A soil conditioner and a method of making the same

Abstract

The present application relates to the technical field of soil remediation, and discloses a soil conditioner and a preparation method thereof, and provides a soil conditioner, the granule has a core-shell structure, and sequentially comprises a nutrient slow-release inner core, a pH buffering isolation intermediate layer and a rhizosphere pH response passivation outer shell from inside to outside; the nutrient slow-release inner core comprises a biochar carrier, plant required nutrients loaded on the biochar carrier, and a non-pH response slow-release coating layer coated on the outer surface of the biochar carrier; the non-pH response slow-release coating layer comprises a hydrophobic polymer; the pH buffering isolation intermediate layer comprises a pH buffering material; and the rhizosphere pH response passivation outer shell comprises a pH response type high molecular gel skeleton and a soil passivator dispersed in the pH response type high molecular gel skeleton. The soil conditioner provided by the present application integrates plant required nutrients and soil passivators, realizes simultaneous fertilization and remediation by one-time application, and reduces labor cost.

Description

Technical Field

[0001] This invention relates to the field of soil remediation technology, specifically to a soil conditioner and its preparation method. Background Technology

[0002] Heavy metal pollution in arable land is a prominent issue, and moderately polluted arable land urgently requires technical solutions for simultaneous production and remediation without fallowing or yield reduction. Existing soil conditioners (such as lime, biochar, sepiolite, and phosphate rock powder) primarily reduce the available form of heavy metals in the soil through adsorption, precipitation, and complexation, and are widely used in the remediation of polluted arable land. However, traditional soil conditioners have the following significant drawbacks in practical applications: First, traditional soil conditioners have limited functionality and poor agronomic compatibility (complex application methods). Lacking nutrient supply capabilities, traditional soil conditioners are typically applied separately from the nutrients required by plants, necessitating two separate field operations by farmers. This not only increases labor costs but also hinders mechanized simultaneous application, limiting large-scale promotion and application. Furthermore, separate application leads to inconsistent spatial distribution of soil conditioners and fertilizers in the soil, reducing the in-situ control effect of soil conditioners on rhizosphere pollution.

[0003] Secondly, traditional soil conditioners lack the ability to respond to and release in response to the rhizosphere microenvironment. The release of passivating components in existing soil conditioners is either one-time or continuous, lacking a mechanism to sense and trigger release based on dynamic changes in the crop's rhizosphere microenvironment. The physicochemical properties of the crop's rhizosphere microenvironment, such as pH and redox potential, can experience short-term, drastic fluctuations due to factors such as fertilization (especially the nitrification of ammonium nitrogen fertilizer), irrigation, and root exudates (e.g., rhizosphere pH can decrease by 0.5-1.5 units). These fluctuations represent the critical window for heavy metal activation and subsequent crop absorption. However, existing products cannot sense these dynamic changes in the rhizosphere microenvironment, failing to respond quickly to heavy metal activation and resulting in ineffective consumption of soil conditioners during non-activation periods. This leads to poor rhizosphere inhibition control, low remediation efficiency, and significant material waste.

[0004] In summary, there is an urgent need to develop a new type of soil conditioner that integrates nutrient supply and passivation functions, and can intelligently sense changes in the rhizosphere microenvironment and precisely release passivation components, so as to achieve efficient, economical and green remediation of farmland pollution. Summary of the Invention

[0005] This invention provides a soil conditioner, its preparation method, and its application, to solve the problems of existing soil conditioners having single functions, poor agronomic compatibility, and lack of rhizosphere microenvironment response and release capabilities.

[0006] In a first aspect, the present invention provides a soil conditioner, wherein the particles of the soil conditioner have a core-shell structure, comprising, from the inside out: a nutrient slow-release core, a pH buffering and isolating intermediate layer, and a rhizosphere pH-responsive passivating shell; the rhizosphere pH-responsive passivating shell is in a contracted and compacted state to seal the soil passivating agent when the pH of the rhizosphere microenvironment is higher than 6.0, and can reversibly swell to release the soil passivating agent when the pH of the rhizosphere microenvironment drops below 6.0.

[0007] The nutrient slow-release core includes a biochar carrier, plant-required nutrients loaded on the biochar carrier, and a non-pH-responsive slow-release coating layer covering the outer surface of the biochar carrier. The non-pH-responsive slow-release coating layer refers to a hydrophobic polymer coating material whose water permeability and nutrient diffusion resistance do not change significantly with changes in environmental pH. The molecular chains of the hydrophobic polymer do not contain ionized functional groups that can be protonated or deprotonated in the pH range of 4.0-9.0. The absolute value of the rate of change of the water permeability coefficient of the non-pH-responsive slow-release coating layer in the pH range of 4.0-9.0 is ≤20%.

[0008] The non-pH-responsive sustained-release coating layer comprises a hydrophobic polymer; The pH buffering isolation intermediate layer includes a pH buffering material; the pH buffering material refers to a material that can consume or adsorb the H2 produced by the release of nutrients from the core through chemical reactions (such as acid neutralization and alkali neutralization). + or OH - Functional materials that stabilize the pH of their microenvironment within a neutral range (pH=6.5-7.5).

[0009] The rhizosphere pH-responsive passivation shell includes a pH-responsive polymeric gel framework and a soil passivating agent dispersed in the pH-responsive polymeric gel framework; the pH-responsive polymeric gel framework refers to a polymeric cross-linked gel material whose swelling degree or porosity of a three-dimensional network structure can undergo reversible changes with changes in environmental pH; the pH-responsive polymeric gel framework is formed by polymeric cross-linking containing ionizable functional groups (-COOH).

