Soil conditioner for soda saline-alkali soil as well as preparation method and application of soil conditioner

Abstract

The invention belongs to the technical field of soil improvement, and particularly relates to a soil conditioner for soda saline-alkali soil as well as a preparation method and application of the soil conditioner. The soil conditioner comprises an inner core and a shell layer coating the surface of the inner core, the inner core comprises a zwitterionic polymer and a load precursor dispersed in the zwitterionic polymer; the load precursor is acidified biochar loaded with powdered sulfur and a microbial agent; the shell layer is a pH responsive polymer; the pH responsive polymer is a copolymer of methacrylic acid, ethyl acrylate and methyl methacrylate. The soil conditioner provided by the invention has salt-resistant and water-absorbing properties, can meet the requirements of soda saline-alkali soil restoration on water retention performance, and meanwhile, improves the survival rate of functional microorganisms in soda saline-alkali soil.

Description

Technical Field

[0001] This invention belongs to the field of soil improvement technology, specifically relating to a soil conditioner for soda saline-alkali land, its preparation method, and its application. Background Technology

[0002] Soda saline-alkali land (concentrated in areas such as the Songnen Plain in China) is widely recognized as the "cancer" of soil improvement due to the dual stress of high pH (usually >9.0) and high exchangeable sodium ion content. To solve the remediation problem of soda saline-alkali land, the existing technical system has gradually formed three major schools of thought: physical leaching, chemical modification, and bioremediation. Among them, chemical modification technology, which mainly uses gypsum, acid conditioners, and other modifiers, is currently the most widely used technology. However, after the modifiers are applied to the soil, they easily react with calcium ions in the environment to form calcium carbonate precipitates, which leads to passivation of the modifier surface and significantly reduces its long-term improvement effect. In bioremediation technology, microbial agents are subjected to strong alkaline stress in the early stage of colonization in a high saline-alkali environment, which leads to rapid loss or even inactivation of bacterial activity, making it difficult to achieve stable colonization and function. Water-retaining materials, which are indispensable in physical-chemical synergistic remediation, also face severe challenges. In the high ionic strength of soda saline-alkali environment, traditional water-retaining materials will have a significant decrease in water retention performance due to the charge shielding effect generated by the counterion compression of the polymer double layer.

[0003] Currently, the mainstream agricultural and forestry water-retaining agents on the market are all potassium / sodium polyacrylate and their copolymers. Their water absorption mechanism essentially relies on the electrostatic repulsion between anionic groups on the polymer chain, causing the polymer network to be in an extended state, thereby absorbing water through osmotic pressure. This type of water-retaining agent exhibits excellent water absorption performance in conventional freshwater environments, with an equilibrium swelling rate of 400-500 times in pure water. However, in the actual application scenario of soda saline-alkali land, due to the high content of sodium carbonate and sodium bicarbonate in the soil solution, according to the polyelectrolyte solution theory, a large number of counterions in the environment will rapidly compress the double layer on the polymer chain. The strong charge shielding effect significantly weakens or even cancels the electrostatic repulsion between polymer chains, causing the polymer chain to rapidly change from an extended state to a coiled state, the network pores to collapse, and the water absorption performance to drop sharply. Actual test data show that the equilibrium swelling rate of this type of traditional water-retaining agent in 0.9% NaCl solution has dropped to 40-50 times, while in soda saline-alkali soil extract, its water absorption ratio can only reach 10-20 times, and in some cases even lower, which is completely unable to meet the water retention performance requirements of soda saline-alkali land remediation. Summary of the Invention

[0004] The purpose of this invention is to provide a soil conditioner for soda saline-alkali land, its preparation method and application. The soil conditioner provided by this invention has salt tolerance and water absorption, which can meet the water retention requirements of soda saline-alkali land remediation, and at the same time improves the survival rate of functional microorganisms in soda saline-alkali land.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a soil conditioner for soda-saline-alkali land, comprising a core and a shell coating the surface of the core; the core comprises an amphoteric polymer and a loaded precursor dispersed in the amphoteric polymer; the loaded precursor is acidified biochar loaded with sulfur powder and microbial inoculant; the shell comprises a pH-responsive polymer; the pH-responsive polymer is a copolymer of methacrylic acid, ethyl acrylate and methyl methacrylate.

[0006] Preferably, the zwitterionic polymer is obtained by polymerizing zwitterionic monomers; the zwitterionic monomers include betaine monomers.

