Composite soil conditioner and preparation method thereof

Abstract

The present invention provides a composite soil conditioner and a preparation method thereof, belonging to the field of agricultural technology. The method comprises the following steps: Step S1, preparing a multi-arm polymer; Step S2, preparing modified biochar; Step S3, preparing slow-release microcapsules; and Step S4, mixing the modified biochar, slow-release microcapsules, and a sodium carboxymethyl cellulose solution, and granulating the mixture to obtain the composite soil conditioner. The present invention can achieve the purpose of the soil conditioner efficiently absorbing heavy metals, regulating soil pH, and helping soil retain water.

Description

Technical Field

[0001] The present invention relates to the technical field of agriculture, and in particular to a composite soil conditioner and a preparation method thereof. Background Art

[0002] Currently, soil degradation is becoming increasingly severe, with issues such as heavy metal pollution, acidification, salinization, and organic matter loss, particularly those that require urgent resolution. Acidic soils, due to their low pH, are susceptible to the dissolution and migration of heavy metals (such as cadmium and lead), which in turn, through crop accumulation, threaten agricultural product safety and human health. While traditional soil conditioners such as lime and gypsum can adjust pH, they require large application amounts, have a single effect, and are susceptible to soil compaction or salinization. Furthermore, their effectiveness in enhancing beneficial elements such as selenium is limited. Furthermore, while early synthetic materials can improve soil structure, they carry environmental risks and high costs. Existing conditioners are mostly single-function, making it difficult to address multiple objectives. Their narrow scope of application makes it difficult to address the needs of improving complex soil conditions.

[0003] The patent application document with publication number CN111233571A discloses a soil conditioner, which is a mixture of seaweed residue fermented by microorganisms, carbonized bagasse, carbonized sugarcane leaves, sugar factory filter mud, silicon potash fertilizer and attapulgite, and then dried, crushed and stirred. The mixture is made according to the following mass percentages of each component: seaweed residue 25%-55%, carbonized bagasse 5%-20%, carbonized sugarcane leaves 5%-20%, bone char 5%-10%, sugar factory filter mud 10%-30%, silicon potash fertilizer 10%-20%, and attapulgite 5%-20%. The soil conditioner prepared by this scheme mainly uses waste as raw materials, achieving the effect of waste utilization and resource conservation, but its function is relatively single, and it still lacks the heavy metal adsorption, water retention and other functions of the soil conditioner.

[0004] Therefore, it is necessary to provide a preparation method of a composite soil conditioner to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0005] In view of this, the present invention provides a composite soil conditioner and a preparation method thereof, which can achieve the purpose of the soil conditioner efficiently absorbing heavy metals, adjusting soil pH and helping soil retain water.

[0006] The specific scheme of the present invention is as follows: a method for preparing a composite soil conditioner, comprising the following steps:

[0007] Step S1, dissolving pentaerythritol tetraacrylate, N-isopropylacrylamide, acrylic acid, copper bromide, and pentamethyldiethylenetriamine in anhydrous ethanol, heating and stirring under a nitrogen atmosphere, then adding ether, collecting the precipitate, purifying, and vacuum drying to obtain a multi-arm polymer;

[0008] Step S2: mixing the crushed bamboo and coffee grounds, performing gradient pyrolysis under a nitrogen environment, sieving to obtain biochar, immersing the biochar in mixed acid, heating the mixture to react, filtering, and drying to obtain carboxylated biochar. The carboxylated biochar is then immersed in MES buffer, mixed evenly, and then a multi-arm polymer is added to react, filtered, and dried to obtain modified biochar.

[0009] Step S3, placing the oyster shell powder and humic acid into a ball mill for ball milling, then sieving to obtain core particles, adding the core particles to a chitosan solution, washing, then adding to a TPP solution, washing, repeating the process three times, and drying to obtain sustained-release microcapsules;

[0010] Step S4: mixing the modified biochar, the slow-release microcapsules and the sodium carboxymethyl cellulose solution, and granulating the mixture to obtain a composite soil conditioner.

[0011] Bamboo and coffee grounds are pyrolyzed to produce multi-level porous biochar materials, which can simultaneously adsorb heavy metal ions of different particle sizes, enhancing the adsorption of heavy metals in the soil by soil conditioners. Carboxyl groups are introduced on the surface of biochar through mixed acid oxidation to obtain carboxylated biochar, which fixes heavy metals through ion exchange and complexation. Carboxyl groups can be protonated in acidic soils and can react with positively charged Cd 2+ Plasma generates electrostatic attraction, further enhancing the adsorption of heavy metals in the soil by soil conditioners.

