Salt-resistant water-retention composite functional sustained and controlled release fertilizer and preparation method thereof

Abstract

The invention relates to a salt-resistant water-retention composite functional controlled release fertilizer and a preparation method thereof, and the preparation method comprises the following steps: step 1, sieving urea particles, and placing in a disc for coating; step 2, adding ethyl cellulose and lactic acid into an ethanol solution to prepare a mixed solution, so as to obtain a coated mixed solution; step 3, rotating the disc, uniformly spraying the coating mixed solution on the surfaces of the urea particles in a spray form, drying, and repeating for multiple times to obtain first coated fertilizer particles; step 4, crushing the salt-resistant water-retaining agent by using a crusher, and granulating to obtain second coated fertilizer particles; and step 5, drying. Compared with the traditional composite coated fertilizer, the fertilizer disclosed by the invention has more obvious salt resistance and water-retaining property.

Description

Technical Field

[0001] The invention relates to the field of fertilizers, and in particular to a salt-resistant and water-retaining composite functional slow-release fertilizer and a preparation method thereof. Background Art

[0002] my country has a serious shortage of arable land resources, and soil fertility is generally low. Medium and low-yield fields account for as much as 2 / 3, and natural fertility cannot meet the needs of crop growth in terms of quantity and quality. Problems such as drought, water shortage, and land salinization are becoming increasingly prominent, seriously restricting the sustainable development of my country's agriculture. Abiotic stress causes various physiological disorders of crops, affects the permeability of crop cells, causes physiological drought and ion toxicity, affects crop nutrient absorption, leads to soil nutrient deficiency, and causes crop failure or reduced yields. Functional slow-release fertilizers that have the ability to slowly and continuously supply nutrients to meet the needs of crop growth have become an important measure to improve nutrient utilization efficiency and soil improvement.

[0003] Super absorbent polymer (SAP) contains hydrophilic macromolecules with a three-dimensional network structure. It can significantly improve the effectiveness of soil nutrients and water by slowly releasing nutrients in combination with slow-release fertilizers. Traditional acrylic acid and acrylamide copolymer cross-linked water-retaining polymers have high water absorption, but their raw materials are non-renewable resources, poor degradability, and have a certain impact on the environment; polyamino acid-based natural macromolecular self-polymer cross-linked water-retaining polymers have the disadvantages of high cost, high requirements for preparation process and conditions, and too fast degradation rate.

[0004] The quick-acting fertilizers in the blended water-retaining controlled-release fertilizers tend to reduce the water absorption capacity of the water-retaining agent; the loaded water-retaining controlled-release fertilizers use highly absorbent resins to encapsulate or absorb fertilizer nutrients to form a fertilizer supply system, but their nutrient release characteristics and content are difficult to stabilize; composite coated water-retaining controlled-release fertilizers: highly absorbent resins are coated on the surface of fertilizer particles through a specific process, but it is difficult to resolve the contradiction between controlled-release performance and water absorption. Summary of the invention

[0005] In view of the problems existing in the prior art, the object of the present invention is to provide a salt-resistant and water-retaining composite functional slow-release fertilizer and a preparation method thereof.

[0006] The purpose of the present invention is achieved by adopting the following technical solutions:

[0007] In a first aspect, the present invention discloses a method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer, comprising the following steps:

[0008] Step 1, sieving urea granules and placing them in a disc for coating;

[0009] Step 2, adding ethyl cellulose and lactic acid to an ethanol solution to prepare a mixed solution, stirring the solution with a magnetic stirrer until the solution is completely dissolved to obtain a coating mixed solution;

[0010] Step 3, rotating the disc to evenly spray the coating mixed liquid on the surface of the urea particles in the form of a spray, drying, and repeating multiple times to form a first coating layer on the surface of the urea particles to obtain first coated fertilizer particles;

[0011] Step 4, crushing the salt-resistant water-retaining agent with a pulverizer, adding it to the disc, rotating the disc, and making the salt-resistant water-retaining agent powder evenly attached to the first coated fertilizer particles under the action of atomized water, drying, and repeating multiple times, so that the composite water-retaining agent forms a second coating layer on the outer layer, and obtains second coated fertilizer particles;

[0012] Step 5, drying the prepared second coated fertilizer particles again in a forced air drying oven to obtain a salt-resistant and water-retaining composite functional slow-release fertilizer.

