A soil conditioner for improving saline-alkali soil and a preparation method and application thereof

Abstract

This invention provides a soil conditioner for saline-alkali land, its preparation method, and its application method. The soil conditioner is composed of the following raw materials in parts by weight: 25-35 parts of organic-inorganic modified zeolite, 15-20 parts of organic carbon, 5-15 parts of organic acid-calcium complex, 10-15 parts of phosphogypsum, 0.1-0.3 parts of humic acid-nano zero-valent iron, 8-12 parts of bentonite, 2-5 parts of compound microbial agent, 5-10 parts of ammonium sulfate, and 0.1-0.2 parts of polyacrylamide. The components of the soil conditioner of this invention work synergistically to address the problems of difficult sodium removal, slow pH reduction, severe compaction, low fertility, accumulation of reducing toxins, and low microbial activity in saline-alkali land.

Description

Technical Field

[0001] This invention relates to the field of fertilizer technology, and in particular to a soil conditioner for saline-alkali land, its preparation method, and its application. Background Technology

[0002] Saline-alkali land is mainly distributed in arid, semi-arid, and coastal areas. Due to multiple obstacles such as high salinity, high pH, ​​poor physical structure, low organic matter content, poor nutrient availability, and accompanying reducing toxicity (in waterlogged areas), crop growth is inhibited, yields are extremely low, and even crop failure occurs. Therefore, developing efficient and systematic saline-alkali land improvement and fertilization technologies is of great significance for ensuring national food security and the sustainable use of arable land resources.

[0003] Currently, existing saline-alkali land management mainly focuses on engineering salt removal, chemical amendment, physical amendment, organic fertilizer enrichment, and bioremediation. While engineering salt removal technology can reduce total salt content, its effect on improving alkaline soil is limited, and it cannot improve soil structure and fertility, while also consuming large amounts of freshwater resources. Chemical amendment technology involves a displacement reaction or acid-base neutralization reaction with exchangeable sodium in the soil. Commonly used chemical amendments include calcium-based amendments, acidic amendments, and organic-inorganic composite amendments. However, existing chemical amendment technologies have significant shortcomings; a single amendment cannot simultaneously address multiple obstacles such as high salinity, high pH, ​​compaction, infertility, and reducing toxicity.

[0004] Existing solutions mostly target single factors and fail to organically integrate multiple mechanisms such as chemical improvement, physical improvement, organic fertilization, and bioremediation, lacking systematic synergy; they are not targeted enough for reducing saline-alkali land; the improved soil is prone to salinization, lacks a long-term fertilization mechanism, and there are compatibility conflicts between effective components on the market, making it impossible to achieve high-activity compounding; therefore, it is very important to study a systematic soil conditioner for saline-alkali land and its preparation and application methods. Summary of the Invention

[0005] One objective of this invention is to provide a soil conditioner for improving saline-alkali land through a multi-mechanism synergistic approach, simultaneously addressing multiple obstacles such as high salinity and alkalinity, soil compaction, low fertility, and the coexistence of redox toxicity.

[0006] Another objective of this invention is to provide a highly efficient physical adsorption treatment material and its preparation method, which uses hydrochloric acid and hexadecyltrimethylammonium bromide to treat zeolite, resulting in an organic-inorganic modified zeolite that can be used for physical adsorption treatment of saline-alkali land.

[0007] Another objective of this invention is to provide an organic acid-calcium complex and its preparation method, wherein citric acid, humic acid and calcium oxide are reacted and complexed to obtain an organic acid-calcium complex for application in saline-alkali land for salt reduction and fertilization.

[0008] Another objective of this invention is to provide a method for preparing a soil conditioner for improving saline-alkali land. This method can effectively prepare the soil conditioner, avoid component antagonism, and maximize and prolong the improvement effect.

[0009] To achieve the above objectives, a soil conditioner for improving saline-alkali land comprises, by weight, 25-35 parts of organic-inorganic modified zeolite, 15-20 parts of organic carbon, 5-15 parts of organic acid-calcium complex, 10-15 parts of phosphogypsum, 0.1-0.3 parts of humic acid-nano zero-valent iron, 8-12 parts of bentonite, 2-5 parts of compound microbial agent, 5-10 parts of ammonium sulfate, and 0.1-0.2 parts of polyacrylamide. This invention's soil conditioner is a multi-mechanism synergistic system designed based on the characteristics of saline-alkali land: high sodium, high pH, ​​compaction, infertility, and reducing toxicity. Organic-inorganic modified zeolite acts as the framework of aggregates, increasing porosity. Bentonite, upon contact with water, fills the gaps between zeolite particles, binding fine-grained soil. Organic carbon, a porous carbon framework with a rough surface, increases the binding of organic matter and minerals, enhancing the organic carbon content of aggregates. Polyacrylamide stabilizes the modified zeolite, bentonite, and organic carbon together through molecular forces, reducing soil bulk density, improving water-stable large aggregates, and significantly enhancing resistance to water erosion and compaction. The organic acid in the organic acid-calcium complex reacts directly with the alkali salts in the saline-alkali land, rapidly lowering pH. Ammonium sulfate provides long-term physiological acidity in the soil, and microorganisms living in the soil also provide trace amounts of weak acid. These three components work synergistically to achieve short-term and long-term pH reduction. Phosphogypsum and organic acid-calcium complexes can provide calcium ions for sodium removal. Organic acid ions can rapidly chelate sodium ions and prevent the adsorption of calcium ions released from phosphogypsum. Simultaneously, organic acids can provide an initial carbon source for microorganisms. Organic-inorganic modified zeolite exhibits high selective adsorption of sodium ions and can synergistically capture free sodium ions under displacement, preventing their adsorption to soil colloids. Phosphogypsum, organic acid-calcium, ammonium sulfate, modified zeolite, bentonite, and organic carbon are used for initial chemical modification, reducing salinity, lowering pH, and initially improving soil structure. Humic acid-nano zero-valent iron acts as a redox regulator, consuming oxidizing substances in the soil, improving the soil reducing environment, promoting organic matter transformation, and the generated iron oxides can fix salt ions. Compound microbial agents are used for bioremediation, restoring the soil microecology. Through initial chemical modification, mid-term oxidation, and late-term biological control to improve saline-alkali soil, the synergistic effect of this composition is not a simple additive of independent components, but rather a six-fold mechanism of chemical replacement, physical adsorption, organic chelation, oxidation regulation, structural stabilization, and biological activation to treat saline-alkali land.

