Modified straw organic fertilizer for improving saline-alkali soil geology and fertility and preparation method thereof

Abstract

The invention belongs to the technical field of soil improvement, and relates to a modified straw organic fertilizer for improving saline-alkali soil geology and fertility and a preparation method thereof.Plant straw is modified with alkali liquor and a polyglutamic acid solution, and the water retention and ion exchange capacity of the plant straw are enhanced; potassium permanganate oxidized humic acid is compounded with chitosan, and humic acid-chitosan powder is obtained; then the complex microbial inoculant is coated by a microencapsulation technology, so that the survival ability of thalli in a high saline-alkaline environment is improved; meanwhile, soybean meal and rape seed cakes are subjected to enzymolysis pretreatment, and carbon and nitrogen nutrients easy to use are released; and finally, mixing the components according to an optimized proportion, and performing two-stage temperature-controlled fermentation to obtain a finished product. The fertilizer can effectively break soil hardening, continuously reduce salt harm, enhance soil microbial activity, promote granular structure formation and provide slow-release nutrients, and synergistic improvement of the soil structure, chemical properties and biological activity of the saline-alkali soil is achieved.

Description

Technical Field

[0001] This invention belongs to the technical field of soil improvement, and relates to a modified straw organic fertilizer for improving the fertility of saline-alkali land and its preparation method. Background Technology

[0002] Saline-alkali land is a global soil degradation problem characterized by the presence of soluble salts (such as Na+) in the soil. + Cl - Excessive accumulation of alkaline substances (such as sodium carbonate) leads to an increase in soil pH (usually >8.5), resulting in soil compaction, poor aeration and permeability, low organic matter content, and inhibited microbial activity, ultimately causing reduced crop yields or even crop failure. While existing methods for improving saline-alkali land and the use of organic fertilizers have some effect, they still have many shortcomings: Current technologies often employ physical measures such as deep plowing, turning, and drainage to wash away salt. While these can temporarily reduce surface salinity, they involve large-scale engineering, high costs, and the effects are not lasting. Salt easily rises back to the surface with water movement, leading to a "salinization" phenomenon, which cannot fundamentally improve soil structure. Furthermore, physical methods fail to provide the soil with the necessary organic matter and nutrients, thus having a limited effect on improving soil fertility.

[0003] Current technologies commonly use chemical amendments such as gypsum, phosphogypsum, and sulfur to reduce soil pH and sodium ion content through ion exchange or neutralization reactions. However, long-term use of these chemicals may lead to the loss of beneficial ions such as calcium and magnesium from the soil, causing secondary pollution and exacerbating soil compaction. Furthermore, chemical amendments cannot provide the necessary nutrient environment for soil microorganisms, thus contributing little to the restoration of the soil ecosystem.

[0004] While traditional organic fertilizers (such as farmyard manure and direct straw return to the field) can increase soil organic matter, their effects are poor in saline-alkali soils. Untreated straw decomposes slowly and may even exacerbate the imbalance of soil carbon-nitrogen ratio in high-salt environments, attracting salt accumulation and further reducing microbial activity. In addition, traditional organic fertilizers have poor water and fertilizer retention capacity and cannot effectively adsorb and fix sodium ions, thus having limited effect on improving soil structure.

[0005] Microbial fertilizers containing beneficial bacteria (such as Bacillus and Actinomycetes) can theoretically promote soil health. However, the high salinity and high pH environment of saline-alkali soils severely inhibit or kill microorganisms, leading to inactivation of the microbial agents. Existing microbial fertilizers lack effective protection mechanisms, resulting in low survival rates and weak colonization capabilities of the microorganisms in the soil, thus failing to exert a sustained soil-improving effect.

[0006] Some existing compound fertilizers attempt to integrate multiple components, but often lack specific design for saline-alkali soils. For example, while ordinary humic acid fertilizers can improve soil structure, their ion exchange capacity and sodium ion adsorption efficiency are insufficient in saline-alkali soils; and some fertilizers with added microbial agents are ineffective under high salt stress because they do not consider the issue of microbial protection. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a modified straw organic fertilizer for improving the fertility of saline-alkali land and its preparation method, specifically including the following steps: Step 1: Crush the plant straw into 1-2cm pieces, wash with deionized water 3-5 times to remove dust, mud, and soluble impurities, dry at 60-70℃ until the moisture content is <10%, then mix with alkaline solution and soak at 50-60℃ for 2.5-3 hours to destroy the lignin and cellulose structure, increase the specific surface area and reactivity, filter, remove the filtrate, wash the filter residue with deionized water until the washing liquid is neutral, then mix with a 2-3% polyglutamic acid solution and soak at 60-70℃ for 2.5-3 hours. Polyglutamic acid is a natural, biodegradable polymer that tightly wraps the surface of straw fibers through hydrogen bonds and van der Waals forces, introducing a large number of carboxyl and amino functional groups. This modification process greatly enhances the water retention capacity and ion exchange capacity of straw, enabling it to effectively adsorb and fix sodium ions in saline-alkali soil, while slowly releasing water, breaking up soil compaction, filtering, removing filtrate, and drying the filter residue at 50-60℃ to a moisture content of <8%, thus obtaining modified straw.

