Method for leaching and desalting plough layer soil by using compaction type plough pan in cooperation with concealed conduit

Abstract

The invention relates to a method for leaching and desalting plough layer soil by utilizing a compaction type plough pan in cooperation with a concealed conduit. The method comprises the following steps: ploughing, removing impurities and tedding a target field; excavating a soil profile with a designed inclination angle; constructing a plow pan, and compacting a soil profile; a compacted rectangular soil pit is excavated and constructed; buried pipes are buried; paving a gravel layer and a coarse sand layer; constructing a cohesive soil water retaining surface at the tail end of the field; and backfilling the plough layer soil. According to the method, the concave-surface compaction type plow pan is constructed below the near-surface plow layer, the perforated water-permeable concealed pipes are buried at the bottom of the concave surface, in the rainfall or irrigation process, salt-containing leaching water infiltrated through the plow layer is collected to the concave surface to form a saturated water-containing zone, the pressure water head at the saturated zone is increased along with the increase of the water accumulation degree, and the salt-containing leaching water in the water-containing zone is drained. Water is discharged out of the soil body through the water-permeable concealed pipe, targeted leaching of a plough layer is achieved, and the water-saving leaching effect is achieved; in addition, directional collection of the leaching water is realized in a concealed pipeline shunting manner, so that secondary pollution caused by the leaching water can be avoided.

Description

Technical Field

[0001] The invention relates to the technical field of farmland drainage and soil leaching, and in particular to a method for leaching and desalting a cultivated layer of soil by utilizing a compacted plow bottom layer in conjunction with a concealed pipe. Background Art

[0002] Dryland farmland has a high evaporation intensity. Frequent irrigation with inferior water (such as brackish water and urban sewage) and the application of pesticides and fertilizers cause a large amount of soluble salt to accumulate in the soil, causing crops to suffer from salt stress. Therefore, without affecting the current water and fertilizer mode, the use of appropriate field engineering to regulate soil salinity is the only way to improve the sustainability of dryland farmland production capacity.

[0003] Irrigation leaching is a common desalination method for saline farmland. It involves injecting a large amount of low-salt water into the target field, causing the salt accumulated in the shallow soil to infiltrate into the deep soil along with the water, thus achieving desalination of the soil in the near-surface cultivated layer. However, the soil moisture content in dryland farmland is generally low, and soil leaching consumes too much irrigation resources, resulting in low water resource utilization efficiency. In addition, the infiltrating high-salt leached water may induce secondary groundwater pollution. Therefore, it is necessary to simultaneously consider water conservation during leaching and the harmless treatment of high-salt leached water.

[0004] Concealed pipe drainage is a common field project for directional regulation of soil moisture in farmland. It involves burying permeable pipes with holes horizontally in the soil. When the groundwater level rises to the buried depth of the concealed pipe, the soil around the pipe is in a saturated state. The moisture in the soil enters the pipe through the pipe wall and is discharged horizontally along the pipe, thus achieving regulation of the groundwater level.

[0005] The Chinese patent application with publication number CN 1765169A discloses a system engineering technology for improving saline-alkali land by using a concealed pipe drainage method. The main purpose is to discharge the leaching solution from the soil by laying concealed pipes underground to avoid secondary pollution caused by high-salt leaching water. However, the above scheme consumes a large amount of irrigation resources during the salt leaching process, and the leaching benefits of soil salt are low. Secondly, if the concealed pipe technology is used in areas with shallow groundwater levels, it is easy to cause the salt-containing leaching water to infiltrate and destroy the groundwater quality, and it is not conducive to the centralized treatment of farmland sewage drainage.

[0006] Based on this, the present invention reduces the buried depth of the concealed pipe through a scientific method, and constructs a low permeable soil layer (such as the plow bottom layer) underneath it, so as to artificially create the supersaturated conditions required for concealed pipe drainage during the farmland leaching process, thereby achieving targeted leaching of soil salt in the cultivated layer and regularization of subsequent leaching water. Summary of the invention

[0007] Technical problems solved: In view of the technical problems existing in the prior art, such as large leaching water consumption and difficulty in recycling drainage, the present invention proposes a method for leaching and desalting the cultivated layer soil by using a compacted plow bottom layer and a concealed pipe. By constructing a concave compacted plow bottom layer below the cultivated layer near the surface, a permeable concealed pipe with holes is buried at the bottom of the concave surface. During rainfall or irrigation, the salty leached water that infiltrates through the cultivated layer is collected at the concave surface to form a saturated water-containing zone. As the degree of water accumulation increases, the pressure head in the saturated zone increases, and the salty leached water is discharged from the soil through the permeable concealed pipe, realizing targeted leaching of the cultivated layer. Compared with the traditional leaching of the entire soil profile, the method of the present invention has the effect of water-saving leaching; secondly, the high-compacted plow bottom layer and the shallow buried concealed pipe reduce the infiltration of high-salt leached water and avoid groundwater pollution. In addition, the directional collection of leached water is achieved by using the concealed pipe diversion method to avoid secondary pollution caused by leached water.

