Saline-alkali soil treatment method

Abstract

The invention discloses a saline-alkali land treatment method, and belongs to the technical field of saline-alkali land treatment, and the saline-alkali land treatment method comprises the following steps: determining the initial salt content, soluble salt ion composition and pH value of surface soil, middle soil and deep soil by adopting a soil profile sampling detection method; a three-dimensional latticed layout is adopted for laying a percolation concealed pipe drainage system layer by layer; constructing a drip irrigation and spray irrigation coupled irrigation system, firstly adopting spray irrigation for salt leaching in moderate and severe areas, and adopting drip irrigation for salt leaching in mild areas and the later stage of improvement; according to data monitored by the layered sensor module, salt-tolerant organisms are planted in stages and areas, and progressive restoration of soil improvement, consolidation and lifting is achieved; the saline-alkali soil is treated in a layered mode through the concealed pipe drainage system, the sensor module is combined to monitor the saline-alkali soil value in real time, the irrigation amount, the modifier applying amount and the vegetation planting type are dynamically adjusted, and the saline-alkali soil restoration treatment effect is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of saline-alkali soil treatment, in particular to a saline-alkali soil treatment method. BACKGROUND

[0002] Salinization not only leads to soil quality degradation, but also causes a series of chain problems such as soil physicochemical property deterioration, vegetation degradation, land desertification, water resource pollution and secondary disasters, which poses a serious threat to the ecological environment, agricultural economy and food security. As a potential developable arable land resource, saline-alkali soil treatment can expand arable land resources, improve regional ecological environment and drive economic transformation in saline-alkali areas.

[0003] A saline-alkali soil treatment and early warning method is disclosed in a patent with publication number CN118940942B. During the improvement period of successfully improved saline-alkali soil, saline-alkali soil data of successfully improved saline-alkali soil is collected. The missing data is filled using the historical saline-alkali soil data of successfully improved saline-alkali soil. A standard curve is established according to the completed saline-alkali soil data of successfully improved saline-alkali soil. The standard curve is corrected according to the difference of the improvement influencing factors to obtain a treatment target curve. Remote sensing data of the to-be-evaluated saline-alkali soil is collected in real time to obtain saline-alkali soil data of the to-be-evaluated saline-alkali soil. The saline-alkali soil data of the to-be-evaluated saline-alkali soil is subtracted from the treatment target curve. If the difference is within the preset range, the to-be-evaluated saline-alkali soil treatment does not need early warning. If the difference exceeds the preset range, a BP neural network is established to predict the saline-alkali soil data of the to-be-evaluated saline-alkali soil at one collection time and give a treatment early warning.

[0004] A saline-alkali soil treatment method and system are disclosed in a patent with publication number CN120240052A. The saline-alkali soil treatment method includes a saline-alkali water field device, which includes a water distribution pipe network and a plurality of buried drip irrigation pipes. The buried drip irrigation pipes are arranged below the surface layer of the to-be-treated saline-alkali soil. The water outlet ends of the water distribution pipe network are in communication with the buried drip irrigation pipes. This saline-alkali soil treatment method includes the step of distributing fresh water into the to-be-treated saline-alkali soil. The buried drip irrigation pipes are used to infiltrate water below the surface layer of the to-be-treated saline-alkali soil, so that the fresh water is uniformly distributed below the surface layer. This method greatly saves water resources and continuously desalinizes the saline-alkali water. The salt content of the saline-alkali water below the ground surface becomes less and less with continuous water use, so that the saline-alkali soil can be completely treated.

[0005] For example, the patent with publication number CN116830845A discloses a saline-alkali soil treatment method, which comprises the following steps: arranging at least one layer of engineering waste soil in a target trench of the saline-alkali soil to obtain an improved soil body, and then restoring the landform of the improved soil body to obtain a cultivable soil body. The present application is aimed at the characteristics of high salt content, soil hardening, poor aeration, low fertility level, poor water and fertilizer retention capacity, and poor economic benefits of saline-alkali land, and fully utilizes the strong water permeability of engineering waste soil to develop a method for improving saline-alkali soil by using engineering waste soil, thereby solving the technical defects of not effectively utilizing the engineering waste soil generated during the construction process and being unable to improve the land utilization rate of saline-alkali soil. The application of engineering waste soil in the improvement of saline-alkali soil not only improves the utilization rate of engineering waste soil, but also realizes the purpose of improving saline-alkali soil into cultivable land. However, in the existing treatment of some saline-alkali soil, only single deep furrow or buried pipe is relied on, and the salt is not completely discharged and is easy to flow back. After irrigation or rainfall, the salt is easy to move upward with water to the surface, and the salt return rate is high. In addition, the irrigation amount and the amount of application of the traditional saline-alkali soil salt washing and improvement agent cannot be dynamically monitored and controlled, the pH value of the local soil fluctuates sharply, the growth of crops is inhibited, and the benign treatment of saline-alkali soil is not conducive.

[0006] In view of the above problems, it is urgent to make innovative design on the basis of the original saline-alkali soil treatment method. SUMMARY

[0007] The present application aims to provide a saline-alkali soil treatment method to solve the problems of incomplete salt discharge and easy salt flowback in the existing treatment of some saline-alkali soil, easy salt upward movement with water to the surface after irrigation or rainfall, high salt return rate, and the like. In addition, the irrigation amount and the amount of application of the traditional saline-alkali soil salt washing and improvement agent cannot be dynamically monitored and controlled, the pH value of the local soil fluctuates sharply, the growth of crops is inhibited, and the benign treatment of saline-alkali soil is not conducive.

[0008] To achieve the above-mentioned purpose, the present application provides the following technical scheme: a saline-alkali soil treatment method, which comprises the following steps: The initial salt content, soluble salt ion composition and pH value of the surface soil, middle soil and deep soil are determined by soil profile sampling detection method, the underground water level is ascertained, the light, moderate and severe saline-alkali regions are divided, the surface soil is deeply ploughed to break the hardening layer, the soil permeability is increased, the salt downward infiltration is promoted, the mulch is covered on the surface of the surface soil to block the water and salt upward movement and inhibit the soil evaporation.

[0009] The three-dimensional grid layout is adopted, and the infiltration buried pipe drainage system is layered laid in the surface soil, middle soil and deep soil. The water collecting well is arranged at the edge of the treatment plot to collect the brackish water discharged by the drainage system, and the submersible pump and the brackish water storage pool are matched to realize the separation of salt and fresh water.

[0010] The irrigation system is coupled with drip irrigation and sprinkler irrigation, the moderate and severe areas are first washed with salt by sprinkler irrigation, the light area and the improved later period are washed with salt by drip irrigation, a salt-content-flow-rate-water-level three-in-one sensor module is arranged in the middle of the drainage system to monitor the salt content and flow rate of the salt water in the pipe in real time, the data is transmitted to the central control system through the wireless transmission module, the irrigation quota, irrigation cycle and the amount of improvement agent are dynamically adjusted based on the soil salinization dynamic model according to the numerical change.

[0011] The irrigation system dissolves the soluble salt in the surface soil, middle soil and deep soil of the fresh water to form salt water runoff, which is infiltrated into the underground drainage system, collected into the water collecting well through gravity flow, and realizes the salt content disposal in different places.