[0013] Preferably, in step 1, the sieving is through a 20-28 mesh sieve.

[0014] Preferably, in step 2, the mass ratio of ethyl cellulose, lactic acid and ethanol solution is 5:2-3:100-150, and the mass fraction of ethanol solution is 50%-70%.

[0015] Preferably, in step 2, the purity of ethyl cellulose (EC) is higher than 99%, the viscosity is 220 mPa·s (solvent with a weight ratio of ethanol:toluene of 1:4), and the degree of substitution is 2.4; and the lactic acid is a mixture of one or more of L-lactic acid, D-lactic acid, and DL-lactic acid.

[0016] Preferably, in step 3, the thickness of the first coating layer is 0.3-0.5 mm.

[0017] Preferably, in step 4, the salt-resistant water-retaining agent is crushed by a crusher and passed through a 100-150 mesh sieve, and the thickness of the second coating layer is 0.4-0.6 mm.

[0018] Preferably, in step 4, the preparation method of the salt-resistant water-retaining agent comprises:

[0019] S1. Preparation of amino starch:

[0020] Weigh corn starch and dimethyl sulfoxide, mix them, heat them to 80-90°C, stir them thoroughly until a uniform mixed solution is formed, then drop the aminosilane coupling agent solution, keep the mixture warm and stir for 1-2 hours after the dropwise addition, then cool it to room temperature, discharge it in anhydrous ethanol, centrifuge, wash and dry it to obtain amino starch;

[0021] S2, preparation of allyl alcohol starch:

[0022] Weigh allyl alcohol glycidyl ether and dimethyl sulfoxide, mix them, stir them well, gradually add amination starch, heat them to 80-90°C, keep them warm and stir for 3-5h, then cool them to room temperature, discharge them in anhydrous ethanol, centrifuge, wash and dry them to obtain allyl alcohol starch;

[0023] S3, preparation of glucomannan monomer:

[0024] Weigh konjac glucomannan, acrylic anhydride and deionized water, add alkali solution to adjust the pH value of the solution to 8-9, stir for 15-30 hours in an ice water bath, and after the reaction is completed, discharge the material in anhydrous ethanol, centrifuge, wash and dry to obtain glucomannan monomer (KGM monomer);

[0025] S4, preparation of salt-resistant water-retaining agent:

[0026] Add allyl alcohol starch to deionized water for gelatinization treatment, then add glucomannan monomer and acrylamide, stir evenly, introduce nitrogen as protective gas, add thermal initiator, keep warm and stir to react for 1-2 hours, then add photoinitiator and cross-linking agent, treat under ultraviolet light for 10-20 minutes, and spray dry to obtain salt-resistant water-retaining agent.

[0027] Preferably, in S1, the purity of corn starch is ≥98%, the water content is ≤14%, and the acidity is ≤1.8.

[0028] Preferably, in S1, the mass ratio of corn starch, dimethyl sulfoxide and aminosilane coupling agent solution is 1:60-80:20-40.

[0029] Preferably, in S1, the aminosilane coupling agent solution is obtained by mixing KH-550 and deionized water in a mass ratio of 1:8-12.

[0030] Preferably, in S2, the mass ratio of amination starch, allyl alcohol glycidyl ether and dimethyl sulfoxide is 1:0.22-0.44:40-60.

[0031] Preferably, in S3, the mass ratio of konjac glucomannan, acrylic anhydride and deionized water is 1:8-12:60-100.

[0032] Preferably, in S3, the alkali solution is a sodium hydroxide solution with a mass fraction of 10%-20%.

