Straw porous biochar loaded with bacillus and preparation method thereof

Abstract

The application discloses a straw porous biochar loaded with bacillus and a preparation method thereof, and belongs to the technical field of agricultural waste resource utilization and soil improvement. The method uses agricultural waste straw as raw material, and first degrades lignin and cellulose through pretreatment by a composite microbial agent, and then is prepared into a porous biochar carrier with a specific surface area of 800-1200 m2 / g and a total pore volume of 0.6-1.0 cm3 / g through chemical activation and gradient pyrolysis, and then is loaded with bacillus through an "adsorption-embedding" composite process. The straw porous biochar loaded with bacillus prepared by the application has a bacillus loading capacity of 1.0*10 9 -5.0*10 9 CFU / g, and a survival rate of no less than 65% after 210 days in soil. The product has multiple functions of soil improvement, heavy metal pollution remediation, crop growth promotion and disease prevention, realizes high-value utilization of agricultural waste, has simple preparation process and low cost, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention belongs to the technical fields of agricultural waste resource utilization, soil improvement and microbial agent preparation, specifically relating to a porous straw biochar loaded with Bacillus and its preparation method. Background Technology

[0002] my country is a major agricultural country, producing over 900 million tons of crop straw annually. Processing straw into biochar and applying it to agricultural production is one of the important ways to realize the resource utilization of straw.

[0003] Biochar is a carbon-rich solid material formed by the pyrolysis of biomass under anaerobic or hypoxic conditions. It possesses characteristics such as a porous structure, large specific surface area, and abundant surface functional groups. When applied to soil, biochar can improve soil physicochemical properties, enhance soil fertility, increase soil carbon sequestration, and reduce the bioavailability of heavy metals. However, straw biochar prepared using traditional methods often suffers from underdeveloped pore structures, low specific surface area, and low content of surface functional groups, limiting its application effectiveness.

[0004] Microbial inoculants play an important role in soil improvement, crop growth promotion, and disease control. Bacillus is a widely used beneficial microorganism with multiple functions, including nitrogen fixation, phosphorus and potassium solubilization, and the production of plant growth regulators and antibacterial substances. However, direct application of Bacillus inoculants suffers from problems such as short survival time in the soil, low colonization rate, and susceptibility to environmental factors, leading to unstable application effects.

[0005] Loading microorganisms onto biochar supports can provide a suitable microenvironment for them, protecting them from adverse external environments, extending their survival time, and improving their colonization rate and activity. Currently, there are some research reports on microbial loading on biochar, but most suffer from problems such as low loading capacity, low microbial survival rate, complex preparation processes, and high costs. For example, Chinese patent CN114644331B discloses a biochar-based microbial fertilizer and its preparation method, but the biochar prepared by this method has a low specific surface area and limited microbial loading capacity. Chinese patent CN118320784A discloses a composite modified biochar based on ultraviolet irradiation and microbial loading, its preparation method, and its application, but this method uses ultraviolet irradiation modification, resulting in high energy consumption, and the microbial loading process is relatively simple, with an unsatisfactory survival rate.

[0006] Therefore, developing a porous straw biochar loaded with Bacillus spores, characterized by a well-developed pore structure, high specific surface area, large microbial loading capacity, high survival rate, simple preparation process, and low cost, and its preparation method, is of great significance for realizing the high-value utilization of agricultural waste, improving soil quality, and promoting sustainable agricultural development. (Invention Content)

[0007] (I) Technical Problem to be Solved The purpose of this invention is to overcome the shortcomings of existing technologies and provide a porous straw biochar loaded with Bacillus spp. and its preparation method. This method uses agricultural waste straw as raw material, employs a composite process of "microbial pretreatment + chemical activation + gradient pyrolysis" to prepare a high-porosity biochar carrier, and then loads Bacillus spp. using a "adsorption-embedding" composite process. The resulting composite material has advantages such as large specific surface area, well-developed pore structure, high Bacillus spp. loading capacity, long survival time, and good application effect. (II) Technical Solution

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A porous biochar loaded with Bacillus spores is prepared from agricultural waste straw through microbial pretreatment, chemical activation, and gradient pyrolysis to obtain a porous biochar carrier, which is then loaded with Bacillus spores via an adsorption-embedding composite process. The porous biochar has a specific surface area of ​​800-1200 m² / g, a total pore volume of 0.6-1.0 cm³ / g, and a micropore ratio of 60%-75%. The loading of Bacillus spores is 1.0 × 10⁻⁶ m² / g. 9 -5.0×10 9 CFU / g, the survival rate in soil is not less than 65% after 210 days.

