A method for leaching and removing salt by using compacted plow bottom layer to realize soil matching hidden pipe for tillage layer

Abstract

A method for leaching and salt removal by using a compacted plough bottom layer to realize farmland layer soil and hidden pipe, comprising ploughing, removing impurities and ploughing and drying the target field; excavating a soil profile with a designed inclination; constructing a plough bottom layer and compacting the soil profile; excavating and constructing a compacted rectangular soil pit; burying a hidden pipe; laying a gravel layer and a coarse sand layer; constructing a clay soil water retaining surface at the tail end of the field; and backfilling the farmland layer soil. The method constructs a concave compacted plough bottom layer below the near-surface farmland layer, and buries a water-permeable hidden pipe at the bottom of the concave surface. During rainfall or irrigation, the salt-containing leaching water that infiltrates through the farmland layer collects at the concave surface to form a saturated water zone. With the increase of water accumulation, the pressure head at the saturated zone increases, and the water is discharged from the soil through the water-permeable hidden pipe, thereby realizing targeted leaching of the farmland layer and achieving water-saving leaching. In addition, the method realizes directional collection of leaching water by using the hidden pipe to shunt, thereby avoiding secondary pollution caused by leaching water.

Description

Technical Field

[0001] This invention relates to the field of farmland drainage and soil leaching technology, specifically to a method for leaching and desalinizing topsoil using a compacted plow pan and underground pipes. Background Technology

[0002] Dryland farming experiences high evaporation rates, and frequent irrigation with substandard water (such as brackish water and urban sewage) along with the application of pesticides and fertilizers leads to the accumulation of large amounts of soluble salts in the soil, causing crops to suffer from salt stress. Therefore, without affecting the current water and fertilizer management practices, adopting appropriate field engineering methods to regulate soil salinity is the only way to improve the sustainability of dryland farming productivity.

[0003] Irrigation leaching is a common desalination method used in saline-alkali farmland. It involves injecting large amounts of low-salt water into the target field, causing salts accumulated in the shallow soil to infiltrate into deeper soil layers, thus desalinizing the near-surface topsoil. However, soil moisture content is generally low in dryland farmland, and soil leaching consumes excessive irrigation water, resulting in low water resource utilization efficiency. Furthermore, the high-salt leachate may induce secondary groundwater pollution. Therefore, it is necessary to simultaneously consider water conservation during leaching and the harmless treatment of high-salt leachate.

[0004] Subsurface drainage is a common field engineering project for the targeted regulation of soil moisture in farmland. It involves horizontally burying perforated water-permeable pipes in the soil. When the groundwater level rises to the depth of the buried pipe, the soil around the pipe is saturated. The water in the soil enters the pipe through the pipe wall and is discharged horizontally along the pipe, thereby regulating the groundwater level.

[0005] Chinese patent application CN 1765169A discloses a system engineering technology for improving saline-alkali land using underground pipe drainage. This technology primarily involves laying underground pipes to drain leachate from the soil, avoiding secondary pollution caused by high-salt leaching. However, this method requires significant irrigation water during salt leaching, resulting in low leaching efficiency. Furthermore, in areas with shallow groundwater levels, underground pipe technology can easily lead to the infiltration of saline leaching water, damaging groundwater quality, and is also unfavorable for the centralized treatment of wastewater from farmland.

[0006] Based on this, the present invention reduces the burial depth of the underground pipes through scientific methods and constructs a low-permeability soil layer (such as the plow pan) below them, thereby artificially creating the supersaturated conditions required for underground pipe drainage during the farmland leaching process, achieving targeted leaching of soil salts in the topsoil and the subsequent leaching of water. Summary of the Invention

[0007] Technical Problem Solved: Addressing the issues of high water consumption and difficulty in wastewater recovery in existing leaching techniques, this invention proposes a method for desalination of the topsoil using a compacted plow pan and underground pipes. This involves constructing a concave, compacted plow pan below the near-surface topsoil, and burying perforated, permeable underground pipes at the bottom of this concave surface. During rainfall or irrigation, saline leached water infiltrating the topsoil collects at the concave surface, forming a saturated zone. As water accumulation increases, the pressure head within the saturated zone rises, and the saline leached water is discharged through the permeable underground pipes, achieving targeted leaching of the topsoil. Compared to traditional leaching of the entire soil profile, this method is water-saving. Furthermore, the high-compact plow pan combined with shallowly buried underground pipes reduces the infiltration of high-salt leached water, preventing groundwater pollution. Additionally, the underground pipe system diverts the leached water for directional collection, preventing secondary pollution.

