ASSESSING THE SURFACE-COMPOSITION OF SOIL PARTICLES FROM SOME PODZOLIC SOILS BY X-RAY PHOTOELECTRON-SPECTROSCOPY

We have applied X-ray photoelectron spectroscopy (XPS) to assess the s urface composition of soil particles in the AB, Bf, and Bhf horizons o f some Podzolic soils from British Columbia, Canada. Since the analysi s is restricted to a 'depth' of < 10 nm from the particle surface, thi s technique is uniquely suited to this purpose. For the soils used her e, the elements detected in decreasing order of abundance are oxygen ( 46-54%), carbon (13-38%), silicon (3.2-20%), aluminium (4.8-14%), iron (1.0-4.4%), and nitrogen (0.4-2.9%). Small amounts of sodium and magn esium are also measured. In comparison with the corresponding values f or the bulk soils, the surface of soil particles is enriched in C, N, and Al. As C and N may be assigned to organic matter (OM), this findin g is strongly indicative of the presence of Al-organic complexes as a coating over soil particle surfaces. Unlike Al, Fe is relatively deple ted at the surface of soil particles probably because Fe tends to prec ipitate as an oxyhydroxide phase in the pH range (4.1-5.3) of the soil s sampled. Silicon is also depleted at soil particle surfaces but the extent of depletion is smaller for the AB than for the underlying Bf h orizons. (C) 1998 Elsevier Science B.V. All rights reserved.