Accumulation of organic matter in the mineral layers of permafrost-affected soils of coastal lowlands in East Siberia

On the basis of a large volume of literature and original data, the high content (1–7%) of organic matter in the mineral layer of loamy permafrost-affected soils of coastal lowlands in East Siberia (from the lower reaches of the Lena River to the lower reaches of the Kolyma River) has been statistically proved. In most cases, the reserves of C_org in the mineral layer of these soils exceed those in the surface organic horizons and constitute 60–90% of the total soil pool of C_org. The enrichment of the mineral layer with C_org is due to the cryogenic retention (retenization) of humus (the illuviation and accumulation of colorless humic substances above permafrost) and the cryogenic mass exchange (mechanical admixture of organic matter from the upper organic horizons into the mineral layers). The analysis of 60 soil profiles showed that the accumulation of organic matter above the permafrost table is observed in 43% of cases; in general, the organic matter distribution in the soil profiles is highly variable. A specific type of colorless humus is accumulated above the permafrost table. The mechanisms of its precipitation and transformation in the profile require further studies.     

Soil formation in the technogenic forest-steppe landscapes of the Nazarovskaya Depression in western Siberia

The soil formation was studied in the 21- to 35-year-old pine plantations created on the overburden dumps of the Nazarovskaya Depression without applying the material of the humus horizon. The surface technogenic formations under the pine plantations belong to the group of naturfabricats (surface formations devoid of the humus horizon and composed of natural substrate). The morphological characteristics, bulk chemical and particle-size compositions, and labile properties of the soils indicate that the accumulation and transformation of organic matter are dominant processes in the artificially planted forests. The accumulation of organic residues and destruction and humification are tightly related to the environmental conditions transformed by the technogenesis and conceal other processes forming the soil profiles. Quasizems created for agricultural production purposes were the objects of the study. They were formed by covering the technically planned overburden rocks with the material of humus layers. The thickness of the humus horizons of the quasizems varies greatly (25–64%); the variation of the humus reserves in them is 34–122%. Middle-profile horizons have not been formed by the present time.     

Anthropogenic evolution of dark gray forest-steppe soils in the southern part of the Central Russian Upland

A sequence of dark gray forest soils developing under a virgin broadleaved forest and under croplands used for 100 and 150 years was studied in the southern part of the forest-steppe zone on the Central Russian Upland. The application of multiple study methods for these objects made it possible to trace the evolutionary changes in the soil properties during the 150-year-long period of regular plowing. Several important trends in the soil development under the impact of the cultivation were revealed: (a) an increase in the thickness of the humus layer (according to the measurements at 20 points for each of the objects), (b) an increase in the amount of mole tunnels, (c) a decrease in the coefficient of the textural differentiation of the soil profile (with respect to the clay content), (d) an increase in the contents and reserves of the major nutrients upon a stable pool of humus in the upper meter, and (e) some alkalization and carbonization of the profile. Powdery accumulations of carbonates and whitish calcareous coatings on the faces of prismatic peds appeared at a depth of more than 130 cm. The plowed soils contained thin deep fissures, the surface of which was covered by dark-colored clayey-humus coatings at the depth of 50–110 cm. The radiocarbon age of the humus in these coatings was 500–1000 years younger than the age of the humus in the soil mass between the fissures. This set of features attests to the evolution of the plowed dark gray forest soils into chernozems under the impact of plowing.     

The formation of the humus profile of chernozems in the Azov province

The regularities of the formation of the humus profiles in chernozems of the Azov province (“priazovskii chernozems”) were revealed from studying the paleosols of burial mounds (archeological monuments) of the Bronze Age, Early Iron Age, and Middle Ages. The principal differences in the geneses of different parts of the humus profiles were revealed. From 40 to 70% of the current humus reserves in the 1-m-thick layer were shown to be accumulated by the late 3rd and early 2nd millennia BC. In the following 4000 thousand years, the development of the upper soil layers was cyclic. In favorable climatic periods, the humus content increased and accumulation processes predominated. Under aridization, the humus mineralization was intensified, the humus content decreased to 3%, and its reserves did not exceed 18 kg/m². The fluctuations in the humus reserves in the past were not higher than 30% as compared to the recent reference soils. They were most actively replenished from the 1st to the 8th centuries A.D., and the rate of this process reached 0.5 kg/m² for 100 years. In the same period, the thickness of the layer with the humus content above 1% drastically increased. The illuviation of peptized organic matter and its further bioturbation upon the development of the solonetzic process had the greatest importance in the formation of the lower part of the humus profiles.     

