Preparation method of slow-release fertilizer

Abstract

The invention provides a preparation method of a slow-release fertilizer, and belongs to the technical field of fertilizer.The preparation method of the slow-release fertilizer comprises the following steps that calcium silicate is added into potassium chloride or potassium sulfate and other potassium fertilizer solutions to be stirred and mixed to be uniform, then modified filler and inorganic fertilizer are sequentially added, stirring continues to be conducted, and slurry is obtained; the slurry is sprayed out through a slurry spraying machine and then falls into a rolling disc, and particles with smooth appearance are formed; feeding the particles into a roller, and spraying a small amount of slow-release coating liquid to form a coating layer, so as to obtain coated particles; and baking the coated particles, screening the particles, and packaging to obtain the slow-release fertilizer. Wherein the small amount of slow-release coating liquid is prepared from castor oil polyhydric alcohol, polymethylene polyphenyl polyisocyanate and oxalyl diamine. The prepared slow-release fertilizer has an excellent slow-release effect on inorganic fertilizers, the nutrient release time of the fertilizer can be effectively prolonged, the utilization rate of the fertilizer is increased, and crop growth is better promoted.

Description

Technical Field

[0001] The invention belongs to the technical field of fertilizers, and in particular relates to a method for preparing a slow-release fertilizer. Background Art

[0002] As modern agriculture pursues efficient and environmentally friendly production methods, slow-release fertilizers, as a new type of fertilizer technology, have gradually become a research hotspot in the agricultural field. Although traditional chemical fertilizers can quickly provide the nutrients needed by crops, due to their high solubility and fast release rate, nutrients are easily lost or volatilized with rainwater, resulting in low utilization rate, which not only increases agricultural production costs, but also causes serious pollution to the environment, such as eutrophication of water bodies and soil degradation. Slow-release fertilizers control the release rate of nutrients to match them with the growth needs of crops, thereby significantly improving the utilization efficiency of fertilizers and reducing resource waste and environmental pollution. The core advantage of slow-release fertilizers lies in their long-term effectiveness and stability, which can provide crops with a continuous and balanced supply of nutrients and avoid poor crop growth caused by insufficient or excessive nutrient supply. In addition, slow-release fertilizers can reduce the number of fertilizations and labor costs, providing important support for the sustainable development of modern agriculture.

[0003] At present, the preparation methods of slow-release fertilizers mainly include coating method, chemical synthesis method and matrix method. The coating method is to control the release of nutrients by coating a layer of polymer or sulfur and other materials on the surface of fertilizer particles, but its preparation process is complicated and costly, and the degradation performance of the coating material is difficult to accurately control, which may lead to uneven nutrient release. The chemical synthesis method uses low-solubility compounds such as urea-formaldehyde as slow-release carriers, but its production process has high energy consumption, and the release rate is greatly affected by environmental factors, which is difficult to meet the needs of different crops. The matrix method is to embed nutrients into organic or inorganic matrices and achieve nutrient slow release through the decomposition of the matrix, but this method has problems such as unstable matrix decomposition rate and uncontrollable nutrient release. In addition, the existing slow-release fertilizer technology generally has the disadvantages of high production cost, complex process, poor environmental adaptability, etc., which limits its large-scale promotion and application.

[0004] In order to overcome the shortcomings of existing slow-release fertilizer technology, improvements can be made in terms of material selection, process optimization and release mechanism. For example, develop biodegradable coating materials to reduce environmental burden, or use nanotechnology to regulate nutrient release rate to improve accuracy. In addition, the use of natural organic substances such as lignin, chitosan, etc. as slow-release carriers has also become a research hotspot because of their wide sources, low cost and environmental friendliness. However, these improved methods still face many challenges, such as insufficient mechanical properties of biodegradable materials, difficulty in large-scale production of nanotechnology, limited nutrient loading capacity of natural organic substances, etc., and the existing technology is difficult to take into account the long-term effect, stability and economy of slow-release fertilizers, resulting in unsatisfactory results in practical applications. Therefore, there is an urgent need for a new method for preparing slow-release fertilizers, which is not only simple in process and low in cost, but also can take into account the long-term effect and stability of slow-release fertilizers. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a slow-release fertilizer, which further improves the slow-release performance of the slow-release fertilizer by adopting a specific modified filler to work synergistically with calcium silicate and combining a coating treatment with a small amount of slow-release coating liquid, thereby effectively extending the nutrient release time of the fertilizer, improving the utilization rate of the fertilizer, and better promoting crop growth.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a slow-release fertilizer, comprising the following steps:

[0008] 90-100 parts of calcium silicate are added to 2-20 parts by weight of potassium chloride or potassium sulfate and stirred for 0.3-30 hours, and then 0-5 parts by weight of modified filler and 0-600 parts by weight of inorganic fertilizer are added in sequence and stirred for 0.5-10 hours to obtain slurry; the slurry is sprayed out by a spraying machine and then falls into a rolling plate to form particles with smooth appearance;

[0009] The particles are fed into a drum, and a small amount of slow-release coating liquid is sprayed to form a coating layer to obtain coated particles; the small amount of slow-release coating liquid is composed of castor oil polyol, polymethylene polyphenyl polyisocyanate and oxalyl diamide; the coated particles are baked, the particles are sieved, and packaged to obtain the slow-release fertilizer.

[0010] Preferably, a method for preparing a slow-release fertilizer comprises the following steps:

[0011] 90-100 parts by weight of calcium silicate are added to 180-220 parts by weight of 23-28wt% hydrochloric acid solution, stirred at 200-300r / min for 1-2h, then 7-12 parts by weight of potassium chloride or potassium sulfate are added and stirred for 0.3-1h, then 12-18 parts by weight of modified filler and 500-600 parts by weight of inorganic fertilizer are added in sequence and stirred for 0.5-1.5h to obtain slurry; the slurry is sprayed out by a spraying machine and then falls into a rolling plate to form particles with smooth appearance;

[0012] The particles are fed into a drum, and a small amount of slow-release coating liquid is sprayed to form a coating layer to obtain coated particles; the coated particles are baked, the particles are sieved, and they are packaged to obtain the slow-release fertilizer.

[0013] Preferably, the method for preparing the modified filler comprises the following steps:

[0014] Adding nano-silicon dioxide to a hydroxypropyl chitosan aqueous solution, performing ultrasonic treatment, filtering, and drying to obtain pretreated nano-silicon dioxide; adding nano-montmorillonite to a hexadecyltrimethylammonium chloride aqueous solution, heating and stirring, filtering, and drying to obtain pretreated nano-montmorillonite;

[0015] 3-acryloxypropylmethyldimethoxysilane, allyltriethoxysilane and ethanol aqueous solution are uniformly mixed, and then pretreated nano-silica and pretreated nano-montmorillonite are added in sequence for ultrasonic treatment, and then gamma-polyglutamic acid is added for heating and stirring, filtered, and dried to obtain a modified filler.

[0016] The present invention significantly improves the slow-release performance of the slow-release fertilizer by adding the modified filler prepared by the above method, and synergistically acts with calcium silicate, thereby effectively extending the nutrient release time of the fertilizer, improving the utilization rate of the fertilizer, better promoting crop growth, and improving the soil and increasing the fertility of the soil. Among them, the modified filler is composited by nano-silicon dioxide, nano-montmorillonite and γ-polyglutamic acid, and after surface modification and chemical cross-linking treatment, the mechanical strength of the fertilizer particles is significantly improved. After the nano-silicon dioxide is modified by hydroxypropyl chitosan, the compatibility with the polymer matrix is ​​enhanced to form a stable physical network structure; after the nano-montmorillonite is modified by hexadecyltrimethylammonium chloride intercalation, the hydrophobicity and dispersibility are significantly improved, and the compression resistance and wear resistance of the particles are further improved. This improvement in mechanical properties helps to reduce the breakage of fertilizer particles during application. At the same time, the nanomaterials in the modified filler have high specific surface area and good dispersibility, which can be filled into the micropores inside the fertilizer particles and optimize the pore distribution. This optimized pore structure plays an important role in regulating nutrient release: on the one hand, dense pores can slow down the diffusion rate of nutrients; on the other hand, the existence of pores provides a channel for water penetration, ensuring that nutrients are gradually released under suitable conditions. Furthermore, γ-polyglutamic acid has abundant carboxyl and amino functional groups, which can bind to nutrient ions such as nitrogen, phosphorus, and potassium through electrostatic action or hydrogen bonding, temporarily fixing them inside the fertilizer particles. This chemical adsorption slows down the release rate of nutrients and reduces the loss caused by leaching or volatilization, thereby improving the utilization rate of fertilizers. In addition, the nanomaterials and γ-polyglutamic acid in the modified filler are gradually converted into soil organic matter or functional substances during the decomposition of fertilizers, improving soil structure and enhancing soil water and fertilizer retention capacity; γ-polyglutamic acid can also promote soil microbial activity, accelerate organic matter decomposition and nutrient conversion, and further improve soil fertility.