[0008] Preferably, the plant straw includes one or more of soybean straw, wheat straw, peanut straw, rice straw, and corn straw. Most preferably, the plant straw is rice straw and corn straw, with a mass ratio of (1-3):(1-3).

[0009] Preferably, the mass ratio of the plant straw, alkali solution and polyglutamic acid solution is 1:(5-6):(5-6).

[0010] Preferably, the alkaline solution is a sodium hydroxide solution or potassium hydroxide solution with a mass fraction of 0.8-1.0%.

[0011] Step 2: Mix humic acid with a 0.4-0.6% (w / w) potassium permanganate solution and react at 35-45℃ for 1-2 hours. Potassium permanganate acts as an oxidant, increasing the content of carboxyl and phenolic hydroxyl groups in the humic acid molecules, enhancing its ion exchange and complexing capacity, thereby better adsorbing sodium ions and heavy metals in saline-alkali soil. After the reaction, filter the mixture. Wash the filter residue with deionized water and mix it with a chitosan solution. Stir at 55-65℃ and 100-200 rpm for 1.5-2.5 hours. Chitosan binds to humic acid through electrostatic interactions and hydrogen bonds, introducing amino functional groups to form a humic acid-chitosan complex. This complex not only enhances the selective adsorption and slow-release performance of humic acid for specific ions in saline-alkali soil, but also utilizes the film-forming properties of chitosan to provide a better protective carrier for subsequent microbial agents. After stirring, filter the mixture. Dry the filter residue at 60-70℃ until the moisture content is ≤8%, and pulverize it to 80-120 mesh to obtain humic acid-chitosan powder.

[0012] Preferably, the mass ratio of the humic acid, potassium permanganate solution, and chitosan solution is 1:(3-4):(5-6). Most preferably, the chitosan solution comprises chitosan, acetic acid, and water in a mass ratio of (1-2):(1-2):100.

[0013] Step 3: After activating and culturing the compound bacterial powder, the bacterial cells are collected by centrifugation at 8000-10000 rpm. Then, the mixture is combined with sodium alginate, humic acid-chitosan powder, and water, and spray-dried (inlet temperature 115-125℃, outlet temperature 50-60℃) to obtain compound bacterial powder microcapsules. The outer shell of these microcapsules is composed of sodium alginate and humic acid-chitosan. The addition of humic acid-chitosan significantly enhances the mechanical strength and stability of the microcapsules and provides additional protection for the microorganisms using its functional groups, greatly improving the survival rate, colonization ability, and sustained-release properties of the bacteria under high salinity and alkalinity stress.

[0014] Preferably, the bacterial cells, sodium alginate, humic acid-chitosan powder, and water are in a mass ratio of (0.8-1.2):(0.1-0.2):(0.02-0.03):10.

[0015] Preferably, the activation culture is performed by resuspending the compound bacterial powder in an activation culture medium to a concentration of 60-80 mg / mL, and then incubating at 35-39°C with shaking at 100-150 rpm for 10-14 hours. Most preferably, the activation culture medium, based on water, comprises 0.4-0.6% glucose, 0.1% yeast extract, and 0.04-0.06% potassium dihydrogen phosphate.

[0016] Preferably, the compound bacterial powder is Bacillus subtilis powder, Bacillus megaterium powder and Bacillus jellyoides powder, with a mass ratio of (1-3):(1-3):(1-3).

[0017] Step 4: Crush soybean meal and rapeseed cake into 2-4 mm particles, then soak them in a 70-75% (v / v) ethanol solution at 50-60°C for 2-3 hours. The ethanol removes oil and soluble anti-nutritional factors. After soaking, rinse with deionized water to remove any remaining ethanol. Then mix with a compound enzyme solution and enzymatically hydrolyze at 40-50°C for 2.5-3.5 hours. The enzyme degrades the cellulose and hemicellulose in the soybean meal and rapeseed cake, releasing more soluble sugars and amino acids, thus enhancing their value as a microbial carbon and nitrogen source. After the reaction is complete, filter the mixture and dry the filter residue at 40-50°C for 1-2 hours to obtain enzymatically hydrolyzed soybean meal-rapeseed cake.

