Composite soil conditioner and preparation method thereof

Abstract

The invention provides a composite soil conditioner and a preparation method thereof, and belongs to the technical field of agriculture, and the preparation method comprises the following steps: step S1, preparing a multi-arm polymer; step S2, preparing modified biochar; step S3, preparing a sustained-release microcapsule; s4, mixing the modified biochar, the sustained-release microcapsules and the sodium carboxymethyl cellulose solution, and granulating to obtain the composite soil conditioner. The soil conditioner disclosed by the invention can achieve the purposes of efficiently adsorbing heavy metals, adjusting the pH value of soil and helping the soil to retain water.

Description

Technical Field

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

[0002] At present, the situation of soil degradation is becoming increasingly severe, especially problems such as heavy metal pollution, acidification, salinization and organic matter loss need to be solved urgently. Due to the low pH value, acidic soil is likely to cause the dissolution and migration of heavy metals (such as cadmium and lead), and then threaten the safety of agricultural products and human health through crop enrichment. Although traditional soil conditioners such as lime and gypsum can adjust the pH, they have problems such as large application amounts, single functions, easy soil compaction or salinization, and limited improvement effects on beneficial elements such as selenium. In addition, although early synthetic materials can improve the soil structure, they have defects such as environmental risks and high costs. Most of the existing conditioners are mainly single-functional, difficult to balance multiple objectives, and have a narrow application range, making it difficult to meet the improvement requirements of complex soil conditions.

[0003] A patent application document with the publication number of CN111233571A discloses a soil conditioner, which is a mixture made by fermenting seaweed residues through microorganisms and then adding carbonized bagasse, carbonized sugarcane leaves, sugar mill filter mud, silicon potassium fertilizer and attapulgite clay through drying, pulverizing and stirring and mixing. The mixture is made according to the following mass percentages of each component: 25%-55% of seaweed residues, 5%-20% of carbonized bagasse, 5%-20% of carbonized sugarcane leaves, 5%-10% of bone charcoal, 10%-30% of sugar mill filter mud, 10%-20% of silicon potassium fertilizer, and 5%-20% of attapulgite clay. The soil conditioner prepared by this scheme mainly uses waste as raw materials, achieving the effect of waste utilization and resource conservation. However, its function is relatively single, and there are still deficiencies in the functions of heavy metal adsorption and water retention of the soil conditioner.

[0004] Therefore, a preparation method of a composite soil conditioner is needed 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 purposes of high-efficiency heavy metal adsorption, soil pH adjustment and soil water retention of the soil conditioner.

[0006] The specific scheme of the present invention is as follows. A preparation method of a composite soil conditioner includes the following steps: Step S1: Dissolve pentaerythritol tetraacrylate, N-isopropylacrylamide, acrylic acid, copper bromide and pentamethyldiethylenetriamine in absolute ethanol. Under a nitrogen atmosphere, heat and stir to react, then add ether, collect the precipitate, purify it, and vacuum dry it to obtain a multi-arm polymer; Step S2: Mix the crushed bamboo with coffee grounds, and carry out gradient pyrolysis under a nitrogen atmosphere. After sieving, biochar is obtained. Immerse it in a mixed acid, raise the temperature for reaction, filter, and obtain carboxylated biochar after drying. Then immerse the carboxylated biochar in MES buffer solution. After mixing evenly, add multi-arm polymer and carry out the reaction. Filter and dry to obtain modified biochar; Step S3: Put oyster shell powder and humic acid into a ball mill for ball milling, and then sieve to obtain core particles. Add the core particles to chitosan solution, wash, and then add to TPP solution, wash, repeat three times, and dry to obtain slow-release microcapsules; Step S4: Mix the modified biochar, slow-release microcapsules and sodium carboxymethylcellulose solution, and granulate to obtain a composite soil conditioner.

