Chemodestructive fractionation of humus as an indicator of the functional state of soil organic matter

Abstract

The content, composition, and properties of humus are the most important characteristics that reflect the features of modern soil formation, the genesis and evolution of soils, and their agrogenic transformation. The main criteria for assessing soil fertility are traditionally the content and reserves of organic matter in soils. At the same time, the decrease in soil fertility is associated not so much with a decrease in the total content of humus, but with the loss of its labile forms, which determine the life of the soil, its most important agronomic properties and crop yields. One of the integral indicators characterizing the state and functioning of soil organic matter (SOM) is the ratio of stable and labile forms of organic compounds obtained by chemodestructive analysis. The determination of the bichromate oxidizability of humus showed that the virgin soils of the Southern Cis-Baikal region contain an equal amount of stable and labile forms of organic compounds. Accordingly, the humus in them is a stable and balanced system in relation to external influences. Plowing led to a significant decrease in the easily and hardly hydrolysable humus fractions. In the fallow areas, the upper part of the humus horizon, in terms of the ratio of humus fractions, approaches virgin soils, and the lower part approaches the arable horizons of agricultural soils. The method of permanganate oxidizability of humus revealed a noticeable enrichment in easily oxidizable forms of virgin and, especially, fallow soils of the region. Compared to them, agricultural soils contained noticeably less labile humus, which indicates a sharp decrease in their fertility.