Acid soil conditioner and preparation method thereof

Abstract

The invention provides an acid soil conditioner and a preparation method thereof, and belongs to the technical field of soil conditioners. The soil conditioner is prepared from the following raw materials in parts by weight: 30-40 parts of pH-sensitive hydrogel, 3-7 parts of slow-release nitrogen-fixing bacteria microcapsules, 5-8 parts of soil improvement bacteria, 10-20 parts of a chitosan / sodium alginate modified compound, 17-20 parts of fly ash and 18-22 parts of phosphogypsum. According to the prepared acid soil conditioner, the microorganism and chemical improvement effect is adopted, the pH value of soil can be obviously increased, the granular structure of the soil is improved, the buffering capacity of the soil is enhanced, the fertility of the soil is improved, the heavy metal content of the soil is reduced, the quality of the soil is improved, and the crop yield is increased, so that the acid soil conditioner has wide application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of soil conditioners, and particularly relates to an acidic soil conditioner and a preparation method thereof. Background Art

[0002] Soil acidification has become one of the most serious land degradation problems in the global agricultural system, and up to 40% of the cultivated land globally is affected by acidification. Acidic soil is a general term for soils with a low pH value. In areas with acidic soil, precipitation is abundant, the leaching effect is strong, base ions are leached in large quantities, the base saturation is low, and the high concentrations of H + , A1 3+ , Mn 2+ and Fe 2+ in acidic soil have a direct toxic effect on plants. Another serious problem of acidic soil is the lack of available nutrients, and the types of nutrients involved are relatively many. For example, acidic soil generally lacks nitrogen, phosphorus and potassium, many acidic soils lack calcium and magnesium, and some acidic soils also lack molybdenum.

[0003] Currently, the main methods for improving acidic soil are: using quicklime to neutralize acidity, planting green manure to increase organic matter, applying organic fertilizers such as farmyard manure, increasing the number of irrigation times, applying alkaline fertilizers, etc. However, these methods all have great defects. For example, using quicklime to neutralize acidity will destroy the soil microbial population structure, and a large amount of organic fertilizer needs to be applied to exert its effect. The amount of alkaline fertilizer applied is limited and the improvement effect is not obvious.

[0004] Chinese invention patent CN104926565B discloses a preparation and application method of an acidic soil conditioner. The waste calcium mud and magnesium mud generated by the chemical fertilizer industry are respectively dried to reduce their water content to 13%-15%, and then crushed to less than 10 meshes; 15-25 parts of the prepared calcium mud, 20-30 parts of magnesium mud, 10-15 parts of commercial urea, 5-8 parts of commercial monoammonium phosphate, and 2-3 parts of commercial potassium sulfate are weighed by mass. After all the raw materials are mixed evenly, they are granulated and dried to a water content of 10%-12%, and then packaged to obtain the finished product. However, the application amount of the prepared acidic soil conditioner per hectare per year is 300 kg - 600 kg; when the pH value of acidic soil is 4.5 - 5, it is recommended to apply 600 kg - 900 kg per hectare per year. The application amount is large and the improvement effect on acidic soil is not good. Summary of the Invention

[0005] The purpose of the present invention is to provide an acidic soil conditioner and a preparation method thereof, which can significantly increase the pH value of the soil, improve the soil aggregate structure, enhance the soil buffering capacity, increase the soil fertility, reduce the soil heavy metal content, improve the soil quality and crop yield by using the microbial + chemical improvement effect, and has broad application prospects.

[0006] The technical solution of the present invention is realized as follows: The present invention provides an acidic soil conditioner, which is prepared from the following raw materials by weight: 30-40 parts of pH-sensitive hydrogel, 3-7 parts of slow-release nitrogen-fixing bacteria microcapsules, 5-8 parts of soil-improving bacteria, 10-20 parts of chitosan / sodium alginate modified complex, 17-20 parts of fly ash, and 18-22 parts of phosphogypsum.

[0007] As a further improvement of the present invention, the preparation method of the pH-sensitive hydrogel is as follows: S1. Dissolve sodium carboxymethyl cellulose in water to obtain solution A; S2. Dissolve chitosan in an acid solution to obtain solution B; S3. Crush the straw, add it to water, add tetrabutyl titanate, stir and react, centrifuge, wash, dry, calcine, and ball mill to obtain biochar-supported titanium dioxide; S4. Mix solution A and solution B, add biochar-supported titanium dioxide, stir and mix evenly, dropwise add calcium chloride solution, stir and crosslink, and dry to obtain pH-sensitive hydrogel.

[0008] As a further improvement of the present invention, in step S1, the concentration of sodium carboxymethyl cellulose in solution A is 5-7 wt%; in step S2, the concentration of chitosan in solution B is 3-5 wt%, and the acid solution is acetic acid or lactic acid solution with a concentration of 1-2 wt%; in step S3, the mass ratio of straw to tetrabutyl titanate is 10-12:5-8, the calcination temperature is 750-850 °C, the time is 2-4 h, and the ball milling time is 1-2 h; in step S4, the mass ratio of solution A, solution B and biochar-supported titanium dioxide is 10:15-20:0.2-0.5, and the stirring and crosslinking time is 2-4 h.

