Oxamido multi-nutrient core-shell structure long-acting slow-release fertilizer and preparation method thereof

Abstract

The invention relates to the technical field of slow-release fertilizers, in particular to an oxamido multi-nutrient core-shell structure long-acting slow-release fertilizer and a preparation method thereof. The slow release fertilizer is of a core-shell structure and comprises a shell, an inner layer unit and a core layer, the inner layer unit comprises n inner layer groups, each inner layer group comprises an odd number of layers and an even number of layers, the shell comprises the following raw materials: oxamide and a biological agent, and the raw material of the even number of layers is oxamide; the odd layers comprise the following raw materials: a nitrogen source, a phosphorus source, a potassium source, organic matters, medium trace elements and polyhydroxy acid; components of the core layer are the same as those of the odd layers. Through the unique core-shell structure design, the nitrogen utilization rate reaches 40%-80%, and compared with traditional urea, the nitrogen utilization rate is remarkably improved. The nitrogen fertilizer can effectively meet the requirement of crops for nitrogen in the whole growth period, and also can remarkably reduce waste caused by loss of nutrient elements, so that the agricultural production cost is reduced while the agricultural production efficiency is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of slow-release fertilizer, in particular to a long-acting slow-release fertilizer with oxamide-based multi-nutrient core-shell structure and a preparation method thereof. BACKGROUND

[0002] Traditional nitrogen fertilizers such as urea have significant defects in the application process: the nitrogen utilization rate is usually only 30%-40%, of which ammonia volatilization loss accounts for 30%-50%, and nitrate nitrogen leaching loss accounts for 20%-40%. To solve this problem, the prior art mainly uses physical coating (such as sulfur-coated urea, which completely decomposes in soil with pH <5.5 within 3 months) or chemical modification (such as adding urease inhibitor DCD, which has a half-life of 40-60 days) to delay nutrient release, but there are problems such as uncontrollable degradation of coating materials (such as sulfur-coated urea, which has a release rate fluctuation of ±40% in acid soil), inhibitor residues interfering with soil microbial communities (DCD reduces soil urease activity by 50%-70%), etc., resulting in an average annual decrease of 0.5%-1.2% in soil organic matter content and an increase of 15%-25% in soil compaction index.

[0003] Oxamide (CONH2)2 as a new type of slow-release nitrogen source, its amide bond (C=O and N-H) in the molecular structure needs to be hydrolyzed to NH4 + and H2C2O4 by amidoase, which is regulated by soil temperature (optimum 35-40℃), humidity (water content >60%) and microbial activity, achieving the synchronization of nutrient release and crop demand period. However, its industrial application faces two major bottlenecks: one is high synthesis cost, and the other is that single nitrogen source slow release is difficult to meet the synchronous demand of crops for phosphorus and potassium. When the proportion of oxamide in the existing compound fertilizer formula exceeds 15%, the release peak of phosphorus and potassium elements deviates from the nitrogen release curve by more than 40%.

[0004] Oxamide is a poorly water-soluble organic nitrogen compound with low water solubility at room temperature, and is a high-efficiency slow-release nitrogen fertilizer with high nitrogen utilization rate and slow-release nitrogen characteristics. Oxamide has high cost and is suitable for high-end application scenarios and economic crops when used alone. To expand the large-area application scenarios of oxamide and improve the utilization rate of other instant fertilizers, developing a slow-release fertilizer with oxamide-based and multi-nutrient synergistic effect is one of the future development directions.

[0005] Patent ammonium phosphate solution spraying preparation of slow-release fertilizer (CN202110301388.9) takes high-concentration phosphorus ammonium emulsion (containing N and P) as the bonding-granulating core, and obtains 2.5-4.5 mm granules through the spray granulation method. The solid raw material can contain 3%-5% of carbon ammonium; the drying temperature is 100-250 DEG C; and the finished product particle size is 2.5-4.5 mm. This method basically uses quick-acting nitrogen and phosphorus fertilizer, lacks slow-release effect, and the nitrogen release rate is too fast, which cannot meet the long life period of crops once base fertilizer application, causes the increase of labor, increases the cost of base fertilizer and topdressing, and the overall fertilizer efficiency is low, and the nitrogen utilization rate is insufficient.

[0006] The oxamide slow-release nitrogen fertilizer disclosed in patent CN102304003A only realizes slow release through simple mixing of oxamide and urea, and does not involve multi-nutrient synergy and soil micro-ecological improvement.

