Ammonium polyphosphate-containing double-layer slow-release compound fertilizer as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of fertilizers, and particularly relates to an ammonium polyphosphate-containing double-layer slow-release compound fertilizer and a preparation method and application thereof.The ammonium polyphosphate-containing double-layer slow-release compound fertilizer is sequentially composed of a fertilizer core, a first coating, a surface layer and a second coating from inside to outside, fertilizer particles in the fertilizer core are ammonium polyphosphate particles, the coating is made of a slow-release material, and the surface layer is made of a slow-release material; the surface layer comprises nitrogen fertilizer, phosphate fertilizer and potash fertilizer. Through the double-layer structure, the direct contact area of the phosphate fertilizer and soil is reduced, so that the fixation and loss of the phosphate fertilizer are reduced, the effective utilization rate of the phosphate fertilizer is improved, and compared with common phosphate fertilizer, the diffusion distance of ammonium polyphosphate in the soil is remarkably increased (from 1-2 mm to 4-5 cm), so that plant root systems absorb phosphorus elements more easily, and the yield of the phosphate fertilizer is increased. Therefore, the absorption efficiency of phosphorus is improved. Meanwhile, the use of the fertilizer is also beneficial to reducing environmental pollution and promoting the sustainable development of agriculture.

Description

Technical Field

[0001] The invention belongs to the technical field of fertilizers, and in particular relates to a double-layer slow-release compound fertilizer containing ammonium polyphosphate and a preparation method and application thereof. Background Art

[0002] Phosphate fertilizer is an indispensable nutrient in the growth of crops and plays a vital role in improving crop yield and quality. However, the application of traditional phosphate fertilizer in agricultural production faces many challenges, and its low utilization rate has become an important factor restricting agricultural production efficiency and sustainable development.

[0003] On the one hand, after traditional phosphate fertilizers are applied to the soil, their phosphate ions easily react chemically with metal cations (such as iron, aluminum, calcium, magnesium, etc.) in the soil to form insoluble phosphate precipitates. These precipitates significantly reduce the mobility of phosphorus, making it difficult for crop roots to effectively absorb and utilize it, resulting in a significant decrease in the utilization rate of phosphate fertilizers. This not only increases agricultural production costs, but also aggravates the environmental burden, such as causing environmental problems such as eutrophication of water bodies.

[0004] On the other hand, phosphate fertilizers are easily adsorbed by the soil solid phase, further reducing the supply of effective phosphorus in the soil. This phenomenon is particularly evident in areas where soil phosphorus is scarce. Despite the large amount of phosphate fertilizers applied, the actual absorption of phosphorus by crops is very limited. This not only affects the normal growth and development of crops, but may also lead to the accumulation of soil phosphorus, causing long-term adverse effects on the ecological environment.

[0005] With the continuous growth of the global population and the continuous increase in food demand, agricultural production has become increasingly dependent on phosphate fertilizers. Especially in some areas with low soil phosphorus content, the application of phosphate fertilizers has become a key measure to improve crop yields and quality. However, the production of phosphate fertilizers mainly depends on non-renewable phosphate rock resources. Excessive exploitation and use may not only lead to resource depletion, but also cause a series of environmental problems.

[0006] Although existing technologies have made some progress in improving the utilization rate of phosphate fertilizers, there are still many limitations. For example, the supply of traditional phosphate fertilizers is uneven during the crop growth period, making it difficult to meet the nutrient needs of crops throughout the entire growth period; at the same time, most phosphate fertilizers lack an effective slow-release mechanism, resulting in rapid release of phosphorus in the soil, which cannot be fully absorbed and utilized by crops. In addition, some phosphate fertilizers may cause environmental pollution during production and use, which does not meet the current requirements of sustainable development.

