Effect of soil salinity on eco-meliorative condition

. This article represents recommendations for the gradual acceleration of agricultural production, the rational use of land resources, the solution of problems related to increasing the productivity and economic efficiency of each hectare of irrigated land, as well as practical advice.


Actuality
The main tasks of land reclamation in Central Asia, including Uzbekistan, are to prevent soil salinity and swamping, develop protected lands, combat water and wind erosion. Land recultivation, prevention of soil densification and reduction of humus content, fight against soil pollution and desertification and other negative processes are considered as the main goals. The systems of reclamation activities are different for regions with different natural conditions.The development of these activities requires a deep knowledge of soil formation and their properties [1].
Consistent acceleration of production in agriculture, rational use of the land fund, development of solutions to problems related to increase the productivity of each irrigated hectare and its economic efficiency are of great importance. In this regard, maintaining soil fertility and increasing it regularly every year is one of the important tasks of agriculture, primarily for soil reclamation specialists. [1]

Objects and methods
The productivity of the irrigated soils of our republic significantly decreased in the next ten years. During this period the area of medium and low-quality lands have increased by 14.0%. One of the main reasons for this negative situation is, first of all, the deterioration of the reclamation condition of irrigated soils. Over the next twenty years, the area of saline lands increased by 850,000 hectares, and the total area exceeded 2,446,000 hectares, which is almost half of the irrigated land. Accumulation of salts and soil salinity is increasing in the region of desert and pale gray soils. For example, in the Republic of Karakalpakstan, Khorezm, Bukhara, Syrdarya and other regions. In addition, the exploitation of gypsum soils causes land subsidence and rapid removal from the composition of agricultural lands [2,3].
As it was mentioned above, today in very large areas of Mirzachul, Malikchol and Karshi deserts, irrigable lands are developed and cotton, grain and other agricultural crops are grown. The development of Karshi and Malikchul is carried out at the expense of the newly built water reservoirs of Amudarya (Talimarjon, Tudakul, Kuyimozor) and requires the economical use of water resources. As a result of the commissioning of the Amu-Bukhara channel, the possibility of using the land resources of Bukhara and Navoi regions has doubled,and this is a clear proof of our opinion. The amount of humus in the soils scattered in the deserts of our republic is small, their indicator does not exceed 0.4-0.8%. Brown soils with a brown color occupy a large part of the desert region of our country. When developing these soils for irrigation, it is necessary to study their composition. As a result of the dissolution of carbonates and gypsum in brown soils with irrigated color, the surface layer of the soil sinks, as a result, their microrelief plane is disturbed and it becomes difficult to observe agrotechnical rules in crop care. Therefore, in the desert region, it is recommended to thoroughly wash the gypsum and salt mixtures in newly developed soils [4,5].
Development of measures to improve the ecological and reclamation conditions of old and newly developed soils in the territory of the Republic of Uzbekistan, especially the properties of saline soils in Mirzachul, Karshi, Bukhara oasis, Surkhan-Sherabad desert, Amudarya delta and other areas. In addition, a great attention is being paid to scientific research works on the detailed study of their characteristics, their comprehensive analysis, and recommendations are being made.

Result and analysis
According to the given data, the following anthropogenic evolutionary changes are taking place in the irrigated soil cover of the regions of the Republic of Uzbekistan (Syr Darya, Jizzakh, Navai, Bukhara, Kashkadarya, Khorezm) under the influence of irrigation: -The increase in the level of mineralization of irrigation water, the introduction of chemicals into the soil (fertilizers, pesticides, herbicides) increases the processes of soil salinity and pollution; -As a result of the increase of irrigation water, the approach of the level of seepage water located under medium, heavy and clay soils with a mechanical composition (1-3 m) to the surface of the earth and the weakening of their flow in the soils of the newly developed areas of our country; -Therefore, the most urgent but extremely complex problem in the newly developed areas is to study the changes in the degree of salt resistance of crops, taking into account the watersalt regime of the soil, the forms of salinization processes, and the period of their areas. it is necessary to strengthen scientific-research works on; -The development of secondary salinization and sedimentation processes is observed in the newly developed brown soils with a reddish hue. This requires the analysis of differentiated soil cover in the meso-and micro-relief forms of the newly developed areas (meadow, saline and saline, non-gypsum, non-saline) and their evolutionary changes; -Taking into account the properties and characteristics of various soil types and types and their characteristic changes in the different soil and climate conditions of our country, it helps to develop measures based on modern scientific and technological achievements and creates an opportunity to increase soil productivity in farms.
There are a number of difficulties in the effective use of meadow alluvial, brownish brown and desert sandy soils in the Bukhara oasis. The most important of these are the high consumption of irrigation water, the observation of secondary salinization processes in the soil and the formation of primary grazing processes in microrelief forms, and the decrease in crop productivity.

