A chives continuous cropping soil conditioner and a preparation method thereof

Abstract

This invention relates to the field of soil conditioner technology, specifically a soil conditioner for continuous cropping of scallions and its preparation method, comprising the following components: composite microspheres, alkaline mineral powder, humic acid, composite microbial inoculant, sodium alginate, and trace element additives. This invention uses chitosan-coated biochar alkaline composite particles as the functional component. It utilizes the protonation characteristics of chitosan amino groups under acidic conditions to simultaneously drive the coating to swell and release alkaline substances, while the surface positive charge inhibits the activity of Fusarium oxysporum. This allows the acid-regulating and antibacterial functions to originate from the same chemical response and synergistically change with the degree of soil acidification, thereby breaking the vicious cycle of mutually reinforcing soil acidification and root rot in continuous cropping of scallions.

Description

Technical Field

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

[0002] Scallions are one of the main varieties used in continuous cropping of greenhouse vegetables in southern my country. With increasing years of continuous cropping, severe soil acidification commonly occurs in scallion-growing areas. After more than three years of continuous cultivation, the soil pH typically drops from an initial 6.5–7.0 to 4.5–5.5. Soil acidification inhibits normal root growth and metabolism in scallions and also activates Al in the soil. 3 + Fe 3+ Metal ions, including free metal ions, cause cell damage in the root tip region, forming numerous micro-wounds. Simultaneously, continuous cropping of scallions leads to a high incidence of root rot, with *Fusarium oxysporum* being the main pathogen. This fungus exhibits strong adaptability to acidic soil environments; furthermore, soil acidification increases root micro-wounds and reduces the activity of rhizosphere antagonistic microorganisms, further exacerbating the risk of infection. Acidification-induced root micro-wounds provide a convenient entry channel for the pathogen. After infection, the pathogen further weakens root function, leading to increased susceptibility of organic acids in root exudates to A... 3+ Fe 3+ The chelating and passivation capacity of the fertilizer decreases, the concentration of free acidifying metal ions increases, and the degree of soil acidification is further aggravated. In addition, the excessive application of ammonium nitrogen fertilizer to compensate for yield loss continuously releases H2 during its nitrification process. + This further accelerates soil acidification, which, combined with the above-mentioned cycle, constitutes the core reason why the problem of continuous cropping obstacles of scallions cannot be eradicated by a single measure.

[0003] In existing technologies, soil conditioners for acidification caused by continuous cropping often utilize lime, calcium silicate powder, or alkaline industrial byproducts. For example, CN105154100A discloses an acidic soil conditioner that neutralizes acidifying ions in the soil with alkaline components and adds compound microbial agents to improve the soil microecology. Furthermore, CN119613196A discloses a soil conditioner for acidified soil remediation that improves acidified soil by using calcined alkaline slag powder and biochar-based composite materials. However, the acid-regulating and antibacterial components in these solutions are independent of each other, lacking a coordinated response mechanism. When soil acidification is most severe, the antibacterial effect cannot be enhanced synchronously, making it difficult to sustainably block the reproduction and invasion of pathogens in the rhizosphere. Summary of the Invention

[0004] (1) Technical problems to be solved The purpose of this invention is to provide a soil conditioner for continuous cropping of scallions and its preparation method, so as to solve the vicious cycle problem of acidification stress exacerbating root rot infection caused by long-term monoculture in the process of continuous cropping of scallions. In particular, it solves the defect of existing technology that the acid-regulating function and antibacterial function are independent and cannot respond synergistically with changes in soil acidity.

[0005] (2) Technical solution To achieve the above objectives, on the one hand, the present invention provides a soil conditioner for continuous cropping of scallions, comprising the following components by weight: 20-40 parts of chitosan-coated biochar alkaline composite granules, 15-30 parts of alkaline mineral powder, 10-20 parts of humic acid, 5-15 parts of composite microbial inoculant, 2-8 parts of sodium alginate, and 1-5 parts of trace element additives. The chitosan-coated biochar alkaline composite particles are pH-responsive coated particles prepared by a fluidized bed coating process using a mixture of activated biochar and carbide slag as the core material and chitosan as the coating material. The carbide slag is dried, pulverized, and sieved through a 200-mesh sieve before use, and its effective alkali content, calculated as CaO, is ≥60%.

