Changes in the geometric structure of pores and aggregates as indicators of the structural degradation of cultivated soils

As shown by the example of loamy soils of the European territory of Russia, the geometric parameters of soil structure, along with the agrophysical soil parameters, should be taken into account for the comprehensive assessment of the physical degradation of cultivated soils. Different variants of the geometric transformation of soil structure in the plow horizons are analyzed. The shape and orientation of soil pores in thin sections prepared from undisturbed oriented soil samples are considered to be the main diagnostic indices. A computer-aided analysis of soil pores in thin sections made it possible to distinguish and characterize different levels of the geometric transformation of soil structure upon soil compaction: (a) without the disturbance of the shape and orientation of the aggregates, (b) with the transformation of soil aggregates from the crumb (granular) to the angular blocky shape, (c) with the development of a platy structure characterized by the predominantly horizontal orientation of the pores and aggregates, and (d) the complete disappearance of separate aggregates with the formation of a massive soil structure. The validity of the assessments of the geometric transformation of the soil pore space against the background of a considerable spatial variability in the geometric properties of soil structure in the plow horizon is discussed. The structural-functional specificity of the distinguished levels of the geometric transformation of soil structure is outlined.