A quantitative morphological study of pores in a dark gray soil with the second humus horizon (Luvic Retic Greyzemic Phaeozem (Loamic) [14]) in Kashira district of Moscow oblast was performed. This study was aimed at establishing specific features of the spatial organization of soil pores as new diagnostic features of polygenetic soils with the second humus horizon (SHH) in the East European Plain. A laboratory microtomograph Bruker SkyScan 1172 was applied. It was shown that the level of mesopores and fine macropores is more informative than the level of coarse macropores to diagnose the pore-structural state of the SHH. For pores of d = 0.03-2 mm, the analysis of closed tomographic porosity revealed the dual nature of the SHH: the volume of closed porosity in the SHH differed little from that in the AU3el horizon, whereas the proportion of closed porosity in the pore space was close to that in the to the BT1el horizon. The diagnostic significance of the shape of soil pores was confirmed. In the SHH, more than half of the pores of d = 0.1-2 mm were represented by isometric dissected packing voids of crumb-granular aggregates. Because of this, the arithmetic mean of the pore shape factor F reached 0.5 for fine macropores in this horizon. The difference between the SHH and the modern humus horizon in the shape of fine macropores can be regarded as an additional argument in favor of the relict origin of the SHH.
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