Genesis and age of mineralogical profiles of Moldavian chernozems

In chernozems developed in the autonomous positions in Moldova, the mineralogy of their silicate component has some features indicative of stronger transformations than those that could be expected for the chernozems formed by the Holocene pedogenesis. The mineralogical profiles testify to the eluvial nature of the main subtypes of chernozems. It is suggested that the revealed changes are not due to the Holocene pedogenesis. According to the probable age of the mineralogical profiles calculated from the volumes of aluminosilicates removed, these profiles originated in the early and middle Late Pleistocene, i.e., about 50 000–120 000 years ago. The effect of forest pedogenesis in the past epochs on the mineralogy of the northern subtypes of chernozems also cannot be excluded. The presented data characterize the chernozems under study as polygenetic soil formations.     

Characterization of the carbonate-calcium status of chernozems in the Kamennaya Steppe

Features of the carbonate-calcium status of ordinary chernozems under different plant communities and anthropogenic impacts were considered. Soil solutions were usually supersaturated with calcite. The carbonate status of chernozems was closely related to the local pedogenesis conditions developed in every specific case: the position of soil in the relief, the type of vegetation, and the local weather conditions.     

Assessment of biological activity in agrogenic and natural chernozems of Kabardino-Balkaria

Parameters of biological activity (humus and microbial biomass reserves, potential intensity of the CO₂ emission, and enzyme activity) have been determined in arable and natural chernozems on the plains of Kabardino-Balkaria as a part of the system for the ecological assessment of the state of the soil cover. Integral parameters of the eco-biological state of studied soils have been calculated on the basis of obtained data, and the level of changes in their total biological activity has been determined. A statistically significant decrease of the values of all the considered biological properties under the impact of tillage has been found. The data of two-way ANOVA suggest a stronger influence of agricultural management in comparison with genetic features of chernozems at the level of subtype. Differential approach is insufficient for evaluating the total level of soil biological activity, because there are many biological properties of soil, and the degrees of their changes in agrogenic soils are different. An integral approach has been used; it integrates the obtained data into a single integral assessment parameter. In arable soils, this integral parameter decreases by 39–46% and makes it possible to assess the degree of disturbance of the ecological functions of soils and their capacity for self-restoration.     

Humus status and distribution of the underground phytomass in eroded chernozems of the Cis-Salair region

It is shown that humus loss may reach 1.7 t/ha per year as a result of plowing of leached chernozems and erosion development. Distribution of underground phytomass in uneroded and eroded chernozems and slightly aggraded meadow-chernozemic soils of dissected areas in the Cis-Salair region is analyzed. It is shown that an increase in the degree of soil erosion is accompanied by a decrease in the total phytomass reserves, whereas the average depth of the root zone increases.     

The effect of irrigation on the content and mineralogical composition of clays in chernozems of Rostov oblast (Bagaevsko-Sadkovskaya Irrigation System)

The content and mineralogical composition of clays in the irrigated and nonirrigated pre-Caucasian chernozems in Rostov oblast were studied by X-ray diffraction analysis. Irrigation caused an increase in the content of this fraction in plow layers. The main changes in the mineralogical composition comprised a decrease in the quantity of illites and increase in labile minerals.     

Biological mineralization of organic matter in the modern virgin and plowed chernozems,buried chernozems,and fossil chernozems

The phenomenon of mineralization (biological mineralization) of organic matter in chernozems has been studied. A decrease in the content of C_org with time can be considered an index of the organic matter mineralization. It is suggested that the humus horizons of modern chernozems contain the pools of organic matter of different ages: easily decomposable organic matter, labile biologically active humus, stable biologically active humus, and relatively inert humus. The composition and mean residence times of these pools and their contribution to the total organic matter content have been estimated. The particular types of the biological mineralization have been determined on the basis of the comparison between the velocities of mineralization (M) and humification (H) processes: total unidirectional mineralization (M ≫ H), equilibrium mineralization (M ∼ H), nonequilibrium mineralization (M> <H), and zero mineralization. The separation of subtypes is based on data on the relative rates (%) of the organic matter mineralization. On the basis of available experimental data on chernozems buried under kurgans and in loess sediments (with the age of up to 800 ka), the quantitative relationship of the humus content in the buried soils on their age has been found; it has an exponential shape. During the first 100 ka after the soil burial, the soil humus content gradually (with a slowing intensity) decreases from 100–75 to 6.5% of its content in the virgin chernozems. Then, 100–1000 ka after the soil burial, the soil humus content remains approximately constant (6.5% of the initial level, or 0.3% of the soil mass). The rates of mineralization have been estimated. It is shown that the elemental composition (C, H, N, O) of humic acids remains relatively stable for a long time due to the regeneration of the chemical structure of humus (matric restoration of humus). It is suggested that several different forms of humus related to pedogenesis should be distinguished in the biosphere. The renewable humus in the equilibrium state with the environment is typical of the open biospheric (soil) systems. The fossil humus, whose content decreases with time, and whose composition remains stable, is typical of the semiclosed and closed systems. With time, it transforms into residual humus, whose content and composition remain stable. The fossilized organic matter in the fossil soils and sediments of the past geological epochs (Mesozoic and Paleozoic) considerably differs from the renewable, fossil, and residual humus.     

