Special composite microbial fertilizer for saline-alkali soil remediation

Abstract

The application discloses a kind of saline-alkali soil repair special-purpose compound microbial fertilizer, adopt salt-tolerant complex function flora to match porous modified biochar carrier, acid-base buffer regulator and organic synergistic component compound technical scheme;By optimizing adaptation saline-alkali extreme environment's halophilic bacillus, alkali-eliminating nitrogen-fixing bacteria, phosphorus and potassium-eliminating bacteria complex flora, cooperate with the pore lock bacteria of modified biochar and keep alive structure, with multiple buffer system stabilizing soil pH value, realize the multiple effects of flora long-acting planting, sustained salt reduction and alkali adjustment, soil nutrient activation;The fertilizer can survive and reproduce in saline-alkali soil with salt content of 0.3%-0.8% and pH of 8.5-9.8 for a long time, effectively reduce soil salt content and pH value, improve soil aggregate structure, solve the defects of short repair period, poor effect and insufficient stability of traditional fertilizer, have dual effects of soil repair and crop growth promotion, wide application range, strong repair durability, have significant application value.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology for saline-alkali land improvement, specifically relating to a compound microbial fertilizer for saline-alkali land remediation. Background Technology

[0002] Saline-alkali lands generally suffer from problems such as high soil salinity, high pH, ​​severe soil compaction, low organic matter content, lack of microbial communities, and poor nutrient availability, resulting in low crop emergence rates, poor growth, and sharp reductions in yield, which seriously restricts the sustainable development of regional agriculture.

[0003] Currently, the main methods for remediating and improving saline-alkali land are divided into three categories: physical improvement, chemical improvement, and biological improvement. Among them, microbial fertilizers have become the mainstream technology for ecological restoration of saline-alkali land due to their advantages of being green and environmentally friendly, having no secondary pollution, and being able to improve soil in a long-term manner. Existing microbial fertilizers for saline-alkali land are mostly prepared by compounding conventional agricultural microbial communities. Although they can improve the soil microenvironment in the short term, they have core technical problems: conventional microbial communities have low salt and alkali tolerance thresholds and are easily inactivated and decomposed in the extreme environment of high-salt and high-alkali saline-alkali soils. They cannot stably establish themselves and continuously metabolize and reproduce, resulting in short-term fertilizer improvement effects and rapid decay. The effects of soil salinization, alkali adjustment, and nutrient activation after a single application of fertilizer can only be maintained for 1-2 months, requiring frequent topdressing. This results in high restoration costs, incomplete improvement, and difficulty in achieving long-term ecological restoration of saline-alkali land and steady improvement of arable land fertility.

[0004] In existing technologies, to improve the survival rate of microbial communities, simple carriers are often used to adsorb the microbial communities to prepare microbial fertilizers. However, ordinary carriers have a simple pore structure and poor adsorption stability, which cannot isolate the damage to the microorganisms caused by salt and alkali stress. Moreover, without a matching acid-base buffer system, fluctuations in soil pH will further accelerate the inactivation of microorganisms. At the same time, single-function microbial communities cannot simultaneously meet the multiple needs of salt reduction, alkali regulation, phosphorus and potassium solubilization, nitrogen fixation, and growth promotion, further exacerbating the problems of poor remediation effect and insufficient sustainability, which greatly limits the large-scale application of microbial fertilizers in the remediation of moderate to severe saline-alkali land. Summary of the Invention

