A saline-alkali resistant plant-based biochar soil amendment and a preparation method thereof

Abstract

This invention relates to the field of agricultural environmental materials technology, and in particular to a salt-tolerant plant-based biochar soil conditioner and its preparation method. The conditioner uses salt-tolerant plant *Ilex chinensis* as the biochar raw material, which is prepared by compounding with porous mineral carrier diatomaceous earth and modifying with chitosan solution. The preparation method includes: washing, desalinating, drying, and pulverizing *Ilex chinensis*, followed by pyrolysis under limited oxygen conditions to obtain a biochar matrix; mixing the biochar and diatomaceous earth in a certain mass ratio, and achieving mechanical dispersion by wet ball milling; impregnating with chitosan acetic acid solution; and finally, separating the solid and liquid, drying, and solidifying to obtain a powdered product. This invention can effectively reduce soil pH and electrical conductivity, increase organic matter content, and significantly promote crop growth. It has the advantages of readily available raw materials, simple process, and long-lasting improvement effect, and is suitable for ecological restoration and agricultural utilization of coastal saline-alkali land.

Description

Technical Field

[0001] This invention relates to the field of agricultural environmental materials technology, and in particular to a salt-tolerant plant-based biochar soil conditioner and its preparation method. Background Technology

[0002] Saline-alkali land degradation is a global land management challenge, especially in China's coastal areas. High salinity, high pH, ​​and poor soil structure severely restrict crop growth. Traditional improvement methods, such as applying gypsum, organic fertilizers, or chemical leaching, can alleviate saline-alkali stress in the short term, but they have problems such as high cost, easy secondary pollution, and unsustainable effects. With the advancement of ecological agriculture concepts, the development of green and long-lasting soil conditioners has become an urgent need.

[0003] In recent years, biochar has been introduced into the field of saline-alkali land improvement due to its porous structure and adsorption properties. However, single biochar materials have obvious limitations: First, ordinary plant-derived biochar (such as straw char) is inherently highly alkaline, and direct application may exacerbate the increase in soil pH; second, its pore structure is easily blocked by salt, and its effectiveness diminishes with long-term use; third, it lacks salt and alkali tolerance and cannot specifically adsorb sodium ions. In addition, existing composite amendments mostly use common raw materials (such as reeds and Suaeda salsa), lack in-depth development of special halophyte resources, and the modification process is simple (such as simple acid washing), failing to achieve the synergy of physical adsorption and chemical regulation.

[0004] Therefore, a composite soil conditioner designed specifically for saline-alkali soil is needed. Its core lies in: selecting plant raw materials with natural salt-alkali tolerance mechanisms and preserving their functional components through pyrolysis; constructing an integrated "adsorption-buffering-regulation" system through the combination of porous mineral carriers and polymer modifiers; and optimizing the preparation process to ensure the synergistic effect of the conditioner in reducing pH, controlling salt content, and increasing fertility. Based on these needs, this invention proposes using special halophytes such as *Ilex chinensis* as a base, and through diatomaceous earth composite and chitosan modification, overcoming the limitations of existing technologies. Summary of the Invention

[0005] To address the problems mentioned in the background section, this invention provides a salt-tolerant plant-based biochar soil conditioner with significant improvement effects, long-lasting effects, and environmental friendliness, as well as its preparation method.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a salt-tolerant plant-based biochar soil conditioner is provided, comprising the following steps: S1. Raw material pretreatment and biochar preparation: Salt-tolerant plant materials are washed, desalinated, dried and pulverized; the pretreated plant materials are pyrolyzed under limited oxygen conditions to obtain biochar matrix. S2. Preparation of composite carrier: The biochar matrix and porous mineral carrier are mixed at a mass ratio of (6:4)-(8:2) and mechanically dispersed to ensure uniform mixing; S3. Modification treatment: The mixed composite is impregnated with a natural polymer modifier solution, followed by solid-liquid separation and drying to obtain the powdered soil conditioner.

