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

Qian Fang,Hanlie Hong,Chaowen Wang,Stephanie Kukolich,Ke Yin,Lulu Zhao

doi:10.1155/2018/3168974

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).

Highlights

Soils are open, complex, and dynamic systems as well as fundamental natural environments for animals, plants, microorganisms, and human interaction [1]
Soil mineralogy is still a minor topic in soil sciences. is may be due partly to the unjustified assumption that a given soil mineral will have the same properties as those of its better-crystallized counterpart that formed in a more “geologic” context [4]
Clay minerals in soils are more complex and less well crystallized than those in sedimentary rocks. Traditional characterization methods such as X-ray diffraction (XRD) are usually expensive and time-consuming, whereas visible and near-infrared reflectance spectroscopy (VNIR) is a quick, cost-efficient, and nondestructive technique for analyzing the soil mineralogic properties of large datasets. e major strength of soil mineralogy studies is that there is a direct relationship between soil minerals and their spectra, since the diagnostic absorption bands of soil minerals lie within the VNIR region

Summary

Introduction

Complex, and dynamic systems as well as fundamental natural environments for animals, plants, microorganisms, and human interaction [1]. According to Churchman [3], clay minerals in the soil context are “secondary inorganic compounds of

Objectives

Methods

Conclusion