A medium-element fertilizer composition for soil improvement and its preparation method

Abstract

This invention relates to the field of fertilizer technology, specifically to a medium-element fertilizer composition for soil improvement and its preparation method. Specifically, a first component is used to encapsulate a second component in a fluidized bed, followed by impregnation and encapsulation of a third component. The first component provides a calcium and magnesium nutrient pool; the chelating effect of polyaspartic acid and the electrostatic adsorption between montmorillonite layers combine to encapsulate calcium... 2+ and Mg 2+ The first component is fixed, preventing the migration of medium-level elements upwards during freeze-thaw cycles. The citric acid hydrolysis in the second component creates an acidic environment, promoting the absorption of Ca from the first component. 2+ and Mg 2+ The released nutrients are recaptured by potassium humate, facilitating absorption by organic acids secreted by plant roots. Alginate can induce root secretion of organic acids, and its hydroxyl groups form a hydrogen bond network with the resin, enhancing gel stability. In the third component, the thermosensitive water-absorbing resin protects the fertilizer granules at low temperatures and releases nutrients as the temperature rises.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically a medium-element fertilizer composition for soil improvement and its preparation method. Background Technology

[0002] In existing technologies, conventional micronutrient fertilizers are mostly in the form of simple inorganic salts (such as calcium nitrate and magnesium sulfate). After being applied to the soil, the nutrient ions are in a free state. However, in northern my country, winters are long and cold, and the soil undergoes frequent seasonal freeze-thaw cycles. When the soil freezes from top to bottom, the water in the unfrozen soil below carries dissolved calcium due to the temperature gradient and the suction of the soil mechanism. 2+ Mg 2+ Medium-level element ions migrate towards the freezing front. With repeated freeze-thaw cycles, these salts gradually accumulate in the topsoil, forming a high-salt crust. This not only inhibits seed germination and seedling growth, but also solidifies and crystallizes the migrated medium-level element ions on the surface, leading to nutrient depletion in the deeper soil layers and severely affecting crop yield and quality. Summary of the Invention

[0003] (1) Technical problems to be solved

[0004] The purpose of this invention is to provide a medium-element fertilizer composition for soil improvement and its preparation method, so as to solve the problem of upward migration of medium elements during freeze-thaw cycles.

[0005] (2) Technical solution

[0006] To achieve the above objectives, in one aspect, the present invention provides a method for preparing a medium-element fertilizer composition for soil improvement, comprising the following steps:

[0007] S1. Preheat the first component to 50~55℃, place it in a fluidized bed, spray the second component onto the surface of the first component, control the fluidized bed temperature at 55℃, and continue coating to obtain the first mixture;

[0008] S2. Preheat the first mixture to 45°C, immerse it in the third component at 50°C, remove it and transfer it to a fluidized bed for drying. Repeat the immersion-drying process and vacuum drying to obtain a medium-element fertilizer composition.

[0009] The first component is a polyaspartic acid-modified montmorillonite-calcium carbonate / magnesium oxide composite material;

[0010] The second component is a physical blend of citric acid-modified potassium humate and seaweed oligosaccharides;

[0011] The third component is a thermosensitive water-absorbing resin-modified starch complex.

[0012] Furthermore, the mass ratio of the first component, the second component, and the third component in the medium-element fertilizer composition is 8~9:5~6:4~5.

[0013] Furthermore, the preparation method of the first component includes the following steps:

[0014] S11. Disperse montmorillonite in an ethanol / water mixed solvent, add aminopropyltriethoxysilane, stir the reaction, centrifuge and wash the resulting reaction solution, vacuum dry it, grind and sieve it to obtain aminated montmorillonite;

[0015] S12. Polyaspartic acid was dissolved in MES buffer, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added. The mixture was activated in the dark to obtain an activated polyaspartic acid solution. Aminated montmorillonite was ultrasonically dispersed in MES buffer, and the activated polyaspartic acid solution was added. The pH was adjusted with dilute HCl, and the mixture was heated in a water bath with stirring. The resulting reaction solution was centrifuged, washed, and freeze-dried to obtain polyaspartic acid-modified montmorillonite.

[0016] S13. Place polyaspartic acid-modified montmorillonite, calcium carbonate powder and magnesium oxide powder in a mixer and dry mix them evenly. While stirring, spray in PVA solution, place the resulting product in a granulator to granulate, and dry to obtain the first component.