[0008] Technical solution: A method for leaching and desalting the cultivated soil layer by using a compacted plow bottom layer and a concealed pipe. The leaching and desalting method is based on dryland farmland, where the head of the farmland is adjacent to the irrigation channel and the tail of the farmland is adjacent to the drainage ditch. The specific method is as follows:

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

[0010] Step 2: excavate a soil profile with a designed inclination angle: the vertical direction from the head of the field adjacent to the irrigation channel to the end of the field adjacent to the drainage ditch is regarded as the longitudinal direction of the target field, and the horizontal direction between the ridges on both sides is regarded as the transverse direction of the target field. First, longitudinal excavation is carried out from the head of the field to the end of the field. The excavated transverse profile is a bilaterally symmetrical V-shaped concave surface. The slopes on both sides correspond to the same slope angle, and the angle range is 5° to 10°, so as to obtain the slope profile of the plow bottom layer with a designed inclination angle;

[0011] Step 3: Construct the plow bottom layer and compact the soil profile: After the plow bottom layer slope profile with the designed inclination is excavated, the soil is compacted using a compacting device;

[0012] 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 layer, lay a clay layer on the bottom of the rectangular pit, and compact the clay layer. Then, construct a slope with a slope angle of 45° to 60° on the inner side of the rectangular pit and at the junction of the plow bottom layer and the rectangular pit, so that the transverse cross-section of the rectangular pit is in the shape of an inverted trapezoid to prevent leaching water from leaking at the junction.

[0013] Step 5: Bury the underground pipe: Place the drainage underground pipe with holes and water permeability on the upper surface of the rectangular pit, and the buried height of the underground pipe at the head of the field is higher than that at the end of the field;

[0014] Step 6: Lay gravel and coarse sand layers: To prevent fine particles in the upper soil from moving downward and blocking the permeable underground pipe, lay a gravel layer on the underground pipe, and lay a coarse sand layer 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 retaining surface at the end of the field: After the soil pit is filled, construct a clay retaining surface at the end of the field to prevent water from seeping out of the soil at the end of the field;

[0016] Step 8: Backfill the cultivated soil layer: After the clay soil retaining surface is constructed, backfill the topsoil layer evenly and level it. The backfill soil bulk density is 1.2-1.3 g / cm 3 ;

[0017] Step 9. During rainfall or irrigation, the saline leached water that seeps through the surface tillage layer gathers at the concave surface of the plow bottom layer, forming a saturated water zone. As the degree of water accumulation increases, the pressure head in the saturated zone increases, and the saline leached water is discharged from the soil through permeable concealed pipes to achieve targeted leaching of the tillage layer.

[0018] Furthermore, the plowing, weeding and drying of the target field in step one are specifically as follows: the land of the target field is leveled and debris is removed, the topsoil cultivation layer within a depth of 30 cm below the surface of the target field is pushed up and placed in a temporary soil pile area near the target field, and then the soil within a depth of 60 cm below the surface is plowed, crushed, leveled and debris is cleared to prepare for the construction of the plow bottom layer.

[0019] Furthermore, when the V-shaped transverse profile is excavated in step 2, the maximum excavation depth at the transverse midpoint of the field is calculated by the following formula (I):

[0020] h=tanβ×l(I)

[0021] In the formula, h is the maximum excavation depth at the horizontal midpoint, cm; β is the slope angle, °, which is 5°~10°; l is half of the width of the field, cm.

[0022] Furthermore, in step 3, the soil is compacted by a compactor, specifically as follows: one round of rolling from the head of the field to the end of the field is considered as one round, and the bulk density of the soil 20 cm thick below the compacted surface is measured once after each round of compaction to confirm that the compacted bulk density of the constructed slope surface reaches the expected target, that is, the compacted bulk density of the plow bottom soil is greater than 1.5 g / cm 3 After the soil compaction density meets the standard, collect original soil samples of the column at random positions to measure the infiltration rate of water. The water infiltration rate of the constructed plow bottom layer is required to be less than 15cm / d. If the soil water infiltration rate does not meet the standard, re-compact it and slightly increase the compaction density until the soil water infiltration rate meets the standard.

