Saline-alkali soil treatment method

Abstract

The invention relates to a saline-alkali soil treatment method, which aims at saline-alkali soil, especially coastal saline-alkali soil, firstly, clay separation walls are arranged in the saline-alkali soil to separate land parcels, so that the problems of concentration of surrounding salt to a treatment area and rebalance of water-salt movement are prevented, and the limitation of the terrain of a flat terrain area on soil preparation is solved. Besides, comprehensive treatment is carried out on the saline-alkali soil from the source through measures of arranging a gravel salt-resistant permeable cushion layer under the cultivation soil, arranging a drainage concealed pipe under the clay separation wall, treating the collected seepage water through ion exchange and the like, and a remarkable treatment effect is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of saline-alkali land treatment, and in particular to a saline-alkali land treatment method. Background Art

[0002] Salt-alkali land is a concrete manifestation of land degradation. Natural factors and unreasonable human development are important forms of land salinization. my country has a large area of ​​coastal saline-alkali land. The vast coastal areas have low terrain and poor drainage. They are infiltrated by seawater, and a large amount of salt is retained in the soil. With the capillary action of the soil and the evaporation of water, the salt in the soil is transferred from the bottom of the soil to the surface and enriched in the surface soil, which greatly affects the growth of plants and the transformation of fertile fields.

[0003] The salt content of coastal saline-alkali land is mainly chloride. According to the research of Liu Qingsheng et al. (Liu Qingsheng, Liu Gaohuan, Xue Kai et al. A brief analysis of soil salinization characteristics of geomorphic units of different scales in the Yellow River Delta in modern and contemporary times [J]. Chinese Agricultural Science Bulletin, 2006, (11): 34-39.), the groundwater depth is 0.5-1m, the mineralization degree is 5-15g / l, the topsoil salt content is 0.6-1%, and the ion composition is mainly Cl - and Na + , K + The main elements are 80-90% of the total anions and cations, respectively. The medium groundwater level is 0.5-1m, the mineralization is 5-10g / l, the salt content of the topsoil is 0.2-0.4%, and Cl - Accounting for 70-80% of the total anions, Na + , K + It accounts for 80% of the total cations, and the farther away from the coastline, the lower the groundwater level and soil salinity.

[0004] The existing coastal saline-alkali land treatment technologies are mainly divided into three categories. The first is to apply improvers to the soil, including various bacterial agents that improve the physical and chemical properties of the soil and desulfurized gypsum that mainly adjusts the soil pH value, such as Zhao Huili (Zhao Huili, Yu Jinyi, Liu Tao, et al. Improving the physical and chemical properties of saline-alkali land in the Yellow River Delta by applying straw and desulfurized gypsum [J]. Environmental Science: 1-18); the second is to achieve the treatment of saline-alkali land by setting up a pipe and drainage system and washing salt through irrigation; the third is to achieve the treatment of saline-alkali land by supporting soil improvement through the drainage system. Based on this, Li Ya, Shen Weidong, and Xu Luwei proposed "A method for improving and draining salt from saline-alkali land" (CN112840786B), that is, to preliminarily treat the soil and inject water into the soil. After the soil absorbs the injected water, the soil surface is leveled and a plastic drainage board is driven in. Counterweights are placed between adjacent drainage boards to extract the accumulated water on the soil surface, and sponges are placed above the soil to drain salt. Li Lixia et al. proposed "a method for treating severe saline-alkali land" (CN113575013A), that is, to draw lines according to the location of the impermeable interlayer of the soil for plowing, prepare purification liquid, and pre-bury pipes in the soil, and promote the treatment of saline-alkali land by fertilizing and cooperating with crops. Ge Chunhui et al. proposed "a saline-alkali land improver and its preparation method and application" (CN103275731A), that is, to produce the improver by granulating biochar, phosphogypsum, ammonium humate, urea and citric acid in a certain proportion. In recent years, a large number of experimental studies have been carried out by using desulfurized gypsum, slag, etc. as saline-alkali land improvement matrices, which have achieved certain results. However, my country has a vast territory, and the substances contained in coal and other materials in different regions vary greatly. Although a limited number of studies have not found problems such as heavy metal pollution in the above-mentioned mineral wastes, it is undeniable that some slags contain heavy metals to varying degrees. Therefore, there are huge risks in large-scale engineering applications as saline-alkali land improvement matrices.

