Том 52, № 5 (2019)

The main trends in the development of soil mapping methods are discussed, and the major problems are identified. By the present time, the transition from the paper-based soil maps to digital soil-geographical databases has already been completed. The digital mapping of soils and their properties is now accepted as the main method at all the levels of generalization. The approaches of digital soil mapping, as well as of the traditional one, are based on the ideas of V.V. Dokuchaev about the dependence of soils on soil-forming factors. However, in digital soil mapping, new achievements of mathematical statistics and mathematical modeling are being widely applied. This provides for a greater objectivity and reproducibility of the digital soil maps in comparison with the traditional soil maps. At the same time, all unsolved problems of soil cartography related to the lack of field observation data, scale, soil taxonomy, spatial microheterogeneity, and mapping of individual soil properties are preserved. Partially, these problems can be solved by using remote sensing data. When the soil geographical information is used to assess the quality of soil resources, the interpretation of remote sensing data for mapping purposes seems to be more preferable in comparison with the methods of digital soil mapping.

In the middle part of the profiles of light gray soils (non-gleyed, deeply gleyed, weakly and strongly gleyed) on silty loamy sandy two-layered deposits of the river terraces in the Tambov Plain, placic layers are formed. Nodules are confined to the arable layer, if surface water stagnation occurs. Angular black nodules of less than 2 mm in size with a high Mn content are specific for weakly gleyed soils, grayish brown nodules of 7–10 mm in size are common in strongly gleyed soils. The Cd and Pb accumulation coefficients in the nodules reach 100–300, those for Co and Mo are 10–100; for Zn and Cu, 2–5; the content of P₂O₅ is 1.0–1.5%, the content of organic matter in the nodules is 1.8–2.5%, and it has a fulvic nature (C_ha/C_fa < 0.4). The placic layer density reaches 1.6 g/cm³, and the aeration porosity is reduced to 3–6%. They are highly acidic, 1.5 to 3 times higher in the contents of clay, Al, Fe, Mn, and trace elements than the enclosing material. A reliable quantitative criterion for the evaluation of the agroecological status of light gray surface-gley soils can be the Fe/Mn ratio in 1 N sulfuric acid extract from the nodules (bogging factor according to Zaidelman and Ogleznev).

Concentrations of total carbon and nitrogen were measured by gas chromatography method, and the carbon content of inorganic compounds was determined by the volumetric method in soils of undisturbed coastal landscapes of the Barents Sea (Khaypudyrskaya Bay). Two groups of soils were specified. The first group included saline marsh soils formed under flooding by tidewater and surging seawater. The second group included soils of tundra ecosystems, which were subjected to precipitation of marine aerosols. In the first group, the content of C_org varied from 5 to 75 g/kg, the content of N total varied from 1 to 5 g/kg, and the C_org/N_tot ratio varied from 10 to 18. Humus-accumulative horizons buried under recent marine sediments were described in the middle part of the marsh soil profile. In the second group, the contents of C_org was 430–470 g/kg and N_tot 4–7 g/kg. The C_org/N_tot ratio in the surface peat horizons equaled to 64–95 g/kg and decreased by three–seven times in the deeper layers. The soils of the low-level marshes flooded each tide and especially their surface horizons contained more inorganic carbon than any other soils. Mass fraction of inorganic carbon varied from 4 to 20% of the total carbon content. Seawater and carbonate-containing rocks could be the source of the inorganic carbon. A correlation was found between the contents of C_org and N_tot in soils and in plant communities growing on these soils. Additional input of C_org and N_tot into marsh soils was due to the living activity of birds and to organic substances in seawater.

Soil salinity is an increasing threat to agriculture and is a major factor in reducing plant productivity in arid and semi-arid regions. Knowledge of the transport process of mass and energy in subsurface soil is vital for understanding the environmental and economic impact of agricultural practices in these areas. A finite difference model, WASH_1D, was applied to evaluate various transport mechanisms associated with temporal variations in soil water content and soil salinity in 5 cm sandy soil columns. Experiment was conducted in a laboratory with fixed temperature and relative humidity. Soil columns were initially saturated with distilled water or 3000 ppm NaCl solution. The accuracy of the model was evaluated using measured soil water content and soil salinity at seven depths 0.2, 0.6, 1.2, 1.7, 2.4, 3.4 and 4.4 cm at the end of the experiment. Simulated cumulative evaporation was compared with the data measured with an electronic balance. Results showed that the liquid flux of distilled water treatment was sharply declined sooner than NaCl solution treatment which was associated with decreasing in moisture diffusivity. The contribution of the water vapor flux to the total moisture flux was 0.01 and 0.2% for distilled water and solution treatments, respectively. The RMSE values between simulated and measured cumulative evaporation lines were 0.77 and 1.08 (g) for the distilled water and solution treatments, respectively. It was observed that the solution treatment significantly reduced total cumulative evaporation up to 11% as compared to the distilled water treatment. Simulated results demonstrated that the model predicted soil water content and salinity with adequate accuracy.