[0006] Furthermore, the alkaline mineral powder is composed of 50% calcined oyster shell powder, 30% calcium silicate, and 20% fly ash; wherein the calcined oyster shell powder is obtained by calcining oyster shells at 900℃ for 2 hours and then pulverizing them through a 200-mesh sieve; and the fly ash contains As≤10mg / kg, Cd≤3mg / kg, Pb≤50mg / kg, Cr≤150mg / kg, and Hg≤2mg / kg.

[0007] Furthermore, the compound microbial agent is composed of 50% Bacillus subtilis, 30% Bacillus amyloliquefaciens, and 20% Trichoderma longifolia; the effective viable count of each strain is independently ≥5 billion / g.

[0008] Furthermore, the humic acid is biochemical potassium fulvate with a weight-average molecular weight of 3500 Da; the trace element additive consists of 55% boric acid and 45% ammonium molybdate.

[0009] Furthermore, the preparation method of the chitosan-coated biochar alkaline composite particles includes the following steps: N11. Pyrolyze rice husks or straw under an inert atmosphere, grind and sieve after natural cooling to obtain primary biochar; place the primary biochar in a container with a 10% phosphoric acid solution, soak and activate, wash with deionized water, and dry to obtain activated biochar. N12. Activated biochar and calcium carbide slag powder are mixed to obtain a mixture; then deionized water is added, stirred, and aged to obtain an aged wet mixture; the aged wet mixture is granulated by an extrusion granulator, the resulting wet particles are dried, cooled, and sieved to obtain core material particles; N13. Chitosan is dissolved in an aqueous solution of acetic acid with a volume fraction of 1% to obtain a chitosan coating solution; the chitosan coating solution is sprayed onto the surface of the core material particles; after spraying, fluidized drying is continued to obtain chitosan-coated biochar alkaline composite particles.

[0010] Further, in step N11, the solid-liquid ratio of the initial biochar to the 10% phosphoric acid solution is 1g:10mL; in step N12, the mass ratio of the activated biochar to the carbide slag powder is 6:4; in step N13, the degree of deacetylation of the chitosan is ≥90%, and its weight-average molecular weight is 100,000 to 200,000 Da; the mass of the chitosan is 10 to 15% of the mass of the core material particles.

[0011] On the other hand, the present invention also provides a method for preparing a soil conditioner for continuous cropping of scallions, comprising the following steps: N1. Alkaline mineral digestion and premixing: Alkaline mineral powder is added to deionized water, stirred, aged, dried, and cooled to obtain digested mineral powder; humic acid and trace element additives are added and mixed to obtain mineral-humic acid premix. N2. Granulation and drying of matrix particles: The mineral-humic acid premix is ​​mixed with sodium alginate to obtain a mixture; then deionized water is added, and the mixture is granulated by an extrusion granulator; the resulting wet particles are dried and sieved to obtain matrix particles; N3. Composite particle mixing: Chitosan-coated biochar alkaline composite particles are mixed with matrix particles to obtain mixed particles; N4. Microbial agent coating: After the mixed particles have cooled, the compound microbial agent is applied to the surface of the mixed particles by spraying or rolling coating. After mixing, the scallion continuous cropping soil conditioner is obtained.

[0012] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. Synergistic Effect of Slow-Release in Achieving Acidification and Micro-Area Antibacterial Action: The chitosan coating in the chitosan-coated biochar alkaline composite particles of this invention acts as a physical barrier, enabling the continuous slow release of alkaline substances. The release rate matches the soil's alkali-consuming needs due to acidification, avoiding the problems of sudden pH increases and short effective periods caused by concentrated alkali release in traditional lime-based conditioners, thus extending the effective acidification cycle of a single application. Simultaneously, the positive charge carried by the protonated amino groups under acidic conditions inhibits the germination and hyphal extension of Fusarium oxysporum spores in the rhizosphere micro-domain, and the antibacterial activity increases with increasing acidification. This spatially complements the biological antagonistic effect of the composite microbial agent, effectively blocking the vicious cycle of mutually reinforcing soil acidification and root rot in continuous cropping of scallions.

