The soil diversity of coastal depressions of pulsating highly mineralized chloride lakes of the Uldza–Torey closed basin (on the example of the Lake Babie) within the Southeastern Transbaikalia area was studied. It has been established that 3 main soil types dominate: quasigley solonchaks, saline humus-quasigley soils and light-humus saline soils. The soils under study, especially the quasigley solonchaks, are characterized by unfavorable physicochemical and agrochemical properties and a high degree of salinity in most horizons with the excessive content of Na+ and Cl– toxic ions. Very high concentrations of N, Ca, Mg, S, and Na+ and Cl– ions were revealed in the upper saline layer (0–5 cm) of the quasigley solonchaks. A low content of the most important nutritional elements, including nitrogen and phosphorus available for plants was defined mainly in soils studied, so as biogenic microelements in humus-quasigley saline and light humus saline soils. Therefore, these soils have an extremely low level of both potential and effective fertility based on the agrochemical assessment of their production ability. When considering the ecological uniqueness and medicinal value of the lake and its lakeside ecosystems, it is recommended to exclude these soils and land resources from agricultural practice. They must be used in the form of specially protected natural landscape components as a part of reproduction areas, nature reserves, territories of medical and balneological resorts and other health care facilities.

Впервые проведены комплексные исследования почв, растительного покрова и микробиоты прибрежных понижений высокоминерализованных бессточных хлоридных озер юго-восточного Забайкалья (Даурия, оз. Бабье). Выявлено, что формирование приозерных экосистем степной зоны связано с циклическими изменениями уровня озер и происходящей при этом смене химического состава. Определенное влияние оказывает эоловый фактор. Исследованы динамические свойства и вещественный состав почв супераквально-субаквальных, супераквальных и элювиально-супераквальных позиций, выявлено проявление на них современного континентального засоления различного химизма и гидрогенного окарбоначивания. Изучение пространственной структуры фитоценозов и их видового состава в зависимости от их рельефного расположения в приозерных понижениях, почвенных условий и галогенеза показало приуроченность пионерных гипергалофитных и галофитных сообществ к солончакам квазиглеевым. На супераквальной части приозерного понижения произрастают растительные сообщества с преобладанием галофитов и мезофитов с участием гликоолигогалофитов и мезоксерофитов. На светлогумусовых почвах сформирована ковыльно-разнотравно-вострецовая (Leymus chinensis, Artemisia frifida, Bupleurum bicaule, Stipa krylovi) степь с участием мезофитов и ксерофитов, близкая по составу к зональным степям. Установлено, что в динамически эволюционирующих приозерных почвах в зависимости от абиотических факторов формируются различные микробобиоморфные комплексы. Высокоминерализованные хлоридные озерные воды способствуют образованию близких микробных сообществ в донных осадках оз. Бабье и сильнозасоленных горизонтах солончака квазиглеевого. При этом во всех почвенных образцах обнаружена большая доля неклассифицируемых прокариот. Этот важный неизученный микробный компонент представлен на уровне домена Bacteriaв солончаках (до 22 %), гумусово-квазиглеевой засоленной (до 15 %) и светло-гумусовой засоленной (до 16 %) почвах. Структура микробиома в гумусово-квазиглеевой почве характеризуется присутствуем галобактерий и кренархеот. В светлогумусовой засоленной почве установлена значительная доля таксонов, участвующих в круговоротах углерода и азота и играющих важную роль в глобальных биогеохимических циклах. Также в этом типе почв выявлено отсутствие галобактерий, что связано с незначительным содержанием легкорастворимых солей в гумусовом и переходном горизонтах. Complex studies of soils, vegetation cover, and microbiota of coastal depressions of highly mineralized drainless chloride lakes in Southeastern Transbaikal Region (Dauria, Lake Babie) were performed for the first time. It was revealed that the lakeside ecosystems formed within the steppe zone under cyclic changes in the level of lakes and the resulting change in the lake water chemical composition. The eolian factor has a certain influence. The dynamic properties and material composition of soils of superaqueous-subaqueous, superaqueous, and eluvial-superaqueous positions have been studied. Current continental salinization of various chemistry and hydrogenous carbonization has been revealed there. The study of the spatial structure of phytocenoses and their species composition, depending on relief location in lakeside depressions, soil conditions and halogenesis revealed the confinement of pioneer hyperhalophytic and halophytic communities to quasigley solonchaks. Within the superaquatic part of the lakeside depression, plant communities grow with a predominance of halophytes and mesophytes with the participation of glyco-oligohalophytes and mesoxerophytes. The feather-grass-forb-leymus (Leymus chinensis, Artemisia frifida, Bupleurum bicaule, Stipa krylovi) steppe was formed on the light-humus soils, similar in composition to zonal steppes, with the presence of mesophytes and xerophytes. Various microbiomorphic complexes have been established to be in dynamically evolving lakeside soils, depending on abiotic factors. Highly mineralized chloride lake waters contribute to forming of similar microbial communities in the bottom sediments of the Lake Babie and highly saline horizons of the quasigley solonchak. At the same time, a large proportion of unclassified prokaryotes were found in all soil samples. This important unstudied microbial component is present at the level of the Bacteria domain in solonchaks (up to 22 %), saline humus-quasigley (up to 15 %), and light-humus saline (up to 16 %) soils. The microbiome structure in humus-quasigley soil is characterized by the presence of halobacteria and krenarcheotes. A significant proportion of taxa involved in carbon and nitrogen cycles, and play an important role in global biogeochemical cycles, have been established in light-humus saline soil. Also, halobacteria were no revealed in this type of soil due to insignificant content of easily soluble salts in the humus and transitional horizons.

