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Soil Systems
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Using Synchrotron Radiation to Perform Phosphate Speciation in Soils
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Using Synchrotron Radiation to Perform Phosphate Speciation in Soils

A special issue of Soil Systems (ISSN 2571-8789).

Deadline for manuscript submissions: closed (10 January 2020) | Viewed by 29065

Special Issue Editor

Prof. Dr. Derek Peak

E-Mail Website
Guest Editor
Department of Soil Sciences, University of Saskatchewan, Saskatoon, SK, Canada
Interests: application of molecular-scale spectroscopic tools to perform chemical speciation in terrestrial systems; improving food security via nutrient stewardship and climate-smart approaches; optimizing in-situ bioremediation utilizing advanced soil characterization; development of novel spectroscopic tools for soil analysis; role of mineralogy in cycling of light elements in soils; molecular agronomic science

Special Issue Information

 Dear Colleagues,

Scope: This Special Issue will focus on the application of synchrotron-based spectroscopy to understand the linkage between the chemical form of P and its behavior in the soil environment. This is an issue of vital concern for both agronomic and environmental researchers.

Summary: Phosphorous (P) is a macronutrient that is integral to all life; as it is utilized in cellular energy transfer, constitutes the backbone of DNA/RNA, is a major component of cell walls, and provides structural integrity to bones. Phosphorus is a finite resource that often limits crop production, which pressures a high demand on its efficient usage and tightly couples P nutrient efficiency to global food demands. When P is present in excess, however, it promotes the rapid growth of microbial and plant life, producing eutrophication and algal blooms that are detrimental to the environment. Phosphorus differs enormously in its solubility, bioavailability and mobility, depending on its chemical form in soils. Therefore, understanding the fate of P in the soil environment requires techniques capable of directly measuring the solid-state speciation of P. Synchrotron approaches have proven especially capable in this regard; this Special Issue will highlight current research into the application of synchrotron-based x-ray absorption spectroscopy (XAS) in terrestrial ecosystems.

Prof. Dr. Derek Peak
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Phosphorus speciation
  • XANES
  • EXAFS
  • Quantitative speciation
  • Phosphate fixation
  • Phosphate mineralogy
  • Nutrient stewardship

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Published Papers (5 papers)