[0005] Coastal saline-alkali land has typical zonal characteristics, with most of the terrain being flat and the groundwater level being high. The high salt content of the groundwater provides a continuous supply of salt to the soil. Therefore, a single technology cannot solve the problem of salinization of coastal saline-alkali land and the continuous improvement of saline-alkali land.

[0006] By applying soil conditioners to adjust the pH value and change the soil structure, the physical and chemical properties of the soil can be changed to a certain extent, the permeability of the soil can be improved, and the pH value of the soil can be lowered. However, it faces major problems. First, the soil improvement process requires a large amount of conditioners, and the cost of tilling and applying conditioners is high, which limits large-scale use. Second, after the conditioners are applied, since it is impossible to cut off the external salt supply, the salt in a larger area will quickly dilute the conditioners with the movement and rebalancing of groundwater salt, reducing the improvement effect and causing soil salt reversion.

[0007] Traditional saline-alkali land improvement also includes large-scale terraced land preparation and drainage engineering construction, but most of the coastal saline-alkali land has flat terrain, making it difficult to carry out terraced land preparation. Drainage engineering requires the establishment of a step-by-step pumping and drainage system, which is not only a huge amount of work, but also requires a steady supply of electricity for continuous pumping and drainage, and faces great challenges in operation and management. At the same time, groundwater is mobile, and the surrounding water will be quickly replenished after local groundwater is pumped out. In the rainy season, groundwater rises rapidly, and it is impossible to quickly pump out the groundwater level. When it reaches the range of soil capillary action, the salt in the groundwater will be quickly raised to the ground through evaporation, forming salt spots and other salt return phenomena.

[0008] It is precisely because of the above-mentioned problems that the management of saline-alkali land, especially coastal saline-alkali land, has always been difficult to manage on a large scale and apply engineering applications. Summary of the invention

[0009] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for treating saline-alkali land. For saline-alkali land, especially coastal saline-alkali land, clay isolation walls are first set in the saline-alkali land to separate the plots, so as to prevent the surrounding salt from concentrating in the treatment area and the problem of water-salt movement rebalancing, thereby solving the limitation of the terrain on land preparation in flat areas. In addition, by setting a gravel salt-blocking and permeable cushion layer under the cultivated soil, setting a drainage pipe under the clay isolation wall, and treating the collected infiltration water through ion exchange, the saline-alkali land is comprehensively treated from the source, and a significant treatment effect is achieved.

[0010] In order to achieve the above object, the present invention provides a method for treating saline-alkali land, the method comprising the following steps:

[0011] (1) Digging trenches on the saline-alkali land to be treated, dividing the target land into multiple rectangular plot units; the length and width of the plot unit are 30-50m respectively, the trench width is 30-40cm, and the depth is 150-200cm;

[0012] (2) concealed drainage pipes are arranged at the bottom of the trenches and connected to each other to form a drainage network;

[0013] (3) Filling clay on the external permeation filter layer of the drainage pipe to form a clay isolation wall, wherein the clay isolation wall itself is 100-150 cm high and the top is more than 30 cm below the soil cultivation surface;

[0014] (4) Open-pit land preparation is adopted for each block unit and a gravel salt-blocking and water-permeable cushion layer is laid on the lower layer. The thickness of the gravel salt-blocking and water-permeable cushion layer is 20-30 cm, and the top is 80-120 cm below the soil cultivation surface;

[0015] (5) The outlet of the drainage network is connected to the main drainage pipe, and the collected infiltration water is used for recycling irrigation after ion removal.

[0016] The height of the clay isolation wall can be adjusted according to the groundwater level. In principle, the bottom of the clay isolation wall should be 30 cm lower than the annual groundwater level. After the sandwich clay isolation wall is set up, the entire treatment plot is divided and enclosed into independent treatment units to block the treatment area from the outside world and the lateral supply of salt inside the treatment area. Since the clay isolation wall is set underground and 30 cm below the ground, it will not affect the surface vegetation or crop planting.