[0017] Furthermore, the mass ratio of polyaspartic acid to aminated montmorillonite is 0.25~0.4:1; the mass ratio of polyaspartic acid-modified montmorillonite, calcium carbonate powder, and magnesium oxide powder is 2:6:1.

[0018] Furthermore, the preparation method of the second component includes the following steps:

[0019] S21. Dissolve sodium alginate in deionized water, add alginate lyase, perform enzymatic hydrolysis, heat the resulting reaction solution to inactivate the enzyme, cool it and filter it through an ultrafiltration membrane, collect the permeate, concentrate it and spray dry it to obtain seaweed oligosaccharide.

[0020] S22. Potassium humate and anhydrous citric acid are thoroughly dry-mixed, protected by nitrogen, and the temperature is slowly increased while stirring. The resulting product is cooled and crushed, dissolved in deionized water, precipitated and purified by adding ethanol, pH is adjusted with KOH, and spray-dried to obtain modified potassium humate.

[0021] S23. Place seaweed oligosaccharide, modified potassium humate and magnesium sulfate monohydrate in a mixer and dry mix evenly to obtain a composite powder. Add the composite powder to a PVP ethanol solution under stirring, gradually add deionized water to adjust the solid content, and continue stirring to obtain the second component.

[0022] Furthermore, the mass ratio of the seaweed oligosaccharide, modified potassium humate, and magnesium sulfate monohydrate is 3:9:5.

[0023] Furthermore, the preparation method of the third component includes the following steps:

[0024] S31. Under ice bath and stirring, acrylic acid is added to deionized water, KOH solution is slowly added dropwise to adjust the pH, N-isopropylacrylamide, N-tert-butylacrylamide and N,N'-methylenebisacrylamide are added, stirred to dissolve, deionized water is added, nitrogen gas is purged to remove oxygen, potassium persulfate is added after heating, the reaction is stirred, the resulting reaction solution is poured into ethanol to precipitate, allowed to stand to dehydrate, filtered and washed, vacuum dried, ground and sieved to obtain temperature-sensitive water-absorbing resin;

[0025] S32. Dissolve corn starch in deionized water, adjust the pH with NaOH, slowly add sodium hypochlorite solution, stir the reaction, add sodium sulfite solution to the resulting reaction solution, adjust the pH with dilute HCl, filter, wash, and dry to obtain oxidized starch;

[0026] S33. Disperse oxidized starch in deionized water, add sodium sulfate, adjust the pH with NaOH, add propylene oxide, seal the reaction, adjust the pH of the resulting reaction solution with dilute HCl, filter, wash, and dry to obtain oxidized-etherified dual-modified starch;

[0027] S34. Add the oxidized-etherified double-modified starch to hot water, stir and gelatinize to obtain starch paste, add thermosensitive water-absorbing resin, glycerin, calcium stearate and defoamer while stirring, homogenize and disperse, and degas under vacuum to obtain the third component.

[0028] Furthermore, the mass ratio of the thermosensitive water-absorbing resin to the oxidized-etherified dual-modified starch is 2:3.

[0029] In the first component, montmorillonite was modified with aminopropyltriethoxysilane, introducing active amino groups onto the montmorillonite surface to provide reaction sites for the modification of polyaspartic acid. The combined effect of the chelating action of polyaspartic acid and the electrostatic adsorption between montmorillonite layers allows Ca to be modified... 2+ and Mg 2+ It fixes and effectively prevents the upward migration of medium-level elements under freeze-thaw conditions. Calcium carbonate and magnesium oxide, as calcium and magnesium sources, are slowly released into the soil.

[0030] The second component is a physical blend of citric acid-modified potassium humate and seaweed oligosaccharides. The citric acid groups release H+ through hydrolysis. + By creating an acidic environment locally, it promotes the formation of calcium carbonate, magnesium oxide, and chelated Ca in the first component. 2+ and Mg 2+ The dissolution allows for controlled release of nutrients. The released Ca... 2+ and Mg 2+ Recaptured by potassium humate, humic acid and Ca2+ Mg 2+ The resulting chelate is a weak chelate, ensuring that secondary elements are not adsorbed and fixed by soil colloids or moved upwards with freeze-thaw moisture, but can be displaced and absorbed by organic acids secreted by plant roots. Simultaneously, seaweed oligosaccharides are themselves highly effective plant immune activators, activating jasmonic acid and salicylic acid signaling pathways, inducing systemic resistance in plants, and significantly improving their resistance to frost damage and diseases. Furthermore, by inducing roots to secrete more organic acids, they accelerate the rhizosphere release of humic acid-chelated nutrients, and the hydroxyl groups of seaweed oligosaccharides form a hydrogen bond network with the resin, enhancing gel stability. Magnesium sulfate monohydrate provides both magnesium and sulfur sources.