[0007] In order to solve the above problems, it is urgent to develop a new type of fertilizer that can improve the utilization rate of phosphate fertilizer and reduce resource waste, thereby promoting the sustainable development of agriculture. Summary of the invention

[0008] The purpose of the present invention is to provide a double-layer slow-release compound fertilizer containing ammonium polyphosphate and a preparation method and application thereof. The compound fertilizer is made from ammonium polyphosphate as a raw material, can significantly improve the utilization efficiency of phosphate fertilizer, reduce resource waste, and increase crop yield. At the same time, the use of this new fertilizer also helps to reduce environmental pollution and promote the sustainable development of agriculture.

[0009] The objective of the present invention is achieved through the following technical solutions: The invention provides a double-layer slow-release compound fertilizer containing ammonium polyphosphate. The double-layer slow-release compound fertilizer containing ammonium polyphosphate consists of a fertilizer core, a first coating, a surface layer and a second coating from the inside to the outside. The fertilizer particles in the fertilizer core are ammonium polyphosphate particles, the coating is composed of a slow-release material, and the surface layer includes nitrogen fertilizer, phosphate fertilizer and potassium fertilizer.

[0010] Furthermore, the ammonium polyphosphate-containing double-layer slow-release compound fertilizer also includes a binder.

[0011] Furthermore, the slow-release material includes polyvinyl alcohol or polylactic acid, the nitrogen fertilizer includes urea or ammonium chloride, the phosphate fertilizer includes polyammonium phosphate or diammonium phosphate, and the potash fertilizer includes potassium sulfate, potassium nitrate or potassium chloride.

[0012] Furthermore, the binder includes humic acid.

[0013] Furthermore, the ammonium polyphosphate-containing double-layer slow-release compound fertilizer comprises the following components by mass: 23 parts of urea, 5-15 parts of ammonium polyphosphate, 8 parts of potassium chloride, 8-15% of the total mass of the fertilizer of polylactic acid, and 5-15% of the total mass of the fertilizer of humic acid.

[0014] Furthermore, the particle size of the fertilizer core is 1-2 mm, the thickness of the coating is 0.1-0.2 mm, and the particle size of the double-layer slow-release compound fertilizer containing ammonium polyphosphate is 3-5 mm.

[0015] The present invention also provides a method for preparing a double-layer slow-release compound fertilizer containing ammonium polyphosphate, comprising the following steps: S1 uses extrusion granulation process to prepare ammonium polyphosphate fertilizer core, and obtains ammonium polyphosphate granules by accurately controlling granulation parameters; S2 dissolves the sustained-release material in a solvent to form a coating liquid, and performs coating treatment on the ammonium polyphosphate particles; S3: mixing the coated ammonium polyphosphate particles with nitrogen fertilizer, potassium fertilizer, phosphate fertilizer and a binder and granulating them to obtain ammonium polyphosphate slow-release compound fertilizer particles; S4 dissolves the slow-release material in a solvent to form a coating liquid, and performs coating treatment on the ammonium polyphosphate slow-release compound fertilizer particles; After screening and quality inspection, S5 is packed in bags to obtain a double-layer slow-release compound fertilizer containing ammonium polyphosphate; Wherein, in step S2 and step S4, when the sustained-release material used is polyvinyl alcohol, the solvent used for dissolving is water, and when the sustained-release material used is polylactic acid, the solvent used for dissolving is ethyl acetate.

[0016] Furthermore, the content of ammonium polyphosphate in each ammonium polyphosphate slow-release compound fertilizer granule is 0.0105g-0.021g, coated polylactic acid is 0.01g-0.0118g, surface nitrogen fertilizer is 0.0605g, potassium fertilizer is 0.0211g, phosphate fertilizer is 0.0079g-0.0158g and humic acid is 0.00895g-0.00974g.

[0017] The invention also provides an application of the ammonium polyphosphate-containing double-layer slow-release compound fertilizer in improving corn yield.

[0018] Furthermore, during the application process, the fertilization depth of the double-layer slow-release compound fertilizer containing ammonium polyphosphate is 10-20 cm.

