A biochar-based soil conditioner, its preparation method and application

Abstract

This invention discloses a biochar-based soil conditioner, its preparation method, and its application. The biochar-based soil conditioner comprises the following components: biochar granules, an alkaline neutralizer, calcium magnesium phosphate fertilizer, and humic acid; the biochar-based soil conditioner comprises the following components in parts by weight: 100 parts biochar granules, 5-15 parts alkaline neutralizer, 20-40 parts calcium magnesium phosphate fertilizer, and 15-30 parts humic acid. The biochar-based soil conditioner proposed in this invention can be flexibly adjusted according to soil obstacles, climate characteristics, and soil improvement needs in different regions, improving problems such as poor soil structure, salinization and acidification, and nutrient deficiency, ensuring long-term stable agricultural production.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement technology, specifically relating to a biochar-based soil conditioner, its preparation method, and its application. Background Technology

[0002] Soil, as the most basic production material in agriculture, directly impacts food security and sustainable agricultural development. To improve degraded soils, soil conditioners are commonly applied. Currently, commonly used conditioners mainly include organic, inorganic, and organic-inorganic composites, with raw materials encompassing lime, minerals, humic acid, and industrial and agricultural waste. Among these, biochar-based soil conditioners, made primarily from biochar produced through the thermal pyrolysis of agricultural and forestry waste (such as straw and livestock manure) and compounded with other functional materials, have become a promising new type of soil amendment. Biochar possesses a well-developed pore structure, high chemical stability, and excellent adsorption properties. When applied to the soil, it helps improve soil aggregate structure, regulate pH, enhance water and fertilizer retention capacity, increase soil microbial activity, and realize the resource utilization of agricultural waste, thus providing dual benefits of soil improvement and ecological recycling.

[0003] However, despite the widespread experimentation and application of biochar-based soil conditioners in practice, there is still a lack of unified and standardized technical standards for their preparation and application. Current applications are mostly empirical and rudimentary, lacking a scientifically sound system for raw material selection, formulation optimization, process control, and application methods. This not only affects the stability of the soil improvement effect but may also pose potential soil risks.

[0004] Furthermore, existing standards primarily focus on the testing of biochar's inherent properties or specific product specifications, while a systematic technical procedure for the preparation of biochar-based soil conditioners remains lacking, severely lagging behind production practices and promotional needs. Therefore, it is urgent to establish a scientific and operable preparation process to ensure product quality, improve application effectiveness, and promote the healthy standardization and industrialization of this technology. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a biochar-based soil conditioner, which can be flexibly adjusted according to soil obstacles, climate characteristics, and soil improvement needs in different regions, to improve problems such as poor soil structure, salinization and acidification, and nutrient deficiency, and ensure long-term stable agricultural production.

[0006] The present invention also proposes a method for preparing the above-mentioned biochar-based soil conditioner.

[0007] This invention also proposes the application of the above-mentioned biochar-based soil conditioner.

[0008] According to a first aspect of the present invention, a biochar-based soil conditioner is provided, the biochar-based soil conditioner comprising the following components: biochar particles, an alkaline neutralizer, calcium magnesium phosphate fertilizer, and humic acid.

[0009] In some embodiments of the present invention, the biochar-based soil conditioner comprises the following components in parts by weight: 100 parts biochar granules, 5-15 parts alkaline neutralizer, 20-40 parts calcium magnesium phosphate fertilizer, and 15-30 parts humic acid.

[0010] In some embodiments of the present invention, the biochar-based soil conditioner comprises the following components in parts by weight: 100 parts biochar granules, 8-12 parts alkaline neutralizer, 25-35 parts calcium magnesium phosphate fertilizer, and 15-25 parts humic acid.

[0011] In some embodiments of the present invention, the pH value of the biochar particles is greater than 9.0.

[0012] In some embodiments of the present invention, the pH value of the biochar particles is 10-11.

[0013] In some embodiments of the present invention, the biochar particles have a particle size of 20-60 mesh.

[0014] In some embodiments of the present invention, the specific surface area of ​​the biochar particles is 400-500 m². 2 / g.

[0015] In some embodiments of the present invention, the alkaline neutralizing agent includes quicklime and / or oyster shell powder.

[0016] According to a second aspect of the present invention, a method for preparing a biochar-based soil conditioner is provided, the method comprising the following steps: S1: Primary carbonization of agricultural and forestry waste to obtain primary biochar; S2: The primary biochar obtained in step S1 is first screened, and the material under 4-10 mesh is collected for secondary carbonization to obtain secondary carbonized biochar particles. S3: The biochar particles obtained from the secondary carbonization in step S2 are subjected to secondary sieving to collect medium-sized biochar particles of 20-60 mesh. S4: Mix the granular biochar, alkaline neutralizer, calcium magnesium phosphate fertilizer and humic acid obtained in step S3 to obtain the biochar-based soil conditioner.

[0017] In some embodiments of the present invention, the agricultural and forestry waste mentioned in step S1 includes at least one of tree roots, branches, grass roots, straw, rice husks, and livestock and poultry manure.

[0018] In some embodiments of the present invention, the agricultural and forestry waste described in step S1 is pretreated before being placed on the carbonization equipment.