[0005] The purpose of this invention is to solve the technical problems of poor salt and alkali tolerance of functional microbial communities in existing saline-alkali land microbial fertilizers, which are prone to inactivation in saline-alkali environments, resulting in short-term, poor-lasting, and incomplete fertilizer remediation effects. The invention provides a compound microbial fertilizer specifically for saline-alkali land remediation, which enables functional microbial communities to establish themselves and continuously metabolize in saline-alkali land, and stably and effectively complete soil desalination and alkali adjustment, soil fertility improvement, and ecological restoration.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A compound microbial fertilizer specifically for saline-alkali land remediation, comprising, by weight, the following components: 8-15 parts of salt-alkali tolerant compound functional microbial agent, 25-35 parts of modified biochar carrier, 12-18 parts of acid-base buffer regulator, 30-40 parts of organic synergistic matrix, 2-5 parts of trace element adjuvant, and 1-3 parts of binder; wherein the salt-alkali tolerant compound functional microbial agent is composed of halophilic Bacillus, alkali-solubilizing nitrogen-fixing Bacillus, mucilage Bacillus, and megaterium in a viable count ratio of 2:1:1.5:1, with an effective viable count ≥2.0 × 10⁻⁶. 10 CFU / g; the modified biochar carrier is a porous mesh structure carrier prepared by acid-base composite modification and high-temperature activation of straw biochar, with a specific surface area ≥380m² / g; the acid-base buffer regulator is composed of potassium humate, calcium dihydrogen phosphate, citric acid, and bentonite in a weight ratio of 3:2:1:4; the organic synergistic matrix is ​​prepared by mixing well-rotted cow and sheep manure, well-rotted straw, and seaweed extract in a weight ratio of 5:3:2.

[0008] In a preferred embodiment of the present invention, the optimal component ratio by weight is: 12 parts of salt-alkali resistant composite functional bacterial agent, 30 parts of modified biochar carrier, 15 parts of acid-base buffer regulator, 38 parts of organic synergistic matrix, 4 parts of trace element additive, and 2 parts of binder.

[0009] In a preferred embodiment of the present invention, the halophilic Bacillus is tolerant to soil salinity of 0-0.9% and pH of 8.0-10.0, and can metabolize to produce organic acids and extracellular polysaccharides, thereby degrading soil salinity and improving soil aggregate structure; the alkali-solubilizing nitrogen-fixing bacteria are adapted to high-alkali environments and have the functions of nitrogen fixation and neutralization of soil alkaline substances; the mucilaginous Bacillus and megaterium can efficiently solubilize phosphorus and potassium in saline-alkali environments, thereby activating soil to fix nutrients.

[0010] In a preferred embodiment of the present invention, the method for preparing the modified biochar carrier includes: carbonizing corn stalks, crushing them through an 80-100 mesh sieve, soaking them in a 0.5 mol / L sodium hydroxide solution for 1.5 h, rinsing them with deionized water until neutral, soaking them in a 0.3 mol / L dilute sulfuric acid solution for 1 h, rinsing them again until neutral, activating them at a high temperature of 450-500℃ for 2 h, and cooling them to obtain porous mesh modified biochar.

[0011] In a preferred embodiment of the present invention, the trace element additive is a compound of zinc sulfate, ferrous sulfate, boric acid and ammonium molybdate in a weight ratio of 2:3:1:1.

[0012] In a preferred embodiment of the present invention, the binder is sodium carboxymethyl cellulose, which is used to improve the stability of fertilizer granule forming and extend the slow release period of microorganisms and nutrients.

[0013] A method for preparing a compound microbial fertilizer specifically for saline-alkali land remediation includes the following steps: Step S1, Preparation of modified biochar carrier: Prepare porous mesh modified biochar according to claim 4, for later use; Step S2, Preparation of salt- and alkali-tolerant compound functional bacterial agent: The screened and purified halophilic Bacillus, alkali-solubilizing nitrogen-fixing Bacillus, mucilaginous Bacillus, and megaterium were inoculated into their respective salt- and alkali-tolerant liquid culture media and cultured at 28-32℃ and 180r / min for 48h to obtain single bacterial solutions. After compounding according to the ratio of viable bacteria, the compound bacterial agent was prepared by low-temperature concentration and set aside for later use. Step S3, Preparation of mixed matrix: The organic synergistic matrix, acid-base buffer regulator and trace element additive are added to the stirring equipment in sequence and stirred at room temperature for 20-30 minutes until they are mixed evenly to obtain the basic mixed matrix; Step S4, Loading microbial community: Add the modified biochar carrier to the basic mixed matrix, stir evenly, slowly spray the salt and alkali resistant composite functional microbial agent, stir at low speed for 15 minutes, so that the microbial community can be fully adsorbed and fixed in the porous structure of biochar. Step S5, Granulation and molding: Add binder, stir and mix well, then use a disc granulator to prepare 2-4mm granules, dry at 40℃, and control the fertilizer moisture content to ≤12%; Step S6, sieving and packaging: Sieve to remove powder and large particles, test the number of effective viable bacteria and moisture content, and seal and package after passing the test to obtain the finished compound microbial fertilizer.

