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Soil salinization is an excessive accumulation of electrolyte (dissolved or absorbed) salts in the root layer, which inhibit or destroy agricultural plants, reduce the quality and quantity of the crop. According to the FAO (Food and Agriculture Organization of the United Nations), saline soils occupy vast areas in the world - about 25% of the entire land surface.
To date, significant arrays of saline soils are located in South Kazakhstan, Central Asia, in the western United States, in especially arid regions of South America and Australia, in North Africa. Soils in deserts and semi-deserts are characterized by a particularly high degree of salinity; in dry or arid climates.
Soil salinization is the process of accumulation in the soil of more than 0.25% of its mass of salts that are harmful to plants (chlorides, sodium carbonates, sulfates). This process is most common in arid regions, usually in depressions.
FAO experts are sure that salinization is a global problem for humanity. Soil salinization, both natural and secondary in conditions of irrigated agriculture, is one of the factors intensifying the process of desertification. However, it is both a cause and a consequence of other problems. Agriculture. Salinization is associated with drainage problems, destruction of irrigation and drainage systems; inefficient use of water resources; growing demand for agricultural products, which leads to increased pressure on agricultural land; obsolete technologies that do not meet the requirements of today's production systems and many other factors.
The fight against soil salinization is now considered in combination with other activities aimed at sustainable intensification of agriculture, which is one of the foundations of food security.
The situation in the Russian Federation
According to the Russian Academy of Sciences, the total area of saline lands in the Russian Federation is more than 40 million hectares. Salt soils in Russia include solonchaks, solonchakous, saline and deeply saline soils, solonetzes, solonetsous soils, solods and solodized soils. They are widespread in the southeast of the European part of Russia, especially in the Middle and Southern Volga regions, in the Northeastern Ciscaucasia, in the south of Western and Eastern Siberia, in Yakutia.
In Russia, the regions of the Volga region and Western Siberia turned out to be the richest in saline soils, where their areas are 11.6 and 10.2 million hectares.
In the steppe zone of the Pre-Altai province on the territory of the Altai Territory, the total area of saline soils is about two million hectares.
Of course, not all of these areas are idle. Basically, agricultural producers use them in field and fodder crop rotations, or as hayfields and pastures. There is only one reason - low natural productivity, on average it ranges from 2 to 6 centners per hectare.
natural salinity
Currently, a distinction is made between primary or natural salinization and secondary or accelerated salinization due to human activities.During primary salinization, the distribution of salts in the soil occurs as a result of a wide variety of processes.
Natural salinization is a rather slow natural process during which salts are pulled from groundwater to the surface layers of the soil during the upward movement of moisture. This process is influenced by the nature of the soil-forming rock and the depth of saline groundwater.
With a close occurrence of groundwater, a constant upward flow of water is formed, which, evaporating, deposits salts in the soil. The greatest depth of the groundwater level at which soil salinization begins is called the critical depth.
Capillary salinization of the soil is the more intense, the greater the evaporation, the higher the salinity of the water and the longer the evaporation process.
Groundwater is evaporated by soil and plants if the capillary fringe of groundwater is in contact with the root-inhabited soil layer, but if the fringe lies below the root-inhabited layer, then groundwater does not evaporate and soil salinization does not occur.
The natural factors that determine the development of primary soil salinization include: climate, topography, drainage of the territory, salinity of soil-forming and underlying rocks, and the presence of mineralized groundwater. The climate, as a factor determining the development of the salinization process, is characterized by the predominance of evaporation over precipitation. Under these conditions, the process of moisture and salt transfer is activated and an evaporative geochemical barrier is formed, leading to the process of salt accumulation.
In areas with a high amount of precipitation, salts are usually washed into the underlying soil layers and are carried away by underground groundwater to lower places, to the seas or oceans. Groundwater with good permeability of soils and deep occurrence of water-resistant layers move down the slope, taking salt with it.
However, in areas with insufficient precipitation (typical for zones of arid agriculture), salts are not washed out into the underlying layers and can accumulate on its surface. In low, flat areas, easily soluble salts accumulate not only in the upper layers of the soil, but also in subsoil groundwater. Therefore, a significant excess of water consumption over its inflow and the difficulty in the flow of surface and groundwater are the main cause of soil salinization. As a result, soil salinization is most widespread in semi-deserts and deserts.
These places are characterized by a long frost-free period, high temperatures and very little precipitation. These climatic features create conditions for intensive water consumption by soil and plants. Water in the form of precipitation far from covers the entire flow here, so water is drawn up from the underlying salt-bearing layers. Along with the water, the salts dissolved in it also move, but the water evaporates, and the salts, precipitating, accumulate on the surface of the soil.
The most severe salinization of the soil occurs in large intermountain pits and insufficiently drained plains. Weak drainage of the territory contributes to the slowdown of lateral landscape-geochemical flows, the rise in the level of groundwater and the activation of salinization processes in arid, semi-arid zones. The presence of easily soluble salts in the rocks in the zone of active moisture exchange contributes to the formation of saline soils. In these places, lakes with self-planting salt are often formed, where mining is usually organized mainly table salt. The soil around the lakes is covered with a snow-white coating of salt.
