A cadmium-reducing lead soil conditioner, a preparation method thereof and a soil conditioning method

Abstract

The application provides a cadmium-reducing lead soil conditioner and a preparation method and soil conditioning method thereof, and relates to the technical field of soil conditioning. The application comprises the following components by weight: 16-24 parts of bacteria-algae particles, 8-12 parts of pH-responsive hydrogel, 5-10 parts of calcium alginate, 10-15 parts of hydroxyapatite-urea composite microspheres, and 20-25 parts of ammonia-modified mesoporous carbon. The bacteria-algae particles are obtained by mixing and culturing chlorella and bacillus subtilis at a ratio of 1:1, and then treating the mixture with a citric acid solution; the pH-responsive hydrogel is an acrylic acid-chitosan copolymer; and the hydroxyapatite-urea composite microspheres are obtained by wrapping nano-hydroxyapatite and urea in a gel network formed by cross-linking sodium alginate and calcium ions. The application can realize efficient removal of cadmium and lead in the soil through the synergistic effect of the multiple mechanisms of adsorption, fixation, regulation and efficiency preservation, and can overcome the limitations of single-functioning conditioning agents. The application can be applied to different types of soil and has high persistence. The preparation method is simple and convenient to apply.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil conditioning, in particular to a cadmium and lead reducing soil conditioner, a preparation method thereof and a soil conditioning method. BACKGROUND

[0002] Soil heavy metal pollution is one of the current environmental problems, among which cadmium (Cd) and lead (Pb) pose a threat to soil ecosystems and human health due to their high toxicity, non-degradability and bioaccumulation. Existing soil heavy metal remediation technologies mainly include physical remediation, chemical remediation, biological remediation and other methods.

[0003] In the chemical remediation method, the application of soil conditioner is the most widely used, which mainly reduces the content of available heavy metals in soil through adsorption, precipitation, complexation and other actions. However, the existing conditioners have problems such as single function, limited remediation efficiency, poor persistence and the like: for example, although hydroxyapatite can fix heavy metals, it has poor persistence.

[0004] Chinese patent document CN103242849A discloses a comprehensive conditioner for remediation of copper and cadmium contaminated acidic soil and a preparation method thereof. The comprehensive conditioner has a pH of more than 10 and is composed of the following components by weight: organic fertilizer 95-96%, limestone powder or alkali residue 3-5%, and nano-hydroxyapatite 0.2-1.0%. The preparation method is to uniformly stir and sieve the components to obtain the conditioner. The conditioner proposed in the scheme is mainly used to reduce the content of copper and lead in soil, and the raw materials are simply mixed, the components are easy to separate and lose, and the effective period is short.

[0005] Chinese patent document CN109097059A discloses a bacterial source mesoporous carbon material, a preparation method thereof and application thereof in remediation of heavy metal contaminated water systems or soil. In the scheme, the bacterial bodies are pyrolyzed under a protective atmosphere to obtain a bacterial source carbon material with a large specific surface, a graphite-like sheet structure and rich mesopores, and the bacterial source carbon material can release orthophosphate ions in soil water phase. The bacterial source carbon material can be used for remediation of heavy metal pollution in soil water phase through adsorption, passivation and fixation, and can also release phosphorus, but it cannot be applied to different soil pH environments, and the nutrients are single, only phosphorus can be released, and other key nutrients such as nitrogen are not involved. In addition, although activated carbon adsorption materials can adsorb heavy metals, they are easy to release heavy metals again due to environmental changes; although biological remediation agents are environmentally friendly, they have a long remediation period and low efficiency.

[0006] Therefore, it is urgent to develop a cadmium and lead reducing soil conditioner which can comprehensively play the multiple roles of adsorption, fixation, regulation and the like, is suitable for different soil types, and has a long-acting and stable remediation effect. SUMMARY

[0007] The technical problem solved by the present application is to provide a cadmium and lead reducing soil conditioner, a preparation method thereof and a soil conditioning method in view of the defects of the prior art.

[0008] To solve the above technical problems, the present application adopts the following technical solutions:

[0009] In a first aspect, the present application provides a multi-component synergistically stable cadmium and lead reducing soil conditioner, comprising the following components by weight:

[0010] 16-24 parts of bacterial algal particles, 8-12 parts of pH responsive hydrogel, 5-10 parts of calcium alginate, 10-15 parts of hydroxyapatite-urea composite microspheres, and 20-25 parts of ammonia modified mesoporous carbon;

[0011] The bacterial algal particles are prepared by mixing Chlorella vulgaris and Bacillus subtilis at a ratio of 1:1, treating the mixture with a 10% citric acid solution at 55-65 DEG C for 1.8-2.2 hours, centrifuging and freeze-drying.

[0012] The pH responsive hydrogel is an acrylic acid-chitosan copolymer.

[0013] The hydroxyapatite-urea composite microspheres are prepared by the following method: mixing nano-hydroxyapatite and urea at a weight ratio of 4:1, adding a 2% sodium alginate aqueous solution, ultrasonic dispersion to prepare a suspension; using the suspension as the water phase, adding 3% Tween-80 cyclohexane as the oil phase, the volume ratio of the water phase to the oil phase being 1:5, emulsifying to form an O / W microemulsion; adding 10% calcium chloride anhydrous ethanol solution dropwise into the microemulsion, the molar ratio of calcium chloride to sodium alginate being 1:1, stirring to crosslink sodium alginate and calcium ions (Ca 2+ ) to form a gel network, which encapsulates nano-hydroxyapatite and urea; filtering and collecting the microspheres, dehydrating, drying and sieving to obtain the hydroxyapatite-urea composite microspheres.

[0014] The ammonia modified mesoporous carbon is prepared by first preparing a carbon precursor using sucrose as the carbon source, then carbonizing the carbon precursor to obtain mesoporous carbon, and then immersing the mesoporous carbon in an ammonia solution to load amino groups onto the surface of the mesoporous carbon.

[0015] Further, the acrylic acid-chitosan copolymer is prepared by mixing acrylic acid and chitosan at a weight ratio of 2:1, adding 0.5-1 part of a crosslinking agent N,N'-methylenebisacrylamide, and stirring uniformly; under the protection of an inert atmosphere, adding an initiator, and stirring in a 60 DEG C water bath for 3-4 hours. Preferably, the inert atmosphere is nitrogen, argon or helium, more preferably nitrogen; preferably, the initiator is a water-soluble free radical initiator, such as potassium persulfate or ammonium persulfate; more preferably, the initiator is potassium persulfate.