[0014] In a preferred embodiment of the present invention, in step S2, the pH value of the salt-alkali tolerant liquid culture medium is adjusted to 8.5-9.0, and the salt content is 0.5%, which is used to acclimate the strain to salt and alkali tolerance and improve the strain's environmental adaptability.

[0015] An application of a special compound microbial fertilizer for saline-alkali land remediation is applicable to the remediation of mild, moderate and severe saline-alkali land. It is applied as a base fertilizer before spring sowing or after autumn harvest during deep plowing and land preparation, with an application rate of 40-60 kg per mu. The soil should be plowed to a depth of 20-25 cm to ensure that the fertilizer is fully mixed with the soil. It should be applied once a year.

[0016] In a preferred embodiment of the present invention, after the fertilizer is applied, the annual average salinity of saline-alkali soil can be reduced by 0.25%-0.35%, the annual average pH value of the soil can be reduced by 0.8-1.2, and the number of effective viable bacteria in the soil can be stably maintained at 1.0 × 10⁻⁶. 10 With a CFU / g or higher, the repair effect lasts for more than 12 months.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention precisely addresses the core problems of existing technologies, such as the weak salt and alkali tolerance of microbial communities, their susceptibility to inactivation in saline-alkali environments, and their short-lived repair effects. By screening for highly salt- and alkali-tolerant strains with specific functions, and combining them with the physical protective structure of porous modified biochar, the damage to the microorganisms caused by salt and alkali stress is isolated, significantly improving the survival rate and colonization ability of the microbial community in high-salt and high-alkali environments. The survival period of the microbial community is extended from the traditional 1-2 months to 8-12 months, achieving long-term and continuous repair.

[0018] 2. This invention sets up a multi-element acid-base buffer system, which can dynamically adjust the soil pH value, buffer the fluctuation of soil acidity and alkalinity, provide a stable micro-ecological environment for the metabolism and reproduction of functional microbial communities, and continuously neutralize soil alkalinity and replace soil soluble salts, thereby improving the physical and chemical properties of saline-alkali soil from the root, with a long-lasting and non-rebounding repair effect, overcoming the defect of rapid rebound of soil salinity and alkalinity after traditional fertilizer improvement.

[0019] 3. The compound microbial community has complementary functions, with multiple effects such as reducing salt and alkali, fixing nitrogen, solubilizing phosphorus and potassium, activating soil, and promoting growth and stress resistance. When combined with organic enhancement substrate, it can simultaneously increase soil organic matter content, optimize soil aggregate structure, and restore soil microbial community diversity, so as to achieve simultaneous ecological restoration and soil fertility improvement of saline-alkali land. It does not require the use of multiple soil amendments, and is convenient to apply and low in cost.

[0020] 4. This invention adopts low-temperature granulation and low-temperature drying processes, which avoids damage to microbial activity by high temperature throughout the process. The fertilizer has a high content of effective live bacteria, good stability, wide applicability, and can be adapted to saline-alkali land of different degrees. It is green and has no secondary pollution, meets the needs of sustainable development of ecological agriculture, and has extremely high industrialization and promotion value. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments or prior art, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram showing the component ratio of a special compound microbial fertilizer for saline-alkali land remediation provided in an embodiment of the present invention.

[0023] Figure 2 Scanning electron microscope image of the micropore structure of the modified biochar support provided in this embodiment of the invention.

[0024] Figure 3 This invention provides a flowchart of a method for preparing a special compound microbial fertilizer for saline-alkali land remediation.

