Straw-based biochar composite slow-release fertilizer for saline-alkali soil improvement and preparation method of straw-based biochar composite slow-release fertilizer

Abstract

The invention belongs to the technical field of organic fertilizers, and particularly relates to a straw-based biochar composite slow-release fertilizer for saline-alkali soil improvement and a preparation method of the straw-based biochar composite slow-release fertilizer. The preparation method comprises the following steps: (1) uniformly mixing sheep manure and pigeon manure, mixing the mixed manure with crushed corn straw to obtain a total material, inoculating bacillus subtilis, and composting and fermenting to obtain a primary organic matter; (2) fermenting the primary organic matter by using aspergillus niger, trichoderma reesei and saccharomyces cerevisiae to obtain a submerged fermentation organic matter; (3) crushing the submerged fermentation organic matter to prepare particles; the composite coating powder is scattered into the submerged fermentation organic matter, coating is conducted, and the coated organic matter is obtained; and (4) uniformly mixing the coated fermented organic matter, biochar, desulfurized gypsum, humus soil, a water-retaining agent and ammonium dihydrogen phosphate to obtain the straw-based biochar composite slow-release fertilizer for saline-alkali soil improvement. The organic fertilizer can improve the pH value of saline-alkali soil, reduce the salt content and increase the organic matter content.

Description

A straw-based biochar compound slow-release fertilizer for saline-alkali land improvement and its preparation method Technical Field

[0001] This invention belongs to the field of organic fertilizer technology, specifically relating to a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement and its preparation method. Background Technology

[0002] Saline-alkali land is one of my country's important marginal land resources. Its soil is characterized by high pH, ​​high salinity, compacted structure, and nutrient deficiency, severely restricting normal crop growth and the sustainable development of agricultural production. In recent years, the use of organic materials to improve saline-alkali land has become a research hotspot. Corn stalks and livestock manure, as abundant and inexpensive agricultural waste resources, are widely used to prepare organic fertilizers to improve soil physical and chemical properties and enhance soil fertility.

[0003] However, in practical applications, the use of corn stalks and livestock manure faces numerous technical bottlenecks. First, corn stalks are rich in lignin and cellulose, making them difficult to degrade and requiring a long natural composting period. Without effective pretreatment, they are difficult to fully decompose during conventional composting, resulting in a large amount of undecomposed coarse fiber remaining in the compost product, affecting fertilizer release and soil integration. Second, while livestock manure is rich in nitrogen and organic matter, it suffers from insufficient maturity, inadequate acid production during fermentation, and an inability to effectively neutralize the alkalinity of saline-alkali soils. Furthermore, it lacks the targeted conversion of active components.

[0004] Chinese patent CN120247628A describes a special cow manure organic fertilizer for saline-alkali land and its preparation method, which can improve the performance of saline-alkali land. However, traditional organic fertilizers are mostly applied in the form of exposed granules or powder, lacking an effective coating structure. This type of uncoated fertilizer has obvious defects in saline-alkali environments: on the one hand, its nutrients are easily leached away by irrigation water, making it difficult to achieve slow-release supply under high-salt and high-alkali conditions; on the other hand, uncoated organic particles cannot effectively isolate salt ions, and after rapid dispersion in the soil, they may aggravate local salt accumulation and weaken the improvement effect. Summary of the Invention

[0005] The purpose of this invention is to provide a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement and its preparation method.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement, comprising the following steps: (1) mixing sheep manure and pigeon manure evenly, crushing corn straw, mixing the mixed manure with the crushed corn straw to obtain total material, inoculating with Bacillus subtilis, composting and fermenting to obtain primary organic matter; (2) fermenting the primary organic matter from step (1) with Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae to obtain deep fermented organic matter; (3) crushing the deep fermented organic matter from step (2) into granules; sprinkling composite coating powder into the deep fermented organic matter, coating to obtain coated organic matter; (4) mixing the coated fermented organic matter from step (3), biochar, desulfurized gypsum, humus, water-retaining agent, and ammonium dihydrogen phosphate evenly to obtain a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement.

