A saline-alkali soil biological improvement fertilizer, a preparation method and application thereof

Abstract

The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and a preparation method and application thereof, and belongs to the field of saline-alkali soil biological improvement. The application discloses a saline-alkali soil biological improvement fertilizer and

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of composite microbial fertilizer, in particular to a saline-alkali soil biological improvement fertilizer, a preparation method and application thereof. BACKGROUND

[0002] It is reported that about 10% of the land in the world is covered by different types of saline-alkali soil, mainly distributed in arid and semi-arid regions. Half of the existing irrigated land is threatened by secondary salinization. In the northeast, north and northwest regions of China, different types of saline-alkali soil are distributed, in addition, various coastal saline soils (such as coastal beach land) are widely distributed along the coast. These types of soil are inherently immature and of poor quality.

[0003] The saline-alkali soil is characterized by containing sodium carbonate and sodium bicarbonate in the soil solution, and containing exchangeable sodium on the soil colloid, so the saline-alkali soil is strongly alkaline, with a pH of more than 9. The soil solution concentration of the saline-alkali soil is too large, greater than the solution concentration of the crop cells, causing the crop cells to lose water and affect the crop cell work. In addition, the saline-alkali soil is easy to be cemented, which makes it difficult for gas to be intermingled in the soil after cementation, resulting in heavy soil and poor permeability, leading to a decrease in the respiratory efficiency of crops. The combination of the above two factors seriously affects the metabolism of crop cells, resulting in insufficient energy of crops, so that the crops lack the absorption power, and thus lack inorganic salts, which seriously affects the growth of crops. The saline-alkali soil often causes the crops to be under-yield, and even causes the crops to be no yield, so the saline-alkali soil has become a low-yield soil in agricultural production, which seriously affects the development of agricultural production.

[0004] In recent years, there are many methods for improving and repairing saline-alkali soil. The main methods include engineering improvement, chemical improvement and biological improvement. The engineering improvement has obvious short-term effect, but the cost is too high and the cost performance is low; the chemical improvement has fast effect, but the cost is high and the side effects are obvious, and improper use will cause secondary pollution to the environment. The biological improvement has the advantages of low cost, environmental friendliness and long-term effect, so the biological improvement of saline-alkali soil has broad prospects.

[0005] The existing biological improvement method has poor tolerance of the strain to the saline-alkali soil, and the capacity of the carrier is limited, so it is impossible to plant a sufficient number of strains in the soil, and the improvement efficiency and range of the soil cannot meet the needs of many plants.

[0006] Therefore, there is an urgent need for a biological improvement fertilizer which can improve the survival rate and the number of strains planted in the soil, and can improve the improvement efficiency and range of the saline-alkali soil. SUMMARY

[0007] Inventive purpose: In view of the defects of the prior art, the purpose of the present application is to provide a saline-alkali soil biological improvement fertilizer which can improve the survival rate and quantity of strains in soil, and improve the efficiency and range of saline-alkali soil improvement, and a preparation method and application thereof.

[0008] Technical scheme:

[0009] The present application provides a saline-alkali soil biological improvement fertilizer, which comprises a composite bacterial agent, an organic-inorganic composite carrier, humic acid, an elemental adjuvant, biochar and organic material.

[0010] The composite bacterial agent comprises Bacillus subtilis, halophilic Bacillus and jelly-like Bacillus.

[0011] The organic-inorganic composite carrier is prepared by modifying cyclodextrin with an amino acid surfactant, and then grafting the modified cyclodextrin on pretreated attapulgite.

[0012] The amino acid surfactant has the following structure shown in formula A:

[0013] .

[0014] The organic-inorganic composite carrier in the present application is grafted on pretreated attapulgite by modified cyclodextrin. On the one hand, based on the excellent inclusion and adsorption capacity of modified cyclodextrin, it can not only effectively adsorb and fix free sodium ions in the soil to improve the soil environment, but also improve the tolerance and loading capacity of the strains to improve the improvement efficiency. On the other hand, based on the porous structure and ion adsorption and replacement capacity of attapulgite, the loading effect of the strains and the soil improvement capacity can be further improved, so that it can be effectively applied to the loading of strains.

