A humic acid-coated slow-release potassium chloride and its preparation method

Abstract

This invention discloses a humic acid-coated slow-release potassium chloride and its preparation method, belonging to the field of biological slow-release organic-inorganic fertilizer technology. The fertilizer raw materials, by weight, are: 40-55 parts potassium chloride, 6-8 parts humic acid, 6-9 parts urea, 0.5-0.8 parts trace elements, and 3.5-5.5 parts slow-release porous coating material. This invention uses ethylenediamine and maleic anhydride as raw materials to prepare functional monomers containing both carboxyl and amino groups. The effective coating material makes the release of potassium ions in the soil slower and more uniform, improving potassium utilization efficiency. This invention's slow-release potassium chloride has a strong slow-release effect, providing crops with sufficient potassium, and can effectively regulate soil ecological activity, improving potassium utilization rate.

Description

Technical Field

[0001] This invention belongs to the field of biological controlled-release organic and inorganic fertilizer technology, specifically relating to a humic acid-coated controlled-release potassium chloride and its preparation method. Background Technology

[0002] The availability of potassium in soil for crops depends on its form and distribution. Besides the potassium transformation within the soil itself, exogenous potassium also affects the release and fixation of potassium in the soil, altering the dynamic balance of interconversion between potassium forms. During crop rotation periods, without potassium fertilizer application, readily available potassium is absorbed, while non-exchangeable potassium is released. Potassium application can increase the content of water-soluble and exchangeable potassium in the soil and convert it towards non-exchangeable potassium. However, traditional potassium chloride and potassium sulfate, once applied to the soil, are easily fixed or converted into less available non-exchangeable and fixed potassium forms, and are easily leached by rainwater or lost through surface runoff, which does not match the potassium requirements of crops. Controlled-release potassium chloride can slowly release potassium, improving the chlorophyll fluorescence characteristics of crops after a single application and increasing the content of readily available potassium in the soil, making it a research hotspot for novel potassium fertilizers.

[0003] Controlled-release potassium chloride refers to the technology used to slow down the release rate of potassium chloride, allowing it to continuously supply the nutrients needed by plants throughout their growth cycle. From a nutritional and environmental perspective, the development of controlled-release potassium chloride is significant for several reasons: ① Improved fertilizer efficiency: Traditional potassium chloride fertilizers release nutrients in a single step, making it difficult to adapt to the changing nutrient requirements of plants at different growth stages. Controlled-release potassium chloride slows down the release rate, allowing it to continuously supply the nutrients needed by plants over a longer period. Therefore, it improves fertilizer utilization efficiency and reduces waste. ② Environmental protection: Traditional potassium chloride fertilizers, due to their inability to control the release rate, easily cause soil pollution. Controlled-release potassium chloride reduces the leaching and retention time of chloride ions in the soil, helping to reduce chloride ion overload in the soil and thus mitigating environmental impact. ③ Improved crop quality: Traditional potassium chloride fertilizers, due to their rapid release rate, can easily cause root burn in crops, and excessive fertilizer intake also has an adverse effect on crop quality. Controlled-release potassium chloride can control the rate of potassium release, avoiding excessive fertilization, thus having a positive effect on crop quality.

[0004] However, current controlled-release potassium chloride products generally only contain potassium chloride and organic or inorganic slow-release materials. On the one hand, their functions are limited, and on the other hand, the controlled-release effect is not ideal and the stability is poor. For example, Chinese patent application CN201810809046.6 discloses a controlled-release potassium chloride with urea as the base coating and its preparation method. The controlled-release potassium chloride with urea as the base coating includes three layers: the core layer is granular potassium chloride, the middle layer is urea coated on the surface of the granular potassium chloride, and the outermost layer is an attapulgite nanocomposite material modified by a silane coupling agent or surfactant.

[0005] Therefore, developing a highly efficient slow-release potassium chloride fertilizer is a technical problem that urgently needs to be solved. Summary of the Invention

[0006] This invention addresses the problems existing in the prior art by providing a novel slow-release potassium chloride. On the one hand, it has a strong slow-release effect, providing crops with sufficient potassium. On the other hand, it can effectively regulate soil ecological activity and improve potassium utilization.

[0007] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows:

[0008] A humic acid-based coated slow-release potassium chloride comprises the following raw materials: potassium chloride, humic acid, urea, trace elements, and a slow-release porous coating material.