[0010] In one alternative embodiment, the biochar carrier is obtained from agricultural waste through pyrolysis.

[0011] In one optional embodiment, the specific surface area of ​​the biochar carrier is ≥100 m². 2 / g.

[0012] In one alternative implementation, the agricultural waste includes one or more of corn stalks, fruit tree branches, and corn cobs.

[0013] In one alternative embodiment, the pyrolysis temperature is 300-700°C.

[0014] In one alternative embodiment, the soil conditioner satisfies at least one of the following conditions: (1) The nutrients required by the plant include one or more of nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer and micronutrient fertilizer; (2) The thickness of the non-pH-responsive sustained-release coating layer is 5-50 μm; (3) The non-pH-responsive sustained-release coating material includes at least one of polylactic acid and ethyl cellulose; (4) The particle size of the soil conditioner is 2-5 mm; (5) The mass ratio of the biochar carrier to the nutrients required by the plant is (20-40): (60-80).

[0015] In one alternative embodiment, the nitrogen fertilizer includes one or more of urea, ammonium sulfate, and ammonium chloride.

[0016] In one optional embodiment, the phosphate fertilizer includes one or more of monoammonium phosphate, superphosphate, and diammonium phosphate.

[0017] In one optional embodiment, the potassium fertilizer includes at least one of potassium sulfate and potassium chloride.

[0018] In one optional embodiment, the micronutrient fertilizer includes one or more of borax, zinc sulfate, and magnesium sulfate; the micronutrient fertilizer refers to a chemical fertilizer or organic material containing medium elements such as calcium, magnesium, and sulfur or micro elements such as boron, zinc, iron, manganese, copper, molybdenum, and chlorine required for plant growth, used to supplement insufficient soil supply and promote nutrient balance.

[0019] In one optional embodiment, the pH buffering material includes one or more of calcium carbonate, kaolin, and dolomite; In one optional embodiment, the thickness of the pH buffer isolation intermediate layer is 50-200 μm; In one alternative embodiment, the pH-responsive polymeric gel backbone comprises an alginate gel.

[0020] In one optional embodiment, the alginate gel includes one or more of calcium alginate gel, ammonium alginate gel, and sodium alginate gel.

[0021] In one optional embodiment, the soil passivating agent includes at least one of phosphate rock powder, phosphate, carbonate, silicate, mercaptochemical, and iron-based materials.

[0022] In one alternative embodiment, the silicate comprises calcium silicate; In one alternative embodiment, the phosphate comprises potassium dihydrogen phosphate; In one optional embodiment, the thiolated material includes at least one of thiolated palygorskite, thiolated diatomaceous earth, and thiolated zeolite.

[0023] In one alternative embodiment, the iron-based material includes at least one of ferrous sulfate, nano-zero valent iron, and iron-modified biochar.

[0024] In one optional embodiment, when the soil conditioner is used on cadmium-contaminated soil, the soil passivating agent includes at least one of phosphate rock powder, carbonate, silicate, and phosphate.

[0025] In one optional embodiment, when the soil conditioner is used on lead-contaminated soil, the soil passivating agent includes at least one of phosphate rock powder, mercaptochemicals, and phosphates.

[0026] In one alternative embodiment, when the soil conditioner is used on arsenic-contaminated soil, the soil passivating agent comprises an iron-based material.

[0027] Secondly, the present invention provides a method for preparing the aforementioned soil conditioner, comprising the following steps: S1. Preparation of a nutrient-slow-release core: S1-1. The biochar carrier is mixed with the nutrients required by the plant, granulated and dried to obtain the substrate granules; S1-2. The matrix is ​​coated for the first time using a non-pH-responsive slow-release coating solution to obtain a nutrient slow-release core; S2. Encapsulated pH buffering and isolation intermediate layer: S2-1. Mix the pH buffer material with the binder to prepare a suspension slurry; S2-2. The nutrient slow-release core in S1 is coated a second time using the suspension slurry to obtain particles coated with a pH buffer isolation intermediate layer; S3. Rhizosphere pH-responsive passivating shell: S3-1. Mix pH-responsive polymeric gel framework, soil passivating agent and surfactant to obtain coating slurry; S3-2. The particles coated with the pH buffer isolation intermediate layer in S2 are coated a third time using the coating slurry, and then cross-linked and cured to obtain the soil conditioner coated with a rhizosphere pH-responsive passivating shell.

[0028] In one alternative implementation, S1 satisfies at least one of the following conditions: (1) The S1-1 further includes pulverizing the biochar carrier before mixing; (2) The particle size of the granules after granulation in S1-1 is 1.5-3.0 mm; (3) The moisture content of the dried granules in S1-1 is <3%; (4) The weight gain of the first coating in S1-2 is 5%-15%; (5) The first coating step in S1-2 also includes a drying process; (6) The non-pH-responsive sustained-release coating solution in S1-2 is prepared by dissolving a hydrophobic organic film-forming material in an organic solvent.

[0029] In one optional embodiment, the particle size of the biochar carrier after pulverization in S1-1 is 80-200 mesh.

[0030] In one optional embodiment, the drying temperature after the first coating in S1-2 is 40-50°C.

[0031] In one alternative embodiment, the hydrophobic organic film-forming material includes at least one of polylactic acid and ethyl cellulose.

[0032] In one alternative embodiment, the organic solvent includes one of dichloromethane and anhydrous ethanol.

