A micro-electric field synergistic graphite / humic acid saline-alkali land improvement system and its construction method

Abstract

This invention provides a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system and its construction method. The saline-alkali land improvement system includes a saline-alkali land improvement fertilizer and a low-voltage power supply system. The saline-alkali land improvement fertilizer is a four-layer composite particle, consisting of a core layer, an inner transition layer, an isolation layer, and an outer layer from the inside out. The outer layer contains modified graphite that has undergone surface hydroxylation and magnetic field-induced alignment treatment. The low-voltage power supply system is used to apply intermittent direct current to the saline-alkali land improvement fertilizer, which is distributed in the soil in an intermittent manner, to establish a micro-electric field between adjacent amendment strips. The saline-alkali land improvement fertilizer of this invention solves the problems of salt rebound and short-term effects of single amendments, and significantly improves the improvement efficiency of severely saline-alkali land. By establishing a micro-electric field inside the soil, a directional driving force is applied to charged salt ions, causing them to quickly detach from the crop root zone and be efficiently captured and fixed by the functional components in the formula, thereby improving the desalination rate and improvement depth.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, specifically to a soil improvement fertilizer and a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system and its construction method. Background Technology

[0002] Saline-alkali land is a major obstacle to sustainable agricultural development and ecological security worldwide. Its high salinity, high pH, ​​compacted structure, and low fertility severely inhibit crop growth and lead to a decline in land productivity. Currently, saline-alkali land improvement technologies mainly include physical, chemical, biological, and hydraulic engineering approaches, but many limitations remain. In terms of chemical improvement, commonly used amendments such as gypsum, humic acid, and organic fertilizers can improve soil physicochemical properties in the short term, but they generally suffer from short-lived effects, easy salt leaching with water, or rapid "salinization" after irrigation. In particular, single amendments struggle to simultaneously achieve multiple goals such as rapid desalination, stable pH adjustment, structural improvement, and fertility enhancement. Long-term application of some chemical amendments may also damage soil microbial communities, exacerbating soil compaction and degradation. Regarding physical and electrochemical improvement, technologies such as direct current desalination can drive salt ion migration through an electric field, but they generally suffer from high energy consumption, electrode corrosion, significant soil structural disturbance, complex equipment, and high costs, making them difficult to promote and apply on large areas of farmland. Existing technologies primarily focus on "externally applied" electric fields, lacking synergistic design with soil amendment components, resulting in limited desalination efficiency and insufficient depth of action. Furthermore, traditional amendments are unevenly dispersed in the soil, have weak binding force with soil particles, and are prone to nutrient loss, making it difficult to create a long-term, stable amended microenvironment in the root zone. For moderately to severely saline-alkali land, existing amendment methods are often slow to take effect and cannot quickly reduce soil salinity to a suitable range within the crop growth cycle. Therefore, there is an urgent need for a comprehensive saline-alkali land management technology that can synergistically achieve rapid desalination, long-term acidification, structural improvement, and ecological restoration, realizing efficient, long-term, and eco-friendly saline-alkali land improvement. Summary of the Invention

[0003] In view of this, the present invention proposes a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system and its construction method to solve the above problems.

[0004] The technical solution of this invention is implemented as follows:

[0005] A micro-electric field synergistic graphite / humic acid saline-alkali land improvement system includes saline-alkali land improvement fertilizer and a low-voltage power supply system.

[0006] Furthermore, the saline-alkali land improvement fertilizer is a four-layer composite particle, consisting of a core layer, an inner transition layer, an isolation layer, and an outer layer, from the inside out. The outer layer contains modified graphite that has undergone surface hydroxylation and magnetic field-induced alignment treatment. The low-voltage power supply system is used to apply intermittent direct current to the saline-alkali land improvement fertilizer, which is distributed in the soil in an intermittent manner, to establish a micro-electric field between adjacent amendment strips.

[0007] Furthermore, the core layer includes the following raw materials by weight: 50-70 parts decomposed organic fertilizer, 20-30 parts activated humic acid, 5-10 parts water-retaining agent, 0.5-2.0 parts compound microbial agent, and 2-4 parts binder.

[0008] Furthermore, the inner transition layer comprises the following raw materials in parts by weight: 60-80 parts humic acid, 15-25 parts zeolite powder, 3-8 parts trace element chelates, and 3-6 parts binder.

[0009] Furthermore, the isolation layer comprises the following raw materials in parts by weight: 40-60 parts gypsum, 30-50 parts calcined clay or diatomaceous earth, and 5-10 parts water-soluble polymer.

[0010] Furthermore, the outer layer comprises the following raw materials in parts by weight: 50-70 parts modified graphite, 20-35 parts zeolite powder and gypsum mixture, 3-8 parts water-retaining agent, 4-8 parts salt-resistant binder, and 2-10 parts short-cut conductive carbon fiber.

[0011] Further, modified graphite is prepared by the following method: natural flake graphite is placed in a drying oven and dried at 60-80℃ for 4-6 hours. The dried graphite is then placed in a 5-15% hydrogen peroxide solution at a material-to-liquid ratio of 1:5-10 and reacted in a water bath at 40-50℃ with stirring at 300-500 rpm for 1-3 hours. The material-to-liquid ratio is expressed in g / mL. After the reaction, the graphite is filtered out, washed 3-4 times with deionized water, and then placed in a drying oven and dried at 60-80℃ for 4-6 hours to obtain pre-oxidized graphite. Graphite oxide and deionized water are mixed at a material-to-liquid ratio of 1:20-30. Sodium polyacrylate (0.5-1.0% by weight of graphite) is added as a dispersant. The mixture is ultrasonically treated at an ultrasonic power of 400-600W for 30-60 minutes to obtain a pre-oxidized graphite suspension slurry. The material-to-liquid ratio is in g / mL. The pre-oxidized graphite suspension slurry is placed in a magnetic field with an intensity of 0.3-0.8T and allowed to stand for 2-4 hours. Then, it is transferred to a drying oven and dried at 40-60℃ for 20-30 hours. Finally, it is ground through a 50-200 mesh sieve to obtain modified graphite particles.