[0009] Furthermore, the proportions of each raw material by weight are as follows: 40-55 parts potassium chloride, 6-8 parts humic acid, 6-9 parts urea, 0.5-0.8 parts trace elements, and 3.5-5.5 parts slow-release porous coating material.

[0010] Furthermore, the trace elements are one or more of magnesium sulfate, calcium sulfate, sodium molybdate, zinc sulfate, ammonium molybdate, and manganese sulfate.

[0011] Furthermore, the method for preparing the sustained-release porous coating material is as follows:

[0012] (1) Preparation of functional monomer: Take 50 mL of acetone and place it in a container. Add 5 mL of ethylenediamine while stirring to obtain a mixture. Take 10 mL of maleic anhydride in acetone, stir and heat at 45-50 °C to dissolve it, and add it dropwise to the mixture. After the addition is complete, continue the reaction for 1 h. Remove the upper liquid, dissolve the product with 30 mL of distilled water, add 80 mL of acetone, shake, let stand and separate the layers, and collect the lower liquid. Then, evaporate the entire solution by rotary evaporation and dry it at 100 °C to obtain the functional monomer.

[0013] (2) Preparation of sustained-release porous coating material: 10g of hexadecyltrimethylammonium bromide and 25g of diatomaceous earth were dispersed in 1L of water. After the dispersion was uniform, 200g of functional monomer and 150g of N,N-methylenebisacrylamide were added and stirred evenly to obtain a mixture. 100mL of rapeseed oil was added to the above mixture and emulsified at 6000r / min at room temperature for 2min. Then, 5g of initiator ammonium persulfate and 0.5g of crosslinking agent N,N,N,N-tetramethylethylenediamine were added and stirred for 10min. The mixture was then transferred to a container and sealed. The mixture was polymerized in a water bath at 70℃ for 24h to obtain a solid polymer. The polymer was extracted by Soxhlet extraction for 24h to completely wash away the oil phase. Finally, it was vacuum dried to constant weight to obtain a sustained-release porous coating material.

[0014] Furthermore, in step (1), the mass concentration of the maleic anhydride acetone solution is 0.5 g / mL.

[0015] A method for preparing humic acid-coated slow-release potassium chloride includes the following preparation steps:

[0016] (1) Potassium chloride, humic acid, urea and trace elements are mixed evenly in a rotating drum according to the weight to obtain a premix. The round particles obtained by disc granulation, drum granulation or spray granulation are preheated to 70-75℃ and sprayed with a polyvinyl alcohol solution with a mass fraction of 2% and a borax solution with a mass fraction of 5%.

[0017] (2) Under stirring, the slow-release porous coating material is heated and sprayed onto the surface of solid particles, and then sealed with a cellulose acetate solution with a mass concentration of 0.03 g / mL;

[0018] (3) Finally, after drying at 40-55℃, humic acid-coated slow-release potassium chloride is obtained.

[0019] Furthermore, in step (1), the amount of polyvinyl alcohol solution used is 1-3% of the mass of the premix, and the amount of borax solution used is 3-7% of the mass of the premix.

[0020] Beneficial effects:

[0021] (1) This invention uses potassium chloride as the main potassium source, and adds humic acid, urea, trace elements and other nutrients as auxiliary materials. Humic acid can activate potassium fertilizer and make it decompose slowly, thereby improving the utilization rate of potassium fertilizer by crops. Compared with ordinary potassium oxide fertilizer, it can better control the release of potassium and prolong its fertilizer effect. Adding a small amount of urea and trace elements, when used in combination, can significantly promote crop growth, balance the nutrients in the soil, and enhance the disease resistance of crops.

[0022] (2) This invention uses ethylenediamine and maleic anhydride as raw materials to prepare functional monomers containing both carboxyl and amino groups. Subsequently, porous polymer materials are prepared through emulsion polymerization. These materials possess abundant macroporous and microporous structures and surface functional groups. The hydrophilic groups (carboxyl, amino, etc.) can form channels for water molecules to enter and exit the coating, thus achieving a controlled release of fertilizer. When potassium chloride is coated using this controlled-release porous coating material, soil moisture enters through the coating agent channels, forming a high-concentration potassium chloride solution. The carboxyl active groups act as potassium ion transporters, and the potassium ions coated inside the coating agent diffuse into the soil outside the coating agent through the chelation and release effects of the carboxyl groups, achieving a long-term controlled release of nutrients, especially potassium. Meanwhile, the amino active groups can adsorb and store exchangeable potassium ions through electrostatic adsorption and π-cation bonds, thereby reducing potassium loss and achieving a controlled-release effect. The synergistic effect of these two mechanisms makes the release of potassium ions in the soil slower and more uniform, improving potassium utilization efficiency.

