Identification of agricultural Mediterranean soils using mid-infrared photoacoustic spectroscopy

This study investigated the use of Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) for rapid identification of agricultural soil samples. The PAS spectra of 166 air-dried samples belonging to five Mediterranean soil types most common in Israeli agriculture were recorded. The various soil types exhibited distinctive mid-IR bands, especially around the 2900–3700 cm− 1, 2500–2550 cm− 1, 1800–2050 cm− 1 and 900–1600 cm− 1 regions. Following smoothing and normalization of the spectra, principal component analysis (PCA) was used to reduce the dimensionality of the data and the PCA scores were used in classifiers based either on linear discriminant analysis or on probabilistic neural networks. The two classifiers based on four PCA scores yielded very similar results and correctly identified over 96% of the 77 validation samples. Comparison with the attenuated total reflectance (ATR) spectra of similar soils used in a previous study showed that the PAS spectra contained more information than the ATR ones, both in terms of the number of soil-specific bands and in terms of the bands' distinctiveness. The results clearly show that FTIR-PAS can be used for rapid soil identification and the abundance of information in the PAS spectra indicates that this technique could be further developed to assess important soil features.