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

[0024] Furthermore, in step five, before placing the concealed pipe, a film is first used to fit and cover the plow bottom layer and the surface of the rectangular pit, and both ends of the film are embedded in the plow bottom layer, and then the concealed pipe is placed on the film.

[0025] Furthermore, the concealed pipe is wrapped with a layer of permeable geotextile, the inner diameter of the concealed pipe is 8 to 11 cm, the upper surface of the concealed pipe is evenly opened with holes, the hole diameter range is 1 to 5 mm, the hole density is 3 to 10% of the pipe area, and no holes are opened on the lower surface of the concealed pipe to facilitate water to flow along the bottom of the pipe.

[0026] Furthermore, in step seven, the clay soil water retaining surface is constructed based on the plow bottom layer and is in a vertical inverted triangle shape. The two sides of the clay soil water retaining surface coincide with the hypotenuse of the plow bottom layer at the end of the field section, and its height is consistent with the elevation difference of the hypotenuse of the transverse V-shaped concave surface of the plow bottom layer at the end of the field.

[0027] Furthermore, after the clay soil retaining surface is constructed, a round of watering is carried out above the plow bottom layer to verify whether the drainage effect of the concealed pipe meets the standard. The standard condition is that the drainage volume of the concealed pipe is not less than 70% of the irrigation volume. If it does not meet the standard, the buried angle of the concealed pipe and whether there is blockage inside it, or check whether there is leakage at the bottom of the rectangular pit and the clay soil retaining surface.

[0028] Furthermore, in the step five, after placing the concealed pipe on the upper surface of the rectangular pit, the pipe opening close to the irrigation channel is blocked, the concealed pipe close to the drainage ditch is extended 20 to 30 cm beyond the ridge, and a Y-type three-way joint is connected to the pipe outlet, the Y-type three-way joint is placed horizontally above the drainage ditch, one side is connected to a branch pipe for discharging the collected leaching water, the leaching water branch pipe is connected to the receiving pool through a leaching ball valve, and the other side of the Y-type three-way joint is connected to a drainage ball valve through a pipe and is located above the drainage ditch for ordinary drainage.

[0029] Beneficial effects:

[0030] (1) The present invention reduces the water consumption of soil salt leaching by combining the compacted plow bottom layer with concealed pipe drainage while improving the salt leaching efficiency, thereby achieving the effect of water saving and salt control.

[0031] (2) The present invention can collect leached water and avoid secondary pollution caused by leached water with high solute content.

[0032] (3) The method provided by the present invention is suitable for 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 angle between the buried drainage pipe of the present invention and the horizontal plane of the field can realize the self-weight flow of water in the pipe, which is conducive to the directional migration of drainage. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 To construct a 3D schematic diagram of the plow bottom layer;

[0035] Figure 2 A cross-sectional schematic diagram for constructing the bottom layer of the plow;

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

[0037] Figure 4 A schematic diagram of the longitudinal section for constructing the bottom layer of the plow;

[0038] Figure 5 This is the layout diagram of the farmland underground pipe leaching and salt drainage facilities;

[0039] Figure 6 The figure is a flow chart of the method of the present invention.

[0040] In the figure: 1: clay soil layer; 2: slope; 3: film; 4: concealed pipe; 5: permeable geotextile; 6: gravel layer; 7: coarse sand layer; 8: plow bottom layer; 9: Y-type three-way joint; 10: elution ball valve; 11: drainage ball valve; 12: clay soil retaining surface; 13: collection pool. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and are not used to limit the scope of protection of the present invention. The specific implementation of the application example of the present invention is introduced below.