[0033] In one alternative implementation, S2 satisfies at least one of the following conditions: (1) S2-1 further includes pulverizing the pH buffer material before mixing; (2) The solid content of the suspended slurry in S2-1 is 20wt%-40wt%; (3) The binder in S2-1 includes at least one of sodium carboxymethyl cellulose and polyvinyl alcohol; (4) The air inlet temperature in the second coating process of S2-2 is 50-70℃; (5) The weight gain of the coating after the second coating in S2-2 is 10%-20%; (6) The second coating step in S2-2 also includes a drying and curing step.

[0034] In one optional embodiment, the particle size of the pH buffer material after pulverization in S2-1 is 300-600 mesh; In one optional embodiment, the drying and curing temperature after the second coating in S2-2 is 60-80°C.

[0035] In one alternative implementation, S3 satisfies at least one of the following conditions: (1) S3-1 further includes mixing the pH-responsive polymeric gel skeleton with the solvent before mixing to obtain a pH-responsive polymeric gel skeleton solution; (2) The mass ratio of pH-responsive polymeric gel skeleton to soil passivating agent in S3-1 is 100:(20-40). (3) The mass ratio of pH-responsive polymeric gel skeleton to surfactant in S3-1 is 100:(0.1-1). (4) The mixing step in S3-1 includes a shearing process; (5) The surfactant in S3-1 includes at least one of Tween 80 and Tween 20; (6) The air inlet temperature in the third coating process in S3-2 is 40-60℃; (7) The cross-linking curing method in S3-2 includes spraying a cross-linking agent; (8) The third coating step in S3-2 also includes a drying process; (9) The thickness of the rhizosphere pH-responsive passivation shell in S3-2 is 50-200 μm; (10) The drying process in S3-2 also includes sieving.

[0036] In one optional embodiment, the mass concentration of the pH-responsive polymeric gel skeleton solution is 1%-5%.

[0037] In one optional embodiment, the solvent in the pH-responsive polymeric gel skeleton solution in S3-1 includes one or more of deionized water, purified water, and distilled water.

[0038] In one optional embodiment, the shearing rate in S3-1 is 1000-2000 rpm.

[0039] In one optional embodiment, the crosslinking agent in S3-2 includes one or more of calcium chloride, barium chloride, and aluminum chloride.

[0040] In one optional embodiment, the temperature of the drying process after the third coating in S3-2 is 40-50°C.

[0041] The technical solution of this invention has the following advantages: 1. The present invention provides a soil conditioner, wherein the soil conditioner particles have a core-shell structure, comprising, from the inside out: a nutrient slow-release core, a pH buffering and isolating intermediate layer, and a rhizosphere pH-responsive passivating shell; the nutrient slow-release core comprises a biochar carrier, plant-required nutrients loaded on the biochar carrier, and a non-pH-responsive slow-release coating layer covering the outer surface of the biochar carrier; the non-pH-responsive slow-release coating layer comprises a hydrophobic polymer; the pH buffering and isolating intermediate layer comprises a pH buffering material; the rhizosphere pH-responsive passivating shell comprises a pH-responsive polymeric gel framework and a soil passivating agent dispersed in the pH-responsive polymeric gel framework.

[0042] The soil conditioner provided by this invention integrates plant-required nutrients with a soil passivating agent, achieving simultaneous fertilization and remediation in a single application, thus reducing labor costs. The pH-responsive polymeric gel framework in the soil conditioner's structure can sense pH fluctuations (especially short-term acidification caused by fertilization and root exudation), releasing the soil passivating agent immediately upon heavy metal activation and retaining it during non-activation periods to prevent ineffective loss. This invention incorporates a pH buffer layer to prevent localized acidification caused by nutrient release from the core from interfering with the outer layer's pH sensing, ensuring that the outer layer only responds to actual rhizosphere microenvironment changes and is not falsely triggered by core release. Furthermore, the product of this invention has similar particle strength (15-20N) and application performance to conventional fertilizers, making it suitable for existing mechanized operations.

[0043] The functions of each component of the soil conditioner are as follows: (1) Nutrient slow-release kernels can release nutrients required for plant growth under different soil pH conditions, ensuring the nutritional needs of crops throughout their entire growth period.

[0044] (2) The function of the pH buffer isolation intermediate layer is to neutralize the H produced by the release of nutrients from the core. + , adsorption of OH - This prevents local pH changes from being transmitted to the outer layer, ensuring that the outer layer senses the true pH of the rhizosphere microenvironment.

[0045] (3) When the pH of the rhizosphere microenvironment is higher than the threshold (6.0), the passivating shell is in a contracted and dense state, sealing the soil passivating agent; when the pH of the rhizosphere microenvironment drops below the threshold (6.0) (such as after fertilization, ammonium nitrogen nitrification, root secretion of organic acids, etc.), it swells or degrades, rapidly releasing the soil passivating agent into the plant rhizosphere soil, fixing the activated heavy metals in situ.

[0046] The functions of each component in a soil conditioner are as follows: (1) Functions of biochar carrier: adsorb and load nutrients to achieve physical slow release; assist in the passivation of heavy metals; improve soil structure. Principle: The porous structure adsorbs nutrients through capillary action, and the surface functional groups complex heavy metal ions.

[0047] (2) Nutrient requirements of plants: Provides nitrogen, phosphorus, potassium and micronutrients required by crops throughout their entire growth period, ensuring yield. Principle: After being adsorbed by the biochar carrier, it diffuses through the non-pH-responsive slow-release coating layer via a concentration gradient, and the rate is independent of pH.

[0048] (3) Function of non-pH-responsive slow-release coating layer: Controls constant nutrient release, unaffected by changes in soil pH. Principle: The permeability coefficient of the non-pH-responsive slow-release coating layer is stable within the pH range of 4-9, and the nutrient release rate does not change drastically with pH fluctuations.

