Sugar refinery filter peat-based slow-release fertilizer for citrus and preparation method of slow-release fertilizer

Abstract

The invention relates to the technical field of fertilizers, in particular to a sugar refinery filter peat-based slow release fertilizer for citrus and a preparation method thereof. According to the invention, a variable-temperature carbonization process is adopted, so that the biochar forms different structures and porosities at different temperature stages, and a coating agent and the biochar are alternately coated during coating, so that not only is the physical strength of fertilizer particles enhanced, but also a coating layer is more stable, and the crushing and loss of the fertilizer in the application process are effectively avoided; the coating agent is combined with the charcoal, so that the fertilizer can continuously and stably provide nutrition in the whole growth season, the utilization rate of the fertilizer is increased, and the environmental pollution is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of fertilizers, and in particular to a sugar mill filtered peat-based slow-release fertilizer for citrus and a preparation method thereof. Background Art

[0002] With the continuous development of agricultural production and the improvement of environmental protection requirements, slow-release fertilizers, as an efficient and environmentally friendly form of fertilizer, have gradually become the mainstream choice for agricultural fertilization. Slow-release fertilizers reduce the volatilization and loss of traditional fertilizers in the soil by controlling the nutrient release rate in the fertilizer, improve the utilization efficiency of nutrients, and reduce pollution to the environment. Especially in the cultivation of fruit trees such as citrus, appropriate fertilization methods can effectively improve soil fertility and promote the healthy growth of fruit trees. However, traditional fertilizers rely on simple chemical fertilizer supply methods, and their use often has problems such as rapid nutrient loss and serious soil pollution. Therefore, the development of new slow-release fertilizers, especially carbon-based slow-release fertilizers combined with biochar and coating technology, has become a hot topic in current agricultural fertilizer technology research.

[0003] Traditional fertilizer application methods mainly include direct application of chemical fertilizers, covering the soil after fertilization, etc. These methods often do not fully consider the slow release and long-term stable supply of nutrients. Conventional chemical fertilizers such as urea, potassium sulfate and superphosphate have a faster dissolution rate and are easy to release a large amount of nutrients in a short time after fertilization, resulting in rapid absorption by crops, but also causing a large amount of nutrients to fail to be fully utilized, but instead are lost with water or evaporated into the air, causing waste and polluting the environment. In order to improve fertilizer utilization, traditional slow-release fertilizer technology usually relies on artificially synthesized polymer coating layers. Although these coating materials can control the nutrient release rate, their environmental friendliness and sustainability still have certain limitations, and the production process is relatively complex and the cost is high. In addition, a single fertilizer release regulation method is usually difficult to meet the nutrient needs of different crops at different growth stages. Summary of the invention

[0004] The object of the present invention is to provide a sugar factory filtered peat-based slow-release fertilizer for citrus and a preparation method thereof in view of the above-mentioned problems.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme: a method for preparing a sugar factory filtered peat-based slow-release fertilizer for citrus, comprising the following steps:

[0006] (1) After air-drying the sugarcane filter mud, crush it, pass it through a 40-mesh sieve, and then carbonize it at 280°C for 4 hours, then increase the temperature to 450°C, continue carbonizing for 4 hours, and finally cool it to 400°C for another 4 hours, and take it out after cooling to obtain biochar;

[0007] (2) Weigh 20-25 parts by weight of urea, 10-15 parts by weight of potassium sulfate and 10-15 parts by weight of superphosphate, dissolve them in 10 parts by weight of water, and grind them into a mixture after air drying for later use;

[0008] (3) Weigh 40 parts by weight of the biochar obtained in step (1), add it to the mixture obtained in step (2), mix and stir the two, put them into a granulator for granulation, and pass them through a 40-mesh sieve to obtain fertilizer core particles of sugarcane peat-based slow-release fertilizer;

[0009] (4) preparing a coating agent;

[0010] (5) Weighing the coating agent, biochar and fertilizer core particles in a weight ratio of 5:4:20; adding the coating agent and biochar to the fertilizer core particles in batches, and the specific operation is as follows: after each addition of the coating agent, stirring the mixture of the fertilizer core particles and the coating agent under hot air, stirring for 3-5 minutes, adding biochar when the coating agent is in a paste state, stirring and mixing until completely dry, repeating the steps of adding the coating agent, hot air stirring, adding biochar, and drying again, until the coating agent and biochar are completely added and the surface of the fertilizer core particles is covered with a dark purple coating; after drying, the slow-release fertilizer is obtained.

[0011] Preferably, in the above preparation method, the preparation method of the coating agent in step (4) is: weigh 80-85 parts by weight of ethyl acetate, add 10-12 parts by weight of polyvinyl alcohol in batches, stir to completely dissolve it, then add 5-6 parts by weight of isocyanate and 1-1.5 parts by weight of sodium dodecylbenzene sulfonate, mix them evenly, and finally add 2 parts by weight of calcium stearate, stir to mix them evenly, to obtain a mixed solution; then weigh 2 parts by weight of carmine, dissolve it in water, and then add it to the mixed solution, stir to make it evenly colored, to obtain the coating agent.

[0012] Preferably, in the above preparation method, the temperature of stirring under hot air in step (4) is 50-60°C.

[0013] The present invention also provides a sugar mill peat-based slow-release fertilizer prepared by the preparation method.

