Water-retention synergistic coated slow-release fertilizer and preparation method thereof

Abstract

The invention discloses a water-retention synergistic coated slow-release fertilizer and a preparation method thereof, and relates to the technical field of water-retention slow-release fertilizers. The coated slow-release fertilizer sequentially comprises a fertilizer core, an inhibitor layer, a slow-release coating layer, a bonding layer and a water-retaining slow-release layer from inside to outside. Wherein the inhibitor layer is composed of a urease / nitrification inhibitor, the slow-release coating layer is composed of organic polymer resin, the bonding layer is composed of an ethyl cellulose binder, and the water-retaining slow-release layer is composed of a modified water-retaining agent. The coated slow-release fertilizer prepared by the invention has good water retention performance, controlled release performance and salt resistance, is suitable for high-salt soil, and can obviously improve the nitrogen fertilizer utilization rate. Meanwhile, the combination of polyglutamic acid and sulfonic acid groups is used for modifying polyacrylic acid to prepare the modified water-retaining agent, so that a synergistic effect on improving the salt resistance of the coated slow-release fertilizer is achieved, the fertilizer efficiency can be improved, the loss is reduced, the soil environment is improved, and the water-retaining capacity of soil and the utilization rate of the fertilizer are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of water-retaining slow-release fertilizers, and particularly to a water-retaining and efficiency-enhancing coated slow-release fertilizer and a preparation method thereof. Background Art

[0002] Slow-release fertilizers have become a research hotspot in modern agricultural technology because they can delay the nutrient release rate, reduce nitrate leaching and nitrogen volatilization, thereby improving fertilizer utilization efficiency. Traditional slow-release fertilizers often have limited improvement in fertilizer utilization efficiency due to insufficient water-retaining performance and mismatch between nutrient release and water supply in arid or saline soils, making it difficult to meet the requirements of coordinated water and fertilizer regulation.

[0003] Currently, water-retaining agents are often used to coat slow-release fertilizers to improve their water-retaining performance. Commercially available water-retaining agents include polyacrylates and polyacrylamides, etc. Among them, both polyacrylate-based and polyacrylamide absorb water by forming hydrogen bonds between carboxylate groups on the polymer chain and water molecules and generating osmotic pressure. However, in high-salt soils, a large number of cations (such as Na+, Ca2+, Mg2+) present in the solution will compete with the carboxylate groups of polyacrylate, neutralize their negative charges and reduce the osmotic pressure difference, thus significantly weakening the water absorption ability of the water-retaining agent.

[0004] In the prior art, CN118619759A discloses a double-layer structured biomass surface-crosslinked water-retaining slow-release fertilizer and a preparation method thereof. The inner layer of the water-retaining slow-release fertilizer is a semi-interpenetrating network-type high water-retaining and slow-release fertilizer formed by polymerizing an acrylic acid-based superabsorbent resin with urea formaldehyde or modified urea formaldehyde linear resin, and the outer layer is coated with a biomass material using surface crosslinking technology. However, the nutrient content in the water-retaining slow-release fertilizer is low, and the internal fertilizer molecules / ions will limit the swelling of the water-retaining agent molecules, resulting in reduced water absorption. CN119350094A discloses a pH-responsive starch-based gel-coated slow-release fertilizer. The coated slow-release fertilizer includes a core fertilizer and a pH-responsive starch-based gel coating wrapped on the surface of the core fertilizer. The coating material is prepared by crosslinking polymerization of amorphous starch, acrylic acid monomer, crosslinking agent and initiator. Although the coating material shows different permeabilities at different pH values to control the nutrient release rate, there is still a problem of poor water absorption when it is used in high-salt soils.

[0005] Therefore, it is particularly important to prepare a coated slow-release fertilizer with high water-retaining performance, salt tolerance and efficiency-enhancing properties, and to ensure that the coated slow-release fertilizer still has good water absorption ability when used in high-salt soils. Summary of the Invention

[0006] In view of the above-mentioned prior art, the object of the present invention is to provide a water-retaining and efficiency-enhancing coated slow-release fertilizer and a preparation method thereof. The coated slow-release fertilizer is prepared by sequentially coating an inhibitor layer, a slow-release coating layer, a bonding layer, and a water-retaining slow-release layer outside the fertilizer core. Among them, the inhibitor layer is composed of urease / nitrification inhibitor, the slow-release coating layer is composed of organic polymer resin, the bonding layer is composed of ethyl cellulose binder, and the water-retaining slow-release layer is composed of modified water-retaining agent. The coated slow-release fertilizer prepared by the present invention has good water-retaining performance and controlled-release performance. When applied to high-salt soil, it can significantly improve the nitrogen fertilizer utilization rate. In addition, the modified water-retaining agent is prepared by using the combination of polyglutamic acid and sulfonic acid groups to modify polyacrylic acid, which not only has a synergistic effect on improving the salt tolerance of the coated slow-release fertilizer, but also can enhance the fertilizer efficiency, reduce losses, improve the soil environment, and improve the soil water-retaining capacity and fertilizer utilization rate.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] In the first aspect of the present invention, there is provided a water-retaining and efficiency-enhancing coated slow-release fertilizer, which sequentially includes from inside to outside: a fertilizer core, an inhibitor layer, a slow-release coating layer, a bonding layer, and a water-retaining slow-release layer;

[0009] The mass ratio of the fertilizer core, the inhibitor layer, the slow-release coating layer, the bonding layer, and the water-retaining slow-release layer is 100:(0.5 - 5):(3 - 7):(0.5 - 1):(5 - 10);

[0010] The water-retaining slow-release layer is composed of a modified water-retaining agent, and the modified water-retaining agent is prepared by the following method:

[0011] Mix the polyglutamic acid solution, acrylic acid solution, and sulfonate, heat and stir, then introduce a protective gas to remove the dissolved oxygen in the solution to obtain a mixed solution; then add an initiator and a cross-linking agent to the mixed solution, mix and heat up to 60 - 80 °C and stir for 2 - 5 min, then stop stirring and continue the reaction under insulation. After the reaction is completed, wash and dry to obtain the modified water-retaining agent.

[0012] Preferably, the fertilizer core is one or more of urea, NPK compound fertilizer, ammonium sulfate, ammonium chloride, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; the particle size of the fertilizer core is 2.5 - 3.5 mm.

[0013] Preferably, the inhibitor layer is composed of a urease inhibitor and a nitrification inhibitor in a mass ratio of 1:(3 - 10).

[0014] More preferably, the urease inhibitor is one or more of hydroquinone, n-butyl thiophosphoryl triamide, thiophosphoric triamide, and phenylphosphoryldiamine alcohol; the nitrification inhibitor is one or several of dicyandiamide, 3,4-dimethylpyrazole phosphate, 1-methylcarbamoyl-3-methylpyrazole, and guanylthiourea.

[0015] Preferably, the slow-release coating layer is composed of epoxy resin and / or polyurethane.

[0016] Preferably, the adhesive layer is composed of an ethyl cellulose binder, and the ethyl cellulose binder is prepared by the following method: ethyl cellulose and absolute ethanol are mixed at a material-liquid ratio of 1 g:(10 - 50) mL, and then stirred to obtain the ethyl cellulose binder.

