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Innovative methods in soil phosphorus research: A review.

Kruse J, Abraham M, Amelung W, Baum C, Bol R, Kühn O, Lewandowski H, Niederberger J, Oelmann Y, Rüger C, Santner J, Siebers M, Siebers N, Spohn M, Vestergren J, Vogts A, Leinweber P - J Plant Nutr Soil Sci (1999) (2015)

Bottom Line: Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development.This review provides an overview of advanced state-of-the-art methods currently used in soil P research.Required experimental set-ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.

View Article: PubMed Central - PubMed

Affiliation: Soil Science, Faculty for Agricultural and Environmental Sciences, University of Rostock Justus-von-Liebig Weg 6, 18051 Rostock, Germany ; Institute of Crop Science and Resource Conservation, Soil Science and Soil Ecology, University of Bonn Nussallee 13, 53115 Bonn, Germany.

ABSTRACT

Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state-of-the-art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q-TOF MS/MS, high resolution-MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum-chemical modeling, microbial biomass P, enzymes activity, DGT, (33)P isotopic exchange, (18)O isotope ratios). Required experimental set-ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.

No MeSH data available.


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(a) Stacked and normalized P K-XANES fluorescence yield spectra of selected soil-relevant P reference compounds and (b) the respective P L2,3-edge spectra. (c) Long-range scan of amorphous Ca-phosphate at the P K-edge visualizing the XANES and the EXAFS region of the spectrum in energy space, (d) respective k-space transformed, and (e) Fourier transformed χ(k) data of amorphous Ca-phosphate, giving information on the type and distances of bondings (Kruse, 2013, unpublished).
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fig09: (a) Stacked and normalized P K-XANES fluorescence yield spectra of selected soil-relevant P reference compounds and (b) the respective P L2,3-edge spectra. (c) Long-range scan of amorphous Ca-phosphate at the P K-edge visualizing the XANES and the EXAFS region of the spectrum in energy space, (d) respective k-space transformed, and (e) Fourier transformed χ(k) data of amorphous Ca-phosphate, giving information on the type and distances of bondings (Kruse, 2013, unpublished).

Mentions: X-ray absorption spectroscopy is based on measuring the variation of the absorption coefficient of a sample as a function of the applied X-ray energy in order to obtain an absorption spectrum. This can be done either directly or indirectly. The direct method monitors the intensity of the beam transmitted through the sample (transmission mode). Indirect methods include monitoring the emitted total or partial fluorescence yield (FLY), or the sample drain current as total (TEY) or partial electron yield (PEY). Generally, spectra obtained by these different detection modes are comparable but differ in their analytical depth; TEY and PEY measure the surface of the samples whereas FLY is rather a bulk method (P L2,3-edge: TEY ≈ 5 nm vs. FLY, ≈ 70 nm: P K-edge TEY ≈ 20 nm vs. FLY, ≈ 200 nm) (Kruse et al., 2009). For soil P analyses, FLY is often more valuable, since the lower background of the FLY signal results in a better signal-to-background ratio and spectra are not affected by surface charging as often observed for TEY (Stöhr, 1992). Conversely, it should be noted that spectra recorded in FLY mode for highly concentrated and thick samples can be distorted by self-absorption effects (e.g., Shober et al., 2006; Toor et al., 2006). Essentially, these effects are attributed to a reduction in the penetration depth, causing re-absorption of the fluorescence photons; this is not an issue for spectra recorded in TEY mode. Therefore, samples with high P concentrations should be diluted or analyzed using the TEY detection mode. However, it should be noted that for samples where surface structure is different from that of the bulk material, TEY and FLY spectra may differ in their spectral features; this is a direct consequence of the much shallower sampling depth of TEY (see above) (e.g., shown for vivianit in Toor et al., 2006). Furthermore, due to the generally low penetration depth (a few microns) of the X-rays used for P XAS measurements, data collection in transmission mode is often impractical. The relatively low X-ray energy used for collecting P XAS spectra requires measurements under high vacuum conditions (P K- & L2,3-edges) or under ambient pressure in He-purged (P K-edge) chambers to minimize attenuation effects by the air. The latter condition also enables solid-state in-situ measurements of moist or liquid samples (Kelly et al., 2008); whereas solid samples must be dried in advance for measurements under vacuum. Liquids must be inserted into a liquid cell (Rouff et al., 2009) that seals the liquid from the vacuum by an appropriate P-free thin film (e.g., ultralene). One of the main advantages of XAS is the relatively straightforward preparation, simply by powdering and spreading a few milligrams as a thin film on a double adhesive tape which is attached to a sample holder. An example of a P XAS spectra recorded at the P K-edge (i.e., electrons from the K-shell or 1s are exited) and L2,3-edges are shown in Fig.9a,b.


Innovative methods in soil phosphorus research: A review.

