Use of mid‐infrared spectroscopy in the diffuse‐reflectance mode for the prediction of the composition of organic matter in soil and litter

Abstract

Mid-infrared spectroscopy (MIRS) is assumed to be superior to near-infrared spectroscopy (NIRS) for the prediction of soil constituents, but its usefulness is still not sufficiently explored. The objective of this study was to evaluate the ability of MIRS to predict the chemical and biological properties of organic matter in soils and litter. Reflectance spectra of the mid-infrared region including part of the near-infrared region (7000-400 cm -1 ) were recorded for 56 soil and litter samples from agricultural and forest sites. Spectra were used to predict general and biological characteristics of the samples as well as the C composition which was measured by 13 C CPMAS-NMR spectroscopy. A partial least-square method and cross-validation were used to develop equations for the different constituents over selected spectra ranges after several mathematical treatments of the spectra. Mid-infrared spectroscopy predicted well the C : N ratio: the modeling efficiency EF was 0.95, the regression coefficient (a) of a linear regression (measured against predicted values) was 1.0, and the correlation coefficient (r) was 0.98. Satisfactorily (EF ≥ 0.70, 0.8 ≤ a ≤ 1.2, r ≥ 0.80) assessed were the contents of C, N, and lignin, the production of dissolved organic carbon, and the contents of carbonyl C, aromatic C, O-alkyl C, and alkyl C. However, the N mineralization rate, the microbial biomass and the alkyl-to-aromatic C ratio were predicted less satisfactorily (EF < 0.70). Limiting the sample set to mineral soils did generally not result in improved predictions. The good and satisfactory predictions reported above indicate a marked usefulness of MIRS in the assessment of chemical characteristics of soils and litter, but the accuracies of the MIRS predictions in the diffuse-reflectance mode were generally not superior to those of NIRS.

Recent applications of vibrational mid-Infrared (IR) spectroscopy for studying soil components: a review

“…This technique was introduced by Nguyen, et al (1991) for studying soil chemical composition and was subsequently used to investigate SOM and the chemical composition of humic substances, as well as the effect of amendment practice on soil (Aguiar, et al, 2013;Calderon, et al, 2011aCalderon, et al, , 2011bDemyan, et al, 2012;Ellerbrock, et al, 2009;Ferrari, et al, 2011;Janik, et al, 2007a;Kaiser, et al, 2007;Leue, et al, 2010;Ludwig, et al, 2008;Minasny, et al, 2008;Reeves III and Smith, 2009). It has also been applied to study many other agricultural related aspects such as the composition of different coal ranks (Chen, et al, 2012;Li, et al, 2010) and their soluble SOM fraction (Gezic, et al, 2012;Ghosh, et al, 2009), the chemistry of waste and compost materials (Huber-Humer, et al, 2011;Salati, et al, 2013;Smidt and Meissl, 2007), the decomposition processes of forest litter (Duboc, et al, 2012;Nault, et al, 2009;Osono, et al, 2011;Tatzber, et al, 2010), the chemical structure of pyrogenic organic matter (OM) Nocentini, et al, 2010) and the behaviour of chemical compounds adsorbed on clays (Aochi and Farmer, 2011;Dorado, et al, 2010).…”

“…KBr-pellet), DRIFT or ATR, depends on parameters such as the sample size, the information needed (bulk versus surface analysis) or the time required for the sample preparation. Currently, the improved design of DRIFT accessories has made this technique widely used for studying soil compounds (Aguiar, et al, 2013;Calderon, et al, 2011aCalderon, et al, , 2011bDemyan, et al, 2012;Ellerbrock, et al, 2009;Francioso, et al, 2009;Leue, et al, 2010;Ludwig, et al, 2008;Minasny, et al, 2008); ATR is also now being widely used (Artz, et al, 2008;Gezic, et al, 2012;Neves-Fernandes, et al, 2010;Vergnoux, et al, 2011).…”

“…The critical point is how to identify single functional group vibrations or the presence of well defined molecular structures. Normalization, baseline correction and smoothing are the first steps to process a spectrum (Demyan, et al, 2012;Du and Zhou, 2009;FernandezGetino, et al, 2013;Ludwig, et al, 2008;Tatzber, et al, 2010;Vegnoux, et al, 2011).…”

“…Strong correlations were found between FTIR spectra and soil parameters: C/N ratio, C and N content, lignin, HA, soil organic carbon (SOC), inorganic carbon, metals, pH, and others. In the last few years, many papers have dealt with the applications of PCA and PLS to the quantitative determination of the above-mentioned parameters on different soil layers and litter, as well as on particulate OM and on OM different fractions (Bornemann, et al, 2010;Calderon, et al, 2011a;D'Acqui, et al, 2010;Fernandez-Getino, et al, 2013;Ludwig, et al, 2008;Tatzber, et al, 2010). MIR spectroscopy predicted the C/N ratio well; the contents of C, N, and lignin, the production of dissolved OC, and the contents of carbonyl-C, aromatic C, O-alkyl -C, and alkyl-C were satisfactorily assessed.…”

“…MIR spectroscopy has frequently been applied to investigate soil properties and soil organic matter (SOM) characteristics (Aguiar, et al, 2013;Bellon-Maurel and McBratney, 2011;Calderon, et al, 2011aCalderon, et al, , 2011bDemyan, et al, 2012;Du and Zhou, 2009;Francioso, et al, 2009;Haberhauer and Gerzabek, 1999;Kaiser, et al, 2011). Currently, the combination of multivariate statistical methods used for the Fourier Transform IR (FTIR) spectra analysis has provided a powerful method for the discrimination and identification and/or quantification of single components in soils (Aguiar, et al, 2013;Bellon-Maurel and McBratney, 2011;Bornemann, et al, 2010;Calderon, et al, 2011aCalderon, et al, , 2011bD'Acqui, et al, 2010;Fernandez-Getino, et al, 2013;Janik, et al, 2007aJanik, et al, , 2007bLudwig, et al, 2008;Minasny, et al, 2008;Pirie, et al, 2005;Reeves III, 2010;Stumpe, et al, 2011;Tatzber, et al, 2010;Viscarra Rossel, et al, 2006;Yang, et al, 2012). The representation of MIR spectra is not uniform in the literature.…”