[0010] Preferably, the organic-inorganic modified zeolite is zeolite modified with hydrochloric acid and hexadecyltrimethylammonium bromide, wherein the concentration of hydrochloric acid is 30%-35% and the purity of hexadecyltrimethylammonium bromide is 99%-99.5%. Hydrochloric acid removes impurities such as calcium, magnesium, and iron ions from the zeolite channels, unblocks the channels, and increases the specific surface area. Hexadecyltrimethylammonium bromide enters the zeolite channels and surface through ion exchange, forming an organic phase covering layer. This results in a positively charged surface organic layer that shields the negatively charged inner layer. Long-chain alkyl groups occupy the pore openings and channels, forming a water transport barrier layer and cation competitive exchange, allowing sodium ions to easily pass through, thus achieving sodium removal. It can also capture chloride and sulfate ions. The modified zeolite particles form a rigid framework, synergistically increasing soil porosity, reducing bulk density, improving water permeability and aeration, and promoting salt leaching in conjunction with bentonite and polyacrylamide.

[0011] Preferably, the organic carbon is rice husk char-algae biochar, with a ratio of rice husk char to algae biochar of 4-6:1; the organic acid-calcium complex is a citric acid-humic acid-calcium complex, prepared from citric acid, humic acid, and calcium oxide in a ratio of 1-2:1:0.5-1; the citric acid has a purity of 98.0%-99.0% and a particle size range of 80-120 mesh; the humic acid has a content of 60.0%-65.0% and a particle size range of 80-120 mesh; and the calcium oxide has a content of 85.0%-90.0% and a particle size range of 100-200 mesh. Organic carbon prepared from rice husk biochar and algal biochar can provide readily available organic matter, buffer soil pH, adsorb sodium ions, and promote aggregate formation. Rice husk biochar is rich in silicon, which can improve the salt tolerance of crops. Algal biofilms chelate sodium ions, which can improve soil salinity and introduce stress-resistant algae to secrete large amounts of auxin, promoting root growth and crop growth. In organic acid-calcium complexes, calcium ions coordinate with citric acid and humic acid to form a ternary coordination structure. Citric acid rapidly neutralizes alkalinity, while humic acid buffers pH, preventing soil alkalinity rebound. It can provide both readily available and long-lasting calcium ions, efficiently replace sodium ions, and in addition, it can chelate sodium ions, activate nutrients, cement soil particles, and serve as a microbial carbon source.

[0012] Preferably, the humic acid-nano zero-valent iron has an iron content of 95%-99% and a particle size of 40-80 nm; the phosphogypsum has a purity of 82%-85% and a phosphorus content of 0.4%-0.8%; the bentonite has a montmorillonite content of 60%-70%; and the ammonium sulfate has an nitrogen content of 20.5%-21.0%. Humic acid-nano zero-valent iron is a composite material that utilizes the carboxyl and phenolic hydroxyl groups of humic acid to coat, stabilize, and functionalize nano-zero-valent iron. Its preparation method is as follows: S1. First, prepare a humic acid solution with a concentration of 5-10 g / L and adjust the pH to 8-10. S2, Add iron salts (FeSO4·7H2O, FeCl2·4H2O) with a ferrous ion to humic acid mass ratio of 1:0.2; S3. Introduce an inert gas, then slowly add sodium borohydride (NaBH4) as a reducing agent. The molar ratio of sodium borohydride to ferrous ions is 2:1. The reaction temperature is 20-30℃, and the reaction time is 30-120 min. S4. Separation and drying: First, magnetic separation is performed, then washing is done with deionized water and anhydrous ethanol, and finally vacuum freeze drying is performed.

[0013] Preferably, the compound microbial agent is composed of *Lactiplantibacillus plantarum*, *Saccharomycodes sinenses*, *Bacillus subtilis*, and *Aspergillus niger* in a ratio of 1-1.5:1-1.5:1.5-2:1; the *Lactiplantibacillus plantarum* is catalog number CGMCC1.2437, deposited at the China General Microbiological Culture Collection Center on December 22, 1999; the *Saccharomycodes sinenses* is catalog number CGMCC2.1395, deposited at the China General Microbiological Culture Collection Center on December 22, 1999; the *Bacillus subtilis* is catalog number CGMCC1.15792, deposited at the China General Microbiological Culture Collection Center on July 10, 2016; the *Aspergillus niger ... The compound microbial agent (CGMCC3.11571) is deposited at the China General Microbiological Culture Collection Center on July 14, 2008. Before use, the compound microbial agent undergoes activation treatment, including: thoroughly mixing the compound microbial agent powder with sterile water, controlling the concentration of the compound microbial agent to 10–50 g / L, adding 1%–3% molasses or glucose as an activation carbon source, and culturing at 25–35℃ for 4–12 h to restore the metabolic activity of the cells, thus obtaining the activated microbial solution.

[0014] This invention also provides a method for preparing a soil conditioner for saline-alkali land, comprising the following steps: A) Preparation of organic-inorganic modified zeolites; B) Preparation of organic carbon; C) Preparation of organic acid-calcium complexes; D) Pretreatment with phosphogypsum, bentonite, ammonium sulfate, polyacrylamide, and compound microbial agents; E) Place the organic-inorganic modified zeolite, phosphogypsum, organic carbon, organic acid-calcium complex, bentonite, and ammonium sulfate in a mixer according to their weight parts and mix for 20-30 minutes. After mixing evenly, the basic modified carrier is obtained. F) Take humic acid-nano zero-valent iron and compound microbial agent. Mix humic acid-nano zero-valent iron at low speed and add it to the basic soil amendment carrier. Mix for 20-30 minutes to obtain a mixture. Then spray the compound microbial agent on the surface of the obtained mixture and keep the moisture content at 8%-12% to obtain a soil amendment.

[0015] Preferably, the method for preparing the organic-inorganic modified zeolite includes the following steps: 1) Mix zeolite and hydrochloric acid at a solid-liquid ratio of 1:2.5-3.5 and stir at room temperature for 2-4 hours; allow to stand and precipitate, filter to obtain solid, wash with deionized water 1-2 times, and then dry at 110-120℃ to obtain acid-modified zeolite. 2) Weigh hexadecyltrimethylammonium bromide and acid-modified zeolite at a mass ratio of 0.05-0.15:1. Dissolve hexadecyltrimethylammonium bromide in deionized water and heat to 40-50℃. Add the acid-modified zeolite to the hexadecyltrimethylammonium bromide solution and stir in a water bath at 60-80℃ for 4-6 hours. After the reaction, filter to obtain a solid, wash with deionized water 1-2 times, dry at 110-120℃, and grind through a 100-mesh sieve to obtain organic-inorganic modified zeolite.

[0016] Preferably, the method for preparing the organic carbon includes the following steps: 1) Pyrolyze rice husks under limited oxygen conditions at 500-600℃, keep warm for 1-2 hours, cool and then pulverize through 80 mesh to obtain rice husk charcoal; 2) Add rice husk charcoal and algal biochar to a mixer at a mass ratio of 4-6:1, mix for 15-20 minutes, add 10%-15% water by solid mass, extrude and granulate to a particle size of 2-4 mm, and dry at 60-80℃ to obtain organic carbon.

