A saline-alkali soil remediation fertilizer based on soybean acidified oil sludge and biochar, and a preparation method and application thereof

Abstract

The present application relates to a kind of saline-alkali soil remediation fertilizer based on soybean acidified oil sludge and biochar and its preparation method and application, the present application is harmless to soybean acidified oil sludge by subsection gradient extraction process and nutrient enrichment extraction, then the extraction product is accurately compounded with modified biochar, functional additive, and is prepared into saline-alkali remediation fertilizer by specific process;The fertilizer not only realizes the resource recycling of soybean acidified oil sludge, but also can extend the industrial chain, create green low-carbon circular economy, the prepared product can reduce the water-soluble salt content of saline-alkali soil, supplement soil organic matter, improve soil physical and chemical properties, improve soil microbial function, and preparation process is simple, low in cost, no secondary pollution, and can be adapted to different types of saline-alkali soil, and the repair efficiency is high, and the effective period is long, with significant economic, environmental and social benefits, can be widely applied in saline-alkali soil improvement and agricultural sustainable development field.

Description

Technical Field

[0001] This invention relates to a fertilizer for remediating saline-alkali soil based on soybean acidified sludge and biochar, its preparation method and application, belonging to the field of agricultural waste resource utilization and soil remediation technology. Background Technology

[0002] my country is a major global producer of soybean oil, generating a large amount of byproducts during the processing. Currently, extracting acidified oil from these byproducts is one of the main technological pathways for resource recycling. However, the extraction of acidified oil still produces a large amount of sludge. This sludge is not only rich in organic components such as free fatty acids, oils, proteins, and cellulose, but also contains abundant organic nitrogen, phosphorus, potassium, and other nutrients, possessing considerable resource potential.

[0003] Currently, the main methods for treating acidified oil sludge include incineration, landfill, and biodegradation. However, these methods generally suffer from high processing costs and low resource utilization rates. In particular, chemical treatment processes are prone to causing secondary pollution, making it difficult to meet the practical needs of large-scale disposal. It is worth noting that acidified soybean oil sludge originates from a byproduct of vegetable oil processing and possesses natural and pollution-free characteristics. If it is thoroughly mixed and fermented with other low-moisture organic wastes and compounded with functional materials such as biostimulants, it has a good foundation for developing bio-fertilizers.

[0004] Meanwhile, my country has a vast area of ​​saline-alkali soil, accounting for about 10% of the total land area, mainly concentrated in the Northeast, North China, Northwest China and coastal areas. Among them, the area of ​​saline-alkali soil with potential for improvement and utilization is about 200 million mu (approximately 13.3 million hectares). Due to its high salt content, high pH value, poor structure, low organic matter content and insufficient nutrients, this type of soil seriously inhibits crop growth and restricts the improvement of land productivity, and has become one of the key limiting factors affecting the sustainable development of agriculture in my country.

[0005] Currently, saline-alkali soil remediation technologies mainly fall into three categories: engineering improvement, chemical remediation, and bioremediation. Among them, chemical improvement methods are widely used due to their ease of operation and significant effects, but traditional amendments such as gypsum and phosphogypsum have drawbacks such as limited effectiveness, easy inducing soil compaction, and nutrient loss. Bioremediation is characterized by a scarcity of targeted products, long improvement cycles, and a lack of products designed specifically for different types of saline-alkali land, and existing bio-organic fertilizer products have limited adaptability. Although engineering improvement measures have certain effects, they are costly, have limited applicability, and are difficult to promote on a large scale.

[0006] In summary, exploring a synergistic approach for the treatment of acidified oil sludge and the improvement of saline-alkali soil that combines environmental friendliness with efficient resource utilization has significant practical implications and promising application prospects.

[0007] In recent years, the preparation of soil remediation fertilizers from agricultural waste has become a research hotspot. This strategy helps alleviate the environmental pressure caused by waste and promotes resource recycling. Currently, studies have reported the use of materials such as soybean sludge or biochar to prepare fertilizers, but the following shortcomings remain: 1. The treatment of acidified soybean sludge is insufficient, failing to effectively extract the nutrients and large amounts of small organic molecules, thus underutilizing its potential as a fertilizer resource; 2. Biochar is mostly prepared from a single raw material, lacking targeted modification treatment, resulting in limited adsorption and regulation capabilities for saline-alkali soils, making it difficult to simultaneously achieve multiple objectives such as salinization, pH adjustment, and nutrient replenishment; 3. Fertilizer formulations lack targeted design, failing to fully consider the compositional characteristics of acidified soybean sludge and the actual needs of saline-alkali soil remediation, leading to unsatisfactory remediation effects and short-lasting effects; 4. The lack of differentiated application schemes for different types of saline-alkali soils limits its adaptability and promotional value in practical applications. Summary of the Invention

[0008] In response to the shortcomings of existing technologies, especially the difficulties in disposing of acidified sludge, a byproduct of soybean oil processing, the lack of resource recycling technologies, and the scarcity of special fertilizers for saline-alkali soils with poor improvement effects and low organic matter content, this invention provides a saline-alkali soil remediation fertilizer based on acidified soybean sludge and biochar, its preparation method, and its application.