[0009] As a further improvement of the present invention, the preparation method of the slow-release nitrogen-fixing bacteria microcapsules is as follows: T1. Preparation of carboxylated chitosan nanocrystals: Mix chitosan, acid solution, Tempo reagent, and sodium bromide and stir, then add sodium hypochlorite, adjust the pH value of the solution, stir and react, add ethanol to terminate the reaction, centrifuge, wash, and dry to obtain carboxylated chitosan nanocrystals; T2. Slow-release nitrogen-fixing bacteria microcapsules: Add carboxylated chitosan nanocrystals, waterborne polyurethane, and emulsifier to water, stir and disperse evenly, add nitrogen-fixing bacteria, mix evenly, then dropwise add to fish oil, emulsify, freeze-dry, and filter to obtain slow-release nitrogen-fixing bacteria microcapsules.

[0010] As a further improvement of the present invention, in step T1, the mass ratio of chitosan, Tempo reagent, sodium bromide, and sodium hypochlorite is 1:0.01 - 0.02:0.1 - 0.15:4 - 6, the acid solution is an acetic acid or lactic acid solution with a concentration of 1 - 2 wt%, the pH value of the adjustment solution is 9.5 - 10.5, and the stirring reaction time is 18 - 20 h; in step T2, the mass ratio of carboxylated chitosan nanocrystals, aqueous polyurethane, emulsifier, and nitrogen-fixing bacteria is 5 - 10:20 - 40:0.5 - 1:12 - 15, the aqueous polyurethane is Impranil RSC 1380, the emulsifier is selected from at least one of Tween-20, Tween-40, Tween-60, and Tween-80, and the nitrogen-fixing bacteria are at least one of Azotobacter chroococcum, Frankia, Rhizobium, Azospirillum brasilense, Azospirillum lipoferum, Klebsiella, and Clostridium pasteurianum.

[0011] As a further improvement of the present invention, the preparation method of the chitosan / sodium alginate modified composite is as follows: U1. Preparation of biochar: Crush the straw, carbonize it, and ball-mill it to obtain biochar; U2. Preparation of the modified composite: Mix the biochar and basalt powder evenly, add them to ethanol, add a silane coupling agent, heat and stir for reaction, centrifuge, wash, and dry to obtain the modified composite; U3. Preparation of the chitosan / sodium alginate modified composite: Dissolve chitosan in the acid solution, add the modified composite and sodium alginate, dropwise add calcium chloride solution, stir and crosslink, dry, and crush to obtain the chitosan / sodium alginate modified composite.

[0012] As a further improvement of the present invention, in step U1, the temperature of carbonization is 700 - 800 °C, the time is 3 - 5 h, and the time of ball-milling is 1 - 3 h; in step U2, the mass ratio of biochar, basalt powder, and silane coupling agent is 10 - 15:8 - 12:3 - 5, the silane coupling agent is selected from at least one of KH550, KH602, and KH792, the temperature of the heating and stirring reaction is 40 - 50 °C, and the time is 2 - 4 h; in step U3, the acid solution is an acetic acid or lactic acid solution with a concentration of 1 - 2 wt%, the mass ratio of chitosan, modified composite, and sodium alginate is 10 - 12:7 - 10:4 - 7, and the time of stirring and crosslinking is 1 - 3 h.

[0013] As a further improvement of the present invention, the soil-improving bacteria are at least one of Alcaligenes faecalis, Bacillus subtilis, and Bacillus licheniformis. These soil-improving bacteria have good acid tolerance, and at the same time can more effectively decompose organic substances, fix nutrients, inhibit harmful microorganisms, etc., and increase the pH value of the soil.

[0014] The present invention further protects a preparation method of the above-mentioned acid soil conditioner, which comprises the following steps: (1) Mix the slow-release nitrogen-fixing bacteria microcapsules and soil improvement bacteria evenly to obtain a compound bacteria preparation; (2) Stir and mix the pH-sensitive hydrogel, chitosan / sodium alginate modified composite, fly ash, and phosphogypsum evenly, add the compound bacteria preparation at low temperature, and stir and mix evenly to obtain the acid soil conditioner.

[0015] As a further improvement of the present invention, the low temperature is 3-5°C.

[0016] The present invention has the following beneficial effects: The present invention prepares a pH-sensitive hydrogel, which is prepared by cross-linking carboxymethyl cellulose sodium containing abundant carboxyl groups and chitosan to obtain a hydrogel matrix, and then adding biochar prepared by carbonizing straw. The biochar prepared by carbonization has advantages such as a large specific surface area, can load more titanium dioxide. The prepared pH-sensitive hydrogel will swell and gradually decompose in the acid soil medium. In addition, the presence of titanium dioxide can also promote the decomposition of the hydrogel, releasing the slow-release nitrogen-fixing bacteria microcapsules and soil improvement bacteria buried inside it. In addition, the hydrogel can also adsorb heavy metal ions in the soil, reduce the content of soil heavy metal ions, and slowly release to increase the soil organic matter and nitrogen content, long-term improve the soil fertility, avoid the loss of multi-element nutrients, and accelerate the degradation and transformation of corrupt substances in the soil, improve the water storage capacity of the soil, can adsorb a part of smaller aggregates to form larger aggregate structures, effectively increase the content of water-stable aggregates in the soil, and have a certain retention effect on water and nutrients.