[0012] Biochar is grafted with multi-arm polymers. These polymers absorb water and swell, allowing them to store large amounts of water. Under drought conditions, they contract and release water, enabling the soil conditioner to dynamically regulate soil moisture. The multi-arm polymer network structure provides more attachment sites for microorganisms, allowing them to adsorb and enrich bacteria such as nitrogen-fixing and phosphate-solubilizing bacteria, thereby helping to maintain soil nutrients.

[0013] When the soil pH drops below 5, the chitosan in the outer layer of the microcapsules protonates and swells, releasing the oyster shell powder inside. This rapidly neutralizes the pH, improves soil acidity, and quickly brings the soil pH to a neutral level. The carboxyl groups in humic acid, through dissociation equilibrium, absorb or release protons, acting as a buffer and helping to maintain the soil pH between 6.5 and 7.5 for extended periods. Furthermore, the aromatic rings in humic acid can undergo π-π interactions with heavy metals, while the carboxyl groups can also form chelates with metal ions, inhibiting plant absorption of heavy metals. This synergistic effect with biochar's adsorption of metal ions significantly reduces the migration of metal ions in the soil. Furthermore, humic acid can serve as a natural organic fertilizer to promote plant root development. Encapsulated in microcapsules, it acts as a soil conditioner, slowly releasing humic acid to meet plant growth needs while preventing nutrient loss.

[0014] Preferably, in step S1, the heating and stirring reaction is carried out at a speed of 300-400 rpm, a temperature of 60-65° C., and a time of 32-36 h.

[0015] Preferably, in step S2, the ratio of bamboo to coffee grounds is 3:1; the pyrolysis comprises the following steps: immersing the mixed bamboo and coffee grounds in a citric acid solution, then placing the mixture in a muffle furnace, heating to 400°C under a nitrogen environment, then introducing CO2, and continuing to heat to 700°C.

[0016] Mesopores are formed at 400℃, while micropores are promoted at 700℃, resulting in a gradient pore size.

[0017] Preferably, the concentration of the citric acid is 0.5 mol / L; and the heating rate to 400° C. is 10° C. / min.

[0018] Preferably, after heating to 400° C., maintain the temperature for 30 minutes; after heating to 700° C., maintain the temperature for 20 minutes.

[0019] Preferably, in step S2, the mesh size used for sieving is 200 mesh; the mixed acid is prepared by compounding nitric acid and sulfuric acid in a ratio of 1:3; the temperature of the temperature-raising reaction is 75-85° C., and the time is 1.5-3 hours.

[0020] Preferably, in step S2, EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide) and NHS (N-hydroxysuccinimide) are also dissolved in the MES (2-(N-morpholino)ethanesulfonic acid) buffer; and γ-Fe2O3 nanoparticles are loaded on the carboxylated biochar before adding the multi-arm polymer.

[0021] EDC and NHS can promote the grafting modification of multi-arm polymers into carboxylated biochar.

[0022] Preferably, the loading comprises the following steps: adding the modified biochar to a 0.8 wt% γ-Fe2O3 solution, ultrasonically dispersing for 30 minutes, and drying to obtain the modified biochar loaded with γ-Fe2O3.

[0023] γ-Fe2O3 nanoparticles loaded on modified biochar materials can be slowly oxidized to Fe in the slightly acidic environment of plant roots. 2+ , Fe 2+ It can be absorbed by plants and participate in the synthesis of chlorophyll, helping to improve the iron deficiency and chlorosis symptoms of plants. In addition, γ-Fe2O3 is magnetic and can be used to recycle soil conditioners in a magnetic field environment.

[0024] Preferably, in step S3, the ball milling speed is 250-400 rpm and the time is 3-5 h.

[0025] Preferably, in step S4, the concentration of the carboxymethyl cellulose solution is 3-5 wt %.

[0026] It helps to control the particle shape and size of soil conditioners and reduce the fragmentation and deformation of soil conditioners.

[0027] To achieve the above object, the present invention further provides a composite soil conditioner prepared by the above method for preparing a composite soil conditioner, comprising the following components in parts by weight:

[0028] 30-45 parts of modified biochar, 18-27 parts of slow-release microcapsules and 50-75 parts of carboxymethyl cellulose solution.