[0016] Further, in the preparation process of the hydroxyapatite-urea composite microspheres, the solid-liquid ratio of the mixture of nano-hydroxyapatite and urea and the sodium alginate aqueous solution is 1:10 g / mL, and the ultrasonic dispersion condition is 250-350 W ultrasonic treatment for 10-20 min.

[0017] Further, in the preparation process of the hydroxyapatite-urea composite microspheres, the dehydration and drying conditions of the collected microspheres are as follows: dehydrated with anhydrous ethanol and vacuum dried at 40°C, which can satisfy the condition of not damaging the microsphere structure.

[0018] Further, in the preparation process of the hydroxyapatite-urea composite microspheres, the emulsification treatment condition of the water phase and the oil phase is 25-35°C emulsification at a speed of 1000-1500 r / min for 15-25 min.

[0019] Further, the specific preparation method of the ammonia-modified mesoporous carbon comprises the following steps: (1) taking sucrose as a carbon source, dissolving sucrose and water at a mass-volume ratio of 1:3, and performing hydrothermal reaction at 160-180°C for 10-15 h, and then centrifuging and drying after cooling to obtain a carbon precursor; (2) placing the carbon precursor in a tube furnace, and increasing the temperature to 750-850°C at a heating rate of 5°C / min, and then carbonizing at a constant temperature for 1.5-2.5 h in an inert atmosphere, and then naturally cooling to obtain mesoporous carbon; (3) soaking the mesoporous carbon in a 25% ammonia water solution, and stirring at 55-65°C for 5-8 h to load amino groups onto the surface of the mesoporous carbon; after the reaction, washing with deionized water until neutral, and then drying at 75-85°C to obtain ammonia-modified mesoporous carbon, and the specific surface area of the ammonia-modified mesoporous carbon is 800-1200 m 2 / g. Preferably, the inert atmosphere in the carbonization process is nitrogen, argon or helium, and more preferably, nitrogen.

[0020] In a second aspect, the present application further provides a preparation method of the soil conditioner for reducing cadmium and lead as described above, comprising the following steps:

[0021] S1, taking the pH-responsive hydrogel according to the weight parts, adding deionized water at a solid-liquid ratio of 1:5 g / mL, and swelling at 20-30°C for 1.5-2.5 h to form a hydrogel suspension;

[0022] S2, according to the mass ratio of the pH-responsive hydrogel to the bacteria-algae particles of 1:2, adding bacteria-algae particles to the hydrogel suspension, stirring at 400-600 r / min at 25-35°C for 12-18 min, so that the bacteria-algae particles are wrapped by the hydrogel to form a core-shell structure, and then removing the free water by vacuum filtration to obtain a hydrogel-bacteria-algae composite;

[0023] S3, the weight parts of the ammonia modified mesoporous carbon is added into anhydrous ethanol according to a solid-liquid ratio of 1:8 g / mL to form a mesoporous carbon dispersion liquid by ultrasonic dispersion; then the hydrogel-bacterial alga composite of S2 is added, and the mesoporous carbon is uniformly adsorbed on the surface of the hydrogel by stirring, and dried to a moisture content of less than or equal to 5% to obtain a mesoporous carbon-hydrogel-bacterial alga composite;

[0024] S4, the calcium alginate is mixed with deionized water according to a weight ratio of 1:10 to prepare a calcium alginate colloid; the mesoporous carbon-hydrogel-bacterial alga composite of S3 and the hydroxyapatite-urea composite microspheres are added, and the mass ratio of the mesoporous carbon-hydrogel-bacterial alga composite of S3 to the hydroxyapatite-urea composite microspheres to the calcium alginate is 10:3:1.5, and the mixture is obtained by stirring at 150-250 r / min at 35-45 DEG C for 15-25 min, so that the calcium alginate colloid is filled in the interstitial space to form a three-dimensional network structure;

[0025] S5, the mixture of S4 is granulated, and vacuum dried at 35 DEG C to a moisture content of 10-15% to obtain the product.

[0026] Further, the shell thickness of the core-shell structure in S2 is 20-50 um.

[0027] Further, the ultrasonic dispersion condition in S3 is ultrasonic treatment at a power of 180-220 W for 8-12 min.

[0028] Further, the stirring condition after adding the hydrogel-bacterial alga composite in S3 is stirring at 250-350 r / min at 45-55 DEG C for 25-35 min.

[0029] Further, the drying condition in S3 is air drying at 55-65 DEG C.

[0030] Further, the particle size of the calcium alginate in S4 is 50-100 um.

[0031] Further, the granulation particle size in S5 is 1-3 mm, the particle compressive strength is greater than or equal to 2 N, and a stable gel structure can be formed within 30 min after water is added.

[0032] In a third aspect, the application further provides a soil conditioning method, specifically, the conditioning agent or the conditioning agent prepared by the method described above is uniformly applied 7-10 days before ploughing, the application amount is 50-75 kg / acre, and the soil is uniformly mixed with the paddy field soil by ploughing twice after application, an appropriate amount of water is poured to stabilize and mature for 3-5 days, and then rice transplanting is performed.

[0033] The action mechanism of each component in the application is as follows:

[0034] (1) Bacteria-algae particles: The bacteria-algae particle component in the conditioner of the present application is rich in natural organic matter and microbial active substances, which can improve the soil aggregate structure, increase the soil permeability and water retention; at the same time, the functional groups on its surface can complex with heavy metals in the soil, and assist in reducing the activity of cadmium, lead and other heavy metals in the soil, and reducing the absorption of heavy metals by crops.

[0035] (2) pH-responsive hydrogel: The specific pH-responsive material used in the conditioner of the present application is acrylic acid-chitosan copolymer, in acidic soil (pH < 5.5), the carboxyl groups (-COOH) in the copolymer dissociate into -COO - , which combines with cadmium, lead and other heavy metal ions through electrostatic attraction and chelation, and fixes the heavy metals; in neutral / alkaline soil, the carboxyl groups are protonated, the gel shrinks, and the potential toxicity to crop roots can be avoided.