Salts in the soil can also accumulate during the weathering of the minerals that make up rocks released during volcanic eruptions. Also, salts can enter the root-inhabited soil layer from saline soils with salty dust, which is formed when solonchaks are scattered by the wind or from sea water sprayed by storm winds.
Primarily saline soils are developed in our country mainly in the zones of semi-deserts and steppes. In more northerly natural zones, soil salinization manifests itself only locally (in Yakutia, on the coast of the northern seas, etc.). Salinization here is associated with the emergence of salt-bearing rocks on the surface, or with the influx of easily soluble salts from outside.
In areas subject to excessive salinity, even halophytes do not grow, that is, plants confined to highly saline soils. However, the area of such barren soils is relatively small. The main area of saline soils can be developed for agricultural crops through the use of reclamation and agrotechnical measures.
Human factor
Secondary salinization of soils is almost always the result of improper irrigation regime in crop production, occurs as a result of excessive irrigation that increases the level of saline groundwater or irrigation with highly mineralized water. According to the FAO, around 30% of all irrigated lands are subject to secondary salinization and alkalinization worldwide. Secondary salinization is most active in zones of natural salinization development. For example, in the Caspian lowland, the process of salinization of pastures and irrigated lands is actively going on. Due to improper irrigation, today 53% of all irrigated lands are saline in the irrigated regions of Central Asia, and 40% of all irrigated lands in Transcaucasia. In general, the area of saline soils in Russia is 25% of the total area of irrigated land. Soil salinization weakens their contribution to the maintenance of the biological cycle of substances. Many species of plant organisms disappear, new halophyte plants appear (saltwort, etc.). The gene pool of terrestrial populations is decreasing due to the deterioration of the living conditions of organisms, and migration processes are intensifying.
How does secondary salinization occur? Salts in the soil are in a dissolved or absorbed state, so the movement of water in it inevitably causes the movement of salts and the more, the better their solubility in water.
With excessive irrigation, excess moisture goes deep into the soil cover, where it merges with saline groundwater. As a result, there is a capillary rise of salts to the surface layers, there is a migration of salts.
The occurrence of secondary salinization is also promoted by improperly applied agricultural techniques. In particular, a poorly planned field with a close occurrence of saline groundwater is one of the reasons for the occurrence of saline spots. The stronger the excess soil moisture and the higher the level of saline groundwater, the more prerequisites for the occurrence of secondary salinization. On the elevations and hills of the field, a sharp increase in water evaporation is observed. Because of this, salts rise along with water along the capillaries, like a wick. As the water evaporates, the salts precipitate and accumulate in the soil.
Failure to comply with agrotechnical measures and water use rules on soils prone to salinity contributes to the emergence of the so-called patchy salinization. Such salinization is often found in irrigated cotton-growing areas, where varying degrees of soil salinity and solonchak spots are observed in the same field. Spotted salinization is widespread in a number of regions of Central Asia.
Spotted salinization often occurs where there are raised, hilly areas 8–20 cm high on the soil surface. at the same time, groundwater was desalinated, its level increased, and in hilly areas, irrigation water did not reach groundwater, the supply of which was not replenished, and they were not desalinated. As the groundwater that rose to the soil surface evaporated, even areas were practically not salinized, while salts precipitated on the raised salts and thus salinity spots appeared.
Due to the heating of the soil in flat areas of the field, fresh groundwater evaporates, which does not cause soil salinization, while in hilly areas, the evaporation of salty groundwater entails a strong salinization of the soil.
It should be noted that salinization is not an inevitable and mandatory consequence of irrigation. A well-designed irrigation system often contributes to the desalinization of saline soils. However, with excessive irrigation and in the absence of groundwater outflow, the soils become saline, and sometimes become swampy.
It should be noted that improper irrigation, in addition to salinization, can have many other negative consequences: the soil structure is destroyed, leaching, bogging and alkalinization occur, up to complete soil degradation.
Secondary salinization is one of the main degradation processes that determine the ecological state of lands. At the same time, they distinguish: soil salinization itself - excessive accumulation of water-soluble salts and a possible change in the reaction of the environment due to a change in their cation-anion composition; solonetzization - the acquisition of specific morphological and other properties by the soil, due to the incorporation of sodium and magnesium ions into the soil absorbing complex, which is considered as an independent process of adverse changes in soils of the saline series. Soil salinity is assessed: by the depth of the upper boundary of the salt horizon; according to the composition of salts (the chemistry of salinity); according to the degree of salinity; by the percentage of saline soils in the soil contour. According to the depth of the upper boundary of the salt horizon, there are: saline soils containing salts in the upper meter layer of the soil profile and deeply saline - the upper boundaries of the saline horizon are located in the second meter. Potentially saline contain readily soluble salts at a depth of 2–5 m, that is, in parent and underlying rocks. According to the composition of salts (chemistry), soils are divided into predominantly chloride, predominantly sulfate and soda (with the participation or predominance of bicarbonates or sodium carbonates).
