Soils at the Boundary between the Zones of Light Chestnut and Brown Arid Soils in the South of European Russia

The properties of virgin light chestnut and brown arid soils and light solonetzes, located at the boundary between the dry steppes and demideserts of Astrakhan oblast on the right bank of the Volga River near Solenoe Zaimishche village (about 48 N), have been studied. According to climatic zoning (1961), the study area belongs to a region with a hot dry climate (the hydrothermal index is 0.3-0.4); according to the geobotanical data (Safronova, 2003), this area lies at the boundary between dry steppes and deserts (semi-deserts). This area also lies at the boundary between two geomorphological regions of the Caspian lowland: the North Sarpa plain and South Sarpa lowland (Doskach, 1979). Analysis of the soil data has shown that the studied area lies within different soil zones on various soil maps (the subzone of light chestnut soils and the zone of brown arid soils). Our soil descriptions, based on the soil classifications of 1977 and 2004 and on the analytical materials, show that the properties of light chestnut and brown arid soils are very similar (at the zone of their contact), as these soils have similar texture. In our opinion, the difference and similarity between zonal soils (light chestnut and brown arid soils) are mainly determined by the parent material: in the north of the Caspian lowland, they are represented by the Early Khvalyn heavy and medium loams; in the south, they are represented by Late Khvalyn light loams and loamy sands. Light automorphic solonetzes are often found in the context of zonal soils; their formation is related to the outcrops of saline material.