[0036] (3) Calcium alginate: The calcium alginate component in the conditioner of the present application has good water and fertilizer retention performance, can form a three-dimensional network structure in the soil to retain soil moisture and reduce nutrient loss; at the same time, it can provide carbon source for soil microorganisms, promote microbial reproduction, and improve the soil microbial environment.

[0037] (4) Hydroxyapatite (HAP)-urea composite microspheres: The hydroxyapatite in the hydroxyapatite-urea composite microspheres of the present application can form stable phosphate precipitates with cadmium and lead ions, achieving permanent fixation of heavy metals; urea slowly releases nitrogen, making up for the consumption of soil nutrients during the repair process.

[0038] (5) Ammonia-modified mesoporous carbon: The ammonia-modified mesoporous carbon prepared in the present application has a high specific surface area (> 800 m² / g) and a rich mesoporous structure (pore size 2-50 nm), and contains a large number of amino groups after modification with ammonia water, which can form coordination complexes with cadmium and lead through amino groups, efficiently adsorbing heavy metals in the soil; its surface basic functional groups can neutralize acidic soil and adjust the pH value of the soil; in addition, the amino groups can also slowly release nitrogen, providing additional nitrogen nutrition for crop growth.

[0039] The soil conditioner of the present application is configured by the above components, which can comprehensively improve the cadmium and lead contaminated soil. The main effects are as follows: ammonia-modified mesoporous carbon (high specific surface area) rapidly adsorbs free cadmium and lead in the soil, while neutralizing the acidity; pH-responsive hydrogel wraps bacteria-algae particles, chelates heavy metals under acidic conditions, shrinks under neutral / alkaline conditions to avoid root damage, and protects the activity of bacteria-algae; HAP-urea microspheres slowly release HAP (form permanent phosphate precipitates) and urea (supply nitrogen), solving the problems of "adsorption reversibility" and "fertility decline"; calcium alginate forms a three-dimensional network to fix the components and prevent loss, prolonging the effective period.

[0040] Compared with the prior art, the present application has the following beneficial effects:

[0041] 1. The soil conditioner of the present invention achieves efficient removal of cadmium and lead from the soil through the synergistic effect of multiple mechanisms of "adsorption-fixation-regulation-efficacy retention", overcoming the limitations of single-function conditioners.

[0042] 2. Introducing pH-responsive hydrogels can automatically adjust the local pH value according to the soil environment, optimize remediation conditions, improve remediation efficiency, and are suitable for soils with different pH types.

[0043] 3. The soil conditioner of this invention uses hydroxyapatite-urea composite microspheres, which can achieve the dual functions of heavy metal fixation and soil nutrient replenishment, thus avoiding the problem of soil fertility decline after remediation.

[0044] 4. The soil conditioner of the present invention improves the persistence of the conditioner and reduces the risk of secondary pollution through the synergistic effect of its components.

[0045] 5. The preparation method of the soil conditioner of the present invention is simple, convenient to use, and suitable for large-scale promotion and application. Detailed Implementation

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0047] As used in this article:

[0048] "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variation thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0049] When a parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1~5” is disclosed, the described range should be interpreted as including the ranges “1~4”, “1~3”, “1~2”, “1~2 and 4~5”, “1~3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0050] In these examples, the parts and percentages are by mass unless otherwise indicated.

[0051] For the purpose of promoting a fuller understanding of the application, a more complete description of the application is set forth below in connection with specific examples. The application, however, can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

[0052] The main raw materials used in the following examples include Chlorella vulgaris, Bacillus subtilis, acrylic acid, chitosan, crosslinking agent N,N'-methylene bisacrylamide, potassium persulfate, sodium alginate, calcium chloride, nano-hydroxyapatite, urea, sucrose, etc., each of which is a conventional product sold on the market.

[0053] I. Preparation of soil conditioner

[0054] Example 1 Preparation of bacteria-algae granules

[0055] The present application provides a preparation method of bacteria-algae granules, specifically, Chlorella vulgaris and Bacillus subtilis are mixed and cultured at a ratio of 1:1, then treated with a 10% citric acid solution at 55-65℃ for 1.8-2.2h, centrifuged and freeze-dried to obtain carboxylated bacteria-algae porous granules. The Chlorella vulgaris is a brownish yellow powder; the effective viable count of Bacillus subtilis is ≥100 billion CFU / g.

[0056] The Bacillus subtilis in the bacteria-algae granules of the present application has strong resistance due to its spore structure, which can meet the basic activity requirements. In order to avoid the influence of freeze-drying on the activity of the bacteria, 5% sucrose solution is added to protect the bacteria before freeze-drying after centrifugation, because sucrose can form a glass state during freeze-drying, which can wrap the cell membrane of the bacteria and reduce the damage caused by dehydration; the citric acid solution added during preparation mainly plays a role in optimizing and selecting effective bacteria.

[0057] Since the upper limit of the temperature tolerance of the spores of Bacillus subtilis is about 70℃, and the spore germination rate will decrease when the temperature exceeds 70℃, and the efficiency of bacteria selection and functional group optimization of citric acid is insufficient when the temperature is lower than 50℃; and the citric acid needs to be maintained at a specific temperature for a sufficient time to fully react with the surface groups of the bacteria (such as carboxylation modification), and if the time is too short (<1.8h), the functional group modification will not be sufficient, and if the time is too long (>2.2h), the bacteria proteins may be excessively decomposed, reducing the content of organic matter. Therefore, the treatment conditions of the citric acid solution are 55-65℃ for 1.8-2.2h. This embodiment is a preferred embodiment, and 60℃ for 2h is specifically used as an example for illustration.

[0058] Example 2 Preparation of pH-responsive hydrogel

[0059] The pH-responsive hydrogel in the scheme of the application is specifically an acrylic acid-chitosan copolymer, acrylic acid CAS 79-10-7. The degree of deacetylation of chitosan is greater than or equal to 90%, CAS 9012-76-4. The crosslinking agent is N,N'-methylenebisacrylamide, CAS 110-26-9, with a density of 1.235 g / cm 3 . The concentration of potassium persulfate is 0.01 mol / L.

