For the test monitoring site on the territory of the Oroshaemaya Experimental Station in the south of the Volga Upland (Volgograd oblast, Russia), the estimates of the baseline contents and stocks of soil organic carbon (Corg) and soil bulk density and characteristics of their spatial variability and vertical distribution patterns within the upper 40 cm encompassing the entire humus layer are presented. The specified indicators characterize arable land in crop rotation under dry and irrigated farming practices and a 50-year-old fallow at seven dynamic monitoring plots with light chestnut soils. The studied soils have two types of profile horizonation: P–BMK–BCAnc (agrochestnut soils) and Pca–BCAnc (carbonate-accumulative agrozems); they are silty loamy and develop from yellowish brown sandy silt loams. In the WRB system, they are classified as Haplic Kastanozems (Loamic, Aric). The map of the coefficients of multitemporal soil line, retrospective analysis of remote sensing data for 40 years, and the results of field soil survey have been used to select the monitoring plots. Each plot 30 × 30 m includes nine individual sampling points, at which soil sampling from thin (5 or 10 cm) layers has been performed to a depth of 40 cm. The coefficient of spatial variation in the Corg content increases from 5–10 to 30–40

The aim of this study is to present data on the salinity status of soils, sediments, and groundwater on irrigated rice fields of the Karkinit Lowland in Krasnoperekopskii district of Crimea in 2015–2018, 2–5 years after the irrigation stopped. Most of solonetzic microcatenas were transformed into rice paddies and irrigated by flooding during half a century; as a result, the soils were leached from soluble salts to a depth of 3–3.5 m. In 2015–2018, the groundwater table dropped below the critical level. Since 2017, a depression cone of the groundwater table has been formed at the seashore. This area is under the impact of seawater head of up to 0.8–1.1 m. The occurrence frequency of horizons with clusters of fine-grained gypsum crystals has increased in the vadose zone, and slight salinity has restored in sediments of the depression cone at a depth of 3.5–4.5 m. In rice paddies elevated by less than 2 m above seas level, the contents of soluble salts exceeded the low limit of slight salinity in the middle and deep parts of soil profiles on the fifth year after the cessation of irrigation. The maximum of soluble salts in the profile is accompanied by the appearance of calcium and magnesium chlorides in pore solutions and by the accumulation of fine gypsum grains (farinaceous gypsum).

The aim of the article is to submit data about ground water table and soil salinity of the rice irrigated systems at the Sivash seashore in Nyzhnegorsky district of Crimea in 2017–2018 which is 4–5 years from irrigation cease. It was found that many soil cover patterns with salt-affected solonetz at the rice system were leached from salts to the depth about 3–3.5 m by flooding irrigation during half a century. In 2017–2018 ground water tables were deeper than the critical depth. Ground water mineralization is characterized by mosaic spatial distribution, varying from 1.9 to 7.4 g/l with a tendency to growth as ground water depth increases. Depression funnel of ground water table was formed at the seashore. The bottom water drive is up to 0.8–1.6 m relatively sea level. The first symptoms of the salinity returning in grounds of vadose zone were found: (1) appearance of calcium and magnesium chlorides in pore solutions of formally no saline or weakly saline horizons; (2) increasing trend of sodium and chloride ion activity measured in pastes with moisture 50% (w) at the dynamic plots in 2018 as compared with 2017; (3) frequency of grounds with clustered gypsum crystals is increased.

Statistical cumulative distributions of indices for shrinkage curve of 324 monoliths from Vertisols and Vertic Solonetzes are created. Natric and vertic horizons have similar range of shrinkage indices, with that natric ones have higher values of pore volume weakly changed during water evaporation and lower bulk density at shrinkage limit.

