A method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer

Abstract

The present invention relates to the technical field of soil function improvement, specifically a method for increasing carbon and expanding the capacity of paddy field soil based on biochar-based organic fertilizer. The method comprises: crushing the biomass raw material, pyrolyzing and cooling it to obtain biochar; immersing the biochar in a functional bacterial solution containing actinomycetes and bacillus for activation treatment to obtain modified biochar; mixing the modified biochar with decomposed straw for composting and fermentation to obtain organic fertilizers of different particle sizes; applying large-particle organic fertilizers to the deep soil, laying straw on the soil and covering it with soil, and applying small-particle organic fertilizers to the surface soil. The present application uses layered application to enable large-particle biochar to repair the deep soil structure and expand the carbon pool capacity. At the same time, the carbon-nitrogen synergistic metabolism driven by functional bacteria improves carbon stability, thereby achieving soil carbon increase and expansion while improving carbon sequestration efficiency, solving the contradiction between carbon sequestration and structural degradation and nutrient imbalance in traditional carbon increase and expansion technologies, and promoting the coordinated improvement of carbon sink function and agricultural productivity.

Description

Technical Field

[0001] The present invention relates to the technical field of soil function enhancement, and in particular to a method for increasing carbon and expanding the capacity of paddy soil based on biochar-based organic fertilizer. Background Art

[0002] In recent years, with the deepening of soil ecosystem research and the growing demand for sustainable agricultural development, increasing carbon and expanding soil storage capacity has become a key path to improving soil quality. Biochar, rich in carbon, not only increases carbon when applied to soil, but its porous structure also optimizes soil pore conditions, expanding soil storage capacity, and thereby systematically improving the soil's physical, chemical, and biological properties.

[0003] However, traditional technologies usually apply organic fertilizer or biochar evenly to the surface or shallow soil. Due to the lack of oxygen in the deep soil, anaerobic bacteria dominate the microorganisms, and their decomposition ability is significantly limited. The mineralization rate of organic carbon loaded by large-particle biochar is extremely low, and carbon and nitrogen nutrients are retained in the deep layer for a long time, which is misaligned with the needs of the rice root distribution area (0-20 cm surface), causing the risk of nutrient leaching.

[0004] To address this issue, existing methods attempt to adjust large-particle biochar fertilizers to smaller particles. While small-particle biochar can improve carbon sequestration efficiency in the surface layer, once applied deeper, the fine particles tend to combine with clay minerals to form a dense aggregate structure, significantly reducing soil porosity and hindering water infiltration and gas exchange. The anoxic environment in the deep soil further inhibits the metabolic activity of aerobic functional bacteria while stimulating the methanogenesis pathway dominated by anaerobic bacteria, ultimately leading to negative chain reactions such as soil acidification and structural degradation. Summary of the Invention

[0005] Given that in existing technologies, traditional soil carbon enhancement technology has a single application strategy, which leads to low carbon sequestration efficiency in deep soil, structural degradation, aggravated acidification and compaction, and mismatch between carbon and nitrogen nutrient supply and demand, and has negative technical problems.

[0006] This application describes a method for increasing carbon content in paddy soil using biochar-based organic fertilizer, including:

[0007] Step 1: crush the biomass raw material and pyrolyze it at 500-700℃ for 5-8 hours, then cool it to obtain biochar;

[0008] Step 2: Prepare a functional bacterial solution containing actinomycetes and Bacillus according to the ratio of (1–3):1. The number of viable bacteria in the functional bacterial solution should be ≥ ;

[0009] Step 3: immersing the biochar in a functional bacterial solution for activation treatment, controlling the volume ratio of the functional bacterial solution to the biochar to be 1:(2-3) to obtain modified biochar;

[0010] Step 4: composting and fermenting the modified biochar and the decomposed straw, and then granulating and screening the compost to obtain organic fertilizers with different particle sizes;

[0011] Step 5: Use large-particle organic fertilizer and apply it to the deep soil. Spread pretreated straw on the soil and cover it with soil. Use small-particle organic fertilizer and apply it to the surface soil.

