopy Center, Texas A&M Univ., College Station, TX 77843
    Soil and Crop Sciences Dep., Texas A&M Univ., College Station, TX 77843



The composition and crystallinity of Fe oxides in soils determines the reactivity and toxicity of Fe through redox and solubility reactions. The mineralogy and crystallinity of Fe oxides seasonally precipitating on ped surfaces and within soil pores and those forming around rice (Oryza sativa L.) roots were investigated by x-ray diffraction, electron microscopy, and electron microprobe analyses. Iron oxides precipitated on exposed surfaces of the League soil (fine, montmorillonitic, hyperthermic Oxyaquic Dystrudert), which is flooded during rice production, differed from Fe phases precipitated around rice roots. Iron oxides precipitated on ped surfaces and within soil pores were relatively poorly crystallized while those precipitated on rice-root surfaces were well crystallized. The presence of soluble Si and P during flooding may be responsible for precipitation of the less crystalline Fe oxides. Infrared and electron-diffraction data on the precipitate suggest the presence of PO4 groups either adsorbed or coprecipitated with Fe oxide. Depletion of Si and P from the rhizosphere is believed to contribute to the formation of well-crystallized lepidocrocite on root surfaces. The poorly crystalline Fe-oxide precipitate that forms on ped surfaces upon draining and oxidation of the League soil has adsorbed or occluded Si and P. Thus, Fe oxides may influence the mobility of Si and P in alternately flooded and drained soils. Electron-diffraction data suggests that some of the Fe may be precipitated as strengite. Upon reduction and dissolution, these oxides release Fe, Si, and P into the soil solution and influence the nutrient dynamics in the rhizosphere of the rice plant.

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