It was found that low humus content and low biological activity of virgin chestnut soils of Western Transbaikalia cause a low gross amount of sulfur. The distribution of sulfur along the profile gradually decreases with some accumulation in the carbonate horizon. Prolonged irrigation caused by an increase in humus content and biological activity contributed to an increase in the amount of sulfur, which practically increases with the depth of the profile. The stock of mobile sulfates irrigated in a layer of 0–20 cm was three times higher than in virgin soil (7.3 and 2.4 kg/ha, respectively); it also was 1.3 times higher in the 0–50 cm layer and 2.9 times higher in the 0–100 cm layer. According to the content and reserves of mobile sulfur, chestnut soils in a layer of 0–20 cm are classified as low-income. After 3 years of using increasing doses of sulfur fertilizers (against the background of NPK) for irrigated potatoes, the content of all forms of sulfur in the soil increased depending on the dose size. The following pattern was revealed: the amount of Sorg in the soil and the enrichment of humus with it increased with an increase in the dose and the ratio C : Sorg decreased. A negative sulfur balance was found in the control and in the background versions. The introduction of the lowest dose of S15 has already formed a positive balance, but it is necessary to apply a dose of S30 (against the background of NPK) in compliance with irrigation standards because chestnut soils are depleted of mobile sulfur.

Over the past half century, global warming has become one of humanity’s serious problems, which is accompanied by ecosystem reactions, that is, climate aridization and subsequent desertification of landscapes. In southeastern Transbaikalia (Dauria) and the bordering regions of Mongolia and China, the problem is intensified by regionally occurring cyclical (approximately 30-year) humid (transgressive) and arid (regressive) climate phases. In these territories there are more than 500 drainless salt and brackish lakes of various chemical compositions and varying degrees of mineralization. Naturally, all the ongoing climate changes are clearly reflected in the hydrology and chemical composition of these reservoirs and in the landscapes of lake depressions, including the soil cover. During the regressive climate phase, we conducted studies of the main types of soils in the lakeside depression of the pulsating chloride Lake Bab’e. Their morphology, particle size distribution, physicochemical and other properties, composition, and salinity chemistry were studied for the first time. It has been established that these soils form a genetically related series of saline soils: quasi-gley solonchaks of the chloride type of salinity–humus-quasi-gley saline soils–light humus saline soils. It was revealed that the formation of salt marshes is directly influenced by highly mineralized lake waters. Humus-quasi-gley saline soils formed in superaquatic positions are periodically affected by lake waters and are active only in the humid climate phase. Also, the research results indicated that in humus-quasi-gley and light humus soils, chloride–soda and soda-chloride salinization of the lower horizons was noted. The obtained materials will be necessary for monitoring saline soils and ecosystems of lakeside depressions of cyclically pulsating highly mineralized drainless reservoirs in the transboundary territories of Transbaikalia (Russia), Mongolia, and China during global and regional climate changes.