[0033] Preferably, in S4, during the gelatinization process, the mass ratio of allylated starch to deionized water is 1:40-60, the gelatinization temperature is 60-70° C., and the gelatinization time is 0.5-1 h.

[0034] Preferably, in S4, the mass ratio of allylated starch, glucomannan monomer and acrylamide is 3:1-2:2-4.

[0035] Preferably, in S4, the thermal initiator is one of sodium persulfate, ammonium persulfate and potassium persulfate.

[0036] Preferably, in S4, the photoinitiator is benzoin diethyl ether or benzoin dimethyl ether; and the cross-linking agent is N,N-methylenebisacrylamide.

[0037] Preferably, in S4, the amount of thermal initiator added is 2.3%-4.6% of the mass of the allylated starch, the amount of photoinitiator added is 1.8%-3.6% of the mass of the allylated starch, and the amount of cross-linking agent added is 1.5%-3% of the mass of the allylated starch.

[0038] Preferably, in S4, the power of the ultraviolet light is 125 W and the wavelength is 365 nm.

[0039] In a second aspect, the present invention discloses a salt-resistant and water-retaining composite functional slow-release fertilizer, which is prepared by the above-mentioned preparation method.

[0040] The beneficial effects of the present invention are:

[0041] 1. The present invention prepares a coated slow-release fertilizer, the inner core material of which is urea granules, and the outer surface of the urea granules is coated with a double-layer structure, the inner layer is a composite layer formed by ethyl cellulose and lactic acid, and the outer layer is a salt-resistant and water-retaining layer formed by a salt-resistant and water-retaining agent. Compared with traditional composite coated fertilizers, the fertilizer of the present invention has more obvious salt resistance and water retention.

[0042] 2. As the inner coating layer of the slow-release fertilizer, the composite layer formed by ethyl cellulose and lactic acid, the lactic acid is acidic and can adjust the pH of the soil. It can also effectively inhibit the reproduction of bacteria and improve the quality of the fertilizer. Ethyl cellulose is used as a binder to improve the processing performance and stability of the coating layer.

[0043] 3. Starch is a natural substance whose nutrients can meet the needs of plant growth and act as a fertilizer. In addition, starch has good moisture retention and water retention, which can keep the soil moist. The present invention first performs an amination treatment on starch to obtain amino starch; then the epoxy group in allyl alcohol glycidyl ether is combined with the amino group of the amino starch to obtain allyl alcohol starch; then the allyl alcohol starch, glucomannan monomer and acrylamide are polymerized to finally obtain a salt-resistant water-retaining agent. Compared with conventional starch coatings, the modified starch coating prepared by the present invention has more excellent salt resistance and water retention, and has better yield-increasing properties for agricultural products such as corn. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is described below through specific examples. It should be understood that the one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combination step or the insertion of other method steps between these explicitly mentioned steps; it should also be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to limit the scope of the present invention. The change or adjustment of the relative relationship thereof shall also be regarded as the scope of the present invention without substantially changing the technical content.

[0045] In order to better understand the above technical scheme, the exemplary embodiments of the present invention are described in more detail below. Although exemplary embodiments of the present invention are shown, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to enable the scope of the present invention to be fully communicated to those skilled in the art.

[0046] The ethyl cellulose (EC) used in the embodiment of the present invention has a purity higher than 99%, a viscosity of 220 mPa·s (solvent with a weight ratio of ethanol to toluene of 1:4), and a degree of substitution of 2.4.

[0047] The corn starch used in the embodiment of the present invention has a purity of ≥98%, a water content of ≤14%, and an acidity of ≤1.8.

[0048] The present invention will be further described below in conjunction with the following examples.

