A structural modifier for heavy and compacted soils

Abstract

The application provides a structural modifier for heavy and compacted soil, which is prepared by reasonably compounding and combining biochar, phosphate rock powder, straw short fibers, water-retaining agent and microbial liquid, and has the advantages of synergistically improving soil structure, enhancing water and fertilizer retention capacity, promoting nutrient slow release and utilization, and activating beneficial microbial community, and can effectively improve acidified, compacted and infertile soil, and improve soil fertility and crop growth conditions.

Description

Technical Field

[0001] This invention belongs to the field of agricultural resources, environment and soil improvement technology, specifically, it relates to a composite structural improver for improving heavy and compacted soil. Background Technology

[0002] Soil is the foundation of agricultural production and the health of ecosystems. Heavy clay soils (such as Quaternary red clay) are widely distributed in southern my country, characterized by their heavy texture, fine particles, and low porosity. Under natural conditions or under unreasonable cultivation, irrigation, and external pressure, these soils are highly susceptible to compaction.

[0003] Soil compaction refers to the phenomenon where the soil surface becomes hardened due to the destruction of its structure and the dispersion of soil materials under the influence of natural or human factors, and the soil surface hardens under the influence of cohesion after drying. Its main harms are: (1) Deterioration of physical properties: Poor soil permeability hinders water infiltration, exacerbates surface runoff and soil erosion; at the same time, it affects soil gas exchange, leading to root hypoxia. (2) Imbalance of chemical properties: Compacted soil has a strong adsorption and fixation effect on nutrients, slow conversion of effective nutrients, low fertilizer utilization rate, resulting in increased agricultural production costs and non-point source pollution. (3) Reduction of biological activity: The harsh physical and chemical environment inhibits the activity of soil microorganisms and animals, destroys the balance of the soil ecosystem, and reduces the natural fertility of the soil. (4) Restriction of crop growth: The hard soil layer seriously hinders the root system of crops from penetrating, resulting in poor crop development, poor resistance to adverse conditions, and ultimately reduced yield and quality.

[0004] Currently, measures to improve soil compaction mainly include: Physical methods: such as deep plowing and deep loosening. These methods are direct but short-lived, costly to repeat, and may cause secondary soil compaction. Chemical methods: applying traditional soil conditioners, such as gypsum and lime. These mainly promote soil aggregation through cation exchange, but their effectiveness is limited for soils with extremely low organic matter content, and long-term, large-scale use may cause soil pH imbalance or secondary salinization. Biological methods: increasing the application of organic fertilizers (such as farmyard manure and straw return to the field). This is the most ideal method, but organic fertilizer sources are limited, the decomposition period is long, and the dosage is large (often several tons per acre to see results), resulting in slow effects and failing to meet the needs of rapid soil improvement in modern agriculture. In recent years, polymeric conditioners (such as polyacrylamide, PAM) have been used, offering good water and fertilizer retention, but they are expensive and difficult to degrade in the environment, potentially posing a risk of secondary pollution.

[0005] Therefore, there is an urgent need in the current technological field for a high-efficiency, long-lasting, environmentally friendly, and cost-effective composite soil structure conditioner. It should comprehensively address the physical structure problems of heavy, compacted soils while simultaneously achieving multiple objectives such as improving soil fertility and stimulating soil biological activity, overcoming the limitations of existing single-type conditioners.

[0006] Existing plant amendments have diverse raw material sources, mainly including inorganic materials (such as gypsum, lime, zeolite, etc.), organic materials (such as humic acid, organic fertilizer, straw, etc.), and high molecular polymers (such as polyacrylamide, polyvinyl alcohol, etc.). Among them, the development of plant amendments using agricultural waste resources has become a research hotspot, especially materials represented by biochar and straw, which show broad application prospects.

[0007] Biochar is a carbon-rich material produced by the pyrolysis of biomass under anaerobic conditions. Recycling agricultural waste (such as straw and rice husks) to produce biochar not only enables the high-value utilization of waste resources and reduces environmental pollution, but also significantly improves soil structure. Biochar possesses a porous structure, high specific surface area, and stable properties. When applied to the soil, it enhances aggregate formation, increases porosity and permeability, and adsorbs nutrients, reducing nutrient loss. Furthermore, biochar provides habitats for microorganisms, stimulates soil biological activity, and achieves carbon sequestration and emission reduction, aligning with the development direction of green agriculture and the circular economy.

[0008] Returning straw to the field is a traditional biological amendment method, and its recycling is of great significance for improving soil compaction. Straw is rich in organic matter and nutrients, which can increase soil organic carbon content, promote soil aggregate formation, enhance water and fertilizer retention capacity, and alleviate soil compaction. Straw resources are abundant and inexpensive, and large-scale return to the field can also reduce environmental pollution from burning and achieve the recycling of agricultural waste. However, direct straw return to the field has problems such as slow decomposition, limited short-term effects, and the potential to carry pathogens. Fermentation treatment or compounding with other amendments is necessary to improve its application effect. Through technological optimization, straw-based amendments have broad prospects in improving soil quality and promoting sustainable development.

[0009] Water-retaining agents are functional materials with high water absorption and retention capacity. Common types include synthetic polymers (such as polyacrylates and polyacrylamide) and naturally modified types (such as cellulose-based and starch-based). Composite water-retaining agents are usually enhanced through physicochemical modification or multi-component compounding (such as adding mineral powders and biochar). The main functions of water-retaining agents are to improve soil water holding capacity, reduce water evaporation and seepage, enhance drought resistance, and promote nutrient use efficiency through water regulation, thereby supporting crop growth. However, single water-retaining agents often suffer from poor degradability (synthetic types), weak salt tolerance, high cost, or insufficient duration of effect; while composite water-retaining agents improve overall performance to some extent, they still face challenges such as complex processes and unclear environmental adaptability. In water-scarce areas, water-retaining agents are of great significance for improving agricultural water use efficiency and ensuring crop yield, and are an important component of soil conditioner research and development.

[0010] In conclusion, developing composite soil conditioners based on waste resources such as biochar and straw, combined with multifunctional materials that retain water and promote granulation, offers advantages such as environmental friendliness, resource recycling, cost-effectiveness, and long-lasting improvement. This is an important development direction for solving the problem of compacted clay soils. Summary of the Invention

[0011] This invention discloses a structural improver for heavy, compacted soil to solve any of the aforementioned or potential problems in the prior art. To solve the above-mentioned technical problems, the improver of this application is specifically prepared as follows:

[0012] Add 50-60 parts by weight of composite biochar, 30-40 parts by weight of phosphate rock powder, and 10-20 parts by weight of short straw fiber into a mixer and run it at a low speed of 20-30 rpm for 15-20 minutes. Then add 5-8 parts by weight of water-retaining agent and continue mixing at a speed of 20-30 rpm for 10-15 minutes. Dilute 5-10 parts by weight of microbial mixed bacterial solution with 1-2 times its weight of sterile water and spray the diluted bacterial solution onto the mixture. At the same time, keep the mixture stirring at a low speed of 10-15 rpm. After the bacterial solution is added, continue running the mixer at a low speed of 10-15 rpm for 5 minutes. Transfer the mixed improver to a cool, dark place and let it stand and mature for 24-48 hours.