[0017] Preferably, the sulfonate is one or more of 2-acrylamido-2-methylpropane sulfonic acid, sodium p-styrene sulfonate, and β-aminoethanesulfonic acid.

[0018] Preferably, the polyglutamic acid solution is prepared by mixing polyglutamic acid and deionized water at a material-liquid ratio of (0.1 - 1) g:100 mL.

[0019] Preferably, the neutralization degree of the acrylic acid solution is 40 - 70%, and the acrylic acid solution is prepared by mixing acrylic acid and a 10% KOH solution by mass fraction.

[0020] Preferably, the heating temperature is 35 - 45°C, and the stirring time is 4 - 6 min.

[0021] Preferably, the protective gas is nitrogen, and the time for introducing the protective gas is 12 - 18 min.

[0022] Preferably, the crosslinking agent is one or several of divinylbenzene, diisocyanate, N,N'-methylenebisacrylamide, dimethylacrylamide, and polyethylene glycol; the initiator is one or several of potassium persulfate, ammonium persulfate, and sodium persulfate.

[0023] Preferably, the continued reaction time is 3 - 4 h.

[0024] Preferably, the washing operation is as follows: the reaction product is washed 2 - 3 times with deionized water and then soaked for 24 h to remove the unreacted monomers in the reaction product.

[0025] Preferably, the drying temperature is 50 - 70°C.

[0026] Preferably, the addition amounts of the acrylic acid solution, polyglutamic acid solution, sulfonate, initiator, and crosslinking agent are 100 mL:(0.5 - 10) g:(0.1 - 10) g:(0.1 - 5) g:(0.01 - 1) g.

[0027] In the second aspect of the present invention, a preparation method of the above water-retaining and efficiency-enhancing coated slow-release fertilizer is provided, including the following steps:

[0028] (1) Spray the inhibitor solution on the surface of the preheated fertilizer core, and after drying, an inhibitor layer is formed on the surface of the fertilizer core, obtaining the inhibitor-coated fertilizer;

[0029] (2) Spray the coating solution on the surface of the preheated inhibitor-coated fertilizer, and after curing, a slow-release coating layer is formed on the surface of the inhibitor-coated fertilizer, obtaining the inhibitor-coated and double-controlled release fertilizer;

[0030] (3) After spraying the binder on the surface of the inhibitor-coated and double-controlled release fertilizer, then spray the modified water-retaining agent on the inhibitor-coated and double-controlled release fertilizer with the binder on its surface, and dry it, and a bonding layer and a water-retaining and slow-release layer are sequentially formed on the surface of the inhibitor-coated and double-controlled release fertilizer, obtaining the water-retaining and efficiency-enhancing coated slow-release fertilizer.

[0031] Preferably, in step (1), during the preheating process of the fertilizer core: the preheating rotation speed is 20 - 40 rpm, the preheating temperature is 70 - 85 °C, and the preheating time ≥ 5 min.

[0032] Preferably, in step (1), the preparation method of the inhibitor solution is: dissolve the inhibitor in absolute ethanol by stirring at a temperature of 60 - 80 °C, obtaining the inhibitor solution; wherein, the material ratio of the inhibitor to absolute ethanol is 1 g : (20 - 50) mL.

[0033] Preferably, in step (1), the drying time ≥ 20 min.

[0034] Preferably, in step (1), the mass ratio of the inhibitor to the fertilizer core is (0.5 - 5) : 100.

[0035] Preferably, in step (2), the coating solution is prepared by mixing solution A and solution B in a mass ratio of (1 - 10) : (1 - 5); solution A is isocyanate and / or epoxy resin; solution B is polyol and / or triethylenetetramine.

[0036] More preferably, the polyol is selected from vegetable oil polyol or polyether polyol; the vegetable oil polyol is selected from at least one of castor oil polyol, soybean oil polyol, and palm oil polyol; the polyether polyol is selected from at least one of polyethylene glycol, polyether tetrol, polyurea triol, and polyvinyl alcohol; the isocyanate is selected from at least one of polymethylene polyphenyl isocyanate (PAPI), toluene diisocyanate (TDI) trimer, toluene diisocyanate (TDI), and isophorone diisocyanate (IPDI) trimer.

[0037] Preferably, in step (2), during the preheating process of the inhibitor-coated fertilizer, the preheating rotation speed is 20 - 40 rpm, the preheating temperature is 70 - 85 °C, and the preheating time is ≥ 5 min.

[0038] Preferably, in step (2), the curing temperature is 75 - 85 °C and the curing time is 12 - 18 min.

[0039] Preferably, in step (3), the drying temperature is 60 - 85 °C and the drying time ≥ 20 min.

[0040] Advantages of the present invention:

[0041] 1. The present invention prepares a water - retaining and efficiency - enhancing coated slow - release fertilizer by sequentially coating an inhibitor layer, a slow - release coating layer, a bonding layer, and a water - retaining and slow - release layer outside the fertilizer core. Among them, the inhibitor layer is composed of urease / nitrification inhibitor, the slow - release coating layer is composed of organic polymer resin - polyurethane and / or epoxy resin, the bonding layer is composed of ethyl cellulose binder, and the water - retaining and slow - release layer is composed of a modified water - retaining agent, and the modified water - retaining agent is prepared by co - modifying polyacrylic acid with polyglutamic acid and sulfonate. The coated slow - release fertilizer prepared by the present invention has good water - retaining performance, controlled - release performance, and salt - tolerance performance. When applied to high - salt soil, it can significantly improve the nitrogen fertilizer utilization rate. Specifically, when the application rate is 0.5 - 2%, it can increase the maximum water - holding rate of the soil by 64.2 - 74.7%; compared with the soil without applying the coated water - retaining and slow - release fertilizer of the present invention, the water - retaining ability of the soil after applying the coated water - retaining and slow - release fertilizer of the present invention is increased by 42.7%; the coated water - retaining and slow - release fertilizer of the present invention has good slow - release performance. The time required for the nutrient release amount of the coated water - retaining and slow - release fertilizer of the present invention to reach 80% is 43 - 50 days, while the uncoated urea particles release more than 80% of the fertilizer nutrients within 35 days.

[0042] 2. Although urease / nitrification inhibitor can delay the hydrolysis of nitrogen fertilizer in the soil and the conversion of ammonium nitrogen to nitrate nitrogen, there are problems such as adsorption fixation and degradation after it is applied to the soil. Therefore, the present invention combines urease / nitrification inhibitor with organic polymer resin for coating, which can not only improve the controlled - release performance of the fertilizer but also effectively improve the nitrogen fertilizer utilization rate.

[0043] The release of the coated fertilizer is a water - driven cross - interface diffusion mechanism of nutrients. By coating a water - retaining and slow - release layer on the outermost layer, the present invention can keep the surface of the fertilizer always in a water - vapor - saturated state. It not only has excellent water - retaining effect, making the actual release law of the coated fertilizer easier to be consistent with the designed release law in the laboratory, but also ensures that in the burst - release stage, the swollen water - retaining agent will be filled with high - concentration fertilizer and inhibitor, having a buffering effect and slowing down the nutrient diffusion rate.

