title: Addition of carboxylic acids modifies phosphate sorption on soil and boehmite surfaces: a solution chemistry and XANES spectroscopy study.
abstract: Soil acidification is a globally significant agricultural issue, as the plant availability of phosphorus (P) is decreased through increased P sorption onto aluminium (Al) hydroxides and other solid phase binding sites. X-ray absorption near edge structure (XANES) spectroscopy generated new information on the speciation of Al and P in the presence of carboxylic acids on soil and boehmite (gamma-AlOOH) surfaces. XANES spectra were acquired in the soft X-ray regime at the P and Al L(2,3)-edges, and the Al K-edge, respectively. Adding oxalic acid to soil enhanced Al dissolution and exposed previously occluded soil P, while hydroxybenzoic and coumaric acids did not compete with P for surface binding sites. Boehmite strongly adsorbed carboxylic acids in the absence of applied phosphorus. However, when P was applied with carboxylic acids, the carboxylics were unable to compete with P for binding, especially hydroxybenzoic and coumaric acids. Using XANES in both total electron yield and fluorescence yield modes provided valuable information on both surface and near-surface processes of P and Al due to different information depths. The Al K-edge XANES provided baseline information on the solid-phase matrix. XANES in total electron yield mode and at the P L-edge shows promise for speciation of elements on soil surfaces due to enhanced sensitivity for speciation of surface-adsorbed species compared to the commonly used P K-edge XANES.
authors.affiliation: Future Farming Systems Research Division, Department of Primary Industries, Rutherglen Centre, Victoria 3685, Australia. cassandra.schefe@dpi.vic.gov.au
authors.forename: C R
authors.initials: CR
authors.lastname: Schefe
authors.forename: P
authors.initials: P
authors.lastname: Kappen
authors.forename: L
authors.initials: L
authors.lastname: Zuin
authors.forename: P J
authors.initials: PJ
authors.lastname: Pigram
authors.forename: C
authors.initials: C
authors.lastname: Christensen