Milkheev E.Yu., Tsybikova E.V. MOLECULAR STRUCTURE OF HUMIC ACIDS OF KASHTANOZEMS OF TRANSBAIKALIA // Arid Ecosystems. 2025. Vol. 31. № 2 (103). P. 53-60. | PDF

Bioclimatic conditions of soil formation in the cryoarid climate zone of Western Transbaikalia determine the specific composition of humic substances. However, the heterogeneity of these compounds, as well as the widely used classical methods of organic matter analysis, does not allow us to sufficiently determine the structure of high-molecular organic compounds in soils. ¹³C-NMR spectroscopy of humic acid preparations from kashtanozems made it possible to identify ranges of chemical shifts of carbon atoms from various functional groups and molecular fragments. The peculiarity of humus formation in kashtanozems is humic acids with a fairly high content of C, N, O, that occur despite the harsh conditions, such as the influence of long-term seasonal permafrost or continental climate. The macromolecules of humic acids in arable samples of kashtanozems are characterized by a less developed peripheral part and a high degree of benzoyl in comparison to humic acids of the virgin variant. This happens due to the environmental conditions of soil formation and the component composition of humification precursors. An increase in the proportion of aliphatic structures and a decrease in the proportion of aromatic fragments allow us to talk about a simplification of the structure of the humic acid macromolecules. A short vegetation period, insufficient moisture in combination with a light granulometric composition significantly reduce the rate of transformation of organic matter and lead to an increase in the proportion of unoxidized aliphatic fragments.

Keywords: soil organic matter, elemental composition, NMR spectroscopy, cryoarid kashtanozems, Western Transbaikalia.

DOI: 10.24412/1993-3916-2025-2-53-60

EDN: JGUGBG