[0044] It can be seen that the water-retaining and efficiency-enhancing slow-release fertilizer provided by the present invention is a physical carrier of water and fertilizer regulation technology. The inhibitor and resin are combined for coating, reducing nutrient loss and improving nitrogen fertilizer utilization rate. The addition of the water-retaining layer not only delays nutrient release but also improves water utilization rate. Therefore, the water-retaining and efficiency-enhancing slow-release fertilizer combines fertilizer, inhibitor, and water-retaining agent, giving full play to the interaction between nutrients and water, achieving the effect of promoting fertilizer with water and regulating fertilizer with water.

[0045] 3. The present invention introduces polyglutamic acid and sulfonic acid groups into the polyacrylic acid (PAA) hydrogel network, and uses a method of constructing a physical and chemical double cross-linked network to synergistically improve the performance of the water-retaining agent, preparing a water-retaining agent with salt tolerance, fertilizer efficiency enhancement, and strong water absorption. Specifically, the combination of polyglutamic acid and sulfonic acid groups modifies polyacrylic acid, which not only has a synergistic effect on improving the salt tolerance of coated slow-release fertilizers but also can enhance fertilizer efficiency, reduce losses, improve the soil environment, and improve soil water retention capacity and fertilizer utilization rate. It can be seen that the modified water-retaining agent prepared by the present invention successfully solves the deficiencies of commercially available water-retaining agents with poor salt tolerance and single function.

[0046] 4. The present invention uses ethyl cellulose as a binder. Coating it on the surface of the fertilizer can significantly reduce the release rate of the fertilizer and extend the release time of the fertilizer. Therefore, ethyl cellulose can not only be used as a binder between the coated fertilizer and the water-retaining layer but also further extend the controlled-release period of the fertilizer and enhance the controlled-release effect of the fertilizer. Description of the Drawings

[0047] Figure 1 : Scanning electron microscope images of the coated slow-release fertilizers prepared in Example 3 and Comparative Example 2. Among them, (a) is the scanning electron microscope image of the coated slow-release fertilizer prepared in Comparative Example 2, and (b) is the scanning electron microscope image of the coated slow-release fertilizer prepared in Example 3;

[0048] Figure 2 : FTIR spectrum of the coated slow-release fertilizer prepared in Example 3;

[0049] Figure 3 : Swelling degrees of the coated slow-release fertilizers prepared in Example 3 and Comparative Examples 2-4; among them, (a) is the swelling degrees of the coated slow-release fertilizers prepared in Example 3 and Comparative Examples 2-4 in deionized water at different times; (b) is the swelling degrees of the coated slow-release fertilizers prepared in Example 3 and Comparative Examples 2-4 at different pH values; (c) is the swelling degrees of the coated slow-release fertilizers prepared in Example 3 and Comparative Examples 2-4 in salt solutions with different concentrations;

[0050] Figure 4 : Maximum water-holding capacity diagrams of the mixed soils of the coated slow-release fertilizers prepared in Example 3 and Comparative Examples 2-4 in different proportions;

[0051] Figure 5:Water retention capacity diagrams of the coated slow-release fertilizers prepared from Example 3 and Comparative Examples 2-4 in different proportions; among them, (a) is the water retention capacity diagram corresponding to Comparative Example 2; (b) is the water retention capacity diagram corresponding to Comparative Example 3; (c) is the water retention capacity diagram corresponding to Comparative Example 4; (d) is the water retention capacity diagram corresponding to Example 3;

[0052] Figure 6 :Nitrogen release behavior diagrams of the coated slow-release fertilizers prepared from Example 3 and Comparative Examples 2-4. Detailed implementation manners

[0053] It should be noted that the following detailed descriptions are all illustrative and are intended to provide further explanations for the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs.

[0054] In order to enable those skilled in the art to more clearly understand the technical solutions of the present invention, the technical solutions of the present invention will be described in detail below in conjunction with specific embodiments.

[0055] The experimental materials used in the embodiments of the present invention are all conventional experimental materials in the art and can all be obtained through commercial channels.

[0056] Example 1: Water retention and efficiency-enhancing coated slow-release fertilizer

[0057] 1. Composition

[0058] The water retention and efficiency-enhancing coated slow-release fertilizer sequentially includes from the inside to the outside: a fertilizer core, an inhibitor layer, a slow-release coating layer, a bonding layer, and a water retention and slow-release layer; the mass ratio of the fertilizer core, the inhibitor layer, the slow-release coating layer, the bonding layer, and the water retention and slow-release layer is 100:2.208:3:0.6:6;

[0059] The fertilizer core is urea with a particle size of 2.5-3.5 mm; the inhibitor layer is composed of 3,4-dimethylpyrazole phosphate and n-butyl thiophosphoryl triamide mixed in a mass ratio of 0.368 g:1.84 g; the slow-release coating layer is composed of polyurethane; the bonding layer is composed of an ethyl cellulose binder, and the water retention and slow-release layer is composed of a modified water-retaining agent;

[0060] The preparation method of the ethyl cellulose binder is as follows:

[0061] After mixing ethyl cellulose and absolute ethanol at a material-liquid ratio of 1 g:10 mL, stir for 30 min to obtain the ethyl cellulose binder;

[0062] The preparation method of the modified water-retaining agent is as follows:

[0063] After mixing 0.15 g of γ-polyglutamic acid with 100 mL of deionized water and ultrasonically dispersing for 25 min, a polyglutamic acid solution was obtained;

[0064] Mix 15 mL of acrylic acid solution and 44.55 mL of 10% KOH solution by mass for reaction to obtain an acrylic acid solution with a neutralization degree of 40%;

[0065] After mixing the polyglutamic acid solution, acrylic acid solution and sodium p-styrenesulfonate, heat and stir at 40 °C for 5 min, and pass nitrogen to remove dissolved oxygen in the solution to obtain a mixed solution. Add ammonium persulfate and dimethylacrylamide to the mixed solution, heat up to 60 °C after mixing and stir for 2 min, stop stirring, keep the temperature at 60 °C for heat preservation reaction for 4 h. After the reaction is completed, wash the reaction product 3 times with deionized water and soak for 24 h to remove unreacted monomers in the reaction product, and then dry and pulverize at 60 °C to obtain the modified water retaining agent;

[0066] Among them, the addition ratio of the polyglutamic acid solution, acrylic acid solution, sodium p-styrenesulfonate, ammonium persulfate and dimethylacrylamide is 0.15 g: 15 mL: 0.15 g: 0.09 g: 0.012 g.