Soil development on the Crimean Peninsula in the Late Holocene

The study of soils of different ages in different physiographic regions of the Crimean Peninsula made it possible to reveal the main regularities of pedogenesis in the Late Holocene (in the past 2800 years). With respect to the average rate of the development of soil humus horizons, the main types of soils in the studied region were arranged into the following sequence: southern chernozems and dark chestnut soils > mountainous forest brown soils > gravelly cinnamonic soils. In the newly formed soils, the accumulation of humus developed at a higher rate than the increase in the thickness of humus horizons. A sharp decrease in the rates of development of soil humus profiles and humus accumulation took place in the soils with the age of 1100-1200 years. The possibility for assessing the impact of climate changes on the pedogenetic process on the basis of instrumental meteorological data was shown. The potential centennial fluctuations of the climate in the Holocene determined the possibility of pulsating shifts of soil-geographic subzones within the steppe part of the Crimea with considerable changes in the rates of the development of soil humus horizons in comparison with those in the Late Holocene.     

Light Gray Surface-Gleyed Loamy Sandy Soils of the Northern Part of Tambov Plain: Agroecology,Properties, and Diagnostics

Light gray soils of Tambov oblast mainly develop from sandy and loamy sandy parent materials; these are the least studied soils in this region. Despite their coarse texture, these soils are subjected to surface waterlogging. They are stronger affected by the agrogenic degradation in comparison with chernozems and dark gray soils. Morphology, major elements of water regime, physical properties, and productivity of loamy sandy light gray soils with different degrees of gleyzation have been studied in the northern part of Tambov Plain in order to substantiate the appropriate methods of their management. The texture of these soils changes at the depth of 70–100 cm. The upper part is enriched in silt particles (16–30%); in the lower part, the sand content reaches 80–85%. In the nongleyed variants, middle-profile horizons contain thin iron-cemented lamellae (pseudofibers); in surface-gleyed variants, iron nodules are present in the humus horizon. The removal of clay from the humus horizon and its accumulation at the lithological contact and in pseudofibers promote surface subsidence and formation of microlows in the years with moderate and intense winter precipitation. The low range of active moisture favors desiccation of the upper horizons to the wilting point in dry years. The yield of cereal crops reaches 3.5–4.5 t/ha in the years with high and moderate summer precipitation on nongleyed and slightly gleyed light gray soils and decreases by 20–50% on strongly gleyed light gray soils. On light gray soils without irrigation, crop yields are unstable, and productivity of pastures is low. High yields of cereals and vegetables can be obtained on irrigated soils. In this case, local drainage measures should be applied to microlows; liming can be recommended to improve soil productivity.     

Radiometric Study of Soil Profiles in the Infrared Band

The applicability of radiometric survey of soil profiles in the infrared range for the analysis of soil physical properties was studied. Radiometric data were obtained for different dates of the growing season for a number of soil profiles. The specificity of temperature profiles of texture-differentiated soils (Luvisols and Retisols) as related to weather conditions of the growing season was examined. The correlation analysis showed a close relationship between the air and surface soil temperatures and between the radiometric and thermodynamic soil temperatures in the upper 10 cm. In the studied profiles, the gradient of radiometric temperatures reached 0.5–0.8°C/cm in the humus horizons and sharply decreased at the depth of more than 15–20 cm. The gradient analysis of radiometric images made it possible to outline the boundaries of soil horizons. For the texture-differentiated soils, the most distinct boundaries were established between the gray-humus AY horizon and the underlying eluvial EL horizon in podzolic soils and between the AY horizon and the underlying humus-eluvial AEL horizon in gray soils.     

Changes in soil properties at different levels of soil structural arrangement under the impact of irrigation

Processes taking place at different levels of the soil structural arrangement in irrigated and rainfed soils of the Lower Volga region are analyzed. Interactions between these processes and the dependence of their rates on the duration of irrigation are discussed. It is shown that irrigation-induced changes are more pronounced and proceed faster in soils of poorly drained landscapes in comparison with well-drained landscapes. Interaction of the processes taking place at different hierarchical levels of soil arrangement is observed. At the ionic-molecular level, migration and transformation of the composition of soil humus and soluble salts and various exchange reactions take place; at the level of elementary soil particles, the processes of disintegration, peptization, transformation, and the destruction of minerals; at the aggregate level, changes in the water stability of soil aggregates and the degree of soil micro- and macroaggregation; at the level of particular morphological elements, horizons, and pedons, reorganization of soil material (changes in the thickness and bulk density of soil horizons, synthesis and destruction of various neoformations, etc.); finally, at the level of the soil cover pattern, irrigation leads to a higher complexity of the soil cover; the degree of contrast in the soil cover pattern increases, and the soil development at different sites proceeds with different velocities.     

