Articles

Soil respiration, which is one of the main fluxes in the global carbon cycle, is characterized by high temporal and spatial variability. Based on the year-round continuous 21-year monitoring of the respiration of soddy weakly-podzolic soil in the forest and meadow coenoses of the southern taiga zone, an assessment of the temporal variability of CO₂ fluxes from soils was made at different time levels: monthly, seasonal, and annual. The values of total respiration of soddy weakly-podzolic soil varied most significantly at the monthly averaging level (coefficient of variation, CV=25–56%), while the variability of the annual respiration of soils was 20–22%. At the seasonal averaging level, the highest variability (CV=39–44%) was noted for winter CO₂ fluxes from soils, whereas the variability of total soil respiration in the other calendar seasons was close and amounted to 26–29%. The effect of the type of cenosis on the total CO₂ fluxes from the soddy weakly-podzolic soil was statistically significant both at the annual averaging level and in all calendar seasons of the year, except for winter. The most stable indicator characterizing the seasonal distribution of CO₂ fluxes within a year is the contribution of the warm period (May–October) to the total annual CO₂ flux from soils, which averages 73–77%. Its variability over 21 years of observation in both coenoses was 8%. It can be recommended to use this indicator to obtain estimates of annual CO₂ fluxes from soils based on field measurements carried out only within the growing season. The numerical experiments performed have shown that continuous measurements of CO₂ emission from soils for five consecutive years reduces the variability of annual and seasonal CO₂ fluxes from soils by more than 2 times compared to a one- or two-year measurement period. This makes it possible to recommend a five-year observation period as the optimal required for obtaining adequate values of annual and seasonal CO₂ fluxes from the soils of the southern taiga zone. 

The current state of the problem of soil mapping is considered. It is shown that there has been a replacement of traditional soil mapping methods by methods based on geoinformation digital and remote sensing technologies. The main advantages and disadvantages of the currently used soil mapping methods are outlined, and the necessity of taking into account the level of generalization of the information used in the process of soil mapping is demonstrated. We demonstrated the errors arising in soil maps when digital spatial data with different levels of information generalization is used. The most promising directions in the development of soil mapping methods are identified. It is shown that the primary attention should be paid to the development of digital soil mapping methods based on remote sensing data, which contain the most accurate information on the spatial variation of the surface soil horizon properties. The use of methods of spatial interpolation of point data is less accurate than the use of remotely sensed data. But the latter allows us to confidently detect only certain soil properties and not all of those necessary to create soil maps in the traditional form. Mapping individual soil properties is a more promising approach. Maps of individual soil properties are more convenient and accurate for evaluating soil and land resources. In the future, they can be used as a basis both for the re-creation of soil units in terms of accepted soil classification and for the creation of soil maps in traditional form (with the reflection of classification units of soils on them). But for a complete transition to the mapping of soil properties, it is necessary to deepen research in studying the spectral reflectance of the soil surface and its relationship with the properties of the underlying soil horizons.

The article is a review of the scientific problems that the Honored Professor of the Lomonosov Moscow state university Evgeny Anatolyevich Dmitriev. The main area of his scientific interests is the genesis of soil and land cover data. Numerous works carried out under his supervision convincingly demonstrate the influence of sampling methods on the results of determining certain soil properties. As a consequence, this influence also extends to the final conclusions, which can be highly distorted if the method of obtaining them is not taken into account. In an attempt to solve the question “What classifies soil classification?”, he develops the concept of “single soil”, which can be the object of soil classifications, not being directly a soil body, but acting as a kind of standard element of sampling. Theoretical understanding of the influence of heterogeneity of soils and soil cover at all hierarchical levels on the features of its “life” is the subject of the second part of the scientific legacy of E.A. Dmitriev. He puts forward the concept of soil bodies of different dimensions, shows the influence of the dimensional characteristics of these bodies on soil regimes and, in particular, on the water regime, and discusses the need to study soil regimes at different hierarchical levels. To fix the heterogeneity of the soil and soil cover, he developed special devices, with the help of which studies were carried out on soddy-podzolic, gray forest, chestnut, and other soils.