[0012] Furthermore, in step 1, the lignin content of the biomass raw material is ≥30%, and after crushing, it is sieved using a 15-20 mesh screen, and the particle size of the crushed biomass raw material particles is ≤5 mm.

[0013] Furthermore, in step 1, the pyrolysis time is controlled to be 6-7 hours; after the pyrolysis is completed, nitrogen is introduced to cool the biomass raw material, and the cooling time is controlled to be less than 30 minutes.

[0014] Furthermore, in step 3, the ambient temperature of the activation treatment is controlled to be 25-30°C, and the treatment is carried out at a constant temperature of 25-30°C for 18-24 hours to dehydrate the modified biochar to a moisture content between 5% and 10%.

[0015] Furthermore, in step 4, the modified biochar, decomposed straw compost, and edible fungus residue are added in a ratio of (5-6): (3-4): 1, calculated by mass percentage, and mixed evenly until the uniformity is ≥ 95%. The moisture content of the material is adjusted to 50%-60%, and the composting and fermentation is continued for 5-7 days. The pile temperature is controlled between 55-65°C, and the pile is turned once a day.

[0016] Further, in step 5, the particle size of the large-particle organic fertilizer is 4 to 6 mm, and the particle size of the small-particle organic fertilizer is 2 to 4 mm;

[0017] Apply large-grained organic fertilizer to a depth of 20 to 30 cm in the soil at a rate of 1,200 kg ± 50 kg per hectare;

[0018] Spread pre-treated straw at a rate of 2,000 kg ± 100 kg per hectare on a 10 to 20 cm soil layer;

[0019] Apply small-particle organic fertilizer to the topsoil at a rate of 800 kg ± 30 kg per hectare, to a depth of 0 to 10 cm.

[0020] Furthermore, in step 5, the straw pretreatment step is to cut the whole straw into short segments of 2-5 cm and dry them naturally in the sun until the moisture content is ≤30%.

[0021] Furthermore, in step 4, the pretreatment of the decomposed straw includes: mixing the decomposed straw with a composting agent at a mass ratio of (10-15):1, adjusting the carbon-nitrogen ratio to (25-30):1, and stacking and fermenting for 2-3 days before use; the composting agent contains a composite bacterial agent of Bacillus subtilis and Aspergillus oryzae, and the number of viable bacteria is ≥ .

[0022] Furthermore, during the composting fermentation process in step 4, the pH value of the material is monitored and adjusted to 6.5-7.5, straw powder is added during daily turning to adjust aeration, and fermentation is terminated when the cellulose degradation rate in the material is ≥60%.

[0023] Furthermore, in step 5, after fertilization, the surface soil is covered with a pre-treated straw layer with a thickness of 3-5 cm, and regular sprinkler irrigation is performed to maintain the soil moisture content at 60%-70% for 15-20 days.

[0024] The beneficial effects of this application are:

[0025] The present application mentions a method for increasing carbon and expanding the capacity of paddy field soil based on biochar-based organic fertilizer, comprising: crushing the biomass raw materials, pyrolyzing and cooling them to obtain biochar; preparing a functional bacterial solution containing actinomycetes and Bacillus; immersing the biochar in the functional bacterial solution for activation treatment to obtain modified biochar; mixing the modified biochar with decomposed straw for composting and fermentation, and after completion, granulating and screening to obtain organic fertilizers of different particle sizes; using large-particle organic fertilizers, applying them to deep soil, laying pretreated straw on the soil and covering it with soil, and using small-particle organic fertilizers, mixing them into the surface soil.

