Preparation method of slow-release fertilizer based on silkworm excrement carrier simultaneously loading urea and urease inhibitor

Abstract

The invention discloses a preparation method of a slow-release fertilizer based on a silkworm excrement carrier simultaneously loaded with urea and a urease inhibitor. The method comprises the following steps: firstly, by taking silkworm excrement as a raw material, adding phanerochaete chrysosporium, aspergillus niger and bacillus subtilis complex microbial inoculants for fermentation; and fermenting at 30-35 DEG C for 3-4 days. After fermentation is finished, weighing the crushed fermented silkworm excrement, urea and a urease inhibitor according to the mass ratio of (6-7): 1: 0.08, adding water, and stirring and mixing, so that the urea and the urease inhibitor are fully loaded into a pore structure of the silkworm excrement; and drying and granulating to obtain the silkworm excrement-based slow-release fertilizer. And the loaded fertilizer realizes slow release of nitrogen by virtue of the synergistic effect of a silkworm excrement hydrogen bond polymerization structure and the urease inhibitor, has a remarkable effect on crops with long growth cycle and high nitrogen demand, and has both environmental protection and economic benefits.

Description

Technical Field

[0001] The invention belongs to the field of fertilizer preparation, and particularly relates to a method for preparing a slow-release fertilizer based on a silkworm excrement carrier that simultaneously loads urea and a urease inhibitor. Background Art

[0002] In global agricultural production, fertilizers play a critical role in achieving high crop yields. However, the overuse of traditional fertilizers, especially chemical fertilizers, has caused numerous problems. For one thing, chemical fertilizers release nutrients rapidly, preventing crops from fully absorbing them in time, leading to significant nutrient loss. According to statistics, the average utilization rate of nitrogen fertilizers in my country is only 30%-35%, phosphate fertilizers 10%-25%, and potash fertilizers 35%-50%. This nutrient loss not only wastes resources but also creates serious environmental problems, such as eutrophication of water bodies and soil acidification and compaction, disrupting ecological balance and threatening sustainable agricultural development. Furthermore, frequent fertilization increases labor and material costs, placing a financial burden on farmers. Therefore, the development of efficient, environmentally friendly, and economical slow-release fertilizers is urgent.

[0003] Guangxi, a major province in my country's sericulture industry, produces a huge amount of silkworm feces. Rich in nutrients essential for plant growth, such as nitrogen, phosphorus, and potassium, as well as organic matter and bioactive substances, silkworm feces are theoretically a high-quality fertilizer raw material. However, the processing and utilization of silkworm feces have long been plagued by numerous problems. Most silkworm feces are carelessly discarded or simply landfilled or composted, resulting in not only a waste of resources but also soil and water pollution due to the odor and leachate produced by fermentation. Furthermore, silkworm feces contain a certain proportion of lignin, cellulose, and hemicellulose. These components limit the release of nutrients from silkworm feces and their ability to adsorb other fertilizer components, hindering their efficient application in the fertilizer sector.

[0004] To address the challenges of silkworm feces utilization, it can be modified through biodegradation technology. During the silkworm feces pretreatment process, simple physical crushing is first performed to increase its specific surface area and improve the efficiency of subsequent reactions. White-rot fungi or other compound preparations are then added during the fermentation process. White-rot fungi, for example, secrete a series of extracellular enzymes, such as lignin peroxidase, manganese peroxidase, and laccase, which specifically degrade lignin. At the same time, the cellulase system secreted by white-rot fungi, including endoglucanases, exoglucanases, and β-glucosidases, synergistically decomposes cellulose and hemicellulose. Through biodegradation, the internal structure of silkworm feces is reshaped, creating more pores and active sites, significantly enhancing its adsorption capacity and creating favorable conditions for the subsequent loading of fertilizers and other functional ingredients. Compared to chemical treatment methods, biodegradation is more environmentally friendly, has mild reaction conditions, and is relatively low-cost, in line with the concept of green agricultural development.

[0005] In the fertilizer system, urea is a widely used nitrogen fertilizer, but after urea is applied to the soil, it will be rapidly hydrolyzed into ammonia and carbon dioxide by urease in the soil, resulting in serious ammonia volatilization losses, reducing the utilization rate of nitrogen fertilizers and polluting the environment. The addition of urease inhibitors can effectively solve this problem. It can bind to the urease active center, inhibit urease activity, slow down the hydrolysis rate of urea, and enable nitrogen to be supplied to crops more sustainably and stably. Combining urease inhibitors with biodegradable silkworm feces to prepare a slow-release fertilizer that couples biodegradation and enzyme inhibition can give full play to the advantages of both, achieve accurate and long-term release of fertilizer nutrients, improve fertilizer utilization, reduce the number of fertilizations, reduce agricultural production costs, and promote green and efficient development of agriculture. This is also an important starting point and goal of the research and development of this technical solution. Summary of the Invention