[0007] Preferably, the corn stalks are crushed using a shredder until they pass through a 20-mesh sieve.

[0008] This invention uses a specific strain for two-stage fermentation. The first fermentation uses Bacillus subtilis, which efficiently decomposes cellulose in corn stalks and nitrogenous organic matter in feces. The second fermentation uses a complex of Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae, which work together to degrade insoluble components. The dual fermentation improves the conversion rate of organic matter, helps to lower the pH of saline-alkali land, and also helps to reduce salinity.

[0009] Preferably, in step (1), by weight, the proportions are: 20-25 parts sheep manure, 10-15 parts pigeon manure, and 15-20 parts corn stalks.

[0010] Preferably, in step (1), Bacillus subtilis is inoculated at an inoculation amount of 0.5% of the total material mass.

[0011] Preferably, in step (1), composting is carried out at 25-35℃ for 15-20 days. When the internal temperature of the pile exceeds 50℃, it is turned over immediately; if the threshold is not reached, it is turned over once every 3 days.

[0012] Preferably, the three strains of Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae used in step (2) are in an effective viable count ratio of 1:(1-1.2):(0.4-0.6).

[0013] This invention uses waste materials to construct a slow-release barrier, using cassava starch residue, soybean meal powder, and kelp polysaccharide waste as coating powders to form a porous film structure. This not only prevents the rapid leaching of organic acids and nutrients but also provides channels for ion exchange. The coating layer extends the release cycle of active components, achieving a long-term synergistic effect of reducing salt content, conserving fertilizer, and improving structure, thus solving the problem of easy rebound in the improvement effect of saline-alkali land.

[0014] Preferably, 2-3 parts of cassava starch residue, 0.5-1 part of soybean meal powder, and 0.3-0.5 parts of kelp polysaccharide are mixed evenly to prepare a composite coating powder. The amount of the composite coating powder used is 3%-8% of the mass of the deep-fermented organic matter.

[0015] The coating powder raw materials used in this invention are all industrial by-products. Cassava starch residue is waste from cassava processing, soybean meal powder comes from filter residue in the brewing industry, and kelp polysaccharide is a by-product of seaweed food / pharmaceutical processing. Traditional treatment methods for these wastes mainly involve landfilling and incineration, which not only occupy land but also easily cause leachate pollution and air pollution. This invention uses them as the core raw material for the coating powder, significantly improving resource utilization. Furthermore, its coating effect is superior to that of commonly used raw materials in existing technologies.

[0016] Preferably, by weight, 45-55 parts of coated fermented organic matter, 6-8 parts of biochar, 8-12 parts of desulfurized gypsum, 10-15 parts of humus, 0.3-0.8 parts of water-retaining agent, and 1-3 parts of ammonium dihydrogen phosphate are mixed evenly to obtain a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement.

[0017] Preferably, in step (2), the fermentation temperature is controlled at 28-32℃, an intermittent ventilation mode is adopted, the air volume is 324-648m³ / h, and the process is carried out for 5-10 minutes, then stopped for 50-60 minutes, for continuous solid-state fermentation for 5-7 days.

[0018] The preparation method described above produces a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement.

[0019] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: 1. The present invention uses a gradient two-stage fermentation with specific strains. The first fermentation uses Bacillus subtilis, which efficiently decomposes corn stalk cellulose and nitrogen-containing organic matter in feces. The second fermentation uses a complex strain of Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae, which work together to degrade insoluble components. The dual fermentation improves the conversion rate of organic matter, helps to lower the pH of saline-alkali land, and also helps to reduce salt content.