[0060] The application provides a preparation method of an acrylic acid-chitosan copolymer, specifically as follows: acrylic acid and chitosan are mixed at a weight ratio of 2:1, 0.5-1 parts of a crosslinking agent N,N'-methylenebisacrylamide is added, and stirring is uniform. Then, 0.2 g of potassium persulfate is added as an initiator under nitrogen protection, stirring is performed in a 60℃ water bath for 4 h, and an acrylic acid-chitosan copolymer hydrogel is obtained. The hydrogel is repeatedly washed with deionized water to remove unreacted monomers and impurities, and then freeze-drying and crushing to a particle size of less than 50 mesh are performed to obtain a pH-responsive hydrogel. In order to study the influence of the weight fraction of the added crosslinking agent on the conditioner performance, different examples are set, and the specific parameters are shown in Table 1.

[0061] Example 3: Preparation of calcium alginate

[0062] It is prepared by using conventional techniques from sodium alginate and calcium chloride. The crosslinking reaction occurs between the carboxyl group in sodium alginate and the calcium ion in calcium chloride to form calcium alginate precipitate which is insoluble in water. After filtration, washing and drying, it is obtained. The sodium alginate is aqueous with an active substance content of greater than or equal to 90%. The calcium chloride is a conventional product available on the market, CAS 10035-04-8.

[0063] Example 4: Preparation of hydroxyapatite (HAP)-urea composite microspheres

[0064] Raw material parameters: nano-hydroxyapatite (HAP) particle size 20-50 nm, purity greater than or equal to 99.5%, CAS 1306-06-5. Urea N content 46%.

[0065] The application provides a preparation method of hydroxyapatite-urea composite microspheres, specifically as follows: nano-hydroxyapatite (HAP) and urea are mixed at a weight ratio of 4:1, 2% sodium alginate aqueous solution is added, and a suspension is prepared by ultrasonic dispersion. The ultrasonic dispersion conditions are 250-350 W ultrasonic treatment for 10-20 min. As a preferred example, the ultrasonic dispersion conditions use the following parameters: 300 W ultrasonic treatment for 15 min, which is used as an example for illustration.

[0066] The microemulsion is prepared by adding 3% Tween-80 in cyclohexane as the oil phase to the aqueous phase, and emulsifying the mixture to form an O / W microemulsion, with the volume ratio of the aqueous phase to the oil phase being 1:5; the emulsification is carried out at a speed of 1000-1500 r / min for 15-25 min at 25-35℃. As a preferred embodiment, the emulsification is carried out at a speed of 1200 r / min for 20 min at 30℃.

[0067] A 10% calcium chloride solution in pure anhydrous ethanol is added dropwise to the microemulsion, with the molar ratio of calcium chloride to sodium alginate being 1:1, and the mixture is stirred for 30 min, so that the sodium alginate and the calcium chloride form a gel network to encapsulate the nano-hydroxyapatite and urea; the mixture is dehydrated with anhydrous ethanol and dried in a vacuum at 40℃, and the composite microspheres with a particle size of 5-20 μm are obtained by sieving. 2+ The gel network is crosslinked to encapsulate the nano-hydroxyapatite and urea; the mixture is dehydrated with anhydrous ethanol and dried in a vacuum at 40℃, and the composite microspheres with a particle size of 5-20 μm are obtained by sieving.

[0068] Example 5: Preparation of ammonia-modified mesoporous carbon

[0069] The density of the selected sucrose is 1.587 g / cm 3 The present application provides a method for preparing ammonia-modified mesoporous carbon, which comprises the following steps: (1) dissolving sucrose and water in a mass / volume ratio of 1:3 to obtain a carbon precursor by hydrothermal reaction at 160-180℃ for 10-15 h; (2) heating the carbon precursor to 750-850℃ at a rate of 5℃ / min in a tube furnace, and carbonizing the carbon precursor in an inert atmosphere for 1.5-2.5 h to obtain mesoporous carbon; and (3) soaking the mesoporous carbon in a 25% ammonia solution, and stirring the mixture at 55-65℃ for 5-8 h to load amino groups onto the surface of the mesoporous carbon; after the reaction, the mesoporous carbon is washed with deionized water until neutral, and then dried at 75-85℃ to obtain ammonia-modified mesoporous carbon with a specific surface area of 800-1200 m² / g.

[0070] As a preferred embodiment, the following parameters are used in this example: in step (1), the sucrose and water are hydrothermally reacted at 180℃ for 12 h to obtain a carbon precursor; in step (2), the carbon precursor is heated to 800℃ at a rate of 5℃ / min, and carbonized in a nitrogen atmosphere for 2 h to obtain mesoporous carbon; and in step (3), the mesoporous carbon is soaked in an ammonia solution and stirred at 60℃ for 6 h to load amino groups onto the surface of the mesoporous carbon; the drying temperature is 80℃. The specific surface area of the ammonia-modified mesoporous carbon obtained in this example is about 1000 m 2 / g.

[0071] Example 6 Preparation of soil conditioner

[0072] The application also provides a method for preparing a soil conditioner, comprising the following steps:

[0073] S1, the pH-responsive hydrogel prepared in Example 2 is added to deionized water at a solid-liquid ratio of 1:5 g / mL, and swelled at 20-30°C for 2-2.5 h to form a hydrogel suspension; in order to study the effect of swelling time on the performance of the conditioner, different examples are set, and the specific parameters are shown in Table 1, and the swelling temperature of the specific examples is 25°C.

[0074] S2, according to the mass ratio of pH-responsive hydrogel to bacterial algal particles of 1:2, bacterial algal particles prepared in Example 1 are added to the hydrogel suspension, and stirred at 400-600 r / min at 25-35°C for 12-18 min (as a preferred example, the following parameters are used in this example: stirring at 500 r / min at 30°C for 15 min, which is used as an example for explanation), so that the bacterial algal particles are wrapped by the hydrogel to form a core-shell structure, the shell thickness of the core-shell structure is 20-50 um, and the free water is removed by vacuum filtration (0.22 um filter membrane) to obtain a hydrogel-bacterial algal composite.