[0012] Further, activated humic acid is prepared by the following method: humic acid and deionized water are mixed at a material-to-liquid ratio of 1:5-8, and stirred at 100-200 rpm for 30-60 min to obtain a humic acid slurry. The material-to-liquid ratio is expressed in g / mL. Ammonia water, accounting for 25-28% of the slurry volume, is slowly added dropwise to the humic acid slurry. The reaction system is heated to 50-65℃ and stirred at 300-500 rpm for 2-4 h. Then, the temperature is lowered to 40-50℃ and the mixture is stirred at 150-250 rpm for 1-2 h to mature. The matured slurry is subjected to solid-liquid separation using a plate and frame filter press. The filtrate is collected, and the filter residue is washed 1-2 times. The washing liquid is combined with the filtrate, and then the filtrate is concentrated to 30-40% of the original volume under conditions of 60-70℃ and vacuum degree of -0.06 to -0.08MPa to obtain a concentrated liquid. The concentrated liquid is then spray-dried with an inlet air temperature of 180-200℃ and an outlet air temperature of 80-90℃, and then dried at 70-80℃ for 1-2 hours. Finally, it is pulverized through an 80-100 mesh sieve to obtain activated humic acid.

[0013] Furthermore, the water-retaining agent in the core layer is a starch-grafted acrylate copolymer, the composite microbial agent is composed of Azotobacter chrysophyllariae, Bacillus megaterium, and Pseudomonas fluorescens in a mass ratio of (5-6):(3-4):(1-2), and the binder is sodium carboxymethyl cellulose.

[0014] Furthermore, the trace element chelate in the inner transition layer is composed of ethylenediaminetetraacetic acid and hydroxyethylethylenediaminetriacetic acid in a mass ratio of (6-7.5):(2.5-4).

[0015] Furthermore, the water-soluble polymer in the isolation layer is polyvinyl alcohol.

[0016] Furthermore, the salt-resistant binder in the outer layer is oxidized starch or acetate starch; the mass ratio of zeolite powder to gypsum in the zeolite powder and gypsum mixture is (6-7):(4-3); the water-retaining agent is polyacrylamide with a molecular weight of 8 million-15 million and a water absorption rate of saturation within 30 seconds; and the length of the short-cut conductive carbon fiber is 3-10 mm.

[0017] Furthermore, the saline-alkali land improvement fertilizer is prepared by the following method:

[0018] A1. Weigh the raw materials of the core layer according to the weight parts, put them into a three-dimensional motion mixer, stir and mix at 200-300 rpm for 15-20 minutes, spray deionized water into the uniformly mixed material, control the total moisture content at 18-22%, then put it into a granulator, and make 1.0-1.5 mm spherical particles at 30-40℃ and 30-50 rpm, and then dry at 50-55℃ for 30-60 minutes to obtain the core layer particles;

[0019] A2. Weigh the transition layer raw material according to the weight ratio, add deionized water to make the solid content 40-50%, stir at 1000-1500 rpm for 15-25 min to make the transition layer slurry; put the core layer particles into the fluidized bed coating equipment, spray the inner transition layer slurry onto the particle surface, control the air inlet temperature to 60-70℃ and the material temperature to 45-55℃, after the spraying is completed, fluidize and dry at 50-60℃ for 10-15 min to obtain double-layer particles;

[0020] A3. Weigh the raw materials for the isolation layer according to the weight proportions. First, prepare the water-soluble polymer in it into an aqueous solution with a concentration of 5-8%, and then mix it with other raw materials. Stir at 500-800 rpm for 15-25 minutes to make an isolation layer slurry. Place the double-layer particles into a fluidized bed coating equipment, preheat it to 45-50℃, and spray the isolation layer slurry onto the surface of the double-layer particles. Control the air inlet temperature to 65-75℃ and the material temperature to 50-60℃ to obtain three-layer particles.

[0021] A4. Weigh out the outer layer raw materials according to the weight percentage and put them into a three-dimensional motion mixer. Stir and mix at 100-150 rpm for 20-30 minutes to obtain the outer coating powder. Preheat the three-layer granules to 40-45℃ and transfer them into a drum coating equipment. Spray 3-5% of the weight of deionized water onto the surface of the three-layer granules to wet the surface. Add the outer coating powder during the rolling process. Alternately perform the spray-powder addition operation 3-5 times. After the coating is completed, dry the granules at 50-60℃ until the moisture content is ≤8% to obtain a four-layer structure saline-alkali land improvement fertilizer.

[0022] Furthermore, the above-mentioned method for constructing a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system includes the following steps:

[0023] B1. Place saline-alkali land improvement fertilizer in the soil to form intermittently distributed electrode strips;

[0024] B2. Install a low-voltage power supply system on the formed electrode strips to establish a micro-electric field between adjacent electrode strips, thus completing the construction of the saline-alkali land improvement system.

[0025] Furthermore, the fertilizer for improving saline-alkali land in B1 is arranged in strips or concentric circles.

[0026] Furthermore, the low-voltage power supply system includes a DC power supply, wires, and corrosion-resistant electrode connectors; the DC power supply operates in an intermittent DC power mode, with power supplied for 4-12 hours per day.

[0027] Furthermore, the DC power supply is solar-powered.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. Outstanding synergistic improvement effect: Modified graphite and humic acid form a core synergistic system, which solves the pain points of salt rebound and short-term effect of single amendments, and significantly improves the improvement efficiency of severely saline-alkali land.

[0030] 2. Highly eco-friendly: The formula does not contain harmful chemicals, will not damage the soil microbial environment, avoids soil compaction, and can improve soil health with long-term use.

