Biochar-based microbial soil conditioner and preparation method thereof

Abstract

The invention discloses a biochar-based microbial soil conditioner and a preparation method thereof, and relates to the technical field of soil improvement. The preparation method comprises the following steps: firstly, carrying out alkali-acid treatment and segmented pyrolysis on raw materials such as wood chips to obtain primary biochar, and then carrying out chemical activation, nano material modification and plasma treatment to obtain the composite modified biochar. Meanwhile, probiotics such as bacillus subtilis and the like are subjected to activation, expanding culture and saline-alkali domestication to obtain directional domestication bacterial liquid, and the directional domestication bacterial liquid is solidified into microspheres by adopting a composite embedding carrier. And finally, mixing the composite modified biochar, the composite embedded microspheres, potassium humate and other auxiliary materials, drying, and sieving to obtain the soil conditioner. The soil conditioner disclosed by the invention can realize an improvement effect on saline-alkali soil and reduce the total salt content; meanwhile, directionally domesticated microorganisms secrete organic acid to neutralize alkaline components, the pH of the soil is adjusted to the range suitable for crop growth, and salt and alkali stress is relieved.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, belonging to patent classification number C09K17 / 40, specifically to a biochar-based microbial soil conditioner and its preparation method. Background Technology

[0002] Soil salinization and impoverishment have become one of the core challenges restricting sustainable agricultural development and threatening ecological restoration worldwide. According to statistics from the Food and Agriculture Organization of the United Nations, the global area of ​​saline-alkali soils has exceeded 950 million hectares and is increasing at a rate of 10 million hectares per year. In my country, the total area of ​​saline-alkali land has also reached over 100 million hectares, widely distributed in Northwest, North, and coastal regions. These degraded soils not only disrupt the osmotic pressure of crop roots due to high salinity ions, leading to low seedling emergence rates and sharp yield reductions, but also cause a chain reaction of problems due to the destruction of soil aggregate structure and the depletion of organic matter content, resulting in a decline in water and fertilizer retention capacity and a decrease in ecosystem stability. These issues pose a serious challenge to food security strategies and the construction of ecological barriers.

[0003] To overcome these challenges, researchers have developed various technical solutions, including physical, chemical, and biological amendments. Among these, biochar-based amendments have become a research hotspot and application focus in soil remediation due to their advantages such as wide availability of raw materials (utilizing agricultural straw, forestry waste, and other biomass resources), environmental friendliness (carbon sequestration and emission reduction during preparation, with no secondary pollution after application), and diverse improvement effects (simultaneously improving soil structure and nutrient status). These amendments utilize the porous structure of biochar to adsorb soil salinity and regulate pH balance. Combined with the metabolic activities of microbial agents, they activate soil nutrients and promote crop growth, forming a synergistic "physical adsorption-biological regulation" amendment mechanism. This has shown considerable application potential in the remediation of mildly saline-alkali soils.

[0004] However, the practical application of biochar-based soil conditioners is still constrained by many technical bottlenecks that urgently need to be overcome, severely limiting their effectiveness and long-term sustainability in moderately to severely salinized and infertile soils. Existing biochar has insufficient adsorption sites and limited diffusion channels for high-concentration salt ions in soil, resulting in a short adsorption saturation period. This makes it impossible to achieve continuous fixation and leaching control of salt, and the improvement effect is prone to rebound with irrigation or rainfall.

[0005] In the application of microbial agents, current technologies generally adopt the direct addition of untreated, unacclimated agents. However, the highly alkaline environment, high osmotic pressure, and low organic matter (content below 0.5%) of high-salt-alkali soils differ significantly from the suitable living environment of microbial agents. This results in rapid cell dehydration and enzyme activity inhibition after application, leading to a survival rate typically below 10%. Furthermore, the lack of effective protective carriers makes surviving microorganisms susceptible to soil mechanical action and competition from native microorganisms, hindering the formation of stable colonies. Their functional metabolic cycle lasts only 1-2 months, failing to establish a dominant microbial community that can sustainably function in the soil. Consequently, nitrogen fixation, phosphorus solubilization, and growth promotion functions cannot be sustained long-term, hindering the long-term regulation and stable maintenance of soil nutrient cycling. This severely restricts the industrial application and technological value enhancement of biochar-based amendments. Summary of the Invention

[0006] The purpose of this invention is to provide a biochar-based microbial soil conditioner and its preparation method, so as to solve the technical problems mentioned in the background.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing a biochar-based microbial soil conditioner includes the following steps:

[0009] S1. After crushing sawdust, corn stalks and peanut shells, they are treated with sodium hydroxide solution and hydrochloric acid solution in sequence, washed and dried to obtain a refined precursor. The refined precursor is subjected to staged pyrolysis under a nitrogen atmosphere, and then switched to a carbon dioxide atmosphere for further pyrolysis to obtain primary biochar.

[0010] S2. Primary biochar is chemically activated sequentially with potassium hydroxide and phosphoric acid solutions, washed and dried to obtain chemically activated biochar. The chemically activated biochar is dispersed in water, and nano-hydroxyapatite and graphene oxide are added to react. After drying, nano-modified biochar is obtained. The nano-modified biochar is subjected to plasma treatment to obtain composite modified biochar.

[0011] S3. Bacillus subtilis, Bacillus mucilaginosus, and Pseudomonas fluorescens were activated and cultured to obtain pure culture solutions. The pure culture solutions were then mixed and acclimated in a saline-alkali culture medium to obtain a directional acclimation mixed culture solution.

[0012] S4. Chitosan, sodium alginate, montmorillonite, β-cyclodextrin and L-glutamic acid were prepared into a composite embedding carrier matrix. The directional domestication mixed bacterial solution was mixed with the composite embedding carrier matrix and dripped into calcium chloride solution to solidify and form primary microspheres. Then, crosslinking was performed with glutaraldehyde solution. After washing, the composite embedding microspheres were obtained.