[0015] Further, the amino acid surfactant is prepared by the following steps: in a reactor, 4-phenylbutyryl chloride and oxaline acid are added, sodium hydroxide solution is added to adjust the pH to 10-11, after stirring uniformly, the temperature is raised to 40-50 DEG C, and after reaction for 8-12 hours, the temperature is cooled, hydrochloric acid is added to adjust the pH to 1-2, and after filtration, washing and drying, the amino acid surfactant is obtained.

[0016] The mass concentration of the sodium hydroxide solution is 10-15%;

[0017] The mass concentration of the hydrochloric acid is 30-40%;

[0018] The molar ratio of 4-phenylbutyryl chloride to oxaline acid is 1:1.2-1.5.

[0019] The amino acid surfactant in the application can not only improve the adsorption and loading capacity of the cyclodextrin and the attapulgite respectively, but also can make the cyclodextrin be uniformly and effectively grafted on the surface of the attapulgite, and can play the effects of ion exchange and inclusion fixation, and can significantly improve the improvement efficiency and range of the material for the saline-alkali soil.

[0020] Further, the specific preparation method of the organic-inorganic composite carrier is:

[0021] (1) in the reactor, the amino acid surfactant, the catalyst and the deionized water are added, stirred until dissolved, then the β-cyclodextrin is added, heated to 70-80℃, and after 6-8 hours of incubation, cooling, filtration, washing and drying, the modified cyclodextrin is prepared;

[0022] (2) in the reactor, the attapulgite and sulfuric acid are added, and after 6-8 hours of standing, washing and drying, the pretreated attapulgite is prepared by adding it into the sodium hydroxide solution, adjusting the pH to 10-11, and stirring and reacting at 60-70℃ for 2-3 hours;

[0023] (3) in the reactor, the pretreated attapulgite, the modified cyclodextrin and the deionized water are added, heated to 50-60℃, reacted for 18-24 hours, then cooled, filtered, washed and dried to prepare the organic-inorganic composite carrier.

[0024] The amino acid surfactant is used for surface modification of the cyclodextrin, which can expand the cavity volume and enhance the inclusion capacity, so that the bacteria can be effectively loaded on the surface of the carrier, and a protective layer with a certain coating structure is formed, thereby avoiding direct contact of the bacteria with the high concentration environment of the saline-alkali soil, and improving the survival rate; on the other hand, the hydrophobicity of the cyclodextrin cavity is enhanced, thereby improving the adsorption and inclusion capacity of the carrier for the free sodium ions in the soil, and reducing the salt concentration to improve the soil environment.

[0025] Further, the catalyst in step (1) is selected from one of sodium hypophosphite or potassium hypophosphite; the mass ratio of the amino acid surfactant and the β-cyclodextrin is 1:12-15.

[0026] Further, the mass concentration of sulfuric acid in step (2) is 40-60%; the mass concentration of the sodium hydroxide solution is 10-15%.

[0027] Further, the mass ratio of the pretreated attapulgite and the modified cyclodextrin in step (3) is (5-8):(2-3).

[0028] Further, the element additive is selected from at least one of urea, monoammonium phosphate, potassium sulfate and potassium chloride; the organic material is selected from at least one of wheat straw, corn straw and shiitake mushroom residue.

[0029] Further, the effective viable bacteria number in the saline-alkali soil biological improvement fertilizer is not less than 5*10 9 CFU / g;

[0030] The effective viable bacteria number ratio of Bacillus subtilis, Bacillus halodurans and Bacillus gellwangenensis in the compound microbial agent is (3-5):(1-2):(2-3).

[0031] The Bacillus subtilis in the compound microbial agent can accelerate the mineralization of organic matter, improve the soil structure and reduce the toxicity of salt stress on crops; the Bacillus halodurans can stably survive in a high-salt environment and create a low-osmotic-pressure microenvironment for other bacterial species; the Bacillus gellwangenensis can reduce the soil pH and activate the phosphorus and potassium elements fixed by the saline-alkali soil; the EPS can improve the aggregate structure and improve the water-retention and salt-repelling capacity.

