Oksana O. Plotnikova

In this work, we present the Chernozem Soil Aggregates Micromorphometrical Parameters Dataset for specific areas located in the Central Russian Upland that can be utilized for the development of a digital twin of Chernozem. The present dataset represents a collection of soil aggregates’ micromorphometrical parameters (aggregate total area, minimal and maximal Feret diameters, form factor, elongation, unevenness, orientation) obtained through segmentation of soil thin sections’ digital images. Also, the dataset represents the data on physical and chemical properties of the studied soils (organic carbon content, inorganic carbon content, clay, silt, and sand fractions content, mean weight diameter of aggregates). Soil excavation and sampling were conducted in two stages: 24–25 April 2023 and 4 June 2024. Soil sampling sites were selected to provide a comparison of virgin Chernozem soils with plowed, non-eroded, and severely eroded ones. Soil sections were excavated at 9 key points. Laboratory analysis yielded 60 sets of data on physical and chemical properties and over 51,000 micromorphometric values for soil aggregates.

To create a digital soil twin, we should define and formalize as many indicators as possible that characterize soil functioning in the landscape and various soil degradation and progradation processes. The aim of this study is to identify the influence of soil properties—the contents of clay, silt, and sand fractions; organic carbon (C_org); and carbon of carbonates (C_carb)—on the morphometric parameters (MPs) of aggregates in the plow and subplow layers of uneroded and severely eroded typical chernozems of Kursk oblast. A significant positive correlation with the minimum diameter of aggregates has been found for C_carb of severely eroded chernozems and C_org of noneroded Chernozems. Within all size classes of aggregates, the effect of the contents of C_org and C_carb and various particle-size fractions, as well as the degree of erosion (on the binary scale noneroded/severely eroded) on MPs has not been found.. 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 of soil aggregates 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 impact on the physical and chemical properties of the upper horizons of plowed chernozems. However, a detailed analysis of the MPs of soil aggregates indicates that in the presence of such a strong factor as regular tillage, 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 resilience of most of the MPs of aggregates in chernozems to water erosion, if it is accompanied by annual soil tillage. It is shown that the unevenness of the boundary of aggregates largely depends on their size than on the degree of soil erosion. Presumably, the processes of water erosion and tillage practices indirectly affect this morphometric parameter via regulating the composition of the size fractions of soil aggregates.

The period since the mid-1970s is considered as the period of modern global warming, and 1976 is conventionally taken as its beginning. Southern and arid regions are known to be especially sensitive to climate changes. In this context, the aim of our study was to identify the features of climate warming in the area of the Dzhanybek Plain and to characterize changes in soil properties associated with the established climatic trends. The object of the study is represented by a microcatena of chestnut solonetzic soils (Someric Calcic Luvic Kastanozems (Loamic, Sodic) and Mollic Salic Calcic Solonetzes (Loamic)) on the territory of the Dzhanybek Experimental Station of the Institute of Forest Science of the Russian Academy of Sciences. Data on the climate of the study area for the period of 1914–2021 are summarized. It is shown that the period from 1976 to 2021 compared to the period from 1914 to 1975 is characterized by an increase in the mean annual air temperature by 1°C, the mean annual precipitation by 18.3 mm, the mean air temperature of the cold season by 1.5°C, and the mean precipitation of the warm season by 39.5 mm. The results of terrain study together with micromorphological and chemical data suggest that in the past 54 years, the groundwater table has risen by 1 m, the groundwater mineralization and salinity have increased by at least two times, soil salinization and calcification have also become higher, and the depths of soil processing by mesofauna and root penetration have increased, though these changes have not yet been reflected in the soil organic carbon content. If the identified climate trends continue, the studied soils are expected to become saline and effervescent from the surface, and the content and stock of carbon in them will increase. However, to confirm this assumption, further more comprehensive study and continuation of stationary observations are required.

