Profile of desert sandy soils formed in the Aral Sea dried-up seabed

. In subsequent years, as a result of the strengthening of natural and anthropogenic factors, the inability of the Amu Darya and Sir Darya waters to flow into the Aral Sea, the mechanical composition of desert sandy soils, the type of salinization, the degree of salinization, the variety of humus content in the soils common in the soil covers of the dried seabed were studied. During the study of the study area soils, the strong salinization of soils was noted by the chloride-sulfate salinization type and the salinization in the surface layer of the soil profile section No. 47, that is, in the layers 0-9 cm and 9-50 cm deep, and weak salinization by the sulfate-chloride salinization type and the salinization in the lower layer of the soil profile. In the surface layer of the studied desert sandy soils, that is, by 0-9 cm and 9-50 cm, the humus content ranged from 0.418% to 0.528%. On the dried bottom of the Aral Sea, because of strong evaporation of groundwater in the soil profile, an intensive process of accumulation of salt crystals took place, and desert sandy soils became highly saline.


Introduction
The total area of pasture lands worldwide is 1910 million hectares.Of these, 246 million hectares (12.8%) are in varying degrees of degradation, 62 million hectares (33.6%) are in poor condition, and 1022 million hectares (53.5%) require land in stable condition.In arid regions of the globe, the main factors leading to soil degradation include soil erosion, salinization, depletion of humus and nutrients, and contamination with toxic and heavy elements.Changes in the state of the natural environment under human influence, changes under the influence of strong anthropogenic factors on living and non-living components have caused local, regional and global environmental problems.As a result of such impacts, the ecological imbalance in the region was lost, which led to the "Aral problem", which is considered the most dangerous in the crisis.Today, as a result of global climate change, the risk of salinization, desertification and degradation in the areas of sea water retreat is increasing from year to year.In particular, the negative impact on the health of habitants of the Aral Sea region was found.
As a result of the Aral Sea drainage, significant changes in the soil cover have been observed since the 1970s.In subsequent years, climate change, especially with less precipitation, led to the disruption of the salt and water balance in the Aral Sea region, salinization of land, and, as a consequence, the relative decrease in fertility and crop yields

Materials and methods
Identification on the basis of chemical analyses of desert sandy ground soils formed on the dried-up bottom of the Aral Sea, freed from water as a result of the increased natural and anthropogenic factors.
In the areas of the dried-up bottom of the Aral Sea, field soil studies were carried out, during which the morphological structure of the soil profile, newly formed structures, the main signs and geographical location in the excavated section were studied, soil samples were taken for laboratory and analytical studies.The work on chemical analysis was carried out on the basis of the "Instructions for conducting soil survey and drawing up soil maps for maintaining the state land cadastre [1] on the basis of the accepted methods.
When determining the degree of salinity, considering the types of salinity, the classification of N.I.Bazilevich and E.I. Pankova was used.

Results and discussion
Morphogenetic structure of the seabed ground soils -ground-soil groups also began to form under the influence of various river sediments in the areas of the dried-up bottom of the Aral Sea that retreated from the water [2].The formed ground soils developed depending on the soil and climatic conditions of the territory, lithological and hydrogeological, as well as agrolandscape structure.Of course, it was noticed that the sea laid various layered hard rocks on its way and formed large layers.
When studying the morphogenetic features of ground soils developing at the new stage in the central part of the Aral Sea, it was noted that desert sandy ground soil types were formed there [3;4].The main attention was paid to the soil and ground covers of the Aral Sea, as well as desert sandy soils characteristic of its dried bottom (Figure 1).

