A facility farmland salt leaching system based on soil profile rapid convergence interlayer and a construction method thereof

Abstract

The application discloses a kind of based on soil profile quick convergence interlayer's facility farmland salt leaching system and its construction method, belong to farmland irrigation and drainage technical field, the system includes arc concave, the arc concave is arranged in facility farmland, with arc concave as foundation and is equipped with soil interlayer, the central position of the arc concave is equipped with pumping well pipe device, the pumping well pipe device is communicated with arc concave by water-permeable sand column;The arc concave has the fastest drop line configuration characteristics, and the soil interlayer is the soil interlayer with high density on compaction upper low down.The system of the present application improves water collection efficiency, significantly inhibits deep percolation;Avoid interlayer salt accumulation, strengthen system sustainability;Realize single field leaching water independent control and accurate processing;Achieve pumping intensity and interlayer water convergence intensity Dynamic synergistic regulation.

Description

Technical Field

[0001] This invention belongs to the field of farmland irrigation and drainage technology, specifically relating to a facility farmland salt leaching system based on a rapid confluence layer of soil profile and its construction method. Background Technology

[0002] In facility-based farmland environments isolated from natural rainfall, the widespread adoption of intensive production models involving high multiple cropping indices, excessive fertilization, and frequent irrigation has led to increasingly prominent problems of secondary soil salinization and groundwater eutrophication. Simultaneously, these problems trigger a chain reaction of soil compaction, nutrient imbalances, and dysregulation of the microbial community structure, further inhibiting crop growth and development, ultimately resulting in a decline in the overall productivity of farmland.

[0003] Currently, soil leaching using flood irrigation is a conventional technique to alleviate excessive solute accumulation in greenhouse farmland. However, in humid irrigation areas with high groundwater levels and abundant rainfall, this gravity-driven vertical leaching method has significant drawbacks: on the one hand, it easily causes the leaching of nutrients such as nitrogen and phosphorus into deeper soil layers, thereby exacerbating the risk of agricultural non-point source pollution; on the other hand, traditional leaching methods only achieve the downward migration of salts along the soil profile, without truly removing solutes from the soil. When encountering irrigation, rainfall, or human disturbance, the salts that have already migrated downwards are very likely to move upwards again, causing repeated stress to the crop root zone.

[0004] Therefore, in the practice of salinity control in facility farmland, it is urgent to optimize the drainage path of leachate, enhance the lateral migration and directional discharge efficiency of solutes, reduce the vertical accumulation and diffusion of salts below the topsoil layer, and avoid secondary pollution to deep soil and groundwater environments. Simultaneously, efforts should be made to improve the utilization efficiency of leachate by achieving directional migration and centralized discharge of salts, thereby reducing ineffective leachate volume and ultimately conserving agricultural water resources. Summary of the Invention

[0005] Technical Problem Solved: To address the aforementioned technical problems, this invention provides a salt leaching system for facility farmland based on a rapid confluence layer in the soil profile and its construction method. The system involves excavating an arc-shaped concave surface with the brachistochrone (maximum descent) structural characteristic within the facility farmland, and constructing a compacted soil layer with a high-to-low density distribution based on this concave surface. On one hand, when water seeps vertically into the soil after surface irrigation, it can converge at the bottom of the arc-shaped concave surface at the fastest speed upon contact with the layer, shortening the residence time of the infiltrated water on the layer surface and thus inhibiting the formation of deep seepage. On the other hand, during non-irrigation periods, relying on the dense-to-sparse pore structure of the soil layer, the salt-containing solution retained within the layer can move upwards under capillary force, preventing salt from seeping into the deeper layers with the water. In addition, by setting up vertical drainage pipe wells in the center of the field, the leachate collected at the bottom of the arc-shaped concave surface is centrally pumped out, and the pumping intensity is dynamically adjusted according to the water level changes in the drainage pipe wells. This effectively reduces the energy consumption of pumping while avoiding the risk of secondary pollution of farmland water areas caused by gravity drainage.

[0006] Technical solution: In a first aspect, the present invention provides a facility farmland salt leaching system based on a rapid confluence layer of soil profile, including an arc-shaped concave surface, which is set in the facility farmland. A soil layer is set on the arc-shaped concave surface as a base. A pumping well pipe device is set at the center of the arc-shaped concave surface. The pumping well pipe device is connected to the arc-shaped concave surface through a permeable sand column. The arc-shaped concave surface has the structural characteristics of the brachistochrone line, and the soil layer is a soil layer with a higher compaction density at the top and a lower compaction density at the bottom.

[0007] Preferably, the pumping well pipe device includes a PVC hollow pipe, which is open at the upper end and closed at the lower end. Several water-permeable holes are formed on the lower side wall of the PVC hollow pipe, and a non-woven fabric layer is provided outside the water-permeable holes. A central control system is provided at the upper end of the PVC hollow pipe. A water-permeable baffle is provided inside the PVC hollow pipe, dividing the PVC hollow pipe into a first cavity and a second cavity. A water level monitoring device is provided in the first cavity, and a small water pump is provided in the second cavity. The small water pump and the central control system are respectively connected to the water level monitoring device via signals. A drainage outlet is formed on the side wall of the PVC hollow pipe forming the second cavity.