[0049] (4) pH-responsive polymeric gel framework function: triggers the release of passivating agents when the rhizosphere is acidified, and seals them at normal pH, thus achieving on-demand response. Principle: Gels such as calcium alginate shrink and compact at pH > 6 (seal-in), and swell and dissolve carboxyl groups at pH < 6 (release), and the process is reversible.

[0050] (5) Function of soil passivating agents: They fix heavy metals activated in the rhizosphere and prevent their migration to crops. Principle: Soil passivating agents react with heavy metal ions to form precipitates or coordination complexes, reducing bioavailability.

[0051] The soil conditioner provided by this invention has the following advantages: (1) Traditional soil conditioners either focus on improving the overall properties of the soil or on optimizing the intrinsic properties of the conditioner materials. However, the critical period for plants to absorb heavy metals is when the rhizosphere microenvironment becomes acidic in the short term due to fertilization, root secretion, etc. Therefore, this invention proposes a soil conditioner that senses changes in the rhizosphere microenvironment and responds accordingly, with the dynamic changes in the plant rhizosphere microenvironment as the triggering condition for the conditioner.

[0052] (2) This invention integrates fertilizer and remediation agent into one structure for the first time, realizing the dual effect of fertilization and soil remediation with one application; a pH buffer isolation middle layer is set to solve the problem of nutrient interference from the nutrient slow-release core to sense the change of pH in the rhizosphere microenvironment; the rhizosphere pH-responsive passivated shell can intelligently sense the change of soil rhizosphere microenvironment and intelligently release soil passivating agent, realizing a breakthrough from passive application to dynamic release.

[0053] (3) In terms of function, it realizes the integration of continuous nutrient supply and precise rhizosphere response passivation repair through a single fertilization. It has a mechanism that senses dynamic changes in the crop rhizosphere microenvironment and releases the trigger. The nutrients in the nutrient slow-release core will not be affected by soil pH and will continuously release the nutrients required by the plant. The outer rhizosphere pH response passivation shell senses changes in the rhizosphere soil microenvironment. When the pH is lower than the set threshold, it will intelligently sense and respond to release the soil passivating agent.

[0054] (4) At the application level, it can achieve one-time base fertilizer, which is effective throughout the season, reduces labor costs, and is suitable for mechanized fertilization. Attached Figure Description

[0055] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0056] Figure 1 This is a schematic diagram of the soil conditioner particle structure in Embodiment 1 of the present invention.

[0057] Explanation of reference numerals in the attached figures: 1. Nutrient slow-release core; 2. Non-pH-responsive slow-release coating layer; 3. pH-buffered isolation intermediate layer; 4. Rhizosphere pH-responsive passivating shell. Detailed Implementation

[0058] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0059] Unless otherwise specified, all experimental steps or conditions in the examples were performed according to conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0060] The raw materials and their sources used in the embodiments and comparative examples of this application are as follows: Urea (total nitrogen (N) content ≥46%, particle size 1.18-3.35mm), manufacturer: Hubei Saning Chemical Co., Ltd. Monoammonium phosphate (Standard 11-47-0, total nutrients (N+P2O5) ≥55%), manufacturer: Hubei Yihua Group Co., Ltd. Potassium chloride (K2O≥60%, industrial grade), manufacturer: Qinghai Salt Lake Industry Co., Ltd. Polylactic acid (4032D, melt index 3-5 g / 10 min), manufacturer: Zhejiang Hisun Biomaterials Co., Ltd. Ethyl cellulose (EC7FP, viscosity 7 mPa·s), manufacturer: Ashland Chemical (Nanjing) Co., Ltd. Calcium carbonate (analytical grade, ≥99%, 400 mesh), manufacturer: Sinopharm Chemical Reagent Co., Ltd. Sodium carboxymethyl cellulose (viscosity 300-800 mPa·s, purity ≥99%), manufacturer: Shanghai Aladdin Biochemical Technology Co., Ltd. Sodium alginate (chemically pure, viscosity 200-500 mPa·s), manufacturer: Qingdao Mingyue Algae Group Co., Ltd. Deionized water, conductivity ≤0.1 μS / cm; Phosphate rock powder (P2O5 content: 20-35%, passed through 100-mesh sieve, moisture ≤3%), manufacturer: Yichang Dongsheng Industrial Co., Ltd. Calcium silicate (available silicon ≥25%, CaO ≥30%), manufacturer: Jinwoyuan Fertilizer Co., Ltd. Tween 80 (chemically pure, HLB value 15), manufacturer: Sinopharm Chemical Reagent Co., Ltd. Calcium chloride (anhydrous, analytical grade, ≥96%), manufacturer: Sinopharm Chemical Reagent Co., Ltd.

[0061] Example 1 This embodiment provides a method for preparing a soil conditioner, including the following steps: S1. Preparation of a nutrient-slow-release core: S1-1. The biochar carrier (corn stalk charcoal, obtained by pyrolyzing corn stalks at 500℃, pulverizing, and passing through a 100-mesh sieve, with a specific surface area ≥150 m²) is used. 2 The powder (g) is crushed to 80 mesh and mixed with the nutrients required by the plant (the mass ratio of each substance is urea, monoammonium phosphate, potassium chloride = 30:20:15) at a mass ratio of 20:80. The mixture is then granulated and dried until the moisture content is <3%, resulting in granules with a particle size of 1.5 mm.

