The analysis of literature sources and a database on soil physical properties collected by the Department of Soil Physics and Amelioration of Soils of the Faculty of Soil Science of Moscow State University made it possible to compare three major constituents of the particle-size distribution analysis (PSDA): (a) the classification of soil separates with respect to their sizes and the classification of soil textures, (b) the procedures used to prepare soil samples for the PSDA, and (c) the specificity of the determination of the particle-size distribution by different methods. It was shown that there are good physical and statistical grounds for the conversion of data on the particle-size distribution from the Russian classification system into other systems. Much larger problems are related to the pretreatment of soil samples for the PSDA. The diversity of existing methods, classification schemes, and technical devices based on different physical principles (sedimentation and laser diffractometry) should be taken into account in the analysis and quantitative conversion of particle-size distribution data from a given classification system into another system. The Russian classification of soil textures and soil particle-size groups developed by N.A. Kachinskii has certain advantages and can be easily converted into other systems. In the choice of a particular system, it is important to take into account the goals of the study. Agreement between soil scientists concerning the major constituents of the PSDA has to be reached.

With the help of computed X-ray microtomography with a resolution of 2.75 μm, changes in the microstructure and pore space of aggregates of 3 mm in diameter from the virgin soddy-podzolic soil...

Comparison of the particle-size distributions in different soils showed that the sedimentation method (Kachinskii pipette method) gives higher (by 1.5–5 times) values of the clay content than the laser diffraction method. This is related to the significant variation in density of soil solids, which is taken to be constant in the sedimentation method. Therefore, particles of significantly larger size and lower density fall into this fraction. Using optical, electron, and confocal microscopy, it was shown that the low density of soil particles of silt size falling into the sedimentometric clay fraction is related to the organomineral shell (film) around the soil microparticles. This shell contributes to the linking of microparticles into aggregates at the lower average density. As a result, these aggregates have significantly larger size and lower density and settle with the same velocity as the small particles with the average density of the solid phase during the sedimentation particle-size analysis.

The potential, state of the art, and outlooks of using the pedotransfer functions concept in soil science were analyzed. Current methods of developing the pedotransfer functions and their statistical and functional testing were considered. Problems related to the spatially distributed estimates of soil properties and parameters and their use in predictive modeling and soilscape assessment are discussed.