Assessment of the mineralogical status of silicate components in chernozems

An approach to assess the mineralogical status of chernozems is discussed. It is based on ten characteristics of the main groups of minerals composing the silicate part of the soil and allows us to give a comprehensive assessment of the mineralogical status of chernozems and its transformation under the impact of pedogenetic processes. The obtained data may be used for determining the soil genesis; improving soil classification; and solving various applied problems, including the assessment of the adverse effect of irrigation of chernozems on the state of their minerals, the irrigation-induced degradation of smectites and illite formation, illite formation upon the nonexchangeable fixation of potassium from fertilizers, etc. The principles of this approach may also be applied to other soils with due consideration for their mineralogical composition.     

Microbial activity in the profiles of gray forest soil and chernozems

Soil samples were taken from the profiles of a gray forest soil (under a forest) and southern chernozems of different textures under meadow vegetation. The microbial biomass (MB) was determined by the method of substrate-induced respiration; the basal respiration (BR) and the population density of microorganisms on nutrient media of different composition were also determined in the samples. The microbial metabolic quotient (qCO₂ = BR/MB) and the portion of microbial carbon (C mic) in C org were calculated. The MB and BR values were shown to decrease down the soil profiles. About 57% of the total MB in the entire soil profile was concentrated in the layer of 0–24 cm of the gray forest soil. The MB in the C horizon of chernozems was approximately two times lower than the MB in the A horizon of these soils. The correlation was found between the MB and the C org (r = 0.99) and between the MB and the clay content (r = 0.89) in the profile of the gray forest soil. The C mic/C org ratio in the gray forest soil and in the chernozems comprised 2.3–6.6 and 1.2–9.6%, respectively. The qCO₂ value increased with the depth. The microbial community in the lower layers of the gray forest soil was dominated (88–96%) by oligotrophic microorganisms (grown on soil agar); in the upper 5 cm, these microorganisms comprised only 50% of the total amount of microorganisms grown on three media.     

The effect of paleocryogenesis on the profiles of chernozems in the Kamennaya Steppe

It is shown that the history of sedimentation and development of soil-forming materials exerts a great effect on the modern pedogenic processes. Paleocryogenic microtopography inherited from the Late Valdai stage predetermines many morphological features of modern chernozems. Morphological differences between the soils on microelevations and in microdepressions are described. Nine main morphological distinctions in the morphology of soils developed on different elements of the microtopography are are specified.     

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.     

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.     

Genesis of light-colored acid eluvial horizons in soil profiles

General ideas concerning the formation of light-colored acid eluvial horizons in soil profiles are considered. In Russia, the current concept is related to the polygenetic origin of these horizons due to processes of acid hydrolysis, lessivage, and gley. Based on the original and literature data summarized by the author, the conclusion was drawn that the acid hydrolysis cannot provide the reduction of Fe (III) to Fe (II) under aerobic conditions or its further transfer to the soil solution. Lessivage, which governs the formation of light-colored acid eluvial horizons, is not an obligatory factor, as its features are often absent in the profile of these soils. Under conditions of a stagnant-percolative water regime, gley may be considered to be the only process responsible for the eluviation of Fe, Mn, and Al and removal of iron hydroxide and iron oxide coatings from mineral grains, resulting in an increase in the relative Si content and the appearance of a whitish color. This factor is the only cause for the formation of light-colored eluvial (podzolic) horizons. Therefore, they are monogenetic in origin.     

Biological activity in the profiles of chernozems as dependent on the character of their agricultural use and microtopography

The biological activity of soil samples taken from genetic horizons of plowed and virgin chernozems in the Kamennaya Steppe Reserve was determined as the amount evolved from the soil upon its incubation in laboratory conditions. In the top humus horizons, the biological activity of virgin chernozem was two to three times higher as compared with that in the plowed chernozem. The intensity of biological processes and the microbial biomass in the soil profile was mainly controlled by the quantity and quality of soil organic matter. Long-term agricultural use exerted a weaker effect on the biological properties of chernozems developed on microelevations (blocks) of the paleocryogenic microtopography in comparison with chernozems developed in the microdepressions between the blocks. The factor analysis showed that soil characteristics related to the biological processes comprise more than 50% of the total variance of factor loads and are distinctly differentiated in the soil profile.     