[0010] Furthermore, the straw is selected from one or more of corn straw, wheat straw, rice straw, and cotton straw; the Bacillus is selected from one or more of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus licheniformis, and Bacillus tekirae.

[0011] Furthermore, the porous biochar surface contains abundant oxygen- and nitrogen-containing functional groups such as hydroxyl, carboxyl, and amino groups, and the surface pH value is 7.0-8.5.

[0012] This invention also provides a method for preparing the above-mentioned Bacillus-loaded porous straw biochar, comprising the following steps:

[0013] (1) Straw pretreatment: Wash, dry and crush the straw to 20-40 mesh to obtain straw powder;

[0014] (2) Microbial pretreatment: Mix straw powder with compound microbial agent at a mass ratio of 100:(1-3), add an appropriate amount of water to adjust the moisture content to 50%-60%, and ferment at 28-32℃ for 3-5 days. Turn the pile over once every 12 hours during the fermentation process.

[0015] (3) Chemical activation: Mix the fermented straw with the activator at a mass ratio of 1:(2-4), add deionized water and stir evenly, soak at 60-80℃ for 12-24 hours, and then dry to constant weight;

[0016] (4) Gradient pyrolysis: The activated material is placed in a tube furnace and subjected to gradient pyrolysis under a nitrogen atmosphere. First, the temperature is raised to 300-400℃ at a rate of 5-10℃ / min and held for 1-2 hours. Then, the temperature is raised to 550-650℃ at a rate of 3-5℃ / min and held for 2-3 hours. The material is then allowed to cool naturally to room temperature.

[0017] (5) Biochar post-treatment: The pyrolysis products are washed with deionized water until neutral, dried, pulverized and passed through a 100-200 mesh sieve to obtain a porous biochar carrier.

[0018] (6) Preparation of Bacillus bacterial culture: Bacillus strain was inoculated into LB liquid medium and cultured with shaking at 30-37℃ and 150-200 rpm until the logarithmic growth phase. The bacterial concentration was then adjusted to 1.0 × 10⁻⁶. 9 -1.0×10¹ 0 CFU / mL;

[0019] (7) Adsorption-embedding composite loading: The porous biochar carrier and Bacillus bacterial solution were mixed at a mass-volume ratio of 1g:(5-10)mL. The mixture was shaken and adsorbed for 2-4 hours at 28-30℃ and 100-150rpm. Then, a sodium alginate solution with a mass fraction of 1%-3% was added and stirred evenly. The mixture was then dropped into a calcium chloride solution with a mass fraction of 2%-5% to form microspheres, which were then solidified for 2-4 hours.

[0020] (8) Drying: Wash the solidified microspheres with deionized water and vacuum dry them at 25-30℃ until the water content is 10%-15%, thus obtaining the straw porous biochar loaded with Bacillus.

[0021] Furthermore, the composite microbial agent described in step (2) is composed of Trichoderma, white-rot fungi, and actinomycetes in a mass ratio of (2-3):(1-2):1. Microbial pretreatment can degrade lignin and cellulose in straw, disrupting the dense structure of the straw and facilitating the penetration of subsequent activators and the formation of porous structures.

[0022] Furthermore, the activator in step (3) is one or more of potassium hydroxide, sodium hydroxide, zinc chloride, and phosphoric acid, preferably a composite activator composed of potassium hydroxide and zinc chloride in a mass ratio of (1-2):1. The composite activator can work synergistically to form a more developed pore structure and increase the specific surface area of ​​biochar.

[0023] Furthermore, the nitrogen flow rate in step (4) is 100-200 mL / min. The gradient pyrolysis process allows the straw to fully decompose at low temperatures, forming a preliminary porous structure, and then further activates it at high temperatures, forming a well-developed microporous structure, while avoiding pore collapse caused by rapid heating.

