Том 51, № 12 (2018)

The results of morphosubstantive genetic study of a soil–sedimentary sequence with four buried soils in the Boguty River basin (southeastern Altai) are discussed. A comparative analysis of the surface and buried soils in the valley of a tributary of the Boguty River allows us to distinguish between the following stages of the development of valley landscapes: (1) 11–8 ka BP, humid to semihumid stage with the warmest climate and widespread development of forest vegetation with the formation of texture-differentiated soils with a dark humus horizon; (2) 8–7 ka BP, the stage of relative cooling and humidization of the climate; disturbance of the valley landscapes by a mudflow; the formation of thin short-living dark-humus gleyic soils with cryogenic features under the meadow-steppe vegetation; (3) about 7 ka BP, the stage of transformation of the earlier formed profiles by solifluction processes; (4) 7–<2.7 ka BP, the stage of stabilization of the slopes and the development of cold meadow-steppe/steppe pedogenesis under conditions of a small deficit of moisture; (5) about 2.7 ka BP, a short stage of aridization and activation of eolian followed by stage (6) Al–Fe-humus pedogenesis under the tundra/meadow-steppe phytocenoses with a shift from humid to arid climatic conditions of the next (7) stage of the cryoaridic steppe pedogenesis. Modern pedogenesis proceeds under the cold and dry conditions that are most severe since the beginning of the Holocene. The obtained data are in agreement with the existing notions about the evolution of geosystems in the southeastern Altai in the Holocene and make them more detailed.

Exchangeable acidity in samples from organic and mineral horizons of taiga and bog soils with strongly acid reaction (pH_KCl < 3.3 and \({\text{p}}{{{\text{H}}}_{{{{{\text{H}}}_{2}}{\text{O}}}}}\) ≤ 4.4) was determined by the Sokolov method of potentiometric titration of KCl extract before and after the addition of a sodium fluoride solution. In the same extracts, the contents of Al, Fe, and Mn ions were determined by the atomic emission method. NaF was added in an amount sufficient for binding all metal ions into fluoride complex compounds. It was found that the content of metals determined by atomic emission is lower than that calculated from titration results in 1.5–2 times in organic horizons and by 20–25% in mineral horizons. Even a higher difference between the two methods was observed for exchangeable protons: from the titration data, their content in organic horizons was 10–12% of the content determined as the difference between total exchangeable acidity and total metal ions determined by atomic emission, and 3–15% in mineral horizons. The revealed differences were attributed to the underestimated results of determining exchangeable protons in the presence of NaF, which was confirmed by the potentiometric titration of model solutions of strong and weak acids prepared from a KCl solution. It was found that the addition of NaF during the titration with a strong acid results in reaching the point of equivalence after the addition of a smaller amount of base. Reasons for the shift of the point of equivalence during titration with a strong acid in the presence of NaF require special investigations. It is recommended to estimate the exchangeable acidity of strongly acid soils due to metal ions by atomic emission or other adequate methods.

Data on the СО₂ emission from the surface of iron-illuvial podzol (Albic Podzol) under an 84‑year-old cowberry–lichen pine forest of the middle taiga in the northeast of European Russia (the Komi Republic) during the growing seasons of 2014–2017 are discussed. Interannual differences in weather conditions were estimated from records of the Syktyvkar weather station. The emission of СО₂ was measured by an infrared analyzer LI-COR 8100. In 2016, the duration of the growing season, mean air temperature, and the sums of effective (>5°С) and biologically active (>10°С) temperatures were 1.1–1.3 times higher than the long-term averages. Droughty seasons were absent in the studied period. The intensity of the CO₂ emission correlated with the soil temperature at the depth of 10 cm; the correlation coefficient varied from 0.79 to 0.86 (p < 0.05). The temperature coefficient Q₁₀ varied from 2.2 to 3.7; soil respiration at the temperature of 10°C, from 1.2 to 1.5 g С–СО₂/(m² 24 h); at the temperature of 20°C, from 2.6 to 5.3 g С–СО₂/(m² 24 h), the mean rate of soil respiration during the growing season, from 1.3 to 1.7 g С–СО₂/(m² 24 h). The total emission of carbon in the form of CO₂ from the surface of iron-illuvial podzol varied from 246 to 389 g/m² with the maximum during the hot summer season of 2016.