[0017] Preferably, the method for preparing the organic acid-calcium complex includes the following steps: 1) Weigh out citric acid, humic acid and calcium oxide in proportion. Dissolve citric acid in water, with the mass of water being twice that of citric acid. Add humic acid while stirring, then slowly add calcium oxide. Place in a room temperature water bath and continue stirring for 1-2 hours to obtain a paste. 2) Dry the paste at 75-85℃, pulverize it and pass it through a 60-mesh sieve to obtain an organic acid-calcium complex.

[0018] The application of a soil conditioner for saline-alkali land to improve saline-alkali soil.

[0019] The beneficial effects of this invention are: 1.1 The soil conditioner of this invention can significantly reduce the exchangeable sodium content, alkalinity, and pH of the soil. Phosphogypsum and organic acid-calcium provide fast-acting and slow-release calcium ions to replace sodium ions in soil colloids. Organic-inorganic modified zeolite has high selective adsorption of sodium ions, and organic acids can also chelate free sodium ions to prevent sodium ions from being re-adsorbed into the soil, thus effectively desalinizing the soil. The organic acids in the soil conditioner of this invention can rapidly reduce soil pH, the physiological acidification effect of ammonium sulfate can continuously reduce rhizosphere pH, humic acid buffers against pH rebound, and the compound microbial agent ferments for biological treatment of the soil. 2. The soil conditioner of the present invention uses organic-inorganic modified zeolite and rice husk charcoal as rigid particles, bentonite to fill the gaps, and polyacrylamide to bind them together to form water-stable macroaggregates; thereby comprehensively improving the physical structure of the soil and enhancing its permeability and water retention capacity. 3. The rice husk char in the soil conditioner of this invention provides long-lasting stable carbon, and algal biochar provides fast-acting activated carbon; ammonium sulfate, algal biochar, phosphogypsum and organic acids - calcium and sulfur, and rice husk char release active silicon; citric acid and humic acid chelate trace elements such as iron, zinc and manganese, and the compound microbial agent activates the fixed phosphorus in the soil, improving the availability of soil organic matter and nutrients. 4. The soil conditioner of this invention systematically solves the problems of difficult sodium removal, slow pH reduction, severe compaction, low fertility, accumulation of reducing toxins, and low microbial activity in the process of saline-alkali land treatment through the synergistic effect of six mechanisms: chemical replacement, physical adsorption, organic chelation, oxidation regulation, structural stabilization, and biological activation. It not only achieves rapid desalination and dealkali removal in the short term, but also provides fertilizer in a long-term and stable manner, making it suitable for the improvement of large areas of saline-alkali land in my country. Attached Figure Description

[0020] Figure 1 Characteristics of soil pH distribution in arable land; Figure 2 Nutrient content and distribution characteristics of arable land soil; Figure 3 Microbial carbon and nitrogen characteristics of cultivated land and their correlation with soil pH; Detailed Implementation

[0021] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0022] Example 1: This embodiment provides a formula, preparation method, and application method for an agent to improve saline-alkali soil; Soil conditioner formula: 30 parts organic-inorganic modified zeolite, 18 parts organic carbon, 10 parts organic acid-calcium complex, 13 parts phosphogypsum, 0.2 parts humic acid-nano zero-valent iron, 10 parts bentonite, 3 parts compound microbial agent, 8 parts ammonium sulfate, and 0.15 parts polyacrylamide. Compound microbial agent: Composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1:1:2:1.

[0023] Preparation method of soil conditioner: Preparation of organic-inorganic modified zeolites: Zeolite and hydrochloric acid were mixed at a solid-liquid ratio of 1:3, stirred at room temperature for 3 hours, allowed to stand and precipitate, filtered to obtain a solid, washed 1-2 times with deionized water, and then dried at 115℃ to obtain acid-modified zeolite. Hexadecyltrimethylammonium bromide and acid-modified zeolite were weighed at a mass ratio of 0.1:1. Hexadecyltrimethylammonium bromide was dissolved in deionized water and heated to 45°C. The acid-modified zeolite was then added to the hexadecyltrimethylammonium bromide solution and stirred in a water bath at 70°C for 5 hours. After the reaction, the solid was obtained by filtration, washed 1-2 times with deionized water, dried at 115°C, and ground through a 100-mesh sieve to obtain organic-inorganic modified zeolite. Preparation of organic carbon: Rice husks were pyrolyzed at 550℃ under limited oxygen conditions and kept at that temperature for 1.5 hours. After cooling, the husks were pulverized through an 80-mesh sieve to obtain rice husk charcoal. Rice husk charcoal and algal biochar were added to a mixer at a mass ratio of 5:1 and mixed for 18 minutes. Water at 13% of the solid mass was added and extruded to granulate with a particle size of 3 mm. The mixture was then dried at 70°C to obtain organic carbon. Preparation of organic acid-calcium complexes: Weigh out citric acid, humic acid, and calcium oxide in a ratio of 1.5:1:0.8. Dissolve citric acid in water, with the water mass being twice that of citric acid. Add humic acid while stirring, then slowly add calcium oxide. Heat in a 25°C water bath and stir for 1.5 hours to obtain a paste. The paste was dried at 80°C and pulverized through a 60-mesh sieve to obtain an organic acid-calcium complex.

[0024] Phosphogypsum was dried at 55℃ for 3 hours, initially passed through a 10-mesh sieve, and then pulverized and passed through a 100-mesh sieve; bentonite was pulverized using a crusher, then pulverized using a grinding mill, and passed through a 200-mesh sieve; ammonium sulfate was pulverized and passed through a 20-mesh sieve.

[0025] Organic-inorganic modified zeolite, phosphogypsum, organic carbon, organic acid-calcium complex, bentonite, and ammonium sulfate were placed in a mixer according to their weight parts and mixed for 25 minutes. After mixing evenly, the mixture was sealed and stored for later use. Take humic acid-nano zero-valent iron and compound microbial agent, add humic acid-nano zero-valent iron to the basic soil amendment carrier at low speed, mix for 25 minutes to obtain a mixture, and then spray the compound microbial agent on the surface of the obtained mixture, keeping the moisture content at 10%, to obtain a soil amendment.

[0026] Application method of a soil conditioner for improving saline-alkali land and enriching soil: The general application rate is 2000 kg / hm². 2 ~5000 kg / hm 2 (Dry weight), in this example and the following examples, 3000 kg / hm² was applied. 2 .