A specific swelling clayey strongly alkaline soil with gilgai microtopography is characterized. The profile of this soil displays diagnostic features of both Solonetzes and Vertisols. In the Russian soil classification system, it is classified as a crusty quasigley slitic (vertic) sulfate–sodic clayey dark solonetz. In the WRB-2015 system, it can be defined as a Nudinatric Vertic Stagnic Protosalic Solonetz (Clayic, Columnic, Cutanic, Humic, Hypernatric). The area with this soil is found on the northern spurs of the Kalach Upland in the Kamennaya Steppe (Talovskii district of Voronezh oblast). Data on the particle-size distribution, soil density, composition of extracts from water-saturated pastes, and the content of exchangeable cations in the soil profile are analyzed. The 2D distribution of the morphological features indicated by symbols of the soil diagnostic horizons and features is presented. Data on the contents of organic carbon and calcium carbonates; the activities of sodium, calcium, and chloride ions and their ratios; the contents of oxalate- and dithionite-soluble iron compounds and their ratios, and the swelling capacity of ground samples are also presented. Three levels of morphologically manifested deformation structures are identified in the soil profile. Their impact on the spatial distribution of the physical and chemical properties is discussed.

Data on the morphology and radiocarbon ages of humus of dark vertic quasigley nonsaline clayey soils with alternating bowl-shaped (Pellic Vertisols (Humic, Stagnic)) and diapiric (Haplic Vertisols (Stagnic, Protocalcic)) structures are discussed, and the genetic concept for these soils is suggested. The studied soils develop on loesslike medium clay in the bottom of a large closed depression on the Eisk Peninsula in the lowest western part of the Kuban–Azov Lowland. The lateral and vertical distribution of humus in the studied gilgai catena displays a lateral transition of a relatively short humus profile of the accumulative type with a maximum near the surface and with a sharp increase in 14 C dates of humus in the deeper layers within the diapiric structure to the extremely deep humus profile with a maximum at the depth of 40–80 cm, with similar mean residence time of carbon within this maximum, and with a three times slower increase in 14 C dates of humus down the profile within the bowl-shaped structure. The development of the gilgai soil combination is specified by the joint action of the lateral–upward squeezing of the material of the lower horizons from the nodes with an increased horizontal stress toward the zones a decreased horizontal stress, local erosional loss of soil material from the microhighs and its accumulation in the adjacent microlows, leaching of carbonates from the humus horizons in the microlows, and the vertical and lateral ascending capillary migration of the soil solutions with precipitation of calcium carbonates in the soils of microhighs.

Five variants of the distribution of clay (<0.001 mm) and physical clay (<0.01 mm) fractions along the vertical profiles of Vertisols (slitozems) and vertic soils (slitic subtypes of different soil types) from the European part of Russia are distinguished: (1) accumulative, (2) even, (3) regressive, (4) with a maximum in the middle-profile horizon and with their approximately equal contents in the upper and the lower horizons, and (5) eluvial–illuvial. These distribution patterns are related to the lithological specificity of sedimentation and formation of parent materials composed of swelling clays of different geneses and ages. Solonetzic, eluvial- gley, and solodic processes contribute to the development of the eluvial–illuvial and, partly, regressive variants of clay distribution. All the five variants with a predominance of the even distribution pattern can be found in Vertisols. Most of Vertisols in the European part of Russia have a medium clayey or a heavy clayey texture in the entire profile. The regressive distribution pattern is typical of the group of vertic soils. In the upper horizons of Vertisols, where slickensides do not form, the texture is usually heavier than that in the analogous horizons of vertic soils. The middle-profile and lower horizons with slickensides have similar statistical distributions of particle-size fractions in Vertisols proper and in vertic soils. However, in Vertisols, a tendency for a more frequent occurrence of the soils with a higher content of the clay fraction and with a higher portion of this fraction in the physical clay fraction is observed (as compared with the vertic soils).

Properties and mineralogy of fine fractions separated from agrochernozems forming a three-component noncontrasting soil combination in the Kamennaya Steppe have been characterized. The soil cover consists of zooturbated (Haplic Chernozems (Clayic, Aric, Pachic, Calcaric)), migrational-mycelial (Haplic Chernozems (Clayic, Aric, Pachic)), and clay-illuvial (Luvic Chernozems (Clayic, Aric, Pachic)) agrochernozems. All the soils are deeply quasi-gleyed because of periodical groundwater rise. The mineralogy of the fraction <1μm includes irregular mica–smectite interstratifications, di- and trioctahedral hydromicas, imperfect kaolinite, and magnesium–iron chlorite. The profile distribution of these minerals slightly varies depending on the subtype of spot-forming soils. A uniform distribution of clay minerals is observed in zooturbated agrochernozem; a poorly manifested eluvial–illuvial distribution of the smectite phase is observed in the clay-illuvial agrochernozem. The fractions of fine (1–5 μm) and medium (5–10 μm) silt consist of quartz, micas, potassium feldspars, plagioclases, kaolinite, and chlorite. There is no dominant mineral, because the share of each mineral is lower than 35–45%. The silt fractions differ in the quartz-to-mica ratio. The medium silt fraction contains more quartz, and the fine silt fraction contains more micas.