[0026] This application solves the synergistic contradiction between carbon sequestration and nutrient utilization in deep soil by using a differentiated strategy of layered application of large-particle and small-particle biochar, combined with the directional regulation of hypoxia-tolerant functional bacteria. Large-particle biochar forms a slow-release barrier in the deep layer, reducing carbon decomposition and nutrient loss. Its porous structure improves deep soil aeration, promotes the metabolic activity of anaerobic bacterial communities, and accelerates carbon-nitrogen conversion efficiency. Small-particle biochar optimizes the pore network of surface soil, enhances water penetration and root interaction, and alleviates the inhibition of compaction on microbial activity. Functional bacteria enhance the decomposition of organic matter by secreting extracellular enzymes, accurately adapting to the nutrient needs of the crop growth cycle. This application uses a layered application strategy to enable large-particle biochar to repair deep soil structure and expand carbon storage capacity. At the same time, the carbon-nitrogen synergistic metabolism driven by functional bacteria improves carbon stability, thereby achieving soil carbon expansion while improving carbon sequestration efficiency, solving the contradiction between carbon sequestration and structural degradation and nutrient imbalance in traditional carbon expansion technologies, and promoting the synergistic improvement of carbon sink function and agricultural productivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments of the present invention in conjunction with the accompanying drawings.

[0028] Figure 1 This is a process flow chart of a method for increasing carbon and expanding the capacity of paddy soil based on biochar-based organic fertilizer mentioned in the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the examples are not intended to limit the present invention.

[0030] For this purpose, refer to Figure 1 This application discloses a method for increasing carbon content in paddy soil using biochar-based organic fertilizer, comprising:

[0031] Step 1: crush the biomass raw material, pyrolyze it at 500-700℃ for 5-8h, and then cool it to obtain biochar.

[0032] It should be noted that high-temperature pyrolysis at 500-700°C promotes thermochemical decomposition of biomass feedstock, converting complex organic matter such as lignin into a stable aromatic carbon structure, forming porous biochar with a high specific surface area. High-temperature cracking produces micropores and mesopores, forming a porous structure that enhances the physical adsorption capacity of biochar and provides a microenvironment for subsequent microbial colonization. The aromatic ring structure enhances carbon stability, resists microbial decomposition, reduces deep soil carbon mineralization, and achieves long-term carbon fixation. During the pyrolysis process, some nitrogen and phosphorus are converted into slow-release states, preserving inert nutrients and reducing the risk of deep nutrient loss.

[0033] It's important to note that the biochar pyrolysis temperature is controlled between 500-700°C to avoid excessive decarboxylation and the production of highly alkaline ash at temperatures exceeding 800°C. Furthermore, high-temperature pyrolysis provides a high-surface-area carrier for subsequent microbial loading, and its porous structure enhances microbial attachment. The alkaline environment (pH 8-10) created by high-temperature carbonization can partially inactivate pathogens, reducing bacterial contamination during the composting fermentation stage.

[0034] In this technical solution, in step 1, the biomass feedstock has a lignin content of ≥30%. High-lignin feedstocks offer greater carbon stability and resistance to decomposition after pyrolysis. Straw or rice husks can be used as the biomass feedstock. After crushing, the biomass feedstock is screened using a 20-mesh sieve. The crushed biomass feedstock has a particle size of ≤5 mm to increase pyrolysis uniformity, avoid partial incomplete carbonization, and increase the contact area during subsequent bacterial activation.

[0035] In step 1, the pyrolysis time is controlled to 6-7 hours. After the pyrolysis is complete, nitrogen gas or spray cooling is applied to the biomass feedstock, keeping the cooling time to <30 minutes. Rapid cooling reduces high-temperature oxidation, preserves surface oxygen-containing functional groups such as carboxyl and phenolic hydroxyl groups, and enhances the biochar's ability to attract functional bacteria.

[0036] Step 2: Prepare a functional bacterial solution containing actinomycetes and Bacillus according to the ratio of (1-3):1. The number of viable bacteria in the bacterial solution should be ≥ ;

[0037] For example, in this application, Streptomyces can be selected as the actinomycete, and Bacillus amyloliquefaciens can be selected as the Bacillus. Actinomycetes secrete cellulases and chitinases, which decompose complex organic matter and promote humus formation. They also produce biosurfactants, which improve soil particle aggregation. Bacillus can antagonize soil-borne pathogens, induce systemic resistance in plants, and regulate nitrogen forms through nitrification and denitrification, reducing the risk of deep anaerobic methanogenesis.