[0042] The embodiment of the present invention provides a method for leaching and desalting the cultivated layer soil by using a compacted plow bottom layer in conjunction with a concealed pipe. The leaching and desalting method is based on dryland farmland, where the head of the farmland is adjacent to an irrigation channel, and the tail of the farmland is adjacent to a drainage ditch. Figure 6 , the specific method is as follows:

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

[0044] Step 2: excavate a soil profile with a designed inclination angle: the vertical direction from the head of the field adjacent to the irrigation channel to the end of the field adjacent to the drainage ditch is regarded as the longitudinal direction of the target field, and the horizontal direction between the ridges on both sides is regarded as the transverse direction of the target field. First, longitudinal excavation is carried out from the head of the field to the end of the field. The excavated transverse profile is a bilaterally symmetrical V-shaped concave surface. 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 slope profile of the plow bottom layer with a designed inclination angle;

[0045] Step 3: Constructing the plow bottom layer and compacting the soil profile: After the plow bottom layer slope profile with the designed inclination is excavated, the soil is compacted using a compaction device to obtain the plow bottom layer 8. The 3D schematic diagram of constructing the plow bottom layer is shown in FIG. Figure 1 , see the cross-sectional diagram of the construction of the plow bottom layer Figure 2 ;

[0046] Step 4: Dig and construct a compacted rectangular pit. For an enlarged view of the rectangular pit, see Figure 3 : A rectangular pit is excavated in the longitudinal direction at the bottom of the concave surface of the plow bottom layer, and a clay layer 1 is laid on the bottom of the rectangular pit, and the clay layer 1 is compacted. Subsequently, a slope 2 with a slope angle of 45° to 60° is constructed at the inner side of the rectangular pit and at the junction of the plow bottom layer 8 and the rectangular pit, so that the transverse cross-section of the rectangular pit is in the shape of an inverted trapezoid to prevent leaching water from leaking at the junction;

[0047] Step 5: Bury the concealed pipe: Place a permeable drainage concealed pipe 4 on the upper surface of the rectangular pit, and the buried height of the concealed pipe 4 at the head of the field is higher than that at the end of the field;

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

[0049] Step 7: Constructing a clay retaining surface at the end of the field: After the soil pit is filled, construct a clay retaining surface 12 at the end of the field to prevent water from seeping out of the soil at the end of the field;

[0050] Step 8: Backfill the cultivated soil layer: After the clay soil retaining surface 12 is constructed, the topsoil layer is evenly backfilled and leveled. The backfill soil bulk density is 1.2-1.3 g / cm 3 ;

[0051] Step 9. During rainfall or irrigation, the saline leached water that seeps through the surface tillage layer gathers at the concave surface of the plow bottom layer 8, and then forms a saturated water zone here. As the degree of water accumulation increases, the pressure head in the saturated zone increases, and the saline leached water will be discharged from the soil through permeable concealed pipes to achieve targeted leaching of the tillage layer soil.

[0052] Furthermore, as one of the preferred embodiments of the present invention, the plowing, weeding and drying of the target field in step one are specifically as follows: the land of the target field is leveled and debris is removed, the topsoil cultivation layer within 30 cm below the surface of the target field is pushed up and placed in a temporary soil pile area near the target field, and then the soil within 60 cm below the surface is plowed, crushed, leveled and debris is cleared to prepare for the construction of the plow bottom layer.

[0053] Further, as one of the preferred embodiments of the present invention, when excavating a V-shaped transverse profile, the maximum excavation depth at the transverse midpoint of the field is calculated by the following formula (I):

[0054] h=tanβ×l(I)

[0055] In the formula, h is the maximum excavation depth at the horizontal midpoint, cm; β is the slope angle, °, which is 5°~10°; l is half of the width of the field, cm.

[0056] Further, as one of the preferred embodiments of the present invention, in step 3, the soil is compacted by a compacting device, specifically as follows: one round of rolling from the head of the field to the end of the field is considered as one round, and the bulk density of the soil 20 cm thick below the compacted surface is measured once for each round of compaction to confirm that the compacted bulk density of the constructed slope surface reaches the expected target, that is, the compacted bulk density of the plow bottom soil is greater than 1.5 g / cm 3 After the soil compaction density meets the standard, collect original soil samples of the column at random positions to measure the infiltration rate of water. The water infiltration rate of the constructed plow bottom layer is required to be less than 15cm / d. If the soil water infiltration rate does not meet the standard, re-compact it and slightly increase the compaction density until the soil water infiltration rate meets the standard.

[0057] Furthermore, as one of the preferred embodiments of the present invention, before compacting the soil, the water content of the soil to be compacted is adjusted to 60-80%.

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

[0059] Furthermore, as one of the preferred embodiments of the present invention, the concealed pipe 4 is wrapped with a layer of permeable geotextile 5, the inner diameter of the concealed pipe 4 is 8 to 11 cm, the upper surface of the concealed pipe is evenly opened with holes, the hole diameter range is 1 to 5 mm, the opening density is 3 to 10% of the pipe area, and no holes are opened on the lower surface of the concealed pipe to facilitate water to flow along the bottom of the pipe.

