A sorghum straw biochar for saline-alkali land improvement and its preparation method

Abstract

This invention belongs to the field of saline-alkali soil improvement technology, and discloses a sorghum straw biochar for saline-alkali soil improvement and its preparation method. The method uses sorghum straw as raw material, and prepares a modified biochar carrier through low-temperature plasma surface activation, in-situ hydrothermal growth of silicon-doped hydroxyapatite, and stepwise oxygen-limited pyrolysis. Then, a composite microorganism is loaded through an alkali-resistant composite encapsulation process to obtain the target product. This product can be used in moderately to severely saline-alkali soils, simultaneously achieving sodium ion adsorption, pH regulation, and slow nutrient release. It can improve the survival stability of the composite microorganisms in high-salt and high-alkali environments, achieving long-term improvement of saline-alkali soils.

Description

Technical Field

[0001] This invention belongs to the field of saline-alkali soil improvement technology, and relates to a sorghum straw biochar for saline-alkali soil improvement and its preparation method. Background Technology

[0002] Saline-alkali land is a typical type of land with low to medium yields. Its high pH, ​​high salinity, and low fertility severely restrict agricultural production. With the increasing scarcity of arable land resources, the improvement and utilization of saline-alkali land has become an important direction for ensuring food security.

[0003] Straw biochar has been widely used in saline-alkali land improvement research due to its wide availability and low cost, as well as its adjustable pore structure and strong adsorption capacity. Current technologies enhance the sodium ion adsorption capacity of straw biochar through metal loading modification or by loading functional microorganisms to improve soil fertility. Some studies have also attempted to combine modification with microbial loading to achieve comprehensive improvement effects. However, existing technologies still face significant bottlenecks. For the high salinity and alkalinity of saline-alkali land, the sodium ion adsorption capacity of conventionally modified biochar is limited, failing to meet the high-load desalination requirements of moderately to severely saline-alkali land. Furthermore, in conventional microbial loading techniques, the encapsulating material is easily degraded in high pH environments, leading to rapid inactivation of functional microorganisms after application, hindering long-term colonization. Simultaneously, the various modification steps in existing technologies are mostly applied independently, lacking sufficient synergy between different technologies. This prevents the simultaneous achievement of multiple functions such as desalination, alkali regulation, and fertilization, thus limiting the comprehensive improvement needs of moderately to severely saline-alkali land and restricting the application scope of straw biochar in the improvement of such land.

[0004] Therefore, developing comprehensive improvement materials that can be adapted to moderately to severely saline-alkali land and solving the problems of insufficient adsorption capacity and poor microbial survival stability in existing technologies has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The technical problem to be solved by this invention is that conventional straw biochar has a limited sodium ion adsorption capacity in the process of improving moderately to severely saline-alkali land, which cannot meet the high salt load of moderately to severely saline-alkali land. At the same time, functional microorganisms are easily deactivated in high-salt and high-alkali environments and cannot achieve long-term colonization. Moreover, existing modification technologies are mostly applied independently and lack synergy, and cannot simultaneously achieve multiple functions such as desalination, alkali adjustment and fertilization. This invention provides a sorghum straw biochar for improving saline-alkali land and its preparation method, so as to achieve long-term and efficient improvement of moderately to severely saline-alkali land.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] In a first aspect, the present invention provides a sorghum straw biochar for saline-alkali land improvement. Using sorghum straw as raw material, the modified biochar carrier is obtained through plasma activation, in-situ growth of silicon-doped hydroxyapatite, and stepwise pyrolysis. The carrier is loaded with composite microorganisms, and the specific surface area of ​​the carrier is 400-600 m². 2 / g, has a hierarchical porous structure.

[0008] Secondly, the present invention provides a method for preparing the above-mentioned sorghum straw biochar, comprising the following steps: raw material pretreatment, low-temperature plasma surface activation, in-situ hydrothermal growth of silicon-doped hydroxyapatite, stepwise oxygen-limited pyrolysis carbonization, loading of composite microbial agents, and alkali-resistant encapsulation.

[0009] Furthermore, in the preparation method, the raw material pretreatment includes drying and pulverizing.

[0010] Furthermore, in the preparation method, the power of the low-temperature plasma surface activation is 100~150W, the processing time is 120~240s, the processing distance is 8~12mm, and the working gas is argon.

[0011] Furthermore, in the preparation method, the molar ratio of calcium nitrate, diammonium hydrogen phosphate, and sodium silicate in the precursor solution for in-situ hydrothermal growth is 1.5~1.8:1:0.2~0.3, the reaction temperature is 160~200℃, and the reaction time is 4~8h.