[0014] In summary, due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0015] 1. Compared with traditional fertilizer technology, the scheme of the present invention uses biochar as a carrier and combines it with coating technology to convert sugarcane filter mud into carbon-based slow-release fertilizer. It combines biochar, coating technology and fertilizer slow-release principle, which not only improves the nutrient utilization rate of fertilizer, but also significantly improves the soil quality and crop growth environment of the citrus industry, and successfully solves the problems of fast fertilizer loss, uneven nutrient release and environmental pollution in the prior art. First of all, the biochar obtained by the variable temperature carbonization process has a high specific surface area and rich pore structure. The introduction of biochar not only improves the physical properties of fertilizer particles, improves its ability to adsorb and store nutrients, so that it can effectively adsorb and store nutrients in fertilizers, but also prolongs the release cycle of fertilizers through its unique pore structure, reducing nutrient loss; this slow-release characteristic reduces the common nutrient loss problem in the use of traditional fertilizers, ensures that fertilizers provide a stable nutrient supply at different growth stages, and contributes to the healthy growth and yield increase of citrus trees. Secondly, through the application of the coating agent, the slow-release effect of the fertilizer is further guaranteed, the environmental adaptability of the fertilizer is further improved, the release cycle of the fertilizer is extended, and the release rate of the fertilizer is effectively controlled by regulating the thickness and material composition of the coating layer, ensuring that the fertilizer can still maintain a good slow-release effect under high temperature or humid conditions. Finally, the present invention alternately coats the coating agent and biochar during coating, which not only enhances the physical strength of the fertilizer particles, but also makes the coating layer more stable, effectively avoiding the breakage and loss of the fertilizer during application; the use of the coating agent combined with biochar enables the fertilizer to provide nutrition continuously and stably throughout the growing season, thereby improving the utilization rate of the fertilizer and reducing environmental pollution. This innovative technology breaks through the bottleneck of traditional slow-release fertilizers that rely on a single chemical material coating, not only improves the slow-release effect, but also has a higher environmental friendliness, providing a more sustainable, economical and efficient fertilization scheme for modern agriculture. The scheme of the present invention not only improves the use efficiency and environmental protection of the fertilizer, but also provides a sustainable, economical and efficient fertilization solution for the citrus industry, promoting agricultural production to develop in a more efficient and greener direction.

[0016] 2. The present invention solves the problems of rapid nutrient loss, low fertilizer utilization rate, and serious environmental pollution during the application of traditional fertilizers through innovative carbonization process and coating technology. By adopting a variable temperature carbonization process, the biochar forms different structures and porosities at different temperature stages, so as to improve the slow-release ability of the fertilizer and make it better suitable for the citrus industry. By utilizing the high specific surface area and pore structure of biochar, combined with the coating technology of slow-release fertilizer, it can not only significantly extend the nutrient release cycle of the fertilizer, improve the nutrient utilization efficiency of the fertilizer, and reduce the negative impact of the fertilizer on the environment, but also improve the physical properties of the soil, improve soil health, and promote the balanced growth and high yield of crops such as citrus. The present invention aims to provide an environmentally friendly, economical and efficient fertilizer solution for agricultural production, promote the sustainable development of agriculture, and provide an optimized fertilization technology for the citrus industry.

[0017] 3. The preparation method of the sugarcane peat-based slow-release fertilizer disclosed in the present invention is applied to citrus. Compared with traditional fertilization, the addition of the sugarcane peat-based slow-release fertilizer greatly reduces the use of chemical fertilizers, increases the content of nitrogen and phosphorus nutrients in the soil, and reduces the loss rate of nutrients. While reducing the risk of environmental pollution, it improves the economic benefits of the citrus industry and promotes the green and sustainable development of the citrus industry and the sugar industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The present invention is a flow chart of the preparation process of the sugar factory filtered peat-based slow-release fertilizer for citrus. DETAILED DESCRIPTION

[0019] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present application.

[0020] The process flow chart of the preparation of the sugar mill peat-based slow-release fertilizer for citrus of the present invention is as follows: Figure 1 As shown, the specific preparation process includes the following steps:

[0021] (1) After the sugarcane filter mud is naturally air-dried, it is crushed and passed through a 40-mesh sieve to remove impurities such as glass and plastic, in order to ensure the purity and particle consistency of the initial raw material and provide uniform reaction conditions for subsequent carbonization; then 500 parts by weight of the sieved sugarcane filter mud is weighed and first placed in a carbonization furnace for carbonization, and then taken out after cooling to obtain biochar; the carbonization process adopts segmented temperature control to optimize the pore structure and adsorption performance of the biochar, and the carbonization process includes the following three temperature change stages:

[0022] ① The initial temperature is set at 280 degrees Celsius and carbonization is continued for 4 hours. The main purpose of this stage is to remove moisture and volatile substances from the raw materials. The degree of removal of volatile substances can be monitored by the following formula:

[0023]

[0024] Among them, M v represents the volatile matter removal rate, m i is the initial mass of raw materials, m f is the mass after stage carbonization; by calculating M v , the dehumidification and devolatilization efficiency in the initial stage of carbonization can be dynamically evaluated to ensure that the first stage is fully completed;

[0025] ② Raise the temperature to 450℃ and continue carbonization for 4 hours. In this stage, the organic matter is further decomposed by high temperature and a preliminary carbonized skeleton structure is formed. In this process, in order to evaluate the pore formation effect, the porosity can be calculated by the following formula:

[0026]

[0027] Where P is the porosity, V g is the total pore volume of biochar, V o is the volume of the solid after carbonization, and m is the sample mass; optimizing the carbonization temperature and time can effectively improve the porosity, thereby increasing the adsorption capacity of biochar and the slow-release effect of nutrients. ③ Cool down to 400℃ and carbonize for another 4 hours. The main purpose of this stage is to stabilize the internal structure of biochar and further adjust the pore morphology to make it more suitable as an adsorption carrier for slow-release fertilizers; the total porosity and specific surface area of ​​the obtained biochar can be significantly improved by segmented carbonization control, the porosity can be increased from 30% to 60%, and the specific surface area can be increased from 220 square meters per gram to 350 square meters per gram, thereby providing a larger contact area and longer release time for the active ingredients of slow-release fertilizers.

[0028] (2) Weigh 20-25 parts by weight of urea, 10-15 parts by weight of potassium sulfate and 10-15 parts by weight of superphosphate, dissolve them in 10 parts by weight of water, and grind them into powder after air drying for later use.

