Enhanced soil profile visualization using portable X-ray fluorescence (PXRF) spectrometry

Abstract

Soil horizonation has traditionally relied upon morphological description, field sampling, and laboratory analysis as a means of establishing key diagnostic horizons and features within a soil profile. While this technique is useful for many soil properties, other quantifiable properties associated with elemental abundance may be visually imperceptible. Portable X-ray fluorescence (PXRF) spectrometry allows for rapid elemental data acquisition in-situ, providing more than 20 elements commonly detectable within a soil profile. In this study, a grid containing 130 cells was physically imposed upon two soil profiles in West Texas, USA. PXRF was used to sequentially scan each grid cell and acquire elemental data. The profiles were morphologically described by a panel of soil scientists, sampled, and subjected to traditional laboratory characterization. Data from the PXRF and field sampling were statistically compared, then visualized as depth functions. A data visualization tool was created to overly elemental data on top of a digital photograph of the soil profile in semitransparency. Using elemental data as a proxy, PXRF data was able to detect both argillic and calcic horizons within one soil profile and visually illustrate their extent and assist in delineating horizons in a second profile with nondescript horizons. The soil visualization tool has other features as well such as correlation analysis between elements, adjustable correlation threshold in real time, rasterized vs. smoothed data overlay, and box-plots of elemental concentrations. Summarily, this research developed a new tool for PXRF data visualization in support of soil pedon description, allowing for elemental data which may be visually imperceptible to be considered during soil profile characterization. Future advancements will seek to integrate this tool directly into the PXRF software for on-site visualization of any element specified by the analyst. Applications of such could include real-time mapping of contaminant metals in soil profiles.