Environment-friendly organic slow-release fertilizer and preparation method thereof

Abstract

The invention relates to the technical field of agricultural fertilizers, and discloses an environment-friendly organic slow-release fertilizer and a preparation method thereof, the environment-friendly organic slow-release fertilizer comprises the following raw materials by mass: 55-65% of a decomposed straw carrier; 20%-30% of a slow release carrier; 8%-12% of a microencapsulated bacterial agent; 3%-5% of a cross-linking agent; and 2%-4% of an auxiliary additive. The porosity of the decomposed straw carrier is larger than or equal to 65%, the carbon nitrogen ratio is (25-28): 1, the particle size is 0.5-1.5 mm, and the water holding capacity is larger than or equal to 2.5 g / g. The environment-responsive supramolecular slow-release system is constructed, supramolecular host-guest interaction and temperature-responsive polymer synergism are utilized, the fertilizer release rate can be dynamically regulated and controlled along with the crop rhizosphere temperature, nitrogen can be accurately released in the crop fertilizer demand peak period, the matching degree of a nitrogen release curve and crop demand is increased to 90% or above, and the nitrogen release rate is increased to 90% or above. Compared with the traditional organic fertilizer with the problems of uncontrolled nutrient release, excessive nutrient loss in the early stage and insufficient supply in the later stage, the fertilizer realizes the high conformity of nutrient release and crop requirements.

Description

Technical Field

[0001] The invention relates to the technical field of agricultural fertilizers, in particular to an environmentally friendly organic slow-release fertilizer and a preparation method thereof. Background Art

[0002] In agricultural production, the rational use of fertilizers is crucial to improving crop yield and quality. With the increasing awareness of environmental protection and the demand for sustainable agricultural development, environmentally friendly organic slow-release fertilizers have gradually become a hot topic in research and application.

[0003] Although traditional organic fertilizers can improve soil structure and fertility, the nutrient release rate is difficult to control, and they are often released in large quantities in a short period of time, resulting in excessive nutrient supply in the early stage, causing waste and environmental pollution, and insufficient supply in the later stage, which cannot meet the needs of crop growth. From the perspective of the preparation process of fertilizers, the prior art is insufficient in ensuring the activity of microorganisms and the stability of organic matter. Some preparation processes have too high temperatures, which can easily lead to the inactivation of microorganisms and reduce the biological activity of fertilizers. For example, in the high-temperature granulation process, the activity of beneficial microorganisms in fertilizers, such as Bacillus subtilis, will be seriously affected, and even die in large numbers, thereby weakening the improvement effect of fertilizers on the soil ecological environment. At the same time, some processes may cause pyrolysis of organic matter during the preparation process, resulting in the loss of effective ingredients in the fertilizer, and reducing the quality and fertilizer efficiency of the fertilizer.

[0004] In terms of the ecological safety of fertilizers, some existing slow-release fertilizers use materials that pose potential risks. For example, some polymer coating materials used are difficult to degrade and remain in the soil to form microplastics. Long-term accumulation will destroy the soil structure, affect the air permeability and water permeability of the soil, and further affect the growth of crop roots and the absorption of nutrients. Moreover, these microplastics may enter the human body through the food chain, posing a threat to the ecological environment and human health. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides an environmentally friendly organic slow-release fertilizer and a preparation method thereof, which solves the problem that some processes may cause pyrolysis of organic matter during the preparation process, resulting in loss of effective ingredients in the fertilizer and reduced fertilizer quality and fertilizer efficiency.

[0006] To achieve the above objectives, the present invention is implemented through the following technical scheme: an environmentally friendly organic slow-release fertilizer comprises the following raw materials in percentage by mass: 55% to 65% of the decomposed straw carrier; 20% to 30% sustained-release carrier; 8% to 12% microencapsulated bacterial agent; 3% to 5% cross-linking agent; 2% to 4% auxiliary additives.

[0007] Preferably, the porosity of the composted straw carrier is ≥65%, the carbon-nitrogen ratio is 25-28:1, the particle size is 0.5-1.5 mm, and the water holding capacity is ≥2.5 g / g.

[0008] Preferably, the main body of the slow-release carrier is cyclodextrin, and the guest is N-isopropylacrylamide.

[0009] Preferably, the cross-linking agent is geniposide, the cross-linking density is 0.8-1.2 mmol / g, and the gel storage modulus G'≥0.8 kPa.

[0010] Preferably, the auxiliary additive is nano-montmorillonite, its specific surface area is ≥200 m² / g, and the layer spacing is 1.2-1.5 nm.