[0027] Example 2: Formula of soil conditioner for saline-alkali land: 25 parts organic-inorganic modified zeolite, 20 parts organic carbon, 13 parts organic acid-calcium complex, 15 parts phosphogypsum, 0.3 parts humic acid-nano zero-valent iron, 12 parts bentonite, 5 parts compound microbial agent, 10 parts ammonium sulfate, and 0.2 parts polyacrylamide. Compound microbial agent: Composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1.5:1.5:2:1.

[0028] Preparation method of soil conditioner: Preparation of organic-inorganic modified zeolites: Zeolite and hydrochloric acid were mixed at a solid-liquid ratio of 1:2.5 and stirred at room temperature for 2.5 hours. After settling, the solid was filtered and washed 1-2 times with deionized water and then dried at 110°C to obtain acid-modified zeolite. Hexadecyltrimethylammonium bromide and acid-modified zeolite were weighed at a mass ratio of 0.15:1. Hexadecyltrimethylammonium bromide was dissolved in deionized water and heated to 40°C. The acid-modified zeolite was then added to the hexadecyltrimethylammonium bromide solution and stirred in a water bath at 65°C for 4 hours. After the reaction, the solid was obtained by filtration, washed 1-2 times with deionized water, dried at 110°C, and ground through a 100-mesh sieve to obtain organic-inorganic modified zeolite. Preparation of organic carbon: Rice husks were pyrolyzed at 600℃ under limited oxygen conditions, kept at the temperature for 1 hour, cooled, and then pulverized through an 80-mesh sieve to obtain rice husk char. Rice husk charcoal and algal biochar were added to a mixer at a mass ratio of 4.5:1 and mixed for 20 minutes. Water of 15% by solid mass was added and extruded to form granules with a particle size of 2 mm. The granules were then dried at 60°C to obtain organic carbon. Preparation of organic acid-calcium complexes: Weigh out citric acid, humic acid, and calcium oxide in a ratio of 1:1:1. Dissolve citric acid in water, with the water mass being twice that of citric acid. Add humic acid while stirring, then slowly add calcium oxide. Heat in a 25°C water bath and stir for 2 hours to obtain a paste. The paste was dried at 85°C and pulverized through a 60-mesh sieve to obtain an organic acid-calcium complex.

[0029] Phosphogypsum was dried at 55℃ for 3 hours, initially passed through a 10-mesh sieve, and then pulverized and passed through a 100-mesh sieve; bentonite was pulverized using a crusher, then pulverized using a grinding mill, and passed through a 200-mesh sieve; ammonium sulfate was pulverized and passed through a 20-mesh sieve.

[0030] Organic-inorganic modified zeolite, phosphogypsum, organic carbon, organic acid-calcium complex, bentonite, and ammonium sulfate were placed in a mixer according to their weight parts and mixed for 25 minutes. After mixing evenly, the mixture was sealed and stored for later use. Take humic acid-nano zero-valent iron and compound microbial agent, add humic acid-nano zero-valent iron to the basic soil amendment carrier at low speed, mix for 25 minutes to obtain a mixture, and then spray the compound microbial agent on the surface of the obtained mixture, keeping the moisture content at 10%, to obtain a soil amendment.

[0031] Example 3: Formula of soil conditioner for saline-alkali land: 35 parts organic-inorganic modified zeolite, 15 parts organic carbon, 5 parts organic acid-calcium complex, 10 parts phosphogypsum, 0.1 parts humic acid-nano zero-valent iron, 8 parts bentonite, 2 parts compound bacterial agent, 5 parts ammonium sulfate, and 0.1 parts polyacrylamide. Compound microbial agent: Composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1.2:1.3:1.8:1.

[0032] Preparation method of soil conditioner: Preparation of organic-inorganic modified zeolites: Zeolite and hydrochloric acid were mixed at a solid-liquid ratio of 1:3.5, stirred at room temperature for 2 hours, allowed to stand and precipitate, filtered to obtain a solid, washed 1-2 times with deionized water, and then dried at 120℃ to obtain acid-modified zeolite. Hexadecyltrimethylammonium bromide and acid-modified zeolite were weighed at a mass ratio of 0.05:1. Hexadecyltrimethylammonium bromide was dissolved in deionized water and heated to 50°C. The acid-modified zeolite was then added to the hexadecyltrimethylammonium bromide solution and stirred in a water bath at 60°C for 6 hours. After the reaction, the solid was obtained by filtration, washed 1-2 times with deionized water, dried at 120°C, and ground through a 100-mesh sieve to obtain organic-inorganic modified zeolite. Preparation of organic carbon: Rice husks were pyrolyzed at 500℃ under limited oxygen conditions, kept at that temperature for 2 hours, cooled, and then pulverized through an 80-mesh sieve to obtain rice husk char. Rice husk charcoal and algal biochar were added to a mixer at a mass ratio of 4:1 and mixed for 15 minutes. Then, 10% water by solid mass was added and the mixture was extruded and granulated to a particle size of 4 mm. The granules were then dried at 80°C to obtain organic carbon. Preparation of organic acid-calcium complexes: Weigh out citric acid, humic acid, and calcium oxide in a ratio of 2:1:0.5. Dissolve citric acid in water, with the water mass being twice that of citric acid. Add humic acid while stirring, then slowly add calcium oxide. Heat in a 25°C water bath and stir for 2 hours to obtain a paste. The paste was dried at 75°C and pulverized through a 60-mesh sieve to obtain an organic acid-calcium complex.

[0033] Phosphogypsum was dried at 55℃ for 3 hours, initially passed through a 10-mesh sieve, and then pulverized and passed through a 100-mesh sieve; bentonite was pulverized using a crusher, then pulverized using a grinding mill, and passed through a 200-mesh sieve; ammonium sulfate was pulverized and passed through a 20-mesh sieve.

[0034] Organic-inorganic modified zeolite, phosphogypsum, organic carbon, organic acid-calcium complex, bentonite, and ammonium sulfate were placed in a mixer according to their weight parts and mixed for 25 minutes. After mixing evenly, the mixture was sealed and stored for later use. Take humic acid-nano zero-valent iron and compound microbial agent, add humic acid-nano zero-valent iron to the basic soil amendment carrier at low speed, mix for 25 minutes to obtain a mixture, and then spray the compound microbial agent on the surface of the obtained mixture, keeping the moisture content at 10%, to obtain a soil amendment.

[0035] Comparative Example 1: Soil conditioner formulation: 30 parts ordinary zeolite, 18 parts organic carbon, 10 parts organic acid-calcium complex, 13 parts phosphogypsum, 0.2 parts humic acid-nano zero-valent iron, 10 parts bentonite, 3 parts compound microbial agent, 8 parts ammonium sulfate, and 0.15 parts polyacrylamide; the compound microbial agent is the same as in Example 1. Preparation method of soil conditioner: Preparation of organic-inorganic modified zeolite: This comparative example uses ordinary zeolite, so this step is omitted; Other preparation methods are the same as in Example 1; The application method of the soil conditioner for saline-alkali land in this comparative example is the same as that in Example 1.