[0023] (3) Subsequently, polyvinyl alcohol solution and borax solution are used for coating. The ions in borax will cross-link with polyvinyl alcohol (PVA) molecules to form a three-dimensional network structure. This structure has good mechanical properties and self-healing ability, which makes the fertilizer particles have good physical properties and slow-release properties.

[0024] (4) Finally, the fertilizer particles are sealed with cellulose acetate solution. The cellulose acetate solution can form a smooth and delicate film, which can effectively wrap the fertilizer particles, thereby slowing down the release rate of nutrients. At the same time, the fertilizer particles coated with cellulose acetate solution have low leaching solubility in the soil, which means that the nutrients in the fertilizer are not easily washed away by rainwater, thereby improving the utilization rate of fertilizer. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope image of the sustained-release porous coating material prepared in this invention, where (ac) represents three different sampling points of the same sample.

[0026] Figure 2 The release curve of the sample in Example 1 of this invention in still water at 25°C;

[0027] Figure 3 The results of soil leaching tests are shown in the embodiments and comparative examples of this invention. Detailed Implementation

[0028] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0029] Example 1

[0030] A humic acid-based coated slow-release potassium chloride comprises the following raw materials: potassium chloride, humic acid, urea, trace elements, and a slow-release porous coating material. The weight proportions of each raw material are as follows: 40 parts potassium chloride, 8 parts humic acid, 6 parts urea, 0.5 parts trace elements, and 3.5 parts slow-release porous coating material.

[0031] The trace elements are obtained by mixing magnesium sulfate, calcium sulfate, sodium molybdate, zinc sulfate, ammonium molybdate, and manganese sulfate in a mass ratio of 10:5:1:0.5:0.3:0.5.

[0032] The method for preparing the sustained-release porous coating material is as follows:

[0033] (1) Preparation of functional monomer: Take 50 mL of acetone and place it in a container. Add 5 mL of ethylenediamine while stirring to obtain a mixture. Take 10 mL of maleic anhydride in acetone, stir and heat at 45-50 °C to dissolve it, and add it dropwise to the mixture. After the addition is complete, continue the reaction for 1 h. Remove the upper liquid, dissolve the product with 30 mL of distilled water, add 80 mL of acetone, shake, let stand and separate the layers, and collect the lower liquid. Then, evaporate the entire solution by rotary evaporation and dry it at 100 °C to obtain the functional monomer.

[0034] (2) Preparation of sustained-release porous coating material: 10g of hexadecyltrimethylammonium bromide and 25g of diatomaceous earth were dispersed in 1L of water. After the dispersion was uniform, 200g of functional monomer and 150g of N,N-methylenebisacrylamide were added and stirred evenly to obtain a mixture. 100mL of rapeseed oil was added to the above mixture and emulsified at 6000r / min at room temperature for 2min. Then, 5g of initiator ammonium persulfate and 0.5g of crosslinking agent N,N,N,N-tetramethylethylenediamine were added and stirred for 10min. The mixture was then transferred to a container and sealed. The mixture was polymerized in a water bath at 70℃ for 24h to obtain a solid polymer. The polymer was extracted by Soxhlet extraction for 24h to completely wash away the oil phase. Finally, it was vacuum dried to constant weight to obtain a sustained-release porous coating material.

[0035] The mass concentration of maleic anhydride in acetone solution is 0.5 g / mL.

[0036] A method for preparing humic acid-coated slow-release potassium chloride includes the following preparation steps;

[0037] (1) Potassium chloride, humic acid, urea and trace elements are mixed evenly in a rotating drum according to the weight to obtain a premix. The round particles obtained by disc granulation, drum granulation or spray granulation are preheated to 70-75℃ and sprayed with a polyvinyl alcohol solution with a mass fraction of 2% and a borax solution with a mass fraction of 5%.

[0038] (2) Under stirring, the slow-release porous coating material is heated and sprayed onto the surface of solid particles, and then sealed with a cellulose acetate solution with a mass concentration of 0.03 g / mL;

[0039] (3) Finally, after drying at 40-55℃, humic acid-coated slow-release potassium chloride is obtained.