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Research

17 pages, 1397 KiB  
Article
A Probabilistic Approach to Phosphorus Speciation of Soils Using P K-edge XANES Spectroscopy with Linear Combination Fitting
by Jon Petter Gustafsson, Sabina Braun, J. R. Marius Tuyishime, Gbotemi A. Adediran, Ruben Warrinnier and Dean Hesterberg
Soil Syst. 2020, 4(2), 26; https://doi.org/10.3390/soilsystems4020026 - 24 Apr 2020
Cited by 36 | Viewed by 6222
Abstract
A common technique to quantitatively estimate P speciation in soil samples is to apply linear combination fitting (LCF) to normalized P K-edge X-ray absorption near-edge structure (XANES) spectra. Despite the rapid growth of such applications, the uncertainties of the fitted weights are still [...] Read more.
A common technique to quantitatively estimate P speciation in soil samples is to apply linear combination fitting (LCF) to normalized P K-edge X-ray absorption near-edge structure (XANES) spectra. Despite the rapid growth of such applications, the uncertainties of the fitted weights are still poorly known. Further, there are few reports to what extent the LCF standards represent unique end-members. Here, the co-variance between 34 standards was determined and their significance for LCF was discussed. We present a probabilistic approach for refining the calculation of LCF weights based on Latin hypercube sampling of normalized XANES spectra, where the contributions of energy calibration and normalization to fit uncertainty were considered. Many of the LCF standards, particularly within the same standard groups, were strongly correlated. This supports an approach in which the LCF standards are grouped. Moreover, adsorbed phytates and monetite were well described by other standards, which puts into question their use as end-members in LCF. Use of the probabilistic method resulted in uncertainties ranging from 2 to 11 percentage units. Uncertainties in the calibrated energy were important for the LCF weights, particularly for organic P, which changed with up to 2.7 percentage units per 0.01 eV error in energy. These results highlight the necessity of careful energy calibration and the use of frequent calibration checks. The probabilistic approach, in which at least 100 spectral variants are analyzed, improves our ability to identify the most likely P compounds present in a soil sample, and a procedure for this is suggested in the paper. Full article
(This article belongs to the Special Issue Using Synchrotron Radiation to Perform Phosphate Speciation in Soils)
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13 pages, 2248 KiB  
Article
The Influences of Magnesium upon Calcium Phosphate Mineral Formation and Structure as Monitored by X-ray and Vibrational Spectroscopy
by David M. Hilger, Jordan G. Hamilton and Derek Peak
Soil Syst. 2020, 4(1), 8; https://doi.org/10.3390/soilsystems4010008 - 29 Jan 2020
Cited by 9 | Viewed by 4690
Abstract
Calcium phosphate minerals are typically the solubility-limiting phase for phosphate in calcareous soils. Magnesium (Mg), despite being present in high concentrations in calcareous soils, has been largely neglected in the study of formation and stabilization of soil phosphate minerals due to the high [...] Read more.
Calcium phosphate minerals are typically the solubility-limiting phase for phosphate in calcareous soils. Magnesium (Mg), despite being present in high concentrations in calcareous soils, has been largely neglected in the study of formation and stabilization of soil phosphate minerals due to the high solubility of pure Mg phosphate phases. In this study, a series of four common calcium and magnesium phosphate minerals, hydroxyapatite/bobierrite and brushite/newberyite were synthesized in the presence of widely varying Mg concentrations to examine the effects of Mg substitution upon the local bonding environment and overall structure of the precipitates. Phosphorus K-edge X-Ray absorption near edge structure (XANES) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) provide insight into the local coordination environment, whereas synchrotron powder X-Ray diffraction (SP-XRD) and transmission electron microscopy (TEM) were used for structural analysis. In acidic to neutral pH, Mg-bearing brushite phases formed over a wide range of Ca:Mg ratios. In neutral to high pH systems, a short-range order amorphous calcium phosphate (ACP) with a local structure analogous with hydroxyapatite precipitated for a wide range of Ca to Mg ratios. It can be inferred that the presence of Mg in soils leads to stabilization of metastable phases: via cation substitution in brushite and via poisoning of crystal growth propagation for hydroxyapatite. Full article
(This article belongs to the Special Issue Using Synchrotron Radiation to Perform Phosphate Speciation in Soils)
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19 pages, 2181 KiB  
Article
Molecular Scale Studies of Phosphorus Speciation and Transformation in Manure Amended and Microdose Fertilized Indigenous Vegetable Production Systems of Nigeria and Republic of Benin
by Abimfoluwa Olaleye, Durodoluwa Oyedele, Pierre Akponikpe, Gourango Kar and Derek Peak
Soil Syst. 2020, 4(1), 5; https://doi.org/10.3390/soilsystems4010005 - 8 Jan 2020
Cited by 3 | Viewed by 4007
Abstract
This study investigated the speciation, transformation, and availability of P during indigenous vegetable production by employing a combination of chemical and spectroscopic techniques. The study focused on sites in two ecozones of SSA, the dry savanna (lna, Republic of Benin) and rainforest (Ilesha, [...] Read more.
