Suzanne Beauchemin*,a,d, Dean Hesterbergb, Jeff Chouc, Mario Beauchemina,d, Régis R. Simarde and Dale E. Sayersf
a Natural Resources Canada, CANMET, 555 Booth Street, Office 332A, Ottawa, ON, Canada K1A 0G1
b Department of Soil Science, North Carolina State University, Box 7619, 3235 Williams Hall, Raleigh, NC 27695-7619
c National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, NC 27709
d Canada Centre for Remote Sensing, 588 Booth Street, 4th floor, Ottawa, ON, Canada K1A 0Y7
e Soil Science Department, University of Manitoba, 362 Ellis Building, Winnipeg, MB, Canada R3T 2N2
f Department of Physics, North Carolina State University, Box 8202, Raleigh, NC 27695-8202
Knowledge of phosphorus (P) species in P-rich soils is usefulfor assessing P mobility and potential transfer to ground waterand surface waters. Soil P was studied using synchrotron X-rayabsorption near-edge structure (XANES) spectroscopy (a nondestructivechemical-speciation technique) and sequential chemical fractionation.The objective was to determine the chemical speciation of Pin 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 agrosystemsin the province of Québec, Canada. The soils containedbetween 800 and 2100 mg total P kg-1. Distinct XANES featuresfor Ca-phosphate mineral standards and for standards of adsorbedphosphate made it possible to differentiate these forms of Pin the soil samples. The XANES results indicated that phosphateadsorbed on Fe- or Al-oxide minerals was present in all soils,with a higher proportion in acidic than in slightly alkalinesamples. Calcium phosphate also occurred in all soils, regardlessof pH. In agreement with chemical fractionation results, XANESdata showed that Ca-phosphates were the dominant P forms inone acidic (pH 5.5) and in the two slightly alkaline (pH 7.4–7.6)soil samples. X-ray absorption near-edge structure spectroscopydirectly identified certain forms of soil P, while chemicalfractionation provided indirect supporting data and gave insightson additional forms of P such as organic pools that were notaccounted for by the XANES analyses.
Abbreviations: Alox and Feox, ammonium oxalate–extractable aluminum or iron • HCl-P, phosphorus extracted with 1 M HCl • IHP, inositol hexametaphosphate • LCF, linear combination fitting • M3P, Mehlich III–extractable phosphorus • NaOH-P, phosphorus extracted with 0.1 M NaOH • PCA, principal component analysis • Pi, inorganic phosphorus • Po, organic phosphorus • Pt, total soil phosphorus • XANES, X-ray absorption near-edge structure
J. Environ. Qual. 32:1809-1819 (2003). © 2003 ASA, CSSA, SSSA.