[0060] Furthermore, as one of the preferred embodiments of the present invention, the clay water retaining surface 12 in the step seven is constructed based on the plow bottom layer 8 and is in a vertical inverted triangle shape. The two sides of the clay water retaining surface 12 coincide with the hypotenuse of the plow bottom layer 8 at the end of the field, and its height is consistent with the elevation difference of the hypotenuse of the transverse V-shaped concave surface of the plow bottom layer 8 at the end of the field.

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

[0062] Further, as one of the preferred embodiments of the present invention, in step 5, see Figure 4 and Figure 5 After placing the concealed pipe 4 on the upper surface of the rectangular pit, the pipe opening close to the irrigation channel is blocked, and the concealed pipe close to the drainage ditch extends 20 to 30 cm from the ridge, and a Y-type three-way joint 9 is connected to the pipe outlet. The Y-type three-way joint 9 is placed horizontally above the drainage ditch, and one side is connected to a branch pipe for discharging the collected leaching water. The leaching water branch pipe is connected to the receiving pool 13 through a leaching ball valve 10. The other side of the Y-type three-way joint 9 is connected to a drainage ball valve 11 through a pipe and is located above the drainage ditch for ordinary drainage.

[0063] The specific embodiments are as follows:

[0064] Example 1

[0065] This embodiment provides a method for using a compacted plow bottom layer to achieve leaching and desalination of the cultivated layer soil in conjunction with a concealed pipe. The leaching and desalination method is based on dryland farmland, where the head of the farmland is adjacent to an irrigation channel and the tail of the farmland is adjacent to a drainage ditch. Figure 6 , the specific method is as follows:

[0066] (1) Step 1: Ploughing, weeding and drying the target field: First, use a rotary tiller to treat the soil in the target field, and then remove the impurities of crops and animal residues in the soil. Then, level the land, push up the soil 30 cm below the surface and transport it to a temporary soil pile area near the field.

[0067] After the soil layer with a thickness of 30 cm below the surface of the target field is transported away, the soil with a thickness of 60 cm below the surface of the target field is plowed, crushed, cleared of debris and leveled to prepare for the construction of the plow bottom layer 8.

[0068] (2) Step 2: Excavate a soil profile with a designed inclination: the vertical direction from the beginning of the field adjacent to the irrigation channel to the end of the field adjacent to the drainage ditch is regarded as the longitudinal direction of the target field, and the horizontal direction between the ridges on both sides (not the ridges at the beginning and end of the field) is regarded as the transverse direction of the target field.

[0069] In order to facilitate the collection of water, longitudinal excavation is first carried out from the head to the end of the field. The cross-sectional shape of the excavation is a bilaterally symmetrical V-shaped concave surface, and the slopes on both sides correspond to the same slope angle, which can be 5° to 10°. The slope profile of the plow bottom layer with a designed inclination angle is obtained, and the maximum excavation depth at the horizontal midpoint of the field is calculated as follows:

[0070] h=tanβ×l

[0071] In the formula, h is the maximum excavation depth at the horizontal midpoint, cm; β is the slope angle, °, which is 5°~10°; l is half of the width of the field, cm.

[0072] (3) Step 3: Constructing the plow bottom layer and compacting the soil profile: After the soil profile for the plow bottom layer 8 to be constructed is excavated, the soil is compacted using a compaction device to obtain the plow bottom layer 8. For a 3D schematic diagram of constructing the plow bottom layer, see Figure 1 , see the cross-sectional diagram of the construction of the plow bottom layer Figure 2 .

[0073] After the soil treatment of the construction plow bottom layer 8 is completed, the water content of the soil needs to be measured. Soil samples are taken using the five-point sampling method in the field, and the mass water content of the soil samples taken is measured by the drying method.

[0074] It is known from field experience that the suitable soil mass moisture content for constructing the plow bottom layer 8 is 60% to 80% of the field water holding capacity of the target field. Therefore, before compacting the soil, the soil mass moisture content to be compacted needs to be adjusted to this range.

[0075] Soil bulk density is an important influencing parameter affecting the water seepage characteristics of the constructed plow bottom layer 8. The change of soil bulk density in different soil types has different effects on water infiltration. The following 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) are used as references, as shown in Table 1.