[0040] Step (1) The amount of polyvinyl alcohol solution used is 1% of the mass of the premix, and the amount of borax solution used is 3% of the mass of the premix.

[0041] Example 2

[0042] A humic acid-based coated slow-release potassium chloride comprises the following raw materials: potassium chloride, humic acid, urea, trace elements, and a slow-release porous coating material. The weight proportions of each raw material are as follows: 44 parts potassium chloride, 6 parts humic acid, 8 parts urea, 0.7 parts trace elements, and 4.5 parts slow-release porous coating material.

[0043] The trace elements are obtained by mixing magnesium sulfate, calcium sulfate and zinc sulfate in a mass ratio of 10:1:0.5.

[0044] The method for preparing the sustained-release porous coating material is as follows:

[0045] (1) Preparation of functional monomer: Take 50 mL of acetone and place it in a container. Add 5 mL of ethylenediamine while stirring to obtain a mixture. Take 10 mL of maleic anhydride in acetone, stir and heat at 45-50 °C to dissolve it, and add it dropwise to the mixture. After the addition is complete, continue the reaction for 1 h. Remove the upper liquid, dissolve the product with 30 mL of distilled water, add 80 mL of acetone, shake, let stand and separate the layers, and collect the lower liquid. Then, evaporate the entire solution by rotary evaporation and dry it at 100 °C to obtain the functional monomer.

[0046] (2) Preparation of sustained-release porous coating material: 10g of hexadecyltrimethylammonium bromide and 25g of diatomaceous earth were dispersed in 1L of water. After the dispersion was uniform, 200g of functional monomer and 150g of N,N-methylenebisacrylamide were added and stirred evenly to obtain a mixture. 100mL of rapeseed oil was added to the above mixture and emulsified at 6000r / min at room temperature for 2min. Then, 5g of initiator ammonium persulfate and 0.5g of crosslinking agent N,N,N,N-tetramethylethylenediamine were added and stirred for 10min. The mixture was then transferred to a container and sealed. The mixture was polymerized in a water bath at 70℃ for 24h to obtain a solid polymer. The polymer was extracted by Soxhlet extraction for 24h to completely wash away the oil phase. Finally, it was vacuum dried to constant weight to obtain a sustained-release porous coating material.

[0047] The mass concentration of maleic anhydride in acetone solution is 0.5 g / mL.

[0048] A method for preparing humic acid-coated slow-release potassium chloride includes the following preparation steps;

[0049] (1) Potassium chloride, humic acid, urea and trace elements are mixed evenly in a rotating drum according to the weight to obtain a premix. The round particles obtained by disc granulation, drum granulation or spray granulation are preheated to 70-75℃ and sprayed with a polyvinyl alcohol solution with a mass fraction of 2% and a borax solution with a mass fraction of 5%.

[0050] (2) Under stirring, the slow-release porous coating material is heated and sprayed onto the surface of solid particles, and then sealed with a cellulose acetate solution with a mass concentration of 0.03 g / mL;

[0051] (3) Finally, after drying at 40-55℃, humic acid-coated slow-release potassium chloride is obtained.

[0052] Furthermore, in step (1), the amount of polyvinyl alcohol solution used is 1% of the mass of the premix, and the amount of borax solution used is 5% of the mass of the premix.

[0053] Example 3

[0054] A humic acid-based coated slow-release potassium chloride comprises the following raw materials: potassium chloride, humic acid, urea, trace elements, and a slow-release porous coating material. The weight proportions of each raw material are as follows: 55 parts potassium chloride, 8 parts humic acid, 9 parts urea, 0.8 parts trace elements, and 5.5 parts slow-release porous coating material.

[0055] The trace elements are obtained by mixing magnesium sulfate, calcium sulfate, sodium molybdate, zinc sulfate, ammonium molybdate, and manganese sulfate in a mass ratio of 10:6:2:0.3:0.5:0.2.

[0056] The method for preparing the sustained-release porous coating material is as follows:

[0057] (1) Preparation of functional monomer: Take 50 mL of acetone and place it in a container. Add 5 mL of ethylenediamine while stirring to obtain a mixture. Take 10 mL of maleic anhydride in acetone, stir and heat at 45-50 °C to dissolve it, and add it dropwise to the mixture. After the addition is complete, continue the reaction for 1 h. Remove the upper liquid, dissolve the product with 30 mL of distilled water, add 80 mL of acetone, shake, let stand and separate the layers, and collect the lower liquid. Then, evaporate the entire solution by rotary evaporation and dry it at 100 °C to obtain the functional monomer.

