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Soil Science Society of America Journal Abstract - DIVISION S-4-SOIL FERTILITY & PLANT NUTRITION

Phosphorus Fractionation in Biosolids-Amended Soils Relationship to Soluble and Desorbable Phosphorus


This article in SSSAJ

  1. Vol. 64 No. 6, p. 2018-2024
    Received: Mar 27, 2000

    * Corresponding author(s): rmaguire@udel.edu
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  1. R. O. Maguire *a,
  2. J. T. Simsa and
  3. F. J. Coaleb
  1. a Dep. Plant and Soil Sci., Univ. of Delaware, Newark, DE 19717-1303 USA
    b Dep. Nat. Res. Sci., Univ. Maryland, College Park, MD 20742-5821 USA


Phosphorus has been identified as a major factor involved in decreasing water quality through its role in eutrophication, and there is now a focus on controlling nonpoint agricultural P sources. This work was conducted to identify how biosolids applications under current regulations have affected the forms and release potential of P in agricultural soils. We collected samples from eight farms with a history of biosolids amendments, selecting fields that had setback areas (where biosolids applications were not permitted) to allow comparison of amended and unamended soils. We analyzed these soils for P fractions (soluble P, Al-P, Fe-P, reductant soluble P, and Ca-P; their sum equals total P), sequentially desorbable P (Fe-strip), oxalate P, Al and Fe, Mehlich-1 P, and the degree of P saturation. Our results show that following a N-based biosolids nutrient management plan can significantly increase total P (from 403 to 738 mg kg−1) and initially desorbable P (from 32 to 61 mg kg−1). The main soil components associated with P retention (Alox and Feox) also tended to be increased by biosolids amendment and this may help mitigate P release. Biosolids amendment significantly increased Fe-P (from 137 to 311 mg kg−1), probably due to Fe added to biosolids during production, and there was also a strong trend for higher Al-P where biosolids had been applied. Desorbable P was initially greatest from biosolids sites, but with increasing extractions, the release converged towards that from the setback areas. Mehlich-1 P and Pox were good predictors of desorbable P release, as measured by one and five sequential extractions with Fe-strips. Desorbable P, by both one and five Fe-strip extractions, was more closely correlated with Al-P than Fe-P, especially in setback areas, indicating that Al-P is probably the most important source of desorbable P independent of biosolids amendment. This work indicates the importance of considering P availability at agricultural biosolids application sites and of maintaining setback areas near water bodies, where no biosolids may be applied, to reduce the risk of P losses.

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