Soil moisture, nutrients and environmental conditions have extremely vital effects on vegetation growth and microbial activities in terrestrial ecosystems. To study the changes of soil physical and chemical properties as affected by degradation along the eastern margin of the Tibetan Plateau, using the largest wetland in Ruoergai as the research sample for two consecutive years, we tested the soil bulk density, the soil moisture content, the pH value, the content of organic C, total N and total P of 0~20 cm and 20~40 cm in different degradation degree (light, moderate, serious and non-degraded alpine meadow). The results show that: (1) Degradation had profound effects on the soil physical properties and chemical properties. with the intensification of the alpine meadow degradation in the eastern margin of the Qinghai-Tibet Plateau, the soil organic carbon, total nitrogen, total phosphorus and soil water content decreased significantly but soil bulk density increased significantly. (2) the soil organic carbon, total nitrogen, total phosphorus contents and soil water content increased with the increase of soil depth, however, the soil bulk density show the opposite regular. (3) The correlation analysis indicated that there was an extremely significant positive correlation between soil organic carbon and total nitrogen, total phosphorus, soil water, and the correlation coefficients were 0.822, 0.907 and 0.885 respectively (P < 0.01). There was an extremely significant positive relationship between the pH and the soil bulk density (r = 0.488, p < 0.01), while a significant negative relationship between pH and soil water (r = –0.387, p < 0.05). Overall, these results suggested that soil degradation not only changed the soil physical properties but also affected the soil chemical properties indirectly. Protecting surface vegetation and reducing wind erosion could be a good way to curb degradation.

The osmotic pressure and electrical conductivity were determined with the use of instrumental methods (centrifuging, conductometry, and cryoscopy) in equilibrium soil solutions as the functions of moisture (the mass ratio between solid and liquid phases) for the soils of different geneses and textures. These functions proved to have a nonlinear character with one extremum. A theoretical substantiation to this phenomenon is suggested. It is based on the concept of competing interphase interactions in soil and develops the classical ideas by A.A. Rode. Upon the low soil water content, surface (molecular and ion-electrostatic) forces of the solid phase bind water molecules and prevent them from hydrating ions and dissolving electrolyte salts in the soil solution; as a result, electrical conductivity and osmotic pressure values approach zero in this case. With an increase in the water content, water molecules escape gradually from the energy field of surface forces, and their activity (chemical potential) and dissolving capacity also increase. This results in the expected growth of the electrical conductivity and osmotic pressure of the equilibrium solution extracted from the soil. The maximum values of the studied parameters are observed at the water content approximately equal to the maximum molecular water capacity (or to the boundary zone, within which capillary gravitational forces influencing the soil liquid phase become prevailing over the surface interphase interaction forces). The further increase in the soil water content lowers the electrical conductivity and osmotic pressure of equilibrium solution because of dilution of the fixed mass of electrolyte salts. For quantitative description of the revealed functional dependence, we suggest an empirical mathematical model in the form of modified equation of lognormal distribution.

The research was performed in the center of the Baraba Plain. It was demonstrated that soil salinity exerts a considerable effect on oribatid mites. Several stages of changes in the population of oribatid mites upon soil evolution on the dried bottom of salt lake in the forest-steppe zone of Western Siberia were identified. At the stage of solonchakous meadow soils (Mollic Gleysols (Salic)), oribatid mites formed a multi-species low-number group. At the stage of medium-deep solonetzes (Gleyic Solonetzes) and chernozemic meadow soils (Luvic Chernozems), the species richness and abundance of oribatid mites increased by about 2–3.5 times. The appeared species were sensitive to high soil salinity and could not survive in the meadow soil. Changes in the soil salinity led to changes in the ecological status of species: some of them occupied dominant positions, and others lost them.

Soil aggregates are key elements of soil structure that play an important role in several soil processes. One of the major factors that affect soil structure are the anthropogenic activities. Such modifications can be studied by different scales of analysis, macro, meso and microscale; and measured through different soil properties. The aim of our work is to perform description at submicroscopic scale of the soil aggregates matrices of Luvic Phaeozems affected by the different uses in the southeastern part of Buenos Aires, Argentina. The descriptions were made taking into account: (a) characteristics of aggregates matrix, (b) elemental composition of matrix and (c) organics components (plant residues, other carbon components) and microbiogical components. In natural and forested soils, the content of organic carbon in the aggregate matrices is higher, while in cultivated soils there is a decrease, which results in a decrease in their structural stability. The observations under MEB and the EDAXs have contributed to defining the morphological characteristics of the aggregate matrices from granular porous organic ones in non-tilled soils to compact ones in cultivated plots.