[0029] The purpose of this step is to provide sufficient nitrogen, potassium and phosphorus, the three basic nutrients for the slow-release fertilizer. During the preparation process, urea provides the nitrogen source, potassium sulfate provides the potassium source, and superphosphate adds the phosphorus source to the fertilizer. The ratio of these three components directly affects the nutrient supply capacity of the slow-release fertilizer and the release rate of nutrients in the soil; in order to ensure the dissolution effect, the amount of water used must be sufficient to dissolve these salt components to avoid precipitation or crystallization. The dissolved mixture needs to be air-dried for further grinding to make its particle size suitable for mixing with biochar and other ingredients. The solubility of each component in the dissolved formula and the concentration of the aqueous solution are key factors. The concentration change of the solution can be calculated by the following formula:

[0030]

[0031] Among them, C represents the concentration of the solution, m is the mass of the dissolved substance, and V is the volume of the solvent. By adjusting the mass of urea, potassium sulfate and superphosphate and the volume of water, the concentration of the fertilizer solution can be accurately controlled to ensure the uniform dissolution of each fertilizer component, thereby avoiding unnecessary waste caused by uneven nutrition or excessive ingredients. In this process, ensuring the appropriate concentration of each component is a crucial link in the preparation process. If the concentration is too high, the solubility will reach saturation, resulting in some fertilizer components not being completely dissolved, affecting the fertilizer effect. The air-dried mixture needs to be further ground into more uniform particles for subsequent mixing with biochar and granulation to form the core particles of slow-release fertilizer. This link can fully distribute the nutrients of the fertilizer in the particles, ensuring that the fertilizer can be gradually released according to crop needs during application.

[0032] This concentration needs to be precisely controlled to ensure that the solubility of each component and the proportion in the solution are appropriate, further achieving the scientificity and stability of the formula. The solution is ground after air drying, which is convenient for mixing with other ingredients, and finally forms slow-release particles of fertilizer, thereby achieving efficient and continuous supply of fertilizer. By controlling the concentration and component ratio of the fertilizer solution through this process, the utilization rate of the fertilizer can be effectively improved, thereby enhancing the effect and applicability of the entire fertilizer preparation process.

[0033] (3) Weigh 40 parts by weight of the biochar obtained in step (1), add the mixture obtained in step (2) into the biochar obtained in step (1), mix and stir the two, put them into a granulator for granulation, and pass through a 40-mesh sieve to obtain fertilizer core particles of sugarcane peat-based slow-release fertilizer.

[0034] The purpose of this step is to evenly adsorb nutrients on the surface of biochar and ensure that the fertilizer has sufficient operability and stability in the subsequent granulation process; the surface of biochar has a rich pore structure, which enables it to adsorb and store water-soluble fertilizer components, thereby slowing down the rate of nutrient release; therefore, biochar is not only a carrier of fertilizer, but also plays an important role in improving the slow-release characteristics of fertilizer.

[0035] During mixing, ensuring uniform distribution of biochar in the mixture can be assessed by the following formula:

[0036]

[0037] Where H is the mixing uniformity index, C i represents the concentration of nutrients in each sample, and n is the total number of samples. The purpose of this formula is to evaluate the uniformity of the mixing process by measuring the fertilizer concentration in each particle; ideally, H should be close to the ideal concentration value of the fertilizer, which means that the nutrients are evenly distributed in each particle; during the mixing process, excessive mixing should be avoided to prevent biochar breakage or loss of nutrients, while ensuring that each particle can evenly absorb enough nutrients.

[0038] After stirring, the mixture is placed in a granulator for granulation, and the fertilizer core particles are obtained after being sieved through a 40-mesh sieve. The key to this link is the optimization of the granulation process, which directly determines the shape, strength and subsequent use effect of the fertilizer particles. During the granulation process, the material will aggregate and form particles under the action of external forces to form fertilizer particles with good structure. In order to ensure the granulation quality and particle uniformity, the crushing strength of the particles can be evaluated, and the formula is:

[0039]

[0040] Among them, S is the crushing strength of the particles, F is the crushing force, and A is the contact area of ​​the particles. By controlling the granulation pressure and material ratio, the fertilizer particles can have higher strength to avoid breaking during transportation and application. The granulated particles need to be screened to ensure the consistency of particle size, and 40 mesh is used to screen out particles that meet the standards.

[0041] For example, if the average crushing strength of 100 fertilizer particles is 2.5N and the contact area of ​​each particle is 0.5cm 2 , then the crushing strength can be calculated as:

[0042]

[0043] This value indicates that the particles can maintain better stability during application and reduce breakage.

[0044] Through this series of operations, not only the nutrients of the fertilizer are evenly distributed, but also the stability and applicability of the fertilizer particles are improved, which helps to further enhance the slow-release effect in the citrus industry. In the overall framework, the use of biochar not only enhances the storage capacity of the fertilizer, but also ensures the efficient and continuous release of fertilizer particles by optimizing the mixing and granulation process, meeting the nutritional needs of citrus crops.

[0045] (4) Weigh 80-85 parts by weight of ethyl acetate, add 10-12 parts by weight of polyvinyl alcohol in batches, stir to completely dissolve, then add 5-6 parts by weight of isocyanate and 1-1.5 parts by weight of sodium dodecylbenzene sulfonate, mix them evenly, finally add 2 parts by weight of calcium stearate, stir to mix them evenly, weigh 2 parts by weight of carmine, add a little water to just dissolve the carmine to show pink, then add to the above mixture and stir to evenly color it, to obtain a coating agent.

[0046] In this step, the key to the preparation of the coating agent is to form a stable coating by accurately proportioning different ingredients to coat the fertilizer particles and enhance their slow-release properties and environmental adaptability. First, 80-85 parts by weight of ethyl acetate is used as a solvent and mixed with 10-12 parts by weight of polyvinyl alcohol to ensure that the polyvinyl alcohol is completely dissolved. The molecular structure of polyvinyl alcohol contains polar groups, which can form a strong interaction force with the molecules in the solvent, helping to improve the uniformity and stability of the coating layer. In this process, the choice of solvent is crucial, because ethyl acetate can effectively dissolve PVA and has moderate volatility, which is convenient for the subsequent operation of the coating agent.

[0047] To further improve the durability and reactivity of the coating layer, 5-6 parts by weight of isocyanate is added. The -NCO group in the isocyanate molecule can react with moisture or other components under certain conditions to form a strong polyurethane chemical bond, which not only enhances the firmness of the coating, but also improves its resistance to hydrolysis, thereby prolonging the slow-release effect of the fertilizer. The rate of this chemical reaction can be evaluated by the following formula:

[0048] r=k[C][NCO]

[0049] Where r represents the reaction rate, k is the reaction rate constant, [C] is the water concentration, and [NCO] is the isocyanate concentration. This formula shows that the reaction rate is proportional to the product of the water concentration and the isocyanate concentration. By controlling the ratio of these components and the stirring time, the progress of the coating reaction and the structure of the final film layer can be precisely controlled to ensure that it has ideal physical and chemical properties.