[0011] In addition, the present invention also provides a preparation method of an environment-friendly organic slow-release fertilizer, comprising the following steps: S1. Copolymer synthesis: Humic acid (HA) and N-isopropylacrylamide (NIPAM) are mixed in a molar ratio of 1:10-1:15, deionized water / ethanol mixture (volume ratio 3:1) is used as a solvent, and 0.5-1.0 mol% of 2,2'-azobis(2-methylpropionamidine) dihydrochloride (AIBA) is added as an initiator, and the reaction is carried out at a temperature of 60-70 °C for 6-8 h; S2. Cyclodextrin functionalization modification, making CD and 2-hydroxyethyl acrylate are mixed in a molar ratio of 1:1.2-1:1.5, 2-4 mol% of p-toluenesulfonic acid (PTSA) is added as a catalyst, and the reaction is carried out at a temperature of 40-50 °C for 4-6 h; S3. Click chemistry cross-linking: HA-PNIPAM and acrylated CD are mixed in a molar ratio of 1:0.8-1:1.2, 0.1-0.3 wt% of a photoinitiator is added, and irradiated under the condition of a UV irradiation intensity of 10-15 mW / cm² for 2-4 min; S4. Urea inclusion and gel loading: A urea solution with a concentration of 35%-45% (w / v) is prepared, and at a temperature of 55-65 °C, stirred at a stirring rate of 200-300 rpm for 2-3 h to make cyclodextrin include urea; S5. Inner layer solution preparation: A sodium alginate solution with a concentration of 1.5%-2.5% (w / v) is prepared, a bacterial suspension with an OD600 of 5.0-7.0 is prepared, a bacterial strain is selected, and the viable bacteria count is ≥5×10 8 CFU / g, and the inner layer solution is passed through a microfluidic device, and the flow rate is controlled at 0.5-1.0 mL / min; S6, preparing the outer layer solution, dissolving chitosan in 1% acetic acid to prepare a solution with a concentration of 1.0% to 2.0% (w / v), adding 0.5% to 1.5% (w / v) nanohydroxyapatite with a particle size of 30 to 70 nm to the outer layer solution, and passing the outer layer solution through a microfluidic device with a flow rate controlled at 1.5 to 2.5 mL / min; S7, cross-linking and curing, prepare a concentration of 1.5 to 2.5M Solution, under the atomization pressure of 0.1~0.3MPa, the microcapsules are Solidify in solution for 10 to 20 minutes; S8, carrier surface activation, using low-temperature plasma with a power of 250-350W to treat the decomposed straw carrier for 80-100s; S9, electrostatic layer-by-layer self-assembly, adjusting the pH of the HA-PNIPAM solution to 3.5-4.5 to form a positive layer, and adjusting the pH of the straw carrier solution to 8.0-9.0 to form a negative layer; S10, low-temperature drying and molding, placing the material that has undergone electrostatic layer-by-layer self-assembly into a fluidized bed, drying it at a temperature of 40° C. to 50° C., and adding geniposide and nano-montmorillonite at the same time.

[0012] Preferably, during the preparation of the inner layer solution, the bacterial species selected is Bacillus subtilis.

[0013] Preferably, in the cross-linking and curing step, the particle size of the microcapsules is between 50 μm and 150 μm.

[0014] Preferably, in the carrier surface activation step, the carboxyl density on the carrier surface is made ≥7.5 μmol / m².

[0015] Preferably, in the low-temperature drying and molding step, the fluidized bed drying controls the final moisture content to be 10% to 12% (w / w).

[0016] The present invention provides an environmentally friendly organic slow-release fertilizer and a preparation method thereof, which has the following beneficial effects: 1. The present invention constructs an environment-responsive supramolecular slow-release system, utilizes supramolecular host-guest interaction and temperature-responsive polymers in coordination, and the fertilizer release rate can be dynamically regulated with the root temperature of the crop. During the peak period of crop fertilizer demand, such as tillering and booting, nitrogen can be accurately released, so that the matching degree between the nitrogen release curve and the crop demand is improved to more than 90%. Compared with the problem of uncontrolled nutrient release of traditional organic fertilizers, which easily causes excessive nutrient loss in the early stage and insufficient supply in the later stage, this fertilizer achieves a high degree of fit between nutrient release and crop demand, improves fertilizer utilization, and reduces fertilizer waste and environmental pollution.

[0017] 2. The present invention uses a microfluidic aerosol encapsulation technology to prepare microencapsulated microbial agents, with the viable count of Bacillus subtilis ≥ 5×10 8 CFU / g and the embedding rate ≥ 95%. The microcapsule structure provides a stable microenvironment for the survival of microorganisms, effectively resisting the influence of external adverse factors on the microbial activity. During the use of fertilizers, the microorganisms continuously play a role, participating in the transformation and decomposition of substances in the soil, promoting the release and absorption of nutrients by crops, enhancing soil fertility, and improving the soil microecological environment, which is a microbial synergistic function not possessed by ordinary fertilizers.