The features of anthropogenic transformation of natural chestnut soils and genesis of urban soils and conditions of the dry-steppe natural zone on the territory of Volgograd were studied in detail. The study was carried out by comparing the morphological characteristics of natural soils and their anthropogenic-modified counterparts. A morphological description was carried out for each of the 16 transects. The morphological characteristics of urban soils and chestnut soils of the city outskirts were compared. Under the influence of urban pedogenesis, natural light humus horizons AJ disappear, and the average thickness of diagnostic xerometamorphic horizons BMK decreases. The upper boundary of accumulative-carbonate horizon BCA lowered relative to the surface by an average of 32 cm compared to natural chestnut soils. Under the influence of urban-techno-pedogenesis there appeared inclusions represented by debris of building materials and garbage, accumulated in the process of human settlements functioning, the structure, density, nature of boiling from HCl 10% have changed. Modern surface horizons often boil off HCl 10%. In the landscaped recreational areas of the city, carbonate leaching has occurred due to irrigation of the area. The variants of morphological transformation of chestnut soils formed on the territory of Volgograd as a result of urban pedogenesis have been revealed. The first variant - soils of initial stages of technotransformation, with changes at the level of the upper horizons. The second option — soils with thick urban horizons, overlapping the preserved diagnostic horizons. The third option — burial of natural rocks by man-made soils of varying thickness with almost complete destruction (removal) of natural soil horizons. The fourth option — soils with thick humus horizons formed at the expense of intensive infusion of organic matter in underpourings of compost. It is noted that most of the soils of the city have profiles, completely formed on man-made sediments, and do not contain natural soil horizons in the upper 1,5 m thickness. According to the Field Identification of Soils of Russia, the studied soils of the first variant of transformation are defined as urban-stratified. The soils of the other options of transformation can be attributed to man-made surface formations. The content of organic carbon in the urban, technogenic, and replanted horizons averages 1,1, 0,25, and 1,6%, respectively. Chemical analysis of urbic, reclamation, and technogenic horizons revealed a low content of readily soluble salts — 0,14% and carbonates — 0,9%. Density in UR and RAT horizons is on average 1,4─1,43 g/cm³, in TCH horizons — 1,55 g/cm³. Buried horizons average density is 1,43 g/cm³ in AJ, 1,49 g/cm³ in BMK, 1,62 g/cm³ in B, and 1,54 g/cm³ in BCA, which is higher than average density for native chestnut soils. Also for the buried horizons is characterized by leaching from salts (mid. 0,2%) lower values of calcium carbonate content than in the background, alkalinization of the environment, as well as a decrease in organic carbon by an average of 0,35% in the AJ, BMK, and B horizons, and by 0,28% in BCA. The average CaCO3 content in the upper humus and median horizons is 1,4% and in the carbonate horizon 4,3%. The obtained results allow us to study in more detail the peculiarities of the genesis of urban soils and the anthropogenic transformation of natural chestnut soils in urban conditions of the dry-steppe natural zone.

Water-soluble organic substances (WSOM) of sod and humus horizons of Mollic Gleysol artificially saturated to full moisture capacity were isolated by sequential centrifugation from pores with a diameter of more than and less than 30 microns. The total concentration of carbon and phenolic compounds, the absorption and fluorescence spectra of the solutions do not differ significantly, but a strong variation in the parameters (the ratio of maximum and minimum values is 415 times) indicates the heterogeneity of the composition of the extracted substances. The concentration of simple phenolic acids in solutions of large pores of the humus horizon is 48 times higher than in smaller ones, salicylic, benzoic and cinnamic acids predominate (75% of the total amount). In small pores, p-hydroxybenzoic and benzoic acids predominate (67% of the total amount). Dissolved organic matter (DOM) of soil solution of the Podzolic soil (ELBTg horizon, moisture 22%), were obtained by tension lysimeters from pores with a diameter of more and less than 14.7 microns. DOM in solutions from large pores contain more C, N, phenolic compounds and, according to the absorption spectra, have a large molecular weight and a degree of aromaticity. Organic substances from small pores are more hydrophobic and are characterized by a greater C:N ratio; these features potentially promote DOM resistance to decomposition. Predominant localization of phenolic substances in large pores is favourable for the conservation in soil since transport with water flows assist their chemical stabilization in the lower horizons as organo-mineral compounds. 

Under the conditions of a laboratory incubation experiment, the effect of the introduction of crop residues (rye straw) and mineral nitrogen fertilizer on the formation of nitrous oxide by Albic Retisols was studied. It was found that the increase in the carbon content of microbial biomass is linearly related to the mass of introduced plant residues. An important indicator characterizing the system under study is the C:N ratio of microbial biomass and its dynamics both with changes in the amount of crop residues introduced and over time. At the ratio C:N = 40 in plant residues at the early stages of their decomposition in the soil, the predominant process of microbial nitrogen immobilization is replaced by the predominance of the process of mineralization of organic nitrogen compounds. It is shown that the maximum immobilization "capacity" of microbial biomass in relation to nitrogen is achieved at a ratio of C:N in the substrate equal to 20-40. The dependence of the intensity of nitrous oxide emission by soils on the amount of crop residues introduced has been established. It is shown that the maximum values of the emission factor are characteristic of the experimental variants with the introduction of a substrate enriched with nitrogen (C:N = 7,5-10), which may be associated with better decomposition of plant residues under conditions of better nitrogen supply.

The features of the ground cover in connection with the use of care in typical urban plantings in Moscow are determined. The character of plantings care determines the main features of ground cover more than the type of tree species. As a result of planting care, nemoral shade-tolerant species in the grass layer are actively replaced by meadow nitrophilic and ruderal species belonging to annuals and turf grasses, which contributes to an increase the biological cycle intensity.  In urban ecosystems, the indicative role of plants in relation to soil properties is reduced due to the lack of direct long-term relationships between these components.

Within the landscapes of the upper reaches of the Klyazma River, the long-term component composition of natural waters in the system has been studied: snow waters — soil solutions — soil-ground waters — surface waters. It has been determined that the regular excess of the content of the main macro- and microelements in soil solutions in comparison with snow waters at subsequent stages is first replaced by an increase in the concentration of components in soil-ground water, followed by a decrease in the content in surface waters — streams and river waters. It is shown that the relatively high mobility of sodium, magnesium, potassium and calcium, and of the anions chloride and nitrate ions, is accompanied by a significant decrease in the mobility of elements of the family of iron, copper and zinc at the transition from groundwater to surface water. This explains the wide distribution of segregated forms, presented in the form of nodules in soils of semi-hydromorphic landscapes, up to ortsands, and in the boggy conditions of near-terrace depressions on the border with the super-aquatic landscape, the formation of typical bog ores. Thus, the composition of natural waters and its change serves not only as a good, but also a necessary tool for explaining the features of migration of elements in the soil — natural water system.