[0050] Next, 1-1.5 parts by weight of sodium dodecylbenzene sulfonate is added. This emulsifier can effectively improve the compatibility between different solvents and promote the uniform dispersion of the film-forming agent. The role of the emulsifier is not only to improve the rheological properties of the solution, but also to change the surface tension of the solution, so that the coating effect of the coating agent is more uniform, further ensuring the uniformity of the coating layer.

[0051] Finally, 2 parts by weight of calcium stearate, an organophosphorus compound, is added to enhance the hydrophobicity of the coating and improve the strength of the film. To ensure the color consistency and traceability of the coating agent, 2 parts by weight of carmine is added and completely dissolved in a small amount of water and stirred evenly, so that the coating agent presents a distinct pink color. The color of the coating agent not only helps to monitor the uniformity during the production process, but also serves as an indicator for quality control.

[0052] Through the above steps, the coating agent finally obtained has strong stability, excellent adhesion and adaptability, and can be effectively coated on the surface of fertilizer particles to delay the release of nutrients from the fertilizer. In other words, the proportion of the coating agent is adjusted to an ideal state, and a uniform coating can be formed when coating the fertilizer core particles, so that the nutrients of the fertilizer are slowly released under environmental conditions. By controlling the viscosity and reaction rate of the coating agent, it is ensured that it can maintain a long release cycle under different temperature and humidity conditions, effectively improving the slow-release effect of the entire fertilizer system.

[0053] (5) Weigh the coating agent, biochar and fertilizer core particles in a weight ratio of 5:4:20, and add the coating agent and biochar to the fertilizer core particles in batches. The specific operation is as follows: after each addition of the coating agent, stir the mixture of the fertilizer core particles and the coating agent under hot air at 50-60°C. After stirring for 3-5 minutes, add biochar when the coating agent is in a paste state, stir and mix until completely dry, and repeat the steps of adding the coating agent, hot air stirring, adding biochar, and drying until the coating agent and biochar are completely added and the surface of the fertilizer core particles is covered with a dark purple coating; after air drying, shake slightly to separate the adhering particles to obtain a sugarcane peat-based slow-release fertilizer.

[0054] In step (5), during the mixing and coating process of the coating agent and the fertilizer core particles, ensuring uniform coating and encapsulation of the fertilizer particles is the key to achieving a slow-release effect. The purpose of adding biochar is to increase the adsorption of the fertilizer particles through the characteristics of the biochar itself, and further promote the slow release of nutrients. The addition of biochar, especially during the process of adding the coating agent in batches, helps to improve the physical strength and stability of the fertilizer. Biochar has a high specific surface area and rich pore structure, which makes the nutrient release of the coated fertilizer more uniform and lasting.

[0055] After each addition of the coating agent, the mixture of the fertilizer core particles and the coating agent needs to be stirred under hot air at 50-60°C. The hot air not only accelerates the evaporation of the solvent of the coating agent, causing it to solidify quickly and form a solid film layer, but also prevents excessive moisture from remaining in the coating, thus avoiding the fragility and peeling of the coating. In this process, the formation rate of the coating layer can be evaluated by the following formula:

[0056]

[0057] Where R represents the rate of coating formation, dM / dt is the rate of transfer of the coating agent from the liquid phase to the surface of the solid particles, k is the rate constant, and C s is the saturation concentration, and C is the actual concentration. By adjusting the heating temperature, stirring speed, and concentration of the coating agent, the speed of coating formation can be accurately controlled to make the coating layer uniform and avoid film cracks or particle shedding caused by over-drying.

[0058] When the coating layer is about to dry, a small amount of biochar is added to further enhance the structural stability of the particles and promote the long-term release of the fertilizer. The amount of biochar added is adjusted according to the desired slow-release effect to ensure that the overall structure of the fertilizer is strengthened without affecting the uniform release of nutrients. At this time, the mixture continues to dry under hot air and the coating layer gradually forms. During the drying process, the alternating addition of coating agent and biochar can enhance the thickness and adhesion of the film layer, thereby improving the durability and effect of the fertilizer.

[0059] Finally, after the mixture is completely dried, the adhering particles are separated by slight shaking to obtain the final fertilizer particles. The surface of the fertilizer particles is covered with a layer of dark purple coating, indicating that the coating agent has been evenly covered on the fertilizer core particles and the coating process has achieved the desired effect.

[0060] For example, if the mass of each batch of fertilizer core particles is 100 grams, after stirring and drying, the total amount of coating agent and biochar added is 45 grams (including 25 grams of coating agent and 20 grams of biochar), then the coating layer of each fertilizer core particle will significantly improve its slow-release performance. For example, the formation of the coating layer extends the release time of the fertilizer from the conventional 3 days to 7 days. By controlling the addition ratio of the coating agent and biochar, the release rate of the fertilizer can be adjusted according to the needs of different crops, so as to achieve the purpose of optimizing agricultural production.

[0061] Through the above operation steps, the present application effectively combines the coating agent and biochar, so that the fertilizer can continuously release nutrients after application, improve the utilization rate of the fertilizer, reduce nutrient loss, and ultimately achieve optimized application in the citrus industry. This slow-release fertilizer technology not only improves the efficiency of fertilizer use, but also provides technical support for sustainable agricultural development.

[0062] In order to express the present invention more clearly, the present invention is further described below through specific examples.