[0006] The present invention relates to a method for preparing a slow-release fertilizer based on a silkworm excrement carrier that simultaneously loads urea and a urease inhibitor. This method solves the problems of existing fertilizers, such as rapid nutrient release, low utilization rate, and difficulty in handling silkworm excrement waste. The slow-release fertilizer combines two technologies: biodegradation and enzyme inhibition. The biodegradation process turns silkworm excrement into an efficient fertilizer carrier that slowly releases adsorbed fertilizer nutrients, prolongs the fertilizer's effective period, and reduces nutrient loss. The urease inhibitor inhibits the activity of urease in the soil, slows the hydrolysis of urea to ammonia, reduces ammonia volatilization losses, and improves nitrogen fertilizer utilization. The two act synergistically to match fertilizer nutrient release with crop growth requirements, improve crop nutrient absorption efficiency, and simultaneously achieve resource utilization of silkworm excrement waste, reduce environmental pollution, and have significant economic and environmental benefits. The present invention uses physical crushing to reduce the silkworm excrement particle size, thereby effectively increasing its surface area. By precisely controlling the ratio of the composite bacterial agent and creating a suitable fermentation environment, the enzymes are encouraged to fully function during the fermentation process, degrading the lignin, cellulose, and hemicellulose in the silkworm excrement. During this process, the internal structure of the silkworm excrement is reshaped, creating abundant pores and significantly enhancing its adsorption capacity. After fermentation, the ratio of urea to urease inhibitor is precisely controlled, and the fermented silkworm excrement is placed in a saturated solution of urea and urease inhibitor. The silkworm excrement's swelling properties allow it to fully absorb the urea and urease inhibitor in the solution. Subsequently, through filtration and low-temperature drying, the urea and urease inhibitor are firmly attached to the silkworm excrement.

[0007] The technology of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a slow-release fertilizer based on a silkworm excrement carrier simultaneously loaded with urea and a urease inhibitor comprises the following steps:

[0009] (1) Silkworm excrement collection and pretreatment

[0010] Collect fresh silkworm excrement and spread it flat on the cement floor, removing visible impurities such as mulberry branch and leaf fragments, pebbles, etc. Dry the cleaned silkworm excrement in the sun or air to reduce the moisture content to 15%-20%;

[0011] (4) Quicklime covering and disinfection

[0012] Lay a layer of plastic film on the silkworm excrement accumulation site, evenly spread the air-dried silkworm excrement on the film to a thickness of 20-30 cm; use 2-3 kg of quicklime per cubic meter of silkworm excrement, evenly sprinkle the quicklime on the surface of the silkworm excrement, then cover it tightly with plastic film, compacting it on all sides to seal it; maintain the sealed state for 3-5 days, using the quicklime to release heat when it comes into contact with water and the strong alkaline calcium hydroxide environment it generates to effectively kill harmful microorganisms, insect eggs, and weed seeds in the silkworm excrement;

[0013] (5) Bacteria activation

[0014] The solid inoculum of Phanerochaete chrysosporium was inoculated into a culture dish containing potato dextrose agar medium, and cultured in a constant temperature incubator at 28°C-30°C for 3-5 days. After the colonies grew and had good morphology, some mycelium was picked and transferred to a new potato dextrose agar liquid medium, and cultured in a shaker at a speed of 150-180 r / min and 28°C for 2-3 days to fully activate the strain and prepare for subsequent fermentation.

[0015] Take the freeze-dried powder or slant culture of Bacillus subtilis and inoculate it into nutrient broth medium. Incubate it in a constant temperature shaker at 35℃ and 180 rpm for 18-24 hours. Activation is complete when the bacterial solution becomes turbid and a large number of cells grow.

[0016] Inoculate Aspergillus niger spores onto a potato dextrose agar medium plate, place in a 30°C constant temperature incubator and culture for 3-5 days. When the plate is covered with black spores, pick out the spores and inoculate them into a potato dextrose liquid medium. Incubate in a 30°C constant temperature shaker at 150 rpm for 2-3 days until the bacterial solution becomes turbid and mycelium grows, indicating that activation is complete.

[0017] (7) Preparation of compound bacterial agents

[0018] The activated Phanerochaete chrysosporium liquid, Bacillus subtilis liquid, and Aspergillus niger liquid were mixed in a volume ratio of 5:3:2; during the mixing process, the mixture was slowly added dropwise with continuous stirring; a magnetic stirrer was used with a stirring speed of 80-100 r / min and a stirring time of 30-45 minutes to ensure that the bacterial agent and the enzyme preparation were evenly mixed; the mixed composite bacterial agent should be stored at a low temperature of 4°C-8°C and used within 24 hours to maintain its activity;

[0019] (8) Inoculation and fermentation treatment

[0020] Sprinkle the prepared composite bacterial agent evenly on the surface of the above-mentioned mixed materials, and then use a mixer to fully stir; transfer the inoculated materials to the fermentation tank and pile them into a pile with a height of 1-1.2m; insert a thermometer in the pile to closely monitor temperature changes; in the early stage of fermentation, the temperature of the pile will gradually rise. When the temperature reaches 35°C, turn the pile for the first time to ensure uniform ventilation of the material; after that, control the fermentation temperature between 30°C and 35°C, turn the pile once every 24 hours, and continue fermentation for 3-4 days; regularly check the pH value and microbial count.

[0021] (9) Crushing and loading processing

[0022] After the fermentation is completed, the fermented silkworm excrement is crushed into a particle size of 2-5 mm using a crusher; the crushed fermented silkworm excrement, urea and urease inhibitor are weighed according to a mass ratio of 6-7:1:0.08; the urea and urease inhibitor are first added to an appropriate amount of water, stirred and dissolved at 40°C-50°C to prepare a mixed solution, and the amount of water used is based on the ability to completely dissolve the urea and urease inhibitor and subsequently evenly soak the silkworm excrement; the crushed fermented silkworm excrement is slowly added to the above mixed solution, and a stirring device is turned on at the same time, and stirred at a speed of 100-150 r / min for 30-45 minutes to ensure that the urea and urease inhibitor are fully loaded into the pore structure of the silkworm excrement; after completing the auxiliary loading, the material is dried and granulated to obtain the silkworm excrement-based slow-release fertilizer.