[0007] Preferably, in step S1, the salt-tolerant plant material is sea lettuce, a seaweed halophyte; the desalination treatment includes rinsing and soaking repeatedly with deionized water at least 3 times until the conductivity of the material drops below 1.0 mS / cm.

[0008] Preferably, in step S1, the pyrolysis reaction conditions are: heating from room temperature to 450-550°C at a heating rate of 5-15°C / min, and maintaining the temperature at this temperature for 1-3 hours; the oxygen-limiting conditions are carried out in a nitrogen or argon atmosphere, and the oxygen concentration in the reaction system is controlled to be ≤0.5%.

[0009] Preferably, in step S2, the porous mineral carrier is diatomaceous earth; the mass ratio of the biochar matrix to the diatomaceous earth is (6:4)-(7:3), more preferably 7:3.

[0010] Preferably, the mechanical dispersion treatment adopts wet ball milling; the process parameters of the wet ball milling are: ball-to-material ratio (8:1)-(12:1), rotation speed 200-300 rpm, grinding time 1-3 hours; the solid-liquid ratio of the composite slurry formed during ball milling is 1:5-1:10.

[0011] Preferably, in step S3, the natural polymer modifier is chitosan; the concentration of the chitosan solution is 0.5%-2.0% (w / v), and the solvent is an acidic aqueous solution containing 0.5%-1.0% (v / v) acetic acid; the process parameters for the impregnation treatment are: impregnation temperature 20-30℃, impregnation time 12-36 hours, solid-liquid ratio 1:8-1:12, supplemented by shaking or stirring.

[0012] Preferably, the drying and curing conditions are: drying to constant weight at 100–110℃; and the particle size of the powdered soil conditioner is ≤0.15mm.

[0013] The present invention also provides a salt-tolerant plant-based biochar soil conditioner prepared by the above method, the composition of which, on a dry weight basis, includes: 50-70% biochar, 20-40% diatomaceous earth, and 5-10% chitosan.

[0014] Preferably, the modifier has a pH value of 7.5-8.5 and an electrical conductivity of ≤1.0 mS / cm.

[0015] The beneficial effects of this invention are: 1. In this invention, the sea lettuce biochar itself is rich in silicates and alkaline metal oxides, and its surface functional groups can effectively fix Na in the soil solution through ion exchange and electrostatic adsorption. + Diatomaceous earth, as a porous mineral carrier, provides a dispersed framework for biochar particles with its abundant mesoporous and macroporous structures, preventing pore blockage of the biochar itself. This significantly extends the diffusion path of water and salt ions within the amendment, promoting the slow release and leaching of salts. Furthermore, the numerous amino groups on the chitosan molecular chain can be protonated to -NH3 in the soil environment. + It can effectively reduce the inherent alkalinity of biochar and regulate soil pH through neutralization reactions, and further enhance its resistance to Na+ through complexation. + Fixed capacity.

[0016] 2. In this invention, a homogeneous composite formed by ball milling biochar and diatomaceous earth serves as the "core," containing an interconnected conductive carbon network and a silica framework, providing stable structural support and electron transfer channels. The outer chitosan polymer layer acts as the "shell," tightly adhering to the composite surface and pores through hydrogen bonds and physical entanglement, forming a pH-responsive smart gel layer. After the soil conditioner is applied, the chitosan outer layer absorbs water and swells first, creating a local microenvironment, and then gradually degrades to release H2O. + It achieves gentle and long-term regulation of soil pH, while the internal biochar-diatomite "core" serves as a persistent pore pool and adsorption pool, continuously optimizing soil aggregate structure and ion balance.

[0017] 3. In this invention, regarding the core performance of improving saline-alkali soil, this product can significantly and continuously reduce soil pH and electrical conductivity, effectively passivating sodium ion activity. In terms of improving soil physical structure, its porous characteristics help reduce soil bulk density, increase porosity, and enhance aeration and water permeability. In terms of improving soil fertility, this product is not only rich in organic carbon, but also provides an excellent habitat for soil microorganisms, thereby activating soil nutrients. For crop growth, it directly promotes seed germination, root development, and plant growth by creating a more suitable rhizosphere environment, thereby enhancing the crop's salt and alkali tolerance.