[0063] 1. Preparation Example

[0064] Embodiment 1:

[0065] The preparation method of the sugar mill peat-based slow-release fertilizer provided by the present invention is as follows:

[0066] (1) After the sugarcane filter mud is naturally air-dried, it is crushed and impurities such as glass and plastic are removed from it through a 40-mesh sieve. 500 g of the sieved sugarcane filter mud is weighed and placed in a carbonization furnace. It is carbonized at 280°C for 4 hours, then the temperature is increased to 450°C for another 4 hours, and finally the temperature is reduced to 400°C for another 4 hours. After cooling, it is taken out to obtain 200 g of biochar;

[0067] The volatile matter removal rate calculated by the formula is 60%, that is, 60% of the volatile matter is removed, and the porosity P is 35%. When this biochar is combined with fertilizer core particles, it can effectively improve the slow-release performance, making it more suitable for the long-term nutritional needs of the citrus industry. Through this variable temperature carbonization process, not only the resource utilization rate of sugarcane filter mud is improved, but also the biochar has excellent slow-release carrier characteristics, providing a reliable foundation for the efficient application of the overall solution;

[0068] (2) Weigh 25 g of urea, 12 g of potassium sulfate and 12 g of superphosphate, dissolve them in 10 ml of water, and use the formula to calculate the concentration of the fertilizer solution obtained after dissolution: After drying, grind the mixture and set aside;

[0069] (3) Weigh 40 g of the biochar obtained in step (1), add it to the mixture obtained in step (2), mix and stir the two, put them into a granulator for granulation, and pass them through a 40-mesh sieve to obtain fertilizer core particles of sugarcane peat-based slow-release fertilizer;

[0070] (4) Weigh 80 g of ethyl acetate, add 10 g of polyvinyl alcohol in batches, stir to completely dissolve, then add 5 g of isocyanate and 1 g of sodium dodecylbenzene sulfonate, mix evenly, and finally add 2 g of calcium stearate, stir to mix evenly, to obtain a mixed solution; then weigh 2 g of carmine, add a little water until the carmine is just dissolved and turns pink, then add to the above mixed solution, stir to color evenly, to obtain a coating agent;

[0071] (5) Weigh 25 grams of coating agent, 20 grams of biochar and 100 grams of fertilizer core particles, and add the coating agent and biochar to the fertilizer core particles in batches. The specific operation is as follows: after each addition of the coating agent, stir the mixture of the fertilizer core particles and the coating agent under hot air at 60°C. After stirring for 3-5 minutes, add a little biochar when the coating agent is in a paste state, stir and mix until completely dry, and repeat the steps of adding the coating agent, hot air stirring, adding biochar, and drying again until the coating agent and biochar are completely added and the surface of the fertilizer particles is covered with a uniform dark purple coating. After the mixture is completely dry, gently shake to separate the sticky fertilizer particles to obtain the final sugar factory filter peat-based slow-release fertilizer. At this time, the surface of the fertilizer particles is completely covered with the coating, and the color of the coating is dark purple, indicating the completion of the slow-release fertilizer. Through screening and air drying, ensure that the particle size of the fertilizer particles is uniform and suitable for application.

[0072] Embodiment 2:

[0073] The preparation method of the sugar mill peat-based slow-release fertilizer provided by the present invention is as follows:

[0074] (1) Biochar was prepared using the same method as in Example 1;

[0075] (2) Weigh 20 g of urea, 15 g of potassium sulfate and 15 g of superphosphate, dissolve them in 10 ml of water, and use the formula to calculate that the concentration of the fertilizer solution obtained after dissolution is 4.7 g / ml. After air drying, grind the mixture and set aside;

[0076] (3) Weigh 40 g of the biochar obtained in step (1), add it to the mixture obtained in step (2), mix and stir the two, put them into a granulator for granulation, and pass them through a 40-mesh sieve to obtain fertilizer core particles of sugarcane peat-based slow-release fertilizer;

[0077] (4) Weigh 85 g of ethyl acetate, add 12 g of polyvinyl alcohol in batches, stir to completely dissolve, then add 6 g of isocyanate and 1.5 g of sodium dodecylbenzene sulfonate, mix evenly, and finally add 2 g of calcium stearate, stir to mix evenly, to obtain a mixed solution; then weigh 2 g of carmine, add a little water until the carmine is just dissolved and turns pink, then add to the above mixed solution, stir to color evenly, to obtain a coating agent;

[0078] (5) Weigh 30 grams of coating agent, 24 grams of biochar and 120 grams of fertilizer core particles, and add the coating agent and biochar to the fertilizer core particles in batches. The specific operation is as follows: after each addition of the coating agent, stir the mixture of the fertilizer core particles and the coating agent under hot air at 50°C. After stirring for 3-5 minutes, add a little biochar when the coating agent is in a paste state, stir and mix until completely dry, and repeat the steps of adding the coating agent, hot air stirring, adding biochar, and drying again until the coating agent and biochar are completely added and the surface of the fertilizer particles is covered with a uniform dark purple coating. After the mixture is completely dry, gently shake to separate the sticky fertilizer particles to obtain the final sugar factory filter peat-based slow-release fertilizer. At this time, the surface of the fertilizer particles is completely covered with the coating, and the color of the coating is dark purple, indicating the completion of the slow-release fertilizer. Through screening and air drying, ensure that the particle size of the fertilizer particles is uniform and suitable for application.

[0079] Embodiment 3:

[0080] The preparation method of the sugar mill peat-based slow-release fertilizer provided by the present invention is as follows:

[0081] (1) Biochar was prepared using the same method as in Example 1;

[0082] (2) Weigh 23 g of urea, 10 g of potassium sulfate and 10 g of superphosphate, dissolve them in 10 ml of water, and use the formula to calculate that the concentration of the fertilizer solution obtained after dissolution is 4.3 g / ml. After air drying, grind the mixture and set aside;

[0083] (3) Weigh 40 g of the biochar obtained in step (1), add it to the mixture obtained in step (2), mix and stir the two, put them into a granulator for granulation, and pass them through a 40-mesh sieve to obtain fertilizer core particles of sugarcane peat-based slow-release fertilizer;

[0084] (4) preparing a coating agent using the same method as in Example 1;

[0085] (5) Weigh 20 grams of coating agent, 16 grams of biochar and 80 grams of fertilizer core particles, and add the coating agent and biochar to the fertilizer core particles in batches. The specific operation is as follows: after each addition of the coating agent, stir the mixture of the fertilizer core particles and the coating agent under hot air at 50°C. After stirring for 3-5 minutes, add a little biochar when the coating agent is in a paste state, stir and mix until completely dry, and repeat the steps of adding the coating agent, hot air stirring, adding biochar, and drying again until the coating agent and biochar are completely added and the surface of the fertilizer particles is covered with a uniform dark purple coating. After the mixture is completely dry, gently shake to separate the sticky fertilizer particles to obtain the final sugar factory filter peat-based slow-release fertilizer. At this time, the surface of the fertilizer particles is completely covered with the coating, and the color of the coating is dark purple, indicating the completion of the slow-release fertilizer. Through screening and air drying, ensure that the particle size of the fertilizer particles is uniform and suitable for application.