The most toxic is soda salinity. According to the percentage of saline soils, the territories are distinguished: with a predominance of saline soils (the area of saline soils is more than 50% of the contour area); with high participation of saline soils (50–20%); with the participation (20-5%) of saline soils; with local manifestation of saline soils (less than 5%).
Soil fertility and high yields on saline soils are out of the question - the basis of fertility is humus is lost, mineralized, soil moisture binds, physical properties soils become unfavorable for plants, the activity of soil organisms is inhibited.
To be continued
Soil salinity is one of the biggest problems you can face on your own plots. Even trees or bushes for such soil are difficult to pick up, and perennials and flowering plants at all. True, this is not entirely fair: just among herbaceous plants there are also such Spartans who are not afraid of the abundance of mineral salts and polluted environment. The correct selection of plant species will allow you to create a full-fledged landscaping even in such problem areas.
Soil salinity, as well as polluted air, gas pollution, are considered very dangerous factors that complicate landscaping and lead to great difficulties in selecting plants. The accumulation of salt in the soil cannot be noticed without special studies; it manifests itself apparently only by its effect on plants and their development.
In private gardens, the problem of salting is typical not only where the plots are laid out on salt marshes, located near the sea or ocean coast. Salinity is a problem of improper de-icing or the proximity of the garden to sidewalks, roadsides, public roads - any objects where salts are used for winter de-icing. Salinization can also occur when unsuitable water with a high concentration of minerals is used for irrigation. Any soil is considered saline if the concentration of easily soluble mineral salts in it exceeds 0.1%.
The accumulation of salt in the soil leads to damage to the roots, disruption and stunting, drying out and loss of decorativeness in most of the plants we are used to. cultivated plants, but not all of them. The range of horticultural crops is wide not only in terms of size, style, foliage type, flowering characteristics, lighting preferences, but also in terms of requirements for soil characteristics. Along with plants that are sensitive to the composition and parameters of garden soils, there are also crops that are undemanding to the soil, and even more - ready to put up with conditions that are unfavorable for most of their competitors. Right choice plants allows you to find suitable candidates for landscaping even the most problematic areas. And salinization of the soil for them is no exception.
When selecting plants that can tolerate an increased level of salts in the soil, they always first of all focus on bushes and trees that can be used for hedges and protective plantings along the perimeter of the site. But it is not necessary to be limited to giants, as well as to abandon plans to create lush narrow flower beds or flower beds, colorful and cheerful compositions. Nobody canceled the style of the garden, its color scheme, the design concept, including for saline areas. And the task of landscaping in areas with a high salt content will help to solve correctly selected herbaceous perennials.
Despite the prejudice, it is herbaceous plants, and not evergreen conifers or typical garden shrubs and trees, that cope better with salinity. This happens due to several factors:
- Until the time when it is time to deal with snow marks and icing, the aerial parts of herbaceous perennials are already dying off, drying up, and a period of their complete rest begins.
- In order for the salts to go deeper, below the level of the roots of perennial plants, good moistening with melt water is sufficient (or in the spring it is enough to carry out several very plentiful waterings).
- Such crops are easier to replace and adjust plantings if the early selected species grow poorly and do not live up to expectations.
When choosing options for lush landscaping of saline areas, it is worth simplifying your task as much as possible and provide for the possibility of changing compositions in the future. For saline areas, it is better to choose not complex compositions, but choose a combination of 3-7 most reliable plants that contrast with each other and reveal the style of garden design, making up a simple rapport from them (in the sense of a repeating pattern) - a rectangle, square or circle. To fill the entire area, the selected scheme is simply repeated, duplicated, beaten off, reaching the desired size. The same planting pattern will allow, if necessary, to easily replace one plant with another, determine the number planting material and make the necessary adjustments in time.
When growing herbaceous perennials in saline areas, it is important not to forget about timely care. Removing dry and damaged parts of plants in spring, timely rejuvenation and planting, maintaining a high-quality mulch layer of organic fertilizers will allow plants to maintain their decorative effect for many years. Watering in the spring will help to cope with new salt deposits, and during the summer - to maintain the attractiveness of greenery. Otherwise, care is similar to any other flower garden and comes down to weeding, loosening the soil, and removing fading flowers. If the plants are planted in places where splashes of dirty water from under the wheels of cars can fall on them, then a protective layer of straw, spruce branches, needles is used as mulch, which are periodically changed and destroyed. In winter, such mulching will help to reduce the level of salinity near the road.
The most spectacular perennials for saline areas
Day-lily (Hemerocallis) is one of the favorite universal herbaceous perennials, the flowering of which is by no means inferior to the beauty of the linear basal leaves collected in dense bunches.