[0067] 2. Preparation method:

[0068] (1) After mixing the inhibitor and absolute ethanol according to the material-liquid ratio of 1 g: 20 mL and stirring and mixing evenly at 70 °C, an inhibitor solution was obtained. Load the urea granules into a coating machine and rotate and preheat to 75 °C at 40 rpm; Spray the inhibitor solution evenly on the surface of the preheated urea granules and dry for 20 min, and an inhibitor layer is formed on the surface of the urea granules to obtain the inhibitor-coated fertilizer;

[0069] (2) Mix soybean oil polyol and polymethylene polyphenyl isocyanate according to a mass ratio of 5:2 to obtain a coating solution; Load the inhibitor-coated fertilizer into a coating machine and rotate and preheat to 75 °C at 40 rpm; Spray the coating solution evenly on the surface of the preheated inhibitor-coated fertilizer and cure at 80 °C for 15 min. Repeat the spraying and curing operations multiple times, and a slow-release coating layer is formed on the surface of the inhibitor-coated fertilizer to obtain the inhibitor-coated and double-controlled release fertilizer;

[0070] Among them, in each spraying process, the dosage of the coating solution is 1 wt% of the mass of the urea granules;

[0071] (3) Evenly spray the ethyl cellulose binder on the inhibitor-coated and double-controlled release fertilizer, and then evenly spray the modified water retaining agent on the inhibitor-coated and double-controlled release fertilizer with a binder-coated surface. Dry at 70 °C for 20 min, and a binder layer and a water retention and slow-release layer are successively coated on the surface of the inhibitor-coated and double-controlled release fertilizer to obtain the water retention and efficiency-enhanced coated slow-release fertilizer.

[0072] Example 2: Water-retention and efficiency-enhancing coated slow-release fertilizer

[0073] 1. Composition

[0074] The water-retention and efficiency-enhancing coated slow-release fertilizer successively includes from inside to outside: a fertilizer core, an inhibitor layer, a slow-release coating layer, a bonding layer, and a water-retention and slow-release layer; the mass ratio of the fertilizer core, the inhibitor layer, the slow-release coating layer, the bonding layer, and the water-retention and slow-release layer is 100: 3.312: 3: 0.9: 9;

[0075] The fertilizer core is urea with a particle size of 2.5 - 3.5 mm; the inhibitor layer is composed of an inhibitor, and the inhibitor is formed by mixing hydroquinone and dicyandiamide according to a mass ratio of 0.552: 2.76; the slow-release coating layer is composed of epoxy resin; the bonding layer is composed of ethyl cellulose binder; the water-retention and slow-release layer is composed of a modified water-retaining agent;

[0076] The preparation method of ethyl cellulose is as follows:

[0077] After mixing ethyl cellulose and absolute ethanol according to a material-liquid ratio of 1 g: 10 mL, stir for 30 min to obtain the ethyl cellulose binder;

[0078] The preparation method of the modified water-retaining agent is as follows:

[0079] After mixing 0.75 g of γ-polyglutamic acid and 100 mL of deionized water, ultrasonically disperse for 25 min to obtain a polyglutamic acid solution;

[0080] Mix 15 mL of acrylic acid solution and 78 mL of 10% KOH solution by mass for reaction to obtain an acrylic acid solution with a neutralization degree of 70%;

[0081] After mixing the polyglutamic acid solution, the acrylic acid solution, and β-aminoethanesulfonic acid, heat and stir at 40 °C for 5 min, and introduce nitrogen to remove the dissolved oxygen in the solution to obtain a mixed solution. Add ammonium persulfate and diisocyanate to the mixed solution, mix and then raise the temperature to 60 °C and stir for 2 min, stop stirring, keep the temperature at 60 °C for a reaction for 4 h. After the reaction ends, wash the reaction product 3 times with deionized water and soak for 24 h to remove the unreacted monomers in the reaction product, and then dry and pulverize at 60 °C to obtain the modified water-retaining agent;

[0082] Among them, the addition amount ratio of polyglutamic acid, acrylic acid solution, β-aminoethanesulfonic acid, ammonium persulfate, and diisocyanate is 0.75 g: 15 mL: 1.5 g: 0.06 g: 0.009 g.

[0083] 2. Preparation method:

[0084] (1) Mix the inhibitor and absolute ethanol at a material-liquid ratio of 1 g: 50 mL, stir and mix evenly at 70 °C to obtain an inhibitor solution. Load the urea granules into a coating machine, rotate and preheat to 75 °C at 40 rpm; evenly spray the inhibitor solution on the surface of the preheated urea granules, and dry for 20 min, that is, an inhibitor layer is formed on the surface of the urea granules, and a fertilizer coated with the inhibitor is obtained. Among them, the mass ratio of the inhibitor to the urea granules is 3.312: 100;

[0085] (2) Mix epoxy resin and triethylenetetramine at a mass ratio of 10: 3 to obtain a coating solution; load the fertilizer coated with the inhibitor into a coating machine, rotate and preheat to 75 °C at 40 rpm; evenly spray the coating solution on the surface of the fertilizer coated with the inhibitor after preheating, and cure at 80 °C for 15 min. Repeat the spraying and curing operations multiple times, that is, a slow-release coating layer is formed on the surface of the fertilizer coated with the inhibitor, and a double-controlled release fertilizer coated with the inhibitor is obtained;

[0086] Among them, during each spraying process, the dosage of the coating solution is 1 wt% of the mass of the urea granules;

[0087] (3) Evenly spray the ethyl cellulose binder on the double-controlled release fertilizer coated with the inhibitor, and then evenly spray the modified water-retaining agent on the double-controlled release fertilizer coated with the inhibitor and having a binder on the surface. Dry at 70 °C for 20 min, that is, a binder layer and a water-retaining and slow-release layer are sequentially coated on the surface of the double-controlled release fertilizer coated with the inhibitor, and a water-retaining and efficiency-enhancing coated slow-release fertilizer is obtained.

[0088] Example 3: Water-retaining and efficiency-enhancing coated slow-release fertilizer

[0089] 1. Composition

[0090] The water-retaining and efficiency-enhancing coated slow-release fertilizer sequentially includes from the inside to the outside: a fertilizer core, an inhibitor layer, a slow-release coating layer, a binder layer and a water-retaining and slow-release layer; the mass ratio of the fertilizer core, the inhibitor layer, the slow-release coating layer, the binder layer and the water-retaining and slow-release layer is 100: 2.208: 3: 0.9: 9;

[0091] The fertilizer core is urea with a particle size of 2.5 - 3.5 mm; the inhibitor layer is composed of an inhibitor, and the inhibitor is composed of hydroquinone and dicyandiamide mixed at a mass ratio of 0.368 g: 1.84 g; the slow-release coating layer is composed of polyurethane; the binder layer is composed of an ethyl cellulose binder, and the water-retaining and slow-release layer is composed of a modified water-retaining agent;

[0092] The preparation method of ethyl cellulose is:

[0093] Mix ethyl cellulose and absolute ethanol at a material-liquid ratio of 1 g: 10 mL, and stir for 30 min to obtain an ethyl cellulose binder;

[0094] The preparation method of the modified water retaining agent is as follows:

[0095] After mixing 0.45 g of γ-polyglutamic acid and 100 mL of deionized water, ultrasonic dispersion is carried out for 25 min to obtain a polyglutamic acid solution;

[0096] Mix 15 mL of acrylic acid solution and 66.91 mL of 10% KOH solution by mass for reaction to obtain an acrylic acid solution with a neutralization degree of 60%;

[0097] After mixing the polyglutamic acid solution, acrylic acid solution and 2-acrylamido-2-methylpropanesulfonic acid, heat and stir at 40 °C for 5 min, and introduce nitrogen to remove the dissolved oxygen in the solution to obtain a mixed solution. Add ammonium persulfate and N,N'-methylenebisacrylamide to the mixed solution, mix and then raise the temperature to 60 °C and stir for 2 min. Stop stirring and keep the reaction at 60 °C for 4 h. After the reaction is completed, wash the reaction product 3 times with deionized water and soak for 24 h to remove the unreacted monomers in the reaction product, and then dry and pulverize at 60 °C to obtain the modified water retaining agent;

[0098] Among them, the addition ratio of polyglutamic acid, acrylic acid, 2-acrylamido-2-methylpropanesulfonic acid, ammonium persulfate and N,N'-methylenebisacrylamide is 0.45 g: 15 mL: 0.75 g: 0.075 g: 0.0105 g.