[0086] Comparative Example 1

[0087] The method for preparing the sugar mill peat-based slow-release fertilizer provided in this comparative example is similar to that in Example 1, the only difference being the method for preparing biochar in step (1), and the other steps being the same as those in Example 1.

[0088] In this comparative example, the preparation method of biochar is as follows:

[0089] After the sugarcane filter mud is naturally air-dried, it is crushed and passed through a 40-mesh sieve to remove impurities such as glass and plastic. 500 g of the sieved sugarcane filter mud is weighed and put into a carbonization furnace. It is carbonized at 280°C for 12 hours and taken out after cooling to obtain 300 g of biochar.

[0090] Comparative Example 2

[0091] The method for preparing the sugar mill peat-based slow-release fertilizer provided in this comparative example is similar to that in Example 1, the only difference being the method for preparing biochar in step (1), and the other steps being the same as those in Example 1.

[0092] In this comparative example, the preparation method of biochar is as follows:

[0093] After the sugarcane filter mud is naturally air-dried, it is crushed and passed through a 40-mesh sieve to remove impurities such as glass and plastic. 500 g of the sieved sugarcane filter mud is weighed and put into a carbonization furnace. It is carbonized at 450°C for 12 hours and taken out after cooling to obtain 260 g of biochar.

[0094] Comparative Example 3

[0095] The method for preparing the sugar mill peat-based slow-release fertilizer provided in this comparative example is similar to that in Example 1, the only difference being the method for preparing biochar in step (1), and the other steps being the same as those in Example 1.

[0096] In this comparative example, the preparation method of biochar is as follows:

[0097] After the sugarcane filter mud is naturally air-dried, it is crushed and passed through a 40-mesh sieve to remove impurities such as glass and plastic. 500 g of the sieved sugarcane filter mud is weighed and put into a carbonization furnace. It is carbonized at 400 °C for 12 hours and taken out after cooling to obtain 350 g of biochar.

[0098] Comparative Example 4

[0099] The preparation method of the sugar mill filtered peat-based slow-release fertilizer provided in this comparative example is similar to that of Example 1, the only difference being the amount of coating agent and fertilizer core particles used in coating the fertilizer core particles in step (5), and the other steps being the same as those of Example 1.

[0100] In this comparative example, the dosage of the coating agent, biochar and fertilizer core particles is 100 g, 20 g and 100 g, respectively.

[0101] Comparative Example 5

[0102] The preparation method of the sugar mill filtered peat-based slow-release fertilizer provided in this comparative example is similar to that of Example 1, the only difference being the amount of coating agent and fertilizer core particles used in coating the fertilizer core particles in step (5), and the other steps being the same as those of Example 1.

[0103] In this comparative example, the dosage of the coating agent, biochar and fertilizer core particles is 200 g, 20 g and 100 g, respectively.

[0104] Comparative Example 6

[0105] The preparation method of the sugar mill filtered peat-based slow-release fertilizer provided in this comparative example is similar to that of Example 1, the only difference being the amount of coating agent and fertilizer core particles used in coating the fertilizer core particles in step (5), and the other steps being the same as those of Example 1.

[0106] In this comparative example, the dosage of the coating agent, biochar and fertilizer core particles is 25 grams, 20 grams and 150 grams respectively.

[0107] Comparative Example 7

[0108] The preparation method of the sugar mill filtered peat-based slow-release fertilizer provided in this comparative example is similar to that of Example 1, the only difference being the coating method of the fertilizer core particles in step (5), and the other steps being the same as those of Example 1.

[0109] In this comparative example, the specific method for coating the fertilizer core particles is as follows:

[0110] Weigh 25 grams of coating agent and 100 grams of fertilizer core particles, add the coating agent to the fertilizer core particles in batches, and specifically stir the mixture of the fertilizer core particles and the coating agent under 60° C. hot air after each addition of the coating agent, stir and mix until completely dry, repeat the steps of adding the coating agent and drying again, until the coating agent and biochar are completely added and the fertilizer core particles are coated with a dark purple coating, shake slightly after air drying to separate the sticky particles, and obtain the sugar factory peat-based slow-release fertilizer.

[0111] 2. Effect Verification

[0112] In order to further illustrate the promotion and application value of the sugar mill peat-based slow-release fertilizer of the present invention, various indicators of the slow-release fertilizers obtained in Examples 1-3 and Comparative Examples 1-7 were evaluated.

[0113] 1. The biochars obtained in Example 1 and Comparative Examples 1-3 were compared, and the results are shown in Table 1:

[0114] Table 1

[0115] Biochar Volatile matter removal rate Porosity <![CDATA[Specific surface area (m 2 / g) <!-- 9 -->]]> Example 1 60％ 35％ 350 Comparative Example 1 40％ 25％ 220 Comparative Example 2 48％ 30％ 300 Comparative Example 3 30％ 22％ 230

[0116] As can be seen from Table 1, the removal rate of volatile matter in the biochar prepared in Comparative Example 1 can only reach about 40%, which is much lower than the removal rate of about 60% achieved in Example 1. At the same time, since the temperature was not effectively increased to promote the deep decomposition of organic matter, the pore structure of the formed biochar was not fully developed, and its porosity was only about 25%, and the specific surface area was about 220 square meters per gram, which was significantly different from the biochar prepared in Example 1 of the present application (porosity 35%, specific surface area 350 square meters per gram).

[0117] Under the carbonization conditions of Comparative Example 2, although the organic matter can be decomposed quickly, the internal structure of the biochar is unstable due to the lack of temperature gradient change in the present application. Long-term high temperature causes some pores to be blocked or collapsed due to excessive carbonization. The porosity is measured to be about 30%, and the specific surface area is about 300 square meters per gram, which is also very different from the biochar prepared in Example 1.

[0118] In comparative example 3, sugarcane was peatified at 400°C for 12 hours, but the removal of moisture and volatile substances was insufficient, and the removal rate of volatile substances was about 30%. The degree of organic matter decomposition was limited, the carbonization skeleton of biochar was not well constructed, the pore structure was poor, the porosity was only about 22%, and the specific surface area was about 230 square meters per gram.