Kruse J, Abraham M, Amelung W, Baum C, Bol R, Kühn O, Lewandowski H, Niederberger J, Oelmann Y, Rüger C, Santner J, Siebers M, Siebers N, Spohn M, Vestergren J, Vogts A, Leinweber P - J Plant Nutr Soil Sci (1999) (2015)

(a) Stacked and normalized P K-XANES fluorescence yield spectra of selected soil-relevant P reference compounds and (b) the respective P L2,3-edge spectra. (c) Long-range scan of amorphous Ca-phosphate at the P K-edge visualizing the XANES and the EXAFS region of the spectrum in energy space, (d) respective k-space transformed, and (e) Fourier transformed χ(k) data of amorphous Ca-phosphate, giving information on the type and distances of bondings (Kruse, 2013, unpublished).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4497464&req=5

fig09: (a) Stacked and normalized P K-XANES fluorescence yield spectra of selected soil-relevant P reference compounds and (b) the respective P L2,3-edge spectra. (c) Long-range scan of amorphous Ca-phosphate at the P K-edge visualizing the XANES and the EXAFS region of the spectrum in energy space, (d) respective k-space transformed, and (e) Fourier transformed χ(k) data of amorphous Ca-phosphate, giving information on the type and distances of bondings (Kruse, 2013, unpublished).
Mentions: X-ray absorption spectroscopy is based on measuring the variation of the absorption coefficient of a sample as a function of the applied X-ray energy in order to obtain an absorption spectrum. This can be done either directly or indirectly. The direct method monitors the intensity of the beam transmitted through the sample (transmission mode). Indirect methods include monitoring the emitted total or partial fluorescence yield (FLY), or the sample drain current as total (TEY) or partial electron yield (PEY). Generally, spectra obtained by these different detection modes are comparable but differ in their analytical depth; TEY and PEY measure the surface of the samples whereas FLY is rather a bulk method (P L2,3-edge: TEY ≈ 5 nm vs. FLY, ≈ 70 nm: P K-edge TEY ≈ 20 nm vs. FLY, ≈ 200 nm) (Kruse et al., 2009). For soil P analyses, FLY is often more valuable, since the lower background of the FLY signal results in a better signal-to-background ratio and spectra are not affected by surface charging as often observed for TEY (Stöhr, 1992). Conversely, it should be noted that spectra recorded in FLY mode for highly concentrated and thick samples can be distorted by self-absorption effects (e.g., Shober et al., 2006; Toor et al., 2006). Essentially, these effects are attributed to a reduction in the penetration depth, causing re-absorption of the fluorescence photons; this is not an issue for spectra recorded in TEY mode. Therefore, samples with high P concentrations should be diluted or analyzed using the TEY detection mode. However, it should be noted that for samples where surface structure is different from that of the bulk material, TEY and FLY spectra may differ in their spectral features; this is a direct consequence of the much shallower sampling depth of TEY (see above) (e.g., shown for vivianit in Toor et al., 2006). Furthermore, due to the generally low penetration depth (a few microns) of the X-rays used for P XAS measurements, data collection in transmission mode is often impractical. The relatively low X-ray energy used for collecting P XAS spectra requires measurements under high vacuum conditions (P K- & L2,3-edges) or under ambient pressure in He-purged (P K-edge) chambers to minimize attenuation effects by the air. The latter condition also enables solid-state in-situ measurements of moist or liquid samples (Kelly et al., 2008); whereas solid samples must be dried in advance for measurements under vacuum. Liquids must be inserted into a liquid cell (Rouff et al., 2009) that seals the liquid from the vacuum by an appropriate P-free thin film (e.g., ultralene). One of the main advantages of XAS is the relatively straightforward preparation, simply by powdering and spreading a few milligrams as a thin film on a double adhesive tape which is attached to a sample holder. An example of a P XAS spectra recorded at the P K-edge (i.e., electrons from the K-shell or 1s are exited) and L2,3-edges are shown in Fig.9a,b.

Bottom Line: Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development.This review provides an overview of advanced state-of-the-art methods currently used in soil P research.Required experimental set-ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.

View Article: PubMed Central - PubMed

Affiliation: Soil Science, Faculty for Agricultural and Environmental Sciences, University of Rostock Justus-von-Liebig Weg 6, 18051 Rostock, Germany ; Institute of Crop Science and Resource Conservation, Soil Science and Soil Ecology, University of Bonn Nussallee 13, 53115 Bonn, Germany.

ABSTRACT

Phosphorus (P) is an indispensable element for all life on Earth and, during the past decade, concerns about the future of its global supply have stimulated much research on soil P and method development. This review provides an overview of advanced state-of-the-art methods currently used in soil P research. These involve bulk and spatially resolved spectroscopic and spectrometric P speciation methods (1 and 2D NMR, IR, Raman, Q-TOF MS/MS, high resolution-MS, NanoSIMS, XRF, XPS, (µ)XAS) as well as methods for assessing soil P reactions (sorption isotherms, quantum-chemical modeling, microbial biomass P, enzymes activity, DGT, (33)P isotopic exchange, (18)O isotope ratios). Required experimental set-ups and the potentials and limitations of individual methods present a guide for the selection of most suitable methods or combinations.

No MeSH data available.


Related in: MedlinePlus