[0036] Comparative Example 2: Soil conditioner formula: 30 parts organic-inorganic modified zeolite, 10 parts organic acid-calcium complex, 13 parts phosphogypsum, 0.2 parts humic acid-nano zero-valent iron, 10 parts bentonite, 3 parts compound microbial agent, 8 parts ammonium sulfate, and 0.15 parts polyacrylamide. Compound microbial agent: composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1:1:2:1; Preparation method of soil conditioner: No organic carbon was added to the soil conditioner for saline-alkali land in this comparative example, so this step was omitted. Other preparation methods are the same as in Example 1; The application method of the soil conditioner for saline-alkali land in this comparative example is the same as that in Example 1.

[0037] Comparative Example 3: Soil conditioner formula: 30 parts organic-inorganic modified zeolite, 18 parts organic carbon, 13 parts phosphogypsum, 0.2 parts humic acid-nano zero-valent iron, 10 parts bentonite, 3 parts compound microbial agent, 8 parts ammonium sulfate, and 0.15 parts polyacrylamide. Compound microbial agent: composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1:1:2:1; Preparation method of soil conditioner: This comparative example of saline-alkali soil conditioner does not contain organic acid-calcium complex, so this step is omitted; Other preparation methods are the same as in Example 1; The application method of the soil conditioner for saline-alkali land in this comparative example is the same as that in Example 1.

[0038] Comparative Example 4: Soil conditioner formula: 30 parts organic-inorganic modified zeolite, 18 parts organic carbon, 10 parts organic acid-calcium complex, 0.2 parts humic acid-nano zero-valent iron, 10 parts bentonite, 3 parts compound microbial agent, 8 parts ammonium sulfate, and 0.15 parts polyacrylamide. Compound microbial agent: composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1:1:2:1; This comparative example removes phosphogypsum. The preparation and application methods are the same as in Example 1, except that the corresponding phosphogypsum is removed. Everything else is the same as in Example 1.

[0039] Comparative Example 5: Soil conditioner formula: 30 parts organic-inorganic modified zeolite, 18 parts organic carbon, 10 parts organic acid-calcium complex, 13 parts phosphogypsum, 10 parts bentonite, 3 parts compound microbial agent, 8 parts ammonium sulfate, and 0.15 parts polyacrylamide. Compound microbial agent: Composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1:1:2:1; This comparative example lacks humic acid-nano zero-valent iron, so this step is omitted; The application method of the soil conditioner for saline-alkali land in this comparative example is as follows: Step 2) shallowly till to a depth of 10-15 cm, then apply polyacrylamide, irrigate with a small amount of water, and wait for 7-10 days. The rest is the same as in Example 1.

[0040] Comparative Example 6: Soil conditioner formula: 30 parts organic-inorganic modified zeolite, 18 parts organic carbon, 10 parts organic acid-calcium complex, 13 parts phosphogypsum, 0.2 parts humic acid-nano zero-valent iron, 3 parts compound microbial agent, 8 parts ammonium sulfate, and 0.15 parts polyacrylamide. Compound microbial agent: composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1:1:2:1; This comparative example removes bentonite. The preparation and application methods are the same as in Example 1, except that the corresponding bentonite is removed. Everything else is the same as in Example 1.

[0041] Comparative Example 7: Soil conditioner formula: 30 parts organic-inorganic modified zeolite, 18 parts organic carbon, 10 parts organic acid-calcium complex, 13 parts phosphogypsum, 0.2 parts humic acid-nano zero-valent iron, 10 parts bentonite, 3 parts compound microbial agent, and 0.15 parts polyacrylamide. Compound microbial agent: Composed of *Lactobacillus plantarum*, *Saccharomyces cerevisiae*, *Bacillus subtilis*, and *Aspergillus niger* in a ratio of 1:1:2:1; This comparative example removes ammonium sulfate. The preparation and application methods are the same as in Example 1, except that the corresponding ammonium sulfate is removed.

[0042] Comparative Example 8: Soil conditioner formula: 30 parts organic-inorganic modified zeolite, 18 parts organic carbon, 10 parts organic acid-calcium complex, 13 parts phosphogypsum, 0.2 parts humic acid-nano zero-valent iron, 10 parts bentonite, 3 parts compound microbial agent, and 8 parts ammonium sulfate. Compound microbial agent: composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1:1:2:1; The preparation method of this comparative example is the same as that of Example 1; This comparative example removed polyacrylamide.

[0043] Comparative Example 9: Soil conditioner formula: 30 parts organic-inorganic modified zeolite, 18 parts organic carbon, 10 parts organic acid-calcium complex, 13 parts phosphogypsum, 0.2 parts humic acid-nano zero-valent iron, 10 parts bentonite, 8 parts ammonium sulfate, and 0.15 parts polyacrylamide. This comparative example removes the compound microbial agent. The preparation method and application method are the same as in Example 1, except that the corresponding compound microbial agent and its usage process are removed. Everything else is the same as in Example 1.

[0044] Comparative Example 10: Calcium oxide was used instead of the organic acid-calcium complex, and the other components and steps were the same as in Example 1.

[0045] Comparative Example 11: Hydrochloric acid-modified zeolite and / or CTAB-modified zeolite were used instead of organic-inorganic modified zeolite, and all other aspects were the same as in Example 1.

[0046] Field experiments were conducted using the saline-alkali soil fertilization methods described in Examples 1-3 and Comparative Examples 1-14. The experimental fields were located in Longshan Town, Cixi City, Ningbo City, Zhejiang Province, and the soil type was coastal silty saline-alkali soil. The land area of ​​each experimental field was 50 m². 2 The basic physicochemical properties of the topsoil in the 0-30cm layer are as follows: total salt content is 4.8 g / kg, pH value (1:5 water immersion) is 8.5-8.8, organic matter content is 11.2 g / kg, soil electrical conductivity (EC, 1:5 soil-water ratio) is 0.85 dS / m, sodium chloride content is 3.2 g / kg, and water-stable macroaggregate content (>0.25 mm) is 8%. The crop planted is rice. Note: In addition to Examples 1-3 and Comparative Examples 1-11, there is also a control group of ordinary planting by local farmers. The following data are the differences between Examples 1-3 and Comparative Examples 1-11 and the control group of ordinary planting by local farmers.