[0008] Technical solution: A method for desalination of topsoil using a compacted plow pan and underground pipes, wherein the desalination method is based on dryland farmland, with the field head adjacent to irrigation canals and the field tail adjacent to drainage ditches. The specific method is as follows:

[0009] Step 1: Till, remove weeds, and dry the target field;

[0010] Step 2: Excavate a soil profile with the designed inclination angle: The vertical direction between the field head adjacent to the irrigation canal and the field tail adjacent to the drainage ditch is regarded as the longitudinal direction of the target field, and the horizontal direction between the two field ridges is regarded as the transverse direction of the target field. First, longitudinal excavation is carried out from the field head to the field tail. The transverse profile of the excavation is a V-shaped concave surface with left and right symmetry. The slopes on both sides correspond to the same slope angle, with the angle range being 5° to 10°, to obtain the outline of the plow bottom slope surface with the designed inclination angle.

[0011] Step 3: Constructing the plow pan and compacting the soil profile: After the plow pan slope with the designed inclination angle has been excavated, the soil is compacted using compaction equipment.

[0012] Step 4: Excavate and construct a compacted rectangular pit: Excavate a through rectangular pit longitudinally at the bottom of the concave surface of the plow bottom, and lay a layer of cohesive soil on the bottom surface of the rectangular pit and compact the cohesive soil layer. Then, construct a slope with an angle of 45° to 60° on the inner side of the rectangular pit and at the junction of the plow bottom and the rectangular pit, so that the transverse cross section of the rectangular pit is inverted trapezoidal to prevent leaching water from seeping at the junction.

[0013] Step 5: Install underground drainage pipes: Place perforated drainage pipes on the upper surface of the rectangular pit, and the underground pipes at the beginning of the field should be installed at a higher height than those at the end of the field.

[0014] Step 6: Laying gravel and coarse sand layers: To prevent fine particles from the upper soil layer from moving down and clogging the permeable pipe, a gravel layer is laid on the pipe, and a coarse sand layer is laid on top of the gravel layer until the rectangular pit is filled. The thickness of the gravel layer and the coarse sand layer is set in a ratio of 3:7.

[0015] Step 7: Construct a clay water barrier at the end of the field: After the pit is filled, construct a clay water barrier at the end of the field to prevent water from seeping out from the soil on the end side of the field.

[0016] Step 8: Backfilling the topsoil: After the cohesive soil retaining surface is constructed, evenly backfill and level the topsoil layer. The bulk density of the backfill soil should be 1.2–1.3 g / cm³. 3 ;

[0017] Step 9: During rainfall or irrigation, the salt-containing leached water that infiltrates from the topsoil layer collects at the concave surface of the plow layer, forming a saturated water zone. As the water accumulation increases, the pressure head at the saturated zone increases, and the salt-containing leached water is discharged from the soil through permeable pipes to achieve targeted leaching of the topsoil layer.

[0018] Furthermore, the specific steps of tilling, removing debris, and drying the target field in step one are as follows: level the land of the target field and remove debris; push up the topsoil cultivation layer within 30cm of the target field surface and place it in a temporary mound area near the target field; then till, break up, level, and remove debris from the soil within 60cm of the surface surface to prepare for the construction of the plow pan.

[0019] Furthermore, in step two, the maximum excavation depth at the midpoint of the field's transverse profile during the V-shaped cross-section excavation is calculated using the following formula (I):

[0020] h=tanβ×l(I)

[0021] In the formula, h is the maximum excavation depth at the midpoint of the transverse direction, in cm; β is the slope angle, in °, ranging from 5° to 10°; and l is half the width of the field, in cm.

[0022] Furthermore, in step three, soil compaction is carried out using compaction equipment, specifically as follows: One round of compaction from the beginning to the end of the field constitutes one cycle. After each cycle, the bulk density of the soil 20cm below the compacted surface is measured to confirm that the compacted bulk density of the constructed slope reaches the expected target, i.e., the bulk density of the compacted plowshare soil is >1.5g / cm³. 3 After the soil compaction density meets the standard, undisturbed soil samples are collected from the column at random locations to measure the infiltration rate of water. The infiltration rate of water in the constructed plow layer is required to be <15cm / d. If the soil water infiltration rate does not meet the standard, compaction is carried out again, and the compaction density is slightly increased until the soil water infiltration rate meets the standard.

[0023] Furthermore, before compacting the soil, the moisture content of the soil to be compacted is adjusted to 60-80%.