Changes in the physical status of the typical and leached chernozems of Kursk oblast within 40 years

The changes in the physical properties of the chernozems in the Central Russian province of the forest-steppe zone (Kursk oblast) that took place from 1964 to 2002 are analyzed in relation to the corresponding changes in the agrotechnology, agroeconomy, and agroecology. Three periods of the soil transformation are distinguished. The first period was characterized by the use of machines with relatively small pressure on the soil and by the dynamic equilibrium between the physical state of the soils and the processes of the humification-mineralization of the soil organic matter. The use of power-intensive machines in the next period resulted in greater soil compaction with negative changes in the soil physical properties. At the same time, the physical properties of the chernozems remained close to optimum on the fields where heavy machines were not used. The third period was characterized by the use of heavy machines and by the decrease in the rates of the organic and mineral fertilizers and certain disturbances in the crop rotation systems because of the economic difficulties. The negative tendencies of the changes in the soil physical properties observed during the preceding period continued.     

Analysis of the long-term dynamics of moisture balance components in typical chernozems of the reserved steppe area in Kursk region

The long-term dynamics (1947–2006) of parameters characterizing the income and expenditure components of moisture balance in deep (3 m) chernozems of the reserved steppe area subject to annual hay cutting have been analyzed by methods of moving averages and resolution of data sets into time series. The results provide evidence for the cyclic patterns of these dynamics and their dependence on changes in weather conditions over the past few decades, referred to as recent climate warming. An increase is noted in the occurrence frequency of long time series (about 7 years) with parameters of soil moisture balance deviating (either positively or negatively) from long-term average values, during which changes in soil properties (in particular, carbonate status) may well leave their mark in the soil profile. The long-term dynamics of individual components of soil moisture balance have a specific pattern accounted for by the mutual influence of these components on each other as well as by the combined effect of changing environmental factors. An analysis of the moving-average curves of these components has revealed the tendency indicating that the period of increased moisture supply to chernozem soils (characteristic of the past few decades) is coming to an end.     

The effect of pollution with oil and oil products on the biological status of ordinary chernozems

The effect of pollution of an ordinary chernozem with oil and oil products depends on the nature and concentration of the pollutants, their distribution in the soil profile, and the period of the pollution. The soil contamination causes a rise in the number of microorganisms and changes in their species composition: a decrease in the diversity of micromycetes and an increase in the diversity of bacteria. In most cases, it inhibits the activity of soil enzymes. Oxidoreductases are more sensitive to oil pollution than hydrolases. The soil ecological functions are disturbed under the impact of contamination.     

Potassium status and clay mineralogy in ordinary chernozems treated with different rates of potassium fertilizers

The effect of a single instance of potassium fertilization at rates of 0, 70, 140, and 280 kg/ha on the potassium status and clay mineralogy was studied in a field experiment on ordinary chernozems. The content of exchangeable potassium determined by the Maslova method and the potassium potential vary with greatest reliability in response to increasing fertilizer rates. The content of easily exchangeable potassium and the potassium-buffering capacity are insignificantly affected by the application rate of potassium fertilizers. The chernozems under study without fertilization are characterized by a low supply of available potassium. When potassium fertilizers are applied at rates of 70 and 140 kg/ha, the soils pass into the category of unstable or high supply according to different gradation systems. The lower limit of the high or optimal supply category is reached only at the application of 280 kg/ha of potassium fertilizer. However, even in this case, chernozems are characterized by a low potassium supply according to the value of potassium potential and the content of nonexchangeable potassium. A single application of potassium fertilizers does not cause significant changes in the contents of illites in the clay fraction.     

Nonhydrolyzable residue in humus of chernozems

Mismanagement of chernozems results in a decreasing humus content at the expense of the carbon of the nonhydrolyzable residue (the humin fraction). This conclusion is proved by the original data obtained by the authors and by other scientists. It is also shown that the newly formed humus is dominated by the carbon of nonhydrolyzable residue. These facts attest to the presence of labile humus compounds subjected to mineralization in the humin fraction of chernozems.     