[0031] The third component is composed of a thermosensitive superabsorbent polymer (SUP) and an oxidized-etherified dual-modified starch. At low temperatures, the SUP maintains a hydrophilic swelling state, acting as a protective outer shell for the fertilizer. Furthermore, the gel adheres to surrounding soil particles, increasing frictional resistance within the soil matrix and mitigating frost damage during freeze-thaw cycles. During the crop's growing season, as temperatures rise, the porosity and permeability of the SUP gel layer increase, accelerating the release of nutrients from the first and second components into the rhizosphere. Oxidation of the modified starch improves processability, while etherification ensures durability. As a biodegradable matrix, it gradually decomposes during the growing season and does not remain in the soil for extended periods.

[0032] The fertilizer prepared by this invention not only provides a balanced supply of medium-quantity elements such as calcium, magnesium, and sulfur, but also the humic acid, montmorillonite residue, and reaction products in its components work together to improve the soil. Humic acid promotes the formation of aggregate structure and stimulates microbial activity, while montmorillonite enhances water and fertilizer retention capacity.

[0033] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0034] 1. The first component provides a calcium and magnesium nutrient pool, which utilizes the chelating effect of polyaspartic acid and the electrostatic adsorption between montmorillonite layers to bind calcium and magnesium. 2+ and Mg 2+ It fixes and effectively prevents medium-level elements from migrating upwards during freeze-thaw cycles.

[0035] 2. In the second component, citric acid hydrolysis creates an acidic environment, promoting the dissolution of calcium carbonate and magnesium oxide in the first component, releasing Ca... 2+ and Mg 2+ After being recaptured by potassium humate, it is replaced and absorbed by organic acids secreted by plant roots. Alginate acts as a signaling molecule to activate the root system, inducing the root system to secrete organic acids and accelerating the rhizosphere release of humic acid-chelated nutrients. At the same time, its hydroxyl groups form a hydrogen bond network with the resin, which can enhance gel stability.

[0036] 3. In the third component, the temperature-sensitive water-absorbing resin protects the fertilizer granules at low temperatures and releases nutrients when the temperature rises. Attached Figure Description

[0037] Figure 1 This is a photograph of the medium-element fertilizer composition prepared in Example 1 of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] Example 1: This example discloses a method for preparing a medium-element fertilizer composition for soil improvement, comprising the following steps:

[0040] S1. Preheat the first component to 50~55℃, place it in a fluidized bed, spray the second component onto the surface of the first component, control the fluidized bed temperature at 55℃, and continue coating to obtain the first mixture;

[0041] S2. Preheat the first mixture to 45°C, immerse it in the third component at 50°C, remove it and transfer it to a fluidized bed for drying. Repeat the immersion-drying process and vacuum drying to obtain a medium-element fertilizer composition.

[0042] The first component is a polyaspartic acid-modified montmorillonite-calcium carbonate / magnesium oxide composite material;

[0043] The second component is a physical blend of citric acid-modified potassium humate and seaweed oligosaccharides;

[0044] The third component is a thermosensitive water-absorbing resin-modified starch complex.

[0045] It should be noted that, as Figure 1 The image shown is a physical picture of the medium-element fertilizer composition prepared in Example 1 of the present invention. The medium-element fertilizer composition prepared in the present invention needs to be applied by deep application. It should be applied to a soil layer of 15-30cm after the autumn crop harvest and before the soil freezes, that is, the area where the main root system of the crop is distributed, so that the fertilizer has enough time to form a stable combination with the soil.

[0046] The mass ratio of the first component, the second component, and the third component in the medium-element fertilizer composition is 9:6:5.

[0047] The preparation method of the first component includes the following steps:

[0048] S11. Disperse 2 kg of montmorillonite in 20 L of ethanol / water mixed solvent (volume ratio 4:1), add 0.3 kg of aminopropyltriethoxysilane, stir at 60 °C for 6 h, centrifuge the resulting reaction solution, wash with ethanol, vacuum dry at 80 °C, grind through a 200 mesh sieve to obtain aminated montmorillonite.