[0019] The beneficial effects of the present invention are: After the ammonium polyphosphate double-layer slow-release compound fertilizer is applied to the soil in the present invention, the ammonium polyphosphate therein can be combined with metal ions such as iron, aluminum, calcium, and magnesium in the soil, reduce the fixation of phosphorus, enhance the mobility of phosphorus, enable more phosphate ions to move to the root of the crop, and improve the absorption efficiency of phosphorus by the crop, and the orthophosphate in the ammonium polyphosphate will be absorbed and utilized by the crop first, and pyrophosphate, tripolyphosphate, tetrapolyphosphate, etc. will gradually be converted into orthophosphate after hydrolysis, for continuous absorption by the crop, therefore, the ammonium polyphosphate can continuously provide nutrients in the entire growth period of the crop, with a long-term fertilizer effect, and at the same time, a large amount of phosphate ions are distributed on the ammonium polyphosphate molecular chain, which can be chelated with metal ions such as calcium, magnesium, iron, manganese, and other trace elements in the soil. This not only provides major nutrients such as nitrogen and phosphorus for crops, but also can provide trace elements through chelation, promoting the comprehensive growth of crops.

[0020] When corn is deficient in phosphorus, it will start an adaptive metabolic mechanism, and its roots will activate the insoluble phosphates in the soil by secreting organic acids such as citric acid and malic acid. The continuous release of these organic acids will cause the pH value of the rhizosphere microenvironment to drop significantly (usually to 4.5-5.5), forming a local acidic microdomain. Under such acidic conditions, the crystalline area of ​​the polylactic acid (PLA) coating material containing the polyphosphate double-layer slow-release ammonium compound fertilizer in the present invention gradually disintegrates, eventually leading to the collapse of the three-dimensional network structure. After the coating is degraded, the fertilizer core originally wrapped is released. At this time, the corn root system is just in the critical growth period when it is in urgent need of phosphorus, forming a precise matching mechanism of "demand-response-supply".

[0021] The present invention reduces the direct contact area between phosphate fertilizer and soil through the double-layer structure, thereby reducing the fixation and loss of phosphate fertilizer and improving the effective utilization rate of phosphate fertilizer. Compared with ordinary phosphate fertilizer, the diffusion distance of ammonium polyphosphate in the soil is significantly increased (from 1-2 mm to 4-5 cm), which makes it easier for plant roots to absorb phosphorus, thereby improving the absorption efficiency of phosphorus.

[0022] In addition, the present invention uses degradable PLA (polylactic acid) as the coating material. This material can be naturally degraded in the soil, reducing pollution to the environment and meeting the requirements of sustainable development. At the same time, the demand for phosphorus by corn increases in the later stages of growth, and the ammonium polyphosphate fertilizer core can continuously release phosphorus, providing sufficient nutrient support for corn growth, thereby significantly increasing corn yields.

[0023] In summary, the double-layer slow-release compound fertilizer of the present invention not only improves the utilization efficiency of phosphate fertilizer, but also reduces the negative impact on the environment through environmentally friendly materials and slow-release technology, while meeting the nutrient requirements of corn in the later stage of growth, and ultimately achieving a significant increase in corn yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 The present invention is a structural diagram of a double-layer slow-release ammonium polyphosphate compound fertilizer, wherein the numbers in the figure are: 1-fertilizer core, 2-envelope 1, 3-surface layer, 4-envelope 2. DETAILED DESCRIPTION

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to the skilled artisan. The present invention description and examples are exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] The specific structure of the double-layer slow-release compound fertilizer containing ammonium polyphosphate in the present invention is as follows Figure 1 As shown, from the inside to the outside, there are fertilizer core, coating one, surface layer and coating two, among which, the fertilizer particles in the fertilizer core are ammonium polyphosphate particles with a particle size of 1-2mm; the coating is composed of slow-release material; the surface layer contains nitrogen fertilizer, phosphorus fertilizer and potassium fertilizer particles, and the particles are formed with a binder.