[0013] The microbial mixed bacterial solution is prepared by mixing Bacillus megaterium, Bacillus colloidis, and Trichoderma harzianum in equal proportions, with a viable count ≥10. 8 CFU / mL.

[0014] The preparation of composite biochar is as follows: Wood chips and rice husks are prepared, washed, dried, pulverized, and sieved through a 100-mesh sieve; white phosphogypsum powder is added to deionized water to form a uniformly dispersed suspension, with a white phosphogypsum to water mass ratio of 1:20 and a biochar to white phosphogypsum dry weight addition ratio of 2-5:1. The mixture is placed in a constant temperature shaker and shaken at 40-60℃ and 150-200 rpm for 4-12 hours. After shaking, the mixture is vacuum filtered or centrifuged to separate the solid composite; the solid composite is placed in an oven at 105℃ and dried for 24 hours until completely dry, yielding a preliminary composite powder.

[0015] The composite powder is placed in a muffle furnace, and nitrogen gas is introduced to raise the temperature from room temperature to 300-400℃ at a rate of 5-10℃ / min, and the temperature is maintained for 1-2 hours. After cooling to room temperature, it is ground and passed through a 20-40 mesh sieve to obtain composite biochar.

[0016] The preparation process of straw short fiber is as follows: Straw is dried, shredded into 3-5 cm pieces, and then the straw pieces are placed in a cooking tank. A 5%-15% NaOH solution is prepared in the cooking tank, controlling the weight ratio of the solution to straw at 4-6:1. A cooking aid of 0.05%-0.1% by weight is added to the mixture. The temperature is raised to 110-120℃ at a rate of 1-1.5℃ / min and held for 20-30 minutes. Then, the temperature is increased by 2- The temperature is increased to 150-170℃ at a rate of 5℃ / min, and the pressure is maintained at 0.6-1.0MPa. Under these conditions, the temperature and pressure are maintained for 1-3 hours. Then, the slurry is instantly depressurized to 0.2-0.3MPa and discharged into the spray chamber. It is repeatedly washed with hot water at 50-60℃ until the water is clear and the pH is neutral to obtain fiber slurry. It is centrifuged to dehydrate to a moisture content of 35%-40%, and then placed in a drum dryer and dried at 105-120℃ to a moisture content of ≤10% to obtain short straw fibers.

[0017] Straw includes rice, wheat, and corn stalks.

[0018] The cooking aid is anthraquinone.

[0019] The water-retaining agent is composed of alkali lignin, glycidyltrimethylammonium chloride, and attapulgite.

[0020] The preparation process of the water-retaining agent includes:

[0021] Alkali lignin pretreatment: 100 parts by mass of alkali lignin powder and deionized water were mixed at a ratio of 1:15. NaOH solution was slowly added under stirring to adjust the pH to 10-11, forming a homogeneous system. The mixture was stirred at 60℃ for 1 hour, and then the temperature was raised to 68-72℃. 30-40 parts by mass of glycidyltrimethylammonium chloride were added dropwise to the system. After the addition was completed, the mixture was stirred at 70℃ and 200 rpm for 3-4 hours. Then, dilute hydrochloric acid was added to adjust the pH to neutral. The precipitate was collected by vacuum filtration. The precipitate was washed three times with 50% ethanol solution. The washed precipitate was dried in an oven at 60-70℃ to constant weight. The dried block product was pulverized with a pulverizer to obtain quaternized alkali lignin powder for later use.

[0022] Water-retaining agent mixing: Mix quaternized alkali lignin powder with deionized water at a mass ratio of 1:20, stir at 50℃ for 2 hours, add attapulgite clay with a mass of 2-4 times that of quaternized alkali lignin powder, and stir with a high-speed mixer at a speed of 500-800 rpm for 30-45 minutes to form a slurry; spread the mixed slurry evenly on a tray, put it in an oven, and dry at 85℃ to obtain a block composite material, crush it with a pulverizer, and pass it through a 20-40 mesh sieve to obtain the final composite water-retaining agent.

[0023] The implementation method of the structure modifier is as follows:

[0024] Mix the soil conditioner with the soil at a depth of 20-30 cubic meters per acre, 5-8 cm above the soil surface. After letting the soil stand for 7-10 days, mix it again with the soil at a depth of 20-25 cm, at a depth of 40-50 cubic meters per acre.

[0025] The advantages and beneficial effects of this invention are as follows:

[0026] 1. The soil conditioner in this application achieves a synergistic improvement in soil structure, nutrient efficiency, and microbial environment through the scientific and orderly compounding of composite biochar, phosphate rock powder, straw short fiber, water-retaining agent, and microbial inoculum. This conditioner can quickly and effectively break up soil compaction, significantly reduce soil bulk density, increase porosity, optimize the three-phase structure, and promote the formation of durable and stable aggregates. Simultaneously, by enhancing water retention and ion exchange capacity, it greatly improves the soil's water and fertilizer retention capacity and nutrient utilization rate. The highly active microbial community further stimulates soil microbial activity, improves the micro-ecological environment, and inhibits the reproduction of pathogens. This product is environmentally friendly, uses widely available and renewable raw materials, has a simple and low-cost preparation process, and is suitable for the ecological restoration and soil fertility improvement of acidified, compacted, and infertile soils, demonstrating significant comprehensive improvement effects and application prospects.

[0027] 2. In this application, the composite biochar uses sawdust and rice husks as biochar precursors, which are not only widely available and inexpensive, but also an effective way to utilize agricultural waste resources. Furthermore, white phosphogypsum, a naturally rich phosphorus mineral, is introduced. Through its composite treatment with biochar, the functions of organic carbon materials and inorganic minerals are integrated, providing a sustained and efficient phosphorus supply for the modifier. A robust composite of white phosphogypsum and biochar is achieved through a combination of liquid-phase loading and medium-temperature pyrolysis. First, the mixture is subjected to oscillation in a liquid-phase suspension system, using mechanical action and temperature conditions to promote the full dispersion of white phosphogypsum particles and their attachment to the surface and internal channels of the biochar's porous structure. Subsequently, controlled-temperature pyrolysis is carried out under an inert atmosphere. This process not only carbonizes the biochar precursor to form a stable porous structure, but also promotes a stronger physicochemical bond between the white phosphogypsum and the carbon matrix through thermodynamic action, thereby significantly improving the stability and functionality of the composite material.