Under description is a profile configuration represented by stratified bowllike morphostructures with the increased thickness of darkgray humus horizons and diaperlike morphostructures consisted of the olive-brown material ascending from the lower horizons in Vertisols developed on the bottom of a huge closed depression (padi) in Eisk peninsula. Histograms are presented to show statistic distribution and non-parametric statistic indices for morphometric characteristics of the above morphostructures. The statistic relationship between the morphometric indices is estimated. Under discussion is also the genesis of such morphostructures in Vertisols.

В почвах Кубано-Приазовской низменности, которые на почвенных картах выделены под названием “слитые” и “уплотненные”, установлено наличие диагностических признаков, используемых для идентификации типа темных слитых почв и подтипов слитизированных почв по классификации почв России, а также реферативной почвенной группе (РПГ) Vertisols и почв других групп с главным квалификатором (principal qualifier) Vertic по WRB: поверхностей скольжения (сликенсайдов) и клиновидной структуры на фоне глинистого гранулометрического состава всего почвенного профиля и образования трещин усадки при высыхании. Установлено, что темные слитые квазиглеевые почвы (Vertisols по WRB) встречаются в центральной части днища обширных (длина большой оси более 1.5 км) замкнутых понижений (падей). Гумусово-квазиглеевые слитизированные почвы (Vertic Stagnic Phaeozems (Clayic, Pachic)) приурочены к периферии днищ падей и к днищам замкнутых понижений с длиной большой оси 0.8–1.5 км. Гумусово-квазиглеевые глубокослитизированные почвы и черноземы глинисто-иллювиальные глубокослитизированные (Bathyvertic Stagnic Phaeozems (Clayic, Pachic)), в которых верхняя граница появления поверхностей скольжения (сликенсайдов) наблюдается на глубине от 100 до 200 см, обычно встречаются по периферии замкнутых понижений среднего размера, в днищах замкнутых понижений с длиной большой оси менее 0.6–0.8 км и в днищах и на склонах неглубоких балок. На Кубано-Приазовской низменности выделено 8 почвенных районов по распространению вертисолей и вертиковых почв. В пяти из них указанные почвы занимают от 0.1 до 12.1% площади района.

The soils shown on Russian soil maps of the Kuban-Azov Lowland under the names of slitic (vertic) and compacted soils contain diagnostic features characteristic of the type of dark slitozems and subtypes of slitic soils in the new Russian soil classification system, or Vertisols and Vertic soils in the WRB system. These are slickensides, wedge-shaped structure, clayey texture through the entire soil profile, and shrinkage cracks formed during soil drying. It was found that dark quasi-gley slitozems (Vertisols) occur in the central parts of the bottoms of large (> 1.5 km along the longest axis) closed depressions. Humus quasi-gley slitozems (Vertic Stagnic Phaeozems (Clayic, Pachic)) are confined to the peripheral parts of the bottoms of these depressions and to the bottoms of smaller (0.8–1.5 km) closed depressions. Deeply slitic humus—quasi-gley soils and deeply slitic clay-illuvial chernozems (Bathyvertic Stagnic Phaeozems (Clayic, Pachic)), in which the upper boundary of slickensides is found at the depths from 100 to 200 cm, usually occur in the bottoms of closed depressions with the longest axis of less than 0.6–0.8 km and in the bottoms and on slopes of shallow flat-bottomed ravines. With respect to the distribution of Vertisols and Vertic soils, the Kuban-Azov Lowland can be subdivided into eight soil districts. In five of them, these soils occupy from 0.1% to 12.1% of the territory.