[0047] Table 1. Data metrics for Examples 1-3 and Comparative Examples 1-11

[0048] As can be seen from the table above, the saline-alkali land formula of the present invention can significantly reduce the salinity of the soil. Through Examples 1-3, it can be seen that the saline-alkali land formula of the present invention has an excellent effect on reducing the salinity of saline-alkali land. Combined with Comparative Examples 1-11, it can be seen that phosphogypsum, organic acid-calcium, and organic carbon have a significant impact on reducing the salinity of saline-alkali land. The three work synergistically, acting in three stages: rapid effect, slow release, and long-term effect. Phosphogypsum and organic acid-calcium provide calcium ions, which replace sodium ions and other salt particles through chemical replacement. Organic carbon performs physical adsorption, improves the structure, promotes leaching, and improves the problem of high salinity in the long term. The absence of any one of the three components will make the salinity reduction effect of the present invention worse. The formula adapted for saline-alkali land in this invention can significantly reduce soil pH. As can be seen from Comparative Examples 1-11, organic acid-calcium is the core of pH reduction and can rapidly reduce pH in a short period of time. Humic acid in organic carbon can reduce pH in a long-term, slow-release manner. Compound microbial agents reduce pH from a biological perspective. Modified zeolite also works synergistically with organic acid-calcium to reduce pH. Phosphogypsum and ammonium sulfate are components that assist in reducing pH. The formula reduces pH through chemical replacement and physiological acidification, and works in conjunction with organic acid-calcium to reduce soil pH. The soil conditioner formulation adapted for saline-alkali land of this invention can improve soil structure and increase the content of water-stable macroaggregates in the soil. Organic carbon and modified zeolite are the key components for improving soil structure. Rice husk char in the organic carbon provides a rigid framework and enhances physical support. Humic acid binds soil particles. Zeolite, after acidification and organic phase modification, can enhance its binding capacity and also provides a rigid framework. The two work synergistically to increase the content of water-stable macroaggregates. Bentonite acts as a flexible colloid to fill the gaps in the framework, and polyacrylamide connects the particles into a stable network, thereby synergistically improving the content of water-stable macroaggregates. The absence of any component will limit or reduce the effect of this fertilization on improving the content of water-stable macroaggregates in the soil.

[0049] The soil conditioner applicable to saline-alkali land of this invention can increase crop yield and increase soil organic matter. Rice husk char and algal biochar in organic carbon are the material basis for increasing soil organic matter. When they are missing, the organic matter decreases. Compound microbial agents can convert organic matter into soil accumulation. When they are missing, although the organic matter increases, the amount of increase is much smaller. Phosphogypsum, organic acid-calcium, modified zeolite, and ammonium sulfate promote the accumulation of organic matter by improving the soil environment and providing nutrients. The synergistic effect of each component can achieve the best fertilization effect.

[0050] In Example 1 and Comparative Example 5, the black root rate of rice was additionally tested. The black root rate of Example 1 was 2.7%, and the black root rate of Comparative Example 5 was 15.3%. Obviously, the soil conditioner of the present invention can regulate the redox environment of saline-alkali soil, reduce the oxidative damage induced by salt stress, and significantly reduce root toxicity.

[0051] Examples 1 and Comparative Example 12 show that using inorganic alternatives to organic acid complexes leads to a significant pH rebound. This is because the organic acid-calcium complex of the present invention forms a citric acid-humic acid-calcium complex with a ternary coordination structure. In this structure, calcium ions simultaneously form bidentate coordination with the α-hydroxycarboxylic acid group of citric acid and the phenolic hydroxyl and / or carboxyl groups of humic acid. This structure results in a non-linear characteristic of calcium ion release rate that is fast at the beginning and slow at the end, ensuring rapid initial replacement of sodium ions while preventing calcium ions from being rapidly fixed by soil colloids and becoming ineffective. According to Examples 1 and Comparative Example 13, if hydrochloric acid-modified zeolite and / or CTAB-modified zeolite are used to replace the organic modified zeolite of this application, the soil pH change will be uneven, resulting in the destruction of the soil conditioner's persistence.

[0052] The results above show that the soil conditioner for saline-alkali land of the present invention can systematically solve the problems of high soil salt content, alkaline soil, soil compaction, poor soil quality, and reducing toxicity in one go; the components work synergistically, and the absence of any one component will reduce the effect.

[0053] Example 4: Experiment on the continuous treatment of saline-alkali land using the fertilization method of the present invention: Soil conditioner formula: 33 parts organic-inorganic modified zeolite, 19 parts organic carbon, 13 parts organic acid-calcium complex, 14 parts phosphogypsum, 0.1 parts humic acid-nano zero-valent iron, 9 parts bentonite, 3 parts compound microbial agent, 9 parts ammonium sulfate, and 0.1 parts polyacrylamide. Compound microbial agent: composed of Lactobacillus plantarum, Chinese yeast, Bacillus subtilis, and Aspergillus niger in a ratio of 1:1:2:1; The preparation method is the same as in Example 1.

[0054] Soil sample collection: The selected area is 1466.7 hm². 2 The core area for saline-alkali land remediation, based on "every 66.7 hm² 2 Following the principle of "one sampling point per location," a total of 22 sampling points were established using a quincunx pattern. Soil samples were collected annually from October to November (after grape harvest and before the application of base fertilizer and soil conditioner), for four consecutive years from 2019 to 2023. The period from 2019 to 2020 was the baseline monitoring phase before the implementation of the saline-alkali land management demonstration project, while the period from 2020 to 2023 was the improvement phase. Each year after grape harvest (November-December), 2250 kg / hm² of soil conditioner was applied to the saline-alkali land at a depth of 10–15 cm, ensuring uniform mixing of the conditioner with the topsoil. Other agricultural activities remained consistent with the farmers' routine management practices.

[0055] Five sampling points were evenly distributed within each sampling unit, collecting soil samples from the 0–40 cm topsoil layer. The subsamples from each point were thoroughly mixed and then quartered to approximately 1 kg to form a mixed soil sample for that location. The samples were air-dried in a well-ventilated, shady place. Plant debris, roots, stones, and plastic fragments were manually removed. The samples were then ground in an agate mortar and pestle, passed through a 100-mesh nylon sieve (0.15 mm aperture), and stored in a sealed bag away from light. This was used to determine soil pH, organic matter, total nitrogen, available phosphorus, and available potassium. A separate fresh soil sample was passed through a 2 mm sieve and stored at 4°C for determining soil microbial biomass carbon and nitrogen, substrate-induced respiration, and soil enzyme activity.