[0075] S3, the ammonia-modified mesoporous carbon prepared in Example 5 is added to anhydrous ethanol at a solid-liquid ratio of 1:8 g / mL, and ultrasonic dispersion is formed to form a mesoporous carbon dispersion liquid, the ultrasonic dispersion conditions are ultrasonic treatment at 180-220 W power for 8-12 min, as a preferred example, the following parameters are used in this example: ultrasonic treatment at 200 W power for 10 min, which is used as an example for explanation. Then add the hydrogel-bacterial algal composite of S2, and stir to uniformly adsorb the mesoporous carbon on the surface of the hydrogel, the stirring conditions are 250-350 r / min at 45-55°C for 25-35 min, as a preferred example, the following parameters are used in this example: stirring at 300 r / min at 50°C for 30 min, which is used as an example for explanation. 60°C air drying to moisture content ≤5%, to obtain a mesoporous carbon-hydrogel-bacterial algal composite;

[0076] S4, the calcium alginate (particle size of 50-100 um) of Example 3 is mixed with deionized water at a weight ratio of 1:10 to prepare a calcium alginate colloid; the mesoporous carbon-hydrogel-benthic algae composite of S3 and the hydroxyapatite-urea composite microspheres prepared in Example 4 are added, the mass ratio of the mesoporous carbon-hydrogel-benthic algae composite of S3: the hydroxyapatite-urea composite microspheres: the calcium alginate is 10:3:1.5, and the mixture is prepared by stirring at 150-250 r / min at 35-45°C for 15-25 min, so that the calcium alginate colloid is filled in the interstitial space to form a three-dimensional network structure. As a preferred embodiment, the following parameters are used in this embodiment: the mixture is prepared by stirring at 200 r / min at 40°C for 20 min, and this is used as an example for illustration.

[0077] S5, the mixture of S4 is granulated by a granulator, and vacuum dried at 35°C until the moisture content is 10-15%, to obtain the final soil conditioner, the particle compression strength of which is ≥2 N, and the particle size is 1-3 mm; the stable gel structure can be formed within 30 min when the soil conditioner is contacted with water.

[0078] The weight fractions of the benthic algae particles, the acrylic acid-chitosan copolymer, the calcium alginate, the hydroxyapatite (HAP)-urea composite microspheres and the ammonia-modified mesoporous carbon in this embodiment are shown in Table 1.

[0079]

[0080] As shown in Table 1, the present application also provides Examples 7, 8 and 9 to verify the effects of the adjustment of the weight fractions of the components and the key parameters of the hydrogel preparation on the soil conditioner, and the specific component composition and parameters are shown in Table 1.

[0081] Meanwhile, in order to study the effects of the components on the performance of the soil conditioner, Comparative Examples 1-4 are provided. Among them, Comparative Example 1 differs from Example 6 in that the acrylic acid-chitosan copolymer (pH-responsive hydrogel) is not used in the components; Comparative Example 2 differs from Example 6 in that the ammonia-modified mesoporous carbon is not used in the components; Comparative Example 3 differs from Example 1 in that the conventional hydroxyapatite (HAP) is used instead of the hydroxyapatite (HAP)-urea composite microspheres in the scheme of the present application; and Comparative Example 4 only uses the single component hydroxyapatite (HAP)-urea composite microspheres, and the specific component composition is shown in Table 1.

[0082] Note: (1) Example 9 is a process adjustment group, that is, the amount of crosslinking agent N,N'-methylenebisacrylamide in the (pH-responsive hydrogel) acrylic acid-chitosan copolymer is adjusted to verify the flexibility and stability of the "key process parameters" in the present application. The pH-responsive hydrogel is the core part of the present application (responsible for "chelating heavy metals in acidic soil, shrinking and avoiding in neutral / alkaline soil"), and its performance (such as crosslinking degree, swelling capacity, response sensitivity) directly depends on the preparation process parameters: the amount of crosslinking agent (N,N'-methylenebisacrylamide) determines the "strength and swelling degree" of the hydrogel - too little will cause the gel to break easily and the heavy metal chelating site to be lost; too much will cause the gel to be too hard and not enough to swell, unable to wrap the bacterial algal particles. Example 9 selects an intermediate value (0.8 parts) above the patent limited range (0.5-1 parts) to verify whether reasonable fluctuations in the amount of crosslinking agent within the process interval protected by the patent will affect the function of the hydrogel.

[0083] Hydrogel swelling time: determines the "efficiency of wrapping bacterial algal particles", insufficient swelling will result in poor gel wrapping and easy loss of bacterial algal particles; excessive swelling will result in too high a gel viscosity, increasing the difficulty of subsequent compounding with mesoporous carbon. Example 9 extends the swelling time from 2h to 2.5h (still within the reasonable operating range) to verify whether minor deviations in swelling time in actual production will destroy the core-shell structure of the "hydrogel-bacterial algal composite" and thus affect the final repair effect.

[0084] (2) Comparative Example 3 uses "pure HAP particles" to replace "HHA-urea microspheres" to verify the "permanent fixation + nutrient supplement integration" effect of HAP-urea microspheres.

[0085] II. Soil conditioner rice plot test

[0086] In order to verify the feasibility and effectiveness of the present application, the soil conditioners prepared in the above examples and comparative examples were subjected to the following rice plot test:

[0087] A plot test was carried out in a cadmium and lead combined pollution paddy field near a certain town in a certain county in Fujian Province. Nine treatments were set up, with three replicates for each treatment, a total of 27 plots, randomly arranged in a randomized block design. The plot size was 6m long and 4m wide, and 2.5m wide protection rows were set up around the test field, separated by a field ridge, with agricultural film and single row single irrigation to prevent water and fertilizer from mixing between plots.

[0088] The basic physicochemical properties of the test soil were as follows: soil pH was 5.1, organic matter was 26.94g / kg, total cadmium was 1.85mg / kg, available cadmium was 1.21mg / kg, total lead was 246mg / kg, and available lead was 94.5mg / kg. The rice variety was Jingliangyouhuazhan (late rice).