[0049] S12. Dissolve 0.5 kg of polyaspartic acid in 10 L of 0.1 M MES buffer, add 0.075 kg of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 0.0375 kg of N-hydroxysuccinimide, and activate in the dark for 30 min to obtain an activated polyaspartic acid solution; disperse 2 kg of aminated montmorillonite in 20 L of 0.1 M MES buffer, add the activated polyaspartic acid solution, adjust the pH to 6 with dilute HCl, heat in a 40 °C water bath, stir and react for 10 h, centrifuge the resulting reaction solution, wash with deionized water, freeze dry to obtain polyaspartic acid modified montmorillonite;

[0050] S13. Place 2 kg of polyaspartic acid modified montmorillonite, 6 kg of calcium carbonate powder and 1 kg of magnesium oxide powder in a mixer and dry mix them evenly. While stirring, spray in 5% PVA solution. Place the resulting product in a granulator to granulate and dry at 80℃ for 12 h to obtain the first component.

[0051] The mass ratio of polyaspartic acid to aminated montmorillonite is 0.25:1; the mass ratio of polyaspartic acid-modified montmorillonite, calcium carbonate powder, and magnesium oxide powder is 2:6:1.

[0052] The preparation method of the second component includes the following steps:

[0053] S21. Dissolve 12 kg of sodium alginate in 400 L of deionized water, add 0.5 kg of alginate lyase, and perform enzymatic hydrolysis at 38 °C for 5 h. Heat the resulting reaction solution to 85 °C to inactivate the enzyme for 20 min, cool it, filter it through an ultrafiltration membrane, collect the permeate, concentrate it under reduced pressure to a solid content of 20%, and spray dry it to obtain seaweed oligosaccharide.

[0054] S22. Mix 18 kg of potassium humate and 5.4 kg of anhydrous citric acid thoroughly, purge with nitrogen, slowly heat to 150 °C, stir for 6 h, cool and crush the product, dissolve in deionized water, add ethanol for precipitation and purification, adjust pH to 9.5 with KOH, spray dry to obtain modified potassium humate.

[0055] S23. Place 6 kg of seaweed oligosaccharide, 18 kg of modified potassium humate and 10 kg of magnesium sulfate monohydrate into a mixer and dry mix evenly to obtain a composite powder. Add the composite powder to 2 kg of 10% PVP ethanol solution under stirring, gradually add deionized water to adjust the solid content to 30%, and continue stirring to obtain the second component.

[0056] The mass ratio of the seaweed oligosaccharide, modified potassium humate, and magnesium sulfate monohydrate is 3:9:5.

[0057] The preparation method of the third component includes the following steps:

[0058] S31. Under ice bath and stirring, 1.8 kg of acrylic acid was added to 20 L of deionized water, and 40% KOH solution was slowly added dropwise to adjust the pH to 7. 7 kg of N-isopropylacrylamide, 1.2 kg of N-tert-butylacrylamide and 0.1 kg of N,N'-methylenebisacrylamide were added and stirred to dissolve. 30 L of deionized water was added, nitrogen gas was purged to remove oxygen, the temperature was raised to 60 °C, and 0.1 kg of potassium persulfate was added. The reaction was stirred for 4 h, and the resulting reaction solution was poured into ethanol to precipitate. After standing for 2 h to dehydrate, the solution was filtered, washed with ethanol, dried under vacuum at 60 °C, and pulverized through an 80-mesh sieve to obtain a thermosensitive water-absorbing resin.

[0059] S32. Dissolve 12 kg of corn starch in 24 L of deionized water, adjust the pH to 9.5-10 with 3% NaOH, slowly add 24 kg of 10% sodium hypochlorite solution at 35 °C, stir and react for 2 h, add sodium sulfite solution to terminate the reaction, adjust the pH to 6.5 with dilute HCl, filter, wash, and dry to obtain oxidized starch.

[0060] S33. Disperse 12 kg of oxidized starch in 32 L of deionized water, add 0.5 kg of sodium sulfate, adjust the pH to 11-11.5 with NaOH, add 0.96 kg of propylene oxide, seal and react at 45 °C for 12 h, adjust the pH of the resulting reaction solution to 6.5-7 with dilute HCl, filter, wash, and dry to obtain oxidized-etherified dual-modified starch;

[0061] S34. Add 12 kg of oxidized-etherified double-modified starch to 35 L of hot water, stir and gelatinize at 85 °C for 30 min to obtain starch paste. Add 8 kg of thermosensitive water-absorbing resin, 3 kg of glycerol, 1 kg of calcium stearate and 0.5 kg of defoamer while stirring, homogenize and disperse for 10 min, and degas under vacuum for 15-20 min to obtain the third component.

[0062] The mass ratio of the thermosensitive water-absorbing resin to the oxidized-etherified dual-modified starch is 2:3.

