Method for improving clayed soil

Abstract

The invention relates to the technical field of soil improvement methods, and discloses a clayey soil improvement method which comprises the following stages: S1-S4. Through a synergistic improvement mode, the content of organic matters in the soil is increased, the content of heavy metals in the soil is reduced, the hardening rebound rate is reduced, meanwhile, the pH value of the soil is adjusted to a suitable range of 6.0-7.5, and the comprehensive improvement effect is remarkable; meanwhile, contour line operation, multi-ditch drainage, straw covering and the like are arranged, so that the device can adapt to mountainous and hilly terrains and rainy and high-humidity climate in the southwest, and water and soil loss and modifier loss are effectively prevented; ecological materials such as bamboo fibers, earthworms and straws are adopted, so that the dosage of chemical reagents is greatly reduced, secondary pollution is avoided, and adverse effects are reduced after leaching agent residues are subjected to drainage and biodegradation; an improved closed loop is formed through later measures such as crop rotation, regular compensation and improvement, permeability maintenance and the like, rebounding after short-term effectiveness is avoided, and the improvement effect is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the field of soil improvement methods, specifically a method for improving clayey soil. Background Technology

[0002] Clay soils, due to their high clay content (usually >35%), suffer from poor pore structure, poor aeration and water permeability, and are prone to compaction, severely restricting crop root growth and hindering water infiltration and nutrient migration. Clay soils in Southwest China also face unique challenges: the mountainous and hilly terrain easily leads to soil erosion; the rainy and humid environment causes soil amendments to be lost and soil to be washed away; and some plots have excessive levels of heavy metals such as Cu, Pb, and Ni due to industrial activities or agricultural pollution.

[0003] Existing methods for improving clayey soils have many limitations: traditional physical amendments (such as simply adding sand) have short-lived effects and are prone to rebound; chemical amendments (such as gypsum or quicklime alone) require large quantities, which may lead to soil salinization or pH imbalance; biological amendments often use single microbial strains or organic fertilizers, failing to achieve synergistic effects; leaching technologies for heavy metal pollution are not integrated with conventional amendments, and there is a lack of technical solutions adapted to the terrain and climate of Southwest China. Furthermore, existing methods often neglect post-construction maintenance and site adaptation, resulting in unsustainable improvement effects and failing to meet the needs of diverse scenarios such as farmland, orchards, and lawns.

[0004] Therefore, there is an urgent need to develop a method for improving clay soil that takes into account ecological sustainability, targeted approach, long-term effectiveness, and scenario adaptability, and to solve the improvement problems caused by clay soil compaction, nutrient deficiency, heavy metal pollution, and the special environment of Southwest China through multi-technology collaboration. Summary of the Invention

[0005] This invention provides a method for improving cohesive soil, which solves the problems of existing methods for improving cohesive soil, such as short-lived effects, poor adaptability, and failure to address heavy metal pollution.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for improving clayey soil includes the following stages: S1. Pollution Screening and Enhanced Pretreatment: Soil pH, clay content, organic matter content, and heavy metal content (Cu, Pb, Ni, Zn, Cr) are tested and classified according to the results. If areas with excessive heavy metals are found during this stage, targeted leaching treatment is employed. Subsequently, stones and weed roots are removed from the soil, and the soil is deeply plowed 25-30cm along contour lines, followed by sun-drying or freezing for 15-20 days. After leaching or sun-drying, sufficient soil moisture is applied until the soil moisture content reaches 20-25%. The S1 stage is conducted 2-3 months before sowing or transplanting (after the rainy season) to lay the foundation for core improvement. Specifically, soil samples are collected from the 0-20cm topsoil layer to test pH, clay content, organic matter content, and heavy metal content (Cu, Pb, Ni, Zn, Cr). According to the test results, soils with a clay content >40% are classified as high-clay soils; soils with a pH <6.5 are acidic soils, and soils with a pH >7.5 are alkaline soils; soils with heavy metal content higher than Table 1 in (GB15618-2018) but equal to or lower than Table 3, and for which control measures can be taken, are considered agricultural soils with excessive heavy metals that can be improved. Heavy metal pollution in clay soils in Southwest China is mainly caused by Cu, Pb, Ni, Zn, and Cr, while Hg and As exceedances are mostly concentrated in specific industrial pollution sites, such as areas surrounding mercury mines and gallium arsenide production areas. These are low-frequency pollutions and are not considered. During deep plowing and weed removal, severely compacted plots are plowed twice with a 10-day interval to break up the compacted layer. Sun-dried clods are plowed in summer and then left fallow for 15-20 days to allow high-temperature weathering and particle dispersal; frozen clods are plowed in winter and then left fallow for 15-20 days to break up clay aggregates through freeze-thaw cycles. Among these measures, the leaching agent should not be used simultaneously with strongly alkaline materials such as quicklime, and an interval of more than 7 days is required. During the rainy season, approximately from May to September, deep plowing and leaching should not be carried out to avoid soil erosion and loss of the amendment.