[0007] Pyrolysis of bamboo and coffee grounds yields a hierarchical porous biochar material, which can enable the biochar material to adsorb heavy metal ions of different particle sizes simultaneously, enhancing the adsorption of heavy metals in the soil by the soil conditioner. Through mixed acid oxidation, carboxyl groups are introduced onto the biochar surface to obtain carboxylated biochar. Heavy metals are fixed through ion exchange and complexation. Carboxyl groups can be protonated in acidic soil and can electrostatically attract positively charged Cd 2+ and other ions, further enhancing the adsorption of heavy metals in the soil by the soil conditioner.

[0008] Introduce multi-arm polymer to graft-modify the biochar. The multi-arm polymer absorbs water and swells, and can store a large amount of water. Under drought conditions, the multi-arm polymer shrinks and releases water, enabling the soil conditioner to have the ability to dynamically regulate soil moisture. The network structure of the multi-arm polymer can provide more attachment sites for microorganisms, and can adsorb and enrich nitrogen-fixing bacteria, phosphorus-solubilizing bacteria and other bacterial groups, contributing to the maintenance of soil nutrients.

[0009] When the pH of the soil < 5, the chitosan on the outer layer of the microcapsule is protonated and swells, releasing the internal oyster shell powder, which can quickly neutralize the pH, improve the acidity of the soil, and rapidly bring the pH of the soil to a neutral level. The carboxyl groups and phenolic hydroxyl groups in humic acid can absorb or release protons through dissociation equilibrium, playing a buffering role, and contributing to maintaining the soil pH at 6.5 - 7.5 for a long time. In addition, the aromatic rings in humic acid can have π-π interactions with heavy metals, and at the same time, carboxyl groups can form chelates with metal ions, inhibiting the absorption of heavy metals by plants, and having a synergistic effect with the adsorption of metal ions by biochar, greatly reducing the migration of metal ions in the soil. Moreover, humic acid can also promote the development of plant roots as a natural organic fertilizer. Through microcapsule encapsulation, it can achieve the slow release of humic acid by the soil conditioner, meet the growth needs of plants and avoid nutrient loss.

[0010] Preferably, in the step S1, the speed of the heating and stirring reaction is 300 - 400 rpm, the temperature is 60 - 65 °C, and the time is 32 - 36 h.

[0011] Preferably, in the step S2, the ratio of bamboo to coffee grounds is 3:1; the pyrolysis includes the following steps: the mixed bamboo and coffee grounds are immersed in a citric acid solution, and then placed in a muffle furnace. Under a nitrogen atmosphere, it is heated to 400 °C, and then CO2 is introduced, and it is continuously heated to 700 °C.

[0012] Mesopores are formed at the 400 °C stage, and the formation of micropores is promoted at the 700 °C stage to obtain a gradient pore size.

[0013] Preferably, the concentration of the citric acid is 0.5 mol / L; the heating rate to 400 °C is 10 °C / min.

[0014] Preferably, after heating to 400 °C, it is maintained for 30 min; after heating to 700 °C, it is maintained for 20 min.

[0015] Preferably, in the step S2, the mesh number 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-rising reaction is 75 - 85 °C, and the time is 1.5 - 3 h.

[0016] Preferably, in the step S2, EDC (1-(3-dimethylaminopropyl)-3-ethylcarbodiimide) and NHS (N-hydroxysuccinimide) are also dissolved in the MES (2-(N-morpholino)ethanesulfonic acid) buffer solution; before adding the multi-arm polymer, γ-Fe2O3 nanoparticles are loaded on the carboxylated biochar.

[0017] EDC and NHS can promote the grafting modification of the multi-arm polymer on the carboxylated biochar.

[0018] Preferably, the loading includes the following steps: the modified biochar is added to a 0.8 wt% γ-Fe2O3 solution, ultrasonically dispersed for 30 min, and dried to obtain the modified biochar loaded with γ-Fe2O3.

[0019] The γ-Fe2O3 nanoparticles loaded on the modified biochar material, γ-Fe2O3 can be slowly oxidized to obtain Fe 2+ Fe 2+ in the slightly acidic environment of the plant roots, and Fe

[0020] can be absorbed by plants and participate in the synthesis of chlorophyll, which helps to improve the iron-deficiency chlorosis symptoms of plants. In addition, γ-Fe2O3 has magnetism and can also recycle the soil conditioner in a magnetic field environment.

