Method for treating saline-alkali soil by using biomass combined microbial fertilizer

Abstract

The application provides a method for treating saline-alkali soil by using biomass combined microbial fertilizer, and belongs to the technical field of soil improvement. The core layer of the improver provides long-acting nutrients for crops in the whole growth period. The first coating layer rapidly reduces the pH value and sodium content of the soil by calcium-sodium replacement and acid-alkali neutralization. The second coating layer adsorbs salt by relying on the porous structure of magnesium modified biochar and creates a good habitat for microorganisms. The third coating layer realizes precise controlled release and protects the internal microbial agent from the influence of chemical improvers. At the same time, the magnesium modified biochar is used as a microbial carrier. The abundant functional groups and developed pores of the magnesium modified biochar resist high-salt and high-alkali stress, slowly release magnesium ions to promote microbial metabolism, greatly improve the survival rate and colonization rate of the microbial agent, and finally construct a low-salt, high-fertilizer and microbe-rich microzone suitable for growth in the rhizosphere of crops, effectively promote the growth of roots and enhance the salt tolerance of crops.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement technology, and in particular relates to a method for treating saline-alkali land by combining biomass with microbial fertilizer. Background Technology

[0002] Soil salinization is one of the major ecological and environmental problems facing the world. Saline-alkali lands, due to their high salt content, abnormally high pH value, deteriorated soil structure, low organic matter content, and poor microbial activity, seriously affect plant growth, leading to low crop yields or even crop failure, and restricting the sustainable development of regional agriculture and ecological security.

[0003] Existing methods for saline-alkali land management mainly include water-based improvement, chemical improvement, physical improvement, and biological improvement. Water-based improvement reduces soil salinity through salt leaching and drainage, but it suffers from high water consumption, high costs, and a tendency for salt to return to the soil. Chemical improvement neutralizes soil alkalinity and replaces sodium ions by applying amendments such as gypsum, desulfurized gypsum, and humic acid, but long-term application can lead to soil compaction and secondary pollution. Physical improvement improves soil structure through deep plowing and sand mixing, but it is labor-intensive and its effects are not lasting.

[0004] Biological improvement is a rapidly developing technology for saline-alkali land management in recent years, mainly involving planting salt-tolerant plants and applying microbial fertilizers. Microbial fertilizers reduce soil salinity, improve soil structure, enhance soil fertility, and strengthen plant resistance through the metabolic activities of microorganisms, offering advantages such as low cost, environmental friendliness, and long-lasting effects. However, existing microbial fertilizers have the following problems in saline-alkali land applications: 1. Lack of intelligent release mechanisms, with effective components being released even in non-saline-alkali environments, resulting in low utilization rates; 2. Low survival rate and difficulty in colonization of microorganisms in high-salt-alkali environments, leading to unstable fertilizer effects; 3. Single strains or simple compound strains have limited functions, making it difficult to meet the comprehensive improvement needs of saline-alkali land. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for treating saline-alkali land by combining biomass with microbial fertilizer.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a soil conditioner for saline-alkali land, comprising a 30-40% core layer, a 25-35% first coating layer, a 20-30% second coating layer, and a 5-15% third coating layer; The core layer comprises the following components by weight: 20-30 parts slow-release nitrogen fertilizer, 15-25 parts slow-release phosphate fertilizer, 10-20 parts slow-release potassium fertilizer, 5-10 parts trace elements, and 3-5 parts binder. The first coating layer comprises the following components in parts by weight: 40-60 parts desulfurized gypsum, 20-30 parts ferrous sulfate, 10-20 parts humic acid, and 5-10 parts citric acid; The second coating layer comprises the following components in parts by weight: 70-85 parts magnesium-modified biochar, 10-20 parts composite salt-tolerant microbial agent, and 5-10 parts seaweed polysaccharide; The third coating layer comprises the following components in parts by weight: 40-60 parts polyglutamic acid, 20-30 parts chitosan, 5-10 parts crosslinking agent, and 3-5 parts plasticizer.

[0007] Preferably, the composite salt-tolerant microbial agent includes Haloxylon ammodendron, Azotobacter chrysogenum, Pseudomonas fluorescens, Bacillus mucilaginosus, Azotobacter brasiliensis, Bacillus megaterium, and Trichoderma echinosporum, wherein the mass ratio of Haloxylon ammodendron, Azotobacter chrysogenum, Pseudomonas fluorescens, Azotobacter mucilaginosus, Azotobacter brasiliensis, Bacillus megaterium, and Trichoderma echinosporum is 1~3:1:1:1:1:1:1~3.

