IntroductionAs a natural system, each terrain has important properties: self-organization, self-regulation, and selfrenewal -all of which facilitate sustainable development of an ecosystem and its ability to resist degradation and crisis processes. Sustainability of terrain is associated with the ability of its components to conserve their structure and function under external influences [1].At present, the impact of anthropogenic factors often exceeds maximal permissible limits, destroying natural ecosystems. First of all, land degradation results in expanded water and wind erosion, reduction of groundwater level, pollution, water logging and salinity of irrigated and non-irrigated soils [2]. Especially in arid regions where productivity of agricultural production is dependent on land irrigation, and soils are mostly subjected to salinity. The following six groups of degradation have been outlined in the World Atlas of Desertification [3]: water erosion, wind erosion, soil fertility decreases, salinization, Pol. J. Environ. Stud. Vol. 25, No. 6 (2016), 2469-2475 Original Research Dynamics of Soil Salinity in Irrigation AbstractThe analysis has been conducted of possibility of determining the extent of soil salinity by indirect and direct decoding of satellite images Pleiades 1A / 1B (in the year of survey) and LANDSATTM (archive). It was found that indirect decoding of salinity based on spectral char-acteristics of vegetation images is strongly dependent on crop growth phase (period of shoot-ing). LANDSAT archive images with normalized soil salinity index (NDSI) allow to develop salinity maps and soil salinity dynamics maps at semi-quantitative level. Based on computer analysis of LANDSAT images it was determined that soil salinity at study object during the pe-riod from 1987 to 2014 has increased due to significant decrease of the area of non-saline soil by 41.5% and increasing of the areas of low and moderately saline soils by 34.9%, also regions with heavily saline soils at 6.6% of total surveyed area have been detected, which previously were absent.

Salinization of soil cover and the constant increase in their area have become one of the most pressing problems year after year for irrigated agriculture regions. The degradation processes caused by the salinity of soils negatively affect the growth and development of food crops. Therefore, this study focused on the effects of soil salinity in the midstream of the Syrdarya on the growth and development of maize where the climate is continental and mostly arid, and the cultivation of crops is possible under irrigation conditions. The study made harmonious use of remote sensing and field survey methods based on modern and traditional approaches in terms of time and space. Based on Sentinel-2 satellite images, regression analysis was carried out to determine the dependency of vegetation indices on soil electronegativity and maize biomass from 73 sampling points in the representative area. As a result, in the study of the growth and development of maize, it was found that the dependence of the Normalized Difference Vegetation Index (NDVI) on maize biomass within 18 vegetation indices was "high" (R2 = 0.76) in spring. The dynamics of maize biomass grown on soils of different salinity levels were developed. NDVI dynamics, which covers the entire growth phases of corn, showed that compared to corn grown in unsalted soils, it slows down the growth of corn in slightly saline soils-up to 11 days, in moderately saline soils -35 days, and in heavily (highly) saline soils -45 days. Characterization of soil salinity and other factors having a positive and negative influence on the growth and development of maize yield in the studied object is also given.

The water regime is the main factor contributing to the formation of landscapes in the river deltas of arid zones, any fluctuations in which lead to a change in the integral hydromorphic landscape. After the construction of the Kapshagai reservoir, the anthropogenic load on the ecosystem of the Ili River delta increased, as a result of which degradation processes, such as drying out and salinization, intensified. In the short term, this phenomenon may lead to the desertification of about 1 million ha of land in the modern river delta. In this regard, the main goal of this study is to look at the processes of desertification in the modern delta of the Ili River, using remote sensing data, which allows for quick identification of the long-term dynamics of degradation processes. For this, the authors used satellite data from Landsat 1-5 MSSS and Landsat 8OLI satellites for 1979 and 2019 and soil analysis data obtained through the ground (field) surveys. Using regression analysis of space and soil data, predictors for interpreting space images were identified and maps of landscape drying and soil salinization were compiled, reflecting the changes that have occurred over the past 40 years. As a result, it was found that in 2019, compared to 1979, the area of landscapes covered with vegetation had decreased by 12% and there was a transformation of hydromorphic landscapes into salt marshes and solonetzes. Over the past 40 years, the volume of non-saline soils has decreased by 41.3% and the volume of saline soils has increased to varying degrees. That is, at present, on the territory of the modern delta, a difficult land improvement situation has developed associated with the cessation of spring and summer floods due to the intensive water use at the Chinese and Kazakh sides.

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