[0049] Example 1

[0050] A method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer comprises the following steps:

[0051] Step 1, urea granules are passed through a 25-mesh sieve and placed in a disc for coating;

[0052] Step 2, adding ethyl cellulose (EC) and L-lactic acid to a 60% ethanol solution, wherein the mass ratio of ethyl cellulose, L-lactic acid and ethanol solution is 5:2.5:125, to prepare a mixed solution, stirring the mixture with a magnetic stirrer until the mixture is completely dissolved, to obtain a coating mixed solution;

[0053] Step 3, rotating the disc to evenly spray the coating mixed liquid on the surface of the urea particles in the form of a spray, drying, and repeating multiple times to form a first coating layer with a thickness of 0.4 mm on the surface of the urea particles to obtain first coated fertilizer particles;

[0054] Step 4, crushing the salt-resistant water-retaining agent with a pulverizer, passing through a 120-mesh sieve, adding it to a disc, rotating the disc, and making the salt-resistant water-retaining agent powder evenly attached to the first coated fertilizer particles under the action of atomized water, drying, and repeating multiple times, so that the composite water-retaining agent forms a second coating layer with a thickness of 0.5 mm on the outer layer, and obtaining second coated fertilizer particles;

[0055] Step 5, drying the prepared second coated fertilizer particles again in a forced air drying oven to obtain a salt-resistant and water-retaining composite functional slow-release fertilizer.

[0056] In the above step 4, the preparation method of the salt-resistant water-retaining agent comprises:

[0057] S1. Preparation of amino starch:

[0058] Weigh corn starch and dimethyl sulfoxide, mix them, heat them to 85°C, stir them thoroughly until a uniform mixed solution is formed, and then drop an aminosilane coupling agent solution, the aminosilane coupling agent solution is obtained by mixing KH-550 and deionized water in a mass ratio of 1:10, and the mass ratio of corn starch, dimethyl sulfoxide and aminosilane coupling agent solution is 1:70:30. After the dropwise addition, stir them at room temperature for 1.5 hours, then cool them to room temperature, discharge them in anhydrous ethanol, centrifuge, wash and dry them to obtain amino starch;

[0059] S2, preparation of allyl alcohol starch:

[0060] Weigh allyl alcohol glycidyl ether and dimethyl sulfoxide, mix them, stir them thoroughly, gradually add amination starch, the mass ratio of amination starch, allyl alcohol glycidyl ether and dimethyl sulfoxide is 1:0.33:50, heat to 85°C, keep stirring for 4 hours, then cool to room temperature, discharge in anhydrous ethanol, centrifuge, wash and dry to obtain allyl alcohol starch;

[0061] S3, preparation of glucomannan monomer:

[0062] Weigh konjac glucomannan (molecular weight 1 million), acrylic anhydride and deionized water, mix them in a mass ratio of 1:10:80, add 15% sodium hydroxide solution dropwise to adjust the solution pH to 8.5, stir in an ice-water bath for 24 hours, and after the reaction is completed, discharge the mixture in anhydrous ethanol, centrifuge, wash and dry to obtain glucomannan monomer (KGM monomer);

[0063] S4, preparation of salt-resistant water-retaining agent:

[0064] The allyl alcohol starch is added to deionized water for gelatinization treatment, the mass ratio of the allyl alcohol starch to the deionized water is 1:50, the gelatinization temperature is 65°C, and the gelatinization time is 0.6h. Subsequently, glucomannan monomer and acrylamide are added, and the mass ratio of the allyl alcohol starch, glucomannan monomer and acrylamide is 3:1.5:3. The mixture is stirred evenly, nitrogen is introduced as a protective gas, sodium persulfate is added in an amount of 3.4% of the mass of the allyl alcohol starch, and the mixture is stirred and reacted for 1.5h at a temperature of 2.4% of the mass of the allyl alcohol starch and 2.5% of the mass of the allyl alcohol starch. The mixture is irradiated with ultraviolet light for 15min, the power of the ultraviolet light is 125W, and the wavelength is 365nm. The mixture is spray-dried to obtain a salt-resistant water-retaining agent.