[0099] 2. Preparation method:

[0100] (1) After mixing the inhibitor and absolute ethanol according to the material-liquid ratio of 1 g: 50 mL, stir and mix evenly at 70 °C to obtain an inhibitor solution. Load the urea granules into a coating machine and rotate and preheat to 75 °C at 40 rpm; Spray the inhibitor solution evenly on the surface of the preheated urea granules and dry for 20 min, that is, an inhibitor layer is formed on the surface of the urea granules to obtain the inhibitor-coated fertilizer, among which the mass ratio of the inhibitor to the urea granules is 2.208: 100;

[0101] (2) Mix soybean oil polyol and polymethylene polyphenyl isocyanate according to a mass ratio of 3: 2 to obtain a coating solution; Load the inhibitor-coated fertilizer into a coating machine and rotate and preheat to 75 °C at 40 rpm; Spray the coating solution evenly on the surface of the preheated inhibitor-coated fertilizer and cure at 80 °C for 15 min. Repeat the spraying and curing operations multiple times, that is, a slow-release coating layer is formed on the surface of the inhibitor-coated fertilizer to obtain the inhibitor-coated and double-controlled release fertilizer;

[0102] Among them, in each spraying process, the dosage of the coating solution is 1 wt% of the mass of the urea granules;

[0103] (3) The ethyl cellulose binder was evenly sprayed on the inhibitor-coated double-controlled release fertilizer, and then the modified water-retaining agent was evenly sprayed on the inhibitor-coated double-controlled release fertilizer with the binder coated on the surface. It was dried at 70 °C for 20 min, and thus a binder layer and a water-retaining and slow-release layer were successively coated on the surface of the inhibitor-coated double-controlled release fertilizer, and a water-retaining and efficiency-enhancing coated slow-release fertilizer was prepared.

[0104] Comparative Example 1:

[0105] The difference between this comparative example and Example 3 is that: the coated slow-release fertilizer includes, from the inside to the outside: a fertilizer core, a slow-release coating layer, and a binder layer; the specific preparation method is as follows:

[0106] (1) The urea granules were loaded into a coating machine and preheated to 75 °C by rotating at 40 rpm; the soybean oil polyol and polymethylene polyphenyl isocyanate were mixed in a mass ratio of 3:2 to obtain a coating solution; the coating solution was evenly sprayed on the surface of the preheated urea granules and cured at 80 °C for 15 min. The spraying and curing operations were repeated multiple times, and thus a slow-release coating layer was formed on the surface of the urea granules, and a coated controlled-release fertilizer was prepared;

[0107] Among them, in each spraying process, the dosage of the coating solution was 1 wt% of the mass of the urea granules;

[0108] (2) The ethyl cellulose binder was evenly sprayed on the surface of the coated controlled-release fertilizer and dried at 70 °C for 20 min, and thus a binder layer was formed on the surface of the coated controlled-release fertilizer, and the coated slow-release fertilizer was obtained.

[0109] Comparative Example 2:

[0110] The difference between this comparative example and Example 3 is that the water-retaining and slow-release layer in the coated slow-release fertilizer is composed of a water-retaining agent, and the water-retaining agent is potassium polyacrylate, which is prepared by the following method:

[0111] 15 mL of acrylic acid solution and 66.91 mL of 10% by mass KOH solution were mixed and reacted to obtain an acrylic acid solution with a neutralization degree of 60%;

[0112] Ammonium persulfate and N,N'-methylenebisacrylamide were added to the acrylic acid solution. After mixing, the temperature was raised to 60 °C and stirred for 2 min, then the stirring was stopped, and the reaction was carried out at 60 °C for 4 h. After the reaction was completed, the reaction product was washed 3 times with deionized water and soaked for 24 h to remove the unreacted monomers in the reaction product, and then dried and pulverized at 60 °C to obtain the water-retaining agent;

[0113] Among them, the addition ratio of the acrylic acid solution, ammonium persulfate, and N,N'-methylenebisacrylamide was 15 mL: 0.075 g: 0.0105 g.

[0114] Comparative Example 3:

[0115] The difference between this comparative example and Example 3 is that the water-retaining and slow-release layer in the coated slow-release fertilizer is composed of a sulfonic acid group-modified water-retaining agent, and the sulfonic acid group-modified water-retaining agent is prepared by the following method:

[0116] Mix 15 mL of acrylic acid solution and 66.91 mL of 10% KOH solution by mass for reaction to obtain an acrylic acid solution with a neutralization degree of 60%;

[0117] After mixing the acrylic acid solution and 2-acrylamido-2-methylpropanesulfonic acid, heat and stir at 40 °C for 5 min, and introduce nitrogen to remove dissolved oxygen in the solution to obtain a mixed solution. Add ammonium persulfate and N,N'-methylenebisacrylamide to the mixed solution, mix and then raise the temperature to 60 °C and stir for 2 min. Stop stirring and keep the reaction at 60 °C for 4 h. After the reaction is completed, wash the reaction product 3 times with deionized water and soak for 24 h to remove unreacted monomers in the reaction product, and then dry and pulverize at 60 °C to obtain the sulfonic acid group-modified water-retaining agent;

[0118] Among them, the addition ratio of the acrylic acid solution, 2-acrylamido-2-methylpropanesulfonic acid, ammonium persulfate, and N,N'-methylenebisacrylamide is 15 mL:0.75 g:0.075 g:0.0105 g.

[0119] Comparative Example 4:

[0120] The difference between this comparative example and Example 3 is that the water-retaining and slow-release layer in the coated slow-release fertilizer is composed of a polyglutamic acid-modified water-retaining agent, and the polyglutamic acid-modified water-retaining agent is prepared by the following method:

[0121] After mixing 0.45 g of γ-polyglutamic acid and 100 mL of deionized water, ultrasonically disperse for 25 min to obtain a polyglutamic acid solution;

[0122] Mix 15 mL of acrylic acid solution and 66.91 mL of 10% KOH solution by mass for reaction to obtain an acrylic acid solution with a neutralization degree of 60%;

[0123] After mixing the polyglutamic acid solution and the acrylic acid solution, heat and stir at 40 °C for 5 min, and introduce nitrogen to remove dissolved oxygen in the solution to obtain a mixed solution. Add ammonium persulfate and N,N'-methylenebisacrylamide to the mixed solution, mix and then raise the temperature to 60 °C and stir for 2 min. Stop stirring and keep the reaction at 60 °C for 4 h. After the reaction is completed, wash the reaction product 3 times with deionized water and soak for 24 h to remove unreacted monomers in the reaction product, and then dry and pulverize at 60 °C to obtain the modified water-retaining agent;

[0124] Among them, the addition amounts of polyglutamic acid, acrylic acid solution, ammonium persulfate, and N,N-methylenebisacrylamide are in a ratio of 0.45 g: 15 mL: 0.075 g: 0.0105 g.