Meadow-alluvialsoils
In the delta of the Zarafshan river or in the lower reaches of this river, there are soils of various degrees of salinity, which have been used for irrigation agriculture for many centuries. These soils differ from other irrigated soils distributed in the Bukhara oasis by the clear and sharp separation of the following morphological genetic horizons in their soil profile: Ax -Axos -AV -AV1 -AV2 -AV3 -G. Here Ax is arable layer; Axos -arable layer; AVtransitional horizon and AV1, AV2 and AV3 agroirrigated layers and Gglaciated horizon.These soils, suitable for this morpho-genetic structure, differ from each other in their mechanical composition, salinity level, location of the salt layer in the soil profile, supply of nutrients, absorption capacity and properties. The following are the main signs, properties and characteristics of these soils: 1) periodic and constant wetting of soil horizons under the influence of irrigation, 2) settling of seepage waters at a depth of 1-3 m and 3) accumulation of salt in the upper, middle and lower layers of the soil as a result of their evaporation in hot periods. monitoring of processes.Such a change in the mechanical composition of these soils is directly related to the accumulation of suspended liquid particles of different sizes in the fields of micro-and nanorelief forms. Usually, in the lower parts of the Bukhara oasis, soils with heavy and medium mechanical composition are developed, on the contrary, in relatively high areas of these landforms, soils with light mechanical composition are developed.
Therefore, in these irrigated micro-and nanoreliefs, in soils with different mechanical composition, salinization processes develop in places in seasonal spotty and permanent spotty forms, and the total amount of salt (dry residue), HCO3--, Cl-, SO4-ions, Ca++, Mg++ and Na+ cations and easily soluble salts (MgSO4, Na2SO4, NaCl) formed from their compounds differ from each other in terms of content and quantity (see Appendix 1).
The mechanical composition of anciently irrigated meadow alluvial soils is light, medium, heavy sand and clay. The amount of <0.001 mm particles in the soil profile varies. In terms of their quantity, there is no clear pattern of distribution or accumulation in a separate soil genetic horizon (see Table 1). The degree of salinity of the studied saline soils, the location and type of salinity in the upper and lower layers of saline horizons, the State Committee for Land Resources, Geodesy, Cartography and State Cadastre ("O'zyergeodezkadastr") of the Republic of Uzbekistan, "Uzdavyerloyiha" Institute, subsidiary company "Land Cadastre", It was carried out on the basis of the "Instructions on conducting soil surveys and drawing up soil maps for the state land cadastre" prepared by the employees of the State Research Institute of Soil Science and Agrochemistry in 2005.
Based on this "Instruction", the results of the research conducted on this topic were divided into groups of non-saline, low-saline, and highly saline soils, and the resistance of cotton to the salinization process was thoroughly analyzed. The рN index of the described soils is low-alkaline, and its value fluctuates around 7.21 -7.43 in the soil horizons. The amount of carbonates in the soil profile is 6.78-9.67%.
In alluvial soils of old irrigated meadows, humus is 1.09-1.39% in the uppermost arable layer, and its amount does not exceed 0.93-0.47% in the middle and lower horizons. Nitrogen content is also 0.098 -0.044% in the soil profile and decreases gradually from the upper layer to the lower horizon, like the humus content.
The amount of Na+ and K+ in the absorption capacity is 10-15%. Depending on the level of soil salinity, the composition of salts in medium and low salinity meadow alluvial soils mainly consists of CaSO4, Na2SO4. As the soil salinity increases, the amount of NaCl salts in them also increases. The amount of MgSO4 salt in the soils to be described in both of the above-mentioned cases does not change to any great extent. In addition, Mg(HCO3)2, MgCl2, Na2CO3 salts are not found in the alluvial moderately saline soils, which have been irrigated since ancient times.
After leaching of medium salinity soils, their composition of anions and cations changes dramatically. These changes are clearly observed first of all in the 0-30 and 30-100 cm layers of the soil and in the reduction of the mineralized level of seepage waters.

Conclusion
Since the recommended agromelioration and agrotechnical methods for meadow-alluvial, brown and desert sandy soils developed in multi-layered agro-irrigation deposits are less effective. These measures used in some cases have to be repeated and requires consideration. To achieve these goals, it is necessary to perform the following tasks.
-Studying the morphology, physical and chemical properties of saline soils distributed in the Bukhara oasis before and after leaching of newly reclaimed desert sandy irrigated brown and old irrigated meadow-alluvial soils determination of tolerance characteristics of cotton varieties to salinity levels based on the study of properties and characteristics; -Taking measures for studied soils and the processes of salinization and desalination to prevent negative ecological conditions in the soil during the phases of cotton growth, development, harvest and others.

Suggestions and recommendations
After the completion of the cotton harvest in the areas of widely irrigated and saline meadow-alluvial, brownish-brown, desert-sandy soils in the Bukhara oasis, it is recommended to divide the contours of the fields into separate checks and carry out salt washing works in these areas on the basis of high agro-technologies: 1. In areas with highly saline soils, where underground seepage waters are located at a depth of 100-250 cm, with mineralization levels of 5-10 g/l and more, before washing the salt of this area, ensure the drainage of water in the collector and drainage networks around the crop fields; 2. It is necessary to wash the freshly developed highly saline desert-sandy, newly developed highly saline brown-brown soils at the rate of 2500-3000 and 3000-3500 m3/ha, and 5500-6500 m3/ha in meadow-alluvial strongly saline soils. ; 3.In exchange for adding 35-40 tons of rotted manure, 270 kg of nitrogen, 170 kg of phosphorus and 100 kg of potash fertilizers to each hectare of land in order to continuously increase their water-salt and nutrient regimes and productivity after washing highly saline soils. Fortunately, the value cotton varieties such as" Buxoro-8","Omad","S-4727" increases 1.5-1.7 times. 4. It was found that the influence of soil types and salinity levels on some ecophysiological characteristics of cotton varieties studied in soils with different levels of salinity differed within varieties. Depending on soil types and levels of salinity, the total amount of water in the leaves, the rate of respiration, the density of cell sap, the water deficit of plants, and the increase in the viscosity of protoplasm were noted.The value of all studied parameters was found to be higher in all (weak, medium, strong) salted variants compared to non-salted variants. It was revealed that the change in the value of physiological indicators is different depending on the biological characteristics of the varieties.