Chernozems are the most fertile soils in Russia. Most of the territory of Kursk oblast is covered with chernozems, half of the territory is plowed, and app

Since Chernozems are among the most fertile soils in the world, the study of their degradation is of great interest. However, the microstructure and composition of the soil organic matter (SOM) in eroded Chernozems have not yet been sufficiently studied. We studied the SOM and aggregate states of eroded Chernozems using the example of two catenas with arable Haplic Chernozems in the Kursk region of Russia. In the plow horizons (the part of the soil most susceptible to water erosion), we determined the mean-weighted aggregate diameter (MWD), structure and water stability coefficients (SC and WS; dry and wet sieving, respectively), soil organic carbon (SOC) content, and SOM composition and content (qualitative and quantitative micromorphological analyses, respectively). It was shown that with an increase in the degree of erosion, the content of SOC decreased significantly, according to both chemical and micromorphological methods of evaluation. No significant relationships were found between the degree of erosion and the indicators of the structure (except for WS, which was significantly lower in non-eroded Chernozem than in slightly and moderately eroded soils). With the increasing degree of erosion, the humus state of these soils deteriorates at the microlevel, the intensity of humification decreases, the depth of the appearance of assimilated biogenic aggregates with finely dispersed calcite in the profile increases, the structure is destroyed, lumpy aggregates form, and the proportion of planar voids increases. The downslope transport of the soil solid phase under the impact of erosion is accompanied by the accumulation of the transformation products of carbohydrates in the Chernozems in the lower part of the catena. In the Chernozems located in the transit position of the slope, the composition of SOM is characterized by the predominance of lipids and nitrogen-containing compounds. Our unique results contribute to a deeper understanding of the formation of structure and water resistance in eroded soils.

In the closed depressions of the forest-steppe, unique soils form that differ significantly in their properties from the zonal Chernozems. These soils have a light-colored, acidic Albic horizon and the complete absence of carbonates. They resemble podbels, which are formed in the southern Far East of Russia, with their different soil-forming processes, regimes, and genesis. The aim of this study is to interpret the genesis of the soils in the center of the closed depression by analyzing their morphological, micromorphological, chemical, physical, and physico-chemical properties. This will help to determine the main diagnostic criteria for their classification. The depression is located in the Oka-Don Lowland, in Tambov Oblast (52.0398°N, 41.1839°E, See Fig. 1a). We collected a total of 39 samples, from three walls of soil pit, at 10-centimeter intervals, to a depth of 130 centimeters. For micromorphology, we took samples from all genetic horizons, in triplicate (12 samples). In the pre-dried and homogenized samples, we determined pH values, total dissolved salts and soluble salt content (conductivity), particle size distribution (laser granulometry, with preliminary ultrasonic treatment at an energy level of 450 joules per milliliter), total carbon (by dry combustion), cation exchange capacity, exchangeable cation composition (using Pfeffer's method), and iron content in oxalate extracts (Tamm's method) and dithionite-citrate extracts (Mehra-Jackson method). We also calculated the Schwertmann ratio and and the degree of hydromorphism were calculated as indicators of soil overmoisture. The diagnostic properties of the studied soil (See Fig. 1b) include: (1) a thick (30 cm) mollic horizon, rich in organic carbon, with a loosely aggregated structure and varying degrees of organic matter decomposition; this horizon is overlain by a (2) light-colored albic horizon, which has signs of humus leaching and contains up to 5% of small-sized iron-rich concretions, and (3) an illuvial horizon that has a weaker structure and a higher concentration of concretions than the overlying horizon. This horizon also has cutans along the edges of ped. The soil demonstrates a sharp decrease in carbon and a gradual increase in pH from slightly acidic to neutral values with depth (See Fig. 2). The middle part of the profile has a slightly higher clay content compared to the mollic horizon. The top 10 cm of the soil contains soluble salts at a concentration of 106 mg/ L (0.14% of soil dry mass), classifying this layer as slightly saline and chloride-magnesium. However, at the lower boundary of the soil surface (20-30 cm), the salt content drops sharply to 27 mg/L (0.04% of the dry soil mass) and does not exceed 50 mg/L in deeper layers, indicating that the soil is not saline. The anion-cation composition of the soil in the depression remains consistent throughout the profile. There are two peaks in the cation exchange capacity, one in the humus layer and another at a depth of 100-130 centimeters. This latter peak is likely due to an increase in exchangeable Ca2+, which is probably caused by its influx from solutions in the underlying carbonate parent material. The relatively high content of soluble salts and exchangeable sodium in the topsoil can be attributed to lateral water flow from surrounding depressions with solonetz and meadow-chernozem soils. Based on the Schwertmann's and hydromorphic criteria, the upper part of the soil profile, particularly the mollic and albic horizons, experience prolonged surface overmoisture. These coefficients decrease sharply in the gleic horizon. Based on a comprehensive study of soil properties, we can conclude that the light-colored horizon of the depression soil we studied is predominantly eluvio-gleyic in nature, with concretions (See Fig. 3 d, f) and cutans (See Fig. 3 c, e). In the underlying horizon, Schwertmann and hydromorphic criteria indicate seasonal surface overmoistening and periods of drying. The additional factor contributing to the formation of the light-colored horizon may be the presence of sodium in the upper horizons of the soil-absorbing complex, ranging from 4 to 14%. The soil profile formula of the studied depression soil is AH- AHel-ELhi,g-BTg (according to WRB, Ah-Eg-Btg); in terms of the genetic horizons it is absent in the Russian Soil Classification, partially corresponding to darkhumus pseudo-gleyic (AH-EL-BTg-BCA-Q; Calcic Albic Mollic Planosol, A-Eg-BtBk-Bgk), dark-humus podbel gleyic (AU-ELg-BTg; Mollic Albic Stagnosol, A-EgBtg). Unlike the dark-humus pseudo-gleyic soil, the studied soil does not contain carbonates, which are leached from the soil due to its large catchment area (55 hectares). Different from dark-humus podbel gleyic, the studied soil differs in the nature of the upper horizon and less pronounced processes of iron segregation in the lightened horizon (a lower quantity of concretions). We hypothesize that the water regime of the depression soils is less contrasting, with a smoother alternation of periods of overmoistening and drying compared to the podbels of the Far East, which may explain the lower quantity of concretions in the depression soil. Following the classical tradition of Russian soil science – reflection of the major soil-forming processes in the soil name – the studied depression soil can be termed as dark-humus elluvial gleyeic. With the expansion of soil studies in depressions and the identification of soils with a similar profile structure, introduction of an independent type of peat-dark-humus gleic soils into the Russian Soil Classification may be proposed.