[0007] S2. Co-processing: Mix 200-300 kg of fine sand, 300-400 kg of fine slag, and 300-450 kg of crushed straw per acre, then rotary tillage to achieve physical loosening and reduce stickiness. During this stage, apply chemical amendments to adjust the pH based on soil acidity / alkalinity. Construct an ecological biological system of "highly absorbent bamboo fiber, earthworms, and chicory," supplemented with 1500-2000 kg of well-rotted farmyard manure to replenish organic matter. This stage is carried out 15 days after pretreatment and 30 days before sowing / transplanting. Specifically, select fine sand with a particle size of 0.5-2 mm, sieve the fine slag, and control the length of the crushed straw to 1-3 cm. First, spread the fine sand on the surface to a thickness of 2-3 cm, then rotary till to a depth of 15-20 cm. Next, mix in the slag and straw and rotary till again to ensure no stratification and to construct a breathable framework.

[0008] S3, Cultivation Adaptation: Construct raised beds 15-25cm high along contour lines, equipped with furrows, waist ditches (when the bed length exceeds a certain threshold), and perimeter ditches to form a multi-ditch drainage system; level the soil and moderately compact it; cover the soil after sowing or transplanting to retain moisture; this stage is approximately 10-20 days after the S2 stage improvement, before sowing / transplanting. Specifically, the multi-ditch drainage system can prevent water accumulation in the beds, which can lead to the re-agglomeration of clay particles and reduce the risk of soil compaction. Specifically, leveling and moderately compacting the soil involves: leveling the bed surface with a rake, and compacting with a light roller (pressure ≤0.5MPa) to ensure close contact between the soil and the seed / seedling roots, while keeping the surface loose; attention should be paid to moisture regulation during this process. If the soil moisture is <15%, spray a small amount of water to bring the moisture content to 20-25%, which is beneficial for seed germination and the effectiveness of the soil conditioner.

[0009] S4. Post-planting maintenance: Adopt a three-year crop rotation system of "leguminous crops - deep-rooted crops - gramineous crops" for rotation optimization; manage soil moisture and nutrients and regularly aerate soil to maintain permeability; conduct regular monitoring and remediation. Crop rotation helps leguminous crops fix nitrogen, deep roots activate deep-rooted nutrients, and gramineous crops balance nutrient consumption, avoiding soil compaction and nutrient imbalance caused by continuous cropping. Specifically, soil moisture and nutrient management includes: timely clearing of ditches during the rainy season to ensure smooth drainage; watering frequently in small amounts during the dry season to avoid flooding; applying 10 kg / mu of urea as top dressing during the crop growing season, combined with foliar spraying of 0.2% potassium dihydrogen phosphate to avoid excessive chemical fertilizers leading to soil salinization; and replanting 300 kg / mu of straw every quarter, shallowly tilling to a depth of 5 cm to continuously replenish organic matter. Regular monitoring and remediation are revised as follows: test soil indicators every 6 months. If the pH deviates from 6.0-7.5, apply 50 kg / mu of wood ash for acidic soil and 30 kg / mu of ferrous sulfate for alkaline soil. If the aeration decreases, apply 1 kg / mu of bamboo fiber and 10,000 earthworms / mu, and lightly till and mix them. If heavy metals rebound, apply a targeted leaching solution once.