[0013] S5. Mix the composite modified biochar with the composite encapsulated microspheres evenly, then add potassium humate, zeolite powder and L-glutamic acid and stir until evenly mixed. Add deionized water to adjust the moisture content and then vacuum dry. Finally, pulverize and sieve to obtain the biochar-based microbial soil conditioner.

[0014] In this invention, the biochar undergoes a multi-level synergistic modification process involving precursor refining, staged pyrolysis, composite chemical activation, nano-loading, and plasma etching. This significantly increases the specific surface area and porosity, forming a multi-level interconnected pore structure. This structure not only efficiently adsorbs free salt and alkali ions in the soil, reducing the total soil salinity, but also reduces salt migration to crop roots through the physical retention of pores, alleviating salt stress. Simultaneously, the rich pore structure significantly improves soil aeration porosity, reduces soil bulk density, and improves soil... The modified biochar improves soil permeability and water retention, reduces water leakage and evaporation loss, and provides ample space for crop roots to extend and respire. The large number of active functional groups such as hydroxyl and phosphate groups introduced on the surface of the modified biochar can form stable bonds with nutrient molecules such as nitrogen, phosphorus, and potassium in the soil, reducing nutrient leaching and loss and improving nutrient utilization. In addition, the stable carbon element rich in biochar can directly replenish soil organic matter, improve soil buffering capacity, regulate soil pH to a more balanced state, and provide a stable habitat substrate for soil microorganisms.

[0015] On the other hand, the compound microbial agent, through salt-alkali acclimation, exhibits significantly enhanced tolerance to 4% NaCl concentration and strongly alkaline environments. Further encapsulation with chitosan-sodium alginate-montmorillonite and cross-linking with glutaraldehyde creates a structurally stable microsphere carrier, increasing the agent's survival rate in the soil and achieving long-term microbial survival and slow release. After release, Bacillus subtilis, Bacillus mucilage, and Pseudomonas fluorescens can rapidly adapt to the harsh environments of saline-alkali and infertile soils and multiply rapidly. The extracellular polysaccharides produced by the strains act as binders for soil particles, efficiently linking fine soil particles to form stable aggregate structures, further increasing the proportion of soil aggregates and enhancing soil erosion resistance and structural stability. Microbial metabolism... The organic acids secreted during the process can gradually neutralize the alkaline components of the soil, adjusting the soil pH to the suitable range for crop growth of 7.0-7.2. At the same time, they can decompose insoluble minerals in the soil (such as phosphate rock and potassium feldspar), converting insoluble phosphorus and potassium into readily available phosphorus and potassium that crops can absorb, activating potential nutrients in the soil, and supplementing the supply of effective nutrients in the soil. In addition, the proliferation of a large number of functional microorganisms can enrich the diversity of soil microbial communities, enhance the efficiency of soil material cycling and energy conversion, inhibit the growth of harmful pathogens, and improve the stability of the soil ecosystem. From the aspects of improving biological activity, optimizing soil structure, regulating pH, activating nutrients, and strengthening ecological functions, the process achieves deep soil improvement, ensuring the durability and stability of the improvement effect.

[0016] Preferably, in step S1, the mass ratio of sawdust, corn stalks and peanut shells is 32:(20-25):(10-15).

[0017] Preferably, in step S1, the sodium hydroxide solution has a mass fraction of 5% and the hydrochloric acid solution has a mass fraction of 3%.

[0018] Preferably, in step S2, the mass ratio of primary biochar to potassium hydroxide is 1:(0.5-1).

[0019] Preferably, in step S2, the mass ratio of nano-hydroxyapatite to graphene oxide is 3:(0.5-2.0).

[0020] Preferably, in step S3, the saline-alkali culture medium includes a first saline-alkali culture medium, a second saline-alkali culture medium, a third saline-alkali culture medium, and a fourth saline-alkali culture medium.

[0021] Preferably, the sodium chloride concentration in the first saline-alkali culture medium is 1%, the sodium chloride concentration in the second saline-alkali culture medium is 2%, the sodium chloride concentration in the third saline-alkali culture medium is 3%, and the sodium chloride concentration in the fourth saline-alkali culture medium is 4%.

[0022] Preferably, in step S5, the mass ratio of the composite modified biochar to the composite encapsulated microspheres is 4:(0.5-1.5).

[0023] Preferably, in step S5, the composite modified biochar undergoes pretreatment, including the following steps:

[0024] The composite modified biochar was added to deionized water to prepare a suspension, and then γ-aminopropyltriethoxysilane and polyethylene glycol were added. The mixture was heated and stirred to react, and the product was obtained.

[0025] In the technical solution of this invention, the research and development team further discovered that the pores of biochar are mainly mesopores and micropores, while the particle size (1-2 mm) of the microbial-embedded microspheres is far larger than the pore size. They can only weakly adhere to the surface of biochar and cannot enter the pores to colonize. As a result, the salts and nutrients adsorbed by microorganisms and biochar are difficult to act synchronously in the soil micro-domain. That is, the salt and alkali ions adsorbed by biochar cannot be rapidly metabolized and neutralized by nearby microorganisms. The organic acids and extracellular polysaccharides produced by microorganisms are also difficult to synergistically optimize the soil structure with biochar, which ultimately affects the synergistic effect of the above two aspects and limits the maximization of the improvement effect. To further address this technical problem, this invention pre-treats the composite modified biochar: post-treatment involving γ-aminopropyltriethoxysilane grafting and polyethylene glycol pore expansion resolves the challenge of synergistic effects between the two. After hydrolysis, KH550 forms Si-OC covalent bonds with the hydroxyl groups on the biochar surface, uniformly grafting amino groups onto the biochar surface and pore walls. This eliminates the hydrophilic / hydrophobic difference between the hydrophobic surface of the biochar and the hydrophilic surface of the microspheres, allowing them to form a dual bonding mode of chemical bonding and hydrogen bonding synergistic through amidation and hydrogen bonding, thereby enhancing their synergistic effects. In addition to performance, the pore-expanding effect of PEG significantly increases the proportion of macropores in biochar, thereby achieving a match between its pore size and the microsphere particle size. This allows the microspheres to transition from slight surface adhesion to strong colonization within the pores, gaining physical barrier protection to enhance survival stability. After colonization within the pores, the microspheres form a close-range microenvironment with the salt and alkali ions and nutrients adsorbed by the biochar. Microorganisms can rapidly metabolize and neutralize the salt, and the organic acids and extracellular polysaccharides they produce can also synergistically optimize soil structure with the biochar, further enhancing the synergistic effect of both.