[0031] 3. High nutrient utilization rate: The combination of the adsorption properties of modified graphite and the chelating effect of humic acid reduces nutrient loss with water, significantly improving fertilizer utilization rate.

[0032] 4. Micro-electric field synergistic driving: By establishing a micro-electric field inside the soil, a directional driving force is applied to charged salt ions (such as Na⁺, Cl⁻), causing them to quickly detach from the crop root zone and be efficiently captured and fixed by the functional components in the formula, thereby significantly improving the desalination rate and improvement depth.

[0033] 5. Wide range of applications: It can be adapted to different types and degrees of saline-alkali land, and can meet the growth needs of a variety of crops at the same time, making it highly versatile.

[0034] 6. Low cost of use: The improvement effect is long-lasting, and there is no need for frequent reapplication. The overall cost of use is 15%-20% lower than that of existing products. Detailed Implementation

[0035] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0036] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0037] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0038] Example 1

[0039] A micro-electric field synergistic graphite / humic acid saline-alkali land improvement system includes a saline-alkali land improvement fertilizer and a low-voltage power supply system. The saline-alkali land improvement fertilizer is a four-layer composite particle, consisting of a core layer, an inner transition layer, an isolation layer, and an outer layer, from the inside out. The outer layer contains modified graphite that has undergone surface hydroxylation and magnetic field-induced alignment treatment. The low-voltage power supply system applies intermittent direct current to the saline-alkali land improvement fertilizer, which is distributed in the soil in an intermittent manner, to establish a micro-electric field between adjacent improvement agent strips.

[0040] The core layer comprises the following raw materials by weight: 50 parts decomposed organic fertilizer, 20 parts activated humic acid, 5 parts water-retaining agent, 0.5 parts compound microbial inoculant, and 2 parts binder. The inner transition layer comprises the following raw materials by weight: 60 parts humic acid, 15 parts zeolite powder, 3 parts trace element chelates, and 3 parts binder. The isolation layer comprises the following raw materials by weight: 40 parts gypsum, 30 parts calcined clay, and 5 parts water-soluble polymer. The outer layer comprises the following raw materials by weight: 50 parts modified graphite, 20 parts a mixture of zeolite powder and gypsum, 3 parts water-retaining agent, 4 parts salt-resistant binder, and 2 parts chopped conductive carbon fiber.

[0041] The modified graphite described above was prepared by the following method: Natural flake graphite was placed in a drying oven and dried at 60°C for 6 hours. The dried graphite was then placed in a 5% hydrogen peroxide solution at a material-to-liquid ratio of 1:5 and reacted at 300 rpm for 3 hours under a 40°C water bath. The material-to-liquid ratio was measured in g / mL. After the reaction, the graphite was filtered out, washed three times with deionized water, and then placed in a drying oven and dried at 60°C for 6 hours to obtain pre-oxidized graphite. The pre-oxidized graphite was mixed with deionized water at a material-to-liquid ratio of 1:20, and 0.5% sodium polyacrylate (by weight of graphite) was added as a dispersant. The mixture was ultrasonically treated at 400W for 60 minutes to obtain a pre-oxidized graphite suspension slurry. The material-to-liquid ratio was measured in g / mL. The pre-oxidized graphite suspension slurry was placed in a magnetic field with a strength of 0.3T and allowed to stand for 4 hours. It was then transferred to a drying oven and dried at 40°C for 30 hours. Finally, it was ground through a 50-mesh sieve to obtain modified graphite particles.

[0042] The activated humic acid was prepared by the following method: Humic acid and deionized water were mixed at a material-to-liquid ratio of 1:5 and stirred at 100 rpm for 60 min to obtain a humic acid slurry. The material-to-liquid ratio was expressed in g / mL. Ammonia water, accounting for 25% of the slurry volume, was slowly added dropwise to the humic acid slurry. The reaction system was heated to 50°C and stirred at 300 rpm for 4 h. Then, the temperature was lowered to 40°C and stirred at 150 rpm for 2 h to mature the slurry. The matured slurry was then subjected to solid-liquid separation using a plate and frame filter press. The filtrate was collected, and the filter residue was washed once. The washing liquid was combined with the filtrate. The filtrate was then concentrated to 40% of the original volume at 60°C and a vacuum of -0.06 MPa to obtain a concentrated solution. The concentrated solution was spray-dried at an inlet air temperature of 180°C and an outlet air temperature of 80°C for 2 h. Finally, it was pulverized and passed through an 80-mesh sieve to obtain activated humic acid.

[0043] The core layer contains a starch-grafted acrylate copolymer as the water-retaining agent, a composite microbial agent consisting of *Azotobacter chrysophagus*, *Bacillus megaterium*, and *Pseudomonas fluorescens* in a mass ratio of 5:3:1, and a sodium carboxymethyl cellulose binder as the binder. The inner transition layer contains a trace element chelate consisting of ethylenediaminetetraacetic acid (EDTA) and hydroxyethyl ethylenediaminetriacetic acid (HEAT) in a mass ratio of 6:2.5. The isolation layer contains a polyvinyl alcohol as the water-soluble polymer. The outer layer contains an oxidized starch binder, a zeolite powder and gypsum mixture in a zeolite powder to gypsum mass ratio of 6:4, a polyacrylamide with a molecular weight of 8 million and a water absorption rate saturating within 30 seconds, and short-cut conductive carbon fibers with a length of 3 mm.

[0044] The above-mentioned fertilizer for improving saline-alkali land is prepared by the following method:

[0045] A1. Weigh the raw materials of the core layer according to the weight parts, put them into the three-dimensional motion mixer, stir and mix at 200 rpm for 20 minutes, spray deionized water into the uniformly mixed material, control the total moisture content at 18%, then put it into the granulator, and make 1.0 mm spherical particles at 30℃ and 30 rpm, and then dry at 50℃ for 60 minutes to obtain the core layer particles.