[0017] The present invention can obtain carboxylated chitosan nanocrystals by the Tempo oxidation method. This is a rod-shaped crystalline nanoparticle with the characteristics of a high aspect ratio and high modulus. Its surface contains a large number of polar groups such as hydroxyl groups and amino groups, and can form hydrogen bonds with waterborne polyurethane to serve as an embedding shell material for nitrogen-fixing bacteria. Nitrogen-fixing bacteria can fix nitrogen in the air and effectively increase the nitrogen content in the soil. However, it is not acid-resistant, and some are even sensitive to acid. Therefore, it needs to be embedded and protected. When the soil pH value slowly rises and approaches neutrality, the shell material will swell and release nitrogen-fixing bacteria. At the same time, the shell material has good environmental protection and is safe and non-toxic.

[0018] The present invention prepares a chitosan / sodium alginate modified composite, using biochar obtained by carbonizing straw and basalt as the core materials. Silicate rocks such as basalt produce alkaline substances during weathering, reducing soil acidification caused by overuse of ammonium fertilizers, elemental sulfur fertilizers, urea, and repeated harvesting of crops, and improving organic matter sequestration by increasing the organic carbon input of roots and mycorrhizal fungi, contributing to the restoration of soil health. At the same time, it can both improve soil acidity and correct soil available silicon and crop silicon deficiency. The highly alkaline cations in biochar can combine with acidic anions in acidic soil to reduce the concentration of acidic ions, thereby increasing the pH value of the soil. Biochar has a good pore structure and permeability, and after being added to acidic soil, it can increase the porosity and permeability of the soil, thus improving the soil structure. Biochar is rich in trace elements and organic substances and can be added to the soil as a fertilizer to improve soil fertility. After being modified with an amino coupling agent on the surface, it can be compounded and fixed with chitosan and sodium alginate. On the one hand, sodium alginate and chitosan have a certain flocculation effect, which can promote the aggregation of soil particles and improve the soil aggregate structure, thereby enhancing the aeration and water retention of the soil; chitosan itself is a weak alkaline substance, which can neutralize some acidic substances in the soil, thus increasing the pH value of the soil to a certain extent; chitosan can provide nutrients for beneficial microorganisms in the soil and promote their growth and reproduction. Sodium alginate molecules contain a large number of carboxyl (-COO - ), hydroxyl (-OH) and other active groups. These groups can chemically react with acidic substances in the soil, adsorb and fix acidic substances, thereby reducing the concentration of acidic ions in the soil solution and increasing the pH value of the soil. At the same time, such substances can also significantly fix the content of soil heavy metal ions, achieving the effect of reducing soil pollution.

[0019] Phosphogypsum has higher solubility than lime and can react with soil colloids to displace OH - to neutralize soil acidity. Combining lime with trace elements, small molecule polymers, and humus helps to improve the soil aggregate structure, enhance the soil buffering capacity, and increase soil quality and crop yield.

[0020] Fly ash contains alkaline substances such as calcium oxide. When applied to acidic soil, these alkaline substances will undergo a neutralization reaction with acidic components in the soil, thereby increasing the pH value of the soil and reducing soil acidity. Its fine particles can fill the pores in the soil, increasing the porosity and aeration of the soil, improving the physical structure of the soil. After being applied to the soil, it can improve the physical and chemical properties of the soil and indirectly affect the activity of microorganisms in the soil.

[0021] The present invention adds the synergistic action of nitrogen-fixing bacteria and soil-improving bacteria, which can more effectively decompose organic substances, fix nutrients, inhibit harmful microorganisms, etc., increase the pH value of the soil, and the slow and controlled release technology also greatly improves the tolerance of the bacteria to the soil, playing a better role in soil improvement. Moreover, it can avoid the problem of soil compaction caused by applying alkaline substances and affecting soil vitality, which is the microbial effect.

[0022] The present invention prepares an acidic soil conditioner, which adopts the microbial + chemical improvement effect, can significantly increase the pH value of the soil, improve the soil aggregate structure, enhance the soil buffering capacity, increase the soil fertility, reduce the soil heavy metal content, improve the soil quality and crop yield, and has broad application prospects. Specific embodiments

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] The bacteria used in the following embodiments of the present invention are: Azotobacter chroococcum, CGMCC 1.502, 10 billion cfu / g; Alcaligenes faecalis, ATCC 8750, 10 billion cfu / g.

[0025] Preparation Example 1: Preparation of pH-sensitive hydrogel, the method is as follows: S1. Dissolve 5 g of sodium carboxymethylcellulose in 100 mL of water to obtain solution A; S2. Dissolve 3 g of chitosan in 100 mL of 1 wt% acetic acid solution to obtain solution B; S3. Crush 10 g of corn straw, add it to 200 mL of water, add 5 g of tetrabutyl titanate, stir and react for 1 h, centrifuge, wash, dry, calcine at 750 °C for 2 h, and ball mill for 1 h to obtain biochar-supported titanium dioxide; S4. Mix 100 g of solution A and 150 g of solution B, add 2 g of biochar-supported titanium dioxide, stir and mix evenly, dropwise add 30 mL of 2 wt% calcium chloride solution, stir and crosslink for 2 h, and dry to obtain pH-sensitive hydrogel.

