Preparation method of saline-alkali soil improvement slow-release fertilizer

Abstract

The invention relates to the technical field of saline-alkali soil improvement, and particularly discloses a preparation method of a saline-alkali soil improvement slow-release fertilizer, which comprises the following steps: (1) uniformly mixing carbon powder, a plant nutrient solution, molasses and alginic acid powder, granulating the obtained mixture, mixing the obtained particles with the carbon powder again, and coating to obtain a coated material; and separating out the particles, and drying to obtain the nutrition core. (2) uniformly mixing gypsum powder, carbon powder and water to form coating slurry; and coating the surface of the nutrition core with the slurry, and drying to obtain precursor particles. (3) uniformly mixing boric acid or lactic acid, carbon powder, gypsum powder and water to form coating slurry; and coating the slurry on the surfaces of the precursor particles, and drying to obtain the alkaline land soil improvement slow-release fertilizer. The slow-release fertilizer prepared by the process disclosed by the invention not only can improve the exchange capacity of sodium ions in soil, but also can improve the nutrient degree and the air permeability of the soil, and is beneficial to better growth of plants.

Description

Technical Field

[0001] The invention relates to the technical field of saline-alkali soil improvement, and in particular to a method for preparing a slow-release fertilizer for improving saline-alkali soil. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Salt-alkali land improvement generally refers to the transformation and utilization of saline soil, alkaline soil and salinized land. After soil salinization, the soil becomes unsuitable for plant growth due to excessive salt and alkaline substances in it, especially in arid and semi-arid areas with low precipitation and high evaporation. Salt migrates to the soil surface with water and then the water evaporates, causing salt to accumulate on the soil surface to form saline-alkali soil. In addition, long-term use of brackish water or industrial wastewater with high salt content for irrigation, as well as unreasonable irrigation methods, can easily lead to soil salinization. The main reason for the alkalinity and high salt content of saline-alkali soil is the high content of carbonate ions and sodium ions in it. Carbonate ions become alkaline after hydrolysis, causing the soil to become alkaline.

[0004] The use of gypsum to improve saline-alkali soil is currently a common method. Its principle is to use the Ca released by gypsum to improve saline-alkali soil. 2+ Exchangeable Na in soil colloids + A replacement reaction occurs, making the less soluble Na + It is converted into easily soluble sodium sulfate, which can effectively reduce the pH value and alkalinity of the soil after being leached and drained away by water. However, the inventors found that a problem in the above process is that the calcium ions released by gypsum are more easily captured by carbonate ions in the soil to form calcium carbonate, thereby solidifying the calcium ions and causing the Na in the soil colloid to be damaged. + The replacement capacity is insufficient. In addition, gypsum is difficult to solve the problem of poor saline-alkali soil, compaction and poor air permeability. Therefore, the traditional method of using gypsum to improve saline-alkali soil still has many shortcomings. Summary of the Invention

[0005] The present invention provides a method for preparing a slow-release fertilizer for improving saline-alkali soil, which not only improves the exchange capacity of sodium ions in the soil, but also increases the nutrient content and air permeability of the soil, thereby promoting better plant growth. Specifically, the technical solution of the present invention is as follows.

[0006] A method for preparing a slow-release fertilizer for improving saline-alkali soil comprises the following steps: (1) Carbon powder, plant nutrient solution, molasses, and alginic acid powder are uniformly mixed, and the resulting mixture is granulated. The resulting granules are mixed with carbon powder again for coating, and the granules are separated and dried to obtain the nutrient core for later use.

[0007] (2) Gypsum powder, carbon powder, and water are uniformly mixed to form a coating slurry. The slurry is then coated on the surface of the nutrient core and dried to obtain precursor particles.

[0008] (3) Boric acid or lactic acid, carbon powder, gypsum powder, and water are uniformly mixed to form a coating slurry. The slurry is then coated on the surface of the precursor particles and then dried to obtain the alkaline soil improving slow-release fertilizer.

[0009] Furthermore, in step (1), the ratio of the carbon powder, plant nutrient solution, molasses, and alginic acid powder is 1g: 0.2-0.3g: 0.15-0.35g: 0.1-0.18. Optionally, the fineness of the carbon powder is 50-80 mesh. The plant nutrient solution can be a commercially available product as needed.