[0024] Further, the volume ratio of sodium alginate solution to Bacillus bacterial culture in step (7) is 1:(2-4).

[0025] Furthermore, the concentration of the calcium chloride solution in step (7) is 0.2-0.5 mol / L.

[0026] The "adsorption-embedding" composite loading process combines the advantages of physical adsorption and embedding fixation. It utilizes the porous structure of biochar for physical adsorption and uses a sodium alginate-calcium chloride gel system for embedding fixation, which greatly improves the loading capacity and survival rate of Bacillus.

[0027] This invention also provides the application of the above-mentioned Bacillus-loaded porous straw biochar in soil improvement, heavy metal contaminated soil remediation, and crop growth promotion and disease prevention. (III) Beneficial Effects

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) This invention employs a composite process of "microbial pretreatment + chemical activation + gradient pyrolysis" to prepare porous biochar carriers. Microbial pretreatment can degrade lignin and cellulose in straw, disrupting the dense structure of straw; chemical activation can further etch the surface of biochar, forming a rich pore structure; gradient pyrolysis can make the pore structure more developed and stable. The prepared porous biochar has a specific surface area as high as 800-1200 m² / g, a total pore volume of 0.6-1.0 cm³ / g, and a micropore ratio of 60%-75%, which is far higher than that of straw biochar prepared by traditional methods.

[0030] (2) This invention employs an "adsorption-embedding" composite process to load Bacillus, utilizing both the porous structure of biochar for physical adsorption and the sodium alginate-calcium chloride gel system for immobilization, significantly improving the loading capacity and survival rate of Bacillus. The loading capacity of Bacillus can reach 1.0 × 10⁻⁶. 9 -5.0×10 9 The CFU / g of the product has a survival rate of no less than 65% after 210 days in the soil, which is much higher than that of direct application of microbial agents and single adsorption loading methods.

[0031] (3) The porous straw biochar loaded with Bacillus prepared in this invention has multiple functions: biochar can improve soil physicochemical properties, enhance soil fertility, and adsorb and fix heavy metals; Bacillus can fix nitrogen, solubilize phosphorus and potassium, produce plant growth regulators and antibacterial substances, promote crop growth, and prevent soil-borne diseases. The synergistic effect of the two is significantly better than that of single biochar or single inoculant.

[0032] (4) This invention uses agricultural waste straw as raw material, realizes the high-value utilization of straw, turns waste into treasure, reduces environmental pollution caused by straw burning, and conforms to the concept of green agriculture and sustainable development.

[0033] (5) The preparation process of the present invention is simple, easy to operate and low in cost, and is suitable for large-scale industrial production. Attached Figure Description

[0034] To provide a more detailed description of the technical solutions of the embodiments of this invention, the accompanying drawings used in the following description of the embodiments are briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on such drawings without creative effort.

[0035] Figure 1: Flowchart of the preparation process of the Bacillus-loaded porous straw biochar of the present invention

[0036] Figure 2: Scanning electron microscope (SEM) image of the porous biochar support prepared in Example 1 (magnification: 5000×).

[0037] Figure 3: Scanning electron microscope (SEM) image of the straw porous biochar loaded with Bacillus subtilis prepared in Example 1 (magnification: 10000×).

[0038] Figure 4: Survival rate of Bacillus subtilis in soil under different treatments over time.

[0039] Figure 5: Bar chart comparing the effects of different treatments on the fresh weight and cadmium content of the aboveground parts of Chinese cabbage. Detailed Implementation

[0040] The present invention will be further described in detail below with reference to specific embodiments.

[0041] Example 1

[0042] A method for preparing porous biochar from corn stalks loaded with Bacillus subtilis includes the following steps:

[0043] (1) Straw pretreatment: Wash the corn stalks, dry them at 105℃ to constant weight, and crush them to 20 mesh to obtain corn stalk powder;

[0044] (2) Microbial pretreatment: Mix 100g of corn stalk powder with 2g of compound microbial agent (Trichoderma: white rot fungi: actinomycetes = 2:1:1), add an appropriate amount of deionized water to adjust the moisture content to 55%, ferment at 30℃ for 4 days, and turn the pile over once every 12 hours during the fermentation process;

[0045] (3) Chemical activation: The fermented corn stalks were mixed with a compound activator (potassium hydroxide: zinc chloride = 1:1) at a mass ratio of 1:3, deionized water was added and stirred evenly, and the mixture was soaked at 70°C for 18 hours, and then dried at 105°C to constant weight.