[0025] Figure 4This is a comparison curve of the survival rates of the compound microbial community, single microbial community, and commercially available conventional microbial community of the present invention in saline-alkali gradient soil. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0027] like Figure 1 As shown in the figure, this invention provides a special compound microbial fertilizer for saline-alkali land remediation, comprising the following components by weight: 8-15 parts of salt-alkali tolerant compound functional bacterial agent, 25-35 parts of modified biochar carrier, 12-18 parts of acid-base buffer regulator, 30-40 parts of organic synergistic matrix, 2-5 parts of trace element adjuvant, and 1-3 parts of binder; the salt-alkali tolerant compound functional bacterial agent is composed of halophilic Bacillus, alkali-solubilizing nitrogen-fixing Bacillus, mucilage Bacillus, and megaterium in a viable count ratio of 2:1:1.5:1, with an effective viable count ≥2.0×10⁻⁶. 10 CFU / g; the modified biochar carrier is a porous mesh structure carrier prepared by acid-base composite modification and high-temperature activation of straw biochar, with a specific surface area ≥380m² / g; the acid-base buffer regulator is composed of potassium humate, calcium dihydrogen phosphate, citric acid, and bentonite in a weight ratio of 3:2:1:4; the organic synergistic matrix is ​​prepared by mixing well-rotted cow and sheep manure, well-rotted straw, and seaweed extract in a weight ratio of 5:3:2. This invention's fertilizer uses the porous structure of modified biochar to physically lock in and preserve bacteria, combined with a multi-element acid-base buffer system to stabilize the soil microenvironment. This solves the technical problems of existing microbial fertilizers, such as weak salt and alkali tolerance, easy inactivation under saline-alkali environments, and short-term remediation effects, achieving long-term remediation of saline-alkali land.

[0028] The optimal composition ratio by weight is: 12 parts salt-alkali resistant composite functional bacterial agent, 30 parts modified biochar carrier, 15 parts acid-base buffer regulator, 38 parts organic synergistic matrix, 4 parts trace element adjuvant, and 2 parts binder.

[0029] Halophilic Bacillus can tolerate soil salinity of 0-0.9% and pH of 8.0-10.0. It can metabolize organic acids and extracellular polysaccharides to degrade soil salinity and improve soil aggregate structure. Alkali-solubilizing and nitrogen-fixing bacteria are adapted to high-alkaline environments and have the functions of nitrogen fixation and neutralization of soil alkaline substances. Mucilaginous Bacillus and Megalosporus can efficiently solubilize phosphorus and potassium in saline-alkali environments and activate soil to fix nutrients.

[0030] The preparation method of the modified biochar carrier includes: carbonizing corn stalks, pulverizing them through an 80-100 mesh sieve, soaking them in a 0.5 mol / L sodium hydroxide solution for 1.5 h, rinsing them with deionized water until neutral, then soaking them in a 0.3 mol / L dilute sulfuric acid solution for 1 h, rinsing them again until neutral, activating them at 450-500℃ for 2 h, and cooling them to obtain porous network modified biochar. (Reference) Figure 2 .

[0031] The trace element adjuvant is a compound of zinc sulfate, ferrous sulfate, boric acid, and ammonium molybdate in a weight ratio of 2:3:1:1. It supplements the soil and crops with trace nutrients and synergistically enhances soil activity.

[0032] The binder is sodium carboxymethyl cellulose, which is used to improve the stability of fertilizer granule formation and extend the slow release period of microorganisms and nutrients.

[0033] like Figure 3 As shown in the figure, this invention provides a method for preparing a special compound microbial fertilizer for saline-alkali land remediation, comprising the following steps: Step S1, Preparation of modified biochar carrier: Prepare porous mesh modified biochar according to the above method, for later use; Step S2, Preparation of salt- and alkali-tolerant compound functional bacterial agent: The screened and purified halophilic Bacillus, alkali-solubilizing nitrogen-fixing Bacillus, mucilaginous Bacillus, and megaterium were inoculated into their respective salt- and alkali-tolerant liquid culture media and cultured at 28-32℃ and 180r / min for 48h to obtain single bacterial solutions. After compounding according to the ratio of viable bacteria, the compound bacterial agent was prepared by low-temperature concentration and set aside for later use. Step S3, Preparation of mixed matrix: The organic synergistic matrix, acid-base buffer regulator and trace element additive are added to the stirring equipment in sequence and stirred at room temperature for 20-30 minutes until they are mixed evenly to obtain the basic mixed matrix; Step S4, Loading microbial community: Add the modified biochar carrier to the basic mixed matrix, stir evenly, slowly spray the salt and alkali resistant composite functional microbial agent, stir at low speed for 15 minutes, so that the microbial community can be fully adsorbed and fixed in the porous structure of biochar. Step S5, Granulation and molding: Add binder, stir and mix well, then use a disc granulator to prepare 2-4mm granules, dry at 40℃, and control the fertilizer moisture content to ≤12%; Step S6, sieving and packaging: Sieve to remove powder and large particles, test the number of effective viable bacteria and moisture content, and seal and package after passing the test to obtain the finished compound microbial fertilizer.