[0029] The components of the present invention are used in the above-mentioned weight proportions to achieve the optimal effect, so that the performance of the composite soil conditioner is optimized.

[0030] Preferably, the modified biochar comprises the following components in parts by weight:

[0031] 55-65 parts of biochar and 1-2 parts of multi-arm polymer.

[0032] Preferably, the modified biochar further comprises the following raw materials in parts by weight:

[0033] 60-70 parts of 0.8wt% γ-Fe2O3 solution.

[0034] The above technical solution of the present invention includes at least the following beneficial effects:

[0035] (1) The multi-level porous biochar material prepared by pyrolysis can simultaneously adsorb heavy metal ions of different particle sizes, thereby enhancing the adsorption of heavy metals in the soil by soil conditioners. The carboxylated biochar obtained by mixed acid oxidation can fix heavy metals through ion exchange and complexation, further enhancing the adsorption of heavy metals in the soil by soil conditioners.

[0036] (2) Multi-arm polymers can absorb water and swell, storing large amounts of water. Under drought conditions, the polymers shrink and release water, giving the soil conditioner the ability to dynamically regulate soil moisture. The network structure of multi-arm polymers can provide more attachment sites for microorganisms, adsorbing and enriching bacteria such as nitrogen-fixing bacteria and phosphate-solubilizing bacteria, thereby helping to maintain soil nutrients.

[0037] (3) The chitosan in the outer layer of the slow-release microcapsules protonates and swells when the pH is less than 5, releasing the oyster shell powder inside, which can quickly neutralize the pH and improve the acidity of the soil. The carboxyl and phenolic hydroxyl groups in humic acid act as a buffer through dissociation equilibrium, helping to maintain a neutral soil pH. In addition, humic acid can also be used as a natural organic fertilizer to promote plant root development. Through microencapsulation, it can act as a soil conditioner to slowly release humic acid, meeting the needs of plant growth and preventing nutrient loss. DETAILED DESCRIPTION

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention. All other embodiments obtained by ordinary technicians in this field based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0039] Example 1

[0040] 1.8 g of pentaerythritol tetraacrylate, 20 g of N-isopropylacrylamide, 1.4 g of acrylic acid, 0.05 g of copper bromide and 0.07 g of pentamethyldiethylenetriamine were dissolved in 500 mL of anhydrous ethanol, and nitrogen was introduced to deoxygenate. The mixture was heated to 65° C. in an oil bath and stirred at 350 rpm. The reaction was carried out for 36 h, and ether was slowly added dropwise. The precipitate was collected, purified, and vacuum dried to obtain a multi-arm polymer.

[0041] Take 60g of crushed bamboo and 20g of coffee grounds in a ratio of 3:1, soak them in 0.5mol / L citric acid solution for 12h, dry them, put them into a muffle furnace, and pyrolyze them in a nitrogen environment. Heat them to 400℃ at a rate of 10℃ / min, keep them for 30min, introduce CO2 and continue heating to 700℃, keep them for 20min; cool them, crush and sieve them (200 mesh) to obtain multi-level porous biochar.

[0042] 60 g of biochar was immersed in 60 mL of mixed acid (HNO3:H2SO4=1:3), heated to 80°C, refluxed for 2 h, filtered, washed, and dried to obtain carboxylated biochar, which was then immersed in 120 mL of MES buffer containing 2 g of EDC and 0.6 g of NHS, stirred at room temperature for 30 min, 1.5 g of multi-arm polymer was added, reacted for 12 h, filtered, washed, dried, added to 65 parts of 0.8 wt% γ-Fe2O3 solution, ultrasonically dispersed, and dried to obtain modified biochar.

[0043] 25 g of oyster shell powder and 10 g of humic acid were placed in a ball mill, 200 mL of citric acid solution was added, and the mixture was ball-milled at 300 rpm for 4.5 h. After drying, the mixture was crushed through a 100-mesh sieve to obtain core particles. The core particles were dissolved in chitosan solution, washed, dissolved in TPP solution, washed, and repeated three times. The mixture was dried to obtain sustained-release microcapsules.

[0044] 30 g of modified biochar material, 18 g of slow-release microcapsules and 55 g of sodium carboxymethyl cellulose solution were mixed and granulated to obtain a composite soil conditioner.

