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This article in SSSAJ

  1. Vol. 58 No. 4, p. 1184-1189
    Received: June 2, 1993

    * Corresponding author(s):
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Phosphorus Relationships in Flooded Rice Soils with Low Extractable Phosphorus

  1. H. Shahandeh,
  2. L. R. Hossner  and
  3. F. T. Turner
  1. Soil and Crop Sciences Dep., College Station, TX 77843
    Texas A&M Research and Extension Center, Beaumont, TX 77713



Rice (Oryza sativa L.) grain yields on some flooded soils are not increased by P fertilizer despite their low soil test P status determined on air-dry soils by soil test methods such as Bray, Olsen, or Texas A&M. Conventional soil test methods apparently do not accurately assess the capacity of these soils to supply P to rice grown under flooded conditions. To test the possibility of an Fe-P association, oxalate extractant (which would extract noncrystalline Fe and its associated P) was used to provide a more accurate measure of available P in flooded soil. Phosphorus response experiments were conducted on 10 rice soils under greenhouse and field conditions and related to the oxalate-extractable Fe and P, P uptake, P adsorption, and P desorption under aerobic and anaerobic conditions. Oxalate-extractable Fe significantly increased under anaerobic conditions in all soils including the soils that were nonresponsive to P and had low levels of extractable P using conventional extractants. Phosphorus adsorption and desorption data confirmed the importance of oxalate extractant in predicting P availability following anaerobiosis. The inability of Bray 1, Olsen, and Texas A&M soil test methods to accurately predict P availability in flooded rice soil appears to be due to their failure to extract the active reductant-soluble P fraction. The measurement of P associated with poorly crystalline Fe by oxalate extractant is a useful soil test method for predicting the availability of P in flooded rice soils.

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