[0032] Among them, the nitrogen fertilizer in the above-mentioned ammonium polyphosphate double-layer slow-release compound fertilizer includes urea or ammonium chloride; the phosphorus fertilizer includes ammonium polyphosphate or diammonium phosphate; the potash fertilizer includes potassium sulfate, potassium nitrate or potassium chloride; the slow-release material includes polyvinyl alcohol (PVA) or polylactic acid (PLA), which is used for coating one and coating two, and the thickness is 0.1-0.2mm; the binder includes humic acid or polyvinyl alcohol; the nitrogen, phosphorus and potassium nutrient content of the above-mentioned ammonium polyphosphate double-layer slow-release compound fertilizer is ≥45%, and the particle size is 3-5mm. Among them, when the slow-release material used is polyvinyl alcohol, the solvent used for dissolution is water, and when the slow-release material used is polylactic acid, the solvent used for dissolution is ethyl acetate.

[0033] The method for preparing the double-layer slow-release compound fertilizer containing ammonium polyphosphate in the present invention comprises the following steps: (1) Material preparation: prepare the basic materials needed for the preparation of ammonium polyphosphate double-layer slow-release compound fertilizer, including 23 parts of urea, 5-15 parts of ammonium polyphosphate, 8 parts of potassium chloride, 8-15% of the total weight of polylactic acid and 5-15% of the total weight of humic acid; (2) Fertilizer core preparation: The ammonium polyphosphate fertilizer core is prepared by extrusion granulation process. By precisely controlling the granulation parameters, a fertilizer core product with a particle size range of 1-2 mm is obtained. The content of ammonium polyphosphate in each fertilizer core is strictly controlled between 0.0105g and 0.021g, ensuring that the product has stable nutrient release characteristics and good physical properties; (3) Coating process: dissolve the sustained-release material polylactic acid in a solvent to form a coating liquid, put the ammonium polyphosphate particles into a fluidized bed coating machine, spray the coating liquid evenly, and form an outer coating after drying. The thickness is controlled at 0.1-0.2 mm, and the coating material for each fat core is 0.00105 g-0.0021 g; (4) stirring treatment: placing the fertilizer core particles obtained above in a disc granulator, and then adding a uniform mixture of nitrogen fertilizer, potassium fertilizer, phosphorus fertilizer and humic acid to granulate, so as to obtain ammonium polyphosphate slow-release compound fertilizer particles, the fertilizer particles have a diameter range of 2-4 mm, and each particle of the surface fertilizer contains 0.0605 g of nitrogen fertilizer, 0.0211 g of potassium fertilizer, 0.0079 g-0.0158 g of phosphorus fertilizer, and 0.00895 g-0.00974 g of humic acid; (5) Coating process: dissolve the slow-release material polylactic acid in a solvent to form a coating liquid, put the ammonium polyphosphate slow-release compound fertilizer particles into a fluidized bed coating machine, spray the coating liquid evenly, and form an outer coating after drying. The thickness is controlled at 0.1-0.2mm, and the coating material per fertilizer particle is 0.00895g-0.00974g; (6) Screening and quality inspection: Screen to remove oversized or undersized particles (control the particle size to 3-5 mm), ensure uniform particle size, and test the particle compressive strength (>15N); (7) Bagging: The finished product of the double-layer slow-release compound fertilizer containing ammonium polyphosphate obtained in step (6) is bagged by compound fertilizer bagging equipment to obtain a packaged double-layer slow-release compound fertilizer containing ammonium polyphosphate.

[0034] The present invention will be further described below by way of examples.

[0035] Example 1 In this embodiment, a double-layer slow-release compound fertilizer containing ammonium polyphosphate is prepared, which includes the following components: 23 parts of urea, 7 parts of ammonium polyphosphate, 8 parts of potassium chloride, polylactic acid accounting for 8-15% of the total mass of the fertilizer, and humic acid accounting for 5-15% of the total mass of the fertilizer.