[0023] Furthermore, the nutrient broth culture medium in step (3) is 10 g of peptone, 3 g of beef extract, 5 g of sodium chloride, and 1000 mL of distilled water, with a pH of 7.2-7.4.

[0024] Furthermore, the total inoculation amount of the composite bacterial agent in step (5) is 10% of the dry weight of silkworm excrement.

[0025] Furthermore, in step (6), 40% urea solution is prepared by dissolving 400 g urea in 600 mL deionized water and stirring until completely dissolved, and then adding 2% of the mass of urea water-retaining agent PAAS and stirring in a 60° C. water bath for 30 min to form a homogeneous solution.

[0026] Furthermore, during the fermentation process, the compost is mechanically turned once every 24 hours to ensure that the oxygen concentration is greater than 15%, and the moisture content is regulated to 60% by spraying with sterile water.

[0027] Furthermore, samples were taken daily during the fermentation process to ensure that the pH fluctuation range was between 5.0 and 6.0.

[0028] In the laboratory, the present invention can first place the loaded material on a tray, uniformly control the thickness of the material to 1-2 cm, and then place it in an ordinary oven and set the temperature to 40°C-50°C to achieve the drying process. Since ordinary ovens rely on hot air convection heating, the temperature rises relatively slowly, and the drying process takes a long time, generally 8-12 hours, until the moisture content of the material is reduced to below 5%. After drying, the material forms a loose block or powdery semi-finished product. If further shaping is required, a granulator can be used to granulate at a pressure of 3-5MPa to produce a slow-release fertilizer product of a specific shape (such as cylindrical or spherical).

[0029] The slow-release fertilizer obtained by the preparation method of the present invention is used in the slow-release of fertilizers for crops during their growth cycle.

[0030] Phanerochaete chrysosporium is a typical white rot fungus with strong degradation ability and can adapt to the fermentation requirements of silkworm feces. Therefore, the present invention selects Phanerochaete chrysosporium for the fermentation process.

[0031] Lignin peroxidases and laccases secreted by white-rot fungi specifically attack the carbon-carbon and ether bonds within lignin, gradually degrading its complex structure. Cellulases secreted by Aspergillus niger during fermentation act on the β-1,4-glycosidic bonds of cellulose, breaking it down into smaller molecules such as glucose. Hemicellulases, on the other hand, break down the side and main chains of hemicellulose. These degradation processes disrupt the tightly bound hydrogen-bonded structure of lignin, cellulose, and hemicellulose within the silkworm excrement, allowing the previously tightly entangled macromolecular segments to unfold. Bacillus subtilis, a Gram-positive bacterium, produces amylases that break down starch in the excrement into sugars, and proteases that break down proteins into amino acids, providing nutritional support for the overall fermentation process. Furthermore, organic acids (such as oxalic acid and citric acid) produced by microbial metabolism during fermentation, in the slightly acidic environment, promote the formation of new hydrogen bonds within the excrement, enabling internal polymerization of hydrogen bonds and creating a loose, porous structure, significantly increasing the carrier's loading capacity. The loaded fertilizer achieves slow release of nitrogen through the synergistic effect of the hydrogen bond polymerization structure of silkworm feces and urease inhibitors, which is effective for crops with long growth cycles and high nitrogen requirements, and has both environmental and economic benefits.

[0032] The principle behind this invention is to produce a highly efficient, environmentally friendly, and optimized silkworm feces-based slow-release fertilizer suitable for sugarcane cultivation. The key to this invention lies in a multi-step process that taps into the potential value of silkworm feces and optimizes their performance. The key to silkworm feces processing lies in the fermentation step, which involves the addition of a complex microbial agent, such as white-rot fungi. These fungi secrete enzymes like lignin peroxidase and manganese peroxidase, which specifically attack the complex structure of lignin, breaking it down into small molecules and breaking down the lignin's encapsulation of cellulose and hemicellulose. Simultaneously, other microorganisms in the complex microbial agent secrete cellulases and hemicellulases, which hydrolyze cellulose and hemicellulose into monosaccharides such as glucose and xylose, respectively. The synergistic action of these microorganisms reshapes the internal structure of silkworm feces, creating abundant pores and significantly enhancing their adsorption properties, making them an ideal fertilizer carrier. Nitrogen fertilizer is a key nutrient for sugarcane cultivation, and urea is a commonly used nitrogen fertilizer. However, urea is rapidly hydrolyzed by soil urease, leading to significant ammonia volatilization losses, reducing fertilizer utilization and polluting the environment. The present invention utilizes the swelling properties of fermented silkworm excrement by carefully formulating a urease inhibitor and a urea solution, uniformly loading the two onto the excrement. The urease inhibitor binds to the urease active center, effectively inhibiting urease activity and slowing the hydrolysis of urea, resulting in a more sustained and stable nitrogen release. When the silkworm excrement-based slow-release fertilizer loaded with urea and a urease inhibitor is applied to sugarcane cultivation, the organic nutrients retained in the silkworm excrement after fermentation and the adsorbed urea are gradually released, providing balanced nutrition for sugarcane at all growth stages. Furthermore, the urease inhibitor plays a role in reducing nitrogen loss, ensuring efficient nutrient utilization in the fertilizer, promoting the healthy growth of sugarcane, and improving sugarcane yield and quality. This also enables resource utilization of silkworm excrement waste, reduces environmental pollution, and promotes sustainable agricultural development.