Already at the time of the growth of young foliage of daylilies, the bushes look very elegant. The greenery of this perennial, creating original arrays, brings order and elegance to any flower garden. The daylily looks great in summer, and the leaves emphasize the beauty of flowering, reminiscent of royal lilies in shape. Daylily flowers bloom for just one day (it’s not for nothing that we call the plant a beautiful day), but continuous flowering continues from early to mid-summer, and sometimes daylilies allow you to enjoy a second wave of flowering. In autumn, they quickly leave the garden scene, but it is not easy to forget their summer parade.
Steller's Wormwood (Artemisia stelleriana) is a spectacular perennial with widely spread shoots and amazingly beautiful carved greenery, the silvery lace of which can delight anyone. This is an excellent ground cover that demonstrates its talents on saline soils.
Even young wormwood looks like luxurious silver lace. Wormwood pleases with young leaves in the first half of spring, without losing its attractiveness until the end of the garden season. The foliage looks especially luxurious in summer, when the beauty of the edge on the leaves is fully manifested. The flowering of wormwood is inconspicuous, the greenish-yellow apical inflorescences do not spoil the plants, but do not draw attention from the main stars in the neighborhood. Pruning inflorescences, a light haircut will allow wormwood not only not to lose its attractiveness throughout the summer, but also to remain a decoration of the site even with the advent of winter.
This salt-tolerant plant can only be used to decorate well-lit areas.
Coreopsis whorled (Coreopsis verticillata) - one of the brightest perennials with basket inflorescences, which conquers primarily with its dense and lush greenery. This hardy look distinguished by its durability.
Whorled coreopsis may not be limited to 1 m in height. Branched shoots are not visible due to the abundance of narrow, needle-shaped, bright green leaves that form a continuous lacy texture. The inflorescences are star-shaped, radiant, light yellow, they seem to be scattered over dense greenery like shining stars. Coreopsis will delight with decorative foliage only in the second half of spring. But on the other hand, you will not find such a bright, dazzling green color in other perennials. And when the baskets of inflorescences begin to bloom at the beginning of summer, they seem to illuminate the places along the paths and sidewalks.
This salt-tolerant plant can only be used to decorate well-lit areas.
stonecrops (Sedum) conquer with their undemanding and endurance. The possibility of using sedums in garden design is not limited even to saline areas. But more resistant to salinity than stonecrop rock (Sedum rupestre), no other species can boast.
Stonecrop rock is one of the compact types of sedum that can form solid rugs. The height is limited to a maximum of 25 cm. The shoots are recumbent, with awl-linear leaves. Colors are usually very bright. Stonecrops with their light juicy leaves in neat pillows in the second half of spring pleasantly enliven the compositions. To achieve even greater expressiveness and pomp, it is better to cut stonecrops in early summer.
This salt-tolerant plant can be used to decorate both well-lit and shaded areas.
Euphorbia multicolor (Euphorbia epithymoides) is one of the most spectacular types of euphorbia. Dazzling flowering and neat hemispheres of lace bushes make this euphorbia the best spring plant for decorating any site, including those with saline soils.
This type of milkweed in height can exceed half a meter. Euphorbia reach the greatest decorativeness in the spring. Multicolor spurge with its bright, yellow tops of shoots in young bushes attracts attention already in early spring, although it only reaches its peak of decorativeness closer to summer. The flowering of milkweed in early summer significantly spoils the decorativeness of the plant. But it will already fulfill its function in full on saline areas, and the growing neighbors can easily compensate for this shortcoming. Pruning at this time will allow you to preserve the splendor and beauty of greenery, enjoying the fall autumn palette.
This salt-tolerant plant can only be used to decorate well-lit areas.
Aquilegia canadensis (Aquilegia canadensis) is one of the “special” types of watershed. Its flowering, and the splendor of the bushes, are pleasantly different from other varieties and modern hybrids, as well as undemanding to growing conditions.
Canadian aquilegia is a tall perennial (up to 60 cm) with a densely spreading bush, reddish or green shoots, beautifully dissected dark leaves and single, large, narrow drooping flowers up to 5 cm long with an atypical red-yellow color and yellow stamens sticking out of the flower. Aquilegia blooms by mid-spring. The touching and magical caps of her inflorescences have given rise to so many fabulous nicknames for a reason. Elven caps, although of an unusual shape and color, look great not only in landscape design. And to keep the aquilegia looking great, it can be partially or completely cut off after flowering to encourage the growth of new greenery and shoots.
This salt-tolerant plant can be used to decorate partially shaded or shady areas.
Liriope muscari (Liriope muscari) is one of the most unusual perennials in any garden collection. Non-standard foliage and flowering, high decorativeness, unique growth form allows the use of liriope as a unique accent. And resistance to salinity pleasantly surprises even experienced gardeners.