[0009] This invention employs a segmented gradient extraction process to harmlessly treat and effectively extract nutrients from acidified soybean sludge, achieving the resource-based and harmless utilization of the sludge. Simultaneously, it can efficiently improve saline-alkali soil, enhance soil fertility, reduce remediation costs, and provide technical support for sustainable agricultural development. The sludge after segmented extraction, combined with composite modified biochar possessing adsorption and regulation functions, yields a fertilizer that combines nutrient supply and saline-alkali remediation functions, achieving a triple benefit of "waste resource utilization, saline-alkali soil remediation, and increased agricultural production," demonstrating significant innovation and practicality.

[0010] To achieve the above objectives, the present invention adopts the following technical solution:

[0011] A method for preparing a saline-alkali soil remediation fertilizer based on soybean acidified sludge and biochar includes the following steps:

[0012] (1) Pretreatment of soybean acidified sludge: The acidified sludge, a byproduct generated during soybean oil processing, is dried, crushed, and impurities are removed to obtain pretreated sludge;

[0013] (2) Segmented gradient extraction: The pretreated sludge is subjected to segmented gradient extraction using a first-stage extraction and a second-stage extraction process. The extraction yields a first-stage extract, a second-stage extract, and a second-stage residue. The first-stage extract and the second-stage extract are mixed, heated, and fractionated to recover the extractant and obtain an extract concentrate. The second-stage residue is dried to obtain an extract residue powder.

[0014] (3) Preparation of modified biochar:

[0015] Apple branches were used as biochar precursors. After crushing the apple branches, they were soaked in phosphoric acid solution, drained, and placed in a carbonization furnace. They were then heated and carbonized under a nitrogen atmosphere and cooled to room temperature to obtain primary biochar. A composite modifier was added to the primary biochar for heating and modification. After modification, the biochar was cooled and crushed to obtain modified biochar.

[0016] (4) Preparation of saline-alkali remediation fertilizer:

[0017] The following components are mixed evenly according to mass fractions to obtain a compound mixture: 25-35 parts of extract concentrate, 5-15 parts of modified biochar, 30-40 parts of mixture of fungal residue and rice bran powder, 8-12 parts of extract residue powder, 3-5 parts of functional additives, and 2-4 parts of binder.

[0018] Deionized water was added to the compound mixture, granulated, dried, cooled to room temperature, and then sieved to obtain saline-alkali soil remediation fertilizer.

[0019] According to a preferred embodiment of the present invention, in step (1), the soybean acidified sludge contains 20-40% oil, 10-20% protein, 10-20% free fatty acids, 5-10% free amino acids, and 5-10% organic nitrogen, phosphorus, and potassium nutrients.

[0020] According to a preferred embodiment of the present invention, in step (1), drying is performed by air drying in a cool and ventilated place, controlling the moisture content after air drying to be 20-25%, and pulverization is performed by putting the air-dried acidified sludge into a pulverizer for pulverization, and then passing the pulverized sludge through an 80-mesh sieve. The moisture content of the acidified sludge after drying is controlled to be 20-25%. If the moisture content is too high, the extractant will easily become ineffective in the subsequent extraction process, and if the moisture content is too low, the nutrient extraction efficiency will be reduced.

[0021] According to a preferred embodiment of the present invention, in step (2), the primary extraction specifically involves: adding extractant A to the pretreated sludge, wherein the mass ratio of the pretreated sludge to extractant A is 1:3-5; placing the mixture in a constant temperature water bath, controlling the temperature at 45-55°C; using a bidirectional circulating stirring method, with a stirring speed of 1200-1500 r / min; after stirring, placing it in a centrifuge, controlling the speed at 3500 r / min, centrifuging for 30 min, and separating the primary extract and the primary residue; wherein the primary extract mainly contains free fatty acids, small molecule fat-soluble nutrients, and the extractant A is a mixture of n-hexane and ethyl acetate with a volume ratio of 3:1.

[0022] The extractant A of this invention has extremely strong solubility for free fatty acids and small molecule oils in acidified sludge, and is non-toxic and easy to recycle. Compared with a single extractant, the extraction efficiency is increased by more than 20%.

[0023] A further preferred method is to use a bidirectional circulating stirring method, which involves stirring in the forward direction for 15 minutes, stopping for 5 minutes, and stirring in the reverse direction for 15 minutes, repeating the cycle 3 times.

[0024] According to a preferred embodiment of the present invention, in step (2), the secondary extraction specifically involves: adding extractant B to the primary residue, wherein the mass ratio of the primary residue to extractant B is 1:2-3, controlling the constant temperature water bath temperature at 60-70℃, stirring at 1000-1200 r / min, and stirring continuously for 40-50 min; after stirring, centrifuging to obtain the secondary extract and the secondary residue, wherein the extractant B is a mixture of ethanol and deionized water with a volume ratio of 2:1.

[0025] The present invention can efficiently dissolve water-soluble nutrients such as proteins and amino acids, while avoiding protein denaturation and preserving their activity.

[0026] Further optimized, the centrifugation speed is 4500 r / min, and the time is 25 min. The secondary extract mainly contains water-soluble nutrients such as proteins, amino acids, and organic nitrogen, phosphorus, and potassium, while the secondary residue mainly contains cellulose and ash.

[0027] According to a preferred embodiment of the present invention, in step (2), the heating fractionation is to mix the primary extract and the secondary extract, pour them into a fractionation apparatus, and fractionate them for 60 minutes at 80-90°C and normal pressure.

[0028] The extract concentrate obtained by this invention is rich in fat-soluble and water-soluble nutrients and can be directly used as a nutrient source for fertilizers.

