Satellite estimates of the impact of secondary salinization on agriculture sustainability in irrigated soils of Golodnaya Steppe (Kazakhstan); [Спутниковые оценки влияния вторичного засоления пашни на устойчивость растениеводства в ирригационном массиве «Голодная степь» (Казахстан)]

Secondary salinization and lack of water resources for large (140 thousand ha) irrigation massif “Golodnaya Steppe” (Kazakhstan), located in the Syrdarya river basin, negatively affects crop cultivation. Assessment of the trend of recent years in the state of agricultural vegetation is of considerable interest. To combat secondary salinization, winter soil washing is practiced in the region. When it is carried out, water mirrors are formed on fields during January-February, which can be registered by satellites. Thus, it is possible operatively identify fields designated for soil washing at the end of the season due to secondary soil salinization. Sentinel-2 satellite data with 10 m resolution for the period 2017–2022 were used to analyze seasonal maximums of NDVI (Normalized Difference Vegetation Index) for two groups of fields: those with crops of the whole region, and fields with saline soils selected by farmers at the end of the year for winter soil washing. Sentinel-1, -2 and Landsat-8, -9 satellite imagery obtained for January-February 2017–2023 was used as a basis for compiling water surface masks on the fields. The directionality and significance of the trend of the difference between seasonal NDVI maxima for the most saline fields and for all fields in the region was assessed. A decreasing trend of this difference was recorded, with reliability of linear approximation R2 = 0.93, and Fisher-Snedekor factor value F = 56.2 (F = 8.47; α = 0.01). It was found that about 30 % of arable soils in the region are annually washed from secondary salinization. Dynamics of the state of agricultural vegetation on the fields with saline soils during the period 2017–2022 was characterized by pronounced determinism and trend to reduce differences with other fields of the region. Thus, during the last 6 years (2017–2022), crop production in the irrigation massif “Golodnaya Steppe” (Kazakhstan) demonstrated stability of agrotechnical level and resistance to seasonal variations in weather conditions and water content of the Syr Darya River. © 2023 Space Research Institute of the Russian Academy of Sciences. All rights reserved.