[0063] Example 2: This example is based on Example 1, but differs from Example 1 in that the mass ratio of the first component, the second component, and the third component in the medium-element fertilizer composition described in this example is 8.5:5.5:4.5.

[0064] The other components and preparation methods are the same as in Example 1.

[0065] Example 3: This example is based on Example 1, but differs from Example 1 in that the mass ratio of the first component, the second component, and the third component in the medium-element fertilizer composition described in this example is 8:5:4.

[0066] The other components and preparation methods are the same as in Example 1.

[0067] Example 4: This example is based on Example 1, but differs from Example 1 in that the mass ratio of polyaspartic acid to aminated montmorillonite is 0.4:1; and the mass ratio of polyaspartic acid-modified montmorillonite, calcium carbonate powder and magnesium oxide powder is 2:6:1.

[0068] The other components and preparation methods are the same as in Example 1.

[0069] Comparative Example 1: This comparative example differs from Example 1 in that the first component in this comparative example is aminated montmorillonite-calcium carbonate / magnesium oxide.

[0070] The preparation method of the first component includes the following steps:

[0071] S11. Disperse 2 kg of montmorillonite in 20 L of ethanol / water mixed solvent (volume ratio 4:1), add 0.3 kg of aminopropyltriethoxysilane, stir at 60 °C for 6 h, centrifuge the resulting reaction solution, wash with ethanol, vacuum dry at 80 °C, grind through a 200 mesh sieve to obtain aminated montmorillonite.

[0072] S12. Place 2 kg of aminated montmorillonite, 6 kg of calcium carbonate powder and 1 kg of magnesium oxide powder in a mixer and dry mix them evenly. While stirring, spray in 5% PVA solution. Place the resulting product in a granulator to granulate and dry at 80℃ for 12 h to obtain the first component.

[0073] Comparative Example 2: This comparative example is based on Example 1, but unlike Example 1, the second component of this comparative example does not contain seaweed oligosaccharides.

[0074] The preparation method of the second component includes the following steps:

[0075] S21. Thoroughly dry mix 18 kg of potassium humate and 5.4 kg of anhydrous citric acid, purge with nitrogen, slowly heat to 150 °C, stir and react for 6 h, cool and crush the product, dissolve in deionized water, add ethanol for precipitation and purification, adjust pH to 9.5 with KOH, spray dry to obtain modified potassium humate.

[0076] S22. Place 18 kg of modified potassium humate and 10 kg of magnesium sulfate monohydrate in a mixer and dry mix evenly to obtain a composite powder. Add the composite powder to 2 kg of 10% PVP ethanol solution under stirring, gradually add deionized water to adjust the solid content to 30%, and continue stirring to obtain the second component.

[0077] The other components and preparation methods are the same as in Example 1.

[0078] Comparative Example 3: This comparative example is based on Example 1, but differs from Example 1 in that the second component, potassium humate, is not modified with citric acid.

[0079] The preparation method of the second component includes the following steps:

[0080] S21. Dissolve 12 kg of sodium alginate in 400 L of deionized water, add 0.5 kg of alginate lyase, and perform enzymatic hydrolysis at 38 °C for 5 h. Heat the resulting reaction solution to 85 °C to inactivate the enzyme for 20 min, cool it, filter it through an ultrafiltration membrane, collect the permeate, concentrate it under reduced pressure to a solid content of 20%, and spray dry it to obtain seaweed oligosaccharide.

[0081] S22. Place 6 kg of seaweed oligosaccharide, 18 kg of potassium humate and 10 kg of magnesium sulfate monohydrate into a mixer and dry mix evenly to obtain a composite powder. Add the composite powder to 2 kg of 10% PVP ethanol solution under stirring, gradually add deionized water to adjust the solid content to 30%, and continue stirring to obtain the second component.

[0082] The other components and preparation methods are the same as in Example 1.

[0083] Comparative Example 4: This comparative example is based on Example 1, except that the citric acid-modified potassium humate is replaced with potassium citrate.

[0084] The preparation method of the second component includes the following steps:

[0085] S21. Dissolve 12 kg of sodium alginate in 400 L of deionized water, add 0.5 kg of alginate lyase, and perform enzymatic hydrolysis at 38 °C for 5 h. Heat the resulting reaction solution to 85 °C to inactivate the enzyme for 20 min, cool it, filter it through an ultrafiltration membrane, collect the permeate, concentrate it under reduced pressure to a solid content of 20%, and spray dry it to obtain seaweed oligosaccharide.