[0029] According to a preferred embodiment of the present invention, in step (2), the secondary residue drying is performed by drying in an oven at 85°C for 40 minutes.

[0030] According to a preferred embodiment of the present invention, in step (3), the phosphoric acid solution has a mass concentration of 4-8%, the soaking time is 24 hours, and the carbonization is carried out by heating to 500-600°C at a heating rate of 5°C / min for 2-3 hours. The phosphoric acid solution of the present invention can pretreat the precursor and increase the pore structure in the subsequent carbonization process.

[0031] According to a preferred embodiment of the present invention, in step (3), the mass ratio of the amount of primary biochar added to the composite modifier is 10:1-2, the temperature modification is carried out at 200-250℃ for 1.5-2 hours, and after cooling, it is pulverized through a 100-mesh sieve. The composite modifier is a mixture of diatomaceous earth, bentonite and Fe3O4 nanoparticles, and the mass ratio of diatomaceous earth, bentonite and Fe3O4 nanoparticles is (4-6):(2-5):(1-3).

[0032] In the composite modifier of this invention, diatomaceous earth and bentonite increase the specific surface area and adsorption performance of biochar, efficiently adsorbing sodium and chloride ions in saline-alkali soil and reducing soil salinity. Fe3O4 nanoparticles enhance the conductivity and microbial affinity of biochar, promote soil microbial activity, and replenish iron in the soil, improving soil nutrient structure. Testing shows that the modified biochar prepared by this invention has a specific surface area of ​​245-260 m² / g, and compared to unmodified biochar, its adsorption capacity is increased by more than 35%, with an adsorption rate of over 85% for sodium ions.

[0033] According to a preferred embodiment of the present invention, in step (4), the functional additive is a mixture of humic acid, polyglutamic acid and arbuscular mycorrhizal fungi (AMF), and the mass ratio of humic acid, polyglutamic acid and arbuscular mycorrhizal fungi is 4:3:3.

[0034] In the functional adjuvants of this invention, humic acid can regulate soil pH, improve soil aggregate structure, and enhance soil water and fertilizer retention capacity; polyglutamic acid can promote nutrient absorption by crop roots, improve fertilizer utilization, and inhibit soil salt accumulation; arbuscular mycorrhizal fungi (AMF) can form a symbiotic relationship with crop roots, enhance crop photosynthesis, improve root vitality, increase plant salt tolerance, promote plant biomass accumulation, and work synergistically with modified biochar to further enhance the remediation effect of saline-alkali soil.

[0035] The mixture of mushroom residue and rice bran powder described in this invention is conventionally pulverized edible mushroom residue and rice bran, which belongs to the category of agricultural processing waste recycling.

[0036] According to a preferred embodiment of the present invention, in step (4), the binder is modified starch. Modified starch is a natural green binder with zero salt and neutral pH, has good binding properties, can form fertilizer granules, and can be used as soil organic matter after degradation without causing secondary pollution.

[0037] According to a preferred embodiment of the present invention, in step (4), deionized water is added to the compound mixture to adjust the moisture content of the mixture to 30-35%, granulation is performed to control the particle size to 2-4 mm, drying is performed by placing the granulated particles in an oven at 70-80℃ to dry, and controlling the moisture content of the dried particles to ≤10%, and sieving is performed by passing through 10-mesh and 20-mesh sieves to remove unqualified particles that are too large or too small.

[0038] This invention controls the moisture content of the dried granules to be ≤10%. Excessive moisture content can easily lead to granule clumping and mold growth, while excessively low moisture content makes the granules brittle.

[0039] A fertilizer for remediating saline-alkali soil based on acidified soybean sludge and biochar was prepared using the method described above.

[0040] Application of soybean acidified sludge and biochar-based fertilizer for saline-alkali soil remediation in saline-alkali land improvement.

[0041] According to a preferred embodiment of the present invention, one of the specific application methods is as follows:

[0042] 1) For mild saline-alkali soil: Evenly spread the saline-alkali remediation fertilizer on the soil surface at a rate of 200-250 kg / mu, then use a rotary tiller to plow to a depth of 15-20 cm to ensure the fertilizer is thoroughly mixed with the soil; after plowing, water the soil to control the soil moisture content to 20-25% and soak the soil for 3-5 days, then sow crops as usual; after sowing, apply fertilizer every 30 days at a rate of 50-80 kg / mu, for two consecutive applications to ensure a continuous supply of soil nutrients and consolidate the remediation effect;

[0043] 2) For moderate / severe saline-alkali soil: First, mix the saline-alkali remediation fertilizer with the top 0-20cm soil at a mass ratio of 1:10 to make a remediation substrate; evenly cover the soil surface with the remediation substrate to a thickness of 5-8cm, and then use a rotary tiller to turn the soil to a depth of 20-25cm to ensure that the remediation substrate is fully mixed with the deeper soil; after turning the soil, water it for 3-5 days, drain the water, and then let it dry for 2-3 days to reduce the soil moisture content to 20-25% before sowing crops; apply fertilizer once 15 days after sowing, at a rate of 100-120kg / mu, and apply fertilizer three times consecutively to gradually improve the physical and chemical properties of the soil and enhance soil fertility.

[0044] According to the preferred embodiment of the present invention, slightly saline-alkali soil has the following characteristics: soil salt content ≤0.3% and pH value 7.5-8.5. The soil structure is relatively good, and it is suitable for crops such as wheat, corn, and cotton.