[0019] In some embodiments of the present invention, the pretreatment includes crushing and / or drying.

[0020] In some embodiments of the present invention, the crushing process includes cutting the agricultural and forestry waste to a length of 5-8 cm.

[0021] In some embodiments of the present invention, the drying process includes adjusting the moisture content of tree roots, branches, grass roots, straw, and rice husks to below 30%.

[0022] In some embodiments of the present invention, the drying process includes adjusting the moisture content of tree roots, branches, grass roots, straw, and rice husks to 10%-15%.

[0023] In some embodiments of the present invention, the drying process includes adjusting the moisture content of livestock and poultry manure to below 20%.

[0024] In some embodiments of the present invention, the drying process includes adjusting the moisture content of livestock and poultry manure to 15%-18%.

[0025] In some embodiments of the present invention, the stacking is carried out in a layered, intersecting, grid-like manner, and the apparent density of the resulting pile is 160-200 kg / m³. 3 .

[0026] In some embodiments of the present invention, the bottom of the stacked body has an overhead layer with a height of 15-25 cm.

[0027] In some embodiments of the present invention, the pretreated agricultural and forestry waste is tested for moisture content and heavy metal content before initial carbonization.

[0028] In some embodiments of the present invention, the heating procedure for the initial carbonization in step S1 includes: first heating to 130°C-170°C at a rate of 5°C-10°C / h and maintaining it for 0.5-1.5 h, then heating to 380°C-420°C at a rate of 20°C-30°C / h and holding it at that temperature for 2-3 h.

[0029] In some embodiments of the present invention, the initial carbonization in step S1 is carried out under oxygen-limited conditions with an oxygen volume concentration of <5%.

[0030] The initial carbonization step involves programmed heating and oxygen-limited pyrolysis of the raw material pile arranged according to a preset structure to provide a stable intermediate for the subsequent secondary carbonization process. During this process, the organic components in the raw material undergo pyrolysis to generate biochar particles rich in porous structure. After the initial carbonization is completed, the material is allowed to cool naturally to room temperature before proceeding to the next step.

[0031] The initial screening process involves sieving the biochar particles after initial carbonization to separate products that meet the particle size requirements. Mechanical screening of the initially carbonized and cooled products ensures precise separation of materials based on carbonization degree and particle size, guaranteeing homogeneity of the feed for subsequent secondary carbonization processes. This screening ensures that the material entering the secondary carbonization process has a consistent particle size range (2.00-4.75 mm) and high carbonization uniformity, providing a stable reaction matrix for the core modification steps and avoiding performance fluctuations caused by material inhomogeneity.

[0032] In some embodiments of the present invention, the heating process for secondary carbonization in step S2 includes: heating to 600℃-640℃ at a rate of 10-15℃ / min and holding at that temperature for 40-60 min.

[0033] After initial screening, the biochar particles enter a secondary carbonization stage, a process designed to further optimize their pore structure and chemical stability. This secondary carbonization step, under strictly oxygen-limited conditions, involves high-temperature, deep thermal modification of the medium-sized primary biochar obtained from the initial screening to directionally enhance its pore structure and surface activity.

[0034] In some embodiments of the present invention, the secondary carbonization in step S2 is carried out under oxygen-limited conditions with an oxygen volume concentration of <2%.

[0035] Due to the adoption of the above-mentioned secondary carbonization process, the medium-sized biochar prepared by this invention has a 2-3 times higher specific surface area compared with traditional one-step carbonization products, and its ability to retain nutrients and moisture is significantly enhanced; moreover, its structure is highly aromatic, and its degradation half-life in the soil is greatly extended, achieving a long-lasting carbon fixation and improvement effect.

[0036] The secondary screening involves multi-stage precision screening of the high-performance biochar matrix after secondary carbonization, achieving product shaping and functional pre-grading based on particle size, and providing raw materials with standardized physical specifications for subsequent targeted compounding.

[0037] In some embodiments of the present invention, the biochar-based soil conditioner in step S4 comprises the following components in parts by weight: 100 parts of medium-particle biochar obtained in step S3, 5-15 parts of alkaline neutralizer, 20-40 parts of calcium magnesium phosphate fertilizer and 15-30 parts of humic acid.

[0038] In some embodiments of the present invention, the biochar-based soil conditioner in step S4 comprises the following components in parts by weight: 100 parts of medium-particle biochar prepared in S3, 8-12 parts of alkaline neutralizer, 25-35 parts of calcium magnesium phosphate fertilizer and 15-25 parts of humic acid.

[0039] In some embodiments of the present invention, the proportion of the biochar-based soil conditioner is determined based on a neutralization curve established in a preliminary experiment.

[0040] According to a third aspect of the present invention, the role of the biochar-based soil conditioner described in the first aspect of the present invention or the biochar-based soil conditioner prepared by the preparation method described in the second aspect of the present invention in soil improvement is proposed.

[0041] In some embodiments of the present invention, the target soil for soil improvement includes hyperacidic soil.

[0042] In some embodiments of the present invention, the pH of the hyperacidic soil is 3-5.