[0007] The double-layer coated compound fertilizer of patent CN115677409A only focuses on the improvement of nitrogen content, and lacks the synergistic matching of phosphorus, potassium and trace elements.

[0008] Therefore, the current slow-release fertilizer mainly has the following problems: 1. Single slow-release system, nitrogen source is mainly quick-acting. Phosphorus ammonium, carbon ammonium and urea are all water-soluble and release quickly, which is mismatched with the high fertilizer demand peak of crops in the middle and later stages, and multiple topdressing is required, and the nitrogen utilization rate is low; 2. Physical and chemical technology is used for coating: the existing technology does not combine biological agents with the slow-release system, and cannot simultaneously realize nutrient supply and soil micro-ecological restoration; 3. Lack of special formula, different crops have large differences in N-P-K demand, and the fertilizer efficiency is not matched. It is urgent to provide a slow-release fertilizer with high nitrogen utilization rate and without the need for multiple topdressing. SUMMARY

[0009] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a long-acting slow-release fertilizer with oxamide-based multi-nutrient core-shell structure and a preparation method thereof, which is used to solve the problems of low nitrogen utilization rate and the need for multiple topdressing in the prior art.

[0010] To achieve the above-mentioned purposes and other related purposes, the present application is obtained through the following technical solutions.

[0011] The first aspect of the present application provides an oxamide-based multi-nutrient core-shell structure long-acting slow-release fertilizer, the slow-release fertilizer is a core-shell structure, including an outer shell, an inner layer unit and a core layer, the inner layer unit includes n inner layer groups (n≥0), each of the inner layer groups includes an odd layer and an even layer, the outer shell includes the following raw materials: oxamide, biological agent, the even layer raw material is oxamide; the odd layer includes the following raw materials: a nitrogen source, a phosphorus source, a potassium source, organic matter, trace elements, polyhydroxy acid, the components of the core layer are the same as those of the odd layer; when n≥1, the odd layer in the inner layer group closest to the outer shell is adjacent to the outer shell layer, and the even layer in the inner layer group closest to the core layer is adjacent to the core layer, and the odd layer and the even layer in the inner layer unit are staggered.

[0012] The second aspect of the present application provides a preparation method of an oxamide-based multi-nutrient core-shell structure long-acting slow-release fertilizer, including the following steps:

[0013] (1) mix part of oxamide and part of an auxiliary agent, crush, and then mix with water and biological agent to obtain an outer shell layer mixed slurry with a solid content;

[0014] (2) mix the remaining oxamide, the remaining auxiliary agent and water to obtain an even layer slow-release slurry;

[0015] (3) mix quick-acting nitrogen, quick-acting phosphorus, quick-acting potassium, trace elements, humic acid, fulvic acid and polyhydroxy acid to obtain a mixture;

[0016] (4) divide the mixture of step (3) into 1 part of core layer raw material and n parts of odd layer raw material; divide the even layer slow-release slurry obtained in step (2) into n parts; wherein n≥0;

[0017] (5) put the core layer raw material into a rotary disc for granulation to obtain spherical material one;

[0018] (6) spray the first part of the even layer slow-release slurry to the spherical material one, dry to form a slow-release shell, and obtain spherical material two;

[0019] (7) put the first part of the odd layer raw material into a rotary disc to mix and granulate with the spherical material two, and obtain spherical material three;

[0020] (8) repeat steps (6)-(7) to obtain spherical material 2n+1;

[0021] (9) spray the outer shell layer mixed slurry obtained in step (1) to the surface of the spherical material 2n+1, dry, cool and sieve to obtain an oxamide-based multi-nutrient core-shell structure long-acting slow-release fertilizer.

[0022] The third aspect of the present application is to provide the oxamide-based multi-nutrient core-shell structure long-acting slow-release fertilizer and / or the application of the slow-release fertilizer prepared by the preparation method of the oxamide-based multi-nutrient core-shell structure long-acting slow-release fertilizer in grain crops and / or economic crops.

[0023] As described above, the oxamide-based multi-nutrient core-shell structure long-acting slow-release fertilizer and the preparation method thereof have the following beneficial effects:

[0024] (1) In terms of nutrient utilization efficiency, the present application has significantly improved the nitrogen utilization rate to 40% to 80% through the unique core-shell structure design, compared with the traditional urea (the nitrogen utilization rate is about 30%). This efficient nutrient utilization effect not only effectively meets the demand of crops for nitrogen during the whole growth period, but also significantly reduces the waste caused by the loss of nutrient elements, thereby improving the efficiency of agricultural production while reducing the cost of agricultural production.

