ИСТИНА

Structure is the most complex soil property having dualistic nature. It determines all the soil processes, and also is their reflection. Each structure level is characterized by specific interactions, processes, and functions that can be used as criteria for their separation. Mechanistic understanding of soil structure enables to include it into dynamic soil models. The goal of this study is describing of the mechanisms of soil microstructure organization and dynamics for 10 main zonal soil types - from Podzols to Ferrasols. X-ray microtomography of macroaggregates has allowed to separate functional zones of microstructures by its density. These zones save their spatial positions after wetting/drying cycles, while connectivity density of pore network increases in saturated condition and decreases in dried condition. In Chernozems for example, large (>425 µm) zones with high density are mainly localized on the outer shell of the aggregates, whereas intermediate size (210-425 µm) zones of medium density regularly fill the internal shell. The smallest (<210 µm) zones with the lowest density form the film under surface pore channels inside of the aggregates. Laser diffraction analyses combined with chemical, ultrasonic and hydraulic stresses on soil samples allowed to distinguish three types of microstructures and their relationships with physico-chemical properties. Soil organic carbon (SOC) was closely linearly correlated (R²=0.83) to the differences between elementary particle size distribution (obtained after pretreatment by ultrasonic energy equal of 450 J・ml-1; Yudina et al., 2018) and microaggregate size distribution (obtained after intense stirring (2500 min-1) of water suspension after 10 minutes). SOC however, is not unique binding agent for the formation of such elementary soil particles. Particles in Ferralsols are strongly bound by organic matter (OM), whereas elementary soil particles in Retisols, Phaeozems and Vertisols are not really bound by OM and presented by particulated organic matter because of complete oxidation of such particles. Microaggregate content (sum of differences between microaggregate size distribution and elementary particle size distribution) in Retisols has a positive relationship (R²=0.60) with content of crystalline Fe oxides and negative (R²=0.68) with amorphous Fe oxides. Microaggregation in Chernozems increases in AB horizon and occurs under specific ratio of SOC and carbonate content. Thus, types of soil microstructures and their sizes and localization were described. Combination of our knowledge about soil hierarchical structure organization with data, obtained by X-ray microtomography, will allow to develop 3D-model of soil structure organization.