[0010] Furthermore, in step (1), the mass ratio of the particles to the carbon powder is 1:0.5-0.7. Optionally, the fineness of the carbon powder is 200-500 mesh; the size of the particles is 5-15 mm, and particles of any other suitable size can also be prepared as needed.

[0011] Furthermore, in step (1), the drying temperature is 70-100° C., and the drying time is 20-40 min.

[0012] Furthermore, in step (2), the mass ratio of the gypsum powder to the carbon powder is 1:0.21-0.33. Optionally, the fineness of the carbon powder is 100-150 mesh.

[0013] Furthermore, in step (2), the solid content of the coating slurry is 50-65 wt.%.

[0014] Furthermore, in step (2), the nutritional core and the coating slurry are mixed in a mass ratio of 1g:1.8~2.5.

[0015] Furthermore, in step (2), the drying temperature is 70-100° C., and the drying time is 20-40 min.

[0016] Furthermore, in step (3), the mass ratio of the boric acid or lactic acid, carbon powder, and gypsum powder is 1-2:3-5.5:1-1.5. Optionally, the fineness of the carbon powder is 50-80 mesh.

[0017] Furthermore, in step (3), the solid content of the coating slurry is 52-65 wt.%.

[0018] Furthermore, in step (3), the precursor particles and the coating slurry are mixed in a mass ratio of 1:1.3-1.6.

[0019] Furthermore, in step (3), the drying temperature is 80-95° C., and the drying time is 20-35 min.

[0020] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects: The slow-release fertilizer for improving saline-alkali soil of the present invention first uses carbon powder, plant nutrient solution, molasses, and alginic acid to form a nutrient core, and then coats the surface of the inner coating layer formed by gypsum powder and carbon powder, and then coats the outer coating layer formed by boric acid or lactic acid, carbon powder, and gypsum powder. The outer coating layer is a structure formed by a zeolite aggregate formed by cementation under the action of the hydration product of gypsum and the boric acid or lactic acid distributed therein. After this improved slow-release fertilizer is applied to saline-alkali soil, on the one hand, the outer coating layer releases the boric acid or lactic acid therein under the action of water, consumes the carbonate ions in the soil, and converts it into carbon dioxide, which is easily discharged from the soil, reducing the content of carbonate ions in the soil. At the same time, the gypsum in the outer coating layer can also release some calcium ions to further consume the remaining carbonate ions in the soil, thereby reducing the capture of calcium ions released by the inner coating layer and improving the exchangeable Na in the soil colloid. + As the boric acid or lactic acid and gypsum in the outer coating layer dissolve, the outer coating layer is converted into a porous structure, which facilitates the contact between the gypsum in the inner coating layer and the moisture in the soil, thereby dissolving and releasing more Ca into the soil. 2+ Exchangeable Na in soil colloids + Replacement is carried out, thereby reducing the pH value and alkalinity of the soil. After the aforementioned improvement steps, the inner coating layer is also constructed into a slow-release shell due to the dissolution of part of the gypsum, so that the nutrients in the nutrient kernel are gradually released into the soil. At the same time, the released molasses can also provide carbon and nitrogen sources for microorganisms in the soil, improve the living environment of microorganisms, and thus help to improve the soil structure. At the same time, the alginic acid reacts with the sodium ions in the soil under an alkaline environment to form sodium alginate, which forms an insoluble gel after cross-linking under the action of calcium ions, thereby achieving the solidification of sodium ions, which helps to further reduce the pH value and alkalinity of the soil. In addition, the gypsum component in the present invention has undergone hydration in the process of forming the coating layer, so that after entering the soil, there will be no phenomenon of cementing the soil particles, thereby well avoiding the problem of easily aggravating soil compaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute undue limitations thereon. The embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a sample diagram of the slow-release fertilizer for improving saline-alkali soil prepared in Example 1 below. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0023] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. The reagents and raw materials used in the present invention can be purchased through conventional channels. Unless otherwise specified, the reagents and raw materials used in the present invention are used in accordance with conventional methods in the art or in accordance with the product instructions.