[0020] 2. This invention uses waste materials to construct a slow-release barrier, forming a porous membrane structure that prevents rapid leaching of organic acids and nutrients while providing channels for ion exchange. The coating layer extends the release period of active components, achieving a long-term synergistic effect of salt reduction, fertilizer retention, and structural improvement, thus solving the problem of easy rebound in the improvement effect of saline-alkali land.

[0021] 3. The coating powder raw materials used in this invention are all industrial by-products. Traditional treatment methods for these wastes mainly involve landfilling and incineration, which not only occupy land but also easily cause leachate pollution and air pollution. This invention uses them as the core raw material for coating powder, significantly improving resource utilization. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described 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.

[0023] The raw materials used in the following embodiments of the present invention are all commercially available products: water-retaining agent: model PY-7050, from Shuangcheng Chemical Products Factory, Renqiu City.

[0024] Biochar: Corn stalk biochar, 20 mesh, Henan Lanri Environmental Protection Co., Ltd.

[0025] Bacillus subtilis: strain number: ZKCC10117, Beijing Zhongke Quality Inspection Biotechnology Co., Ltd.

[0026] Aspergillus niger: strain number: ZKCC13077, Beijing Zhongke Quality Inspection Biotechnology Co., Ltd.

[0027] Trichoderma reesei: Strain number: ZKCC12990, Beijing Zhongke Quality Inspection Biotechnology Co., Ltd.

[0028] Saccharomyces cerevisiae: strain number: ZKCC15672, Beijing Zhongke Quality Inspection Biotechnology Co., Ltd.

[0029] Cassava starch residue: Beibu Gulf soybean residue supplier, moisture content 3wt%, 80 mesh.

[0030] Soybean meal powder: A powdery substance made from soybean meal, 80 mesh.

[0031] Kelp polysaccharide: Shanghai Shifeng Biotechnology Co., Ltd.

[0032] Desulfurized gypsum: Hubei Puhui Building Materials Co., Ltd., passed through a 325-mesh sieve.

[0033] Humus soil: Harbin Qingwomeng Agricultural Technology Co., Ltd.

[0034] Bacillus pumilus: strain number: ZKCC16577, Beijing Zhongke Quality Inspection Biotechnology Co., Ltd.

[0035] *Procambarus chrysosporus*: No. BNCC189286, Beina Chuanglian Biotechnology Co., Ltd.

[0036] Candida tropicalis: Product code: BNCC335988, Beina Chuanglian Biotechnology Co., Ltd.