[0046] A2. Weigh the transition layer raw material according to the weight ratio, add deionized water to make the solid content 40%, stir at 1000 rpm for 25 min to make the transition layer slurry; put the core layer particles into the fluidized bed coating equipment, spray the inner transition layer slurry onto the particle surface, control the air inlet temperature to 60℃ and the material temperature to 45℃, after the spraying is completed, fluidize and dry at 50℃ for 15 min to obtain double-layer particles;

[0047] A3. Weigh the raw materials for the isolation layer according to the weight parts. First, prepare the water-soluble polymer in it into an aqueous solution with a concentration of 5-8%. Then mix it with other raw materials and stir at 500 rpm for 25 minutes to make an isolation layer slurry. Place the double-layer particles into a fluidized bed coating equipment, preheat it to 45°C, and spray the isolation layer slurry onto the surface of the double-layer particles. Control the air inlet temperature to 65°C and the material temperature to 60°C to obtain three-layer particles.

[0048] A4. Weigh the outer layer raw materials according to the weight percentage and put them into a three-dimensional motion mixer. Stir and mix at 100 rpm for 30 minutes to obtain the outer coating powder. Preheat the three-layer granules to 40°C and transfer them into a drum coating equipment. Spray 3% of the weight of deionized water onto the surface of the three-layer granules to wet the surface. Add the outer coating powder during the rolling process. Alternately perform the spray-powder addition operation 3 times. After the coating is completed, dry the granules at 50°C to a moisture content of 8% to obtain a four-layer structure saline-alkali land improvement fertilizer.

[0049] The above-mentioned method for constructing a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system includes the following steps:

[0050] B1. Apply the saline-alkali soil improvement fertilizer to the soil in strips to form spaced electrode strips. The electrode strips are 20cm wide, with a center-to-center distance of 100cm between adjacent strips, and are placed 10cm below the soil surface.

[0051] B2. Install a low-voltage power supply system on the existing electrode strips to establish a micro-electric field between adjacent electrode strips, completing the construction of the saline-alkali land improvement system. The low-voltage power supply system includes a DC power supply, wires, and corrosion-resistant electrode connectors. The DC power supply operates in intermittent DC mode, providing power for 4 hours daily. Solar power is selected for the DC power supply. A solar photovoltaic power supply unit, including photovoltaic panels, a controller, and a battery, is installed at the site edge and connected to a control box with integrated timing function. The power output is safe DC power, using corrosion-resistant electrode connectors to reliably electrically connect the positive and negative output terminals of the power supply system to the spaced-apart improvement agent electrode strips using an "alternating polarity connection method." That is, connect the first electrode strip to the positive terminal, the adjacent second to the negative terminal, the third to the positive terminal, and so on, creating a potential difference between any two adjacent electrode strips.

[0052] Example 2

[0053] A micro-electric field synergistic graphite / humic acid saline-alkali land improvement system includes a saline-alkali land improvement fertilizer and a low-voltage power supply system. The saline-alkali land improvement fertilizer is a four-layer composite particle, consisting of a core layer, an inner transition layer, an isolation layer, and an outer layer, from the inside out. The outer layer contains modified graphite that has undergone surface hydroxylation and magnetic field-induced alignment treatment. The low-voltage power supply system applies intermittent direct current to the saline-alkali land improvement fertilizer, which is distributed in the soil in an intermittent manner, to establish a micro-electric field between adjacent improvement agent strips.

[0054] The core layer comprises the following raw materials by weight: 60 parts decomposed organic fertilizer, 25 parts activated humic acid, 8 parts water-retaining agent, 1.2 parts compound microbial inoculant, and 3 parts binder. The inner transition layer comprises the following raw materials by weight: 70 parts humic acid, 20 parts zeolite powder, 5.5 parts trace element chelates, and 4.5 parts binder. The isolation layer comprises the following raw materials by weight: 50 parts gypsum, 40 parts diatomaceous earth, and 7.5 parts water-soluble polymer. The outer layer comprises the following raw materials by weight: 60 parts modified graphite, 28 parts a mixture of zeolite powder and gypsum, 5.5 parts water-retaining agent, 6 parts salt-resistant binder, and 6 parts chopped conductive carbon fiber.

[0055] The modified graphite described above was prepared by the following method: Natural flake graphite was placed in a drying oven and dried at 70°C for 5 hours. The dried graphite was then placed in a 10% hydrogen peroxide solution at a material-to-liquid ratio of 1:7.5 and reacted at 400 rpm for 2 hours under a water bath at 45°C. The material-to-liquid ratio was expressed in g / mL. After the reaction was completed, the graphite was filtered out, washed four times with deionized water, and then placed in a drying oven and dried at 70°C for 5 hours to obtain pre-oxidized graphite. Pre-oxidized graphite and deionized water were mixed at a material-to-liquid ratio of 1:25. Sodium polyacrylate (5% by weight of graphite) was added as a dispersant. The mixture was ultrasonically treated at an ultrasonic power of 500W for 45 minutes to obtain a pre-oxidized graphite suspension slurry. The material-to-liquid ratio was measured in g / mL. The pre-oxidized graphite suspension slurry was placed in a magnetic field with a strength of 0.6T and allowed to stand for 3 hours. Then, it was transferred to a drying oven and dried at 50°C for 25 hours. Finally, it was ground through a 120-mesh sieve to obtain modified graphite particles.

