The literature and the author's own experimental data on the properties of the microaggregates in a typical chernozem are considered. On the basis of the differences in their composition and properties and in accordance with their sizes, it is stated that the formation of these microaggregates can be described by two fundamentally different mechanisms. The first of these resembles the well-known colloidal-chemical theory, one of whose authors was N.A. Kachinskiy. This is a complex process of gradual accretion of the mechanical elements into micro- and macroaggregates and their fixing, accompanied by differentiation of the composition, structure, and properties of the structural units, and ending in the formation of a water-stable macroaggregate about 3-5 mm in size. The other aggregation mechanism, which produces coarser and larger structural units of quite uniform composition and properties, can be regarded as the analogue of the physicomechanical theory of fragmentation of a soil mass.
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