[0012] Furthermore, in the preparation method, the stepwise oxygen-limited pyrolysis carbonization includes: first heating to 200~250℃ and holding at that temperature for 0.5~1.5h, then heating to 450~500℃ and holding at that temperature for 1~2h, with heating rates of 3~7℃ / min and 6~10℃ / min respectively; the protective gas is nitrogen.

[0013] Furthermore, in the preparation method, the embedding solution used for alkali-resistant composite embedding load includes carboxymethyl cellulose and gelatin, wherein the mass fraction of carboxymethyl cellulose is 1.5~2.5%, the mass fraction of gelatin is 0.5~1.5%, and the volume ratio of the two is 2.5~3.5:1.

[0014] Furthermore, in the preparation method, the composite microorganisms include: halophilic Bacillus, Bacillus megaterium, and Bacillus subtilis, with a volume ratio of 0.8~1.2:0.8~1.2:0.8~1.2 for each bacterial solution.

[0015] Thirdly, this invention seeks protection for the application of the above-mentioned sorghum straw biochar in the improvement of moderately to severely saline-alkali soil.

[0016] Furthermore, in the above applications, the pH of the saline-alkali land is 7.0~10.0, and the salt content is ≥0.3%.

[0017] Compared with the prior art, the present invention has significant beneficial effects: This invention achieves uniform loading of silicon-doped hydroxyapatite on straw carriers through the synergistic effect of plasma activation and in-situ hydrothermal growth, significantly improving the sodium ion adsorption capacity of biochar to 72 mg / g, which is higher than that of conventional modified biochar. It can effectively adapt to the high salt load of moderate to severe saline-alkali land and achieve rapid desalination and pH control.

[0018] Meanwhile, the alkali-resistant composite encapsulation system used in this invention can remain stable in a wide pH range of 4-11. Combined with the stress-resistant protection of trehalose and the colonization effect of the hierarchical pores of biochar, it achieves triple stress-resistant protection for microorganisms, enabling the functional microorganisms to maintain a density of 2.5 × 10⁻⁶ even after 90 days of application. 7 The effective viable count of CFU / g is far higher than the survival level of conventional encapsulated bacterial agents, solving the problem of rapid inactivation of microorganisms in moderately to severely saline-alkali land and realizing the long-term colonization of functional microorganisms.

[0019] Furthermore, the technical solution of this invention achieves multiple functions of desalination, alkali adjustment, and fertilization synergistically. While improving soil salinity, it can simultaneously increase the content of available phosphorus, available potassium, and available silicon in the soil, effectively solving the problem of fertility deficiency in moderately to severely saline-alkali land. Moreover, the raw materials used in this invention are widely available, and the microorganisms used are all conventional commercial strains that can be publicly obtained. The process parameters are clear and well-defined, making it easy to implement on a large scale. It can effectively promote the improvement and development of moderately to severely saline-alkali land, providing new technical support for expanding arable land resources and ensuring food security. Detailed Implementation

[0020] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; unless otherwise specified, the reagents and materials described are commercially available.

[0022] The microbial information used in the examples is as follows: Salt-resistant Bacillus ( Bacillus halotolerans ), deposited at the China General Microbiological Culture Collection Center, accession number: CGMCC No.30804, sourced as a gift, see CN119752735A for details; Bacillus megaterium ( Bacillus megaterium ), deposited at the China General Microbiological Culture Collection Center, accession number: CGMCC NO.22296, sourced as a gift, see CN115710561A for details; Bacillus subtilis ( Bacillus subtilis (), deposited at the China Center for Type Culture Collection, accession number: CCTCC NO: M 2022679, sourced as a gift, see CN120060043A for details.

[0023] Example 1 This embodiment provides a method for preparing sorghum straw biochar, the specific steps of which are as follows: 1. Raw material pretreatment After harvesting, remove the soil, sand and other impurities adhering to the surface of the sorghum stalks, rinse them with clean water, place them in a forced-air drying oven, and dry them to constant weight at 60℃. Then, use a universal pulverizer to pulverize them and pass them through a 40-mesh standard sieve to obtain sorghum stalk powder for later use.

[0024] 2. Low-temperature atmospheric pressure plasma surface activation pretreatment Take 100g of the above sorghum straw powder and spread it evenly on the sample stage of the atmospheric pressure low temperature plasma processor, controlling the spreading thickness to be 2mm to ensure the uniformity of the treatment; introduce 99.99% pure argon gas as the working gas, set the plasma treatment power to 120W, the treatment distance to 10mm, and the treatment time to 180s; after the treatment is completed, collect the activated straw powder for later use.