[0008] Preferably, the preparation method of the magnesium-modified biochar is as follows: agricultural waste straw is pyrolyzed at 400~500℃ for 2~3h to obtain biochar; the biochar is mixed with 1~2mol / L magnesium chloride solution at a solid-liquid ratio of 1:5~10, stirred at 60~80℃ for 2~3h, filtered, washed until neutral, and dried at 100~110℃ for 5~15min to obtain magnesium-modified biochar.

[0009] Preferably, the trace elements include calcium, magnesium, sulfur, zinc, and boron; the binder includes bentonite; the crosslinking agent includes glutaraldehyde; and the plasticizer includes glycerin.

[0010] The present invention also provides a method for preparing the aforementioned saline-alkali soil conditioner, comprising the following steps: (1) Mix slow-release nitrogen fertilizer, slow-release phosphorus fertilizer, slow-release potassium fertilizer and trace elements in proportion, add binder, stir evenly, granulate, and obtain core layer; (2) Mix desulfurized gypsum, ferrous sulfate, humic acid and citric acid in proportion, crush them, add water to make a slurry, coat the core layer surface evenly, dry it, and complete the first coating layer coating. (3) Mix magnesium-modified biochar, composite salt-tolerant microbial agent and seaweed polysaccharide evenly, add water to make a slurry, evenly coat the surface of the first coating layer, dry, and complete the second coating layer coating. (4) Dissolve polyglutamic acid and chitosan in acetic acid solution, add crosslinking agent and plasticizer, stir evenly to obtain film-forming liquid, spray the film-forming liquid evenly on the surface of the second coating layer, dry, complete the second coating layer coating, and obtain the saline-alkali soil conditioner.

[0011] Preferably, the diameter of the granulation in step (1) is 2~3mm; the amount of water used in step (2) is 25%~35% of the total mass of desulfurized gypsum, ferrous sulfate, humic acid and citric acid; the drying temperature is 40~50℃, and the drying is carried out until the moisture content is ≤5%.

[0012] Preferably, the amount of water used in step (3) is 30% to 40% of the total mass of magnesium-modified biochar, composite salt-tolerant microbial agent and seaweed polysaccharide; the drying temperature is 30 to 40°C, and the drying is carried out until the moisture content is ≤8%.

[0013] Preferably, the concentration of the acetic acid solution in step (4) is 1~3%, and the amount of the acetic acid solution used is 10~20 times the total mass of polyglutamic acid and chitosan; the drying temperature is 30~40℃, and the drying is carried out until the moisture content is ≤5%.

[0014] The present invention also provides the application of the aforementioned saline-alkali soil conditioner in the improvement of saline-alkali land.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Salt-triggered slow-release mechanism: The outermost polyglutamic acid-chitosan composite membrane is salt-sensitive. In high-salt environments, it swells, allowing the release of internal active ingredients; in low-salt environments, it maintains a dense structure, slowing down the release rate. This release mechanism can automatically adjust the release rate according to the soil salinity concentration, improving the utilization rate of active ingredients and prolonging the improvement effect.

[0016] 2. Synergistic effect of four-layer core-shell structure: The core layer provides long-term nutrient supply to meet the nutritional needs of crops throughout their growth period; the first coating layer rapidly reduces soil pH and sodium content through calcium-sodium exchange and acid-base neutralization; the second coating layer uses the porous structure of magnesium-modified biochar to adsorb salts while providing a good habitat for microorganisms, improving their survival and colonization rates; the third coating layer achieves controlled release and protects the internal microbial agents from the effects of chemical amendments.

[0017] 3. High-efficiency microbial immobilization technology: Magnesium-modified biochar is used as a microbial carrier. Its abundant functional groups and well-developed porous structure provide protection for microorganisms, preventing damage from high-salt and high-alkali environments. Simultaneously, it slowly releases magnesium ions, promoting microbial growth and metabolism. Compared with direct application of inoculants, this increases the survival rate of microorganisms.

[0018] 4. Construction of a suitable rhizosphere micro-domain: The amendment slowly releases active ingredients around the crop roots, forming a low-salt, high-fertilizer, and microbial-rich rhizosphere micro-domain, which promotes crop root growth and improves crop salt tolerance.

