Visible – NIR reflectance for evaluation of luvisols and phaeozems

M. Todorova1*, M. Mihalache2, L. Ilie2, S. Atanassova3

1Department of Plant Production, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria
2Faculty of Agriculture, University of Agronomic Sciences and Veterinary Medicine, Bucharest, Romania
3Department of Biochemistry, Microbiology and Physics, Faculty of Agriculture, Trakia University, 6000 Stara Zagora, Bulgaria

Abstract. Near infrared spectra of soils with differences in soil colour, organic matter and clay mineral content showed differences in the spectral region from 700 to 1700 nm. The objective of the present study was to describe the information content of soil vis-NIR spectra of two soil types Luvisols and Phaeozems from Romania to assist soil surveys. The samples were collected from each horizon of the soil profiles. The diffuse reflectance spectra of the air-dried and sieved soil samples were obtained using both spectrophotometers – USB 4000 (OceanOptics, Inc.) into spectral range 450 – 1100 nm and NIRQuest (OceanOptics, Inc.) into spectral range 900 – 1700 nm. The diffuse reflectance, R, was transformed to absorbance using log (1/R). All of these samples have location information and a set of soil chemical and physical analytical data. Similarities and differences in absorption maxima of soil spectra from the different soil taxonomic classes using 2nd derivative of raw spectra are discussed. Principal Component Analysis (PCA) and SIMCA – soft independent modeling of class analogy was used for qualitative analysis. The obtained results showed that specific differences in Vs-NIR spectral data of Luvisols and Phaeozems from Romania existed. These spectral data could be used to develop models for soil discrimination according to soil taxonomic classes.