[0026] Preparation Example 2: Preparation of pH-sensitive hydrogel, the method is as follows: S1. Dissolve 7 g of sodium carboxymethylcellulose in 100 mL of water to obtain solution A; S2. Dissolve 5 g of chitosan in 100 mL of 2 wt% lactic acid solution to obtain solution B; S3. Crush 12 g of corn straw, add it to 200 mL of water, add 8 g of tetrabutyl titanate, stir and react for 3 h, centrifuge, wash, dry, calcine at 850 °C for 4 h, and ball mill for 2 h to obtain titanium dioxide supported on biochar; S4. Mix 100 g of solution A and 200 g of solution B, add 5 g of titanium dioxide supported on biochar, stir and mix evenly, dropwise add 30 mL of 2 wt% calcium chloride solution, stir and crosslink for 4 h, dry to obtain a pH-sensitive hydrogel.

[0027] Preparation Example 3: Preparation of a pH-sensitive hydrogel, the method is as follows: S1. Dissolve 6 g of sodium carboxymethyl cellulose in 100 mL of water to obtain solution A; S2. Dissolve 4 g of chitosan in 100 mL of 1.5 wt% acetic acid solution to obtain solution B; S3. Crush 11 g of corn straw, add it to 200 mL of water, add 6 g of tetrabutyl titanate, stir and react for 2 h, centrifuge, wash, dry, calcine at 800 °C for 3 h, and ball mill for 1.5 h to obtain titanium dioxide supported on biochar; S4. Mix 100 g of solution A and 170 g of solution B, add 3 g of titanium dioxide supported on biochar, stir and mix evenly, dropwise add 30 mL of 2 wt% calcium chloride solution, stir and crosslink for 3 h, dry to obtain a pH-sensitive hydrogel.

[0028] Comparative Preparation Example 1: Compared with Preparation Example 3, the difference is that corn straw is not added in step S3. Specifically as follows: S1. Dissolve 6 g of sodium carboxymethyl cellulose in 100 mL of water to obtain solution A; S2. Dissolve 4 g of chitosan in 100 mL of 1.5 wt% acetic acid solution to obtain solution B; S3. Add 6 g of tetrabutyl titanate to 200 mL of water, stir and react for 2 h, centrifuge, wash, dry, calcine at 500 °C for 3 h, and ball mill for 1.5 h to obtain titanium dioxide; S4. Mix 100 g of solution A and 170 g of solution B, add 3 g of titanium dioxide, stir and mix evenly, dropwise add 30 mL of 2 wt% calcium chloride solution, stir and crosslink for 3 h, dry to obtain a pH-sensitive hydrogel.

[0029] Comparative Preparation Example 2: Compared with Preparation Example 3, the difference is that titanium dioxide supported on biochar is not added in step S4. Specifically as follows: S1. Dissolve 6 g of sodium carboxymethyl cellulose in 100 mL of water to obtain solution A; S2. Dissolve 4 g of chitosan in 100 mL of 1.5 wt% acetic acid solution to obtain Solution B; S3. Mix 100 g of Solution A and 170 g of Solution B, stir to mix evenly, add dropwise 30 mL of 2 wt% calcium chloride solution, stir and crosslink for 3 h, and dry to prepare a pH-sensitive hydrogel.

[0030] Test Example 1: Perform performance tests on the pH-sensitive hydrogels prepared in Preparation Examples 1-3 and Comparative Preparation Examples 1-2, and the results are shown in Table 1.

[0031] (1) Water absorbency in aqueous solutions with different pH values: Take equal masses of the pH-sensitive hydrogel, soak it in different pH aqueous solutions (pH = 2, pH = 7, pH = 10) at room temperature, and measure the liquid absorption ratio after swelling by absorbing liquid for 3 h.

[0032] Method for measuring the liquid absorption ratio: Immerse 0.1 g of the sample in 500 mL of liquid and let it stand at room temperature until swelling equilibrium is reached. Then filter with a filter screen for 15 min to filter off the excess water other than the sample, and calculate the water absorption ratio of the pH-sensitive hydrogel using the following formula: Q = (m2 - m1) / m1, In the formula, Q: water absorption ratio, g / g; m1: mass of the dry gel taken, g; m2: mass of the gel after swelling equilibrium, g.

[0033] (2) Degradation performance: Place the pH-sensitive hydrogel with a weight of m0 in an aqueous solution, and carry out the degradation test in an air bath shaker at a temperature of 37 °C and a shaking speed of 100 rpm. At regular intervals, take out the sample, dry it, and weigh the weight as m1. Then replace it with a new degradation solution. When (m0 - m1 / m0) is greater than 0.99, it is considered to be completely degraded. Record the complete degradation time.

[0034] Table 1

[0035] As can be seen from the above table, the pH-sensitive hydrogels prepared in Examples 1-3 of the present invention have the largest liquid absorption ratio under acidic conditions and a short degradation time. The degradation time in Comparative Preparation Examples 1-2 is extended, indicating that the participation of titanium dioxide shortens the degradation time of the hydrogel.

[0036] Preparation Example 4: Preparation of slow-release nitrogen-fixing bacteria microcapsules, the method is as follows: T1. Preparation of carboxylated chitosan nanocrystals: Mix 1 g of chitosan, 100 mL of 1 wt% acetic acid solution, 0.01 g of 1 mol% Tempo reagent, and 0.1 g of sodium bromide, and stir. Then add 4 g of sodium hypochlorite, adjust the pH value of the solution to 9.5, stir and react for 18 h, add 10 mL of ethanol to terminate the reaction, centrifuge, wash, and dry to obtain carboxylated chitosan nanocrystals; T2. Slow-release azotobacter microcapsules: Add 5 g of carboxylated chitosan nanocrystals, 20 g of aqueous polyurethane Impranil RSC1380, and 0.5 g of Tween-40 to 500 mL of water, stir and disperse for 15 min, add 12 g of Azotobacter chroococcum, mix well, then dropwise add to 1 L of fish oil, emulsify at 8000 r / min for 15 min, freeze-dry, and filter to obtain slow-release azotobacter microcapsules.