[0038] In addition, the bacterial liquid is combined with biochar in step 3 to form a "carbon-bacteria" complex, and the pore structure of biochar is used to protect microorganisms from being inhibited by the anaerobic environment in deep soil, thereby extending their functional activity cycle.

[0039] Step 3: Immerse the biochar in a functional bacterial solution for activation treatment, and control the volume ratio of the bacterial solution to the biochar to be 1: (2-3) to obtain modified biochar.

[0040] In this technical solution, in step 3, the ambient temperature of the activation treatment is controlled to 25-30°C, and the treatment is carried out at a constant temperature of 25-30°C for 24 hours to dehydrate the modified biochar to a moisture content between 5% and 10%.

[0041] Controlling the moisture content between 5% and 10% can prevent wet charcoal from clumping in the compost and affecting aeration; at the same time, retaining enough moisture to maintain the dormant activity of the bacterial community.

[0042] It is important to note that immersion activation is performed at a constant temperature of 25-30°C, with a volume ratio of bacterial solution to biochar of 1:(2-3). Avoid excessive bacterial solution, which can overwet the biochar and affect pore aeration, or insufficient bacterial load, which can lead to insufficient bacterial populations. The bacterial solution penetrates the biochar pores, where microorganisms colonize and form a biofilm structure, enhancing microbial tolerance to stresses such as drought and hypoxia. Actinomycete enzymes bind to carboxyl and hydroxyl groups on the biochar surface, thereby increasing the activation efficiency of phosphorus and potassium. Bacillus metabolites can chelate insoluble soil nutrients. A 24-hour constant temperature treatment promotes uniform water evaporation, dehydration, and moisture control, preventing biochar particle agglomeration and maintaining pore connectivity.

[0043] Step 4: composting and fermenting the modified biochar and the decomposed straw, and then granulating and screening the compost to obtain organic fertilizers with different particle sizes;

[0044] In the present technical solution, in step 4, the modified biochar, decomposed straw compost, and edible fungus residue are added in a ratio of (5-6): (3-4): 1, calculated by mass percentage, and mixed evenly until the uniformity is ≥ 95%. The moisture content of the material is adjusted to 50%-60%. A moisture content below 50% will restrict microbial activity, and a moisture content above 60% will lead to anaerobic fermentation. The composting and fermentation lasts for 5-7 days, and the pile temperature is controlled between 55-65°C to promote thermophilic bacteria to degrade cellulose. Excessive pile temperature will inactivate functional bacteria, and the pile needs to be turned to dissipate heat.

[0045] It should be noted that modified biochar is mixed with decomposed straw and edible fungus residue in a ratio of (5-6):(3-4):1, and composted at 55-65°C to achieve synergistic nutrient release. Microbial action decomposes straw cellulose into humic acid, which then binds to the surface functional groups of the biochar, undergoing a humification process and forming a stable organic-inorganic composite colloid, improving the soil's ability to retain water and fertilizer. The fungus residue provides a readily available nitrogen source, the straw provides a carbon skeleton, and the biochar fixes ammonia and nitrogen, balancing nutrients and reducing nitrogen volatilization losses during composting. The high temperature phase (above 55°C for three days) kills weed seeds and pathogens, while the adsorption effect of the biochar reduces ammonia release.

[0046] In step 4, the pretreatment of the composted straw includes: mixing the composted straw with a composting agent at a mass ratio of (10-15):1, adjusting the carbon-nitrogen ratio to (25-30):1, and stacking and fermenting for 2-3 days before use; the composting agent contains a composite bacterial agent of Bacillus subtilis and Aspergillus oryzae at a mass ratio of 1:1, and the number of viable bacteria is ≥ .

[0047] During the composting process, actinomycetes degrade lignin by secreting enzymes such as laccase and manganese peroxidase, breaking down the stubborn structure of straw. Simultaneously, Bacillus bacteria hydrolyze cellulose into glucose using cellulase enzymes. Bacillus bacteria provide a carbon source for the actinomycetes, while biochar acts as a carrier, anchoring the bacteria and buffering pH. It also absorbs degradation intermediates through its pores, preventing feedback inhibition.