[0089] Treatment 1 (CK): conventional fertilization, without applying any conditioner

[0090] Treatment 2: conventional fertilization + soil conditioner prepared in Example 6, 50 kg / acre base application

[0091] Treatment 3: conventional fertilization + soil conditioner prepared in Example 7, 50 kg / acre base application

[0092] Treatment 4: conventional fertilization + soil conditioner prepared in Example 8, 50 kg / acre base application

[0093] Treatment 5: conventional fertilization + soil conditioner prepared in Example 9, 50 kg / acre base application

[0094] Treatment 6: conventional fertilization + soil conditioner prepared in Comparative Example 1, 50 kg / acre base application

[0095] Treatment 7: conventional fertilization + soil conditioner prepared in Comparative Example 2, 50 kg / acre base application

[0096] Treatment 8: conventional fertilization + soil conditioner prepared in Comparative Example 3, 50 kg / acre base application

[0097] Treatment 9: conventional fertilization + soil conditioner prepared in Comparative Example 4, 50 kg / acre base application

[0098] On the basis of conventional fertilization, the conditioner was uniformly applied on the field surface by manual or mechanical spreading 7-10 days before plowing, and was mixed with the soil by plowing twice with a rotary cultivator, and was stabilized and matured by watering for 3-5 days, and then rice transplanting was performed. During the growth of rice, weeding, fertilization, pesticide spraying, and irrigation were performed according to the local production management mode.

[0099] When the rice was mature, 1-1.5 kg of soil samples were collected, naturally dried, ground, and passed through a 20-mesh sieve (for pH value) and a 100-mesh sieve (for analysis of effective cadmium and effective lead content in soil), mixed, and stored in sealed bags for use.

[0100] 1-1.5 kg of rice samples were collected, and rice was obtained after dehulling by a huller, and the rice was dried, ground, and passed through an 80-mesh sieve to remove impurities and particles, and stored in sealed bags for use.

[0101] Soil pH value determination, effective cadmium and effective lead, rice yield determination, and cadmium and lead content in rice were performed. The detection methods are as follows:

[0102] Soil pH determination method: water was used as the extraction agent, a small amount of soil was collected, and water and soil were mixed in a mass ratio of 2.5:1, and the pH value was determined by potentiometry (referring to NY / T1377-2007).

[0103] Determination of available cadmium and lead in soil: refer to "Determination of Available Cadmium and Lead in Soil-Atomic Absorption Spectrometry" (GB / T 23739-2009).

[0104] Rice yield determination: refer to "Operation Specification for Determination of Rice Yield" (DB33 / T 2517-2022).

[0105] Rice cadmium determination method: refer to "National Food Safety Standard-Determination of Cadmium in Food" (GB 5009.15-2023).

[0106] Rice lead determination method: refer to "National Food Safety Standard-Determination of Lead in Food" (GB 5009.12-2017).

[0107] 1. Effect of different treatments on soil pH

[0108] The test results of the effect of different treatment groups on soil pH are as follows in Table 2:

[0109]

[0110] As can be seen from Table 2, the soil pH value of treatment 1 (CK) is 5.1. Compared with treatment 1, treatments 2, 3, 4, 5, 6, 8, and 9 all increased the soil pH value to a certain extent, and treatment 4 > treatment 2 > treatment 5 > treatment 3 > treatment 6 > treatment 8 > treatment 9 > treatment 7 = treatment 1, while treatment 7 and treatment 1 had almost no difference.

[0111] 2. Effect of different treatments on soil available cadmium and lead content

[0112] The test results of the effect of different treatment groups on soil available cadmium and lead content are as follows in Table 3:

[0113]

[0114] As can be seen from Table 3, the soil available cadmium content of treatment 1 (CK) is 1.20 mg / kg, and the available lead content is 93.3 mg / kg. Compared with treatment 1, treatments 2, 3, 4, 5, 6, 7, 8, and 9 all reduced the soil available cadmium and lead content to a certain extent.

[0115] Soil available cadmium reduction effect: treatment 4 > treatment 2 > treatment 5 > treatment 3 > treatment 8 > treatment 6 > treatment 7 > treatment 9 > treatment 1

[0116] Soil available lead reduction effect: treatment 4 > treatment 2 > treatment 5 > treatment 3 > treatment 6 > treatment 8 > treatment 7 > treatment 9 > treatment 1.

[0117] The fixation of lead mainly depends on the formation of lead phosphate precipitate by HAP and adsorption depends on mesoporous carbon, so the sequence is highly consistent with "effective cadmium", but the amount of HAP has a more significant effect.

[0118] 3. Effect of different treatments on rice yield

[0119] The test results of the effect of different treatment groups on rice yield are as follows in Table 4:

[0120]

[0121] As can be seen from Table 4, the rice yield of treatment 1 (CK) is 521.2 kg / acre. Compared with treatment 1, treatments 2, 3, 4, 5, 6, 7, 8 and 9 all improve the rice yield to a certain extent, and the improvement effect is treatment 4 > treatment 2 > treatment 5 > treatment 3 > treatment 6 > treatment 8 > treatment 7 > treatment 9.

[0122] 4. Effect of different treatments on cadmium and lead content in rice

[0123] The test results of the effect of different treatment groups on cadmium and lead content in rice are as follows in Table 5:

[0124]

[0125] As can be seen from Table 5, the cadmium content in rice of treatment 1 (CK) is 0.41 mg / kg, and the lead content in rice is 0.48 mg / kg. Compared with treatment 1, treatments 2, 3, 4, 5, 6, 7, 8 and 9 all reduce the cadmium and lead content in rice to a certain extent.

[0126] Among them, the cadmium reduction effect in rice is treatment 4 > treatment 2 > treatment 5 > treatment 3 > treatment 8 > treatment 6 > treatment 7 > treatment 9 > treatment 1.

[0127] The lead reduction effect in rice is treatment 4 > treatment 2 > treatment 5 > treatment 3 > treatment 6 > treatment 8 > treatment 7 > treatment 9 > treatment 1.

[0128] The results are analyzed as follows:

[0129] The examples are better than the comparative examples: all examples meet the standards of "effective cadmium and lead reduction", "yield improvement" and "rice safety", and are much better than the comparative examples, which shows that the components in the soil conditioning agent of the present application have a "multi-component synergistic" effect.

[0130] The internal difference of the embodiment: treatment 4 (embodiment 3) > treatment 2 (benchmark example 1) > treatment 5 (process adjustment example 4) > treatment 3 (low component dosage example 2), which proves that reasonable increase of component dosage can enhance the effect; the effect of the process adjustment example and the benchmark example is not much different, which shows that the process adjustment will not affect the industrialization application of the patent product.

[0131] The obvious short board of the comparative example: the comparative example missing key components (such as mesoporous carbon, HAP) or single function, the effect is greatly reduced; the blank control is completely ineffective.