[0013] 2. Synergistically fixes metal ions, reduces wounds, and cuts off pathogen infection channels: The alkaline component of calcium hydroxide in the carbide slag in the core material can neutralize free Al in the soil. 3+ Fe 3+ Precipitation and fixation activate the oxygen-containing functional groups on the surface of biochar, which further adsorb residual ions. The synergistic effect of both reduces the concentration of free acidifying metal ions in the rhizosphere, lessens damage to scallion root tip cells, and reduces micro-wounds in the roots from the source, thereby reducing the main entry point for Fusarium oxysporum through these wounds.

[0014] 3. Optimizing the rhizosphere microecology to create suitable conditions for biological disease control: The porous structure formed by the activated biochar in the core material after phosphate activation can physically adsorb allelopathic autotoxic substances accumulated in continuously cropped soils, reducing their effective concentration in the rhizosphere. Simultaneously, humic acid can complex mineral nutrients and buffer rhizosphere pH, while trace elements such as boron and molybdenum remain stable and effective under alkaline conditions. These combined effects improve the rhizosphere microecological environment, providing suitable conditions for the colonization and antagonistic activity of compound microbial agents, thus enhancing the actual control effect against root rot. Attached Figure Description

[0015] Figure 1 This is a flowchart illustrating the preparation process of the scallion continuous cropping soil conditioner of the present invention. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: This example discloses a soil conditioner for continuous cropping of scallions, comprising the following components by weight: 30 parts of chitosan-coated biochar alkaline composite granules, 23 parts of alkaline mineral powder, 15 parts of humic acid, 10 parts of composite microbial agent, 5 parts of sodium alginate, and 3 parts of trace element additives. The chitosan-coated biochar alkaline composite particles are pH-responsive coated particles prepared by a fluidized bed coating process using a mixture of activated biochar and carbide slag as the core material and chitosan as the coating material. The carbide slag is dried, pulverized, and sieved through a 200-mesh sieve before use, and its effective alkali content, calculated as CaO, is ≥60%.

[0018] The alkaline mineral powder is composed of 50% calcined oyster shell powder, 30% calcium silicate, and 20% fly ash; wherein the calcined oyster shell powder is obtained by calcining oyster shells at 900℃ for 2 hours and then crushing them through a 200-mesh sieve; the fly ash contains As≤10mg / kg, Cd≤3mg / kg, Pb≤50mg / kg, Cr≤150mg / kg, and Hg≤2mg / kg.

[0019] The compound microbial agent is composed of 50% Bacillus subtilis, 30% Bacillus amyloliquefaciens, and 20% Trichoderma longifolia; the effective viable count of each strain is independently ≥5 billion / g.

[0020] The humic acid is biochemical potassium fulvic acid with a weight-average molecular weight of 3500 Da; the trace element additive consists of 55% boric acid and 45% ammonium molybdate.

[0021] The preparation method of the chitosan-coated biochar alkaline composite particles includes the following steps: N11. Place rice husks or straw in a tube furnace and heat to 550℃ at a rate of 5℃ / min under a nitrogen atmosphere. Maintain the temperature for 2.5h and allow to cool naturally. Grind the raw biochar through a 150-mesh sieve to obtain primary biochar. Place the primary biochar and a 10% phosphoric acid solution in a container and soak and activate at room temperature for 4h. Wash repeatedly with deionized water until the pH of the washing solution is 6.5-7.0. Dry at 105℃ to constant weight to obtain activated biochar. N12. Mix activated biochar and calcium carbide slag powder evenly to obtain a mixture; then add 25-30% deionized water according to the total mass of the mixture, stir thoroughly until the material is uniform and plastic, and let it stand at room temperature for 1 hour to obtain an aged wet mixture; granulate the aged wet mixture by extrusion granulator (granulation aperture of 1.5-2.0 mm, screw speed of 20-40 r / min), place the obtained wet granules in a fluidized bed at 60℃ to dry to a moisture content of ≤5%, cool to room temperature, and sieve to obtain granules with a particle size of 1-2 mm to obtain core material granules; N13. Dissolve chitosan in a 1% (v / v) aqueous solution of acetic acid to prepare a 2% (w / w) chitosan coating solution. Place the core material particles in a fluidized bed coating machine, control the inlet air temperature at 45-50℃ and the atomization pressure at 0.2-0.3MPa, and uniformly spray the chitosan coating solution onto the surface of the core material particles at a rate of 10-15mL / min. After spraying, continue fluidizing and drying at 50℃ for 40min, and repeat the spraying-drying cycle 2-3 times until the discharged particles have no obvious acetic acid odor, thus obtaining chitosan-coated biochar alkaline composite particles.