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.     

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.     

Gully development in the Moldavian Plateau of Romania

Gully erosion has been recognized as an important environmental threat in the Moldavian Plateau of Eastern Romania. The main objective of this study was to define the process-based gully development by providing quantitative information from long-term field measurements in small catchments.Three main areas of monitoring gullies were explored: aerial photographs of flights in 1960 and 1970, classical leveling and repeated survey through a particular close stakes grid after 1980. The Caesium-137 technique has been used effectively in the areas of deposition of gully sediments to obtain reliable information on dating specific levels of sediments and to provide chronological measures of gully development.Most of the discontinuous gullies exhibit both proper gullying, mainly if not exclusively by gully head advance, and aggradation of the gully basin floor. Results indicated that the mean gully head retreat was 0.92 m year^− 1 and the mean areal gully growth was 17.0 m² year^− 1. Both values indicate a slow erosion rate for this area. The average annual regime of gullying is pulsatory, one that is best described by great fluctuations. Conventional measurements on sedimentation over the period 1987–1997 indicate a higher rate of aggradation in the upper half of the gully floor. Information on the Caesium-137 depth profile was used to provide estimates of a mean sedimentation rate of 4.4 cm year^− 1 over the period 1963–1996 and 2.5 cm year^− 1 after 1986 for the short successive discontinuous gullies. A new classification of the discontinuous gullies based on two criteria, respectively, the field patterns and the rate of aggradation within the gully basin floor was established.For continuous gullies, linear gully head retreat, areal gully growth and eroded material rates were quantified for three periods (1961–1970, 1971–1980 and 1981–1990). Results indicate that gully erosion has decreased since 1960. This gullying decline is due to the rainfall distribution, and the increased influence of soil conservation practices. The mean gully head retreat of 12.5 m year^− 1 between 1961–1990 was accompanied by a mean areal gully growth of 366.8 m² year^− 1 and a mean erosion rate of 4168 t year^− 1. As with discontinuous gullies, continuous gullies showed pulsatory development.The critical period for gullying over 1981–1996 covers 4 months from Mid March to Mid July in an area with mean annual precipitation around 500 mm. Another main finding of this 16-year stationary monitoring was that 57% of the total gullying occurred during the cold season, with the remainder during the warm season. Of the total gully growth, 66% results from only four years (1981, 1988, 1991 and 1996), when a greater amount of precipitation fell.     

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.     

Specific features of water permeability in virgin and cultivated chernozems

The tendency and type of quantitative changes in the main characteristics of the water permeability of automorphic (typical and ordinary) chernozems in the central part of the Russian Plain have been studied in the system of virgin soil (long-term fallow), rainfed plowland, and irrigated plowland. It is shown that irrigation exerts the most pronounced adverse effect on the water permeability of chernozems. The revealed causes of unfavorable changes in the water permeability of chernozems in the region are related to their agricultural use.     

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.     

Comparative characterization of the optimum and actual parameters of Ukrainian chernozems

Positive and negative characteristic of chernozems have been revealed from the database on the properties of Ukrainian soils, which includes information about more than 2000 soil profiles (considered as the most probable and characterizing the current state of the soils) and the optimal parameters of soils. The main problems that hamper the production of high crop yields on these soils are as follows: the deficit of productive moisture, the moderate reserves and negative balances of nutrients, and degradation processes as a result of unbalanced and unsatisfactory land use. The chernozems are characterized by the risk of overcomepaction (especially in the under-seed layer of the soils in the spring because of the water content being close to that of the soil physical maturity and the decreased bulk density and clodding during the basic cultivation. The water stability of the soil structure of chernozems is significantly lower than that of their natural analogues. The maintenance and sustainable use of chernozems in Ukraine require a corresponding strategy: programs, laws, monitoring, the newest conservation technologies, and tight control of their implementation.     

