Application of X-ray Photoelectron Spectroscopy (XPS) to Assess Soil Organic Matter Under Different Land Uses

Soil carbon sequestration is suggested as a mechanism to remove CO2 from the atmosphere; however, uncertainty persists regarding the residence time of the stored carbon. Different land uses on the same soil series were selected to compare the amount and properties of soil carbon present and to evaluate the soil-sorbed carbon by loss on ignition estimation and X-ray photoelectron spectroscopy. Surface horizon soil samples were collected from a second-growth cedar forest, mowed grassland, hybrid poplar forest, perennial strawberry field, and an annually cropped wheat field at Totem Field at the University of British Columbia in Vancouver, British Columbia. Soils were analyzed using loss on ignition (LOI), X-ray diffraction (XRD), and angle-resolved X-ray photoelectron spectroscopy (XPS). Results indicate high variability in soil properties and carbon storage across different land uses. Specifically, perennial vegetation exhibited lower soil bulk density and higher soil carbon content compared to agriculturally managed fields, correlating with differences in soil pH. XPS indicated major differences in the amount of C-C and C=O bonds and minor differences in the amount O-C=O and Pi-Pi bonds associated with soil in the different land uses. This study contributes valuable insights that help to inform the relationship between land use practices and soil carbon storage potential.