Unusual rhizomes and stolons on liriope roots are just one of the features of this non-standard perennial. Rigid, linear, dark emerald green leaves, gracefully curving in arcs in curtains and dotted with small, bead-like flowers, inflorescences up to 30 cm high, attract admiring glances to Muscari liriope. The showy liriope inflorescences and its thin leaves look great throughout the summer, and the plant itself looks like green fountains. Violet-blue liriope candles place touching accents on the sod and emphasize the freshness of the plant. Liriope looks good even in winter, so it is better not to rush to cut the plant in autumn.
This salt-tolerant plant can be used to decorate places with both good and secluded lighting.
Soft cuff (Alchemilla mollis) is one of the main decorative and deciduous perennials and partners for flowering plants. Undemanding to conditions, the ability to grow in her are equally valuable.
The cuff is soft - an upright perennial up to half a meter high with rounded, soft, pleasantly velvety bright green leaves. The spring bloom of the cuff looks like solid lace. The green and yellow lush show looks amazing and lights up even the darkest corners. After flowering, it is better to cut the cuff in order to enjoy a repeated colorful show a little later. Its bright foliage looks great, in the fall the cuff dies off only when the air temperature drops to -5 degrees.
This salt-resistant plant can be used to decorate any, including shady areas.
Nippon nomad(today reclassified as Anisocampium niponicum, but deprecated name Athyrium niponicum also common) - one of the most beautiful ferns. Its leaves are so beautiful and unusual that it is very difficult to believe that a pleasant “bonus” is also attached to the spectacular appearance of the plant - the ability to grow on saline soils.
The young leaves of the nomad plant attract admiring glances already in the spring, spectacularly unfolding from sprouts with a purple tint. But even in summer, gray carved leaves look just fine. Red or reddish-brown sori, surprisingly graceful feathery lobes of wai, and a constant metallic sheen turn the green of the Nippon nodules into a perfect shade decoration. The carved wonder of the nomad looks great and is highly frost-resistant. Usually the height of the plant is limited to 40-60 cm.
This salt-tolerant plant can be used to decorate places with secluded lighting.
It is also worth paying attention to other plants that are promising in terms of their tolerance of saline soil - eryngium, veronica, gaillardia, cimicifuga, yellow lamb, Chinese astilba, hellebore hybrids, santolina, periwinkle, Schmidt's wormwood, evergreen iberis, seaside armeria, geyhera, yarrow felt, large-flowered foxglove, trifoliate waldstein, stonecrop Kamchatka, Byzantine chistets.
Soil salinization control methods
Ignoring the very problem of soil salinity is very dangerous. Suitable plants can be found for any area in the garden, but if these problems are severely neglected, the lack of measures to minimize salinity levels will lead to the fact that even the hardiest stars can not withstand the concentration of salts. Therefore, in addition to choosing suitable crops, it is worth taking care of measures to prevent the aggravation of such a situation:
- stop using salts or minimize their amount;
- try to deal with excess snow in a timely manner and remove it from sidewalks and paths in order to avoid situations where it is impossible to cope without anti-ice chemistry;
- replace the usual salts with safer means - sand, potassium chloride or calcium-magnesium acetate;
- install wind protection and high fences if your garden is located in coastal areas, etc.
UDC 631.445.52
- SANIIRI ,
(Karshi Engineering and Economic Institute, Uzbekistan)
ENVIRONMENTAL PROBLEMS OF IRRIGATED LAND
SUBJECT TO SALT
The article lists the problems and reasons for the decline in the productivity of irrigated lands due to the causes of the emergence and development of soil salinization, deterioration of water quality. Based on the analysis of the situation, the authors show the role of reclamation in increasing the productivity of saline lands and give suggestions for a strategy to improve their reclamation state.
Problems and causes of efficient lowering of irrigated soils for beginning and developing soil salinity, making worse water quality are enumerated in the article. On the base situation analyze the authors showed the role of melioration in raising efficiency of salinity soils and are made an offer for strategy of improvement their meliorative state.
In our region, located in the arid zone, there are a lot of problems associated with irrigation and melioration. Irrigated agriculture is the backbone of the region's agriculture. Against the background of a wide variety of natural conditions in the irrigated zone, poor water management at various functional levels of irrigation systems creates many problems that worsen soil fertility and the quality of lands in agricultural use, as well as aggravate environmental issues, expressed in salinization and pollution of irrigated soils, groundwater and water sources.
Irrigated agriculture in Uzbekistan, before the start of mass land development, which began approximately from the middle of the last century, was confined to river valleys, their first and second terraces and deltas. This was due to the weak technical capabilities of water intake at that time and the relatively favorable hydrogeological and soil features of the territory. Only the peripheries of the so-called alluvial cones and delta areas of ancient irrigation were subject to surface salinization.
The main arrays of saline soils in Uzbekistan are confined to regional zones of groundwater wedging out, even with a relatively low mineralization of 2–5 g/l, as well as to river deltas and local relief depressions. Here the formation of solonchaks took place.
Among the most typical depressions in the steppe and desert zones, which have significant areas of solonchaks, are the Shuruzyak and Arnasay depressions in the Golodnaya steppe, the Charagyl and Dengizkul depressions in the Karshi steppe, as well as the Tudakul, Shorsay and Shorkul depressions in the Bukhara oasis.