Desert sandy soils
These soil formations were formed on the previously exposed (water-free) seabed, where scattered sand dunes are currently forming, tamarix, halostachys and saxaul grow, but the plants are rare and drying up, because the groundwater level has decreased (Figure 2).
Section No. 47. 2022.20.05.A.Dusaliev., A.Ismonov.On the Surgul-Muynak road, 37 km from Muynak region.In the north, there is the left side of the highway, the plain.At the altitude of 46 m above sea level (measured from the Baltic Sea level).The landscape is deserted, overgrown with saxaul and tamarisk.The environment consists of finely scattered sands and shells.The section is located on the surface of alluvial deposits.0-9 cm.Gray sand, the surface is dry, with fixed sands with the bark and shells admixture, the layer is medium-dense, dry sandy, sabulous dusty-porous, loose, rarely covered with vegetation.The transition to the next layer is obvious in color.9-50 cm.Yellow sand, slightly moist fine sand is porous, there are few roots, there are rotten plant roots, a lot of rust spots.The transition to the next layer is obvious in density.
50-100 cm.Yellow sand, slightly moist, porous sand, slightly compacted, sometimes there are rust spots, the roots are rare and small, the transition to the next layer is gradual.100-200 cm; (100-158 cm).Yellow enlarged sand, slightly moist, roots are rare, porous, mouldy, there are shells and weakly compacted rust spots.
There is very little moisture in the profile of desert sandy soils on the water-free lands of the dried-up bottom of the Aral Sea, and in the extremely arid climate they undergo the process of transformation into automorphic soils, but it has been observed that hydromorphic (or halophytic) plants currently survive due to periodic humidity and reduce their range [5,6].There are no new formations on these soils, they are spread mouldy on the soil.Agrochemical properties of ground seabed soils.In the 2022 studies, the agrochemical and physico-chemical properties of ground soils formed on the dried bottom of the Aral Sea were studied on the basis of soil samples presented in the field studies.Desert sandy ground soil groups located in various geomorphological areas are common on large areas of the dried-up bottom of the Aral Sea.According to the results of the chemical analysis of the presented soil samples, the analysis of the mechanical composition of soils, water absorption, humus and other chemical analyses were carried out.Based on the soil samples studied below, taken from the areas of retreat of the waters of the Aral Sea, agrochemical and other properties of desert sandy ground soils will be highlighted [8,9].
Desert sandy ground soils -belong to the group of automorphic soils of the desert zone, the mechanical composition of which consists mainly of light loams and sands.The emergence and development of these soils on exposed marine lands is associated with deposits of Aeolian sands or ancient alluvial rocks with a light mechanical composition [7; 8].The porosity of the soil composition has led to the occurence of several properties.Due to the high water permeability, deep humidification allows capillary moisture to rise to a small height, as well as to release constant moisture under it.Due to the presence of favorable natural conditions among the automorphic soils of the desert zone, vegetation is constantly growing.But it is poor in humus, moisture and heat contribute to the rapid mineralization of plant residues.The mechanical composition of desert sandy soils is given below (Table 1).
It is noted that the ground soils of the studied bottom of the Aral Sea, which have undergone various degrees of salinization, degradation and dehumidification processes, intensively undergo desertification processes.The ongoing processes of desertification have negative impact on the ecological and reclamation state of the soil cover [9].In addition, studies have noted that the lack of natural moisture in hydromorphic soils in conditions of water scarcity leads to their transition to the type or group of automorphic soils.As a result of water lack, high heat levels for many years, transitions to highly saline salt marshes were noted in places, and in the lower layers of the section profile, according to the degree of salinity of the soil -medium and low salinity (Table 2).
It was also noted that erosion processes caused by the drying of natural vegetation continued in the areas of the Aral Sea, as a result of which a large number of dust and salt particles settled from the surface of saline soils in the form of aerosols, which spread to the territory of the Aral Sea region [10].It has been established that the ground soils found in all areas where sea waters recede are subject to degradation to varying degrees.
All currently studied soils develop at the stage of transition from hydromorphic regime to a semi-hydromorphic and automorphic one.As a result of the drying up of the Aral Sea and the lowering of the groundwater level, a specific soil formation occurred in the region, which led to the intensive processes of desertification and degradation.In the first periods of soil formation, as a result of evaporation of water in the hydromorphic regime, salts rise into the upper layers, as a result of which various layered salt marshes, simple salt marshes were formed.Then, as a result of the lowering of the groundwater level, the rise of salts in the upper layers stopped.After a decrease in the total soil moisture, wind erosion began, processes that, in turn, also caused a strong volatility of salts.

Conclusion
Summing up, we can say that in the mechanical composition of the desert sandy soil soils studied in studies, dust particles average 58.1-81.5%,sand particles-16.5-20.2%,silt particles-9.3-12.5%.In the upper layers of the studied desert sandy soils, i.e. 0-9 cm and 9-50 cm, the humus content ranges from 0.418% to 0.528%, and in the lower layer of the soil profile 125-158 cm -0.44%.They are poor in humus, but moisture and heat contribute to the rapid mineralization of plant residues.In the areas of the dried-up bottom of the Aral Sea, as a result of strong evaporation of groundwater in the soil profile, the intensive process of accumulation of salt crystals took place, and desert sandy soils became highly saline, and sometimes very saline, in which the dry residue averaged from 0.439% to 1.147%, while it was noted that the type the salinity was sulfate-chloride.

Fig. 2 .
Fig. 2. General view of the desert-sandy soils of the dried-up bottom of the Aral Sea, 2023.

Table 1 .
Mechanical composition of desert sandy soils of the dried-up bottom of the Aral Sea, in %.

Table 2 .
Water composition, salinity levels and types of ground soils of the dried bottom of the Aral Sea (47th section).