[0019] 5. Resource utilization and environmental friendliness: Using industrial and agricultural waste such as desulfurized gypsum and agricultural waste straw as the main raw materials, the system realizes the resource utilization of waste, reduces production costs, and avoids secondary pollution. Detailed Implementation

[0020] This invention provides a soil conditioner for saline-alkali land, comprising a 30-40% core layer, a 25-35% first coating layer, a 20-30% second coating layer, and a 5-15% third coating layer; The core layer comprises the following components by weight: 20-30 parts slow-release nitrogen fertilizer, 15-25 parts slow-release phosphate fertilizer, 10-20 parts slow-release potassium fertilizer, 5-10 parts trace elements, and 3-5 parts binder. The first coating layer comprises the following components in parts by weight: 40-60 parts desulfurized gypsum, 20-30 parts ferrous sulfate, 10-20 parts humic acid, and 5-10 parts citric acid; The second coating layer comprises the following components in parts by weight: 70-85 parts magnesium-modified biochar, 10-20 parts composite salt-tolerant microbial agent, and 5-10 parts seaweed polysaccharide; The third coating layer comprises the following components in parts by weight: 40-60 parts polyglutamic acid, 20-30 parts chitosan, 5-10 parts crosslinking agent, and 3-5 parts plasticizer.

[0021] In this invention, the amount of the core layer is preferably 32-38%, more preferably 35%; the amount of the slow-release nitrogen fertilizer is preferably 22-28 parts, more preferably 25 parts; the amount of the slow-release potassium fertilizer is preferably 12-18 parts, more preferably 15 parts; the amount of the trace elements is preferably 6-9 parts, more preferably 8 parts; the trace elements include calcium, magnesium, sulfur, zinc, and boron; the amount of the binder is preferably 3.5-4.5 parts, more preferably 4 parts; the binder includes bentonite.

[0022] In this invention, the amount of the first coating layer is preferably 28-32%, more preferably 30%; the amount of the desulfurized gypsum is preferably 45-55 parts, more preferably 50 parts; the amount of the ferrous sulfate is preferably 22-28 parts, more preferably 25 parts; the amount of the humic acid is preferably 12-18 parts, more preferably 15 parts; and the amount of the citric acid is preferably 6-9 parts, more preferably 8 parts.

[0023] In this invention, the amount of the second coating layer is preferably 22-28%, more preferably 25%; the amount of the magnesium-modified biochar is preferably 75-80 parts; the preparation method of the magnesium-modified biochar is as follows: agricultural waste straw is pyrolyzed at 400-500℃ for 2-3 hours to obtain biochar; the biochar is mixed with 1-2 mol / L magnesium chloride solution at a solid-liquid ratio of 1:5-10, stirred at 60-80℃ for 2-3 hours, filtered, washed until neutral, and dried at 100-110℃ for 5-15 minutes to obtain magnesium-modified biochar. The preferred pyrolysis temperature is 420~480℃, more preferably 450℃; the preferred pyrolysis time is 2.5h; the preferred concentration of the magnesium chloride solution is 1.5mol / L; the preferred solid-liquid ratio is 1:6~9, more preferably 1:8; the preferred stirring temperature is 65~75℃, more preferably 70℃; the preferred stirring time is 2.5h; the preferred drying temperature is 102~108℃, more preferably 105℃; the preferred drying time is 8~12min, more preferably 10min. The preferred dosage of the composite salt-tolerant microbial agent is 12-18 parts, more preferably 15 parts; the composite salt-tolerant microbial agent includes Haloxylon ammodendron, Azotobacter chrysogenum, Pseudomonas fluorescens, Bacillus mucilaginosus, Azotobacter brasiliensis, Bacillus megaterium, and Trichoderma echinosporum, the mass ratio of Haloxylon ammodendron, Azotobacter chrysogenum, Pseudomonas fluorescens, Azotobacter mucilaginosus, Azotobacter brasiliensis, Bacillus megaterium, and Trichoderma echinosporum is 1-3:1:1:1:1:1:1-3, preferably 2:1:1:1:1:1:1:2; the preferred dosage of the seaweed polysaccharide is 6-9 parts, more preferably 8 parts.