[0132] III. Soil conditioner soil culture test

[0133] In order to further verify that the application is suitable for different pH type soils, in addition to acidic soil, neutral and alkaline soils are also selected for soil culture test, and the groups of each embodiment and comparative example and the rice plot test are consistent.

[0134] Cadmium and lead contaminated soils collected from Fujian, Jiangxi, Hebei and other regions are used for indoor soil culture test.

[0135] Among them, the soil in Fujian region: the soil pH is 5.1, the organic matter is 26.94g / kg, the total cadmium is 1.85mg / kg, the available cadmium is 1.21mg / kg, the total lead is 246mg / kg, and the available lead is 94.5mg / kg.

[0136] The soil in Jiangxi region: the soil pH is 6.7, the organic matter is 24.13g / kg, the total cadmium is 1.57mg / kg, the available cadmium is 1.05mg / kg, the total lead is 213mg / kg, and the available lead is 85mg / kg.

[0137] The soil in Hebei region: the soil pH is 8.2, the organic matter is 26.72g / kg, the total cadmium is 1.48mg / kg, the available cadmium is 0.83mg / kg, the total lead is 186mg / kg, and the available lead is 74.5mg / kg.

[0138] Each type of regional soil is set up 9 treatments:

[0139] Treatment 1 (CK): conventional fertilization, without any conditioner

[0140] Treatment 2: add the soil conditioner prepared in example 6 at a dosage of 5g / kg of soil (dry weight)

[0141] Treatment 3: add the soil conditioner prepared in example 7 at a dosage of 5g / kg of soil (dry weight)

[0142] Treatment 4: add the soil conditioner prepared in example 8 at a dosage of 5g / kg of soil (dry weight)

[0143] Treatment 5: The soil conditioner prepared in Example 9 was added at a dosage of 5 g / kg of soil (dry weight)

[0144] Treatment 6: The soil conditioner prepared in Comparative Example 1 was added at a dosage of 5 g / kg of soil (dry weight)

[0145] Treatment 7: The soil conditioner prepared in Comparative Example 2 was added at a dosage of 5 g / kg of soil (dry weight)

[0146] Treatment 8: The soil conditioner prepared in Comparative Example 3 was added at a dosage of 5 g / kg of soil (dry weight)

[0147] Treatment 9: The soil conditioner prepared in Comparative Example 4 was added at a dosage of 5 g / kg of soil (dry weight)

[0148] Each treatment was set up in triplicate. Each replicate used a plastic culture bottle containing 7.5 kg of soil, to which the corresponding material was added, mixed evenly, and the soil was kept at a moisture content of 60-80% of the field capacity.

[0149] The plastic culture bottles containing the soil were placed in a constant temperature incubator, and the incubation temperature was controlled at about 25°C. After 20 days of incubation, a suitable amount of soil sample (about 10 g) was taken from each replicate in each treatment group, using a quartering method, and was air-dried, ground, and sieved through a 0.149 mm sieve, and then the soil pH and heavy metal content were determined. The determination method was the same as that for the initial soil sample.

[0150] The changes in soil pH, soil cadmium and lead content in different soils were as follows:

[0151] 1. Changes in soil pH, soil available cadmium and lead content in acidic region soil

[0152] After testing, the effects of different treatment groups on the soil pH, soil available cadmium and lead content in acidic region soil were as shown in Table 6 below:

[0153]

[0154] 2. Changes in soil pH, soil available cadmium and lead content in neutral region soil

[0155] After testing, the effects of different treatment groups on the soil pH, soil available cadmium and lead content in neutral region soil were as shown in Table 7 below:

[0156]

[0157] 3. Changes in soil pH, soil available cadmium and lead content in alkaline region soil

[0158] The test results of the effects of different treatment groups of the alkaline region soil on the soil pH, soil available cadmium and soil available lead contents are as follows in Table 8:

[0159]

[0160] The changes of the above three types of soil pH, soil available cadmium and soil available lead show that the results are analyzed as follows:

[0161] (1) The soil conditioner has the intelligence of pH adjustment.

[0162] Acid soil: the pH of the example group is increased by 1.0-1.2 (mesoporous carbon alkaline functional group + hydrogel carboxyl dissociation), avoiding excessive acidification;

[0163] Neutral soil: the pH is only increased by 0.3-0.4 (hydrogel shrinkage, mesoporous carbon mild adjustment), without the risk of alkalization;

[0164] Alkaline soil: the pH is stable at 8.2-8.4 (hydrogel completely shrinks, mesoporous carbon amino slow release), without destroying the alkaline soil ecology.

[0165] Treatment 6 (comparative example 1) (lack of pH hydrogel) in neutral / alkaline soil appears excessive increase of pH (neutral soil pH 7.2, alkaline soil pH 8.5), which proves that the pH responsive hydrogel has the "environmental adaptation core effect" and is suitable for different types of soil.

[0166] (2) The soil conditioner has the stability of reducing effective cadmium and lead

[0167] In the three types of pH soil, the effective cadmium reduction rate of the example group is 61%-77%, the effective lead reduction rate is 60%-74%, the fluctuation range is <10%, and the effect is much higher than that of the prior art (CN103242849A); and the reduction rate of the comparative example group (lack of key components) is generally lower than 40%, and the fluctuation is large in different pH soils, such as treatment 7 (comparative example 2) in acid soil, the lead reduction rate is 28.3%, and in alkaline soil, the lead reduction rate is 24%, which proves that the soil conditioner provided by the application has the adaptability to different pH soils through "multi-component cooperation", and the repair effect is stable and has high persistence.