[0012] According to the monitoring data of the layered sensor module, salt-tolerant organisms are planted in stages and regions, the salt secretion, nitrogen fixation and decomposition of fallen branches and leaves of the biological root system are utilized, and the rhizosphere growth promoting agent is used to construct the soil-plant-microorganism collaborative repair system, so that the progressive repair of soil improvement, consolidation and promotion is realized.

[0013] Preferably, the surface soil physical improvement method is as follows: for the hardened soil, a heavy deep plough is used for deep ploughing of 25-30 cm depth to break the plough sole and reduce the soil bulk density to 1.2-1.4 g / cm³ to improve the soil porosity; after deep ploughing, a rotary tiller is used for shallow rotary tillage of 15-20 cm to make the soil particles uniform and fine, and reduce the soil fissure development; 0.08 mm thick polyethylene mulch is covered on the surface soil, the mulch joints are compacted with soil to block the water and salt upward channel and inhibit the salt surface accumulation.

[0014] Preferably, the underground drainage system includes capillary pipes embedded in the surface soil, branch pipes embedded in the middle soil and main pipes embedded in the deep soil to form a three-dimensional drainage network for deep water level control, middle salt discharge and surface salt reduction; the capillary pipe has a buried depth of 30-40 cm, a pipe diameter of 50-75 mm and a spacing of 5-8 m, and is used for quickly discharging the surface salt water after salt washing for the surface high salt area; the branch pipe has a buried depth of 60-80 cm, a pipe diameter of 110-160 mm and a spacing of 20-30 m, and covers the middle salt area; the main pipe has a buried depth of 80-100 cm, a pipe diameter of 160-200 mm and a spacing of 50-80 m, and is responsible for collecting the deep salt water.

[0015] Preferably, the capillary pipe, the branch pipe and the main pipe are all provided with permeable holes for salt washing and drainage, and the longitudinal connection of the capillary pipe, the branch pipe and the main pipe is provided with an electrically operated regulating valve, which dynamically adjusts the drainage flow rate according to the layered pH monitoring data, specifically: during the salt washing period, the valve is fully opened, the drainage flow rate is increased to 1.2-1.5 m³ / h to accelerate the salt discharge; during the biological repair period, the valve is half open, and the flow rate is controlled at 0.3-0.5 m³ / h to avoid excessive drainage leading to soil drought.

[0016] Preferably, the outer part of the underground drainage system is wrapped with a gradient filter, which includes an inner layer of water-permeable non-woven fabric and an outer layer of geotextile wrapped outside the underground drainage system, and a middle layer of zeolite particles filled between the inner and outer layers; the inner layer of water-permeable non-woven fabric is used to prevent fine soil particles from entering; the middle layer of zeolite particles is used to adsorb salt in water and reduce the salinity of the drainage; and the outer layer of geotextile is used to filter coarse particles and prolong the service life of the underground pipe.

[0017] Preferably, the underground drainage system is laid in a trench filled with a modified substrate composed of humus soil, straw fragments, and salt-tolerant microbial inoculants. The humus soil and straw fragments improve soil structure and promote root growth, and the microbial inoculants decompose salt around the pipe to prevent the formation of salt stains around the underground drainage system.

[0018] Preferably, the irrigation system is combined with a modifier for application. The chemical modifier is selected and applied as follows: for alkaline saline-alkali soil, desulfurized gypsum and humic acid composite modifier are selected, desulfurized gypsum provides calcium ions, and humic acid adjusts soil structure and reduces pH value; for acidic saline-alkali soil, lime and wood ash composite modifier are selected to neutralize soil acidity and supplement potassium and calcium elements; the application method is to crush the modifier and dissolve it in irrigation water, then apply it through the irrigation system to avoid uneven manual application, and the concentration of the modifier is set according to the initial pH value of the soil.

[0019] Preferably, the salt washing and pressing process of the irrigation system is as follows: first salt washing, for moderate and severe areas, use sprinkler irrigation to continuously irrigate 300-400 cubic meters of fresh water per mu, dissolve the salt in the surface and middle layers, and the salt will infiltrate with water to the underground pipe layer and be discharged through the water collection well; cyclic salt washing, repeat the salt washing once every 7-10 days for 2-3 cycles, during the treatment period, continuously drain the underground water through the underground pipe to control the underground water level below 1.5m to prevent salt backflow; precise acid adjustment, simultaneously apply chemical modifiers during salt washing, detect the soil pH value after each irrigation, and if it does not reach the target range, adjust the concentration of the modifier and irrigate again.

[0020] Preferably, the irrigation system comprises a water source treatment unit, a pipe network conveying unit, an irrigator unit and an intelligent control unit, each of which is optimized for saline-alkali land characteristics, specifically: the water source treatment unit is equipped with a sand filter, a laminated filter and an activated carbon filter to remove silt, algae and organic matter in the water; the pipe network conveying unit includes a main water conveying pipeline laid along the edge of the land, fishbone-shaped sprinkler branch pipes laid in moderate and severe saline-alkali areas, and drip irrigation branch pipes laid in parallel to the crop planting rows in light saline-alkali areas and improved later-stage land; the irrigator unit includes rotary sprinkler irrigators selected in moderate and severe areas, and inner-inlaid laminated sprinkler irrigators selected in light areas and improved later-stage areas; the intelligent control unit is configured with one PLC controller in each irrigation subarea to collect data such as soil humidity, pressure and flow in the subarea, receive central control system instructions, control start and stop and parameter adjustment, deploy a central control platform on the cloud and a local server, support Web and mobile access, and have functions of irrigation plan making, real-time data monitoring, equipment state early warning and historical data query, and the platform is built-in with a soil salinization dynamic model to provide algorithm support for regulation and control decisions.

[0021] Preferably, the progressive repair method is: a first stage of severe improvement period, applicable conditions are that the soil surface salt content is greater than 0.4%, pH is greater than 8.5 or less than 5.5, salt-tolerant pioneer plants are planted, direct seeding and seedling transplanting are combined, the seeding amount per mu is 2-3 kg, and salt-tolerant microbial inoculants are applied; the pioneer plant roots penetrate into the soil layer to absorb salt, and the microorganisms decompose the residual improvement agent to stabilize the soil pH value; a second stage of moderate consolidation period, applicable conditions are that the soil surface salt content is 0.2%-0.4%, the pH is 6.0-8.0, salt-tolerant green manure and salt-tolerant crops are rotated, the green manure is turned under after being planted for 2 months, the soil organic matter is supplemented, the salt content is further reduced, and the soil aggregate structure is improved to lay a foundation for planting conventional crops; a third stage of light improvement period, applicable conditions are that the soil surface salt content is less than 0.2%, the pH is 6.5-7.5, the three-layer pH value is stable, conventional crops are planted, and salt-tolerant protective forests are planted at the edges of the land to form an ecological system of crops and forests, the residual salt is absorbed by the crops, the forests conserve water and reduce evaporation, and long-term and stable soil is realized.

[0022] Compared with the prior art, the beneficial effects of the present application are: Deep salt control, cutting off the supply source: the layered underground drainage system forms a three-dimensional network of rapid surface drainage, continuous middle layer drainage and limited deep layer drainage, the main drainage pipe stably controls the underground water level at 1.8-2.0 m through water pumping by the water collecting well, cuts off the deep salt upward channel, and greatly reduces the return salt rate after treatment.