[0119] 2. Verification of the effect of slow-release fertilizer on citrus growth

[0120] Citrus plants with the same production conditions were selected, and under the same conditions, the slow-release fertilizers obtained in Examples 1-3 and Comparative Examples 1-7 were applied respectively, and the plant growth, fruit quality and fruit yield were observed to verify the effects of the slow-release fertilizers on citrus growth. The verification results are shown in Table 2.

[0121] Table 2 Comparison of the effects of various slow-release fertilizers on citrus growth

[0122]

[0123]

[0124] As can be seen from Table 2, the citrus fruits that were applied with the slow-release fertilizers prepared in Examples 1-3 of the present application had a higher yield. This is because the biochar obtained by the temperature-variable carbonization process of the slow-release fertilizers prepared in Examples 1-3 of the present application has a high specific surface area and a rich pore structure, which enables it to effectively adsorb and store nutrients in the fertilizer and release them slowly over a long period of time. This slow-release characteristic reduces the common nutrient loss problem in the use of traditional fertilizers, ensures that the fertilizer provides a stable supply of nutrients at different growth stages, and contributes to the healthy growth and yield improvement of citrus trees; and the alternating coating of the coating agent and biochar not only enhances the physical strength of the fertilizer particles, but also makes the coating layer more stable, effectively avoiding the breakage and loss of the fertilizer during the application process; in addition, the introduction of the coating agent further improves the environmental adaptability of the fertilizer, prolongs the release cycle of the fertilizer, and ensures that the fertilizer can still maintain a good slow-release effect under high temperature or humid conditions.

[0125] The preparation method of the slow-release fertilizer in Comparative Example 1-7 is different from that in Example 1-3, which results in various problems after being applied to citrus fruits. The specific analysis is as follows:

[0126] Table 3

[0127]

[0128] The sugar factory filtered peat-based slow-release fertilizer prepared by the method of Comparative Example 1 has limited adsorption capacity for nutrients such as nitrogen, phosphorus, and potassium, which significantly reduces the slow-release performance of the fertilizer in the soil. As shown in Table 3, in the citrus planting test, within one week after the slow-release fertilizer of Comparative Example 1 was applied, the nitrogen content in the soil quickly increased to a peak value, and then rapidly decreased; while the slow-release fertilizer prepared by Examples 1-3 of the present application had a relatively gentle increase in nitrogen content within the same period of time and could be maintained at a certain level for a long time, effectively meeting the continuous demand for nitrogen in the early stage of citrus growth. Because the nitrogen content of the sugar factory filtered peat-based slow-release fertilizer prepared in Comparative Example 1 was released too quickly in the early stage, it was unable to provide a stable nutrient supply for the entire growth process of citrus, resulting in slow growth of citrus plants, yellow and thin leaves, poor fruit development, and a yield reduced by about 30% compared with the slow-release fertilizer using Examples 1-3 of the present application.

[0129] As can be seen from the comparison of the total phosphorus content in the soil in Table 3, the sugar factory filtered peat-based slow-release fertilizer prepared by the method of Comparative Example 2 has an initial nutrient release rate in the soil that is too fast. For example, the phosphorus release in the first three days after fertilization reaches 40% of the total phosphorus content, while the slow-release fertilizer prepared in Examples 1-3 only releases about 15% during the same period. This leads to excessive phosphorus absorption and fertilizer damage in the early stages of citrus growth, which is manifested as stunted root development and scorched spots on the leaves. Over time, due to the damage to the pore structure, the nutrient release rate drops sharply again, and it is unable to meet the nutrient demand of citrus in the middle and late stages of growth, resulting in uneven size of citrus fruits and reduced sweetness. The fruit yield is reduced by about 25% compared to the slow-release fertilizers of Examples 1-3 of the present application, and the fruit quality is significantly reduced.

[0130] The sugar mill peat-based slow-release fertilizer prepared by the method of comparative example 3 has poor stability of fertilizer particles in the soil, and nutrients are very easy to dissolve. In the simulated rainfall test, the dissolution rates of nitrogen and potassium nutrients in the slow-release fertilizer obtained in comparative example 3 reached 30% and 25% respectively within 1 hour, while the dissolution rates of nitrogen and potassium nutrients in the slow-release fertilizer prepared by examples 1-3 of the present application were only 5% and 3% within 1 hour. The excessively high nitrogen and potassium dissolution rates of the slow-release fertilizer obtained in comparative example 3 cause serious loss of fertilizer nutrients, and the utilization rate is extremely low, and it is unable to provide long-term nutrient support for citrus growth, so that citrus shows obvious symptoms of fertilizer deficiency during growth, such as short plants, slow growth of new shoots, thin leaves and light green color, etc., which ultimately leads to a reduction of about 30% in citrus yield, and the fruit quality does not meet market requirements.

[0131] In Comparative Example 4, the mass ratio of the coating agent to the fertilizer core particles is 1:1. This ratio results in a large excess of the coating agent, which makes the coating layer on the surface of the fertilizer particles too thick. The coating layer thickness can be measured to be about 3 times that of Examples 1-3 of the present application. On the one hand, the production cost is greatly increased, about 2.5 times that of Examples 1-3 of the present application; on the other hand, the overly thick coating seriously hinders the diffusion of nutrients. As shown in Table 3, after 10 days of fertilization in the soil, the rate of nitrogen diffusion outward from the inside of the fertilizer core particles is only 20% of that of Examples 1-3 of the present application, resulting in slow growth of citrus seedlings, delayed germination of new shoots, and plant growth lagging behind normal fertilization by about 15 days. Moreover, the overly thick coating layer degrades slowly and remains in the soil for a long time. After a growth cycle, the amount of coating agent residue in the soil is 5 times that of Examples 1-3 of the present application, which has an adverse effect on the physical structure and microbial environment of the soil. Long-term use may lead to soil compaction and imbalance of microbial communities.