[0045] Example 2

[0046] 1.8 g of pentaerythritol tetraacrylate, 20 g of N-isopropylacrylamide, 1.4 g of acrylic acid, 0.05 g of copper bromide and 0.07 g of pentamethyldiethylenetriamine were dissolved in 500 mL of anhydrous ethanol, nitrogen was introduced to deoxygenate, the oil bath was heated to 60° C., stirring was started at 300 rpm, the reaction was carried out for 40 h, ether was slowly added dropwise, the precipitate was collected, purified, and vacuum dried to obtain a multi-arm polymer.

[0047] Take 60g of crushed bamboo and 20g of coffee grounds in a ratio of 3:1, soak them in 0.5mol / L citric acid solution for 12h, dry them, put them into a muffle furnace, and pyrolyze them in a nitrogen environment. Heat them to 400℃ at a rate of 10℃ / min, keep them for 30min, introduce CO2 and continue heating to 700℃, keep them for 20min; cool them, crush and sieve them (200 mesh) to obtain multi-level porous biochar.

[0048] 65 g of biochar was immersed in 60 mL of mixed acid (HNO3:H2SO4=1:3), heated to 80°C, refluxed for 2 h, filtered, washed, and dried to obtain carboxylated biochar, which was then immersed in 120 mL of MES buffer containing 2 g of EDC and 0.6 g of NHS, stirred at room temperature for 30 min, added with 1 g of multi-arm polymer, reacted for 12 h, filtered, washed, dried, added to 60 parts of 0.8 wt% γ-Fe2O3 solution, ultrasonically dispersed, and dried to obtain modified biochar.

[0049] 25 g of oyster shell powder and 10 g of humic acid were placed in a ball mill, 200 mL of citric acid solution was added, and the mixture was ball-milled at 350 rpm for 3.5 h. After drying, the mixture was crushed through a 100-mesh sieve to obtain core particles. The core particles were dissolved in chitosan solution, washed, dissolved in TPP solution, washed, and repeated three times. The mixture was dried to obtain sustained-release microcapsules.

[0050] 45 g of modified biochar material, 27 g of slow-release microcapsules and 75 g of sodium carboxymethyl cellulose solution were mixed and granulated to obtain a composite soil conditioner.

[0051] Example 3

[0052] 1.8 g of pentaerythritol tetraacrylate, 20 g of N-isopropylacrylamide, 1.4 g of acrylic acid, 0.05 g of copper bromide and 0.07 g of pentamethyldiethylenetriamine were dissolved in 500 mL of anhydrous ethanol, nitrogen was introduced to deoxygenate, the oil bath was heated to 62° C., stirring was started at 400 rpm, the reaction was carried out for 32 h, ether was slowly added dropwise, the precipitate was collected, purified, and vacuum dried to obtain a multi-arm polymer.

[0053] Take 60g of crushed bamboo and 20g of coffee grounds in a ratio of 3:1, soak them in 0.5mol / L citric acid solution for 12h, dry them, put them into a muffle furnace, and pyrolyze them in a nitrogen environment. Heat them to 400℃ at a rate of 10℃ / min, keep them for 30min, introduce CO2 and continue heating to 700℃, keep them for 20min; cool them, crush and sieve them (200 mesh) to obtain multi-level porous biochar.

[0054] 65 g of biochar was immersed in 60 mL of mixed acid (HNO3:H2SO4=1:3), heated to 80°C, refluxed for 2 h, filtered, washed, and dried to obtain carboxylated biochar, which was then immersed in 120 mL of MES buffer containing 2 g of EDC and 0.6 g of NHS, stirred at room temperature for 30 min, 1.5 g of multi-arm polymer was added, reacted for 12 h, filtered, washed, dried, added to 70 parts of 0.8 wt% γ-Fe2O3 solution, ultrasonically dispersed, and dried to obtain modified biochar.

[0055] 25 g of oyster shell powder and 10 g of humic acid were placed in a ball mill, 200 mL of citric acid solution was added, and the mixture was ball-milled at 250 rpm for 5 h. After drying, the mixture was crushed through a 100-mesh sieve to obtain core particles. The core particles were dissolved in chitosan solution, washed, dissolved in TPP solution, washed, and repeated three times. The mixture was dried to obtain sustained-release microcapsules.