[0023] Prevent clogging, ensure long-term salt discharge: The gradient filter of the underground drainage system is composed of inner layer water-permeable non-woven fabric, middle layer zeolite particles and outer layer geotextile. Zeolite absorbs salt while preventing clogging, prolonging the service life of the pipeline and ensuring long-term salt discharge efficiency.

[0024] Dynamic adjustment, fast response: The irrigation system, amendment application and saline-alkali land monitoring are combined. According to the data changes monitored by the sensor module in the saline-alkali land treatment, the irrigation mode, irrigation amount, amendment application type and amendment concentration are dynamically adjusted to realize the coupling regulation and control of irrigation and amendment.

[0025] Timing optimization, shortening the salt washing period: The salt washing is accelerated by alternating sprinkler irrigation and drip irrigation to accelerate the downward migration of salt to the underground pipe, reducing the salt content in the surface layer.

[0026] Layered monitoring, directional selection of species: Based on the layered pH and salt content sensor data, when the salt content in the surface layer is greater than 0.4%, pioneer plants such as tamarisk are planted, when the salt content is reduced to 0.2%-0.4%, salt-tolerant crops such as alfalfa and sugar beet are planted, and when the salt content is less than 0.2%, conventional crops such as salt-tolerant wheat are planted. The species selection is completely matched with the soil conditions. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 It is a schematic diagram of the multi-layer structure of the soil of the present application.

[0028] Figure 2 It is a schematic diagram of the external filter structure of the underground drainage system of the present application.

[0029] Figure 3 It is a schematic diagram of the laying structure of the capillary tube, branch pipe and main drainage pipe of the present application.

[0030] Figure 4 It is a schematic diagram of the sensor module structure of the present application.

[0031] Figure 5 It is a treatment flowchart of the present application.

[0032] In the figure: 11, surface soil; 12, middle layer soil; 13, deep layer soil; 14, mulch; 2, underground drainage system; 21, capillary tube; 22, branch pipe; 23, main drainage pipe; 3, infiltration hole; 41, inner layer water-permeable non-woven fabric; 42, middle layer zeolite particles; 43, outer layer geotextile; 5, water collection well; 6, irrigation system; 7, sensor module. DETAILED DESCRIPTION

[0033] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] This application provides a method for treating saline-alkali land. The core of this method involves using soil profile sampling to determine the initial salinity, soluble salt ion composition, and pH value of the topsoil 11, middle soil 12, and deep soil 13; identifying the groundwater level; dividing the land into mild, moderate, and severe saline-alkali areas; deeply tilling the topsoil 11 to break up the compacted layer, increasing soil permeability and promoting salt infiltration; covering the surface of the topsoil 11 with a mulch film 14 to block the upward movement of water and salt and inhibit soil evaporation; employing a three-dimensional grid layout, laying a layered infiltration drainage system 2 in the topsoil 11, middle soil 12, and deep soil 13; setting up collection wells 5 at the edges of the treated area to collect the saline water discharged from the drainage system 2; and using submersible pumps and saline water storage tanks to achieve salinity separation; and constructing an irrigation system 6 that couples drip and sprinkler irrigation. Sprinkler irrigation is used to wash away salt in moderate and severe areas first, while drip irrigation is used to wash away salt in mild areas and during the later stages of improvement. In the drainage system 2, a sensor module 7 that integrates salt content, flow rate, and water level detection is installed at intervals to monitor the salt content and flow rate of saline water in the pipe in real time. The data is synchronized to the central control system via a wireless transmission module. Based on the dynamic model of soil salinization, the irrigation quota, irrigation cycle, and amount of soil conditioner are dynamically adjusted according to the numerical changes. The fresh water irrigated by the irrigation system 6 dissolves soluble salts in the topsoil 11, middle soil 12, and deep soil 13, forming saline water runoff. This runoff seeps down into the underground drainage system 2 and is collected by gravity flow to the collection well 5, achieving off-site treatment of salt. Based on the monitoring data of the layered sensor module 7, salt-tolerant organisms are planted in stages and areas. The salt secretion and nitrogen fixation of the biological roots, as well as the decomposition and improvement effects of fallen leaves and branches, combined with rhizosphere growth-promoting bacteria, construct a soil-plant-microorganism synergistic remediation system to achieve progressive remediation of soil improvement, consolidation, and enhancement.

[0035] Example 1: To better understand the above technical solution, the following will provide a detailed description of the technical solution in conjunction with the accompanying drawings and specific implementation methods. (Refer to...) Figures 1-5 As shown in this embodiment of the present application, a method for treating saline-alkali land includes: S1. The initial salinity, soluble salt ion composition and pH value of the topsoil 11, middle soil 12 and deep soil 13 are determined by soil profile sampling and testing method. The groundwater level is determined and the areas of mild, moderate and severe salinity are divided. The topsoil 11 is deeply tilled to break up the compacted layer, increase soil permeability and promote salt infiltration. The surface of the topsoil 11 is covered with mulch film 14 to block the upward movement of water and salt and inhibit soil evaporation.

[0036] In this embodiment, the physical improvement method for the topsoil 11 is as follows: For compacted soil, a heavy-duty deep tillage machine is used to perform deep tillage at a depth of 25-30cm to break up the plow pan, reduce the soil bulk density to 1.2-1.4g / cm³, and increase soil porosity; after deep tillage, a rotary tiller is used to perform shallow tillage at a depth of 15-20cm to make the soil particles uniformly broken and reduce the development of soil cracks; a 0.08mm thick polyethylene film is covered on the topsoil, and the seams of the film are compacted with soil to block the upward channels of water and salt and inhibit the accumulation of salt on the surface.

[0037] It should be noted that the core of stratified drainage is to accurately match the salt migration patterns of each soil layer, specifically including: Surface capillary pipes (30-40cm) quickly drain surface salt after leaching. The surface layer (0-40cm) of saline-alkali land is the area with the highest salt concentration, accounting for 40%-60% of the total salt content. Traditional capillary pipes (60-80cm) cannot drain the saline water after surface leaching in time, which can easily lead to salt re-infiltration. During the leaching period (after sprinkler irrigation), surface capillary pipes 21 can drain surface saline water within 24 hours, which is 3-4 times faster than traditional capillary pipes. The time for the surface salt content to drop from 0.6%-0.8% to 0.2%-0.3% is shortened by 50%.

[0038] The middle layer (60-80cm) of underground pipes blocks the upward migration of salt. The middle layer (40-80cm) is the channel for soil salt to rise. When the groundwater level rises, salt tends to accumulate in this layer. The middle layer branch pipe 22 can continuously discharge the saline water from the middle layer, keeping the groundwater level stable at 1.5-1.8m. Traditional underground pipes can only control the groundwater level at 1.2-1.5m, reducing the amount of salt that rises to the surface with the water. In addition, when combined with the application of chemical amendments, soluble salts produced by the amendment reaction, such as sodium sulfate, are quickly discharged, avoiding soil compaction caused by amendment residues.

