Bioactive fertilizer capable of improving soil and preparation method thereof

Abstract

The invention relates to the field of fertilizers, in particular to a bioactive fertilizer capable of improving soil and a preparation method thereof. Compared with a conventional starch coating layer, starch is modified in the coating layer, the stability and the slow release effect of the coating layer are improved, meanwhile, a certain amount of nitrogen phosphorus potassium salt is added, and nutrients needed by plants in the early stage can be provided. The prepared fertilizer is moderate in slow-release effect, the slow-release days reach about 4 months, the fertilizer can adapt to plant growth, and the growth requirements of plants are fully met.

Description

Technical Field

[0001] The invention relates to the field of fertilizers, and in particular to a biologically active fertilizer capable of improving soil and a preparation method thereof. Background Art

[0002] With the rapid development of modern agriculture, soil degradation problems are becoming increasingly serious, including soil salinization, acidification, nutrient imbalance and decreased microbial diversity. These problems have seriously affected the growth and yield of crops, and also threatened the sustainable development of agriculture. Therefore, improving soil and increasing soil fertility and biological activity have become important tasks in agricultural production.

[0003] Bioactive fertilizer, as a new type of soil conditioner, combines the advantages of organic fertilizer and microbial fertilizer. It can not only provide nutrients needed for crop growth, but also improve soil structure, increase soil biological activity and promote nutrient circulation through the action of microorganisms. The large number of beneficial microorganisms contained in bioactive fertilizers, such as nitrogen-fixing bacteria, phosphate-solubilizing bacteria and potassium-solubilizing bacteria, can increase the availability of nutrients such as nitrogen, phosphorus and potassium in the soil. At the same time, their metabolites can improve the physical properties of the soil and improve the soil's water and fertilizer retention capacity. Research progress on the effects of bio-organic fertilizers on farmland soil characteristics, crop yield and quality shows that the application of bio-organic fertilizers can increase soil moisture content, reduce soil bulk density and compactness, improve soil physical properties; balance the soil carbon-nitrogen ratio, improve soil pH, and increase the content of effective nutrient elements in the soil; increase the microbial activity and enzyme activity in the soil and promote nutrient conversion in the soil.

[0004] Therefore, as an important means of improving soil, the research and application of bioactive fertilizers are of great significance for improving soil quality, ensuring food security and promoting sustainable agricultural development. Although biofertilizers have many advantages such as improving fertilizer utilization and crop quality, protecting the ecological environment and soil health, there is a problem of unstable product effects during use, which often leads to the application of biofertilizers failing to achieve the expected results. Summary of the invention

[0005] In view of the problems existing in the prior art, the object of the present invention is to provide a biologically active fertilizer capable of improving soil and a preparation method thereof.

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a biologically active fertilizer capable of improving soil, comprising the following steps:

[0008] Step 1, preparing epoxidized starch:

[0009] Weigh corn starch and dimethyl sulfoxide, mix them, stir them evenly, adjust the system to be alkaline, add epichlorohydrin, stir and treat at 45-55° C. for 3-8 hours, and after the reaction is completed, cool to room temperature, precipitate, wash and dry to obtain epoxidized starch;

[0010] Step 2, preparing modified starch:

[0011] Epoxidized starch and amino polyethylene glycol hydroxyl (NH2-PEG-OH) are mixed in dimethyl sulfoxide, heated and stirred, precipitated, washed and dried to prepare modified starch;

[0012] Step 3, preparation of compound fertilizer granules:

[0013] The composite bacterial agent, fermented soybean meal and urea solution are mixed, fully mixed, and then granulated to obtain composite bacterial fertilizer granules;

[0014] Step 4, coating treatment:

[0015] The modified starch and nitrogen, phosphorus and potassium salts are mixed in a mixer, and then water and propylene glycol are added. After being fully stirred, a film liquid is prepared, which is then sprayed on the surface of the composite bacterial fertilizer particles. After drying, a biologically active fertilizer is obtained.

[0016] Preferably, in step 1, the corn starch is industrial grade corn starch with a particle size of 20-30 microns, a moisture content of ≤14%, and an ash content of ≤0.15%.