[0028] 3. The composite of white phosphogypsum and biochar significantly improves phosphorus utilization efficiency. The porous structure of biochar provides a good dispersion carrier for white phosphogypsum, effectively preventing the agglomeration and fixation of phosphate rock powder. Simultaneously, biochar itself has an adsorption and protective effect on phosphorus in the soil. The two work synergistically to reduce phosphorus fixation and loss in the soil, achieving slow release and long-term supply of phosphorus. Secondly, the pore structure of the composite biochar is optimized, and the introduction of white phosphogypsum further enriches its surface chemical properties, enhancing its adsorption capacity and retention capacity for nutrient elements, providing a more suitable habitat for microorganisms. Thirdly, this composite material combines the soil-amortizing properties of biochar with the phosphorus supply function of white phosphogypsum, avoiding the component separation or unevenness problems that may result from simple physical mixing. When applied to soil conditioners, this composite biochar can significantly improve soil fertility and structure, and promote crop root development and nutrient absorption.

[0029] 4. The processing technology for short straw fibers employs an alkaline cooking method combined with anthraquinone adjuvant. Adding anthraquinone as a cooking adjuvant effectively promotes lignin removal and fiber softening. Anthraquinone undergoes a redox reaction in an alkaline environment, cyclically disrupting the lignin structure and protecting carbohydrates from degradation, thereby significantly improving fiber yield and strength. Compared to traditional methods without anthraquinone or using other adjuvants, this mechanism achieves more complete fiber separation under lower alkali dosage and milder process conditions, reducing damage to cellulose from strong alkali, while also lowering energy and chemical consumption. Secondly, the use of anthraquinone adjuvant enhances the penetration of the cooking solution into the straw and the uniformity of the reaction, making subsequent thermomechanical treatment easier. After cooking, a large amount of lignin and hemicellulose dissolves from the fiber pulp, resulting in a more intact fiber morphology and increased surface area, which is beneficial for subsequent washing and drying processes. This process ensures good flexibility and dispersibility of the straw fibers.

[0030] 5. In this application, quaternized alkali lignin, attapulgite, and a microbial community support system are selected as the three core components of the composite water-retaining agent. This fully leverages the inherent properties of each material and achieves performance enhancement through their interaction. After modification, quaternized alkali lignin possesses an amphiphilic structure, containing hydrophilic groups to effectively capture water while also exhibiting colloidal stability and ion exchange capacity, thus delaying water evaporation and reducing nutrient loss. Attapulgite, as a natural mineral material, has a unique layered chain structure and abundant internal surface pores, enabling it to physically adsorb large amounts of water while enhancing the mechanical stability of the matrix and preventing the rapid degradation of organic components. Although the mixed microbial solution does not directly participate in the formation of the water-retaining agent, its presence is closely related to the functional performance of the water-retaining agent after application, providing a foundation for subsequent soil microecological restoration.

[0031] 6. Quaternized alkali lignin and attapulgite can form an organic-inorganic hybrid network at the interface. Attapulgite, as a nanoscale reinforcing phase, can be dispersed in the matrix formed by quaternized alkali lignin. This increases the specific surface area and porosity of the material, thereby improving the overall water absorption capacity and rate. It also enhances the mechanical strength of the gel network, allowing it to maintain good structural integrity after water absorption and preventing collapse and failure. Furthermore, the functional groups carried by quaternized alkali lignin may interact with the surface of attapulgite, further stabilizing the composite system. This composite water-retaining agent has multiple advantages over existing conventional technologies. Traditional water-retaining agents often focus on a single water absorption function, and the material types are mostly synthetic polymers or single minerals. Although the water absorption rate may be high, they generally suffer from problems such as difficult degradation, poor environmental compatibility, single function, and potential damage to soil structure with long-term use.

[0032] 7. This water-retaining agent not only efficiently absorbs and retains moisture, but its three-dimensional network structure also serves as a sanctuary and carbon source for soil microorganisms, providing a favorable environment for the survival and colonization of beneficial microorganisms such as Bacillus megaterium, Bacillus mucilaginosus, and Trichoderma harzianum. This means that while performing water-saving functions, this water-retaining agent also has multiple functions such as improving soil structure, promoting nutrient activation, and stimulating crop growth, achieving an integrated system of water retention, fertilizer retention, and growth promotion.

[0033] 8. In summary, the advantage of this combined strategy lies in its ingenious integration of the potential of organic modified materials, inorganic mineral materials, and biological functions. Through the synergistic effect of multiple components, it not only optimizes water retention performance but also expands its comprehensive benefits in soil health and fertility improvement, representing a more systematic and sustainable direction for the design of agricultural improvement materials.

[0034] 9. Furthermore, the method of using the soil conditioner in this application firstly involves rapidly creating a loose, water-retaining, and fertilizer-retaining seedbed layer in the shallow layer, which is conducive to seed germination and early root growth of seedlings; subsequently, before the crop roots penetrate deep, the deep soil is thoroughly improved, breaking up the plow pan, significantly enhancing soil permeability, water retention capacity, and fertilizer supply potential, thereby creating a uniform, fertile, and well-developed optimized environment for the entire crop growth period, achieving increased yield and efficiency. Detailed Implementation

[0035] The present invention will be further described in detail below with reference to the embodiments.

[0036] Example 1

[0037] Preparation of composite biochar: Wood chips and rice husks were prepared, washed, dried, pulverized, and sieved through a 100-mesh sieve. White phosphogypsum powder was added to deionized water to form a uniformly dispersed suspension. The mass ratio of white phosphogypsum to water was 1:20, and the dry weight ratio of biochar to white phosphogypsum was 3:1. The mixture was placed in a constant-temperature shaker and shaken at 180 rpm for 8 hours at 50°C. After shaking, the mixture was vacuum filtered or centrifuged to separate the solid composite. The solid composite was placed in an oven at 105°C and dried for 24 hours until completely dry, yielding a preliminary composite powder. The composite powder was placed in a muffle furnace, and nitrogen gas was introduced to raise the temperature from room temperature to 50°C at a rate of 8°C / min, and held for 1.5 hours. After cooling to room temperature, the mixture was ground and passed through a 30-mesh sieve to obtain composite biochar.

[0038] Preparation of short straw fibers: Rice, wheat, and corn stalks were dried and shredded into 4 cm pieces. The straw pieces were then placed in a digester, where a 10% NaOH solution was prepared. The weight ratio of the solution to the straw was controlled at 5:1. Anthraquinone (0.08% by mass) was added to the mixture. The temperature was increased to 115℃ at a rate of 1.2℃ / min and held for 25 min. Then, the temperature was increased to 160℃ at a rate of 4℃ / min, and the pressure was maintained at 0.8 MPa. The temperature and pressure were maintained for 2 h. The pulp was then instantly depressurized to 0.2 MPa and discharged into a spray chamber. It was repeatedly washed with 55℃ hot water until the water was clear and the pH was neutral to obtain fiber pulp. The pulp was centrifuged to remove water until the moisture content was 38%. Then, it was placed in a drum dryer and dried at 112℃ until the moisture content was 10% to obtain short straw fibers.