[0024] In this invention, the amount of the third coating layer is preferably 7-12%, more preferably 10%; the amount of polyglutamic acid is preferably 45-55 parts, more preferably 50 parts; the amount of chitosan is preferably 22-28 parts, more preferably 25 parts; the amount of the crosslinking agent is preferably 6-9 parts, more preferably 8 parts; the crosslinking agent includes glutaraldehyde; the amount of the plasticizer is preferably 3.5-4.5 parts, more preferably 4 parts; the plasticizer includes glycerol.

[0025] The present invention also provides a method for preparing the aforementioned saline-alkali soil conditioner, comprising the following steps: (1) Mix slow-release nitrogen fertilizer, slow-release phosphorus fertilizer, slow-release potassium fertilizer and trace elements in proportion, add binder, stir evenly, granulate, and obtain core layer; (2) Mix desulfurized gypsum, ferrous sulfate, humic acid and citric acid in proportion, crush them, add water to make a slurry, coat the core layer surface evenly, dry it, and complete the first coating layer coating. (3) Mix magnesium-modified biochar, composite salt-tolerant microbial agent and seaweed polysaccharide evenly, add water to make a slurry, evenly coat the surface of the first coating layer, dry, and complete the second coating layer coating. (4) Dissolve polyglutamic acid and chitosan in acetic acid solution, add crosslinking agent and plasticizer, stir evenly to obtain film-forming liquid, spray the film-forming liquid evenly on the surface of the second coating layer, dry, complete the second coating layer coating, and obtain the saline-alkali soil conditioner.

[0026] In this invention, slow-release nitrogen fertilizer, slow-release phosphate fertilizer, slow-release potassium fertilizer, and trace elements are mixed in a certain proportion, a binder is added, the mixture is stirred evenly, and then granulated to obtain the core layer. The diameter of the granules is 2-3 mm.

[0027] In this invention, desulfurized gypsum, ferrous sulfate, humic acid, and citric acid are mixed in a certain proportion, pulverized, and water is added to form a slurry. This slurry is then uniformly coated onto the surface of the core layer and dried to complete the first coating layer. The amount of water used is 25% to 35% of the total mass of the desulfurized gypsum, ferrous sulfate, humic acid, and citric acid, preferably 28% to 32%, and more preferably 30%. The drying temperature is 40 to 50°C, preferably 42 to 48°C, and more preferably 45°C. The drying process continues until the moisture content is ≤5%.

[0028] In this invention, magnesium-modified biochar, a composite salt-tolerant microbial agent, and seaweed polysaccharide are mixed evenly, water is added to form a slurry, and the slurry is evenly coated onto the surface of the first coating layer and dried to complete the second coating layer. The amount of water used is 30% to 40% of the total mass of the magnesium-modified biochar, the composite salt-tolerant microbial agent, and the seaweed polysaccharide, preferably 32% to 38%, and more preferably 35%; the drying temperature is 30 to 40°C, preferably 32% to 38°C, and more preferably 35°C; the drying is carried out until the moisture content is ≤8%.

[0029] In this invention, polyglutamic acid and chitosan are dissolved in an acetic acid solution, a crosslinking agent and a plasticizer are added, and the mixture is stirred until homogeneous to obtain a film-forming solution. This film-forming solution is then uniformly sprayed onto the surface of a second coating layer and dried to complete the second coating layer coating, thus obtaining the saline-alkali soil conditioner. The concentration of the acetic acid solution is 1-3%, preferably 1.5-2.5%, more preferably 2%; the amount of acetic acid solution used is 10-20 times the total mass of polyglutamic acid and chitosan, preferably 12-18 times, more preferably 15 times; the drying temperature is 30-40℃, preferably 32-38℃, more preferably 35℃; and the drying process continues until the moisture content is ≤5%.

[0030] The present invention also provides the application of the aforementioned saline-alkali soil conditioner in the improvement of saline-alkali land.

[0031] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0032] Haloxylon ammodendron 1A05923 was purchased from the China Marine Microbial Culture Collection Center; Azotobacter chrysogenum (bio-110198) and Pseudomonas fluorescens (bio-51826) were purchased from Beijing Bio-Biobio Biotechnology Co., Ltd.; Azotobacter brasiliensis PJZ542 was purchased from Shanghai Bohu Biotechnology Co., Ltd.; Bacillus mucilaginosus (SHMCC D12018), Bacillus megaterium (SHMCC D82777), and SHMCC D62489 were purchased from Shanghai Preservation Microbial Co., Ltd.