[0024] Furthermore, in step five, before placing the hidden pipe, a film is first used to cover the plow bottom and the surface of the rectangular pit, and the two ends of the film are embedded inside the plow bottom. Then, the hidden pipe is placed on the film.

[0025] Furthermore, the underground pipe is wrapped with a layer of permeable geotextile. The inner diameter of the underground pipe is 8-11cm. The upper half of the underground pipe has uniformly opened holes with a hole diameter range of 1-5mm and an opening density of 3-10% of the pipe body area. The lower half of the underground pipe has no holes to facilitate the flow of water along the bottom of the pipe.

[0026] Furthermore, in step seven, the cohesive soil water-retaining surface is constructed based on the plow layer and is in the shape of a vertical inverted triangle. The two sides of the cohesive soil water-retaining surface coincide with the inclined side of the plow layer in the field tail profile, and its height is consistent with the elevation difference of the inclined side of the transverse V-shaped concave surface of the plow layer on the field tail side.

[0027] Furthermore, after the cohesive soil water-retaining surface is constructed, a round of water is injected above the plow layer to verify whether the drainage effect of the underground pipe meets the standard. The standard condition is that the drainage volume of the underground pipe is not less than 70% of the injection volume. If it does not meet the standard, the burial angle of the underground pipe and whether there is blockage inside it are inspected, or the bottom of the rectangular pit and the cohesive soil water-retaining surface are checked for leakage.

[0028] Furthermore, in step five, after placing the underground pipe on the upper surface of the rectangular pit, the pipe opening on the side near the irrigation channel is sealed, and the underground pipe on the side near the drainage ditch extends 20-30cm out of the field ridge. A Y-type tee is connected to the outside of the pipe outlet. The Y-type tee is placed horizontally above the drainage ditch, with one side connected to a branch pipe for discharging and collecting leachate. The leachate branch pipe is connected to the collection tank through a rinsing ball valve. The other side of the Y-type tee is connected to a drainage ball valve located above the drainage ditch for ordinary drainage.

[0029] Beneficial effects:

[0030] (1) This invention reduces the water consumption for soil salt leaching by combining compacted plow pan with underground drainage pipes, while improving salt leaching efficiency, thus achieving the effect of water conservation and salt control.

[0031] (2) The present invention can realize the collection of leachate, avoiding secondary pollution caused by leachate with high solute content.

[0032] (3) The method provided by the present invention is applicable to dryland crops with shallow root systems such as wheat and soybeans, and can provide guidance for soil salinity adjustment of dryland crops.

[0033] (4) The drainage pipes buried in this invention have an angle between them and the horizontal plane of the field, which enables the water in the pipes to flow by gravity, which helps the drainage to move in a directional manner. Attached Figure Description

[0034] Figure 1 A 3D diagram illustrating the construction of the plowshare's subsurface;

[0035] Figure 2 A schematic diagram of the cross section for constructing the plowshare's subsoil;

[0036] Figure 3 This is an enlarged view of the rectangular pit;

[0037] Figure 4 A schematic diagram of the longitudinal section for constructing the plowshare's subsurface;

[0038] Figure 5 Layout diagram of underground pipe leaching and salt removal facilities in farmland;

[0039] Figure 6 This is a flowchart of the method of the present invention.

[0040] In the diagram: 1: Cohesive soil layer; 2: Slope; 3: Membrane; 4: Underground pipe; 5: Permeable geotextile; 6: Gravel layer; 7: Coarse sand layer; 8: Plow bottom layer; 9: Y-type tee joint; 10: Shower ball valve; 11: Drainage ball valve; 12: Cohesive soil water-retaining surface; 13: Collection pool. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Specific implementation methods of the embodiments of the present invention are described below.

[0042] This invention provides a method for desalination of topsoil using a compacted plow pan combined with underground pipe leaching. This desalination method is based on dryland farmland where the field head is adjacent to irrigation canals and the field tail is adjacent to drainage ditches. (See also...) Figure 6 The specific method is as follows:

[0043] Step 1: Till, remove weeds, and dry the target field;

[0044] Step 2: Excavate a soil profile with the designed inclination angle: The vertical direction between the field head adjacent to the irrigation canal and the field tail adjacent to the drainage ditch is regarded as the longitudinal direction of the target field, and the horizontal direction between the two field ridges is regarded as the transverse direction of the target field. First, longitudinal excavation is carried out from the field head to the field tail. The transverse profile of the excavation is a V-shaped concave surface with left and right symmetry. The slopes on both sides correspond to the same slope angle, and the angle range can be 5° to 10°, so as to obtain the outline of the plow bottom slope with the designed inclination angle.