Postpyrogenic Polycyclic Soils in the Forests of Yakutia and Transbaikal region

Periodical forest fires are typical natural events under the environmental and climatic conditions of central and southern Yakutia and Transbaikal region of Russia. Strong surface fires activate exogenous geomorphological processes. As a result, soils with polycyclic profiles are developed in the trans-accumulative landscape positions. These soils are specified by the presence of two–three buried humus horizons with abundant charcoal under the modern humus horizon. This indicates that these soils have been subjected to two–three cycles of zonal pedogenesis during their development. The buried pyrogenic humus horizons accumulate are enriched in humus; nitrogen; total and oxalate-extractable iron; exchangeable bases (Са⁺² and Mg⁺²); and the fractions of coarse silt, physical clay (<0.01 mm), and clay (<0.001 mm) particles in comparison with the neighboring mineral horizons of the soil profile. The humus of buried pyrogenic horizons is characterized by the increased content of humic acids, particularly, those bound with mobile sesquioxides (HA-1) and calcium (HA-2) and by certain changes in the type of humus.     

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.     

Radiocarbon pollution and self-purification of humus in chernozems of the East-European plain in 1900–2008

The dynamics of the ¹⁴C content in the humus of chernozems in 1900?C2008 are considered. The elevated ¹⁴C content in the atmosphere because of nuclear weapons tests has led to the contamination of humus with bomb radiocarbon. In 1966?C1968, the ¹⁴C reserves in the profiles of chernozems exceeded the background ones by 15%; in 1978, by 12%; and, in 1998, by 2%. By the year of 2008, its reserves became equal to the background ones. The ¹⁴C distribution along the soil profiles changed. By 1978, the 0- to 30-cm-thick soil layer became free from radiocarbon due to its self-purification; however, at depths of 40?C70 and 100?C115 cm, its weak accumulation was registered. By 2008, the whole soil profile was free from ¹⁴C. The main mechanism of the soil self-purification from radiocarbon is suggested to be the constant substitution of fragments of humus compound structures for those of fresh organic matter entering the soils with the ¹⁴C content being in equilibrium with the atmospheric one, i.e., due to the renewal of the carbon in the humus. The rate of the carbon renewal and its migration in the soils are assed based on the ¹⁴C concentrations in the humus.     

Soils of the loess region in China

The loess region of northwestern China is located in the middle reaches of the Huanghe River and is mostly composed of the loess plateau. The region has a loess cover largely ranging in thickness from 30 to 80 m. Main broad groups of soils formed in loess are the heilu soils, huangmian soils, lou soils, sierozem, castanozem, and drab soils. Distribution of the soils tends to parallel that of climate but is also affected by topography and past farming practices. All soils are calcareous to the surface, a reflection of the semiarid and arid climates. Calcic horizons are well expressed in sierozems, evident in castanozems and drab soils and not clearly defined in heilu soils. Average thickness of the surface, humus layer ranges from 30 cm in sierozems to 100 cm in heilu soils. The lou soils are distinctive in having one humus layer at the surface due to additions of earthy manure during long periods of cultivation plus a deeper humus layer from the original drab soil profile. Clay distribution curves show a distinct maximum in drab soil profiles and slight or no maxima in the others.Water is limiting for plant growth over most of the region, although drought hazards become progressively greater from southeast to northwest. In the middle of the region and for some distance to the northwest, cultivation must include fallowing during summers or for entire years to store water for crops. Further to the northwest, layers of sand about 10 cm thick are spread over fields to increase infiltration and reduce moisture losses. In the extreme northwestern part, crops are not grown and the soils are in meadow for grazing livestock.Amounts of nutrient elements in the soils have a rather wide range. Nitrogen is deficient generally and must be added for successful production. Biological fixation of the element by legumes is the most effective method of adding the element. Total phosphorus is not low but available forms are; phosphorus fertilization increases crop yields. Potassium supplies are currently adequate in the soils. Amounts of zinc, manganese, boron, copper and molybdenum in available forms seem to be low in many soils but their applications are limited.     