[0036] The method for preparing the above-mentioned double-layer slow-release compound fertilizer containing ammonium polyphosphate comprises the following steps: Step 1: material preparation, preparing the basic materials required for the preparation of the ammonium polyphosphate double-layer slow-release compound fertilizer; Step 2: Preparation of fertilizer cores: preparing ammonium polyphosphate fertilizer cores by extrusion granulation process to obtain fertilizer core products with a particle size range of 1-2 mm. The content of ammonium polyphosphate in each fertilizer core is strictly controlled to be around 0.0105 g; Step 3, coating process, dissolving the sustained-release material polylactic acid in a solvent to form a coating liquid, placing the ammonium polyphosphate particles in a fluidized bed coating machine, spraying the coating liquid evenly, and forming an outer coating after drying, with a thickness controlled at 0.1-0.2mm, and 0.00105g of coating material per fat core; Step 4: stirring, placing the fertilizer core particles obtained above in a disc granulator, and then adding a uniform mixture of nitrogen fertilizer, potassium fertilizer, phosphorus fertilizer and humic acid for granulation, so as to obtain ammonium polyphosphate slow-release compound fertilizer particles, the fertilizer particles have a diameter range of 2-4 mm, and each particle of the surface fertilizer contains 0.0605 g of nitrogen fertilizer, 0.0211 g of potassium fertilizer, 0.0079 g of phosphorus fertilizer, and 0.00895 g of humic acid; Step 5, coating process, dissolving the slow-release material polylactic acid in a solvent to form a coating liquid, placing the ammonium polyphosphate slow-release compound fertilizer particles in a fluidized bed coating machine, spraying the coating liquid evenly, and forming an outer coating after drying, with a thickness controlled at 0.1-0.2mm, and 0.00895g of coating material per fertilizer particle; Step 6: Screening and quality inspection, screen to remove oversized or undersized particles (control the particle size to 3-5mm), ensure uniform particle size, and test the particle compressive strength (>15N); Step seven, bagging operation, bagging the finished ammonium polyphosphate slow-release compound fertilizer obtained in step six by compound fertilizer bagging equipment to obtain a packaged double-layer slow-release compound fertilizer containing ammonium polyphosphate.

[0037] The fertilization depth of the double-layer slow-release compound fertilizer containing ammonium polyphosphate prepared in this embodiment is surface fertilization.

[0038] Example 2 Compared with Example 1, the only difference is that the fertilization depth of the double-layer slow-release compound fertilizer containing ammonium polyphosphate prepared in this example is 0-10 cm.

[0039] Example 3 Compared with Example 1, the only difference is that the fertilization depth of the double-layer slow-release compound fertilizer containing ammonium polyphosphate prepared in this example is 10-20 cm.

[0040] Example 4 Compared with Example 1, the only difference is that the ammonium polyphosphate in this embodiment is 14 parts. Among them, the content of ammonium polyphosphate in each fertilizer core is about 0.021g, the first layer of coating polylactic acid is 0.0021g, the surface layer of nitrogen fertilizer is 0.0605g, potassium fertilizer is 0.0211g, phosphate fertilizer is 0.0158g and humic acid is 0.00974g, and the second layer of coating polylactic acid is 0.00974g.

[0041] Example 5 Compared with Example 4, the only difference is that the fertilization depth is 0-10 cm.

[0042] Example 6 Compared with Example 4, the only difference is that the fertilization depth is 10-20 cm.

[0043] Example 7 Compared with Example 1, the only difference is that ammonium polyphosphate is not used in this embodiment, but diammonium phosphate with the same addition amount is used.

[0044] Example 8 Compared with Example 1, the only difference is that ammonium polyphosphate is not used in this embodiment, but diammonium phosphate is used in the same addition amount, and the fertilization depth is 0-10 cm.

[0045] Example 9 Compared with Example 1, the only difference is that ammonium polyphosphate is not used in this embodiment, but diammonium phosphate is used in the same addition amount, and the fertilization depth is 10-20 cm.

[0046] Example 10 Compared with Example 4, the only difference is that ammonium polyphosphate is not used in this embodiment, but diammonium phosphate with the same addition amount is used.

[0047] Embodiment 11 Compared with Example 4, the only difference is that ammonium polyphosphate is not used in this embodiment, but diammonium phosphate is used in the same addition amount, and the fertilization depth is 0-10 cm.