[0039] The water-retaining agent is composed of alkali lignin, glycidyltrimethylammonium chloride, and attapulgite. The preparation process is as follows:

[0040] (1) Alkali lignin pretreatment: 100 parts of alkali lignin powder were mixed with deionized water at a mass ratio of 1:15. NaOH solution was slowly added under stirring to adjust the pH to 10.5 to form a homogeneous system. The mixture was stirred at 60℃ for 1 h, and then heated to 70℃. 35 parts of glycidyltrimethylammonium chloride were added dropwise to the system. After the addition was completed, the mixture was stirred at 70℃ for 200 rpm for 3.5 h. Then, dilute hydrochloric acid was added to adjust the pH to neutral. The precipitate was collected by vacuum filtration. The precipitate was washed three times with 50% ethanol solution. The washed precipitate was dried in an oven at 65℃ to constant weight. The dried block product was crushed with a pulverizer to obtain quaternized alkali lignin powder for later use.

[0041] (2) Water-retaining agent mixing: Quaternized alkali lignin powder and deionized water are mixed at a mass ratio of 1:20 and stirred at 50°C for 2 hours. Add attapulgite clay with a mass of 3 times that of quaternized alkali lignin powder and stir at 650 rpm for 38 minutes to form a slurry. Spread the mixed slurry evenly on a tray, put it in an oven, and dry it at 85°C to obtain a block composite material. Crush it with a pulverizer and pass it through a 30-mesh sieve to obtain the final composite water-retaining agent.

[0042] 55 parts by weight of composite biochar, 35 parts by weight of phosphate rock powder, and 15 parts by weight of short straw fiber were added to a mixer and run at a low speed of 25 rpm for 18 minutes. Then, 6 parts by weight of water-retaining agent were added, and mixing continued at 25 rpm for 12 minutes. The microbial mixed inoculum was prepared by mixing Bacillus megaterium, Bacillus colloidis, and Trichoderma harzianum in equal proportions, with a viable count ≥10. 8 For CFU / mL, dilute 8 parts by weight of the microbial mixed bacterial solution with 1.5 times its weight of sterile water. Spray the diluted bacterial solution onto the mixture while stirring the mixture at a low speed of 12 rpm. After the bacterial solution is added, continue to run the mixer at a low speed of 12 rpm for 5 minutes. Transfer the mixed improver to a cool, dark place and let it stand for 36 hours to mature.

[0043] Example 2

[0044] Preparation of composite biochar: Wood chips and rice husks were prepared, washed, dried, pulverized, and sieved through a 100-mesh sieve. White phosphogypsum powder was added to deionized water to form a uniformly dispersed suspension. The mass ratio of white phosphogypsum to water was 1:20, and the dry weight ratio of biochar to white phosphogypsum was 2:1. The mixture was placed in a constant-temperature shaker and shaken at 150 rpm for 12 hours at 60°C. After shaking, the mixture was vacuum filtered or centrifuged to separate the solid composite. The solid composite was placed in an oven at 105°C and dried for 24 hours until completely dry, yielding a preliminary composite powder. The composite powder was placed in a muffle furnace, and nitrogen gas was introduced to raise the temperature from room temperature to 400°C at a rate of 10°C / min, holding for 1 hour. After cooling to room temperature, the mixture was ground and passed through a 20-mesh sieve to obtain composite biochar.

[0045] Preparation of short straw fibers: Rice, wheat, and corn stalks were dried and shredded into 5 cm pieces. The straw pieces were then placed in a cooking tank, where a 5% NaOH solution was prepared. The weight ratio of the solution to the straw was controlled at 6:1. Anthraquinone (0.05% by mass) was added to the mixture. The temperature was increased to 110℃ at a rate of 1.5℃ / min and held for 30 min. Then, the temperature was increased to 150℃ at a rate of 5℃ / min, and the pressure was maintained at 1.0 MPa. The temperature and pressure were maintained for 1 h. The pulp was then instantly depressurized to 0.3 MPa and discharged into a spray chamber. It was repeatedly washed with 60℃ hot water until the water was clear and the pH was neutral to obtain fiber pulp. The pulp was centrifuged to remove water until the moisture content was 35%. Then, it was placed in a drum dryer and dried at 120℃ until the moisture content was 5% to obtain short straw fibers.

[0046] The water-retaining agent is composed of alkali lignin, glycidyltrimethylammonium chloride, and attapulgite. The preparation process is as follows:

[0047] (1) Alkali lignin pretreatment: 100 parts of alkali lignin powder were mixed with deionized water at a mass ratio of 1:15. NaOH solution was slowly added under stirring to adjust the pH to 10 to form a homogeneous system. The mixture was stirred at 60℃ for 1 h, and then heated to 72℃. 30 parts of glycidyltrimethylammonium chloride were added dropwise to the system. After the addition was completed, the mixture was stirred at 70℃ for 200 rpm for 4 h. Then, dilute hydrochloric acid was added to adjust the pH to neutral. The precipitate was collected by vacuum filtration. The precipitate was washed three times with 50% ethanol solution. The washed precipitate was dried in an oven at 60℃ to constant weight. The dried block product was crushed with a pulverizer to obtain quaternized alkali lignin powder for later use.

[0048] (2) Water-retaining agent mixing: Quaternized alkali lignin powder and deionized water are mixed at a mass ratio of 1:20 and stirred at 50°C for 2 hours. Attapulgite clay with a mass of 4 times that of quaternized alkali lignin powder is added and stirred at 500 rpm for 45 minutes using a high-speed mixer to form a slurry. The mixed slurry is evenly spread on a tray, placed in an oven, and dried at 85°C to obtain a block composite material. The block composite material is crushed by a pulverizer and passed through a 20-mesh sieve to obtain the final composite water-retaining agent.

[0049] Add 50 parts by weight of composite biochar, 40 parts by weight of phosphate rock powder, and 10 parts by weight of short straw fiber to a mixer and run at a low speed of 30 rpm for 15 minutes. Then add 8 parts by weight of water-retaining agent and continue mixing at a speed of 20 rpm for 15 minutes. The microbial mixed bacterial solution is prepared by mixing Bacillus megaterium, Bacillus colloidis, and Trichoderma harzianum in equal proportions, with a viable count ≥10. 8For CFU / mL, dilute 5 parts by weight of the microbial mixed bacterial solution with twice its weight of sterile water. Spray the diluted bacterial solution onto the mixture while stirring the mixture at a low speed of 10 rpm. After the bacterial solution is added, continue to run the mixer at a low speed of 15 rpm for 5 minutes. Transfer the mixed improver to a cool, dark place and let it stand for 24 hours to mature.

