Limitations and potential of spectral subtractions in Fourier-transform infrared spectroscopy of soil samples

Soil science research is increasingly applying Fourier transform infrared (FTIR) spectroscopy for analysis of soil organic matter (SOM). However, the compositional complexity of soils and the dominance of the mineral component can limit spectroscopic resolution of SOM and other minor components. The use of spectral subtraction is an established technique for isolating specific components of multicomponent spectra, and as such is a powerful tool to improve and expand the potential of spectroscopy of soil samples. To maximize the utility of spectral subtraction and avoid its misuse, consideration must be given to the general and soil-specific limitations of FTIR spectroscopy and subtractions, as well as specific experimental objectives. This review summarizes the history of subtractions in FTIR spectroscopy of soil samples, identifies and qualifies misconceptions and limitations on its use, and highlights trade-offs, recent developments, and future directions on the potential of spectral subtractions to improve and expand FTIR applications in soil science.