Moisturizing slow-release fertilizer and preparation method thereof

Abstract

The invention belongs to the field of fertilizers, and particularly relates to a moisturizing type slow release fertilizer and a preparation method thereof. Urea; potassium nitrate; potassium sulfate; trehalose; calcium dihydrogen phosphate; citric acid; humic acid; medium trace element salts; konjac glucomannan; glycerol; sodium hydroxide; bentonite; vermiculite; a coupling agent; a polycaprolactone; starch; an antioxidant; a coating agent; a water-retaining agent; an adhesive; and a filler. According to the invention, by enhancing the moisture retention capability and slow release capability of the fertilizer, the possibility of root burning of crops in a high-temperature drought environment can be reduced.

Description

Technical Field

[0001] This invention belongs to the field of fertilizers, specifically relating to a moisture-retaining slow-release fertilizer and its preparation method. Background Technology

[0002] Fertilizers can be divided into base fertilizers and top dressings. Base fertilizers are applied before sowing, before transplanting, or at the beginning of the growing season, through methods such as furrow application, hole application, or broadcasting, combined with soil tillage. After being applied to the soil, base fertilizers provide basic nutrients to crops, ensuring that crops obtain sufficient various growth elements in the early stages of growth, reducing nutrient deficiency, and promoting crop growth.

[0003] When applying chemical fertilizers as base fertilizer, the soil usually needs to be watered. The water penetrates to the area around the fertilizer particles, which on the one hand promotes the decomposition of the base fertilizer and converts the nutrients in the base fertilizer into a form that crops can absorb. For example, elements such as nitrogen, phosphorus, and potassium need to be dissolved into their corresponding ionic states before they can be absorbed by the crop roots. On the other hand, it dilutes the concentration of the fertilizer and prevents the fertilizer from causing excessively high osmotic pressure in the local soil solution, which would lead to water loss in the crop root cells and cause the crop to wilt, blacken roots, and damage the root system during the seedling stage.

[0004] In areas with higher temperatures and lower rainfall, the soil moisture is easily lost quickly after watering due to vigorous infiltration and evaporation. This can lead to fertilizer not being absorbed by the roots or frequent root burn, which is detrimental to the healthy growth of crops. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a moisture-retaining slow-release fertilizer and its preparation method. This invention utilizes the action of konjac glucomannan, glycerin, water-retaining agents, etc. to form a three-dimensional moisture-retaining network, thereby improving the water retention capacity of fertilizer granules. Furthermore, by combining urea-formaldehyde resin coating of urea, trehalose coating of calcium dihydrogen phosphate, polycaprolactone, starch, etc. to form a double-layer coating, the slow-release capacity of fertilizer granules can be enhanced. This invention reduces the possibility of excessive fertilizer release in a short period of time and the inability to absorb nutrients or burn roots due to water loss, from both the perspectives of moisture retention and slow release.

[0006] The technical solution adopted by the present invention to solve the above problems is as follows: A moisture-retaining slow-release fertilizer comprises the following components in parts by weight: 20-25 parts urea-formaldehyde resin; 8-10 parts urea; 7-10 parts potassium nitrate; 7-10 parts potassium sulfate; 1.2-1.4 parts trehalose; 10.8-12.6 parts calcium dihydrogen phosphate; 1-2 parts citric acid; 2-3 parts humic acid; 1-3 parts trace element salts; 6-7.5 parts konjac glucomannan; 1-2 parts glycerol; 0.05-0.06 parts sodium hydroxide; 3-4 parts bentonite; 3-4 parts vermiculite; 0.3-0.4 parts coupling agent; 1-1.3 parts polycaprolactone; 3-4 parts starch; 0.01-0.02 parts antioxidant; 3-4 parts coating agent; 3-5 parts water-retaining agent; 0.2-0.3 parts binder; and 15-20 parts filler.