[0026] A biochar-based microbial soil conditioner is prepared by the method described above.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. By using multi-stage modified biochar to adsorb salt and alkali ions in the soil, the total salt content is reduced; at the same time, the directed domesticated microorganisms secrete organic acids to neutralize alkaline components, adjusting the soil pH to a range suitable for crop growth and alleviating salt and alkali stress.

[0029] 2. The multi-level porous structure of biochar improves soil aeration porosity, reduces bulk density, alleviates compaction, and enhances permeability and water retention; the extracellular polysaccharides produced by microbial metabolism promote the formation of soil aggregates, further improving soil stability and erosion resistance.

[0030] 3. The active functional groups on the surface of biochar can fix nutrients such as nitrogen, phosphorus, and potassium, reducing their loss; microorganisms can activate insoluble minerals and convert them into readily available nutrients. Attached Figure Description

[0031] Figure 1 This is a SEM image of the soil conditioner prepared in Example 1 of the present invention.

[0032] Figure 2 The image shows the XPS spectrum of the soil conditioner prepared in Example 1 of this invention. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1

[0035] A method for preparing a biochar-based microbial soil conditioner includes the following steps:

[0036] Step 1: Weigh 32 parts sawdust, 24 parts corn stalks, and 14 parts peanut shells, crush them to 80-100 mesh, add 5% sodium hydroxide solution (solid-liquid ratio 1:10, g / mL), stir in a 60℃ water bath for 2 hours, filter and wash with deionized water until neutral; then add 3% hydrochloric acid solution (solid-liquid ratio 1:8, g / mL), stir in a 50℃ water bath for 1.5 hours, filter and wash until neutral, and dry in a forced-air dryer at 70℃ until the moisture content is ≤5% to obtain a refined precursor; place the refined precursor in a tube furnace, introduce nitrogen gas (flow rate 60 mL / min), heat to 250℃ at 5℃ / min and hold for 1 hour, then heat to 400℃ at 4℃ / min and hold for 2 hours, switch to carbon dioxide gas (flow rate 40 mL / min), heat to 750℃ at 3℃ / min and hold for 3 hours, and cool naturally to room temperature to obtain primary biochar.

[0037] Step 2: Mix primary biochar and potassium hydroxide at a mass ratio of 1:0.9, add deionized water to adjust the water content to 60% to form a paste, stir in an 85℃ water bath for 2.5 hours, filter, and dry at 105℃; then mix with a 25% phosphoric acid solution at a solid-liquid ratio of 1:6 (g / mL), reflux at 105℃ for 5 hours, filter and wash until the pH of the filtrate is 6.5-7.0, and dry at 110℃ to constant weight to obtain chemically activated biochar; disperse the chemically activated biochar in deionized water to prepare 10g of the solution. The suspension was ultrasonically dispersed at 350W for 45 min, 3 parts of nano-hydroxyapatite and 1.8 parts of graphene oxide were added, and the mixture was stirred in a water bath at 65℃ for 4 h. The pH was adjusted to 7.2-7.5 with 0.1 mol / L sodium hydroxide solution, filtered, and vacuum dried at 100℃ for 3 h to obtain nano-modified biochar. The nano-modified biochar was placed in a plasma treatment instrument, argon gas was introduced (flow rate 25 mL / min), and the treatment was carried out at 180W for 20 min. After natural cooling, composite modified biochar was obtained.

[0038] Step 3: Take lyophilized powders of Bacillus subtilis, Bacillus mucilage, and Pseudomonas fluorescens, respectively, and inoculate them into LB medium (10 g / L peptone, 5 g / L yeast extract, 5 g / L NaCl, pH=7.0). Incubate at 31℃ with shaking at 190 rpm for 20 h to obtain single-strain activated solutions. Transfer the single-strain activated solutions to expansion medium (15 g / L peptone, 8 g / L yeast extract, 5 g / L glucose, pH=7.2) and incubate at 30℃ for 30 h until the bacterial concentration is ≥10. 9 CFU / mL was used to obtain pure bacterial culture. The three pure bacterial cultures were mixed at a volume ratio of 2:1:1 to obtain the initial mixed bacterial culture. The culture was then inoculated into the first to fourth saline-alkali culture media (NaCl mass concentrations of 1%, 2%, 3%, and 4%, respectively, each containing 3 g / L yeast extract, 10 g / L sucrose, and 0.5 g / L KH2PO4). Each saline-alkali culture medium was inoculated at 5% and cultured at 30℃ with shaking for 24 h. This process was repeated 3 times to obtain the directional acclimatization mixed bacterial culture.

[0039] Step 4: Dissolve chitosan in 1.2% acetic acid solution to prepare a 2.5% concentration solution, and keep it in a 60℃ water bath; dissolve sodium alginate in deionized water to prepare a 1.5% concentration solution, heat to 85℃ to dissolve, and then cool to 60℃; add montmorillonite to deionized water to prepare a 6% concentration dispersion, and ultrasonically disperse at 300W for 35 min; mix the three solutions (6 parts) at a volume ratio of 3:2:1, add 1.5 parts β-cyclodextrin and 0.6 parts L-glutamic acid, and stir at 60℃ for 1.5 h to obtain a composite embedding carrier matrix; mix the directional domestication mixed bacterial solution with the carrier matrix at a volume ratio of 1:4, stir evenly at 120 r / min, and drip into a 2.5% calcium chloride solution using a peristaltic pump (flow rate 6 mL / min), and let it stand to solidify for 2 h to form primary microspheres; transfer the primary microspheres into a 0.8% glutaraldehyde solution, stir and crosslink at room temperature for 1.5 h, and wash 4 times to obtain composite embedding microspheres.