[0033] Compared with the prior art, the advantages of the present invention are:

[0034] 1. Improved slow-release fertilizer performance: Existing sugarcane fertilizers have difficulty in releasing nutrients in a manner that matches sugarcane growth. This invention utilizes a composite bacterial agent to ferment silkworm excrement, optimizing its structure. After loading it with urease inhibitors and urea, the silkworm excrement slows down urea release through pore adsorption, while the urease inhibitor controls hydrolysis, prolonging fertilizer effectiveness and stabilizing nitrogen supply, surpassing traditional fertilizer release methods.

[0035] 2. Realize waste resource utilization: In traditional agriculture, silkworm feces are often discarded and pollute the environment. This invention physically crushes and ferments them, degrading the complex components to produce a high-value-added fertilizer carrier, alleviating environmental pressure and reducing costs. Compared with fertilizers made from new raw materials, it is environmentally friendly and economical.

[0036] 3. Enhanced soil eco-friendliness: Traditional fertilizers can easily cause soil compaction and acidification. The silkworm excrement-based slow-release fertilizer of this invention contains humus to improve soil structure, beneficial microorganisms produced by fermentation to regulate the soil community, and urease inhibitors to reduce ammonia volatilization, improving the overall soil ecology and outperforming existing fertilizers that have negative impacts. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The invention relates to silkworm feces-based slow-release fertilizer granules prepared by extrusion in the embodiment 1.

[0038] Figure 2 Infrared spectra of silkworm excrement before and after fermentation in Example 1.

[0039] Figure 3 This is the infrared spectrum of urea loaded after fermentation of silkworm excrement in Example 1.

[0040] Figure 4 Scanning electron micrographs of fermented silkworm excrement and urea adsorbed and immobilized on it; (a) SEM image of fermented silkworm excrement; (b) Urea adsorbed and immobilized on the interior and surface of silkworm excrement; DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments, but the scope of protection claimed by the present invention is not limited to the scope of protection of the embodiments.

[0042] Example 1

[0043] Silkworm excrement collection and pretreatment

[0044] Fresh silkworm excrement is collected from local sericulture farms and spread on a clean cement floor with a thickness of about 5 cm to remove impurities. It is then exposed to sunlight for 3 days for preliminary sterilization and drying to reduce the moisture content of the silkworm excrement to about 15%.

[0045] Quicklime covering disinfection

[0046] On a site covered with alkali-resistant and puncture-resistant film, the exposed silkworm feces are spread to a thickness of 20-30 cm, and lumps of quicklime are sprinkled at 2-3 kg per cubic meter. The film is sealed for 3-5 days for sterilization, and then the disinfection effect is tested by microbial culture.

[0047] Preparation of compound microbial agents

[0048] Purified strains of Phanerochaete chrysosporium solid inoculum, Aspergillus niger (a cellulolytic bacterium), and Bacillus subtilis were purchased and activated on PDA medium (for the Phanerochaete chrysosporium solid inoculum and Aspergillus niger) and beef extract peptone medium (for Bacillus subtilis). The activated strains were then mixed in a volume ratio of 5:3:2 for white rot fungus:Bacillus subtilis:Aspergillus niger to create a composite inoculum.

[0049] Silkworm feces fermentation

[0050] Place 10 kg of pre-treated and disinfected silkworm excrement into a large plastic bucket. Add 5 liters of sterile water and stir thoroughly. Add 500 ml of a compound bacterial inoculant and stir again to ensure full contact between the inoculant and the excrement. Seal the bucket with plastic film and poke a few small holes in the bucket for ventilation. Place the bucket in a constant temperature incubation room at 28°C for 10 days to ferment. Remove the film and stir every three days to ensure even fermentation.

[0051] Preparation of urea and urease inhibitor solution

[0052] Weigh 5 kg of urea and 50 g of N-butylthiophosphoric triamide (NBPT, urease inhibitor), put them into a large plastic container, add 20 liters of deionized water, and stir with a stirrer until they are completely dissolved.

[0053] Load process

[0054] Pour the fermented silkworm excrement into the urea and urease inhibitor solution and soak and stir for 8 hours to allow the silkworm excrement to fully absorb the solution. Then, filter the silkworm excrement with a filter to remove excess solution.

[0055] Crushing and drying

[0056] Use a small grinder to physically crush the loaded silkworm excrement to control the particle size to 3-5 mm. Spread the crushed silkworm excrement on a tray and put it into a 40°C oven to dry to constant weight to obtain a silkworm excrement-based slow-release fertilizer (such as Figure 1 shown).

[0057] Sugarcane planting application

[0058] In a 1-mu (approximately 1.5-acre) sugarcane experimental field, the prepared slow-release fertilizer was evenly spread on the soil surface before planting, then plowed into the soil to a depth of approximately 20 centimeters. Sugarcane was planted according to conventional planting density and methods, and no additional nitrogen fertilizer was applied throughout the growing season.

