Underassessed phosphorus fixation mechanisms in soil sand fraction

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• 作者：Yuji Arai^a ; ^{yarai@clemson.edu} ; Ken J. Livi^b ; ¹ ; ^{klivi@jhu.edu}
• 关键词：Phosphorus ; Fixation ; Sand fraction ; Coatings ; XAS ; STEM
• 刊名：Geoderma
• 出版年：2013
• 出版时间：January, 2013
• 年：2013
• 卷：192
• 期：Complete
• 页码：422-429
• 全文大小：1103 K

文摘

Eutrophication caused by phosphorus (P) rich leachate from sandy soils has been one of the major agro-environmental issues in the world. In predicting P bioavailability in soils, P reactivity in soil clay fractions (e.g., iron oxyhydroxides) has been a major focus of soil chemistry research in the past. However, the role of sand fraction has been rarely investigated to accurately understand the retention and release mechanisms of P in soils, and remains poorly understood. In this case study, we report here on macroscopic and spectroscopic evidence for environmentally important P partitioning mechanisms in soil sand fractions. In the high P sandy soils, total desorbable P from the sand fraction was as high as ~ 50 % of total desorbable P from the whole soils, and these bioavailable P were associated with ammonium oxalate extractable Al and Fe. Scanning transmission electron microscopy/energy-dispersive X-ray analysis further revealed that P was associated with amorphous mixed Fe/Al/Si precipitates in the sand grain coating, and was not present with crystalline iron oxyhydroxides like goethite. Bulk- and microfocused-Fe K-edge X-ray absorption spectroscopy analysis showed that average FeO₆ coordination environments in the grain coating did not exactly coincide with that in synthetic goethite, hematite, and ferrihydrite. The coordination numbers of second and third Fe shells were slightly larger/smaller than those in reference iron oxyhydroxides (hematite and goethite), suggesting the perturbation of local chemical structure of FeO₆ linkages by Si/Al/P. Our research findings suggest that amorphous Al/Si/Fe grain coatings in soil sand fractions might be important in predicting the release of labile P in the surface and subsurface environment.