[0008] Furthermore, the water level monitoring device includes a device body, which is a hollow cavity structure. The lower end of the device body is detachably connected to a probe fixing seat, which has three probe mounting holes extending vertically and parallel to each other. A short probe, a medium probe, and a long probe are respectively installed in the probe mounting holes. The upper end of the device body is provided with a signal transmission component, which includes an integrated wiring and three signal transmission lines. One end of each of the three signal transmission lines is electrically connected to the short probe, the medium probe, and the long probe, respectively. The integrated wiring is electrically connected to the central control system.

[0009] Furthermore, the small water pump is connected to the drain outlet via a drain pipe, and a rubber plug is provided inside the drain outlet; the power supply line of the small water pump forms a signal transmission circuit with the short probe, medium probe and long probe.

[0010] Secondly, the present invention provides a method for constructing a facility farmland salinity leaching system based on a rapid confluence layer of soil profiles as described in the first aspect, comprising the following steps: S1. Design of an arc-shaped concave surface with brachistochrone characteristics, including the establishment of a spatial coordinate system and the generation of parametric equations for the brachistochrone; S2, Arc-shaped concave excavation and soil isolation layer construction; S3. Layout and control of the drainage system.

[0011] Preferably, the specific process of step S1 is as follows: S1-1. Establishment of Spatial Coordinate System The length of the rectangular farmland is set to l Width is w ; Taking the upper left endpoint A of the cross-section at the beginning of the field along the width direction as the origin (0, 0), establish the x-axis along the width direction (left to right) and the z-axis along the vertical direction (up to down) to construct a two-dimensional xz coordinate system; Based on the depth h of the main root system layer of the crops planted in the facility farmland, the maximum excavation depth corresponding to the midpoint of the surface layer of the cross-section at the beginning of the field is defined as h, and this excavation depth point is denoted as B ( w / 2, h ); S1-2, Generation of the parametric equations for the brachistochrone curve Construct the brachistochrone line from top to bottom using the line connecting points A and B. Generate the parametric equation of the brachistochrone line along the cross-section of the field width. The expression in the above xz coordinate system is: , Where, x 横 z 横 The coordinates of the point in the xz coordinate system r 横 Let be the radius of the circle that generates the cycloid in the xz coordinate system; i 横 The roll angle is the angle a circle rotates as it rolls along a straight line, expressed in radians. i B The angle that the circle corresponding to the cycloid moves to point B can be obtained by the following calculation process: or ; ;because It is monotonically increasing in the interval (0, 2π), and All are greater than 0, therefore i B There exists a unique solution in the interval (0, 2π), corresponding to r. 横 Its value is also unique; Using the vertical centerline of the Tianshou section passing through point B as the axis of symmetry, the brachistochrone line from point A to point B is mirrored to form the brachistochrone line from point B to the upper right end point C (w, 0) of the Tianshou section. Similarly, for the longitudinal section along the length of the field, with the upper endpoint A at the beginning of the field as the origin (0, 0), a y-axis is established along the horizontal line of the ground surface along the length of the field (beginning to end), and a z-axis is established vertically (up to down) along the left endpoint, constructing a two-dimensional yz coordinate system; based on the depth h of the main root layer of the crop, the excavation depth corresponding to the midpoint of the surface layer of the longitudinal section is set as h, and this excavation depth point is denoted as D(l / 2, h); the steepest descent line from point A to point D is constructed, generating the parametric equation of the steepest descent line in the yz coordinate system of the longitudinal section along the length of the field, the expression of which is: , Among them, y 纵 z 纵 The coordinates of the point in the yz coordinate system. r 纵 Let be the radius of the circle that generates the cycloid in the yz coordinate system; i 纵 The roll angle is the angle a circle rotates as it rolls along a straight line, expressed in radians. i D The angle that the circle corresponding to the cycloid moves to point D can be obtained by the following calculation process: or ; ; Similarly, r 纵 There exists a unique solution. i D There exists a unique solution; taking the vertical centerline of the side longitudinal section passing through point D as the axis of symmetry, the brachistochrone line from point A to point D is mirrored to form the brachistochrone line from point D to the upper left end point E(l, 0) of the Tianwei section. Based on the ABC arc of the cross section at the beginning of the field, the ADE arc of the longitudinal section on the side is moved from the beginning of the field to the end of the field, and finally an arc-shaped concave surface with the characteristics of the steepest descent line is constructed in the soil layer. The four vertices of the arc-shaped concave surface coincide with the four endpoints of the rectangular field surface, and the center point is the deepest point of excavation, with a depth of 2h.