[0050] Example 3

[0051] Preparation of composite biochar: Wood chips and rice husks were prepared, washed, dried, pulverized, and sieved through a 100-mesh sieve. White phosphogypsum powder was added to deionized water to form a uniformly dispersed suspension. The mass ratio of white phosphogypsum to water was 1:20, and the dry weight ratio of biochar to white phosphogypsum was 5:1. The mixture was placed in a constant-temperature shaker and shaken at 200 rpm for 4 hours at 40°C. After shaking, the mixture was vacuum filtered or centrifuged to separate the solid composite. The solid composite was placed in an oven at 105°C and dried for 24 hours until completely dry, yielding a preliminary composite powder. The composite powder was placed in a muffle furnace, and nitrogen gas was introduced to raise the temperature from room temperature to 300°C at a rate of 5°C / min, and held for 2 hours. After cooling to room temperature, the mixture was ground and passed through a 40-mesh sieve to obtain composite biochar.

[0052] Preparation of short straw fibers: Rice, wheat, and corn stalks were dried and shredded into 3 cm pieces. The straw pieces were then put into a cooking tank, where a 15% NaOH solution was prepared. The weight ratio of the solution to the straw was controlled at 4:1. Anthraquinone (0.1% by mass) was added to the mixture. The temperature was increased to 120℃ at a rate of 1℃ / min and held for 20 min. Then, the temperature was increased to 170℃ at a rate of 2℃ / min, and the pressure was maintained at 0.6 MPa. The temperature and pressure were maintained for 3 h. The pulp was then instantly depressurized to 0.2 MPa and discharged into a spray chamber. It was repeatedly washed with 50℃ hot water until the water was clear and the pH was neutral to obtain fiber pulp. The pulp was centrifuged to remove water until the moisture content was 40%. Then, it was placed in a drum dryer and dried at 105℃ until the moisture content was 8% to obtain short straw fibers.

[0053] The water-retaining agent is composed of alkali lignin, glycidyltrimethylammonium chloride, and attapulgite. The preparation process is as follows:

[0054] (1) Alkali lignin pretreatment: 100 parts of alkali lignin powder were mixed with deionized water at a mass ratio of 1:15. NaOH solution was slowly added under stirring to adjust the pH to 11 to form a homogeneous system. The mixture was stirred at 60°C for 1 h, and then heated to 68°C. 40 parts of glycidyltrimethylammonium chloride were added dropwise to the system. After the addition was completed, the mixture was stirred at 70°C for 200 rpm for 3 h. Then, dilute hydrochloric acid was added to adjust the pH to neutral. The precipitate was collected by vacuum filtration. The precipitate was washed three times with 50% ethanol solution. The washed precipitate was dried in an oven at 70°C to constant weight. The dried block product was crushed with a pulverizer to obtain quaternized alkali lignin powder for later use.

[0055] (2) Water-retaining agent mixing: Quaternized alkali lignin powder and deionized water are mixed at a mass ratio of 1:20 and stirred at 50°C for 2 hours. Attapulgite clay with a mass of 2 times that of quaternized alkali lignin powder is added and stirred at 800 rpm for 30 minutes using a high-speed mixer to form a slurry. The mixed slurry is evenly spread on a tray, placed in an oven, and dried at 85°C to obtain a block composite material. The block composite material is crushed by a pulverizer and passed through a 40-mesh sieve to obtain the final composite water-retaining agent.

[0056] Add 60 parts by weight of composite biochar, 30 parts by weight of phosphate rock powder, and 20 parts by weight of short straw fiber into a mixer and run at a low speed of 20 rpm for 20 minutes. Then add 5 parts by weight of water-retaining agent and continue mixing at 30 rpm for 10 minutes. The microbial mixed inoculum is prepared by mixing Bacillus megaterium, Bacillus colloidis, and Trichoderma harzianum in equal proportions, with a viable count ≥10. 8 For CFU / mL, dilute 10 parts by weight of the microbial mixed bacterial solution with 1 times its weight of sterile water. Spray the diluted bacterial solution onto the mixture while stirring the mixture at a low speed of 15 rpm. After the bacterial solution is added, continue to run the mixer at a low speed of 10 rpm for 5 minutes. Transfer the mixed improver to a cool, dark place and let it stand for 48 hours to mature.

[0057] Comparative Example 1

[0058] Preparation of composite biochar: Prepare sawdust and rice husk raw materials, wash, dry, crush and sieve through 100 mesh; put them into a muffle furnace, introduce nitrogen gas and raise the temperature from room temperature to 50℃ at a rate of 8℃ / min, and keep it at this temperature for 1.5h; after cooling to room temperature, grind and pass through a 30-mesh sieve to obtain biochar.

[0059] Preparation of short straw fibers: Rice, wheat, and corn stalks were dried and shredded into 4 cm pieces. The straw pieces were then put into a cooking tank, where a 10% NaOH solution was prepared, with the weight ratio of the solution to the straw controlled at 5:1. The temperature was increased to 115℃ at a rate of 1.2℃ / min and held for 25 min. Then, the temperature was increased to 160℃ at a rate of 4℃ / min, and the pressure was maintained at 0.8 MPa. The temperature and pressure were maintained for 2 h. The pulp was then instantly depressurized to 0.2 MPa and discharged into a spray chamber. It was repeatedly washed with 55℃ hot water until the water was clear and the pH was neutral to obtain fiber pulp. The pulp was centrifuged to remove water until the moisture content was 38%, and then placed in a drum dryer and dried at 112℃ until the moisture content was 10% to obtain short straw fibers.

[0060] The water-retaining agent is composed of alkali lignin, glycidyltrimethylammonium chloride, and attapulgite. The preparation process is as follows:

[0061] (1) Alkali lignin pretreatment: 100 parts of alkali lignin powder were mixed with deionized water at a mass ratio of 1:15. NaOH solution was slowly added under stirring to adjust the pH to 10.5 to form a homogeneous system. The mixture was stirred at 60℃ for 1 h, and then heated to 70℃. 35 parts of glycidyltrimethylammonium chloride were added dropwise to the system. After the addition was completed, the mixture was stirred at 70℃ for 200 rpm for 3.5 h. Then, dilute hydrochloric acid was added to adjust the pH to neutral. The precipitate was collected by vacuum filtration. The precipitate was washed three times with 50% ethanol solution. The washed precipitate was dried in an oven at 65℃ to constant weight. The dried block product was crushed with a pulverizer to obtain quaternized alkali lignin powder for later use.

[0062] (2) Water-retaining agent mixing: Quaternized alkali lignin powder and deionized water are mixed at a mass ratio of 1:20 and stirred at 50°C for 2 hours. Add attapulgite clay with a mass of 3 times that of quaternized alkali lignin powder and stir at 650 rpm for 38 minutes to form a slurry. Spread the mixed slurry evenly on a tray, put it in an oven, and dry it at 85°C to obtain a block composite material. Crush it with a pulverizer and pass it through a 30-mesh sieve to obtain the final composite water-retaining agent.