[0017] Furthermore, the preparation method of the modified filler comprises the following steps:

[0018] 10-15 parts by weight of nano-silicon dioxide are added to 70-120 parts by weight of 1-2wt% hydroxypropyl chitosan aqueous solution, ultrasonically treated for 2-4h at an ultrasonic power of 100-200W and an ultrasonic frequency of 20-40kHz, filtered, and dried to obtain pretreated nano-silicon dioxide; 4-6 parts by weight of nano-montmorillonite are added to 60-80 parts by weight of 2-5wt% hexadecyltrimethylammonium chloride aqueous solution, stirred for 3-5h at 60-70°C and 100-150r / min, filtered, and dried to obtain pretreated nano-montmorillonite;

[0019] 0.5-0.7 parts by weight of 3-acryloxypropylmethyldimethoxysilane, 0.3-0.5 parts by weight of allyltriethoxysilane and 80-90 parts by weight of 45-60wt% ethanol aqueous solution are uniformly mixed, and then 4-6 parts by weight of pretreated nano silicon dioxide and 2-4 parts by weight of pretreated nano montmorillonite are added in sequence, and ultrasonic treatment is performed for 30-50 minutes under the conditions of ultrasonic power of 100-200W and ultrasonic frequency of 20-40kHz, and then 0.5-1.5 parts by weight of gamma-polyglutamic acid are added, and stirring is performed for 40-60 minutes under the conditions of 55-60°C and 100-300r / min, and filtering and drying are performed to obtain a modified filler.

[0020] Preferably, the inorganic fertilizer is a mixture of urea, potassium dihydrogen phosphate and diammonium hydrogen phosphate in a weight ratio of (2-4):(2-3):1.

[0021] Preferably, the pressure of the shotcrete machine is 0.2-0.6 MPa, and the rotation speed of the rolling plate is 2-20 r / min.

[0022] Furthermore, the pressure of the shotcrete machine is 0.3-0.6 MPa, and the rotation speed of the rolling plate is 5-15 r / min.

[0023] Preferably, the coating layer accounts for 0-4% of the total weight of the particles.

[0024] Furthermore, the coating layer accounts for 2-4% of the total weight of the particles.

[0025] Preferably, the rotation speed of the drum is 5-15 r / min; the spraying pressure is 7-10 MPa, and the spraying temperature is 70-80°C.

[0026] Preferably, the baking conditions are: pre-baking at 90-100° C. for 0.5-10 h, and then baking at 100-120° C. for 0.5-10 h.

[0027] Furthermore, the baking conditions are: pre-baking at 90-100° C. for 10-30 min, and then baking at 100-120° C. for 20-40 min.

[0028] Preferably, the particle screening is to screen out qualified particles with a particle size of 2-4 mm.

[0029] Preferably, the small amount of sustained-release coating liquid is composed of castor oil polyol, polymethylene polyphenyl polyisocyanate and oxalyl diamide.

[0030] The present invention also uses a small amount of slow-release coating liquid to coat the fertilizer particles, further improving the slow-release performance of the slow-release fertilizer. Compared with ordinary coating liquid, it can better prevent the release of nutrients, and can make the compound fertilizer have a sufficiently long nutrient release time to meet the demand for nutrients in the crop growth cycle. Among them, castor oil polyol is used to react with polymethylene polyphenyl polyisocyanate to generate a polyurethane with a three-dimensional network structure. This network structure is dense and stable, and can effectively wrap the fertilizer particles to form a solid protective layer to prevent the rapid release of nutrients; oxalyl diamide can be used as a functional auxiliary agent to enhance the degree of cross-linking between molecules, so that the mechanical properties and hydrolysis resistance of the coating material are significantly improved. In the coating material used in the present invention, castor oil polyol is derived from natural vegetable oil and has biodegradability. With the action of soil microorganisms, the coating layer gradually degrades and releases the internal nutrients. The presence of oxalyl diamide not only enhances the stability of the coating, but also gradually decomposes into nutrient nitrogen during the degradation process. The degradation products of the coating material such as carbon dioxide, water and a small amount of nitrogen are friendly to the soil environment and will not cause pollution. In addition, the coating layer of the present invention has flexibility and elasticity, can adapt to the changes in mechanical stress under different soil conditions, and reduce the damage caused by external forces, thereby ensuring the stability of the slow-release effect.