[0024] In addition, any methods and materials similar or equivalent to those described herein can be applied to the method of the present invention. The present invention will now be further described with reference to the accompanying drawings and specific embodiments. The preferred implementation methods and materials described herein are for demonstration purposes only.

[0025] Example 1 A method for preparing a slow-release fertilizer for improving saline-alkali soil comprises the following steps: (1) Mix carbon powder (fineness 80 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.25g:0.3g:0.14g and stir evenly. Then granulate the resulting mixture. Mix the resulting particles with a particle size of 5-10mm with carbon powder (fineness 300 mesh) in a ratio of 1g:0.55g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 90°C for 30 minutes to obtain the nutrient core, which is then set aside.

[0026] (2) Gypsum powder, carbon powder (fineness 120 mesh), and water were mixed to form a coating slurry with a solid content of 60 wt.%, wherein the mass ratio of gypsum powder to carbon powder was 1:0.28. The nutrient core and the coating slurry were then mixed in a mass ratio of 1:2 and tumbled to uniformly coat the surface of the nutrient core with the slurry. After completion, the obtained particles were removed and dried at 75°C for 30 minutes to obtain precursor particles for later use.

[0027] (3) Lactic acid powder, 50-mesh carbon powder, gypsum powder, and water are mixed evenly to form a coating slurry with a solid content of 60 wt.%, wherein the mass ratio of lactic acid powder, carbon powder, and gypsum powder is 1.6:4.5:1.2. Then, the precursor particles are mixed with the coating slurry at a mass ratio of 1:1.5 and rolled to uniformly coat the surface of the precursor particles with the slurry. After completion, the obtained particles are taken out and dried at 90°C for 30 minutes to obtain the alkaline soil improving slow-release fertilizer (such as Figure 1 shown).

[0028] A saline-alkali soil with a pH of 8.51 was used as the experimental object. The alkaline soil improving slow-release fertilizer prepared in this example was added at a rate of 350 kg / mu. After mixing evenly, the soil was sprinkled with water to moisten it. The soil was then left to stand for 30 days (sprinkled with water every three days). The pH of the soil was then tested. 20 and salt content (CO3 2- 、Na + 、Cl - ), calculate the desalination rate. The results are as follows: pH 20 =7.28, desalination rate = 64.36%.

[0029] Example 2 A method for preparing a slow-release fertilizer for improving saline-alkali soil comprises the following steps: (1) Mix carbon powder (fineness 60 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.2g:0.35g:0.18g and stir evenly. Then granulate the resulting mixture. Mix the resulting particles with a particle size of 5-10 mm with carbon powder (fineness 200 mesh) in a ratio of 1g:0.7g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 100°C for 20 minutes to obtain the nutrient core, which is then set aside.

[0030] (2) Gypsum powder, carbon powder (fineness 150 mesh), and water were mixed to form a coating slurry with a solid content of 50 wt.%, wherein the mass ratio of gypsum powder to carbon powder was 1:0.21. The nutrient core and the coating slurry were then mixed at a mass ratio of 1:1.8 and tumbled to uniformly coat the surface of the nutrient core with the slurry. After completion, the obtained particles were removed and dried at 70°C for 40 minutes to obtain precursor particles for later use.

[0031] (3) Lactic acid powder, 80-mesh carbon powder, gypsum powder, and water were uniformly mixed to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of lactic acid powder, carbon powder, and gypsum powder was 1.0:3.0:1.0. The precursor particles were then mixed with the coating slurry at a mass ratio of 1:1.6 and tumbled to uniformly coat the surface of the precursor particles with the slurry. After completion, the obtained particles were removed and dried at 95°C for 20 minutes to obtain the alkaline soil improving slow-release fertilizer.

[0032] A saline-alkali soil with a pH of 8.51 was used as the experimental object. The alkaline soil improving slow-release fertilizer prepared in this example was added at a rate of 350 kg / mu. After mixing evenly, the soil was sprinkled with water to moisten it. The soil was then left to stand for 30 days (sprinkled with water every three days). The pH of the soil was then tested. 20 and salt content (CO3 2- 、Na + 、Cl - ), calculate the desalination rate. The results are as follows: pH 20 =7.42, desalination rate = 61.79%.

