Estimation of elemental composition of agricultural soils from West Azerbaijan, Iran, using mid-infrared spectral models

Abstract

Characterizing the elemental composition provides useful information about the weathering degree of soils. In Miandoab County, Northern Iran, this characterization was missing, and thus the objectives of this work were to evaluate the weathering degrees for the most typical soils in the area from their elemental compositions, and to estimate this elemental composition using Fourier transform infrared spectroscopy and Random Forest models. Five soil profiles, including Aridisols and Inceptisols, were selected as the most representative of the area. Major elemental oxides were determined in each genetic horizon by X-ray fluorescence, showing that these soils were at early developmental stages. Only Al2O3 and CaO were accurately estimated, with R2 values of 0.8, and out-of-bag mean square errors of 0.2 and 1.1, respectively. The other oxides were not predicted satisfactorily, probably due to small differences in their elemental compositions. Random Forest provided the important spectral bands related to the content of each element. For Al2O3, these bands were between 500 and 650 cm-1, which represent out-of-plane OH bending vibrations and Al-O gibbsite and alumino-silicate vibrations. For CaO, the most important bands are related to carbonate content. A combination of Fourier transform infrared spectra and Random Forest models can be used as a rapid and low-cost technique to estimate the elemental composition of arid and semi-arid soils of Northern Iran.

Mid-Infrared Spectroscopy Supports Identification of the Origin of Organic Matter in Soils

“…This result suggests possible influences from the other physicochemical soil components important for pedogenic processes, such as carbonates and clay minerals [39]. However, the placement of some samples indicated the soil transformation (analyzed as the change from the bottom towards topsoil layers of the buried soil) from Chernozem through Phaeozem towards Luvisol (kurgan K3) and from Phaeozem towards Luvisol (kurgans K1 and K2), which is consistent with opinions regarding the transformations of chernozemic soils during the Holocene period [19,29,40,41]. Clear discrimination of the topsoil horizons of modern soils into non-overlapping classes referring to the land use and soil type has confirmed the potential of non-destructive spectroscopic methods in paleopedological studies.…”