[0017] Furthermore, the material of the permeable filter layer outside the drainage pipe includes crushed sand, ceramsite, zeolite and / or fiber balls. The fiber balls can be spherical filter materials formed by tying fibers such as polyester, polypropylene or acrylic fibers. The permeable filter layer is used to cover the drainage pipe to support and filter and prevent the holes of the drainage pipe from being blocked. The preferred materials include crushed sand, ceramsite and / or zeolite. The drainage pipe can be made of PVC, and the drainage pipe is connected to the horizontal drainage pipes at the bottom of the barrier treatment units on both sides to form a drainage network.

[0018] In one embodiment, the thickness of the permeation filtration layer is 2-5 cm.

[0019] Furthermore, an anti-seepage sandwich layer is provided in the clay isolation wall to increase the barrier effect. The sandwich layer can be an anti-seepage cloth or an anti-seepage coating layer, such as a waterproof coating layer of polyurethane, epoxy resin, polyester, etc. The anti-seepage sandwich layer can be laid out simultaneously when the clay isolation wall is formed.

[0020] Furthermore, the thickness of the clay isolation wall is 30-40 cm. Preferably, the thickness of the clay isolation wall is the same as the width of the groove.

[0021] Furthermore, the gravel salt-blocking and water-permeable cushion layer is a single-graded gravel cushion layer with a particle size of 5-10 mm; or a continuously graded gravel cushion layer with a particle size of 5-40 mm.

[0022] Furthermore, the gravel salt-blocking and water-permeable cushion layer is connected to the external permeable filter layer of the drainage concealed pipe, so that the salt-containing moisture passing through the gravel salt-blocking and water-permeable cushion layer can enter the drainage concealed pipe through the permeable filter layer.

[0023] In one embodiment, the bottom of the gravel salt blocking and permeable cushion layer is lower than the top of the permeable filter layer outside the drainage concealed pipe. Therefore, the gravel salt blocking and permeable cushion layer and the permeable filter layer have an overlapping part in height, so there is a directly connected part between the two at the bottom of the clay isolation wall.

[0024] In one embodiment, the bottom of the gravel salt-blocking and permeable cushion layer is higher than the top of the permeable filter layer outside the drainage concealed pipe, and the gravel salt-blocking and permeable cushion layer is provided with a connecting portion extending downward to the permeable filter layer along the inner side wall of the clay isolation wall. The connecting portion may be the same as the composition of the gravel salt-blocking and permeable cushion layer, or may be composed of the same material as the permeable filter layer, such as crushed sand, ceramsite and / or zeolite. Thus, the gravel salt-blocking and permeable cushion layer is connected to the permeable filter layer through the connecting portion, and the salt-containing moisture of the gravel salt-blocking and permeable cushion layer can be quickly introduced into the drainage concealed pipe.

[0025] When the gravel salt-blocking and permeable cushion layer is provided with a connection portion extending downward along the inner side wall of the clay isolation wall, the connection portion extending downward can be formed before the construction of the corresponding portion of the clay isolation wall. For example, before filling clay on the permeable filter layer outside the drainage concealed pipe, a layer of vertical connection portion, such as a vertical layer of crushed gravel, ceramsite and / or zeolite, is formed on the corresponding portion of the groove side wall.

[0026] Furthermore, the outlet of the drainage network is connected to the main drainage pipe via a forced drainage well. A liquid level monitoring device is provided in the forced drainage well. When the liquid level in the forced drainage well exceeds the liquid level warning line, the forced drainage pump is automatically turned on to pump out the liquid in the forced drainage well (such as collected infiltration water and / or groundwater).

[0027] The drainage network may have multiple outlets, each of which may be connected to the main drainage pipe via a different forced drainage well to increase the accuracy of liquid level detection and the pumping efficiency. Of course, according to different construction requirements, two or more of the outlets of the drainage network may also be connected to one forced drainage well.