[0048] Furthermore, during the composting process in step 4, monitor the pH of the material and adjust it to 6.5-7.5. Add straw powder during daily turning to adjust aeration. Stop fermentation when the cellulose degradation rate in the material is ≥60%. Acidic environments with a pH <6.5 inhibit actinomycetes, while alkaline environments with a pH >7.5 reduce cellulase activity. Maintaining a cellulose degradation rate of ≥60% ensures that the straw is fully decomposed and avoids nitrogen competition after application to the soil.

[0049] Step 5: Use large-particle organic fertilizer and apply it into the deep soil. Spread pre-treated straw on the soil and cover it with soil. Use small-particle organic fertilizer and mix it into the surface soil.

[0050] In the present technical solution, in step 5, the particle size of the large-particle organic fertilizer is 4 to 6 mm, and the particle size of the small-particle organic fertilizer is 2 to 4 mm.

[0051] Apply large-particle organic fertilizer at a rate of 1,200 kg ± 50 kg per hectare to a depth of 20 to 30 cm. Large particles slowly decompose at depth, forming a long-term carbon reservoir and reducing CO2 emissions. Apply pretreated straw at a rate of 2,000 kg ± 100 kg per hectare to a 10 to 20 cm soil layer. Short straw segments facilitate even laying, and their low moisture content prevents heat generation from fermentation and root burns. Apply small-particle organic fertilizer at a rate of 800 kg ± 30 kg per hectare to a depth of 0 to 10 cm in the topsoil. The small particles quickly release nutrients, promoting early rice growth.

[0052] In the present technical solution, in step 5, the straw pretreatment step is to cut the whole straw into short segments of 2-5 cm and dry them naturally in the sun until the moisture content is ≤30%.

[0053] In this application, a differentiated application of large- and small-particle organic fertilizers was implemented, combined with straw pretreatment. Large-particle organic fertilizer (4-6 mm) was applied deep (20-30 cm). Large-particle biochar increased soil porosity, alleviated anaerobic conditions, and inhibited methanogen activity. The slow-release nitrogen, phosphorus, and potassium loaded in the biochar diffused with water to the lateral root zone, releasing nutrients and reducing surface nutrient competition. Small-particle organic fertilizer (2-4 mm) was applied to the surface (0-10 cm). Small-particle biochar filled surface pores, retaining carbon within the micropores, reducing water evaporation and nutrient leaching. It also reflected sunlight and lowered surface temperature fluctuations. Mixed with pretreated straw (2-5 cm short segments), it promoted interaction between rice shallow roots and microorganisms. Straw pretreatment involved cutting short segments and air-drying them to reduce moisture content, accelerate field decomposition, and prevent excessive surface soil compaction.

[0054] Pyrolysis and carbonization achieve physical stabilization, while the microbial load is activated, and composting and humification achieve chemical equilibrium. Deep, large-particle carbon improves aeration, while surface, small-particle carbon inhibits compaction, and straw pretreatment bridges the organic matter gradient.

[0055] In step 5, after fertilization, the surface soil is covered with a 3-5 cm thick layer of pre-treated straw, and regular sprinkler irrigation is used to maintain the soil moisture content at 60%-70% for 15-20 days.

[0056] The straw mulch is 3-5 cm thick. The mulch layer can reduce water evaporation, and sprinkler irrigation maintains microbial activity and accelerates the mineralization of organic fertilizer.

[0057] This application solves the synergistic contradiction between deep soil carbon sequestration and nutrient utilization through a differentiated strategy of layered application of large- and small-particle biochar, combined with the targeted regulation of hypoxia-tolerant functional bacteria: large-particle biochar forms a slow-release barrier in the deep layer, reducing carbon decomposition and nutrient loss. Its porous structure improves deep soil aeration, promotes the metabolic activity of anaerobic bacterial communities, and accelerates carbon-nitrogen conversion efficiency; small-particle biochar optimizes the surface soil pore network, enhances water penetration and root interaction, and alleviates the inhibition of compaction on microbial activity. Functional bacteria enhance the decomposition of organic matter by secreting extracellular enzymes, accurately adapting to the nutrient needs of the crop growth cycle, and simultaneously improving deep carbon stability and surface soil health, ultimately achieving two-way optimization of carbon sequestration efficiency and agricultural productivity.