[0037] Preparation Example 5: Preparation of slow-release azotobacter microcapsules, the method is as follows: T1. Preparation of carboxylated chitosan nanocrystals: Mix 1 g of chitosan, 100 mL of 2 wt% lactic acid solution, 0.02 g of 1 mol% Tempo reagent, and 0.15 g of sodium bromide, and stir. Then add 6 g of sodium hypochlorite, adjust the pH value of the solution to 10.5, stir and react for 20 h, add 10 mL of ethanol to terminate the reaction, centrifuge, wash, and dry to obtain carboxylated chitosan nanocrystals; T2. Slow-release azotobacter microcapsules: Add 10 g of carboxylated chitosan nanocrystals, 40 g of aqueous polyurethane Impranil RSC 1380, and 1 g of Tween-60 to 500 mL of water, stir and disperse for 15 min, add 15 g of Azotobacter chroococcum, mix well, then dropwise add to 1 L of fish oil, emulsify at 8000 r / min for 15 min, freeze-dry, and filter to obtain slow-release azotobacter microcapsules.

[0038] Preparation Example 6: Preparation of slow-release azotobacter microcapsules, the method is as follows: T1. Preparation of carboxylated chitosan nanocrystals: Mix 1 g of chitosan, 100 mL of 1.5 wt% acetic acid solution, 0.015 g of 1 mol% Tempo reagent, and 0.12 g of sodium bromide, and stir. Then add 5 g of sodium hypochlorite, adjust the pH value of the solution to 10, stir and react for 19 h, add 10 mL of ethanol to terminate the reaction, centrifuge, wash, and dry to obtain carboxylated chitosan nanocrystals; T2. Slow-release azotobacter microcapsules: Add 7 g of carboxylated chitosan nanocrystals, 30 g of aqueous polyurethane Impranil RSC1380, and 0.7 g of Tween-80 to 500 mL of water, stir and disperse for 15 min, add 13 g of Azotobacter chroococcum, mix well, then dropwise add to 1 L of fish oil, emulsify at 8000 r / min for 15 min, freeze-dry, and filter to obtain slow-release azotobacter microcapsules.

[0039] Comparative Preparation Example 3: Compared with Preparation Example 6, the difference lies in that carboxylated chitosan nanocrystals were not added in step T2. Specifically as follows: 737 g of aqueous polyurethane Impranil RSC 1380 and 0.7 g of Tween-80 were added to 500 mL of water, stirred and dispersed for 15 min, 13 g of Azotobacter chroococcum was added, and after mixing evenly, it was dropped into 1 L of fish oil, emulsified at 8000 r / min for 15 min, freeze-dried, and filtered to obtain slow-release Azotobacter chroococcum microcapsules.

[0040] Test Example 2: 1 g of the slow-release Azotobacter chroococcum microcapsules prepared in Preparation Examples 4-6 of the present invention and Comparative Preparation Example 3 were respectively added to 10 mL of phosphate buffer solution with pH = 2, 10 mL of phosphate buffer solution with pH = 6, and 10 mL of phosphate buffer solution with pH = 10, and reacted at 30 °C and 50 r / min for 2 h respectively. The survival rate was calculated according to the following formula: The release rate was calculated according to the following formula: Release rate (%) = (W0 - W t ) / W0 × 100%, wherein, W0 is the initial weight of the sample; W t is the weight of the sample after reacting in different buffer solutions for a certain time.

[0041] The results are shown in Table 2.

[0042] Table 2

[0043] As can be seen from the above table, the slow-release Azotobacter chroococcum microcapsules prepared in Preparation Examples 4-6 of the present invention have a low release rate under acidic conditions, and the release rate is significantly increased under neutral and alkaline conditions.

[0044] Preparation Example 7: Preparation of chitosan / sodium alginate modified composite, the method is as follows: U1. Preparation of biochar: Corn straw was crushed, carbonized at 700 °C for 3 h, and ball-milled for 1 h to obtain biochar; U2. Preparation of modified composite: 10 g of biochar and 8 g of basalt powder were mixed evenly, added to 200 mL of ethanol, 3 g of silane coupling agent KH792 was added, heated to 40 °C, stirred and reacted for 2 h, centrifuged, washed, and dried to obtain the modified composite; U3. Preparation of chitosan / sodium alginate modified composite: Dissolve 10 g of chitosan in 500 mL of acetic acid solution with a concentration of 1 wt%, add 7 g of modified composite and 4 g of sodium alginate, dropwise add 50 mL of 2 wt% calcium chloride solution, stir and crosslink for 1 h, dry, and pulverize to obtain chitosan / sodium alginate modified composite.

