Remote Sensing of the Carbonate Content in Irrigated Soils of the Dry Steppe Zone in Volgograd Oblast

Data on the spatial distribution of calcium carbonates (CaCO3) in the surface layer and in the profiles of irrigated soils at two key plots of the Svetloyarsk irrigation system in Volgograd oblast are presented. The key plots are located in different natural areas of the dry-steppe zone: the Yergeni Upland and the Caspian Lowland. The fields at both plots are characterized by patchiness on satellite images both for the bare soil surface and for the vegetation cover. One of the main reasons for the patchiness on the image is the different content of carbonates in the surface soil layer. Two mechanisms of the appearance of carbonates near the surface of irrigated soils have been established. The first mechanism is related to the cutting of the soils of arching areas of micro- and mesotopography in the course of surface leveling during the construction of irrigation systems with the exposure of calcareous horizons in the middle part of the soil profile and the movement of the cut material, including carbonates, to neighboring areas. The second mechanism is the ascending migration of soil solutions to the surface layer with the deposition of carbonates during the long period of irrigation in a dry hot climate. The combined use of remote sensing data and ground-based field surveys of soils along transects that intersect areas with different patchiness and spectral brightness of the images makes it possible to identify soils with different contents of carbonates in the plow horizon.