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This article in JEQ

  1. Vol. 37 No. 6, p. 2100-2107
    Received: Oct 12, 2007

    * Corresponding author(s): jan.siemens@tu-berlin.de
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Is Colloid-Facilitated Phosphorus Leaching Triggered by Phosphorus Accumulation in Sandy Soils?

  1. Jan Siemens *,
  2. Katrin Ilg,
  3. Holger Pagel and
  4. Martin Kaupenjohann
  1. Dep. of Soil Science, Institute of Ecology, Berlin Univ. of Technology, Salzufer 11-12, D-10587 Berlin, Germany


The leaching of colloidal phosphorus (Pcoll) contributes to P losses from agricultural soils. In an irrigation experiment with undisturbed soil columns, we investigated whether the accumulation of P in soils due to excess P additions enhances the leaching of colloids and Pcoll from sandy soils. Furthermore, we hypothesized that large concentrations of Pcoll occur at the onset of leaching events and that Pcoll mobilized from topsoils is retained in subsoils. Soil columns of different P saturation and depth (0–25 and 0–40 cm) were collected at a former disposal site for liquid manure and at the Thyrow fertilization experiment in northeastern Germany. Concentrations of total dissolved P, Pcoll, Fecoll, Alcoll, optical density, zeta potential, pH, and electrical conductivity of the leachates were determined. Colloidal P concentrations ranged from 0.46 to 10 μmol L−1 and contributed between 1 and 37% to total P leaching. Large Pcoll concentrations leached from the P-rich soil of the manure disposal site were rather related to a large P-content of colloids than to the mobilization of additional colloids. Concentrations of colloids and Pcoll in leachates from P-poor and P-rich columns from Thyrow did not differ significantly. In contrast, accumulation of P in the Werbellin and the Thyrow soil consistently increased dissolved P concentrations to maximum values as high as 300 μmol L−1 We observed no first-flush of colloids and Pcoll at the beginning of the leaching event. Concentrations of Pcoll leached from 40-cm soil columns were not smaller than those leached from 25-cm columns. Our results illustrate that an accumulation of P in sandy soils does not necessarily lead to an enhanced leaching of colloids and Pcoll, because a multitude of factors independent from the P status of soils control the mobility of colloids. In contrast, P accumulation generally increases dissolved P concentrations in noncalcareous soils due to the saturation of the P sorption capacity. This indicates that leaching of dissolved P might be a more widespread environmental problem in areas with P-saturated sandy soils than leaching of Pcoll

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