[0007] Preferably, the betaine monomer is at least one of sulfobetaine methacrylate, carboxybetaine methacrylate, and phosphate betaine methacrylate.

[0008] Preferably, the sulfur powder has a particle size ≤30 micrometers; the microbial agent includes Bacillus amyloliquefaciens and Thiobacillus thiophanate-methyl.

[0009] Preferably, the mass ratio of the acidified biochar loaded with sulfur powder and microbial agent to the zwitterionic polymer is 1:(2~5); the coating weight gain rate of the shell is 10%~20% of the core mass, and the thickness of the shell is 20~50 micrometers.

[0010] This invention also provides a method for preparing the soil conditioner described in the above technical solution, comprising the following steps: After mixing acidified biochar and sulfur powder, microbial agents are adsorbed under vacuum to obtain a loaded precursor. The supported precursor, an aqueous solution of the zwitterionic monomer, the first initiator and the accelerator are mixed and then subjected to in-situ polymerization, granulation and drying in sequence to obtain the core. The soil conditioner is obtained by spraying a pH-responsive polymer emulsion onto the core surface and then subjecting it to heat treatment.

[0011] Preferably, the aqueous solution of the zwitterionic monomer includes a betaine monomer, a crosslinking agent, and water; the crosslinking agent includes N,N'-methylenebisacrylamide; the first initiator includes ammonium persulfate; and the in-situ polymerization temperature is 40~60℃, and the time is 3~6h.

[0012] Preferably, the pH-responsive polymer emulsion is obtained by copolymerizing methacrylic acid, ethyl acrylate, and methyl methacrylate; the molar ratio of methacrylic acid, ethyl acrylate, and methyl methacrylate is 35:45:20.

[0013] Preferably, the heat treatment temperature is 50~70℃ and the time is 0.5~2h.

[0014] The present invention also provides the application of the soil conditioner described in the above technical solution or the soil conditioner prepared by the preparation method described in the above technical solution in the improvement of soda saline-alkali land and the increase of crop yield.

[0015] This invention provides a soil conditioner for soda-saline-alkali land, comprising a core and a shell coating the surface of the core; the core comprises an amphoteric polymer and a loaded precursor dispersed in the amphoteric polymer; the loaded precursor is acidified biochar loaded with sulfur powder and microbial inoculant; the shell comprises a pH-responsive polymer; the pH-responsive polymer is a copolymer of methacrylic acid, ethyl acrylate, and methyl methacrylate, which has the following advantages compared to existing soil conditioners: (1) Overcoming technical bias in salt-resistant water absorption: By utilizing the physical property of "salt-induced expansion" of zwitterionic polymers, the industry problem of "salt-induced shrinkage" in traditional products is solved. In soda saline-alkali soil extract, the equilibrium swelling rate of this invention can reach more than 60g / g, and the water absorption rate is better than that of traditional products.

[0016] (2) Micron-level in-situ acidification and anti-passivation: Sulfur micropowder is dispersed in the pores of biochar and combined with sulfur-removing bacteria. After the shell dissolves, the sulfur powder can not only provide a long-lasting acid source, but also greatly increase the specific surface area by dispersing the micron-level sulfur powder in the pores of biochar. Furthermore, the biochar provides a "house" for microorganisms, ensuring that microorganisms can continuously contact and oxidize the sulfur powder.

[0017] (3) Breakthrough improvement in microbial colonization rate: Through the three-step strategy of “isolation-release-environment creation”, a smooth transition period from dormancy to recovery was provided for microorganisms, which significantly improved the survival rate in extreme soil with pH 9.8.

[0018] (4) The soil conditioner provided by the present invention does not contain calcium, thus avoiding the surface passivation problem of traditional gypsum-based conditioners. Detailed Implementation

[0019] This invention provides a soil conditioner for soda-saline-alkali land, comprising a core and a shell coating the surface of the core; the core comprises an amphoteric polymer and a loaded precursor dispersed in the amphoteric polymer; the loaded precursor is acidified biochar loaded with sulfur powder and microbial inoculant; the shell is a pH-responsive polymer; the pH-responsive polymer is a copolymer of methacrylic acid, ethyl acrylate and methyl methacrylate.