[0056] 35 g of modified biochar material, 25 g of slow-release microcapsules and 60 g of sodium carboxymethyl cellulose solution were mixed and granulated to obtain a composite soil conditioner.

[0057] Example 4

[0058] 1.8 g of pentaerythritol tetraacrylate, 20 g of N-isopropylacrylamide, 1.4 g of acrylic acid, 0.05 g of copper bromide and 0.07 g of pentamethyldiethylenetriamine were dissolved in 500 mL of anhydrous ethanol, and nitrogen was introduced to deoxygenate. The oil bath was heated to 65° C. and stirred at 400 rpm. The reaction was carried out for 36 hours. Ether was slowly added dropwise, and the precipitate was collected, purified, and vacuum dried to obtain a multi-arm polymer.

[0059] Take 60g of crushed bamboo and 20g of coffee grounds in a ratio of 3:1, soak them in 0.5mol / L citric acid solution for 12h, dry them, put them into a muffle furnace, and pyrolyze them in a nitrogen environment. Heat them to 400℃ at a rate of 10℃ / min, keep them for 30min, introduce CO2 and continue heating to 700℃, keep them for 20min; cool them, crush and sieve them (200 mesh) to obtain multi-level porous biochar.

[0060] 55 g of biochar was immersed in 60 mL of mixed acid (HNO3:H2SO4=1:3), heated to 80°C, refluxed for 2 h, filtered, washed, and dried to obtain carboxylated biochar, which was then immersed in 120 mL of MES buffer containing 2 g of EDC and 0.6 g of NHS, stirred at room temperature for 30 min, 2 g of multi-arm polymer was added, reacted for 12 h, filtered, washed, dried, added to 60 parts of 0.8 wt% γ-Fe2O3 solution, ultrasonically dispersed, and dried to obtain modified biochar.

[0061] 25 g of oyster shell powder and 10 g of humic acid were placed in a ball mill, 200 mL of citric acid solution was added, and the mixture was ball-milled at 400 rpm for 3 h. After drying, the mixture was crushed through a 100-mesh sieve to obtain core particles. The core particles were dissolved in chitosan solution, washed, dissolved in TPP solution, washed, and repeated three times. The mixture was dried to obtain sustained-release microcapsules.

[0062] 45 g of modified biochar material, 27 g of slow-release microcapsules and 70 g of sodium carboxymethyl cellulose solution were mixed and granulated to obtain a composite soil conditioner.

[0063] Example 5

[0064] 1.8 g of pentaerythritol tetraacrylate, 20 g of N-isopropylacrylamide, 1.4 g of acrylic acid, 0.05 g of copper bromide and 0.07 g of pentamethyldiethylenetriamine were dissolved in 500 mL of anhydrous ethanol, nitrogen was introduced to deoxygenate, the oil bath was heated to 60° C., stirring was started at 350 rpm, the reaction was carried out for 36 h, ether was slowly added dropwise, the precipitate was collected, purified, and vacuum dried to obtain a multi-arm polymer.

[0065] Take 60g of crushed bamboo and 20g of coffee grounds in a ratio of 3:1, soak them in 0.5mol / L citric acid solution for 12h, dry them, put them into a muffle furnace, and pyrolyze them in a nitrogen environment. Heat them to 400℃ at a rate of 10℃ / min, keep them for 30min, introduce CO2 and continue heating to 700℃, keep them for 20min; cool them, crush and sieve them (200 mesh) to obtain multi-level porous biochar.

[0066] 60 g of biochar was immersed in 60 mL of mixed acid (HNO3:H2SO4=1:3), heated to 80°C, refluxed for 2 h, filtered, washed, and dried to obtain carboxylated biochar, which was then immersed in 120 mL of MES buffer containing 2 g of EDC and 0.6 g of NHS, stirred at room temperature for 30 min, 2 g of multi-arm polymer was added, reacted for 12 h, filtered, washed, dried, added to 70 parts of 0.8 wt% γ-Fe2O3 solution, ultrasonically dispersed, and dried to obtain modified biochar.

[0067] 25 g of oyster shell powder and 10 g of humic acid were placed in a ball mill, 200 mL of citric acid solution was added, and the mixture was ball-milled at 320 rpm for 4 h. After drying, the mixture was crushed through a 100-mesh sieve to obtain core particles. The core particles were dissolved in chitosan solution, washed, dissolved in TPP solution, washed, and repeated three times. The mixture was dried to obtain sustained-release microcapsules.