[0010] Furthermore, in the S1 stage, the specific operations for targeted leaching include: using a 0.1 mol / L ferric chloride solution when Cu, Ni, and Pb exceed the standard; using an oxalic acid solution when Zn exceeds the standard; and preparing a leaching agent separately according to the soil pH when Cr exceeds the standard, and mixing it with the ferric chloride solution and oxalic acid solution in the appropriate ratio; spraying the leaching agent at a water-to-soil ratio of 10:1 (w / w), then shallowly tilling to a depth of 5 cm and keeping it moist for 1 hour; repeating the leaching process at 7-day intervals, for a total of 3 leachings, followed by drainage after leaching. Specifically, when Cr exceeds the standard, the leaching agent is prepared according to the soil pH: for pH ≤ 6.5, a mixture of 0.1 mol / L ferric chloride (FeCl3): 0.05 mol / L oxalic acid: 0.03 mol / L ferrous sulfate (FeSO4) in a 2:1:1 ratio is used; for pH > 6.5, a mixture of 0.1 mol / L FeCl3: 0.05 mol / L oxalic acid: 0.02 mol / L EDTA-2Na in a 2:1:1 ratio is used.

[0011] Furthermore, in the S2 stage, the amount of the ecological biological system used is as follows: 24-30g / ㎡ of highly absorbent bamboo fiber, 20-25 earthworms / ㎡, and 3g / ㎡ of chicory seeds. When placing the bamboo fiber, first turn it shallowly into the soil, then cover it with earthworms mixed with decomposed organic fertilizer, and then sow the chicory seeds in rows.

[0012] Furthermore, in the S2 stage, after the ecological biological system is established, the use of high-concentration pesticides is avoided, and the soil moisture is maintained at 20-25% for 3 days after the earthworms are released.

[0013] Furthermore, in the S2 stage, the application scheme of chemical amendments is as follows: When pH < 6.5, apply 50-80 kg of quicklime or 150 kg of wood ash and 50-80 kg of ferrous sulfate. When Cr exceeds the standard, the amount of ferrous sulfate is increased to 100-150 kg / mu; When pH 6.5-7.5, apply 40-60 kg of gypsum and 1000 g of soil loosening agent. When Cr exceeds the standard, add an additional 80-100 kg / mu of humic acid; When pH > 7.5, apply 80-100 kg of humic acid and 100 kg of superphosphate. When Cr exceeds the standard, the amount of humic acid is increased to 120-150 kg / mu.

[0014] Furthermore, in the S3 stage, the mulching and moisture-retaining operation after sowing or transplanting includes: covering the bed surface with 5-8cm of straw or straw mats to prevent rainwater from washing away the topsoil, reduce water evaporation, and inhibit weed growth; specifically, during the dry season, mulch film can be used and the edges should be compacted, while during the rainy season, straw mulch should be retained. Furthermore, in the S3 stage, the specifications of the multi-ditch drainage system are as follows: the furrow ditch is 30-40cm wide and 15-20cm deep. When the land length exceeds 30m, a waist ditch is set with a width of 40cm and a depth of 30cm. The surrounding ditch is 50cm wide and 40-50cm deep. The multiple ditches are interconnected and gradually deepened.

[0015] Furthermore, in the S4 stage, the drilling maintenance operation includes: at the end of summer, using a drill with a hole diameter of 15-20mm, drilling holes at 20cm×20cm intervals, to a depth of 25-35cm, and then filling them with crushed straw. This structure allows for the filling of crushed straw after drilling, creating long-lasting aeration channels and improving the permeability of deep soil layers.

[0016] Furthermore, for steep mountain slopes, the deep tillage depth is adjusted to 20cm in stage S1, and the straw cover thickness is increased to 8-10cm in stage S3, with the spacing of waist ditches increased to 25m; for low-lying river valleys, the ridge height is increased to 25cm in stage S3, and the amount of organic fertilizer used is adjusted to 1000-1500kg / mu in stage S2, with the amount of gypsum used increased to 80kg / mu.