[0007] Through the above technical solutions, urea-formaldehyde resin can coat urea, and trehalose can coat calcium dihydrogen phosphate, thus forming an inner single-nutrient coating. Urea-formaldehyde resin, with its densely cross-linked molecular structure, forms the first slow-release barrier for urea. Under soil moisture, the urea-formaldehyde resin coating slowly swells rather than rapidly ruptures, allowing for the stable release of ammonia and nitrate nitrogen produced by urea decomposition, avoiding the phenomenon of large initial releases and sudden increases in local nutrient concentrations seen with traditional fertilizers. Trehalose, relying on its hydrophilic groups, forms hydrogen bonds with calcium dihydrogen phosphate, preventing rapid solidification and deactivation of calcium dihydrogen phosphate in the soil, and extending the phosphorus release cycle through the slow degradation of trehalose, ensuring phosphorus supply throughout the crop's growth period. Polycaprolactone, starch, etc., can form an outer coating. This outer coating, together with the urea-formaldehyde resin coating of urea and the trehalose coating of calcium dihydrogen phosphate, forms a double barrier for slow-release and controlled release, slowing down the nutrient release rate and preventing root burn caused by large local dissolution of nutrients in a short period. Bentonite and vermiculite can actively adsorb free potassium and calcium ions in the soil, preventing nutrients from being leached into deeper soil layers with small amounts of irrigation water. Simultaneously, through a dynamic balance of adsorption and desorption, they maintain a uniform concentration of effective nutrients in the soil solution, preventing localized nutrient accumulation and avoiding nutrient buildup around the roots. This, in turn, stabilizes soil osmotic pressure and reduces the likelihood of root cell water loss. The synergistic effect of konjac glucomannan, glycerol, and water-retaining agents constructs a three-dimensional moisture-retaining network covering the fertilizer granules, soil pores, and crop roots. After glycerol modification, konjac glucomannan forms a three-dimensional gel structure with a water absorption rate of 30-40 times its own weight. It can form an elastic water film on the surface of fertilizer granules, reducing water evaporation loss at high temperatures, thereby enhancing the fertilizer's water retention capacity and reducing the possibility of root burn in crops.

[0008] Furthermore, the trace element salts include at least one of calcium sulfate, magnesium sulfate, and zinc sulfate.

[0009] By using the above technical solutions, the selection of micronutrient salts such as calcium sulfate, magnesium sulfate, and zinc sulfate can not only accurately supplement crops with the three key micronutrients of calcium, magnesium, and zinc, but also specifically address the "element deficiency syndrome" caused by the obstruction of nutrient absorption in crops under high temperature and drought conditions, thus ensuring the normal operation of crop physiological functions.

[0010] Furthermore, the coupling agent is any one of silane coupling agent KH-550, silane coupling agent KH-560, and silane coupling agent KH-602.

[0011] Through the above technical solution, the silane coupling agent molecule has both inorganic affinity groups (such as siloxane groups) and organic affinity groups (such as amino and epoxy groups). The inorganic affinity groups can form covalent bonds with the hydroxyl groups on the surface of bentonite and vermiculite, while the organic affinity groups can chemically bond or physically entangle with the hydroxyl groups of konjac glucomannan and the ester groups of polycaprolactone, thereby eliminating the interfacial tension between inorganic particles and organic polymers and avoiding the stratification and delamination of fertilizers during mixing, granulation and storage.

[0012] Furthermore, the antioxidant is at least one of pentaerythritol ester [β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], 2,6-di-tert-butyl-p-cresol, vitamin E, and tea polyphenols.

[0013] Through the above technical solutions, under high temperature and drought conditions, oxygen and ultraviolet rays can easily cause the molecular chain of the organic coating layer to break (such as the hydrolysis and oxidation of the ester bond of polycaprolactone and the breakage of the glycosidic bond of starch). Antioxidants can reduce the degradation of the coating layer by capturing free radicals and terminating the oxidation chain reaction, thereby reducing the cracking rate of the coating layer.

[0014] Furthermore, the coating agent is poly(N-isopropylacrylamide).

[0015] Through the above technical solution, poly(N-isopropylacrylamide) can quickly cure into a film after spraying. On the one hand, it tightly coats the surface of fertilizer nutrient particles, forming a uniformly thick inner film that reduces the evaporation of water inside the particles. On the other hand, some of the coating agent will penetrate into the soil surface with irrigation water, forming a transparent "soil film" that blocks the direct contact between free water in the soil and air, reduces the evaporation rate at high temperatures, and prolongs the soil's water retention time. Poly(N-isopropylacrylamide) exhibits a "shrinkage state" at 32–35℃ (typical temperature for high temperature and drought), with reduced pore size in the membrane structure, further reducing water loss. When a small amount of water is added to the soil, the membrane structure will swell moderately, allowing water and nutrients to slowly penetrate, thus preventing rapid water loss and ensuring that nutrients can dissolve into absorbable ionic states.

[0016] Furthermore, the water-retaining agent includes at least one of L-proline and anhydrous betaine.