[0058] For a better understanding of the technical solution, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

[0059] Implementation location and materials;

[0060] Location: Black soil area of ​​Heilongjiang Province, typical black soil, normal pH 5.5-6.0, organic matter content 3%-4%.

[0061] Materials: The biomass raw materials include rice straw and composted pig manure straw; the functional bacterial liquid includes a 1:1 ratio of Streptomyces griseus to Bacillus amyloliquefaciens.

[0062] Three parallel experiments were set up in each group, with a total experimental period of 12 months. The experiments included straw crushing, biochar preparation, and composted straw pretreatment; stratified fertilization, soil covering, and rice planting (variety: Longjing 20); and data collection was conducted every three months.

[0063] Experimental design;

[0064] Example group: large-particle organic fertilizer (4-6 mm) was applied deep (20-30 cm) + small-particle organic fertilizer (2-4 mm) was applied on the surface (0-10 cm) + straw mulch (3-5 cm) + functional bacterial liquid activation treatment.

[0065] Control group 1: conventional chemical fertilizer (NPK), conventional single fertilization.

[0066] Control group 2: Layered fertilization (large particle size + small particle size organic fertilizer) + surface covering soil, but no functional bacterial solution was added.

[0067] implementation method;

[0068] For biochar preparation, rice straw was crushed to ≤5 mm, pyrolyzed at 500 °C for 6 h, protected by nitrogen, cooled to room temperature, and pulverized to pass through a 20-mesh sieve.

[0069] Composted straw pretreatment, composted straw and composting agent, containing Bacillus subtilis + Aspergillus oryzae in a mass ratio of 1:1, viable bacteria count , mixed at a ratio of 10:1, adjusted to a C / N ratio of 25:1, and composted for 3 days. Modified biochar (5-6 mm), decomposed straw compost, and edible fungus residue were mixed at a ratio of 6:3:1, adjusted to a moisture content of 55%, and composted for 7 days, turning the pile daily.

[0070] Field fertilization: Example group: large-particle organic fertilizer (1200 kg / ha) was applied in the deep layer (20-30 cm), small-particle organic fertilizer (800 kg / ha) was applied in the surface layer (0-10 cm), and pretreated straw (3-5 cm) was covered after covering with soil;

[0071] Control group 1: NPK fertilizer (300 kg / ha) was applied uniformly on the surface;

[0072] Control group 2: The same amount of fertilizer was applied as in the example group, but no functional bacterial solution was added.

[0073] Carbon enrichment efficiency determination: The total organic carbon (TOC) content of soil samples was determined using the potassium dichromate oxidation-external heating method. After air-drying, grinding, and sieving (2 mm), the soil samples were oxidized with concentrated sulfuric acid and potassium dichromate solution, and the TOC content was determined by titration. The aqueous extract was filtered through a 0.45 μm filter membrane, and the dissolved carbon (DOC) content in the filtrate was determined using a total organic carbon analyzer. The data are shown in Table 1.

[0074] ;

[0075] Referring to Table 1, the TOC of the Example group was 25.3 g / kg, compared to 18.7 g / kg in Control 1, a 35.3% increase (p < 0.05). The porous structure of the pyrolyzed biochar adsorbs organic molecules, reducing microbial decomposition. Scanning electron microscopy verified pore filling. Large-particle organic fertilizers were applied deep into the soil, reducing tillage disturbance and promoting the physical protective bonding of biochar with soil minerals. The TOC of the Example group was significantly higher than that of Control 1. This is because the adsorption of biochar reduces the decomposition of organic carbon, thereby increasing its storage in the soil.

[0076] The DOC of the example group was 0.38 g / kg, while that of the control group 2 was 0.29 g / kg, a 31.0% increase. Actinomycetes secreted extracellular polysaccharides (EPS), indicating that the functional bacteria promoted short-term carbon retention.