The effects of agricultural use on the structure and physical properties of three soil types

This investigation was carried out to determine the influence of the use of soils on their morphological structure and properties. Three soil types (i.e. Haplic Phaeozem derived from loess, Orthic Luvisol derived from loess and Orthic Luvisol derived from sandy loam) were involved. In each soil unit, profiles lying at a small distance from one another were taken for detailed examination. The main difference between the soils within each unit was the use to which they were put. The following soils were selected for evaluation: (A) soil from natural forest habitat; (B) soil cultivated in farms with a very low level of mechanisation; (C) soil cultivated in farms which had been completely mechanised for many years; (D) soil used for many years in a vegetable garden, similar to hortisol.

In the selected profiles the morphological features, soil structure in all genetic horizons, granulometric composition, humus content, pH, density, air and water capacity and air permeability were analysed.

It was found that the transition from forest soil management to agricultural use leads not only to the formation of an arable-humus horizon and to changes in structure but also to changes of the physico-chemical properties of soils. Soils under agricultural use manifest a lower level of acidification than forest soils, as well as a different distribution of organic matter. In all agricultural soils, increased compaction of humus horizons was observed, compared with the corresponding horizons of forest soils, as well as changes in other physical features. The use of heavy machines over many years in field operations results in increased density of the soil and deterioration of soil structure. This effect is greater in soils with low colloids and organic matter contents.     

Assessment and prediction of changes in the reserves of organic carbon in abandoned soils of European Russia in 1990–2020

Experimental studies and the analysis of published data have shown that carbon reserves in soils generally increase upon soil exclusion from agricultural use. The rate of carbon accumulation in the abandoned soils depends on the soil type, the time elapsed since the soil abandoning (the restoration period), and the thickness of the layer for which the rate of carbon accumulation is determined. For the upper 20-cm-thick layer, it varies from 66 to 175 g C/m² per year in dependence on the type of soil and averages 111 g C/m² per year. The highest rate is typical of the first 10–15 years of soil restoration. According to our calculations, the carbon sequestration in the upper 20-cm-thick layer of Russian soils due to changes in land use was 184–673 Mt C in 1990–2005 and may reach 282–1030 Mt C by 2020.     

Erosion resistance of irrigated soils in the republic of Azerbaijan

It was found that the average size of water-stable aggregates in irrigated soils varies in the range 0.23–2.0 mm, and the eroding flow velocity is 0.03–0.12 m/s. A five-point scale was used for assessing erosion resistance, predicting irrigation erosion, and developing erosion control measures on irrigated soils. According to this system, gray-brown soils and light sierozems were classified as the least erosion-resistant, sierozemic and meadow-sierozemic soils as low erosion-resistant, gray-cinnamonic soils as moderately erosion-resistant, mountain gray-cinnamonic soils as highly erosion-resistant, and steppe mountain cinnamonic soils as very highly erosion-resistant ones. The determination of the erosion resistance of soils is of great importance for assessing the erosion-resistance potential of irrigated areas and developing erosion control measures.     

Microbial biomass carbon in the profiles of forest soils of the southern taiga zone

In the mineral horizons of the soils under different southern taiga forests (oak, archangel spruce, and aspen in the Kaluzhskie Zaseki Reserve of Kaluga region and the green moss spruce and spruce-broadleaved forests of the Zvenigorod Biological Station of Moscow State University in Moscow region), the carbon content in the microbial biomass (C_mic), the rate of the basal respiration (BR), and the specific microbial respiration (qCO₂= BR/C_mic) were determined. The C_mic content was measured using the method of substrate-induced respiration (SIR). In the upper humus horizons of the soils, the C_mic content amounted to 762–2545 μg/g and the BR ranged from 1.59 to 7.55 μg CO₂-C/g per h. The values of these parameters essentially decreased down the soil profiles. The portion of C_mic in the organic carbon of the humus horizons of the forest soils was 4.4 to 13.2%. The qCO₂values increased with the depth in the soils of the Biological Station and did not change in the soils of the Reserve. The pool of C_mic and C_org and the microbial production of CO₂ (BR) within the forest soil profiles are presented.     