[0031] Furthermore, the small amount of sustained-release coating solution is composed of 20-30 parts by weight of castor oil polyol, 30-35 parts by weight of polymethylene polyphenyl polyisocyanate and 5-10 parts by weight of oxalyl diamide.

[0032] The invention also provides a slow-release fertilizer prepared by the method.

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

[0034] 1. The present invention provides a method for preparing a slow-release fertilizer. By using a modified filler composed of nano-silicon dioxide, nano-montmorillonite and γ-polyglutamic acid, the modified filler and calcium silicate work together to not only enhance the mechanical strength of the fertilizer particles, but also optimize the internal pore structure, thereby providing a better physical barrier for the controlled release of nutrients. In addition, a small amount of slow-release coating liquid composed of castor oil polyol, polymethylene polyphenyl polyisocyanate and oxalyl diamide is used for coating treatment, which can not only further delay the release of nutrients, but also protect the fertilizer from the influence of the external environment such as rain, thereby significantly prolonging the effective action time of the fertilizer. The slow-release fertilizer prepared by the present invention has a slow-release performance that is better than the requirements of the national standard GB / T 23348-2009 "Slow-release Fertilizer".

[0035] 2. The modified filler prepared by the present invention is a composite of nano-silica, nano-montmorillonite and γ-polyglutamic acid. After surface modification and chemical cross-linking treatment, the mechanical strength of the fertilizer particles is significantly improved. After the nano-silica is modified by hydroxypropyl chitosan, the compatibility with the polymer matrix is ​​enhanced to form a stable physical network structure. After the nano-montmorillonite is modified by hexadecyltrimethylammonium chloride intercalation, the hydrophobicity and dispersibility are significantly improved, and the compression resistance and wear resistance of the particles are further improved. At the same time, the nanomaterial in the modified filler has a high specific surface area and good dispersibility, and can be filled into the micropores inside the fertilizer particles to optimize the pore distribution. On the one hand, the dense pores can slow down the diffusion rate of nutrients. On the other hand, the existence of the pores provides a channel for water penetration, ensuring that the nutrients are gradually released under suitable conditions.

[0036] 3. Compared with ordinary coating liquid, the small amount of slow-release coating liquid used in the present invention can better prevent the release of nutrients, so that the compound fertilizer has a sufficiently long nutrient release time to meet the nutrient demand during the crop growth cycle. Among them, castor oil polyol is reacted with polymethylene polyphenyl polyisocyanate to generate a polyurethane with a three-dimensional network structure. This network structure is dense and stable, and can effectively wrap the fertilizer particles to form a solid protective layer to prevent the rapid release of nutrients; oxalyl diamide as a functional additive can enhance the degree of cross-linking between molecules, so that the mechanical properties and hydrolysis resistance of the coating material are significantly improved. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] Calcium silicate is prepared by the method of basic example 1 in patent CN202510033993.0.

[0039] Polymethylene polyphenyl polyisocyanate, viscosity (25°C): 500-800 mPa·s, average functionality: 2.5-3, isocyanate content: 30-32 wt%.

[0040] Castor oil polyol, viscosity (25°C): 400-600 mPa·s, average functionality: 2.5-3, hydroxyl value: 150-200 mgKOH / g, acid value: 0.5-1.5 mgKOH / g.

[0041] Hydroxypropyl chitosan, viscosity (25°C, 1wt% aqueous solution): 50-150mPa·s, deacetylation degree: ≥85%, hydroxypropyl substitution degree: ≥75%.

[0042] Nano-silicon dioxide, average particle size: 20-40nm.

[0043] Nano-montmorillonite, average particle size: 100-200nm.

[0044] γ-Polyglutamic acid, average molecular weight: 100000-400000.

