Speciation of phosphorus in phosphorus-enriched agricultural soils using X-ray absorption near-edge structure spectroscopy and chemical fractionation.
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.
Beauchemin
Suzanne
S
Natural Resources Canada, CANMET, 555 Booth Street, Office 332A, Ottawa, ON, Canada K1A 0G1. sbeauche@nrcan.gc.ca
Hesterberg
Dean
D
Chou
Jeff
J
Beauchemin
Mario
M
Simard
Régis R
RR
Sayers
Dale E
DE
D000327:Adsorption; D000383:Agriculture; D002623:Chemistry Techniques, Analytical / Q000379:methods; D004784:Environmental Monitoring / Q000379:methods; D010710:Phosphates / Q000032:analysis / Q000737:chemistry; D010758:Phosphorus / Q000032:analysis* / Q000737:chemistry*; D012987:Soil; D013052:Spectrometry, X-Ray Emission
D010710:Phosphates; D012987:Soil; D010758:Phosphorus