[0017] Beneficial effects: Through synergistic improvement, it increases soil organic matter content, removes heavy metals, reduces soil compaction rebound rate, and adjusts soil pH to a suitable range of 6.0-7.5, resulting in significant comprehensive improvement effects. Furthermore, by implementing contour line planting, multi-ditch drainage, and straw mulching, it adapts to the hilly terrain and rainy, humid climate of southwestern China, effectively preventing soil erosion and soil amendment loss. The use of ecological materials such as bamboo fiber, earthworms, and straw greatly reduces the amount of chemical reagents used, avoids secondary pollution, and reduces the adverse effects of leaching agent residues after drainage and biodegradation. Finally, through post-improvement measures such as crop rotation, regular replanting, and permeability maintenance, a closed-loop improvement system is formed, preventing rebound after short-term effects and effectively extending the improvement effect. Detailed Implementation

[0018] The technical solution of a method for improving cohesive soil according to the present invention will be further described in detail below with reference to embodiments.

[0019] Example 1: Steep slope sandstone and shale area in Bijie mountains Background: The soil is red soil developed from sandstone and shale, with a pH of 5.3, clay content of 41%, Cu exceeding the standard by 1.5 times, Pb exceeding the standard by 2 times, and an annual rainfall of 1300 mm.

[0020] Improvement measures: S1 Pretreatment: Deep plowing to 20cm along contour lines in winter (two deep plowings, 10 days apart), sun-drying the soil for 15 days, and irrigating to a soil moisture level of 22%. Targeted leaching: For Cu / Pb compound pollution, a mixture of 0.1mol / L FeCl3 and 0.05mol / L oxalic acid (1:1) was used with a water-to-soil ratio of 10:1. Leaching was performed three times in total, with an interval of 7 days.

[0021] S2 Collaborative Improvement: Physical Improvement: 200 kg / mu of fine sand, 300 kg / mu of fine slag, and 450 kg / mu of crushed straw (1-3 cm), mixed by rotary tillage. Ecosystem: 24 g / m² of bamboo fiber, 20 earthworms / m², and 3 g / m² of chicory seeds.

[0022] Chemical improvement: Apply 60 kg / mu of quicklime and 100 kg / mu of ferrous sulfate at pH 5.3 (Cr content not exceeded).

[0023] S3 Cultivation Adaptation: Construct double-layer contour beds: the upper bed is 15cm high, and the lower bed is covered with a biological hedge (vetiver grass, spaced 5m apart). Multiple drainage ditches: bed ditches are 30cm wide and 15cm deep; waist ditches are 40cm wide and 30cm deep, spaced 20m apart; perimeter ditches are 50cm wide and 40cm deep. Mulching: Cover with a 6cm layer of straw mat after sowing corn.

[0024] S4 Post-Grain Maintenance: Crop Rotation: Corn-Vetch-Ryegrass three-year rotation. Hole Drilling Maintenance: Drill holes at the end of summer (15mm diameter × 25cm depth) and fill with crushed straw.

[0025] Results: Soil pH increased to 6.1, Cu / Pb removal rates reached 82% / 78%, and runoff erosion decreased by 65%. Corn yield increased by 23%, and vetch nitrogen fixation increased soil organic matter to 1.8%.

[0026] Example 2: Karst Peak-Cluster Depression in Huanjiang, Guangxi Background: The rocky desertification rate is 40%, the carbonate rocks are developed into yellow limestone soil, the pH is 7.4, the clay content is 35%, the Pb exceeds the standard by 3 times, and the Zn exceeds the standard by 1.2 times.

[0027] Improvement measures: S1 Pretreatment: Deep plowing to 25cm in spring (avoiding the rainy season), freezing the soil for 20 days, and irrigating to a soil moisture level of 24%. Targeted leaching: For Pb exceeding the standard, use a mixture of 0.1mol / L FeCl3 and 0.05mol / L oxalic acid (3:1), with a water-to-soil ratio of 10:1, and leach twice.

[0028] S2 Collaborative Improvement: Physical Improvement: 250 kg / mu of fine sand, 150 kg / mu of slag, and 400 kg / mu of crushed straw (1-3 cm). Ecosystem: 28 g / m² of bamboo fiber, 22 earthworms / m², and 3 g / m² of chicory seeds. Chemical Improvement: 50 kg / mu of gypsum and 1000 g / mu of soil loosening agent (Cr content not exceeding the standard).