[0077] Acidification inhibition determination; pH was determined using the potentiometric method. Soil samples were air-dried and passed through a 2 mm sieve. The soil samples were mixed with deionized water at a mass ratio of 1:2.5 and stirred for 30 minutes. After standing for 30 minutes, the pH value of the suspension was measured using a calibrated pH meter.

[0078] Determination of exchangeable acid by potassium chloride exchange method and hydrolytic acid 2.5 g of air-dried soil sample passed through a 2 mm sieve was taken, 50 mL of 1 mol / L KCl solution was added, and the mixture was shaken for 2 hours; the supernatant was separated by centrifugation, and the exchangeability was determined by neutralization titration. concentration (in cmol / kg);

[0079] The oxalic acid concentration was determined by high performance liquid chromatography (HPLC). The supernatant was collected by centrifugation and purified by C18 solid-phase extraction column. The product was concentrated and dissolved in the mobile phase (0.1% formic acid aqueous solution: acetonitrile = 90:10). The oxalic acid concentration was quantified by HPLC (UV detector, λ = 210 nm). The data are shown in Table 2.

[0080] ;

[0081] Referring to Table 2, the pH of the example group was 6.8, and that of the control group 1 was 5.2, which was an increase of 30.8% (p<0.05); the ash produced by high-temperature pyrolysis of biochar was rich in 、 , neutralize the soil through ion exchange The exchangeable acid in the example group was 70.5% of that in the control group 1, indicating that biochar effectively reduced aluminum ions. The oxalic acid concentration in the example group was 12.3 mg / kg, while that in the control group 2 was 22.1 mg / kg, a decrease of 65.5%, because the microorganisms preferentially utilize organic acids as carbon sources.

[0082] Anti-caking test verification;

[0083] Determination method of compaction relief index: Take the original soil sample of 0-20 cm soil layer and use volume Cut the aluminum box in layers to ensure the integrity of the soil structure; weigh the fresh soil mass, record it, and then place it in an oven (105°C) to a constant weight for 48 hours; calculate the bulk density: soil bulk density = dry soil mass (g) / ring cutter volume .

[0084] Take 20 g of air-dried soil sample that has passed through a 2 mm sieve, place it in a sedimentation cylinder, and add a 0.25 mm pore size sieve; inject distilled water until the soil is submerged and let it stand for 10 minutes to simulate field moisture conditions; slowly shake the sieve to separate aggregates, and collect the fine particles that pass through the sieve holes; dry and weigh the sample, and calculate the proportion of aggregates larger than 0.25 mm: mass of aggregates > 0.25 mm (g) / total soil sample mass (g) × 100%.

[0085] Take an undisturbed soil column 10 cm high and 10 cm in diameter and place it in a permeameter. Inject distilled water into the upper ring to maintain saturation, while the lower ring collects the leaking water. Record the stable seepage time (approximately 30 minutes) and calculate the hydraulic conductivity: , where Q is the flow rate, L is the height of the soil column, A is the cross-sectional area, and h is the head difference. The above data are shown in Table 3.

[0086] ;

[0087] Referring to Table 3, the bulk density of the embodiment group is , control group 1 was , decreased by 20.7% (p < 0.05) due to biochar filling pores and forming a granular structure. The proportion of aggregates larger than 0.25 mm was 50% in the Example group, compared to 42% in the Control group 2, a 19.0% increase. The hydraulic conductivity was 8.2 cm / h in the Example group, compared to 3.5 cm / h in the Control group 1, a 134% increase. The bulk density of the Example group decreased by 20.7% compared to the Control group 1, indicating that the reduction in permeability caused by compaction was alleviated.

[0088] Obviously, the above examples are merely provided for clarity of explanation and are not intended to limit the embodiments. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to enumerate all embodiments here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

[0089] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0090] In the description of this specification, the terms "one", "some", "example", "specific example" or "some examples" refer to the specific features, structures, materials or characteristics described in conjunction with the example or example included in at least one or an example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more or examples in a suitable manner. In addition, those skilled in the art can combine and combine different examples and features of different examples described in this specification without contradiction.