[0034] This invention provides an application method for the above-mentioned compound microbial fertilizer for saline-alkali land remediation, which is suitable for the remediation of mild, moderate and severe saline-alkali land. It is applied as a base fertilizer before spring sowing or after autumn harvest during deep plowing and land preparation, with an application rate of 40-60 kg per mu. The fertilizer is then plowed to a depth of 20-25 cm to ensure that it is fully mixed with the soil. It is applied once a year.

[0035] After fertilizer application, the annual average salinity of saline-alkali soil can be reduced by 0.25%-0.35%, the annual average pH value can be reduced by 0.8-1.2, and the number of effective viable bacteria in the soil can be stably maintained at 1.0×10⁻⁶. 10 With a CFU / g or higher, the repair effect lasts for more than 12 months.

[0036] Example 1 A special compound microbial fertilizer for saline-alkali land remediation, by weight, is composed of the following components: 12 parts of salt-alkali tolerant compound functional bacterial agent, 30 parts of modified biochar carrier, 15 parts of acid-base buffer regulator, 38 parts of organic synergistic matrix, 4 parts of trace element adjuvant, and 2 parts of binder.

[0037] The salt- and alkali-tolerant compound functional bacterial agent is a mixture of halophilic Bacillus, alkali-fixing nitrogen-fixing bacteria, mucilage Bacillus, and megaterium in a viable count ratio of 2:1:1.5:1, with an effective viable count ≥2.0×10⁻⁶. 10 CFU / g.

[0038] Preparation of modified biochar carrier: Corn stalks were crushed and carbonized at 550℃ for 2 hours, passed through a 90-mesh sieve, soaked in 0.5 mol / L NaOH solution for 1.5 hours, rinsed with deionized water until neutral, soaked in 0.3 mol / L dilute sulfuric acid for 1 hour, rinsed until neutral, activated at 480℃ for 2 hours, and cooled for later use.

[0039] The acid-base buffer is a compound of potassium humate, calcium dihydrogen phosphate, citric acid, and bentonite in a weight ratio of 3:2:1:4.

[0040] The organic enhancement matrix is ​​prepared by mixing well-rotted cow and sheep manure, well-rotted straw, and seaweed extract in a weight ratio of 5:3:2.

[0041] The trace element additive is a compound of zinc sulfate, ferrous sulfate, boric acid and ammonium molybdate in a weight ratio of 2:3:1:1, and the binder is sodium carboxymethyl cellulose.

[0042] Preparation method: Step S1, prepare modified biochar carrier for later use; Step S2, culture four salt- and alkali-tolerant bacterial strains separately, and concentrate them according to the ratio to obtain a compound bacterial agent; Step S3, mix and stir the organic synergistic matrix, acid-base buffer regulator, and trace element adjuvant for 25 min to obtain the basic matrix; Step S4, add modified biochar and mix well, spray the compound bacterial agent, and stir at low speed for 15 min to complete the bacterial colony loading; Step S5, add binder and mix well, granulate in a disc to prepare 3 mm particles, and dry at 40℃ until the moisture content is ≤12%; Step S6, screen, test, seal and package to obtain the finished fertilizer.

[0043] Example 2 A special compound microbial fertilizer for saline-alkali land remediation, by weight, is composed of the following components: 8 parts of salt-alkali tolerant compound functional bacterial agent, 25 parts of modified biochar carrier, 12 parts of acid-base buffer regulator, 30 parts of organic synergistic matrix, 2 parts of trace element adjuvant, and 1 part of binder. The proportions and preparation methods of the remaining components are the same as in Example 1.

[0044] Example 3 A special compound microbial fertilizer for saline-alkali land remediation, by weight, is composed of the following components: 15 parts of salt-alkali tolerant compound functional bacterial agent, 35 parts of modified biochar carrier, 18 parts of acid-base buffer regulator, 40 parts of organic synergistic matrix, 5 parts of trace element adjuvant, and 3 parts of binder. The proportions and preparation methods of the remaining components are the same as in Example 1.