[0039] Deep underground pipes (80-100cm) control groundwater levels and deep salinity. Deep (below 80cm) saline water layers are the source of salt replenishment for saline-alkali land. Deep main drainage pipes can extract deep saline water, lower the groundwater level from 1.0-1.2m to 1.8-2.0m, and cut off the salt replenishment path. For coastal saline-alkali land, deep underground pipes can discharge high-concentration saline water with a salt content greater than 3.0% brought by seawater backflow, thus preventing the aggravation of deep soil salinization.

[0040] In practice, deep plowing and mulching (14) improve the physical properties of the topsoil (11), reduce salt accumulation, and ensure the effectiveness of subsequent underground drainage and irrigation for salt leaching. To address the issue of topsoil compaction (11), a heavy-duty moldboard plow is used for deep plowing to a depth of 25-30 cm, breaking up the plow pan below 20 cm and connecting it with the middle soil layer (12). After deep plowing, a rotary tiller is used for shallow tilling to a depth of 15-20 cm, ensuring uniform and fine soil particle breakage, increasing soil porosity from 30% to over 40%. Enhanced air permeability promotes the downward penetration of salt into the middle soil layer 12 during salt leaching, and then discharges it through branch pipes, preventing cracking of the surface soil layer 11. Cracks would cause deep salt to rise rapidly with capillary water, creating a flat base for mulch film 14 coverage. In severely saline-alkali areas, after deep plowing, 200-300 kg of well-rotted straw fragments are spread per acre and mixed into the soil. After the straw is decomposed, it can increase the organic matter content of the surface soil layer 11 to more than 1.2%, further improving the granular structure and delaying salt back-infiltration.

[0041] It should be noted that 0.08mm thick aging-resistant polyethylene mulch film with a width of 1.2-1.5m should be selected to match the crop planting row spacing. Black mulch film should be preferred in severely saline-alkali areas, as it has both shading and weed suppression effects, reducing soil evaporation. When laying the mulch film, the ground surface should be flat, and the seams of the mulch film 14 should overlap by 5-8cm and be compacted with soil to prevent it from being blown away by strong winds. The edge of the mulch film 14 should be buried in the soil 10-15cm deep, slightly shallower than the lower boundary of the surface soil 11, forming a sealed layer that blocks the upward path of water and salt from the deep soil 13 to the middle soil 12 to the surface soil 11, reducing the evaporation of the surface soil 11 by more than 60%.

[0042] The mulch film 14 and the underground drainage system 2 work together to reduce the evaporation of the surface soil 11, thereby reducing the drainage load of the underground pipes. In slightly saline-alkali areas, after the mulch film 14 is used for mulching, the salt infiltration rate of the surface soil 11 is accelerated, and the drainage cycle of the branch pipes 22 can be extended from 7 days to 10 days, reducing energy consumption. In severely saline-alkali areas, the mulch film 14, in conjunction with the capillary pipes 21 for drainage, can prevent the rapid rebound of the surface soil 11 salt after leaching, thus shortening the time for the surface salt content to reach the standard.

[0043] S2. A three-dimensional grid layout is adopted, and the infiltration underground pipe drainage system 2 is laid in layers in the top soil 11, middle soil 12 and deep soil 13. A water collection well 5 is set at the edge of the treatment plot to collect the saline water discharged by the drainage system 2. A submersible pump and a saline water storage tank are provided to achieve the separation of fresh and salt water.

[0044] In this embodiment, the underground drainage system 2 includes capillary pipes 21 buried in the topsoil 11, branch pipes 22 buried in the middle soil 12, and main pipes 23 buried in the deep soil 13, forming a three-dimensional drainage network for deep water level control, middle salt discharge, and surface salt reduction. The capillary pipes 21 are buried at a depth of 30-40cm, with a diameter of 50-75mm and a spacing of 5-8m, and are used to quickly discharge surface saline water after salt washing in high-salt areas. The branch pipes 22 are buried at a depth of 60-80cm, with a diameter of 110-160mm and a spacing of 20-30m, covering the middle salt zone. The main pipes 23 are buried at a depth of 80-100cm, with a diameter of 160-200mm and a spacing of 50-80m, and are responsible for collecting deep saline water.

[0045] In this embodiment, the capillary tube 21, branch pipe 22 and main pipe 23 are all provided with permeable holes 3 for salt washing drainage, and electric regulating valves are installed at the longitudinal connection of the capillary tube 21, branch pipe 22 and main pipe 23 to dynamically adjust the drainage flow rate according to the stratified pH monitoring data. Specifically, during the salt washing period, the valve is fully open and the drainage flow rate is increased to 1.2-1.5 m³ / h to accelerate salt discharge; during the bioremediation period, the valve is half open and the flow rate is controlled at 0.3-0.5 m³ / h to avoid excessive drainage leading to soil drought.

[0046] In this embodiment, the underground pipe drainage system 2 is externally wrapped with gradient filter material, which includes an inner layer of permeable nonwoven fabric 41 and an outer layer of geotextile 43 wrapped around the outside of the underground pipe drainage system 2. A middle layer of zeolite particles 42 is filled between the inner layer of permeable nonwoven fabric 41 and the outer layer of geotextile 43. The inner layer of permeable nonwoven fabric 41 is used to prevent fine soil particles from entering. The middle layer of zeolite particles 42 is used to adsorb salt in the water and reduce the salinity of the drainage. The outer layer of geotextile 43 is used to filter coarse particles and extend the service life of the underground pipe.

[0047] It should be noted that the filter media distribution and installation process is as follows: The inner layer of permeable non-woven fabric 41 is wrapped around the outer wall of the main pipe 23, with the overlaps sewn together using a sewing machine at a stitch spacing of 5mm to ensure a tight, gapless fit. Alternatively, it can be hand-sewn with nylon thread at 3 stitches per centimeter. After sewing, check that the non-woven fabric adheres tightly to the pipe wall without wrinkles to avoid dead corners that could lead to fine soil accumulation. The middle layer of zeolite particles 42 is filled by evenly filling the space between the inner non-woven fabric 41 and the outer geotextile 43 using a filling funnel. During filling, gently tamp the material with a wooden stick to prevent particles from becoming airtight and ensure uniform filling density. The filling amount error per meter should be less than 5%. The filling height should match the width of the underground pipe trench. For example, if the trench width is 30cm, the diameter of the filter media after filling should be controlled at 25-28cm, leaving 2-5cm of space for subsequent soil backfilling. The outer layer of geotextile 43 is then used to cover and fix the filter media. The outer layer of geotextile 43 is wrapped around the outer wall of the middle layer of zeolite particles 42, with an overlap of 10cm. It is secured with nylon cable ties every 60cm, with the cable ties being tight enough to prevent loosening when lightly pulled, avoiding excessive tightness that could compress the zeolite particles and affect the adsorption effect. At the joint between the main pipe 23 and the branch pipe 22, an additional 3 turns of geotextile are wrapped and the cable ties are tightened, with a spacing of 20cm, to prevent the filter material from loosening at the joint. For the underground pipe entering the trench and backfilling the soil, the main pipe 23 wrapped with filter material is placed into the pre-excavated trench to a depth of 80-100cm. The slope of the underground pipe is adjusted to maintain a drainage slope of 0.2%-0.3%. Then, the soil is backfilled in layers: first, a 10cm thick layer of fine soil is backfilled, covered with the outer layer of geotextile 43, and gently compacted to avoid over-compaction that could clog the filter material pores. Then, a mixture of the middle layer soil 12 and the deep layer soil 13 is backfilled, following the original soil layer sequence to reduce damage to the soil structure.