[0018] 3. The temperature of the entire preparation process of the present invention is ≤ 70°C, avoiding the inactivation of microorganisms and the pyrolysis of organic substances, and ensuring the activity and function of each component. At the same time, the degradation period of the supramolecular gel is synchronized with the crop growth period, which is 120 - 150 days, and there is no microplastic residue. It will not cause an additional burden on the environment during the production process, and will not leave harmful substances that are difficult to degrade in the soil after use, meeting the environmental protection requirements, achieving ecological friendliness throughout the entire process from production to use, and providing strong support for the sustainable development of agriculture. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flowchart of the preparation method in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0021] Please refer to the attached Figure 1 , the embodiments of the present invention provide an environmentally friendly organic slow-release fertilizer, including the following raw materials by mass percentage: 55% - 65% of decomposed straw carrier; 20% - 30% of slow-release carrier; 8% - 12% of microencapsulated microbial agent; 3% - 5% of cross-linking agent; 2% - 4% of auxiliary additive.

[0022] The porosity of the decomposed straw carrier is ≥ 65%, the carbon-nitrogen ratio is 25 - 28:1, the particle size is 0.5 - 1.5 mm, and the water holding capacity is ≥ 2.5 g / g.

[0023] The main body of the slow-release carrier is cyclodextrin, and the guest is N-isopropylacrylamide.

[0024] The crosslinking agent is geniposide, the crosslinking density is 0.8 - 1.2 mmol / g, and the gel storage modulus G'≥0.8 kPa.

[0025] The auxiliary additive is nano-montmorillonite, its specific surface area ≥200 m² / g, and the layer spacing is 1.2 - 1.5 nm.

[0026] In addition, the present invention also provides a preparation method of an environment-friendly organic slow-release fertilizer, comprising the following steps: S1. Copolymer synthesis: Mix humic acid (HA) and N-isopropylacrylamide (NIPAM) in a molar ratio of 1:10 - 1:15, use a deionized water / ethanol mixture (volume ratio 3:1) as the solvent, add 0.5 - 1.0 mol% of azobisisobutyramidine hydrochloride (AIBA) as the initiator, and react at a temperature of 60 - 70 °C for 6 - 8 h; S2. Cyclodextrin functionalization modification, make CD and hydroxyethyl acrylate are mixed in a molar ratio of 1:1.2 - 1:1.5, add 2 - 4 mol% of p-toluenesulfonic acid (PTSA) as the catalyst, and react at a temperature of 40 - 50 °C for 4 - 6 h; S3. Click chemistry crosslinking: Mix HA-PNIPAM and acrylated CD in a molar ratio of 1:0.8 - 1:1.2, add 0.1 - 0.3 wt% of photoinitiator, and irradiate under the condition of UV irradiation intensity of 10 - 15 mW / cm² for 2 - 4 min; S4. Urea inclusion and gel loading: Prepare a urea solution with a concentration of 35% - 45% (w / v), at a temperature of 55 - 65 °C, stir at a stirring rate of 200 - 300 rpm for 2 - 3 h, so that Cyclodextrin includes urea; S5. Inner layer solution preparation: Prepare a sodium alginate solution with a concentration of 1.5% - 2.5% (w / v), prepare a bacterial suspension with an OD600 of 5.0 - 7.0, select Bacillus subtilis, so that the viable cell count ≥5×10 8 CFU / g, pass the inner layer solution through a microfluidic device, and control the flow rate at 0.5 - 1.0 mL / min; S6. Outer layer solution preparation: Dissolve chitosan in 1% acetic acid to prepare a solution with a concentration of 1.0% - 2.0% (w / v), add 0.5% - 1.5% (w / v) of nano-hydroxyapatite with a particle size of 30 - 70 nm to the outer layer solution, pass the outer layer solution through a microfluidic device, and control the flow rate at 1.5 - 2.5 mL / min; S7. Crosslinking and curing: Prepare a solution with a concentration of 1.5 - 2.5 M of The solution is atomized at a pressure of 0.1 - 0.3 MPa to solidify the microcapsules in the solution for 10 - 20 min, and the particle size of the microcapsules is 50 μm - 150 μm; S8. Activation of the carrier surface: The decomposed straw carrier is treated with low-temperature plasma at a power of 250 - 350 W for 80 - 100 s to make the carboxyl density on the carrier surface ≥ 7.5 μmol / m²; S9. Electrostatic layer-by-layer self-assembly: The pH of the HA-PNIPAM solution is adjusted to 3.5 - 4.5 to form a positive layer, and the pH of the straw carrier solution is adjusted to 8.0 - 9.0 to form a negative layer; S10. Low-temperature drying and forming: The material after electrostatic layer-by-layer self-assembly is put into a fluidized bed and dried at a temperature of 40°C - 50°C. At the same time, geniposide and nano-montmorillonite are added, and the final moisture content of the fluidized bed drying is controlled at 10% - 12% (w / w).