[0063] 55 parts by weight of composite biochar, 35 parts by weight of phosphate rock powder, and 15 parts by weight of short straw fiber were added to a mixer and run at a low speed of 25 rpm for 18 minutes. Then, 6 parts by weight of water-retaining agent were added, and mixing continued at 25 rpm for 12 minutes. The microbial mixed inoculum was prepared by mixing Bacillus megaterium, Bacillus colloidis, and Trichoderma harzianum in equal proportions, with a viable count ≥10. 8For CFU / mL, dilute 8 parts by weight of the microbial mixed bacterial solution with 1.5 times its weight of sterile water. Spray the diluted bacterial solution onto the mixture while stirring the mixture at a low speed of 12 rpm. After the bacterial solution is added, continue to run the mixer at a low speed of 12 rpm for 5 minutes. Transfer the mixed improver to a cool, dark place and let it stand for 36 hours to mature.

[0064] Comparative Example 2

[0065] Preparation of composite biochar: Prepare sawdust and rice husk raw materials, wash, dry, crush and sieve through 100 mesh; put them into a muffle furnace, introduce nitrogen gas and raise the temperature from room temperature to 50℃ at a rate of 8℃ / min, and keep it at this temperature for 1.5h; after cooling to room temperature, grind and pass through a 30-mesh sieve to obtain biochar.

[0066] Preparation of short straw fibers: Rice, wheat, and corn stalks were dried and shredded into 4 cm pieces. The straw pieces were then placed in a digester, where a 10% NaOH solution was prepared. The weight ratio of the solution to the straw was controlled at 5:1. Anthraquinone (0.08% by mass) was added to the mixture. The temperature was increased to 115℃ at a rate of 1.2℃ / min and held for 25 min. Then, the temperature was increased to 160℃ at a rate of 4℃ / min, and the pressure was maintained at 0.8 MPa. The temperature and pressure were maintained for 2 h. The pulp was then instantly depressurized to 0.2 MPa and discharged into a spray chamber. It was repeatedly washed with 55℃ hot water until the water was clear and the pH was neutral to obtain fiber pulp. The pulp was centrifuged to remove water until the moisture content was 38%. Then, it was placed in a drum dryer and dried at 112℃ until the moisture content was 10% to obtain short straw fibers.

[0067] The water-retaining agent is composed of alkali lignin, glycidyltrimethylammonium chloride, and attapulgite. The preparation process is as follows:

[0068] (1) Alkali lignin pretreatment: 100 parts of alkali lignin powder were mixed with deionized water at a mass ratio of 1:15. NaOH solution was slowly added under stirring to adjust the pH to 10.5 to form a homogeneous system. The mixture was stirred at 60℃ for 1 h, and then heated to 70℃. 35 parts of glycidyltrimethylammonium chloride were added dropwise to the system. After the addition was completed, the mixture was stirred at 70℃ for 200 rpm for 3.5 h. Then, dilute hydrochloric acid was added to adjust the pH to neutral. The precipitate was collected by vacuum filtration. The precipitate was washed three times with 50% ethanol solution. The washed precipitate was dried in an oven at 65℃ to constant weight. The dried block product was crushed with a pulverizer to obtain quaternized alkali lignin powder for later use.

[0069] (2) Water-retaining agent mixing: Quaternized alkali lignin powder and deionized water are mixed at a mass ratio of 1:20 and stirred at 50°C for 2 hours. Add attapulgite clay with a mass of 3 times that of quaternized alkali lignin powder and stir at 650 rpm for 38 minutes to form a slurry. Spread the mixed slurry evenly on a tray, put it in an oven, and dry it at 85°C to obtain a block composite material. Crush it with a pulverizer and pass it through a 30-mesh sieve to obtain the final composite water-retaining agent.

[0070] 55 parts by weight of composite biochar, 35 parts by weight of phosphate rock powder, and 15 parts by weight of short straw fiber were added to a mixer and run at a low speed of 25 rpm for 18 minutes. Then, 6 parts by weight of water-retaining agent were added, and mixing continued at 25 rpm for 12 minutes. The microbial mixed inoculum was prepared by mixing Bacillus megaterium, Bacillus colloidis, and Trichoderma harzianum in equal proportions, with a viable count ≥10. 8 For CFU / mL, dilute 8 parts by weight of the microbial mixed bacterial solution with 1.5 times its weight of sterile water. Spray the diluted bacterial solution onto the mixture while stirring the mixture at a low speed of 12 rpm. After the bacterial solution is added, continue to run the mixer at a low speed of 12 rpm for 5 minutes. Transfer the mixed improver to a cool, dark place and let it stand for 36 hours to mature.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that in this comparative example, leucobrycete is replaced with hydroxyapatite; otherwise, it is the same as in Example 1.

[0073] Comparative Example 4

[0074] Preparation of composite biochar: Wood chips and rice husks were prepared, washed, dried, pulverized, and sieved through a 100-mesh sieve. White phosphogypsum powder was added to deionized water to form a uniformly dispersed suspension. The mass ratio of white phosphogypsum to water was 1:20, and the dry weight ratio of biochar to white phosphogypsum was 3:1. The mixture was placed in a constant-temperature shaker and shaken at 180 rpm for 8 hours at 50°C. After shaking, the mixture was vacuum filtered or centrifuged to separate the solid composite. The solid composite was placed in an oven at 105°C and dried for 24 hours until completely dry, yielding a preliminary composite powder. The composite powder was placed in a muffle furnace, and nitrogen gas was introduced to raise the temperature from room temperature to 50°C at a rate of 8°C / min, and held for 1.5 hours. After cooling to room temperature, the mixture was ground and passed through a 30-mesh sieve to obtain composite biochar.

[0075] Preparation of short straw fibers: Rice, wheat, and corn stalks were dried and shredded into 4 cm pieces. The straw pieces were then put into a cooking tank, where a 10% NaOH solution was prepared, with the weight ratio of the solution to the straw controlled at 5:1. The temperature was increased to 115℃ at a rate of 1.2℃ / min and held for 25 min. Then, the temperature was increased to 160℃ at a rate of 4℃ / min, and the pressure was maintained at 0.8 MPa. The temperature and pressure were maintained for 2 h. The pulp was then instantly depressurized to 0.2 MPa and discharged into a spray chamber. It was repeatedly washed with 55℃ hot water until the water was clear and the pH was neutral to obtain fiber pulp. The pulp was centrifuged to remove water until the moisture content was 38%, and then placed in a drum dryer and dried at 112℃ until the moisture content was 10% to obtain short straw fibers.