[0048] In practice, the filter media parameters are dynamically adjusted based on the texture and salinity data of the deep soil 13. If the deep soil 13 is clay soil, fine soil particles are easily migrated with the water flow. Therefore, the pore size of the inner permeable nonwoven fabric 41 needs to be reduced to 0.1mm, and the outer geotextile 43 needs to be double-layered. At the same time, the filling thickness of the middle layer zeolite particles 42 is increased from 10-15cm to 15-20cm to improve the anti-clogging ability. If the salinity of the deep soil 13 is greater than 0.6%, modified zeolite particles 42 with higher adsorption capacity need to be selected. After modification by soaking in hydrochloric acid, the adsorption capacity is increased to 18-20mg / g. 5% activated carbon particles are added to the filter media layer of the main discharge pipe to enhance the adsorption of Cl ions and further reduce the EC value of the discharged saline water.

[0049] In this embodiment, the trench of the underground pipe drainage system 2 is filled with an improved substrate consisting of a combination of humus, straw fragments and salt-tolerant microbial agents. The humus and straw fragments improve the soil structure and promote root growth, while the microbial agents decompose the salt around the pipe, preventing the formation of salt spots around the underground pipe drainage system 2.

[0050] It should be noted that the specific governance and protection measures are as follows: regular maintenance, cleaning the underground drainage system 2, external filter media and water collection well 5 every 3 months to avoid blockage, and calibrating the pH sensor every 6 months; nutrient supplementation, applying organic fertilizer in conjunction with biological planting, 1000-1500 kg per mu, to improve the soil's salt resistance; emergency treatment, if a sudden rebound in pH value is detected, immediately start emergency irrigation, supplement the soil conditioner, suspend crop planting, and switch back to pioneer phytoremediation.

[0051] In practice, for sloping saline-alkali land, traditional horizontal underground pipes are prone to water accumulation in low-lying areas. Instead, the pipes can be laid according to the terrain gradient, with shallower burial depth (50-60cm) on the uphill section and deeper burial depth (70-90cm) on the downhill section, maintaining an overall drainage slope of 0.2%-0.3%. Salt collection wells 5 (spaced 30-50m apart) are added in low-lying areas and connected to branch pipes 22 to centrally discharge the high-concentration saline water (which can reduce the salt content by 20%-30%).

[0052] It should be noted that for short-term improvement plots, such as crop rotation areas within 5 years, the capillary pipe 21, branch pipe 22 and main pipe 23 adopt a detachable concealed pipe installation structure, with the pipes connected in sections (each section 1-2m), and the joints are fixed with clips. After the improvement is completed, they can be removed and recycled and reused in other plots.

[0053] S3. Construct an irrigation system 6 that couples drip irrigation and sprinkler irrigation. Sprinkler irrigation is used to wash away salt in moderate and severe areas first, while drip irrigation is used to wash away salt in mild areas and in the later stages of improvement. A sensor module 7 that detects salt content, flow rate and water level is installed at intervals in the drainage system 2 to monitor the salt content and flow rate of the saline water in the pipe in real time. The data is synchronized to the central control system through a wireless transmission module. Based on the dynamic model of soil salinization, the irrigation quota, irrigation cycle and amount of soil conditioner are dynamically adjusted according to the changes in the values.

[0054] In this embodiment, the irrigation system 6 is used in conjunction with the soil amendment. The selection and application method of the chemical amendment are as follows: For alkaline saline-alkali land, a composite amendment of desulfurized gypsum and humic acid is selected. The desulfurized gypsum provides calcium ions, and the humic acid adjusts the soil structure and lowers the pH value. For acidic saline-alkali land, a composite amendment of lime and wood ash is selected to neutralize the soil acidity and supplement potassium and calcium elements. The application method is to crush the amendment and dissolve it in the irrigation water, and apply it in a directional manner through the irrigation system 6 to avoid the problem of uneven application by manual spreading. The concentration of the amendment is set according to the initial pH value of the soil.

[0055] In this embodiment, the irrigation system 6 includes a water treatment unit, a pipeline delivery unit, an emitter unit, and an intelligent control unit. Each unit is specifically optimized for the characteristics of saline-alkali land. Specifically, the water treatment unit is equipped with a sand filter, a disc filter, and an activated carbon filter to remove silt, algae, and organic matter from the water; the pipeline delivery unit includes a main water supply pipeline laid along the edge of the plot, sprinkler branch pipes laid in a herringbone pattern in moderate and severe saline-alkali areas, and drip irrigation branch pipes laid parallel to the crop planting rows in mild saline-alkali areas and in plots in the later stages of improvement; the emitter unit includes units in moderate and severe saline-alkali areas... The selected rotary sprinkler irrigation system uses embedded patch sprinkler irrigation systems in mildly affected areas and later stages of improvement. Each irrigation zone is equipped with a PLC controller for the intelligent control unit, which collects data on soil moisture, pressure, and flow rate within the zone. It receives commands from the central control system to control start / stop operations and parameter adjustments. A central control platform is deployed in the cloud and on a local server, supporting access via web and mobile devices. It features irrigation plan creation, real-time data monitoring, equipment status alerts, and historical data query functions. The platform incorporates a dynamic soil salinization model, providing algorithmic support for regulatory decisions.

[0056] It should be noted that sensor module 7 acts as a data bridge between irrigation system 6 and underground drainage system 2, achieving closed-loop control through wireless transmission. The core process is as follows: One sensor module 7 is installed every 15m in capillary pipe 21 to monitor the parameters of saline water after surface salt washing, suitable for sprinkler irrigation areas; one sensor module 7 is installed every 20m in branch pipe 22 to monitor the parameters of mixed saline water in the middle layer, suitable for drip irrigation / sprinkler irrigation transition areas; one sensor module 7 is installed every 30m in main pipe 23 to monitor the parameters of deep high-salinity saline water, suitable for heavily saline areas; salinity, flow rate, and water level are collected every 10 minutes and uploaded to the central control system via LoRa wireless transmission module.

[0057] If the flow rate monitored by sensor module 7 in branch pipe 22 of the moderate zone decreases from 0.8 m³ / h to 0.6 m³ / h, the model predicts that the rate of salinity reduction will slow down by 50%, the irrigation cycle will be shortened from 10 days to 7 days, and the concentration of soil amendment will be increased from 1.0% to 1.2% simultaneously. If the pH monitored by sensor module 7 in branch pipe 22 of the mild zone is 8.0, the model calculates that 0.1% lime amendment needs to be added. The concentration in the dissolving tank will be automatically adjusted from 0.3% to 0.4% through the drip irrigation system, and the application time will be extended by 5 minutes to ensure that the amendment penetrates evenly into the middle soil layer 12.