[0045] According to the preferred embodiment of the present invention, moderately / severely saline-alkali soil has the following characteristics: soil salinity 0.3-1.0% and pH value 8.5-10.0. The soil is severely compacted and has extremely low organic matter content, making it suitable for crops such as salt-tolerant forage grasses, sunflowers, and sugar beets.

[0046] Based on the differences in salinity and pH value of different types of saline-alkali soil, this invention designs two targeted application methods to improve the remediation effect and adapt to the planting needs of different crops.

[0047] Technical features and advantages of the present invention:

[0048] 1. Unique segmented gradient extraction process: Targeting the compositional characteristics of soybean acidified sludge, a "two-way circulating stirring + segmented extraction" method is adopted. A special mixed extractant is selected to extract fat-soluble nutrients (free fatty acids, small molecule oils) and water-soluble nutrients (proteins, amino acids) separately. The extraction efficiency is high (effective nutrient extraction rate ≥85%). At the same time, harmful substances in the acidified sludge are removed, achieving harmless treatment. This solves the problems of incomplete treatment and easy secondary pollution of existing acidified sludge. Moreover, the extractant can be recycled, reducing costs.

[0049] 2. Preparation of composite modified biochar: Using waste biomass apple branches as a precursor, combined with diatomaceous earth, bentonite and Fe3O4 nanoparticles for composite modification, not only is the secondary resource utilization of soybean oil processing by-products realized, but the adsorption capacity, nutrient supply capacity and microbial affinity of biochar are also significantly improved. Compared with the existing single modified biochar, the adsorption rate of sodium ions in saline-alkali soil is increased by more than 30%, and it can simultaneously achieve "salt reduction, pH adjustment and microbial promotion".

[0050] 3. Compound formulation of fertilizer for saline-alkali soil remediation: Combining the nutrient characteristics of soybean acidified oil sludge extract with the needs of saline-alkali soil remediation, the extract concentrate, modified biochar, microbial residue and rice bran powder, extract residue powder and functional adjuvants (humic acid + polyglutamic acid + AMF) are precisely compounded to form a unique formula that achieves the three-in-one effect of "nutrient supply, saline-alkali remediation and soil improvement", solving the problems of single remediation effect and short duration of traditional fertilizers;

[0051] 4. Adaptive Application: Specialized application methods are designed for different types of saline-alkali soil (mild, moderate / severe), and the application rate and frequency of topdressing are adjusted according to crop type to improve remediation efficiency, expand the scope of application, and solve the problems of single application methods and limited applicability of existing fertilizers;

[0052] 5. Full-process resource utilization: The entire process uses acidified sludge, a byproduct of soybean oil processing, as the main raw material, realizing the full-process resource utilization and harmless treatment of waste without secondary pollution. At the same time, it reduces the cost of saline-alkali soil remediation and fertilizer preparation. Compared with traditional saline-alkali soil remediation technology, the cost is reduced by more than 40%.

[0053] 6. Solving environmental problems: It realizes the harmless and resource-based utilization of soybean acidified oil sludge, avoiding environmental pollution caused by landfill and incineration. At the same time, it uses waste biomass to prepare biochar, further promoting the resource recycling of agricultural waste, which is in line with the concept of green development.

[0054] 7. Excellent remediation effect: The prepared saline-alkali remediation fertilizer can simultaneously reduce the salinity of saline-alkali soil, regulate pH value, replenish soil organic matter and nutrients, improve soil aggregate structure, and enhance soil microbial activity. Experimental verification shows that after applying the fertilizer of this invention, the salinity of mild saline-alkali soil is reduced by more than 45% and the pH value is reduced to 7.0-7.5, the salinity of moderate / severe saline-alkali soil is reduced by more than 35% and the pH value is reduced to 7.5-8.5, and the soil organic matter content is increased by more than 60%.

[0055] 8. High fertilizer utilization rate: The "slow-release" formula is designed to match the nutrient release rate with the crop absorption rate, increasing fertilizer utilization rate by more than 30%, reducing nutrient loss, and reducing agricultural non-point source pollution;

[0056] 9. Low cost: The main raw material is soybean processing by-product, which is widely available and inexpensive. The extractant can be recycled, the preparation process is simple and does not require complicated equipment, and large-scale production is highly feasible. Compared with traditional saline-alkali soil remediation fertilizers, the preparation cost is reduced by more than 40%.

[0057] 10. Wide applicability: It is suitable for different types of saline-alkali soil (light, medium / severe) and can be used for planting a variety of crops such as wheat, corn, cotton, and salt-tolerant forage grass. After restoration, soil productivity is significantly improved, and crop yield increases by more than 25%, which has significant economic, environmental and social benefits. Detailed Implementation

[0058] The present invention will be further described in detail below with reference to specific embodiments, comparative examples and experimental examples. The scope of protection of the present invention is not limited to the following embodiments.

[0059] Example 1

[0060] A method for preparing a saline-alkali soil remediation fertilizer based on soybean acidified oil sludge and biochar, comprising the following steps:

[0061] (1) Pretreatment of soybean acidified sludge: Place the soybean acidified sludge in a cool and ventilated place to air dry naturally until the moisture content is 22%, crush it and pass it through an 80-mesh sieve to remove impurities, and obtain pretreated sludge.

