Volume IV of the Proceedings of the Institute of Soil Science of the Academy of Sciences of the Kazakh Soviet Socialist Republic contains part of the results of soil investigations conducted in the Northern Caspian region during 1951-1952. The studies were carried out in the Volga-Ural interfluve, south of 50° north latitude and east of 48°30′ east longitude, including the Ural-Kushum watershed, the Bolshoy Uzen and Maly Uzen rivers, the Kamysh-Samar lake system, the ancient and modern deltas of the Ural River, the southern part of the Volga-Ural sands, and the easternmost section of the Volga Delta. Approximately 5 million hectares were surveyed, and soil maps at the corresponding scales were compiled. This work was undertaken to support irrigation and water supply development in the Northern Caspian region, in accordance with decisions of government agencies and assignments from the Leningrad Institute for Water Engineering Planning and Design. The research materials were transferred to that institute for design purposes. These materials included soil maps and soil reclamation zoning maps, descriptions of soils and soil regions, data on soil water-physical properties, classifications of soil reclamation and agricultural productivity characteristics, data on areas suitable for irrigation, as well as basic recommendations concerning land use patterns and irrigation methods. Because the authors were occupied with other more urgent work, the processing, final editing, and preparation of the published results for printing were delayed. This volume of the Proceedings presents only part of the collected materials, including the principal findings on the water-physical properties and organic matter composition of Northern Caspian soils, the conditions of soil formation in sandy areas, and the reclamation characteristics of lands suitable for irrigation. The article by L. I. Pachkina presents the results of field semi-stationary and laboratory studies of the hydrophysical, chemical, and other properties of soils in the Ural River floodplain and the Ural Delta. The research covered the most important and widespread soils, including light chestnut calcareous soils, brown calcareous soils, meadow-steppe soils, and meadow soils, as well as their associations and complexes with solonetz, solonetzic, and saline soils. Studies of this kind involving different soils across such an extensive territory have been relatively rare and were conducted in this region for the first time. The extensive and detailed factual material collected by the author clearly demonstrates the hydrophysical and agricultural-reclamation properties of the soils and parent materials studied and is of considerable scientific and practical value. This work is both useful and necessary for a deeper understanding of soil genesis and soil reclamation characteristics. The article by I. I. Yemelyanov on the organic matter of Northern Caspian soils contains factual data on root biomass and aboveground plant biomass, as well as on the component and fraction composition of organic matter in various soils. The article attempts to explore the interrelationships and interdependencies among these data. However, the amount of factual material collected during a single season, together with the absence of related microbiological and biochemical investigations (which were not included in the author's research program), prevented him from fully explaining the complex processes of humus formation in the soils studied. Nevertheless, these data remain highly valuable and fill a major gap in knowledge concerning organic matter in the desert-steppe soils of Western Kazakhstan. The article by A. M. Petzhelina is devoted to the study of the characteristics of soil formation in the sandy areas of the Northern Caspian region. Based on field observations and soil chemical analyses, the author attempts to establish a direct relationship between soil development and the history of land-surface evolution following the retreat of the Caspian Sea. The author's principal view is that the steppification of the Northern Caspian lowland plain and the development of its soils were not associated with a sharp climatic shift toward greater aridity. Rather, they were related to the regression of the Caspian Sea, the lowering of the erosion base level and groundwater table, and the effects of water and wind erosion, which together caused certain local climatic changes. The collective paper by U. U. Uspanov, A. A. Sokolov, and N. M. Vladimirov characterizes soil reclamation categories of lands that are suitable for irrigation to varying degrees. The land classification was developed on the basis of analysis and synthesis of soil and hydrogeological research materials. Materials on the soil reclamation classification of lands, accompanied by soil maps of individual districts and statistical contour tables indicating the areas and principal reclamation indicators, were transferred to the Leningrad Institute for Water Engineering Planning and Design, the Guryev Regional Water Administration, and the Institute of Economics of the Academy of Sciences of the Kazakh SSR, where they were used for practical purposes. Some revisions were made when these materials were printed here, and the appendices have not been included.