Atmospheric dust affects both human health and climate change. Therefore, the study of atmospheric dust is one of the important tasks of many scientific fields. The aim of our research was to indirectly assess the relation of atmospheric dust over arable lands of two test sites in Tver and Tula regions of Russia with soils. Dust was analyzed on aspirator filters after pumping specified volumes of air at the level of 20–30 cm above the arable surface. Its spectral reflectance was used as a criterion of soil origin of dust, which was compared with the reflectance of the size fraction (50–200 nm) of soils isolated by dry sieving of a sample of arable soil horizon. The spectral reflectance of dust was calculated based on approaches of linear separation of spectral mixture, taking into account the projective coverage of dust particles on filters, which was determined by analyzing microscope photographs of the filters in GIS. As a result, it was found that the recovered dust spectra on the filters correlate well with the spectra of the same size soil fraction separated by dry sieving, which indirectly confirms the predominance of specifically soil dust on the filters. Spearman correlation coefficient is within the range of 0.84–0.90, Kendall's Tau correlation coefficient varies within 0.70–0.79 (at significance level p < 0.05). Under the conditions of insignificant atmospheric dust load and when collecting a sufficient amount of dust for direct analysis is time and labour consuming, the approach used may serve as an alternative for indirect confirmation of the soil origin of dust in the near ground layer of the atmosphere. In the future, this approach can be used as a basis for monitoring of arable soils deflation.

Micromorphological Characterization of Soils of the Solonetzic Complex (Dzhanybek Plain) Микроморфологическая характеристика почв солонцового комплекса (Джаныбекская равнина)

A comparative analysis of physicochemical properties and micromorphological features in virgin soils of the dry-steppe solonetzic soil complex sampled in 1968 as a starting point of soil monitoring in 1968–2022 is suggested. The study of climatic parameters for 1914–1968 demonstrated that over 54 years preceding the sampling, soils had been developing under relatively stable climatic conditions. Analysis of soil properties showed that on an almost flat area with the height difference of only 3.6 cm at a distance of 229 cm, soils differ significantly in the depth and degree of salinity, degree of solonetzization, set of humus microforms, organic matter content, presence and size of clay coatings, and degree of micromass mobility. This confirms the patterns of moisture redistribution described in numerous studies in this area, even with very small elevation differences. Based on the set of available indicators, it can be concluded that soils of the microcatena belong to different taxonomic units. The soil of the lower part of the microslope can be attributed to light chestnut soils according to the classification of soils of the Soviet Union (1977) or to Haplic Kastanozems (Loamic) according to the international classification WRB (2015). Soils with a high content of exchangeable sodium and the presence of clay coatings are found in the middle and upper parts of the microslope and belong to Solonetzes according to both classification systems.