[0056] The activated humic acid was prepared by the following method: Humic acid and deionized water were mixed at a material-to-liquid ratio of 1:6.5 and stirred at 150 rpm for 45 min to obtain a humic acid slurry. The material-to-liquid ratio was expressed in g / mL. Ammonia water, accounting for 26.5% of the slurry volume, was slowly added dropwise to the humic acid slurry. The reaction system was heated to 58°C and stirred at 400 rpm for 3 h. Then, the temperature was lowered to 45°C and stirred at 200 rpm for 1.5 h to mature the slurry. The matured slurry was then subjected to solid-liquid separation using a plate and frame filter press. The filtrate was collected, and the filter residue was washed twice. The washings were combined with the filtrate. The filtrate was then concentrated to 35% of the original volume at 65°C and a vacuum of -0.07 MPa to obtain a concentrated solution. The concentrated solution was spray-dried at an inlet air temperature of 190°C and an outlet air temperature of 85°C, and then dried at 75°C for 1.5 h. Finally, the solution was pulverized and passed through a 90-mesh sieve to obtain activated humic acid.

[0057] The core layer contains a starch-grafted acrylate copolymer as the water-retaining agent, a composite microbial agent composed of *Azotobacter chrysophagus*, *Bacillus megaterium*, and *Pseudomonas fluorescens* in a mass ratio of 5.5:3.5:1.5, and a sodium carboxymethyl cellulose binder as the binder. The inner transition layer contains a trace element chelate composed of ethylenediaminetetraacetic acid and hydroxyethylethylenediaminetriacetic acid in a mass ratio of 6.7:3.2. The isolation layer contains a polyvinyl alcohol as the water-soluble polymer. The outer layer contains an oxidized starch binder, a zeolite powder and gypsum mixture in a zeolite powder to gypsum mass ratio of 6.5:3.5, a polyacrylamide with a molecular weight of 12 million and a water absorption rate saturating within 30 seconds, and short-cut conductive carbon fibers with a length of 7 mm.

[0058] The above-mentioned fertilizer for improving saline-alkali land is prepared by the following method:

[0059] A1. Weigh the raw materials of the core layer according to the weight parts, put them into the three-dimensional motion mixer, stir and mix at 250 rpm for 17.5 min, spray deionized water into the uniformly mixed material, control the total moisture content at 20%, then put it into the granulator, and make 1.2 mm spherical particles at 35℃ and 40 rpm, and then dry at 52℃ for 45 min to obtain the core layer particles.

[0060] A2. Weigh the transition layer raw material according to the weight ratio, add deionized water to make the solid content 45%, stir at 1200 rpm for 20 min to make the transition layer slurry; put the core layer particles into the fluidized bed coating equipment, spray the inner transition layer slurry onto the particle surface, control the air inlet temperature to 65℃ and the material temperature to 50℃, after the spraying is completed, fluidize and dry at 55℃ for 12 min to obtain double-layer particles;

[0061] A3. Weigh the raw materials for the isolation layer according to the weight parts. First, prepare the water-soluble polymer in it into an aqueous solution with a concentration of 6.5%. Then mix it with other raw materials and stir at 650 rpm for 20 minutes to make an isolation layer slurry. Place the double-layer particles into a fluidized bed coating equipment, preheat it to 48°C, and spray the isolation layer slurry onto the surface of the double-layer particles. Control the air inlet temperature to 70°C and the material temperature to 55°C to obtain three-layer particles.

[0062] A4. Weigh the outer layer raw materials according to the weight percentage and put them into a three-dimensional motion mixer. Stir and mix at 120 rpm for 25 minutes to obtain the outer coating powder. Preheat the three-layer granules to 43°C and transfer them into a drum coating equipment. Spray 4% of the weight of deionized water onto the surface of the three-layer granules to wet the surface. Add the outer coating powder during the rolling process. Alternately perform the spray-powder addition operation 4 times. After the coating is completed, dry the granules at 55°C to a moisture content of 7% to obtain a four-layer structure saline-alkali land improvement fertilizer.

[0063] The above-mentioned method for constructing a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system includes the following steps:

[0064] B1. Apply the saline-alkali soil improvement fertilizer to the soil in strips to form spaced electrode strips. The electrode strips are 30cm wide, with a center-to-center distance of 150cm between adjacent strips, and are placed 15cm below the soil surface.

[0065] B2. Install a low-voltage power supply system on the existing electrode strips to establish a micro-electric field between adjacent electrode strips, completing the construction of the saline-alkali land improvement system. The low-voltage power supply system includes a DC power supply, wires, and corrosion-resistant electrode connectors. The DC power supply operates in intermittent DC mode, providing power for 8 hours daily. Solar power is selected for the DC power supply. A solar photovoltaic power supply unit, including photovoltaic panels, a controller, and a battery, is installed at the site edge and connected to a control box with integrated timing function. The power output is safe DC power, using corrosion-resistant electrode connectors to reliably electrically connect the positive and negative output terminals of the power supply system to the spaced-apart improvement agent electrode strips using an "alternating polarity connection method." That is, connect the first electrode strip to the positive terminal, the adjacent second to the negative terminal, the third to the positive terminal, and so on, creating a potential difference between any two adjacent electrode strips.

[0066] Example 3

[0067] A micro-electric field synergistic graphite / humic acid saline-alkali land improvement system includes a saline-alkali land improvement fertilizer and a low-voltage power supply system. The saline-alkali land improvement fertilizer is a four-layer composite particle, consisting of a core layer, an inner transition layer, an isolation layer, and an outer layer, from the inside out. The outer layer contains modified graphite that has undergone surface hydroxylation and magnetic field-induced alignment treatment. The low-voltage power supply system applies intermittent direct current to the saline-alkali land improvement fertilizer, which is distributed in the soil in an intermittent manner, to establish a micro-electric field between adjacent improvement agent strips.