[0033] Example 1

[0034] A soil conditioner for saline-alkali land comprises the following components: 35% core layer (25 parts slow-release nitrogen fertilizer, 20 parts slow-release phosphate fertilizer, 15 parts slow-release potassium fertilizer, 8 parts trace elements (calcium, magnesium, sulfur, zinc, boron), 4 parts bentonite), 30% first coating layer (50 parts desulfurized gypsum, 25 parts ferrous sulfate, 15 parts humic acid, 8 parts citric acid), and 25% second coating layer (80 parts magnesium-modified biochar (obtained by pyrolyzing agricultural waste straw at 450℃ for 2.5h; the biochar is then dissolved in 1.5mol / L magnesium chloride solution)). The liquid was mixed at a solid-liquid ratio of 1:8, stirred at 70℃ for 2.5h, filtered, washed until neutral, and dried at 105℃ for 10min to obtain magnesium-modified biochar, 15 parts of composite salt-tolerant microbial agent (Haloxylon ammodendron, Azotobacter chrysogenum, Pseudomonas fluorescens, Bacillus mucilaginosus, Azotobacter brasiliensis, Bacillus megaterium, Trichoderma echinosporum in a mass ratio of 2:1:1:1:1:1:2), 8 parts of seaweed polysaccharide, and 10% of the third coating layer (50 parts of polyglutamic acid, 25 parts of chitosan, 8 parts of glutaraldehyde, and 4 parts of glycerol).

[0035] The preparation method of the saline-alkali soil conditioner is as follows: (1) Mix slow-release urea, slow-release superphosphate, slow-release potassium chloride and trace elements in proportion, add bentonite, stir evenly, and form particles with a diameter of 2 mm through a disc granulator as the core layer. (2) First coating layer coating: Modified desulfurized gypsum, ferrous sulfate, humic acid and citric acid are mixed in proportion, crushed to 150 mesh, and water of 30% of the total mass of desulfurized gypsum, ferrous sulfate, humic acid and citric acid is added to make a slurry, which is then uniformly coated on the surface of the core layer and dried at 45°C to a moisture content of 5%; (3) Second coating layer coating: Corn stalks were pyrolyzed at 450℃ for 2.5 hours to obtain biochar; the biochar was mixed with 1.5mol / L magnesium chloride solution at a solid-liquid ratio of 1:8, stirred at 70℃ for 2.5 hours, filtered, washed until neutral, and dried at 105℃ to obtain magnesium-modified biochar; the magnesium-modified biochar was pulverized to 250 mesh, mixed evenly with composite salt-tolerant microbial agent and seaweed polysaccharide, and water was added at 35% of the total mass of magnesium-modified biochar, composite salt-tolerant microbial agent and seaweed polysaccharide to make a slurry, which was evenly coated on the surface of the first coating layer and dried at 35℃ to a moisture content of 8%; (4) Third coating layer coating: Polyglutamic acid and chitosan are dissolved in 2% acetic acid solution (15 times the total mass of polyglutamic acid and chitosan) in proportion, glutaraldehyde and glycerol are added, and the mixture is stirred evenly to obtain film-forming liquid; the film-forming liquid is evenly sprayed onto the surface of the second coating layer and dried at a low temperature of 35°C to a moisture content of 5% to obtain the saline-alkali soil conditioner.

[0036] Example 2

[0037] A soil conditioner for saline-alkali land comprises the following components: 30% core layer (20 parts slow-release nitrogen fertilizer, 15 parts slow-release phosphate fertilizer, 10 parts slow-release potassium fertilizer, 5 parts trace elements (calcium, magnesium, sulfur, zinc, boron), and bentonite), 25% first coating layer (40 parts desulfurized gypsum, 20 parts ferrous sulfate, 10 parts humic acid, and 5 parts citric acid), 20% second coating layer (70 parts magnesium-modified biochar, 10 parts compound salt-tolerant microbial agent (Haloxylon ammodendron, Azotobacter chrysophagus, Pseudomonas fluorescens, Bacillus mucilaginosus, Azotobacter brasiliensis, Bacillus megaterium, and Trichoderma echinosporum in a mass ratio of 1:1:1:1:1:1:1), and 5 parts seaweed polysaccharide), and 5% third coating layer (40 parts polyglutamic acid, 20 parts chitosan, 5 parts glutaraldehyde, and 3 parts glycerol).