[0059] Example 2

[0060] Silkworm excrement collection and pretreatment

[0061] Fresh silkworm excrement is collected at the sericulture base and transported to a spacious, well-ventilated pre-processing area. The excrement is evenly spread on a dust-proof surface, approximately 5 cm thick. Air-drying is done for 3-4 days in the mild local climate. A moisture meter is used to ensure the excrement's moisture content is reduced to 15%-18%. A drum screen is then used to remove any remaining impurities.

[0062] Quicklime covering disinfection

[0063] After pre-treatment, lay alkali-resistant plastic sheeting in the storage area for silkworm excrement, spreading the excrement into a 20-30 cm thick layer. Evenly sprinkle lumps of quicklime at a rate of 2.5 kg per cubic meter of excrement, then cover tightly with plastic sheeting and compact it tightly. Maintain this seal for four days. The quicklime, when in contact with water, releases heat and creates a strong alkaline environment, effectively killing harmful microorganisms and insect eggs. After disinfection is complete, samples can be collected for microbiological testing to confirm the effectiveness of the disinfection.

[0064] Preparation of compound microbial agents

[0065] Purified strains of Phanerochaete chrysosporium, Bacillus subtilis, and Aspergillus niger were purchased. They were activated using PDA medium (for Phanerochaete chrysosporium and Aspergillus niger) and nutrient broth medium (for Bacillus subtilis), respectively. After activation, the strains were mixed in a volume ratio of 5:3:2 for Phanerochaete chrysosporium:Bacillus subtilis:Aspergillus niger to prepare a composite inoculum.

[0066] Silkworm feces fermentation

[0067] Place 15 kg of disinfected silkworm excrement into a large plastic bucket with a sealed lid. Add 7 liters of boiled, cooled sterile water and stir thoroughly with a paddle. Add 700 ml of a compound inoculant to the bucket and stir again to thoroughly blend the inoculant and silkworm excrement. Seal the lid and poke 10-12 holes, 2-3 mm in diameter, evenly throughout for ventilation. Place the bucket in an incubation room maintained at 28°C and ferment for 12 days. Open the lid every four days and stir thoroughly with a long-handled stirring tool to ensure even fermentation.

[0068] Preparation of urea and urease inhibitor solution

[0069] Weigh 6 kg of urea and 60 g of N-butylthiophosphoric triamide (NBPT, urease inhibitor), place them in a large-capacity plastic container, add 25 liters of deionized water, and stir with an electric stirrer until they are completely dissolved.

[0070] Loading and forming

[0071] The fermented silkworm excrement is poured into a solution of urea and urease inhibitor, soaked and stirred for 10 hours to promote sufficient adsorption. It is then filtered through a 25-mesh stainless steel filter to remove excess solution. The filtered silkworm excrement is placed in a low-temperature vacuum drying oven and dried to constant weight at 40°C and a vacuum of 0.07 MPa. The dried silkworm excrement is processed into granules with a particle size of 4-5 mm using an extrusion granulator to produce silkworm excrement slow-release fertilizer.

[0072] Sugarcane planting application

[0073] Application was carried out in a 1-mu sugarcane experimental field. Before planting, a rotary tiller was used to evenly spread the prepared slow-release fertilizer on the soil surface. Plowing was then performed to a depth of 23 cm to ensure thorough mixing of the fertilizer and soil. The Liucheng 05-136 sugarcane variety, suitable for the local climate, was selected for planting according to local sugarcane planting density and methods. No additional nitrogen fertilizer was applied throughout the growing season. Sugarcane growth was regularly observed, and growth indicators such as tiller number and internode length were recorded.

[0074] Example 3

[0075] Silkworm excrement collection and pretreatment

[0076] Silkworm feces were collected from multiple small silkworm farmers and placed in a well-ventilated warehouse to dry in the shade for one week. With the help of a humidity detector, the moisture content was reduced to about 18%.

[0077] Quicklime covering disinfection

[0078] After pre-treatment, lay alkali-resistant plastic sheeting in the storage area for silkworm excrement, spreading the excrement into a 20-30 cm thick layer. Evenly sprinkle lumps of quicklime at a rate of 2.5 kg per cubic meter of excrement, then cover tightly with plastic sheeting and compact it tightly. Maintain this seal for four days. The quicklime, when in contact with water, releases heat and creates a strong alkaline environment, effectively killing harmful microorganisms and insect eggs. After disinfection is complete, samples can be collected for microbiological testing to confirm the effectiveness of the disinfection.

[0079] Preparation of compound microbial agents

[0080] Purchase Phanerochaete chrysosporium, Bacillus subtilis, and Aspergillus niger from a professional strain collection. Activate them using PDA medium (for Phanerochaete chrysosporium and Aspergillus niger) and nutrient broth medium (for Bacillus subtilis), respectively. After activation, mix Phanerochaete chrysosporium: Bacillus subtilis: Aspergillus niger in a volume ratio of 5:3:2 to prepare a composite inoculum.

[0081] Silkworm feces fermentation

[0082] Place 15 kg of disinfected silkworm excrement into a sealed plastic fermentation barrel. Add 8 liters of sterile brown sugar water (5% concentration) and stir thoroughly. Add 750 ml of a composite bacterial inoculant and stir thoroughly to mix the inoculant and silkworm excrement evenly. Seal the barrel lid and drill 6-8 small holes, approximately 5 mm in diameter, evenly in the barrel wall for ventilation. Place the fermentation barrel in a room at 27°C for 11 days. Open the barrel lid and stir every four days to ensure even fermentation.