[0068] The core layer comprises the following raw materials by weight: 70 parts decomposed organic fertilizer, 30 parts activated humic acid, 10 parts water-retaining agent, 2.0 parts compound microbial inoculant, and 4 parts binder. The inner transition layer comprises the following raw materials by weight: 80 parts humic acid, 25 parts zeolite powder, 8 parts trace element chelates, and 6 parts binder. The isolation layer comprises the following raw materials by weight: 60 parts gypsum, 50 parts diatomaceous earth, and 10 parts water-soluble polymer. The outer layer comprises the following raw materials by weight: 70 parts modified graphite, 35 parts a mixture of zeolite powder and gypsum, 8 parts water-retaining agent, 8 parts salt-resistant binder, and 10 parts chopped conductive carbon fiber.

[0069] The modified graphite described above was prepared by the following method: Natural flake graphite was placed in a drying oven and dried at 80°C for 4 hours. The dried graphite was then placed in a 15% hydrogen peroxide solution at a material-to-liquid ratio of 1:10 and reacted at 500 rpm for 1 hour under a 50°C water bath. The material-to-liquid ratio was expressed in g / mL. After the reaction, the graphite was filtered out, washed four times with deionized water, and then placed in a drying oven and dried at 80°C for 4 hours to obtain pre-oxidized graphite. Pre-oxidized graphite and deionized water were mixed at a material-to-liquid ratio of 1:30. Sodium polyacrylate (1.0% by weight of graphite) was added as a dispersant. The mixture was ultrasonically treated at an ultrasonic power of 600W for 30 minutes to obtain a pre-oxidized graphite suspension slurry. The material-to-liquid ratio was measured in g / mL. The pre-oxidized graphite suspension slurry was placed in a magnetic field with a strength of 0.8T and allowed to stand for 2 hours. Then, it was transferred to a drying oven and dried at 60°C for 20 hours. Finally, it was ground through a 200-mesh sieve to obtain modified graphite particles.

[0070] The activated humic acid was prepared by the following method: Humic acid and deionized water were mixed at a material-to-liquid ratio of 1:6.5 and stirred at 150 rpm for 45 min to obtain a humic acid slurry. The material-to-liquid ratio was expressed in g / mL. Ammonia water at 28% of the slurry volume was slowly added dropwise to the humic acid slurry. The reaction system was heated to 65°C and stirred at 500 rpm for 2 h. Then, the temperature was lowered to 50°C and stirred at 250 rpm for 1 h to mature the slurry. The matured slurry was then subjected to solid-liquid separation using a plate and frame filter press. The filtrate was collected, and the filter residue was washed twice. The washings were combined with the filtrate. The filtrate was then concentrated to 30% of the original volume at 70°C and a vacuum of -0.08 MPa to obtain a concentrated solution. The concentrated solution was spray-dried at an inlet air temperature of 200°C and an outlet air temperature of 90°C for 1 h. Finally, it was pulverized and passed through a 100-mesh sieve to obtain activated humic acid.

[0071] The core layer contains a starch-grafted acrylate copolymer as the water-retaining agent, a composite microbial agent consisting of *Azotobacter chrysophagus*, *Bacillus megaterium*, and *Pseudomonas fluorescens* in a mass ratio of 6:4:2, and a sodium carboxymethyl cellulose binder. The inner transition layer contains a trace element chelate consisting of ethylenediaminetetraacetic acid (EDTA) and hydroxyethyl ethylenediaminetriacetic acid (HEAT) in a mass ratio of 7.5:4. The isolation layer contains a polyvinyl alcohol as the water-soluble polymer. The outer layer contains a salt-resistant binder of acetate starch, a zeolite powder and gypsum mixture in a zeolite powder to gypsum mass ratio of 7:3, a polyacrylamide with a molecular weight of 15 million and a water absorption rate saturating within 30 seconds, and short-cut conductive carbon fibers with a length of 10 mm.

[0072] The above-mentioned fertilizer for improving saline-alkali land is prepared by the following method:

[0073] A1. Weigh the raw materials of the core layer according to the weight parts, put them into a three-dimensional motion mixer, stir and mix at 200-300 rpm for 15-20 minutes, spray deionized water into the uniformly mixed material, control the total moisture content at 18-22%, then put it into a granulator, and make 1.0-1.5 mm spherical particles at 30-40℃ and 30-50 rpm, and then dry at 50-55℃ for 30-60 minutes to obtain the core layer particles;

[0074] A2. Weigh the transition layer raw material according to the weight ratio, add deionized water to make the solid content 50%, stir at 1500 rpm for 15 min to make the transition layer slurry; put the core layer particles into the fluidized bed coating equipment, spray the inner transition layer slurry onto the particle surface, control the air inlet temperature to 70℃ and the material temperature to 45℃, after the spraying is completed, fluidize and dry at 60℃ for 10 min to obtain double-layer particles;

[0075] A3. Weigh the raw materials for the isolation layer according to the weight parts. First, prepare the water-soluble polymer in it into an aqueous solution with a concentration of 5-8%. Then mix it with other raw materials and stir at 800 rpm for 15 minutes to make an isolation layer slurry. Place the double-layer particles into a fluidized bed coating equipment, preheat it to 50°C, and spray the isolation layer slurry onto the surface of the double-layer particles. Control the air inlet temperature to 75°C and the material temperature to 60°C to obtain three-layer particles.

[0076] A4. Weigh the outer layer raw materials according to the weight percentage and put them into a three-dimensional motion mixer. Stir and mix at 150 rpm for 20 minutes to obtain the outer coating powder. Preheat the three-layer granules to 45°C and transfer them into a drum coating equipment. Spray 5% of the weight of deionized water onto the surface of the three-layer granules to wet the surface. Add the outer coating powder during the rolling process. Alternately perform the spray-powdering operation 5 times. After the coating is completed, dry the granules at 60°C to a moisture content of 6% to obtain a four-layer structure saline-alkali land improvement fertilizer.

[0077] The above-mentioned method for constructing a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system includes the following steps:

[0078] B1. Apply saline-alkali land improvement fertilizer to the soil in a concentric circle pattern, forming spaced electrode strips. Each electrode strip is 40cm wide, with a center-to-center distance of 200cm between adjacent strips, and is placed 20cm below the soil surface.