[0012] Preferably, the specific process of step S2 is as follows: S2-1, Arc-shaped concave excavation Before excavation, a spiral drill bit is used to advance along the length of the field and loosen the soil through rotary tillage. Every 10-50 cm of advance, the depth of rotation is adjusted according to the horizontal position of the drill bit to ensure that the soil profile after rotary tillage conforms to the brachistochrone structural characteristics. After the entire farmland is rotary tilled, the loosened soil is removed to expose the arc-shaped concave surface that meets the design requirements. S2-2, Construct a compacted interlayer with a higher density at the top and a lower density at the bottom. The concave surface was further loosened by rotary tillage using an auger bit, maintaining the concave shape. The tillage depth was no less than 20.0 cm, and the soil bulk density in the tilled area did not exceed 1.25 g / cm³. 3 Subsequently, a roller is used to roll back and forth along the length of the field to compact and smooth the concave surface. Taking advantage of the characteristic that the compaction effect decreases with depth, the compacted layers are designed with a "dense on top, loose on the bottom" density distribution: the upper dense layer is 5.0–10.0 cm thick with a density not less than 1.50 g / cm³; the lower loose layer is 5.0–10.0 cm thick with a density not exceeding 1.35 g / cm³. 3 The "dense on top and sparse on the bottom" structure can form a capillary gradient effect. After rinsing, the solute in the unsaturated layer can move upward under the stronger capillary action in the upper part. During the next round of water rinsing, the water flowing above the layer can preferentially rinse the salt accumulated in the upper part and discharge it, avoiding the accumulation of salt in the layer.

[0013] Preferably, the specific process of step S3 is as follows: S3-1. Layout of the pumping well casing and permeable sand column After compaction, a cylindrical permeable sand column is piled at the bottom center of the concave surface, and a PVC hollow pipe is vertically inserted into the center of the permeable sand column; the top of the PVC hollow pipe is 40-60 cm above the farmland surface; then, the concave surface is backfilled to ensure that the average bulk density of the backfill soil is close to 1.30 g / cm³. S3-2, Water Level Monitoring and Pumping Control The control logic is as follows: when the water level in the PVC hollow pipe rises to submerge the long probe but does not contact the middle probe, the small water pump does not start; when the water level rises to contact the top of the middle probe, the small water pump starts in low-power operation mode until the water level drops below the top of the long probe and then stops; if the water level continues to rise and contacts the top of the short probe, the small water pump switches to high-power operation mode until the water level drops below the top of the middle probe, then switches back to low-power operation mode to continue pumping until the water level drops below the top of the long probe and then stops.

[0014] Beneficial effects: (1) Improve water collection efficiency and significantly inhibit deep leakage. Setting a compacted barrier layer in the soil profile is an effective technical means to improve the targeting of salt leaching, save water resources and prevent groundwater pollution. However, traditional barriers tend to prolong the retention time of infiltrated water on the surface, which not only increases the risk of deep leakage, but also weakens the water blocking and water conduction effects. The present invention designs the profile structure based on the principle of the steepest descent line, so that water flows rapidly along the direction of gravity after contacting the barrier layer. Macroscopically, it follows the energy dissipation law of moving from high water potential area to low water potential area, which can effectively shorten the retention time of water on the surface of the barrier layer and greatly reduce the risk of deep leakage. (2) Prevent salt accumulation in the interlayer and enhance system sustainability. Salt-containing leached water easily accumulates in the interlayer after seeping into it, affecting the long-term performance of the interlayer. This invention reduces the bulk density of a specific thickness of soil layer by excavating an arc-shaped concave surface with the characteristics of the steepest descent line in the facility farmland and performing rotary tillage. Then, combined with vibration and rolling compaction technology, a "dense on top and sparse on the bottom" pore structure and a "high on top and low on the bottom" bulk density distribution are constructed. In the unsaturated stage of the soil, this structure makes the soil water suction in the interlayer present a distribution characteristic of high on top and low on the bottom, which can drive the salt to migrate upward under the action of matrix potential, making it easier for the solute to be removed in the subsequent leaching process, thereby completely preventing the accumulation of salt in the interlayer and ensuring the long-term stable operation of the system; (3) Achieve independent control and precise treatment of leaching water from a single field. In view of the characteristics of diverse crop types, complex water and fertilizer management models, and large differences in leaching solute composition in facility agriculture, this invention takes an independent field as the basic unit and sets up a vertical pumping well in the center of the field to achieve separate pumping and discharge of leaching water; at the same time, a dedicated water storage and treatment system can be built to achieve classified collection and targeted treatment of drainage from different fields, effectively avoid the risk of secondary pollution, and protect the water environment quality around the farmland. (4) Achieving dynamic and coordinated control of pumping intensity and interlayer water collection intensity. After irrigation, there is a lag effect in soil moisture infiltration and collection, which can easily lead to fluctuations in the water collection rate of vertical wells. This invention monitors the water level changes in the pumping well in real time and adopts a segmented power control strategy: when the water level is high, a high-power pumping mode is activated to prevent the water level from being too high and inhibiting the collection efficiency; when the water level is low, it switches to a low-power operation mode, which can significantly save energy consumption, reduce the number of frequent pump starts and stops, and extend the service life of the equipment. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of a facility farmland salt leaching system based on a rapid confluence layer of soil profile according to the present invention; Figure 2 A diagram showing the spatial coordinate system setup for constructing an arc-shaped concave surface with the characteristics of the steepest descent line in this invention; Figure 3 This is a schematic diagram of the longitudinal section of a rectangular field block based on the brachistochrone line; Figure 4 This is a schematic diagram of the transverse cross-section along the width direction at the head end of a rectangular field based on the brachistochrone line. Figure 5 A schematic diagram of a pumping pipeline device based on water level changes; Figure 6 This is a flowchart illustrating the construction and operation of a facility farmland salt leaching system based on a rapid confluence layer in soil profile, as described in this invention. In the diagram: 1. Arc-shaped concave surface; 2. Permeable sand column; 3. Pumping well pipe device; 31. Central control system; 32. PVC hollow pipe; 321. Permeable baffle; 33. Drainage outlet; 34. Water level monitoring device; 341. Short probe; 342. Medium probe; 343. Long probe; 344. Probe mounting base; 345. Main body of the device; 346. Signal transmission component; 35. Small water pump; 351. Drainage pipe; 352. Power supply line. Detailed Implementation