[0017] Preferably, in step 1, adjusting the system to be alkaline is to use triethylamine to adjust the pH of the system to 11-12.

[0018] Preferably, in step 1 and step 2, precipitation is performed by pouring the reaction system into 2-3 times the volume of water and collecting the precipitate; washing is performed by washing at least three times with pure water; and drying is performed under vacuum conditions.

[0019] Preferably, in step 1, the mass ratio of corn starch, epichlorohydrin and dimethyl sulfoxide is 1:0.32-0.64:15-25.

[0020] Preferably, in step 2, the temperature of the heating and stirring treatment is 55-60° C. and the time is 4-6 hours.

[0021] Preferably, in step 2, the molecular weight of amino polyethylene glycol hydroxyl group (NH2-PEG-OH) is 2000-5000.

[0022] Preferably, in step 2, the mass ratio of epoxidized starch, aminopolyethylene glycol hydroxyl group and dimethyl sulfoxide is 1:0.3-0.8:10-20.

[0023] Preferably, in step 3, the composite bacterial agent comprises a Bacillus amyloliquefaciens preparation, a Bacillus subtilis preparation, a Bacillus mucilaginosus preparation, and a Bacillus licheniformis preparation; and the effective viable bacterial count of each bacterial preparation in the composite bacterial agent is greater than 1×10 10 CFU / g; the mass ratio of the Bacillus amyloliquefaciens preparation, the Bacillus subtilis preparation, the Bacillus mucilaginosus preparation, and the Bacillus licheniformis preparation is 2-4:1-3:1-2:1-2.

[0024] Preferably, in step 3, the urea solution is an aqueous solution of urea with a mass fraction of 30%-50%.

[0025] Preferably, in step 3, the mass ratio of the composite bacterial agent, the fermented soybean meal and the urea solution is 1:30-50:6-10.

[0026] Preferably, in step 4, the nitrogen, phosphorus and potassium salts are monoammonium phosphate, diammonium phosphate and potassium nitrate in a mass ratio of 0.2-0.5:0.1-0.3:1-2.

[0027] Preferably, in step 4, the mass ratio of modified starch, nitrogen, phosphorus and potassium salt, glycerol and water is 3-8:5-10:0.5-1:10.

[0028] Preferably, in step 4, the particle size of the composite bacterial fertilizer particles is 1.5-4.5 mm, and the spraying thickness of the membrane liquid on the surface of the composite bacterial fertilizer particles is 0.3-0.6 mm.

[0029] In a second aspect, the present invention provides a biologically active fertilizer capable of improving soil, which is prepared by the above-mentioned preparation method.

[0030] The beneficial effects of the present invention are:

[0031] 1. The present invention prepares a biologically active fertilizer that can improve soil. The fertilizer is a slow-release coated fertilizer, wherein the inner core is composed of a composite bacterial agent and a biological fertilizer, and the coating layer is composed of modified starch and nitrogen, phosphorus and potassium salts. Compared with the conventional starch coating layer, the starch is modified in the coating layer of the present invention, which improves the stability and slow-release effect of the coating layer, and a certain amount of nitrogen, phosphorus and potassium salts are added to provide the nutrients required by the plant in the early stage. The fertilizer prepared by the present invention has a moderate slow-release effect, and the slow-release days reach about 4 months, which can adapt to the growth of plants and fully meet the growth needs of plants.

[0032] 2. Traditional starch-coated fertilizers are made by directly coating the surface of fertilizer particles with gelatinized starch. However, the gelatinized starch is easy to peel off, and the water absorption is also poor after recrystallization, resulting in unstable effect of slow-release fertilizer. The present invention modifies the starch by epoxidizing the starch first, and then grafting it with amino polyethylene glycol hydroxyl groups to obtain a starch structure grafted with polyethylene glycol groups, which enhances the structural stability and water retention, and performs better in the slow-release application process.

[0033] 3. The inner core of the biological active fertilizer of the present invention is a mixture of a composite bacterial agent and a biological fertilizer. The biological fertilizer is fermented soybean meal, which has a high bioavailability and can provide nutrition for the composite bacterial agent. The decomposition product can be used as an excellent fertilizer. The composite bacterial agent uses a variety of Bacillus to form a suitable probiotic environment, which not only improves the soil's ability to retain fertilizer and water, but also increases soil looseness and promotes the growth of plant roots. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to limit the scope of the present invention. The change or adjustment of the relative relationship thereof shall also be regarded as the scope of the present invention without substantially changing the technical content.