[0062] (2) Segmented gradient extraction of soybean acidified sludge:

[0063] S21. Primary extraction: Add extractant A (n-hexane:ethyl acetate = 3:1, volume ratio) to the pretreated sludge. The mass ratio of pretreated sludge to extractant A is 1:4. Control the temperature at 50℃, the stirring speed at 1300 r / min, stir forward for 15 min, stop for 5 min, stir backward for 15 min, repeat 3 times, and centrifuge (3500 r / min, 30 min) to obtain primary extract and primary residue.

[0064] S22. Secondary extraction: Add extractant B (ethanol:deionized water = 2:1, volume ratio) to the primary residue. The mass ratio of primary residue to extractant B is 1:2.5. Control the temperature at 65℃, the stirring speed at 1100 r / min, stir for 45 min, and then centrifuge (4500 r / min, 25 min) to obtain secondary extract and secondary residue.

[0065] S23. Extraction liquid treatment: Mix the primary extract and the secondary extract, fractionate at 85°C and atmospheric pressure for 60 min, recover the extractant, and obtain the extract concentrate;

[0066] S24. Residue treatment: Dry the secondary residue at 85℃ for 40 min, pulverize it through a 100-mesh sieve to obtain extraction residue powder;

[0067] (3) Preparation of modified biochar:

[0068] S31. Preparation of biochar precursor: Apple branches were crushed, soaked in 5% phosphoric acid solution for 24 hours, drained and placed in a carbonization furnace. Under nitrogen atmosphere, the temperature was increased to 550℃ at 5℃ / min and carbonized for 2.5 hours. After cooling to room temperature, primary biochar was obtained.

[0069] S32. Composite modification: Add a modifier (diatomaceous earth: bentonite: Fe3O4 nanoparticles = 5:3:2, mass ratio) to primary biochar. The mass ratio of primary biochar to modifier is 10:1.5. After mixing evenly, modify at 220℃ for 1.8h. After cooling, pulverize through a 100-mesh sieve to obtain modified biochar.

[0070] (4) Compounding and preparation of saline-alkali remediation fertilizers:

[0071] S41. Compound formulation: Mix evenly by mass parts: 30 parts of extract concentrate, 5 parts of modified biochar, 40 parts of mixture of fungal residue and rice bran powder, 8 parts of extract residue powder, 4 parts of functional additives, and 3 parts of binder.

[0072] S42. Granulation: Add deionized water, adjust the moisture content to 32%, and granulate by extrusion to a particle size of 3mm;

[0073] S43. Drying: Dry in an oven at 75℃ until the moisture content is 8%, cool and sieve to obtain the finished salt-alkali remediation fertilizer.

[0074] Application method of saline-alkali remediation fertilizer: For slightly saline-alkali soil with a salt content of 0.25% and pH of 8.0, when planting wheat: spread the fertilizer evenly on the soil surface at a rate of 220 kg / mu, till to a depth of 18 cm, water until the soil moisture content is 22%, soak for 4 days, and then sow wheat; apply 70 kg / mu as a top dressing 30 days after sowing and 70 kg / mu as a top dressing 60 days after sowing.

[0075] Example 2

[0076] A method for preparing a saline-alkali soil remediation fertilizer based on soybean acidified oil sludge and biochar, comprising the following steps:

[0077] (1) Pretreatment of soybean acidified sludge: Soybean acidified sludge was air-dried to a moisture content of 20%, crushed and passed through an 80-mesh sieve to remove impurities, and pretreated sludge was obtained.

[0078] (2) Segmented gradient extraction of soybean acidified sludge:

[0079] S21. Primary extraction: The pretreated sludge and extractant A (n-hexane: ethyl acetate = 3:1) were mixed at a mass ratio of 1:3. The temperature was 45℃, the stirring speed was 1200 r / min, the stirring was carried out for 15 min in the forward direction, stopped for 5 min, and then reversed for 15 min, for a total of 3 cycles. The mixture was then centrifuged (3500 r / min, 30 min) to obtain the primary extract and primary residue.

[0080] S22. Secondary extraction: The mass ratio of primary residue to extractant B (ethanol:deionized water = 2:1) is 1:2. The temperature is 60℃, the stirring speed is 1000r / min, the stirring is carried out for 40min, and then the mixture is centrifuged (4500r / min, 25min) to obtain secondary extract and secondary residue.

[0081] S23. Extraction liquid treatment: Mix the extract liquid, fractionate at 80℃ and atmospheric pressure for 60 min, recover the extractant, and obtain the extract concentrate;

[0082] S24. Residue treatment: The secondary residue is dried at 85℃ for 40 min, pulverized and passed through a 100-mesh sieve to obtain extraction residue powder;

[0083] (3) Preparation of modified biochar:

[0084] S31. Preparation of biochar precursor: Apple branches were crushed and soaked in 5% phosphoric acid solution for 24 h. Under nitrogen atmosphere, the temperature was increased to 500℃ at 5℃ / min and carbonized for 2 h. After cooling, primary biochar was obtained.

[0085] S32. Composite modification: Primary biochar and modifier (diatomaceous earth: bentonite: Fe3O4 nanoparticles = 5:3:2) in a mass ratio of 10:1, modified at 200℃ for 1.5h, cooled and pulverized through a 100-mesh sieve to obtain modified biochar;

[0086] (4) Compounding and preparation of saline-alkali remediation fertilizers:

[0087] S41. Compound: 35 parts of concentrated extract, 10 parts of modified biochar, 35 parts of a mixture of mushroom residue and rice bran powder, 12 parts of extract residue powder, 5 parts of functional additives, and 3 parts of binder, mixed evenly;

[0088] S42. Granulation: Adjust the moisture content to 30%, extrude granulation, particle size 2mm;

[0089] S43. Drying: Dry at 70℃ to a moisture content of 9%, then sieve to obtain the finished product.