[0022] In step N11, the solid-liquid ratio of the initial biochar to the 10% phosphoric acid solution is 1g:10mL; in step N12, the mass ratio of the activated biochar to the calcium carbide slag powder is 6:4; in step N13, the degree of deacetylation of the chitosan is ≥90%, and its weight-average molecular weight is 100,000 to 200,000 Da; the mass of the chitosan is 10 to 15% of the mass of the core material particles.

[0023] The preparation method of the scallion continuous cropping soil conditioner includes the following steps: N1. Alkaline mineral digestion and premixing: Alkaline mineral powder is added to 10% of its mass of deionized water, stirred thoroughly, and aged at room temperature for 1 hour. It is then dried at 60°C until the moisture content is ≤5%, and cooled to room temperature to obtain digested mineral powder. After confirming that the temperature of the digested mineral powder is not higher than 35°C, humic acid and trace element additives are added and mixed evenly to obtain mineral-humic acid premix. N2. Granulation and drying of matrix particles: The mineral-humic acid premix and sodium alginate are mixed evenly in a three-dimensional mixer to obtain a mixture; then 15% to 25% of deionized water is added to the total mass of the mixture, and the mixture is granulated by an extrusion granulator; the resulting wet particles are dried in a fluidized bed dryer at 40 to 45°C until the moisture content is ≤5%, and then sieved to obtain matrix particles; N3. Composite Particle Mixing: Chitosan-coated biochar alkaline composite particles and matrix particles are added to a three-dimensional mixer and mixed at a speed of 200-400 r / min for 15-20 min to obtain mixed particles with a moisture content of ≤5%. N4. Microbial agent coating: After the mixed granules have cooled to below 35°C, the compound microbial agent is evenly applied to the surface of the mixed granules by spraying or rolling coating, and fluidized and mixed at below 35°C for 10-15 minutes to obtain the scallion continuous cropping soil conditioner.

[0024] Example 2: This example is based on Example 1, but differs from Example 1 in that it includes the following components by weight: 20 parts of chitosan-coated biochar alkaline composite particles, 15 parts of alkaline mineral powder, 10 parts of humic acid, 5 parts of composite microbial agent, 2 parts of sodium alginate, and 1 part of trace element additive; other components and preparation methods are the same as in Example 1.

[0025] Example 3: This example is based on Example 1, but differs from Example 1 in that it includes the following components by weight: 40 parts of chitosan-coated biochar alkaline composite particles, 30 parts of alkaline mineral powder, 20 parts of humic acid, 15 parts of composite microbial agent, 8 parts of sodium alginate, and 5 parts of trace element additives; other components and preparation methods are the same as in Example 1.

[0026] Comparative Example 1: This comparative example is based on Example 1, but differs from Example 1 in that the chitosan-coated biochar alkaline composite particles in this comparative example are replaced with an equal amount of uncoated core material particles (i.e., step N13 is omitted, and chitosan coating is not performed). Other components and preparation methods are the same as in Example 1.

[0027] Comparative Example 2: This comparative example is based on Example 1, but differs from Example 1 in that the core material in this comparative example does not contain activated biochar, but only uses carbide slag powder (i.e., the mass ratio of activated biochar to carbide slag powder in step N12 is adjusted to 0:10, and the missing part is made up with inert quartz sand to maintain granulation and molding properties). Other components and preparation methods are the same as in Example 1.