[0025] 3. In-situ hydrothermal growth of silicon-doped hydroxyapatite To prepare the precursor solution, calcium nitrate, diammonium hydrogen phosphate, and sodium silicate were dissolved in deionized water at a molar ratio of 1.67:1:0.25 to prepare a mixed solution with a calcium ion concentration of 0.2 mol / L. The pH of the solution was then adjusted to 10.0 using 25% ammonia. Plasma-activated straw powder was added to the precursor solution at a solid-liquid ratio of 1:10 (g / mL). After stirring evenly, the mixture was transferred to a hydrothermal reactor lined with polytetrafluoroethylene. The reaction temperature was set at 180℃ and the reaction was carried out at a constant temperature for 6 hours. After the reaction was completed, the mixture was allowed to cool naturally to room temperature. The solid material was filtered and separated. The mixture was then washed three times with deionized water to remove any unreacted precursor solution remaining on the surface, yielding a straw precursor with in-situ silicon-doped hydroxyapatite.

[0026] 4. Stepwise oxygen-limited pyrolysis carbonization The in-situ loaded straw precursor was placed in a tube furnace, and high-purity nitrogen gas at a flow rate of 100 mL / min was introduced as a protective gas to fully remove air from the furnace. The heating rate was controlled at 5℃ / min, and the temperature was first raised to 220℃ and pre-carbonized at a constant temperature for 1 h to preferentially decompose the hemicellulose in the straw and initially open the internal pore structure. Then, the temperature was raised to 480℃ at a heating rate of 8℃ / min and carbonized at a constant temperature for 1.5 h to complete the full carbonization of cellulose and lignin, while stabilizing the crystal structure of hydroxyapatite. After pyrolysis, the product was naturally cooled to room temperature under a nitrogen atmosphere and the solid product was taken out. The product was repeatedly washed with deionized water until the pH of the filtrate was neutral, and then dried in a 70℃ oven to constant weight to obtain a silicon-doped hydroxyapatite-modified sorghum straw biochar carrier.

[0027] 5. Preparation of compound microbial agents Salt-tolerant Bacillus, Bacillus megaterium, and Bacillus subtilis were inoculated into LB liquid medium and cultured in a constant temperature shaker at 37℃ and 180 rpm for 24 h to obtain bacterial suspensions of the three strains. The OD values ​​of each bacterial suspension were adjusted. 600 The concentration was adjusted to 0.8, and then the mixture was prepared by mixing the bacterial culture at a volume ratio of 1:1:1 to obtain a composite microbial culture. Subsequently, 0.5% trehalose was added to the culture as a stress-resistant agent for the microorganisms, and the mixture was stirred evenly for later use.

[0028] 6. Alkali-resistant composite embedding and loading 1) Preparation of alkali-resistant embedding solution: Dissolve carboxymethyl cellulose in deionized water to prepare a 2% carboxymethyl cellulose solution; dissolve gelatin in deionized water to prepare a 1% gelatin solution; mix the two solutions at a volume ratio of 3:1, heat to 45℃, and stir evenly to obtain an alkali-resistant composite embedding solution.

[0029] 2) Mixing of bacterial culture: Add the above-mentioned compound microbial culture with added trehalose to the alkali-resistant embedding solution at a volume ratio of 1:10, stir evenly, and obtain the bacterial-embedding mixture.

[0030] 3) Pore loading: The modified sorghum straw biochar obtained in step 4 was added to the above-mentioned microbial-embedding mixture at a solid-liquid ratio of 1:6 (g / mL), and stirred at 30℃ for 40 min to allow the mixture to fully penetrate into the hierarchical pore structure of the biochar.

[0031] 4) Cross-linking and curing: The mixture is then added dropwise to a cross-linking solution containing 2% calcium chloride and 1% borax, and cross-linked and cured at 4°C for 3 hours to complete the embedding and fixation of microorganisms.

[0032] 5) Drying the finished product: Filter to separate the solid product, rinse three times with deionized water to remove the residual crosslinking agent on the surface, and dry in a vacuum drying oven at 30℃ until constant weight to obtain the final sorghum straw biochar product for improving moderately to severely saline-alkali land.

[0033] The performance of the product prepared in this embodiment was tested, and the results are shown in the table below: Table 1: Performance Test Results

[0034] As shown in Table 1, the modified biochar support prepared in this embodiment has a specific surface area of ​​up to 550 m². 2 The product contains 42% micropores (<2nm) and 31% macropores (>50nm), exhibiting a typical hierarchical pore structure. This structure provides ample active sites for sodium ion adsorption and a stable colonization space for functional microorganisms. The product boasts a static sodium ion adsorption capacity of up to 72 mg / g, demonstrating excellent sodium ion adsorption capabilities and effectively meeting the high-salinity desalination needs of moderately to severely saline-alkali lands. Furthermore, the initial effective viable count reaches 3.2 × 10⁻⁶ cells / g. 8 With a CFU / g content, the functional microbial load is sufficient, providing a robust microbial foundation for subsequent soil nutrient activation.