[0021] Preferably, in the step S4, the concentration of the carboxymethyl cellulose solution is 3-5 wt%.

[0022] It helps to control the particle shape and size of the soil conditioner and reduce the fragmentation and deformation of the soil conditioner.

[0023] To achieve the above object, the present invention also provides a composite soil conditioner prepared by the preparation method of the above-mentioned composite soil conditioner, 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.

[0024] The components of the present invention in the above parts by weight can achieve the optimal effect, making the performance of the composite soil conditioner reach the best.

[0025] Preferably, the modified biochar comprises the following components in parts by weight: 55-65 parts of biochar and 1-2 parts of multi-arm polymer.

[0026] Preferably, the modified biochar further comprises the following raw materials in parts by weight: 60-70 parts of 0.8 wt% γ-Fe2O3 solution.

[0027] The above technical solutions of the present invention at least include the following beneficial effects: (1) The hierarchical porous biochar material is prepared by pyrolysis, which can enable the biochar material to adsorb heavy metal ions with different particle sizes at the same time, enhancing the adsorption of heavy metals in the soil by the soil conditioner. 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 the soil conditioner.

[0028] (2) The multi-arm polymer can absorb water and swell, storing a large amount of water. Under drought conditions, the polymer shrinks and releases water, enabling the soil conditioner to have the ability to dynamically regulate soil moisture. The network structure of the multi-arm polymer can provide more attachment sites for microorganisms, and can adsorb and enrich nitrogen-fixing bacteria, phosphorus-solubilizing bacteria and other bacterial groups, which helps to maintain soil nutrients.

[0029] (3) The chitosan on the outer layer of the slow-release microcapsule protonates and swells at pH < 5, releasing the internal oyster shell powder, which can quickly neutralize the pH and improve the acidity of the soil; the carboxyl groups and phenolic hydroxyl groups in humic acid play a buffering role through dissociation equilibrium, which helps to maintain the soil pH at neutral. In addition, humic acid can also promote the development of plant roots as a natural organic fertilizer. Through microcapsule encapsulation, the slow release of humic acid by the soil conditioner can be achieved, meeting the growth needs of plants and avoiding nutrient loss. Specific embodiments

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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 part of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention fall within the scope of protection of the present invention.

[0031] Example 1 Dissolve 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 in 500 mL of absolute ethanol. Purge with nitrogen to remove oxygen, heat in an oil bath to 65 °C, start stirring at a speed of 350 rpm, react for 36 h, slowly drop in diethyl ether, collect the precipitate, purify, and vacuum dry to obtain a multi-arm polymer.

[0032] Take 60 g of crushed bamboo and mix it with 20 g of coffee grounds in a ratio of 3:1. Soak it in a 0.5 mol / L citric acid solution for 12 h. After drying, put it into a muffle furnace and pyrolyze it in a nitrogen environment. Heat it to 400 °C at a rate of 10 °C / min, hold for 30 min, pass in CO2 and continue heating to 700 °C, maintain for 20 min; cool, crush and sieve (200 mesh) to obtain hierarchical porous biochar.

[0033] Immerse 60 g of biochar in 60 mL of mixed acid (HNO3:H2SO4 = 1:3), heat to 80 °C, reflux and react for 2 h, filter, wash, and dry to obtain carboxylated biochar. Immerse it in 120 mL of MES buffer solution containing 2 g of EDC and 0.6 g of NHS, stir at room temperature for 30 min, add 1.5 g of multi-arm polymer, react for 12 h, filter, wash, and dry. Add it to 65 parts of a 0.8 wt% γ-Fe2O3 solution, disperse by ultrasonic treatment, and dry to obtain modified biochar.