[0058] After the soil conditioner is infiltrated into the soil by sprinkler / drip irrigation, salt ions such as Na⁺ are first filtered by the outer layer of geotextile 43 of the underground pipe, and then adsorbed by the middle layer of zeolite particles 42. Finally, the EC value of the discharged saline water is reduced by 20%-30% compared with that without filter material, reducing the load on the saline water treatment tank. When the sensor module 7 detects a decrease in the flow rate of the underground pipe, the irrigation system 6 automatically starts the low-pressure flushing mode. The water flow impacts the pores of the filter material, and with the physical adsorption of zeolite particles 42, the drainage capacity is restored, and the blockage treatment time is shortened to within 2 hours. The central control system compares the irrigation parameters with the drainage data fed back by the sensor module 7. If the EC value of the discharged saline water does not meet the target, the concentration of the soil conditioner is automatically adjusted to form a closed loop of "irrigation-drainage-monitoring-control" to ensure a stable decrease in soil salinity.

[0059] S4. The fresh water irrigated by the irrigation system 6 dissolves soluble salts in the topsoil 11, middle soil 12 and deep soil 13, forming saline runoff. The water seeps down into the underground drainage system 2 and is collected by gravity into the collection well 5, thus achieving off-site treatment of salt.

[0060] In this embodiment, the salt washing and suppression process of irrigation system 6 is as follows: First salt washing: For moderate to severe areas, continuous sprinkler irrigation is used, with 300-400 cubic meters of fresh water per acre to dissolve the surface and middle layers of salt. The salt seeps down to the underground pipe layer with the water and is discharged through the collection well 5; Circular salt washing: Salt washing is repeated once every 7-10 days, for a total of 2-3 rounds. During the treatment, drainage is continuously carried out through the underground pipe to control the groundwater level below 1.5m to prevent salt backflow; Precise acid adjustment: Chemical amendments are applied simultaneously with salt washing. The soil pH value is tested after each round of irrigation. If it does not reach the target range, the concentration of the amendment is adjusted and irrigation is carried out again.

[0061] It should be noted that the collection well 5, as the connecting node between the underground drainage system 2 and the external treatment process, undertakes functions such as temporary storage, water quality monitoring, and pressurized transportation to achieve off-site treatment of salinity. The saline water transported by the main discharge pipe 23 flows into the collection well 5 by gravity through the pipeline. When the sensor detects that the water level reaches 1.5m (60% of the volume of the collection well 5), the submersible pump is automatically started. If the EC value sensor detects that the saline water concentration is greater than 5ms / cm, the off-site treatment mode is activated; if it is less than 5ms / cm, the circulating irrigation mode is switched. Water samples are collected from the collection well 5 and the saline water treatment tank regularly to test the salt content and ion composition, ensuring that the salt removal rate reaches 60%-70% after off-site treatment. At the same time, the water discharge indicators after treatment are monitored to ensure compliance with environmental protection standards.

[0062] In practice, irrigation during the growing season includes: dynamic adjustment of quotas: 50 m³ / mu (20 cm wetness depth) during the sowing period, 80 m³ / mu (30 cm wetness depth) during the flowering and boll-forming period, and 40 m³ / mu during the maturity period, matching the drainage volume of the branch pipes to avoid water retention; and the injection of soil conditioner, adding a low-concentration conditioner (0.3% lime and 0.2% wood ash) once every two drip irrigations, which adsorbs residual salts through the gradient filter media of the branch pipes to maintain the soil pH at 6.5-7.5.

[0063] S5. Based on the monitoring data of the layered sensor module 7, salt-tolerant organisms are planted in stages and areas. The salt secretion and nitrogen fixation of the biological roots and the decomposition and improvement of dead branches and fallen leaves are utilized. Combined with rhizosphere growth-promoting bacteria, a soil-plant-microorganism synergistic remediation system is constructed to achieve progressive remediation of soil improvement, consolidation and enhancement.

[0064] In this embodiment, the progressive remediation method is as follows: The first stage is the severe improvement period, applicable when the surface soil salinity is >0.4% and pH is >8.5 or <5.5. Salt-tolerant pioneer plants are planted using a combination of direct seeding and seedling transplanting, with a seeding rate of 2-3 kg per acre. Simultaneously, salt-tolerant microbial agents are applied. The pioneer plant roots penetrate deep into the soil to absorb salt, and the microorganisms decompose the residual conditioner, rapidly stabilizing the soil pH. The second stage is the moderate consolidation period, applicable when the surface soil salinity is 0.2%-0.4% and pH is 6.0- 8.0, rotate salt-tolerant green manure and salt-tolerant crops. Two months after planting the green manure, plow it back into the field to replenish soil organic matter, further reduce salt content, improve soil aggregate structure, and lay the foundation for conventional crop planting. The third stage is the mild improvement period, which is applicable when the surface salt content of the soil is <0.2%, the pH is 6.5-7.5, the pH value of the three layers is stable, conventional crops are planted and salt-tolerant protective forests are planted at the edge of the plots to form an ecosystem of crops and trees. Through the absorption of residual salt by crops and the conservation of water sources and reduction of evaporation by trees, long-term soil stability is achieved.

[0065] In practice, sensor module 7 monitors pH values ​​24 and 72 hours after irrigation, and every 3 days during non-irrigation periods, with data automatically uploaded to the cloud platform. The dynamic control rules are as follows: if the surface pH is greater than 8.0 or less than 6.5, the dosage of the corresponding amendment is increased, and the irrigation interval is shortened from 7 days to 5 days; if the pH of the middle layer is abnormal, the irrigation time is adjusted and extended by 10-20 minutes to ensure that the amendment penetrates into the middle layer; if the pH of the deep layer is stable and the salinity is less than 0.2%, the amount of salt leaching irrigation is reduced, and the process transitions to the bioremediation stage.

[0066] Example 2: This application provides a method for treating saline-alkali land, the method comprising: The initial salinity, soluble salt ion composition, and pH value of the topsoil 11, middle soil 12, and deep soil 13 were determined by soil profile sampling and testing method. The groundwater level was determined, and the areas of mild, moderate, and severe salinity were divided. The topsoil 11 was deeply tilled to break up the compacted layer, increase soil permeability, and promote salt infiltration. The surface of the topsoil 11 was covered with mulch film 14 to block the upward movement of water and salt and inhibit soil evaporation.

[0067] A three-dimensional grid layout is adopted, and the infiltration underground pipe drainage system 2 is laid in layers in the top soil 11, middle soil 12 and deep soil 13. A water collection well 5 is set at the edge of the treatment plot to collect the saline water discharged by the drainage system 2. A submersible pump and a saline water storage tank are provided to achieve the separation of fresh and salt water.

[0068] An irrigation system 6 combining drip irrigation and sprinkler irrigation is constructed. Sprinkler irrigation is used to wash away salt in moderate and severe areas first, while drip irrigation is used to wash away salt in mild areas and in the later stages of soil improvement. A sensor module 7 that detects salt content, flow rate and water level is installed at intervals in the drainage system 2 to monitor the salt content and flow rate of the saline water in the pipe in real time. The data is synchronized to the central control system through a wireless transmission module. Based on the dynamic model of soil salinization, the irrigation quota, irrigation cycle and soil amendment application amount are dynamically adjusted according to the numerical changes.