[0018] Preferably, the mass ratio of soybean meal, rapeseed cake, ethanol solution, and compound enzyme solution is (4-6):(2-4):(25-30):(30-40). Most preferably, the compound enzyme solution comprises, based on water, 0.4-0.6% by mass of cellulase, 0.3-0.5% by mass of xylanase, and 0.5-0.7% by mass of protease.

[0019] Step 5: Mix the modified straw, compound microbial powder microcapsules, and enzymatically hydrolyzed soybean meal-rapeseed cake at a mass ratio of (30-40):(10-15):(15-20) until homogeneous. Stir at 60-90 rpm for 25-35 minutes. Pile the mixture into a fermentation pile 1-1.5m high, adjust the moisture content to 55-60%, and ferment at 55-60℃ for 2-3 days, turning the pile once a day. This stage mainly utilizes thermophilic microorganisms to rapidly degrade easily decomposable organic matter and kill potential pathogens. Simultaneously, the water-retaining properties of polyglutamic acid in the modified straw effectively maintain the humidity of the internal microenvironment of the pile, ensuring the smooth progress of high-temperature fermentation. Continue fermenting at 45-50℃ for 3-4 days. This stage is crucial for the large-scale formation of humus and the optimization of the microbial community structure. Due to the protection of the microcapsule shell and ample food, microorganisms multiply rapidly and secrete extracellular polymers during this stage, further cross-linking with other components to form a stable, loose aggregate structure precursor. After fermentation, the material is dried at 35-38°C until the moisture content is ≤12%, and then made into 2-4mm granules to obtain the finished organic fertilizer.

[0020] The present invention has the following advantages: (1) Significantly improves soil structure, breaks up compaction, and enhances water retention capacity. This invention modifies straw with polyglutamic acid, introducing a large number of carboxyl and amino functional groups, giving the straw fibers super water retention capacity and ion exchange capacity. This modified straw can effectively adsorb and fix sodium ions in saline-alkali soil, while slowly releasing water, continuously breaking up soil compaction and improving soil porosity and aeration. Compared with unmodified straw, the fertilizer of this invention can maintain soil microenvironment humidity for a long time, promote the formation of aggregate structure, and thus create favorable conditions for plant root growth.

[0021] (2) Efficient adsorption and immobilization of salt ions, reducing the harm of salt: The humic acid-chitosan complex in this invention, through potassium permanganate oxidation treatment, increases the content of carboxyl and phenolic hydroxyl groups in the humic acid molecules, significantly enhancing its complexing and adsorption capacity for sodium ions and heavy metal ions. The introduction of chitosan further improves the selectivity and slow-release performance of the complex, enabling the fertilizer to target and adsorb harmful ions in saline-alkali soil and slowly release nutrients, preventing soil salinity from rising again. This advantage ensures that the fertilizer will not cause negative effects during long-term use and can sustainably reduce soil conductivity and pH.

[0022] (3) Significantly improves the survival rate and colonization capacity of microorganisms, and activates the soil ecosystem. This invention uses microencapsulation technology to encapsulate compound bacterial powder (Bacillus subtilis, Bacillus megaterium, etc.) in a sodium alginate and humic acid-chitosan shell, which significantly enhances the mechanical strength and stability of the bacterial cells. This microencapsulation structure can effectively protect microorganisms from high salt and high alkali stress, ensuring the survival, reproduction and colonization of the microorganisms in the soil. At the same time, the humic acid-chitosan shell provides additional nutrition and protection for microorganisms, further improving their ability to secrete extracellular polymers and promote soil aggregation, thereby activating the entire soil microbial community and accelerating the decomposition of organic matter and nutrient cycling.

[0023] (4) Accelerating nutrient release and improving fertilizer utilization efficiency: This invention pre-degrades cellulose, hemicellulose, and protein in soybean meal and rapeseed cake through enzymatic hydrolysis, releasing a large amount of soluble sugars and amino acids. These readily available carbon and nitrogen sources not only provide high-quality nutrition for microorganisms but also promote rapid mineralization and nutrient release of fertilizer in the soil. Compared with unhydrolyzed raw materials, the fertilizer of this invention can be utilized by plants and microorganisms more quickly, significantly improving the bioavailability of nutrients such as nitrogen, phosphorus, and potassium, and reducing fertilizer waste.