[0086] S22. Place 6 kg of seaweed oligosaccharide, 7.5 kg of potassium citrate and 10 kg of magnesium sulfate monohydrate into a mixer and dry mix evenly to obtain a composite powder. Add the composite powder to 2 kg of 10% PVP ethanol solution under stirring, gradually add deionized water to adjust the solid content to 30%, and continue stirring to obtain the second component.

[0087] The other components and preparation methods are the same as in Example 1.

[0088] Comparative Example 5: This comparative example is based on Example 1, but unlike Example 1, the third component of this comparative example does not contain thermosensitive water-absorbing resin.

[0089] The preparation method of the third component includes the following steps:

[0090] S31. Place 12 kg of corn starch in 24 L of deionized water, adjust the pH to 9.5-10 with 3% NaOH, slowly add 24 kg of 10% sodium hypochlorite solution at 35 °C, stir and react for 2 h, add sodium sulfite solution to terminate the reaction, adjust the pH to 6.5 with dilute HCl, filter, wash, and dry to obtain oxidized starch;

[0091] S32. Disperse 12 kg of oxidized starch in 32 L of deionized water, add 0.5 kg of sodium sulfate, adjust the pH to 11-11.5 with NaOH, add 0.96 kg of propylene oxide, seal and react at 45 °C for 12 h, adjust the pH of the resulting reaction solution to 6.5-7 with dilute HCl, filter, wash, and dry to obtain oxidized-etherified dual-modified starch;

[0092] S33. Add 12 kg of oxidized-etherified double-modified starch to 35 L of hot water, stir and gelatinize at 85 °C for 30 min to obtain starch paste. Add 3 kg of glycerol, 1 kg of calcium stearate and 0.5 kg of defoamer while stirring, homogenize and disperse for 10 min, and degas under vacuum for 15-20 min to obtain the third component.

[0093] The other components and preparation methods are the same as in Example 1.

[0094] Comparative Example 6: This comparative example is based on Example 1, but the corn starch in this comparative example is not modified.

[0095] The preparation method of the third component includes the following steps:

[0096] S31. Under ice bath and stirring, 1.8 kg of acrylic acid was added to 20 L of deionized water, and 40% KOH solution was slowly added dropwise to adjust the pH to 7. 7 kg of N-isopropylacrylamide, 1.2 kg of N-tert-butylacrylamide and 0.1 kg of N,N'-methylenebisacrylamide were added and stirred to dissolve. 30 L of deionized water was added, nitrogen gas was purged to remove oxygen, the temperature was raised to 60 °C, and 0.1 kg of potassium persulfate was added. The reaction was stirred for 4 h, and the resulting reaction solution was poured into ethanol to precipitate. After standing for 2 h to dehydrate, the solution was filtered, washed with ethanol, dried under vacuum at 60 °C, and pulverized through an 80-mesh sieve to obtain a thermosensitive water-absorbing resin.

[0097] S32. Add 12kg of corn starch to 35L of hot water and stir and gelatinize at 85℃ for 30min to obtain starch paste. Add 8kg of thermosensitive water-absorbing resin, 3kg of glycerin, 1kg of calcium stearate and 0.5kg of defoamer while stirring. Homogenize and disperse for 10min and degas under vacuum for 15~20min to obtain the third component.

[0098] The other components and preparation methods are the same as in Example 1.

[0099] Comparative Example 7: This comparative example is based on Example 1, but differs from Example 1 in that it prepares a medium-element fertilizer composition through physical blending.

[0100] The preparation method includes the following steps:

[0101] S1. Place the first component, the second component, and the third component in a mixer and dry mix them evenly. Transfer the mixture to a granulator and, while stirring, slowly and gradually add 5% PVP binder and glycerin using a spray device. Granulate the mixture and dry it at 60-70°C for 12-24 hours to obtain a medium-element fertilizer composition.

[0102] The other components and preparation methods are the same as in Example 1.

[0103] Comparative Example 8: This comparative example is based on Example 1, but differs from Example 1 in that it is a conventional medium-element fertilizer composition.

[0104] The preparation method includes the following steps:

[0105] S1. Place 63.8 kg of calcium nitrate powder, 25 kg of magnesium sulfate powder, 6 kg of potassium sulfate powder, and 5.2 kg of kaolin in a mixer and dry mix evenly. Transfer the mixture to a granulator and slowly and evenly add 5% PVP binder liquid using a spray device while stirring. Granulate the mixture and dry it at 60~70℃ for 12~24 hours to obtain a medium-element fertilizer composition.