[0035] In order to better understand the above technical scheme, the exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0036] The present invention will be further described below in conjunction with the following examples.

[0037] Example 1

[0038] A biologically active fertilizer capable of improving soil, the preparation method of which comprises the following steps:

[0039] Step 1, preparing epoxidized starch:

[0040] Weigh industrial-grade corn starch (particle size of 25 microns, moisture ≤14%, ash ≤0.15%) and dimethyl sulfoxide, mix them, stir them evenly, use triethylamine to adjust the pH of the system to 11, then add epichlorohydrin dropwise, the mass ratio of corn starch, epichlorohydrin and dimethyl sulfoxide is 1:0.48:20, gradually heat to 50°C, keep warm and stir for 5 hours, after the reaction is completed, cool to room temperature, pour the reaction solution into 3 times the volume of water, collect the precipitate, wash it with water three times, and dry it under vacuum to obtain epoxidized starch;

[0041] Step 2, preparing modified starch:

[0042] Add epoxidized starch and aminopolyethylene glycol hydroxyl (NH2-PEG-OH) with a molecular weight of 3000 into dimethyl sulfoxide, the mass ratio of epoxidized starch, aminopolyethylene glycol hydroxyl and dimethyl sulfoxide is 1:0.5:15, stir and mix thoroughly, then gradually heat to 58°C, keep stirring for 5 hours, cool to room temperature, pour into 3 times volume of water, collect precipitate, wash three times with water, and dry under vacuum to obtain modified starch;

[0043] Step 3, preparing compound fertilizer granules:

[0044] The composite bacterial agent, fermented soybean meal and 40% urea aqueous solution were mixed, the mass ratio of the composite bacterial agent, fermented soybean meal and urea solution was 1:40:8, the composite bacterial agent included Bacillus amylolyticus preparation, Bacillus subtilis preparation, Bacillus mucilaginosus preparation and Bacillus licheniformis preparation in a mass ratio of 3:2:1:2, and the effective live bacteria count of each single bacterial preparation was greater than 1×10 10 CFU / g, after being fully mixed, wet granulation was performed in a drum, and sieved after drying. The sieved particle size was 3mm to obtain composite bacterial fertilizer granules;

[0045] Step 4, coating treatment:

[0046] Monoammonium phosphate, diammonium phosphate and potassium nitrate are mixed into nitrogen, phosphorus and potassium salts in a mass ratio of 0.3:0.2:1.5, modified starch and nitrogen, phosphorus and potassium salts are mixed in a blender, and then water and glycerol are added. The mass ratio of modified starch, nitrogen, phosphorus and potassium salts, glycerol and water is 5:8:0.6:10. After being fully stirred, a film liquid is made, and then it is sprayed on the surface of the composite bacterial fertilizer particles with a spraying thickness of 0.4 mm. After drying, a biologically active fertilizer is obtained.

[0047] Example 2

[0048] A biologically active fertilizer capable of improving soil, the preparation method of which comprises the following steps:

[0049] Step 1, preparing epoxidized starch:

[0050] Weigh industrial-grade corn starch (particle size of 25 microns, moisture ≤14%, ash ≤0.15%) and dimethyl sulfoxide, mix them, stir them evenly, use triethylamine to adjust the pH of the system to 12, then add epichlorohydrin dropwise, the mass ratio of corn starch, epichlorohydrin and dimethyl sulfoxide is 1:0.4:20, gradually heat to 50°C, keep warm and stir for 6 hours, after the reaction is completed, cool to room temperature, pour the system into a large amount of water, collect the precipitate, wash it with water three times, and dry it under vacuum to obtain epoxidized starch;

[0051] Step 2, preparing modified starch:

[0052] Add epoxidized starch and aminopolyethylene glycol hydroxyl (NH2-PEG-OH) with a molecular weight of 25000 into dimethyl sulfoxide, the mass ratio of epoxidized starch, aminopolyethylene glycol hydroxyl and dimethyl sulfoxide is 1:0.4:12, stir and mix thoroughly, then gradually heat to 55°C, keep stirring for 5 hours, cool to room temperature, pour the system into a large amount of water, collect the precipitate, wash it three times with water, and dry it under vacuum to obtain modified starch;

[0053] Step 3, preparing compound fertilizer granules:

[0054] The composite bacterial agent, fermented soybean meal and 30%-50% urea aqueous solution are mixed, the mass ratio of the composite bacterial agent, fermented soybean meal and urea solution is 1:45:7, the composite bacterial agent includes amylolytic Bacillus preparation, subtilis preparation, mucilaginous Bacillus preparation and licheniformis preparation in a mass ratio of 3:1:2:2, and the effective live bacteria count of each bacterial preparation is greater than 1×10 10 CFU / g, after fully mixing, wet granulation, drying and sieving, the sieving particle size is 2.5mm, and the composite fertilizer granules are obtained;

[0055] Step 4, coating treatment:

[0056] Monoammonium phosphate, diammonium phosphate and potassium nitrate are mixed into nitrogen, phosphorus and potassium salts in a mass ratio of 0.3:0.1:2, modified starch and nitrogen, phosphorus and potassium salts are mixed in a blender, and then water and glycerol are added. The mass ratio of modified starch, nitrogen, phosphorus and potassium salts, glycerol and water is 4:6:0.6:10. After being fully stirred, a film liquid is prepared, and then it is sprayed on the surface of the composite bacterial fertilizer particles with a spraying thickness of 0.5 mm. After drying, a biologically active fertilizer is obtained.

[0057] Example 3

[0058] A biologically active fertilizer capable of improving soil, the preparation method of which comprises the following steps:

[0059] Step 1, preparing epoxidized starch:

[0060] Weigh industrial-grade corn starch (particle size of 25 microns, moisture ≤14%, ash ≤0.15%) and dimethyl sulfoxide, mix them, stir them evenly, use triethylamine to adjust the pH of the system to 12, then add epichlorohydrin dropwise, the mass ratio of corn starch, epichlorohydrin and dimethyl sulfoxide is 1:0.53:25, gradually heat to 55°C, keep warm and stir for 4 hours, after the reaction is completed, cool to room temperature, pour the system into a large amount of water, collect the precipitate, wash it three times with water, and dry it under vacuum to obtain epoxidized starch;

[0061] Step 2, preparing modified starch:

[0062] Epoxidized starch and aminopolyethylene glycol hydroxyl (NH2-PEG-OH) with a molecular weight of 4000 are added to dimethyl sulfoxide, the mass ratio of epoxidized starch, aminopolyethylene glycol hydroxyl and dimethyl sulfoxide is 1:0.6:18, and the mixture is fully stirred and mixed, and then the temperature is gradually raised to 60°C, and after being kept and stirred for 6 hours, the temperature is lowered to room temperature, and the system is poured into a large amount of water, and the precipitate is collected, washed with water three times, and dried under vacuum conditions to obtain modified starch;

[0063] Step 3, preparing compound fertilizer granules:

[0064] The composite bacterial agent, fermented soybean meal and 50% urea aqueous solution were mixed, the mass ratio of the composite bacterial agent, fermented soybean meal and urea solution was 1:40:6, the composite bacterial agent included Bacillus amyloliquefaciens preparation, Bacillus subtilis preparation, Bacillus mucilaginosus preparation and Bacillus licheniformis preparation in a mass ratio of 2.5:2:1.5:1.5, and the effective live bacteria count of each single bacterial preparation was greater than 1×10 10 CFU / g, after fully mixing, wet granulation, drying and sieving, the sieved particle size is 3.5mm, and the composite fertilizer granules are obtained;

[0065] Step 4, coating treatment:

[0066] Monoammonium phosphate, diammonium phosphate and potassium nitrate are mixed into nitrogen, phosphorus and potassium salts in a mass ratio of 0.4:0.2:1, modified starch and nitrogen, phosphorus and potassium salts are mixed in a blender, and then water and glycerol are added. The mass ratio of modified starch, nitrogen, phosphorus and potassium salts, glycerol and water is 6:7:0.8:10. After being fully stirred, a film liquid is prepared, and then it is sprayed on the surface of the composite bacterial fertilizer particles with a spraying thickness of 0.4 mm. After drying, a biologically active fertilizer is obtained.