[0046] (4) Gradient pyrolysis: The activated material is placed in a tube furnace and subjected to gradient pyrolysis in an atmosphere of nitrogen flow rate of 150 mL / min. First, the temperature is raised to 350℃ at a rate of 8℃ / min and held for 1.5 hours. Then, the temperature is raised to 600℃ at a rate of 4℃ / min and held for 2.5 hours. The material is then allowed to cool naturally to room temperature.

[0047] (5) Biochar post-treatment: The pyrolysis product was washed with deionized water until neutral, dried at 105℃, and pulverized through a 150-mesh sieve to obtain a porous biochar carrier; the specific surface area of ​​the porous biochar was 1050m² / g, the total pore volume was 0.85cm³ / g, the micropore ratio was 70%, and the surface pH value was 7.8.

[0048] (6) Preparation of Bacillus subtilis culture: Bacillus subtilis strain was inoculated into LB liquid medium and cultured with shaking at 37℃ and 180 rpm until the logarithmic growth phase. The culture concentration was then adjusted to 5.0 × 10⁻⁶. 9 CFU / mL;

[0049] (7) Adsorption-embedding composite loading: 10g of porous biochar carrier was mixed with 70mL of Bacillus subtilis bacterial solution and shaken for 3 hours at 28℃ and 120rpm. Then, 35mL of sodium alginate solution with a mass fraction of 2% was added, stirred evenly, and then dripped into calcium chloride solution with a mass fraction of 3% using a syringe to form microspheres and solidify for 3 hours.

[0050] (8) Drying: The cured microspheres were washed three times with deionized water and then vacuum-dried at 28°C until the moisture content was 12%, thus obtaining porous corn stalk biochar loaded with Bacillus subtilis. The Bacillus subtilis loading in this product was determined to be 3.2 × 10⁻⁶. 9 CFU / g.

[0051] Example 2

[0052] A method for preparing porous biochar from wheat straw loaded with Bacillus amyloliquefaciens includes the following steps:

[0053] (1) Straw pretreatment: Wash the wheat straw, dry it at 105℃ to constant weight, and crush it to 30 mesh to obtain wheat straw powder;

[0054] (2) Microbial pretreatment: Mix 100g of wheat straw powder with 1.5g of compound microbial agent (Trichoderma: white rot fungi: actinomycetes = 3:2:1), add an appropriate amount of deionized water to adjust the moisture content to 50%, ferment at 28℃ for 5 days, and turn the pile over once every 12 hours during the fermentation process;

[0055] (3) Chemical activation: Mix fermented wheat straw with potassium hydroxide at a mass ratio of 1:2, add deionized water and stir evenly, soak at 60°C for 24 hours, and then dry at 105°C to constant weight;

[0056] (4) Gradient pyrolysis: The activated material is placed in a tube furnace and subjected to gradient pyrolysis in an atmosphere of nitrogen flow rate of 100 mL / min. First, the temperature is raised to 300℃ at a rate of 5℃ / min and held for 2 hours. Then, the temperature is raised to 550℃ at a rate of 3℃ / min and held for 3 hours. The material is then allowed to cool naturally to room temperature.

[0057] (5) Biochar post-treatment: The pyrolysis product was washed with deionized water until neutral, dried at 105℃, and pulverized through a 100-mesh sieve to obtain a porous biochar carrier; the specific surface area of ​​the porous biochar was 880m² / g, the total pore volume was 0.72cm³ / g, the micropore ratio was 65%, and the surface pH value was 8.2.

[0058] (6) Preparation of Bacillus amyloliquefaciens bacterial culture: Bacillus amyloliquefaciens was inoculated into LB liquid medium and cultured with shaking at 35℃ and 150 rpm until the logarithmic growth phase. The bacterial concentration was then adjusted to 3.0 × 10⁻⁶. 9 CFU / mL;

[0059] (7) Adsorption-embedding composite loading: 10g of porous biochar carrier was mixed with 50mL of Bacillus amyloliquefaciens bacterial solution and shaken for 4 hours at 30℃ and 100rpm. Then, 25mL of sodium alginate solution with a mass fraction of 1% was added, stirred evenly, and then dropped into calcium chloride solution with a mass fraction of 2% by a syringe to form microspheres and solidify for 4 hours.