In addition to the earlier known vertic alluvial soils (slitozems) of the Volga-Akhtuba floodplain, 44 new areas of Vertisols and vertic soils (according to the WRB), or dark slitozems (according to the new Russian soil classification system), have been found in the Middle and Lower Volga regions from the forest-steppe to the semidesert zones. Though these soils occupy relatively small areas, they are regularly found in the studied regions. Vertisols developed from the clayey alluvial sediments occur in widened parts of the central floodplain in the areas of strong meandering of the river downstream from the areas, where it washes out ancient swelling clay sediments. Many areas of Vertisols and vertic soils are confined to the second Khvalyn terrace of the Volga River composed of the chocolate-brown swelling Khvalyn clay. These soils do not occupy the entire terrace. They have an insular-type distribution and highly diverse in their properties. In the soils developed from the eluvium of the microlayered chocolate-brown marine clay within the Privolzhskaya Upland, vertic features are absent. The destruction of the lithogenic layering in the course of the redeposition of the marine clay with the formation of the new Quaternary clayey sediments creates conditions for the development of vertic soils. The northernmost area of Vertisols proper has been found in the area of the Samara Arc (53.231° N, 049.322° E). The soils with vertic features have been found in Mordovia and Samara oblast even further to the north (up to 54.2° N). Morphometric data on the slickensides, wedge-shaped structure, and depth of the soil cracking are presented.

На территории Среднего и Нижнего Поволжья в дополнение к известным аллювиальным слитым почвам Волго-Ахтубинской поймы выявлено 44 новых ареала вертисолей и вертиковых почв по WRB или темных слитых и слитизированных почв по Российской классификации в различных ландшафтных условиях от полупустыни до лесостепи. В Поволжье рассматриваемые почвы являются редкими, но встречаются регулярно. Вертисоли на аллювиальных глинистых отложениях приурочены к расширениям центральной поймы на участках сильного меандрирования русла реки, выше по течению которых река размывает более древние осадки набухающих глин. Много ареалов вертисолей и вертиковых почв обнаружено на шоколадных глинах второй хвалынской террасы Волги. Они не занимают всю поверхность террасы и отличаются разнообразием в силу неоднородности шоколадных глин и особенностей их островного распространения. В почвах, развитых на элювии микрослоистых набухающих глин морского происхождения, распространенных на Приволжской возвышенности, признаки вертигенеза отсутствуют. Устранение исходной микрослоистости в ходе переотложения этих пород и формирования из их материала четвертичных глинистых отложений создает предпосылки для развития вертигенеза в почвах в новых условиях. Наиболее северный ареал собственно вертисолей найден на Самарской Луке (53.231° с.ш., 049.322° в.д.). Ареалы вертиковых почв обнаружены еще севернее в Мордовии и Самарской обл. на северной широте около 54.2°. Представлены морфометрические показатели поверхностей скольжения, клиновидной структуры и глубины проникновения трещин в изученных почвах.

The most spread are soils with vertic properties at the territory of Kamennaya Steppe (Voronezh region, Talovsky district) being confined to four landscape positions within 11 different soil combinations derived from clayey or two-layered heavy loam-clayey parent materials. These soils have developed: (A) on bottoms of deep and closed depressions covered by spotted soil combinations in flat watersheds; (B) on some depression bottoms in spotted combinations without solonetzic soils; (C) in different relief elements occupied by chernozemic hydromorphic solonetz complexes and (D) in concave (in long and cross directions) relief elements in the topolithomosaic composition confined to exposed re-deposition products of Dnieper moraine on the slope of Talovaya narrow. Occupying only 0.2% from the total area of agro-forest landscapes, the vertic soils can account for 0.7% to 15% within a separate soil combination and reveal a great diversity. The latter is associated with vertic properties developed together with features of gleying and quasi-gleying, accumulation of calcium carbonates and, on the contrary, clay illuviation against the background of calcium carbonate leaching, solonetz process, salinization, humus formation and the topsoil eluviations. Such a diversity may be adequately reflected both in the soil classification of Russia and in WRB.