[0132] In Comparative Example 5, the mass ratio of the coating agent to the fertilizer core particles is 2:1, which results in a serious excess of the coating agent, and the coating layer thickness is about 4 times that of Examples 1-3 of the present application. In addition to the above problems, due to the viscosity of the coating agent, the prepared fertilizer particles have serious adhesion phenomenon, which makes it difficult to disperse evenly during the fertilization process, resulting in excessive fertilizer concentration in local areas, which can easily cause fertilizer damage, causing citrus leaves to burn and curl. At the same time, insufficient fertilizer in other areas affects the overall growth balance of citrus, resulting in excessive differences in fruit size, a reduction of about 35% in the rate of high-quality fruit, and a reduction of about 30% in yield.

[0133] In Comparative Example 6, the mass ratio of the coating agent to the fertilizer core particles is 1:6. In this comparative example, the coating agent is too little, and the coating layer of the fertilizer particles is thin and incomplete, and can only cover about 60% of the surface of the fertilizer core particles. This causes the slow-release effect of the fertilizer in the soil to be lost, and the nutrient release rate is no different from that of ordinary fertilizers. Under irrigation conditions, the potassium loss rate is as high as 40% within 2 days after fertilization, while the potassium loss rate of the slow-release fertilizer obtained in Examples 1-3 of the present application is less than 5% during the same period; the rapid loss of nutrients causes the fertilizer utilization rate of the slow-release fertilizer obtained in Comparative Example 6 to be less than 30%, while the fertilizer utilization rate of the slow-release fertilizer obtained in Examples 1-3 of the present application is as high as more than 70%. It can be seen that the fertilizer utilization rate of the slow-release fertilizer obtained in Comparative Example 6 is much lower than the fertilizer utilization rate of the slow-release fertilizer provided in the present application, which leads to frequent fertilizer deficiency in citrus during growth, poor fruit development, small size, sour taste, and a yield reduction of about 50%.

[0134] In the coating process of Comparative Example 7, no biochar was added, and the coating layer was formed only by the coating agent. Due to the lack of high specific surface area and rich pore structure of biochar, the coating layer has weak ability to adsorb and fix nutrients. In the soil environment simulation test, after the fertilizer particles obtained in Comparative Example 7 were soaked in water for 1 hour, the dissolution rates of nitrogen, phosphorus and potassium nutrients reached 25%, 18% and 20%, respectively, while the slow-release fertilizer obtained in Example 1 of the present application was soaked in water for 1 hour, and the dissolution rates of nitrogen, phosphorus and potassium nutrients were 5%, 3% and 3%, respectively. The excessively high dissolution rate resulted in extremely poor slow-release effect of the fertilizer obtained in Comparative Example 7 in the soil, and rapid and uneven nutrient release. In the citrus planting experiment, the soil nutrient concentration was too high in a short period of time after fertilization, and the citrus roots showed reverse osmosis, and the root cells lost water, resulting in obstructed root growth and even rot in some roots. As time goes by, due to the lack of a continuous supply of nutrients, the growth of citrus plants stagnates, the leaves turn yellow and fall off, and the fruits fall in large numbers. Ultimately, the yield is reduced by about 60%, the quality of the fruit is severely reduced, and it almost loses its commercial value.

[0135] In summary, the sugar mill peat-based slow-release fertilizer prepared in Examples 1-3 of the present invention can be applied according to the different needs of crops. The fertilizer has good slow-release properties, and achieves long-term nutrient release through the action of biochar, reduces the loss and volatilization of traditional fertilizers, and effectively improves the utilization rate of fertilizers. The effect evaluation after application shows that the use of this slow-release fertilizer can significantly increase the growth rate, yield and quality of crops, and can also improve the physical and chemical properties of the soil. It shows that the present invention successfully provides an efficient and environmentally friendly slow-release fertilizer solution, which not only optimizes the use effect of the fertilizer, but also provides strong support for the sustainable development of agriculture.

[0136] The above description is a detailed description of the preferred feasible embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modified changes completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A method for preparing a sugar factory filtered peat-based slow-release fertilizer for citrus, characterized in that: The following steps are involved: (1) After air-drying the sugarcane filter mud, crush it, pass it through a 40-mesh sieve, and then carbonize it at 280°C for 4 hours, then increase the temperature to 450°C, continue carbonizing for 4 hours, and finally cool it to 400°C for another 4 hours, and take it out after cooling to obtain biochar; (2) Weigh 20-25 parts by weight of urea, 10-15 parts by weight of potassium sulfate and 10-15 parts by weight of superphosphate, dissolve them in 10 parts by weight of water, and grind them into a mixture after air drying for later use; (3) Weigh 40 parts by weight of the biochar obtained in step (1), add it to the mixture obtained in step (2), mix and stir the two, put them into a granulator for granulation, and pass them through a 40-mesh sieve to obtain fertilizer core particles of sugarcane peat-based slow-release fertilizer; (4) preparing a coating agent; (5) Weighing the coating agent, biochar and fertilizer core particles in a weight ratio of 5:4:20; adding the coating agent and biochar to the fertilizer core particles in batches, and the specific operation is as follows: after each addition of the coating agent, stirring the mixture of the fertilizer core particles and the coating agent under hot air, stirring for 3-5 minutes, adding biochar when the coating agent is in a paste state, stirring and mixing until completely dry, repeating the steps of adding the coating agent, hot air stirring, adding biochar, and drying again, until the coating agent and biochar are completely added and the surface of the fertilizer core particles is covered with a dark purple coating; after drying, the slow-release fertilizer is obtained.

2. The preparation method according to claim 1, characterized in that: The preparation method of the coating agent in step (4) is as follows: weigh 80-85 parts by weight of ethyl acetate, add 10-12 parts by weight of polyvinyl alcohol in batches, stir to completely dissolve it, then add 5-6 parts by weight of isocyanate and 1-1.5 parts by weight of sodium dodecylbenzene sulfonate, mix them evenly, and finally add 2 parts by weight of calcium stearate, stir to mix them evenly, and obtain a mixed solution; then weigh 2 parts by weight of carmine, dissolve it in water, and then add it to the mixed solution, stir to make it evenly colored, and obtain the coating agent.

3. The preparation method according to claim 1, characterized in that: The stirring temperature under hot air in step (4) is 50-60°C.

4. The sugar mill peat-based slow-release fertilizer prepared according to the preparation method described in any one of claims 1 to 3.

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