[0045] Step 3: Constructing the plow pan and compacting the soil profile: After the plow pan slope outline with the designed inclination angle is excavated, the soil is compacted using compaction equipment to obtain the plow pan 8. See the 3D diagram of the plow pan construction for reference. Figure 1 See the schematic diagram of the cross-section of the plowshare sublayer. Figure 2 ;

[0046] Step 4: Excavate and construct a compacted rectangular pit. See the enlarged view of the rectangular pit. Figure 3 A rectangular pit is excavated longitudinally at the bottom of the concave surface of the plow layer, and a layer of cohesive soil 1 is laid on the bottom surface of the rectangular pit and compacted. Then, a slope 2 with a slope angle of 45° to 60° is constructed on the inner side of the rectangular pit and at the junction of the plow layer 8 and the rectangular pit, so that the transverse cross section of the rectangular pit is inverted trapezoidal to prevent leaching water from seeping at the junction.

[0047] Step 5: Install underground pipes: Place perforated drainage pipes 4 on the upper surface of the rectangular pit, and the underground pipes 4 at the beginning of the field are buried at a higher height than those at the end of the field.

[0048] Step 6: Laying gravel and coarse sand layers: To prevent fine particles from the upper soil layer from moving down and clogging the permeable underground pipe, a gravel layer 6 is laid on the underground pipe 4, and a coarse sand layer 7 is laid on top of the gravel layer 6 until the rectangular pit is filled. The thickness of the gravel layer 6 and the coarse sand layer 7 is set in a ratio of 3:7.

[0049] Step 7: Construct a clay water barrier at the end of the field: After the pit is filled, construct a clay water barrier 12 at the end of the field to prevent water from seeping out from the soil on the end side of the field.

[0050] Step 8: Backfilling the topsoil: After the cohesive soil retaining surface 12 is constructed, evenly backfill and level the topsoil layer. The bulk density of the backfill soil should be 1.2–1.3 g / cm³. 3 ;

[0051] Step 9: During rainfall or irrigation, the salt-containing leached water that infiltrates from the topsoil layer gathers at the concave surface of the plow layer 8, thus forming a saturated water zone. As the water accumulation increases, the pressure head in the saturated zone increases, and the salt-containing leached water will be discharged into the soil through permeable pipes to achieve targeted leaching of the topsoil.

[0052] Furthermore, as a preferred embodiment of the present invention, the specific steps of tilling, removing debris, and drying the target field in step one are as follows: leveling the land of the target field and removing debris, pushing up the topsoil cultivation layer within 30cm of the target field surface and placing it in a temporary mound area near the target field, and then tilling, breaking up, leveling, and cleaning the soil within 60cm of the surface surface to prepare for the construction of the plow pan.

[0053] Furthermore, as a preferred embodiment of the present invention, the maximum excavation depth at the midpoint of the field's transverse profile during V-shaped excavation is calculated using the following formula (I):

[0054] h=tanβ×l(I)

[0055] In the formula, h is the maximum excavation depth at the midpoint of the transverse direction, in cm; β is the slope angle, in °, ranging from 5° to 10°; and l is half the width of the field, in cm.

[0056] Furthermore, as a preferred embodiment of the present invention, in step three, soil compaction is performed using a compaction device, specifically as follows: one round of compaction from the beginning to the end of the field constitutes one cycle. After each cycle, the bulk density of the soil 20cm below the compacted surface is measured to confirm that the compacted bulk density of the constructed slope reaches the expected target, i.e., the bulk density of the compacted plowshare soil is >1.5g / cm³. 3 After the soil compaction density meets the standard, undisturbed soil samples are collected from the column at random locations to measure the infiltration rate of water. The infiltration rate of water in the constructed plow layer is required to be <15cm / d. If the soil water infiltration rate does not meet the standard, compaction is carried out again, and the compaction density is slightly increased until the soil water infiltration rate meets the standard.

[0057] Furthermore, as a preferred embodiment of the present invention, the moisture content of the soil to be compacted is adjusted to 60-80% before compaction.

[0058] Furthermore, as a preferred embodiment of the present invention, in step five, before placing the hidden pipe 4, a film 3 is first used to cover the plow bottom layer 8 and the surface of the rectangular pit, and the two ends of the film 3 are embedded inside the plow bottom layer 8, and then the hidden pipe 4 is placed on the film 3.

