Elemental Composition and Structure of Humic Acids in Virgin and Arable Soddy-Podzolic Soils of the Cis-Urals

摘要

The elemental composition and structure of humic acids isolated from virgin and arable soddy-podzolic soils (Eutric Albic Retisols (Abruptic, Loamic, Cutanic)) were studied in the Perm Krai in stationary sites under mixed forest and plots of a long-term experiment started in 1978. The content of carbon in the humic acids of the soddy-podzolic soil varies from 30.7 to 34.6 at %; of hydrogen, from 43.3 to 47.3 at %; of oxygen, from 18.0 to 19.7 at %; and of nitrogen, from 2.1 to 2.6 at %. The humic acids of virgin soddy-podzolic soil have the maximum H : C ratio (1.54), which suggests the prevalence of aliphatic structures in their composition. The soil amendment with increasing doses of mineral fertilizers increases the share of aromatic structures with the highest carbon content in humic acids; in the N150P150K150 variant, the H : C ratio reaches 1.25. This variant shows the maximum degree of oxidation of humic acids (-0.15). The FTIR spectra of humic acids isolated from the plots of the long-term stationary experiment display the absorption bands of carboxyl, hydroxyl, methyl, methylene, methoxyl, and other groups in a wide wavelength range but they differ from the spectrum of the humic acids in virgin soil in the intensity of stretching vibrations of the groups. The vibrations of the C=O group of aromatic rings in the range of 1605-1670 cm(-1) are considerably more intensive, confirming a higher content of aromatic fragments in humic acids of arable soil as compared with virgin soil.