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This article in JEQ

  1. Vol. 26 No. 6, p. 1548-1554
     
    Received: Oct 17, 1996
    Published: Nov, 1997


    * Corresponding author(s): crltocaj@uco.es
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doi:10.2134/jeq1997.00472425002600060014x

Iron-Related Phosphorus in Overfertilized European Soils

  1. J. M. Ruiz,
  2. A. Delgado and
  3. J. Torrent *
  1. Departamento de Ciencias y Recursos Agrícolas y Forestales, Universidad de Córdoba, Apdo. 3048, 14080 Córdoba, Spain.

Abstract

Abstract

Iron-related P forms directly influence the amount of phosphate released from soils and sediments, particularly when subjected to reduction. In this work, we examined such P forms in 12 overfertilized, widely different European soils by using various single and sequential extraction techniques, including the use of a mild and a strong reductant (ascorbate and dithionite, respectively). Reductant-soluble P (defined as the amount of P released by the specific action of a strong reductant) ranged from 2 to 63% of the total amount of P extracted by the sequential extraction procedure of Olsen and Sommers. More than 50% of reductant-soluble P was released by the specific effect of ascorbate in most of the soils studied. The results of the sequential extractions suggest that, on average, about one-half of the reductant-soluble P was occluded in Fe oxides. Poorly crystalline and crystalline Fe oxides generally contained similar amounts of occluded P in absolute terms. However, P/Fe mole ratios were higher in poorly crystalline than in crystalline Fe oxides (X̄ = 5.9 and 1.7 × 10−2, respectively). We suggest that fertilizer P may have been occluded in Fe oxides, particularly in the poorly crystalline forms. The contribution of the parent material, pedogenesis, and fertilization to occluded P build-up is difficult to assess. Though obtained in vitro, our results suggest that reduction of overfertilized soil materials in aquatic environments can release significant amounts of P; these in turn increase saturation of reduction-resistant P-adsorbing surfaces and thus help increase the P equilibrium concentration in solution.

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