[0032] The compound microbial agent in the application can effectively improve the survival capacity of the bacterial species in the saline-alkali soil through the synergistic effect of salt-tolerant, alkali-reducing and fertilizer-increasing of the three bacteria, and can improve the structure and fertility of the saline-alkali soil, so that the saline-alkali soil can be effectively improved.

[0033] The application further provides a preparation method of the saline-alkali soil biological improvement fertilizer.

[0034] (1) The element aid and the organic material are crushed, then mixed with the biochar and the humic acid according to the proportion, uniformly mixed, granulated and dried for standby use;

[0035] (2) The compound microbial agent is sprayed on the surface of the organic-inorganic composite carrier and left for 6-8 hours, then mixed with the material in step (1) to prepare the saline-alkali soil biological improvement fertilizer;

[0036] According to the total mass fraction of 100%, the mass percentage of each component in the saline-alkali soil biological improvement fertilizer is:

[0037] Compound microbial agent 8-12%

[0038] Organic-inorganic composite carrier 12-15%

[0039] Humic acid 8-12%

[0040] Element aid 15-20%

[0041] Biochar 10-15%

[0042] The balance is the organic material.

[0043] Finally, the application further provides the application of the saline-alkali soil biological improvement fertilizer in the improvement of the saline-alkali soil.

[0044] Advantages:

[0045] (1) The saline-alkali soil biological improvement fertilizer provided by the application can effectively improve the inclusion capacity of the carrier for the microbial agent and the tolerance of the microbial agent to the saline-alkali environment by loading the compound microbial agent on the organic-inorganic composite carrier and making the biological fertilizer, has excellent adsorption capacity, can effectively adsorb free sodium ions in the soil and fix them, thereby significantly reducing the salt concentration of the soil, improving the saline-alkali soil improvement efficiency and range, and can be widely applied in the field of improvement of saline-alkali soil by compound microbial fertilizer.

[0046] (2) The saline-alkali soil biological improvement fertilizer provided by the application has a synergistic effect of salt tolerance, alkali reduction and fertilizer increase by the three of Bacillus subtilis, halophilic Bacillus and jelly-like Bacillus, can effectively improve the survival ability of the strain in the saline-alkali soil, and can improve the structure and fertility of the saline-alkali soil, so that the saline-alkali soil can be effectively improved.

[0047] (3) The organic-inorganic composite carrier of the saline-alkali soil biological improvement fertilizer provided by the application grafts modified cyclodextrin on pretreated attapulgite, on the one hand, based on the excellent inclusion and adsorption capacity of the modified cyclodextrin, it can effectively adsorb and fix free sodium ions in the soil, improve the soil environment, and improve the tolerance and loading capacity of the strain, thereby improving the improvement efficiency; on the other hand, based on the porous structure and ion adsorption and replacement capacity of attapulgite, the loading effect of the strain and the soil improvement capacity can be further improved, so that it can be effectively applied in the loading of the strain.

[0048] (4) The saline-alkali soil biological improvement fertilizer provided by the application modifies cyclodextrin with an amino acid surfactant, on the one hand, it can enlarge the cavity volume and enhance the inclusion capacity, so that it can effectively load the microbial agent on the surface of the carrier and form a protective layer with a certain coating structure, thereby avoiding direct contact of the strain with the high-concentration environment of the saline-alkali soil and improving the survival rate; on the other hand, it can enhance the hydrophobicity of the cyclodextrin cavity, thereby improving the adsorption and inclusion capacity of the carrier for free sodium ions in the soil, reducing the salt concentration and improving the soil environment. (5) The saline-alkali soil biological improvement fertilizer provided by the application can not only improve the adsorption and loading capacity of cyclodextrin and attapulgite respectively, but also make the cyclodextrin graft uniformly and effectively on the surface of attapulgite, synergistically play the effects of ion exchange and inclusion fixation, and significantly improve the improvement efficiency and range of the material for saline-alkali soil. DETAILED DESCRIPTION

[0049] The present application will be described in detail below in conjunction with specific embodiments. It should be noted that the following examples are used to illustrate the present application and are not intended to limit the present application. Other combinations and various modifications within the concept of the present application can be made without departing from the spirit or scope of the present application.