The soils, vegetation cover, and microbiota of coastal depressions of highly mineralized drainless chloride lakes in southeastern Transbaikalia (Dauria and Lake Bab’e) have been comprehensively studied for the first time. It is revealed that the lakeside ecosystems of the steppe zone are formed under cyclic changes in the level of lakes and the resulting change in the lake water chemical composition. The aeolian factor exerts a certain influence. The dynamic properties and substance composition of soils of superaqual–subaqual, superaqual, and eluvial–superaqual positions have been studied. The current continental salinization of various chemical composition and hydrogenous carbonization has been revealed there. A study of the spatial pattern of phytocenoses and their species composition, depending on location in the relief of lakeside depressions, soil conditions, and halogenesis, shows the allocation of pioneer hyperhalophytic and halophytic communities to quasigley solonchaks. Within the superaquatic part of the lakeside depression, plant communities are predominated by halophytes and mesophytes with the participation of glyco-oligohalophytes and mesoxerophytes. The feather-grass–forb–leymus (Leymus chinensis, Artemisia frifida, Bupleurum bicaule, and Stipa krylovii) steppe with the participation of mesophytes and xerophytes is formed on light-humus soils, similar in composition to zonal steppes. It has been revealed that various microbiomorphic complexes are formed in dynamically evolving lakeside soils, depending on abiotic factors. Highly mineralized chloride lake waters contribute to the formation of similar microbial communities in the bottom sediments of Lake Bab’e and in highly saline horizons of the quasigley solonchak. A large proportion of unidentified prokaryotes has been found in all soil samples. This important unstudied microbial component is present at the level of the Bacteria domain in solonchaks (to 22

The influence of sowing cereal-legume mixtures and application of mineral fertilizers on technozem created after the liquidation of the tailing dump of the Dzhida Tungsten-Molybdenum Works (Republic of Buryatia) on the change of trace element concentrations in plants and formation of sod limiting the spread of pollutants and reducing environmental risks was assessed. The content of total and mobile forms of some trace elements in the upper loamy sand layer of technozem was higher than in the background soil, exceeded the median background for the soils of Transbaikalia and in some cases the maximum permissible concentrations, and was characterized as moderately hazardous by the coefficient of total contamination (Zc = 18.8); the lower loamy layer was nonhazardous (Zc = 4). It was revealed that the application of fertilizers reduced the concentration of trace elements and their accumulation coefficients in plants. According to the intensity of biological uptake, most of the elements in the aboveground phytomass belonged to the group of medium capture; in the underground phytomass, to the group of medium and intense uptake, which indicates its phytostabilization role. Bioproductivity of cereal–legume mixtures in the control was low. Fertilizer application increased the bioproductivity of the mixtures year to the moderate level on the second year and to the high level on the third year; the dense sod layer fixing the surface and contributing to the increase in the soil organic matter content in comparison with its initial amount was formed on the fourth year. The results of this study can be applied in remediation works on overburden dumps with the creation of technozems for phytostabilization and initiation of organic matter accumulation in these soils by sowing high-yielding perennial herbs and applying mineral fertilizers.

