Soil Catena Characterization using pXRF and Vis-NIR Spectroscopy in Northwest Turkey

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Abstract Soil profile characterization using Vis-NIR and pXRF provides relatively quick measurements, and can be conducted in-situ. The objectives of this study were to i) characterize soil profiles along a catena using soil data and individual or combined Vis-NIR and pXRF data and ii) compare soil color, chemical properties, physical properties, weathering indices, elemental concentrations, Vis-NIR spectra, pXRF8 spectra, pXRF45 spectra, and combined data to determine useful variables for explaining soil variations along the catena using principal component analysis (PCA). Four soil profiles were described and sampled along a catena in the Central Anatolia Region, Eskişehir, Turkey. Soil samples were collected from delineated horizons and analyzed for the content of sand, silt, clay, electrical conductivity (EC), pH, soil organic matter (SOM), CaCO3, and scanned by Vis-NIR (350–2500 nm) and pXRF (0–8 kV and 0–45 kV) spectrometers. The soil profiles were described as Lithic Xeropsamments, Typic Xeropsamments, and Typic Haploxerepts. It was found that color coordinates (R, G, B, L* and V), physical properties (silt and clay), chemical properties (EC, pH, and CaCO3), weathering indices (SAF and DI), and elemental concentrations (Fe, Ca, K, Ti, Zn, Rb, Sr, Zr, and Ba) increased from P1 to P3 along the soil catena (summit to backslope) in both topsoil and subsoil. Soil depth, the thickness of soil horizons, and the darkness of soil color increased downslope along the catena. Soil physical properties such as sand, silt, and clay content were more useful variables to characterize soil variation along the catena than chemical properties such as EC, pH, SOM, and CaCO3. We conclude that proximal soil sensors such as Vis-NIR and pXRF spectra can be successfully used for pedological characterization of young and developing soils along a catena.