[0106] Experimental verification:

[0107] Experiment 1: Freeze-thaw simulation cycle test

[0108] A transparent plexiglass column (10cm inner diameter, 40cm height) with drainage holes and a mesh screen at the bottom is filled with homogeneous farmland soil that has passed through a 2mm sieve and has a bulk density of 1.3g / cm³. 3 A high-salt crust was artificially created in the top 0-5cm soil layer (NaCl solution was added, EC > 4dS / m). The medium-element fertilizer compositions prepared in the examples and comparative examples were applied to the soil layer of 15-30cm, with the amount of CaO calculated at 80kg / ha. 20 freeze-thaw cycles of -5℃ / 12h to 10℃ / 12h were performed, with each treatment repeated 3 times.

[0109] (1) After each cycle, samples were taken from the soil at a depth of 15-30 cm to analyze the Ca content. 2+ Mg 2+ Content, calculate the Ca content in the soil at a depth of 15-30 cm after 20 cycles. 2+ Mg 2+ Increase rate;

[0110] (2) After every 5 cycles, the position of the uppermost interface of the medium-element fertilizer composition marked with colored markings is recorded by the scale marks on the side of the soil column, and the average upward displacement depth is calculated.

[0111] (3) After 20 cycles, the electrical conductivity (EC) of the 0-15cm soil layer and the disintegration rate of fertilizer particles were measured.

[0112] Table 1. Results of freeze-thaw cycle test:

[0113]

[0114] The results of the freeze-thaw cycle test are shown in Table 1. As can be seen from the table, the nutrient retention effects of Comparative Examples 1 and 4 decreased significantly, indicating that the chelation and fixation effect of polyaspartic acid and the recapture effect of citric acid-modified potassium humate are key to nutrient retention. Comparative Example 8 (conventional fertilizer) showed the greatest upward migration depth, indicating that the present invention effectively inhibited the upward migration of fertilizer during the freeze-thaw process. The soil EC value of the examples was significantly reduced, indicating that the present invention effectively prevented salt migration and accumulation to the surface. Furthermore, compared with Comparative Example 7, Example 1 had a lower particle disintegration rate, indicating that the three-layer encapsulation of the first, second, and third components has good structural stability.

[0115] Experiment 2: Field Trial

[0116] Experimental location: A typical freeze-thaw agricultural area (a region with an average annual ground temperature ≤3℃, where the main soil freeze-thaw process occurs from November to April of the following year, with the freeze-thaw effect mainly concentrated in the 0-20cm topsoil layer, where 8-10 freeze-thaw cycles were observed).

[0117] Crop planted: Spring wheat;

[0118] Experimental period: one complete growing season (sowing in April to harvesting in August);

[0119] Cell design: randomized block design, 3 replicates, cell area 20m² (4m×5m).

[0120] Fertilization method: All treatments were basal applied at equal amounts of CaO 80 kg / ha and MgO 40 kg / ha.

[0121] (1) On the 20th day after sowing, the number of seedlings in the three quadrats with fixed markings in each plot was counted and the seedling rate was calculated by comparing it with the theoretical number of seeds sown.

[0122] (2) During the flowering period of the crop, three points were taken in each plot at a depth of 0-40cm to measure the average root length density and the root dry weight of a single plant.

[0123] (3) In the middle 2m×4m area of ​​the actual harvest plot, the grain yield and thousand-grain weight were measured.

[0124] Table 2. Results of field trials:

[0125]

[0126] The results of the field trials are shown in Table 2. The table shows that the experimental results were significantly better than the control group in terms of seedling emergence, root development, and yield. This indicates that the medium-element fertilizer composition prepared in this invention can effectively inhibit the upward migration of nutrients in freeze-thaw soil environments, achieving long-term slow release and stable supply of nutrients, and significantly promoting crop growth and yield increase.