[0034] Put 25 g of oyster shell powder and 10 g of humic acid into a ball mill, add 200 mL of citric acid solution, ball mill at a speed of 300 rpm for 4.5 h, dry and then crush and sieve through a 100-mesh sieve to obtain core particles. Dissolve the core particles in a chitosan solution, wash, dissolve in a TPP solution, wash, repeat three times, and dry to obtain slow-release microcapsules.

[0035] Mix 30 g of modified biochar material, 18 g of slow-release microcapsules, and 55 g of sodium carboxymethylcellulose solution, and granulate to obtain a composite soil conditioner.

[0036] Example 2 Dissolve 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 in 500 mL of absolute ethanol, purge with nitrogen to remove oxygen, heat in an oil bath to 60 °C, start stirring at a speed of 300 rpm, react for 40 h, slowly drop in ether, collect the precipitate, purify, and vacuum dry to obtain a multi-arm polymer.

[0037] Take 60 g of crushed bamboo and 20 g of coffee grounds, mix them in a ratio of 3:1, soak them in 0.5 mol / L citric acid solution for 12 h, dry them and put them into a muffle furnace, pyrolyze them in a nitrogen environment, heat them to 400 °C at a rate of 10 °C / min, hold for 30 min, pass in CO2 and continue heating to 700 °C, maintain for 20 min; cool, crush and sieve (200 mesh) to obtain hierarchical porous biochar.

[0038] Immerse 65 g of biochar in 60 mL of mixed acid (HNO3:H2SO4 = 1:3), raise the temperature to 80 °C, reflux and react for 2 h, filter, wash, dry to obtain carboxylated biochar, immerse it in 120 mL of MES buffer solution containing 2 g of EDC and 0.6 g of NHS, stir at room temperature for 30 min, add 1 g of multi-arm polymer, react for 12 h, filter, wash, dry, add it to 60 parts of 0.8 wt% γ-Fe2O3 solution, ultrasonically disperse, dry to obtain modified biochar.

[0039] Put 25 g of oyster shell powder and 10 g of humic acid into a ball mill, add 200 mL of citric acid solution, ball mill at a speed of 350 rpm for 3.5 h, dry and then crush and sieve through a 100-mesh sieve to obtain core particles, dissolve the core particles in chitosan solution, wash, dissolve in TPP solution, wash, repeat three times, and dry to obtain sustained-release microcapsules.

[0040] Mix 45 g of modified biochar material, 27 g of sustained-release microcapsules and 75 g of sodium carboxymethylcellulose solution, granulate to obtain a composite soil conditioner.

[0041] Example 3 Dissolve 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 in 500 mL of absolute ethanol, purge with nitrogen to remove oxygen, heat in an oil bath to 62 °C, start stirring at a speed of 400 rpm, react for 32 h, slowly drop in ether, collect the precipitate, purify, and vacuum dry to obtain a multi-arm polymer.

[0042] Take 60 g of crushed bamboo and 20 g of coffee grounds, mix them in a ratio of 3:1, soak them in 0.5 mol / L citric acid solution for 12 h, dry them and then put them into a muffle furnace. Pyrolyze them under a nitrogen environment, heat them to 400 °C at a rate of 10 °C / min, hold for 30 min, introduce CO2 and continue heating to 700 °C, maintain for 20 min; cool, crush and sieve (200 mesh) to obtain hierarchical porous biochar.

[0043] Immerse 65 g of biochar into 60 mL of mixed acid (HNO3:H2SO4 = 1:3), raise the temperature to 80 °C, reflux for 2 h, filter, wash, and dry to obtain carboxylated biochar. Immerse it into 120 mL of MES buffer solution containing 2 g of EDC and 0.6 g of NHS, stir at room temperature for 30 min, add 1.5 g of multi-arm polymer, react for 12 h, filter, wash, dry, add it to 70 parts of 0.8 wt% γ-Fe2O3 solution, disperse by ultrasonic wave, and dry to obtain modified biochar.