In arid climate, the most powerful and permanent source of salinization of irrigated soils is readily soluble salts in river waters. With an increase in the degree of use of the surface runoff of rivers for irrigation, their accumulation in soils and underlying sediments increases. On regularly irrigated lands, the place of salt accumulation can be micro elevations resulting from poor-quality field surface planning, poorly irrigated or non-irrigated areas adjacent to irrigated areas, as well as depressions to which there is a constant inflow of groundwater from neighboring irrigated areas.
Irrigation of fields has a decisive influence on the transfer of salts in soils. Irrigation water is also a powerful source of salts for the soil (since about 80% of it is spent on evaporation, and the salts remain in the soil) and, at the same time, they “transport” them into the deep subsoil layers with regular and timely irrigation. The economic well-being of irrigated lands and the ecological state of irrigated territories depend on how irrigation is carried out, how much it replenishes the natural moisture deficit of the soil layer, and is not useless, bypassing the surface of the field, nourishes groundwater with losses. . Insufficient irrigation of local areas always leads to their salinization due to inflow from adjacent, well-irrigated territories.
The conditions for the transport of salts from the mountains towards the reservoirs of the final runoff under natural conditions, under the intensive influence of irrigation and drainage, change dramatically, both at the local and regional levels. Hydrogeological processes in irrigated areas and the hydrological regime of soils are changing. This is that:
Irrigation canals of reclamation systems create sources of concentrated flow of water losses into groundwater, thereby forming their local pressure;
Imperfect irrigation technique is not able to ensure uniform distribution of water over the fields, water losses in the fields are confined to the initial (deep discharge) and end (surface discharge) sections of the furrows, which causes local soil salinization;
Drainage in, basically, does not work to divert the outflow of water that has entered the fields, but removes groundwater that has risen from losses from canals or discharges from fields. Therefore, it does not so much maintain the balance of salts in the soil layer in the fields, as it diverts all non-productive water losses (by % back to water sources!).
For the formation of the water-salt regime of the soil, it is very important in what way and how it gets into it. Nevertheless, at present, in a real existing situation, seasonal salinization of irrigated lands almost everywhere occurs not so much due to the quality of irrigation lands, but due to the pulling up of salts dissolved in groundwater, which occurs as a result of a violation of the irrigation regime. During evaporation, more salts are often introduced into the root zone from groundwater than during irrigation even with mineralized water.
The rapid development of irrigated agriculture since the middle of the last century has contributed to the development of modern views on the methods of reclamation of saline soils. Faced with the problems of the occurrence of "secondary" salinization of lands, for the most part initially saline or subject to salinization, caused by the imperfection of the applied methods of irrigation and poor drainage of territories at the beginning of the mass development of new lands, scientists and engineers began to look for ways out of this situation.
The method of flushing by flooding was borrowed from the past experience of farmers and mechanically transferred to new conditions, completely different in terms of water supply, the degree of use of the land fund and, most importantly, hydrogeological conditions.
In themselves, these ideas were reasonable enough, but their implementation by imperfect methods of water distribution in the fields led, as we now see, to disastrous consequences.
The point is that they were overlooked and unresolved the two main, most complex and costly problems are irrigation techniques and salt removal.
The first problem is related to the fact that the uniform distribution of water across the field and the strict rationing of irrigation water with the help of perfect irrigation facilities is expensive (although it pays off if we consider the system as a whole).
The second problem is the unresolved issues of drainage and waste water disposal at the regional and global level.
The discharge of these waters, as mentioned above, falls, for the most part, back into the water sources, which turns the idea of a leaching mode of soil irrigation into an absurdity, since the salts removed by expensive drainage from some massifs have become a source of salt accumulation in others.
These two problems are currently key in the reclamation of saline lands.
Research materials on the Golodnaya and Karshi steppes and other regions show that the success of development often depends not on the initial depth and degree of desalination of the root horizon, but on the irrigation regime and agricultural technology of those crops that are cultivated after leaching. Therefore, flushing should be considered not as an independent measure, but as an element of the integrated development of saline lands in conjunction with the engineering solutions adopted for the operational period. This will allow assessing the acceptability of one or another method in terms of the minimum cost of material and human resources per unit of output. At the same time, it is necessary, if possible, to manage when carrying out washings with the fleet of mechanisms that are available on the farms, since this is the most economical.
With a shortage of equipment, water and an unsatisfactory condition of drainage systems, such flushing with large norms is carried out less and less. In the current conditions, the principles of primary reclamation should be reconsidered, since the problem of salinization is becoming even more urgent than before, and the issues of reconstruction of systems, water shortages and material and technical means are becoming more problematic.