[0020] In one embodiment of the present invention, the zwitterionic polymer is obtained by polymerization of zwitterionic monomers; the zwitterionic monomers include betaine monomers; the betaine monomers are at least one selected from sulfobetaine methacrylate, carboxybetaine methacrylate, and phosphate betaine methacrylate. In another embodiment of the present invention, the zwitterionic polymer exhibits anti-polyelectrolyte properties, meaning that its equilibrium swelling ratio in a 0.1~1.0 mol / L electrolyte solution is significantly higher than its equilibrium swelling ratio in deionized water.

[0021] In one embodiment of the present invention, the sulfur powder has a particle size ≤30 micrometers; in another embodiment of the present invention, the microbial agent may include Bacillus amyloliquefaciens and Thiobacillus thiophanate-methyl.

[0022] In this invention, the pores of the biochar particles are loaded with micron-sized sulfur powder and Bacillus amyloliquefaciens and alkali-loving sulfur-oxidizing bacteria, which serve as both a carrier and a pH buffer.

[0023] In one embodiment of the present invention, the mass ratio of the acidified biochar loaded with sulfur powder and microbial agent to the zwitterionic polymer can be 1:(2~5), specifically 1:2, 1:3, 1:4 or 1:5.

[0024] In one embodiment of the present invention, the coating weight gain rate of the shell layer is 10% to 20% of the core mass (dry weight of the shell polymer / dry weight of the core particles), and the thickness of the shell layer can be 20 to 50 micrometers, specifically 20 micrometers, 30 micrometers, 40 micrometers or 50 micrometers.

[0025] In this invention, the shell is insoluble in an environment with a pH value < 8.5 due to intramolecular hydrogen bonding and hydrophobic interactions formed by carboxyl protonation; in an environment with a pH value > 9.0, the carboxyl groups dissociate, and electrostatic repulsion disrupts the hydrophobic association, leading to rapid hydration, swelling and disintegration of the shell.

[0026] In one embodiment of the present invention, the soil conditioner has an equilibrium swelling rate of greater than 60 g / g in a soda saline-alkali soil extract with a pH of 9.8.

[0027] This invention also provides a method for preparing the soil conditioner described in the above technical solution, comprising the following steps: After mixing acidified biochar and sulfur powder, microbial agents are adsorbed under vacuum to obtain a loaded precursor. The supported precursor, an aqueous solution of the zwitterionic monomer, the first initiator and the accelerator are mixed and then subjected to in-situ polymerization, granulation and drying in sequence to obtain the core. The soil conditioner is obtained by spraying a pH-responsive polymer emulsion onto the core surface and then subjecting it to heat treatment.

[0028] This invention involves mixing acidified biochar and sulfur powder, followed by vacuum adsorption of microbial broth to obtain a loaded precursor.

[0029] In one embodiment of the present invention, the acidified biochar is obtained by acidifying biochar with an acidifying reagent; in another embodiment, the biochar can be derived from agricultural or forestry waste; the acidifying reagent can be a citric acid solution or a phosphoric acid solution; the concentration of the citric acid solution or phosphoric acid solution can be independently 1-3 mol / L, specifically 1 mol / L, 2 mol / L, or 3 mol / L. In this invention, citric acid acidification not only removes the ash from the biochar but also attaches carboxyl groups to the surface of the biochar, increasing its hydrophilicity and cation exchange capacity.

[0030] After obtaining the supported precursor, the present invention mixes the supported precursor, an aqueous solution of the zwitterionic monomer, a first initiator and an accelerator, and sequentially performs in-situ polymerization, granulation and drying to obtain the core.

[0031] In one embodiment of the present invention, the aqueous solution of the zwitterionic monomer comprises a betaine monomer, a crosslinking agent, and water. In another embodiment of the present invention, the crosslinking agent comprises N,N'-methylenebisacrylamide; the first initiator comprises ammonium persulfate; and the accelerator comprises N,N,N',N'-tetramethylethylenediamine (TMEDA). In another embodiment of the present invention, the in-situ polymerization temperature can be 40~60℃, specifically 45℃, and the time can be 3~6h, specifically 4h; the granulation involves crushing the hydrogel obtained from the in-situ polymerization and granulating it using an extrusion granulator with a pore size of 3mm.

[0032] In one embodiment of the present invention, the drying temperature can be 50°C.

[0033] The present invention involves spraying a pH-responsive polymer emulsion onto the core surface and then subjecting it to heat treatment to obtain the soil-improving microspheres.

[0034] In one embodiment of the present invention, the pH-responsive polymer emulsion is obtained by copolymerization of methacrylic acid, ethyl acrylate and methyl methacrylate; the molar content of the pH-responsive carboxyl functional group monomer (methacrylic acid) is 25%~45%, and the glass transition temperature of the pH-responsive polymer is 30~50°C.