[0058] (2) Preparation of sustained-release porous coating material: 10g of hexadecyltrimethylammonium bromide and 25g of diatomaceous earth were dispersed in 1L of water. After the dispersion was uniform, 200g of functional monomer and 150g of N,N-methylenebisacrylamide were added and stirred evenly to obtain a mixture. 100mL of rapeseed oil was added to the above mixture and emulsified at 6000r / min at room temperature for 2min. Then, 5g of initiator ammonium persulfate and 0.5g of crosslinking agent N,N,N,N-tetramethylethylenediamine were added and stirred for 10min. The mixture was then transferred to a container and sealed. The mixture was polymerized in a water bath at 70℃ for 24h to obtain a solid polymer. The polymer was extracted by Soxhlet extraction for 24h to completely wash away the oil phase. Finally, it was vacuum dried to constant weight to obtain a sustained-release porous coating material.

[0059] The structural characteristics of the sustained-release porous coating material were observed using scanning electron microscopy, such as... Figure 1 As shown, the material surface and the whole exhibit a distinct porous structure, which facilitates the slow release of nutrients.

[0060] The mass concentration of maleic anhydride in acetone solution is 0.5 g / mL.

[0061] A method for preparing humic acid-coated slow-release potassium chloride includes the following preparation steps;

[0062] (1) Potassium chloride, humic acid, urea and trace elements are mixed evenly in a rotating drum according to the weight to obtain a premix. The round particles obtained by disc granulation, drum granulation or spray granulation are preheated to 70-75℃ and sprayed with a polyvinyl alcohol solution with a mass fraction of 2% and a borax solution with a mass fraction of 5%.

[0063] (2) Under stirring, the slow-release porous coating material is heated and sprayed onto the surface of solid particles, and then sealed with a cellulose acetate solution with a mass concentration of 0.03 g / mL;

[0064] (3) Finally, after drying at 40-55℃, humic acid-coated slow-release potassium chloride is obtained.

[0065] Step (1) The amount of polyvinyl alcohol solution used is 3% of the mass of the premix, and the amount of borax solution used is 7% of the mass of the premix.

[0066] Comparative Example 1

[0067] A humic acid-based coated slow-release potassium chloride comprises the following raw materials: potassium chloride, humic acid, urea, trace elements, and a slow-release porous coating material. The weight proportions of each raw material are as follows: 40 parts potassium chloride, 8 parts humic acid, 6 parts urea, 0.5 parts trace elements, and 3.5 parts slow-release porous coating material.

[0068] The preparation method of the sustained-release porous coating material is as follows: 10g of hexadecyltrimethylammonium bromide and 25g of diatomaceous earth are dispersed in 1L of water. After uniform dispersion, 200g of acrylic acid and 150g of N,N-methylenebisacrylamide are added and stirred evenly to obtain a mixture. 100mL of rapeseed oil is added to the above mixture and emulsified at 6000r / min at room temperature for 2min. Then, 5g of initiator ammonium persulfate and 0.5g of crosslinking agent N,N,N,N-tetramethylethylenediamine are added and stirred for 10min. The mixture is then transferred to a container and sealed. It is polymerized in a water bath at 70℃ for 24h to obtain a solid polymer. The polymer is extracted using Soxhlet extraction for 24h to completely wash away the oil phase. Finally, it is vacuum dried to constant weight to obtain the sustained-release porous coating material.

[0069] In this comparative example, except that conventional acrylic acid is used as the monomer in the preparation method of the sustained-release porous coating material, the other raw materials and preparation methods are the same as in Example 1.

[0070] Comparative Example 2

[0071] A humic acid-coated slow-release potassium chloride comprises the following raw materials: potassium chloride, humic acid, urea, trace elements, and coating material. The weight proportions of each raw material are as follows: 40 parts potassium chloride, 8 parts humic acid, 6 parts urea, 0.5 parts trace elements, and 3.5 parts coating material.

[0072] The coating material is a common resin, such as epoxy resin.