[0079] B2. Install a low-voltage power supply system on the existing electrode strips to establish a micro-electric field between adjacent electrode strips, completing the construction of the saline-alkali land improvement system. The low-voltage power supply system includes a DC power supply, wires, and corrosion-resistant electrode connectors. The DC power supply operates in intermittent DC mode, providing power for 12 hours daily. Solar power is selected for the DC power supply. A solar photovoltaic power supply unit, including photovoltaic panels, a controller, and a battery, is installed at the site edge and connected to a control box with integrated timing function. The power output is safe DC power, using corrosion-resistant electrode connectors to reliably electrically connect the positive and negative output terminals of the power supply system to the spaced-apart improvement agent electrode strips using an "alternating polarity connection method." That is, connect the first electrode strip to the positive terminal, the adjacent second to the negative terminal, the third to the positive terminal, and so on, creating a potential difference between any two adjacent electrode strips.

[0080] Comparative Example 1

[0081] This comparative example differs from Example 2 in that it does not use modified fertilizer.

[0082] Comparative Example 2

[0083] The difference between this comparative example and Example 2 is that an equal mass of humic acid was used instead of the saline-alkali land improvement fertilizer in this scheme.

[0084] Comparative Example 3

[0085] The difference between this comparative example and Example 2 is that the graphite in the outer layer is not modified.

[0086] Experimental verification

[0087] A saline-alkali land plot with a salt content of 3.5-4.0% and a pH value of 9.0-9.5 was selected and divided into 6 treatment groups. Each treatment group was treated according to Examples 1-3 and Comparative Examples 1-3, with 3 replicates per treatment group, for a total of 18 experimental plots. The area of ​​each plot was 6m × 1m. The amount of soil conditioner or humic acid used was 200 kg / mu. Wheat and corn were rotated in each plot, with 1800 wheat plants and 48 corn plants planted in each plot. Soil salinity and soil pH were measured before planting, 3 months after planting, 6 months after planting, and 12 months after planting. The average values ​​for each treatment group were recorded in Table 1. After 12 months of planting, the total organic matter content, microbial residue carbon content, refractory carbon content, available nitrogen content, available phosphorus content, available potassium content, wheat yield, and corn yield were measured in each treatment group, and the average values ​​were recorded in Table 2.

[0088] Table 1

[0089]

[0090] As can be seen from Table 1, Examples 1-3 of the present invention can rapidly reduce the salinity and pH value of saline-alkali soil, and the improvement effect is stable and does not rebound in the long term.

[0091] Table 2

[0092]

[0093] As shown in Table 2, Examples 1-3 of this invention not only achieve rapid desalination and acidification of saline-alkali land, but also achieve synergistic breakthroughs in three dimensions: soil fertility improvement, ecological restoration, and high crop yield, realizing an efficient integrated solution of "improvement-fertilization-yield increase." This invention, through a synergistic mechanism, reshapes the soil organic matter composition of saline-alkali land, significantly increasing the content and proportion of stable carbon pool components such as microbial residual carbon and persistent carbon. This invention creatively integrates four mechanisms—electrochemical driving, physicochemical adsorption, biotransformation, and physical slow release—to achieve synergistic effects, fundamentally changing the "infertile, compacted, and poor fertilizer retention" properties of saline-alkali land. It achieves rapid, comprehensive, and lasting improvement in soil fertility, enabling the soil to move from simple "desalination" to a multi-effect stage of "fertilization" and "ecological function restoration."

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A micro-electric field synergistic graphite / humic acid saline-alkali land improvement system, characterized in that, The system includes a fertilizer for improving saline-alkali land and a low-voltage power supply system. The fertilizer is a four-layer composite particle, consisting of a core layer, an inner transition layer, an isolation layer, and an outer layer from the inside out. The outer layer contains modified graphite that has undergone surface hydroxylation and magnetic field-induced alignment treatment. The low-voltage power supply system is used to apply intermittent direct current to the fertilizer for improving saline-alkali land, which is distributed in the soil in an intermittent manner, to establish a micro-electric field between adjacent fertilizer strips. The core layer comprises the following raw materials in parts by weight: 50-70 parts of decomposed organic fertilizer, 20-30 parts of activated humic acid, 5-10 parts of water-retaining agent, 0.5-2.0 parts of compound microbial agent, and 2-4 parts of binder; the inner transition layer comprises the following raw materials in parts by weight: 60-80 parts of humic acid, 15-25 parts of zeolite powder, 3-8 parts of trace element chelate, and 3-6 parts of binder; the isolation layer comprises the following raw materials in parts by weight: 40-60 parts of gypsum, 30-50 parts of calcined clay or diatomaceous earth, and 5-10 parts of water-soluble polymer; the outer layer comprises the following raw materials in parts by weight: 50-70 parts of modified graphite, 20-35 parts of a mixture of zeolite powder and gypsum, 3-8 parts of water-retaining agent, 4-8 parts of salt-resistant binder, and 2-10 parts of short-cut conductive carbon fiber; The modified graphite is prepared by the following method: natural flake graphite is placed in a drying oven and dried at 60-80℃ for 4-6 hours. The dried graphite is then placed in a 5-15% hydrogen peroxide solution at a material-to-liquid ratio of 1:5-10 and reacted by stirring at 300-500 rpm for 1-3 hours in a water bath at 40-50℃. The material-to-liquid ratio is expressed in g / mL. After the reaction, the graphite is filtered out, washed 3-4 times with deionized water, and then placed in a drying oven and dried at 60-80℃ for 4-6 hours to obtain pre-oxidized graphite. Graphite oxide and deionized water are mixed at a material-to-liquid ratio of 1:20-30. Sodium polyacrylate (0.5-1.0% by weight of graphite) is added as a dispersant. The mixture is ultrasonically treated at an ultrasonic power of 400-600W for 30-60 minutes to obtain a pre-oxidized graphite suspension slurry. The material-to-liquid ratio is expressed in g / mL. The pre-oxidized graphite suspension slurry is placed in a magnetic field with an intensity of 0.3-0.8T and allowed to stand for 2-4 hours. Then, it is transferred to a drying oven and dried at 40-60℃ for 20-30 hours. Finally, it is ground through a 50-200 mesh sieve to obtain modified graphite.