[0035] Specifically, the preparation method of the pH-responsive polymer emulsion includes the following steps: mixing water, sodium dodecyl sulfate, methacrylic acid, ethyl acrylate, methyl methacrylate, and a second initiator to carry out a copolymerization reaction to obtain the pH-responsive polymer emulsion. As one embodiment of the present invention, the second initiator includes potassium persulfate; the copolymerization reaction temperature can be 70~90℃, specifically 80℃, and the time can be 3~5 hours, specifically 4 hours.

[0036] In one embodiment of the present invention, the pH-responsive polymer emulsion is insoluble in an aqueous medium with a pH value less than 8.0, but soluble in an aqueous medium with a pH value greater than 9.0.

[0037] In one embodiment of the present invention, the temperature of the heat treatment can be 50~70℃, specifically 60℃, and the time can be 0.5~2h, specifically 1h.

[0038] This invention constructs an improved microsphere capable of recognizing high pH, ​​high salt water absorption, and in-situ acid production by introducing the "anti-polyelectrolyte effect" of zwitterionic polymers and a smart pH-responsive shell.

[0039] The present invention also provides the application of the soil conditioner described in the above technical solution or the soil conditioner prepared by the above preparation method in the improvement of soda saline-alkali land and the increase of crop yield.

[0040] To further illustrate the present invention, the following detailed description of the embodiments is provided in conjunction with the present invention, but these descriptions should not be construed as limiting the scope of protection of the present invention.

[0041] Example 1 (1) After pyrolyzing the corn stalks at 500℃, the corn stalks were passed through a 100-mesh sieve to obtain corn stalk biochar; 100g of corn stalk biochar was dispersed in 500mL of 1.0M citric acid solution and magnetically stirred for 24h to obtain acidified biochar.

[0042] (2) Mix 50g of acidified biochar with 25g of sublimed sulfur with a particle size of 20 micrometers to obtain a carbon-sulfur mixture.

[0043] (3) Prepare a mixed spore solution of Bacillus amyloliquefaciens and Bacillus thiophanate-methyl (referred to as bacterial solution). Place the carbon-sulfur mixture in a vacuum container, spray in the bacterial solution, and repeatedly evacuate the vacuum three times (-0.08 MPa). Use the pressure difference to force the bacterial solution into the microporous structure of the biochar. The mixture changes from loose powder to moist lumps, but no obvious liquid flows out, indicating that the bacterial solution has completely entered the pores. After freeze-drying, loaded biochar is obtained.

[0044] (4) Weigh 20g of sulfobetaine methacrylate and dissolve it in 60mL of deionized water. Add 0.08g of N,N'-methylenebisacrylamide to obtain an aqueous solution of zwitterionic monomer.

[0045] (5) Add 5g of the loaded biochar to the aqueous solution of the zwitterionic monomer, and ultrasonically disperse for 30 min. Then, pass nitrogen gas into the reactor containing the reaction mixture to remove oxygen for 30 min. Then, add 0.1g of ammonium persulfate and 40 μL of N,N,N',N'-tetramethylethylenediamine, and react in a constant temperature water bath at 45℃ for 4 h to obtain a black hydrogel.

[0046] (6) Granulation and drying: The hydrogel is chopped, granulated by an extrusion granulator (3 mm aperture), and dried in a fluidized bed at 50 °C to obtain core particles.

[0047] (7) Add 100g of water and 0.5g of sodium dodecyl sulfate to the reaction vessel, then add 43mL of mixed monomers dropwise, and finally add 0.2g of potassium persulfate as an initiator. The molar ratio of methacrylic acid, ethyl acrylate and methyl methacrylate in the mixed monomers is 35:45:20. Then react at 80℃ for 4h to obtain a milky white latex with a blue sheen and a solid content of 30%, with a pH of about 3.5.

[0048] (8) Place the core particles in a bottom-spray fluidized bed with an inlet air temperature of 45°C and a material temperature of 35°C. Spray (spraying speed is 2 mL / min) the emulsion obtained in step (7) until the coating weight gain reaches 12%.

[0049] (9) After coating, heat treatment at 60°C for 1 hour promotes polymer chain diffusion, eliminates micropores, and forms a dense film with a thickness of 30 micrometers.