Data on saline soils of drainless lakeside depressions, which are formed in areas of extra continental climate with a cyclic 25–30-year change in the level of lakes within the arid and humid climatic phases, were obtained first. Different types of soils are shown to be formed on the landscapes adjacent to highly mineralized chloride lakes of southeastern Trans-Baikal Region: on superaqueous–subaqueous positions– gleyic solonchaks (Gleyic Solonchak (Loamic, Chloridic)); on superaqueous – humus–gley saline soils (Calcaric Mollic Gleysol (Arenic, Endosalic, Sodic)); on eluvial-superaqueous – light-humus saline soils (Fluvic Kastanozem (Epiarenic, Amphiloamic, Sodic)). Salinity degree of the soils under the study is different. Salinity chemistry is sodium taking into account cations. Anion content in solonchaks and upper horizon of humus-gley soil is mostly chloride. Soda-chloride and chloride-soda anion composition prevail in other soils. Gleyic solonchaks have strongly alkaline pH values, high content of carbonates, and a sharp dominance of Na+ among exchangeable cations. Many chemical elements are concentrated in the solonchakous horizon (Sr, S, Li, Mg, Ca); a high content of As is a regional feature. The humus-gley saline soil has the same properties as the light-humus saline soil in terms of physico-chemical parameters, and in terms of elemental composition and texture as solonchaks. This is due to it functions periodically in a semihydromorphic or hydromorphic regimes when changing the arid and humid phases. The high level of groundwater contributes to the enrichment of soils with the elements typomorphic for lake waters. The paleohydromorphic stage of development has been established to be recorded in lower layers of light-humus saline soil in the form of a high content of easily soluble salts and carbonates. The geochemical specialization of soil-forming rocks is associated with the significant accumulation of As, as well as concentration of Li, Ba, and Pb. It was also revealed that low Ca/Sr ratio is their geochemical feature. The use of cluster analysis of indicators of soils under the study revealed that both dynamic and stable soil parameters are reflected in humus-gley soil and it is recommended for monitoring of the dynamics of endorheic lakeside ecosystems in Central Asia with cyclic climatic phases.

Application of sulfur fertilizers at the doses of 15 and 30 kg/ha (with NPK) for irrigated potatoes on chestnut soils of Western Transbaikalia is the most effective for production of marketable tubers with the maximum value of bioenergy coefficient. With increasing the doses of sulfur, in spite of the insignificant increase of crude protein content, the amount of amino acids and the index of essential acids significantly increased in comparison with the control and the background. Replacement of limiting sulfur-containing amino acids (methionine + cystine) with leucine was noted. The highest biological value of potato protein at the level of 72–74% was found at the doses of 15 and 30 S kg/ha (with NPK).

The factors of formation and patterns of spatial differentiation of soils within the floodplain landscapes of the River Selenga and its tributaries (on the territory of Mongolia and Russian Federation) depending on zonal–belt location are revealed. This factor has been established to significantly affect the genesis, structure, morphology, and properties of soils within river floodplains. Soil diversity is due to different types of synlithogenic trunk of the alluvial section and the trunk of primary soil formation of the department of underdeveloped soils. Soils of halomorphic section of the postlithogenic trunk are of a landscape significance in steppe and dry-steppe zones. Alluvial dark-humus soils are close to optimal in properties and regimes Alluvial humus–gley soils develop under excessive flood–ground moisture, the influence of the permafrost–thermal factor, and the low activity of soil microbiota. It is proposed to include the type of alluvial light-humus soils, which are quite widespread in the floodplain landscapes of the region, in the soil classification. These soils develop under conditions of sufficient heat supply, but severe moisture deficit and intensive mineralization of organic matter, and are characterized by low humus content. A comprehensive agrochemical assessment of the level of fertility of alluvial soils and hydromorphic solonchaks and the biological productivity of natural meadow communities is given.