[0076] The water-retaining agent is composed of alkali lignin, glycidyltrimethylammonium chloride, and attapulgite. The preparation process is as follows:

[0077] (1) Alkali lignin pretreatment: 100 parts of alkali lignin powder were mixed with deionized water at a mass ratio of 1:15. NaOH solution was slowly added under stirring to adjust the pH to 10.5 to form a homogeneous system. The mixture was stirred at 60℃ for 1 h, and then heated to 70℃. 35 parts of glycidyltrimethylammonium chloride were added dropwise to the system. After the addition was completed, the mixture was stirred at 70℃ for 200 rpm for 3.5 h. Then, dilute hydrochloric acid was added to adjust the pH to neutral. The precipitate was collected by vacuum filtration. The precipitate was washed three times with 50% ethanol solution. The washed precipitate was dried in an oven at 65℃ to constant weight. The dried block product was crushed with a pulverizer to obtain quaternized alkali lignin powder for later use.

[0078] (2) Water-retaining agent mixing: Quaternized alkali lignin powder and deionized water are mixed at a mass ratio of 1:20 and stirred at 50°C for 2 hours. Add attapulgite clay with a mass of 3 times that of quaternized alkali lignin powder and stir at 650 rpm for 38 minutes to form a slurry. Spread the mixed slurry evenly on a tray, put it in an oven, and dry it at 85°C to obtain a block composite material. Crush it with a pulverizer and pass it through a 30-mesh sieve to obtain the final composite water-retaining agent.

[0079] 55 parts by weight of composite biochar, 35 parts by weight of phosphate rock powder, and 15 parts by weight of short straw fiber were added to a mixer and run at a low speed of 25 rpm for 18 minutes. Then, 6 parts by weight of water-retaining agent were added, and mixing continued at 25 rpm for 12 minutes. The microbial mixed inoculum was prepared by mixing Bacillus megaterium, Bacillus colloidis, and Trichoderma harzianum in equal proportions, with a viable count ≥10. 8For CFU / mL, dilute 8 parts by weight of the microbial mixed bacterial solution with 1.5 times its weight of sterile water. Spray the diluted bacterial solution onto the mixture while stirring the mixture at a low speed of 12 rpm. After the bacterial solution is added, continue to run the mixer at a low speed of 12 rpm for 5 minutes. Transfer the mixed improver to a cool, dark place and let it stand for 36 hours to mature.

[0080] Comparative Example 5

[0081] The difference between this comparative example and Example 1 is that anthraquinone is replaced with triethanolamine in this comparative example; otherwise, it is the same as in Example 1.

[0082] Comparative Example 6

[0083] The difference between this comparative example and Example 1 is that in this comparative example, the water-retaining agent consists of sodium lignosulfonate and attapulgite. Sodium lignosulfonate and deionized water are mixed at a mass ratio of 1:20 and stirred at 50°C for 2 hours. Three times the mass of attapulgite is added to the mixture, which is then stirred at 650 rpm for 38 minutes using a high-speed mixer to form a slurry. The mixed slurry is evenly spread on a tray, placed in an oven, and dried at 85°C to obtain a block composite material. This block composite material is then pulverized using a pulverizer and passed through a 30-mesh sieve to obtain the final composite water-retaining agent. The rest is the same as in Example 1.

[0084] Comparative Example 7

[0085] The difference between this comparative example and Example 1 is that the water-retaining agent in this comparative example consists of alkali lignin and glycidyltrimethylammonium chloride. The preparation process is as follows: 100 parts of alkali lignin powder are mixed with deionized water at a mass ratio of 1:15. NaOH solution is slowly added under stirring to adjust the pH to 10.5 to form a homogeneous system. The mixture is stirred at 60°C for 1 hour, and then heated to 70°C. 35 parts by mass of glycidyltrimethylammonium chloride are added dropwise to the system. After the addition is complete, the mixture is stirred at 70°C and 200 rpm for 3.5 hours. Then, dilute hydrochloric acid is added to adjust the pH to neutral. The precipitate is collected by vacuum filtration. The precipitate is washed three times with 50% ethanol solution. The washed precipitate is dried in an oven at 65°C to constant weight. The dried block product is pulverized with a pulverizer to obtain quaternized alkali lignin powder for use as a water-retaining agent. The rest is the same as in Example 1.

[0086] Experiment 1: Soil property testing

[0087] On heavy, compacted soils, the soil conditioners obtained in Examples 1-3 and Comparative Examples 1-7 were used. First, the conditioner prepared in Example 1 was mixed with the soil at a rate of 25 cubic meters per acre at a depth of 6 cm on the soil surface. After the soil was left to stand for 8 days, it was mixed again at a depth of 22 cm on the soil surface at a rate of 45 cubic meters per acre. After 3 months, the soil bulk density, pH value, and field water holding capacity were tested. At the same time, the effect of the conditioner in Example 1 was tested by applying it in one step on the same heavy, compacted soil. Specifically, the one-step application involved adding 70 cubic meters per acre of the conditioner prepared in Example 1 at a depth of 22 cm on the soil surface and then mixing it with the soil.

[0088] Soil bulk density was determined using the ring sampler method, referring to "Soil Testing Part 4: Determination of Soil Bulk Density" NY / T 1121.4-2006; soil pH was determined using the water extraction method (soil-to-water ratio of 1:2.5) according to HJ962-2018; field capacity was determined according to "Soil Testing Part 22: Determination of Soil Field Capacity - Ring Sampler Method" (NY / T 1121.22-2010). The changes before and after the experiment are shown in Table 1.

[0089] Table 1

[0090] Sample processing <![CDATA[Soil bulk density (g / cm 3 )]]> Soil pH Field water holding capacity (%) Before the experiment 1.51 5.5 22.48 One application 1.18 6.5 33.29 Example 1 1.09 6.8 36.75 Example 2 1.13 6.6 35.18 Example 3 1.15 6.7 35.62 Comparative Example 1 1.32 6.1 25.43 Comparative Example 2 1.26 6.3 30.74 Comparative Example 3 1.23 6.4 32.05 Comparative Example 4 1.34 6.2 25.83 Comparative Example 5 1.28 6.5 31.69 Comparative Example 6 1.35 6.0 24.37 Comparative Example 7 1.20 6.6 32.42

[0091] Experiment 2: Soil activity test results

[0092] (1) Soil organic matter: determined by the dilution thermal method of potassium dichromate (NY / T85-1988).

[0093] (2) Soil EC: The soil EC was determined by the HJ802-2016 water extraction method (soil-water mass ratio of 1:5). The results are shown in Table 2.