[0035] Example 2 This embodiment verifies the application method and improvement effect of sorghum straw biochar prepared in Example 1 on saline-alkali land improvement. The test site is a saline-alkali experimental field in Dalad Banner, Ordos City, Inner Mongolia Autonomous Region. This plot is a typical severely saline-alkali land in the area. The initial basic physicochemical properties of the soil are as follows: pH 8.85, salt content 0.4%, organic matter content 8.2 g / kg, available phosphorus content 4.5 mg / kg, available potassium content 68 mg / kg, and available silicon content 85 mg / kg.

[0036] The experiment consisted of three treatment groups, with each treatment having three replicate cells, each cell measuring 30m². 2 A 1-meter-wide isolation zone is set up between the treatment areas to avoid mutual interference between them. The settings of each treatment area are as follows: Treatment Group 1: Sorghum straw biochar prepared in Example 1 of this invention was applied at a rate of 1.5 t / mu; Control group 1: Commercially available magnesium-modified straw biochar was applied at a rate of 1.5 t / mu; Control group 2: No modifier was applied, serving as a blank control.

[0037] The application method was consistent across all treatment groups: the corresponding soil conditioner was evenly spread on the soil surface of the plot, followed by tilling with a rotary tiller to a depth of 20cm to ensure that the conditioner was fully mixed with the soil in the 0-20cm topsoil layer. After that, regular irrigation was carried out, and corn was sown after the soil moisture was suitable. Other field management measures (such as regular base fertilizer application, pest and disease control, etc.) were kept consistent across all plots.

[0038] Soil samples from the 0-20cm topsoil layer were collected from each plot before application, 30 days after application, and 90 days after application. Soil pH, salinity, available phosphorus, available potassium, and available silicon content were measured. The number of viable bacteria in the soil was also measured. The results are shown in the table below. Table 2: Soil Improvement Effects

[0039] The experimental results show that, compared with conventional soil conditioners and blank controls, the sorghum straw biochar of the present invention can rapidly reduce the pH and salinity of severely saline-alkali land, while significantly increasing the nutrient content of the soil. Moreover, the functional microorganisms can survive stably in the high-salt and high-alkali soil environment for a long time, realizing the long-term, efficient and comprehensive improvement of severely saline-alkali land. The effect is significantly better than the existing conventional improvement technology.

[0040] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A sorghum straw biochar for saline-alkali soil improvement, characterized in that, The modified biochar carrier is obtained by taking corn stalk as raw material, plasma activation, in-situ growth of silicon-doped hydroxyapatite and step-by-step pyrolysis, the carrier is loaded with composite microorganisms, and the specific surface area of the carrier is 400-600 m 2 / g, and the carrier has a hierarchical pore structure.

2. The method for preparing sorghum straw biochar according to claim 1, characterized in that, Includes the following steps: Raw material pretreatment, low-temperature plasma surface activation, in-situ hydrothermal growth of silicon-doped hydroxyapatite, stepwise oxygen-limited pyrolysis carbonization, loading of composite microbial agents, and alkali-resistant encapsulation.

3. The preparation method according to claim 2, characterized in that, Raw material pretreatment includes drying and pulverizing.

4. The preparation method according to claim 2, characterized in that, The power of the low-temperature plasma surface activation is 100~150W, the processing time is 120~240s, the processing distance is 8~12mm, and the working gas is argon.

5. The preparation method according to claim 2, characterized in that, In the precursor solution for in-situ hydrothermal growth, the molar ratio of calcium nitrate, diammonium hydrogen phosphate, and sodium silicate is 1.5~1.8:1:0.2~0.3, the reaction temperature is 160~200℃, and the reaction time is 4~8h.

6. The preparation method according to claim 2, characterized in that, The stepwise oxygen-limited pyrolysis carbonization includes: first heating to 200~250℃ and holding at that temperature for 0.5~1.5h, then heating to 450~500℃ and holding at that temperature for 1~2h, with heating rates of 3~7℃ / min and 6~10℃ / min respectively; the protective gas is nitrogen.

7. The preparation method according to claim 2, characterized in that, The embedding solution used for alkali-resistant composite embedding loads includes carboxymethyl cellulose and gelatin, with a mass fraction of 1.5~2.5% for carboxymethyl cellulose and a mass fraction of 0.5~1.5% for gelatin, and a volume ratio of 2.5~3.5:

1.

8. The preparation method according to claim 2, characterized in that, The composite microorganisms include: halophilic Bacillus, Bacillus megaterium, and Bacillus subtilis, with a volume ratio of 0.8~1.2:0.8~1.2:0.8~1.2 for each bacterial solution.

9. The application of sorghum straw biochar as described in claim 1 in the improvement of moderately to severely saline-alkali soil.

10. The application according to claim 9, characterized in that, The pH of the saline-alkali land is 7.0~10.0, and the salt content is ≥0.3%.

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