[0090] Application method of saline-alkali remediation fertilizer for moderately saline-alkali soil with a salt content of 0.4% and a pH of 8.8, for sunflower planting: Mix the fertilizer with the topsoil at a ratio of 1:10 to make a remediation substrate, cover it with a thickness of 5cm, till it to a depth of 20cm, soak it in water for 3 days, drain it and let it dry for 2 days before sowing sunflowers; apply 100kg / mu as top dressing 15 days after sowing, 100kg / mu as top dressing 30 days after sowing, and 100kg / mu as top dressing 45 days after sowing.

[0091] Example 3

[0092] A method for preparing a saline-alkali soil remediation fertilizer based on soybean acidified oil sludge and biochar, comprising the following steps:

[0093] (1) Pretreatment of soybean acidified sludge: Soybean acidified sludge was air-dried to a moisture content of 25%, crushed and passed through an 80-mesh sieve to remove impurities, and pretreated sludge was obtained.

[0094] (2) Segmented gradient extraction of soybean acidified sludge:

[0095] S21. Primary extraction: The mass ratio of pretreated sludge to extractant A is 1:5, the temperature is 55℃, the stirring speed is 1500r / min, the stirring is carried out for 15min in the forward direction, 5min after stopping, and 15min in the reverse direction, and the cycle is repeated 3 times. The mixture is then centrifuged (3500r / min, 30min) to obtain the primary extract and the primary residue.

[0096] S22. Secondary extraction: The mass ratio of primary residue to extractant B is 1:3, the temperature is 70℃, the stirring speed is 1200r / min, the stirring is carried out for 50min, and then centrifuged (4500r / min, 25min) to obtain secondary extract and secondary residue;

[0097] S23. Extraction liquid treatment: Mix the extract liquid, fractionate at 90℃ and atmospheric pressure for 60 min, recover the extractant, and obtain the extract concentrate;

[0098] S24. Residue treatment: The secondary residue is dried at 85℃ for 40 min, pulverized and passed through a 100-mesh sieve to obtain extraction residue powder;

[0099] (3) Preparation of modified biochar:

[0100] S31. Preparation of biochar precursor: Apple branches were crushed and soaked in 5% phosphoric acid solution for 24 h. Under nitrogen atmosphere, the temperature was increased to 600℃ at 5℃ / min and carbonized for 3 h. After cooling, primary biochar was obtained.

[0101] S32. Composite modification: Primary biochar and modifier are modified at a mass ratio of 10:2, modified at 250℃ for 2 hours, cooled and pulverized through a 100-mesh sieve to obtain modified biochar;

[0102] (4) Compounding and preparation of saline-alkali remediation fertilizers:

[0103] S41. Compound: 35 parts of concentrated extract, 15 parts of modified biochar, 35 parts of a mixture of mushroom residue and rice bran powder, 10 parts of extract residue powder, 5 parts of functional additives, and 3 parts of binder, mixed evenly;

[0104] S42. Granulation: Adjust the moisture content to 35%, extrude granulation, particle size 4mm;

[0105] S43. Drying: Dry at 80℃ to a moisture content of 7%, then sieve to obtain the finished product.

[0106] Application method of saline-alkali remediation fertilizer for severely saline-alkali soil with a salt content of 0.9% and a pH of 9.5, and planting salt-tolerant forage grass: Mix the fertilizer with the topsoil at a ratio of 1:10 to make a remediation substrate, cover it with a thickness of 8cm, till it to a depth of 25cm, soak it in water for 5 days, drain it and let it dry for 3 days before sowing forage grass; apply 120kg / mu as a top dressing 15 days after sowing, 120kg / mu as a top dressing 30 days after sowing, and 120kg / mu as a top dressing 45 days after sowing.

[0107] Comparative Example 1

[0108] The method described in the same way as in Example 1 differs in that:

[0109] In step (2), a segmented gradient extraction process was not used; instead, a single extraction process was used, with extraction agent A (n-hexane: ethyl acetate = 3:1) being used only once. The other steps were carried out as in Example 1, and comparative fertilizer 1 was prepared.

[0110] The application method is the same as in Example 1.

[0111] Comparative Example 2

[0112] The method described in the same way as in Example 1 differs in that:

[0113] In step (3), no composite modified biochar was used, and the rest was carried out according to Example 1 to prepare comparative fertilizer 2;

[0114] The application method is the same as in Example 1.

[0115] Comparative Example 3

[0116] The method described in the same way as in Example 1 differs in that:

[0117] In step (4), no functional additives were added, and the rest was carried out according to Example 1 to prepare comparative fertilizer 3;

[0118] The application method is the same as in Example 1.

[0119] Comparative Example 4

[0120] Commercially available traditional saline-alkali soil remediation fertilizer (main components: gypsum, humic acid, urea) was used, and the application method was in accordance with the product instructions (250 kg / mu for spreading, tilling, and topdressing twice after sowing, 80 kg / mu each time), which is consistent with the application scenario of Example 1 (slightly saline-alkali soil, wheat planting).