[0048] Example 12 Compared with Example 4, the only difference is that ammonium polyphosphate is not used in this embodiment, but diammonium phosphate is used in the same addition amount, and the fertilization depth is 10-20 cm.

[0049] Comparative Example 1 Compared with Example 1, the only difference is that the fertilizer used in this example is a conventional compound fertilizer (26-10-11).

[0050] Comparative Example 2 Compared with Example 1, the only difference is that the fertilizer used in this embodiment is conventional compound fertilizer, and the fertilization depth is 0-10 cm.

[0051] Comparative Example 3 Compared with Example 1, the only difference is that the fertilizer used in this embodiment is conventional compound fertilizer, and the fertilization depth is 10-20 cm.

[0052] Test Example 1 This test example uses the fertilizers and specific fertilization depths prepared in Examples 1-12 and Comparative Examples 1-3 to evaluate their effects on the growth and development of corn. The specific evaluation method is as follows.

[0053] 1.1 Materials and methods 1.1.1 Test materials: The corn variety is Heyu 236. The seedlings have purple sheaths, dark green leaves, purple leaf margins, yellow anthers, and green husks. The plant is compact, with a plant height of 287 cm, an ear height of 106 cm, and 18-19 leaves on mature plants. The ear is cylindrical, 21.5 cm long, 14-16 rows, 5 cm thick, red cob, and yellow grains with horse teeth.

[0054] 1.1.2 Experimental design: The test site is located in Yangchangzi Gacha, Ulanhot City. According to different fertilizer dosages and application methods, the fertilizers prepared in Examples 1-12 and Comparative Examples 1-3 and specific fertilization depths are used for treatment. Each treatment is repeated three times, with a total of 45 treatments.

[0055] In the specific treatment process, the fertilizers prepared in Examples 1-12 and Comparative Examples 1-3 were applied to the soil at one time during ridge formation. The fertilizers were applied according to the corresponding fertilization depth. When sowing, the sowing depth (3-5 cm) of a conventional seeder was used. The corn planting density was 4500 plants / mu. Each treatment area was 16.25 m 2 , other field management methods are exactly the same.

[0056] 1.2 Measurement indicators and methods 1.2.1 Determination of moisture content: Two rows of whole kernels were randomly selected and weighed, and then completely placed in the DSCA-1 Grain Plot Yield Measurement System to calculate the moisture content. Each test was repeated three times.

[0057] 1.2.2 Yield determination: Yield (kg / mu) = ear weight (kg) × seed rate × (1-water content / 100) ÷ 100 ÷ 0.86 ÷ actual harvest area (m 2 )×667(m 2 ) 1.3 Analysis of test results The effects of ammonium polyphosphate compound fertilizer on corn yield and yield components are shown in Table 1:

[0058] Combined with the experimental results obtained in Table 1, it can be seen from the ear traits and 100-grain weight that the ear length, ear thickness, bald tip, ear row number and 100-grain weight of Example 3 are the best, which are 22.26cm, 50.64mm, 4.35mm, 15.73 and 47.07g respectively. According to the depth of fertilization, whether it is a comparative example or an embodiment, the yield of Comparative Example 3, Example 3, Example 6, Example 9 and Example 12 (fertilization depth is 10-20cm) is the highest, which is 7.3%, 11.04%, 24.19%, 23.19% and 1.15% higher than Comparative Example 1, Example 1, Example 4, Example 7 and Example 10 (surface fertilization) respectively. From the perspective of fertilizer types, the yields of Examples 1-3 and Examples 7-9 are higher than those of Examples 4-6 and Examples 10-12. Compared with Examples 1-3 and Examples 7-9, the yields of Comparative Examples 1-3 are 989.03 (Example 3) > 960.26 (Example 9) > 954.61 (Comparative Example 3) from high to low.

[0059] 1.4 Conclusion The application of the compound fertilizer of Example 3 can increase the corn yield by increasing yield factors such as the number of corn cobs and the weight of 100 kernels. Compared with Comparative Example 3, Example 3 increases the yield by 3.61%.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be covered by the scope of the claims of the present invention.