In search of ways to solve the problems of reclamation of saline soils, domestic and foreign researchers have proposed methods for more efficient removal of salts with lower specific costs of washing water, which, using technically simple and relatively cheap methods of distributing water over the surface of fields, combine gradual desalination of soils with improving their water-physical properties. properties and fertility. These include intermittent flushing using various irrigation methods, depending on the permeability of the soil and the surface topography.
In this case, leaching is carried out by separate irrigations at a rate of 2-3 thousand m3/ha at intervals from 3-5 to 10-15 days or more, depending on meteorological and organizational and economic conditions. When filling a free tank, the intervals are determined by the drawdown of groundwater by drainage to a depth of 1.5-2.0 m. At the same time, as experience shows, the flushing effect decreases from irrigation to irrigation, and after 4-5 irrigations, the removal of salts practically stops.
Intermittent water supply allows maximum use of the free capacity of the aeration zone for the accumulation of salts washed out from the upper horizons, due to irrigation rationing, thereby eliminating the need for the construction of temporary drainage. The presence of free capacity ensures uniform desalinization of the upper soil layers along the width of the interdrain, since the rate of absorption in this case will not depend on the distance to the drain (in contrast to the filtration rates when the free capacity is fully saturated).
The combination of high humidity of the leached stratum with good drainage contributes to the development of aerobic processes in the leached strata. After desalination of a layer sufficient for seedlings, it is possible to sow master crops and continue leaching, combined with their cultivation. Intermittent leaching is especially useful in areas where there is an acute shortage of irrigation water.
In the accepted norms for irrigation of agricultural crops, in order to eliminate seasonal salinity, it is recommended to carry out preventive leaching irrigation, which is also water-recharging. The norms of vegetation irrigation, as a rule, are designed for the fact that, in combination with water-recharging and preventive irrigation, they will maintain a "leaching" irrigation regime, when all the salts that enter the field with irrigation water during the year will be removed with groundwater by drainage. In case of violation of the normal irrigation regime of crops in conditions of water shortage during the growing season or for economic reasons, when crops are not grown for a significant part of the hot growing season (for example, re-crops after winter cereals), on lands with relatively close and mineralized groundwater, seasonal salt accumulation.
An obligatory condition that determines the effectiveness of operational leaching is to ensure the drainage of irrigated lands and the normal functioning of the existing collector-drainage network. However, drainage (horizontal, vertical, etc.) creates only conditions for downward filtration in the washed soil layer. The creation of reliable and economical drainage provides a certain reclamation background, but cannot in itself solve the problem of salinization control. To ensure desalinization against the background of drainage, it is necessary to carry out leaching or create a leaching irrigation regime corresponding to the selected reclamation regime by a combination of drainage, water supply and agricultural technology. This combination determines the interaction between irrigation and groundwater and affects the total water consumption.
The soil layer is relatively small in thickness, so irrigation water must be dosed so accurately and evenly over the area of the field in order to create the necessary water and, especially, salt regime in the root layer. The underestimation of this circumstance, to a large extent, led to the difficulties that are observed on irrigated lands subject to salinization in the Aral Sea basin.
Applying the perfect irrigation technique can unravel a whole knot of problems. It saves up to 40% of irrigation water on the field, creates a favorable water-salt regime that almost doubles the yield of agricultural crops, makes it possible to meet the necessary agrotechnical requirements for growing crops, prevents deep and surface water discharge, ensures uniform water distribution over the field area, which contributes to improvement of reclamation state of lands.
Possible ways out of the crisis.
A total reconstruction of irrigation systems that have been created for centuries is not possible today, primarily for economic reasons. All the more problematic is the transfer of irrigation to a perfect irrigation technique. What can and should be done today, practically without high costs?
First of all, to organize the rationing and streamlining of water use, without which, in general, to talk about efficient use water resources are not worth it.
Continue the reconstruction of irrigation and drainage systems, where it is urgently needed.
Create legal and economic incentives to encourage the use of improved irrigation technology, especially for those conditions in which real water savings and real cost recovery can already be obtained today.
Already today, the use of advanced irrigation technology can be cost-effective for individual farmers in systems with high soil permeability and a shortage of irrigation water raised by pumps. This situation is typical for the irrigated adyrs of the Ferghana Valley and other regions similar in natural conditions.
At present, oddly enough, the processes of salt transfer and management are not sufficiently studied. in soils . A new regional concept of their melioration is required, taking into account economic conditions and environmental consequences in the analysis of previously adopted technical solutions. Under the conditions of the Aral Sea crisis, which is largely associated with the depletion of the basin's water resources at the current level of the technical condition of irrigation and drainage systems, these problems become vital for the region. For the operational management of these processes, first of all, the monitoring service of irrigated areas, potentially dangerous for the development of secondary salinization processes, should be strengthened. The development of this service is seen in the application of remote mapping technologies in combination with GIS methods. In addition, methods of ground-based simplified operational control salinity for the purpose of managing soil salinity in specific fields during the growing season.