The characteristics of climatic, lithological and geomorphological conditions of formation of sandy soils of Transbaikalia (Barguzin basin) is given. It has been established that the main soil-forming processes are cryo- and light-humus, accumulative-carbonate and pale-metamorphic. In the soils of deposits, the processes of stratification and abrasion are expressed. Moving sands are not affected by soil formation, but with partial fixation of herbaceous and/or shrub vegetation on them, embryonic underdeveloped soils (layered-eolian, humus psammozems) begin to develop. For the first time, the results of the material composition of the rocks of the Angara-Vitim batholith, soil-forming sand, as well as the composition of minerals of fractions <1.1–5 and >5 µm of cryohumus and light humus soils are presented. It has been determined that the regional features of soil-forming sands are carbonation, alkalinity, and polymineral content, which is inherited from calc-alkaline rocks. The sandy and silty soil fractions have a similar mineralogical composition, which are characterized by a high content of plagioclases and K-feldspars and a low content of quartz. The composition of the silty fraction consists of a mixed-layer phase of illite-smectites interbedded with single chlorite packets, di-trioctadridic illite, ferruginous chlorite, and kaolinite. Modern soil formation is characterized by a low degree of chemical weathering (CWC, CWI, and GM) and weak profile differentiation. A feature of the material composition of sandy soils is an increased content of potassium and sodium. According to the values of total alkalinity, the studied soils are highly alkaline soils. There is a clearly pronounced division of the soil profile according to biological activity. It was revealed that during arable use, sandy soils are potential centers of desertification: in the studied area, all arable lands and fallows located on them are deflated to varying degrees. At the same time, it was found that more than 70

Впервые получены новые данные о разнообразии, морфологическом строении, физико-химических и агрохимических свойствах почв поймы р. Ульдзы (Монголия, Ульдза-Торейская равнина). Установлено преобладание типа аллювиальных среднемощных темногумусовых почв засоленного и квазиглеевого подтипов. Выявлена важнейшая особенность формирования почв - близкий уровень грунтовых вод и легкий гранулометрический состав аллювиальных отложений, определяющие однотипную трансформацию растительных остатков (темногумусовую аккумуляцию). Сделан вывод, что различия между почвами связаны со степенью засоления и типом химизма. Изученные аллювиальные почвы щелочные, слабозасоленные, имеют преимущественно хлоридный и содово-хлоридный тип засоления по анионам и магниево-натриевый или натриево-магниевый по катионам. На наиболее пониженных участках поймы формируются солончаки, имеющие различные типы засоления в генетических горизонтах по анионам и натриевый тип по катионам. На этих почвах произрастают малопродуктивные ценозы, с низким проективным покрытием и обедненным видовым составом, представленным только галофитами. Неблагоприятные факторы функционирования растений обусловливают развитие светлогумусовых процессов, аналогично зональной почве. Выявлен незначительный уровень естественного плодородия изученных почв из-за их маломощного слоистого профиля, неблагоприятных физико-химических и агрохимических свойств, особенно низкого содержания нитратного азота и подвижного фосфора. Представлены деструктивные агрогенные процессы, которые возможны при вовлечении аллювиальных темногумусовых почв в пахотное использование. Данные почвы следует преимущественно использовать как пастбищные и сенокосно-пастбищные угодья, а под пашню рекомендуется отводить «очаговые» участки с соблюдением почвосберегающих мероприятий. Для повышения биопродуктивности пойменных угодий необходимо применение различных видов навоза, компостов, сидератов и минеральных удобрений, в первую очередь азотных и фосфорных. Солончаки типичные обладают неблагоприятными физико-химическими и мелиоративными свойствами и крайне низким уровнем естественного плодородия. В связи с этим их следует отнести к категории мало- или практически непригодных для использования в сельскохозяйственном производстве почв с эпизодическим выпасом сельскохозяйственных животных. Data on the diversity, morphological structure, physical, chemical and agrochemical properties of soils within the Uldz river floodplain (Mongolia, Uldz-Torei plain) have been obtained for the first time. The predominance of alluvial medium-thick dark-humus soil type of saline and quasi-gleic subtypes was established. A very important feature in soil genesis was identified, namely a high level of groundwater and light texture of alluvial deposits, determining the same type of plant residues transformation (dark humus accumulation). It is concluded that the differences between soils are due to the degree of salinity and to the type of chemistry. The alluvial soils under study are alkaline, slightly saline, predominantly of chloride and soda-chloride type of salinity for anions and of magnesium-sodium or sodium-magnesium type for cations. Solonchaks formed in the lower parts of the floodplain have different types of salinity within genetic horizons for anions and sodium type of salinity for cations. Phytocenoses grown on these soils are of low productivity, projective cover and depleted species composition, and are represented only by halophytes. Unfavorable factors for plant growth are responsible for occurrence of light humus processes, similar to the zonal soil. The level of natural fertility of the soils under study was found to be very low because of their thin layered profile, unfavorable physical, chemical and agrochemical properties, and especially low content of nitrate nitrogen and labile phosphorus. Destructive agrogenic processes are described, which are possible when alluval dark-humus soils are involved in durable use possible with alluvial dark-humus soils arable use. These soils should be mainly used as grasslands and hay-pastures, and it is recommended that “focal” plots should be allocated for arable land in compliance with soil conservation measures. For increasing biopoductivity of the floodplain lands, it is necessary to use various types of manure, composts, green manure and mineral fertilizers, primarily nitrogen and phosphorus. Typical solonchaks have unfavorable physical, chemical and meliorative properties and an extremely low level of natural fertility. In this regard, they should be classified as marginal or virtually unsuitable for use in agricultural production with occasional grazing of farm animals.