[0069] The fresh water irrigated by the irrigation system 6 dissolves soluble salts in the topsoil 11, middle soil 12 and deep soil 13, forming saline runoff. The water seeps down into the underground drainage system 2 and is collected by gravity into the collection well 5, thus achieving off-site treatment of salt.

[0070] Based on the monitoring data of the layered sensor module 7, salt-tolerant organisms are planted in stages and areas. By utilizing the salt secretion and nitrogen fixation functions of the biological roots and the decomposition and improvement functions of dead branches and fallen leaves, combined with rhizosphere growth-promoting bacteria, a soil-plant-microorganism synergistic remediation system is constructed to achieve progressive remediation of soil improvement, consolidation and enhancement.

[0071] The three-stage underground pipe system, consisting of capillary pipe 21, branch pipe 22, and main pipe 23, forms a top-down drainage system. Capillary pipe 21 collects surface salt and then flows into the branch pipe. Branch pipe 22 integrates the saline water from the middle and surface layers and then flows into the main pipe 23. Finally, the main pipe 23 discharges the water into the plot. The core logic of this design is to achieve decentralized collection and centralized discharge through a hierarchical layout with increasing pipe diameter and wider spacing, avoiding excessive drainage load on a single pipe, while accurately matching the salt migration patterns of different soil layers.

[0072] The confluence path is a three-stage progressive flow, mainly including: In the first stage, capillary tube 21 collects surface saline water. After the salt-washing period and sprinkler irrigation, the high concentration of surface saline water seeps into the tube through the micropores in the wall of capillary tube 21 and flows towards the end under the action of gravity. The capillary tube is laid with a longitudinal slope of 0.2%, and the surface saline water collection can be completed within 24 hours.

[0073] In the second stage, the branch pipe 22 integrates the surface saline water. The saline water in the capillary pipe 21 flows into the branch pipe 22 through the vertical joint and mixes with the mid-layer saline water collected by the branch pipe 22 itself. It flows along the branch pipe 22 towards the main pipe 23. The longitudinal slope of the branch pipe 22 is 0.2%-0.3%. At this time, the salt content of the mixed saline water in the branch pipe 22 is about 0.5%-0.7%, and the flow rate changes dynamically according to the amount of water flowing into the capillary pipe 21.

[0074] In the third stage, the main drainage pipe 23 centrally transports and discharges the mixed saline water from the branch drainage pipe 22 into the main drainage pipe 23 through the flange joint. At the same time, the main drainage pipe 23 collects deep primary saline water with a salt content of 1.0%-1.5%, eventually forming a mixed water flow with a salt content of 0.7%-1.0%, which is transported to the salt collection well 5 at the edge of the plot. The submersible pump in the salt collection well 5 pressurizes the saline water and discharges it to the external saline water treatment pool.

[0075] Layered underground pipes can promptly remove byproducts generated from the reaction between the soil amendment and the soil, such as sodium sulfate produced by the reaction of gypsum in alkaline soil. This prevents the accumulation of byproducts from affecting the amendment effect. For example, in alkaline soil with a pH greater than 9.0, using layered underground pipes and gypsum amendment can reduce the soil pH to 7.5-8.0 within 3 months, while traditional underground pipes require 6 months, significantly improving the amendment efficiency.

[0076] The combined effect of stratified salt control and synergistic salt reduction is as follows: With no cross-contamination and stratified flow ensuring precise salt control, the vertical connection design of capillary tube 21 and branch pipe 22 prevents high-salt surface water from flowing back into the middle soil layer. The saline water in capillary tube 21 naturally infiltrates downwards by gravity, while the water pressure in branch pipe 22 is lower than that in capillary tube 21. The pump station at the end of the main drain 23 creates negative pressure, preventing saline water from the middle layer from surging to the surface. Actual test data shows that after adopting this connection method, the difference in salt content between the surface and middle soil layers can be stably maintained at 0.2%-0.3%, ensuring the stratified environmental requirements for bioremediation.

[0077] Dynamic adjustment, with the flow rate adapting to the treatment stage. During the salt washing period (0-3 months): the intelligent valve is fully open, increasing the flow rate from the branch pipe to the main pipe to 1.2-1.5 m³ / h, maximizing the discharge efficiency of the main pipe, and quickly reducing the average salinity of the plot from 0.6% to below 0.3%. During the bioremediation period (6-12 months): the valve is partially open, reducing the flow rate to 0.3-0.5 m³ / h, avoiding excessive drainage that could lead to soil drought, and maintaining a moisture content of 18%-22%. At this time, the main pipe only discharges a small amount of deep saline water, reducing energy consumption.

[0078] Traditional single-depth underground pipe treatment is prone to rebound due to the continuous upward movement of deep-layer salts, with surface salt content rising by 30%-40% within 1-2 years. Layered underground pipe treatment can significantly reduce the risk of rebound through three-dimensional salt control. Long-term monitoring data shows that in plots treated with layered underground pipes, the surface salt content rebound rate is less than 5% after 1 year, compared to 25%-30% for traditional underground pipe treatment. After 3 years, the surface salt content can still be maintained at less than 0.2%, and the soil pH is stable at 6.5-7.5. By shortening the treatment cycle, increasing land productivity, and extending service life, the investment payback period can be shortened from 3 years to 1.5 years, resulting in higher long-term benefits.

[0079] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for treating saline-alkali soil, characterized in that, The methods for treating saline-alkali land include: The initial salt content, soluble salt ion composition and pH value of the topsoil (11), middle soil (12) and deep soil (13) were determined by soil profile sampling and testing method. The groundwater level was determined and the areas of mild, moderate and severe salinity were divided. The topsoil (11) was deeply tilled to break up the compacted layer, increase soil permeability and promote salt infiltration. The surface of the topsoil (11) was covered with mulch (14) to block the upward movement of water and salt and inhibit soil evaporation. A three-dimensional grid layout is adopted, and an infiltration underground drainage system (2) is laid in layers in the top soil (11), middle soil (12) and deep soil (13). A water collection well (5) is set at the edge of the treatment plot to collect the saline water discharged by the drainage system (2). A submersible pump and a saline water storage tank are provided to achieve the separation of fresh and salt water. Construct an irrigation system that couples drip irrigation and sprinkler irrigation (6). Sprinkler irrigation is used to wash away salt in moderate and severe areas first, and drip irrigation is used to wash away salt in mild areas and in the later stage of improvement. A sensor module (7) that detects salt content, flow rate and water level is set at intervals in the drainage system (2) to monitor the salt content and flow rate of the saline water in the pipe in real time. The data is synchronized to the central control system through the wireless transmission module. Based on the dynamic model of soil salinization, the irrigation quota, irrigation cycle and amount of soil conditioner are dynamically adjusted according to the numerical changes. The fresh water irrigated by the irrigation system (6) dissolves soluble salts in the topsoil (11), middle soil (12) and deep soil (13), forming saline runoff. The water seeps down into the underground drainage system (2) and is collected by gravity flow to the collection well (5), thus realizing the off-site disposal of salt. Based on the monitoring data of the layered sensor module (7), salt-tolerant organisms are planted in stages and regions. The salt secretion and nitrogen fixation of the biological roots and the decomposition and improvement of dead branches and fallen leaves are utilized. Combined with rhizosphere growth-promoting bacteria, a soil-plant-microorganism synergistic repair system is constructed to achieve progressive repair of soil improvement, consolidation and enhancement.