[0094] Table 2

[0095] Sample processing Organic matter (g / kg) EC (us / cm) Before the experiment 12.58 137.84 One application 18.29 205.63 Example 1 21.81 215.57 Example 2 20.16 210.24 Example 3 20.08 208.81 Comparative Example 1 14.92 148.96 Comparative Example 2 16.37 156.12 Comparative Example 3 17.65 164.78 Comparative Example 4 13.83 146.40 Comparative Example 5 15.70 152.36 Comparative Example 6 14.42 150.57 Comparative Example 7 17.58 197.04

Claims

1. A structural improver for heavy, compacted soil, characterized in that, The specific preparation process is as follows: Add 50 parts by weight of composite biochar, 40 parts by weight of phosphate rock powder, and 10 parts by weight of short straw fiber into a mixer and run at a low speed of 30 rpm for 15 minutes. Then add 8 parts by weight of water-retaining agent and continue mixing at a speed of 20 rpm for 15 minutes. Dilute 5 parts by weight of microbial mixed bacterial solution with twice its weight of sterile water and spray the diluted bacterial solution onto the mixture while keeping the mixture stirred at a low speed of 10 rpm. After the bacterial solution is added, continue running the mixer at a low speed of 15 rpm for 5 minutes. Transfer the mixed improver to a cool, dark place and let it stand and mature for 24 hours. The microbial mixed bacterial solution is prepared by mixing Bacillus megaterium, Bacillus mucilaginosus, and Trichoderma harzianum in equal proportions, with a viable count ≥10⁻⁶. 8 CFU / mL; The preparation of the composite biochar is as follows: Wood chips and rice husks are prepared, washed, dried, pulverized, and sieved through a 100-mesh sieve; white phosphogypsum powder is added to deionized water to form a uniformly dispersed suspension, with a white phosphogypsum to water mass ratio of 1:20 and a wood chip mixture to white phosphogypsum dry weight addition ratio of 2:

1. The mixture is placed in a constant temperature shaker and shaken at 150 rpm for 12 hours at 60°C. After shaking, the mixture is vacuum filtered or centrifuged to separate the solid composite; the solid composite is placed in an oven at 105°C and dried for 24 hours until completely dry, yielding a preliminary composite powder. The composite powder was placed in a muffle furnace, and nitrogen gas was introduced to raise the temperature from room temperature to 400°C at a rate of 10°C / min, and the temperature was maintained for 1 hour. After cooling to room temperature, the powder was ground and passed through a 20-mesh sieve to obtain composite biochar. The preparation process of straw short fiber is as follows: rice, wheat, and corn stalks are dried, shredded into 5 cm segments, and then the straw segments are put into a cooking tank. A 5% NaOH solution is prepared in the cooking tank, and the weight ratio of the solution to straw is controlled at 6:

1. A cooking aid with a mass percentage of 0.05% is added to the mixture. The temperature is raised to 110℃ at a rate of 1.5℃ / min and held for 30 min. Then the temperature is raised to 150℃ at a rate of 5℃ / min, and the pressure is maintained at 1.0 MPa. Under these conditions, the temperature and pressure are maintained for 1 h. The pulp is then instantly depressurized to 0.3 MPa and discharged into a spray chamber. It is repeatedly washed with 60℃ hot water until the water is clear and the pH is neutral to obtain fiber pulp. The pulp is centrifuged to remove water to a moisture content of 35%, and then placed in a drum dryer and dried at 120℃ to a moisture content of 5% to obtain straw short fiber. The water-retaining agent is composed of alkali lignin, glycidyltrimethylammonium chloride, and attapulgite; the preparation process of the water-retaining agent includes: Alkali lignin pretreatment: 100 parts by mass of alkali lignin powder and deionized water were mixed at a ratio of 1:

15. NaOH solution was slowly added under stirring to adjust the pH to 10, forming a homogeneous system. The mixture was stirred at 60°C for 1 hour, and then the temperature was raised to 72°C. 30 parts by mass of glycidyltrimethylammonium chloride were added dropwise to the system. After the addition was completed, the mixture was stirred at 70°C and 200 rpm for 4 hours. Then, dilute hydrochloric acid was added to adjust the pH to neutral. The precipitate was collected by vacuum filtration. The precipitate was washed three times with 50% ethanol solution. The washed precipitate was dried in an oven at 60°C to constant weight. The dried block product was pulverized with a pulverizer to obtain quaternized alkali lignin powder for later use. Water-retaining agent mixing: Quaternized alkali lignin powder and deionized water are mixed at a mass ratio of 1:20 and stirred at 50°C for 2 hours. Attapulgite clay with a mass of 4 times that of quaternized alkali lignin powder is added, and the mixture is stirred at 500 rpm for 45 minutes using a high-speed mixer to form a slurry. The mixed slurry is evenly spread on a tray, placed in an oven, and dried at 85°C to obtain a block composite material. The block composite material is then pulverized using a pulverizer and passed through a 20-mesh sieve to obtain the final composite water-retaining agent.

2. The structural improver for heavy, compacted soil as described in claim 1, characterized in that, In the preparation of the composite biochar, the dry weight ratio of the wood chip mixture to white phosphogypsum is 5:

1. The mixture is placed in a constant-temperature shaker and shaken at 200 rpm for 4 hours at 40°C. The composite powder is then placed in a muffle furnace, and nitrogen gas is introduced to raise the temperature from room temperature to 300°C at a rate of 5°C / min, and the temperature is maintained for 2 hours. The mixture is then passed through a 40-mesh sieve. In the preparation of the straw short fiber, the straw segments are cut into 3 cm segments, the NaOH solution has a mass fraction of 15%, the weight ratio of the solution to the straw is 4:1, the mass percentage of the cooking aid is 0.1%, and the temperature is raised to 120°C at a rate of 1°C / min. The mixture was heated to 170°C at a rate of 2°C / min for 20 minutes, and the pressure was maintained at 0.6 MPa for 3 hours. The pressure was then reduced to 0.2 MPa and discharged. The mixture was washed with 50°C hot water, centrifuged to remove water to a moisture content of 40%, and dried at 105°C to a moisture content of 8%. In the preparation of the water-retaining agent, the pH of the alkali lignin pretreatment was adjusted to 11, the temperature was raised to 68°C, 40 parts by mass of glycidyltrimethylammonium chloride were added, and the mixture was stirred for 3 hours. The precipitate was dried at 70°C. In the water-retaining agent mixture, 2 times the mass of quaternized alkali lignin powder and attapulgite were added, and the mixture was stirred at 800 rpm for 30 minutes and passed through a 40-mesh sieve.

3. A structural improver for heavy, compacted soil as described in claim 1 or 2, characterized in that, The cooking aid is anthraquinone.

4. An embodiment of a structural improver for heavy, compacted soil as described in any one of claims 1-3, characterized in that, The specific implementation process is as follows: mix the soil conditioner with the soil at a depth of 20-30 cubic meters per acre, 5-8 cm above the soil surface. After letting the soil stand for 7-10 days, mix it again with the soil at a depth of 20-25 cm, at a depth of 40-50 cubic meters per acre.