[0045] Comparative Example 1 (Common Commercially Available Microbial Fertilizer for Saline-Alkali Land) It uses commercially available ordinary saline-alkali soil microbial fertilizer, with Bacillus subtilis and organic fertilizer carrier as its main components. It features an unmodified biochar-based microbial locking structure and a multi-element acid-base buffer system, with an effective viable count ≥1.0×10⁻⁶. 10 CFU / g.

[0046] Comparative Example 2 (Single-strain microbial fertilizer) The bacterial fertilizer was prepared using only a single strain of Bacillus halophilus, while the other carriers, adjuvants, and preparation processes were completely consistent with those in Example 1.

[0047] Effect test A moderately saline-alkali land was selected as the experimental plot. The initial soil salinity was 0.52%, pH was 9.2, and organic matter content was 1.12%. A randomized block design was used, with three replicates per group. Fertilizers from Examples 1-3 and Comparative Examples 1-2 were applied at a rate of 50 kg per acre, and the mixture was deeply tilled and thoroughly mixed. Soil indicators and microbial survival rates were monitored continuously for 10 months. The experimental results are as follows: 1. Survival rate of microbial communities: After 10 months of application, the survival rate of microbial communities in Example 1 reached 89.2%, in Example 2 it was 85.7%, and in Example 3 it was 87.5%; the survival rate of microbial communities in Comparative Example 1 was only 18.3%, and in Comparative Example 2 it was 42.6%. This invention's fertilizer can significantly extend the survival period of microbial communities in saline-alkali environments, solving the core problem of easy inactivation of traditional microbial communities. (Reference) Figure 4 .

[0048] 2. Soil improvement effect: After 10 months of application, the soil salinity in Example 1 decreased to 0.21%, the pH decreased to 8.1, and the organic matter content increased to 1.89%; the soil salinity in Example 2 was 0.25%, the pH was 8.2, and the organic matter content was 1.76%; the soil salinity in Example 3 was 0.22%, the pH was 8.1, and the organic matter content was 1.85%; the soil salinity in Comparative Example 1 was 0.43%, the pH was 8.9, and the organic matter content was 1.31%; the soil salinity in Comparative Example 2 was 0.35%, the pH was 8.6, and the organic matter content was 1.52%.

[0049] The experimental results show that the present invention, through the combination of highly salt- and alkali-tolerant compound microbial community with modified biochar microbial locking structure and multi-element buffer system, can maintain the activity of microbial community for a long time, continuously achieve soil salinity reduction, alkali adjustment and fertilization, and the repair effect is significantly better than that of existing conventional products, solving the technical defects of traditional microbial fertilizers in short-term repair effect and easy rebound.

[0050] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A compound microbial fertilizer specifically for saline-alkali land remediation, characterized in that, By weight, it comprises the following components: 8-15 parts of salt- and alkali-tolerant composite functional bacterial agent, 25-35 parts of modified biochar carrier, 12-18 parts of acid- and alkali-buffered regulator, 30-40 parts of organic synergistic matrix, 2-5 parts of trace element adjuvant, and 1-3 parts of binder; the salt- and alkali-tolerant composite functional bacterial agent is a compound of halophilic Bacillus, alkali-fixing nitrogen-fixing Bacillus, mucilage Bacillus, and megaterium in a viable count ratio of 2:1:1.5:1, with an effective viable count ≥2.0 × 10⁻⁶. 10 CFU / g; the modified biochar carrier is a porous mesh structure carrier prepared by acid-base composite modification and high-temperature activation of straw biochar, with a specific surface area ≥380m² / g; the acid-base buffer regulator is composed of potassium humate, calcium dihydrogen phosphate, citric acid, and bentonite in a weight ratio of 3:2:1:4; the organic synergistic matrix is ​​prepared by mixing well-rotted cow and sheep manure, well-rotted straw, and seaweed extract in a weight ratio of 5:3:

2.

2. The compound microbial fertilizer for saline-alkali land remediation according to claim 1, characterized in that, The optimal composition ratio by weight is: 12 parts salt-alkali resistant composite functional bacterial agent, 30 parts modified biochar carrier, 15 parts acid-base buffer regulator, 38 parts organic synergistic matrix, 4 parts trace element adjuvant, and 2 parts binder.