[0044] Put 25 g of oyster shell powder and 10 g of humic acid into a ball mill, add 200 mL of citric acid solution, ball mill at a speed of 250 rpm for 5 h, dry and then crush and sieve through a 100-mesh sieve to obtain core particles. Dissolve the core particles in chitosan solution, wash, dissolve in TPP solution, wash, repeat three times, and dry to obtain slow-release microcapsules.

[0045] Mix 35 g of modified biochar material, 25 g of slow-release microcapsules and 60 g of sodium carboxymethylcellulose solution, and granulate to obtain a composite soil conditioner.

[0046] Example 4 Dissolve 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 in 500 mL of absolute ethanol, purge with nitrogen to remove oxygen, heat in an oil bath to 65 °C, start stirring at a speed of 400 rpm, react for 36 h, slowly drop in ether, collect the precipitate, purify, and vacuum dry to obtain multi-arm polymer.

[0047] Take 60 g of crushed bamboo and 20 g of coffee grounds, mix them in a ratio of 3:1, soak them in 0.5 mol / L citric acid solution for 12 h, dry them and then put them into a muffle furnace. Pyrolyze them under a nitrogen environment, heat them to 400 °C at a rate of 10 °C / min, hold for 30 min, introduce CO2 and continue heating to 700 °C, maintain for 20 min; cool, crush and sieve (200 mesh) to obtain hierarchical porous biochar.

[0048] Immerse 55 g of biochar in 60 mL of mixed acid (HNO3:H2SO4 = 1:3), heat up to 80 °C, reflux for 2 h, filter, wash, and dry to obtain carboxylated biochar. Immerse it in 120 mL of MES buffer solution containing 2 g of EDC and 0.6 g of NHS, stir at room temperature for 30 min, add 2 g of multi-arm polymer, react for 12 h, filter, wash, dry, add it to 60 parts of 0.8 wt% γ-Fe2O3 solution, ultrasonically disperse, and dry to obtain modified biochar.

[0049] Put 25 g of oyster shell powder and 10 g of humic acid into a ball mill, add 200 mL of citric acid solution, ball mill at a speed of 400 rpm for 3 h, dry and crush through a 100-mesh sieve to obtain core particles. Dissolve the core particles in chitosan solution, wash, dissolve in TPP solution, wash, repeat three times, and dry to obtain slow-release microcapsules.

[0050] Mix 45 g of modified biochar material, 27 g of slow-release microcapsules, and 70 g of sodium carboxymethyl cellulose solution, and granulate to obtain a composite soil conditioner.

[0051] Example 5 Dissolve 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 in 500 mL of absolute ethanol, purge with nitrogen to remove oxygen, heat in an oil bath to 60 °C, start stirring at a speed of 350 rpm, react for 36 h, slowly drop in ether, collect the precipitate, purify, and vacuum dry to obtain multi-arm polymer.

[0052] Take 60 g of crushed bamboo and 20 g of coffee grounds, mix them in a ratio of 3:1, soak in 0.5 mol / L citric acid solution for 12 h, dry and put into a muffle furnace, pyrolyze in a nitrogen environment, heat at a rate of 10 °C / min to 400 °C, hold for 30 min, pass in CO2 and continue heating to 700 °C, maintain for 20 min; cool, crush and sieve (200 mesh) to obtain hierarchical porous biochar.

[0053] Immerse 60 g of biochar in 60 mL of mixed acid (HNO3:H2SO4 = 1:3), heat up to 80 °C, reflux for 2 h, filter, wash, and dry to obtain carboxylated biochar. Immerse it in 120 mL of MES buffer solution containing 2 g of EDC and 0.6 g of NHS, stir at room temperature for 30 min, add 2 g of multi-arm polymer, react for 12 h, filter, wash, dry, add it to 70 parts of 0.8 wt% γ-Fe2O3 solution, ultrasonically disperse, and dry to obtain modified biochar.

[0054] Put 25 g of oyster shell powder and 10 g of humic acid into a ball mill, add 200 mL of citric acid solution, ball mill at a speed of 320 rpm for 4 h, dry, crush, and pass through a 100-mesh sieve to obtain core particles. Dissolve the core particles in a chitosan solution, wash, dissolve in a TPP solution, wash, repeat three times, and dry to obtain the sustained-release microcapsules.