[0050] In the soil conditioner prepared in Example 1, the mass ratio of acidified biochar loaded with sulfur powder and microbial agent to zwitterionic polymer was 1:4.

[0051] Application Example 1 In the soda-saline soils of western Jilin, with a pH of 9.8 to 10.2, rice seedlings often suffer from blackening and root rot due to high concentrations of carbonate poisoning after transplanting, resulting in a greening rate of less than 50%.

[0052] The soil conditioner of this invention (30 kg / hm) 2 (and base fertilizer (N-P2O5-K2O = 15-15-15, application rate 200 kg / hm)) 2 The mixture was applied to the transplanting holes, and the various test indicators at 21 days after transplanting are shown in Table 2.

[0053] Comparative Example 1 Blank control: Conventional fertilization treatment, i.e., applying only the same amount of base fertilizer (nitrogen-phosphorus-potassium compound fertilizer, N-P2O5-K2O = 15-15-15) as in Example 1, without applying any soil conditioner.

[0054] Comparative Example 2 The soil conditioner in Application Example 1 was replaced with a traditional conditioner, namely a polyacrylamide-type water-retaining agent, SA-150 type water-retaining agent, whose main component is potassium polyacrylate. The product instructions indicate that its water absorption ratio in deionized water is ≥400 g / g, and the application rate is 30 kg / hm. 2 ).

[0055] Table 2 Field trial data (21 days after transplanting)

[0056] The data in Table 2 prove that the soil conditioner rapidly disintegrates in paddy field water (high pH), and the released sulfur-oxidizing bacteria construct an acidic "refuge" in the rhizosphere microzone. The significant increase in root vitality proves the reduction of toxic ions.

[0057] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A soil conditioner for soda-saline-alkali land, characterized in that, It includes a core and a shell covering the surface of the core; the core includes a zwitterionic polymer and a supported precursor dispersed in the zwitterionic polymer; the supported precursor is acidified biochar supported on sulfur powder and microbial inoculant; the shell is a pH-responsive polymer; the pH-responsive polymer is a copolymer of methacrylic acid, ethyl acrylate and methyl methacrylate.

2. The soil conditioner as described in claim 1, characterized in that, The zwitterionic polymer is obtained by polymerizing zwitterionic monomers; the zwitterionic monomers include betaine monomers.

3. The soil conditioner as described in claim 2, characterized in that, The betaine monomer is at least one of sulfobetaine methacrylate, carboxybetaine methacrylate, and phosphate betaine methacrylate.

4. The soil conditioner as described in claim 1, characterized in that, The sulfur powder has a particle size of ≤30 micrometers; the microbial agent includes Bacillus amyloliquefaciens and Thiobacillus thiophanate-methyl.

5. The soil conditioner as described in claim 1, characterized in that, The mass ratio of the acidified biochar loaded with sulfur powder and microbial agent to the zwitterionic polymer is 1:(2~5); the coating weight gain rate of the shell is 10%~20% of the core mass, and the thickness of the shell is 20~50 micrometers.

6. A method for preparing the soil conditioner according to any one of claims 1 to 5, comprising the following steps: After mixing acidified biochar and sulfur powder, microbial agents are adsorbed under vacuum to obtain a loaded precursor. The supported precursor, an aqueous solution of the zwitterionic monomer, the first initiator and the accelerator are mixed and then subjected to in-situ polymerization, granulation and drying in sequence to obtain the core. The soil conditioner is obtained by spraying a pH-responsive polymer emulsion onto the core surface and then subjecting it to heat treatment.

7. The preparation method according to claim 6, characterized in that, The aqueous solution of the zwitterionic monomer includes a betaine monomer, a crosslinking agent, and water; the crosslinking agent includes N,N'-methylenebisacrylamide; the first initiator includes ammonium persulfate; the in-situ polymerization temperature is 40~60℃ and the time is 3~6h.

8. The preparation method according to claim 6, characterized in that, The pH-responsive polymer emulsion is obtained by copolymerizing methacrylic acid, ethyl acrylate and methyl methacrylate; the molar ratio of methacrylic acid, ethyl acrylate and methyl methacrylate is 35:45:

20.

9. The preparation method according to claim 6, characterized in that, The heat treatment is performed at a temperature of 50~70℃ for a time of 0.5~2h.

10. The application of the soil conditioner according to any one of claims 1 to 5 or the soil conditioner prepared by the preparation method according to any one of claims 6 to 9 in the improvement of soda saline-alkali land and the increase of crop yield.

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