[0024] 5) Achieving synergistic effects of multiple components for sustained improvement of saline-alkali land: This invention mixes modified straw, compound microbial powder microcapsules, and enzymatically hydrolyzed soybean meal-rapeseed cake in an optimized ratio, and uses a two-step fermentation process to ensure full cross-linking and synergistic effects of each component during fermentation. During fermentation, thermophilic microorganisms rapidly degrade organic matter and kill pathogens, while the water-retention properties of the modified straw maintain the moisture content of the compost pile, ensuring smooth fermentation. The subsequent low-temperature fermentation stage promotes the formation of a large amount of humus and the optimization of the microbial community, ultimately forming a stable, loose aggregate structure precursor. This multi-component, multi-stage design enables the fertilizer to continuously improve the physical, chemical, and biological properties of the soil after application, achieving long-term improvement and fertility enhancement of saline-alkali land. Detailed Implementation

[0025] The technical solutions in the embodiments of the invention are described clearly and completely below. 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.

[0026] Example 1 Raw material preparation: Plant straw: rice straw and corn straw, in a mass ratio of 2:1.

[0027] Chitosan solution: chitosan, acetic acid and water in a mass ratio of 1:1:100.

[0028] Compound bacterial powder: Bacillus subtilis powder (purchased from Jinan Yucai Chemical Co., Ltd.), Bacillus megaterium powder (purchased from Weifang Yihao Biotechnology Co., Ltd.), and Bacillus jellyoides powder (purchased from Shandong Yihao Biotechnology Co., Ltd.), with a mass ratio of 3:1:2.

[0029] Activation medium: water-based, consisting of 0.5% glucose, 0.1% yeast extract (purchased from Guangzhou Huayu Biotechnology Co., Ltd.), and 0.05% potassium dihydrogen phosphate.

[0030] Complex enzyme solution: 0.5% cellulase, 0.4% xylanase, and 0.6% protease.

[0031] Preparation method: Step 1: The mass ratio of plant straw, sodium hydroxide solution, and polyglutamic acid solution is 1:5:5.

[0032] Plant straw was crushed into 1-2 cm pieces, washed four times with deionized water, and dried at 65°C until the moisture content was <10%. Then it was mixed with a 0.9% sodium hydroxide solution and soaked at 55°C for 2.75 h. After filtration, the filtrate was removed, and the residue was washed with deionized water until the washing liquid was neutral. Then it was mixed with a 2.5% polyglutamic acid solution and soaked at 65°C for 2.75 h. After filtration, the filtrate was removed, and the residue was dried at 55°C until the moisture content was <8%, thus obtaining modified straw.

[0033] Step 2: The mass ratio of humic acid, potassium permanganate solution, and chitosan solution is 1:4:5.

[0034] Humic acid was mixed with a 0.5% potassium permanganate solution and reacted at 40°C for 1.5 hours. After the reaction was completed, the mixture was filtered. The filter residue was washed with deionized water and then mixed with chitosan solution. The mixture was stirred at 60°C and 150 rpm for 2 hours. After stirring, the mixture was filtered and the filter residue was dried at 65°C until the moisture content was ≤8%. The residue was then pulverized to 100 mesh to obtain humic acid-chitosan powder.

[0035] Step 3: The bacterial cells, sodium alginate, humic acid-chitosan powder, and water are mixed in a mass ratio of 1:0.15:0.025:10.

[0036] The compound bacterial powder was resuspended in the activation medium to make the concentration of the compound bacterial powder 70 mg / mL of the medium. It was cultured at 37℃ and 125 rpm for 12 h with shaking. The bacterial cells were collected by centrifugation at 9000 rpm and then mixed with sodium alginate, humic acid-chitosan powder and water. The mixture was then spray-dried (inlet temperature 120℃, outlet temperature 55℃) to obtain compound bacterial powder microcapsules.

[0037] Step four, the mass ratio of soybean meal, rapeseed cake, ethanol solution and compound enzyme solution is 5:3:27:35.

[0038] Soybean meal and rapeseed cake were crushed into 2-4 mm particles, then soaked in 75% ethanol solution at 55°C for 2.5 h, then mixed with a compound enzyme solution and enzymatically hydrolyzed at 45°C for 3 h. After the reaction was completed, the mixture was filtered and the filter residue was dried at 45°C for 1.5 h to obtain enzymatically hydrolyzed soybean meal-rapeseed cake.