[0043] The present invention has at least the following beneficial effects: The biochar-based soil conditioner provided by this invention solves the problems of unstable performance and crude formulation of existing biochar-based soil conditioners through an innovative "raw material stacking-secondary carbonization-testing feedback" process system. It can produce a soil conditioner with stable structure and precise controllable function, which has a significant effect on improving acidified soils. It can also quickly adjust soil pH in a short time and stabilize soil pH within the optimal range for a long time.

[0044] The preparation method of biochar-based soil conditioner provided by this invention achieves the effects of fine utilization of raw materials, stable product quality and adjustable improvement function through graded carbonization and sieving processes. It makes full use of agricultural waste and is simple and inexpensive. Attached Figure Description

[0045] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is a neutralization curve diagram from Embodiment 1 of the present invention; Figure 2 This is a neutralization curve diagram from Embodiment 2 of the present invention. Detailed Implementation

[0046] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0047] Example 1 This embodiment provides a biochar-based soil conditioner, the preparation method of which is as follows: 1. Raw material selection and pretreatment The raw materials selected are rice straw and livestock and poultry manure.

[0048] The pretreatment steps are as follows: Chop rice straw into 6 cm lengths (5-8 cm is acceptable), spread them out on a hardened surface to dry, reducing their moisture content to 12% (10%-15% is acceptable). Spread livestock and poultry manure out to dry, reducing its moisture content to 16% (15%-18% is acceptable), and test its heavy metal content to ensure it meets the requirements of the industry standard "Organic Fertilizer" NY / T 525-2021.

[0049] The storage of pre-treated raw materials should follow the principle of classified management. Different types of raw materials should be stored in separate areas, with clear labels indicating the raw material name, processing status, and storage date in each area. To prevent the raw materials from getting damp or contaminated by external factors, moisture-proof mats or pallets should be used to isolate the raw materials from the ground during storage, and waterproof cloths should be used for protection. In addition, the stacking height of raw materials should be controlled according to their physical properties to avoid collapse or compaction due to excessive height, which would affect subsequent use. For volatile or odorous raw materials, such as livestock and poultry manure, they should be kept away from other raw material areas as much as possible, and ventilation measures should be strengthened.

[0050] 2. Raw material stacking and initial carbonization To ensure the smooth operation of the preparation process, the site preparation must meet the following requirements: First, a well-ventilated, flat, and easily accessible area should be selected as the operating site to facilitate raw material transportation and equipment layout. Second, the site should have a complete drainage system to prevent rainwater accumulation from affecting the production process. Furthermore, the site needs to be hardened to prevent dust pollution and moisture absorption of raw materials. Simultaneously, functional areas should be divided according to process requirements, including a raw material storage area, a pretreatment area, a carbonization operation area, and a finished product storage area, with clear signage to standardize operating procedures. Finally, necessary fire-fighting facilities and safety protection measures should be provided to ensure that the production process complies with environmental and safety standards.

[0051] Stacking: After site preparation, the pre-treated raw materials need to be stacked properly. On the grate of the carbonization equipment, the rice straw pre-treated in step 1 is stacked in a crisscross pattern. By controlling the stacking density, the apparent density of the pile is stabilized at 190 kg / m³. 3 Left and right. The grate itself forms a bottom raised layer of no less than 20 cm.

[0052] Primary carbonization: A closed carbonization device is used for programmed temperature-controlled carbonization under limited oxygen conditions (oxygen volume concentration <5% by controlling the intake air). First, the temperature is increased to 150℃ at a rate of 8℃ / h (5℃-10℃ / h is acceptable) and maintained for 1 hour to fully remove moisture. Then, the temperature is increased to the target final temperature of 400℃ at a rate of 25℃ / h (20℃-30℃ / h is acceptable) and held at 400±10℃ for 2 hours. After natural cooling and mechanical crushing, primary biochar with a fixed carbon content of 65% and a volatile matter content of 25% is obtained. This homogeneous product is a prerequisite for effective sieving and deep secondary carbonization.

[0053] 3. Initial screening of biochar The primary biochar obtained in step 2 was sieved sequentially using a vibrating screen with double-layered 4-mesh and 10-mesh screens. The material passing through the screen (particle size 2.00 mm-4.75 mm) was collected, while the coarse pieces remaining on the screen were returned to the initial carbonization step for crushing. This step ensured the particle size basis of the feed for subsequent processes.

[0054] 4. Secondary carbonization The primary biochar, after screening in step 3, was transferred to a dedicated secondary carbonization reaction chamber. Nitrogen gas was introduced to replace the air, reducing the oxygen volume concentration inside the chamber to below 2%. Subsequently, under nitrogen protection, the temperature was programmed to rise to 620℃ at a rate of 12℃ / min (10℃-15℃ / min is also acceptable), and held at 620℃±10℃ for 45 minutes to obtain the secondary carbonization product. This process represents deep thermal modification, aiming to significantly improve the pore structure and chemical stability of the biochar.

[0055] 5. Secondary screening and component analysis of biochar Screening: After cooling the secondary carbonization product obtained in step 4, it is classified using a closed airflow sieve to collect the 20-60 mesh (0.25-0.85 mm) B-type biochar particles as the core matrix.