[0029] S3 cultivation adaptation: Construct a deep ditch and raised field system: ridge height 25cm, dig 60cm deep underground drainage ditches, and match with 20cm high ridge planting; multi-ditch drainage: ridge ditch width 30cm×depth 15cm, waist ditch width 40cm×depth 30cm, perimeter ditch width 50cm×depth 40cm; mulching: after transplanting sugarcane, cover with 8cm thick corn stalks, and press the edges with mulch during the rainy season.

[0030] S4 Post-Grain Maintenance: Crop Rotation: Sugarcane-Ryegrass-Vigna Rotation. Hole Drilling Maintenance: Drill holes during the dry season (20mm diameter × 30cm depth) and fill with crushed straw.

[0031] Results: Soil Pb passivation rate 89%, Zn availability reduced by 58%, sugarcane yield increased by 35%. Surface runoff decreased by 72%, and rocky desertification area reduced by 18%.

[0032] Example 3: Alluvial soil in the low-lying river valley of Yibin, Sichuan Background: Groundwater level 1.2m, alluvial soil pH 8.1, clay content 39%, Cr content 0.8 times higher than standard.

[0033] Improvement measures: S1 Pretreatment: Deep plowing to 25cm in summer (completed before the rainy season), sun-drying the soil for 15 days, and irrigating to a soil moisture level of 23%. Targeted leaching: For Cr pollution, a mixture of 0.1mol / L FeCl3:0.05mol / L oxalic acid:0.02mol / L EDTA-2Na in (2:1:1) solution with a water-to-soil ratio of 10:1 was used for leaching 3 times.

[0034] S2 Collaborative Improvement: Physical Improvement: 200 kg / mu of fine sand, 350 kg / mu of fine slag, and 500 kg / mu of crushed straw (1-3 cm). Ecosystem: 30 g / m² of bamboo fiber + 25 earthworms / m², and 3 g / m² of chicory seeds. Chemical Improvement: 120 kg / mu of humic acid and 100 kg / mu of superphosphate.

[0035] S3 Cultivation Adaptation: Construct a high-ridge, underground drainage system: ridge height 25cm, lay 10cm diameter PVC underground pipes (spaced 30m apart), and provide supporting ditches 50cm wide × 40cm deep. Mulching: After rice transplanting, cover with 7cm thick straw; retain the mulch during the dry season to suppress evaporation.

[0036] S4 Post-Grain Maintenance: Crop Rotation: Rice-African Clover-Corn Rotation. Hole Drilling Maintenance: Drill holes (20mm diameter × 35cm depth) at the end of summer and fill with crushed straw.

[0037] Results: Cr residue levels decreased to 0.3 mg / kg, rice yield increased by 28%, groundwater level dropped by 0.8 m, and soil salinization index decreased by 52%.

[0038] Example 4: Complex Pollution in the Purple Soil Hilly Area of ​​Qujing, Yunnan Background: The area has purple soil, pH 6.2, clay content 45%, Cu content 1.2 times higher than standard, Zn content 1.5 times higher than standard, and is adjacent to a chemical industrial park where PAHs (polycyclic aromatic hydrocarbons) pollution exists. The annual rainfall is 1100 mm.

[0039] Improvement measures: S1 Pretreatment: Deep plowing to 20cm along contour lines in winter (two deep plowings, 10 days apart), freezing the soil for 20 days, and irrigating to a soil moisture level of 23%. Targeted leaching: For Cu / Zn composite pollution, FeCl3-oxalic acid (1:1) mixture was used with a water-soil ratio of 10:1, and leaching was performed twice; for PAHs contaminated areas, surfactant (Tween-800.1%) was added to assist leaching.

[0040] S2 Co-processing Improvement: Physical Improvement: 200 kg / mu of fine sand, 300 kg / mu of fine slag, and 450 kg / mu of crushed straw (1-3 cm), mixed thoroughly by rotary tillage. Ecosystem: 24 g / m² of bamboo fiber, 20 earthworms / m², and 3 g / m² of chicory seeds. Chemical Improvement: 50 kg / mu of quicklime, 70 kg / mu of ferrous sulfate (Cr not exceeding the standard), and 100 kg / mu of humic acid (complexing PAHs).