[0039] Step 5: Mix the modified straw, compound microbial powder capsules, and enzymatically hydrolyzed soybean meal-rapeseed cake at a mass ratio of 35:13:18. Stir at 75 rpm for 30 minutes. Pile the mixture into a fermentation pile 1.5m high, adjust the moisture content to 57%, and ferment at 58℃ for 3 days, turning the pile once a day. Then ferment at 57℃ for another 4 days. After fermentation, dry the material at 36°C until the moisture content is ≤12% and make it into 2-4mm granules to obtain the finished organic fertilizer.

[0040] Experimental Example 1 Soil samples were collected from the top 0-20 cm layer of a typical saline-alkali area in the local region. Basic properties: pH 9.2, EC value 4.8 dS / m, organic matter content 5.2 g / kg.

[0041] Test fertilizer: Experimental group: prepared according to the method in Example 1.

[0042] Control group: Unmodified straw and ordinary humic acid (mass ratio 3:1).

[0043] Blank group: No fertilizer was applied.

[0044] Test plants: such as sunflower seeds.

[0045] Experimental Procedure: The collected saline-alkali soil was air-dried, pulverized, and sieved through a 2mm sieve. 500g of soil sample was weighed into a plastic basin (three replicates per treatment). 5g of organic fertilizer was applied to each basin, and the soil moisture content was adjusted to 30%. The basins were placed in a 25℃ constant temperature incubator for 30 days. The soil was weighed weekly, and deionized water was added weekly to maintain a constant moisture content. Soil samples were collected at the beginning (day 0) and end (day 30) of the incubation period for the following analysis. The results are shown in Table 1: pH value: The soil-to-water ratio was 1:2.5, and the pH value was measured using a pH meter.

[0046] EC value: The soil-to-water ratio is 1:5, and the value is measured using a conductivity meter.

[0047] Organic matter content: determined by potassium dichromate oxidation method.

[0048] Soil aggregate stability: Mean weight diameter (MWD) was calculated using the wet sieving method.

[0049] Microbial count: Bacteria, fungi, and actinomycetes (CFU / g) were counted using the dilution plate method.

[0050] Using the same soil and fertilization treatments, each treatment was replicated in 5 groups. Ten sunflower seeds were sown in each pot, and after emergence, seedlings were thinned to 5 plants per pot. The plants were cultured in a greenhouse for 60 days (temperature 25℃, light 12h / d), with regular watering to maintain soil moisture. After the culture period, the following parameters were measured, and the results are shown in Table 2: Plant height and root length: Measured using a ruler.

[0051] Plant biomass: Harvest the aboveground parts and roots, dry them at 65℃ to constant weight, and weigh the dry weight.

[0052] Soil nutrient content: The contents of available nitrogen, available phosphorus, and available potassium were determined.

[0053] Soil enzyme activity: Measurement of urease and phosphatase activity (reflecting microbial metabolic activity).

[0054] Table 1. Results of soil incubation experiment (30 days)

[0055] Note: Bacteria are mainly growth-promoting bacteria with phosphorus-solubilizing, potassium-solubilizing, and nitrogen-fixing functions, including but not limited to Bacillus subtilis, Bacillus megaterium, and gelatinous Bacillus; fungi are mainly cellulose-decomposing bacteria involved in the decomposition of organic matter, such as Trichoderma and Aspergillus. Actinomycetes are mainly species that produce antibiotics and promote humus formation, such as Streptomyces.

[0056] Table 2. Results of the potted plant experiment (60 days)

[0057] As shown in Tables 1-2, the fertilizer of this invention significantly reduced soil pH and EC values, indicating its effective neutralization of alkalinity and adsorption of salts. The increased organic matter content and aggregate stability are attributed to the water retention capacity of the modified straw and the ion exchange capacity of the humic acid-chitosan complex. The microencapsulated microbial agent protected beneficial microorganisms, leading to a significant increase in the number of bacteria, fungi, and actinomycetes, thus enhancing the vitality of the soil ecosystem. The experimental group exhibited the highest plant height, root length, and biomass, confirming that the fertilizer provided sufficient nutrients and a favorable rhizosphere environment. Enzymatic hydrolysis of soybean meal and rapeseed cake promoted rapid nutrient mineralization, significantly increasing the content of alkaline-hydrolyzed nitrogen, available phosphorus, and available potassium.