[0038] The preparation method of the saline-alkali soil conditioner is as follows: (1) Mix slow-release urea, slow-release superphosphate, slow-release potassium chloride and trace elements in proportion, add bentonite, stir evenly, and form particles with a diameter of 3 mm through a disc granulator as the core layer. (2) First coating layer coating: Modified desulfurized gypsum, ferrous sulfate, humic acid and citric acid are mixed in proportion, crushed to 100 mesh, and water of 25% of the total mass of desulfurized gypsum, ferrous sulfate, humic acid and citric acid is added to make a slurry, which is uniformly coated on the surface of the core layer and dried at 40°C to a moisture content of 4%; (3) Second coating layer coating: Agricultural waste straw is pyrolyzed at 400℃ for 2h to obtain biochar; the biochar is mixed with 1mol / L magnesium chloride solution at a solid-liquid ratio of 1:5, stirred at 60℃ for 2h, filtered, washed until neutral, and dried at 100℃ for 5min to obtain magnesium-modified biochar; the magnesium-modified biochar is pulverized to 200 mesh, mixed evenly with composite salt-tolerant microbial agent and seaweed polysaccharide, and water is added at 30% of the total mass of magnesium-modified biochar, composite salt-tolerant microbial agent and seaweed polysaccharide to make a slurry, which is evenly coated on the surface of the first coating layer and dried at 30℃ to a moisture content of 7%; (4) Third coating layer coating: Polyglutamic acid and chitosan are dissolved in 1% acetic acid solution (10 times the total mass of polyglutamic acid and chitosan) in proportion, glutaraldehyde and glycerol are added, and the mixture is stirred evenly to obtain film-forming liquid; the film-forming liquid is evenly sprayed onto the surface of the second coating layer and dried at a low temperature of 30°C to a moisture content of 4% to obtain the saline-alkali soil conditioner.

[0039] Example 3

[0040] A soil conditioner for saline-alkali land comprises the following components: 40% core layer (30 parts slow-release nitrogen fertilizer, 25 parts slow-release phosphate fertilizer, 20 parts slow-release potassium fertilizer, 10 parts trace elements (calcium, magnesium, sulfur, zinc, boron), 5 parts bentonite), 35% first coating layer (60 parts desulfurized gypsum, 30 parts ferrous sulfate, 20 parts humic acid, 10 parts citric acid), and 30% second coating layer (85 parts magnesium-modified biochar, 10-20 parts...). The mixture consists of 1 part of a compound salt-tolerant microbial agent (containing Nocardia halophyte, Azotobacter chrysogenum, Pseudomonas fluorescens, Bacillus mucilaginosus, Azotobacter brasiliensis, Bacillus megaterium, and Trichoderma echinosporum in a mass ratio of 1-3:1:1:1:1:1:1-3), 5-10 parts of seaweed polysaccharide, and 5-15% of a third coating layer (containing 40-60 parts of polyglutamic acid, 20-30 parts of chitosan, 5-10 parts of glutaraldehyde, and 3-5 parts of glycerol).

[0041] The preparation method of the saline-alkali soil conditioner is as follows: (1) Mix slow-release urea, slow-release superphosphate, slow-release potassium chloride and trace elements in proportion, add bentonite, stir evenly, and form particles with a diameter of 2 mm through a disc granulator as the core layer. (2) First coating layer coating: Modified desulfurized gypsum, ferrous sulfate, humic acid and citric acid are mixed in proportion, crushed to 200 mesh, and water of 35% of the total mass of desulfurized gypsum, ferrous sulfate, humic acid and citric acid is added to make a slurry, which is uniformly coated on the surface of the core layer and dried at 50°C to a moisture content of 3%; (3) Second coating layer coating: Agricultural waste straw is pyrolyzed at 500℃ for 3h to obtain biochar; the biochar is mixed with 2mol / L magnesium chloride solution at a solid-liquid ratio of 1:10, stirred at 80℃ for 3h, filtered, washed until neutral, and dried at 110℃ for 15min to obtain magnesium-modified biochar; the magnesium-modified biochar is pulverized to 300 mesh, mixed evenly with composite salt-tolerant microbial agent and seaweed polysaccharide, and water is added to make a slurry with a total mass of 40% of magnesium-modified biochar, composite salt-tolerant microbial agent and seaweed polysaccharide, and evenly coated on the surface of the first coating layer, and dried at 40℃ to a moisture content of 6%; (4) Third coating layer coating: Polyglutamic acid and chitosan are dissolved in 3% acetic acid solution (20 times the total mass of polyglutamic acid and chitosan) in proportion, glutaraldehyde and glycerol are added, and the mixture is stirred evenly to obtain film-forming liquid; the film-forming liquid is evenly sprayed onto the surface of the second coating layer and dried at a low temperature of 40°C to a moisture content of 3% to obtain the saline-alkali soil conditioner.