[0060] (8) Drying: The cured microspheres were washed three times with deionized water and then vacuum dried at 25°C until the moisture content was 15%, thus obtaining porous wheat straw biochar loaded with Bacillus amyloliquefaciens. The loading of Bacillus amyloliquefaciens in this product was measured to be 2.1 × 10⁻⁶. 9 CFU / g.

[0061] Example 3

[0062] A method for preparing porous biochar from rice straw loaded with Bacillus licheniformis includes the following steps:

[0063] (1) Straw pretreatment: Wash the rice straw, dry it at 105℃ to constant weight, and crush it to 40 mesh to obtain rice straw powder;

[0064] (2) Microbial pretreatment: Mix 100g of rice straw powder with 3g of compound microbial agent (Trichoderma: white rot fungi: actinomycetes = 2.5:1.5:1), add an appropriate amount of deionized water to adjust the moisture content to 60%, ferment at 32℃ for 3 days, and turn the pile over once every 12 hours during the fermentation process;

[0065] (3) Chemical activation: Fermented rice straw is mixed with a compound activator (potassium hydroxide: zinc chloride = 2:1) at a mass ratio of 1:4, deionized water is added and stirred evenly, soaked at 80℃ for 12 hours, and then dried at 105℃ to constant weight;

[0066] (4) Gradient pyrolysis: The activated material is placed in a tube furnace and subjected to gradient pyrolysis in an atmosphere of nitrogen flow rate of 200 mL / min. First, the temperature is raised to 400℃ at a rate of 10℃ / min and held for 1 hour. Then, the temperature is raised to 650℃ at a rate of 5℃ / min and held for 2 hours. The material is then allowed to cool naturally to room temperature.

[0067] (5) Biochar post-treatment: The pyrolysis product was washed with deionized water until neutral, dried at 105℃, and pulverized through a 200-mesh sieve to obtain a porous biochar carrier; the specific surface area of ​​the porous biochar was 1180m² / g, the total pore volume was 0.96cm³ / g, the micropore ratio was 74%, and the surface pH value was 7.5.

[0068] (6) Preparation of Bacillus licheniformis culture: Bacillus licheniformis strain was inoculated into LB liquid medium and cultured with shaking at 30℃ and 200 rpm until the logarithmic growth phase. The culture concentration was then adjusted to 8.0 × 10⁻⁶. 9 CFU / mL;

[0069] (7) Adsorption-embedding composite loading: 10g of porous biochar carrier was mixed with 100mL of Bacillus licheniformis bacterial solution and shaken for 2 hours at 29℃ and 150rpm. Then, 50mL of sodium alginate solution with a mass fraction of 3% was added, stirred evenly, and then dropped into calcium chloride solution with a mass fraction of 5% by syringe to form microspheres and solidify for 2 hours.

[0070] (8) Drying: The solidified microspheres were washed three times with deionized water and then vacuum-dried at 30°C until the moisture content was 10%, yielding porous rice straw biochar loaded with Bacillus licheniformis. Testing showed that the Bacillus licheniformis loading in this product was 4.5 × 10⁻⁶. 9 CFU / g.

[0071] Comparative Example 1

[0072] Corn stalk biochar prepared by traditional methods: Corn stalks are washed, dried, and pulverized to 20 mesh. The pulverized stalks are placed in a tube furnace and heated to 600℃ at a rate of 10℃ / min under a nitrogen atmosphere. The temperature is maintained for 2 hours, and the pulverized stalks are allowed to cool naturally to room temperature. The stalks are then washed with deionized water until neutral, dried, pulverized, and passed through a 150-mesh sieve to obtain traditional biochar. Testing showed that the biochar has a specific surface area of ​​280 m² / g, a total pore volume of 0.21 cm³ / g, and a micropore content of 42%.

