No 6 (2024)

Dissolved organic matter is the most mobile part of soil organic matter. At the same time, its change and transformation processes occuring during soil erosion have not been sufficiently studied. The goal of the work was to assess the optical properties of water-extractable organic matter (WEOM) in arable soils of different degree of degradation from erosion and sedimentation in a plowed small arable catchment in the Kursk region. We studied WEOM of arable Protocalcic Chernozems (noneroded and moderately eroded) and their analogue with soil matter sedimentation – Novic Protocalcic Chernozems. WEOM was isolated from aggregates 2–1 and >10 mm. Aqueous extracts were characterized by their organic carbon and nitrogen content. Optical properties were assessed based on absorption spectra and three-dimensional fluorescence spectra. It was shown that in terms of the main quantitative indicators of soil organic matter – the content of organic carbon and nitrogen, as well as the pH value – washed away and reclaimed soils were close to each other and differed significantly from Protocalcic Chernozems. At the same time, both the quantitative and qualitative indicators of WEOM showed a different trend: the WEOM of Novic Protocalcic Chernozems differed significantly from noneroded and moderately eroded Protocalcic Chernozems. Besides, some indicators of WEOM (nitrogen content, SUVA₂₅₄, S_350–400 и S_R) depended on the size of the aggregates from which WEOM was obtained (2–1 or >10 mm). In addition, the fluorescent properties of WEOM depend on the size of the aggregates. The obtained data allow us to conclude that the properties of WEOM in a small arable catchment in the central forest-steppe zone are largely determined by the processes of destruction of non-water-stable aggregates and the consolidation of their particles, as well as the leaching of water-soluble organic matter. When aggregates are destroyed by water, their particles migrate with flows along the slope, and organic matter undergoes decomposition; in depressions, particles accumulate, consolidate into blocky structural units, while the properties of their WEOM change significantly, both due to the degradation of organic matter and as a result of its leaching.

The results of rheological studies of soils on the modular rheometer MCR 302 (Anton Paar, Austria) by the amplitude sweep method (oscillatory method) are considered. Study objects are represented by semi-hydromorphic soils of taiga zone in the Northeast of European part of Russia. We found that the strongest interactions between soil particles are developed in the horizons with high content of mobile humus compounds (fulvic acids) and Al/Fe-humus complexes (ELhi,g–ELg–CRM horizons). Increased structural durability is due to the cementation of soil particles resulting from the intake of humus substances and Al/Fe-humus compounds with the development of strong interparticle bonds in the soils. Another important factor is the freezing-thawing processes. The impact of seasonal freezing on the soil rheology is clearest in the profile of semihydromorphic variants of light soils (Histic Gleyic Stagnosols), in their cryometamorphic (CRM) horizons, where increased rigidity of soil bonds is due to condensation compaction of soil particles as a result of development of freezing veil with long period of temperatures about 0С (“zero curtain”). High values of structural interrelations – Integral Z in the soil profile may be due to weak aggregation of mineral mass caused by a constant surface moisture stagnation in the soil accompanied by an intensive gley process. Disaggregated soils are most at risk of erosion and washout processes, and yet thick moss-peat horizon forming in the upper part of the profile of semihydromorphic soils protects them from negative deformation phenomena. In the northward direction from the textural-differentiated soils of southern taiga to the cryomethamorphic soils of forest-tundra we observe an increasing of the strength or rigidity of interpartical soil bonds. At the latitudinal scale, the strength or durability of soil bonds in the cryometamorphic soils of northern, far northern taiga and forest-tundra is higher than that in the semihydromorphic texture-differentiated soils of southern and middle taiga. This pattern may be due to more active intake of fulvic acids, including complex Al-FA-humic substances, as well as longer freezing of northern soils. It is shown that rheological parameters can be used as additional indicators in the diagnosis and classification of taiga soils.

The dynamics of the temperature of conjugated soils of a paleocryogenic soil complex on chalk sediments in the Orenburg region is studied. Temperature measurements were combined with the investigation of cryogenic features. The freezing point of soil moisture was determined in the laboratory. A significant heterogeneity of the temperature field within the soil complex was revealed. During the autumn–winter, the soil of micro-elevation was colder than the soils of micro-depression and micro-slope, and in the spring-summer period, the micro-slope warmed up faster than the micro-elevation and micro-depression. The differences between the temperature of soils in the frozen layer at micro-elevation and in the micro-depression reached –4.5°C at the beginning of freezing (15.12.2019 at a depth of 15 cm), –4.0°C at the end of winter (10–11.02.2020 at a depth of 5 cm), and –6.5°C during thawing (21–23.03.2020 at a depth of 5 cm). Differentiation of temperature regime along the microrelief were accompanied by differences in the profile distribution of moisture and determined the manifestation of cryogenic processes. Micro-elevations froze deeper, a cryogenic texture was formed across the whole zone of freezing, and was accompanied by frost heaving, cryogenic sorting of coarse fragments, formation of a porous crust on the soil surface, what ensures the maintenance of the microrelief and the structure of the soil cover of chalk polygons. Cryogenic textures determine the formation of a platy soil structure on micro-elevations. In the micro-depressions, freezing was blocked in the middle part of the profile due to relatively high soil temperatures and low soil freezing temperatures. Cryogenic features and processes described for micro-elevations are not expressed in micro-depressions.

A study of the influence of farming practices in the Middle Ages (X–XV AD) on the activities of 11 hydrolytic enzymes involved in the biogeochemical cycles of basic elements in soils was carried out. Agrostratozems of medieval agricultural terraces of mid-mountain Dagestan (Plaggic and Hortic Anthrosol) were chosen as objects of study. In all cases, the enzymatic activity of the studied soils, in all soil layers, decreased in the following order: alkaline phosphatase > phosphodiesterase > acid phosphatase > pyrophosphatase ≥ leucine aminopeptidase > arylsulfatase > chitinase > β-glucosidase > xylanase > α-glucosidase > cellobiohydrolase. The enzymatic activity of the studied soils was primarily determined by the amount of microbial biomass (C_mic). Thus, the activity of enzymes of various groups depended on C_mic by 61–94%. Agricultural practices associated with ploughing, manuring, and irrigation lead to convergence in the activity of nitrogen cycle enzymes in soils of the mountain zone, which is associated with similar features of the nitrogen cycle in agrogenic soils, regardless of bioclimatic conditions. The addition of organic materials has led to an increase in the physiological efficiency of microbial communities and the rate of enzyme production, and high levels of biological activity can persist in soil for about 1000 years. Ploughing with the application of organic fertilizers in the past led to an increase in enzymatic activity expressed per unit of microbial biomass (specific activity), and therefore this indicator can be used as an indicator of agrogenic transformation of soils in the past.

The history of the development of the concept of urban soil services, their current list, anthropocentric and pedocentric approaches to their assessment, and experience of application in various cities are considered. At present, the concept of ecosystem services is a comprehensive tool that allows, by analogy, to translate soil information into the sphere of management decision-making, as well as to maintain the sustainability of urban ecosystems by introducing measures to preserve urban soil services. Despite the accumulated experience in methods for assessing ecosystem services and examples of their application in urban planning in individual cities, there is no unified approach to assessing the services of urban soils. The widespread application of this concept is often hampered by insufficient knowledge of the properties of urban soils with their high spatiotemporal variability, as well as by the insufficient development of the approach itself for assessing soil services. However, the active development of theoretical and practical approaches to integrating information about soil characteristics into management is a prerequisite for optimizing the system of soil resource management in cities and towns.