New experimental data on changes in organic matter content, in soil nutrition regimes, and in productivity of crops in fodder rotation were obtained. Long-term (1995–2005) studies of the effect of different rates of mineral and organic-mineral fertilizers (the control variant without fertilizers; N₁₂₀Р₉₀К₉₀; manure 40 t + N₁₂₀Р₉₀К₉₀; N₂₄₀Р₁₈₀К₁₈₀; and manure 80 t + N₂₄₀P₁₈₀K₁₈₀) in the fodder crop rotation (fallow–turnip–corn–sunflower mixture–spring rape–pea–oats mixture) were performed at the Research Institute of Veterinary Science of Eastern Siberia, Siberian Federal Scientific Center of Agro-Bio Technologies, Russian Academy of Sciences. Their results are discussed in this article. The application of particular norms of organic fertilizers per rotation (80 t of manure and N₂₄₀P₁₈₀K₁₈₀ kg of active substance) resulted in the greatest rise in the nitrate content (by 10–28 mg/kg), available phosphorus (by 21–47), exchangeable potassium (by 12–57 mg/kg of soil), and in organic matter (by 0.08% over the first rotation, by 0.09% over the second one, and by 0.17% over two rotations) in the 0- to 20-cm layer. Productivity of fodder crop rotation increased by 55.4–98.8% over the first rotation and by 58.4–120.6% over the second one.

The ameliorative status of irrigated soils was estimated on the basis of reclamation cadaster data for 2001 and 2016 on 17 state irrigation systems in three nature regions of Volgograd oblast: (1) the Khvalyn clayey plain and Volga sand ridge in the Caspian Lowland, (2) the Volga and Ergeni uplands, and (3) the Volga and Don river valleys. Significant changes took place in the ameliorative status of these systems during the studied period: the total irrigation area sharply decreased (–31%), especially under irrigation by the local runoff (‒44.5%); the groundwater level became lower, and the area with deep (>5 m) groundwater table increased to 77.3%; and the areas of saline and solonetzic soils decreased by 22.9% and 19.3%, respectively. In many cases, the differences in natural conditions determined the ameliorative status of irrigated soils and the intensity of their changes. The changes were the greatest on the initially saline slightly drained soils of the Khvalyn clayey plain and the smallest in the Volga River valley. During the entire period of irrigation, some areas were subjected to secondary salinization and abandoned. Our investigations at the Raigorodsk plot of the Svetloyarsk irrigation system within the Khvalyn clayey plain in 2016 demonstrated that the soils subjected to secondary salinization in the period of maximum irrigation intensity (in 1990) are now at the stage of gradual desalinization.

The depiction of soil delineations on a public cadastral map clearly demonstrates the potentialities of large-scale soil mapping. The development of land legislation involves land accounting by land use and the assessment of land quality in accordance with soils. For the full realization of the potential of soil mapping in solving practical problems concerning delineation and evaluation of agricultural land plots, soil maps must contain essential information. Most of the large-scale soil maps for agricultural lands have been created by state institutes for land management (GIPROZEMs). They have errors of the first and second kind of computer science theory (goal omission and false alarm), and problems with soil taxonomy, i.e., missing soil areas, excessive information, and erroneous soil diagnostics. The combination of these errors significantly complicates the practical application of soil maps. On the soil maps, it is impossible to find the boundaries of the territories, where land use changes are related to soil processes. There are also certain diagnostic and taxonomic difficulties in using soil maps for applied purposes. The development of soil cartography in the form of technology of retrospective monitoring of soil and land cover can significantly improve soil mapping and facilitate the transfer of soil mapping units to cadastral maps.