Modern state of irrigated soils at the south of the Volga upland
The goal is to assess the impact of 50-year irrigation by sprinkling on soil processes occurring in the light-chestnut soils (Luvic Kastanozem (Loamic, Aric, Protosodic, Bathysalic)) of the southern slopes of the Volga upland at the Volga-Don interfluve (FSUE “Oroshaemoe”, the Volgograd region) with deep ground water. Water for irrigation is supplied from the Varvarovsky reservoir of the Volga-Don Canal system. It is characterized by a total dissolved salts of about 1 g/l, a bicarbonate-chloride-sulfate compositionwith an increased sodium content. Detailed morphological description of soil profiles, granulometric composition, content of soluble salts in soils and sediments of the vadoze zone up to the depth of 3.5 m, dynamics of salts in the layer of 0-50 cm for 2011-2019 are presented. Until the autumn of 2015, the studied soils were deep saline, being no saline in the layer of 0-100 cm. In recent years, a weak salinity degree of soda-chloride sodium chemistry has been observed in the 0-50 cm layer as a result of gradual accumulation of irrigation water salts during irrigation organized according to water consumption of agricultural crops. Irrigated soils have acquired a complex of signs of secondary salinity: (1) the presence of light accumulations of sandy and silt mineral grains in the arable horizon, resulting from the destructive effect of irrigation water drops during sprinkling; (2) toxic alkalinity associated with sodium (residual sodium carbonate), according to water extraction 1 : 5 (soil : water), in the horizons from the depth of 10-20 to 60100 cm; (3) abundant humus-clay cutans on the lateral side faces of prismatic structural units in the undisturbed part of the soil profile from 30 to 100 cm.