[0025] (2) In terms of slow-release performance, the slow-release fertilizer of the present application has a controllable slow-release period of 50 to 200 days, which can accurately release nutrients according to different stages of crop growth. This significantly reduced leaching rate indicates that the slow-release fertilizer of the present application has obvious advantages in reducing nutrient loss and improving nutrient utilization efficiency, and also reduces the potential pollution risk to the environment caused by nutrient loss;

[0026] (3) In terms of soil improvement, the present application realizes the significant improvement of soil micro-ecology through the synergistic effect of biological agents and polyhydroxy acids. Biological agents can effectively improve the rhizosphere micro-ecology of crops and promote the growth and reproduction of beneficial microorganisms, thereby enhancing the biological activity of the soil. At the same time, polyhydroxy acids can significantly improve the soil aggregate structure and reduce the occurrence of soil compaction, thereby improving the aeration and water permeability of the soil and creating a better soil environment for the growth of crop roots. This soil improvement effect not only helps to improve the growth quality and yield of crops, but also gradually improves the soil quality in the long-term use process, thereby promoting the sustainable development of agriculture;

[0027] (4) In terms of application operation, the slow-release fertilizer of the present application has significant operational convenience. Through one-time base application, the nutrient demand of crops during the whole growth period can be met, thereby effectively reducing the frequency of traditional fertilization (usually 3 to 4 times). This one-time fertilization method not only saves labor and time costs, but also further protects the soil structure and ecological environment. The slow-release fertilizer of the present application has the characteristics of "reducing amount, slow release, long-acting, and soil improvement for increasing income", excellent particle performance, and environmental friendliness. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1The figure shows a schematic diagram of the oxamide-based multi-nutrient core-shell structure long-acting slow-release fertilizer of the present application.

[0029] Element number explanation

[0030] 1, shell layer; 21, odd layer; 22, even layer; 3, core layer. DETAILED DESCRIPTION

[0031] In order to make the invention purposes, technical solutions and beneficial technical effects of the present application clearer, the present application will be further described in detail below in conjunction with examples, and other advantages and effects of the present application can be easily understood by those skilled in the art from the contents disclosed in the present description.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0033] In the case of using "comprising", "having", and "including" in the description herein, it is intended to cover non-exclusive inclusion, unless using the explicit limitation term, such as "only", "consisting of", etc., another component can be added.

[0034] The words "preferably", "more preferably", "most preferably", "preferably", "more preferably", "most preferably" and the like in the present application mean, in some cases, the embodiments of the present application that can provide certain beneficial effects. However, in the same or other cases, other embodiments can also be preferred. In addition, the description of one or more preferred embodiments does not imply that other embodiments are not available, nor is it intended to exclude other embodiments from the scope of the present application. That is, in the present application, "preferably", "more preferably", "most preferably", "preferably", "more preferably", "most preferably" and the like are only used to describe the implementation or embodiment with better effect, but do not constitute a limitation on the protection scope of the present application.

[0035] In the present application, "further", "more further", "in particular" and the like are used for the purpose of description, indicating differences in content but should not be understood as a limitation on the protection scope of the present application.

[0036] In the present application, "at least one" means one or more, such as one, two and more than two. The meaning of "multiple" or "several" is at least two, such as two, three, etc. The meaning of "multiple layers" is at least two layers, such as two layers, three layers, etc. unless otherwise specifically defined. In the description of the present application, the meaning of "several" is at least one, such as one, two, etc. unless otherwise specifically defined.

[0037] When a numerical range is disclosed herein, the range is intended to include the minimum and maximum values, and every stated value between the minimum and maximum values, unless the context clearly indicates otherwise. Further, when a range is stated to include integers, the range is intended to include every integer within the range, unless the context clearly indicates otherwise. Moreover, when a range is provided, it is intended to include any and all sub-ranges of the range, unless the context clearly indicates otherwise. In other words, unless expressly stated otherwise, any range or

[0038] If not specifically stated, all steps of the present application can be performed in sequence or randomly. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0039] The singular form of a term can include the plural form, unless the context clearly indicates otherwise, and cannot be understood as one in number.

[0040] In the present application, "above" or "below" includes the number itself. For example, 1 below includes 1.

[0041] In the present application, room temperature refers to 0-40°C, including but not limited to 10-40°C, or further 20-30°C.

[0042] In the present application, grain crops refer to crops whose main purpose is to harvest mature fruits (or seeds) and which are directly or indirectly used as human staple food after processing, and are the core of food security. Common grain crops include cereal crops, legume crops and tuber crops.