[0028] Furthermore, the drainage interface of the forced drainage well is connected to the main drainage pipe by a siphon-type one-way drainage pipe, and the water outlet of the siphon-type one-way drainage pipe is lower than the drainage interface of the forced drainage well. The use of a siphon-type one-way drainage pipe can more efficiently discharge the liquid in the forced drainage well to the main drainage pipe. Its active drainage is conducive to the liquid level control in the forced drainage well and can minimize the energy consumption of drainage. In addition, the forced drainage well can also be assisted by an external water pump such as a low-power water pump for drainage, and a one-time comprehensive pumping can be achieved each time it is started for a short time. First, it ensures that the regional groundwater level is always below the fixed height water level line, and second, it can quickly discharge groundwater during surface rainfall and irrigation and salt drainage operations, in order to reduce the salt content of the soil and underground in the enclosed area and solve the problem of salt export.

[0029] Furthermore, the main pipe is connected to a deionization subsystem to remove ions from the collected permeate water; preferably, a permanent inspection well is provided on the main pipe layout line. A permanent inspection well is provided on the main pipe to facilitate inspection and maintenance of the pipe.

[0030] In one embodiment, the deionization system includes an ion exchange device, wherein an ion exchange resin is used to remove ions from the collected permeate water. The ion exchange device includes, for example, a sodium ion exchange device, a calcium ion exchange device, or a comprehensive ion exchange filtration device.

[0031] Furthermore, the separation subsystem is also connected to the composting system and the fresh water supply system to adjust the fertilizer effect components and supply fresh water to the water treated by the separation subsystem; the separation subsystem, the composting system and the fresh water supply system constitute a water, fertilizer and salt regulation center. For example, saline groundwater enters the main drainage pipe through the drainage well and merges into the "water, fertilizer and salt regulation center" through the drainage concealed pipe, and the sodium salt containing sodium chloride is mixed with the water in the composting tank of the composting system after passing through the sodium ion replacement equipment of the "water, fertilizer and salt regulation center". A part of the fresh water can be optionally supplemented through the fresh water supply system and transported to the clay isolation wall enclosed field through the irrigation system for irrigation, collection, salt washing, and water component adjustment to form a circulation loop to achieve the drainage and irrigation cycle of salt in the clay enclosed area.

[0032] In one embodiment, each component system and related equipment in the water, fertilizer and salt regulation center is powered by a photovoltaic system. The photovoltaic system provides green power resources and power configuration, and introduces the photovoltaic system into saline-alkali land management, which is conducive to solving the investment problem of long-term drainage.

[0033] Furthermore, when setting up the drainage concealed pipe and / or laying the gravel salt-blocking and permeable cushion layer, an irrigation pipeline system is also laid out for the plot unit, and the upstream of the irrigation pipeline system is connected to the water, fertilizer and salt regulation center.

[0034] In one embodiment, the main drainage pipe and / or the main trunk pipe of the irrigation pipeline system is laid along the tractor road to facilitate the laying of permanent inspection wells.

[0035] The saline-alkali land treatment method proposed in the present invention belongs to a comprehensive treatment technology of soil treatment and circulating salt water treatment. According to plant growth conditions and the law of water-salt movement, when the salt rises to a height of 40 cm from the ground, the salt in the groundwater will be rapidly lifted to the surface through plant root absorption and soil capillary action, and enriched on the surface. Since the depth of the sandwich clay isolation wall is greater than the gravel salt-blocking and permeable cushion layer, the groundwater in the area surrounding the treatment area penetrates very slowly into the isolation area through the bottom of the clay isolation wall. Under the condition of pumping in the treatment area, the groundwater level inside the clay barrier block can always be maintained at about 80 cm. According to tests, every groundwater level drop in the clay barrier area during the rainy season will produce a significant salt washing effect.

[0036] The beneficial effects of the present invention include:

[0037] 1. The setting of clay isolation wall can change the shortcomings of traditional terraced land preparation, and form a barrier to the movement of water and salt, forming a new underground curtain. The clay isolation wall is set underground, does not affect land cultivation, is convenient for mechanized construction, and the project implementation is simple, which is conducive to large-scale promotion and application.