[0033] Example 3 A method for preparing a slow-release fertilizer for improving saline-alkali soil comprises the following steps: (1) Mix carbon powder (fineness 50 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.3g:0.15g:0.1g and stir evenly. Then granulate the resulting mixture. Mix the resulting particles with a particle size of 10-15mm with carbon powder (fineness 300 mesh) in a ratio of 1g:0.5g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 70°C for 40 minutes to obtain the nutrient core, which is then set aside.

[0034] (2) Gypsum powder, carbon powder (fineness 100 mesh), and water were mixed to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of gypsum powder to carbon powder was 1:0.27. The nutrient core was then mixed with the coating slurry at a mass ratio of 1:2.5 and tumbled to uniformly coat the surface of the nutrient core with the slurry. After completion, the obtained particles were removed and dried at 100°C for 20 minutes to obtain precursor particles for later use.

[0035] (3) Boric acid powder, 60-mesh carbon powder, gypsum powder, and water were uniformly mixed to form a coating slurry with a solid content of 52 wt.%, wherein the mass ratio of boric acid powder, carbon powder, and gypsum powder was 2.0:5.5:1.5. The precursor particles were then mixed with the coating slurry at a mass ratio of 1:1.3 and tumbled to uniformly coat the surface of the precursor particles with the slurry. After completion, the obtained particles were removed and dried at 80°C for 35 minutes to obtain the alkaline soil improving slow-release fertilizer.

[0036] A saline-alkali soil with a pH of 8.51 was used as the experimental object. The alkaline soil improving slow-release fertilizer prepared in this example was added at a rate of 350 kg / mu. After mixing evenly, the soil was sprinkled with water to moisten it. The soil was then left to stand for 30 days (sprinkled with water every three days). The pH of the soil was then tested. 20 and salt content (CO3 2- 、Na + 、Cl - ), calculate the desalination rate. The results are as follows: pH 20 =7.16, desalination rate = 67.56%.

[0037] Example 4 A method for preparing a slow-release fertilizer for improving saline-alkali soil comprises the following steps: (1) Mix carbon powder (fineness 80 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.25g:0.3g:0.14g and stir evenly. Then granulate the resulting mixture. Mix the resulting particles with a particle size of 5-10mm with carbon powder (fineness 300 mesh) in a ratio of 1g:0.55g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 90°C for 30 minutes to obtain the nutrient core, which is then set aside.

[0038] (2) Gypsum powder, carbon powder (fineness 120 mesh), and water are uniformly mixed to form a coating slurry with a solid content of 60 wt.%, wherein the mass ratio of gypsum powder to carbon powder is 1:0.28. The nutrient core and the coating slurry are then mixed in a mass ratio of 1:2 and tumbled to uniformly coat the surface of the nutrient core with the slurry. After completion, the granules are removed and dried at 75°C for 30 minutes to obtain the alkaline soil improving slow-release fertilizer.

[0039] A saline-alkali soil with a pH of 8.51 was used as the experimental object. The alkaline soil improving slow-release fertilizer prepared in this example was added at a rate of 350 kg / mu. After mixing evenly, the soil was sprinkled with water to moisten it. The soil was then left to stand for 30 days (sprinkled with water every three days). The pH of the soil was then tested. 20 and salt content (CO3 2- 、Na + 、Cl - ), calculate the desalination rate. The results are as follows: pH 20 =7.97, desalination rate = 52.07%.

[0040] Example 5 A method for preparing a slow-release fertilizer for improving saline-alkali soil comprises the following steps: (1) Mix carbon powder (fineness 60 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.2g:0.35g:0.18g and stir evenly. Then granulate the resulting mixture. Mix the resulting particles with a particle size of 5-10 mm with carbon powder (fineness 200 mesh) in a ratio of 1g:0.7g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 100°C for 20 minutes to obtain the nutrient core, which is then set aside.