[0045] Example 1

[0046] This embodiment provides a method for preparing a slow-release fertilizer, comprising the following steps:

[0047] 95 parts by weight of calcium silicate are added to 200 parts by weight of 25wt% hydrochloric acid solution, stirred at 250r / min for 1.5h, then 10 parts by weight of potassium chloride are added and stirred for 0.5h, then 15 parts by weight of modified filler and 550 parts by weight of inorganic fertilizer are added in sequence and stirred for 1h to obtain slurry; the inorganic fertilizer is a mixture of urea, potassium dihydrogen phosphate and diammonium hydrogen phosphate in a weight ratio of 3:2.5:1; the slurry is sprayed out by a spraying machine, and then falls into a rolling plate, and forms particles with smooth appearance under the action of rotation; wherein the pressure of the spraying machine is 0.4MPa, and the speed of the rolling plate is 10r / min;

[0048] The particles are fed into a drum, and a small amount of slow-release coating liquid is used for spraying to form a coating layer to obtain coated particles; the coating layer accounts for 3% of the total weight of the particles; the small amount of slow-release coating liquid is composed of 25 parts by weight of castor oil polyol, 32 parts by weight of polymethylene polyphenyl polyisocyanate and 8 parts by weight of oxalyl diamide; wherein the rotation speed of the drum is 10r / min, the spraying pressure is 8.5MPa, and the spraying temperature is 75°C;

[0049] The coated particles are pre-baked at 95° C. for 20 minutes to preliminarily solidify the coating layer, and then baked at 110° C. for 30 minutes to completely solidify the coating layer to obtain baked particles; the baked particles are sieved to select qualified particles with a particle size of 2-4 mm, and packaged to obtain the slow-release fertilizer.

[0050] The preparation method of the modified filler comprises the following steps:

[0051] 12 parts by weight of nano-silicon dioxide are added to 100 parts by weight of a 1.5wt% hydroxypropyl chitosan aqueous solution, ultrasonically treated for 3 hours at an ultrasonic power of 100 W and an ultrasonic frequency of 25 kHz, filtered, and dried to obtain pretreated nano-silicon dioxide; 5 parts by weight of nano-montmorillonite are added to 70 parts by weight of a 3.5wt% hexadecyltrimethylammonium chloride aqueous solution, stirred for 4 hours at 65° C. and 120 r / min, filtered, and dried to obtain pretreated nano-montmorillonite;

[0052] 0.6 parts by weight of 3-acryloxypropylmethyldimethoxysilane, 0.4 parts by weight of allyltriethoxysilane and 85 parts by weight of 50wt% ethanol aqueous solution were uniformly mixed, and then 5 parts by weight of pretreated nano-silica and 3 parts by weight of pretreated nano-montmorillonite were added in sequence, and ultrasonic treatment was performed for 40 minutes under the conditions of ultrasonic power of 100W and ultrasonic frequency of 25kHz, and then 1 part by weight of gamma-polyglutamic acid was added, and stirred for 50 minutes at 56°C and 200r / min, filtered, and dried to obtain a modified filler.

[0053] Example 2

[0054] This embodiment provides a method for preparing a slow-release fertilizer, comprising the following steps:

[0055] 90 parts by weight of calcium silicate are added to 180 parts by weight of 23wt% hydrochloric acid solution, stirred at 200r / min for 1h, then 7 parts by weight of potassium chloride are added and stirred for 0.3h, then 12 parts by weight of modified filler and 500 parts by weight of inorganic fertilizer are added in sequence and stirred for 0.5h to obtain slurry; the inorganic fertilizer is a mixture of urea, potassium dihydrogen phosphate and diammonium hydrogen phosphate in a weight ratio of 2:2:1; the slurry is sprayed out by a spraying machine, and then falls into a rolling plate, and forms particles with a smooth appearance under the action of rotation; wherein the pressure of the spraying machine is 0.3MPa, and the speed of the rolling plate is 5r / min;

[0056] The particles are fed into a drum, and a small amount of slow-release coating liquid is used for spraying to form a coating layer to obtain coated particles; the coating layer accounts for 2% of the total weight of the particles; the small amount of slow-release coating liquid is composed of 20 parts by weight of castor oil polyol, 30 parts by weight of polymethylene polyphenyl polyisocyanate and 5 parts by weight of oxalyl diamide; wherein the rotation speed of the drum is 5r / min, the spraying pressure is 7MPa, and the spraying temperature is 70°C;

[0057] The coated particles are pre-baked at 90° C. for 10 minutes to preliminarily solidify the coating layer, and then baked at 100° C. for 20 minutes to completely solidify the coating layer to obtain baked particles; the baked particles are sieved to select qualified particles with a particle size of 2-4 mm, and packaged to obtain the slow-release fertilizer.

[0058] The preparation method of the modified filler is the same as that of Example 1.