[0045] Preparation Example 8: Preparation of chitosan / sodium alginate modified composite, the method is as follows: U1. Preparation of biochar: Crush corn straw, carbonize at 800 °C for 5 h, and ball mill for 3 h to obtain biochar; U2. Preparation of modified composite: Mix 15 g of biochar and 12 g of basalt powder evenly, add them to 200 mL of ethanol, add 5 g of silane coupling agent KH602, heat to 50 °C, stir and react for 4 h, centrifuge, wash, and dry to obtain modified composite; U3. Preparation of chitosan / sodium alginate modified composite: Dissolve 12 g of chitosan in 500 mL of lactic acid solution with a concentration of 2 wt%, add 10 g of modified composite and 7 g of sodium alginate, dropwise add 50 mL of 2 wt% calcium chloride solution, stir and crosslink for 3 h, dry, and pulverize to obtain chitosan / sodium alginate modified composite.

[0046] Preparation Example 9: Preparation of chitosan / sodium alginate modified composite, the method is as follows: U1. Preparation of biochar: Crush corn straw, carbonize at 750 °C for 4 h, and ball mill for 2 h to obtain biochar; U2. Preparation of modified composite: Mix 12 g of biochar and 10 g of basalt powder evenly, add them to 200 mL of ethanol, add 4 g of silane coupling agent KH550, heat to 45 °C, stir and react for 3 h, centrifuge, wash, and dry to obtain modified composite; U3. Preparation of chitosan / sodium alginate modified composite: Dissolve 11 g of chitosan in 500 mL of lactic acid solution with a concentration of 1.5 wt%, add 8.5 g of modified composite and 5.5 g of sodium alginate, dropwise add 50 mL of 2 wt% calcium chloride solution, stir and crosslink for 2 h, dry, and pulverize to obtain chitosan / sodium alginate modified composite.

[0047] Comparative Preparation Example 4: Compared with Preparation Example 9, the difference is that basalt is not added in step U2. Specifically as follows: U1. Preparation of biochar: Crush corn straw, carbonize at 750 °C for 4 h, and ball mill for 2 h to obtain biochar; U2. Preparation of modified biochar: Add 22 g of biochar into 200 mL of ethanol, add 4 g of silane coupling agent KH550, heat to 45 °C, stir and react for 3 h, centrifuge, wash, and dry to obtain modified biochar; U3. Preparation of chitosan / sodium alginate modified biochar: Dissolve 11 g of chitosan in 500 mL of lactic acid solution with a concentration of 1.5 wt%, add 8.5 g of modified biochar and 5.5 g of sodium alginate, dropwise add 50 mL of 2 wt% calcium chloride solution, stir and crosslink for 2 h, dry, and pulverize to obtain chitosan / sodium alginate modified biochar.

[0048] Comparative Preparation Example 5: Compared with Preparation Example 9, the difference lies in that no biochar was added in step U2. Specifically as follows: U1. Preparation of modified basalt powder: Add 22 g of basalt powder into 200 mL of ethanol, add 4 g of silane coupling agent KH550, heat to 45 °C, stir and react for 3 h, centrifuge, wash, and dry to obtain basalt powder; U3. Preparation of chitosan / sodium alginate modified basalt powder: Dissolve 11 g of chitosan in 500 mL of lactic acid solution with a concentration of 1.5 wt%, add 8.5 g of modified basalt powder and 5.5 g of sodium alginate, dropwise add 50 mL of 2 wt% calcium chloride solution, stir and crosslink for 2 h, dry, and pulverize to obtain chitosan / sodium alginate modified basalt powder.

[0049] Comparative Preparation Example 6: Compared with Preparation Example 9, the difference lies in that no modification with silane coupling agent KH550 was carried out in step U2. Specifically as follows: U1. Preparation of biochar: Crush corn straw, carbonize at 750 °C for 4 h, and ball mill for 2 h to obtain biochar; U2. Preparation of composite: Mix 12 g of biochar and 10 g of basalt powder evenly to obtain a composite; U3. Preparation of chitosan / sodium alginate modified composite: Dissolve 11 g of chitosan in 500 mL of lactic acid solution with a concentration of 1.5 wt%, add 8.5 g of the composite and 5.5 g of sodium alginate, dropwise add 50 mL of 2 wt% calcium chloride solution, stir and crosslink for 2 h, dry, and pulverize to obtain chitosan / sodium alginate modified composite.

[0050] Comparative Preparation Example 7 Compared with Preparation Example 9, the difference lies in that step U3 was not carried out. Specifically as follows: U1. Preparation of biochar: Crush corn straw, carbonize at 750 °C for 4 h, and ball mill for 2 h to obtain biochar; U2. Preparation of the modified composite: Mix 12 g of biochar and 10 g of basalt powder evenly, add them to ethanol, add 4 g of silane coupling agent KH550, heat to 45 °C, stir and react for 3 h, centrifuge, wash, and dry to obtain the modified composite.

[0051] Example 1 A preparation method of an acidic soil conditioner, comprising the following steps: (1) Mix 3 g of the slow-release nitrogen-fixing bacteria microcapsules prepared in Preparation Example 4 and 5 g of Alcaligenes faecalis for 15 min to obtain a composite bacterial preparation; (2) Stir and mix 30 g of the pH-sensitive hydrogel prepared in Preparation Example 1, 10 g of the chitosan / sodium alginate modified composite prepared in Preparation Example 7, 17 g of fly ash, and 18 g of phosphogypsum for 15 min, add the composite bacterial preparation at 3 °C, and stir and mix for 20 min to obtain the acidic soil conditioner.