[0065] Example 2

[0066] A method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer comprises the following steps:

[0067] Step 1, urea granules are passed through a 20-mesh sieve and placed in a disc for coating;

[0068] Step 2, adding ethyl cellulose (EC) and D-lactic acid to a 50% ethanol solution, wherein the mass ratio of ethyl cellulose, D-lactic acid and ethanol solution is 5:2:100, to prepare a mixed solution, stirring the mixture with a magnetic stirrer until the mixture is completely dissolved, to obtain a coating mixed solution;

[0069] Step 3, rotating the disc to evenly spray the coating mixed liquid on the surface of the urea particles in the form of a spray, drying, and repeating multiple times to form a first coating layer with a thickness of 0.3 mm on the surface of the urea particles to obtain first coated fertilizer particles;

[0070] Step 4, crushing the salt-resistant water-retaining agent with a pulverizer, passing through a 100-mesh sieve, adding it to the disc, rotating the disc, and making the salt-resistant water-retaining agent powder evenly attached to the first coated fertilizer particles under the action of atomized water, drying, and repeating multiple times, so that the composite water-retaining agent forms a second coating layer with a thickness of 0.4 mm on the outer layer, and obtaining second coated fertilizer particles;

[0071] Step 5, drying the prepared second coated fertilizer particles again in a forced air drying oven to obtain a salt-resistant and water-retaining composite functional slow-release fertilizer.

[0072] Example 3

[0073] A method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer comprises the following steps:

[0074] Step 1, urea granules are passed through a 28-mesh sieve and placed in a disc for coating;

[0075] Step 2, adding ethyl cellulose (EC) and DL-lactic acid to a 70% ethanol solution, wherein the mass ratio of ethyl cellulose, DL-lactic acid and ethanol solution is 5:3:150, to prepare a mixed solution, stirring the mixture with a magnetic stirrer until the mixture is completely dissolved, to obtain a coating mixed solution;

[0076] Step 3, rotating the disc to evenly spray the coating mixed liquid on the surface of the urea particles in the form of a spray, drying, and repeating multiple times to form a first coating layer with a thickness of 0.5 mm on the surface of the urea particles to obtain first coated fertilizer particles;

[0077] Step 4, crushing the salt-resistant water-retaining agent with a pulverizer, passing through a 150-mesh sieve, adding it to a disc, rotating the disc, and making the salt-resistant water-retaining agent powder evenly attached to the first coated fertilizer particles under the action of atomized water, drying, and repeating multiple times, so that the composite water-retaining agent forms a second coating layer with a thickness of 0.6 mm on the outer layer, and obtaining second coated fertilizer particles;

[0078] Step 5, drying the prepared second coated fertilizer particles again in a forced air drying oven to obtain a salt-resistant and water-retaining composite functional slow-release fertilizer.

[0079] Example 4

[0080] A method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer is different from that of Example 1 in that in step 4, the preparation method of the salt-resistant and water-retaining agent is different, and the rest is the same as the preparation method of Example 1.

[0081] The preparation method of the salt-resistant water-retaining agent comprises:

[0082] S1. Preparation of amino starch:

[0083] Weigh corn starch and dimethyl sulfoxide, mix them, heat them to 80°C, stir them thoroughly until a uniform mixed solution is formed, and then drop an aminosilane coupling agent solution, the aminosilane coupling agent solution is obtained by mixing KH-550 and deionized water in a mass ratio of 1:8, and the mass ratio of corn starch, dimethyl sulfoxide and aminosilane coupling agent solution is 1:60:20. After the dropwise addition, keep warm and stir for 1 hour, then cool to room temperature, discharge in anhydrous ethanol, centrifuge, wash and dry to obtain amino starch;

[0084] S2, preparation of allyl alcohol starch:

[0085] Weigh allyl alcohol glycidyl ether and dimethyl sulfoxide, mix them, stir them thoroughly, gradually add amination starch, the mass ratio of amination starch, allyl alcohol glycidyl ether and dimethyl sulfoxide is 1:0.22:40, heat to 80°C, keep stirring for 3 hours, then cool to room temperature, discharge in anhydrous ethanol, centrifuge, wash and dry to obtain allyl alcohol starch;