[0040] Step 5: Weigh 20 parts of the composite modified biochar, add deionized water to prepare a 12 g / L suspension, ultrasonically disperse at 350 W for 30 min, add 0.4 parts of γ-aminopropyltriethoxysilane and 0.2 parts of polyethylene glycol (PEG-6000), stir in a water bath at 65℃ for 1 h to complete the pretreatment, then add 6 parts of composite embedded microspheres, stir for 20 min to mix evenly; then add 2 parts of potassium humate, 8 parts of zeolite powder and 0.6 parts of L-glutamic acid, stir at 200 r / min for 30 min, add deionized water to adjust the moisture content to 35%; transfer the mixture to a vacuum drying oven, vacuum degree -0.085 MPa, dry at 50℃ until the moisture content is ≤8%; after drying, pulverize to 60-80 mesh, and sieve to obtain biochar-based microbial soil conditioner.

[0041] Example 2

[0042] A method for preparing a biochar-based microbial soil conditioner includes the following steps:

[0043] Step 1: Weigh 32 parts sawdust, 22 parts corn stalks, and 11 parts peanut shells, crush them to 80-100 mesh, add 5% sodium hydroxide solution (solid-liquid ratio 1:10, g / mL), stir in a 60℃ water bath for 2 hours, filter and wash with deionized water until neutral; then add 3% hydrochloric acid solution (solid-liquid ratio 1:8, g / mL), stir in a 50℃ water bath for 1.5 hours, filter and wash until neutral, and dry in a 70℃ forced-air oven until the moisture content is ≤5% to obtain a refined precursor; place the refined precursor in a tube furnace, introduce nitrogen gas (flow rate 60 mL / min), heat to 250℃ at 5℃ / min and hold for 1 hour, then heat to 400℃ at 4℃ / min and hold for 2 hours, switch to carbon dioxide gas (flow rate 40 mL / min), heat to 750℃ at 3℃ / min and hold for 3 hours, and cool naturally to room temperature to obtain primary biochar.

[0044] Step 2: Mix primary biochar and potassium hydroxide at a mass ratio of 1:0.6, add deionized water to adjust the water content to 60% to form a paste, stir in an 85℃ water bath for 2.5 hours, filter, and dry at 105℃; then mix with a 25% phosphoric acid solution at a solid-liquid ratio of 1:6 (g / mL), reflux at 105℃ for 5 hours, filter and wash until the pH of the filtrate is 6.5-7.0, and dry at 110℃ to constant weight to obtain chemically activated biochar; disperse the chemically activated biochar in deionized water to prepare 10g of the solution. The suspension was ultrasonically dispersed at 350W for 45 min, 3 parts of nano-hydroxyapatite and 1.0 part of graphene oxide were added, and the mixture was stirred in a water bath at 65℃ for 4 h. The pH was adjusted to 7.2-7.5 with 0.1 mol / L sodium hydroxide solution, filtered, and vacuum dried at 100℃ for 3 h to obtain nano-modified biochar. The nano-modified biochar was placed in a plasma treatment instrument, argon gas was introduced (flow rate 25 mL / min), and the power was 180W for 20 min. After natural cooling, composite modified biochar was obtained.

[0045] Step 3: Take lyophilized powders of Bacillus subtilis, Bacillus mucilage, and Pseudomonas fluorescens, respectively, and inoculate them into LB medium (10 g / L peptone, 5 g / L yeast extract, 5 g / L NaCl, pH=7.0). Incubate at 31℃ with shaking at 190 rpm for 20 h to obtain single-strain activated solutions. Transfer the single-strain activated solutions to expansion medium (15 g / L peptone, 8 g / L yeast extract, 5 g / L glucose, pH=7.2) and incubate at 30℃ for 30 h until the bacterial concentration is ≥10. 9 CFU / mL was used to obtain pure bacterial culture. The three pure bacterial cultures were mixed at a volume ratio of 2:1:1 to obtain the initial mixed bacterial culture. The culture was then inoculated into the first to fourth saline-alkali culture media (NaCl mass concentrations of 1%, 2%, 3%, and 4%, respectively, each containing 3 g / L yeast extract, 10 g / L sucrose, and 0.5 g / L KH2PO4). Each saline-alkali culture medium was inoculated at 5% and cultured at 30℃ with shaking for 24 h. This process was repeated 3 times to obtain the directional acclimatization mixed bacterial culture.

[0046] Step 4: Dissolve chitosan in 1.2% acetic acid solution to prepare a 2.5% concentration solution, and keep it in a 60℃ water bath; dissolve sodium alginate in deionized water to prepare a 1.5% concentration solution, heat to 85℃ to dissolve, and then cool to 60℃; add montmorillonite to deionized water to prepare a 6% concentration dispersion, and ultrasonically disperse at 300W for 35 min; mix the three solutions (6 parts) at a volume ratio of 3:2:1, add 1.5 parts β-cyclodextrin and 0.6 parts L-glutamic acid, and stir at 60℃ for 1.5 h to obtain a composite embedding carrier matrix; mix the directional domestication mixed bacterial solution with the carrier matrix at a volume ratio of 1:4, stir evenly at 120 r / min, and drip into a 2.5% calcium chloride solution using a peristaltic pump (flow rate 6 mL / min), and let it stand to solidify for 2 h to form primary microspheres; transfer the primary microspheres into a 0.8% glutaraldehyde solution, stir and crosslink at room temperature for 1.5 h, and wash 4 times to obtain composite embedding microspheres.

[0047] Step 5: Weigh 20 parts of the composite modified biochar, add deionized water to prepare a 12 g / L suspension, ultrasonically disperse at 350 W for 30 min, add 0.4 parts of γ-aminopropyltriethoxysilane and 0.2 parts of polyethylene glycol (PEG-6000), stir in a water bath at 65℃ for 1 h to complete the pretreatment, then add 3.5 parts of composite embedded microspheres, stir for 20 min to mix evenly; then add 2 parts of potassium humate, 8 parts of zeolite powder and 0.6 parts of L-glutamic acid, stir at 200 r / min for 30 min, add deionized water to adjust the moisture content to 35%; transfer the mixture to a vacuum drying oven, dry at -0.085 MPa and 50℃ until the moisture content is ≤8%; after drying, pulverize to 60-80 mesh, and sieve to obtain the biochar-based microbial soil conditioner.