[0027] Example: Example 1: Basic responsive formulation The formulation composition is as follows: Table 1: Preparation steps: Synthesis of supramolecular gel: HA-PNIPAM copolymer: The molar ratio of HA to NIPAM is 1:12, the AIBA initiator is 0.8 mol%, and polymerization is carried out at 65°C for 7 h. The product = 15 kDa; CD modification: The molar ratio of CD to 2-hydroxyethyl acrylate is 1:1.3, the PTSA catalyst is 3 mol%, and the reaction is carried out at 45°C for 5 h. The degree of substitution DS = 1.0; Click crosslinking: The molar ratio of HA-PNIPAM to acrylated CD is 1:1.0, irradiated with UV intensity of 12 mW / cm² for 3 min, and the crosslinking degree is 78%; Urea loading: 40% urea solution is included at 60°C for 2.5 h, and the nitrogen loading is 27%.

[0028] Microencapsulation of the microbial agent: Inner layer: 2% sodium alginate + microbial agent solution (OD600 = 6.0), flow rate 0.8 mL / min; Outer layer: 1.5% chitosan + 1.0% nano-hydroxyapatite, flow rate 2.0 mL / min; Crosslinking: 2.0 M Atomization deposition, solidification for 15 min, survival rate 96%.

[0029] Granulation process: Plasma activation: Treated at 300W for 90s, surface carboxyl density 8.0 μmol / m²; Electrostatic self-assembly: Alternately sprayed 5 times (pH4.0 gel particles + pH8.5 carrier), dried between layers at 40°C / 8min; Final drying: Dried in a fluidized bed at 45°C until the moisture content reached 11%.

[0030] Example 2: High bacteria-loading enhanced type The formulation composition is as follows: Table 2: Preparation steps: Enhanced gel: Added 2% nano-montmorillonite; Bacterial agent preparation: Inner layer flow rate 0.6 mL / min, outer layer flow rate 1.8 mL / min, Concentration 2.2M; Example 3: Quick-acting and slow-release dual-mode type The formulation composition is as follows: Table 3: Preparation steps: Quick-acting nitrogen loading: Adsorbed 2% amino acid chelated nitrogen into the pores of the straw carrier; Gel optimization: The molecular weight of HA-PNIPAM was increased to 18 kDa, and the LCST was adjusted to 36°C; Gel synthesis: NIPAM polymerized for 8h, and the product = 18 kDa; Degree of substitution of CD DS = 1.2, crosslinking degree 85%; Granulation process: Spraying cycle 6 times, drying temperature 42°C.

[0031] Comparative example: Comparative example 1 (corresponding to Example 1) Adjusted parameters: Crosslinking agent dosage: Reduced from 5% to 3%, and the total formulation ratio was adjusted to: decomposed straw 62% + gel 25% + bacterial agent 10% + crosslinking agent 3%.

[0032] Click crosslinking time: UV irradiation time shortened from 3min to 1.5min.

[0033] Comparative example 2 (corresponding to Example 2) Adjusted parameters: Microencapsulation process: The outer chitosan / nano-hydroxyapatite coating was cancelled, and only a single layer of sodium alginate embedding was used.

[0034] OD600 of the bacterial suspension: decreased from 6.0 to 3.0.

[0035] Comparative Example 3 (corresponding to Example 3) Adjusted parameters: Type of rapid-release nitrogen source: Replace amino acid chelated nitrogen with an equal amount of ordinary urea (2%).

[0036] LCST of the gel: adjusted from 36 °C to 30 °C.

[0037] Comparative experiment: Experiment 1: Effects of crosslinking agent dosage and crosslinking time on fertilizer performance Experimental setup: Experimental group: Adopt the formulation and preparation steps of Example 1.

[0038] Control group: Adopt the formulation and preparation steps of Comparative Example 1, that is, the crosslinking agent dosage is reduced from 5% to 3%, and the click crosslinking time is shortened from 3 min to 1.5 min.