[0059] Furthermore, as a preferred embodiment of the present invention, the underground pipe 4 is wrapped with a layer of permeable geotextile 5. The inner diameter of the underground pipe 4 is 8-11cm. The upper half of the underground pipe has uniformly opened holes with a hole diameter range of 1-5mm and an opening density of 3-10% of the pipe body area. The lower half of the underground pipe has no holes to facilitate the flow of water along the bottom of the pipe.

[0060] Furthermore, as a preferred embodiment of the present invention, in step seven, the cohesive soil water-retaining surface 12 is constructed based on the plow layer 8 and is in the shape of a vertical inverted triangle. The two sides of the cohesive soil water-retaining surface 12 coincide with the inclined side of the plow layer 8 in the field tail section, and its height is consistent with the elevation difference of the inclined side of the transverse V-shaped concave surface of the plow layer 8 in the field tail side.

[0061] Furthermore, as a preferred embodiment of the present invention, after the cohesive soil water-retaining surface 12 is constructed, a round of water is injected above the plow bottom layer 8 to verify whether the drainage effect of the underground pipe 4 meets the standard. The standard condition is that the drainage volume of the underground pipe is not less than 70% of the water injection volume. If it does not meet the standard, the burial angle of the underground pipe 4 and whether there is blockage inside it are inspected, or the bottom of the rectangular pit and the cohesive soil water-retaining surface 12 are checked for leakage.

[0062] Furthermore, as a preferred embodiment of the present invention, in step five, see... Figure 4 and Figure 5 After placing the underground pipe 4 on the upper surface of the rectangular pit, the pipe opening on the side near the irrigation channel is sealed, and the underground pipe on the side near the drainage ditch extends 20-30cm out of the field ridge. A Y-type tee connector 9 is connected to the outside of the pipe outlet. The Y-type tee connector 9 is placed horizontally above the drainage ditch. One side is connected to a branch pipe for discharging and collecting leachate, and the leachate branch pipe is connected to the collection tank 13 through a rinsing ball valve 10. The other side of the Y-type tee connector 9 is connected to a drainage ball valve 11 above the drainage ditch for ordinary drainage.

[0063] The specific implementation method is as follows:

[0064] Example 1

[0065] This embodiment provides a method for desalination of topsoil using a compacted plow pan and underground pipes. This desalination method is based on dryland farmland where the field head is adjacent to an irrigation canal and the field tail is adjacent to a drainage ditch. (See [link]). Figure 6 The specific method is as follows:

[0066] (1) Step 1: Tilling, removing weeds and drying the target field: First, use a rotary tiller to treat the soil in the target field, and then remove the crop and animal residues contained in the soil. Next, level the land, push up the soil 30cm below the surface and transport it to the temporary soil pile area near the field.

[0067] After the 30cm thick layer of soil below the surface of the target field is removed, the 60cm thick layer of soil below the surface of the target field is tilled, broken up, debris is removed and the soil is leveled to prepare for the construction of the plow pan 8.

[0068] (2) Step 2: Excavate a soil profile with the designed inclination angle: The vertical direction between the field head adjacent to the irrigation channel and the field tail adjacent to the drainage ditch is regarded as the longitudinal direction of the target field, and the horizontal direction between the two field ridges (not the field head and field tail ridge) is regarded as the transverse direction of the target field.

[0069] To facilitate water collection, longitudinal excavation is first carried out from the beginning to the end of the field. The transverse profile of the excavation is a symmetrical V-shaped concave surface, with both sides of the slope corresponding to the same slope angle, which can be taken in the range of 5° to 10°. This results in the outline of the plow pan slope with the designed inclination angle. The maximum excavation depth at the transverse midpoint of the field is calculated using the following formula:

[0070] h=tanβ×l

[0071] In the formula, h is the maximum excavation depth at the midpoint of the transverse direction, in cm; β is the slope angle, in °, ranging from 5° to 10°; and l is half the width of the field, in cm.

[0072] (3) Step 3: Constructing the plowshare and compacting the soil profile: After the soil outline for the plowshare 8 to be constructed is excavated, the soil is compacted using compaction equipment to obtain the plowshare 8. See the 3D schematic diagram of constructing the plowshare. Figure 1 See the schematic diagram of the cross-section of the plowshare sublayer. Figure 2 .

[0073] After the soil treatment of the plow pan 8 is completed, the soil moisture content needs to be measured. Soil samples are collected in the field using a five-point sampling method, and the mass moisture content of the soil samples is determined by the drying method.

[0074] Field experience data shows that the suitable soil moisture content for constructing the plow pan 8 is 60% to 80% of the field water holding capacity of the target field. Therefore, the soil moisture content to be compacted needs to be adjusted to this range before compaction.