[0050] The Bacillus subtilis MES 810 strain in the present application is preserved by the applicant in the China General Microbiological Culture Collection Center (CGMCC) on August 10, 2017, and the preservation number is CGMCC 14514;

[0051] It should be noted that the Bacillus subtilis strain in the present application has been proposed for patent application by the applicant, and the application number is 201710862006.3;

[0052] The Bacillus mucilaginosus MES 803 strain in the present application is preserved by the applicant in the China General Microbiological Culture Collection Center (CGMCC) on August 10, 2017, and the preservation number is CGMCC 14513;

[0053] It should be noted that the Bacillus mucilaginosus MES 803 strain in the present application has been proposed for patent application by the applicant, and the application number is 201710947727.4;

[0054] The Halobacillus salinus strain is purchased from the China General Microbiological Culture Collection Center (CGMCC), and the preservation date is September 17, 2008, and the preservation number is CGMCC 1.8606.

[0055] Preparation of amino acid surfactant

[0056] The amino acid surfactant is prepared by the following steps:

[0057] In a reactor, 0.05 mol of 4-phenylbutyryl chloride and 0.06 mol of oxalamic acid are added, a 15% mass concentration sodium hydroxide solution is added to adjust the pH to 11, and after stirring uniformly, the temperature is raised to 50°C, and after reaction for 8 hours, the temperature is cooled, a 35% mass concentration hydrochloric acid is added to adjust the pH to 1, and after filtration, washing and drying, the amino acid surfactant is prepared;

[0058] Mass spectrometry data of the amino acid surfactant: LC-MS was used to analyze the product, and the m / z of the product was 235.08 (100.0%), 236.15 (14.3%), and 237.06 (1.1%).

[0059] Preparation of the organic-inorganic composite carrier-1:

[0060] The organic-inorganic composite carrier-1 was prepared by the following steps:

[0061] (1) In a reactor, 1 g of the amino acid surfactant, 0.2 g of sodium hypophosphite, and 100 mL of deionized water were added, stirred until dissolved, and then 15 g of β-cyclodextrin was added and heated to 80°C. After 8 hours of incubation, the modified cyclodextrin was prepared by cooling, filtering, washing, and drying.

[0062] (2) In a reactor, 10 g of attapulgite and 100 mL of 50% mass concentration sulfuric acid were added, and after 8 hours of standing, the pretreated attapulgite was prepared by washing and drying, and then adding it to a 15% mass concentration sodium hydroxide solution, adjusting the pH to 11, and stirring at 60°C for 2 hours.

[0063] (3) In a reactor, 5 g of the pretreated attapulgite, 2 g of the modified cyclodextrin, and 100 mL of deionized water were added, heated to 60°C, and reacted for 24 hours. After cooling, filtering, washing, and drying, the organic-inorganic composite carrier-1 was prepared.

[0064] Preparation of the organic-inorganic composite carrier-2

[0065] The preparation of the organic-inorganic composite carrier-1 was basically the same, except that step (1) was not performed, and in step (3), the modified cyclodextrin was replaced with an equal amount of β-cyclodextrin.

[0066] Example 1

[0067] The saline-alkali soil biological improvement fertilizer was prepared by the following steps:

[0068] (1) Urea and wheat straw were crushed and mixed with biochar and humic acid in proportion, granulated and dried for use;

[0069] (2) The composite microbial agent was sprayed onto the surface of the organic-inorganic composite carrier-1 and allowed to stand for 8 hours. After mixing with the material of step (1), the saline-alkali soil biological improvement fertilizer was prepared.

[0070] The effective viable cell count ratio of Bacillus subtilis, Bacillus halophilus, and Bacillus mucosus in the composite microbial agent was 5:2:3

[0071] The effective viable cell count in the saline-alkali soil biological improvement fertilizer was 5×10 9 CFU / g;

[0072] The mass percentage of each component in the saline-alkali soil biological improvement fertilizer is 100% based on the total mass fraction:

[0073] Compound microbial agent 10%

[0074] Organic-inorganic composite carrier-1 15%

[0075] Humic acid 10%

[0076] Urea 20%

[0077] Biochar 15%

[0078] The balance is wheat straw.