[0028] Comparative Example 3: This comparative example is based on Example 1, but differs from Example 1 in that the core material in this comparative example does not contain carbide slag, but only uses activated biochar (i.e., the mass ratio of activated biochar to carbide slag powder in step N12 is adjusted to 10:0, and the missing part is made up with inert quartz sand). Other components and preparation methods are the same as in Example 1.

[0029] Comparative Example 4: This comparative example is based on Example 1, but differs from Example 1 in that the alkaline mineral powder in this comparative example is composed of 60% calcium silicate and 40% fly ash (i.e., no calcined oyster shell powder is added), while the other components and preparation methods are the same as in Example 1.

[0030] Comparative Example 5: This comparative example is based on Example 1, but differs from Example 1 in that the alkaline mineral powder in this comparative example is composed of 62.5% calcined oyster shell powder and 37.5% fly ash (i.e., no calcium silicate is added), while the other components and preparation methods are the same as in Example 1.

[0031] Comparative Example 6: This comparative example is based on Example 1, but differs from Example 1 in that the alkaline mineral powder in this comparative example is composed of 62.5% calcined oyster shell powder and 37.5% calcium silicate (i.e., no fly ash is added), while the other components and preparation methods are the same as in Example 1.

[0032] Comparative Example 7: This comparative example is based on Example 1, except that the calcined oyster shell powder in the alkaline mineral powder is replaced with an equal amount of uncalcined raw oyster shell powder (that is, fresh oyster shells are washed, dried, and directly crushed through a 200-mesh sieve without undergoing calcination at 900°C). The other components and preparation methods are the same as in Example 1.

[0033] Comparative Example 8: This comparative example differs from Example 1 in that activated biochar, carbide slag powder, and chitosan powder are directly mixed, then deionized water is added, and the mixture is granulated once by an extrusion granulator. After drying and sieving, mixed particles without hierarchical structure are obtained. These mixed particles replace the chitosan-coated biochar alkaline composite particles in Example 1. They are mixed with the matrix particles (containing alkaline mineral powder, humic acid, sodium alginate, and trace element additives) prepared according to steps N1-N2 of Example 1, and then coated with composite microbial agents in step N4 to obtain the scallion continuous cropping soil conditioner (i.e., steps N11-N13 are omitted). Other components and preparation methods are the same as in Example 1.

[0034] Experimental verification: I. Experimental Materials Acidified soil tested: Topsoil (0–20 cm) from 5 years of continuous scallion cultivation, air-dried and sieved through a 2 mm sieve. Basic properties: pH 4.52 ± 0.05 (water:soil = 2.5:1), exchangeable Al₂O₃... 3+ 2.48±0.12 cmol·kg -1 (1 mol·L) -1 (KCl extraction), total water-soluble phenols 48.6 ± 3.2 mg·kg -1 (Folin-Ciocalteu method, calculated as gallic acid), Fusarium oxysporum count 1.15 × 10⁻⁶ 4 CFU·g -1 Dry soil (Komada selective medium).

[0035] Test strain: Fusarium oxysporum spp. (allium-specific type), spore suspension concentration adjusted to 1×10⁻⁶. 6 pcs·mL -1 .

[0036] Conditioner samples: 12 conditioners prepared according to Examples 1-3 and Comparative Examples 1-8, and a blank control (CK, no conditioner applied).

[0037] II. Experimental Design Experiment 1: Soil Incubation Experiment Twelve treatments were established: CK, Examples 1-3, and Comparative Examples 1-8. For each treatment, 500g of soil was weighed and mixed evenly with 2% (10g) of the soil mass as a conditioner. The soil moisture content was adjusted to 60% of field capacity. The soil was then incubated at 25℃ for 30 days, with water added every 3 days by weighing. Samples were taken on day 30 to determine pH and exchangeable Al. 3+ Total water-soluble phenols and Fusarium oxysporum count. Each treatment was repeated three times.