[0039] Experimental method: Prepare fertilizer: Synthesize supramolecular gel according to the steps of Example 1: The molar ratio of HA to NIPAM is 1:12, the AIBA initiator is 0.8 mol%, and polymerization is carried out at 65 °C for 7 h to obtain the HA-PNIPAM copolymer; The molar ratio of CD to hydroxyethyl acrylate is 1:1.3, the PTSA catalyst is 3 mol%, and reaction is carried out at 45 °C for 5 h for CD modification; The molar ratio of HA-PNIPAM to acrylated CD is 1:1.0, and click crosslinking is completed by irradiating with a UV intensity of 12 mW / cm² for 3 min; 40% urea solution is included at 60 °C for 2.5 h for urea loading. At the same time, adjust the crosslinking agent dosage and crosslinking time according to Comparative Example 1 for the preparation of supramolecular gel; According to the parameters of Example 1 and Comparative Example 1, carry out the microencapsulation and granulation processes of the bacterial agent respectively. When microencapsulating the bacterial agent, the inner layer is 2% sodium alginate + bacterial solution (OD600 = 6.0), and the flow rate is 0.8 mL / min; the outer layer is 1.5% chitosan + 1.0% nano-hydroxyapatite, and the flow rate is 2.0 mL / min; crosslinking by 2.0M atomization deposition for 15 min for curing. In the granulation process, plasma activation is carried out at 300 W for 90 s, electrostatic self-assembly is alternately sprayed 5 times (pH4.0 gel particles + pH8.5 carrier), drying between layers at 40 °C / 8 min, and final drying in a fluidized bed at 45 °C until the moisture content is 11%.

[0040] Performance test: Nitrogen release rate test: Take two identical glass containers with lids, add equal amounts of the experimental group and control group fertilizers respectively, and then add equal amounts of the culture solution simulating the rhizosphere environment of crops. After sealing, place them in a constant temperature incubator at 35°C. Every 12 hours, use a pipette to suck 10 mL of the culture solution, and use the Kjeldahl method to determine the nitrogen content in it. After the determination, pour the culture solution back into the container and continue the culture.

[0041] Gel performance test: Use a rheometer to measure the storage modulus G' of the supramolecular gel in the two groups of fertilizers, record and compare the values at 25°C.

[0042] Microbial activity test: Weigh 1 g of the experimental group and control group fertilizers respectively, add 9 mL of sterile water, shake evenly, and then perform gradient dilution. Take the appropriate dilution of the bacterial solution and spread it on the beef extract peptone plate. After culturing at 37°C for 24 hours, use the plate counting method to determine the viable count of Bacillus subtilis.

[0043] Experimental data: Table 4: Experimental summary: From the perspective of nitrogen release rate, in the control group, due to the reduction in the amount of cross-linking agent and the shortening of the cross-linking time, the supramolecular gel structure is relatively unstable, and the nitrogen release rate is faster than that of the experimental group. The cross-linking agent plays a key role in click chemistry cross-linking. The reduction in the amount and the shortening of the cross-linking time lead to a decrease in the degree of cross-linking, the gel network structure is not tight enough, and urea is more likely to diffuse out of the gel, so the nitrogen release amount is higher. In terms of gel performance, the higher amount of cross-linking agent and the longer cross-linking time in the experimental group make the gel form a denser network structure, with a larger storage modulus G', showing better mechanical properties. The gel structure of the control group is loose and the storage modulus is lower. For microbial activity, the viable count in the control group is slightly lower than that in the experimental group because the changes in the cross-linking process affect the microenvironment of the microencapsulated microbial agent, which has a certain negative impact on the survival of Bacillus subtilis, but the overall impact is relatively small.

[0044] Comparative experiment 2: Effects of microencapsulation process and bacterial suspension concentration on fertilizer performance Experimental setup: Experimental group: Use the formula and preparation steps of Example 2.

[0045] Control group: Use the formula and preparation steps of Comparative Example 2, that is, cancel the outer chitosan / nano-hydroxyapatite coating, only use sodium alginate monolayer embedding, and reduce the OD600 of the bacterial suspension from 6.0 to 3.0.

[0046] Experimental method: Preparation of fertilizer: According to the formulations of Example 2 and Comparative Example 2, prepare the decomposed straw carrier, CD / HA-PNIPAM supramolecular gel raw materials, microencapsulated microbial agent raw materials (sodium alginate, chitosan, nano-hydroxyapatite, Bacillus subtilis bacterial solution), crosslinking agent and other auxiliary materials. Prepare the supramolecular gel synthesis device, microfluidic device, crosslinking and curing device, nitrogen content detector, scanning electron microscope (SEM), swelling experiment device, and related equipment for microbial culture and detection.