[0016] The present invention will be described in detail below with reference to specific embodiments: Example 1

[0017] A salt leaching system for facility farmland based on a rapid runoff isolation layer in soil profile includes an arc-shaped concave surface 1, which is set in the facility farmland. A soil isolation layer is set on the arc-shaped concave surface 1. A pumping well pipe device 3 is set at the center of the arc-shaped concave surface 1. The pumping well pipe device 3 is connected to the arc-shaped concave surface 1 through a permeable sand column 2. The arc-shaped concave surface 1 has the structural characteristics of the steepest descent line. The soil isolation layer is a soil isolation layer with a higher compaction density at the top and a lower compaction density at the bottom.

[0018] like Figure 5 As shown, the pumping well pipe device 3 includes a PVC hollow pipe 32, which is open at the upper end and closed at the lower end. Several water-permeable holes are provided on the lower side wall of the PVC hollow pipe 32, and a non-woven fabric layer is provided outside the water-permeable holes. A central control system 31 is provided at the upper end of the PVC hollow pipe 32. A water-permeable baffle 321 is provided inside the PVC hollow pipe 32, dividing the PVC hollow pipe 32 into a first cavity and a second cavity. A water level monitoring device 34 is provided in the first cavity, and a small water pump 35 is provided in the second cavity. The small water pump 35 and the central control system 31 are respectively connected to the water level monitoring device 34 via signals. A drainage outlet 33 is provided on the side wall of the PVC hollow pipe 32 forming the second cavity.

[0019] The aforementioned water level monitoring device 34 adopts a three-probe sensing structure design for graded sensing and monitoring of water levels. It includes a device body 345, which is a hollow cavity structure with pre-reserved probe mounting cavities and signal wiring channels to provide mounting carriers and protection for various functional components. The lower end of the device body 345 is detachably connected to a probe mounting base 344, which is made of insulating material and has three vertically extending, parallel probe mounting holes. Each mounting hole contains a short probe 341, a medium probe 342, and a long probe 343. The diameter of the three mounting holes matches the outer diameter of the corresponding probe, and the center-to-center distance between adjacent mounting holes is set to 8-12 mm. mm, to ensure insulation and sensing stability between probes; the short probe 341, medium probe 342 and long probe 343 are all integrally formed of conductive metal, with the same cross-sectional structure and arranged vertically; the effective sensing length of the short probe 341 is L1, the effective sensing length of the medium probe 342 is L2, and the effective sensing length of the long probe 343 is L3, satisfying the relationship L1 < L2 < L3, and the upper ends of the three probes are all embedded in the corresponding probe mounting holes of the probe fixing seat 344 by interference fit, with an embedding depth of not less than 15mm to ensure a firm connection; the lower ends of each probe extend below the probe fixing seat 344, and the end faces of the extended ends are kept flush, forming a graded sensing end.

[0020] The aforementioned signal transmission component 346 includes three signal transmission lines and one integrated wiring. One end of each of the three signal transmission lines is electrically connected to the upper ends of the short probe 341, the medium probe 342, and the long probe 343 respectively by welding. The other end of each line passes through the signal routing channel inside the device body 345 and is connected to the integrated wiring. The integrated wiring is fixed to the upper end of the device body 345 and is detachably electrically connected to the central control system 31, used to transmit the water level sensing signals collected by each probe to the external control module.

[0021] The aforementioned short probe 341, medium probe 342, and long probe 343 are arranged in a linear array on the probe holder 344. The insulation distance between two adjacent probes is not less than 5 mm, which effectively avoids signal interference between adjacent probes caused by the conductivity of water during water level monitoring and ensures that each probe can independently achieve accurate sensing of the corresponding water level threshold.

[0022] The above small water pump 35 is connected to the drainage outlet 33 through a drainage pipe 351, and a rubber plug is provided in the drainage outlet 33. During the non-irrigation leaching stage, the rubber plug is used at the drainage port to prevent soil or debris from entering the drainage pipe 351. When it is necessary to pump and drain the accumulated water after irrigation leaching, a signal conduction loop is constructed by three probes with different lengths of the water level monitoring device 34 and the power supply wire 352. Through the water level induction signal output by this signal conduction loop, the start-stop state of the small water pump 35 is automatically controlled. At the same time, the drainage outlet 33 is connected to a water delivery conduit to realize the outward output of the leachate. Embodiment 2

[0023] For the rectangular farmland as the implementation object, the corresponding length and width are l = 40.0 m and w = 5.0 m respectively, and the main root layer of the planted crops is 0.0 - 0.4 m. The implementation process is as follows: A construction method for a salt leaching system for facility farmland based on a rapid runoff isolation layer in the soil profile, as Figure 6 shown, includes the following steps: S1. Design of the arc concave surface with the characteristics of the brachistochrone S1-1. Establishment of the space coordinate system As Figure 1-Figure 4 shown: To construct the arc concave surface 1 with the characteristics of the brachistochrone, a space coordinate system is established with the upper left surface endpoint A at the head of the field as the origin (0, 0): the surface layer of the cross-section along the width direction at the head of the field is the x-axis (the direction is from left to right), the perpendicular line of the left endpoint is the z-axis (the direction is from top to bottom), and the horizontal line from the upper left endpoint A at the head of the field along the length direction of the field to the tail of the field is the y-axis.