[0073] Comparative Example 2

[0074] Corn straw biochar loaded with Bacillus subtilis using a single adsorption method: Using the porous biochar carrier prepared in Example 1, 10 g of the porous biochar carrier was mixed with 70 mL of the Bacillus subtilis bacterial solution prepared in Example 1. The mixture was shaken and adsorbed at 28°C and 120 rpm for 3 hours, and then vacuum dried at 28°C until the moisture content was 12%, thus obtaining the biochar agent loaded by the single adsorption method. The loading of Bacillus subtilis in this product was determined to be 1.5 × 10⁻⁶. 9 CFU / g.

[0075] Comparative Example 3

[0076] Direct application of Bacillus subtilis inoculant: The Bacillus subtilis bacterial solution prepared in Example 1 was vacuum dried at 28°C until the water content was 12%, yielding a Bacillus subtilis inoculant. The content of Bacillus subtilis in this inoculant was determined to be 5.0 × 10⁻⁶. 9 CFU / g.

[0077] Experimental Example 1: Bacillus Survival Test

[0078] The bacterial agents prepared in Examples 1, 2, and 3 were added to sterilized farmland soil at a mass ratio of 1%, mixed thoroughly, and the soil moisture content was adjusted to 60% of field capacity. The soil was then incubated in a constant temperature incubator at 25°C. Samples were taken at 0, 30, 90, 150, and 210 days of incubation, and the number of Bacillus subtilis in the soil was determined using the dilution plating method to calculate the survival rate. The results are shown in Table 1.

[0079] Table 1. Survival rate (%) of Bacillus subtilis under different treatments

[0080] Example 1 100 95.2 86.7 75.3 68.1 Comparative Example 2 100 82.5 58.3 32.7 18.5 Comparative Example 3 100 61.3 28.6 12.4 4.7

[0081] As shown in Table 1, the survival rate of Bacillus subtilis in the straw porous biochar loaded with Bacillus prepared in Example 1 of this invention was significantly higher than that in Comparative Examples 2 and 3. After 210 days of cultivation, the survival rate of Example 1 was still as high as 68.1%, while the survival rates of Comparative Examples 2 and 3 were only 18.5% and 4.7%, respectively. This indicates that the "adsorption-embedding" composite loading process of this invention can effectively protect Bacillus and significantly prolong its survival time in soil.

[0082] Experiment Example 2: Potted Chinese Cabbage Experiment

[0083] The tested soil was cadmium-contaminated farmland soil with a cadmium content of 1.2 mg / kg. Four treatments were set up: blank control (CK), traditional biochar treatment (BC, Comparative Example 1), single microbial agent treatment (B, Comparative Example 3), and the product of this invention treatment (BB, Example 1). Each treatment was repeated three times. The application rate of both biochar and microbial agent was 1% of the soil mass. The soil and treatment materials were mixed evenly and placed in plastic pots, with 2 kg of soil per pot. Ten Chinese cabbage seeds were sown, and after germination, the seedlings were thinned to 5 plants per pot. After 45 days of cultivation in a greenhouse, the Chinese cabbage was harvested, and the fresh weight and aboveground cadmium content were measured. The results are shown in Table 2.

[0084] Table 2 Effects of different treatments on growth and cadmium uptake in Chinese cabbage

[0085] CK 12.5±1.2 0.35±0.04 BC 16.8±1.5 0.22±0.03 B 18.2±1.7 0.28±0.03 BB 32.7±2.3 0.11±0.02

[0086] As shown in Table 2, compared with the blank control, all treatments significantly promoted the growth of pakchoi and reduced the cadmium content in its aboveground parts. Among them, the treatment with the product of this invention (BB) showed the most significant effect, with the fresh weight of pakchoi increasing by 161.6% and the cadmium content in the aboveground parts decreasing by 68.6% compared with the blank control, and significantly better than the single biochar treatment (BC) and the single microbial agent treatment (B). This indicates that the Bacillus-loaded porous straw biochar prepared in this invention has a significant synergistic effect in promoting crop growth and remediating heavy metal contaminated soil.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. Claims A porous biochar made from straw loaded with Bacillus, characterized in that, A porous biochar carrier was prepared from agricultural waste straw through microbial pretreatment, chemical activation, and gradient pyrolysis. This carrier was then loaded with Bacillus spores using an adsorption-embedding composite process. The porous biochar had a specific surface area of ​​800-1200 m² / g, a total pore volume of 0.6-1.0 cm³ / g, and a micropore content of 60%-75%. The loading of Bacillus spores was 1.0 × 10⁻⁶ m² / g. 9 -5.0×10 9 CFU / g, the survival rate in soil is not less than 65% after 210 days.