Data on the diversity; morphological structure; and physical, chemical, and agrochemical properties of soils within the Uldz River floodplain (Mongolia, Uldz–Torei plain) have been obtained for the first time. The predominance of alluvial medium-thick dark humus soil type of saline and quasi-gleic subtypes is established. A very important feature in soil genesis is identified, namely, a high level of groundwater and light texture of alluvial deposits, determining the same type of plant residues transformation (dark humus accumulations). It is concluded that the differences between soils are due to the degree of salinity and the type of chemistry. The alluvial soils under study are alkaline and slightly saline, predominantly of chloride and soda-chloride type of salinity for anions and of magnesium–sodium or sodium–magnesium type for cations. Solonchaks that form in the lower parts of the floodplain have different types of salinity within genetic horizons for anions and a sodium type of salinity for cations. Phytocenoses grown on these soils are of low productivity, projective cover, and depleted species composition and are represented only by halophytes. Unfavorable factors for plant growth are responsible for the occurrence of light humus processes, similar to the zonal soil. The level of natural fertility of the soils under study is found to be very low because of their thin layered profile; unfavorable physical, chemical, and agrochemical properties; and especially low content of nitrate nitrogen and labile phosphorus. Destructive agrogenic processes are described that are possible when alluvial dark humus soils are involved in arable use. These soils should be mainly used as grasslands and hay pastures, and it is recommended that “focal” plots should be allocated for arable land in compliance with soil conservation measures. To increase the biopoductivity of the floodplain lands, it is necessary to use various types of manure, composts, green manure, and mineral fertilizers (primarily nitrogen and phosphorus). Typical solonchaks have unfavorable physical, chemical, and meliorative properties and an extremely low level of natural fertility. In this regard, they should be classified as marginal or virtually unsuitable for use in agricultural production with the occasional grazing of farm animals.

Data on saline soils of endorheic lacustrine depressions in the areas of ultracontinental climate with 25–30-year-long cycles of lakes level fluctuations are obtained for the first time. Fluctuations correspond to alternating arid and humid climatic phases. Different soils are formed in landscapes adjacent to strongly mineralized chloride lakes of the southeastern Transbaikalia: gley solonchaks (Gleyic Solonchaks (Loamic, Chloride)) in superaqual–subaqual positions; humus-gley saline soils (Calcaric Mollic Gleysols (Arenic, Endosalic, Sodic)) in superaqual positions; and light-humus saline soils (Fluvic Kastanozems (Epiarenic, Amphiloamic, Sodic)) in eluvial-superaqual geochemical positions. Salinity rate of the studied soils varies. The cations are dominated by sodium, and among anions chlorides are most common in solonchaks and in humus-gley topsoils. Soda-chloride and chloride-soda anion composition prevails in other soils. Gley solonchaks are characterized by strongly alkaline pH, high content of carbonates, and predominance of Na + among exchangeable cations. Many chemical elements are concentrated in the solonchakous horizon (Sr, S, Li, Mg, and Ca), and a high content of As is a regional feature. The humus-gley saline soil is similar to the light-humus saline soil by physicochemical parameters and to solonchaks by the element composition and texture. Both features are related to periodical functioning of this soil in semihydromorphic or hydromorphic regimes during arid and humid phases, respectively. The high groundwater level contributes to the enrichment of soils with the elements typomorphic for lake water. The paleohydromorphic formation stage has been recorded in lower layers of light-humus saline soil as a high content of easily soluble salts and carbonates. The geochemical specificity of soil-forming rocks is the significant As accumulation and Li, Ba, and Pb elevated concentrations. It has also been revealed that the low Ca/Sr ratio is inherent to their geochemical composition. The cluster analysis of parameters of the studied soils shows that both dynamic and stable soil parameters are reflected in humus-gley soil, therefore, it is recommended for monitoring the dynamics of endorheic lacustrine ecosystems in Central Asia with cyclic climatic phases.