[0056] Determination of soil physicochemical properties: Soil pH was determined using the potentiometric method. A soil suspension was prepared with a soil-to-water ratio of 2.5:1, thoroughly stirred, and allowed to stand for 30 minutes. The potential value was then measured using a pH meter. Soil total nitrogen content was determined by Kjeldahl distillation-volume method. The sample was digested with concentrated sulfuric acid-catalyst (CuSO4-K2SO4) to convert organic nitrogen into ammonium nitrogen. The total nitrogen content was then calculated by distillation and titration using a fully automated Kjeldahl nitrogen analyzer. The available phosphorus in the soil is 0.5 mol·L⁻¹. -1 The effective phosphorus concentration was determined by NaHCO3 extraction (pH 8.5), with shaking extraction at 25℃ for 30 min. The absorbance of the extract was measured by molybdenum antimony colorimetric method (wavelength 700 nm), and the effective phosphorus concentration was calculated by combining the standard curve. Soil organic matter was determined by the external heating potassium dichromate oxidation-volume method. The soil organic matter was heated in an oil bath (170-180℃) to allow the potassium dichromate to react fully. The remaining potassium dichromate was titrated with a ferrous sulfate standard solution. The organic matter content was calculated based on the stoichiometric relationship of the redox reaction. Available potassium in the soil was extracted using a 1.0 mol·L⁻¹ NH₄OAc solution (pH 7.0), shaken for 30 min, and then filtered. The filtrate was measured using a flame photometer, and the available potassium content was calculated based on the extraction volume.

[0057] Determination of soil microbial biomass: Two 20.0 g samples of fresh soil were weighed into 100 mL plastic bottles. One sample was fumigated with chloroform in a vacuum desiccator for 24 h, while the other was used as a control. The moisture content of the sample was determined simultaneously. Then, 50 mL of 0.5 M K₂SO₄ solution was added for extraction, and the mixture was shaken for 1 h before filtering into a 100 mL plastic bottle; this was the test solution. 10 mL of the test solution was transferred to a digestion tube, and 1.08 g of a mixed catalyst (composed of 100 g potassium sulfate, 10 g copper sulfate, and 1 g selenium) and 5 mL of concentrated sulfuric acid were added sequentially. The tube was sealed with plastic wrap and allowed to stand for 24 h. After digestion at 150 °C for 1 h, the temperature was increased to 320 °C and digestion continued for 3 h. After cooling, the digest was transferred to a 50 mL volumetric flask and diluted to volume with ultrapure water. The solution was then shaken well before analysis. Take 1 mL of the test solution and place it in a 50 mL volumetric flask. Add 1 drop of 2,4-dinitrophenol indicator and shake well. Slowly add 4 M NaOH solution until a pale yellow color appears. Continue to dilute to 50 mL with ultrapure water. Finally, perform analysis using a fully automated discrete chemical analyzer (Cleverchem 380, Dechem-Tech, Germany) to determine the total nitrogen content.

[0058] Two 20.0 g samples of fresh soil were weighed into 100 mL plastic bottles. One sample was fumigated with chloroform in a vacuum desiccator for 24 h, while the other was used as a control. The moisture content was determined simultaneously. Then, 50 mL of 0.5 M K₂SO₄ solution was added for extraction, and after shaking for 1 h, the mixture was filtered into a 100 mL plastic bottle to obtain the test solution. 10 mL of the test solution was transferred to a digestion tube, and 10 mL of 0.018 M K₂CrO₇-H₂SO₄ solution was added. The tube was then placed in silicone oil preheated and kept constant at 175 °C. Timing began after the liquid in the digestion tube boiled, and the tube was slowly removed after 10 min. The liquid in the digestion tube was transferred to an Erlenmeyer flask and rinsed, maintaining a volume of 50 mL in the flask. 5 mL of concentrated sulfuric acid and 2-3 drops of o-phenanthroline indicator were added, bringing the final volume to approximately 60 mL. Titration was performed using (NH₄)₂Fe(SO₄)₂ solution, and the volume consumed was recorded to obtain the organic carbon content.

[0059] Add excess glucose powder (1% of soil weight) to the fresh soil sample and mix well. Place the sample in a sealed container, suspending a small beaker of NaOH solution inside. Incubate at 25°C in the dark for 4 hours; the CO2 released by microbial respiration will be absorbed by the alkali solution. After incubation, titrate the remaining alkali with standard hydrochloric acid and calculate the amount of CO2 released based on the amount of acid consumed.

[0060] according to Figure 1It can be seen that the soil pH box curves in the improved area during the four monitoring periods from 2019–2020 to 2022–2023 showed highly significant differences in soil pH across the years. In the initial stage of remediation in 2019–2020, the soil was generally weakly alkaline, with a median pH of 8.1, indicating significant regional salinization. After implementing salinization remediation measures, the soil pH dropped significantly in 2020–2021, with the median dropping to 6.0, demonstrating the initial effectiveness of soil desalination. In 2021–2022, with continued remediation, the soil pH slightly increased but remained far below the baseline level, showing no trend of salinization rebound. By 2022–2023, the median soil pH had reached its lowest level in four years, with the soil remaining stably in the weakly acidic range. Continuous comprehensive remediation can significantly reduce regional soil pH and effectively reverse the process of soil salinization in the long term.

[0061] according to Figure 2 It can be seen that the average soil organic matter content before improvement (2019–2020) was 21.6 g·kg⁻¹. -1 The samples were mainly distributed in the range of 10~20 g·kg -1 (50%) and 20~30 g·kg -1 (Accounting for 40.9%). The organic matter content of the improved soil increased year by year, reaching an average of 28.0 g·kg⁻¹ in 2022–2023. -1 It is mainly distributed in the range of 20~30 g·kg -1 The range (accounting for 59.1%) was 30~40 g·kg. -1 The proportion of samples meeting the grade increased to 13.6%. The average total nitrogen content in the soil remained consistently between 1.4 and 1.5 g·kg⁻¹ over the four years. -1 The level is high, and there are no significant differences between years; The average available phosphorus content in the soil decreased from 14.5 mg·kg before improvement. -1 Increased to 20.2 mg·kg in 2022-2023. -1 The samples before the improvement were mainly concentrated in the range of 10-20 mg / kg. -1 (45.4%) and 20-40 mg / kg -1 (27.2%) grade; by the third year of improvement, the main sample concentration was 20-40 mg / kg. -1 The high-grade range (accounting for 59.1%), while 10~20 mg·kg -1 The proportion of samples with the highest quality level dropped sharply to 4.5%, indicating a significant improvement in soil phosphorus availability. Over the four years, the average content of available potassium in the soil increased from 78 mg·kg⁻¹ before improvement. -1 Steadily increase to 86 mg / kg in 2022-2023. -130~50 mg·kg -1 The proportion of lower-grade samples decreased year by year (from 13.6% to 0), while the proportion in the 50-100 mg / kg range increased. -1 The proportion of samples at different grades continued to increase (from 59% to 77.3%), 100~150 mg·kg -1 The sample proportion within each interval remained stable at 22.7% to 27.2%.

