Abstract
Visible near-infrared (Vis-NIR) reflection spectroscopy and mid-infrared (mid-IR)
reflection spectroscopy are cost- and time-effective and environmentally friendly techniques
that could be alternatives to conventional soil analysis methods. Successful determination of
spectrally active soil components, including soil organic matter (SOM), depends on the
selection of suitable pretreatment and multivariate calibration techniques. The objective of
the present review is to critically examine the suitability of Vis-NIR (350-2500 nm) and
mid-IR (4000-400 cm<sup>−1</sup>) spectroscopy as a tool for SOM quantity and quality
determination. Particular attention is paid to different pretreatment and calibration
procedures and methods, and their ability to predict SOM content from Vis-NIR and mid-IR data
is discussed. We then review the most recent research using spectroscopy in different
calibration scales (local, regional, or global). Finally, accuracy and robustness, as well as
uncertainty in Vis-NIR and mid-IR spectroscopy, are considered. We conclude that spectroscopy,
especially the mid-IR technique in association with Savitzky-Golay smoothing and
derivatization and the least squares support vector machine (LS-SVM) algorithm, can be useful
in determining SOM quantity and quality. Future research conducted for the standardization of
protocols and soil conditions will allow more accurate and reliable results on a global and
international scale.
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