[0086] S3, preparation of glucomannan monomer:

[0087] Weigh konjac glucomannan, acrylic anhydride and deionized water, mix them in a mass ratio of 1:8:60, drop 10% sodium hydroxide solution to adjust the solution pH to 8, stir for 15 hours in an ice water bath, and after the reaction is completed, discharge the mixture in anhydrous ethanol, centrifuge, wash and dry to obtain glucomannan monomer (KGM monomer);

[0088] S4, preparation of salt-resistant water-retaining agent:

[0089] Add allyl alcohol starch to deionized water for gelatinization treatment, the mass ratio of allyl alcohol starch to deionized water is 1:40, the gelatinization temperature is 60°C, the gelatinization time is 0.5h, then add glucomannan monomer and acrylamide, the mass ratio of allyl alcohol starch, glucomannan monomer and acrylamide is 3:1:2, stir evenly, introduce nitrogen as protective gas, add ammonium persulfate in an amount of 2.3% of the mass of allyl alcohol starch, keep warm and stir for 1h, then add benzoin dimethyl ether in an amount of 1.8% of the mass of allyl alcohol starch, and add N,N-methylenebisacrylamide in an amount of 1.5% of the mass of allyl alcohol starch, treat under ultraviolet light irradiation for 10min, the power of ultraviolet light is 125W, and the wavelength is 365nm, and spray dry to obtain a salt-resistant water-retaining agent.

[0090] Example 5

[0091] A method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer is different from that of Example 1 in that in step 4, the preparation method of the salt-resistant and water-retaining agent is different, and the rest is the same as the preparation method of Example 1.

[0092] The preparation method of the salt-resistant water-retaining agent comprises:

[0093] S1. Preparation of amino starch:

[0094] Weigh corn starch and dimethyl sulfoxide, mix them, heat them to 90°C, stir them thoroughly until a uniform mixed solution is formed, and then drop an aminosilane coupling agent solution, wherein the aminosilane coupling agent solution is obtained by mixing KH-550 and deionized water in a mass ratio of 1:12, and the mass ratio of corn starch, dimethyl sulfoxide and aminosilane coupling agent solution is 1:80:40. After the dropwise addition, stir them at room temperature for 2 hours, then cool them to room temperature, discharge them in anhydrous ethanol, centrifuge, wash and dry them to obtain amino starch;

[0095] S2, preparation of allyl alcohol starch:

[0096] Weigh allyl alcohol glycidyl ether and dimethyl sulfoxide, mix them, stir them well, gradually add amination starch, the mass ratio of amination starch, allyl alcohol glycidyl ether and dimethyl sulfoxide is 1:0.44:60, heat to 90°C, keep stirring for 5 hours, then cool to room temperature, discharge in anhydrous ethanol, centrifuge, wash and dry to obtain allyl alcohol starch;

[0097] S3, preparation of glucomannan monomer:

[0098] Weigh konjac glucomannan, acrylic anhydride and deionized water, mix them in a mass ratio of 1:12:100, drop 20% sodium hydroxide solution to adjust the solution pH to 9, stir for 30 hours in an ice-water bath, and after the reaction is completed, discharge the mixture in anhydrous ethanol, centrifuge, wash and dry to obtain a glucomannan monomer (KGM monomer);

[0099] S4, preparation of salt-resistant water-retaining agent:

[0100] Add allyl alcohol starch to deionized water for gelatinization treatment, the mass ratio of allyl alcohol starch to deionized water is 1:60, the gelatinization temperature is 70°C, and the gelatinization time is 1h. Subsequently, glucomannan monomer and acrylamide are added, and the mass ratio of allyl alcohol starch, glucomannan monomer and acrylamide is 3:2:4. Stir evenly, introduce nitrogen as a protective gas, add potassium persulfate in an amount of 4.6% of the mass of allyl alcohol starch, keep warm and stir for 2h, then add benzoin diethyl ether in an amount of 3.6% of the mass of allyl alcohol starch, and add N,N-methylenebisacrylamide in an amount of 3% of the mass of allyl alcohol starch. Treat under ultraviolet light irradiation for 20min, the power of the ultraviolet light is 125W, and the wavelength is 365nm. After spray drying, a salt-resistant water-retaining agent is obtained.