[0056] Testing: The key indicators for this type B biochar granules were tested as follows: pH value (1:5 water extraction) was 10.5, and BET specific surface area was 435 m². 2 / g, fixed carbon content 81%. All the above indicators meet the quality requirements shown in Table 1, indicating that it can be used as a high-quality raw material in the preparation process.

[0057] Table 1. Test Indicators and Requirements for Biochar Particles After Secondary Screening

[0058] 6. Formulation of biochar-based soil conditioner The formulation ratio of biochar-based soil conditioner is determined based on a "neutralization curve" established through preliminary experiments. Specifically, by measuring the pH values ​​of different ratios of the "biochar matrix-hydrated lime-calcium magnesium phosphate fertilizer" composite material after reaching equilibrium with the target acidic soil, a change curve is plotted, and the proportion of each component corresponding to stabilizing the soil pH in the range of 6.0-6.5 is selected as the final formulation. The advantage of this method is that the slow-release alkali properties of calcium magnesium phosphate fertilizer buffer and supplement the rapid alkali properties of lime, forming a synergistic effect. This ensures a smooth and sustained soil pH improvement process, avoiding the risk of sudden pH changes and rebounds that may occur with single-lime soil improvement.

[0059] Formula calculation logic: First, the neutralization curve established through preliminary experiments determined that 8 parts by weight of quicklime (Ca(OH)2) are required for every 100 parts by weight of the above-mentioned type B biochar particles (pH=10.5) to meet the requirements for rapid neutralization.

[0060] To determine the optimal formulation ratio for a red soil citrus orchard in southern China (pH=4.8), a neutralization curve pre-experiment was conducted before formal production. The B-type biochar particles prepared in step 5 (pH=10.5, specific surface area=435 m²) were used. 2 100 parts by weight of a mixture were prepared, with 30 parts by weight of calcium magnesium phosphate fertilizer (effective P2O5 ≥ 12%, CaO ≥ 25%) and 20 parts by weight of mineral humic acid (humic acid ≥ 50%) added. The amount of quicklime added was set to seven gradients: 0, 4, 6, 8, 10, 12, and 14 parts by weight. The raw material components were mixed using an equal-incremental mixing method. Quicklime was premixed with an equal part by weight of humic acid, then added to the mixer along with the remaining humic acid and calcium magnesium phosphate fertilizer. Finally, all the type B biochar granules were gradually added, and the mixture was stirred in a twin-screw mixer at 25 rpm for 12 minutes to obtain the biochar-based soil conditioner sample to be tested.

[0061] According to the soil conditioner addition amount of 1.5 wt%, each group of samples was mixed with the target acidic soil (pH=4.8) and placed in a constant temperature and humidity incubator. The samples were cultured for 60 days at a temperature of 25℃±2℃ and a humidity of 60%-70% of the maximum field capacity. The soil pH value after equilibrium was measured, and the results are shown in Table 2.

[0062] Table 2 Preliminary Experiment Results

[0063] The neutralization curve plotted based on the data in Table 2 shows ( Figure 1 The optimal amount of quicklime to achieve a soil pH within the target range of 6.0-6.5 is 6-9 kg / 100 kg biochar. Among these, an addition of 8 kg stabilizes the soil pH at 6.5±0.15, which is in the center of the target range and exhibits minimal fluctuation. This indicates that the synergistic effect of the fast-acting alkali (quicklime), slow-acting alkali (calcium magnesium phosphate), and buffer (humic acid) is optimal at this ratio. When the amount of quicklime added exceeds 10 kg, the soil pH exceeds 6.8, entering the risk zone of excessive alkali, which may lead to a later pH rebound or secondary alkali damage.

[0064] The above preliminary experiments confirm that, for the type B biochar granules (pH=10.5) prepared in step 5 of this embodiment, the optimal ratio of 8 parts by weight of slaked lime per 100 parts by weight is to achieve a stable increase in the target soil pH to 6.0-6.5. This ratio, together with calcium magnesium phosphate fertilizer (30 parts by weight) and humic acid (20 parts by weight), forms a fast-slow alkali synergistic and buffering long-lasting improvement system.

[0065] Secondly, to provide a long-lasting buffer and replenish nutrients, 32 parts by weight of calcium magnesium phosphate fertilizer are innovatively introduced. This fertilizer slowly dissolves in the soil and continuously releases alkali, complementing the rapid reaction time of slaked lime. Finally, 22 parts by weight of humic acid are added, utilizing its powerful ion exchange and buffering capacity to stabilize the soil's improvement effect and prevent pH rebound. This compound formula achieves a qualitative leap from "single neutralization" to "rapid-slow synergy, simultaneous improvement of nutrition and soil structure."

[0066] After determining the specific proportions, the final product, biochar-based soil conditioner, was prepared using an equal-incremental mixing method. The specific mixing process is as follows: Uniformity was ensured using an equal-volume incremental method. First, quicklime was premixed with an equal amount of humic acid, then added together with the remaining humic acid and calcium magnesium phosphate fertilizer to a twin-screw mixer. Finally, all the biochar matrix was added. The mixture was stirred at 25 rpm (24-26 rpm is acceptable) for 12 minutes to obtain the biochar-based soil conditioner. Sampling tests showed that the coefficient of variation (CV) for uniformity of this biochar-based soil conditioner was ≤6.5%, and the pH value (1:5 water extraction) was 8.3±0.2.