2. The micro-electric field synergistic graphite / humic acid saline-alkali land improvement system as described in claim 1, characterized in that, The activated humic acid is prepared by the following method: humic acid and deionized water are mixed at a material-to-liquid ratio of 1:5-8, and stirred at 100-200 rpm for 30-60 min to obtain a humic acid slurry. The material-to-liquid ratio is expressed in g / mL. Ammonia water (25-28% of the slurry volume) is slowly added dropwise to the humic acid slurry. The reaction system is heated to 50-65℃ and stirred at 300-500 rpm for 2-4 h. Then, the temperature is lowered to 40-50℃ and the mixture is stirred at 150-250 rpm for 1-2 h to mature. The matured slurry is subjected to solid-liquid separation using a plate and frame filter press. The filtrate is collected, and the filter residue is washed 1-2 times. The washing liquid is combined with the filtrate, and then the filtrate is concentrated to 30-40% of the original volume under conditions of 60-70℃ and vacuum degree of -0.06 to -0.08MPa to obtain a concentrated liquid. The concentrated liquid is then spray-dried with an inlet air temperature of 180-200℃ and an outlet air temperature of 80-90℃, and then dried at 70-80℃ for 1-2 hours. Finally, it is pulverized through an 80-100 mesh sieve to obtain activated humic acid.

3. The micro-electric field synergistic graphite / humic acid saline-alkali land improvement system as described in claim 1, characterized in that, The core layer contains a starch-grafted acrylate copolymer as the water-retaining agent, a composite microbial agent composed of *Azotobacter chrysophagus*, *Bacillus megaterium*, and *Pseudomonas fluorescens* in a mass ratio of (5-6):(3-4):(1-2), and a sodium carboxymethyl cellulose binder. The inner transition layer contains a trace element chelate composed of ethylenediaminetetraacetic acid and hydroxyethyl ethylenediaminetriacetic acid in a mass ratio of (6-7.5):(2.5-4). The isolation layer contains a polyvinyl alcohol as the water-soluble polymer. The outer layer contains an oxidized starch or acetate starch binder, a zeolite powder and gypsum mixture in a mass ratio of (6-7):(4-3), a polyacrylamide with a molecular weight of 8-15 million and a water absorption rate saturated within 30 seconds, and short-cut conductive carbon fibers with a length of 3-10 mm.

4. The micro-electric field synergistic graphite / humic acid saline-alkali land improvement system as described in claim 1, characterized in that, The saline-alkali land improvement fertilizer is prepared by the following method: A1. Weigh the raw materials of the core layer according to the weight parts, put them into a three-dimensional motion mixer, stir and mix at 200-300 rpm for 15-20 minutes, spray deionized water into the uniformly mixed material, control the total moisture content at 18-22%, then put it into a granulator, and make 1.0-1.5 mm spherical particles at 30-40℃ and 30-50 rpm, and then dry at 50-55℃ for 30-60 minutes to obtain the core layer particles; A2. Weigh the transition layer raw material according to the weight ratio, add deionized water to make the solid content 40-50%, stir at 1000-1500 rpm for 15-25 min to make the transition layer slurry; put the core layer particles into the fluidized bed coating equipment, spray the inner transition layer slurry onto the particle surface, control the air inlet temperature to 60-70℃ and the material temperature to 45-55℃, after the spraying is completed, fluidize and dry at 50-60℃ for 10-15 min to obtain double-layer particles; A3. Weigh the raw materials for the isolation layer according to the weight proportions. First, prepare the water-soluble polymer in it into an aqueous solution with a concentration of 5-8%, and then mix it with other raw materials. Stir at 500-800 rpm for 15-25 minutes to make an isolation layer slurry. Place the double-layer particles into a fluidized bed coating equipment, preheat it to 45-50℃, and spray the isolation layer slurry onto the surface of the double-layer particles. Control the air inlet temperature to 65-75℃ and the material temperature to 50-60℃ to obtain three-layer particles. A4. Weigh out the outer layer raw materials according to the weight percentage and put them into a three-dimensional motion mixer. Stir and mix at 100-150 rpm for 20-30 minutes to obtain the outer coating powder. Preheat the three-layer granules to 40-45℃ and transfer them into a drum coating equipment. Spray 3-5% of the weight of deionized water onto the surface of the three-layer granules to wet the surface. Add the outer coating powder during the rolling process. Alternately perform the spray-powder addition operation 3-5 times. After the coating is completed, dry the granules at 50-60℃ until the moisture content is ≤8% to obtain a four-layer structure saline-alkali land improvement fertilizer.

5. A method for constructing a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system as described in any one of claims 1-4, characterized in that, Includes the following steps: B1. Place saline-alkali land improvement fertilizer in the soil to form intermittently distributed electrode strips; B2. Install a low-voltage power supply system on the formed electrode strips, establish a micro-electric field between adjacent electrode strips, and complete the construction of the saline-alkali land improvement system.

6. The method for constructing a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system as described in claim 5, characterized in that, In step B1, the fertilizer for improving saline-alkali land is arranged in strips or concentric circles.

7. The method for constructing a micro-electric field synergistic graphite / humic acid saline-alkali land improvement system as described in claim 5, characterized in that, The power supply system includes a DC power supply, wires, and corrosion-resistant electrode connectors; the DC power supply operates in an intermittent DC power mode, with power supplied for 4-12 hours per day.

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