[0048] Example 3

[0049] A method for preparing a biochar-based microbial soil conditioner includes the following steps:

[0050] Step 1: Weigh 32 parts sawdust, 23 parts corn stalks, and 12 parts peanut shells, crush them to 80-100 mesh, add 5% sodium hydroxide solution (solid-liquid ratio 1:10, g / mL), stir in a 60℃ water bath for 2 hours, filter and wash with deionized water until neutral; then add 3% hydrochloric acid solution (solid-liquid ratio 1:8, g / mL), stir in a 50℃ water bath for 1.5 hours, filter and wash until neutral, and dry in a 70℃ forced-air oven until the moisture content is ≤5% to obtain a refined precursor; place the refined precursor in a tube furnace, introduce nitrogen gas (flow rate 60 mL / min), heat to 250℃ at 5℃ / min and hold for 1 hour, then heat to 400℃ at 4℃ / min and hold for 2 hours, switch to carbon dioxide gas (flow rate 40 mL / min), heat to 750℃ at 3℃ / min and hold for 3 hours, and cool naturally to room temperature to obtain primary biochar.

[0051] Step 2: Mix primary biochar and potassium hydroxide at a mass ratio of 1:0.7, add deionized water to adjust the water content to 60% to form a paste, stir in an 85℃ water bath for 2.5 hours, filter, and dry at 105℃; then mix with a 25% phosphoric acid solution at a solid-liquid ratio of 1:6 (g / mL), reflux at 105℃ for 5 hours, filter and wash until the pH of the filtrate is 6.5-7.0, and dry at 110℃ to constant weight to obtain chemically activated biochar; disperse the chemically activated biochar in deionized water to prepare 10g of the solution. The suspension was ultrasonically dispersed at 350W for 45 min, 3 parts of nano-hydroxyapatite and 1.5 parts of graphene oxide were added, and the mixture was stirred in a water bath at 65℃ for 4 h. The pH was adjusted to 7.2-7.5 with 0.1 mol / L sodium hydroxide solution, filtered, and vacuum dried at 100℃ for 3 h to obtain nano-modified biochar. The nano-modified biochar was placed in a plasma treatment instrument, argon gas was introduced (flow rate 25 mL / min), and the treatment was carried out at 180W for 20 min. After natural cooling, composite modified biochar was obtained.

[0052] Step 3: Take lyophilized powders of Bacillus subtilis, Bacillus mucilage, and Pseudomonas fluorescens, respectively, and inoculate them into LB medium (10 g / L peptone, 5 g / L yeast extract, 5 g / L NaCl, pH=7.0). Incubate at 31℃ with shaking at 190 rpm for 20 h to obtain single-strain activated solutions. Transfer the single-strain activated solutions to expansion medium (15 g / L peptone, 8 g / L yeast extract, 5 g / L glucose, pH=7.2) and incubate at 30℃ for 30 h until the bacterial concentration is ≥10. 9 CFU / mL was used to obtain pure bacterial culture. The three pure bacterial cultures were mixed at a volume ratio of 2:1:1 to obtain the initial mixed bacterial culture. The culture was then inoculated into the first to fourth saline-alkali culture media (NaCl mass concentrations of 1%, 2%, 3%, and 4%, respectively, each containing 3 g / L yeast extract, 10 g / L sucrose, and 0.5 g / L KH2PO4). Each saline-alkali culture medium was inoculated at 5% and cultured at 30℃ with shaking for 24 h. This process was repeated 3 times to obtain the directional acclimatization mixed bacterial culture.

[0053] Step 4: Dissolve chitosan in 1.2% acetic acid solution to prepare a 2.5% concentration solution, and keep it in a 60℃ water bath; dissolve sodium alginate in deionized water to prepare a 1.5% concentration solution, heat to 85℃ to dissolve, and then cool to 60℃; add montmorillonite to deionized water to prepare a 6% concentration dispersion, and ultrasonically disperse at 300W for 35 min; mix the three solutions (6 parts) at a volume ratio of 3:2:1, add 1.5 parts β-cyclodextrin and 0.6 parts L-glutamic acid, and stir at 60℃ for 1.5 h to obtain a composite embedding carrier matrix; mix the directional domestication mixed bacterial solution with the carrier matrix at a volume ratio of 1:4, stir evenly at 120 r / min, and drip into a 2.5% calcium chloride solution using a peristaltic pump (flow rate 6 mL / min), and let it stand to solidify for 2 h to form primary microspheres; transfer the primary microspheres into a 0.8% glutaraldehyde solution, stir and crosslink at room temperature for 1.5 h, and wash 4 times to obtain composite embedding microspheres.

[0054] Step 5: Weigh 20 parts of the composite modified biochar, add deionized water to prepare a 12 g / L suspension, ultrasonically disperse at 350 W for 30 min, add 0.4 parts of γ-aminopropyltriethoxysilane and 0.2 parts of polyethylene glycol (PEG-6000), stir in a water bath at 65℃ for 1 h to complete the pretreatment, then add 5.0 parts of composite embedded microspheres, stir for 20 min to mix evenly; then add 2 parts of potassium humate, 8 parts of zeolite powder and 0.6 parts of L-glutamic acid, stir at 200 r / min for 30 min, add deionized water to adjust the moisture content to 35%; transfer the mixture to a vacuum drying oven, dry at -0.085 MPa and 50℃ until the moisture content is ≤8%; after drying, pulverize to 60-80 mesh, and sieve to obtain the biochar-based microbial soil conditioner.