[0068] 30 g of modified biochar material, 18 g of slow-release microcapsules and 50 g of sodium carboxymethyl cellulose solution were mixed and granulated to obtain a composite soil conditioner.

[0069] Example 6

[0070] 1.8 g of pentaerythritol tetraacrylate, 20 g of N-isopropylacrylamide, 1.4 g of acrylic acid, 0.05 g of copper bromide and 0.07 g of pentamethyldiethylenetriamine were dissolved in 500 mL of anhydrous ethanol, nitrogen was introduced to deoxygenate, the oil bath was heated to 60° C., stirring was started at 350 rpm, the reaction was carried out for 36 h, ether was slowly added dropwise, the precipitate was collected, purified, and vacuum dried to obtain a multi-arm polymer.

[0071] Take 60g of crushed bamboo and 20g of coffee grounds in a ratio of 3:1, soak them in 0.5mol / L citric acid solution for 12h, dry them, put them into a muffle furnace, and pyrolyze them in a nitrogen environment. Heat them to 400℃ at a rate of 10℃ / min, keep them for 30min, introduce CO2 and continue heating to 700℃, keep them for 20min; cool them, crush and sieve them (200 mesh) to obtain multi-level porous biochar.

[0072] 60 g of biochar was immersed in 60 mL of mixed acid (HNO3:H2SO4=1:3), heated to 80°C, refluxed for 2 h, filtered, washed, and dried to obtain carboxylated biochar, which was then immersed in 120 mL of MES buffer containing 2 g of EDC and 0.6 g of NHS, stirred at room temperature for 30 min, 2 g of multi-arm polymer was added, reacted for 12 h, filtered, washed, and dried to obtain modified biochar.

[0073] 25 g of oyster shell powder and 10 g of humic acid were placed in a ball mill, 200 mL of citric acid solution was added, and the mixture was ball-milled at 320 rpm for 4 h. After drying, the mixture was crushed through a 100-mesh sieve to obtain core particles. The core particles were dissolved in chitosan solution, washed, dissolved in TPP solution, washed, and repeated three times. The mixture was dried to obtain sustained-release microcapsules.

[0074] 30 g of modified biochar material, 18 g of slow-release microcapsules and 50 g of sodium carboxymethyl cellulose solution were mixed and granulated to obtain a composite soil conditioner.

[0075] The present invention also carried out comparative examples and related tests.

[0076] Comparative Example 1

[0077] The only difference between Comparative Example 1 and Example 1 is that the multi-arm polymer was not prepared in Comparative Example 1. The other compositions and preparation methods were the same as those in Example 1, and a composite soil conditioner was prepared.

[0078] Comparative Example 2

[0079] The only difference between Comparative Example 2 and Example 1 is that the preparation of slow-release microcapsules was not performed in Comparative Example 2. The other compositions and preparation methods were the same as those in Example 1, and a composite soil conditioner was obtained.

[0080] Comparative Example 3

[0081] The only difference between Comparative Example 3 and Example 1 is that in Comparative Example 3, the carboxylated biochar and the multi-arm polymer are dry-mixed to obtain a mixture of the carboxylated biochar and the multi-arm polymer. The other compositions and preparation methods are the same as those in Example 1 to prepare a composite soil conditioner.

[0082] Performance testing

[0083] The performance of the composite soil conditioner prepared in Examples 1-6 and Comparative Examples 1-3 was tested. 2+ The heavy metal adsorption capacity of soil samples contaminated with Pb (100 mg / kg) and Pb²⁺ (150 mg / kg) was tested by mixing the soil samples with a composite soil conditioner and placing them in a constant temperature and humidity chamber (25°C, 60% humidity) for 30 days. The water retention rate of saturated sandy soil was tested by mixing the composite soil conditioner with the compound soil conditioner. The soil pH was regularly measured to test the pH neutralization capacity of the soil. The nutrient retention capacity of soil supplemented with nitrogen, phosphorus and potassium compound fertilizer was tested by mixing the composite soil conditioner with the compound soil conditioner and then simulating rainfall. The test results are shown in Table 1 below.