2. The method for saline-alkali soil treatment according to claim 1, characterized in that: The physical improvement methods for the topsoil (11) are as follows: For compacted soil, heavy-duty deep tillage machines are used to perform deep tillage operations to a depth of 25-30cm to break up the plow pan, reduce soil bulk density to 1.2-1.4g / cm³, and increase soil porosity. After deep plowing, use a rotary tiller to perform shallow tilling of 15-20cm to make the soil particles uniformly broken and reduce the development of soil cracks. Cover the topsoil with a 0.08mm thick polyethylene film, and compact the soil at the seams of the film to block the upward flow of water and salt and inhibit the accumulation of salt on the surface.

3. The method of claim 1, wherein: The underground drainage system (2) includes capillary pipes (21) pre-buried in the topsoil (11), branch pipes (22) pre-buried in the middle soil (12), and main pipes (23) pre-buried in the deep soil (13), forming a three-dimensional drainage network for deep water level control, middle salt discharge, and surface salt reduction. The capillary tube (21) is buried at a depth of 30-40cm, with a diameter of 50-75mm and a spacing of 5-8m. It is used to quickly drain the surface salt water after washing salt in areas with high surface salinity. Branch pipes (22) are buried at a depth of 60-80cm, with a pipe diameter of 110-160mm and a spacing of 20-30m, covering the middle salt zone; The main drain pipe (23) is buried at a depth of 80-100 cm, has a pipe diameter of 160-200 mm, and a spacing of 50-80 m, and is responsible for collecting deep saline water.

4. The method of claim 3, wherein: The capillary tube (21), the branch drain pipe (22) and the main drain pipe (23) are all provided with permeation holes (3) for salt washing drainage on the surface, and the capillary tube (21), the branch drain pipe (22) and the main drain pipe (23) are longitudinally connected and provided with electrically adjustable valves, the drainage flow is dynamically adjusted according to the stratified pH monitoring data, and specifically: During the salt washing period, the valve is fully opened, the drainage flow is increased to 1.2-1.5 m³ / h, and the salt is accelerated to be discharged; During the biological repair period, the valve is half open, the flow is controlled at 0.3-0.5 m³ / h, and excessive drainage is avoided to cause soil drought.

5. The method of claim 3, wherein: The underground drainage system (2) is externally provided with a gradient filter package, which comprises an inner layer of water-permeable non-woven fabric (41) and an outer layer of geotextile (43) wrapped outside the underground drainage system (2), and the inner layer of water-permeable non-woven fabric (41) and the outer layer of geotextile (43) are filled with middle layer of zeolite particles (42); The inner layer of water-permeable non-woven fabric (41) is used to prevent fine soil particles from entering; The middle layer of zeolite particles (42) is used to adsorb salt in water and reduce the salinity of drainage water; The outer layer of geotextile (43) is used to filter coarse particles and prolong the service life of the underground pipe.

6. The method of claim 5, wherein: The underground drainage system (2) is laid in a trench filled with a modified substrate composed of humus soil, straw fragments and salt-tolerant microbial agents, the humus soil and straw fragments improve soil structure and promote root growth, and the microbial agents decompose salt around the pipe to avoid the formation of salt stains around the underground drainage system (2).

7. The method of claim 1, wherein: The irrigation system (6) is combined with the application of the modifier, and the selection and application method of the chemical modifier is as follows: For alkaline saline-alkali soil, desulfurized gypsum and humic acid composite modifier are selected, the desulfurized gypsum provides calcium ions, and the humic acid adjusts soil structure and reduces pH value; For acid saline-alkali soil, lime and wood ash composite modifier are selected to neutralize soil acidity and supplement potassium and calcium elements; The application mode is to crush the modifier and dissolve it in irrigation water, and then apply it through the irrigation system (6) to avoid the problem of uneven manual application, and the concentration of the modifier is set according to the initial pH value of the soil.

8. The method of claim 1, wherein: The salt washing and salt pressing process of the irrigation system (6) is as follows: For the first time, for the moderate and severe areas, continuous sprinkling irrigation is adopted, 300-400 cubic meters of fresh water per mu is used to dissolve the salt in the surface and middle layers, and the salt is infiltrated to the underground pipe layer with the water, and then discharged through the water collecting well (5); Cyclic salt washing, repeat salt washing once every 7-10 days, a total of 2-3 times, during the treatment period, the underground water level is controlled below 1.5 m to prevent salt backflow; Precise acid adjustment, chemical modifier is applied at the same time of salt washing, soil pH value is detected after each irrigation, if it does not reach the target range, adjust the concentration of the modifier and irrigate again.

9. The method of claim 1, wherein: The irrigation system (6) comprises a water source treatment unit, a pipe network conveying unit, a sprinkler unit and an intelligent control unit, each unit is specially optimized for the characteristics of saline-alkali soil, and specifically: The water source treatment unit is provided with a sandstone filter, a laminated filter and an activated carbon filter to remove silt, algae and organic matter in water; The pipe network conveying unit comprises a main water conveying pipeline laid along the plot edge, a sprinkler branch pipeline laid in a fishbone shape in a moderate and severe saline area, and a drip irrigation branch pipeline laid in parallel to the crop planting row in a mild saline area and a plot after improvement in the later period; The emitter unit comprises a rotary sprinkler emitter selected in a moderate and severe area, and an inner inlaid patch type sprinkler emitter selected in a mild area and after improvement in the later period; The intelligent control unit is configured with one PLC controller in each irrigation subarea, collects data such as soil humidity, pressure and flow in the subarea, receives instructions of the central control system, controls start and stop and parameter adjustment, deploys a central control platform on a cloud and a local server, supports Web and mobile access, has functions of irrigation plan making, real-time data monitoring, equipment state early warning and historical data query, and the built-in soil salinization dynamic model of the platform provides algorithm support for regulation and control decision.

10. The method of claim 1, wherein: The progressive repair method is: In the first stage of severe improvement period, the applicable conditions are that the soil surface salt content is greater than 0.4%, pH is greater than 8.5 or less than 5.5, salt-tolerant pioneer plants are planted, direct seeding and seedling transplanting are combined, the seeding amount per mu is 2-3 kg, salt-tolerant microbial inoculant is applied, the pioneer plant root system penetrates into the soil layer to absorb salt, the microbial decomposition improves the residual of the agent, and the soil pH value is quickly stabilized; In the second stage of moderate consolidation period, the applicable conditions are that the soil surface salt content is 0.2%-0.4%, the pH is 6.0-8.0, salt-tolerant green manure and salt-tolerant crops are rotated, the green manure is turned and applied to the field after being planted for 2 months, the soil organic matter is supplemented, the salt content is further reduced, and the soil aggregate structure is improved to lay a foundation for the planting of conventional crops; In the third stage of mild improvement period, the applicable conditions are that the soil surface salt content is less than 0.2%, the pH is 6.5-7.5, the three-layer pH value is stable, conventional crops are planted, and salt-tolerant protective forests are planted at the plot edge to form an ecological system of crops and forests, the residual salt is absorbed by crops, the water is conserved by forests, and the evaporation is reduced, so that the soil is long-term and stable.

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