[0125] Test Example 1: Structural Characterization

[0126] 1. The coated slow-release fertilizers prepared in Example 3 and Comparative Example 2 were analyzed by electron microscopy scanning, and the results are as Figure 1 shown.

[0127] It can be seen from Figure 1 that the water-retaining agent modified with polyglutamic acid and sulfonic acid groups in Example 3 has a better binding degree with the urea core. The surface of the prepared coated slow-release fertilizer is smooth and flat, without obvious protrusions and impurity particles, the thickness of the film shell is uniform, the wrapping is complete, and there are no obvious gaps.

[0128] 2. The modified water-retaining agent in Example 3 was analyzed by infrared spectroscopy, and the results are as Figure 2 shown.

[0129] It can be seen from Figure 2 that the prepared modified water-retaining agent contains symmetric stretching vibration peaks of S-O and S=O at 1047 cm -1 and 1189 cm -1 , indicating that the sulfonic acid group has been successfully introduced, enhancing the salt tolerance of the water-retaining agent. The stretching vibrations of C=O at 1722 cm -1 , -OH and -NH2 in 3412 cm -1 , and the characteristic absorption peaks of -COOH and -COO- at 1567 cm -1 indicate that the water absorption of the water-retaining agent is enhanced after polyglutamic acid and acrylic acid form an interpenetrating network.

[0130] Test Example 2: Swelling Performance Detection

[0131] The swelling performance of the coated slow-release fertilizers prepared in Example 3 and Comparative Examples 2-4 was tested. The specific steps are as follows:

[0132] (1) Deionized water:

[0133] Put 0.1 g of the coated slow-release fertilizer into a beaker containing 200 mL of deionized water and soak it at 25 °C for 12 h. Place the swollen coated slow-release fertilizer (m1) on a filter screen for 10 min until no more water drips out. Calculate the swelling degree (SD, g / g) of the coated slow-release fertilizer. The results are as Figure 3 (a) shown.

[0134] Among them, the swelling degree of the product is calculated by the following formula:

[0135] SD = (m1 - m0) / m0

[0136] SD represents the water absorption magnification per gram of gel, and m0 and m1 represent the product quality before and after water absorption.

[0137] (2) In media with different pH values:

[0138] Put 0.1 g of the coated slow-release fertilizer into a beaker containing 200 mL of media with different pH values (pH values are 3, 4, 5, 6, 7, 8, 9, 10 respectively), and soak it at 25 °C for 12 h. Place the swollen coated slow-release fertilizer on a filter for 10 min until no water drips out. Calculate the swelling degree of the coated slow-release fertilizer, and the results are as Figure 3 (b) shown, where the calculation formula for the swelling degree is the same as above.

[0139] (3) In media with different salt contents:

[0140] Put 0.1 g of the coated slow-release fertilizer into a beaker containing 200 mL of media with different salt contents (salt contents are 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1% respectively), and soak it at 25 °C for 12 h. Place the swollen coated slow-release fertilizer on a filter for 10 min until no water drips out. Calculate the swelling degree of the coated slow-release fertilizer, and the results are as Figure 3 (c) shown, where the calculation formula for the swelling degree is the same as above.

[0141] It can be seen from Figure 3 that the swelling degrees of the coated slow-release fertilizer prepared in Example 3 in different time, different pH values and salt solution media are all significantly higher than those of Comparative Examples 2-4. Among them, the swelling degree of the coated slow-release fertilizer prepared in Example 3 in the medium with pH 7 is 389 g / g. At the same time, the influence of pH value on the water absorption of the coated slow-release fertilizer prepared in Example 3 is significantly higher than that of the coated slow-release fertilizers prepared in Comparative Examples 2-4.

[0142] The swelling degrees of the coated slow-release fertilizers prepared in Example 3 and Comparative Examples 2-4 all decreased with the increase of the salt concentration in the water-absorbing medium. Among them, the swelling degree of the coated slow-release fertilizer prepared in Example 3 was higher than that of the comparative examples at each salt concentration. Specifically, the swelling degree of the coated slow-release fertilizer prepared in Example 3 in 0.1% NaCl solution was 256 g / g, the swelling degree of the coated slow-release fertilizer prepared in Comparative Example 2 in 0.1% NaCl solution was 88 g / g, the swelling degree of the coated slow-release fertilizer prepared in Comparative Example 3 in 0.1% NaCl solution was 193 g / g, and the swelling degree of the coated slow-release fertilizer prepared in Comparative Example 4 in 0.1% NaCl solution was 140 g / g. Thus, it can be seen that the coated slow-release fertilizer prepared by the present invention has a certain alleviating effect on the influence of the salt concentration in the medium, and the present invention uses polyglutamic acid and sulfonic acid groups to modify polypropylene, which has a synergistic effect in improving the salt tolerance of the coated slow-release fertilizer.

[0143] In summary, the interpenetrating network of polyglutamic acid and acrylic acid increases the water absorption of the water-retaining agent, and the introduction of sulfonic acid groups increases the salt tolerance of the water-retaining agent. Therefore, the combination of the three makes the water-retaining agent obtain more excellent salt tolerance and water absorption.

[0144] Test Example 3:

[0145] The maximum water-holding rate and water retention rate of the coated slow-release fertilizers prepared in Example 3 and Comparative Examples 2-4 were tested as follows:

[0146] 1. Maximum water-holding capacity of soil

[0147] The maximum water-holding capacity of soil was detected by the soil column method. 100.0 g of 20-mesh soil was mixed with the coated slow-release fertilizer particles and transferred into a polyvinyl chloride (PVC) pipe with a diameter of 5.0 cm and a length of 30.0 cm to form a soil column and weighed (W1). After loading the soil column, tap water was slowly poured in from the top of the PVC pipe, and the water penetrated through the entire soil column until water seeped out at the bottom. Then it was left standing, and the mass of the soil column was measured regularly until the mass became constant and the total mass (W2) was recorded. Among them, the mixing ratios of the coated slow-release fertilizer particles and the soil were 0, 0.5, 1.0, and 2.0%, and the maximum water-holding capacity of the soil was calculated. The results are as Figure 4 shown.

[0148] The calculation formula for the maximum water-holding rate (WH%) of soil is as follows:

[0149]

[0150] 2. Water retention rate

[0151] The weighed plastic pipe was placed at 25 °C for 30 d. The weight of the pipe was recorded at an interval of three days and denoted as Wx. Each treatment was repeated 3 times, and the water retention rate was calculated. The results are as Figure 5as shown

[0152] The water retention rate (WR%) is obtained according to the following formula:

[0153]

[0154] From Figure 4 It can be seen that as the dosage of the slow-release coated fertilizer prepared in Example 3 increases, the maximum water holding capacity of the soil continuously increases. And at the same dosage of the slow-release coated fertilizer, the maximum water holding capacity of the soil in Example 3 is much higher than that of the corresponding soil in Comparative Examples 2-4. When the mixing ratio of the slow-release coated fertilizer particles to the soil is 2%, the maximum water holding capacity of the soil in Example 3 is 150.85%, the maximum water holding capacity of the soil in Comparative Example 2 is 87.95%, the maximum water holding capacity of the soil in Comparative Example 3 is 127.45%, and the maximum water holding capacity of the soil in Comparative Example 4 is 134.05%. Thus, it can be seen that the coated slow-release fertilizer prepared by the present invention has good water holding ability.