The realities of today force us to look for certain ways that are most harmless to soils and plants grown on them. Theoretical basis The use of highly mineralized waters for irrigation and flushing is that the concentration of salts in them is much lower than in soil solutions. For irrigated soils, the optimal concentration of salts in soil solutions is 3-5 g/l, at 6 g/l there is a slight inhibition of plant growth, 10-12 g/l - strong inhibition, at 25 g/l it dies. Thus, water with a salt content of up to 3-5 g/l can theoretically (assuming free gravitational flow and continuous water supply) be used without causing damage to plants. However, in practice, the following should be taken into account: the salt tolerance of the crop and the phases of plant development; high evaporation; insufficient operational control of salinity or osmotic potential of the soil; untimely irrigation and low level of their technology; lack of water outflow.
In this regard, water with a mineralization of more than 3 - 5 g/l should be used very carefully and, as a rule, diluted with river water. Be sure to take into account not only the type of irrigated crops, but also varieties that may be more sensitive to salts. The use of drainage water to cover the shortage of irrigation water is more promising for growing salt-tolerant crops (cotton, winter wheat).
When water of increased mineralization is used for irrigation in the soil absorbing complex, calcium is displaced by sodium and magnesium (by 5-6% of the total). It has been established that an increase in the content of absorbed sodium in the soil is associated with an increase in its degree of salinity and is reversible, i.e., when flushed and irrigated with ordinary river water, the ratio of exchangeable sodium and magnesium cations decreases, while calcium increases. If the danger of soil solonetzization processes in the territory under consideration is practically absent when using mineralized waters, then the danger of secondary soil salinization poses a serious threat. Forecasts of the use of mineralized waters on light soils (light loams, sandy loams and sands), carried out on the basis of the condition of maintaining a concentration of salts in the soil solution that does not harm the crop, showed that: with a water mineralization of 2 g / l, the rate should be increased by 5-7%; 3 g / l - by 20%, and at 4 g / l - up to 30-50%. On medium loams, even with a water mineralization of 2 g/l, the water supply must be increased by 10%. How realistic is the possibility of such an increase in the irrigation rate depends on many conditions, but, first of all, on the depth of groundwater and on the drainage of the site, which should ensure the outflow of additional volumes of water.
In the republics of Central Asia, soil properties, water quality and the composition of major agricultural crops in most cases allow relatively safe use of collector-drainage water. Negative Consequence may be mainly salt accumulation. Due to the low sorption properties of soils and a large proportion of calcium salts in water and soil, the processes of soil solonetzization are practically excluded. Salt accumulation, only incidentally, leads to an increase in the proportions of exchangeable sodium and magnesium in the absorbing complex of soils. Experiments show that these processes are reversible during desalinization, however, water with a salinity of more than 3-5 g/l should not be used. If it is necessary to use them, it is necessary to take into account the type of irrigated crops in terms of salt tolerance (which varies in some species according to the phases of development), as well as the water permeability and granulometric composition of the soil. At the same time, it is important to prevent soil salinization by supplying additional volumes of water. In the presence of water and a good outflow from the field, this can be done during the growing season, increasing the frequency of watering or overestimating the "net" norms. In case of insufficient water during the growing season and poor drainage, it is necessary to flush the soils during the non-growing season, choosing the time for flushing when the groundwater is at its deepest.
What possible alternatives for a way out of this situation in the future can be offered?
We have considered schematically several possible options for irrigation development strategies in comparison with existing conditions (option 1). Option 2 represents the ideas implemented in the work , where only partial reconstruction of irrigation systems was considered. Option 3 provides for the use of advanced irrigation techniques without increasing the existing level of sophistication of irrigation canals. Option 4 considers the consequences of applying improved irrigation technology and upgrading the existing level of sophistication of irrigation canals to the world level. That is, option 4 is the limit, above which, with modern crop cultivation technologies, it is hardly possible to rise. These calculations clearly show what opportunities for the development of irrigated agriculture with a limited amount of water resources can be provided by the use of advanced methods of irrigation and reconstruction of irrigation and drainage systems.
Conclusion.
The paper analyzes the natural and technical causes of the ecological crisis in irrigated agriculture in Uzbekistan. The question of changing the concept of reclamation of saline-prone lands has been raised and options for getting out of the current situation in the future by improving irrigation and reclamation systems in various ways have been proposed.
1. Estimated values of irrigation norms for agricultural crops in the basins of the Syrdarya and Amudarya rivers. Tashkent, "Sredazgiprovodkhlopok", 1970. P.292. 2. General scheme for the development of irrigated agriculture and water management of the Republic of Uzbekistan for the period up to 2015. "Vodproekt", Tashkent, 2002. 3. Parfenova NI, Reshetkina N. Ecological principles of regulation of the hydrogeological regime of irrigated lands. .1995, 360 p. 4. , Yamnova I.A., Blagovolin zoning of saline soils of the Aral Sea basin (geography, genesis, evolution. M., 19p. 5. , On the choice of impervious and drainage measures in the design of irrigation systems. Hydraulic engineering and melioration, 1977, No. 5, pp. 44-51.