[0067] Example 4

[0068] A biologically active fertilizer capable of improving soil, the preparation method of which comprises the following steps:

[0069] Step 1, preparing epoxidized starch:

[0070] Weigh industrial-grade corn starch (particle size of 20 microns, moisture ≤14%, ash ≤0.15%) and dimethyl sulfoxide, mix them, stir them evenly, use triethylamine to adjust the pH of the system to 11, then add epichlorohydrin dropwise, the mass ratio of corn starch, epichlorohydrin and dimethyl sulfoxide is 1:0.32:15, gradually heat to 45°C, keep warm and stir for 3 hours, after the reaction is completed, cool to room temperature, pour the system into a large amount of water, collect the precipitate, wash it with water three times, and dry it under vacuum to obtain epoxidized starch;

[0071] Step 2, preparing modified starch:

[0072] Add epoxidized starch and aminopolyethylene glycol hydroxyl (NH2-PEG-OH) with a molecular weight of 2000 into dimethyl sulfoxide, the mass ratio of epoxidized starch, aminopolyethylene glycol hydroxyl and dimethyl sulfoxide is 1:0.3:10, stir and mix thoroughly, then gradually heat to 55°C, keep stirring for 4 hours, cool to room temperature, pour the system into a large amount of water, collect the precipitate, wash with water three times, and dry under vacuum to obtain modified starch;

[0073] Step 3, preparing compound fertilizer granules:

[0074] The composite bacterial agent, fermented soybean meal and 30%-50% urea aqueous solution are mixed, the mass ratio of the composite bacterial agent, fermented soybean meal and urea solution is 1:30:6, the composite bacterial agent includes amylolytic Bacillus preparation, subtilis preparation, mucilaginous Bacillus preparation and licheniformis preparation in a mass ratio of 2:1:1:1, and the effective live bacteria count of each single bacterial preparation is greater than 1×10 10 CFU / g, after fully mixing, wet granulation, drying and sieving, the sieving particle size is 1.5mm, and the composite fertilizer granules are obtained;

[0075] Step 4, coating treatment:

[0076] Monoammonium phosphate, diammonium phosphate and potassium nitrate are mixed into nitrogen, phosphorus and potassium salts in a mass ratio of 0.2:0.1:1, modified starch and nitrogen, phosphorus and potassium salts are mixed in a blender, and then water and glycerol are added. The mass ratio of modified starch, nitrogen, phosphorus and potassium salts, glycerol and water is 3:5:0.5:10. After being fully stirred, a film liquid is prepared, and then it is sprayed on the surface of the composite bacterial fertilizer particles with a spraying thickness of 0.3 mm. After drying, a biologically active fertilizer is obtained.

[0077] Example 5

[0078] A biologically active fertilizer capable of improving soil, the preparation method of which comprises the following steps:

[0079] Step 1, preparing epoxidized starch:

[0080] Weigh industrial-grade corn starch (particle size of 30 microns, moisture ≤14%, ash ≤0.15%) and dimethyl sulfoxide, mix them, stir them evenly, use triethylamine to adjust the pH of the system to 12, then add epichlorohydrin dropwise, the mass ratio of corn starch, epichlorohydrin and dimethyl sulfoxide is 1:0.64:25, gradually heat to 55°C, keep warm and stir for 8 hours, after the reaction is completed, cool to room temperature, pour the system into a large amount of water, collect the precipitate, wash it with water three times, and dry it under vacuum to obtain epoxidized starch;

[0081] Step 2, preparing modified starch:

[0082] Epoxidized starch and aminopolyethylene glycol hydroxyl (NH2-PEG-OH) with a molecular weight of 5000 are added to dimethyl sulfoxide, the mass ratio of epoxidized starch, aminopolyethylene glycol hydroxyl and dimethyl sulfoxide is 1:0.8:20, and the mixture is fully stirred and mixed, and then the temperature is gradually raised to 60°C, and after being kept and stirred for 6 hours, the temperature is lowered to room temperature, and the system is poured into a large amount of water, and the precipitate is collected, washed with water three times, and dried under vacuum conditions to obtain modified starch;