[0083] Preparation of urea and urease inhibitor solution

[0084] Weigh 6 kg of urea and 60 g of hydroquinone (urease inhibitor), place them in a large plastic bucket, add 25 liters of deionized water, and use an electric stirrer to stir at a speed of 300 rpm until they are completely dissolved.

[0085] Load process

[0086] The fermented silkworm excrement was slowly poured into the urea and urease inhibitor solution, stirring while pouring, and soaked for 9 hours. Subsequently, the silkworm excrement was filtered through a nylon filter to remove excess solution.

[0087] Crushing and drying

[0088] The filtered silkworm excrement is crushed using a hammer crusher, and the mesh size of the screen is adjusted to ensure that the excrement particle size is within the range of 4-6 mm. The crushed silkworm excrement is spread evenly on a stainless steel tray and dried in a forced air drying oven set at 42°C to a constant weight to obtain a silkworm excrement-based slow-release fertilizer.

[0089] Sugarcane planting application

[0090] Select a 1.5-mu sugarcane field and, one week before planting, dig planting trenches approximately 30 centimeters deep, with row spacing of 1.2 meters. Evenly spread the prepared slow-release fertilizer at the bottom of the trenches, then cover with a 5-centimeter layer of soil. Plant the sugarcane at a standard planting density, water the fields normally after planting, and avoid applying any additional nitrogen fertilizer during the entire sugarcane growth cycle.

[0091] Example 4

[0092] Silkworm excrement collection and preliminary pretreatment

[0093] Silkworm feces are collected from centralized sericulture parks, and moisture is initially removed using a centrifugal dehydrator. They are then placed in a solar dryer for drying, and the moisture content is reduced to 16% with the help of a high-precision humidity detector.

[0094] Quicklime covering disinfection

[0095] Alkali-resistant plastic sheeting is laid over the pre-treated silkworm excrement storage area, forming a 20-30 cm thick layer. Quicklime blocks are evenly sprinkled on the area at a rate of 2.5 kg per cubic meter of excrement. The area is then tightly covered with plastic sheeting and compacted to seal. This seal is maintained for four days, allowing the quicklime to release heat upon contact with water, creating a highly alkaline environment that effectively kills harmful microorganisms and insect eggs. After disinfection is complete, samples are collected and tested using specialized microbiological testing equipment to confirm the effectiveness of the disinfection.

[0096] Preparation of composite bacterial agents

[0097] Laboratory-selected strains of Phanerochaete chrysosporium, Bacillus subtilis, and Aspergillus niger were used. Phanerochaete chrysosporium and Aspergillus niger were activated using PDA medium (for Phanerochaete chrysosporium and Aspergillus niger) and nutrient broth medium (for Bacillus subtilis), respectively. After activation, the mixture was mixed in a volume ratio of 5:3:2 for Phanerochaete chrysosporium:Bacillus subtilis:Aspergillus niger to produce a composite inoculum.

[0098] Silkworm feces fermentation

[0099] 25 kg of disinfected silkworm excrement is placed in a brick-lined fermentation tank. 12 liters of homemade nutrient solution (rich in amino acids and trace elements) is added, along with 1.2 liters of a compound bacterial agent, and stirred evenly. The fermentation tank is covered with plastic film, compacted with sandbags, and evenly perforated with small holes. Temperature control equipment is used to maintain the tank's temperature at around 31°C. The fermentation is continued for 13 days, with the material being turned over daily with a dedicated turning tool.

[0100] Solution preparation

[0101] Weigh 10 kg of urea and 100 g of N-butylthiophosphoramide, add 40 L of distilled water, and stir with a high-power electric stirrer until completely dissolved.

[0102] Load process

[0103] Immerse the fermented silkworm excrement in the above solution, stir and adsorb for 11 hours, and filter with a stainless steel filter.

[0104] Crushing and drying

[0105] The filtered silkworm excrement is crushed using a double-roll crusher. The equipment parameters are precisely adjusted to control the particle size to 3-5 mm. The crushed silkworm excrement is then dried in a drying room at 43°C to produce a slow-release fertilizer.

[0106] Field application

[0107] In a 3-mu sugarcane field, hole-fertilization was adopted during planting. An appropriate amount of slow-release fertilizer was applied at the bottom of each planting hole. Sugarcane was planted after covering the soil. Subsequent management was carried out according to routine procedures without additional nitrogen fertilizer application.

[0108] Example 5

[0109] Silkworm excrement collection and preliminary pretreatment

[0110] Silkworm feces are collected from multiple scattered small-scale silkworm farmers, piled up in ventilated and bright sheds, and naturally dried for a week. With the help of a humidity detector, the moisture content of the silkworm feces is reduced to approximately 17%.

[0111] Quicklime covering disinfection

[0112] Alkali-resistant plastic sheeting is laid over the pre-treated silkworm excrement storage area, forming a 20-30 cm thick layer. Quicklime blocks are evenly sprinkled on the area at a rate of 2.5 kg per cubic meter of excrement. The area is then tightly covered with plastic sheeting and compacted to seal. This seal is maintained for four days, allowing the quicklime to release heat upon contact with water, creating a highly alkaline environment that effectively kills harmful microorganisms and insect eggs. After disinfection is complete, samples are collected and tested using specialized microbiological testing equipment to confirm the effectiveness of the disinfection.

