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The existing classifications of soil texture are based on the sedimentation data. The aim of this article is to consider the ways to develop soil textural classification on the basis of particle-size distribution (PSD) data obtained by the laser diffraction method. A detailed comparison of PSD data obtained by the classical pipette method and the method of laser diffractometry has been performed. We have shown the reproducibility of the laser diffraction method and the effect of the oxidation stage on the soil texture class. This study is based on eight genetic soil types (overall, 32 full-profile soil pits) forming a zonal soil sequence from Podzols (Subpolar Urals) to ferrallitic soil (southwest Oceania) and differing in their mineralogical compositions, textures, and elementary pedogenetic processes. The direct use of the Kachinskii and USDA classifications with the data of the laser diffraction method leads to mistakes in determining the soil texture class in 43 and 65% of cases, respectively. The increasing complexity of recalculation, introduction of new variables, and accounting for interlaboratory errors allow us to determine correctly the texture class according to the Kachinskii and USDA classifications in no more than 70 and 72% of soil samples, respectively. The most simple and effective approach to solve the classification problem for the laser diffraction method is to calibrate existing classifications directly on the basis of data on soil samples, for which the texture class was determined by the field method.

We summarized the results of studies of pedodiversity and contrast and variability of soil properties based on the analyses of soil maps of different scales for the republics of Karelia and Dagestan and the Moscow region. We used fragments of the Soil Map of the Russian Federation on a scale of 1 : 2 500 000 as a small-scale map and three different medium-scale maps (from 1 : 300 000 to 1 : 500 000). Large-scale maps (1 : 10 000) were compiled for representative plots within the studied territories specifically for the study of pedodiversity. All the maps were digitized, map legends were converted to the new Russian soil classification system and to the World Reference Base for Soil Resources (WRB), and Shannon–Wiener diversity indices were calculated. Comparison of indicators revealed the dependence of the values of the diversity indices on the map scale. The indicators for the large-scale map were relatively low and did not differ much when using Russian and international classification. We concluded that for the successful assessment of soil diversity at different scales, it is important to use several large-scale maps that reflect the heterogeneity of regional soilscapes. Natural boundaries between soilscapes and soil regions can be found using the pedodiversity index map. In almost all cases, maps with a WRB-based legend had lower indicators of pedodiversity than maps with a legend based on the Russian soil classification. This confirms the fact that the international classification is less detailed than the Russian national classification, which was originally intended for large-scale mapping of soils.

The complex studies of hydromorphism features in taiga weakly differentiated soils using morphological (color), chemical (iron content in different extracts, indicators of reducing conditions (IRIS)), and geobotanic (using the Ramenskii scale) methods have led to ambiguous conclusions. In all the soils, surface gleying was manifested. According to the results obtained by different methods, the maximum reduction processes were related to either the sublitter or the next deeper horizon. The Schwertmann coefficient, the criterion of Bodegom, and the Ramenskii scale indicated an increase of hydromorphism in the soils studied in the following sequence: the lower part of the ridge slopes drained by the small gullies < the middle part of the slopes < the flat tops of the ridges < the depression between the ridges. The morphological diagnostics of gleying proved to be a less sensitive method, which can recognize only the most contrasting hydromorphic soils. The lower horizons in some taiga soils have a bluish gray color probably not related to the recent soil hydromorphism.