[0083] Step 3, preparing compound fertilizer granules:

[0084] The composite bacterial agent, fermented soybean meal and 50% urea aqueous solution were mixed, the mass ratio of the composite bacterial agent, fermented soybean meal and urea solution was 1:50:10, the composite bacterial agent included Bacillus amylolyticus preparation, Bacillus subtilis preparation, Bacillus mucilaginosus preparation and Bacillus licheniformis preparation in a mass ratio of 4:3:2:2, and the effective live bacteria count of each single bacterial preparation was greater than 1×10 10 CFU / g, after fully mixing, wet granulation, drying and sieving, the sieved particle size is 4.5mm, and the composite fertilizer granules are obtained;

[0085] Step 4, coating treatment:

[0086] Monoammonium phosphate, diammonium phosphate and potassium nitrate are mixed into nitrogen, phosphorus and potassium salts in a mass ratio of 0.5:0.3:2, modified starch and nitrogen, phosphorus and potassium salts are mixed in a blender, and then water and glycerol are added. The mass ratio of modified starch, nitrogen, phosphorus and potassium salts, glycerol and water is 8:10:1:10. After being fully stirred, a film liquid is made, and then it is sprayed on the surface of the composite bacterial fertilizer particles with a spraying thickness of 0.6 mm. After drying, a biologically active fertilizer is obtained.

[0087] Comparative Example 1

[0088] A bioactive fertilizer, which is different from Example 1 only in that steps 1-2 are omitted and the modified starch in steps 3-4 is replaced by conventional industrial-grade corn starch.

[0089] Comparative Example 2

[0090] A bioactive fertilizer, which differs from Example 1 only in that step 1-2 is omitted, the modified starch in step 3-4 is replaced by a mixture of industrial-grade corn starch and aminopolyethylene glycol hydroxyl with a molecular weight of 3000, and the mass ratio of corn starch to aminopolyethylene glycol hydroxyl is 1:0.5.

[0091] Comparative Example 3

[0092] A bioactive fertilizer, which is different from Example 1 only in that step 2 is omitted and the modified starch in steps 3-4 is replaced by epoxidized starch.

[0093] Experimental example

[0094] For the biologically active fertilizers prepared in Example 1 and Comparative Examples 1-3, the nutrient slow-release effect was tested according to the method of the international standard ISO 18644 "General requirements for controlled-release fertilizers for fertilizers and soil conditioners" (2016), taking nitrogen as an example, and the results are shown in Table 1.

[0095] Table 1 Performance of different bioactive fertilizers

[0096] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Initial 24h nitrogen release rate 1.72％ 1.15％ 2.14％ 1.39％ Nitrogen release rate on the 28th day 12.16％ 38.73％ 46.59％ 7.82％ Total release days 123 days 75 days 61 days 194 days

[0097] Since the bioactive fertilizer coating layer in the present invention contains a certain amount of nitrogen, phosphorus and potassium salts, the nitrogen release rate will be slightly higher than the slow-release fertilizer on the market, but from the comparison results of multiple comparative examples, the slow-release rate of the bioactive fertilizer prepared in Example 1 is more suitable, so that the slow-release days reach about 4 months, which can fully meet the needs of crops and has the best slow-release effect. Specifically, the initial 24h nitrogen release rate in Comparative Example 1 is lower than that in Example 1, but the 28d nitrogen release rate is much higher than that in Example 1, and the total release days are much smaller than that in Example 1, indicating that its slow-release effect in the early stage is poor, but the later stage may be unstable and cracked, resulting in a large number of release days shortened, and the overall performance is not good. In Comparative Example 2, the nitrogen release rate in both the early and late stages is much greater than that in Example 1, indicating that its slow-release effect is poor, which may be caused by the cracking of the coating layer caused by the aminopolyethylene glycol hydroxyl group being more soluble in water. The nitrogen release rates in the early and late stages of Comparative Example 3 are all less than those in Example 1, resulting in too long slow-release days, which easily makes the nutrition during fertilization insufficient, resulting in malnutrition in plants.

