Contemporary advancements in soil characterization: Geochemical, morphological, and spectroscopic approaches

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2020-05

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Abstract

In recent decades, Pedology has advanced from a mostly qualitative method to a more quantitative approach of describing and classifying soil. Complimenting traditional morphological description, the integration of proximal and remote sensors allow modern Pedologists to make laboratory quality readings directly in seconds. However, U.S Soil Taxonomy (USST) was last updated in 1999. Thus, contemporary technological advancements are not currently established methods of classifying soils. Proximal and remote sensors provide voluminous data at minimal cost, which has driven a shift towards quantitative pedology. With the new edition of USST expected in 2022, new approaches are needed to insert contemporary technological advancements into the quantitative USST environment. This research encompasses three different examples of updates needed for the new edition of USST with deference to integration of proximal sensors and novel taxa previously never proposed. Study #1 compared the soil properties of urban and rural playas in the Southern High Plains (SHP) using portable X-ray fluorescence (PXRF) spectroscopy. Playas in the SHP collect runoff and provide habitat for migratory waterfowl. Evaluating playa chemical composition provided information to optimize management for ecological functionality. Rural playas featured higher concentrations of Pb, Cr, As, Zn, Cu, and Ni than urban playas, necessitating different management. Further, clay content of urban playas fell below Vertisol requirements, justifying taxadjuncts or alternate classification with implications for differential playa hydrology. Study #2 established new taxa in northern Alaska. The vast majority of Alaska has not been mapped due to rugged terrain and harsh environment. This study morphologically described and classified ten Gelolls (cold, dark, carbon-rich, fertile soils) previously mapped on only 12.5 ha in Alaska before my research project. Results indicated that more subgroups need to be added to future editions of USST to more appropriately describe Gelolls. A novel concept of Geloll formation was developed inclusive of limestone, calcium rich geology, sufficient drainage, and high coarse fragments (rock) content. Using remote sensing technology and this concept, an estimated 3,100,000 ha of Gelolls in Alaska were identified; therefore, most Gelolls in Alaska have not yet been mapped. Based on this research, the USST working group has expressed interest in using this research to advocate for new additions to the forthcoming version of USST. Study #3 used PXRF and visible near infrared (VisNIR) spectrometry to detect and quantify calcic horizon depth from the mineral soil surface to make soil taxonomic determinations in rural Romania without traditional laboratory methods. PXRF in isolation was adept at identifying calcic horizons directly; combining PXRF + VisNIR data, model stability was improved, but predictive accuracy remained the same. The U.S. Army Engineer Research and Development Center (ERDC) and US Department of Agriculture Soil Survey Staff have both expressed interest in the findings of this study, especially as related to soil taxonomy combined with proximal sensors. These advancements are revolutionizing soil science and classification.

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Keywords

Soil classification, Soil taxonomy, Soil characterization, Playas, Elements, Portable X-ray fluorescence, Geochemistry, Mollisols, gelic temperature regime, Alaska, Gelolls, Transylvanian Plain, Romania, Proximal sensors, Chernisols, Calcic horizons

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