[0055] Mix 30 g of modified biochar material, 18 g of sustained-release microcapsules, and 50 g of sodium carboxymethyl cellulose solution, and granulate to obtain a composite soil conditioner.

[0056] Example 6 Dissolve 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 in 500 mL of absolute ethanol, purge with nitrogen to remove oxygen, heat in an oil bath to 60 °C, start stirring at a speed of 350 rpm, react for 36 h, slowly drop in ether, collect the precipitate, purify, and vacuum dry to obtain the multi-arm polymer.

[0057] Take 60 g of crushed bamboo and 20 g of coffee grounds, mix them in a ratio of 3:1, soak them in 0.5 mol / L citric acid solution for 12 h, dry, put them into a muffle furnace, pyrolyze in a nitrogen environment, heat at a rate of 10 °C / min to 400 °C, hold for 30 min, introduce CO2 and continue heating to 700 °C, maintain for 20 min; cool, crush, and sieve (200 mesh) to obtain the hierarchical porous biochar.

[0058] Immerse 60 g of biochar in 60 mL of mixed acid (HNO3:H2SO4 = 1:3), raise the temperature to 80 °C, reflux and react for 2 h, filter, wash, and dry to obtain carboxylated biochar. Immerse it in 120 mL of MES buffer solution containing 2 g of EDC and 0.6 g of NHS, stir at room temperature for 30 min, add 2 g of multi-arm polymer, react for 12 h, filter, wash, and dry to obtain the modified biochar.

[0059] Put 25 g of oyster shell powder and 10 g of humic acid into a ball mill, add 200 mL of citric acid solution, ball mill at a speed of 320 rpm for 4 h, dry, crush, and pass through a 100-mesh sieve to obtain core particles. Dissolve the core particles in a chitosan solution, wash, dissolve in a TPP solution, wash, repeat three times, and dry to obtain the sustained-release microcapsules.

[0060] Mix 30 g of modified biochar material, 18 g of sustained-release microcapsules, and 50 g of sodium carboxymethyl cellulose solution, and granulate to obtain a composite soil conditioner.

[0061] The present invention also conducted comparative examples and related tests.

[0062] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is only that in Comparative Example 1, the preparation of the multi-arm polymer was not carried out, and the other components and preparation methods were the same as those in Example 1, and a composite soil conditioner was prepared.

[0063] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is only that in Comparative Example 2, the preparation of the slow-release microcapsules was not carried out, and the other components and preparation methods were the same as those in Example 1, and a composite soil conditioner was obtained.

[0064] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is only that in Comparative Example 3, the carboxylated biochar and the multi-arm polymer were dry-mixed to obtain a mixture of carboxylated biochar and multi-arm polymer, and the other components and preparation methods were the same as those in Example 1, and a composite soil conditioner was prepared.

[0065] Performance detection test The composite soil conditioners prepared in Examples 1-6 and Comparative Examples 1-3 were subjected to performance tests. Contaminated soil samples containing Cd 2+ (100 mg / kg) and Pb²⁺ (150 mg / kg) were prepared. After mixing the soil samples with the composite soil conditioner, they were placed in a constant temperature and humidity chamber (25 °C, 60% humidity) for 30 days for heavy metal adsorption capacity testing; after the sandy soil was saturated with water, it was mixed with the composite soil conditioner and placed in an oven at 30 °C for water retention rate testing; the acidic soil (pH 4.5) was mixed with the composite soil conditioner, and the soil pH was measured regularly for pH neutralization capacity testing; after the soil added with nitrogen, phosphorus and potassium compound fertilizer was mixed with the composite soil conditioner, simulated rainfall was carried out for nutrient retention capacity testing. The test results of each item are shown in Table 1 below.