[0075] Soil bulk density is an important parameter affecting the infiltration characteristics of the constructed plow pan. The degree of influence of soil bulk density variation on water infiltration varies in different soil types. The following table shows soil types with different proportions of sand (particle size > 0.02 mm), silt (particle size 0.002-0.02 mm), and clay (particle size < 0.002 mm) as references.

[0076] Table 1 Bulk density and water infiltration rate of different soil types

[0077]

[0078]

[0079] The specific compaction method is as follows: One round of compaction from the beginning to the end of the field constitutes one cycle. After each cycle, the bulk density of the soil at a depth of 20cm below the compacted surface is measured. Confirm that the compacted bulk density of the constructed slope meets the expected target (bulk density of the compacted plow pan soil > 1.5g / cm³). 3After the soil compaction density meets the standard, undisturbed soil samples are collected from random points above the compacted surface to measure the infiltration rate of water. The infiltration rate of water in the constructed plow layer 8 is required to be <15cm / d. If the soil water infiltration rate does not meet the standard, the entire compacted surface is compacted again in multiple rounds until the soil water infiltration rate meets the standard.

[0080] (4) Step 4: Excavate and construct a compacted rectangular pit. See the enlarged view of the rectangular pit. Figure 3 After the soil bulk density and water infiltration rate meet the standards, dig a rectangular pit with a width of 30cm, a depth of 30cm, and a length consistent with the target field at the bottom of the concave surface of the plow layer for burying the underground pipe.

[0081] A layer of cohesive soil 1, approximately 5–10 cm thick, is laid at the bottom of the rectangular pit. This cohesive soil layer 1 is made of cohesive soil with a clay content greater than 50%. After laying the cohesive soil layer 1, it is compacted using a small tamping device, ensuring that the water infiltration rate is less than 7.0 cm / d. Subsequently, a slope 2 with an angle of 45°–60° is pressed onto the inner side of the rectangular pit, at the junction of the plow layer 8 and the rectangular pit, to prevent leakage of leachate during the leaching process at the junction.

[0082] The soil density after the slope body 2 is compacted is consistent with the compacted density of the plow layer 8.

[0083] (5) Step 5: Covering the film and burying the pipe: After the cohesive soil layer 1 and the small slope 2 inside the rectangular pit are compacted, a layer of low-strength, impermeable plastic film 3 is attached to the plow bottom layer 8 and the surface of the rectangular pit, and the two ends of the film 3 are covered with soil and compacted to embed it inside the plow bottom layer 8.

[0084] Subsequently, a rigid, perforated, permeable plastic pipe (underground pipe 4) with an inner diameter of 8–11 cm is placed horizontally above the membrane 3, and a layer of permeable geotextile 5 is wrapped around the outside of the pipe. The underground pipe 4 is buried at a higher height at the beginning of the field than at the end of the field, see [reference needed]. Figure 4 The buried pipe 4 forms a horizontal angle of 1° to 5° with the bottom surface to facilitate water collection. The inner diameter of the buried pipe 4 is 8 to 11 cm. The upper half of the pipe has uniformly distributed perforations with a diameter range of 1 to 5 mm and a perforation density of 3 to 10% of the pipe area. The lower half of the pipe has no perforations to facilitate water flow along the bottom of the pipe.

[0085] (6) Step 6: Laying gravel and coarse sand layers: Lay a gravel layer 6 with a particle size of 2-4 cm above the underground pipe 4, and lay a coarse sand layer 7 with a particle size of 0.2-0.5 cm on top of the gravel layer 6 until the rectangular pit is filled. The thickness ratio of the filled gravel layer 6 to the coarse sand layer 7 is 3:7.

[0086] (7) Step Seven: Constructing a Clay Water Retaining Surface at the End of the Field: After the pit is filled, construct a clay water retaining surface 12 at the end of the field to prevent water from seeping out from the soil on the end side. The clay water retaining surface 12 is constructed based on the plow pan and is in the shape of a vertical inverted triangle. The two sides of the clay water retaining surface 12 coincide with the inclined side of the plow pan in the end profile, and its height is consistent with the elevation difference of the inclined side of the transverse V-shaped concave surface of the plow pan on the end side. The thickness is 5-10 cm. The compaction and inspection indicators of the clay water retaining surface 12 are consistent with those of the clay layer laid in the pit.