[0155] From Figure 5 It can be seen that at 30 d, the water retention rate with an application rate of 0 is 0.74%, while with an application rate of 0.5%, the water retention rate increases by an average of 2.8%, with an application rate of 1%, the water retention rate increases by an average of 7.5%, and with an application rate of 2%, the water retention rate increases by an average of 18.0%, all of which are higher than the maximum water holding rates corresponding to the same addition amounts in the comparative examples. When at 30 d and the application rate is 2%, the soil water retention performance corresponding to the slow-release coated fertilizer in Comparative Example 2 is 14.99%, the soil water retention performance corresponding to the slow-release coated fertilizer in Comparative Example 3 is 16.99%, the soil water retention performance corresponding to the slow-release coated fertilizer in Comparative Example 4 is 18.56%, and the soil water retention performance corresponding to the slow-release coated fertilizer in Example 3 is 21.42%. Thus, it can be seen that the slow-release coated fertilizer prepared by modifying polyacrylic acid with the combination of polyglutamic acid and sulfonic acid groups in the present invention has a synergistic effect in improving the water retention performance of the soil.

[0156] Thus, it can be seen that the slow-release coated fertilizer prepared in Example 3 can improve the water holding ability of the soil and reduce the influence brought by soil evaporation.

[0157] Test Example 4:

[0158] The nitrogen release rates of the coated slow-release fertilizers prepared in Example 3 and Comparative Examples 1-4 were detected. The specific steps are as follows:

[0159] Nutrient release performance: The release rate of the fertilizer was determined by the water dissolution rate method in slow-release fertilizers with reference to GB / T 23348-2009. Specifically, 5.00 g of the coated slow-release fertilizer particles prepared in Example 3 and Comparative Examples 1-4 were accurately weighed and placed into small bags made of 100-mesh nylon mesh. After sealing, the nylon bags were placed into plastic bottles containing 200 mL of deionized water. After sealing, they were placed in a constant temperature incubator at 25°C. Samples were taken on the 1st, 3rd, 5th, 7th, 10th, 14th, 28th, and 42nd days, and then once every 28 days after 42 days until the cumulative nutrient dissolution rate reached over 80%. When sampling, the bottle was inverted 3 times to make the liquid concentration in the bottle uniform, then transferred to another small bottle to measure the nutrient content. Then, 200 mL of water was added to the bottle containing the sample bag, sealed with a cap, and placed back in the constant temperature incubator for continued cultivation. Each treatment was set with 3 replicates. Among them, the nutrient was nitrogen, and the nitrogen was determined by the concentrated sulfuric acid digestion-Kjeldahl method. The results are shown in Table 1.

[0160] Calculation of nutrient release rate: The initial nutrient release rate, denoted as V1:

[0161]

[0162] In the formula: W1—the mass fraction of the nitrogen release amount measured by leaching at 25°C for 1 h, h; W—the mass fraction of total nitrogen, with the value expressed as %.

[0163] The cumulative nutrient release rate during the nutrient release period, denoted as Vt:

[0164]

[0165] In the formula: t—the marked nutrient release period, h;

[0166] Wt—the mass fraction of the cumulative nitrogen measured during nutrient release at 25°C, with the value expressed as %;

[0167] W—the mass fraction of total nitrogen, with the value expressed as %.

[0168] Table 1 Cumulative release of nitrogen by different water-retention and efficiency-enhancing coated urea by static water leaching at 25°C

[0169]

[0170] As can be seen from Table 1, it took about 35 d for Comparative Example 1 to reach a nutrient release amount of over 80%, about 38 d for Comparative Example 2 to reach a nutrient release amount of over 80%, about 43 d for Comparative Examples 3 and 4 to reach a nutrient release of 80%, and about 49 d for Example 3 to reach a nutrient release of 80%. Thus, it can be seen that the coated urea prepared by the present invention not only has water retention ability but also has the effect of slowly releasing fertilizer nutrients.

[0171] Test Example 5:

[0172] In this test, peanuts of the Golden Crown 1 variety were used as test materials, and a two-year test in two locations, Sishui County, Jining City, Shandong Province and Daiyue District, Tai'an City, Shandong Province, was carried out. A total of 4 groups of treatments were designed, with 3 replicates for each treatment. The area of each test plot was 15 m 2 .

[0173] The fertilizers used in the test and their nutrient contents were as follows: superphosphate, purchased from the local fertilizer station, with an N-P2O5-K2O content of 0-12-0; potassium sulfate, purchased from the local fertilizer station, with an N-P2O5-K2O content of 0-0-50; ordinary urea, purchased from the local fertilizer station, with an N-P2O5-K2O content of 46-0-0; the coated urea prepared in Comparative Example 1 had an N-P2O5-K2O content of 44-0-0; the polyurethane-coated controlled-release urea prepared in Examples 1-3 had an N-P2O5-K2O content of 44-0-0.

[0174] The application rates of nitrogen, phosphorus and potassium in each treatment group were the same, specifically N: 202.5 kg / hm 2 , P2O5: 90 kg / hm 2 , K2O: 112.5 kg / hm 2 . Among them, superphosphate was used as the phosphate fertilizer and potassium sulfate was used as the potassium fertilizer, and they were applied as a one-time base fertilizer before sowing. Only different nitrogen fertilizers were used as variables. The specific fertilization operations of each treatment group are shown in Table 2.

[0175] When the peanuts reached the mature stage, the plant height (cm), stem diameter (mm), SPAD, 100-peanut weight (g), 100-kernel weight (g), and yield (kg / mu) of each treatment group were measured. Among them, the plant height was measured with a meter stick, the stem diameter was measured with a vernier caliper, and the SPAD was measured in the field using a portable SPAD meter (model LYS-A).

[0176] Table 2 Fertilization Scheme for the Water Retention and Efficiency Enhancement Coated Urea Test of Peanuts

[0177]

[0178] Results of the Peanut Fertilizer Efficiency Test:

[0179] The test results of the plant height (cm), stem diameter (mm), and SPAD of the peanuts in each treatment group are shown in Table 3. The test results of the number of pods per plant, number of full pods per plant, number of empty pods per plant, number of damaged pods per plant, 100-kernel weight (g), 100-peanut weight (g), and yield (kg / mu) of each treatment group are shown in Table 4. The test results of the partial production of nitrogen fertilizer (g / g), agronomic efficiency of nitrogen fertilizer (g / g), apparent utilization of nitrogen fertilizer (%), soil water storage (cm), and water use efficiency (g / kg) of each treatment group are shown in Table 5.