[0038] Experiment 2: Liquid antibacterial test Take 2.0 g of each of the particle samples from Example 1, Comparative Example 1, and Comparative Example 8, and place them in 250 mL Erlenmeyer flasks with stoppers. Add 100 mL of buffer solution (0.1 mol·L⁻¹) with pH values ​​of 4.0, 5.5, and 7.0, respectively. -1 Citric acid - 0.2 mol·L -1 (Prepared with disodium hydrogen phosphate). At 25℃ and 150 rpm. -1 After shaking for 24 hours, the extract was filtered through a 0.45 μm microporous membrane and collected. 0.2 mL of *Fusarium oxysporum* spore suspension was spread onto a PDA plate, and a sterile Oxford cup was placed in the center of the plate. 200 μL of the extract was added, and the plate was incubated at 28°C for 72 hours, with sterile water as a control. Colony diameters were measured, and the inhibition rate was calculated.

[0039] III. Measurement Methods and Calculation Formulas 1. Soil pH Water:soil mass ratio 2.5:1, determined by glass electrode method.

[0040] 2. Exchangeability Al 3+ Using 1 mol·L -1 KCl solution extraction (soil-to-liquid ratio 1:10, shaking for 30 min), aluminum ions in the extract were determined by aluminum reagent colorimetric method, and a standard curve was plotted using aluminum standard solution for quantification.

[0041] Aluminum fixation rate (%) = (CK exchangeable Al) 3+ - Handling exchangeable AI 3+ ) / CK exchangeability Al 3+ ×100%.

[0042] 3. Water-soluble total phenols Fresh soil was extracted with deionized water (soil-to-water ratio 1:5, shaken for 1 hour), and the color was developed with Folin-Ciocalteu reagent. The color was measured at a wavelength of 765 nm, and the total phenol content was calculated using gallic acid as a standard.

[0043] Phenol adsorption rate (%) = (CK water-soluble total phenols - treated water-soluble total phenols) / CK water-soluble total phenols × 100%.

[0044] 4. Quantity and inhibition rate of Fusarium oxysporum Soil samples were serially diluted with sterile water, spread onto Komada selective medium, and incubated at 28°C for 5 days. Typical colonies were counted and converted to colony-forming units (CFU / g) per gram of dry soil. -1 ).

[0045] Inhibition rate (%) = (CK colony count - treatment colony count) / CK colony count × 100%.

[0046] 5. Plate inhibition rate (Experiment 2) Inhibition rate (%) = (Control colony diameter - Treatment colony diameter) / Control colony diameter × 100%.

[0047] Table 1. Key soil parameters for each treatment after 30 days of incubation: Table 1 shows that the treatments in the examples can stably adjust the pH of acidified soil to a suitable range, improve both aluminum fixation and phenol adsorption rates, and significantly reduce the number of Fusarium oxysporum. In Comparative Examples 1-8: the absence of a coating (Comparative Example 1) led to a sharp increase in pH and a sharp decrease in antibacterial effect; the absence of activated biochar (Comparative Example 2) resulted in a near-complete loss of phenol adsorption capacity; the absence of carbide slag (Comparative Example 3) resulted in almost ineffective aluminum fixation; the absence of calcined oyster shell powder (Comparative Example 4), calcium silicate (Comparative Example 5), and fly ash (Comparative Example 6) in the alkaline mineral powders weakened the acidification and aluminum fixation effects to varying degrees; the substitution of calcined oyster shell powder for raw oyster shell powder (Comparative Example 7) resulted in insufficient calcium oxide activity, leading to a deterioration in the effect; and non-coated mixed granulation (Comparative Example 8) resulted in the loss of both slow-release capacity and antibacterial responsiveness.

[0048] Table 2. Plate inhibition rate of particulate extracts at different pH values: Table 2 shows that the antibacterial rate of the extract in the examples increased as the pH decreased, exhibiting obvious acidity response characteristics; the antibacterial rate was low and lacked responsiveness in uncoated or non-coated granulation, verifying the key role of chitosan coating in achieving dynamic coupling between antibacterial activity and acidification degree.