[0062] S1-2. Place the substrate in a fluidized bed and spray in a non-pH-responsive slow-release coating solution (5g polylactic acid / 100ml dichloromethane) for the first coating. The coating weight increases by 10%, resulting in a non-pH-responsive slow-release coating layer with a thickness of 30μm. Then, dry the coating at 40℃ to prepare the nutrient slow-release core.

[0063] S2. Encapsulated pH buffering and isolation intermediate layer: S2-1. Crush the pH buffer material (calcium carbonate) to 300 mesh and mix it with the binder (2wt% sodium carboxymethyl cellulose aqueous solution) to form a suspension slurry with a solid content of 20wt%.

[0064] S2-2. Place the nutrient slow-release core from S1 in a fluidized bed, spray the above-mentioned suspension slurry for a second coating, the inlet air temperature is 70℃, the coating weight gain is 10%, and then dry and solidify at 60℃ to obtain particles coated with a pH buffer isolation intermediate layer (thickness of 50μm).

[0065] S3. Rhizosphere pH-responsive passivating shell: S3-1. A pH-responsive polymeric gel skeleton (sodium alginate gel) and a solvent (deionized water) were mixed to prepare a 1% (w / w) pH-responsive polymeric gel skeleton solution. Soil passivating agent powder (calcium silicate) and surfactant (Tween 20) were added. The mass ratio of pH-responsive polymeric gel skeleton to soil passivating agent was 100:30, and the mass ratio of pH-responsive polymeric gel skeleton to surfactant was 100:0.1. The solution was dispersed by high-speed shearing (shearing speed of 1000 rpm) to obtain a coating slurry.

[0066] S3-2. Place the particles coated with the pH buffer isolation intermediate layer from S2 into a fluidized bed, spray the above-mentioned coating slurry for a third coating, maintain the inlet air temperature at 60℃, spray the crosslinking agent (0.1mol / L calcium chloride solution) for crosslinking and curing, so that the shell thickness reaches 100μm, then dry at 40℃, pass through a 5-mesh sieve, and obtain a soil conditioner with a particle size of 2-4mm and a particle strength of 20N.

[0067] Figure 1 This is a schematic diagram of the soil conditioner particle structure of Example 1 of the present invention, and its working mechanism is as follows: (1) Normal state (rhizosphere pH above the threshold of 6.0): The nutrient-slow-release core continuously releases nutrients, which penetrate the middle layer and outer shell into the soil for crop absorption; the trace amounts of H produced by the core release... + / OH - It is neutralized by pH buffering material when passing through the intermediate layer; the inner surface of the rhizosphere pH-responsive passivation shell is in contact with the neutral solution buffered by the pH buffering intermediate layer, and the outer surface is in contact with the rhizosphere soil solution; the rhizosphere pH-responsive passivation shell is in a contracted and compacted state, and the soil passivating agent is sealed.

[0068] (2) Rhizosphere acidification (fertilization / root activity causing pH to drop below the threshold): The nutrient-releasing core continues to release nutrients normally, while the pH-buffered intermediate layer continues to buffer the release from the core. The outer surface of the rhizosphere pH-responsive passivating shell directly senses the decrease in pH in the rhizosphere microenvironment, resulting in swelling or degradation. Soil passivating agents are rapidly released into the rhizosphere soil, fixing the activated heavy metals. After the acidification event ends, the rhizosphere pH recovers, the shell returns to its dense state, and the release of soil passivating agents ceases.

[0069] Key features: The structure decouples the functions of "continuous nutrient supply" and "intelligent rhizosphere response and repair", and the middle layer ensures that the outer shell only responds to real changes in the rhizosphere microenvironment and is not disturbed by the core.

[0070] Example 2 This embodiment provides a method for preparing a soil conditioner, including the following steps: S1. Preparation of a nutrient-slow-release core: S1-1. The biochar carrier (fruit tree residue biochar, obtained by pyrolyzing fruit tree residue at 500℃, pulverizing, and passing through an 80-mesh sieve, with a specific surface area ≥100 m²) is used. 2 The powder (g) is crushed to 140 mesh and mixed with the nutrients required by the plant (the mass ratio of each substance is urea, ammonium sulfate, potassium sulfate = 25:20:15) at a mass ratio of 30:70. The mixture is then granulated and dried until the moisture content is <3%, resulting in granules with a particle size of 2.2 mm.

[0071] S1-2. Place the substrate in a fluidized bed and spray in a non-pH-responsive sustained-release coating solution (8g ethyl cellulose / 100ml anhydrous ethanol) for the first coating. The coating weight increases by 5%, resulting in a non-pH-responsive sustained-release coating layer with a thickness of 20μm. Then, dry the coating at 45℃ to prepare the nutrient sustained-release core.

[0072] S2. Encapsulated pH buffering and isolation intermediate layer: S2-1. Crush the pH buffer material (dolomite) to 450 mesh and mix it with the binder (3wt% polyvinyl alcohol solution) to form a suspension slurry with a solid content of 30wt%.

[0073] S2-2. Place the nutrient slow-release core from S1 in a fluidized bed, spray the above-mentioned suspension slurry for a second coating, with an inlet air temperature of 60°C and a coating weight gain of 15%, and then dry and solidify at 80°C to obtain particles coated with a pH buffer isolation intermediate layer (thickness of 125μm).

[0074] S3. Rhizosphere pH-responsive passivating shell: S3-1. A pH-responsive polymeric gel skeleton (sodium alginate gel) and a solvent (deionized water) were mixed to prepare a 3% (w / w) pH-responsive polymeric gel skeleton solution. Soil passivating agent powder (phosphate rock powder, passed through a 200-mesh sieve) and a surfactant (Tween 80) were added. The mass ratio of the pH-responsive polymeric gel skeleton to the soil passivating agent was 100:20, and the mass ratio of the pH-responsive polymeric gel skeleton to the surfactant was 100:0.5. The solution was dispersed by high-speed shearing (shearing speed of 1500 rpm) to obtain a coating slurry.