[0038] 2. The setting of the gravel salt-blocking permeable cushion layer can destroy the soil capillary action while being permeable, preventing and slowing down the rise of salt in groundwater to the surface, and at the same time can play a water-conducting role, meet the drainage permeability requirements, and guide the infiltrated water to the drainage pipe. The bottom height of the gravel salt-blocking permeable cushion layer is higher than the bottom height of the sandwich clay isolation wall, reducing the regional salt water balance effect.

[0039] 3. The setting of drainage network based on drainage concealed pipes, together with a series of subsequent collection, desalination, component adjustment treatments, and irrigation pipe system settings, can realize the extraction, washing and irrigation circulation loop of salt in the clay enclosed area, reduce the salt content in the circulation process, and thus carry out systematic and long-term management of saline-alkali land. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The present invention is a schematic flow chart of a method for treating saline-alkali land in one embodiment of the present invention.

[0041] Figure 2 This is a bar graph of quarterly salt changes in a treatment area using the treatment method of the present invention in one embodiment of the present invention. DETAILED DESCRIPTION

[0042] In order to better understand the above technical solution, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

[0043] Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0044] Example 1

[0045] like Figure 1 As shown, a schematic flow chart of a method for treating saline-alkali land in one embodiment of the present invention is shown. The treatment method comprises the following steps:

[0046] S1. Dig trenches on the saline-alkali land to be treated and divide the target land into multiple rectangular plot units; the length and width of the plot unit are 50m respectively, the trench width is 40cm, and the depth is 200cm;

[0047] S2. Set up horizontal drainage pipes at the bottom of the trench and connect them to form a drainage network. The drainage pipes are made of PVC with an outer diameter of 10 cm. The ceramsite / crushed sand and gravel permeable filter layer on the periphery is about 5 cm thick. When the drainage pipes are laid, the total height of the permeable filter layer on the periphery is about 20 cm.

[0048] S3. Fill clay on the external permeable filter layer of the drainage concealed pipe to form a clay isolation wall. The clay isolation wall is 40 cm wide, 150 cm high, and the top is 30 cm lower than the soil cultivation surface. Therefore, the bottom of the clay isolation wall is at least 180 cm away from the soil surface. Therefore, before filling clay on the permeable filter layer to form an isolation wall, a vertical connection part is formed on the corresponding part of the groove side wall to communicate with the subsequently laid gravel salt-blocking and permeable cushion layer. The thickness of the connection part relative to the groove side wall is about 8 cm, and the height is about 80 cm, and it is formed using ceramsite / crushed sand and stone.

[0049] S4. Open-pit land preparation is adopted for each block unit and a gravel salt-blocking and water-permeable cushion layer is laid on the lower layer. The thickness of the gravel salt-blocking and water-permeable cushion layer is 30 cm, and the top is 100 cm lower than the soil cultivation surface; the gravel salt-blocking and water-permeable cushion layer is a continuously graded gravel cushion layer with a particle size of 10-30 mm;

[0050] S5. Connect the outlet of the drainage network to the main drainage pipe through the forced drainage well. The drainage interface of the forced drainage well is connected to the main drainage pipe using a siphon-type one-way drainage pipe. A liquid level monitoring device is installed in the forced drainage well. When the liquid level in the forced drainage well exceeds the 80cm liquid level warning line, the forced drainage pump is automatically turned on for active pumping. The main drainage pipe is connected to the separation subsystem of the water, fertilizer and salt regulation center. The composting tank and fresh water supply system of the composting system of the water, fertilizer and salt regulation center are connected to the water storage pipe of the separation subsystem, so as to adjust the fertility and concentration of the irrigation water after desalination, and then apply it to the plot unit through the irrigation pipe system. In addition, each component system and related equipment in the water, fertilizer and salt regulation center is powered by a photovoltaic system.