[0049] In summary, this invention effectively blocks the vicious cycle of acidification and root rot exacerbated by continuous cropping of scallions through multi-pathway linkage, by combining the acid-responsive slow release and antibacterial synergy of chitosan coating, the chemical fixation synergy of carbide slag and activated biochar, the three-component complementarity of alkaline mineral powder, and the rhizosphere optimization of porous adsorption and biological antagonism.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A soil conditioner for continuous cropping of scallions, characterized in that, It includes the following components by weight: 20-40 parts of chitosan-coated biochar alkaline composite granules, 15-30 parts of alkaline mineral powder, 10-20 parts of humic acid, 5-15 parts of composite microbial agent, 2-8 parts of sodium alginate, and 1-5 parts of trace element additives. The chitosan-coated biochar alkaline composite particles are pH-responsive coated particles prepared by a fluidized bed coating process using a mixture of activated biochar and carbide slag as the core material and chitosan as the coating material. The carbide slag is dried, pulverized, and sieved through a 200-mesh sieve before use, and its effective alkali content, calculated as CaO, is ≥60%.

2. The scallion continuous cropping soil conditioner according to claim 1, characterized in that, The alkaline mineral powder is composed of 50% calcined oyster shell powder, 30% calcium silicate, and 20% fly ash; wherein the calcined oyster shell powder is obtained by calcining oyster shells at 900℃ for 2 hours and then crushing them through a 200-mesh sieve; the fly ash contains As≤10mg / kg, Cd≤3mg / kg, Pb≤50mg / kg, Cr≤150mg / kg, and Hg≤2mg / kg.

3. The scallion continuous cropping soil conditioner according to claim 1, characterized in that, The compound microbial agent is composed of 50% Bacillus subtilis, 30% Bacillus amyloliquefaciens, and 20% Trichoderma longifolia; the effective viable count of each strain is independently ≥5 billion / g.

4. The scallion continuous cropping soil conditioner according to claim 1, characterized in that, The humic acid is biochemical potassium fulvic acid with a weight-average molecular weight of 3500 Da; the trace element additive consists of 55% boric acid and 45% ammonium molybdate.

5. The scallion continuous cropping soil conditioner according to claim 1, characterized in that, The preparation method of the chitosan-coated biochar alkaline composite particles includes the following steps: N11. Pyrolyze rice husks or straw under an inert atmosphere, grind and sieve after natural cooling to obtain primary biochar; place the primary biochar in a container with a 10% phosphoric acid solution, soak and activate, wash with deionized water, and dry to obtain activated biochar. N12. Activated biochar and calcium carbide slag powder are mixed to obtain a mixture; then deionized water is added, stirred, and aged to obtain an aged wet mixture; the aged wet mixture is granulated by an extrusion granulator, the resulting wet particles are dried, cooled, and sieved to obtain core material particles; N13. Chitosan is dissolved in an aqueous solution of acetic acid with a volume fraction of 1% to obtain a chitosan coating solution; the chitosan coating solution is sprayed onto the surface of the core material particles; after spraying, fluidized drying is continued to obtain chitosan-coated biochar alkaline composite particles.

6. The scallion continuous cropping soil conditioner according to claim 1, characterized in that, In step N11, the solid-liquid ratio of the initial biochar to the 10% phosphoric acid solution is 1g:10mL; in step N12, the mass ratio of the activated biochar to the calcium carbide slag powder is 6:4; in step N13, the degree of deacetylation of the chitosan is ≥90%, and its weight-average molecular weight is 100,000 to 200,000 Da; the mass of the chitosan is 10 to 15% of the mass of the core material particles.

7. A method for preparing a soil conditioner for continuous cropping of scallions according to any one of claims 1 to 6, characterized in that, Includes the following steps: N1. Alkaline mineral digestion and premixing: Alkaline mineral powder is added to deionized water, stirred, aged, dried, and cooled to obtain digested mineral powder; humic acid and trace element additives are added and mixed to obtain mineral-humic acid premix. N2. Granulation and drying of matrix particles: The mineral-humic acid premix is ​​mixed with sodium alginate to obtain a mixture; then deionized water is added, and the mixture is granulated by an extrusion granulator; the resulting wet particles are dried and sieved to obtain matrix particles; N3. Composite particle mixing: Chitosan-coated biochar alkaline composite particles are mixed with matrix particles to obtain mixed particles; N4. Microbial agent coating: After the mixed particles have cooled, the compound microbial agent is applied to the surface of the mixed particles by spraying or rolling coating. After mixing, the scallion continuous cropping soil conditioner is obtained.

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