[0075] S3-2. Place the particles coated with the pH buffer isolation intermediate layer from S2 into a fluidized bed, spray the above-mentioned coating slurry for a third coating, maintain the inlet air temperature at 50°C, spray the crosslinking agent (0.5 mol / L calcium chloride solution) for crosslinking and curing, so that the shell thickness reaches 125 μm, then dry at 45°C, pass through a 4-mesh sieve, and obtain a soil conditioner with a particle size of 4-5 mm and a particle strength of 18 N.

[0076] Example 3 This embodiment provides a method for preparing a soil conditioner, including the following steps: S1. Preparation of a nutrient-slow-release core: S1-1. The biochar carrier (corn cob char, obtained by pyrolyzing corn cobs at 550℃, pulverizing, and passing through a 120-mesh sieve, with a specific surface area ≥100 m²) is used. 2 The powder (g) is crushed to 200 mesh and mixed with the nutrients required by the plant (the mass ratio of each substance is: urea, diammonium phosphate, potassium chloride = 35:20:20) at a mass ratio of 40:60. The mixture is then granulated and dried until the moisture content is <3%, resulting in granules with a particle size of 3.0 mm.

[0077] S1-2. Place the substrate in a fluidized bed and spray in a non-pH-responsive slow-release coating solution (6g polylactic acid / 100ml dichloromethane) for the first coating. The coating weight increases by 15% and the non-pH-responsive slow-release coating layer is 50μm thick. Then dry at 50℃ to prepare the nutrient slow-release core.

[0078] S2. Encapsulated pH buffering and isolation intermediate layer: S2-1. Pulverize the pH buffer material (calcium carbonate: kaolin = 8:2 by mass) to 600 mesh and mix it with the binder (2wt% sodium carboxymethyl cellulose aqueous solution) to form a suspension slurry with a solid content of 40wt%.

[0079] S2-2. Place the nutrient slow-release core from S1 in a fluidized bed, spray the above-mentioned suspension slurry for a second coating, with an inlet air temperature of 50°C and a coating weight gain of 10%, and then dry and solidify at 70°C to obtain particles coated with a pH buffer isolation intermediate layer (thickness of 50μm).

[0080] S3. Rhizosphere pH-responsive passivating shell: S3-1. A pH-responsive polymeric gel skeleton (sodium alginate gel) and a solvent (deionized water) were mixed to prepare a 5% (w / w) solution. Soil passivating agent powder (a 1:1 mixture of phosphate rock powder and potassium dihydrogen phosphate) and a surfactant (Tween 80) were added. The mass ratio of the pH-responsive polymeric gel skeleton to the soil passivating agent was 100:40, and the mass ratio of the pH-responsive polymeric gel skeleton to the surfactant was 100:1. The mixture was then dispersed under high-speed shear (shear speed of 2000 rpm) to obtain a coating slurry.

[0081] S3-2. Place the particles coated with the pH buffer isolation intermediate layer from S2 into a fluidized bed, spray the above-mentioned coating slurry for a third coating, maintain the inlet air temperature at 60℃, spray the crosslinking agent (1.0mol / L calcium chloride solution) for crosslinking and curing, so that the shell thickness reaches 125μm, then dry at 50℃, pass through a 4-mesh sieve, and obtain a soil conditioner with a particle size of 4-5 mm and a particle strength of 16N.

[0082] Comparative Example 1 Soil conditioner 1, manufacturer: Wuhan Wonong Fertilizer Co., Ltd., "Hezhidi" acidic soil conditioner, powder form; The mass percentage of the main components of the product is: CaO≥25%, K2O≥4%, SiO2≥10%; Product pH value: 8.0-10.0.

[0083] Comparative Example 2 Soil Conditioner 2, Manufacturer: Hubei Fuzhiyuan Biotechnology Co., Ltd., Powder form; The mass percentage of the main components of the product is as follows: K2O ≥ 5.0%; CaO ≥ 40.0%; MgO ≥ 5.0%; SiO2 ≥ 10.0%; Product pH value: 10.5-12.5.

[0084] Comparative Example 3 Soil Conditioner 3, Manufacturer: Jinwoyuan Fertilizer Co., Ltd., Silicon-Calcium-Magnesium Soil Conditioner, Powder Form; The mass percentage of the main components of the product is: SiO2 ≥ 25%, CaO ≥ 30%; Product pH value: 8-10.

[0085] Experimental Example 1 Nutrient release rate tests were conducted on the soil conditioner sample prepared in Example 1, the soil conditioner samples of Comparative Examples 1-3, and the combination samples of commercially available rice-specific fertilizer.

[0086] Commercially available rice-specific fertilizer (manufacturer: Hubei Yishizhuang Agricultural Technology Co., Ltd., N-P2O5-K2O 25-10-12, where 25-10-12 refers to the mass percentage of the main components N:P2O5:K2O=25%:10%:12%).

