Organic carbon at soil particle surfaces - Evidence from X-ray photoelectron spectroscopy and surface abrasion

This study aimed at investigating the potential of x-ray photoelectron spectroscopy (XPS) for investigating soil organic matter at secondary soil particles. The XPS was applied to microaggregates of the A horizon of a Typic Haplustoll (<20-mum equivalent diameter, >53-mum maximum real diameter) and to the fine-earth fraction (<2 mm) of the Bs horizon of a Typic Haplorthod. Carbon and N, as well as Si (both samples), Ca (Haplustoll), and Al (Haplorthod) were detected. Removing the particle surface layer (<50 nm) by bombarding with Ar+ resulted in a strong reduction of the signals of C and N, while those attributed to inorganic components increased relatively. Consequently, in both soils, organic matter was concentrated at the surface of soil aggregates. We conclude that Ar+ sputtering followed by XPS analysis is a useful tool in identifying the accumulation of elements at the surfaces of soil particles.