Claims

1. A double-layer slow-release compound fertilizer containing ammonium polyphosphate, characterized in that: The ammonium polyphosphate-containing double-layer slow-release compound fertilizer consists of a fertilizer core, a first coating, a surface layer and a second coating from the inside to the outside. The fertilizer particles in the fertilizer core are ammonium polyphosphate particles, the coating is composed of a slow-release material, and the surface layer includes nitrogen fertilizer, phosphate fertilizer and potassium fertilizer.

2. The double-layer slow-release compound fertilizer containing ammonium polyphosphate as claimed in claim 1, characterized in that: The ammonium polyphosphate-containing double-layer slow-release compound fertilizer also includes a binder.

3. The double-layer slow-release compound fertilizer containing ammonium polyphosphate as claimed in claim 1, characterized in that: The slow-release material includes polyvinyl alcohol or polylactic acid, the nitrogen fertilizer includes urea or ammonium chloride, the phosphate fertilizer includes polyammonium phosphate or diammonium phosphate, and the potash fertilizer includes potassium sulfate, potassium nitrate or potassium chloride.

4. The double-layer slow-release compound fertilizer containing ammonium polyphosphate as claimed in claim 2, characterized in that: The binder includes humic acid.

5. The double-layer slow-release compound fertilizer containing ammonium polyphosphate as claimed in claim 1, characterized in that: The ammonium polyphosphate-containing double-layer slow-release compound fertilizer comprises the following components by weight: 23 parts of urea, 5-15 parts of ammonium polyphosphate, 8 parts of potassium chloride, 8-15% of the total weight of the fertilizer by polylactic acid, and 5-15% of the total weight of the fertilizer by humic acid.

6. The double-layer slow-release compound fertilizer containing ammonium polyphosphate as claimed in claim 1, characterized in that: The particle size of the fertilizer core is 1-2 mm, the thickness of the coating is 0.1-0.2 mm, and the particle size of the ammonium polyphosphate-containing double-layer slow-release compound fertilizer is 3-5 mm.

7. The method for preparing a double-layer slow-release compound fertilizer containing ammonium polyphosphate according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1 uses extrusion granulation process to prepare ammonium polyphosphate fertilizer core, and obtains ammonium polyphosphate granules by accurately controlling granulation parameters; S2 dissolves the sustained-release material in a solvent to form a coating liquid, and performs coating treatment on the ammonium polyphosphate particles; S3: mixing the coated ammonium polyphosphate particles with nitrogen fertilizer, potassium fertilizer, phosphate fertilizer and a binder and granulating them to obtain ammonium polyphosphate slow-release compound fertilizer particles; S4 dissolves the slow-release material in a solvent to form a coating liquid, and performs coating treatment on the ammonium polyphosphate slow-release compound fertilizer particles; After screening and quality inspection, S5 is packed in bags to obtain a double-layer slow-release compound fertilizer containing ammonium polyphosphate; Wherein, in step S2 and step S4, when the sustained-release material used is polyvinyl alcohol, the solvent used for dissolving is water, and when the sustained-release material used is polylactic acid, the solvent used for dissolving is ethyl acetate.

8. The preparation method according to claim 7, characterized in that: The content of ammonium polyphosphate in each ammonium polyphosphate slow-release compound fertilizer granule is 0.0105g-0.021g, coated polylactic acid is 0.01g-0.0118g, surface nitrogen fertilizer is 0.0605g, potassium fertilizer is 0.0211g, phosphate fertilizer is 0.0079g-0.0158g and humic acid is 0.00895g-0.00974g.

9. Use of the double-layer slow-release compound fertilizer containing ammonium polyphosphate as claimed in any one of claims 1 to 6 in increasing corn yield.

10. The use according to claim 9, characterized in that During the application process, the fertilization depth of the double-layer slow-release compound fertilizer containing ammonium polyphosphate is 10-20 cm.

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