Changes in the Ameliorative Status of Irrigated Soils of Volgograd Oblast in the 21st Century

The ameliorative status of irrigated soils was estimated on the basis of reclamation cadaster data for 2001 and 2016 on 17 state irrigation systems in three nature regions of Volgograd oblast: (1) the Khvalyn clayey plain and Volga sand ridge in the Caspian Lowland, (2) the Volga and Ergeni uplands, and (3) the Volga and Don river valleys. Significant changes took place in the ameliorative status of these systems during the studied period: the total irrigation area sharply decreased (-31%), especially under irrigation by the local runoff (44.5%); the groundwater level became lower, and the area with deep (>5 m) groundwater table increased to 77.3%; and the areas of saline and solonetzic soils decreased by 22.9% and 19.3%, respectively. In many cases, the differences in natural conditions determined the ameliorative status of irrigated soils and the intensity of their changes. The changes were the greatest on the initially saline slightly drained soils of the Khvalyn clayey plain and the smallest in the Volga River valley. During the entire period of irrigation, some areas were subjected to secondary salinization and abandoned. Our investigations at the Raigorodsk plot of the Svetloyarsk irrigation system within the Khvalyn clayey plain in 2016 demonstrated that the soils subjected to secondary salinization in the period of maximum irrigation intensity (in 1990) are now at the stage of gradual desalinization.