[0024] S1-2. Generation of the parametric equation of the brachistochrone Combined with the characteristic of the maximum depth of the main root system of 0.4 m in this embodiment, the maximum excavation depth below the midpoint of the surface layer at the head of the field is set to 0.4 m; in the x-z plane at the head of the field, the brachistochrone is the connection line between the two points (0.0, 0.0, 0.0) and (2.5, 0.0, 0.4). According to the cycloid expression, the coordinates of each point satisfy the following relational expressions: When 0 ≤ x < 2.5 m, the relational expression is: ; When 2.5 < x ≤ 5.0 m, with x = 2.5 as the symmetry axis, the brachistochrone of the connection line between the above two points is mirror-imaged, and the relational expression is: ; Similarly, in the y-z plane of the side field section along the length direction, the maximum excavation depth below the midpoint of the surface layer of the side field section is set to 0.4 m, and the brachistochrone is the line connecting the two points (0.0, 0.0, 0.0) and (0.0, 20.0, 0.4). According to the cycloid expression, the coordinates of each point satisfy the following relational expressions: When 0 ≤ y < 20.0 m, the relational expression is: Similarly, in the y-z plane of the side field section along the length direction, the maximum excavation depth below the midpoint of the surface layer of the side field section is set to 0.4 m, and the brachistochrone is the line connecting the two points (0.0, 0.0, 0.0) and (0.0, 20.0, 0.4). According to the cycloid expression, the coordinates of each point satisfy the following relational expressions: When 0 ≤ y < 20.0 m, the relational expression is: ; When 20.0 < y ≤ 40.0 m, with y = 20 as the axis of symmetry, mirror the brachistochrone of the above two-point connection line, and the relational expression is: .

[0025] In summary, based on the horizontal plane formed by the x-y axis, the field is divided into four intervals: Interval 1 (0 ≤ x < 2.5, 0 ≤ y < 20.0), Interval 2 (2.5 < x ≤ 5.0, 0 ≤ y < 20.0), Interval 3 (0 ≤ x < 2.5, 20.0 < y ≤ 40.0), Interval 4 (2.5 < x ≤ 5.0, 20.0 < y ≤ 40.0). The z values (excavation depths) corresponding to different horizontal coordinates in each interval are calculated as follows:

[0026] 1) Interval 1: The excavation depth z1 corresponding to the horizontal position (x1, y1) According to x1 = 0.4323( i 横 -sin i 纵 ) for calculation i 横 , according to y1 = 3.1931( i 纵 -sin i 纵 ) for calculation i 纵 , substitute i 横 , i 纵 into the z value calculation formula to obtain z1.

[0027] 2) Interval 2: The excavation depth z2 corresponding to the horizontal position (x2, y2) According to x² = 5 - 0.4323 ( i 横 -sin i 纵 )calculate i 横 According to y2 = 3.1931 ( i 纵 -sin i 纵 )calculate i 纵 ,Will i 横 , i 纵 Substituting into the formula for calculating the z value, we get z2.

[0028] 3) Interval 3: Excavation depth z3 corresponding to the horizontal position (x3, y3) Based on x3 = 0.4323 ( i 横 -sin i 纵 )calculate i 横 According to y3 = 20 - 3.1931 ( i 纵 -sin i 纵 )calculate i 纵 ,Will i 横 , i 纵 Substituting into the z-value calculation formula, we get z3.

[0029] 4) Interval 4: Excavation depth z4 corresponding to the horizontal position (x4, y4) According to x4 = 5 - 0.4323 ( i 横 -sin i 纵 )calculate i 横 According to y4 = 20 - 3.1931 ( i 纵 -sin i 纵 )calculate i 纵 ,Will i 横 , i 纵 Substituting into the z-value calculation formula, we get z4.

[0030] S2, Arc-shaped concave excavation and compacted interlayer construction S2-1, Arc-shaped concave excavation A rotary tiller equipped with a single, precisely depth-controlled drill bit was used to till and break up the soil above the designed area of ​​the arc-shaped concave surface 1, preparing it for excavation. Tillage began at the left edge of the first end of the field, with an initial depth of 10 cm. The rotary tiller advanced along the length of the field, and every 40 cm, the depth of rotation was dynamically adjusted based on the current horizontal coordinates (x, y) of the drill bit's center point, according to a preset brachistochrone surface equation, to match the designed excavation depth z at that point. After completing one row of rotary tillage, the rotary tiller was moved laterally by one drill bit width, and then rotary tillage was resumed from the beginning to the end of the field, repeating this process until the soil in the entire designed area was loosened and broken up.