[0055] Example 4

[0056] A method for preparing a biochar-based microbial soil conditioner includes the following steps:

[0057] Step 1: Weigh 32 parts sawdust, 25 parts corn stalks, and 15 parts peanut shells, crush them to 80-100 mesh, add 5% sodium hydroxide solution (solid-liquid ratio 1:10, g / mL), stir in a 60℃ water bath for 2 hours, filter and wash with deionized water until neutral; then add 3% hydrochloric acid solution (solid-liquid ratio 1:8, g / mL), stir in a 50℃ water bath for 1.5 hours, filter and wash until neutral, and dry in a 70℃ forced-air oven until the moisture content is ≤5% to obtain a refined precursor; place the refined precursor in a tube furnace, introduce nitrogen gas (flow rate 60 mL / min), heat to 250℃ at 5℃ / min and hold for 1 hour, then heat to 400℃ at 4℃ / min and hold for 2 hours, switch to carbon dioxide gas (flow rate 40 mL / min), heat to 750℃ at 3℃ / min and hold for 3 hours, and cool naturally to room temperature to obtain primary biochar.

[0058] Step 2: Mix primary biochar and potassium hydroxide at a mass ratio of 1:1.0, add deionized water to adjust the water content to 60% to form a paste, stir in an 85℃ water bath for 2.5 hours, filter, and dry at 105℃; then mix with a 25% phosphoric acid solution at a solid-liquid ratio of 1:6 (g / mL), reflux at 105℃ for 5 hours, filter and wash until the pH of the filtrate is 6.5-7.0, and dry at 110℃ to constant weight to obtain chemically activated biochar; disperse the chemically activated biochar in deionized water to prepare 10g of the solution. The suspension was ultrasonically dispersed at 350W for 45 min, 3 parts of nano-hydroxyapatite and 2.0 parts of graphene oxide were added, and the mixture was stirred in a water bath at 65℃ for 4 h. The pH was adjusted to 7.2-7.5 with 0.1 mol / L sodium hydroxide solution, filtered, and vacuum dried at 100℃ for 3 h to obtain nano-modified biochar. The nano-modified biochar was placed in a plasma treatment instrument, argon gas was introduced (flow rate 25 mL / min), and the power was 180W for 20 min. After natural cooling, composite modified biochar was obtained.

[0059] Step 3: Take lyophilized powders of Bacillus subtilis, Bacillus mucilage, and Pseudomonas fluorescens, respectively, and inoculate them into LB medium (10 g / L peptone, 5 g / L yeast extract, 5 g / L NaCl, pH=7.0). Incubate at 31℃ with shaking at 190 rpm for 20 h to obtain single-strain activated solutions. Transfer the single-strain activated solutions to expansion medium (15 g / L peptone, 8 g / L yeast extract, 5 g / L glucose, pH=7.2) and incubate at 30℃ for 30 h until the bacterial concentration is ≥10. 9 CFU / mL was used to obtain pure bacterial culture. The three pure bacterial cultures were mixed at a volume ratio of 2:1:1 to obtain the initial mixed bacterial culture. The culture was then inoculated into the first to fourth saline-alkali culture media (NaCl mass concentrations of 1%, 2%, 3%, and 4%, respectively, each containing 3 g / L yeast extract, 10 g / L sucrose, and 0.5 g / L KH2PO4). Each saline-alkali culture medium was inoculated at 5% and cultured at 30℃ with shaking for 24 h. This process was repeated 3 times to obtain the directional acclimatization mixed bacterial culture.

[0060] Step 4: Dissolve chitosan in 1.2% acetic acid solution to prepare a 2.5% concentration solution, and keep it in a 60℃ water bath; dissolve sodium alginate in deionized water to prepare a 1.5% concentration solution, heat to 85℃ to dissolve, and then cool to 60℃; add montmorillonite to deionized water to prepare a 6% concentration dispersion, and ultrasonically disperse at 300W for 35 min; mix the three solutions (6 parts) at a volume ratio of 3:2:1, add 1.5 parts β-cyclodextrin and 0.6 parts L-glutamic acid, and stir at 60℃ for 1.5 h to obtain a composite embedding carrier matrix; mix the directional domestication mixed bacterial solution with the carrier matrix at a volume ratio of 1:4, stir evenly at 120 r / min, and drip into a 2.5% calcium chloride solution using a peristaltic pump (flow rate 6 mL / min), and let it stand to solidify for 2 h to form primary microspheres; transfer the primary microspheres into a 0.8% glutaraldehyde solution, stir and crosslink at room temperature for 1.5 h, and wash 4 times to obtain composite embedding microspheres.

[0061] Step 5: Weigh 20 parts of the composite modified biochar, add deionized water to prepare a 12 g / L suspension, ultrasonically disperse at 350 W for 30 min, add 0.4 parts of γ-aminopropyltriethoxysilane and 0.2 parts of polyethylene glycol (PEG-6000), stir in a water bath at 65℃ for 1 h to complete the pretreatment, then add 7.5 parts of composite embedded microspheres, stir for 20 min to mix evenly; then add 2 parts of potassium humate, 8 parts of zeolite powder and 0.6 parts of L-glutamic acid, stir at 200 r / min for 30 min, add deionized water to adjust the moisture content to 35%; transfer the mixture to a vacuum drying oven, vacuum degree -0.085 MPa, dry at 50℃ until the moisture content is ≤8%; after drying, pulverize to 60-80 mesh, and sieve to obtain biochar-based microbial soil conditioner.

[0062] Example 5

[0063] A method for preparing a biochar-based microbial soil conditioner includes the following steps:

[0064] Step 1: Weigh 32 parts sawdust, 20 parts corn stalks, and 10 parts peanut shells, crush them to 80-100 mesh, add 5% sodium hydroxide solution (solid-liquid ratio 1:10, g / mL), stir in a 60℃ water bath for 2 hours, filter and wash with deionized water until neutral; then add 3% hydrochloric acid solution (solid-liquid ratio 1:8, g / mL), stir in a 50℃ water bath for 1.5 hours, filter and wash until neutral, and dry in a 70℃ forced-air oven until the moisture content is ≤5% to obtain a refined precursor; place the refined precursor in a tube furnace, introduce nitrogen gas (flow rate 60 mL / min), heat to 250℃ at 5℃ / min and hold for 1 hour, then heat to 400℃ at 4℃ / min and hold for 2 hours, switch to carbon dioxide gas (flow rate 40 mL / min), heat to 750℃ at 3℃ / min and hold for 3 hours, and cool naturally to room temperature to obtain primary biochar.

