Near infrared spectra and soft independent modelling of class analogy for discrimination of Chernozems, Luvisols and Vertisols

The objective of the present study was to use near infrared diffuse reflectance spectroscopy and chemometrics to distinguish three major soil types in Bulgaria - Chernozems, Luvisols and Vertisols. The diffuse reflectance spectra of 78 air-dried and sieved soil samples collected from grasslands and arable agricultural lands and classified as Chernozems, Luvisols and Vertisols were obtained in the spectral range 700-2500 nm. Second-derivative transformation of soil and clay spectra was performed in order to find soil spectral differences based on the clay minerals content. Soft independent modelling of class analogy (SIMCA) was performed to classify samples according to their classes. Results show that the samples can be distinguished according to their classes as the SIMCA models correctly classified 100% of the samples in both calibration and validation sets. According to the discrimination power parameter of the SIMCA procedure, the most important wavelengths in the classification models of Chernozem, Luvisol and Vertisol soils were related to the content of clay minerals such as kaolinite and montmorillonite, smectite minerals, organic matter and carbonates.