[0042] Comparative Example 1

[0043] The difference from Example 1 is that no first coating layer is added.

[0044] Comparative Example 2

[0045] The difference from Example 1 is that no magnesium-modified biochar was added.

[0046] Comparative Example 3

[0047] The difference from Example 1 is that no compound salt-tolerant microbial agent is added.

[0048] Comparative Example 4

[0049] The difference from Example 1 is that no third coating layer is added.

[0050] Experimental Example 1

[0051] The experiment was conducted at the saline-alkali land experimental demonstration base of the Chinese Academy of Agricultural Sciences. Soil conditioners from Examples 1-3 and Comparative Examples 1-4 of this invention were applied according to the method of this invention. After application, planting trials were carried out. A randomized block design was used, with 5 replicates, and each treatment covering 667 m². 2 .

[0052] The crop tested was wheat.

[0053] Soil physicochemical property determination: Sampling was conducted at a depth of 0-20 cm. The determination of total water-soluble salts and pH in the soil was carried out in accordance with NY / T 1121.16-2006 "Soil Testing Part 16: Determination of Total Water-Soluble Salts in Soil". pH was measured using a pH meter method with a water-to-soil ratio of 5:1. Total nitrogen was determined using the semi-micro Kjeldahl method. Available phosphorus was determined using the 0.05 mol / L NaHCO3 solution extraction-UV spectrophotometer colorimetric method. Available potassium was determined using the 1 mol / L NH4Ac solution extraction-flame photometer method. Organic matter content was determined using the potassium dichromate external heating method.

[0054] Wheat yield was measured at maturity at 1.0m in each plot. 2 The number of ears per unit area was investigated within the micro-region; 60 single ears were randomly selected from areas with uniform growth for the number of grains per ear; after wheat harvest, the grains were threshed, air-dried, and adjusted to a moisture content of 10%, which was then used for the thousand-grain weight survey.

[0055] Experimental results are shown in Tables 1 and 2.

[0056] Table 1 Soil property test results

[0057] As shown in Table 1, the application of the soil conditioners of Examples 1-3 of this invention significantly improved the soil's physical and chemical properties, significantly reduced the water-soluble salt content, and decreased the degree of soil salinization. Comparative Examples 1-4, which did not include the first coating layer, magnesium-modified biochar, composite salt-tolerant microbial agent, or third coating layer, showed improvements in all indicators, but the effects were far less than those of Examples 1-3.

[0058] Table 2 Wheat Test Results

[0059] Table 2 shows that the application of the soil conditioners in Examples 1-3 of this invention promoted wheat growth and significantly increased wheat yield in saline-alkali land.

[0060] As can be seen from the above embodiments and experimental examples, the core layer of the amendment of the present invention provides long-lasting nutrients for the entire growth period of crops. The first coating layer rapidly reduces the soil pH and sodium content through calcium-sodium replacement and acid-base neutralization. The second coating layer relies on the porous structure of magnesium-modified biochar to adsorb salt and create a good habitat for microorganisms. The third coating layer achieves precise controlled release and protects the internal inoculants from the influence of chemical amendments. At the same time, magnesium-modified biochar serves as a microbial carrier, utilizing its rich functional groups and well-developed pores to resist high salt and high alkali stress, and slowly releases magnesium ions to promote microbial metabolism, greatly improving the survival rate and colonization rate of the inoculants. Ultimately, it constructs a suitable micro-domain with low salt, high fertilizer, and rich microorganisms in the crop rhizosphere, effectively promoting root growth and enhancing the crop's salt tolerance.