This study investigated the speciation, transformation, and availability of P during indigenous vegetable production by employing a combination of chemical and spectroscopic techniques. The study focused on sites in two ecozones of SSA, the dry savanna (lna, Republic of Benin) and rainforest (Ilesha, Nigeria). Both sites were cultivated with two indigenous vegetable species: local amaranth (Amaranthus cruentus (AC)) and African eggplant (Solanum macrocarpon (SM)). The soils were treated with 5 t/ha poultry manure and urea fertilizer at the rates of 0, 20, 40, 60, and 80 kg N/ha. Soil samples were collected before planting and after harvest. Phosphorus K-edge X-ray absorption near-edge structure (XANES) spectroscopy was used to determine P speciation in these soils. Quantitative analysis showed that adsorbed and organic P were the two dominant P species in the manure amended dry savanna (DS) soils before planting and after harvest in soils cultivated with both AC and SM, with the addition of urea (40 kg N/ha) causing an increase in the organic P form in dry savanna soils cultivated with AC. Soils of the rainforest (RF) cultivated with AC initially had large amounts of apatite P in the manure amended soils prior to planting, which was transformed to adsorbed and organic P after harvest. Urea addition to the rainforest soils shifted the dominant P species from organic P to adsorbed and apatite P, which was likely to limit P availability. Soils cultivated with SM had similar proportions of both organic and adsorbed P forms, with 40 kg N/ha addition slightly increasing the proportion of adsorbed P. Full article
(This article belongs to the Special Issue Using Synchrotron Radiation to Perform Phosphate Speciation in Soils)
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13 pages, 1874 KiB  
Article
Optimization of Data Processing Minimizes Impact of Self-Absorption on Phosphorus Speciation Results by P K-Edge XANES
by Luis Carlos Colocho Hurtarte, Luiz Francisco Souza-Filho, Wedisson Oliveira Santos, Leonardus Vergütz, Jörg Prietzel and Dean Hesterberg
Soil Syst. 2019, 3(3), 61; https://doi.org/10.3390/soilsystems3030061 - 6 Sep 2019
Cited by 15 | Viewed by 5240
Abstract
Bulk soil phosphorus speciation by X-ray absorption spectroscopy (XAS) using fluorescence yield-mode measurements is an important tool for phosphorus research because of the low soil P contents. However, when measuring in fluorescence mode, increasing the concentration of the absorbing atom can dampen the [...] Read more.
Bulk soil phosphorus speciation by X-ray absorption spectroscopy (XAS) using fluorescence yield-mode measurements is an important tool for phosphorus research because of the low soil P contents. However, when measuring in fluorescence mode, increasing the concentration of the absorbing atom can dampen the XAS spectral features because of self-absorption and affect the linear combination (LC) fitting results. To reduce the self-absorption for samples of high P contents, thick boron nitride diluted samples are produced, yet the effects of self-absorption on P speciation results via LC fitting of P K-edge XANES spectroscopy, and the possible benefits of data processing optimization are unknown. Toward this end, we produced a series of ternary standard mixtures (calcium-iron-aluminum phosphates) and an example soil sample both diluted using boron nitride over a range from 1 to ~900 mmol kg−1 for the soil sample and up to ~6000 mmol kg−1 for the standard mixture. We show that by optimizing background subtraction and normalization values, consistent results with less than 10% error can be obtained for samples with up to 300 mmol kg−1 P. Our results highlight the applicability of optimized P K-edge XANES fitting across a wide range of concentrations encountered in natural environments. Full article
(This article belongs to the Special Issue Using Synchrotron Radiation to Perform Phosphate Speciation in Soils)
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17 pages, 4330 KiB  
Article
Phosphate Sorption Speciation and Precipitation Mechanisms on Amorphous Aluminum Hydroxide
by Xiaoming Wang, Brian L. Phillips, Jean-François Boily, Yongfeng Hu, Zhen Hu, Peng Yang, Xionghan Feng, Wenqian Xu and Mengqiang Zhu
Soil Syst. 2019, 3(1), 20; https://doi.org/10.3390/soilsystems3010020 - 20 Mar 2019
Cited by 42 | Viewed by 8194
Abstract
Aluminum (Al) oxides are important adsorbents for phosphate in soils and sediments, and significantly limit Phosphate (P) mobility and bioavailability, but the speciation of surface-adsorbed phosphate on Al oxides remains poorly understood. Here, phosphate sorption speciation on amorphous Al hydroxide (AAH) was determined [...] Read more.
Aluminum (Al) oxides are important adsorbents for phosphate in soils and sediments, and significantly limit Phosphate (P) mobility and bioavailability, but the speciation of surface-adsorbed phosphate on Al oxides remains poorly understood. Here, phosphate sorption speciation on amorphous Al hydroxide (AAH) was determined under pH 3–8 and P concentration of 0.03 mM–15 mM using various spectroscopic approaches, and phosphate precipitation mechanisms were discussed as well. AAH exhibits an extremely high phosphate sorption capacity, increasing from 3.80 mmol/g at pH 7 to 4.63 mmol/g at pH 3. Regardless of reaction pH, with increasing P sorption loading, the sorption mechanism transits from bidentate binuclear (BB) surface complexation with dP-Al of 3.12 Å to surface precipitation of analogous amorphous AlPO4 (AAP), possibly with ternary complexes, such as (≡Al-O)2-PO2-Al, as intermediate products. Additionally, the percentage of precipitated phosphate occurring in AAP linearly and positively correlates with P sorption loading. Compared to phosphate reaction with ferrihydrite, phosphate adsorbs and precipitates more readily on AAH due to the higher solubility product (Ksp) of AAH. The formation of AAP particles involves AlIII release, which is promoted by phosphate adsorption, and its subsequent precipitation with phosphate at AAH surfaces or in the bulk solution. Full article
(This article belongs to the Special Issue Using Synchrotron Radiation to Perform Phosphate Speciation in Soils)
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