[0101] Comparative Example 1

[0102] A method for preparing a slow-release controlled-release fertilizer is different from that of Example 1 in that in step 4, the salt-resistant water-retaining agent used is starch.

[0103] Comparative Example 2

[0104] A method for preparing a slow-release fertilizer, which differs from Example 1 in that in step 4, the salt-resistant water-retaining agent used is amino starch (the preparation is the same as step S1 of Example 1).

[0105] Comparative Example 3

[0106] A method for preparing a slow-release controlled-release fertilizer is different from that of Example 1 in that, in step 4, the salt-resistant water-retaining agent used is konjac glucomannan.

[0107] Comparative Example 4

[0108] A method for preparing a slow-release fertilizer is different from that of Example 1 in that in step 4, the salt-resistant water-retaining agent used is a mixture of konjac glucomannan and amino starch, and the mass ratio of konjac glucomannan to amino starch is 1.5:3.

[0109] Experimental example

[0110] The effects of the fertilizers prepared in the examples and comparative examples on the yield of corn grown in saline-alkali land were determined through field tests.

[0111] The corn variety selected was Kehe 699. The test site was selected in Binzhou City, Shandong Province. The area of ​​each test group was 1 mu. The basic physical and chemical properties of the soil were: pH 7.72, organic matter content 2.17%, available nitrogen 193.2 mg / kg, available phosphorus 21.3 mg / kg, available potassium 273.5 mg / kg, and total salt content 0.083%. The corn was planted on April 23, 2022 and harvested on October 8, 2022. Except for different fertilization, other field management measures such as sowing, irrigation, and weeding were the same for each treatment.

[0112] The emergence rate was tested 10 days after planting; the content of water-stable large aggregates (particle size > 0.25 mm) was randomly tested by wet screening method (30 times / min, 30 min); the yield was calculated from the yield of all corn plants after corn was harvested; the yield increase rate was based on comparative example 1 as a benchmark, compared with the yield increase ratio of comparative example 1.

[0113] The test results are shown in Table 1.

[0114] Table 1 Performance of corn planted in different ways

[0115]

[0116] It can be seen from the results in Table 1 that the slow-release fertilizer of Example 1 of the present invention not only has a higher emergence rate than Comparative Examples 1-3, which can reach 96.4%, but also has a better yield-increasing effect, reaching 25.8% compared to Comparative Example 1. In addition, after using the slow-release fertilizer of Example 1, the content of water-stable macroaggregates in the soil reaches 43.6%, which is much higher than other comparative examples, and the higher the content of water-stable macroaggregates, the better the soil structure stability and the better the water retention, indicating that the slow-release fertilizer prepared in Example 1 of the present invention can enhance the water retention of soil in saline-alkali land.

[0117] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms should not be understood as necessarily being directed to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification.

[0118] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer, characterized in that: The following steps are involved: Step 1, sieving urea granules and placing them in a disc for coating; Step 2, adding ethyl cellulose and lactic acid to an ethanol solution to prepare a mixed solution, stirring the solution with a magnetic stirrer until the solution is completely dissolved to obtain a coating mixed solution; Step 3, rotating the disc to evenly spray the coating mixed liquid on the surface of the urea particles in the form of a spray, drying, and repeating multiple times to form a first coating layer on the surface of the urea particles to obtain first coated fertilizer particles; Step 4, crushing the salt-resistant water-retaining agent with a pulverizer, adding it to the disc, rotating the disc, and making the salt-resistant water-retaining agent powder evenly attached to the first coated fertilizer particles under the action of atomized water, drying, and repeating multiple times, so that the composite water-retaining agent forms a second coating layer on the outer layer, and obtains second coated fertilizer particles; Step 5, drying the prepared second coated fertilizer particles again in a forced air drying oven to obtain a salt-resistant and water-retaining composite functional slow-release fertilizer.

