Comparative Study of Humic Substances and Organic Matter of Physical Fractions of Haplic Chernozem Under Contrasting Land Usesстатья
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Дата последнего поиска статьи во внешних источниках: 10 апреля 2024 г.
Аннотация:The goal of this work is to find out whether the chemical fractions isolated by traditional alkalineextraction are associated with any specific physical fractions. The approach consists in comparison of the specific structural features (assessed according to solid-phase 13C-NMR spectroscopy data) and the contributions of the fractions of both types to total soil organic carbon. The object of the study is Haplic Chernozem of two contrasting land uses: virgin steppe and long-term bare fallow. The investigated chemical fractions are humic acids, humin, and the composite fraction comprising the fulvic acids and organic matter of hydrochloric acid extract, and the colloids precipitated from alkaline extract. The physical fractions obtained according to particle size–density distribution comprise the light fraction occluded in aggregates, clay-sized fraction, and the residue remaining after the separation of light fractions and clay. In the virgin soil, the following fraction pairs have similar structural characteristics of the organic matter and the contributions to soil organic carbon: humic acids–occluded light fraction, composite fraction–clay; humin–residue after physical fractionation.As for the fallow soil, the structural composition of the organic matter is also similar in the above listed pairs but their contributions to the total soil carbon are markedly different. Thus, the chemical fractions in the uncultivated chernozem are associated with particular physical fractions, which is unobservable in degraded bare fallow soil. A comparison of the carbon weight in all fractions of two examined soil variants shows that all fractions lose carbon with soil degradation but the highest loss among the chemical fractions is unexpectedly observed for humin (61%), whereas among versus the physical fractions the highest loss is observed in the occluded light fraction (66%).