[0017] Through the above technical solutions, L-proline can act as an intracellular osmotic regulator in crops, enhancing the water retention capacity of root cells, thereby reducing cell water loss under high temperature and drought conditions and strengthening the crop's resistance to wilting. Anhydrous betaine can promote stomatal closure in crop leaves, reducing transpiration and thus reducing water loss from crops, which in turn reduces the absorption of soil moisture by crops and indirectly reduces soil water consumption.

[0018] Furthermore, the adhesive is any one of polyvinyl alcohol, sodium carboxymethyl cellulose, gum arabic, and guar gum.

[0019] Through the above technical solution, the adhesive molecules can bind to the surface of each component through hydrogen bonds and van der Waals forces, and bind the "loose components" such as urea-formaldehyde resin-coated urea particles, trehalose-coated calcium dihydrogen phosphate particles, and elemental powders into nutrient particles with uniform particle size (2~3mm). This avoids the phenomenon of excessive fine powder or uneven particle size during the granulation process, and facilitates uniform spraying in the subsequent coating process.

[0020] Furthermore, the filler is at least one of talc, kaolin, diatomaceous earth, and mica powder.

[0021] Through the above technical solutions, the filler can adjust the hardness and flowability of fertilizer granules, reduce the possibility of caking and sticking during storage and transportation, and fill the gaps between nutrients and the coating layer, enhance the tightness of the coating layer, and help improve the slow release and moisturizing effect.

[0022] The present invention also provides a method for preparing the above-mentioned moisture-retaining slow-release fertilizer, comprising the following steps: S1. Dilute urea-formaldehyde resin with deionized water to a solid content of 40-60% to obtain a coating solution. Then, put urea into a fluidized bed coating machine. Adjust the temperature of the fluidized bed coating machine to 45-55℃, the air velocity to 1-2m / s, and the atomization pressure to 0.3-0.5MPa. Spray the coating solution at a rate of 2-4mL / min. After spraying, raise the temperature to 60-65℃ and keep it at that temperature for 20-40min. Then, pass the solution through a 10-20 mesh sieve to obtain urea-formaldehyde resin coated urea particles. S2. Dissolve trehalose in deionized water and stir at 100-200 r / min for 5-10 min to obtain a trehalose aqueous solution with a concentration of 10-12%; place calcium dihydrogen phosphate into a fluidized bed coating machine, adjust the temperature of the fluidized bed coating machine to 38-42℃, the air velocity to 0.8-1.2 m / s, the atomization pressure to 0.2-0.4 MPa, and spray the trehalose aqueous solution at a rate of 1.5-2.5 mL / min. After spraying, keep warm and ventilate to dry for 1-1.5 h, then cool and pass through a 15-25 mesh sieve to obtain trehalose-coated calcium dihydrogen phosphate particles; S3. Mix citric acid and humic acid, add five times the total mass of deionized water, heat to 55-65℃, stir at 200-300 r / min for 20-40 min, then add trace element salts, stir for 50-70 min, control the pH to 5.5-6.0 to obtain a mixture, then vacuum concentrate the mixture at a temperature of 65-75℃ and a vacuum degree of -0.08 to -0.09 MPa until the solid content is 75-85%, then spray dry at an inlet air temperature