[0065] Step 2: Mix primary biochar and potassium hydroxide at a mass ratio of 1:0.5, add deionized water to adjust the water content to 60% to form a paste, stir in an 85℃ water bath for 2.5 hours, filter, and dry at 105℃; then mix with a 25% phosphoric acid solution at a solid-liquid ratio of 1:6 (g / mL), reflux at 105℃ for 5 hours, filter and wash until the pH of the filtrate is 6.5-7.0, and dry at 110℃ to constant weight to obtain chemically activated biochar; disperse the chemically activated biochar in deionized water to prepare 10g of the solution. The suspension was ultrasonically dispersed at 350W for 45 min, 3 parts of nano-hydroxyapatite and 0.5 parts of graphene oxide were added, and the mixture was stirred in a water bath at 65℃ for 4 h. The pH was adjusted to 7.2-7.5 with 0.1 mol / L sodium hydroxide solution, filtered, and vacuum dried at 100℃ for 3 h to obtain nano-modified biochar. The nano-modified biochar was placed in a plasma treatment instrument, argon gas was introduced (flow rate 25 mL / min), and the treatment was carried out at 180W for 20 min. After natural cooling, composite modified biochar was obtained.

[0066] Step 3: Take lyophilized powders of Bacillus subtilis, Bacillus mucilage, and Pseudomonas fluorescens, respectively, and inoculate them into LB medium (10 g / L peptone, 5 g / L yeast extract, 5 g / L NaCl, pH=7.0). Incubate at 31℃ with shaking at 190 rpm for 20 h to obtain single-strain activated solutions. Transfer the single-strain activated solutions to expansion medium (15 g / L peptone, 8 g / L yeast extract, 5 g / L glucose, pH=7.2) and incubate at 30℃ for 30 h until the bacterial concentration is ≥10. 9 CFU / mL was used to obtain pure bacterial culture. The three pure bacterial cultures were mixed at a volume ratio of 2:1:1 to obtain the initial mixed bacterial culture. The culture was then inoculated into the first to fourth saline-alkali culture media (NaCl mass concentrations of 1%, 2%, 3%, and 4%, respectively, each containing 3 g / L yeast extract, 10 g / L sucrose, and 0.5 g / L KH2PO4). Each saline-alkali culture medium was inoculated at 5% and cultured at 30℃ with shaking for 24 h. This process was repeated 3 times to obtain the directional acclimatization mixed bacterial culture.

[0067] Step 4: Dissolve chitosan in 1.2% acetic acid solution to prepare a 2.5% concentration solution, and keep it in a 60℃ water bath; dissolve sodium alginate in deionized water to prepare a 1.5% concentration solution, heat to 85℃ to dissolve, and then cool to 60℃; add montmorillonite to deionized water to prepare a 6% concentration dispersion, and ultrasonically disperse at 300W for 35 min; mix the three solutions (6 parts) at a volume ratio of 3:2:1, add 1.5 parts β-cyclodextrin and 0.6 parts L-glutamic acid, and stir at 60℃ for 1.5 h to obtain a composite embedding carrier matrix; mix the directional domestication mixed bacterial solution with the carrier matrix at a volume ratio of 1:4, stir evenly at 120 r / min, and drip into a 2.5% calcium chloride solution using a peristaltic pump (flow rate 6 mL / min), and let it stand to solidify for 2 h to form primary microspheres; transfer the primary microspheres into a 0.8% glutaraldehyde solution, stir and crosslink at room temperature for 1.5 h, and wash 4 times to obtain composite embedding microspheres.

[0068] Step 5: Weigh 20 parts of the composite modified biochar, add deionized water to prepare a 12 g / L suspension, ultrasonically disperse at 350 W for 30 min, add 0.4 parts of γ-aminopropyltriethoxysilane and 0.2 parts of polyethylene glycol (PEG-6000), stir in a water bath at 65℃ for 1 h to complete the pretreatment, then add 2.5 parts of composite embedded microspheres, stir for 20 min to mix evenly; then add 2 parts of potassium humate, 8 parts of zeolite powder and 0.6 parts of L-glutamic acid, stir at 200 r / min for 30 min, add deionized water to adjust the moisture content to 35%; transfer the mixture to a vacuum drying oven, dry at a vacuum degree of -0.085 MPa and 50℃ until the moisture content is ≤8%; after drying, pulverize to 60-80 mesh, and sieve to obtain the biochar-based microbial soil conditioner.

[0069] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that steps 1 and 2 are omitted, and no composite modified biochar is added in step 5.

[0070] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that steps 3 and 4 are omitted, and composite embedded microspheres are not added in step 5.

[0071] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that the composite modified biochar in step 5 is not pretreated.

[0072] Performance testing:

[0073] The original soil was moderately to severely saline-alkali soil (pH=9.2, salt content 0.95%). All tests were conducted after 180 days of cultivation with an amendment applied at a rate of 4% of the soil mass.

[0074] 1. Soil pH test: The potentiometric method was used. 10g of the improved soil sample (passed through a 2mm sieve) was weighed and added to 50mL of deionized water at a soil-to-water ratio of 1:5 (g / mL). The mixture was shaken at 25℃ for 30 minutes and then allowed to stand for 1 hour. The pH value of the supernatant was measured using a calibrated pH meter (accuracy 0.01). Each sample was tested in triplicate, and the average value was taken. The test results are shown in Table 1.

[0075] 2. Soil salinity test: The gravimetric method was used. 20g of air-dried soil sample (passed through a 1mm sieve) was weighed and 200mL of deionized water was added, with a soil-to-water ratio of 1:10 (g / mL). The mixture was shaken at 200 rpm for 60 minutes, then filtered. 100mL of the filtrate was placed in a pre-dried porcelain evaporating dish, evaporated to constant weight in a water bath, and then dried in a 105℃ oven for 4 hours. After cooling to room temperature, the sample was weighed, and the salinity was calculated as follows: Salinity (%) = (Total mass after evaporation - Mass of evaporating dish) / Mass of soil sample × 100%. Each sample was tested in triplicate. The test results are shown in Table 1.