Morphometric profiles of pore space in loamy soils of the forest and steppe zones of European Russia

A computer-based image analysis of vertically oriented thin sections was applied to study changes in the shape and orientation of fine soil macropores (d = 0.2−2.0 mm) in the profiles of soddy-podzolic soils and typical (migrational-mycelial) chernozems. Generalization of the obtained morphometric data was based on the theory of mereology, a scientific discipline studying the structure (part-whole relationships) of classified objects. As a first approximation, generalized data characterized archetypes of morphometric porespace profiles of the studied soils. The archetype of the pore-space profile of the soddy-podzolic soil consists of four components (meronyms) corresponding to the humus-accumulative, eluvial, textural (clay-illuvial), and transitional to the parent material (BC) horizons. Sharp boundaries between the upper horizons specify sharp changes in the studied meronomic indices of the shape and orientation of soil pores. The pore-space profile of the migrational-mycelial chernozem consists of two major components: specific pores in the granular dark-humus (AU) horizon and complex pore space of the BCA and BCca horizons that are poorly differentiated with respect to the shape and orientation of their fine macropores despite clear genetic differences between these horizons. Pore-space patterns in the lower (transitional to the parent material) horizons of the studied soils are characterized by the high degree of similarity (>75%). Pore-space patterns in the upper horizons of the studied soils are different; the level of their similarity does not exceed 24–41.5%. The results obtained in this study hold promise in the use of morphometric characteristics of the pore space in separate genetic soil horizons as meronyms composing archetypes of the pore-space profiles of different soils. Such archetypes may be used for diagnostic purposes as reference pore-space profiles of the particular types of soils.     

灌溉方式对设施土壤总有机碳及其腐殖质组分的影响

通过13年连续的番茄栽培灌溉试验,分析了沟灌、滴灌和渗灌3种灌溉处理0—80cm土层土壤有机碳及其腐殖质组分(胡敏酸、富里酸、胡敏素等)含量,探讨了不同灌溉方法对温室土壤有机质变化的影响。结果表明:3种灌溉处理土壤总有机碳、腐殖质各组分含量剖面变化特征一致,均随土层加深而降低,且这一变化主要集中在0—50cm土层,50—80cm土层变化较小。土壤总有机碳及其组分各灌溉处理间差异明显,将土壤剖面分为0—20,20—80cm上、下2个层次,总体上总有机碳含量上层为渗灌沟灌滴灌,下层滴灌沟灌渗灌;腐殖酸含量上层滴灌沟灌渗灌,下层为渗灌滴灌沟灌;胡敏素上层为沟灌滴灌渗灌,下层为渗灌滴灌沟灌。滴灌处理既能使0—40cm土层土壤有机碳含量保持较高水平,土壤腐殖质含量又高于沟灌、渗灌处理,这对于提升设施土壤肥力水平、保证番茄养分供应是有利的。     

Changes in the physical properties of soils in the Kamennaya Steppe under the impact of shelterbelts

The physical properties of ordinary chernozems and meadow-chernozemic soils under different land management practices (maple, larch, birch, and pine sections of the shelterbelts; continuous (since 1959) fallow; and arable field (since 1952)) were studied in the Kamennaya Steppe. The soils had favorable physicochemical properties, light clayey texture, and high microaggregation independently from the type of land management. The long-term impact of the shelterbelts improved the soil structure in the upper part of the humus horizon: the content of agronomically valuable aggregates increased, the content of coarse aggregates (>10 mm) decreased, the aggregation coefficient increased by 3.7–4.3 times, and the water stability of the aggregates became by 8–12% higher. The soils under the shelterbelts were characterized by minimum values of the bulk density and solid phase density and by maximum values of the total, active, and air porosities. At the same time, no considerable differences between water reserves in the studied range of soils were detected. The ratio of the optimum productive water range to the active (productive) water range (OPWR/AWR) within the upper soil meter varied from 0.42–0.44 to 0.45–0.54. This points to changes in the character of perched water: the content of intra-aggregate capillary-perched water decreases, and content of film perched water increases down the soil profile.     

Mercury in humus horizons of soils in the Transbaikal region

The total mercury content has been determined in gray forest soils, chernozems, chestnut soils, and in different parent materials in the Transbaikal region. The mercury content is below the clarke value in the intrusive, effusive, and alluvial soil-forming rocks (0.004–0.024 mg/kg). In the humus horizons of the soils, it reaches 0.011–0.026 mg/kg, which is higher than the clarke value for the pedosphere. The mean background content of mercury in the soils of the Transbaikal region is 0.018 mg/kg. No significant positive correlation between the mercury content and the humus content of the soils has been revealed.