Soil Salinity Status under Post-Irrigation Conditions at the Generalovskaya Irrigation System in Volgograd Oblast

The aim of this work is to evaluate recent changes in soil salinity status at the Generalovskaya irrigation system in the dry-steppe zone of Volgograd oblast of Russia on the second terrace of the Don River near the Tsimlyansk Reservoir. The studied area has not been irrigated since the mid-1990s. We have used materials of terrain soil survey of the area in 1990 and 2020; data on soil water extracts (1 : 5); measurements of the activities of Na+, Ca2+, and Cl- ions with ion-selective electrodes in soil pastes with a moisture content of 40-45%; and aerial photographs (1990) and satellite image (2020). The studied area was subjected to secondary soil salinization in the 1990s due to the groundwater rise above the critical level. In 25 years after the cessation of irrigation, the groundwater table has descended to a depth of more than 5 m, and secondary-saline soils have been subjected to a gradual desalinization with the development of alkalization in the topsoil. The current soil salinity status inherits the pattern that existed 25 years ago, i.e., the spatial distribution of salts in the studied landscape is generally preserved. We have revealed the presence of calcium chlorides in some soils in 2020, which are identified as evidences of secondary salinization developed by the 1990s. It is shown that the catenary method of terrain soil survey may be used in combination with satellite information and digital data processing for mapping the soil cover under post-irrigation conditions. This enables the reflection of the main soil groups, the depth of the upper saline horizon, and the presence or absence of carbonates on the soil surface. Such information is necessary for the development and selection of optimal reclamation measures.