[0052] Example 2 A preparation method of an acidic soil conditioner, comprising the following steps: (1) Mix 7 g of the slow-release nitrogen-fixing bacteria microcapsules prepared in Preparation Example 5 and 8 g of Alcaligenes faecalis for 15 min to obtain a composite bacterial preparation; (2) Stir and mix 40 g of the pH-sensitive hydrogel prepared in Preparation Example 2, 20 g of the chitosan / sodium alginate modified composite prepared in Preparation Example 8, 20 g of fly ash, and 22 g of phosphogypsum for 15 min, add the composite bacterial preparation at 5 °C, and stir and mix for 20 min to obtain the acidic soil conditioner.

[0053] Example 3 A preparation method of an acidic soil conditioner, comprising the following steps: (1) Mix 5 g of the slow-release nitrogen-fixing bacteria microcapsules prepared in Preparation Example 6 and 7 g of Alcaligenes faecalis for 15 min to obtain a composite bacterial preparation; (2) Stir and mix 35 g of the pH-sensitive hydrogel prepared in Preparation Example 3, 15 g of the chitosan / sodium alginate modified composite prepared in Preparation Example 9, 18 g of fly ash, and 20 g of phosphogypsum for 15 min, add the composite bacterial preparation at 4 °C, and stir and mix for 20 min to obtain the acidic soil conditioner.

[0054] Comparative Example 1 Compared with Example 3, the difference lies in that the pH-sensitive hydrogel is prepared from Comparative Preparation Example 1.

[0055] Comparative Example 2 Compared with Example 3, the difference lies in that the pH-sensitive hydrogel is prepared from Comparative Preparation Example 2.

[0056] Comparative Example 3 Compared with Example 3, the difference lies in that the slow-release nitrogen-fixing bacteria microcapsules are prepared from Comparative Preparation Example 3.

[0057] Comparative Example 4 Compared with Example 3, the difference lies in that the chitosan / sodium alginate modified composite is prepared from Comparative Preparation Example 4.

[0058] Comparative Example 5 Compared with Example 3, the difference lies in that the chitosan / sodium alginate modified composite is prepared from Comparative Preparation Example 5.

[0059] Comparative Example 6 Compared with Example 3, the difference lies in that the chitosan / sodium alginate modified composite is prepared from Comparative Preparation Example 6.

[0060] Comparative Example 7 Compared with Example 3, the difference lies in that the chitosan / sodium alginate modified composite is prepared from Comparative Preparation Example 7.

[0061] Test Example 3 The test site is located in the acidic soil of the vegetable field in Jichang Township, Xixiu District, Anshun City, Guizhou Province. Soil samples are taken respectively to test the following soil indicators: heavy metal content, organic matter content, soil porosity, soil bulk density, soil pH value, exchangeable acidity. Then, the acidic soil amendments prepared in Examples 1-3 and Comparative Examples 1-7 are added, and the addition amount is 20 g / m 3 , to evaluate the soil amendments. The control group does not apply the acidic soil amendment, and the improvement time is 3 months. Among them, the soil bulk density is tested according to the standard NY / T1121.4-2006, the pH value is measured by the standard method of LY / T 1239-1999, and a PHS-3C pH meter is used for determination; the exchangeable acidity is determined by the standard method of LY / T 1240-1999; the heavy metal content in the soil is determined by the TCLP toxicity leaching method; the total porosity of the soil is determined by the core cutter method.

[0062] The results are shown in Table 3.

[0063] Table 3

[0064] As can be seen from the above table, the acidic soil amendments prepared in Examples 1-3 of the present invention can significantly improve the soil quality, increase the organic matter content, reduce the heavy metal content, and increase the soil pH value.

[0065] In addition to the Alcaligenes faecalis and Azotobacter chroococcum described in detail in the above embodiments, although the other soil-improving bacteria and nitrogen-fixing bacteria selected in the present invention are not specifically exemplified in the embodiments, according to existing research, the technical effects of these strains are similar to the action mechanisms of Azotobacter chroococcum and Alcaligenes faecalis. Soil-improving bacteria, such as Bacillus subtilis and Bacillus licheniformis, both have the ability to adjust soil pH and improve soil structure in acidic soil environments. Nitrogen-fixing bacteria, including Azotobacter chroococcum, Frankia, Rhizobium, Azospirillum brasilense, Azospirillum lipoferum, Klebsiella, and Clostridium pasteurianum, all have nitrogenase systems that can convert free nitrogen in the air into ammonia nitrogen that can be absorbed and utilized by plants. In acidic soils, nitrogen is often easily lost due to factors such as leaching. These nitrogen-fixing bacteria supplement the soil nitrogen source through nitrogen fixation, and at the same time, the alkaline substances produced by the metabolism of some nitrogen-fixing bacteria also help to neutralize soil acidity. Therefore, selecting any one or a combination of these soil-improving bacteria and nitrogen-fixing bacteria can achieve efficient improvement of acidic soils. The Alcaligenes faecalis and Azotobacter chroococcum used in the above embodiments are only used to illustrate the feasibility of the technical solution of the present invention. Those skilled in the art can select other single or mixed strains according to actual soil conditions or crop requirements.

[0066] The foregoing is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An acidic soil conditioner, characterized in that, It is prepared from the following raw materials in parts by weight: 30-40 parts of pH-sensitive hydrogel, 3-7 parts of slow-release nitrogen-fixing bacteria microcapsules, 5-8 parts of soil-improving bacteria, 10-20 parts of chitosan / sodium alginate modified composite, 17-20 parts of fly ash, and 18-22 parts of phosphogypsum.

