Visible and Near-Infrared Reflectance Spectroscopy for Investigating Soil Mineralogy: A Review

Abstract

Clay minerals are the most reactive and important inorganic components in soils, but soil mineralogy classifies as a minor topic in soil sciences. Revisiting soil mineralogy has been gradually required. Clay minerals in soils are more complex and less well crystallized than those in sedimentary rocks, and thus, they display more complicated X-ray diffraction (XRD) patterns. Traditional characterization methods such as XRD are usually expensive and time-consuming, and they are therefore inappropriate for large datasets, whereas visible and near-infrared reflectance spectroscopy (VNIR) is a quick, cost-efficient, and nondestructive technique for analyzing soil mineralogic properties of large datasets. The main objectives of this review are to bring readers up to date with information and understanding of VNIR as it relates to soil mineralogy and attracts more attention from a wide variety of readers to revisit soil mineralogy. We begin our review with a description of fundamentals of VNIR. We then review common methods to process soil VNIR spectra and summary spectral features of soil minerals with particular attention to those <2 μm fractions. We further critically review applications of chemometric methods and related model building in spectroscopic soil mineral studies. We then compare spectral measurement with multivariate calibration methods, and we suggest that they both produce excellent results depending on the situation. Finally, we suggest a few avenues of future research, including the development of theoretical calibrations of VNIR more suitable for various soil samples worldwide, better elucidation of clay mineral-soil organic carbon (SOC) interactions, and building the concept of integrated soil mapping through combined information (e.g., mineral composition, soil organic matter-SOM, SOC, pH, and moisture).

The influence of training sample size on the accuracy of deep learning models for the prediction of soil properties with near-infrared spectroscopy data

“…The measured properties include soil texture (sand, silt and clay), organic carbon (OC) and cation exchange capacity (CEC). The soil particle size was quantified by the pipette method, as described in Donagema et al (2011). The method consists of using a 0.1 M NaOH solution as a dispersing agent under high-speed mechanical stirring for 10 min.…”

“…Better generalisation can be made by training the model in a larger data set. However, several studies demonstrated that the performance of the machine learning model did not increase significantly, or it even plateaued, as the calibration sample size increased (Figueroa et al, 2012;Ramirez-Lopez et al, 2014;Ng et al, 2018).…”

Mineralogical and geochemical characterization of hydrocarbon microseepage-induced sediments in part of Assam-Arakan Fold Belt, Cachar area, NE India

“…Among the clay minerals, kaolinite, montmorillonite, illite, vermiculite, and chlorite are the common clay minerals in the hydrocarbon microseepage environments. Clay minerals exhibit diagnostic absorption features near 1400 nm (caused by OH overtones), 1900 nm (overtones caused by water molecules), 2200 nm (due to Al-OH combination tones) and some weaker absorptions in the 2300-2500 nm range due to presence of Fe-or Mg-OH (Clark 1999;Zhao et al 2018;Fang et al 2018). Carbonate minerals show spectral characteristics absorption near 2350 and 2500 nm (Hunt and Salisbury, 1971).…”

Characterization and Identification of Coal and Carbonaceous Shale Using Visible and Near-Infrared Reflectance Spectroscopy

“…Reflectance spectra of these 200 powder samples in 0.5 mm grain size were obtained under the same condition as the sample in Figure 2. e preprocessing method of continuum removal (CR) was employed to remove background noise of the reflectance curves and isolate particular absorption features [17].…”