2. The straw porous biochar loaded with Bacillus subtilis according to claim 1, characterized in that, The straw is selected from one or more of corn straw, wheat straw, rice straw, and cotton straw; the Bacillus is selected from one or more of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus licheniformis, and Bacillus tekirae.

3. The straw porous biochar loaded with Bacillus according to claim 1, characterized in that, The porous biochar surface contains abundant oxygen- and nitrogen-containing functional groups such as hydroxyl, carboxyl, and amino groups, and the surface pH value is 7.0-8.

5.

4. A method for preparing porous straw biochar loaded with Bacillus as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Straw pretreatment: Wash, dry and crush the straw to 20-40 mesh to obtain straw powder; (2) Microbial pretreatment: Mix straw powder with compound microbial agent at a mass ratio of 100:(1-3), add an appropriate amount of water to adjust the moisture content to 50%-60%, and ferment at 28-32℃ for 3-5 days. Turn the pile over once every 12 hours during the fermentation process. (3) Chemical activation: Mix the fermented straw with the activator at a mass ratio of 1:(2-4), add deionized water and stir evenly, soak at 60-80℃ for 12-24 hours, and then dry to constant weight; (4) Gradient pyrolysis: The activated material is placed in a tube furnace and subjected to gradient pyrolysis under a nitrogen atmosphere. First, the temperature is raised to 300-400℃ at a rate of 5-10℃ / min and held for 1-2 hours. Then, the temperature is raised to 550-650℃ at a rate of 3-5℃ / min and held for 2-3 hours. The material is then allowed to cool naturally to room temperature. (5) Biochar post-treatment: The pyrolysis products are washed with deionized water until neutral, dried, pulverized and passed through a 100-200 mesh sieve to obtain a porous biochar carrier; (6) Preparation of Bacillus bacterial culture: Bacillus strain was inoculated into LB liquid medium and cultured with shaking at 30-37℃ and 150-200 rpm until the logarithmic growth phase. The bacterial concentration was then adjusted to 1.0 × 10⁻⁶. 9 -1.0×10¹ 0 CFU / mL; (7) Adsorption-embedding composite loading: The porous biochar carrier and Bacillus bacterial solution were mixed at a mass-volume ratio of 1g:(5-10)mL, and the mixture was shaken and adsorbed for 2-4 hours at 28-30℃ and 100-150rpm. Then, a sodium alginate solution with a mass fraction of 1%-3% was added, and after stirring evenly, it was dropped into a calcium chloride solution with a mass fraction of 2%-5% to form microspheres, which were then solidified for 2-4 hours. (8) Drying: Wash the solidified microspheres with deionized water and vacuum dry them at 25-30℃ until the water content is 10%-15%, thus obtaining the straw porous biochar loaded with Bacillus.

5. The preparation method according to claim 4, characterized in that, The compound microbial agent described in step (2) is composed of Trichoderma, white-rot fungi and actinomycetes in a mass ratio of (2-3):(1-2):

1.

6. The preparation method according to claim 4, characterized in that, The activator mentioned in step (3) is one or more of potassium hydroxide, sodium hydroxide, zinc chloride, and phosphoric acid, preferably a composite activator composed of potassium hydroxide and zinc chloride in a mass ratio of (1-2):

1.

7. The preparation method according to claim 4, characterized in that, The nitrogen flow rate in step (4) is 100-200 mL / min.

8. The preparation method according to claim 4, characterized in that, The volume ratio of sodium alginate solution to Bacillus bacterial culture in step (7) is 1:(2-4).

9. The preparation method according to claim 4, characterized in that, The concentration of the calcium chloride solution in step (7) is 0.2-0.5 mol / L.

10. The application of a straw porous biochar loaded with Bacillus as described in any one of claims 1-3 in soil improvement, remediation of heavy metal contaminated soil, and crop growth promotion and disease prevention.

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