[0067] Example 2 This embodiment provides a biochar-based soil conditioner, targeting soil from a red soil citrus orchard in southern China. The soil has a pH of 4.8 and suffers from calcium and magnesium leaching and compaction. The preparation method of this biochar-based soil conditioner is as follows: 1. Raw material selection and pretreatment Raw material selection: Rice straw and livestock and poultry manure are selected.

[0068] Pretreatment: Chop rice straw into 5-8 cm lengths and spread it out on a hardened surface to dry until its moisture content drops to 10%-15%. Spread livestock and poultry manure out to dry until its moisture content drops to 15%-18%, and test its heavy metal content to ensure it meets the requirements of the industry standard "Organic Fertilizer" NY / T 525-2021.

[0069] The storage of pre-treated raw materials should follow the principle of classified management. Different types of raw materials should be stored in separate areas, with clear labels indicating the raw material name, processing status, and storage date in each area. To prevent the raw materials from getting damp or contaminated by external factors, moisture-proof mats or pallets should be used to isolate the raw materials from the ground during storage, and waterproof cloths should be used for protection. In addition, the stacking height of raw materials should be controlled according to their physical characteristics to avoid collapse or compaction due to excessive height, which would affect subsequent use. For volatile raw materials or those with special odors (such as livestock and poultry manure), they should be kept away from other raw material areas as much as possible, and ventilation measures should be strengthened.

[0070] 2. Raw material stacking and initial carbonization Site preparation: Select a well-ventilated, flat, and easily accessible area as the operating site. The site should have a complete drainage system and be hardened. Divide the site into functional areas according to process requirements, including a raw material storage area, a pretreatment area, a carbonization operation area, and a finished product storage area, and equip it with necessary fire-fighting facilities and safety protection measures.

[0071] Stacking: On the grate of the carbonization equipment, the pretreated rice straw is stacked in a crisscross pattern, and the apparent density of the pile is stabilized within the range of 180-200 kg / m³ (preferably 190 kg / m³) by controlling the density of the stack. The grate itself forms a bottom air gap of not less than 20 cm, and at least one porous ceramic ventilation pipe (diameter ≥10 cm) is longitudinally buried in the center of the bottom of the pile to optimize heat transfer and airflow distribution.

[0072] Primary carbonization: The carbonization equipment is sealed, and programmed temperature-controlled carbonization is performed under limited oxygen conditions (oxygen volume concentration <5% by controlling the intake air). First, the temperature is increased to 150℃ at a rate of 5-10℃ / h and maintained for 1 hour to fully remove moisture. Then, the temperature is increased to the target final temperature of 400℃ at a rate of 20-30℃ / h and held at 400±10℃ for 2 hours. After primary carbonization, the material is allowed to cool naturally to room temperature. The resulting primary biochar has a fixed carbon content of approximately 65% ​​and a volatile matter content of approximately 25%.

[0073] 3. Initial screening of biochar The product after primary carbonization is screened using a vibrating screen equipped with double-layered 4-mesh and 10-mesh screens. Specifically: The material oversize (particle size > 4.75 mm) is mainly coarse lumps that are not fully carbonized and is recycled back to the initial carbonization crushing process. The material passing through the sieve (particle size 2.00-4.75 mm) is a qualified intermediate that is fully carbonized and has a loose structure. It is all collected and transferred to the secondary carbonization process. The undersize material (particle size <2.00 mm) mainly consists of ash and fine carbon, which is collected and used as raw material for high-potassium ash fertilizer or partially mixed back according to the formula requirements.

[0074] This step ensures that the material entering the secondary carbonization process has a consistent particle size range (2.00-4.75 mm) and high carbonization uniformity.

[0075] 4. Secondary carbonization The qualified intermediate obtained after the initial screening in step 3 was transferred to a dedicated secondary carbonization reaction chamber. Nitrogen was introduced to replace the air, reducing the oxygen volume concentration inside the chamber to below 2%. Subsequently, under nitrogen protection, the temperature was programmed to rise to 620±10℃ at a rate of 12℃ / min (10℃-15℃ / min is also acceptable), and held at this temperature for 45 minutes. During the holding period, a trace amount of nitrogen was continuously introduced to maintain positive pressure and remove residual volatiles. This process is a deep thermal modification aimed at significantly improving the pore structure and chemical stability of the biochar.

[0076] 5. Secondary screening and component analysis of biochar Screening: After cooling the secondary carbonization product obtained in step 4, it is classified using a closed airflow sieve to collect the 20-60 mesh (0.25-0.85 mm) B-type biochar particles as the core matrix.

[0077] Testing: The key indicators for this type B biochar granules were tested as follows: pH value (1:5 water extraction) was 10.2, and BET specific surface area was 420 m². 2 / g, fixed carbon content 78%. All the above indicators meet the quality requirements shown in Table 1, indicating that it can be used as a high-quality raw material in the preparation process.