[0087] Test method: Refer to GB / T 8572-2021 and conduct the following experiments: (1) Take 10g of the sample from Example 1 and place it in pH buffer (200mL) with pH=5.0 and pH=7.0 respectively and shake at 25℃ for 56 days; (2) Take 5g of Comparative Example 1 sample and 5g of rice-specific fertilizer and place them in pH buffer solution (200mL) with pH=5.0 and pH=7.0 respectively and shake at 25℃ for 56 days; (3) Take 5g of Comparative Example 2 sample and 5g of rice-specific fertilizer and place them in pH buffer solution (200mL) with pH=5.0 and pH=7.0 respectively and shake at 25℃ for 56 days; (4) Take 5g of the comparative example 3 sample and 5g of rice-specific fertilizer and place them in pH buffer solution (200mL) with pH=5.0 and pH=7.0 respectively and shake at 25℃ for 56 days; The cumulative nutrient release rate of each group of experiments (1)-(4) was measured respectively, and the test results are shown in Table 1.

[0088] Table 1

[0089] The release test lasted 56 days. The cumulative nutrient release rate of Example 1 of this invention was lower than that of the control sample + rice-specific fertilizer at two different pH levels, indicating that the soil conditioner in Example 1 of this invention has a slow-release nutrient function. Since the growth cycle of conventional crops is over 100 days, 30% of the nutrients can be released in the middle and late stages of crop growth, achieving nutrient supply throughout the entire crop growth cycle. Table 1 shows that the difference in the cumulative nutrient release rate of the soil conditioner prepared in Example 1 of this invention at different pH levels is ≤0.8%, proving that the non-pH-responsive slow-release coating layer achieves constant slow release. In contrast, the cumulative nutrient release rate of the soil conditioner combined with rice-specific fertilizer in Control Samples 1-3 was significantly affected by pH (difference 4.4-7.3%), and there was no slow-release effect.

[0090] Experimental Example 2: The soil conditioner samples of Example 1 and Comparative Examples 1-3 were subjected to passivation agent pH-triggered release tests, and the test results are shown in Table 2.

[0091] Test method: (1) Take 10g of the sample from Example 1 and place it in pH buffer (200mL) with pH=5.0 and pH=7.0 respectively, and measure the cumulative release rate of passivating agent within 72h; (2) Take 10g of Comparative Example 1 sample and place it in pH buffer (200mL) with pH=5.0 and pH=7.0 respectively, and determine the cumulative release rate of passivating agent within 72h; (3) Take 10g of Comparative Example 2 sample and place it in pH buffer (200mL) with pH=5.0 and pH=7.0 respectively, and determine the cumulative release rate of passivating agent within 72h; (4) Take 10g of Comparative Example 3 sample and place it in pH buffer (200mL) with pH=5.0 and pH=7.0 respectively, and determine the cumulative release rate of passivating agent within 72h.

[0092] Table 2

[0093] As shown in Table 2, the soil conditioner prepared in Example 1 of this invention showed almost no release of the soil passivator at pH 7.0 (cumulative release rate of passivator = 4.9%), while the release amount of the soil passivator was relatively large at pH 5.0 (cumulative release rate of passivator = 86.3%). The release rate was faster at pH 5.0 within the same time period (72h), indicating that the soil conditioner prepared in Example 1 of this invention is more sensitive to pH changes and responds more precisely, achieving the effect of accurately releasing the conditioner based on the dynamic changes in the pH of the rhizosphere microenvironment. In contrast, the soil conditioners in Comparative Examples 1-3 continuously released the conditioner at all pH levels, showing no intelligent response effect.

[0094] Experimental Example 3: Pot experiments were conducted on the soil conditioner samples of Example 1 and Comparative Examples 1-3. The test items were the cadmium content in brown rice and the rice yield. The test results are shown in Table 3.

[0095] Test method: The tested soil was cadmium-contaminated paddy soil (total cadmium (Cd) content: 0.85 mg / kg, pH=5.8), and the tested crop was rice.

[0096] Usage and dosage for each experimental group: (1) Blank control group 1: Rice was grown in cadmium-contaminated paddy soil without fertilizer or conditioner; (2) Blank control group 2: Rice-specific fertilizer (N-P2O5-K2O 25-10-12, application rate: 40 kg / mu). (3) Comparative Example 1: 100 kg / mu of commercially available soil conditioner 1 was applied, without applying rice-specific fertilizer; (4) Comparative Example 2: 100 kg / mu of commercially available soil conditioner 2 was applied, without applying rice-specific fertilizer; (5) Comparative Example 3: 100 kg / mu of commercially available soil conditioner 3 was applied, without applying rice-specific fertilizer; (6) Separate application group 1: Apply 100 kg / mu of commercially available soil conditioner 1 (comparative ratio 1) + 40 kg / mu of rice-specific fertilizer separately; (7) Separate application group 2: Apply 100 kg / mu of commercially available soil conditioner 2 (comparative ratio 2) + 40 kg / mu of rice-specific fertilizer separately; (8) Separate application group 3: Apply 100 kg / mu of commercially available soil conditioner 3 (comparative ratio 3) + 40 kg / mu of rice-specific fertilizer separately; (9) Example 1: One-time basal application, application rate 58 kg / mu (consistent with the total nitrogen content of blank control group 2); (10) Example 2: One-time basal application, application rate of 83 kg / mu (consistent with the total nitrogen content of blank control group 2); (11) Example 3: One-time basal application, application rate 73 kg / mu (consistent with the total nitrogen content of blank control group 2).

[0097] Table 3

[0098] As shown in Table 3, the single basal application of the soil conditioner in Examples 1-3 of this invention achieved the target cadmium content (0.15-0.17 mg / kg) in brown rice, and the yield increased by 3.4%-5.5% compared to the blank control group 2, realizing the intelligent control effect of simultaneous production and remediation. In contrast, the crop yield of the soil conditioner applied in Examples 1-3 (without rice-specific fertilizer) was close to that of the blank control group 1 (433 kg / mu), proving that it did not contain nutrients and could not guarantee crop yield. Although the separate application of the soil conditioner and rice-specific fertilizer (separate application groups 1-3) could guarantee yield, it required two field fertilization operations, increasing labor costs and making it unsuitable for mechanized fertilization.