[0059] Example 3

[0060] This embodiment provides a method for preparing a slow-release fertilizer, comprising the following steps:

[0061] 100 parts by weight of calcium silicate are added to 220 parts by weight of 28wt% hydrochloric acid solution, stirred at 300r / min for 2h, then 12 parts by weight of potassium chloride are added and stirred for 1h, then 18 parts by weight of modified filler and 600 parts by weight of inorganic fertilizer are added in sequence and stirred for 1.5h to obtain slurry; the inorganic fertilizer is a mixture of urea, potassium dihydrogen phosphate and diammonium hydrogen phosphate in a weight ratio of 4:3:1; the slurry is sprayed out through a spraying machine, and then falls into a rolling plate, and forms particles with a smooth appearance under the action of rotation; wherein the pressure of the spraying machine is 0.6MPa, and the speed of the rolling plate is 15r / min;

[0062] The particles are fed into a drum, and a small amount of slow-release coating liquid is used for spraying to form a coating layer to obtain coated particles; the coating layer accounts for 4% of the total weight of the particles; the small amount of slow-release coating liquid is composed of 30 parts by weight of castor oil polyol, 35 parts by weight of polymethylene polyphenyl polyisocyanate and 10 parts by weight of oxalyl diamide; wherein the rotation speed of the drum is 15r / min, the spraying pressure is 10MPa, and the spraying temperature is 80°C;

[0063] The coated particles are pre-baked at 100° C. for 30 minutes to preliminarily solidify the coating layer, and then baked at 120° C. for 40 minutes to completely solidify the coating layer to obtain baked particles; the baked particles are sieved to select qualified particles with a particle size of 2-4 mm, and packaged to obtain the slow-release fertilizer.

[0064] The preparation method of the modified filler is the same as that of Example 1.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that the preparation method of the modified filler is different, which is as follows: The preparation method of the modified filler comprises the following steps:

[0067] Add 5 parts by weight of nano-montmorillonite to 70 parts by weight of a 3.5 wt% hexadecyltrimethylammonium chloride aqueous solution, stir for 4 hours at 65° C. and 120 r / min, filter, and dry to obtain pretreated nano-montmorillonite;

[0068] 0.6 parts by weight of 3-acryloxypropylmethyldimethoxysilane, 0.4 parts by weight of allyltriethoxysilane and 85 parts by weight of 50wt% ethanol aqueous solution were uniformly mixed, and then 5 parts by weight of nano-silicon dioxide and 3 parts by weight of pretreated nano-montmorillonite were added in sequence, and ultrasonic treatment was performed for 40 minutes under the conditions of ultrasonic power of 100W and ultrasonic frequency of 25kHz, and then 1 part by weight of gamma-polyglutamic acid was added, and stirred for 50 minutes at 56°C and 200r / min, filtered, and dried to obtain a modified filler.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that the preparation method of the modified filler is different, which is as follows: The preparation method of the modified filler comprises the following steps:

[0071] Add 12 parts by weight of nano-silica to 100 parts by weight of a 1.5 wt% hydroxypropyl chitosan aqueous solution, perform ultrasonic treatment for 3 hours at an ultrasonic power of 100 W and an ultrasonic frequency of 25 kHz, filter, and dry to obtain pretreated nano-silica;

[0072] 0.6 parts by weight of 3-acryloxypropylmethyldimethoxysilane, 0.4 parts by weight of allyltriethoxysilane and 85 parts by weight of 50wt% ethanol aqueous solution were uniformly mixed, and then 5 parts by weight of pretreated nano-silica and 3 parts by weight of nano-montmorillonite were added in sequence, and ultrasonic treatment was performed for 40 minutes under the conditions of ultrasonic power of 100W and ultrasonic frequency of 25kHz, and then 1 part by weight of gamma-polyglutamic acid was added, and stirred for 50 minutes at 56°C and 200r / min, filtered, and dried to obtain a modified filler.

[0073] Comparative Example 3

[0074] The difference between this comparative example and Example 1 is that the preparation method of the modified filler is different, which is as follows: The preparation method of the modified filler comprises the following steps:

[0075] 0.6 parts by weight of 3-acryloxypropylmethyldimethoxysilane, 0.4 parts by weight of allyltriethoxysilane and 85 parts by weight of 50wt% ethanol aqueous solution were uniformly mixed, and then 5 parts by weight of nano-silicon dioxide and 3 parts by weight of nano-montmorillonite were added in sequence, and ultrasonic treatment was performed for 40 minutes under the conditions of ultrasonic power of 100W and ultrasonic frequency of 25kHz, and then 1 part by weight of gamma-polyglutamic acid was added, and stirred for 50 minutes at 56°C and 200r / min, filtered, and dried to obtain a modified filler.