[0037] Example 1 This example provides a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement. The preparation method includes the following steps: by mass parts, (1) 23 parts sheep manure and 12 parts pigeon manure are mixed evenly, and 18 parts corn straw are crushed to pass through a 20-mesh sieve using a crusher. The mixed manure and the crushed corn straw are mixed to obtain the total material, which is placed in a fermentation container and stirred evenly. The moisture content is adjusted to 62 wt% of the total material mass. Bacillus subtilis is inoculated at an inoculation rate of 0.5% of the total material mass. The compost is fermented at 30°C. 18 days. When the internal temperature of the pile exceeds 50°C, turn it over immediately. If the threshold is not reached, turn it over once every 3 days. After fermentation, adjust the pH to 7.0 with wood ash, spread the material out to a thickness of 18cm, ventilate naturally for 5 days, turn the pile over once a day to remove moisture and ammonia, and obtain primary organic matter. (2) Adjust the moisture content of the primary organic matter in step (1) to 58wt%. Prepare a mixed bacterial solution by mixing Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae in a ratio of 1:1:0.5 for the effective live bacteria count. The number of live bacteria in the bacterial solution is 1×10 8 CFU / mL, with an inoculation amount of 80mL / kg primary organic matter, the mixed seed liquid was evenly sprayed onto the material with adjusted humidity, and the mixture was thoroughly stirred to ensure uniform distribution of the inoculum. The inoculated material was piled in the fermentation tank, and the fermentation temperature was controlled at 30℃. An intermittent ventilation mode was adopted with an air volume of 350m³ / h. The process was carried out for 10 minutes and stopped for 60 minutes, and the solid-state fermentation was carried out continuously for 6 days. After the fermentation was completed, the fermented material was dried at 65℃ for 3 hours, cooled to room temperature, and then dehydrated by sun exposure to reduce its moisture content to 2wt%, thus obtaining deep fermented organic matter; (3) The deep fermented organic matter in step (2) was crushed to a particle size of less than 60 mesh, and 6wt% water was added as a binder. The material was then lightly granulated using a disc granulator to produce 3mm particles; after granulation, the material was dried at 65℃. The moisture content was 2wt%, and the mixture was placed in a horizontal mixer at a speed of 60r / min. The mixer was turned on and preheated to 35℃. 2.5 parts of cassava starch residue, 0.7 parts of soybean meal powder, and 0.4 parts of kelp polysaccharide were mixed evenly to make a composite coating powder. The speed was kept at 60r / min while stirring. The composite coating powder was evenly sprinkled into the deep fermented organic matter in 3 times. The amount of the composite coating powder was 5% of the mass of the deep fermented organic matter. The interval between each sprinkling was 2min. The mixture was stirred continuously for 6min. The coated material was spread evenly with a thickness of 6cm and dried at 45℃ for 2h to obtain coated organic matter. (4) 50 parts of coated fermented organic matter, 7 parts of biochar, 10 parts of desulfurized gypsum, 12 parts of humus, 0.5 parts of water-retaining agent, and 2 parts of ammonium dihydrogen phosphate were mixed evenly to obtain a straw-based biochar composite slow-release fertilizer for saline-alkali land improvement.

[0038] Example 2 This example provides a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement. The preparation method includes the following steps: by mass parts, (1) 20 parts sheep manure and 15 parts pigeon manure are mixed evenly, and 15 parts corn straw are crushed to pass through a 20-mesh sieve using a crusher. The mixed manure and the crushed corn straw are mixed to obtain the total material, which is placed in a fermentation container and stirred evenly. The moisture content is adjusted to 62 wt% of the total material mass. Bacillus subtilis is inoculated at an inoculation rate of 0.5% of the total material mass. The compost is fermented at 30°C for 1 day. 8 days. When the internal temperature of the pile exceeds 50°C, turn it over immediately. If the threshold is not reached, turn it over once every 3 days. After fermentation, adjust the pH to 7.0 with wood ash, spread the material out to a thickness of 18cm, ventilate naturally for 5 days, turn the pile over once a day to remove moisture and ammonia, and obtain primary organic matter. (2) Adjust the moisture content of the primary organic matter in step (1) to 58wt%. Prepare a mixed bacterial solution by mixing Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae in an effective viable count ratio of 1:1.2:0.4. The number of viable bacteria in the bacterial solution is 1×10 8 CFU / mL, with an inoculation amount of 80mL / kg primary organic matter, the mixed seed liquid was evenly sprayed onto the material with adjusted humidity, and the mixture was thoroughly stirred to ensure uniform distribution of the inoculum. The inoculated material was piled in the fermentation tank, and the fermentation temperature was controlled at 30℃. An intermittent ventilation mode was adopted with an air volume of 350m³ / h. The process was carried out for 10 minutes and stopped for 60 minutes, and the solid-state fermentation was carried out continuously for 6 days. After the fermentation was completed, the fermented material was dried at 65℃ for 3 hours, cooled to room temperature, and then dehydrated by sun exposure to reduce its moisture content to 2wt%, thus obtaining deep fermented organic matter; (3) The deep fermented organic matter in step (2) was crushed to a particle size of less than 60 mesh, and 6wt% water was added as a binder. The material was then lightly granulated using a disc granulator to produce 3mm particles; after granulation, the material was dried at 65℃. Dry to 2wt% moisture content, place in a horizontal mixer at 60r / min speed, start stirring and preheat to 35℃; mix 3 parts cassava starch residue, 0.5 parts soybean meal powder, and 0.3 parts kelp polysaccharide evenly to make composite coating powder; keep the speed at 60r / min while stirring, the amount of the composite coating powder is 4% of the mass of the deep fermented organic matter, sprinkle the composite coating powder evenly into the deep fermented organic matter in 3 times, with an interval of 2min between each sprinkling, and continue stirring for 6min, spread the coated material evenly to a thickness of 6cm, dry at 45℃ for 2h to obtain coated organic matter; (4) mix 55 parts coated fermented organic matter, 8 parts biochar, 12 parts desulfurized gypsum, 10 parts humus, 0.8 parts water-retaining agent, and 1 part ammonium dihydrogen phosphate evenly to obtain straw-based biochar composite slow-release fertilizer for saline-alkali land improvement.