[0047] Preparation of supramolecular gel: According to the requirements of Example 2 and Comparative Example 2, conduct the synthesis of HA-PNIPAM copolymer, cyclodextrin functionalization modification, click chemistry crosslinking, and urea inclusion and gel loading operations, where 2% nano-montmorillonite is added in Example 2 to enhance the gel performance.

[0048] Microencapsulation of microbial agent: The inner layer flow rate in Example 2 is 0.6 mL / min, and the outer layer flow rate is 1.8 mL / min; in Comparative Example 2, the outer layer chitosan / nano-hydroxyapatite coating is removed, and only a single layer of sodium alginate is used for embedding. The OD600 of the bacterial suspension drops from 6.0 to 3.0, and the microencapsulation operation is completed according to the respective parameters.

[0049] Granulation process: Complete granulation according to the steps of Example 2 to ensure that the parameters of each link are accurate.

[0050] Performance testing: Testing of nitrogen release rate: Take two culture bottles of the same specification, respectively put equal amounts of the fertilizers of Example 2 and Comparative Example 2, add an equal amount of simulated soil solution, seal and place them in a constant temperature shaker at 30 °C, and oscillate at a speed of 150 rpm. Every 24 hours, take 10 mL of the solution, measure the nitrogen content by spectrophotometry, and pour the solution back for continued culture after measurement.

[0051] Testing of microcapsule performance: Take out the microencapsulated microbial agent from the two groups of fertilizers, observe the morphological structure of the microcapsules by SEM, measure and count the particle size distribution. Take appropriate amounts of microcapsules and put them into the simulated soil solution respectively, take them out at the set time points (such as 0.5 h, 1 h, 2 h, 4 h, 8 h), dry the surface moisture with filter paper and weigh them, and calculate the swelling ratio.

[0052] Testing of microbial activity: Weigh 1.5 g of the fertilizers of Example 2 and Comparative Example 2 respectively, add 13.5 mL of sterile water, shake and mix evenly, and then dilute them step by step. Take an appropriate dilution of the bacterial solution and spread it on the specific culture medium plate, culture it at 30 °C for 36 hours, and measure the viable bacteria count by plate counting method. At the same time, take a certain amount of the bacterial solution and inoculate it into the culture solution containing a specific substrate, and measure the substrate decomposition rate to evaluate the microbial metabolic activity.

[0053] Experimental data: Table 5: Summary of the experiment: From the perspective of nitrogen release, in Comparative Example 2, due to the change in the microencapsulation process and the decrease in the concentration of the bacterial suspension, the nitrogen release rate is faster than that in Example 2. After removing the outer coating, the encapsulation and slow-release effects of the microcapsules on the nitrogen in the fertilizer are weakened, making it easier for nitrogen to dissolve. The decrease in the concentration of the bacterial suspension also affects the transformation and regulation of substances in the fertilizer by microorganisms, indirectly affecting nitrogen release. In terms of the performance of the microcapsules, the average particle size of the microcapsules in Example 2 is larger, and the swelling ratio is also higher. This is because the double-layer embedding structure and appropriate process parameters enable the microcapsules to better absorb water and swell, and the structure is more stable. In contrast, the single-layer embedding structure in Comparative Example 2 is simple, and its swelling and water retention capabilities are poor. In terms of microbial activity, the viable count and substrate decomposition rate in Example 2 are both higher. The double-layer embedding and higher concentration of the bacterial suspension provide a better living environment and activity guarantee for microorganisms. The changes in Comparative Example 2 disrupt the microenvironment for the survival of microorganisms, resulting in a decrease in activity.

[0054] Comparative Experiment 3: Effects of Quick-Release Nitrogen Source Type and Gel LCST on Fertilizer Performance Experimental Setup: Experimental Group: The formulation and preparation steps of Example 3 are adopted.

[0055] Control Group: The formulation and preparation steps of Comparative Example 3 are adopted, that is, the amino acid chelated nitrogen is replaced with an equal amount of ordinary urea, and the gel LCST is adjusted from 36 °C to 30 °C.

[0056] Experimental Method: Preparation of Fertilizer: According to the formulations of Example 3 and Comparative Example 3, prepare the decomposed straw carrier, CD / HA-PNIPAM supramolecular gel raw materials, microencapsulated microbial agent raw materials, cross-linking agent, nano-montmorillonite, amino acid chelated nitrogen, and ordinary urea materials. Prepare a polymerization reaction device, UV irradiation equipment, microfluidic equipment, nitrogen content detector, temperature control box, crop planting pots, and related growth monitoring equipment.