[0073] A method for preparing humic acid-coated slow-release potassium chloride includes the following preparation steps;

[0074] (1) Potassium chloride, humic acid, urea and trace elements are mixed evenly in a rotating drum according to the weight to obtain a premix. The round particles obtained by disc granulation, drum granulation or spray granulation are preheated to 70-75℃ and sprayed with a polyvinyl alcohol solution with a mass fraction of 2% and a borax solution with a mass fraction of 5%.

[0075] (2) Under stirring, the epoxy resin is heated and sprayed onto the surface of the solid particles, and then sealed with a cellulose acetate solution with a mass concentration of 0.03 g / mL;

[0076] (3) Finally, after drying at 40-55℃, humic acid-coated slow-release potassium chloride is obtained.

[0077] In this comparative example, except that epoxy resin is used as the slow-release material, all other raw materials and preparation methods are the same as in Example 1.

[0078] Performance testing

[0079] Fertilizer samples were prepared using the methods of examples and comparative examples. The potassium fertilizer release effect was tested according to the national standard GB / T23348-2009 for slow-release fertilizers. The results are shown in Table 1.

[0080] Table 1 Test Results

[0081] Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 1-day release % 1.2 1.1 1.1 4.5 10.2 28-day release % 17.8 17.5 17.0 40.2 75.6 140d release % 81.2 81.5 80.6 89.6 95.8

[0082] Potassium release characteristics were further tested using the sample from Example 1. The potassium release characteristics were determined using the static water nutrient extraction method (25°C) in an indoor incubator. The determination was performed according to the method specified in the People's Republic of China Chemical Industry Standard "Controlled Release Fertilizers" "HG / T4215-2011". The results are as follows: Figure 2 As shown.

[0083] Soil leaching performance test:

[0084] 5g of the test sample was evenly buried in 5kg of soil inside a polyethylene drum. The drum was then sealed with a black plastic bag to reduce moisture loss through evaporation. Soil samples were taken within a specified time and dried to constant weight in an electrically heated drying oven. The soil was then pulverized at 105℃. 2g of the pulverized soil, 40mL of soil extractant, and an appropriate amount of soil decolorizing agent were placed in a 100ml Erlenmeyer flask and reacted for 3 minutes under vigorous shaking. The dissolved potassium content of the soil was then tested using a G-61 flame photometer. Figure 3 It can be seen that simple granular potassium chloride is released rapidly into the soil, reaching complete release within 20-30 days. However, the potassium fertilizer in this embodiment of the invention exhibits a significantly longer release period, continuing to release nutrients even after 80 days, demonstrating excellent slow-release performance.

[0085] Field soil slow-release performance test:

[0086] Among various crops, tobacco fields have a relatively high requirement for potassium fertilizer content, therefore, tobacco fields were used as the experimental subject. Samples were applied to tobacco-grown land at a rate of 20 kg / mu. Soil samples were taken at intervals at depths of 10 cm, 20 cm, 30 cm, and 40 cm, dried at 105℃, pulverized, and then the available potassium content of the soil was determined.

[0087] Table 2 Soil available potassium content (mg / kg)

[0088] 10cm 20cm 30cm 40cm Example 1 108.9 179.8 98.5 25.2 Example 2 106.5 178.5 97.2 23.5 Example 3 107.2 185.2 98.1 24.3 Comparative Example 1 105.6 165.2 190.5 210.5 Comparative Example 2 106.2 167.9 215.5 251.3

[0089] As shown in Table 2, there was no significant difference in available potassium content between the control and experimental groups when the soil depth was 10-20 cm. With increasing soil depth, the potassium content in the control group showed an increasing trend. This is because the potassium was released quickly after entering the soil, reaching deeper layers and causing potassium loss. In contrast, the controlled-release potassium fertilizer in the control group released nutrients more slowly, with a release cycle closer to the nutrient requirements of tobacco leaves. Most of the potassium was absorbed by the tobacco leaves, resulting in only a small amount of nutrient loss. An investigation of local tobacco cultivation revealed that the maximum depth at which tobacco roots can absorb nutrients is 20 cm. Nutrients beyond 20 cm in soil depth cannot be absorbed by the tobacco leaves, leading to resource waste. The controlled-release potassium fertilizer maintained a high available potassium content between 10-20 cm in soil depth, with lower levels beyond 20 cm. This had a positive impact on tobacco growth and reduced resource waste, demonstrating excellent field slow-release performance.