[0098] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0099] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a biologically active fertilizer capable of improving soil, characterized in that: The following steps are involved: Step 1, preparing epoxidized starch: Weigh corn starch and dimethyl sulfoxide, mix them, stir them evenly, adjust the system to be alkaline, add epichlorohydrin, stir and treat at 45-55° C. for 3-8 hours, and after the reaction is completed, cool to room temperature, precipitate, wash and dry to obtain epoxidized starch; Step 2, preparing modified starch: Epoxidized starch and aminopolyethylene glycol hydroxyl are mixed in dimethyl sulfoxide, stirred at 55-60° C. for 4-6 hours, precipitated, washed and dried to prepare modified starch; Step 3, preparing compound fertilizer granules: The composite bacterial agent, fermented soybean meal and urea solution are mixed, fully mixed, and then granulated to obtain composite bacterial fertilizer granules; Step 4, coating treatment: The modified starch and nitrogen, phosphorus and potassium salts are mixed in a mixer, and then water and propylene glycol are added. After being fully stirred, a film liquid is prepared, which is then sprayed on the surface of the composite bacterial fertilizer particles. After drying, a biologically active fertilizer is obtained.

2. The method for preparing a biologically active fertilizer capable of improving soil according to claim 1, characterized in that: In the step 1, the system is adjusted to be alkaline by using triethylamine to adjust the pH of the system to 11-12.

3. The method for preparing a biologically active fertilizer capable of improving soil according to claim 1, characterized in that: In the step 1 and the step 2, the precipitation is performed by pouring the reaction system into 2-3 times the volume of water and collecting the precipitate; the washing is performed by washing at least three times with pure water; and the drying is performed under vacuum conditions.

4. The method for preparing a biologically active fertilizer capable of improving soil according to claim 1, characterized in that: In the step 1, the mass ratio of corn starch, epichlorohydrin and dimethyl sulfoxide is 1:0.32-0.64:15-25.

5. The method for preparing a biologically active fertilizer capable of improving soil according to claim 1, characterized in that: In the step 2, the molecular weight of the aminopolyethylene glycol hydroxyl group is 2000-5000; the mass ratio of the epoxidized starch, the aminopolyethylene glycol hydroxyl group and the dimethyl sulfoxide is 1:0.3-0.8:10-20.

6. The method for preparing a biologically active fertilizer capable of improving soil according to claim 1, characterized in that: In step 3, the composite bacterial agent includes a Bacillus amyloliquefaciens preparation, a Bacillus subtilis preparation, a Bacillus mucilaginosus preparation, and a Bacillus licheniformis preparation; the effective viable bacterial count of each bacterial preparation in the composite bacterial agent is greater than 1×10 10 CFU / g; the mass ratio of the Bacillus amyloliquefaciens preparation, the Bacillus subtilis preparation, the Bacillus mucilaginosus preparation, and the Bacillus licheniformis preparation is 2-4:1-3:1-2:1-2.

7. The method for preparing a biologically active fertilizer capable of improving soil according to claim 1, characterized in that: In step 3, the urea solution is an aqueous solution of urea, and the mass fraction is 30%-50%; the mass ratio of the composite bacterial agent, the fermented soybean meal and the urea solution is 1:30-50:6-10.

8. The method for preparing a biologically active fertilizer capable of improving soil according to claim 1, characterized in that: In step 4, the nitrogen, phosphorus and potassium salts are monoammonium phosphate, diammonium phosphate and potassium nitrate in a mass ratio of 0.2-0.5:0.1-0.3:1-2; the mass ratio of modified starch, nitrogen, phosphorus and potassium salts, glycerol and water is 3-8:5-10:0.5-1:

10.

9. The method for preparing a biologically active fertilizer capable of improving soil according to claim 1, characterized in that: In step 4, the particle size of the composite bacterial fertilizer particles is 1.5-4.5 mm, and the spraying thickness of the membrane liquid on the surface of the composite bacterial fertilizer particles is 0.3-0.6 mm.

10. A biologically active fertilizer capable of improving soil, characterized in that: The preparation method according to claim 1 is used for preparation.