[0099] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A soil conditioner, characterized in that, The soil conditioner particles have a core-shell structure, which, from the inside out, includes: a nutrient slow-release core, a pH buffering and isolating intermediate layer, and a rhizosphere pH-responsive passivating outer shell. The nutrient slow-release core includes a biochar carrier, plant-required nutrients loaded on the biochar carrier, and a non-pH-responsive slow-release coating layer covering the outer surface of the biochar carrier; The non-pH-responsive sustained-release coating material includes a hydrophobic polymer; The pH buffer isolation intermediate layer includes a pH buffer material; The rhizosphere pH-responsive passivation shell includes a pH-responsive polymeric gel framework and a soil passivating agent dispersed in the pH-responsive polymeric gel framework.

2. The soil conditioner according to claim 1, characterized in that, The biochar carrier is obtained from agricultural waste through pyrolysis. And / or, the specific surface area of ​​the biochar carrier is ≥100 m². 2 / g.

3. The soil conditioner according to claim 1 or 2, characterized in that, At least one of the following conditions must be met: (1) The nutrients required by the plant include one or more of nitrogen fertilizer, phosphorus fertilizer, potassium fertilizer and micronutrient fertilizer; (2) The thickness of the non-pH-responsive sustained-release coating layer is 5-50 μm; (3) The non-pH-responsive sustained-release coating material includes at least one of polylactic acid and ethyl cellulose; (4) The particle size of the soil conditioner is 2-5 mm; (5) The mass ratio of the biochar carrier to the nutrients required by the plant is (20-40): (60-80).

4. The soil conditioner according to claim 1, characterized in that, The pH buffering material includes one or more of calcium carbonate, kaolin, and dolomite; And / or, the thickness of the pH buffer isolation intermediate layer is 50-200 μm.

5. The soil conditioner according to claim 1, characterized in that, The pH-responsive polymeric gel backbone includes alginate gel.

6. The soil conditioner according to claim 1 or 5, characterized in that, The soil passivating agent includes at least one of phosphate rock powder, phosphate, carbonate, silicate, mercapto-based material, and iron-based material.

7. A method for preparing a soil conditioner according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Preparation of a nutrient-slow-release core: S1-1. The biochar carrier is mixed with the nutrients required by the plant, granulated and dried to obtain the substrate granules; S1-2. The matrix is ​​coated for the first time using a non-pH-responsive slow-release coating solution to obtain a nutrient slow-release core; S2. Encapsulated pH buffering and isolation intermediate layer: S2-1. Mix the pH buffer material with the binder to prepare a suspension slurry; S2-2. The nutrient slow-release core in S1 is coated a second time using the suspension slurry to obtain particles coated with a pH buffer isolation intermediate layer; S3. Rhizosphere pH-responsive passivating shell: S3-1. Mix pH-responsive polymeric gel framework, soil passivating agent and surfactant to obtain coating slurry; S3-2. The particles coated with the pH buffer isolation intermediate layer in S2 are coated a third time using the coating slurry, and then cross-linked and cured to obtain the soil conditioner coated with a rhizosphere pH-responsive passivating shell.

8. The method for preparing the soil conditioner according to claim 7, characterized in that, S1 satisfies at least one of the following conditions: (1) The S1-1 further includes pulverizing the biochar carrier before mixing; (2) The particle size of the granules after granulation in S1-1 is 1.5-3.0 mm; (3) The moisture content of the dried granules in S1-1 is <3%; (4) The weight gain of the first coating in S1-2 is 5%-15%; (5) The first coating step in S1-2 also includes a drying process; (6) The non-pH-responsive sustained-release coating solution in S1-2 is prepared by dissolving a hydrophobic organic film-forming material in an organic solvent.

9. The method for preparing the soil conditioner according to claim 7, characterized in that, S2 satisfies at least one of the following conditions: (1) S2-1 further includes pulverizing the pH buffer material before mixing; (2) The solid content of the suspended slurry in S2-1 is 20wt%-40wt%; (3) The binder in S2-1 includes at least one of sodium carboxymethyl cellulose and polyvinyl alcohol; (4) The air inlet temperature in the second coating process of S2-2 is 50-70℃; (5) The weight gain of the coating after the second coating in S2-2 is 10%-20%; (6) The second coating step in S2-2 also includes a drying and curing step.

10. The method for preparing the soil conditioner according to claim 7, characterized in that, S3 satisfies at least one of the following conditions: (1) S3-1 further includes mixing the pH-responsive polymeric gel skeleton with the solvent before mixing to obtain a pH-responsive polymeric gel skeleton solution; (2) The mass ratio of pH-responsive polymeric gel skeleton to soil passivating agent in S3-1 is 100:(20-40). (3) The mass ratio of pH-responsive polymeric gel skeleton to surfactant in S3-1 is 100:(0.1-1). (4) The mixing step in S3-1 includes a shearing process; (5) The surfactant in S3-1 includes at least one of Tween 80 and Tween 20; (6) The air inlet temperature in the third coating process in S3-2 is 40-60℃; (7) The cross-linking curing method in S3-2 includes spraying a cross-linking agent; (8) The third coating step in S3-2 also includes a drying process; (9) The thickness of the rhizosphere pH-responsive passivation shell in S3-2 is 50-200 μm; (10) The drying process in S3-2 also includes sieving.

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