[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 rolling from the beginning to the end of the field is considered as one round, and the bulk density of the soil 20cm below the compaction surface is measured after each round of compaction. Confirm that the compacted bulk density of the constructed slope surface reaches the expected target (the compacted bulk density of the bottom soil of the plow> 1.5g / cm 3). After the soil compaction density reaches the standard, collect the original soil sample of the column at random points above the compaction surface to measure the infiltration rate of water. The water infiltration rate of the constructed plow bottom layer 8 is required to be less than 15cm / d. If the soil water infiltration rate does not reach the standard, the entire compaction surface is compacted again for multiple rounds until the soil water infiltration rate reaches the standard.

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

[0081] A layer of clay layer 1 with a thickness of about 5 to 10 cm is laid at the bottom of the rectangular pit. The clay layer 1 is made of clay with a clay content of more than 50%. After the clay layer 1 is laid, it is compacted with a small compacting device, and its water infiltration rate is required to be less than 7.0 cm / d. Then, a slope 2 with a slope angle of 45° to 60° is pressed on the inner side of the rectangular pit and at the junction of the plow bottom layer 8 and the rectangular pit to prevent the leached water that infiltrates during the leaching process from leaking at the junction.

[0082] The soil bulk density after the slope 2 is constructed and compacted is consistent with the compacted bulk density of the constructed plow bottom layer 8.

[0083] (5) Step 5: Covering with film and burying concealed pipes: After the clay layer 1 and the small slope 2 inside the rectangular pit are compacted, a layer of low-ductility waterproof plastic film 3 is covered on 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 so that it is embedded in the plow bottom layer 8.

[0084] Then, a hard permeable plastic pipe with an inner diameter of 8 to 11 cm, i.e., a concealed pipe 4, is placed horizontally above the film 3, and a layer of permeable geotextile 5 is wrapped around the outer surface of the pipe. The buried height of the concealed pipe 4 at the head of the field is higher than that at the end of the field. Figure 4 The buried concealed pipe 4 has a horizontal angle of 1° to 5° with the bottom surface to facilitate the collection of water. The inner diameter of the concealed pipe 4 is 8 to 11 cm, and the upper surface of the concealed pipe is evenly perforated with a pore size range of 1 to 5 mm and a perforation density of 3 to 10% of the pipe area. No perforation is made on the lower surface of the concealed pipe to facilitate the flow of water 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 to 4 cm on top of the concealed pipe 4, and lay a coarse sand layer 7 with a particle size of 0.2 to 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 7, constructing a clay retaining surface at the end of the field: After the earth pit is filled, a clay retaining surface 12 is constructed at the end of the field to prevent water from seeping from the soil at the end of the field. The clay retaining surface 12 is constructed based on the plow bottom layer and is in a vertical inverted triangle shape. The two sides of the clay retaining surface 12 coincide with the hypotenuse of the plow bottom layer of the end of the field section, and its height is consistent with the elevation difference of the hypotenuse of the transverse V-shaped concave surface of the plow bottom layer at the end of the field. The thickness is 5 to 10 cm. The compaction and inspection indicators of the clay retaining surface 12 are consistent with those of the clay layer laid in the earth pit.

[0087] After the compaction of the clay soil retaining surface 12 is completed, a round of watering is carried out above the compacted plow bottom layer to verify whether the buried hidden pipe drainage meets the standard (the drainage volume of the hidden pipe is 70% of the watering volume). If it does not meet the standard, the buried angle of the hidden pipe and whether it is blocked inside are inspected, or the bottom of the rectangular pit and the clay soil retaining surface 12 are checked for leakage.

[0088] (8) Step 8: After the above shallow drainage system is tested for its effectiveness, the topsoil layer is evenly backfilled and leveled. The backfill soil has a bulk density of 1.2 to 1.3 g / cm 3 .