[0113] Preparation of compound microbial agents

[0114] Phanerochaete chrysosporium, Bacillus subtilis, and Aspergillus niger were purchased from a professional culture collection. They were activated using PDA medium (for Phanerochaete chrysosporium and Aspergillus niger) and nutrient broth medium (for Bacillus subtilis), respectively. After activation, the mixture was carefully prepared into a composite inoculum by mixing Phanerochaete chrysosporium: Bacillus subtilis: Aspergillus niger at a volume ratio of 5:3:2.

[0115] Silkworm feces fermentation

[0116] Put 12 kg of disinfected silkworm excrement into a sealable plastic barrel, add 6 liters of sterile brown sugar water (concentration of 4%) into the barrel, and stir thoroughly with the help of a stirring rod to mix the two evenly. Then, add 600 ml of the prepared composite bacterial agent and stir again to ensure that the bacterial agent is in full contact with the silkworm excrement. Seal the barrel mouth with a thick plastic film, and evenly poke 8-10 small holes with a diameter of about 4 mm around the barrel wall for ventilation. Place the sealed barrel in a constant temperature room maintained at 29°C for fermentation, and the fermentation time is set to 11 days. During the fermentation period, open the plastic film every 3 days and stir once with a stirring rod to ensure that the silkworm excrement is fermented evenly.

[0117] Preparation of urea and urease inhibitor solution

[0118] Accurately weigh 6 kg of high-quality urea and 60 g of N-butylthiophosphoric triamide (NBPT, a urease inhibitor) into a large plastic container. Next, add 23 liters of deionized water to the container and stir continuously at 250 rpm with an electric stirrer until the urea and NBPT are completely dissolved, forming a homogeneous solution.

[0119] Load process

[0120] The fermented silkworm excrement is slowly poured into the urea and urease inhibitor solution, stirring with a stirrer to fully immerse the silkworm excrement in the solution. Stirring and adsorption are continued for 9 hours. After adsorption is complete, the silkworm excrement is filtered through a stainless steel filter with an appropriate pore size to separate the excess solution.

[0121] Crushing and drying

[0122] A small hammer mill is used to crush the filtered silkworm excrement. The particle size is controlled to 3-5 mm by adjusting the screen. The crushed excrement is evenly spread on a stainless steel tray and placed in a forced air drying oven set at 42°C. Drying is done until the excrement reaches a constant weight, successfully producing the silkworm excrement-based slow-release fertilizer.

[0123] Sugarcane planting application

[0124] A 1.2-mu (approximately 1.2-acre) sugarcane test field was selected. Before planting, trenches were dug with a row spacing of 1.1 meters and a depth of approximately 25 centimeters. Prepared silkworm feces-based slow-release fertilizer was evenly spread along the trenches, followed by a 6-centimeter-thick layer of soil. Sugarcane was planted according to local standard planting density and methods. No additional nitrogen fertilizer was applied throughout the growing season, and only routine field management practices, such as irrigation and pest control, were implemented.

[0125] Material sustained-release performance testing

[0126] The product prepared in Example 1 of the present invention was subjected to characterization analysis and performance test analysis.

[0127] (1) FT-IR spectroscopy characterization

[0128] Fourier transform infrared spectroscopy experiments were performed using a Nicolet Nexus 670 FT-IR spectrometer (ThermoFisher). The purified and dried samples were finely ground and compressed with potassium bromide, and the scanning range was set to 4000–400 cm -1 , the resolution, number of scans and data interval are 4, 32 and 0.482 cm respectively -1 .like Figure 2 、 Figure 3 As shown in the figure, compared with the unfermented silkworm excrement, the carbonyl and carboxyl peaks of the fermented silkworm excrement all shift to higher wavenumbers. This is because the degradation process breaks the tight structure of lignin, cellulose and hemicellulose in the silkworm excrement, which is maintained by hydrogen bonds, allowing the originally tightly entangled macromolecular chains to stretch. Figure 3 As shown in the figure, in addition to the characteristic peaks of silkworm feces itself, there are -1 The original peak will change in this region. This is because there are amino groups (-NH2) in the urea molecule, and the stretching vibration of the NH bond will produce absorption in this region.

[0129] (2) Surface morphology of materials The morphology of the fermented silkworm feces and the urea-adsorbed feces were characterized using a Japanese Hitachi S-3400N low-magnification scanning electron microscope. Figure 3 As shown in (A), the fermented silkworm excrement is in the form of small flakes; (B) shows that urea is heavily loaded on the surface of the silkworm excrement.