[0061] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle 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 soil conditioner for saline-alkali land, characterized in that, It includes a 30-40% core layer, a 25-35% first coating layer, a 20-30% second coating layer, and a 5-15% third coating layer; The core layer comprises the following components by weight: 20-30 parts slow-release nitrogen fertilizer, 15-25 parts slow-release phosphate fertilizer, 10-20 parts slow-release potassium fertilizer, 5-10 parts trace elements, and 3-5 parts binder. The first coating layer comprises the following components in parts by weight: 40-60 parts desulfurized gypsum, 20-30 parts ferrous sulfate, 10-20 parts humic acid, and 5-10 parts citric acid; The second coating layer comprises the following components in parts by weight: 70-85 parts magnesium-modified biochar, 10-20 parts composite salt-tolerant microbial agent, and 5-10 parts seaweed polysaccharide; The third coating layer comprises the following components in parts by weight: 40-60 parts polyglutamic acid, 20-30 parts chitosan, 5-10 parts crosslinking agent, and 3-5 parts plasticizer.

2. The soil conditioner for saline-alkali land according to claim 1, characterized in that, The composite salt-tolerant microbial agent includes Haloxylon ammodendron, Azotobacter chrysogenum, Pseudomonas fluorescens, Bacillus mucilaginosus, Azotobacter brasiliensis, Bacillus megaterium, and Trichoderma echinosporum. The mass ratio of Haloxylon ammodendron, Azotobacter chrysogenum, Pseudomonas fluorescens, Azotobacter mucilaginosus, Azotobacter brasiliensis, Bacillus megaterium, and Trichoderma echinosporum is 1~3:1:1:1:1:1:1~3.

3. The soil conditioner for saline-alkali land according to claim 1, characterized in that, The method for preparing the magnesium-modified biochar is as follows: agricultural waste straw is pyrolyzed at 400-500℃ for 2-3 hours to obtain biochar; the biochar is mixed with 1-2 mol / L magnesium chloride solution at a solid-liquid ratio of 1:5-10, stirred at 60-80℃ for 2-3 hours, filtered, washed until neutral, and dried at 100-110℃ for 5-15 minutes to obtain magnesium-modified biochar.

4. The soil conditioner for saline-alkali land according to claim 1, characterized in that, The trace elements include calcium, magnesium, sulfur, zinc, and boron; the binder includes bentonite; the crosslinking agent includes glutaraldehyde; and the plasticizer includes glycerin.

5. The method for preparing the saline-alkali soil conditioner according to any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Mix slow-release nitrogen fertilizer, slow-release phosphorus fertilizer, slow-release potassium fertilizer and trace elements in proportion, add binder, stir evenly, granulate, and obtain core layer; (2) Mix desulfurized gypsum, ferrous sulfate, humic acid and citric acid in proportion, crush them, add water to make a slurry, coat the core layer surface evenly, dry it, and complete the first coating layer coating. (3) Mix magnesium-modified biochar, composite salt-tolerant microbial agent and seaweed polysaccharide evenly, add water to make a slurry, evenly coat the surface of the first coating layer, dry, and complete the second coating layer coating. (4) Dissolve polyglutamic acid and chitosan in acetic acid solution, add crosslinking agent and plasticizer, stir evenly to obtain film-forming liquid, spray the film-forming liquid evenly on the surface of the second coating layer, dry, complete the second coating layer coating, and obtain the saline-alkali soil conditioner.

6. The preparation method according to claim 5, characterized in that, The diameter of the granulation in step (1) is 2~3mm; the amount of water used in step (2) is 25%~35% of the total mass of desulfurized gypsum, ferrous sulfate, humic acid and citric acid; the drying temperature is 40~50℃, and the drying is carried out until the moisture content is ≤5%.

7. The preparation method according to claim 5, characterized in that, The amount of water used in step (3) is 30% to 40% of the total mass of magnesium-modified biochar, composite salt-tolerant microbial agent and seaweed polysaccharide; the drying temperature is 30 to 40°C, and the drying is carried out until the moisture content is ≤8%.

8. The preparation method according to claim 5, characterized in that, The concentration of the acetic acid solution in step (4) is 1-3%, and the amount of the acetic acid solution used is 10-20 times the total mass of polyglutamic acid and chitosan; the drying temperature is 30-40℃, and the drying is carried out until the moisture content is ≤5%.

9. The application of the saline-alkali soil conditioner according to any one of claims 1 to 4 in the improvement of saline-alkali land.

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