[0076] Comparative Example 4

[0077] The difference between this comparative example and Example 1 is that the preparation method of the modified filler is different, which is as follows: The preparation method of the modified filler comprises the following steps:

[0078] 12 parts by weight of nano-silicon dioxide are added to 100 parts by weight of a 1.5wt% hydroxypropyl chitosan aqueous solution, ultrasonically treated for 3 hours at an ultrasonic power of 100 W and an ultrasonic frequency of 25 kHz, filtered, and dried to obtain pretreated nano-silicon dioxide; 5 parts by weight of nano-montmorillonite are added to 70 parts by weight of a 3.5wt% hexadecyltrimethylammonium chloride aqueous solution, stirred for 4 hours at 65° C. and 120 r / min, filtered, and dried to obtain pretreated nano-montmorillonite;

[0079] Take 85 parts by weight of a 50wt% ethanol aqueous solution, then add 5 parts by weight of pretreated nano-silica and 3 parts by weight of pretreated nano-montmorillonite in sequence, ultrasonically treat for 40 minutes at an ultrasonic power of 100 W and an ultrasonic frequency of 25 kHz, then add 1 part by weight of γ-polyglutamic acid, stir for 50 minutes at 56°C and 200 r / min, filter, and dry to obtain a modified filler.

[0080] Comparative Example 5

[0081] The difference between this comparative example and Example 1 is that the small amount of sustained-release coating liquid is different, specifically as follows: the small amount of sustained-release coating liquid is composed of 25 parts by weight of castor oil polyol and 32 parts by weight of polymethylene polyphenyl polyisocyanate.

[0082] Comparative Example 6

[0083] The difference between this comparative example and Example 1 is that the small amount of sustained-release coating liquid is different, specifically as follows: the small amount of sustained-release coating liquid is composed of 25 parts by weight of castor oil polyol and 8 parts by weight of oxalyl diamide.

[0084] Performance Test 1

[0085] The release rate of the slow-release fertilizers obtained in Examples 1-3 and Comparative Examples 1-6 of the present application was tested in accordance with the national standard GB / T 23348-2009, and the test temperature was 25°C; the stability of the slow-release fertilizers obtained in Examples 1-3 and Comparative Examples 1-6 of the present application was tested, specifically: the slow-release fertilizers were placed in an open environment at a temperature of 40°C and a relative humidity of 65% for 6 months to observe whether adhesion or agglomeration occurred. The results are shown in Table 1.

[0086] Table 1: Test results of slow-release performance and stability of slow-release fertilizers

[0087]

[0088] Performance Test 2

[0089] The slow-release fertilizers obtained in Examples 1-3 and Comparative Examples 1-6 of the present application were tested by field trials, with commercially available rice compound fertilizers as the control group. The application amount was the same, all 60 kg / mu, and applied once 7 days before rice planting. The other field management measures were completely consistent. Among them, the field soil type was typical paddy soil (rice area in the middle and lower reaches of the Yangtze River), with basic physical and chemical properties: pH 6.2, organic matter content 18.52 g / kg, available nitrogen 90.65 mg / kg, available phosphorus 20.81 mg / kg, and available potassium 92.63 mg / kg. The improvement effect of slow-release fertilizers on soil and the yield were analyzed. The results are shown in Table 2.

[0090] Table 2: Field test results of slow-release fertilizers

[0091]

[0092] It can be seen from the above performance test results that the slow-release fertilizers prepared in Examples 1-3 have excellent slow-release performance and stability, can effectively increase crop yields, and promote the improvement of soil fertility, especially the slow-release fertilizer of Example 1 has the most outstanding comprehensive performance. This is because the present invention further improves the slow-release performance of the slow-release fertilizer by adopting a specific modified filler and calcium silicate to act synergistically, and combines a small amount of slow-release coating liquid for coating treatment, thereby effectively extending the nutrient release time of the fertilizer, improving the utilization rate of the fertilizer, and better promoting crop growth.

[0093] In comparison, since the necessary technical solutions were not adopted in Comparative Examples 1-6, the corresponding performance tests were significantly worse than those of Examples 1-3. No modified filler was used in Comparative Examples 1-4, and no specific small amount of slow-release coating liquid was used in Comparative Examples 5-6. It can be seen from the results that the comprehensive performance of the slow-release fertilizer was reduced. The above experimental results further prove the importance of the technical solutions defined in the present invention for its technical effects.