[0018] 4. In this invention, the pore structure is optimized by composite diatomaceous earth to avoid functional failure; and acidic functional groups are introduced by chitosan modification to achieve pH self-regulation, transforming it from a material that may aggravate alkalization into a reliable alkali-reducing material. By constructing a multiple long-term mechanism of action of "physical adsorption-chemical regulation-biological promotion", the stability and durability of the improvement effect are ensured. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, the raw materials used in this invention are all from commercially available conventional products.

[0021] Example 1 S1. Raw material pretreatment and biochar preparation 1. Desalination pretreatment of sea leek raw materials: 1.0 kg of fresh aboveground parts of Triglochin maritima collected from the coastal saline-alkali land of Dongying City, Shandong Province were weighed and rinsed repeatedly with running deionized water three times to remove surface mud and sand. The washed Triglochin maritima was then soaked in 5 L of deionized water, with the water changed every 2 hours, for a total of 3 soakings (6 hours). The desalination endpoint was considered to be reached when the conductivity of the soaking solution stabilized below ≤1.0 mS / cm.

[0022] Place the desalted sea leeks in a forced-air drying oven (model: DHG-9070A) and dry them at 80℃ until constant weight (approximately 16 hours). Use a plant shredder (model: FZ102) to shred the dried sea leeks into pieces 1-3cm in length for later use.

[0023] 2. Preparation of biochar from sea lettuce: Take 200.0g of the above-mentioned sea leek shreds and spread them evenly in a square corundum crucible (the material layer thickness is ≤2cm).

[0024] Place the crucible in a programmable temperature controlled muffle furnace (model: SX2-4-10), seal the furnace chamber and introduce high-purity nitrogen (purity 99.99%, flow rate 1.0L / min) to create an oxygen-limited environment. Set the pyrolysis program: heat from room temperature to 500℃ at a heating rate of 10℃ / min and maintain the temperature at 500℃ for 2 hours.

[0025] After pyrolysis, the power is turned off, and the mixture is allowed to cool naturally to room temperature (<50℃) under nitrogen protection. The lumpy biochar is then ground into powder using an agate mortar and passed through a 100-mesh standard sieve to obtain sea lettuce biochar powder with a particle size ≤0.15mm. The yield (approximately 45-55g) is weighed and recorded, and then sealed for storage.

[0026] S2, Preparation of composite carrier 1. Accurately weigh 35.0g of sea lettuce biochar powder prepared in S1 (corresponding to 70 parts by dry weight) and 15.0g of diatomaceous earth that has passed through a 200-mesh sieve (corresponding to 30 parts by dry weight).

[0027] 2. Add the mixed powder and 200 mL of deionized water (solid-liquid ratio 1:8) to a ball mill jar (volume 500 mL), and add zirconia grinding balls (ball-to-material ratio 10:1).

[0028] 3. Fix the grinding jar onto the planetary ball mill (model: QM-3SP2) and grind for 2 hours at a speed of 250 rpm.

[0029] 4. After ball milling, the slurry is removed to obtain a uniform composite slurry of biochar and diatomaceous earth.

[0030] S3, Chitosan Modification 1. Preparation of chitosan solution: Measure 500mL of deionized water, add 2.5mL of glacial acetic acid (analytical grade), and slowly add 5.0g of chitosan powder with a degree of deacetylation ≥95% while stirring. Continue to stir magnetically at 300rpm for 6 hours to obtain a uniform and transparent 1% (w / v) chitosan acetic acid solution.

[0031] Impregnation: Add all the composite slurry obtained in S2 to the above chitosan solution (at this time the total solid-liquid ratio is about 1:10), place it in a constant temperature shaker (model: HZQ-F160), and shake and impregnate for 24 hours at 25℃ and 150rpm.

[0032] Solid-liquid separation and drying: After impregnation, vacuum filtration was performed using a Buchner funnel and a suction flask to separate the solids. The wet solid product was transferred to a stainless steel tray, spread out, and placed in a forced-air drying oven to dry to constant weight at 105°C (approximately 8 hours).