[0057] Preparation of Supramolecular Gel: In Example 3, the molar ratio of HA to NIPAM is adjusted as required, and the dosage of the AIBA initiator is precisely controlled to polymerize NIPAM for 8 h to obtain HA-PNIPAM with a molecular weight of 18 kDa; CD reacts with hydroxyethyl acrylate in a specific ratio, controlling the dosage of PTSA catalyst to make the degree of substitution DS of CD reach 1.2; HA-PNIPAM and acrylated CD are mixed in a ratio, an appropriate amount of photoinitiator is added, and irradiated under a set UV intensity to make the crosslinking degree reach 85%; 40% urea solution is subjected to urea loading at a specified temperature and time. In Comparative Example 3, except that the rapid-release nitrogen source is replaced with ordinary urea, the gel LCST is also adjusted to 30 °C, and the remaining steps are similar to those in Example 3, but during the preparation of the supramolecular gel, the change of LCST is achieved by adjusting the relevant reaction conditions.

[0058] Microencapsulation and granulation of the microbial agent: According to the established parameters of Example 3 and Comparative Example 3, the microencapsulation and granulation processes of the microbial agent are completed. In Example 3, 2% amino acid chelated nitrogen is adsorbed in the pores of the straw carrier, while in Comparative Example 3, an equal amount of ordinary urea is used instead.

[0059] Performance testing: Testing of nitrogen release rate: Take two identical plastic containers with air holes, respectively fill them with equal amounts of the fertilizers of Example 3 and Comparative Example 3, add an equal amount of simulated rhizosphere soil solution, seal them and place them in a constant temperature incubator at 35 °C. Every 12 hours, accurately pipette 5 mL of the solution, and use spectrophotometry to measure the nitrogen content in the solution. After measurement, carefully pour the solution back into the container and continue the cultivation.

[0060] Testing of temperature-responsive performance: Place the two groups of fertilizers in different temperature control boxes at 25 °C, 30 °C, 35 °C, and 40 °C respectively. According to the above nitrogen release rate testing method, regularly measure the nitrogen release amount at different temperatures and analyze the influence of temperature on the nitrogen release rate.

[0061] Crop growth experiment: Select the same kind of crop seedlings (such as tomato seedlings) with consistent growth conditions and similar sizes, prepare multiple planting pots of the same specification, and fill them with equal amounts of the same soil. Apply the fertilizers of Example 3 and Comparative Example 3 to different planting pots according to the same fertilization amount, and set multiple replicates for each group. Place the planting pots in a greenhouse with consistent environmental conditions of light intensity, temperature, and humidity, water regularly, and keep the soil humidity appropriate. Measure the plant height and number of leaves of the crops once a week, and measure the dry weight of the crops at the end of the experiment.

[0062] Experimental data: Table 6: Experimental summary: In terms of the nitrogen release rate, in the early stage of Example 3, due to the characteristics of amino acid chelated nitrogen, the release is relatively fast, which can provide nutrients for crops in a timely manner. In Comparative Example 3, ordinary urea is used, and the release rate in the early stage is not as good as that in Example 3. As time goes by, the supramolecular gel in Example 3 can effectively regulate nitrogen release according to temperature under the appropriate LCST. When the temperature is high, the release accelerates to meet the crop requirements. After the LCST of the gel in Comparative Example 3 changes, the response to temperature is inaccurate, and the matching degree between nitrogen release and crop requirements is poor.

[0063] In terms of the temperature response performance, the LCST of the gel in Example 3 is 36 °C, which is close to the suitable temperature of the crop rhizosphere. When the temperature rises to 35 °C and above, the gel structure changes, and the nitrogen release rate increases significantly. The LCST of Comparative Example 3 is 30 °C, and more nitrogen is released at a lower temperature. When it comes to the high-temperature stage when crops really need a large amount of nutrients, the release ability is insufficient and cannot well meet the growth of crops.

[0064] From the results of the crop growth experiment, it can be seen that the fertilizer in Example 3 makes the plant height, number of leaves and dry weight of the crops better than those in Comparative Example 3. This is because the fertilizer in Example 3 can supply nitrogen quickly in the early stage and dynamically regulate the release with temperature during the critical growth period of the crops, providing a continuous and appropriate nutrient supply for the crops. In Comparative Example 3, due to the unreasonable nitrogen release, the normal growth and development of the crops are affected.

[0065] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Environmentally friendly organic slow-release fertilizer, characterized in that: The following raw materials are included in percentage by mass: 55% to 65% of the decomposed straw carrier; 20% to 30% sustained-release carrier; 8% to 12% microencapsulated bacterial agent; 3% to 5% cross-linking agent; 2% to 4% auxiliary additives.

2. The environmentally friendly organic slow-release fertilizer according to claim 1, characterized in that: The porosity of the decomposed straw carrier is ≥65%, the carbon-nitrogen ratio is 25-28:1, the particle size is 0.5-1.5 mm, and the water holding capacity is ≥2.5 g / g.

