Transformation of organic matter and clay minerals in cultivated gray forest soils

Mechanisms of the agropedogenic transformation of cultivated gray forest soils are discussed. It is shown that the loss of organic carbon from these soils upon their cultivation is mainly due to the intense mineralization of an easily decomposable fraction having a density of less than 2 g/cm(3) and a characteristic size above 50 mu m. Simultaneously, a certain portion of soil microaggregates is destroyed. Several additional indices of the processes of soil erosion and sediment accumulation on the soil surface (soil aggradation) are suggested. These indices take into account the character of soil clay minerals and soil organic matter. Indicative characteristics of the second humus horizon are suggested on the basis of published materials and new analytical data.