Speciation of Phosphorus in Phosphorus-Enriched Agricultural Soils Using X-Ray Absorption Near-Edge Structure Spectroscopy and Chemical Fractionation
2003
Beauchemin, Suzanne | Hesterberg, Dean | Chou, Jeff | Beauchemin, M. | Simard, Régis R. | Sayers, Dale E.
Knowledge of phosphorus (P) species in P-rich soils is useful for assessing P mobility and potential transfer to ground water and surface waters. Soil P was studied using synchrotron X-ray absorption near-edge structure (XANES) spectroscopy (a nondestructive chemical-speciation technique) and sequential chemical fractionation. The objective was to determine the chemical speciation of P in long-term-fertilized, P-rich soils differing in pH, clay, and organic matter contents. Samples of three slightly acidic (pH 5.5–6.2) and two slightly alkaline (pH 7.4–7.6) soils were collected from A or B horizons in two distinct agrosystems in the province of Québec, Canada. The soils contained between 800 and 2100 mg total P kg⁻¹ Distinct XANES features for Ca-phosphate mineral standards and for standards of adsorbed phosphate made it possible to differentiate these forms of P in the soil samples. The XANES results indicated that phosphate adsorbed on Fe- or Al-oxide minerals was present in all soils, with a higher proportion in acidic than in slightly alkaline samples. Calcium phosphate also occurred in all soils, regardless of pH. In agreement with chemical fractionation results, XANES data showed that Ca-phosphates were the dominant P forms in one acidic (pH 5.5) and in the two slightly alkaline (pH 7.4–7.6) soil samples. X-ray absorption near-edge structure spectroscopy directly identified certain forms of soil P, while chemical fractionation provided indirect supporting data and gave insights on additional forms of P such as organic pools that were not accounted for by the XANES analyses.
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