中国黑钙土地区土地整理方法探讨

黑钙十具有较高肥力,但十地利用方式与自然条件(坡度、气候等)的限制会使黑钙土地区存在一定程度的土壤侵蚀与退化,通过土地整理增强其水土保持能力与耕地生产力.该文将GIS与遥感影像引入土地整理,根据研究区土壤特性与地理要素,通过运用GIS软件并结合模拟分析方法,探讨适宜于黑钙土地区耕地整理中田、水、路、林的设计方法.研究结果:黑钙土地区土地平整应依据实际生产方式与土壤特性采取修改局部地形面方法;农田水利设施需采用喷灌系统进行节水灌溉;田间道路设计须根据实地条件与生产方式最人限度节约耕地;营造防护林以减缓有害风;注重培肥地力、改变耕作方式以改良土壤.研究结论:黑钙土地区耕地整理应针对侵蚀区域进行局部平整,避免大规模表土搬运与平整,同时采用喷灌设施,改善生态环境,并注重土壤改良,保持黑钙土肥力.     

Heavy metals in ordinary chernozems on slopes of different gradients and aspects

The impact of slope aspect and gradient on the contents and distribution of heavy metals (Mn, Cu, Zn, Co, Ni, Pb, and Cd) in the profiles of ordinary chernozem (Haplic Chernozems) was studied in Kursk oblast. Slope aspect was found to be a significant factor controlling the distribution of most of the bulk, mobile, and acid-soluble compounds of heavy metals, whereas the position on the slope (slope gradient) did not exert a significant influence on the distribution of elements. Bulk compounds of Co, Ni, Pb, and Cd showed the eluvial type of distribution in the soil profiles along with accumulation in the lower horizons. Distribution patterns of the mobile Cu, Co, Ni, Pb, and Cd were similar to those of the bulk ones. The latter phenomenon may be attributed to the high content of carbonates, an increased content of clay, and some alkalization of the soil solution in the lower horizons.     

The rates of organic matter renewal in gray forest soils and chernozems

The rates of soil carbon renewal were determined by the method of natural ¹³C abundance in a chernozem under a 40-year-long monoculture of corn and in a gray forest soil after application of corn residues. The mean rate of soil carbon renewal in the chernozem reached 1271–1498 years, whereas in the gray forest soil it depended on the amount of carbon introduced with corn residues and varied from 19 to 63 years. The rate of organic carbon renewal in the chernozem decreased from 697 years in the upper horizon to 2742 years in the layer of 40–60 cm. The mean residence time of organic carbon generally increased with a decrease in the size of particle-size fractions.     

Chemical and mineralogical studies of volcanic ashes

The relationships between rock types and mineralogical properties of volcanic ashes were investigated using many volcanic ash samples from different volcanoes.

The heavy mineral fraction was dominated by two pyroxenes and ferromagnetic minerals In almost all the felsic and Intermediate volcanic ashes. Therefore, It was difficult to determine the rock types of felsic and intermediate volcanic ashes according to their heavy mineral composition. It was assumed that the presence of a large quantity of hornblende was related to the origins of the volcanic ashes. On the other hand, the predominant mineral in the heavy mineral fraction of mafic volcanic ashes was volcanic glass (refractive index about 1.59), followed by olivine.

The refractive indices (γ) of plagioclases and orthopyroxenes were 1.553–1,570 and 1.703–1.715 in the felsic volcanic ashes, 1.558–1.580 and 1.705–1,715 in the intermediate ashes, and 1.565–1.576 and 1.697–1.705 in the mafic ashes, respectively. These results indicate the difficulty of determining the rock types of volcanic ashes according to the optical properties of these minerals.