3. The compound microbial fertilizer for saline-alkali land remediation according to claim 1, characterized in that, The halophilic Bacillus is tolerant of soil salinity of 0-0.9% and pH of 8.0-10.0, and can metabolize to produce organic acids and extracellular polysaccharides, degrading soil salinity and improving soil aggregate structure; the alkali-solubilizing nitrogen-fixing bacteria are adapted to high-alkaline environments and have the functions of nitrogen fixation and neutralization of soil alkaline substances; the mucilaginous Bacillus and megaterium can efficiently solubilize phosphorus and potassium in saline-alkali environments, activating soil to fix nutrients.

4. The compound microbial fertilizer for saline-alkali land remediation according to claim 1, characterized in that, The preparation method of the modified biochar carrier includes: carbonizing corn stalks, crushing them through an 80-100 mesh sieve, soaking them in a 0.5 mol / L sodium hydroxide solution for 1.5 h, rinsing them with deionized water until neutral, soaking them in a 0.3 mol / L dilute sulfuric acid solution for 1 h, rinsing them again until neutral, activating them at a high temperature of 450-500℃ for 2 h, and cooling them to obtain porous mesh modified biochar.

5. The compound microbial fertilizer for saline-alkali land remediation according to claim 1, characterized in that, The trace element additive is a compound of zinc sulfate, ferrous sulfate, boric acid, and ammonium molybdate in a weight ratio of 2:3:1:

1.

6. The compound microbial fertilizer for saline-alkali land remediation according to claim 1, characterized in that, The binder is sodium carboxymethyl cellulose, which is used to improve the stability of fertilizer granule formation and extend the slow release period of microorganisms and nutrients.

7. A method for preparing a compound microbial fertilizer specifically for saline-alkali land remediation as described in any one of claims 1-6, characterized in that, Includes the following steps: Step S1, Preparation of modified biochar carrier: Prepare porous mesh modified biochar according to claim 4, for later use; Step S2, Preparation of salt- and alkali-tolerant compound functional bacterial agent: The screened and purified halophilic Bacillus, alkali-solubilizing nitrogen-fixing Bacillus, mucilaginous Bacillus, and megaterium were inoculated into their respective salt- and alkali-tolerant liquid culture media and cultured at 28-32℃ and 180r / min for 48h to obtain single bacterial solutions. After compounding according to the ratio of viable bacteria, the compound bacterial agent was prepared by low-temperature concentration and set aside for later use. Step S3, Preparation of mixed matrix: The organic synergistic matrix, acid-base buffer regulator and trace element additive are added to the stirring equipment in sequence and stirred at room temperature for 20-30 minutes until they are mixed evenly to obtain the basic mixed matrix; Step S4, Loading microbial community: Add the modified biochar carrier to the basic mixed matrix, stir evenly, slowly spray the salt and alkali resistant composite functional microbial agent, stir at low speed for 15 minutes, so that the microbial community can be fully adsorbed and fixed in the porous structure of biochar. Step S5, Granulation and molding: Add binder, stir and mix well, then use a disc granulator to prepare 2-4mm granules, dry at 40℃, and control the fertilizer moisture content to ≤12%; Step S6, sieving and packaging: Sieve to remove powder and large particles, test the number of effective viable bacteria and moisture content, and seal and package after passing the test to obtain the finished compound microbial fertilizer.

8. The preparation method according to claim 7, characterized in that, In step S2, the pH of the salt-tolerant liquid culture medium is adjusted to 8.5-9.0, and the salt content is 0.5%, which is used to acclimate the strain to salt and alkali tolerance and improve the strain's environmental adaptability.

9. The application of a compound microbial fertilizer specifically for saline-alkali land remediation as described in any one of claims 1-6, characterized in that, Suitable for the remediation of mild, moderate and severe saline-alkali land. Apply as a base fertilizer before spring sowing or after autumn harvest during deep plowing and preparation. The amount of fertilizer applied per acre is 40-60 kg. Plow to a depth of 20-25 cm to ensure that the fertilizer is fully mixed with the soil. Apply once a year.

10. The application according to claim 9, characterized in that, After application, the fertilizer can reduce the salinity of saline-alkali soil by an average of 0.25%-0.35% per year, reduce the soil pH by an average of 0.8-1.2 per year, and maintain the effective viable bacteria count in the soil at a stable level of 1.0 × 10⁻⁶. 10 With a CFU / g or higher, the repair effect lasts for more than 12 months.

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