Spectroscopic characterization of soil organic matter quality in intensively used Chernozems

Chernozems are considered highly productive soils, which are strongly affected by intensive management, erosion processes, and degradation. Three different soil types were classified according to Němeček et al. (2011) along the transect in the field – Calcic Chernozem (control site); Calcaric Regosol (erosion site); and Calcic Chernozem Colluvic (accumulation site). Soil organic matter quality was evaluated using infrared and UV-VIS spectroscopic methods. Humic acids (HAs) were isolated from all three soil samples according to the standard IHSS method. DRIFT spectroscopy (diffuse reflectance infrared Fourier transform spectroscopy) was applied to evaluate HAs chemical composition and hydrophobicity. Both parameters can better characterize HAs stability against microbial degradation, reactivity, and wettability. Results showed that the humification degree was the highest in Calcic Chernozem Colluvic (accumulation site). Less humified were HAs in Calcaric Regosol (erosion site). Higher content of aliphatic labile and hydrophilic groups was in HAs from Calcaric Regosol (erosion site). The content of aromatic stable and resistant components was higher in HAs from Calcic Chernozem (control site) and Calcic Chernozem Colluvic (accumulation site). The highest hydrophobicity index was in HAs from Calcic Chernozem Colluvic (accumulation site). The HAs chemical composition and hydrophobicity are crucial in soil productivity and organic matter stability in a changing environment.