of 170-190℃ and an outlet air temperature of 75-85℃ to obtain elemental powder; S4. Add konjac glucomannan, glycerol, and sodium hydroxide into a reaction vessel, and add deionized water at a ratio of 4 times the total mass of konjac glucomannan, glycerol, and sodium hydroxide. Heat to 75-85℃ and stir at 100-200 r / min for 3.5-4.5 h. After stirring, adjust the pH to 6.8-7.2. Then add 95% ethanol at a ratio of 4 times the total mass of konjac glucomannan, glycerol, and sodium hydroxide. Stir at 100-200 r / min for 20-40 min. After stirring, let stand, filter with a 40-50 mesh filter cloth and collect the precipitate. Dry at 60-70℃ for 2-3 h. After drying, pulverize to 80-100 mesh to obtain glycerol-modified konjac glucomannan powder. S5. Crush bentonite and vermiculite to 200-300 mesh, then transfer them to a mixer and stir at 150-200 r / min for 10-20 min; dilute the coupling agent with 95% ethanol to a concentration of 5-8%, and add the diluted coupling agent to the mixed powder of bentonite and vermiculite; stir at 55-65℃ and 120-180 r / min for 2.5-3.5 h; after stirring, dry at 70-80℃ for 2-2.5 h to obtain the modified bentonite-vermiculite composite. S6. Place polycaprolactone, starch, and antioxidant into a reaction vessel, stir at a temperature of 115-125℃ and a speed of 200-250r / min for 25-35min, cool to room temperature after stirring, and then pulverize to 80-100 mesh to obtain polycaprolactone-starch composite. S7. Place urea granules coated with urea-formaldehyde resin, calcium dihydrogen phosphate granules coated with trehalose, elemental powder, potassium nitrate, potassium sulfate, and filler into a mixer and stir for 20-30 minutes at a temperature of 25-30℃ and a speed of 120-180 r / min. Then add the binder and continue stirring for 10-15 minutes. After stirring, transfer the mixture to a granulator and adjust the temperature of the granulator to 35-45℃ and the speed to 25-35 r / min. Granulate the mixture to a particle size of 2-3 mm to obtain nutrient granules. S8. Dilute the coating agent with 95% ethanol to a concentration of 12-15% and stir at 180-240 r / min for 5-10 min; put the nutrient particles into a fluidized bed coating machine, adjust the temperature of the fluidized bed coating machine to 22-28℃, the air velocity to 1-1.5 m / s, and the atomization pressure to 0.2-0.4 MPa, and spray the coating agent solution at a rate of 2-3 mL / min. After spraying, ventilate and dry to room temperature to obtain inner layer particles; S9. The polycaprolactone-starch composite is placed in a reaction vessel for remelting. The temperature of the reaction vessel is adjusted to 110-120℃, the rotation speed is 120-180 r / min, and the mixture is stirred for 10-15 min to obtain a polycaprolactone-starch fluid. The inner layer particles are placed in a vacuum spraying machine, the vacuum degree is adjusted to -0.07--0.09 MPa, the temperature is 55-65℃, and the polycaprolactone-starch fluid is sprayed at a spraying rate of 3-5 mL / min to obtain double-coated particles. S10. Place the glycerol-modified konjac glucomannan powder, modified bentonite-vermiculite complex, water-retaining agent, and double-coated granules into a mixer. Adjust the temperature of the mixer to 28-32℃ and the rotation speed to 150-200 r / min. Stir for 25-35 min. After stirring, dry at 45-55℃ for 1-1.5 h. After drying, cool to room temperature and pass through a 10-20 mesh sieve to obtain the finished granules.

