Аннотация
The data of two soil and vegetation surveys of flood basins of the Mamai irrigation system performed in 1987 and 2012 are compared. This irrigation system is found within the Caspian Lowland in Western Kazakhstan oblast of Kazakhstan. The thickness of the humus horizon decreased by 4 cm on the average attesting to the first-second stages of soil degradation. The humus content in the A + B1 horizons decreased by 0.3% on the average with variations corresponding to the first-third degradation stages. From 1987 to 2012, the area of saline soils and the content of exchangeable sodium in them also increased attesting to the development of desertification in the studied zone. The flooded portion of flood basins decreased from 84% in 1987 to 69% in 2012, and the groundwater level rose from 3.6–4.0 to 1.8–3.1 m. Soil degradation processes, together with adverse anthropogenic impacts, resulted in a decrease in the projective cover of valuable plant species and the productivity of herbs grown in flood basins.