[0039] The difference between Comparative Example 1 and Example 1 is that 2.5 parts of cassava starch residue, 0.7 parts of soybean meal powder, and 0.4 parts of kelp polysaccharide were mixed evenly to make a composite coating powder, and 2.5 parts of sodium carboxymethyl starch, 0.7 parts of diatomaceous earth, and 0.4 parts of trehalose were mixed evenly to make a composite coating powder.

[0040] The difference between Comparative Example 2 and Example 1 is that Bacillus subtilis is replaced with Bacillus pumilus.

[0041] The difference between Comparative Example 3 and Example 1 is that the three strains of Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae were prepared into a mixed bacterial solution with an effective live cell ratio of 1:1.2:0.4, and were replaced with a mixed bacterial solution prepared with Phanerochaete chrysospora and Candida tropicalis in an effective live cell ratio of 4:1.

[0042] The difference between Comparative Example 4 and Example 1 is as follows: A straw-based biochar compound slow-release fertilizer for saline-alkali land improvement is prepared by the following steps: by mass fraction, (1) 23 parts of sheep manure and 12 parts of pigeon manure are mixed evenly, 18 parts of corn straw are crushed to pass through a 20-mesh sieve using a crusher, the mixed manure and the crushed corn straw are mixed to obtain the total material, placed in a fermentation container, thoroughly stirred evenly, the moisture content is adjusted to 62 wt% of the total material mass, Bacillus subtilis is inoculated at an inoculation rate of 0.5% of the total material mass, composted and fermented at 30℃. After fermentation for 18 days, when the internal temperature of the pile exceeds 50°C, it should be turned over immediately; if the threshold is not reached, it should be turned over once every 3 days. After fermentation, the pH should be adjusted to 7.0 with wood ash, the material should be spread out to a thickness of 18cm, and it should be naturally ventilated for 5 days. The pile should be turned over once a day to remove moisture and ammonia, and primary organic matter should be obtained; (2) The moisture content of the primary organic matter in step (1) should be adjusted to 58wt%, and the three strains of Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae should be mixed into a bacterial solution with an effective live bacteria ratio of 1:1:0.5. The number of live bacteria in the bacterial solution is 1×10 8 CFU / mL, with an inoculation amount of 80mL / kg primary organic matter, the mixed seed liquid was evenly sprayed onto the material with adjusted humidity, and the mixture was stirred thoroughly to ensure that the bacterial strain was evenly distributed. The inoculated material was piled in the fermentation tank, and the fermentation temperature was controlled at 30℃. An intermittent ventilation mode was adopted with an air volume of 350m³ / h. The process was carried out for 10 minutes and stopped for 60 minutes. The solid fermentation was carried out for 6 days. After the fermentation was completed, the fermented material was dried at 65℃ for 3 hours, cooled to room temperature, and then dehydrated by sun exposure to reduce its moisture content to below 2wt% to obtain deep fermented organic matter; (3) 50 parts of deep fermented organic matter, 7 parts of biochar, 10 parts of desulfurized gypsum, 12 parts of humus, 0.5 parts of water-retaining agent, and 2 parts of ammonium dihydrogen phosphate were mixed evenly to obtain straw-based biochar compound slow-release fertilizer for saline-alkali land improvement.