[0023] The present invention has the following beneficial effects: 1. This invention utilizes konjac glucomannan, glycerin, and water-retaining agents to form a three-dimensional moisture-retaining network, enhancing the water-retaining capacity of fertilizer granules. Furthermore, by combining urea-formaldehyde resin coating of urea, trehalose coating of calcium dihydrogen phosphate, polycaprolactone, and starch to form a double-layer coating, the slow-release capacity of fertilizer granules is enhanced. This collectively reduces the possibility of excessive fertilizer release in a short period of time and the inability to absorb nutrients or burn roots due to water loss, thus promoting crop growth. Detailed Implementation

[0024] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to specific examples. However, the scope of protection of this invention is not limited to the following specific embodiments. The described embodiments are merely some, not all, of the embodiments of this invention, and are not intended to limit the invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0025] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0026] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0027] In the quantitative experiments in the following examples, three replicate experiments were set up, and the data are the average of the three replicate experiments or the average ± standard deviation.

[0028] The moisturizing slow-release fertilizer of the present invention includes Examples 1-3 and Comparative Examples 1-7, and the specific components and contents are shown in Table 1, in parts by weight.

[0029] Table 1

[0030] The preparation method of the above embodiments includes the following steps: S1. Dilute urea-formaldehyde resin with deionized water to a solid content of 50% to obtain a coating solution. Then, put urea into a fluidized bed coating machine. Set the temperature of the fluidized bed coating machine to 50℃, the air velocity to 1.5m / s, and the atomization pressure to 0.4MPa. Spray the coating solution at a rate of 3mL / min. After spraying, raise the temperature to 60℃ and keep it at that temperature for 30min to cure. Then, pass the solution through a 10-mesh sieve to obtain urea-formaldehyde resin coated urea particles. S2. Dissolve trehalose in deionized water and stir at 120 r / min for 10 min to obtain a 10% trehalose aqueous solution; put calcium dihydrogen phosphate into a fluidized bed coating machine, set the temperature of the fluidized bed coating machine to 40℃, the air velocity to 1 m / s, and the atomization pressure to 0.3 MPa, and spray the trehalose aqueous solution at a rate of 2 mL / min. After spraying, keep warm and ventilate to dry for 1 h, then cool and pass through a 20-mesh sieve to obtain trehalose-coated calcium dihydrogen phosphate particles; S3. Mix citric acid and humic acid, add 5 times the total mass of deionized water, heat to 60℃, stir at 240 r / min for 30 min, then add calcium sulfate and zinc sulfate, stir for 60 min, control the pH to 6.0, and obtain a mixed solution. Then, vacuum concentrate the mixed solution at a temperature of 70℃ and a vacuum degree of -0.08 MPa until the solid content is 80%. After concentration, spray dry the solution at an inlet air temperature of 180℃ and an outlet air temperature of 80℃ to obtain elemental powder. S4. Add konjac glucomannan, glycerol, and sodium hydroxide into a reaction vessel, and add deionized water at a ratio of 4 times the total mass of konjac glucomannan, glycerol, and sodium hydroxide. Heat to 80℃ and stir at 120 r / min for 4 h. After stirring, adjust the pH to 7.0, then add 95% ethanol at a ratio of 4 times the total mass of konjac glucomannan, glycerol, and sodium hydroxide. Stir at 180 r / min for 30 min. After stirring, let stand, filter with a 50-mesh filter cloth and collect the precipitate. Dry at 65℃ for 2.5 h, and after drying, pulverize to 100 mesh to obtain glycerol-modified konjac glucomannan powder. S5. Crush bentonite and vermiculite to 200-300 mesh, then transfer them to a mixer and stir at 180 r / min for 15 min; dilute silane coupling agent KH-550 with 95% ethanol to a concentration of 5%, and add the diluted silane coupling agent KH-550 to the mixed powder of bentonite and vermiculite, stir at 60℃ and 120 r / min for 3 h, and then dry at 75℃ for 2.5 h to obtain the modified bentonite-vermiculite composite. S6. Polycaprolactone, starch, and 2,6-di-tert-butyl-p-cresol were placed in a reaction vessel and stirred for 30 minutes at 120°C and 240 r / min. After stirring, the mixture was cooled to room temperature and then pulverized to 100 mesh to obtain the polycaprolactone-starch composite. S7. Place urea granules coated with urea-formaldehyde resin, calcium dihydrogen phosphate granules coated with trehalose, elemental powder, potassium nitrate, potassium sulfate, and talc into a mixer and stir for 30 minutes at 30°C and 180 r / min. Then add polyvinyl alcohol and continue stirring for 15 minutes. After stirring, transfer the mixture to a granulator and adjust the temperature of the granulator to 40°C and the speed to 30 r / min. Granulate the mixture to a particle size of 3 mm to obtain nutrient granules. S8. Dilute poly-N-isopropylacrylamide with 95% ethanol to a 15% poly-N-isopropylacrylamide solution and stir at 240 r / min for 10 min; put the nutrient particles into a fluidized bed coating machine, set the temperature of the fluidized bed coating machine to 25℃, the air velocity to 1 m / s, and the atomization pressure to 0.3 MPa, and spray the poly-N-isopropylacrylamide solution at a rate of 3 mL / min. After spraying, ventilate and dry to room temperature to obtain inner layer particles; S9. The polycaprolactone-starch composite was placed in a reaction vessel for remelting. The temperature of the reaction vessel was adjusted to 120℃ and the rotation speed was 180r / min. The mixture was stirred for 10min to obtain a polycaprolactone-starch fluid. The inner layer particles were placed in a vacuum spraying machine. The vacuum degree was adjusted to -0.07MPa and the temperature was 60℃. The polycaprolactone-starch fluid was sprayed at a spraying rate of 3mL / min to obtain double-layer coated particles. S10. Glyceryl-modified konjac glucomannan powder, modified bentonite-vermiculite complex, anhydrous betaine, and double-coated granules are placed in a mixer. The temperature of the mixer is set to 30℃, the speed is set to 180r / min, and the mixture is stirred for 30min. After stirring, the mixture is dried at 50℃ for 1h. After drying, it is cooled to room temperature and passed through a 20-mesh sieve to obtain the finished granules.