[0031] After the soil is completely rotary tilled and broken up, the loosened soil in the area is removed, and the resulting concave surface is the arc-shaped concave surface 1 that meets the design requirements for the steepest descent line. The lowest point of this concave surface is located in the center of the field, and the maximum excavation depth is twice the depth of the main root system of the crop (40.0 cm) (i.e., 80.0 cm). The upper edge coincides with the four corners of the rectangular farmland surface.

[0032] S2-2, Construct a compacted interlayer with a higher density at the top and a lower density at the bottom. Based on the concave surface created by excavation, a secondary rotary tillage of the interlayer area is carried out using a drill bit with a rod length of 20-30 cm. During the rotary tillage process, the designed interlayer shape is maintained, and the soil bulk density after loosening should be lower than 1.25 g / cm³. 3 .

[0033] Subsequently, a roller-type soil roller was used to compact the loose soil layer along the length of the field. Taking advantage of the characteristic that the compaction effect decreases with increasing depth, the compaction parameters were controlled to ensure that the soil bulk density in the range of 5.0–10.0 cm below the upper surface of the interlayer was greater than 1.45 g / cm³. 3 The soil bulk density within 5-10 cm above the bottom of the interlayer should not exceed 1.30 g / cm³. 3 This creates a "higher at the top, lower at the bottom" density distribution, resulting in a "dense at the top, sparse at the bottom" capillary gradient in the soil pores. This structure has dual benefits: firstly, the higher density of the upper layer effectively blocks infiltration water from penetrating the interlayer, reducing deep leakage; secondly, the capillary pore gradient distribution creates a top-to-bottom soil water suction difference during the unsaturated stage, promoting the upward movement of saline water within the interlayer. This facilitates the infiltration water, collected along the concave surface 1, carrying away the salt accumulated in the upper part of the interlayer during the next leaching cycle, thus preventing salt accumulation.

[0034] To achieve the target density distribution, a pre-compaction test must first be conducted: by adjusting the self-weight of the roller soil roller and the number of compaction passes, the process parameters for achieving the target compaction state are determined, and then the optimized parameters are applied to the actual farmland interlayer compaction process.

[0035] S3. Construct a vertical shaft system whose pumping capacity varies with the water catchment volume. S3-1 Construction of a permeable sand column with an arc-shaped concave bottom A cylindrical permeable sand column 2 is installed at the center point of the bottom of the excavated arc-shaped concave surface 1. The permeable sand column 2 is designed to be 30.0 cm high and 15.0 cm in diameter. The construction process is as follows: S3-1-1. Place an acrylic or metal round tube with a wall thickness of 1.0~2.0 cm and an inner diameter of 50.0 cm vertically at the center of the lowest point of the arc-shaped concave surface 1. S3-1-2. Fill the pipe with sorted sand particles with a diameter > 2.0 mm until the sand surface is flush with the pipe opening; S3-1-3. Backfill soil around the outside of the circular pipe, with the backfill height matching that of the pipe, and control the average bulk density of the backfill soil to 1.30 g / cm³. 3 ; S3-1-4. Slowly pull out the round pipe, and promptly fill the gap formed after pulling out the pipe with sand of the same size and compact it to complete the construction of the permeable sand column 2.

[0036] The permeable sand column 2 serves a dual purpose: firstly, it provides bottom support for the subsequently installed pumping well pipe device 3; secondly, it enhances the soil profile's ability to store and collect runoff water.

[0037] S3-2. Pumping Well Casing Structure and Installation S3-2-1. Selection and design of drainage well pipe: Plastic pipe is used, with a wall thickness of 1.0 cm, an inner diameter of 15.0 cm, and a total length of 130.0 cm (calculated based on: 2 × main root layer depth + 50.0 cm above the farmland surface); The pipe adopts a design with one end closed and the other end open. Within a 50.0 cm section extending along the pipe body from the closed end, permeable holes with a diameter of 0.2 cm are evenly opened in a matrix, with a hole spacing of 2.0 cm.

[0038] S3-2-2, Installation Process: (1) Wrap the permeable area of ​​the pipe wall completely with non-woven fabric to prevent fine soil particles from entering and clogging it; (2) A perforated baffle parallel to the pipe diameter is set in the area corresponding to the water permeable hole inside the pipe to evenly divide the inner cavity of the pipe into two independent chambers (one side accommodates a small water pump 35, and the other side is equipped with a water level monitoring device 34). (3) Insert the treated drainage well pipe (i.e., PVC hollow pipe 32) vertically into the center of the pre-set permeable sand column 2, ensuring that the closed end is facing down and the insertion depth is consistent with the height of the permeable sand column (30.0 cm). (4) After the well pipe is installed and in place, backfill the soil to restore the farmland surface to its pre-excavation level, and control the average bulk density of the backfill soil to approximately 1.30 g / cm³. 3 .

[0039] S3-3, Water Level Monitoring and Pumping Control System Both the water level monitoring device 34 and the small water pump 35 are connected to the central control system 31 at the top of the pipe. This system can automatically adjust the operating power of the small water pump 35 based on the real-time water level monitored in the pipe and via the power supply line 352. The water level monitoring device 34 consists of three probes of different lengths: long, medium, and short. These probes are vertically installed in a designated chamber inside the pipe. The difference in probe length can be adjusted according to the expected water collection rate and the drainage capacity of the water pump. During installation, the tip of the long probe 343 is kept 2.0 to 3.0 cm away from the inner wall of the closed end of the pipe.