[0121] Experimental Example

[0122] Experimental Objective

[0123] The purpose of this invention is to verify the remediation effect, fertilizer utilization rate, and crop yield increase effect of the saline-alkali remediation fertilizer prepared by this invention, and to compare the superiority of this invention with the prior art.

[0124] Experimental materials

[0125] Experimental samples: Salt-alkali remediation fertilizers prepared in Examples 1-3 and fertilizers in Comparative Examples 1-4;

[0126] Experimental soils: slightly saline-alkali soil (salt content 0.25%, pH 8.0, organic matter content 1.2%), moderately saline-alkali soil (salt content 0.4%, pH 8.8, organic matter content 0.8%), and severely saline-alkali soil (salt content 0.9%, pH 9.5, organic matter content 0.5%).

[0127] Experimental crops: wheat (slightly saline-alkali soil), sunflower (moderately saline-alkali soil), and salt-tolerant pasture (severely saline-alkali soil).

[0128] Experimental instruments: pH meter, conductivity meter, soil organic matter analyzer, centrifuge, constant temperature water bath, carbonization furnace, etc.

[0129] Experimental Design

[0130] 1. Mild saline-alkali soil remediation experiment: Five treatment groups were set up (Example 1, Comparative Examples 1-4), with three replicates in each treatment group. Each replicate covered an area of ​​1 acre, planted with wheat, and fertilized according to the corresponding application methods. The experimental period was 90 days (wheat growth period).

[0131] 2. Moderate / severe saline-alkali soil remediation experiment: Three treatment groups were set up (Example 2, Example 3, Comparative Example 4), with three replicates in each treatment group. Each replicate covered an area of ​​1 acre, and sunflowers and salt-tolerant forage grasses were planted respectively. Fertilizers were applied according to the corresponding application methods. The experimental period was 120 days.

[0132] 3. Testing indicators: Soil salinity and organic matter content were tested before the start of the experiment (day 0), at 30, 60, and 90 (120) days of the experiment; after the experiment, crop yield and fertilizer utilization rate were tested.

[0133] 4. Testing methods: Soil salinity was determined by electrical conductivity method, pH value was determined by pH meter, soil organic matter content was determined by potassium dichromate titration method, crop yield was determined by on-site harvesting and weighing, and fertilizer utilization rate was calculated by difference method.

[0134] Experimental results

[0135] The results of different treatment groups for the remediation of mildly saline-alkali soil are shown in Table 1.

[0136] Table 1

[0137] As shown in Table 1, the remediation effect of Example 1 is significantly better than that of Comparative Examples 1-4. Example 1 achieved a soil salinity reduction rate of 48.0%, an increase in organic matter content of 8.2%–59%, and a wheat yield of 420 kg / mu, representing a yield increase of 28.8%. In contrast, Comparative Example 1 (without segmented gradient extraction) showed significantly reduced remediation effect and yield increase due to insufficient extraction of effective nutrients. Comparative Example 2 (without composite modified biochar) had poor salinity reduction due to insufficient biochar adsorption capacity. Comparative Example 3 (without functional additives) had limited soil improvement and crop yield increase effects due to a lack of synergistic effects. Comparative Example 4 (using traditional fertilizer) had the worst performance in all indicators, demonstrating the significant technical advantages of this invention.

[0138] The remediation results of different treatment groups for moderate / severe saline-alkali soil are shown in Table 2.

[0139] Table 2

[0140]

[0141] Table 2 shows that the treatment effects of Examples 2 and 3 are better than those of Comparative Example 4, and the performance on moderately saline-alkali soil is better than that on severely saline-alkali soil. Regarding salt reduction, even in moderately saline-alkali soil, Example 1 achieved a salt reduction rate of 35%, while Comparative Example 4 only achieved 22.5%, a significant difference. Although the salt reduction rate was slightly lower in severely saline-alkali soil, it was still effective under high salinity conditions. In terms of yield and organic matter, the moderately saline-alkali soil had 1.17% organic matter and a yield of 280 kg / mu, while the severely saline-alkali soil only had 0.72% and 190 kg / mu, respectively, indicating that lower salinity leads to higher fertility and yield.

Claims

1. A method for preparing a saline-alkali soil remediation fertilizer based on soybean acidified sludge and biochar, comprising the following steps: (1) Pretreatment of soybean acidified sludge: The acidified sludge, a byproduct generated during soybean oil processing, is dried, crushed, and impurities are removed to obtain pretreated sludge; (2) Segmented gradient extraction: The pretreated sludge is subjected to segmented gradient extraction using a first-stage extraction and a second-stage extraction process. The extraction yields a first-stage extract, a second-stage extract, and a second-stage residue. The first-stage extract and the second-stage extract are mixed, heated, and fractionated to recover the extractant and obtain an extract concentrate. The second-stage residue is dried to obtain an extract residue powder. (3) Preparation of modified biochar: Apple branches were used as biochar precursors. After crushing the apple branches, they were soaked in phosphoric acid solution, drained, and placed in a carbonization furnace. They were then heated and carbonized under a nitrogen atmosphere and cooled to room temperature to obtain primary biochar. A composite modifier was added to the primary biochar for heating and modification. After modification, the biochar was cooled and crushed to obtain modified biochar. (4) Preparation of saline-alkali remediation fertilizer: The following components are mixed evenly according to mass fractions to obtain a compound mixture: 25-35 parts of extract concentrate, 5-15 parts of modified biochar, 30-40 parts of mixture of fungal residue and rice bran powder, 8-12 parts of extract residue powder, 3-5 parts of functional additives, and 2-4 parts of binder. Deionized water was added to the compound mixture, granulated, dried, cooled to room temperature, and then sieved to obtain saline-alkali soil remediation fertilizer.

