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This article in SSSAJ

  1. Vol. 63 No. 5, p. 1174-1180
    Received: Aug 26, 1998

    * Corresponding author(s): mlthomps@iastate.edu
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Fractionation of Phosphorus in a Mollisol Amended with Biosolids

  1. Yaobing Suia,
  2. Michael L. Thompson *a and
  3. Chao Shanga
  1.  aDep. of Chemistry and Biochemistry, South Dakota State University, Brookings, SD 57007 USA


Information about soil P fractions is useful to predict the bioavailability of P in soil as well as to predict the likelihood of its transport. In this study, we used a sequential fractionation procedure to investigate the forms of P in a Mollisol amended at the soil surface with biosolids (i.e., anaerobically digested sewage sludge). Soil samples from three depths (0–5, 5–20, and 20–35 cm) were collected from a Cumulic Vertic Endoaquoll in a field experiment with three biosolid application rates, two vegetation treatments [hybrid poplar–cottonwood trees (Populus × euramericana — clone NC-5326) and switchgrass (Panicum virgatum L.)], and four replications per treatment. The Hedley fractionation scheme (dividing soil P into six empirical fractions [water-soluble, NaHCO3-soluble inorganic and organic P; NaOH-soluble inorganic and organic P; HCl-soluble P, and residual P)] was employed. After 6 yr of continuous application of biosolids to poplar plots, the absolute concentrations of all P fractions at the 0- to 5-cm depth increased significantly (P < 0.05). Some P fractions at the 5- to 20-cm depth increased significantly, whereas at the 20- to 35-cm depth, none of the fractions was affected by biosolids amendment. At the 0- to 5-cm depth of both poplar tree and switchgrass plots, the relative concentrations of some of the P fractions (e.g., HCl–P, NaOH–OP, and residual P) decreased rather than increased. Because NaHCO3–IP and H2O–P increased in the biosolids-amended soil at rates disproportionate to their concentrations in the biosolids, we conclude that HCl–P applied with biosolids was transformed to more labile forms.

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