Relationships between the Organic Carbon Content and Structural State of Typical Chernozem

The influence of erosion degree and slope aspect on the structural composition of typical chernozems (Haplic Chernozems) and the qualitative characteristics of organic matter in these soils were studied. We determined the organic carbon content in separate structural units of the soils under different agroecological conditions of Kursk oblast. Aggregates of 3-1 mm in size played the decisive role in the structural state of typical chernozems; their total content and the content of carbon of organic compounds in them were higher than those for the aggregates of 10-3 and <1 mm in size. The contribution of organic matter and labile humic substances to the formation of water-stable soil aggregates was also considered. A tendency for an increase in the diameter of aggregates with an increase in their organic carbon content was displayed in the soils independently from the degree of their erosion. The content of carbon of labile humic substances in water-stable aggregates of the soils on north-facing slopes was higher than that in the soils on south-facing slopes. With an increase in the portion of labile humus participating in the formation of water-stable aggregates of typical chernozems, the diameter of these aggregates increased from 0.5-0.25 to 3-1 mm. This regularity was clearly displayed in the Ap and A horizons of typical chernozems on the interfluve and on the north-facing slope and in the Ap horizon of these soils on the south-facing slopes independently from the degree of soil erosion. The results of this study may be used in methodological recommendations on regulation of the aggregate and humus states of typical chernozems in agrolandscapes with sloping topography.