Changes in acidity parameters of chernozems in the Kamennaya Steppe

The analysis of long-term data on the acidity parameters of chernozems in the Kamennaya Steppe indicated a tendency for some alkalization of the soils.     

Radiocarbon ages of humic substances in chernozems

Data on radiocarbon ages of different fractions of humus (humic acids, fulvic acids, and humin) in the profiles of chernozems are analyzed. A chronoecological grouping of humus in modern and buried (fossil) soils is suggested. An increase in the radiocarbon age of humic substances down the soil profile has a stepwise character. It is shown that the ¹⁴C content in chernozems decreases down the soil profile more somewhat slower than the ¹²C content. The dependence of a decrease in the humus content of buried soils on the age of burying is traced for a time span of 800 ka.     

Biological activity of chernozems in the center of the Russian Plain

Specific features of the microbiological and enzymatic activity of chernozems are considered in genetically associated and technogenic series. The biological processes in chernozems follow the main soil-geographical regularities inherent to the Central Chernozemic region. The biological characteristics of the chernozems reflect the dynamic properties of the microorganisms habitat and are indicators of their technogenic degradation. Plowing of chernozems and their intense agricultural use is accompanied by changes in their biological activity. The disturbances revealed in the biosystem of the chernozems caused by plowing and fertilization were of a functional, i.e., reversible character. The changes in the intensity of the biochemical processes in the chernozems were observed only under the long-term application of fertilizers (for not less than 10 years). A single application of fertilizers caused temporary changes.     

The influence of relief on the humus content in chernozems

Data on the influence of relief on the humus formation in chemozems are given. The insolation coefficient is proposed for the assessment of the solar energy distribution over the ground surface depending on the slope gradient and aspect. Specific features of the humus accumulation in soils on parent rocks different in texture are estimated using the proposed calculated coefficients.     

The development of chernozems on the Dniester-Prut interfluve in the Holocene

The development of forest-steppe and steppe chernozems on the Dniester-Prut interfluve in the Holocene was studied on the basis of data on the paleosols buried under archaeological monuments of different ages. The parameters of the mathematic models of the development of the soil humus horizons in different subtypes of chernozems were calculated. They were used to determine the rate of this process and the age of the soils formed on the surface of Trajan’s lower rampart. The climate-controlled changes in the character of the soil’s development in the Late Holocene were differently pronounced in the different subtypes of chernozems. The suggested differentiation of the trends in the development of the humus horizon in the studied chernozems corresponds to the differences in the soil-forming potential of particular areas (as judged from the energy consumption for pedogenesis).     

Simulation of water permeability processes in chernozems of the Kamennaya Steppe

The physical and hydrophysical properties of ordinary chernozems from the Kamennaya Steppe were studied for the experimental support of a soil water infiltration model. Increased fissuring and density of the plow horizon were noted because of the dry weather conditions, which caused high infiltration values. The soil water retention curve parameters were calculated from the experimentally determined particle-size distribution, the bulk density of the soil, the solid phase density, the organic matter content, and the physicomechanical and soil-hydrological constants using the known pedotransfer functions and the Voronin secant method. A model experiment with different input parameters was performed. It was shown that the best experimental support of the model included parameters calculated by the Voronin method with the following approximation by the van Genuchten function.     

Thermal properties of typical chernozems in Kursk Oblast

Thermal diffusivity and heat capacity of virgin and plowed heavy loamy typical chernozems of Kursk oblast were studied. Thermal diffusivity was determined in the course of step-by-step drying of the initially capillary-saturated samples to the air-dry state. Specific heat capacity was determined for absolutely dry samples. Volumetric heat capacity was calculated according to the de Vries equation. Thermal diffusivity varied within the ranges of (1.15–3.46) × 10^–7 m²/s in the Ap horizon, (1.14–3.35) × 10^–7 m²/s in the А1 horizon, (1.49–3.70) × 10^–7 m²/s in the АВ horizon, (1.49–3.91) × 10^–7 m²/s in the В1 horizon, and (1.60–3.80) × 10^–7 m²/s in the Вса horizon. The thermal diffusivity vs. water content dependencies had distinct maximums and were flattened in the range of low water contents. The maximums were most pronounced for the mineral B1 and Bca horizons; for the A1 and Ap horizons, the curves were rather S-shaped. Volumetric heat capacity of the air-dry soils varied from 0.96 J/(cm³ K) in the A1 horizon to 1.31 J/(cm³ K) in the Bca horizon; in the state of capillary saturation, it varied from 2.79 J/(cm³ K) in the А1 horizon to 3.28 J/(cm³ K) in the Вса horizon. Thermal properties of topsoil horizons were higher in the plowed chernozem compared with the virgin chernozem, which is explained by an increase in the bulk density and a decrease in the organic matter content in the plowed soil.