[0084] Table 1

[0085]

[0086] As can be seen from Table 1 above, the composite soil conditioner prepared in Comparative Example 1 has a significantly decreased water retention capacity and nutrient retention capacity for the soil compared with Example 1, indicating that the water storage capacity and adsorption capacity of the multi-arm polymer on the bacterial flora help to improve the water retention capacity and nutrient retention capacity of the soil conditioner; the pH of the composite soil conditioner prepared in Comparative Example 2 was obviously not maintained in the neutral range compared with Example 1, indicating that the slow-release microcapsules can enhance the pH maintenance ability of the composite soil conditioner, promote the improvement of soil pH and maintain stability; compared with Example 1, the various properties of the composite soil conditioner prepared in Comparative Example 3 have all declined to a certain extent, indicating that the modified biochar obtained by modifying the carboxylated biochar by grafting can promote the soil conditioner to play a better role.

[0087] The above is a preferred embodiment of the present invention. Those skilled in the art may make several improvements and modifications without departing from the principles of the present invention. These improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a composite soil conditioner, characterized in that: The following steps are involved: Step S1, dissolving pentaerythritol tetraacrylate, N-isopropylacrylamide, acrylic acid, copper bromide and pentamethyldiethylenetriamine in anhydrous ethanol, heating and stirring under nitrogen atmosphere, then adding diethyl ether, collecting the precipitate, purifying, and vacuum drying to obtain a multi-arm polymer; Step S2: mixing the crushed bamboo and coffee grounds, performing gradient pyrolysis under a nitrogen environment, sieving to obtain biochar, immersing the biochar in mixed acid, heating the mixture to react, filtering, and drying to obtain carboxylated biochar. The carboxylated biochar is then immersed in MES buffer, mixed evenly, and then a multi-arm polymer is added to react, filtered, and dried to obtain modified biochar. Step S3, placing the oyster shell powder and humic acid into a ball mill for ball milling, then sieving to obtain core particles, adding the core particles to a chitosan solution, washing, and then adding to a TPP solution, washing, repeating this process three times, and drying to obtain sustained-release microcapsules; Step S4: mixing the modified biochar, the slow-release microcapsules, and the sodium carboxymethyl cellulose solution, and granulating the mixture to obtain a composite soil conditioner; The gradient pyrolysis process comprises the following steps: immersing the mixed bamboo and coffee grounds in a citric acid solution, placing the mixture in a muffle furnace, heating the mixture to 400°C under a nitrogen atmosphere, introducing CO2, and continuing to heat the mixture to 700°C; The mixed acid is obtained by compounding nitric acid and sulfuric acid.

2. The method for preparing a composite soil conditioner according to claim 1, characterized in that: In step S1, the heating and stirring reaction is carried out at a speed of 300-400 rpm, a temperature of 60-65° C., and a time of 32-36 h.

3. The method for preparing a composite soil conditioner according to claim 1, characterized in that: In step S2, the ratio of bamboo to coffee grounds is 3:

1.

4. The method for preparing a composite soil conditioner according to claim 3, wherein: The concentration of the citric acid is 0.5 mol / L; the heating rate to 400° C. is 10° C. / min.

5. The method for preparing a composite soil conditioner according to claim 1, wherein: In step S2, the mixed acid is prepared by mixing nitric acid and sulfuric acid in a ratio of 1:3, and the sieve is 200 mesh; the temperature of the temperature-raising reaction is 75-85° C., and the time is 1.5-3 hours.

6. The method for preparing a composite soil conditioner according to claim 1, wherein: In step S2, EDC and NHS are also dissolved in the MES buffer; and γ-Fe2O3 nanoparticles are loaded on the carboxylated biochar before the multi-arm polymer is added.

7. The method for preparing a composite soil conditioner according to claim 6, characterized in that: The loading comprises the following steps: adding the modified biochar to a 0.8 wt % γ-Fe2O3 solution, ultrasonically dispersing for 30 minutes, and drying to obtain the modified biochar loaded with γ-Fe2O3.

8. The method for preparing a composite soil conditioner according to claim 1, wherein: In step S3, the ball milling speed is 250-400 rpm and the time is 3-5 hours.

9. The method for preparing a composite soil conditioner according to claim 1, wherein: In step S4, the concentration of the carboxymethyl cellulose solution is 3-5 wt %.

10. A composite soil conditioner, characterized in that: The composite soil conditioner is prepared by the preparation method of any one of claims 1 to 9, comprising the following components in parts by weight: 30-45 parts of modified biochar, 18-27 parts of slow-release microcapsules and 50-75 parts of carboxymethyl cellulose solution.

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