[0087] After the cohesive soil retaining surface 12 is compacted, a round of water is injected above the compacted plow layer to verify whether the drainage of the buried pipe meets the standard (the drainage volume of the buried pipe is 70% of the injection volume). If it does not meet the standard, the burial angle of the buried pipe and whether there is blockage inside it are inspected, or the bottom of the rectangular pit and the cohesive soil retaining surface 12 are checked for leakage.

[0088] (8) Step 8: After the effectiveness of the above shallow drainage system has been tested, the topsoil layer should be backfilled evenly and leveled. The bulk density of the backfill soil should be 1.2–1.3 g / cm³. 3 .

[0089] See Figure 4 and Figure 5 During the installation of the underground drainage pipe 4, the pipe opening near the irrigation channel is sealed, and the pipe extending 20-30cm from the field ridge on the side closest to the drainage ditch is connected to a Y-type tee connector 9 at the pipe outlet. This tee connector is horizontally positioned above the drainage ditch. A branch pipe for discharging collected leachate is fixedly connected to the side of the Y-type tee connector 9, and a manually adjustable leaching ball valve 10 is installed on the branch pipe. This valve is only opened during soil salinization leaching, and the leachate is connected to the collection tank 13 via an external pipe. The other end of the Y-type tee connector 9, perpendicular to the drainage ditch, is connected to a drainage pipe with a matching drainage ball valve 11. This is used to drain excess water accumulated above the plow pan 8 when waterlogging occurs in the farmland, preventing excessive moisture in the topsoil from stressing the crops. The drainage valve 11 is closed during leaching to prevent leachate from polluting the water in the drainage ditch at the end of the field.

[0090] (9) Step 9: During rainfall or irrigation, the salt-containing leached water that seeps into the topsoil layer collects at the concave surface of the plow layer 8, thus forming a saturated water zone. As the degree of water accumulation increases, the pressure head at the saturated zone increases, and the salt-containing leached water is discharged from the soil through permeable pipes to achieve targeted leaching of the topsoil layer. Applying this method for leaching can effectively reduce the soluble salt content in the original soil layer by more than 60%.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for desalinizing topsoil using a compacted plow pan and combined with leaching through underground pipes, characterized in that, Based on dryland farmland, the head of the farmland is adjacent to the irrigation canal, and the tail of the farmland is adjacent to the drainage ditch. The specific method is as follows: Step 1: Till, remove weeds, and dry the target field; Step 2: Excavate a soil profile with the designed inclination angle: The vertical direction between the field head adjacent to the irrigation canal and the field tail adjacent to the drainage ditch is regarded as the longitudinal direction of the target field, and the horizontal direction between the two field ridges is regarded as the transverse direction of the target field. First, longitudinal excavation is carried out from the field head to the field tail. The transverse profile of the excavation is a V-shaped concave surface with left and right symmetry. The slopes on both sides correspond to the same slope angle, with the angle range being 5°~10°, to obtain the outline of the plow bottom slope surface with the designed inclination angle. Step 3: Constructing the plow bottom and compacting the soil profile: After the plow bottom slope with the designed inclination angle is excavated, the soil is compacted using compaction equipment to obtain the plow bottom (8). Step 4: Excavate and construct a compacted rectangular pit: Excavate a through rectangular pit in the longitudinal direction at the bottom of the concave surface of the plow bottom, and lay a cohesive soil layer (1) on the bottom surface of the rectangular pit and compact the cohesive soil layer (1). Then, construct a slope (2) with a slope angle of 45°~60° on both sides of the inner side of the rectangular pit and the connection between the plow bottom (8) and the rectangular pit, so that the transverse section of the rectangular pit is inverted trapezoidal to prevent leaching water from seeping at the connection. Step 5: Install underground pipes: Place perforated drainage underground pipes (4) on the upper surface of the rectangular pit, and the underground pipes (4) at the beginning of the field are buried at a higher height than those at the end of the field. Step 6: Laying gravel and coarse sand layers: To prevent fine particles from the upper soil from moving down and clogging the permeable underground pipe, a gravel layer (6) is laid on the underground pipe (4), and a coarse sand layer (7) is laid on top of the gravel layer (6) until the rectangular pit is filled. The thickness of the gravel layer (6) and the coarse sand layer (7) is set in a ratio of 3:

