Estimating Fine Resolution Carbon Concentration in an Intact Soil Profile by X-Ray Fluorescence Scanning

Abstract

The link between the small (<mm) scale spatial organisation of soil carbon (C) and the long-term security of the abiotic C store is not well understood. Here we present a methodology that is being developed to map carbon concentration in an intact soil profile of a Cambisol by adapting X-ray fluorescence (XRF) scanning for soils. The main objective was to identify candidate indicators for the estimation of soil C using XRF with intact soil cores 1 m long. Following multiple correlation and regression of XRF elemental counts with carbon concentrations, sulphur emerged as the strongest candidate for the estimation of soil C but a loss of XRF spatial resolution from 200 μm to 1 cm was required for sulphur to achieve a strong relationship with C (R2 = 0.77). It was concluded that XRF measurements using a Cr target tube may increase count rates for lighter elements and improve the accuracy with which elemental counts can predict soil C at the higher spatial scale.