[0041] (2) Lactic acid powder, 80-mesh carbon powder, gypsum powder, and water are uniformly mixed to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of lactic acid powder, carbon powder, and gypsum powder is 1.0:3.0:1.0. The nutrient core and the coating slurry are then mixed in a mass ratio of 1:1.6 and tumbled to uniformly coat the surface of the nutrient core with the slurry. After completion, the granules are removed and dried at 95°C for 20 minutes to obtain the alkaline soil improving slow-release fertilizer.

[0042] A saline-alkali soil with a pH of 8.51 was used as the experimental object. The alkaline soil improving slow-release fertilizer prepared in this example was added at a rate of 350 kg / mu. After mixing evenly, the soil was sprinkled with water to moisten it. The soil was then left to stand for 30 days (sprinkled with water every three days). The pH of the soil was then tested. 20 and salt content (CO3 2- 、Na + 、Cl - ), calculate the desalination rate. The results are as follows: pH 20 =8.04, desalination rate = 30.48%.

[0043] Example 6 A method for preparing a slow-release fertilizer for improving saline-alkali soil comprises the following steps: (1) Mix carbon powder (fineness 50 mesh), plant nutrient solution, molasses, and alginic acid powder in a ratio of 1g:0.3g:0.15g:0.1g and stir evenly. Then granulate the resulting mixture. Mix the resulting particles with a particle size of 10-15mm with carbon powder (fineness 300 mesh) in a ratio of 1g:0.5g and tumble the mixture to coat the particles with carbon powder again. Then remove the particles and dry them at 70°C for 40 minutes to obtain the nutrient core, which is then set aside.

[0044] (2) Gypsum powder, carbon powder (fineness 100 mesh), and water were mixed to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of gypsum powder to carbon powder was 1:0.27. The nutrient core was then mixed with the coating slurry at a mass ratio of 1:2.5 and tumbled to uniformly coat the surface of the nutrient core with the slurry. After completion, the obtained particles were removed and dried at 100°C for 20 minutes to obtain precursor particles for later use.

[0045] (3) Mix 60-mesh carbon powder, gypsum powder, and water to form a coating slurry with a solid content of 52 wt.%, wherein the mass ratio of carbon powder to gypsum powder is 5.5:1.5. Then, mix the precursor particles with the coating slurry in a mass ratio of 1:1.3 and tumble the mixture to uniformly coat the surface of the precursor particles with the slurry. After completion, remove the obtained particles and dry them at 80°C for 35 minutes to obtain the alkaline soil improving slow-release fertilizer.

[0046] A saline-alkali soil with a pH of 8.51 was used as the experimental object. The alkaline soil improving slow-release fertilizer prepared in this example was added at a rate of 350 kg / mu. After mixing evenly, the soil was sprinkled with water to moisten it. The soil was then left to stand for 30 days (sprinkled with water every three days). The pH of the soil was then tested. 20 and salt content (CO3 2- 、Na + 、Cl - ), calculate the desalination rate. The results are as follows: pH 20 =7.85, desalination rate = 55.12%.

[0047] Example 7 A method for preparing a slow-release fertilizer for improving saline-alkali soil comprises the following steps: (1) Mix carbon powder (fineness 60 mesh), plant nutrient solution, and molasses in a ratio of 1g:0.2g:0.35g:0.18g and stir evenly. Then granulate the resulting mixture. Mix the resulting particles with a particle size of 5-10 mm with carbon powder (fineness 200 mesh) in a ratio of 1g:0.7g and tumble them to coat the particles with carbon powder again. Then remove the particles and dry them at 100°C for 20 minutes to obtain the nutrient core, which is then set aside.

[0048] (2) Gypsum powder, carbon powder (fineness 150 mesh), and water were mixed to form a coating slurry with a solid content of 50 wt.%, wherein the mass ratio of gypsum powder to carbon powder was 1:0.21. The nutrient core and the coating slurry were then mixed at a mass ratio of 1:1.8 and tumbled to uniformly coat the surface of the nutrient core with the slurry. After completion, the obtained particles were removed and dried at 70°C for 40 minutes to obtain precursor particles for later use.