[0031] Testing and Inspection The soil used in the experiment was sandy loam, and the ambient temperature was controlled at 32-35℃, relative humidity at 40-50%, and light intensity at 12h / d. There was no rainfall during the planting period to simulate a hot and dry environment.

[0032] 1. Soil water retention time test Test Method: One hundred tomato plants with similar growth were selected and divided into 10 groups. 100g of samples from both the example and comparative studies were mixed with 5kg of planting soil and placed in planting boxes with dimensions of 40cm (length, width, and height). The bottom of each planting box had filter holes, and a filter cloth was laid at the bottom to prevent soil loss. Two tomato seedlings were planted in each planting box and watered with 500mL of water. A soil moisture sensor (accuracy ±0.1%) was then buried at a depth of 10cm in the planting box. Soil moisture content was recorded at the same time every day until it dropped to 15%. The number of days recorded was recorded as the water retention time. The cumulative evaporation when the soil moisture content dropped to 15% was also recorded. Specific test results are shown in Table 2.

[0033] Table 2

[0034] The test results of Examples 1 to 3 show that the fertilizer of the present invention has a long water retention time, and the high cumulative evaporation when the soil moisture content drops to 15% also indicates that the soil retains a higher moisture content, proving that the fertilizer of the present invention has excellent moisture retention ability.

[0035] By comparing the test results of Example 2 with those of Comparative Examples 1 and 2, it can be seen that, compared with not adding either urea-formaldehyde resin or trehalose, the addition of both urea-formaldehyde resin and trehalose enhances the moisture retention capacity of the fertilizer. This indicates that although urea-formaldehyde resin and trehalose mainly play a slow-release role in the fertilizer, the outer film they form can improve the moisture retention capacity of the fertilizer.

[0036] A comparison of the test results of Example 2 and Comparative Example 3 shows that the complex formed by polycaprolactone and starch can enhance the moisture retention capacity of fertilizer.

[0037] By comparing the test results of Example 2 with those of Comparative Examples 4-5, it can be seen that the glycerol-modified konjac glucomannan formed by konjac glucomannan and glycerol can significantly improve the moisture retention capacity of fertilizer and reduce the possibility of root burn in crops.

[0038] 2. Sustained-release performance test Test method: Take 5g of each of the example and comparative sample and place them in a dialysis bag with a molecular weight cutoff of 10000Da. Immerse the dialysis bag in 500mL of deionized water and place it in a constant temperature water bath at 32℃. Then, take 5mL samples on days 1, 3, 7, 14, 21, and 28, respectively. 5mL of deionized water should be added simultaneously with each sample collection. Nitrogen (NH4) is detected using an ion chromatograph (ISC-900). + NO3 - ), phosphorus (PO4) 3- ), potassium (K) + The concentration of ) is used to calculate the cumulative release rate.

[0039] Evaluation criteria: A cumulative nitrogen release rate of 60-70%, a cumulative phosphorus release rate of 55-65%, and a cumulative potassium release rate of 65-75% over 28 days are considered excellent sustained-release performance. Specific test results are shown in Table 3.

[0040] Table 3

[0041] The test results of Examples 1 to 3 show that the fertilizer of the present invention has excellent slow-release properties.

[0042] By comparing the test results of Example 2 with those of Comparative Examples 1 and 2, it can be seen that, compared with adding either urea-formaldehyde resin or trehalose alone, adding both urea-formaldehyde resin and trehalose at the same time can significantly improve the slow-release performance of the fertilizer of the present invention.

[0043] 3. Root burn rate Test method: 100 tomato plants of similar growth were selected and divided into 10 groups. One plant was planted in each 15×15cm seedling pot filled with planting soil. Samples from the example and comparative studies were applied to a depth of 10cm in the soil, with 20g of sample used per pot. 200mL of water was applied on the first day after fertilization, with no further watering. After 15 days of cultivation, the roots were dug up and their color was observed. Blackened or rotten roots indicated root burn, as did wilting or overnight scorching of the plant. The number of roots with burn was counted.

[0044] Calculation method: Root burn rate (%) = (Number of plants with burnn roots / Total number of plants) * 100%. The specific test results are shown in Table 4.

[0045] Table 4

[0046] The test results of Examples 1 to 3 show that the fertilizer of the present invention has excellent root-burn prevention effect, which is beneficial to the smooth growth of crops in hot and dry areas.

[0047] By comparing the test results of Example 2 with those of Comparative Examples 1 and 2, it can be seen that the lack of either urea-formaldehyde resin or trehalose will lead to an increase in the root burn rate of crops, indicating that the slow-release effect can reduce the excessively high local nutrient concentration in crops, thereby reducing the root burn rate of crops.