[0091] It is understood that the above is exemplary and should not be construed as limiting the present invention. Persons skilled in the art may make changes, modifications, substitutions and variations to the above within the scope of the present invention.

Claims

1. A method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer, characterized in that: include: Step 1: crush the biomass raw material and pyrolyze it at 500-700℃ for 5-8h and then cool it to obtain biochar; Step 2: Prepare a functional bacterial solution containing actinomycetes and Bacillus according to the ratio of (1–3):1, and the number of viable bacteria in the functional bacterial solution is ; Step 3: immersing the biochar in the functional bacterial solution for activation treatment, controlling the volume ratio of the functional bacterial solution to the biochar to be 1:(2–3), to obtain modified biochar; Step 4: composting and fermenting the modified biochar and the decomposed straw, and then granulating and screening the compost to obtain organic fertilizers with different particle sizes; Step 5: Use large-particle organic fertilizer to apply to deep soil, lay pretreated straw on the soil and cover it with soil, use small-particle organic fertilizer to apply to the surface soil; In step 3, the ambient temperature of the activation treatment is controlled to 25–30°C, and the treatment is carried out at a constant temperature of 25–30°C for 18–24 hours to dehydrate the modified biochar to a moisture content of 5%–10%.

2. The method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer according to claim 1, characterized in that: In step 1, the biomass raw material has a lignin content of ≥30%, is crushed and sieved using a 15-20 mesh screen, and the particle size of the crushed biomass raw material particles is ≤5 mm.

3. The method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer according to claim 1, characterized in that: In step 1, the pyrolysis time is controlled to be 6-7 hours; after the pyrolysis is completed, nitrogen is introduced to cool the biomass raw material, and the cooling time is controlled to be less than 30 minutes.

4. The method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer according to claim 1, wherein: In step 4, add modified biochar, decomposed straw compost, and edible fungus residue in a ratio of (5–6): (3–4): 1 by mass, mix evenly until the uniformity is ≥ 95%, adjust the moisture content of the material to 50%–60%, and continue composting and fermentation for 5–7 days. Control the pile temperature between 55–65°C and turn the pile once a day.

5. The method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer according to claim 1, characterized in that: In step 5, the particle size of the large-particle organic fertilizer is 4 to 6 mm, and the particle size of the small-particle organic fertilizer is 2 to 4 mm; Apply large-grained organic fertilizer to a depth of 20–30 cm in the soil at a rate of 1,200 ± 50 kg per hectare; Spread pre-treated straw at a rate of 2000±100 kg per hectare on a 10–20 cm soil layer; Apply small-particle organic fertilizer to the topsoil at a rate of 800 ± 30 kg per hectare (0–10 cm).

6. The method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer according to claim 1, characterized in that: In step 5, the straw is pretreated by cutting the whole straw into short segments of 2-5 cm and drying them naturally in the sun until the moisture content is ≤30%.

7. The method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer according to claim 1, characterized in that: In step 4, the pretreatment of the decomposed straw includes: mixing the decomposed straw with a composting agent at a mass ratio of (10-15):1, adjusting the carbon-nitrogen ratio to (25-30):1, and stacking and fermenting for 2-3 days before use; the composting agent contains a composite bacterial agent of Bacillus subtilis and Aspergillus oryzae, and the number of viable bacteria is .

8. The method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer according to claim 1, characterized in that: During the composting fermentation process in step 4, the pH value of the material was monitored and adjusted to 6.5–7.

5. Straw powder was added during daily turning to adjust aeration. Fermentation was terminated when the cellulose degradation rate in the material was ≥60%.

9. The method for increasing carbon content and expanding paddy soil based on biochar-based organic fertilizer according to claim 1, characterized in that: In step 5, after fertilization, the topsoil was covered with a 3–5 cm thick layer of pretreated straw and irrigated regularly to maintain the soil moisture content at 60%–70% for 15–20 days.

Images