The functional role of nitrogen in the formation of crop yield on chernozems under conditions of traditional and direct seeding (DS) cropping systems is considered. In the course of long-term experimental studies of DS cropping system on chernozems, considerable experience has been gained and has found efficient practical application. It is shown that the effect of nitrogen as the most important element in the composition of humic substances influencing the fertility of chernozems depends on the variability of environmental factors, the forms and rates of nitrogen fertilizers, the rotation systems, and the soil treatment technologies. The DS cropping system has been tested for 4–10 years on experimental fields of the Stavropol Agricultural Research Institute and in a number of farms in Stavropol region. The obtained data on the yields of cereal crops and the application of fertilizers attest to the importance of the formation of a mulching layer of plant residues on the surface of ordinary and southern chernozems in the DS systems. This layer contributes to a gradual accumulation of nitrogen, protects the soil from erosion, and increases the number and mass of earthworms. Nitrogen in the DS cropping systems on chernozems in Russia is characterized by the high mobility and the capacity for considerable transformation. In this context, further investigations and special experiments are necessary to gain better knowledge of the behavior of nitrogen in different cropping systems. In particular, the relationships between nitrogen fluxes, agrophysical soil properties (aggregate-size distribution at the macro and micro levels), and specificity of the organic matter in different subtypes of chernozems under different cultivation technologies have to be clarified. In general, the role of DS cropping systems in farming practices has become more significant in the recent years; application of the DS cropping system is considered a positive factor in maintaining and restoring soil fertility.

The current trend in erosion rate of ordinary chernozems in Saratov oblast has been assessed. Detailed studies have been performed in a small catchment area of the Bolshoi Kolyshley River (Medveditsa River basin) using the radiocesium and soil-morphological methods. Data of long-term hydrometeorological observations in the region, reported results of observations of water runoff and soil loss on the runoff plots of the South-Eastern Research Institute of Agriculture (Saratov oblast), results of analysis of the grain size and mineral composition of stratozems developed on the catchment valley bottom were also used for analysis. The quantification of sedimentation rate in the valley bottom during two time windows (1963–1986 and 1986–2017) based on the sediment dating using ¹³⁷Cs as a chronomarker indicates their decrease at least in 4–6 times after 1986, which points to a proportional reduction in erosion rate on the plowed slopes of the catchment area. The analysis of the temporal variability of suspended yields in the regional rivers (Medveditsa and Khopyor) during the period from 1940 to the present time allows us to draw an analogous conclusion for the Volga Upland within Saratov oblast. The decrease in the erosion rate of ordinary chernozems could be mainly caused by the reduction in water runoff from slopes during the spring snowmelt because of reduction in soil freezing depth against the background of rising air temperature in winter and spring. This decrease in erosion rate during the snowmelt period was not balanced by the regional increase in rainfall erosion related to some increase in the rate of runoff-forming rainfalls. In the part of Saratov oblast, located within the Volga Upland, where the studied catchment is situated, on the contrary, even a reduction in the frequency of rains with a rainfall depth of more than 30 mm occurred over the last decades. The reduction in the cultivated land area since the late 1980s because of the abandonment of plowlands on the steepest slopes also contributed to the decrease in total soil loss by erosion at the river basin scale. Within the studied small catchment, the share of perennial grasses in crop rotations increased after 1986, which also led to reduction of the rate of erosion of ordinary chernozems.

It is found that in Belgorod oblast during 2010–2014, cadmium mainly came into agrocenoses with organic fertilizers (0.4 g/ha, or 73.9%) and ameliorants (0.116 g/ha, or 21.4%). The lowest total content of cadmium in the A horizon (0.22 mg/kg) was noted in meadow-chernozemic soil (Greyzemic Stagnic Chernic Phaeozem (Clayic, Pachic)) developed on old alluvial calcareous deposits, and its highest content (0.42 mg/kg) was found in ordinary chernozem (Haplic Chernozem (Clayic, Pachic)), where loess-like clay is the main parent rock. Virgin leached chernozem (Luvic Сhernozem (Loamic, Pachic)) formed on loess-like loam, contained 0.33 mg Cd/kg in the A horizon, which almost coincided with the mean content of this element (0.32 mg/kg) in the plow layer of leached chernozems on reference plots. No exceeding of the tentative permissible concentration of cadmium was revealed in arable soils. In crops, the content of cadmium was highest in sunflower seeds (0.086 mg/kg) and soya beans (0.072 mg/kg), and lowest in peas (0.032 mg/kg) and white lupine beans (0.013 mg/kg). The biological adsorption factor varied within the range from 0.97 (while lupine beans) to 10.8 (sunflower seeds) for target agricultural crops and from 0.41 (while lupine straw) to 4.63 (soya straw) for side products.