[0048] By comparing the test results of Example 2 with those of Comparative Examples 3-5, it can be seen that improving the moisture retention capacity of fertilizer can reduce the osmotic pressure in the soil and reduce the possibility of root burn in crops.

[0049] By comparing the test results of Example 2 with those of Comparative Examples 6 and 7, it can be seen that compared to the absence of either bentonite or vermiculite, the modified bentonite-vermiculite complex formed by the simultaneous addition of bentonite and vermiculite can reduce the root burn rate of crops.

[0050] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0051] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0052] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A moisture-retentive slow-release fertilizer, characterized by comprising: The composition comprises the following components by weight: urea-formaldehyde resin 20-25 parts; urea 8-10 parts; potassium nitrate 7-10 parts; potassium sulfate 7-10 parts; trehalose 1.2-1.4 parts; calcium dihydrogen phosphate 10.8-12.6 parts; citric acid 1-2 parts; humic acid 2-3 parts; trace element salt 1-3 parts; konjac glucomannan 6-7.5 parts; glycerol 1-2 parts; sodium hydroxide 0.05-0.06 parts; bentonite 3-4 parts; vermiculite 3-4 parts; coupling agent 0.3-0.4 parts; polycaprolactone 1-1.3 parts; starch 3-4 parts; antioxidant 0.01-0.02 parts; coating agent 3-4 parts; water-retaining agent 3-5 parts; adhesive 0.2-0.3 parts; filler 15-20 parts.

2. The moisture-retentive slow-release fertilizer according to claim 1, characterized by, The trace element salt comprises at least one of calcium sulfate, magnesium sulfate, and zinc sulfate.

3. The moisture-retentive slow-release fertilizer according to claim 1, characterized by, The coupling agent is any one of silane coupling agent KH-550, silane coupling agent KH-560, and silane coupling agent KH-602.

4. The moisture-retentive slow-release fertilizer according to claim 1, characterized by, The antioxidant is at least one of [beta-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid] pentaerythritol ester, 2,6-di-tert-butyl-p-cresol, vitamin E, and tea polyphenol.

5. The moisture-retentive slow-release fertilizer according to claim 1, characterized in that, The coating agent is poly-N-isopropyl acrylamide.

6. The moisture retaining slow release fertilizer according to claim 1, wherein The water-retaining agent comprises at least one of L-proline and anhydrous betaine.

7. The moisture retaining slow release fertilizer according to claim 1, characterized in that, The adhesive is any one of polyvinyl alcohol, sodium carboxymethyl cellulose, gum arabic, and guar gum.

8. The moisture retaining slow release fertilizer according to claim 1, characterized in that, The filler is at least one of talc, kaolin, diatomite, and mica powder.