[0079] Example 2

[0080] The saline-alkali soil biological improvement fertilizer is basically the same as in Example 1, except that the mass percentage of each component and its mass percentage in the saline-alkali soil biological improvement fertilizer is changed to:

[0081] Compound microbial agent 8%

[0082] Organic-inorganic composite carrier-1 12%

[0083] Humic acid 12%

[0084] Monammonium phosphate 15%

[0085] Biochar 12%

[0086] The balance is corn straw.

[0087] Example 3

[0088] The saline-alkali soil biological improvement fertilizer is basically the same as in Example 1, except that the mass percentage of each component and its mass percentage in the saline-alkali soil biological improvement fertilizer is changed to:

[0089] Compound microbial agent 12%

[0090] Organic-inorganic composite carrier-1 12%

[0091] Humic acid 8%

[0092] Urea 20%

[0093] Biochar 10%

[0094] The balance is wheat straw.

[0095] Comparative Example 1

[0096] The saline-alkali soil biological improvement fertilizer is basically the same as in Example 1, except that the organic-inorganic composite carrier-1 is changed to an equal amount of β-cyclodextrin.

[0097] Comparative Example 2

[0098] The same as Example 1, except that the organic-inorganic composite carrier-1 was replaced by an equal amount of attapulgite.

[0099] Comparative Example 3

[0100] The same as Example 1, except that the organic-inorganic composite carrier-1 was replaced by an equal amount of organic-inorganic composite carrier-2.

[0101] Comparative Example 4

[0102] The same as Example 1, except that the composite microbial agent was replaced by Bacillus subtilis with an effective viable count of 5x10 9 CFU / g.

[0103] Performance test

[0104] Tomato planting test was carried out in saline-alkali soil in Jiangsu coast: tomato fields with an area of 1 mu were selected, and 40 kg / 667 m 2 The products of Examples 1-3 and Comparative Examples 1-5 were added, and the control group was not added. After 3 days, the survival rate of the bacteria in the soil was detected; then the same water and fertilizer management was adopted, and the yield of tomatoes was counted after harvest. Parallel tests were set up, and the crop yield, soil total salt content and average soil pH of different test fields were detected.

[0105] The detection results are as follows:

[0106]

[0107] According to the comparison of the detection results of Examples 1-3 and the control group, the saline-alkali soil biological improvement fertilizer provided by the application not only can effectively improve the survival rate of bacteria in saline-alkali soil, but also has excellent adsorption capacity, can effectively adsorb free sodium ions in the soil and fix them, thereby significantly reducing the salt concentration of the soil, improving the improvement efficiency and range of saline-alkali soil, and can be widely applied in the field of improvement of saline-alkali soil by composite microbial fertilizer.

[0108] According to the comparison of the detection results of Examples 1-3 and Comparative Examples 1-2, the saline-alkali soil biological improvement fertilizer provided by the application can effectively improve the survival rate of bacteria in saline-alkali soil by grafting modified cyclodextrin on pretreated attapulgite as an organic-inorganic composite carrier, and can further improve the improvement effect of the biological improvement fertilizer on saline-alkali soil.

[0109] According to the comparison of the detection results of embodiments 1-3 and comparative example 4, the saline-alkali soil biological improvement fertilizer provided by the application can improve the tolerance of the strains and the improvement effect of the biological improvement fertilizer on the saline-alkali soil by surface modification of cyclodextrin with amino acid surfactant.

[0110] According to the comparison of the detection results of embodiments 1-3 and comparative example 5, the composite microbial agent in the saline-alkali soil biological improvement fertilizer provided by the application can form a synergistic effect of salt tolerance, alkali reduction and fertilizer increase by bacillus subtilis, halophilic bacillus and gelatin-like bacillus, which can effectively improve the survival ability of the strains in the saline-alkali soil, and can improve the structure and fertility of the saline-alkali soil, so as to effectively improve the saline-alkali soil.

[0111] The above embodiments are only for illustrating the technical concept and characteristics of the application, and the purpose is to enable those skilled in the art to understand the content of the application and implement it, and cannot limit the protection scope of the application. Any equivalent changes or modifications made according to the spirit and essence of the application should be covered within the protection scope of the application.