2. The preparation method according to claim 1, characterized in that, In step (1), the soybean acidified sludge contains 20-40% oil, 10-20% protein, 10-20% free fatty acids, 5-10% free amino acids, and 5-10% organic nitrogen, phosphorus, and potassium nutrients. Drying is done by air-drying in a cool and ventilated place, controlling the moisture content to be 20-25% after drying. Crushing is done by putting the air-dried acidified sludge into a crusher and crushing it through an 80-mesh sieve.

3. The preparation method according to claim 1, characterized in that, In step (2), the primary extraction specifically involves: adding extractant A to the pretreated sludge, with a mass ratio of pretreated sludge to extractant A of 1:3-5; placing the mixture in a constant temperature water bath, controlling the temperature at 45-55℃, and using a bidirectional circulating stirring method at a stirring speed of 1200-1500 r / min; after stirring, placing it in a centrifuge, controlling the speed at 3500 r / min, centrifuging for 30 min, and separating the primary extract and the primary residue; wherein, the primary extract mainly contains free fatty acids, small molecule fat-soluble nutrients, and the extractant A is a mixture of n-hexane and ethyl acetate with a volume ratio of 3:

1.

4. The preparation method according to claim 3, characterized in that, In step (2), the secondary extraction specifically involves: adding extractant B to the primary residue, with a mass ratio of primary residue to extractant B of 1:2-3, controlling the constant temperature water bath temperature at 60-70℃, stirring speed at 1000-1200 r / min, and stirring continuously for 40-50 min; after stirring, centrifuging to obtain secondary extract and secondary residue, wherein the extractant B is a mixture of ethanol and deionized water with a volume ratio of 2:

1.

5. The preparation method according to claim 1, characterized in that, In step (2), heating fractionation involves mixing the primary extract with the secondary extract, pouring the mixture into a fractionation apparatus, and fractionating for 60 minutes at 80-90°C and atmospheric pressure. The secondary residue is dried in an oven at 85°C for 40 minutes.

6. The preparation method according to claim 1, characterized in that, In step (3), the phosphoric acid solution has a mass concentration of 4-8% and a soaking time of 24 hours. The carbonization is carried out by heating to 500-600℃ at a heating rate of 5℃ / min for 2-3 hours. The mass ratio of primary biochar to composite modifier is 10:1-2. The temperature modification is carried out at 200-250℃ for 1.5-2 hours. After cooling, the mixture is pulverized through a 100-mesh sieve. The composite modifier is a mixture of diatomaceous earth, bentonite and Fe3O4 nanoparticles. The mass ratio of diatomaceous earth, bentonite and Fe3O4 nanoparticles is (4-6):(2-5):(1-3).

7. The preparation method according to claim 1, characterized in that, In step (4), the functional additive is a mixture of humic acid, polyglutamic acid and arbuscular mycorrhizal fungi (AMF), with a mass ratio of humic acid, polyglutamic acid and arbuscular mycorrhizal fungi of 4:3:

3. The binder is modified starch. Deionized water is added to the compound mixture to adjust the moisture content of the mixture to 30-35%. Granulation is performed to control the particle size to 2-4 mm. Drying is performed by placing the granulated particles in an oven at 70-80℃ to dry them, controlling the moisture content of the dried particles to ≤10%. Sieving is performed by passing the particles through 10-mesh and 20-mesh sieves.

8. A fertilizer for remediating saline-alkali soil based on acidified soybean sludge and biochar, prepared by any one of the methods described in claims 1-7.

9. The application of the saline-alkali soil remediation fertilizer based on soybean acidified sludge and biochar as described in claim 8 in the improvement of saline-alkali land.

10. The application according to claim 9, characterized in that, One of the specific application methods is as follows: 1) For mild saline-alkali soil: Evenly spread the saline-alkali remediation fertilizer on the soil surface at a rate of 200-250 kg / mu, then use a rotary tiller to plow to a depth of 15-20 cm to ensure the fertilizer is thoroughly mixed with the soil; after plowing, water the soil to control the soil moisture content to 20-25% and soak the soil for 3-5 days, then sow crops as usual; after sowing, apply fertilizer every 30 days at a rate of 50-80 kg / mu, for two consecutive applications to ensure a continuous supply of soil nutrients and consolidate the remediation effect; 2) For moderate / severe saline-alkali soil: First, mix the saline-alkali remediation fertilizer with the top 0-20cm soil at a mass ratio of 1:10 to make a remediation substrate; evenly cover the soil surface with the remediation substrate to a thickness of 5-8cm, and then use a rotary tiller to turn the soil to a depth of 20-25cm to ensure that the remediation substrate is fully mixed with the deeper soil; after turning the soil, water it for 3-5 days, drain the water, and then let it dry for 2-3 days to reduce the soil moisture content to 20-25% before sowing crops; apply fertilizer once 15 days after sowing, at a rate of 100-120kg / mu, and apply fertilizer three times consecutively to gradually improve the physical and chemical properties of the soil and enhance soil fertility.

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