[0033] Crushing and Packaging: The dried block product is lightly crushed and passed through a 100-mesh sieve to obtain the final powdered soil conditioner. The finished product is sealed in packaging and stored in a cool, dry place.

[0034] Product characteristics: This modifier is a gray-black homogeneous powder, without lumps, with a pH value of 7.65 and an electrical conductivity (EC) of 0.85 mS / cm.

[0035] Example 2 The difference from Example 1 is that in the S1 biochar preparation step, the pyrolysis temperature is adjusted to 450°C (the lower limit of the range described in claim 3), while the remaining steps and parameters are exactly the same as in Example 1.

[0036] Example 3 The difference from Example 1 is that in the S2 composite carrier preparation step, the weighing mass of sea lettuce biochar and diatomaceous earth is adjusted to 30.0g (60 parts) and 20.0g (40 parts) (i.e., mass ratio 6:4, the lower limit of the range described in claim 4), and the remaining steps and parameters are exactly the same as in Example 1.

[0037] Example 4 The difference from Example 1 is that in the S3 chitosan modification step, when preparing the chitosan solution, the amount of chitosan added is adjusted to 2.5g (i.e., the concentration is 0.5% (w / v), which is the lower limit of the range described in claim 6), while the remaining steps and parameters are exactly the same as in Example 1.

[0038] Example 5 The difference from Example 1 is that the final dosage was adjusted. In the pot experiment, the amount of amendment added in Examples 1-4 and Comparative Examples 1-4 was 1.5% of the dry weight of the soil. In this Example 5, the amount added was adjusted to 1.0% to verify the effect of low dosage. The preparation process was exactly the same as that in Example 1.

[0039] Comparative Example 1 The difference from Example 1 is that S2 and S3 are omitted, that is, only the sea lettuce biochar powder obtained in S1 without any composite modification is prepared and used. In the pot experiment, the same amount of pure sea lettuce biochar as in Example 1 is applied.

[0040] Comparative Example 2 The difference from Example 1 is that the chitosan modification in S3 is omitted. That is, after S1 and S2 are performed to obtain the biochar-diatomite composite, the chitosan solution is not impregnated. Instead, the composite is directly filtered (using water instead of chitosan solution), dried, and pulverized. In the pot experiment, this unmodified composite is applied.

[0041] Comparative Example 3 The difference from Example 1 is that the biochar raw material is replaced. In S1, instead of sea lettuce, an equal amount (1.0 kg dry weight) of ordinary wheat straw is used as the biochar raw material. The washing, drying, crushing, pyrolysis (500℃, 2h) and subsequent S2 and S3 steps are exactly the same as in Example 1.

[0042] Comparative Example 4 The difference from Example 1 is that the modifier is replaced. In S3, instead of using chitosan solution, a 1% (w / v) sodium alginate solution (using deionized water as solvent) is prepared for impregnation treatment. The remaining steps and parameters are exactly the same as in Example 1.

[0043] Comparative Example 5 The difference from Example 1 is that no modifier is applied, but the remaining steps and parameters are exactly the same as in Example 1.