[0078] 6. Formulation of biochar-based soil conditioner Similar to Example 1, this example also establishes a neutralization curve through preliminary experiments to determine the optimal formulation ratio for the target soil.

[0079] The type B biochar particles prepared in step 5 (pH=10.2, specific surface area=420 m²) 2100 parts by weight of (g) were used, with a fixed addition of 35 parts by weight of calcium magnesium phosphate fertilizer and 25 parts by weight of humic acid. The addition of quicklime was set to seven gradients: 0, 4, 6, 8, 10, 12, and 14 parts by weight. The raw material components were mixed using an equal-incremental method. Quicklime was premixed with an equal part by weight of humic acid, then added to the mixer along with the remaining humic acid and calcium magnesium phosphate fertilizer. Finally, all the type B biochar granules were gradually added, and the mixture was stirred in a twin-screw mixer at 25 rpm for 12 minutes to obtain the biochar-based soil conditioner sample to be tested.

[0080] According to the soil conditioner addition of 1.5 wt%, each group of samples was mixed with the target acidic soil (pH≈4.8) and placed in a constant temperature and humidity incubator. It was incubated for 60 days at a temperature of 25℃±2℃ and a humidity maintained at 60%-70% of the maximum field capacity of the soil. The soil pH value after equilibrium was measured and a neutralization curve was plotted. Figure 2 The final formula was determined to be: 100 kg of type B biochar granules, 12 kg of quicklime, 35 kg of calcium magnesium phosphate fertilizer (effective P2O5≥12%, CaO≥25%) + 25 kg of mineral humic acid (humic acid≥50%).

[0081] After determining the specific proportions, the final product, biochar-based soil conditioner, was prepared using an equal-incremental mixing method. The specific mixing process is as follows: Uniformity is ensured by using an equal-volume incremental method. First, quicklime is premixed with an equal amount of humic acid, then added together with the remaining humic acid and calcium magnesium phosphate fertilizer to a twin-screw mixer. Finally, all the biochar matrix is ​​added. The mixture is stirred at 25 rpm for 10 minutes to obtain the biochar-based soil conditioner.

[0082] Sampling tests showed that the biochar-based soil conditioner had a uniformity coefficient of variation (CV) ≤ 6.5%, a pH ≈ 8.5, and slowly released alkaline substances upon contact with water. Pot experiments verified that it could stabilize the pH of simulated acidified soil to 6.0-6.5 within 60 days.

[0083] It should be noted that the biochar particles used in Example 2 have a pH of 10.2, and their alkalinity contribution is slightly lower than that of the biochar particles with a pH of 10.5 used in Example 1. Therefore, under the same target soil conditions (pH=4.8), the amount of quicklime required in Example 2 is slightly higher (12 kg). Verification using its own neutralization curve shows that this ratio can also stabilize the soil pH at 6.0-6.5 (pH≈6.4 after equilibrium). This further confirms the core idea of ​​this invention—precise compounding based on test data—that the formulation ratio needs to be dynamically adjusted according to the measured performance of the biochar matrix, rather than remaining fixed.

[0084] Comparative Example 1 This comparative example provides a biochar-based soil conditioner, the preparation method of which differs from that of Example 1 only in that: during the initial carbonization in step 2, the raw materials are randomly piled on the grate of the carbonization equipment, and no bottom support layer is reserved. The formulation of the biochar-based soil conditioner and the remaining steps are consistent with those of Example 1.

[0085] Comparative Example 2 This comparative example provides a biochar-based soil conditioner, the preparation method of which differs from that of Example 1 only in that the secondary carbonization in step 4 and the secondary sieving in step 5 are omitted, while the formulation and other steps of the biochar-based soil conditioner are consistent with those of Example 1.

[0086] Comparative Example 3 This comparative example provides a biochar-based soil conditioner, the preparation method of which differs from that of Example 1 only in that the initial screening in step 3 and the secondary screening in step 5 are omitted, while the formulation and other steps of the biochar-based soil conditioner are consistent with those of Example 1.

[0087] Comparative Example 4 This comparative example provides a soil conditioner that contains only lime (CaO).

[0088] Comparative Example 5 This comparative example provides a soil conditioner containing only quicklime (Ca(OH)2).

[0089] Comparative Example 6 This comparative example provides a soil conditioner containing only calcium magnesium phosphate fertilizer (effective P2O5 ≥ 12%, CaO ≥ 25%).

[0090] Comparative Example 7 This comparative example provides a biochar-based soil conditioner, which consists of 100 kg of type B biochar particles obtained in step 5 of Example 1 and 8 kg of slaked lime. The preparation method is to directly mix the components.

[0091] Comparative Example 8 This comparative example provides a biochar-based soil conditioner, which consists of 100 kg of type B biochar granules obtained in step 5 of Example 1 and 32 kg of calcium magnesium phosphate fertilizer (effective P2O5 ≥ 12%, CaO ≥ 25%). The preparation method is to directly mix the components.

[0092] Comparative Example 9 This comparative example provides a biochar-based soil conditioner, which consists of: 100 kg of type B biochar granules obtained in step 5 of Example 1, 8 kg of quicklime, and 32 kg of calcium magnesium phosphate fertilizer (effective P2O5 ≥ 12%, CaO ≥ 25%). The preparation method is to directly mix the components.

