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This article in SSSAJ

  1. Vol. 41 No. 2, p. 305-310
     
    Received: July 29, 1976


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doi:10.2136/sssaj1977.03615995004100020026x

Phosphorus Sorption Characteristics of Flooded Soils1

  1. R. A. Khalid,
  2. W. H. Patrick and
  3. R. D. DeLaune2

Abstract

Abstract

Surface soils representing Alfisols and Inceptisols were collected from various parts of Louisiana under rice (Oryza sativa L.) cultivation and incubated under oxidized (aerobic) and reduced (anaerobic) conditions for 2 weeks in a soil to 0.01M CaCl2 solution ratio of 1:5. The release of native soil P and the sorption of added inorganic P was investigated under these conditions. The soils selected for study were characterized for clay content, total carbon, extractable P, pH, and oxalate-extractable Fe, soil properties associated with P sorption. The results show that generally more soil P was released under reduced than oxidized conditions, and this increase in soluble P under reduced conditions was significantly related to Bray no. 2 extractable P, clay content, and oxalate Fe. At high levels of added P, more P was sorbed under reduced conditions than under oxidized conditions in 14 out of 20 soils under study. However, in Midland fine sandy loam essentially all of added P was recovered in the equilibrium solution under both oxidized and reduced conditions, suggesting this soil had no capacity to sorb P. The relationship between P sorbed at 500 µg/g added P and oxalate-extractable Fe was described by fitting two linear curves with different slopes. In the reduced soil samples the slope of Region I (≤ 3,000 µg Fe/g) suggests that 5.4 Fe sorbed 1 P and that this ratio did not change until all of the added P was sorbed. In the oxidized samples this ratio was about 16 Fe/1 P for Region I (≤4,500 µg Fe/g). The slopes for Region II of the linear curves for both reduced and oxidized samples were essentially zero. A closer relationship between P sorbed and oxalate extractable Fe under reduced conditions indicates that poorly crystalline and amorphous oxides and hydroxides of Fe play a primary role in P retention by flooded soils and sediments. A probable greater surface area generated by the transformation of oxyferric hydroxide to more reactive ferrous compounds may be responsible for greater P sorption under reduced conditions.

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