Combined Application of Imaging Methods for Estimating Soil Physicochemical Properties

Abstract

Traditional techniques and methods for evaluation and detection of soil samples are tedious, laborious, expensive, and time-consuming. In comparison, spectroscopic techniques have successfully overcome some of these disadvantages and can supplement or replace them. As soil is a complex media, it is difficult to assign specifically spectral features for physicochemical properties of soil. This study discusses the combined application of Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), and Scanning Electron Microscopy coupled to EDX microprobe (SEM/EDX) methods for estimating soil physicochemical properties. For this purpose, 30 topsoil samples were measured according to standard methods of soil analysis. All spectra were collected in the mid-infrared (MIR) from 4000 to 650 cm-1. Chemometric methods were used in the analysis of multivariate data using the Quant2 package in OPUS 7 software and improved the prediction of soil properties using partial least squares regression (PLSR). The results showed that specific surface area (SSA MB-titration) had the best predictions for the soil properties in ATR-FTIR study with a RPD of 2.08, RMSE of 13.50 m2 g–1, and R2 of 0.77 (very good); followed by cation exchange capacity, organic carbon, SSA (BET), Al, clay, and Ca (good); saturation, sand, silt/clay, electrical conductivity, saturated hydraulic conductivity, K, silt, Fe, C, and Si (fair); O, Mg, pH, bulk density, porosity, total pore volume, and particle density (poor). Also, we found that SEM-EDX is able to perform a rapid simultaneous multielement analysis without any special soil sample preparation. Consequently, modern techniques, such as ATR-FTIR and SEM-EDX can be used for such studies according to the information needed and the time required for the sample preparation.