[0093] Comparative Example 10 This comparative example provides a commercially available lime-based soil conditioner, specifically the Tebe Calcium Soil Conditioner produced by Fujian Mata Agricultural Development Co., Ltd. This lime-based soil conditioner is made from natural marine oyster shells through high-temperature calcination and activation processes. Its main component is active calcium oxide (CaO≥45%), with a pH value of 8.5-10.5, a particle size range of 1.00 mm-4.75 mm, and it is in powder form, white or off-white.

[0094] Comparative Example 11 This comparative example provides a commercially available soil conditioner, specifically an acidic soil conditioner (carbon-based) purchased from Guangdong Dazhong Agricultural Technology Co., Ltd. This product is made from crop straw as raw material, processed into biochar through a single carbonization process (final temperature 450-500℃), and then compounded with mineral-derived alkaline materials. The product is in granular form with a particle size of 1.0-4.75 mm. The biochar matrix has a pH value of 8.0-9.5 (1:5 water extraction) and a specific surface area of ​​80-150 m². 2 / g, with a fixed carbon content of 55%-65%.

[0095] Test case This experiment tested the performance of the soil conditioners provided in Example 1 and Comparative Examples 1-11 in soil improvement. The specific experimental methods and results are as follows: 1. The comprehensive performance of the soil conditioners provided in Example 1 and Comparative Examples 1-4 in soil improvement Test Method: Soil Incubation Experiment. The soil conditioners obtained from Comparative Examples 1-4 and Example 1 were uniformly mixed with typical acidic red soil (initial pH=4.8) at an addition rate of 1.5% (w / w). The mixtures were placed in a constant temperature and humidity incubator and incubated for 60 days at a temperature of 25℃±2℃ and humidity maintained at 60%-70% of the soil's maximum field capacity. The dynamic changes in soil pH and cation exchange capacity (CEC) were monitored. CEC was determined according to the national environmental protection standard "Determination of Soil Cation Exchange Capacity - Hexaamminecobalt Trichloride Leaching-Spectrophotometric Method" (HJ 889-2017). The CEC increase rate was calculated by comparing it with untreated soil.

[0096] Product performance testing: The mixing uniformity (coefficient of variation CV%) of each group of soil conditioners was determined.

[0097] The results are shown in Table 3.

[0098] Table 3. Overall soil improvement performance of the soil conditioners provided in Example 1 and Comparative Examples 1-4

[0099] As shown in Table 3, Example 1 showed the best performance in terms of soil pH improvement, CEC improvement rate and product uniformity. After 60 days, the soil pH stabilized at 6.5, the CEC increased by 45%, and the uniformity CV was only 6.5%, achieving a comprehensive, stable and lasting improvement effect.

[0100] 2. Efficiency and stability tests of soil pH adjustment by the soil conditioners provided in Example 1 and Comparative Examples 5-7 The soil conditioners provided in Example 1 and Comparative Examples 5-7 were mixed evenly with typical acidic red soil (initial pH=4.8) at an addition rate of 1.5% (w / w). The mixtures were placed in a constant temperature and humidity incubator and cultured for 60 days at a temperature of 25℃±2℃ and a humidity maintained at 60%-70% of the soil's maximum field capacity. The dynamic changes in soil pH were monitored, and the results are shown in Table 4.

[0101] Table 4. Efficiency and stability of soil pH adjustment by the soil conditioners provided in Example 1 and Comparative Examples 5-7

[0102] As shown in Table 4, Comparative Example 5 (lime only) showed rapid short-term effects, but this effect could not be sustained, and the pH dropped back to 5.9 after 60 days; Comparative Example 6 (calcium magnesium phosphate fertilizer only) was too slow, and the pH remained below the target after 90 days; Comparative Example 7, due to excessive lime and the lack of slow-release alkali, showed a significantly alkaline pH at 30 days, and the pH dropped back after 90 days. Example 1 of this invention achieves a "fast-slow synergy": the target is reached smoothly in 45 days, with no risk of excessive alkalinity and no subsequent decline, achieving the best balance between regulation efficiency and durability.

[0103] 3. pH-regulating stability of the soil conditioners provided in Example 1 and Comparative Examples 7-9 over a long period of time. The soil conditioners provided in Example 1 and Comparative Examples 7-9 were mixed evenly with typical acidic red soil (initial pH=4.8) at an addition rate of 1.5% (w / w). The mixtures were placed in a constant temperature and humidity incubator and cultured for 120 days at a temperature of 25℃±2℃ and a humidity maintained at 60%-70% of the soil's maximum field capacity. The dynamic changes in soil pH were monitored, and the results are shown in Table 5.

[0104] Table 5. pH adjustment of the soil conditioners provided in Example 1 and Comparative Examples 7-9 over a long period of time.

[0105] As shown in Table 5, Example 1 of the present invention exhibited the smallest pH fluctuation (±0.1) during a long-term observation period of 120 days, demonstrating that the synergistic effect of "fast alkali + slow alkali + buffer" is the key to achieving long-term stability. The absence of any functional component (quick lime, calcium magnesium phosphate fertilizer, humic acid) will lead to increased pH fluctuation or decreased stability.