[0090] After harvesting, tobacco leaves were cured using a three-stage curing method and graded according to the national standard for flue-cured tobacco grade 42 (GB2635-92). 1.5 kg of X2F grade and grade 1.5 kg of tobacco leaves were taken for each grade, and the total nitrogen, potassium, nicotine, and total sugar content were determined. The determinations were performed using tobacco industry standards YC / T1612002, YC / T173-2003, YC / T160-2002, and YC / T159-2002. In the examples and comparative examples, samples were applied at a fertilizer application rate of 20 kg / mu (approximately 13.3 kg / acre), while the blank control received no treatment. All experimental groups were repeated five times, and the results were averaged. The results are shown in Table 3.

[0091] Table 3. Analysis of chemical components in flue-cured tobacco leaves after different treatments.

[0092]

[0093]

[0094] By applying the slow-release fertilizer of this invention, potassium is effectively utilized, which not only reduces the nicotine content in tobacco leaves but also increases the total nitrogen content to varying degrees, thereby achieving the goal of coordinating the chemical components in tobacco leaves and indirectly improving the quality of flue-cured tobacco and tobacco leaves.

[0095] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A humic acid-coated slow-release potassium chloride, characterized in that, The raw materials include: potassium chloride, humic acid, urea, trace elements, and a slow-release porous coating material; the raw materials are distributed in the following weight parts: potassium chloride 40-55 parts, humic acid 6-8 parts, urea 6-9 parts, trace elements 0.5-0.8 parts, and slow-release porous coating material 3.5-5.5 parts; the preparation method of the slow-release porous coating material is as follows: (1) Preparation of functional monomer: Take 50 mL of acetone and place it in a container. Add 5 mL of ethylenediamine while stirring to obtain a mixture. Take 10 mL of maleic anhydride in acetone, stir and heat at 45-50 °C to dissolve it, and add it dropwise to the mixture. After the addition is complete, continue the reaction for 1 h. Remove the upper liquid, dissolve the product with 30 mL of distilled water, add 80 mL of acetone, shake, let stand and separate the layers, and collect the lower liquid. Then, evaporate the entire solution by rotary evaporation and dry it at 100 °C to obtain the functional monomer. (2) Preparation of sustained-release porous coating material: 10g of hexadecyltrimethylammonium bromide and 25g of diatomaceous earth were dispersed in 1L of water. After the dispersion was uniform, 200g of functional monomer and 150g of N,N-methylenebisacrylamide were added and stirred evenly to obtain a mixture. 100mL of rapeseed oil was added to the above mixture and emulsified at 6000 r / min for 2min at room temperature. Then, 5g of initiator ammonium persulfate and 0.5g of crosslinking agent N,N,N,N-tetramethylethylenediamine were added and stirred for 10min. The mixture was then transferred to a container and sealed. The polymer was polymerized in a water bath at 70℃ for 24h to obtain a solid polymer. The polymer was extracted by Soxhlet extraction for 24h to completely wash away the oil phase. Finally, it was vacuum dried to constant weight to obtain the sustained-release porous coating material.

2. The humic acid-coated slow-release potassium chloride according to claim 1, characterized in that, The trace elements mentioned are one or more of magnesium sulfate, calcium sulfate, sodium molybdate, zinc sulfate, ammonium molybdate, and manganese sulfate.

3. The humic acid-coated slow-release potassium chloride according to claim 1, characterized in that, Step (1) The mass concentration of the maleic anhydride acetone solution is 0.5 g / mL.

4. A method for preparing humic acid-coated slow-release potassium chloride according to any one of claims 1-3, characterized in that, The preparation steps include the following: (1) Potassium chloride, humic acid, urea and trace elements are mixed evenly in a rotating drum according to the weight to obtain a premix. The round particles obtained by disc granulation, drum granulation or spray granulation are preheated to 70-75℃ and sprayed with a polyvinyl alcohol solution with a mass fraction of 2% and a borax solution with a mass fraction of 5%. (2) Under stirring, the slow-release porous coating material is heated and sprayed onto the surface of solid particles, and then sealed with a cellulose acetate solution with a mass concentration of 0.03 g / mL; (3) Finally, after drying at 40-55℃, humic acid-coated slow-release potassium chloride is obtained.

5. The method for preparing humic acid-coated slow-release potassium chloride according to claim 4, characterized in that, Step (1) The amount of polyvinyl alcohol solution used is 1-3% of the mass of the premix, and the amount of borax solution used is 3-7% of the mass of the premix.

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