[0044] Performance testing methods and results Pot experiment setup: Test soil: Topsoil (0-20cm) from coastal saline-alkali land in Dongying City, Shandong Province. Its basic physicochemical properties are: pH 8.82, electrical conductivity (EC) 2.53mS / cm, organic matter content 6.52g / kg, sodium adsorption ratio (SAR) 28.65. After air drying, the soil was sieved through a 2mm sieve to remove plant residues and gravel. Experimental design: Polyethylene plastic basins (top diameter × height = 20cm × 25cm) were used, and each basin was filled with 3.0kg of soil. The soil conditioners prepared in Examples 1-5 and Comparative Examples 1-5 were thoroughly mixed with the soil according to the designed dosage (generally 1.5% of the dry weight of the soil, and 1.0% in Example 5). A treatment without any added conditioner was set up as a blank control (Comparative Example 5). Crop cultivation: Sow 15 oat (Avena sativa L.) seeds per pot. After emergence, thin the seedlings to 10 healthy plants per pot. Perform routine water management in the greenhouse (irrigate with deionized water to maintain soil field capacity of 60%-70%). The cultivation period is 60 days. Indicator measurement methods: Soil pH value: After the culture is completed, the soil-water ratio is 1:2.5 (mass-volume ratio) for extraction. The pH value of the extract is measured using a precision pH meter (model: Mettler Toledo Seven Excellence). For specific operation, refer to "Determination of pH value of forest soil" (LY / T 1239-1999). Soil electrical conductivity (EC): Soil-water ratio of 1:5 (mass-volume ratio) was used for extraction, and the electrical conductivity of the extract was measured using an electrical conductivity meter. For specific procedures, please refer to "Determination of Soil Electrical Conductivity" (NY / T 1121.16-2006). Soil organic matter content: determined by potassium dichromate oxidation-external heating method, the specific operation of which is referred to "Determination of Soil Organic Matter" (NY / T 85-1988). Sodium adsorption ratio (SAR): The concentrations of Na+, Ca2+, and Mg2+ in soil leachate were determined using atomic absorption spectrometry and calculated according to the formula SAR=[Na+, Ca2+, and Mg2+]. + ] / √(([Ca 2+ ]+[Mg 2+ The calculation is performed using 1) / 2), where the ion concentration is expressed in mmol / L. Plant height: At the end of the cultivation period, use a ruler to measure the vertical distance from the soil surface to the highest point of the plant (unit: cm). Take the average value after measuring all plants in each pot. Dry weight of aboveground parts of plants: After harvesting the aboveground parts of the plants, they are blanched at 105℃ for 30 minutes and then dried at 80℃ to constant weight. The weight is measured using an electronic balance (unit: g / pot). The results are shown in Tables 1 and 2: Table 1. Results of soil physicochemical property testing (60 days after sowing)

[0045] Table 2. Results of oat growth index measurements (60 days after sowing)

[0046] As shown in Table 1, the soil conditioners prepared in each embodiment of the present invention (especially Example 1) have a significant positive effect on the physicochemical properties of saline-alkali soil. Specifically, compared with the initial soil and the comparative examples, the soil pH value of the example group treated with the conditioner of the present invention decreased significantly from 8.80 (7.65 in Example 1), the electrical conductivity (EC) decreased significantly from 2.50 mS / cm (0.85 mS / cm in Example 1), the soil organic matter content increased significantly (14.2 g / kg in Example 1), and the sodium adsorption ratio (SAR) also decreased effectively from 28.5 to 10.3. These data collectively indicate that the conditioner of the present invention can effectively neutralize soil alkalinity, leach desalination, improve soil fertility, and specifically passivate sodium ion activity. The effects of Comparative Example 1 (single biochar) and Comparative Example 3 (ordinary straw biochar) are far inferior to those of the examples, proving the specificity of sea lettuce raw material and the necessity of combining it with diatomaceous earth and chitosan.

[0047] As shown in Table 2, the improvement of soil physicochemical properties directly promoted crop growth and development. After applying the amendment of this invention, the plant height and aboveground dry weight of oats were significantly improved compared with the blank control (Comparative Example 5). Among them, the oat plant height under the treatment of Example 1 reached 68.5 cm, the aboveground dry weight reached 12.8 g / pot, and the biomass increased by about 110% compared with the blank control. This fully verifies that the amendment of this invention can effectively alleviate salt stress and promote crop photosynthesis and nutrient accumulation by creating a suitable rhizosphere environment, thereby greatly increasing crop yield. Although the crop growth indicators of Comparative Example 2 (without chitosan modification) and Comparative Example 4 (sodium alginate modification) were better than those of the single biochar treatment, they were still significantly lower than those of Example 1, highlighting the irreplaceable key role of chitosan modification in promoting crop growth.