[0127] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a medium-element fertilizer composition for soil improvement, characterized in that, Includes the following steps: S1. Preheat the first component to 50~55℃, place it in a fluidized bed, spray the second component onto the surface of the first component, control the fluidized bed temperature at 55℃, and continue coating to obtain the first mixture; S2. Preheat the first mixture to 45°C, immerse it in the third component at 50°C, remove it and transfer it to a fluidized bed for drying. Repeat the immersion-drying process and vacuum drying to obtain a medium-element fertilizer composition. The first component is a polyaspartic acid-modified montmorillonite-calcium carbonate / magnesium oxide composite material; The second component is a physical blend of citric acid-modified potassium humate and seaweed oligosaccharides; The third component is a thermosensitive water-absorbing resin-modified starch complex; The preparation method of the first component includes the following steps: S11. Disperse montmorillonite in an ethanol / water mixed solvent, add aminopropyltriethoxysilane, stir the reaction, centrifuge and wash the resulting reaction solution, vacuum dry it, grind and sieve it to obtain aminated montmorillonite; S12. Polyaspartic acid was dissolved in MES buffer, and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added. The mixture was activated in the dark to obtain an activated polyaspartic acid solution. Aminated montmorillonite was ultrasonically dispersed in MES buffer, and the activated polyaspartic acid solution was added. The pH was adjusted with dilute HCl, and the mixture was heated in a water bath with stirring. The resulting reaction solution was centrifuged, washed, and freeze-dried to obtain polyaspartic acid-modified montmorillonite. S13. Place polyaspartic acid modified montmorillonite, calcium carbonate powder and magnesium oxide powder in a mixer and dry mix them evenly. While stirring, spray in PVA solution. Place the resulting product in a granulator to granulate and dry it to obtain the first component. The preparation method of the second component includes the following steps: S21. Dissolve sodium alginate in deionized water, add alginate lyase, perform enzymatic hydrolysis, heat the resulting reaction solution to inactivate the enzyme, cool it and filter it through an ultrafiltration membrane, collect the permeate, concentrate it and spray dry it to obtain seaweed oligosaccharide. S22. Potassium humate and anhydrous citric acid are thoroughly dry-mixed, protected by nitrogen, and the temperature is slowly increased while stirring. The resulting product is cooled and crushed, dissolved in deionized water, precipitated and purified by adding ethanol, pH is adjusted with KOH, and spray-dried to obtain modified potassium humate. S23. Place seaweed oligosaccharide, modified potassium humate and magnesium sulfate monohydrate in a mixer and dry mix evenly to obtain a composite powder. Add the composite powder to a PVP ethanol solution under stirring, gradually add deionized water to adjust the solid content, and continue stirring to obtain the second component. The preparation method of the third component includes the following steps: S31. Under ice bath and stirring, acrylic acid is added to deionized water, KOH solution is slowly added dropwise to adjust the pH, N-isopropylacrylamide, N-tert-butylacrylamide and N,N'-methylenebisacrylamide are added, stirred to dissolve, deionized water is added, nitrogen gas is purged to remove oxygen, potassium persulfate is added after heating, the reaction is stirred, the resulting reaction solution is poured into ethanol to precipitate, allowed to stand to dehydrate, filtered and washed, vacuum dried, ground and sieved to obtain temperature-sensitive water-absorbing resin; S32. Dissolve corn starch in deionized water, adjust the pH with NaOH, slowly add sodium hypochlorite solution, stir the reaction, add sodium sulfite solution to the resulting reaction solution, adjust the pH with dilute HCl, filter, wash, and dry to obtain oxidized starch; S33. Disperse oxidized starch in deionized water, add sodium sulfate, adjust the pH with NaOH, add propylene oxide, seal the reaction, adjust the pH of the resulting reaction solution with dilute HCl, filter, wash, and dry to obtain oxidized-etherified dual-modified starch. S34. Add the oxidized-etherified double-modified starch to hot water, stir and gelatinize to obtain starch paste, add thermosensitive water-absorbing resin, glycerin, calcium stearate and defoamer while stirring, homogenize and disperse, and defoam under vacuum to obtain the third component.

2. The method for preparing a medium-element fertilizer composition for soil improvement according to claim 1, characterized in that, The mass ratio of the first component, the second component, and the third component in the medium-element fertilizer composition is 8~9:5~6:4~5.

3. The method for preparing a medium-element fertilizer composition for soil improvement according to claim 1, characterized in that, The mass ratio of polyaspartic acid to aminated montmorillonite is 0.25~0.4:1; the mass ratio of polyaspartic acid-modified montmorillonite, calcium carbonate powder and magnesium oxide powder is 2:6:

1.

4. The method for preparing a medium-element fertilizer composition for soil improvement according to claim 1, characterized in that, The mass ratio of the seaweed oligosaccharide, modified potassium humate, and magnesium sulfate monohydrate is 3:9:

5.

5. The method for preparing a medium-element fertilizer composition for soil improvement according to claim 1, characterized in that, The mass ratio of the thermosensitive water-absorbing resin to the oxidized-etherified dual-modified starch is 2:3.

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