[0066] Table 1

[0067] It can be seen from Table 1 above that compared with Example 1, the composite soil conditioner prepared in Comparative Example 1 has a significant decrease in the water retention capacity and nutrient retention capacity of the soil, indicating that the water storage capacity of the multi-arm polymer and the adsorption capacity for bacteria help to improve the water retention capacity and nutrient retention capacity of the soil conditioner; compared with Example 1, the composite soil conditioner prepared in Comparative Example 2 fails to maintain the pH in the neutral range significantly, 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 performance of the composite soil conditioner prepared in Comparative Example 3 has a certain degree of decline in all aspects, indicating that the modified biochar obtained by grafting the carboxylated biochar can promote the better performance of the soil conditioner.

[0068] The above is the preferred embodiment of the present invention. Without departing from the principle of the present invention, those of ordinary skill in the technical field can also make several improvements and refinements, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a composite soil conditioner, characterized in that It includes the following steps: Step S1: Dissolve pentaerythritol tetraacrylate, N-isopropylacrylamide, acrylic acid, copper bromide, and pentamethyldiethylenetriamine in absolute ethanol. Under a nitrogen atmosphere, heat and stir for reaction, then add ether, collect the precipitate, purify it, and vacuum dry to obtain a multi-arm polymer; Step S2: Mix the crushed bamboo with coffee grounds. Under a nitrogen atmosphere, perform gradient pyrolysis, sieve it to obtain biochar, immerse it in a mixed acid, raise the temperature for reaction, filter it, and dry it to obtain carboxylated biochar. Then immerse the carboxylated biochar in MES buffer, mix evenly, add the multi-arm polymer, react, filter, and dry to obtain modified biochar; Step S3: Put oyster shell powder and humic acid into a ball mill for ball milling, then sieve to obtain core particles. Add the core particles to a chitosan solution, wash, then add it to a TPP solution, wash, repeat three times, and dry to obtain a sustained-release microcapsule; Step S4: Mix the modified biochar, the sustained-release microcapsule, and a sodium carboxymethylcellulose solution, and granulate to obtain a composite soil conditioner.

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

3. The preparation method of a composite soil conditioner according to claim 1, characterized in that In the said Step S2, the ratio of bamboo to coffee grounds is 3:1; the gradient pyrolysis includes the following steps: Immerse the mixed bamboo and coffee grounds in a citric acid solution, then put it into a muffle furnace. Under a nitrogen atmosphere, heat to 400 °C, then introduce CO2 and continue to heat to 700 °C.

4. The preparation method of a composite soil conditioner according to claim 3, characterized in that, The concentration of the said citric acid is 0.5 mol / L; the heating rate to 400 °C is 10 °C / min.

5. The preparation method of a composite soil conditioner according to claim 1, characterized in that, In the said Step S2, the mesh number 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 for raising the temperature for reaction is 75 - 85 °C, and the time is 1.5 - 3 h.

6. The preparation method of a composite soil conditioner according to claim 1, characterized in that In the said Step S2, EDC and NHS are also dissolved in the MES buffer; before adding the multi-arm polymer, γ-Fe2O3 nanoparticles are also loaded on the carboxylated biochar.

7. The preparation method of a composite soil conditioner according to claim 6, wherein The said loading includes the following steps: Add the modified biochar to a 0.8 wt% γ-Fe2O3 solution, ultrasonically disperse for 30 min, and dry to obtain modified biochar loaded with γ-Fe2O3.

8. The preparation method of a composite soil conditioner according to claim 1, characterized in that, In the said Step S3, the speed of ball milling is 250 - 400 rpm, and the time is 3 - 5 h.

9. The preparation method of a composite soil conditioner according to claim 1, characterized in that, In the said Step S4, the concentration of the sodium carboxymethylcellulose solution is 3 - 5 wt%.

10. A composite soil conditioner, characterized in that, Prepared by using the preparation method of a composite soil conditioner according to any one of claims 1 - 9, and it includes the following components in parts by weight: 30 - 45 parts of modified biochar, 18 - 27 parts of sustained-release microcapsule, and 50 - 75 parts of sodium carboxymethylcellulose solution.

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