[0041] S3 Cultivation Adaptation: Construct a terraced-biological hedge composite system: build terraces along contour lines, and plant vetiver grass on the slopes (3m spacing). Multiple drainage ditches: furrows 30cm wide x 15cm deep, side ditches 40cm wide x 30cm deep (densed to 20m), and perimeter ditches 50cm wide x 40cm deep, with a waterproof membrane at the bottom. Mulching: After sowing flue-cured tobacco, cover with 8cm thick straw.

[0042] S4 Post-Grade Maintenance: Crop Rotation: Three-year rotation of flue-cured tobacco, vetch, and milkvetch. Hole Drilling Maintenance: Drill holes during the dry season (15mm diameter × 25cm depth) and fill with crushed straw.

[0043] Results: PAHs removal rate 73%, Cu / Zn removal rate 81% / 79%, soil enzyme activity increased 2.3 times. Soil microbial diversity recovered to 85% of background levels.

[0044] Example 5: Salinization of the Fuling Red Soil Basin in Chongqing Background: Jurassic red soil basin, pH 8.4, clay content 38%, trace Cr (0.6 mg / kg), groundwater depth 0.8 m, average annual evaporation 1800 mm.

[0045] Improvement measures: S1 Pretreatment: Deep plowing to 25cm in spring (completed before the rainy season), sun-drying the soil for 20 days, and irrigating to a soil moisture level of 24%. Targeted leaching: 0.1mol / L FeCl3: 0.05mol / L oxalic acid: 0.02mol / L LEDTA-2Na mixed in a 2:1:1 ratio, with a water-to-soil ratio of 10:1, leaching twice.

[0046] S2 Collaborative Improvement: Physical Improvement: 250 kg / mu of fine sand, 150 kg / mu of fine slag, and 400 kg / mu of crushed straw (1-3 cm). Ecosystem: 28 g / m² of bamboo fiber, 22 earthworms / m², and 3 g / m² of chicory seeds. Chemical Improvement: 150 kg / mu of humic acid and 100 kg / mu of superphosphate.

[0047] S3 cultivation adaptation: Construct a ridge-furrow underground pipe system: ridge height 25cm, lay 10cm diameter PVC underground pipes (spaced 25m apart), and match with a perimeter ditch 50cm wide × 40cm deep. Covering: cover with 7cm thick straw after transplanting the pickled mustard tuber.

[0048] S4 Post-Grain Maintenance: Crop Rotation: Pickled mustard greens-rye grass-vetch rotation. Hole Drilling Maintenance: Drill holes (20mm diameter × 30cm depth) at the end of the rainy season and fill with crushed straw.

[0049] Results: pH decreased to 7.9, Cr passivation rate was 89%. Separate yield of crushed soil increased by 32%, and soil electrical conductivity decreased by 55%.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving clayey soil, characterized in that, Includes the following stages: S1. Pollution Screening and Enhanced Pretreatment: Soil pH, clay content, organic matter content, and heavy metal content (Cu, Pb, Ni, Zn, Cr) are tested and classified according to the results. If any plots exceed heavy metal standards during this stage, targeted leaching treatment is employed. Subsequently, stones and weed roots are removed from the soil, and the soil is deeply plowed 25-30cm along contour lines, followed by sun-drying or freezing for 15-20 days. After leaching or sun-drying, sufficient base moisture is irrigated until the soil moisture content reaches 20-25%. S2. Co-modification: Mix 200-300 kg of fine sand, 300-400 kg of fine slag, and 300-450 kg of crushed straw per acre, and then rotary tillage to achieve physical loosening and reduce stickiness. During this stage, chemical amendments are applied to adjust the pH based on the soil's acidity and alkalinity; an ecological biological system of "highly absorbent bamboo fiber, earthworms, and chicory" is constructed, supplemented with 1500-2000 kg of well-rotted farmyard manure to replenish organic matter; S3. Cultivation adaptation: Construct raised beds with a height of 15-25cm along contour lines, and provide a multi-ditch drainage system with furrows, waist ditches when the land length exceeds a certain threshold, and perimeter ditches; level the soil and compact it appropriately; cover the soil after sowing or transplanting to retain moisture; S4. Post-planting maintenance: Adopt a three-year crop rotation system of "leguminous crops-deep-rooted crops-grass crops" to optimize the rotation; manage soil moisture and nutrients and regularly aerate the soil to maintain permeability; conduct regular monitoring and make improvements.