[0089] See also Figure 4 and Figure 5 During the burial process of the drainage concealed pipe 4, the pipe opening near one end of the irrigation channel is blocked, and the concealed pipe near the drainage ditch extends 20 to 30 cm from the ridge of the field, and a Y-type three-way joint 9 is connected to the pipe outlet, and the three-way joint is placed horizontally above the drainage ditch. Among them, the Y-type three-way joint 9 is laterally fixed to a branch pipe for discharging the collected leaching water, and a manually adjustable elution ball valve 10 is installed on the branch pipe. The valve is only opened when the soil salt is eluted, and the eluted water is connected to the storage pool 13 through an external pipe. The other end of the Y-type three-way joint 9 is perpendicular to the drainage ditch and is connected to a drainage pipe with a matching drainage ball valve 11, which is used to drain the excessive water accumulated above the constructed plow bottom layer 8 when waterlogging occurs in the farmland, so as to avoid excessive water in the arable layer from causing stress to the crops. The valve 11 of the drainage pipe is closed in the elution state to prevent the elution water from polluting the water body 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 through the surface tillage layer gathers at the concave surface of the plow bottom layer 8, thereby 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 a permeable concealed pipe to achieve targeted leaching of the tillage layer. Applying this method for leaching can effectively reduce more than 60% of the soluble salt in the original soil layer.

[0091] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned implementation modes, a person of ordinary skill in the art should understand that the technical solutions described in the aforementioned implementation modes can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the implementation modes of the present invention.

Claims

1. A method for leaching and desalting the cultivated soil layer by using a compacted plow bottom layer and a concealed pipe, characterized in that: Based on dryland farmland, the head of the farmland is adjacent to the irrigation channel, and the tail of the farmland is adjacent to the drainage ditch. The specific methods are as follows: Step 1: plough, remove weeds and dry the target field; Step 2: excavate a soil profile with a designed inclination angle: the vertical direction from the head of the field adjacent to the irrigation channel to the end of the field adjacent to the drainage ditch is regarded as the longitudinal direction of the target field, and the horizontal direction between the ridges on both sides is regarded as the transverse direction of the target field. First, longitudinal excavation is carried out from the head of the field to the end of the field. The excavated transverse profile is a bilaterally symmetrical V-shaped concave surface. The slopes on both sides correspond to the same slope angle, and the angle range is 5° to 10°, so as to obtain the slope profile of the plow bottom layer with a designed inclination angle; Step 3: Constructing the plow bottom layer and compacting the soil profile: After the plow bottom layer slope profile with the designed inclination angle is excavated, the soil is compacted using a compaction device to obtain the plow bottom layer (8); Step 4, excavating and constructing a compacted rectangular pit: excavating a through rectangular pit in the longitudinal direction at the bottom of the concave surface of the plow bottom layer, laying a clay layer (1) on the bottom surface of the rectangular pit, and compacting the clay layer (1), then constructing a slope (2) with a slope angle of 45° to 60° on both sides of the inner side of the rectangular pit and the junction of the plow bottom layer (8) and the rectangular pit, so that the transverse cross-section of the rectangular pit is in the shape of an inverted trapezoid, so as to prevent leaching water from leaking at the junction; Step 5: Bury the concealed pipe: Place a permeable drainage concealed pipe (4) on the upper surface of the rectangular earth pit, and the concealed pipe (4) at the head of the field is buried higher than that at the end of the field; Step 6: Laying gravel layer and coarse sand layer: To prevent fine particles in the upper soil layer from moving downward and blocking the permeable underground pipe, a gravel layer (6) is laid on the underground pipe (4), and a coarse sand layer (7) is laid on the gravel layer (6) until the rectangular pit is filled. The laying thickness of the gravel layer (6) and the coarse sand layer (7) is set in a ratio of 3:7; Step 7: Constructing a clay retaining surface at the end of the field: After the soil pit is filled, construct a clay retaining surface (12) at the end of the field to prevent water from seeping out of the soil at the end of the field; Step 8: Backfill the cultivated soil layer: After the clay soil retaining surface (12) is constructed, the topsoil layer is evenly backfilled and leveled. The backfill soil bulk density is 1.2-1.3 g / cm 3 ; Step 9. During rainfall or irrigation, the saline leached water that seeps through the surface tillage layer gathers at the concave surface of the plow bottom layer (8), thereby forming a saturated water zone. As the degree of water accumulation increases, the pressure head in the saturated zone increases, and the saline leached water is discharged from the soil through a permeable underground pipe to achieve targeted leaching of the tillage layer soil.

2. The method of claim 1, wherein the method utilizes a compacted plow bottom layer to achieve leaching and desalination of the cultivated layer soil in conjunction with a concealed pipe, is characterized in that: The specific steps of plowing, removing weeds 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 below the surface of the target field and place it in a temporary soil pile area near the target field, then plow, break up, level and clean the soil within 60 cm below the surface to prepare for the construction of the plow bottom layer.