3. The environmentally friendly organic slow-release fertilizer according to claim 1, characterized in that: The sustained-release carrier body is Cyclodextrin, the guest is N-isopropylacrylamide.

4. The environmentally friendly organic slow-release fertilizer according to claim 1, characterized in that: The cross-linking agent is geniposide, the cross-linking density is 0.8-1.2 mmol / g, and the gel storage modulus G' is greater than or equal to 0.8 kPa.

5. The environmentally friendly organic slow-release fertilizer according to claim 1, characterized in that: The auxiliary additive is nano-montmorillonite, with a specific surface area of ​​≥200m² / g and an interlayer spacing of 1.2 to 1.5nm.

6. A method for preparing an environmentally friendly organic slow-release fertilizer, characterized in that: The environmentally friendly organic slow-release fertilizer applied to claims 1-5 comprises the following steps: S1. Synthesis of copolymer: humic acid (HA) and N-isopropylacrylamide (NIPAM) were mixed at a molar ratio of 1:10 to 1:15, deionized water / ethanol mixed solution (volume ratio 3:1) was used as solvent, 0.5 to 1.0 mol% of azobisisobutylamidine hydrochloride (AIBA) was added as an initiator, and the mixture was reacted at a temperature of 60 to 70°C for 6 to 8 hours; S2, Functional modification of cyclodextrin CD and hydroxyethyl acrylate are mixed in a molar ratio of 1:1.2 to 1:1.5, 2 to 4 mol% of p-toluenesulfonic acid (PTSA) is added as a catalyst, and the mixture is reacted at a temperature of 40 to 50°C for 4 to 6 hours; S3. Click chemical cross-linking to connect HA-PNIPAM with acryloyl CD is mixed in a molar ratio of 1:0.8 to 1:1.2, a photoinitiator is added in an amount of 0.1 to 0.3 wt%, and irradiated for 2 to 4 minutes under the condition of UV irradiation intensity of 10 to 15 mW / cm²; S4, urea inclusion and gel loading, prepare a urea solution with a concentration of 35% to 45% (w / v), stir at a temperature of 55 to 65°C and a stirring rate of 200 to 300 rpm for 2 to 3 hours. Cyclodextrin inclusion urea; S5. Preparation of inner layer solution: prepare sodium alginate solution with a concentration of 1.5% to 2.5% (w / v), prepare bacterial suspension with OD600 of 5.0 to 7.0, select bacterial species, and make the number of viable bacteria ≥ 5×10 8 CFU / g, the inner layer solution was passed through the microfluidic device with the flow rate controlled at 0.5-1.0 mL / min; S6, preparing the outer layer solution, dissolving chitosan in 1% acetic acid to prepare a solution with a concentration of 1.0% to 2.0% (w / v), adding 0.5% to 1.5% (w / v) nanohydroxyapatite with a particle size of 30 to 70 nm to the outer layer solution, and passing the outer layer solution through a microfluidic device with a flow rate controlled at 1.5 to 2.5 mL / min; S7, cross-linking and curing, prepare a concentration of 1.5 to 2.5M Solution, under the atomization pressure of 0.1~0.3MPa, the microcapsules are Solidify in solution for 10 to 20 minutes; S8, carrier surface activation, using low-temperature plasma with a power of 250-350W to treat the decomposed straw carrier for 80-100s; S9, electrostatic layer-by-layer self-assembly, adjusting the pH of the HA-PNIPAM solution to 3.5-4.5 to form a positive layer, and adjusting the pH of the straw carrier solution to 8.0-9.0 to form a negative layer; S10, low-temperature drying and molding, placing the material that has undergone electrostatic layer-by-layer self-assembly into a fluidized bed, drying it at a temperature of 40° C. to 50° C., and adding geniposide and nano-montmorillonite at the same time.

7. The method for preparing the environmentally friendly organic slow-release fertilizer according to claim 6, characterized in that: During the preparation of the inner layer solution, the bacterial species is selected to be Bacillus subtilis.

8. The method for preparing the environmentally friendly organic slow-release fertilizer according to claim 6, characterized in that: In the cross-linking and curing step, the particle size of the microcapsules is between 50 μm and 150 μm.

9. The method for preparing the environmentally friendly organic slow-release fertilizer according to claim 6, characterized in that: In the carrier surface activation step, the carboxyl density on the carrier surface is made ≥7.5 μmol / m².

10. The method for preparing the environmentally friendly organic slow-release fertilizer according to claim 6, characterized in that: In the low-temperature drying and forming step, the fluidized bed drying controls the final moisture content to 10% to 12% (w / w).

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