Аннотация.Представлена гидрография трансграничной р.Улз-Гол (на территории России -р.Ульдза) и охарактеризованы специфичные эколого-географические условия почвообразования на ее водосборной территории.Важнейшей особенностью формирования почв является близкий уровень грунтовых вод и легкий гранулометрический состав аллювиальных отложений, что способствует своеобразию почв в пойменно-долинных ландшафтах.Установлено, что структура почвенного покрова на изученном участке преимущественно представлена различными подтипами аллювиальных темногумусовых почв.Определенное распространение имеют солончаки типичные

New data on the morphology, chemical and agrochemical properties, classification, and rational use of alluvial soils of floodplains of the mountain rivers of the Pacific Ocean basin (Mongolia, Upper Kerulen Depression) have been obtained. A dense river network in the northern part (subtaiga zone, 1500–1395 m a.s.l.) is formed by the Kerulen River and its tributaries Khoit Khorot, Dund Khorot, Teyun-Gol, Dzor-Gol, and Uvkhiriin-Gol rivers. Thin, rich in humus alluvial soils are formed on the floodplains of the island-braided type with a gravelly bouldery substrate. They are characterized by a poorly pronounced stratification. Soil salinization is is seen in the areas of discharge of chloride–bicarbonate magnesium–sodium groundwater. The differences between soil types within this area are related to the mucky–humus and humus horizons. The types of alluvial humus soils (Fluvisols Humic) and alluvial mucky–humus soils (Folic Fluvisols) have been specified. In the central part of the depression (the forest-steppe zone, 1395–1357 m a.s.l.), the Kerulen River forms an epigenetic valley with poorly developed floodplains. The main floodplains are formed by the Dzun-Burkhiin-Gol, Barun-Burkhiin-Gol, and Delenziin-Gol rivers. Alluvial deposits are of gravelly sandy composition. The soils are characterized by a high humus content, pronounced gleying, and salinization. The types of alluvial dark-humus soils (Eutric Fluvisols Humic) and dark-humus gley soils (Gleyic Fluvisols Humic) have been diagnosed. In the southern part of the basin (the steppe zone, 1357–1306 m a.s.l., floodplain soils are formed mainly on alluvial sands. They are characterized by a slightly alkaline reaction and are saline. The type of alluvial dark-humus gleyed saline soils (Sodic Gleyic Fluvisols Humic)) is formed there. A low fertility of the floodplain soils in the studied region is related to unfavorable water-physical properties and low content of nitrate nitrogen and available phosphorus. A grouping of soils according to their use, mainly for plowing, hayfields, pastures, and poorly available or unavailable for agriculture is proposed. Potential destructive agrogenic processes are described, when these soils are involved in intensive agricultural production. A set of measures is recommended for environmentally safe management of alluvial soils and floodplain ecosystems in the upper reaches of the Kerulen River and its tributaries in grassland farming and agriculture, including the use of various types of manure, composts, and mineral fertilizers (mainly, nitrogen and phosphorus fertilizers).