3. The method of claim 1, wherein the method utilizes a compacted plow bottom layer to achieve leaching and desalination of the cultivated layer soil in conjunction with a concealed pipe, is characterized in that: When the V-shaped transverse profile is excavated in step 2, the maximum excavation depth at the transverse midpoint of the field is calculated by the following formula (I): h=tanβ×l(I) In the formula, h is the maximum excavation depth at the horizontal midpoint, cm; β is the slope angle, °, which is 5°~10°; l is half the width of the field, cm.

4. The method of claim 1, wherein the method utilizes a compacted plow bottom layer to achieve leaching and desalination of the cultivated layer soil in conjunction with a concealed pipe, is characterized in that: In step 3, the soil is compacted by a compactor, specifically as follows: one round of rolling from the head of the field to the end of the field is considered as one round, and the bulk density of the soil 20 cm below the compacted surface is measured once after each round of compaction to confirm that the compacted bulk density of the constructed slope surface reaches the expected target, that is, the compacted bulk density of the plow bottom soil is greater than 1.5 g / cm 3 After the soil compaction density meets the standard, collect original soil samples of the column at random positions to measure the infiltration rate of water. The water infiltration rate of the constructed plow bottom layer is required to be less than 15cm / d. If the soil water infiltration rate does not meet the standard, re-compact it and slightly increase the compaction density until the soil water infiltration rate meets the standard.

5. The method of using compacted plow bottom layer to achieve leaching and desalination of cultivated layer soil in combination with concealed pipes according to 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 of claim 1, wherein the method utilizes a compacted plow bottom layer to achieve leaching and desalination of the cultivated layer soil in conjunction with a concealed pipe, is characterized in that: In the step 5, before placing the concealed pipe (4), a film (3) is first used to fit and cover the plow bottom layer (8) and the surface of the rectangular pit, and the two ends of the film (3) are embedded in the plow bottom layer (8), and then the concealed pipe (4) is placed on the film (3).

7. The method of claim 1, wherein the method utilizes a compacted plow bottom layer to achieve leaching and desalination of the cultivated layer soil in conjunction with a concealed pipe, is characterized in that: The concealed pipe (4) is wrapped with a layer of permeable geotextile (5). The inner diameter of the concealed pipe (4) is 8 to 11 cm. The upper surface of the concealed pipe is evenly perforated with holes in a range of 1 to 5 mm. The perforation density is 3 to 10% of the pipe area. The lower surface of the concealed pipe is not perforated to facilitate water to flow along the bottom of the pipe.

8. The method of claim 1, wherein the method utilizes a compacted plow bottom layer to achieve leaching and desalination of the cultivated layer soil in conjunction with a concealed pipe, is characterized in that: In the step 7, the clay soil water retaining surface (12) is constructed based on the plow bottom layer (8) and is in a vertical inverted triangle shape. The two sides of the clay soil water retaining surface (12) coincide with the hypotenuse of the plow bottom layer (8) at the end of the field, and its height is consistent with the elevation difference of the hypotenuse of the transverse V-shaped concave surface of the plow bottom layer (8) at the end of the field.

9. The method of using compacted plow bottom layer to achieve leaching and desalination of cultivated layer soil in combination with concealed pipes according to claim 8, characterized in that: After the clay soil retaining surface (12) is constructed, a round of watering is carried out above the plow bottom layer (8) to verify whether the drainage effect of the concealed pipe (4) meets the standard. The standard condition is that the drainage volume of the concealed pipe is not less than 70% of the irrigation volume. If it does not meet the standard, the buried angle of the concealed pipe (4) and whether there is blockage inside it, or check whether there is leakage at the bottom of the rectangular pit and the clay soil retaining surface (12).

10. The method of using compacted plow bottom layer to achieve leaching and desalination of cultivated layer soil in conjunction with concealed pipes according to claim 1, characterized in that: In the step 5, after placing the concealed pipe (4) on the upper surface of the rectangular earth pit, the pipe opening close to the irrigation channel is blocked, the concealed pipe close to the drainage ditch extends 20 to 30 cm from the ridge, and a Y-shaped three-way joint (9) is connected to the pipe outlet. The Y-shaped three-way joint (9) is placed horizontally above the drainage ditch, one side of which is connected to a branch pipe for discharging the collected leaching water, and the leaching water branch pipe is connected to the receiving pool (13) through a leaching ball valve (10). The other side of the Y-shaped three-way joint (9) is connected to a drainage ball valve (11) arranged above the drainage ditch through a pipe for ordinary drainage.

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