[0168] The above only describes some preferred embodiments of the application and does not limit the application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A cadmium-reducing lead soil conditioner, characterized by, Components include the following weight parts: The bacteria-algae particles 16~24 parts, the pH responsive hydrogel 8~12 parts, the calcium alginate 5~10 parts, the hydroxyapatite-urea composite microspheres 10~15 parts, and the ammonia modified mesoporous carbon 20~25 parts; The bacteria-algae particles are prepared by mixing Chlorella and Bacillus subtilis in a ratio of 1:1, treating the mixture with a citric acid solution at 55~65 DEG C for 1.8~2.2 hours, centrifuging and freeze-drying. The pH responsive hydrogel is an acrylic acid-chitosan copolymer. The hydroxyapatite-urea composite microspheres are prepared by mixing nano-hydroxyapatite and urea in a weight ratio of 4:1, adding a 2% sodium alginate aqueous solution, and ultrasonic dispersion to form a suspension; using the suspension as the water phase, adding 3% Tween-80 cyclohexane as the oil phase, and emulsifying to form an O / W microemulsion; adding 10% calcium chloride in pure anhydrous ethanol to the microemulsion, with a molar ratio of calcium chloride to sodium alginate of 1:1, and stirring to crosslink the sodium alginate and calcium ions to form a gel network, which encapsulates the nano-hydroxyapatite and urea; The microspheres are collected by filtration, dehydrated, dried, and sieved to obtain the hydroxyapatite-urea composite microspheres. The ammonia modified mesoporous carbon is prepared by using sucrose as a carbon source to prepare a carbon precursor, carbonizing the carbon precursor to obtain mesoporous carbon, and then immersing the mesoporous carbon in an ammonia solution to load amino groups onto the surface of the mesoporous carbon.

2. The soil conditioner for reducing cadmium and lead according to claim 1, wherein The acrylic acid-chitosan copolymer is prepared by mixing acrylic acid and chitosan in a weight ratio of 2:1, adding 0.5~1 parts of a crosslinking agent N,N'-methylenebisacrylamide, and stirring uniformly; under inert atmosphere protection, adding an initiator, and stirring in a 60 DEG C water bath for 3~4 hours.

3. The soil conditioner for reducing cadmium and lead according to claim 1, wherein In the preparation process of the hydroxyapatite-urea composite microspheres, the solid-liquid ratio of the mixture of nano-hydroxyapatite and urea to the 2% sodium alginate aqueous solution is 1:10 g / mL, and the ultrasonic dispersion conditions are 250~350 W ultrasonic treatment for 10~20 minutes.

4. The cadmium-reduced lead soil conditioner of claim 3, wherein, In the preparation process of the hydroxyapatite-urea composite microspheres, the emulsification treatment conditions of the water phase and the oil phase are 25~35 DEG C emulsification at a speed of 1000~1500 r / min for 15~25 minutes.

5. The soil conditioner for reducing cadmium and lead according to claim 3, wherein The specific preparation method of the ammonia-modified mesoporous carbon comprises the following steps: (1) taking sucrose as a carbon source, dissolving sucrose and water according to a mass-volume ratio of 1:3, performing hydrothermal reaction at 160-180 DEG C for 10-15 h, and then performing centrifugal drying after cooling to obtain a carbon precursor; (2) placing the carbon precursor in a tube furnace, increasing the temperature to 750-850 DEG C at a temperature increasing rate of 5 DEG C / min, and then performing carbonization under an inert atmosphere for 1.5-2.5 h, and then naturally cooling to obtain mesoporous carbon; (3) soaking the mesoporous carbon in a 25% ammonia water solution, stirring and reacting at 55-65 DEG C for 5-8 h to load amino groups onto the surface of the mesoporous carbon; after the reaction, washing with deionized water until neutral, and then drying at 75-85 DEG C to obtain ammonia-modified mesoporous carbon, and the specific surface area of the ammonia-modified mesoporous carbon is 800-1200 m 2 / g.

6. A method of preparing a soil conditioner for reducing cadmium in lead as claimed in any one of claims 1 to 5, wherein, The method comprises the following steps: S1, adding deionized water to the pH responsive hydrogel according to a solid-liquid ratio of 1:5 g / mL, swelling at 20~30 DEG C for 1.5~2.5 hours to form a hydrogel suspension; S2, adding bacteria-algae particles to the hydrogel suspension according to a mass ratio of the pH responsive hydrogel to the bacteria-algae particles of 1:2, stirring at 400~600 r / min at 25~35 DEG C for 12~18 minutes to make the bacteria-algae particles encapsulated by the hydrogel to form a core-shell structure, and removing free water by vacuum filtration to obtain a hydrogel-bacteria-algae composite. S3, the weight parts of ammonia-modified mesoporous carbon is added into anhydrous ethanol according to a solid-liquid ratio of 1:8 g / mL to form a mesoporous carbon dispersion liquid by ultrasonic dispersion; then the hydrogel-bacterial alga composite of S2 is added, and the mesoporous carbon is uniformly adsorbed on the surface of the hydrogel by stirring, and dried to a moisture content of ≤5% to obtain a mesoporous carbon-hydrogel-bacterial alga composite; S4, the calcium alginate is mixed with deionized water according to a weight ratio of 1:10 to prepare a calcium alginate colloid; the mesoporous carbon-hydrogel-bacterial alga composite of S3 and the hydroxyapatite-urea composite microspheres are added, and the mass ratio of the mesoporous carbon-hydrogel-bacterial alga composite of S3 to the hydroxyapatite-urea composite microspheres to the calcium alginate is 10:3:1.5, and the mixture is stirred at 150-250 r / min at 35-45°C for 15-25 min to make the calcium alginate colloid fill the interstitial space and form a three-dimensional network structure; S5, the mixture of S4 is granulated, and vacuum dried at 35°C to a moisture content of 10-15% to obtain the soil conditioner.

7. The preparation method of claim 6, wherein the shell thickness of the core-shell structure in S2 is 20-50 um.

8. The preparation method of claim 6, wherein the ultrasonic dispersion conditions in S3 are ultrasonic treatment at a power of 180-220 W for 8-12 min; the stirring conditions after adding the hydrogel-bacterial alga composite are stirring at 250-350 r / min at 45-55°C for 25-35 min; and the drying conditions are air drying at 55-65°C.

9. The preparation method of claim 6, wherein the particle size of the calcium alginate in S4 is 50-100 um; and the granulation particle size in S5 is 1-3 mm, the particle compression strength is ≥2 N, and a stable gel structure can be formed within 30 min after water is added. The soil conditioning method is that the soil conditioner of any one of claims 1-5 or the soil conditioner prepared by the method of any one of claims 6-9 is uniformly applied 7-10 days before ploughing, the application amount is 50-75 kg / acre, the soil conditioner is uniformly mixed with the paddy field soil by ploughing twice after application, an appropriate amount of water is poured to stabilize and mature for 3-5 days, and then rice transplanting is performed. ​ ​ ​ 10. A method of soil conditioning, characterized by, ​

Images