2. The method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer according to claim 1, characterized in that: In the step 2, the mass ratio of ethyl cellulose, lactic acid and ethanol solution is 5:2-3:100-150, and the mass fraction of the ethanol solution is 50%-70%.

3. The method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer according to claim 1, characterized in that: In step 3, the thickness of the first coating layer is 0.3-0.5 mm.

4. The method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer according to claim 1, characterized in that: In the step 4, the salt-resistant water-retaining agent is crushed by a crusher and passed through a 100-150 mesh sieve, and the thickness of the second coating layer is 0.4-0.6 mm.

5. The method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer according to claim 1, characterized in that: In step 4, the preparation method of the salt-resistant water-retaining agent comprises: S1. Weigh corn starch and dimethyl sulfoxide, mix them, heat them to 80-90°C, stir them thoroughly until a uniform mixed solution is formed, then drop the aminosilane coupling agent solution, keep the mixture warm and stir for 1-2h after the addition, then cool it to room temperature, discharge it in anhydrous ethanol, centrifuge, wash and dry it to obtain amino starch; S2, weighing allyl alcohol glycidyl ether and dimethyl sulfoxide, mixing, stirring thoroughly, gradually adding amination starch, heating to 80-90° C., keeping warm and stirring for 3-5 hours, then cooling to room temperature, discharging in anhydrous ethanol, centrifuging, washing and drying to obtain allyl alcohol starch; S3, weigh konjac glucomannan, acrylic anhydride and deionized water, add alkali solution dropwise to adjust the solution pH to 8-9, stir in an ice-water bath for 15-30h, after the reaction is completed, discharge in anhydrous ethanol, centrifuge, wash and dry to obtain glucomannan monomer; S4. Add allyl alcohol starch to deionized water for gelatinization treatment, then add glucomannan monomer and acrylamide, stir evenly, introduce nitrogen as protective gas, add thermal initiator, keep warm and stir to react for 1-2 hours, then add photoinitiator and cross-linking agent, treat under ultraviolet light for 10-20 minutes, and spray dry to obtain salt-resistant water-retaining agent.

6. The method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer according to claim 5, characterized in that: In the S1, the mass ratio of corn starch, dimethyl sulfoxide and aminosilane coupling agent solution is 1:60-80:20-40; the aminosilane coupling agent solution is obtained by mixing KH-550 and deionized water in a mass ratio of 1:8-12.

7. The method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer according to claim 5, characterized in that: In the S2, the mass ratio of the amino starch, allyl alcohol glycidyl ether and dimethyl sulfoxide is 1:0.22-0.44:40-60.

8. The method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer according to claim 5, characterized in that: In S3, the mass ratio of konjac glucomannan, acrylic anhydride and deionized water is 1:8-12:60-100.

9. The method for preparing a salt-resistant and water-retaining composite functional slow-release fertilizer according to claim 5, characterized in that: In S4, during the gelatinization process, the mass ratio of allylated starch to deionized water is 1:40-60, the gelatinization temperature is 60-70°C, and the gelatinization time is 0.5-1h; the mass ratio of allylated starch, glucomannan monomer, and acrylamide is 3:1-2:2-4; the amount of thermal initiator added is 2.3%-4.6% of the mass of allylated starch, the amount of photoinitiator added is 1.8%-3.6% of the mass of allylated starch, and the amount of cross-linking agent added is 1.5%-3% of the mass of allylated starch.

10. A salt-resistant and water-retaining composite functional slow-release fertilizer, prepared by the preparation method according to claim 1.

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