[0130] The above embodiments of the present invention are merely examples to clearly illustrate the present invention and are not intended to limit the embodiments of the present invention. A person skilled in the art will appreciate that various variations or modifications may be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention are intended to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a slow-release fertilizer based on silkworm excrement carriers simultaneously loaded with urea and urease inhibitors, characterized in that: The steps include: (1) Silkworm excrement collection and pretreatment Collect fresh silkworm excrement and remove impurities; sun-dry or air-dry the cleaned silkworm excrement to reduce the moisture content to 15%-20%; (2) Quicklime covering and disinfection Lay a layer of plastic film on the silkworm excrement accumulation site, evenly spread the air-dried silkworm excrement on the film to a thickness of 20-30 cm; use 2-3 kg of quicklime per cubic meter of silkworm excrement, evenly sprinkle the quicklime on the surface of the silkworm excrement, then cover it tightly with plastic film, compacting it on all sides to seal it; maintain the sealed state for 3-5 days, using the quicklime to release heat when it comes into contact with water and the strong alkaline calcium hydroxide environment it generates to effectively kill harmful microorganisms, insect eggs, and weed seeds in the silkworm excrement; (3) Bacteria activation The solid inoculum of Phanerochaete chrysosporium was inoculated into a culture dish containing potato dextrose agar medium, and cultured in a constant temperature incubator at 28°C-30°C for 3-5 days. After the colonies grew and had good morphology, some mycelium was picked and transferred to a new potato dextrose agar liquid medium, and cultured in a shaker at a speed of 150-180 r / min and 28°C for 2-3 days to fully activate the strain and prepare for subsequent fermentation. Take the freeze-dried powder or slant culture of Bacillus subtilis and inoculate it into nutrient broth medium. Incubate it in a constant temperature shaker at 35℃ and 180 rpm for 18-24 hours. Activation is complete when the bacterial solution becomes turbid and a large number of cells grow. Inoculate Aspergillus niger spores onto a potato dextrose agar medium plate, place in a 30°C constant temperature incubator and culture for 3-5 days. When the plate is covered with black spores, pick out the spores and inoculate them into a potato dextrose liquid medium. Incubate in a 30°C constant temperature shaker at 150 rpm for 2-3 days until the bacterial solution becomes turbid and mycelium grows, indicating that activation is complete. (4) Preparation of compound bacterial agents The activated Phanerochaete chrysosporium liquid, Bacillus subtilis liquid, and Aspergillus niger liquid were mixed in a volume ratio of 5:3:2; during the mixing process, the mixture was slowly added dropwise with continuous stirring; a magnetic stirrer was used with a stirring speed of 80-100 r / min and a stirring time of 30-45 minutes to ensure that the bacterial agent and the enzyme preparation were evenly mixed; the mixed composite bacterial agent should be stored at a low temperature of 4°C-8°C and used within 24 hours to maintain its activity; (5) Inoculation and fermentation treatment Evenly sprinkle the prepared composite bacterial agent on the surface of the mixed material, and then use a blender to fully stir. Transfer the inoculated material to the fermentation tank and pile it into a pile with a height of 1-1.2m. Insert a thermometer in the pile to closely monitor temperature changes. In the early stage of fermentation, the temperature of the pile will gradually rise. When the temperature reaches 35°C, turn the pile for the first time to ensure uniform ventilation of the material. After that, control the fermentation temperature between 30°C and 35°C, turn the pile every 24 hours, and continue fermentation for 3-4 days. Regularly test the pH value and microbial count. (6) Crushing and loading processing After the fermentation is completed, the fermented silkworm excrement is crushed into a particle size of 2-5 mm using a crusher; the crushed fermented silkworm excrement, urea and urease inhibitor are weighed according to a mass ratio of 6-7:1:0.08; the urea and urease inhibitor are first added to an appropriate amount of water, stirred and dissolved at 40°C-50°C to prepare a mixed solution, and the amount of water used is based on the ability to completely dissolve the urea and urease inhibitor and subsequently evenly soak the silkworm excrement; the crushed fermented silkworm excrement is slowly added to the above mixed solution, and a stirring device is turned on at the same time, and stirred at a speed of 100-150 r / min for 30-45 minutes to ensure that the urea and urease inhibitor are fully loaded into the pore structure of the silkworm excrement; after completing the auxiliary loading, the material is dried and granulated to obtain the silkworm excrement-based slow-release fertilizer.

2. The method for preparing a slow-release fertilizer based on silkworm excrement carriers simultaneously loaded with urea and urease inhibitors according to claim 1, characterized in that: The nutrient broth culture medium in step (3) is 10 g of peptone, 3 g of beef extract, 5 g of sodium chloride, and 1000 mL of distilled water, with a pH of 7.2-7.

4.

3. The method for preparing a slow-release fertilizer based on silkworm excrement carriers simultaneously loaded with urea and urease inhibitors according to claim 1, characterized in that: The total inoculation amount of the composite bacterial agent in step (5) is 10% of the dry weight of silkworm excrement.

4. The method for preparing a slow-release fertilizer based on silkworm excrement carriers simultaneously loaded with urea and urease inhibitors according to claim 1, characterized in that: In step (6), urea is used to prepare a 40% urea solution: 400 g of urea is dissolved in 600 mL of deionized water, stirred until completely dissolved, and then added with a water-retaining agent PAAS at a concentration of 2% by mass of urea, stirred in a 60° C. water bath for 30 min to form a uniform solution.

5. The method for preparing a slow-release fertilizer based on silkworm excrement carriers simultaneously loaded with urea and urease inhibitors according to claim 1, characterized in that: During the fermentation process, the compost is mechanically turned once every 24 hours to ensure that the oxygen concentration is greater than 15%, and the moisture content is regulated to 60% by spraying with sterile water.

6. The method for preparing a silkworm excrement-based slow-release fertilizer simultaneously loaded with urea and a urease inhibitor based on a silkworm excrement carrier according to claim 1, characterized in that: During the fermentation process, samples were taken daily to ensure that the pH fluctuation range was between 5.0 and 6.

0.

7. Use of the slow-release fertilizer obtained by the preparation method according to any one of claims 1 to 6, characterized in that: Its application in slow release of fertilizers for crops during the growth cycle.

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