Počvovedenie

The profiles and spatial variation of morphological features, ash content, humus content, pH_KCl, granulometric composition, hygroscopic and field moisture in the illuvial-ferruginous and coarse-humus podzols of the North Sakhalin Lowland on sandy soil-forming rocks under specific communities – sparse larch (Larix dahurica) dwarf pine (Pinus pumila), were studied. Statistical characteristics of the variation of indicators for horizons: litter O, coarse humus Oao, podzolic E, illuvial-ferruginous BF, illuvial-humus-ferruginous BHF, transitional BCf, soil-forming rock C, were obtained. It was revealed that the podzolic horizon E has a low thickness, varying from 3 to 11 cm, and its inherent morphological features: whitish color, layered weakly expressed structure, loamy sand and sandy granulometric composition, and a lingual lower border. The horizon BF1 of illuvial-ferruginous podzols is characterized by a rusty brown color, the presence of small Fe–Mn nodules, a humus content of less than 2%, a medium acid reaction, whereas the horizon BHF of coarse-humus podzols has a dark brown color, a humus content of 2–5%, a strongly acidic reaction. Based on the correlation analysis, it was noted that with an increase in the thickness and ash content of the organogenic horizons O, Oao, the humus content increases and the reaction in the illuvial horizons BF1, BHF is acidified. A more acidic reaction of the medium in the O and Oao horizons correlates with an increase in the thickness of the E horizon.

This review examines published data on the composition, properties, dynamics and amounts of DOM formed in the litter of forest soils. The amount and properties of DOM depend on the composition of plant residues forming the litter horizon. In most cases, the leaf litter DOM differs from the fall of needles in a high content of nitrogen, polyphenolic compounds, carbohydrates, hydrophobic acids, higher extinction coefficients and a lower C/N ratio. However, DOM properties and quantity are significantly influenced by the genus and species of plants, leaves and needles age, and growing conditions. In situ the stock of forest litter plays an important role, therefore, DOM concentrations in soil solutions of coniferous litter are higher than deciduous ones. With decomposition of organic residues, DOM quantity and variety of water-soluble organic compounds decreases, the proportion of hydrophobic and hydrophilic acids and aliphatic compounds increases. The composition of the soluble transformation products of litter inherits proportions, structural features and resistance to biodegradation of the original components. Forecasting the composition and rate of production of DOM in forest soils requires taking into account the litter character (ratio of different subhorizons), composition and transformation conditions of the plant debris.

The paper presents the results of measuring the content of clay, humus, and complex permittivity of 23 soil samples in the frequency range from 10 kHz to 8–10 GHz at different moisture. The content of clay (particles smaller than 0.01 mm) in the samples varied from 1.7 to 47.5%, the humus content – from 0.7 to 8%. The processes of dielectric relaxation were studied, correlations between the process parameters and the clay content were found. To estimate the clay content, the intensity of the low-frequency relaxation process and the complex permittivity at a frequency of 100 kHz, measured in a state close to complete capillary saturation, were used. The square of the correlation coefficient of the found average values with those measured by the sedimentation method was 0.89, the average deviation was – 14% with a maximum deviation of 50–60% for two soil samples. In order to estimate the humus content, the values of clay and the maximum amount of bound water found by the dielectric method were used. The maximum amount of bound water was determined by modeling the dielectric spectra using the relaxation-refraction model as the average of the values found at different moisture of the soil samples. The square of the correlation coefficient of the found values with those measured by the Walkley–Black acid digestion method was 0.72, the average deviation was 28% with a maximum deviation of 200% for one soil sample. The reasons for the high errors were discussed.

To create a digital soil twin, it is necessary to define and formalize as many indicators as possible reflecting its functioning in the landscape, as well as various degradation and progradation processes. The aim of the work was to identify the influence of soil properties (the content of silt, dust, sand, organic carbon (C_org) and calcium carbonate (C_carb)) and factors of plowing and water erosion on the morphometric parameters (MP) of aggregates of arable and sub-arable layers of noneroded and severely eroded typical Chernozems (Experimental field, Kursk FARC). A significant positive correlation with the minimum diameter of aggregates was revealed for C_carb of severely eroded Chernozems and C_org of noneroded Chernozems. Within all size classes of aggregates, the effect of the content of C_org and C_carb and various granulometric fractions, as well as the degree of manifestation of erosive processes (on the binary scale noneroded / severely eroded) on MP was not revealed. At the same time, neither the above-mentioned soil factors nor the size class of the aggregate affect the elongation and orientation of the aggregates, while the form factor and the unevenness of the boundary decrease and increase accordingly with increasing size of the aggregates. Our study, which is innovative in many aspects, shows that the factor of water erosion has a significant effect on the physical and chemical properties of the upper horizons of plowed Chernozems. However, a detailed analysis of the MP of soil aggregates revealed that in the presence of such a powerful factor as regular agricultural processing, the factor of water erosion manifests itself only at a depth of 20–30 cm, where the influence of the anthropogenic factor weakens, and the influence of natural soil properties is stronger. At the same time, the results obtained indicate the resistance of most MP aggregates of Chernozems to water erosion if it is accompanied by annual plowing of the soil. We also showed that the unevenness of the boundary of aggregates depends more on their size than on the degree of soil erosion. Presumably, the processes of water erosion and plowing have an indirect effect on this morphometric parameter, regulating the composition of the dimensional fractions of soil aggregates.