[0049] (3) Lactic acid powder, 80-mesh carbon powder, gypsum powder, and water were uniformly mixed to form a coating slurry with a solid content of 65 wt.%, wherein the mass ratio of lactic acid powder, carbon powder, and gypsum powder was 1.0:3.0:1.0. The precursor particles were then mixed with the coating slurry at a mass ratio of 1:1.6 and tumbled to uniformly coat the surface of the precursor particles with the slurry. After completion, the obtained particles were removed and dried at 95°C for 20 minutes to obtain the alkaline soil improving slow-release fertilizer.

[0050] A saline-alkali soil with a pH of 8.51 was used as the experimental object. The alkaline soil improving slow-release fertilizer prepared in this example was added at a rate of 350 kg / mu. After mixing evenly, the soil was sprinkled with water to moisten it. The soil was then left to stand for 30 days (sprinkled with water every three days). The pH of the soil was then tested. 20 and salt content (CO3 2- 、Na + 、Cl - ), calculate the desalination rate. The results are as follows: pH 20 =7.76, desalination rate = 58.23%.

[0051] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a slow-release fertilizer for improving saline-alkali soil, characterized in that: The steps include: (1) mixing carbon powder, plant nutrient solution, molasses, and alginic acid powder uniformly, granulating the obtained mixture, mixing the obtained granules with carbon powder again for coating, separating the granules and drying them, thereby obtaining the nutrient core for later use; (2) Gypsum powder, carbon powder, and water are uniformly mixed to form a coating slurry; the slurry is then coated on the surface of the nutrient core and then dried to obtain precursor particles; (3) Boric acid or lactic acid, carbon powder, gypsum powder and water are uniformly mixed to form a coating slurry; the slurry is then coated on the surface of the precursor particles and then dried to obtain the alkaline soil improving slow-release fertilizer.

2. The method for preparing the slow-release fertilizer for improving saline-alkali soil according to claim 1, wherein: In step (1), the ratio of the carbon powder, plant nutrient solution, molasses, and alginic acid powder is 1g: 0.2-0.3g: 0.15-0.35g: 0.1-0.18; optionally, the fineness of the carbon powder is 50-80 mesh.

3. The method for preparing the slow-release fertilizer for improving saline-alkali soil according to claim 1, characterized in that: In step (1), the mass ratio of the particles to the carbon powder is 1:0.5-0.7; Optionally, in step (1), the fineness of the carbon powder is 200-500 mesh; Optionally, in step (1), the size of the particles is 5-15 mm.

4. The method for preparing the slow-release fertilizer for improving saline-alkali soil according to claim 1, wherein: In step (1), the drying temperature is 70-100°C and the drying time is 20-40 minutes.

5. The method for preparing the slow-release fertilizer for improving saline-alkali soil according to claim 1, characterized in that: In step (2), the mass ratio of the gypsum powder to the carbon powder is 1:0.21~0.33 Optionally, in step (2), the fineness of the carbon powder is 100-150 mesh.

6. The method for preparing the slow-release fertilizer for improving saline-alkali soil according to claim 1, characterized in that: In step (2), the solid content of the coating slurry is 50-65 wt.%.

7. The method for preparing the slow-release fertilizer for improving saline-alkali soil according to claim 1, characterized in that: In step (2), the nutrient core and the coating slurry are mixed in a mass ratio of 1g:1.8-2.5; Optionally, in step (2), the drying temperature is 70-100° C. and the drying time is 20-40 min.

8. The method for preparing the slow-release fertilizer for improving saline-alkali soil according to claim 1, characterized in that: In step (3), the mass ratio of the boric acid or lactic acid, carbon powder, and gypsum powder is 1-2:3-5.5:1-1.5; optionally, the fineness of the carbon powder is 50-80 mesh.

9. The method for preparing the slow-release fertilizer for improving saline-alkali soil according to claim 1, characterized in that: In step (3), the solid content of the coating slurry is 52-65 wt.%.

10. The method for preparing the slow-release fertilizer for improving saline-alkali soil according to any one of claims 1 to 9, characterized in that: In step (3), the precursor particles and the coating slurry are mixed in a mass ratio of 1:1.3-1.6; Optionally, in step (3), the drying temperature is 80-95° C., and the drying time is 20-35 min.

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