[0040] The water level response and pumping control logic are as follows: a) Low water level standby: When the water level in the PVC hollow pipe 32 rises to submerge the top of the long probe 343, but does not contact the middle probe 342, the water pump will not start. b) Medium-power pumping: When the water level continues to rise to the top of the contact probe 342, the pumping pump starts to drain in low-power mode until the water level drops below the top of the long probe 343 and then stops. c) High-power enhanced pumping: If the water level rises rapidly and touches the top of the short probe 341 after contacting the middle probe 342, the small pump 35 immediately switches to high-power mode to quickly lower the water level; when the water level drops below the top of the middle probe 342, it switches back to low-power mode to continue pumping until the water level drops below the top of the long probe 343 and then stops.

[0041] In this embodiment, the bottom suction port of the small water pump 35 is close to the inner wall of the closed end of the pipe to ensure effective drainage of water accumulated at the bottom of the pipe; the outlet is connected to the drain outlet 33 through an independent drain pipe 351. During non-irrigation and leaching periods, the drain outlet 33 is sealed with a rubber stopper to prevent debris or soil from entering; during leaching drainage, the rubber stopper is removed, and the drain outlet 33 is connected to an external water delivery pipe, which can directionally transport the leachate collected at the bottom of the concave surface to a designated discharge point for unified harmless treatment.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A facility farmland salt leaching system based on a rapid runoff buffer layer in soil profile, characterized in that: It includes an arc-shaped concave surface (1), which is set in the facility farmland. A soil partition is provided based on the arc-shaped concave surface (1). A pumping well pipe device (3) is provided at the center of the arc-shaped concave surface (1). The pumping well pipe device (3) is connected to the arc-shaped concave surface (1) through a permeable sand column (2). The arc-shaped concave surface (1) has the characteristics of the steepest descent line structure. The soil partition is a soil partition with a higher compaction density at the top and a lower compaction density at the bottom.

2. The facility farmland salt leaching system based on a rapid soil profile runoff buffer layer according to claim 1, characterized in that: The pumping well pipe device (3) includes a PVC hollow pipe (32), which is open at the top and closed at the bottom. Several water-permeable holes are provided on the lower side wall of the PVC hollow pipe (32), and a non-woven fabric layer is provided outside the water-permeable holes. A central control system (31) is provided at the upper end of the PVC hollow pipe (32). A water-permeable baffle (321) is provided inside the PVC hollow pipe (32). The water-permeable baffle (321) divides the PVC hollow pipe (32) into a first cavity and a second cavity. A water level monitoring device (34) is provided in the first cavity. A small water pump (35) is provided in the second cavity. The small water pump (35) and the central control system (31) are respectively connected to the water level monitoring device (34). A drainage outlet (33) is provided on the side wall of the PVC hollow pipe (32) forming the second cavity.

3. The facility farmland salt leaching system based on a rapid soil profile confluence layer according to claim 2, characterized in that: The water level monitoring device (34) includes a device body (345), which is a hollow cavity structure. The lower end of the device body (345) is detachably connected to a probe fixing seat (344), which has three probe mounting holes that extend vertically and are parallel to each other. The probe mounting holes are respectively provided with a short probe (341), a medium probe (342) and a long probe (343). The upper end of the device body (345) is provided with a signal transmission component (346), which includes an integrated wiring and three signal transmission lines. One end of the three signal transmission lines is electrically connected to the short probe (341), the medium probe (342) and the long probe (343) respectively. The integrated wiring is electrically connected to the central control system (31).

4. The facility farmland salt leaching system based on a rapid soil profile confluence layer according to claim 3, characterized in that: The small water pump (35) is connected to the drain outlet (33) through the drain pipe (351), and the drain outlet (33) is provided with a rubber plug; the power supply line (352) of the small water pump (35) forms a signal transmission circuit with the short probe (341), the medium probe (342) and the long probe (343).

5. A method for constructing a facility farmland salt leaching system based on a rapid soil profile confluence layer as described in claim 4, characterized in that, Includes the following steps: S1. Design of an arc-shaped concave surface with brachistochrone characteristics, including the establishment of a spatial coordinate system and the generation of parametric equations for the brachistochrone; S2, Arc-shaped concave excavation and soil isolation layer construction; S3. Layout and control of the drainage system.

