Phosphorus in sequentially extracted fen peat soils: a K-edge X-ray absorption near edge structure (XANES) spectroscopy study

Autor: Kruse, J., Leinweber, P.
In:

Journal of Plant Nutrition and Soil Science

Bandangabe: 171
Auflage: 4
ISBN: 1522-2624
Seite: 613 - 620
Jahr: 2008

Einordung:
Institut: Professur Bodenkunde
Teilschwerpunkt: Erfassung und Auswertung umweltrelevanter Kenngrößen

Abstract:
The speciation of phosphorus (P) in native and degraded peat soils is an analytical challenge, and synchrotron-based P K-edge X-ray absorption near-edge structure (XANES) is a suitable method to gain information on P species in soils and organic materials. The objective of the present study was to test if P K-edge XANES reflected differences in P fractions in fen peat due to sequential extraction and peat degradation. We investigated each one top- and subsoil sample of a Fibric Histosol, which differed in the degree of humification (H8 vs. H5) and concentration of total P (Pt) (1944 mg kg-1 vs. 436 mg kg-1). In the topsoil, residual P, H2SO4-P, and NaOH-P accounted for roughly the same proportions of Pt (30%). In the subsoil, residual P (64% of Pt) was more abundant than NaOH-P (21% of Pt) and H2SO4-P (10% of Pt). Among many different P reference standards, the P XANES spectra reflected differences in mineral P more distinctive than in organic P compounds. Phosphorus XANES spectra of the residues after each sequential extraction step all showed a prominent white-line peak at around 2152 eV. Stepwise removal of resin-P, NaHCO3-P, and NaOH-P were reflected mainly by the peak intensity but scarcely by distinct spectral features. Extraction with H2SO4 led to the disappearance of spectral features of Ca and Mg phosphates which is a first direct hint to these compounds in the peat. In conclusion, a combined sequential fractionation and spectroscopic (31P NMR, P K- and L-edge XANES with linear-combination fits) approach is proposed to overcome limitations of the present study and gain more insight into the P species in peat soils.
Accepted: 8 October 2007

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