7. Step 7: Construct a clay water barrier at the end of the field: After the pit is filled, construct a clay water barrier (12) at the end of the field to prevent water from seeping out from the soil on the end side of the field. The clay water barrier (12) is constructed based on the plow layer (8) and is in the shape of a vertical inverted triangle. The two sides of the clay water barrier (12) coincide with the inclined side of the plow layer (8) in the end profile of the field. Its height is consistent with the elevation difference of the inclined side of the transverse V-shaped concave surface of the plow layer (8) on the end side of the field. Step 8: Backfilling the topsoil: After the cohesive soil retaining surface (12) is constructed, the topsoil layer is backfilled evenly and leveled. The bulk density of the backfill soil is 1.2~1.3 g / cm³. 3 ; Step 9: During rainfall or irrigation, the salt-containing leached water that seeps into the topsoil layer gathers at the concave surface of the plow layer (8), thus forming a saturated water zone. As the degree of water accumulation increases, the pressure head in the saturated zone increases, and the salt-containing leached water is discharged from the soil through the permeable underground pipe to achieve targeted leaching of the topsoil.

2. The method for desalination of topsoil using a compacted plow pan as described in claim 1, characterized in that, The specific steps of tilling, removing debris, and drying the target field in step one are as follows: level the land of the target field and remove debris; push up the topsoil cultivation layer within 30 cm of the target field surface and place it in a temporary mound area near the target field; then till, break up, level, and remove debris from the soil within 60 cm of the surface surface to prepare for the construction of the plow pan.

3. The method for desalination of topsoil using a compacted plow pan as described in claim 1, characterized in that, The maximum excavation depth at the midpoint of the field's transverse profile during step two is calculated using the following formula (I): （I） In the formula, h The maximum excavation depth at the midpoint of the horizontal direction is in cm; β The slope angle is °, ranging from 5° to 10°; l It is half the width of the field, in cm.

4. The method for desalination of topsoil using a compacted plow pan as described in claim 1, characterized in that, In step three, soil compaction is performed using compaction equipment, specifically as follows: One round trip from the beginning to the end of the field constitutes one cycle. After each cycle, the bulk density of the soil 20 cm below the compacted surface is measured to confirm that the compacted bulk density of the constructed slope meets the expected target, i.e., the bulk density of the compacted plowshare soil > 1.5 g / cm³. 3 After the soil compaction density meets the standard, undisturbed soil samples are collected from the column at random locations to measure the infiltration rate of water. The infiltration rate of water in the constructed plow layer is required to be <15 cm / d. If the soil water infiltration rate does not meet the standard, compaction is carried out again and the compaction density is slightly increased until the soil water infiltration rate meets the standard.

5. The method for desalination of topsoil using a compacted plow pan as described in claim 4, characterized in that, Before compacting the soil, adjust the moisture content of the soil to be compacted to 60-80%.

6. The method for desalination of topsoil using a compacted plow pan as described in claim 1, characterized in that, In step five, before placing the hidden tube (4), a film (3) is used to cover the plow bottom (8) and the surface of the rectangular pit, and the two ends of the film (3) are embedded inside the plow bottom (8), and then the hidden tube (4) is placed on the film (3).

7. The method for desalination of topsoil using a compacted plow pan as described in claim 1, characterized in that, The underground pipe (4) is wrapped with a layer of permeable geotextile (5). The inner diameter of the underground pipe (4) is 8~11cm. The upper half of the underground pipe has uniform holes with a hole diameter range of 1~5 mm and a hole density of 3~10% of the pipe area. The lower half of the underground pipe has no holes to facilitate the flow of water along the bottom of the pipe.

8. A method for desalination of topsoil using a compacted plow pan as described in claim 1, characterized in that, After the cohesive soil water-retaining surface (12) is constructed, a round of water is poured above the plow bottom layer (8) to verify whether the drainage effect of the underground pipe (4) meets the standard. The standard condition is that the drainage volume of the underground pipe is not less than 70% of the water volume. If it does not meet the standard, the burial angle of the underground pipe (4) and whether there is blockage inside it are inspected, or the bottom of the rectangular pit and the cohesive soil water-retaining surface (12) are checked for leakage.

9. A method for desalination of topsoil using a compacted plow pan as described in claim 1, characterized in that, In step five, after placing the underground pipe (4) on the upper surface of the rectangular pit, the pipe opening on the side near the irrigation channel is sealed, and the underground pipe on the side near the drainage ditch extends 20-30cm out of the field ridge. A Y-type tee connector (9) is connected to the outside of the pipe outlet. The Y-type tee connector (9) is placed horizontally above the drainage ditch. One side is connected to the branch pipe for discharging the collected leaching water. The leaching water branch pipe is connected to the collection tank (13) through the rinsing ball valve (10). The other side of the Y-type tee connector (9) is connected to the drainage ball valve (11) above the drainage ditch for ordinary drainage.

Images