[0180] Table 3 Measurement data of water retention and efficiency-enhancing coated urea on peanut growth indicators in different embodiments

[0181]

[0182] As can be seen from Table 3, the fertilizers in Examples 1-3 are superior to those in Control Groups 1-2 in terms of increasing peanut plant height, stem diameter, and SPAD. Thus, it can be seen that the water retention and efficiency-enhancing coated urea prepared by the method of the present invention can significantly promote the growth of peanuts, increase peanut plant height and stem diameter, and the supply of long-acting nitrogen fertilizer enhances the photosynthetic ability of peanuts.

[0183] Table 4 Effects of water retention and efficiency-enhancing coated urea in different embodiments on peanut yield components

[0184]

[0185] As can be seen from Table 4, the fertilizers in Examples 1-3 are superior to those in Control Groups 1-2 in terms of increasing peanut hundred fruit weight, hundred kernel weight, number of full pods per plant, and yield. In addition, the coated urea used in Groups 1-3 of this experiment was not optimized for peanut crops. It can be seen from the table that Groups 1-3 of Examples 1-3 have varying degrees of improvement in terms of the number of full pods per plant, hundred fruit weight, yield, etc. In the actual application process, the types of raw materials and process parameters for preparing the water retention and efficiency-enhancing coated controlled-release fertilizer can be adjusted to obtain a water retention and efficiency-enhancing coated controlled-release fertilizer more suitable for the growth of peanut crops.

[0186] Table 5 Effects of water retention and efficiency-enhancing coated urea in different embodiments on peanut water and nitrogen utilization

[0187]

[0188] As can be seen from Table 5, the fertilizers in Examples 1-3 are superior to those in Control Groups 1-2 in terms of increasing partial factor productivity of nitrogen fertilizer, agronomic efficiency, apparent utilization rate, and water utilization rate. Thus, it can be seen that the water retention and efficiency-enhancing coated urea prepared by the method of the present invention can improve the soil water storage capacity, providing sufficient water conditions for crop growth. And the sufficient water supply can promote nitrogen absorption by crops and the soil, thereby improving nitrogen availability and water-nitrogen utilization efficiency.

[0189] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A water-retaining and efficiency-enhancing coated slow-release fertilizer, which sequentially includes from inside to outside: Fertilizer core, inhibitor layer, slow-release coating layer, bonding layer and water-retaining slow-release layer; The mass ratio of the fertilizer core, inhibitor layer, slow-release coating layer, bonding layer and water-retaining slow-release layer is 100:(0.5 - 5):(3 - 7):(0.5 - 1):(5 - 10); The water-retaining slow-release layer is composed of a modified water-retaining agent, and the modified water-retaining agent is prepared by the following method: Mix the polyglutamic acid solution, acrylic acid solution and sulfonate, heat and stir, then pass in a protective gas to remove the dissolved oxygen in the solution to obtain a mixed solution; then add an initiator and a crosslinking agent to the mixed solution, mix and heat up to 60 - 80 °C and stir for 2 - 5 min, then stop stirring and keep the temperature for continuous reaction. After the reaction is completed, wash and dry to obtain the modified water-retaining agent.

2. The water-retaining and efficiency-enhancing coated slow-release fertilizer according to claim 1, characterized in that, The sulfonate is one or more of 2-acrylamido-2-methylpropanesulfonic acid, sodium p-styrenesulfonate, and β-aminoethanesulfonic acid; The crosslinking agent is one or several of divinylbenzene, diisocyanate, N,N'-methylenebisacrylamide, dimethylacrylamide, and polyethylene glycol; The initiator is one or several of potassium persulfate, ammonium persulfate, and sodium persulfate.

3. The water-retaining and efficiency-enhancing coated slow-release fertilizer according to claim 1, characterized in that The addition amounts of the acrylic acid solution, polyglutamic acid solution, sulfonate, initiator and crosslinking agent are 100 mL:(0.5 - 10) g:(0.1 - 10) g:(0.1 - 5) g:(0.01 - 1) g; The polyglutamic acid solution is prepared by mixing polyglutamic acid and deionized water at a material-liquid ratio of (0.1 - 1) g:100 mL; the acrylic acid solution is prepared by mixing acrylic acid and a 10% KOH solution by mass, and the neutralization degree is 40 - 70%.

4. The water-retaining and efficiency-enhancing coated slow-release fertilizer according to claim 1, wherein The heating temperature is 35 - 45 °C, the stirring time is 4 - 6 min; the continuous reaction time is 3 - 4 h.

5. The water-retaining and efficiency-enhancing coated slow-release fertilizer according to claim 1, characterized in that, The fertilizer core is one or more of urea, NPK compound fertilizer, ammonium sulfate, ammonium chloride, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate, and the particle size of the fertilizer core is 2.5 - 3.5 mm; The inhibitor layer is composed of a urease inhibitor and a nitrification inhibitor at a mass ratio of 1:(3 - 10); The slow-release coating layer is composed of epoxy resin and / or polyurethane; the bonding layer is composed of an ethyl cellulose binder.

6. The water-retaining and efficiency-enhancing coated slow-release fertilizer according to claim 5, characterized in that, The ethyl cellulose binder is prepared by the following method: Mix ethyl cellulose and absolute ethanol at a material-liquid ratio of 1 g:(10 - 50) mL, and stir to obtain the ethyl cellulose binder.

7. The preparation method of the water-retaining and efficiency-enhancing coated slow-release fertilizer according to any one of claims 1-6, characterized in that, Including the following steps: (1) Spray the inhibitor solution on the surface of the preheated fertilizer core, and after drying, an inhibitor layer is formed on the surface of the fertilizer core to obtain the inhibitor-coated fertilizer; (2) Spray the coating solution on the surface of the preheated inhibitor-coated fertilizer, and after curing, a slow-release coating layer is formed on the surface of the inhibitor-coated fertilizer to prepare the inhibitor-coated and double-controlled release fertilizer; (3) Spray the binder on the surface of the inhibitor-coated and double-controlled release fertilizer, and then spray the modified water-retaining agent on the inhibitor-coated and double-controlled release fertilizer with the binder on the surface, and dry to form a bonding layer and a water-retaining slow-release layer in sequence on the surface of the inhibitor-coated and double-controlled release fertilizer to prepare the water-retaining and efficiency-enhancing coated slow-release fertilizer.

8. The preparation method of the water-retaining and efficiency-enhancing coated slow-release fertilizer according to claim 7, characterized in that, In step (1), during the preheating process of the fertilizer core: the preheating rotation speed is 20 - 40 rpm, the preheating temperature is 70 - 85 °C, and the preheating time is ≥ 5 min.

9. The preparation method of the water-retaining and efficiency-enhancing coated slow-release fertilizer according to claim 7, characterized in that, In step (2), the coating solution is prepared by mixing solution A and solution B in a mass ratio of (1 - 10):(1 - 5); solution A is isocyanate and / or epoxy resin; solution B is polyol and / or triethylenetetramine.

10. The preparation method of the water-retaining and efficiency-enhancing coated slow-release fertilizer according to claim 7, characterized in that, In step (2), during the preheating process of the inhibitor-coated fertilizer, the preheating rotation speed is 20 - 40 rpm, the preheating temperature is 70 - 85 °C, and the preheating time is ≥ 5 min.

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