[0058] The modified straw organic fertilizer prepared by this invention exhibits remarkable improvement effects in both physicochemical properties (salt-alkali reduction, nutrient enhancement, and structural modification) and biological properties (microbial promotion and enzyme activity enhancement) through the synergistic effect of multiple components, ultimately significantly promoting the growth of plants on saline-alkali land. Experimental data fully demonstrate its superior comprehensive improvement capabilities and application potential.

[0059] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing modified straw organic fertilizer to improve the fertility of saline-alkali land, characterized in that, Includes the following steps: Step 1: Crush the plant straw, wash it, dry it until the moisture content is <10%, mix it with alkaline solution and soak it, filter it, remove the filtrate, wash the filter residue with water, then mix it with polyglutamic acid solution and soak it, filter it, remove the filtrate, dry the filter residue until the moisture content is <8%, and obtain modified straw. Step 2: Mix humic acid with potassium permanganate solution and react at 35-45℃ for 1-2 hours. Filter the mixture, wash the residue with deionized water, mix and stir it with chitosan solution, filter the mixture, dry the residue to a moisture content of ≤8%, and pulverize it to obtain humic acid-chitosan powder. Step 3: After activating and culturing the compound bacterial powder, the bacterial cells are collected by centrifugation, and then mixed with sodium alginate, humic acid-chitosan powder and water, and spray-dried to obtain compound bacterial powder microcapsules. Step 4: Crush soybean meal and rapeseed cake, then soak them in ethanol solution. After soaking, rinse off the ethanol residue with deionized water, then mix with compound enzyme solution and enzymatically hydrolyze at 40-50℃ for 2.5-3.5 hours. After the reaction is complete, filter and dry the filter residue to obtain enzymatically hydrolyzed soybean meal-rapeseed cake. Step 5: Mix the modified straw, compound microbial powder capsules, and enzymatically hydrolyzed soybean meal-rapeseed cake in a mass ratio of (30-40):(10-15):(15-20), stir, adjust the moisture content to 55-60%, ferment at 55-60℃ for 2-3 days, turning the pile once a day, and then ferment at 45-50℃ for 3-4 days. After fermentation, dry the material to a moisture content of ≤12%, granulate, and obtain the finished organic fertilizer product.

2. The method for preparing modified straw organic fertilizer to improve the fertility of saline-alkali land according to claim 1, characterized in that, The mass ratio of plant straw, alkali solution and polyglutamic acid solution in step one is 1:(5-6):(5-6).

3. The method for preparing modified straw organic fertilizer to improve the fertility of saline-alkali land according to claim 1, characterized in that, The alkaline solution mentioned in step one is a sodium hydroxide solution or potassium hydroxide solution with a mass fraction of 0.8-1.0%.

4. The method for preparing modified straw organic fertilizer to improve the fertility of saline-alkali land according to claim 1, characterized in that, The mass ratio of humic acid, potassium permanganate solution and chitosan solution in step two is 1:(3-4):(5-6).

5. The method for preparing modified straw organic fertilizer to improve the fertility of saline-alkali land according to claim 1, characterized in that, The chitosan solution in step two comprises chitosan, acetic acid, and water in a mass ratio of (1-2):(1-2):

100.

6. The method for preparing modified straw organic fertilizer to improve the fertility of saline-alkali land according to claim 1, characterized in that, In step three, the bacterial cells, sodium alginate, humic acid-chitosan powder, and water are mixed in a mass ratio of (0.8-1.2):(0.1-0.2):(0.02-0.03):

10.

7. The method for preparing modified straw organic fertilizer to improve the fertility of saline-alkali land according to claim 1, characterized in that, The activation culture operation described in step three involves resuspending the compound bacterial powder in the activation culture medium to a concentration of 60-80 mg / mL of the culture medium, and then incubating at 35-39℃ and 100-150 rpm for 10-14 hours with shaking.

8. The method for preparing modified straw organic fertilizer to improve the fertility of saline-alkali land according to claim 1, characterized in that, The mass ratio of soybean meal, rapeseed cake, ethanol solution and compound enzyme solution in step four is (4-6):(2-4):(25-30):(30-40).

9. The method for preparing modified straw organic fertilizer to improve the fertility of saline-alkali land according to claim 1, characterized in that, The complex enzyme solution described in step four, based on water, comprises 0.4-0.6% cellulase, 0.3-0.5% xylanase, and 0.5-0.7% protease by mass fraction.

10. Organic fertilizer prepared by the method according to any one of claims 1-9.

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