[0076] 3. Microbial survival rate test: The plate count method was used. Soil samples were collected 180 days after the application of the soil amendment. 10g of soil was added to 90mL of sterile physiological saline and serially diluted to 10. -6 For concentration, 0.1 mL of the diluted solution was spread onto LB agar plates and incubated at 31°C for 24 h. The number of colonies was counted and the bacterial concentration (CFU / g) was calculated. The microbial survival rate (%) was calculated as (bacterial concentration at a certain time after modification / initial bacterial concentration) × 100%. Each sample was tested in triplicate. The test results are shown in Table 1.

[0077] 4. Soil aggregate test: The wet sieving method was used. 50g of air-dried soil sample (passed through an 8mm sieve to remove stones and roots) was placed on top of a sieve set (2mm and 0.25mm apertures), and then placed in the aggregate analyzer. The sample was first soaked for 5 minutes, then shaken up and down 30 times (3cm amplitude, 1 Hz frequency). Soil particles larger than 0.25mm were collected, dried to constant weight, and then weighed. The proportion of aggregates larger than 0.25mm was calculated as follows: Aggregate proportion (%) = (mass of soil particles larger than 0.25mm / total sample mass) × 100%. Each sample was tested in triplicate. The test results are shown in Table 1.

[0078] 5. Soil organic matter content test: The potassium dichromate titration method with external heating was used. 0.5 g of soil sample (passed through a 0.25 m sieve) was weighed, and 5 mL of 0.8 mol / L potassium dichromate solution and 5 mL of concentrated sulfuric acid were added. The mixture was heated in an oil bath at 170℃ for 5 min. After cooling, 20 mL of deionized water and 3 drops of o-phenanthroline indicator were added. The solution was titrated to the endpoint with 0.2 mol / L ferrous sulfate solution. The organic matter content was calculated based on the titration volume. Each sample was tested in triplicate. The test results are shown in Table 1.

[0079] Table 1:

[0080]

[0081] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. 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. A method of preparing a biochar-based microbial soil amendment, characterized by, The method comprises the following steps: S1, after sawdust, corn straw and peanut shell are crushed, they are treated with sodium hydroxide solution and hydrochloric acid solution in sequence, washed and dried to obtain refined precursor, the refined precursor is subjected to staged pyrolysis under nitrogen atmosphere, and then switched to carbon dioxide atmosphere for continuous pyrolysis to obtain primary biochar; S2, the primary biochar is sequentially subjected to chemical activation treatment with potassium hydroxide and phosphoric acid solution, washed and dried to obtain chemically activated biochar, the chemically activated biochar is dispersed in water, and nano-hydroxyapatite and graphene oxide are added for reaction, and then dried to obtain nano-modified biochar, and the nano-modified biochar is subjected to plasma treatment to obtain composite modified biochar; S3, Bacillus subtilis, Bacillus mucilaginosus and Pseudomonas fluorescens are activated and cultured to obtain pure culture liquid, the pure culture liquid is mixed, and then domesticated in a saline-alkali culture medium to obtain directional domestication mixed liquid; S4, chitosan, sodium alginate, montmorillonite, β-cyclodextrin and L-glutamic acid are prepared into a composite embedding carrier matrix, the directional domestication mixed liquid is mixed with the composite embedding carrier matrix, dropped into a calcium chloride solution for solidification to form primary microspheres, and then crosslinked with glutaraldehyde solution, and washed to obtain composite embedding microspheres; S5, the composite modified biochar and the composite embedding microspheres are uniformly mixed, then potassium humate, zeolite powder and L-glutamic acid are added and uniformly stirred, deionized water is added to adjust the moisture content, and then vacuum dried, and finally crushed and sieved to obtain a biochar-based microbial soil conditioner.

2. A method of preparing a biochar-based microbial soil amendment according to claim 1, characterized in that, In the step S1, the mass ratio of the sawdust, corn straw and peanut shell is 32:(20-25):(10-15).

3. A method of preparing a biochar-based microbial soil amendment according to claim 1, characterized in that, In the step S1, the mass fraction of the sodium hydroxide solution is 5%, and the mass fraction of the hydrochloric acid solution is 3%.

4. The method of claim 1, wherein the biochar-based microbial soil amendment is prepared by, In the step S2, the mass ratio of the primary biochar to potassium hydroxide is 1:(0.5-1).

5. The method for preparing a biochar-based microbial soil conditioner according to claim 1, characterized in that, In the step S2, the mass ratio of the nano-hydroxyapatite to graphene oxide is 3:(0.5-2.0).

6. The method of claim 1, wherein the biochar-based microbial soil amendment is prepared by the steps of: In the step S3, the saline-alkali culture medium comprises a first saline-alkali culture medium, a second saline-alkali culture medium, a third saline-alkali culture medium and a fourth saline-alkali culture medium.

7. A method of preparing a biochar-based microbial soil amendment according to claim 6, characterized in that, In the first saline-alkali culture medium, the mass concentration of sodium chloride is 1%, in the second saline-alkali culture medium, the mass concentration of sodium chloride is 2%, in the third saline-alkali culture medium, the mass concentration of sodium chloride is 3%, and in the fourth saline-alkali culture medium, the mass concentration of sodium chloride is 4%.

8. The method of claim 1, wherein the biochar-based microbial soil amendment is prepared by, In the step S5, the mass ratio of the composite modified biochar to the composite embedding microspheres is 4:(0.5-1.5).

9. The method of claim 1, wherein the biochar-based microbial soil amendment is prepared by, In the step S5, the composite modified biochar is pretreated, comprising the following steps: The composite modified biochar is added into deionized water to prepare a suspension, then γ-aminopropyl triethoxysilane and polyethylene glycol are added, and heated and stirred to react.

10. A biochar-based microbial soil amendment characterized in that, Prepared by the method of any one of the above claims 1-9.

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