[0043] The difference between Comparative Example 5 and Example 1 is that the three strains of Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae were prepared into a mixed bacterial solution in a ratio of 1:1.2:0.4 of effective viable cells, while the three strains of Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae were prepared into a mixed bacterial solution in a ratio of 1.2:0.8:0.8 of effective viable cells.

[0044] The difference between Comparative Example 6 and Example 1 is that 60 parts of coated fermented organic matter, 12 parts of biochar, 6 parts of desulfurized gypsum, 18 parts of humus, 0.2 parts of water-retaining agent, and 4 parts of ammonium dihydrogen phosphate were mixed evenly to obtain a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement.

[0045] Comparative Example 7 is the product of Example 1 in Chinese Patent CN120247628A, "A Special Organic Fertilizer for Saline-Alkali Land and Its Preparation Method".

[0046] Performance testing was conducted on typical saline-alkali soils selected in the Songnen Plain of Northeast China. The soils were divided into several plots, with 0% of the plots being selected. Soil samples from a 20cm depth were collected, and soil pH, salinity, and organic matter content were measured. The initial pH was 9.7, salinity was 0.52%, and organic matter content was 7.24 g / kg. The control group was treated with 500 kg / mu of traditional cow manure, while the experimental group was treated with 500 kg / mu of the organic fertilizer prepared according to this invention. Samples were collected after 30 days. Soil samples from the 20cm depth were collected, and soil pH, salinity, and organic matter content were measured. The results are shown in Table 1.

[0047] Table 1 Performance Test Results

[0048] As shown in Table 1, the organic fertilizers of Examples 1-2 can improve the pH of saline-alkali land, reduce the salt content, and increase the organic matter content by more than 200% compared with the control group, which is better than the products of the existing technology.

[0049] The change in composition of the coating powder in Comparative Example 1 led to a decrease in performance. In Example 1, the kelp polysaccharide carboxyl groups in the coating powder could help reduce alkali, and the soybean meal powder supplemented organic nutrients, while the replaced trehalose had a low carboxyl group content, and diatomaceous earth made no organic contribution; at the same time, the loose film-forming and slow-release effect of cassava starch residue was better than that of sodium carboxymethyl starch, and conventional coating powder made Na + Exchange efficiency and organic matter retention rate decrease.

[0050] In Comparative Example 2, Bacillus subtilis was far more efficient at decomposing straw and manure and produced far more acid than Bacillus pumilus. It could also secrete extracellular polysaccharides to enhance the adsorption capacity of biochar. Bacillus pumilus had weak composting ability, resulting in insufficient organic acid production, low straw degradation rate, and weakened effects of reducing alkali and salt content and increasing organic matter.

[0051] Comparative Example 3 was replaced with *Proteus chrysosporus*, which produces less acid, and *Candida tropicalis*, which has a single function. The ratio of the two was unbalanced, and the total degradation rate and acid production decreased significantly. The improvement effect was worse than that of the strains in Example 1.

[0052] In Comparative Example 4, no coating was applied. Without coating, organic acids leach rapidly, biochar becomes easily saturated, and active components are lost quickly, leading to a rapid rebound in soil alkalinity, insufficient salt leaching, and a decrease in organic matter retention.

[0053] In Comparative Example 5, the reduced proportion of *Trichoderma reesei* led to decreased conversion of recalcitrant components from straw; an excessively high proportion of *Aspergillus niger* exhibited slight antagonism with *Saccharomyces cerevisiae*, resulting in decreased fermentation efficiency and reduced overall yield of active components and Na+. + The ability to bind is weakened.