[0094] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a slow-release fertilizer, characterized in that: The following steps are involved: 90-100 parts by weight of calcium silicate are added to 2-20 parts by weight of potassium chloride or potassium sulfate and stirred for 0.3-30 hours, and then 0-5 parts by weight of modified filler and 0-600 parts by weight of inorganic fertilizer are added in sequence and stirred for 0.5-10 hours to obtain slurry; the slurry is sprayed out by a spraying machine and then falls into a rolling plate to form particles with smooth appearance; The particles are fed into a drum, and a small amount of slow-release coating liquid is sprayed to form a coating layer to obtain coated particles; the small amount of slow-release coating liquid is composed of castor oil polyol, polymethylene polyphenyl polyisocyanate and oxalyl diamide; the coated particles are baked, the particles are sieved, and packaged to obtain the slow-release fertilizer.

2. The method for preparing a slow-release fertilizer according to claim 1, characterized in that: The preparation method of the modified filler comprises the following steps: Adding nano-silicon dioxide to a hydroxypropyl chitosan aqueous solution, performing ultrasonic treatment, filtering, and drying to obtain pretreated nano-silicon dioxide; adding nano-montmorillonite to a hexadecyltrimethylammonium chloride aqueous solution, heating and stirring, filtering, and drying to obtain pretreated nano-montmorillonite; 3-acryloxypropylmethyldimethoxysilane, allyltriethoxysilane and ethanol aqueous solution are uniformly mixed, and then pretreated nano-silica and pretreated nano-montmorillonite are added in sequence for ultrasonic treatment, and then gamma-polyglutamic acid is added for heating and stirring, filtered, and dried to obtain a modified filler.

3. The method for preparing a slow-release fertilizer according to claim 2, characterized in that: The preparation method of the modified filler comprises the following steps: 10-15 parts by weight of nano-silicon dioxide are added to 70-120 parts by weight of 1-2wt% hydroxypropyl chitosan aqueous solution, ultrasonically treated for 2-4h, filtered, and dried to obtain pretreated nano-silicon dioxide; 4-6 parts by weight of nano-montmorillonite are added to 60-80 parts by weight of 2-5wt% hexadecyltrimethylammonium chloride aqueous solution, stirred for 3-5h, filtered, and dried to obtain pretreated nano-montmorillonite; 0.5-0.7 parts by weight of 3-acryloxypropylmethyldimethoxysilane, 0.3-0.5 parts by weight of allyltriethoxysilane and 80-90 parts by weight of 45-60wt% ethanol aqueous solution are uniformly mixed, and then 4-6 parts by weight of pretreated nano-silicon dioxide and 2-4 parts by weight of pretreated nano-montmorillonite are added in sequence, ultrasonically treated for 30-50 minutes, and then 0.5-1.5 parts by weight of gamma-polyglutamic acid are added, stirred for 40-60 minutes, filtered, and dried to obtain a modified filler.

4. The method for preparing a slow-release fertilizer according to claim 1, characterized in that: The small amount of sustained-release coating liquid is composed of 20-30 parts by weight of castor oil polyol, 30-35 parts by weight of polymethylene polyphenyl polyisocyanate and 5-10 parts by weight of oxalyl diamide.

5. The method for preparing a slow-release fertilizer according to claim 1, characterized in that: The inorganic fertilizer is a mixture of urea, potassium dihydrogen phosphate and diammonium hydrogen phosphate in a weight ratio of (2-4):(2-3):

1.

6. The method for preparing a slow-release fertilizer according to claim 1, characterized in that: The coating layer accounts for 0-4% of the total weight of the particles.

7. The method for preparing a slow-release fertilizer according to claim 1, characterized in that: The pressure of the spraying machine is 0.2-0.6MPa, and the rotation speed of the rolling plate is 2-20r / min.

8. The method for preparing a slow-release fertilizer according to claim 1, characterized in that: The rotation speed of the drum is 5-15 r / min; the spraying pressure is 7-10 MPa, and the spraying temperature is 70-80°C.

9. The method for preparing a slow-release fertilizer according to claim 1, characterized in that: The baking conditions are: pre-baking at 90-100° C. for 0.5-10 h, and then baking at 100-120° C. for 0.5-10 h.

10. A slow-release fertilizer, characterized in that: Prepared according to the method described in any one of claims 1 to 9.

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