6. The construction method according to claim 5, characterized in that, The specific process of step S1 is as follows: S1-1. Establishment of Spatial Coordinate System The length of the rectangular farmland is set to l Width is w ; Taking the upper left endpoint A of the cross-section at the beginning of the field along the width direction as the origin (0, 0), establish the x-axis from left to right along the width direction and the z-axis from top to bottom along the vertical direction to construct a two-dimensional xz coordinate system; Based on the root system depth h of the crops planted in the facility farmland, the maximum excavation depth corresponding to the midpoint of the surface layer of the cross-section at the beginning of the field is defined as h, and this excavation depth point is denoted as B ( w / 2, h ); S1-2, Generation of the parametric equations for the brachistochrone curve Construct the brachistochrone line from top to bottom using the line connecting points A and B. Generate the parametric equation of the brachistochrone line along the cross-section of the field width. The expression in the above xz coordinate system is: ， Where, x 横 z 横 The coordinates of the point in the xz coordinate system r 横 Let be the radius of the circle that generates the cycloid in the xz coordinate system; θ 横 The roll angle is the angle a circle rotates as it rolls along a straight line, expressed in radians. θ B The angle that the circle corresponding to the cycloid moves to point B can be obtained by the following calculation process: or ; ;because It is monotonically increasing in the interval (0, 2π), and All are greater than 0, therefore θ B There exists a unique solution in the interval (0, 2π), corresponding to r. 横 Its value is also unique; Using the vertical centerline of the Tianshou section passing through point B as the axis of symmetry, the brachistochrone line from point A to point B is mirrored to form the brachistochrone line from point B to the upper right end point C (w, 0) of the Tianshou section. Similarly, for the longitudinal section along the length of the field, with the upper endpoint A at the beginning of the field as the origin (0, 0), a y-axis is established along the horizontal line of the ground surface from the beginning to the end of the field along the length of the field, and a z-axis is established vertically from top to bottom along the left endpoint, constructing a two-dimensional yz coordinate system; based on the depth h of the main root layer of the crop, the excavation depth corresponding to the midpoint of the surface layer of the longitudinal section is set as h, and this excavation depth point is denoted as D(l / 2, h); the steepest descent line from point A to point D is constructed, generating the parametric equation of the steepest descent line in the yz coordinate system of the longitudinal section along the length of the field, the expression of which is: ， Among them, y 纵 z 纵 The coordinates of the point in the yz coordinate system r 纵 Let be the radius of the circle that generates the cycloid in the yz coordinate system; θ 纵 The roll angle is the angle a circle rotates as it rolls along a straight line, expressed in radians. θ D The angle that the circle corresponding to the cycloid moves to point D can be obtained by the following calculation process: or ; ; Similarly, r 纵 There exists a unique solution. θ D There exists a unique solution; taking the vertical centerline of the side longitudinal section passing through point D as the axis of symmetry, the brachistochrone line from point A to point D is mirrored to form the brachistochrone line from point D to the upper left end point E(l, 0) of the Tianwei section. Based on the ABC arc of the cross section at the beginning of the field, the ADE arc of the longitudinal section on the side is moved from the beginning of the field to the end of the field, and finally an arc-shaped concave surface with the characteristics of the steepest descent line is constructed in the soil layer. The four vertices of the arc-shaped concave surface coincide with the four endpoints of the rectangular field surface, and the center point is the deepest point of excavation, with a depth of 2h.

7. The construction method according to claim 5, characterized in that, The specific process of step S2 is as follows: S2-1, Arc-shaped concave excavation Before excavation, a spiral drill bit is used to advance along the length of the field and loosen the soil through rotary tillage. Every 10-50 cm of advance, the depth of rotation is adjusted according to the horizontal position of the drill bit to ensure that the soil profile after rotary tillage conforms to the brachistochrone structural characteristics. After the entire farmland is rotary tilled, the loosened soil is removed to expose the arc-shaped concave surface that meets the design requirements. S2-2, Construct a compacted interlayer with a higher density at the top and a lower density at the bottom. The concave surface was further loosened by rotary tillage using an auger bit, maintaining the concave shape. The tillage depth was no less than 20.0 cm, and the soil bulk density in the tilled area did not exceed 1.25 g / cm³. 3 Subsequently, a roller is used to roll back and forth along the length of the field to compact and smooth the concave surface. Taking advantage of the characteristic that the compaction effect decreases with depth, the compacted layers are designed with a "dense on top, loose on the bottom" density distribution: the upper dense layer is 5.0–10.0 cm thick with a density not less than 1.50 g / cm³; the lower loose layer is 5.0–10.0 cm thick with a density not exceeding 1.35 g / cm³. 3 .

8. The construction method according to claim 5, characterized in that, The specific process of step S3 is as follows: S3-1. Layout of the pumping well casing and permeable sand column A cylindrical permeable sand column (2) is piled at the bottom center of the compacted arc-shaped concave surface (1), and a PVC hollow pipe (32) is vertically inserted into the center of the permeable sand column (2); the top of the PVC hollow pipe (32) is 40-60 cm above the farmland surface; then, the arc-shaped concave surface (1) is backfilled to ensure that the average bulk density of the backfill soil is close to 1.30 g / cm³. S3-2, Water Level Monitoring and Pumping Control The control logic is as follows: when the water level in the PVC hollow pipe (32) rises to submerge the long probe (343) but does not contact the middle probe (342), the small water pump (35) does not start; when the water level rises to contact the top of the middle probe (342), the small water pump (35) starts in low power operation mode until the water level drops below the top of the long probe (343) and then stops; if the water level continues to rise and contacts the top of the short probe (341), the small water pump (35) switches to high power operation mode until the water level drops below the top of the middle probe (342), then switches back to low power operation mode to continue pumping water until the water level drops below the top of the long probe (343) and then stops.

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