[0054] The change in the component ratio in Comparative Example 6 resulted in a decrease in the effectiveness of the organic fertilizer, indicating that only when the various components are combined in specific ratios can a better synergistic effect be achieved.

[0055] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement, characterized in that, The process includes the following steps: (1) Mix sheep manure and pigeon manure evenly, crush corn stalks, mix the mixed manure with the crushed corn stalks to obtain total material, inoculate with Bacillus subtilis, compost and ferment to obtain primary organic matter; (2) Ferment the primary organic matter from step (1) using Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae to obtain deep fermented organic matter; (3) Crush the deep fermented organic matter from step (2) to make granules; sprinkle composite coating powder into the deep fermented organic matter, coat it, and obtain coated organic matter; (4) Mix the coated fermented organic matter from step (3), biochar, desulfurized gypsum, humus, water-retaining agent, and ammonium dihydrogen phosphate evenly to obtain straw-based biochar compound slow-release fertilizer for saline-alkali land improvement.

2. The method for preparing straw-based biochar compound slow-release fertilizer for saline-alkali land improvement according to claim 1, characterized in that, Crush the corn stalks using a shredder until they pass through a 20-mesh sieve.

3. The method for preparing straw-based biochar compound slow-release fertilizer for saline-alkali land improvement according to claim 1, characterized in that, In step (1), by mass parts: 20-25 parts sheep manure and 10-15 parts pigeon manure are mixed evenly, 15-20 parts corn stalks are crushed, and the mixed manure and crushed corn stalks are mixed to obtain the total material.

4. The method for preparing straw-based biochar compound slow-release fertilizer for saline-alkali land improvement according to claim 1, characterized in that, In step (1), Bacillus subtilis is inoculated at an inoculation rate of 0.5% of the total material mass.

5. The method for preparing straw-based biochar compound slow-release fertilizer for saline-alkali land improvement according to claim 1, characterized in that, In step (1), composting is carried out at 25-35℃ for 15-20 days. When the internal temperature of the pile exceeds 50℃, it should be turned over immediately; if the threshold is not reached, it should be turned over once every 3 days.

6. The method for preparing straw-based biochar compound slow-release fertilizer for saline-alkali land improvement according to claim 1, characterized in that, The effective viable count ratio of the three strains Aspergillus niger, Trichoderma reesei, and Saccharomyces cerevisiae used in step (2) is Aspergillus niger: Trichoderma reesei: Saccharomyces cerevisiae = 1:(1-1.2):(0.4-0.6).

7. The method for preparing straw-based biochar compound slow-release fertilizer for saline-alkali land improvement according to claim 1, characterized in that, Mix 2-3 parts cassava starch residue, 0.5-1 part soybean meal powder, and 0.3-0.5 parts kelp polysaccharide evenly to prepare a composite coating powder; the amount of the composite coating powder is 3%-8% of the mass of the deep fermented organic matter.

8. The method for preparing straw-based biochar compound slow-release fertilizer for saline-alkali land improvement according to claim 1, characterized in that, By weight, 45-55 parts of coated fermented organic matter, 6-8 parts of biochar, 8-12 parts of desulfurized gypsum, 10-15 parts of humus, 0.3-0.8 parts of water-retaining agent, and 1-3 parts of ammonium dihydrogen phosphate are mixed evenly to obtain a straw-based biochar compound slow-release fertilizer for saline-alkali land improvement.

9. The method for preparing straw-based biochar compound slow-release fertilizer for saline-alkali land improvement according to claim 1, characterized in that, In step (2), the fermentation temperature is controlled at 28-32℃, and an intermittent ventilation mode is adopted with an air volume of 324-648m³ / h. The process is carried out for 5-10 minutes, then stopped for 50-60 minutes, and continuous solid-state fermentation is carried out for 5-7 days.

10. A straw-based biochar compound slow-release fertilizer for saline-alkali land improvement prepared by the preparation method according to any one of claims 1-9.

Images