Claims

1. A biological fertilizer for improving saline-alkali soil, characterized in that, This includes compound microbial agents, organic-inorganic composite carriers, humic acid, elemental additives, biochar, and organic materials; The compound microbial agent includes Bacillus subtilis, Halophilic Bacillus salina, and Bacillus mucilaginosus; The organic-inorganic composite carrier is modified with amino acid surfactant to obtain modified cyclodextrin, and then the modified cyclodextrin is grafted onto pretreated attapulgite clay. The amino acid surfactant has the structure shown in Formula A: ； The specific preparation method of the organic-inorganic composite carrier is as follows: (1) In a reactor, add amino acid surfactant, catalyst and deionized water, stir until dissolved, then add β-cyclodextrin and heat to 70-80℃. After reacting at this temperature for 6-8 hours, cool, filter, wash and dry to obtain modified cyclodextrin. (2) Add attapulgite and sulfuric acid to the reactor, let stand for 6-8 hours, wash and dry, add it to sodium hydroxide solution, adjust the pH to 10-11, heat to 60-70℃ and stir for 2-3 hours to obtain pretreated attapulgite. (3) In the reactor, pretreated attapulgite, modified cyclodextrin and deionized water are added, heated to 50-60℃ and reacted for 18-24 hours. After cooling, filtering, washing and drying, the organic-inorganic composite carrier is obtained. In step (1), the catalyst is selected from either sodium hypophosphite or potassium hypophosphite.

2. The biological fertilizer for improving saline-alkali soil according to claim 1, characterized in that, The amino acid surfactant is prepared by the following steps: 4-phenylbutyryl chloride and oxalic acid are added to a reactor, sodium hydroxide solution is added to adjust the pH to 10-11, the mixture is stirred evenly and then heated to 40-50℃. After reacting for 8-12 hours, the mixture is cooled, hydrochloric acid is added to adjust the pH to 1-2, and the mixture is filtered, washed, and dried to obtain the amino acid surfactant. The mass concentration of the sodium hydroxide solution is 10-15%; The mass concentration of the hydrochloric acid is 30-40%; The molar ratio of 4-phenylbutyryl chloride to oxalic acid is 1:1.2-1.

5.

3. The biological fertilizer for improving saline-alkali soil according to claim 1, characterized in that, In step (1), the mass ratio of amino acid surfactant to β-cyclodextrin is 1:12-15.

4. The biological fertilizer for improving saline-alkali soil according to claim 1, characterized in that, In step (2), the mass concentration of sulfuric acid is 40-60%; the mass concentration of the sodium hydroxide solution is 10-15%.

5. The biological fertilizer for improving saline-alkali soil according to claim 1, characterized in that, In step (3), the mass ratio of pretreated attapulgite clay to modified cyclodextrin is (5-8):(2-3).

6. The biological fertilizer for improving saline-alkali soil according to claim 1, characterized in that, The elemental additive is selected from at least one of urea, monoammonium phosphate, potassium sulfate, and potassium chloride; the organic material is selected from at least one of wheat straw, corn straw, and shiitake mushroom residue.

7. The biological fertilizer for improving saline-alkali soil according to claim 1, characterized in that, The bio-fertilizer for improving saline-alkali soil contains no less than 5 × 10⁶ effective live bacteria. 9 CFU / g; The effective viable count ratio of Bacillus subtilis, Bacillus halophilus, and Bacillus mucilaginosus in the compound microbial agent is (3-5):(1-2):(2-3).

8. The method for preparing the bio-improved fertilizer for saline-alkali soil according to any one of claims 1-7, characterized in that, Includes the following steps: (1) After crushing the elemental additives and organic materials, mix them evenly with biochar and humic acid in proportion, granulate and dry for later use; (2) Spray the compound microbial agent onto the surface of the organic-inorganic composite carrier and let it stand for 6-8 hours. Mix it with the material in step (1) to obtain the saline-alkali soil biological improvement fertilizer. Based on a total mass fraction of 100%, the mass percentage of each component in the saline-alkali soil bio-improvement fertilizer is as follows: Compound microbial agent 8-12% Organic-inorganic composite carrier 12-15% Humic acid 8-12% Elemental additives 15-20% Biochar 10-15% The remainder is organic material.

9. The application of the saline-alkali soil biological amendment fertilizer according to any one of claims 1-7 in the improvement of saline-alkali soil.

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