2. The method for improving cohesive soil according to claim 1, characterized in that: In the S1 stage, the specific operations of targeted leaching include: when Cu, Ni, and Pb exceed the standard, use 0.1 mol / L ferric chloride solution; when Zn exceeds the standard, use oxalic acid solution; when Cr exceeds the standard, prepare a leaching agent according to the soil pH and mix it with ferric chloride solution and oxalic acid solution in proportion; spray the leaching agent at a water-to-soil ratio of 10:1 (w / w) and then lightly till 5 cm, keeping it moist for 1 hour; repeat leaching at 7-day intervals, and leach a total of 3 times, and drain the ditch after leaching.

3. The method for improving cohesive soil according to claim 1, characterized in that: In the S2 stage, the amount of the ecological biological system used is as follows: 24-30g / ㎡ of highly absorbent bamboo fiber, 20-25 earthworms / ㎡, and 3g / ㎡ of chicory seeds. When placing the bamboo fiber, first turn it into the soil shallowly, then cover it with earthworms mixed with decomposed organic fertilizer, and then sow the chicory seeds in rows.

4. The method for improving cohesive soil according to claim 1, characterized in that: In the S2 stage, after the ecological biological system is established, avoid using high concentrations of pesticides, and maintain soil moisture at 20-25% for 3 days after earthworm release.

5. The method for improving cohesive soil according to claim 1, characterized in that: In the S2 stage, the application plan for chemical amendments is as follows: When pH < 6.5, apply 50-80 kg of quicklime or 150 kg of wood ash and 50-80 kg of ferrous sulfate. If Cr exceeds the standard, the amount of ferrous sulfate should be increased to 100-150 kg / mu. When pH is 6.5-7.5, apply 40-60 kg of gypsum and 1000 g of soil loosening agent. If Cr exceeds the standard, add an additional 80-100 kg / mu of humic acid. When pH > 7.5, apply 80-100 kg of humic acid and 100 kg of superphosphate. If Cr exceeds the standard, the amount of humic acid should be increased to 120-150 kg / mu.

6. The method for improving cohesive soil according to claim 1, characterized in that: In the S3 stage, the mulching and moisture-retaining operation after sowing or transplanting includes: covering the bed surface with 5-8cm of straw or straw mats to prevent rainwater from washing away the topsoil, reduce water evaporation, and inhibit weed growth; specifically, during the dry season, mulch film can be used and the edges should be compacted, while during the rainy season, straw cover should be retained.

7. The method for improving cohesive soil according to claim 1, characterized in that: In the S3 phase, the specifications of the multi-ditch drainage system are as follows: the furrow ditch is 30-40cm wide and 15-20cm deep. When the land length exceeds 30m, a waist ditch is set with a width of 40cm and a depth of 30cm. The surrounding ditch is 50cm wide and 40-50cm deep. The multiple ditches are interconnected and gradually deepened.

8. A method for improving cohesive soil according to claim 1, characterized in that: In the S4 stage, the drilling maintenance operation includes: at the end of summer, use a hole punch with a hole diameter of 15-20mm to punch holes at a spacing of 20cm×20cm and a depth of 25-35cm. After drilling, crushed straw can be filled in.

9. A method for improving clayey soil according to claim 1, characterized in that: For steep mountain slopes, the deep tillage depth is adjusted to 20cm in stage S1, and the straw cover thickness is increased to 8-10cm in stage S3, with the spacing of the waist ditches increased to 25m. For low-lying river valleys, the ridge height is increased to 25cm in stage S3, and the amount of organic fertilizer used is adjusted to 1000-1500kg / mu in stage S2, while the amount of gypsum used is increased to 80kg / mu.