[0051] Example 2

[0052] The treatment method comprises the following steps:

[0053] S1. Dig trenches on the saline-alkali land to be treated and divide the target land into multiple rectangular plot units; the length and width of the plot unit are 40m respectively, the trench width is 30cm, and the depth is 150cm;

[0054] S2. Set up horizontal drainage pipes at the bottom of the trench and connect them to form a drainage network. The drainage pipes are made of PVC with an outer diameter of 10 cm. The ceramsite / crushed sand and gravel permeable filter layer on the periphery is about 4 cm thick. When the drainage pipes are laid, the total height of the permeable filter layer on the periphery is about 18 cm.

[0055] S3. Fill clay on the external permeation filter layer of the drainage pipe to form a clay isolation wall. The clay isolation wall is 30 cm wide and 102 cm high, and the top is 30 cm lower than the soil cultivation surface;

[0056] S4. For each block unit, open-type land preparation is adopted and a gravel salt-blocking and water-permeable cushion layer is laid on the lower layer. The thickness of the gravel salt-blocking and water-permeable cushion layer is 40 cm, and the top is 100 cm lower than the soil cultivation surface; the gravel salt-blocking and water-permeable cushion layer is a continuously graded gravel cushion layer with a particle size of 10-25 mm; thus, the gravel salt-blocking and water-permeable cushion layer is directly connected with the permeable filtration layer at a height of 8 cm, so there is no need to lay a vertical connection part in the groove;

[0057] S5. Connect the outlet of the drainage network to the main drainage pipe through the forced drainage well. The drainage interface of the forced drainage well is connected to the main drainage pipe using a siphon-type one-way drainage pipe. A liquid level monitoring device is installed in the forced drainage well. When the liquid level in the forced drainage well exceeds the 80cm liquid level warning line, the forced drainage pump is automatically turned on for active pumping. The main drainage pipe is connected to the separation subsystem of the water, fertilizer and salt regulation center. The composting tank and fresh water supply system of the composting system of the water, fertilizer and salt regulation center are connected to the water storage pipe of the separation subsystem, so as to adjust the fertility and concentration of the irrigation water after desalination, and then apply it to the plot unit through the irrigation pipe system. In addition, the various component systems and related equipment in the water, fertilizer and salt regulation center are powered by photovoltaic systems. The main pipes of the main drainage pipe and the irrigation pipe system are laid in conjunction with the mechanized farming road, and permanent inspection wells are set on the laying route.

[0058] Example 3

[0059] Reference Figure 2 As shown, a bar graph of the quarterly salt changes in the treatment area using the treatment method of Example 2 in one embodiment of the present invention is shown. In each quarter, from left to right, clay isolation area 1, clay isolation area 2, clay isolation area 3 and clay isolation area 4 are represented.

[0060] like Figure 2 As shown, after a rainy season, the soil salinity in clay isolation area 1 decreased from 1.32% to 0.42%, and the mineralization of soil leaching water decreased from 3.6 g / l to 1.4 g / l; the soil salinity in clay isolation area 2 decreased from 1.18% to 0.39%, and the mineralization of soil leaching water decreased from 3.2 g / l to 1.3 g / l; the soil salinity in clay isolation area 3 decreased from 1.22% to 0.41%, and the mineralization of soil leaching water decreased from 3.3 g / l to 1.36 g / l; the soil salinity in clay isolation area 4 decreased from 1.16% to 0.44%, and the mineralization of soil leaching water decreased from 3.2 g / l to 1.46 g / l.

[0061] The salinity in each clay isolation zone decreases in the rainy season and then increases in the dry season, but the overall trend is a continuous decline.

[0062] In the saline-alkali land treatment method proposed in the present invention, since the depth of the sandwich clay isolation wall is greater than the gravel salt-blocking and permeable cushion layer, the groundwater in the surrounding area of ​​the treatment area penetrates very slowly into the isolation area through the bottom of the clay isolation wall. Under the condition of drainage in the treatment area, the groundwater level inside the clay barrier block can always be maintained at about 80cm. After each rainy season, the clay barrier area will produce a significant salt washing effect, thereby producing a significant treatment effect on various saline-alkali lands.