[0062] like Figure 3 As shown, before the improvement (2019–2020), the average soil microbial substrate-induced respiration rate was 0.20 mg·kg⁻¹. -1 ·h -1 The average carbon content of microbial biomass was 242.3 mg·kg⁻¹. -1 The average nitrogen content of microbial biomass was 9.73 mg·kg⁻¹. -1 After three years of improvements (2022–2023), the microbial substrate-induced respiration rate was significantly increased to 0.29 mg·kg⁻¹. -1 ·h -1 The microbial biomass carbon content increased to 285.8 mg·kg⁻¹. -1 Microbial biomass nitrogen increased to 13.23 mg·kg⁻¹ -1 In conclusion, improving soil pH is a key driver for promoting microbial activity and increasing microbial biomass.

[0063] It should be noted that the above embodiments and comparative examples are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the present invention.

Claims

1. A soil conditioner for improving saline-alkali land, characterized in that, By weight, the following components are present: 25-35 parts organic-inorganic modified zeolite, 15-20 parts organic carbon, 5-15 parts organic acid-calcium complex, 0.1-0.3 parts humic acid-nano zero-valent iron, 10-15 parts phosphogypsum, 8-12 parts bentonite, 2-5 parts compound microbial agent, 5-10 parts ammonium sulfate, and 0.1-0.2 parts polyacrylamide.

2. The soil conditioner for saline-alkali land according to claim 1, characterized in that, The organic-inorganic modified zeolite is a zeolite modified with hydrochloric acid and hexadecyltrimethylammonium bromide, wherein the concentration of hydrochloric acid is 30%-35% and the purity of hexadecyltrimethylammonium bromide is 99%-99.5%.

3. The soil conditioner according to claim 1, characterized in that, The organic carbon is rice husk char-algae biochar, with a ratio of rice husk char to algae biochar of 4-6:1; the organic acid-calcium complex is a citric acid-humic acid-calcium complex, prepared from citric acid, humic acid, and calcium oxide in a ratio of 1-2:1:0.5-1; the purity of the citric acid is 98.0%-99.0%, with a particle size range of 80-120 mesh; the specifications of the humic acid are 60.0%-65.0% humic acid content and 80-120 mesh particle size; the specifications of the calcium oxide are 85.0%-90.0% calcium oxide content and 100-200 mesh particle size.

4. The soil conditioner according to claim 1, characterized in that, The humic acid-nano zero-valent iron has an iron content of 95%-99% and a particle size of 40-80nm; the phosphogypsum has a purity of 82%-85% and a phosphorus content of 0.4%-0.8%; the bentonite has a montmorillonite content of 60%-70%; and the ammonium sulfate has an nitrogen content of 20.5%-21.0%.

5. A soil conditioner according to claim 1, characterized in that, The compound microbial agent is composed of *Lactiplantibacillus plantarum*, *Saccharomyces sinenses*, *Bacillus subtilis*, and *Aspergillus niger* in a ratio of 1-1.5:1-1.5:1.5-2:

1. The *Lactiplantibacillus plantarum* is cataloged under CGMCC 1.2437, deposited at the China General Microbiological Culture Collection Center on December 22, 1999; the *Saccharomyces sinenses* is cataloged under CGMCC 2.1395, deposited at the China General Microbiological Culture Collection Center on December 22, 1999; the *Bacillus subtilis* is cataloged under CGMCC 1.15792, deposited at the China General Microbiological Culture Collection Center on July 10, 2016; and the *Aspergillus niger*... The accession number (CGMCC3.11571) is CGMCC3.11571, the depositary institution is China General Microbiological Culture Collection Center, and the deposit date is July 14, 2008.

6. A method for preparing a soil conditioner for improving saline-alkali land, characterized in that: Preparation of the saline-alkali soil conditioner according to claims 1-5: (1) Preparation of organic-inorganic modified zeolite; (2) Preparation of organic carbon; (3) Preparation of organic acid-calcium complex; (4) Pretreatment with phosphogypsum, bentonite, ammonium sulfate, polyacrylamide, and compound microbial agent; (5) Place the organic-inorganic modified zeolite, phosphogypsum, organic carbon, organic acid-calcium complex, bentonite, and ammonium sulfate in a mixer according to the weight parts and mix for 20-30 minutes. After mixing evenly, the basic modified carrier is obtained. (6) Take humic acid-nano zero-valent iron and compound microbial agent, mix humic acid-nano zero-valent iron at low speed and add it to the basic improvement carrier, mix for 20-30 minutes to obtain a mixture, and then spray the compound microbial agent on the surface of the obtained mixture, keeping the moisture content at 8%-12% to obtain the soil conditioner.

7. The preparation method according to claim 6, characterized in that, The preparation method of the organic-inorganic modified zeolite includes the following steps: Zeolite and hydrochloric acid are mixed at a solid-liquid ratio of 1:2.5-3.5 and stirred at room temperature for 2-4 hours. After standing and precipitation, the solid is filtered and washed 1-2 times with deionized water. Then it is dried at 110-120℃ to obtain acid-modified zeolite. Weigh hexadecyltrimethylammonium bromide and acid-modified zeolite at a mass ratio of 0.05-0.15:

1. Dissolve hexadecyltrimethylammonium bromide in deionized water and heat to 40-50℃. Add the acid-modified zeolite to the hexadecyltrimethylammonium bromide solution and stir in a water bath at 60-80℃ for 4-6 hours. After the reaction, filter to obtain a solid, wash with deionized water 1-2 times, dry at 110-120℃, and grind through a 100-mesh sieve to obtain organic-inorganic modified zeolite.

8. The preparation method according to claim 6, characterized in that, The method for preparing the organic carbon includes the following steps: Rice husks are pyrolyzed under limited oxygen conditions at 500-600℃ and kept at that temperature for 1-2 hours. After cooling, they are pulverized through an 80-mesh sieve to obtain rice husk charcoal. Rice husk charcoal and algal biochar are added to a mixer at a mass ratio of 4-6:1 and mixed for 15-20 minutes. Then, 10%-15% water by weight of the solids is added and the mixture is extruded and granulated to a particle size of 2-4 mm. The granules are then dried at 60-80℃ to obtain organic carbon.

9. The preparation method according to claim 6, characterized in that, The method for preparing the organic acid-calcium complex includes the following steps: Weigh out citric acid, humic acid, and calcium oxide in the specified proportions. Dissolve citric acid in water, with the water mass being twice that of the citric acid. Add humic acid while stirring, then slowly add calcium oxide. Place the mixture in a room temperature water bath and continue stirring for 1-2 hours to obtain a paste. The paste was dried at 75-85℃ and pulverized through a 60-mesh sieve to obtain an organic acid-calcium complex.

10. The application of a soil conditioner for improving saline-alkali land, characterized in that, The soil conditioner described in claims 1-5 is used to improve saline-alkali farmland.

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