[0106] 4. Long-term comprehensive performance of the soil conditioners provided in Example 1 and Comparative Examples 4, 10, and 11 The soil conditioners provided in Examples 1 and Comparative Examples 4, 10, and 11 were mixed evenly with typical acidic red soil (initial pH = 4.8) at an addition rate of 1.5% (w / w). The mixtures were placed in a constant temperature and humidity incubator and cultured for 120 days at a temperature of 25℃ ± 2℃ and a humidity maintained at 60%-70% of the soil's maximum field capacity. The dynamic changes in soil pH and CEC were monitored, and the results are shown in Table 6.

[0107] Table 6. Long-term comprehensive performance of the soil conditioners provided in Example 1 and Comparative Examples 4, 10, and 11

[0108] As shown in Table 6, Example 1 of the present invention performs excellently in four dimensions: pH adjustment efficiency (reaching the standard in 45 days), long-term stability (pH 6.4 in 120 days), CEC improvement rate (45%), and anti-rebound ability (no rebound). It achieves a synergistic effect of "fast, stable, long-lasting, and fertile" and is significantly better than commercially available products.

[0109] In summary, the beneficial effects of the present invention have been fully demonstrated through the following comparative experiments: 1) Verification of process integrity: Comparative examples 1-3 show that omitting any step in raw material stacking, secondary carbonization, or sieving leads to a significant deterioration in product performance, proving that the process steps of raw material stacking-secondary carbonization-sieving and detection-precise compounding provided by this invention are a complete technical system with each step being interconnected and indispensable.

[0110] 2) Formula synergy verification: Comparative Example 4 shows that conventional lime modification alone cannot achieve long-term pH stability; Comparative Examples 5-6 further confirm that the present invention achieves both high regulation efficiency and long-term stability through the synergistic design of fast alkali (hydrated lime) + slow alkali (calcium magnesium phosphate fertilizer) + buffer (humic acid).

[0111] 3) Verification of comprehensive performance advantages: Comparison Example 7 shows that the present invention is superior to the existing technology in terms of CEC improvement rate and anti-rebound ability, and truly realizes the synergistic effect of "improving and enriching at the same time".

[0112] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

Claims

1. A biochar-based soil conditioner, characterized in that, The biochar-based soil conditioner comprises the following components: biochar granules, alkaline neutralizer, calcium magnesium phosphate fertilizer, and humic acid.

2. The biochar-based soil conditioner according to claim 1, characterized in that, The biochar-based soil conditioner comprises the following components in parts by weight: 100 parts biochar granules, 5-15 parts alkaline neutralizer, 20-40 parts calcium magnesium phosphate fertilizer, and 15-30 parts humic acid.

3. The biochar-based soil conditioner according to claim 1, characterized in that, The biochar particles have a pH value greater than 9.0; Preferably, the biochar particles have a particle size of 20-60 mesh.

4. The biochar-based soil conditioner according to claim 1, characterized in that, The alkaline neutralizing agent includes quicklime and / or oyster shell powder.

5. A method for preparing a biochar-based soil conditioner, characterized in that, The preparation method includes the following steps: S1: Primary carbonization of agricultural and forestry waste to obtain primary biochar; S2: The primary biochar obtained in step S1 is first screened, and the material under 4-10 mesh is collected for secondary carbonization to obtain secondary carbonized biochar particles. S3: The biochar particles obtained from the secondary carbonization in step S2 are subjected to secondary sieving to collect medium-sized biochar particles of 20-60 mesh. S4: Mix the granular biochar, alkaline neutralizer, calcium magnesium phosphate fertilizer and humic acid obtained in step S3 to obtain the biochar-based soil conditioner.

6. The preparation method according to claim 5, characterized in that, Before the initial carbonization, the agricultural and forestry waste mentioned in step S1 is pretreated and then placed on the carbonization equipment. Preferably, the pretreatment includes crushing and / or drying. Preferably, the stacking is carried out in a layered, intersecting tic-tac-toe pattern, resulting in an apparent density of 160-200 kg / m³. 3 .

7. The preparation method according to claim 5, characterized in that, The heating procedure for the initial carbonization in step S1 includes: first, heating to 130℃-170℃ at a rate of 5℃-10℃ / h and maintaining it for 0.5-1.5 h, then heating to 380℃-420℃ at a rate of 20℃-30℃ / h and holding it at that temperature for 2-3 h.

8. The preparation method according to claim 5, characterized in that, The heating procedure for secondary carbonization in step S2 includes: heating to 600℃-640℃ at a rate of 10-15℃ / min and holding at that temperature for 40-60 min.

9. The preparation method according to claim 5, characterized in that, The biochar-based soil conditioner described in step S4 comprises the following components in parts by weight: 100 parts of medium-particle biochar prepared in step S3, 5-15 parts of alkaline neutralizer, 20-40 parts of calcium magnesium phosphate fertilizer, and 15-30 parts of humic acid.

10. The application of the biochar-based soil conditioner according to any one of claims 1-4 or the biochar-based soil conditioner prepared by any one of claims 5-9 in soil improvement.

Images