[0063] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for treating saline-alkali land, characterized in that: The method comprises the following steps: (1) Digging trenches on the saline-alkali land to be treated, dividing the target land into multiple rectangular plot units; the length and width of the plot unit are 30-50m respectively, the trench width is 30-40cm, and the depth is 150-200cm; (2) concealed drainage pipes are arranged at the bottom of the trenches and connected to each other to form a drainage network; (3) Filling clay on the external permeation filter layer of the drainage pipe to form a clay isolation wall, wherein the clay isolation wall itself is 100-150 cm high and the top is more than 30 cm below the soil cultivation surface; (4) Open-pit land preparation is adopted for each block unit and a gravel salt-blocking and water-permeable cushion layer is laid on the lower layer. The thickness of the gravel salt-blocking and water-permeable cushion layer is 20-30 cm, and the top is 80-120 cm below the soil cultivation surface; (5) The outlet of the drainage network is connected to the main drainage pipe, and the collected infiltration water is used for recycling irrigation after ion removal.

2. The method according to claim 1, characterized in that The material of the external permeable filter layer of the drainage concealed pipe includes crushed sand, ceramsite, zeolite and / or fiber balls, and the thickness of the permeable filter layer is 2-5 cm.

3. The method according to claim 1, characterized in that An anti-seepage sandwich layer is arranged in the clay isolation wall. The sandwich layer is an anti-seepage cloth or an anti-seepage coating layer. The anti-seepage sandwich layer is arranged simultaneously when the clay isolation wall is formed.

4. The method according to claim 1, characterized in that: The sand and gravel salt-blocking and water-permeable cushion layer is a single-graded gravel cushion layer with a particle size of 5-10 mm; or a continuously graded gravel cushion layer with a particle size of 5-40 mm.

5. The method according to claim 4, characterized in that The gravel salt blocking and water permeable cushion layer is connected to the external permeable filter layer of the drainage concealed pipe, wherein: The bottom of the gravel salt blocking and permeable cushion layer is lower than the top of the permeable filtration layer, and the gravel salt blocking and permeable cushion layer has an overlapping part in height with the permeable filtration layer; or the bottom of the gravel salt blocking and permeable cushion layer is higher than the top of the permeable filtration layer, and the gravel salt blocking and permeable cushion layer is provided with a connecting part extending downward to the permeable filtration layer along the inner wall of the clay isolation wall, and the connecting part is formed before the construction of the corresponding part of the clay isolation wall.

6. The method according to claim 1, characterized in that The outlet of the drainage network is connected to the main drainage pipe via a forced drainage well. A liquid level monitoring device is provided in the forced drainage well. When the liquid level in the forced drainage well exceeds the liquid level warning line, the forced drainage pump is automatically turned on to pump out the liquid in the forced drainage well. The drainage interface of the forced drainage well is connected to the main drainage pipe by a siphon-type one-way drainage pipe, and the water outlet of the siphon-type one-way drainage pipe is lower than the drainage interface of the forced drainage well.

7. The method according to claim 1, characterized in that The main drainage pipe is connected to the separation subsystem to remove ions from the collected permeated water; a permanent inspection well is arranged on the layout route of the main drainage pipe.

8. The method according to claim 7, characterized in that The separation subsystem is also connected to the composting system and the fresh water supply system to adjust the fertilizer components and supply fresh water to the water treated by the separation subsystem; the separation subsystem, the composting system and the fresh water supply system constitute a water, fertilizer and salt regulation center.

9. The method according to claim 8, characterized in that Each component system and related equipment in the water, fertilizer and salt regulation center is driven by electricity provided by a photovoltaic system.

10. The method according to any one of claims 1 to 9, characterized in that When setting up drainage concealed pipes and / or laying gravel salt-blocking and permeable cushion layers, an irrigation pipe system is also laid out for the plot units, and the upstream of the irrigation pipe system is connected to the water, fertilizer and salt regulation center; the main drainage pipe and / or the main trunk pipe of the irrigation pipe system is laid out along the mechanized farming road.

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