9. A method for producing the moisture-retentive slow-release fertilizer according to any one of claims 1 to 8, characterized by, The method comprises the following steps: S1. diluting the urea-formaldehyde resin with deionized water to a solid content of 40-60% to obtain a coating liquid, placing the urea into a fluidized bed coater, adjusting the temperature of the fluidized bed coater to 45-55°C, the wind speed to 1-2 m / s, and the atomization pressure to 0.3-0.5 MPa, spraying the coating liquid at a rate of 2-4 mL / min, raising the temperature to 60-65°C after spraying, and maintaining the temperature for 20-40 min for solidification, and then passing through a 10-20 mesh sieve to obtain urea-formaldehyde resin-coated urea particles; S2. dissolving the trehalose in deionized water, stirring at a speed of 100-200 r / min for 5-10 min to obtain a trehalose aqueous solution with a concentration of 10-12%, placing the calcium dihydrogen phosphate into a fluidized bed coater, adjusting the temperature of the fluidized bed coater to 38-42°C, the wind speed to 0.8-1.2 m / s, and the atomization pressure to 0.2-0.4 MPa, spraying the trehalose aqueous solution at a rate of 1.5-2.5 mL / min, maintaining the temperature and ventilating to dry for 1-1.5 h after spraying, and then cooling and passing through a 15-25 mesh sieve to obtain trehalose-coated calcium dihydrogen phosphate particles; S3. Citric acid, humic acid are mixed, deionized water is added in an amount of 5 times the total mass of citric acid and humic acid, the temperature is raised to 55-65 DEG C, stirring is carried out at a speed of 200-300 r / min for 20-40 min, then micronutrient salt is added, stirring is carried out for 50-70 min, the pH is controlled to be 5.5-6.0, a mixed solution is obtained, the mixed solution is concentrated in vacuum, the temperature for vacuum concentration is 65-75 DEG C, the vacuum degree is -0.08 to -0.09 MPa, concentration is carried out until the solid content is 75-85%, after concentration, spray drying is carried out, the inlet air temperature for spray drying is 170-190 DEG C, the outlet air temperature is 75-85 DEG C, drying is carried out into powder, element powder is obtained; S4. Konjac glucomannan, glycerol, sodium hydroxide are put into a reaction kettle, deionized water is added in an amount of 4 times the total mass of konjac glucomannan, glycerol and sodium hydroxide, the temperature is raised to 75-85 DEG C, stirring is carried out at a speed of 100-200 r / min for 3.5-4.5 h, after stirring, the pH is adjusted to 6.8-7.2, deionized water is added in an amount of 4 times the total mass of konjac glucomannan, glycerol and sodium hydroxide, the concentration of the deionized water is 95%, stirring is carried out at a speed of 100-200 r / min for 20-40 min, after stirring, standing is carried out, the precipitate is collected by filtering with 40-50 mesh filter cloth, drying is carried out at 60-70 DEG C for 2-3 h, after drying, crushing is carried out to 80-100 mesh, glycerol-modified konjac glucomannan powder is obtained; S5. The bentonite and the vermiculite are crushed to 200-300 mesh, then are transferred into a mixer, stirring is carried out at a speed of 150-200 r / min for 10-20 min; the coupling agent is diluted with 95% ethanol to a concentration of 5-8%, the diluted coupling agent is added into the mixed powder of bentonite and vermiculite, stirring is carried out at a temperature of 55-65 DEG C and a speed of 120-180 r / min for 2.5-3.5 h, after stirring, drying is carried out at 70-80 DEG C for 2-2.5 h, a modified bentonite-vermiculite composite is obtained; S6. Polycaprolactone, starch and antioxidant are put into a reaction kettle, stirring is carried out at a temperature of 115-125 DEG C and a speed of 200-250 r / min for 25-35 min, after stirring, cooling is carried out to room temperature, then crushing is carried out to 80-100 mesh, a polycaprolactone-starch composite is obtained; S7. Urea-formaldehyde resin coated urea particles, trehalose coated calcium dihydrogen phosphate particles, element powder, potassium nitrate, potassium sulfate and filler are put into a mixer, stirring is carried out at a temperature of 25-30 DEG C and a speed of 120-180 r / min for 20-30 min, then the binder is added, stirring is continued for 10-15 min, after stirring, the mixture is transferred into a granulator, the temperature of the granulator is adjusted to 35-45 DEG C, the speed is adjusted to 25-35 r / min, granulation is carried out until the particle size is 2-3 mm, nutrient granules are obtained; S8. dilute the coating agent to a concentration of 12-15% with ethanol at a concentration of 95%, and stir at a speed of 180-240 r / min for 5-10 min; place the nutrient granules into the fluidized bed coating machine, adjust the temperature of the fluidized bed coating machine to 22-28 ℃, the wind speed to 1-1.5 m / s, and the atomization pressure to 0.2-0.4 MPa, spray the coating agent solution at a rate of 2-3 mL / min, and dry after spraying to room temperature to obtain the inner layer granules; S9. melt the polycaprolactone-starch complex in a reaction kettle, adjust the temperature of the reaction kettle to 110-120 ℃ and the rotation speed to 120-180 r / min, and stir for 10-15 min to obtain polycaprolactone-starch flow liquid; place the inner layer granules into a vacuum spraying machine, adjust the vacuum degree to -0.07 to -0.09 MPa and the temperature to 55-65 ℃, and spray the polycaprolactone-starch flow liquid at a spraying rate of 3-5 mL / min to obtain double-layer coated granules; S10. place the glycerol-modified konjac glucomannan powder, modified bentonite-vermiculite complex, water-retaining agent, and double-layer coated granules into a mixing machine, adjust the temperature of the mixing machine to 28-32 ℃ and the rotation speed to 150-200 r / min, and stir for 25-35 min, then dry at 45-55 ℃ for 1-1.5 h after stirring, cool to room temperature after drying, and pass through a 10-20 mesh sieve to obtain the finished granules.