[0048] In summary, the salt-tolerant plant-based biochar soil conditioner provided by this invention constructs an integrated "adsorption-buffering-regulation" improvement system through the synergistic effect of sea lettuce biochar, diatomaceous earth, and chitosan. This system not only improves soil conditions physically (optimizing pore size) and chemically (adjusting pH and fixing Na+), but also... +This invention comprehensively improves saline-alkali soil through multiple dimensions, including biochar and biological methods (enhancing fertility), and can significantly promote crop growth, ultimately achieving ecological restoration and increased agricultural productivity in saline-alkali land. The effects of each comparative example are inferior to those of the implementation examples to varying degrees, which strongly demonstrates the creativity, necessity, and irreplaceability of the raw material selection (sea leek), composite process (biochar-diatomite), and modification treatment (chitosan) in the technical solution of this invention. It provides a green, efficient, and sustainable new technology approach to solve the problem of saline-alkali land management.

[0049] In the description of this specification, the terms "preparation example," "example," "various examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that example or preparation example, which are included in at least one example or preparation example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same example or preparation example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more examples or preparation examples.

[0050] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a salt-tolerant plant-based biochar soil conditioner, characterized in that, Includes the following steps: S1: The salt-tolerant plant materials are washed, desalinated, dried and crushed. S2: The pretreated plant material is subjected to pyrolysis under limited oxygen conditions to obtain biochar matrix; S3: The biochar matrix and porous mineral carrier are mixed at a mass ratio of (6:4)-(8:2) and mechanically dispersed to ensure uniform mixing; S4: The mixed composite is impregnated with a natural polymer modifier solution, followed by solid-liquid separation and drying to obtain a powdered soil conditioner.

2. The preparation method according to claim 1, characterized in that, In S1, the salt-tolerant plant material is sea lettuce, a seaweed plant, and the desalination treatment includes rinsing and soaking repeatedly with deionized water at least 3 times until the conductivity of the material drops below 1.0 mS / cm.

3. The preparation method according to claim 1, characterized in that, In S2, the pyrolysis reaction conditions are as follows: the temperature is increased from room temperature to 450-550℃ at a heating rate of 5-15℃ / min, and then held at this temperature for 1-3 hours. The oxygen-limiting condition is that the reaction is carried out in a nitrogen or argon atmosphere, and the oxygen concentration in the reaction system is controlled to be ≤0.5%.

4. The preparation method according to claim 1, characterized in that, In S3: The porous mineral carrier is diatomaceous earth with a particle size passing through a 200-mesh sieve, and the mass ratio of the biochar matrix to the diatomaceous earth is (6:4) to (8:2).

5. The preparation method according to claim 4, characterized in that, The mass ratio of the biochar matrix to diatomaceous earth is 7:

3.

6. The preparation method according to claim 1 or 4, characterized in that, The mechanical dispersion treatment adopts wet ball milling. The process parameters of the wet ball milling are: ball-to-material ratio (8:1)-(12:1), rotation speed 200-300 rpm, grinding time 1-3 hours, and the solid-liquid ratio of the composite slurry formed during ball milling is 1:5-1:

10.

7. The preparation method according to claim 1, characterized in that, In S4, the natural polymer modifier is chitosan, the degree of deacetylation of the chitosan is ≥90%, the concentration of the chitosan solution is 0.5%-2.0% (w / v), the solvent is an acidic aqueous solution containing 0.5%-1.0% (v / v) acetic acid, and the process parameters of the impregnation treatment are: impregnation temperature 20-30℃, impregnation time 12-36 hours, solid-liquid ratio 1:8-1:12, supplemented by oscillation or stirring at 100-200 rpm.

8. The preparation method according to claim 1, characterized in that: The drying and curing conditions are as follows: drying at 100-110℃ to constant weight, and the particle size of the powdered soil conditioner is ≤0.15mm.

9. A salt-tolerant plant-based biochar soil conditioner prepared by the method according to any one of claims 1-8, characterized in that, Its composition, on a dry weight basis, includes: 50-70% biochar, 20-40% diatomaceous earth, and 5-10% chitosan.

10. The salt-tolerant plant-based biochar soil conditioner as described in claim 9, characterized in that: The modifier has a pH value of 7.5-8.5 and an electrical conductivity of ≤1.0 mS / cm.

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