2. The acid soil conditioner according to claim 1, wherein, The preparation method of the pH-sensitive hydrogel is as follows: S1. Dissolve sodium carboxymethyl cellulose in water to obtain solution A; S2. Dissolve chitosan in an acid solution to obtain solution B; S3. Crush the straw, add it to water, add tetrabutyl titanate, stir and react, centrifuge, wash, dry, calcine, and ball mill to obtain biochar-supported titanium dioxide; S4. Mix solution A and solution B, add biochar-supported titanium dioxide, stir and mix evenly, dropwise add calcium chloride solution, stir and crosslink, and dry to obtain the pH-sensitive hydrogel.

3. The acid soil conditioner according to claim 2, characterized in that, In step S1, the concentration of sodium carboxymethyl cellulose in solution A is 5-7 wt%; in step S2, the concentration of chitosan in solution B is 3-5 wt%, and the acid solution is an acetic acid or lactic acid solution with a concentration of 1-2 wt%; in step S3, the mass ratio of the straw to tetrabutyl titanate is 10-12:5-8, the calcination temperature is 750-850 °C, the time is 2-4 h, and the ball milling time is 1-2 h; in step S4, the mass ratio of solution A, solution B, and biochar-supported titanium dioxide is 10:15-20:0.2-0.5, and the stirring and crosslinking time is 2-4 h.

4. The acid soil conditioner according to claim 1, wherein The preparation method of the slow-release nitrogen-fixing bacteria microcapsules is as follows: T1. Preparation of carboxylated chitosan nanocrystals: Mix and stir chitosan, an acid solution, a Tempo reagent, and sodium bromide, then add sodium hypochlorite, adjust the pH value of the solution, stir and react, add ethanol to terminate the reaction, centrifuge, wash, and dry to obtain carboxylated chitosan nanocrystals; T2. Slow-release nitrogen-fixing bacteria microcapsules: Add carboxylated chitosan nanocrystals, aqueous polyurethane, and an emulsifier to water, stir and disperse evenly, add nitrogen-fixing bacteria, mix evenly, then dropwise add to fish oil, emulsify, freeze-dry, and filter to obtain slow-release nitrogen-fixing bacteria microcapsules.

5. The acid soil conditioner according to claim 4, characterized in that, In step T1, the mass ratio of chitosan, Tempo reagent, sodium bromide, and sodium hypochlorite is 1:0.01-0.02:0.1-0.15:4-6, the acid solution is an acetic acid or lactic acid solution with a concentration of 1-2 wt%, the adjustment of the solution pH value is 9.5-10.5, and the stirring reaction time is 18-20 h; in step T2, the mass ratio of carboxylated chitosan nanocrystals, aqueous polyurethane, emulsifier, and nitrogen-fixing bacteria is 5-10:20-40:0.5-1:12-15, the aqueous polyurethane is Impranil RSC 1380, the emulsifier is selected from at least one of Tween-20, Tween-40, Tween-60, and Tween-80, and the nitrogen-fixing bacteria are at least one of Azotobacter chroococcum, Frankia, Rhizobium, Azospirillum brasilense, Azospirillum lipoferum, Klebsiella, and Clostridium pasteurianum.

6. The acid soil conditioner according to claim 1, wherein The preparation method of the chitosan / sodium alginate modified composite is as follows: U1. Preparation of biochar: Straw was crushed, carbonized, and ball-milled to obtain biochar; U2. Preparation of modified composite: Biochar and basalt powder were mixed evenly, added into ethanol, a silane coupling agent was added, heated and stirred for reaction, centrifuged, washed, and dried to obtain the modified composite; U3. Preparation of chitosan / sodium alginate modified composite: Chitosan was dissolved in an acid solution, the modified composite and sodium alginate were added, a calcium chloride solution was added dropwise, stirred and cross-linked, dried, and pulverized to obtain the chitosan / sodium alginate modified composite.

7. The acid soil conditioner according to claim 6, characterized in that, In step U1, the temperature of the carbonization is 700 - 800 °C, the time is 3 - 5 h, and the time of the ball milling is 1 - 3 h; in step U2, the mass ratio of the biochar, basalt powder, and silane coupling agent is 10 - 15:8 - 12:3 - 5, the silane coupling agent is selected from at least one of KH550, KH602, and KH792, the temperature of the heating and stirring reaction is 40 - 50 °C, and the time is 2 - 4 h; in step U3, the acid solution is an acetic acid or lactic acid solution with a concentration of 1 - 2 wt%, the mass ratio of the chitosan, modified composite, and sodium alginate is 10 - 12:7 - 10:4 - 7, and the time of the stirring and cross-linking is 1 - 3 h.

8. The acid soil conditioner according to claim 1, wherein The soil-improving bacteria are at least one of Alcaligenes faecalis, Bacillus subtilis, and Bacillus licheniformis.

9. A method for preparing the acid soil conditioner according to any one of claims 1-8, characterized in that, It includes the following steps: Mix the slow-release nitrogen-fixing bacteria microcapsules and the soil-improving bacteria evenly to obtain a composite bacterial preparation; Mix the pH-sensitive hydrogel, chitosan / sodium alginate modified composite, fly ash, and phosphogypsum evenly, add the composite bacterial preparation at a low temperature, and stir and mix evenly to obtain an acidic soil conditioner.

10. The preparation method according to claim 9, characterized in that, The low temperature is 3 - 5 °C.

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