[0043] In the present application, economic crops, also known as industrial raw material crops, are crops whose main purpose is to obtain a certain part (such as fiber, seed, rhizome, flower, etc.) as an industrial raw material, or for other non-food purposes. The types of economic crops are as follows: fiber crops (cotton, hemp), oil crops (rape, peanut, soybean, sesame, sunflower), sugar crops (sugarcane, sugar beet), specialty crops (tobacco, tea), medicinal crops (ginseng, wolfberry, radix astragali), rubber crops (rubber tree), beverage crops (coffee, cocoa, tea), etc.

[0044] Existing slow-release fertilizers face numerous problems in practical applications. On the one hand, their nutrient composition is relatively limited, failing to meet the complex nutrient requirements of food and cash crops throughout their entire growth cycle. This can lead to deficiencies in certain key nutrients, impacting yield and quality. On the other hand, the compatibility between biological agents and slow-release systems is poor, hindering their ability to fully improve soil microecology and promote crop growth. Furthermore, the synergistic effect of existing compound fertilizers or slow-release fertilizers on soil microecology is limited. These issues make it difficult to meet the requirements of current sustainable agricultural development. Therefore, there is an urgent need to develop a new type of slow-release fertilizer to overcome the shortcomings of existing technologies, achieve precise supply of multiple nutrients, improve nitrogen utilization, reduce the frequency of topdressing, reduce ammonia volatilization and leaching of nitrogen, phosphorus, and potassium, while also considering particle strength, particle size compliance, and low cost. This would provide comprehensive nutritional support for food and cash crops throughout their entire growth cycle, promoting green and efficient agricultural development.

[0045] To address the problems of existing slow-release fertilizers, the inventors conducted extensive experiments and continuous adjustments and improvements, resulting in the slow-release fertilizer of this invention. This slow-release fertilizer achieves four benefits—reduced dosage, slow release, long-lasting effect, soil nourishment, and increased yield—through its core-shell structure. The synergistic effect of biological agents and polyhydroxy acids enhances nutrient utilization by 1.25 to 1.8 times, with a slow-release period of 50 to 200 days. It significantly improves the utilization rate of nutrients including carbon and nitrogen while reducing nitrogen and carbon emissions to the environment. A single application can meet the needs of the entire growth cycle, making it suitable for both food crops and cash crops, and offering significant economic and environmental benefits.

[0046] The slow-release fertilizer prepared by this invention has the following advantages: (1) the nitrogen fertilizer utilization rate is increased from 20% to more than 80%, significantly improving the utilization rate and fertilizer efficiency of other nutrients such as phosphorus, potassium, carbon and sulfur, and reducing the emission of environmental pollutants; (2) it increases crop yield and regulates soil nutrients and physicochemical properties; (3) it can be applied once or twice during the crop growth cycle, saving labor and time; (4) it is an intelligent fertilizer that synchronizes crop nutrient absorption and nutrient release; (5) it significantly reduces fertilizer usage, improves the nutritional quality of crops, and increases yield; (6) it can be seeded at low altitudes.

[0047] The first aspect of this invention is to provide a long-acting slow-release fertilizer with an oxamide-based multinutrient core-shell structure. The slow-release fertilizer has a core-shell structure, including an outer shell 1, inner layer units, and a core layer 3. The inner layer unit includes n inner layer groups (n≥0), and each inner layer group includes an odd-numbered layer 21 and an even-numbered layer 22. The outer shell 1 includes the following raw materials: oxamide and biological agents. The even-numbered layer 22 is made of oxamide. The odd-numbered layer 21 includes the following raw materials: nitrogen source, phosphorus source, potassium source, organic matter, trace elements, and polyhydroxy acids. The components of the core layer 3 are the same as those of the odd-numbered layer 21. When n≥1, the odd-numbered layer 21 in the inner layer group closest to the outer shell 1 is adjacent to the outer shell layer 1, and the even-numbered layer 22 in the inner layer group closest to the core layer 3 is adjacent to the core layer 3. The odd-numbered layers 21 and even-numbered layers 22 in the inner layer unit are arranged alternately.

[0048] This invention combines oxalamide with other nutrients such as nitrogen, phosphorus, potassium, organic matter, and trace elements to form a core-shell structure, which facilitates synergistic improvement in the utilization rate of the combined quick-dissolving fertilizer.

[0049] In some embodiments of the present invention, the mass percentage of N:P2O5:K2O in the slow-release fertilizer ranges from 3.0-40.8:0.3-20:0.3-20. Specifically, it can be 3-20:0.3-10:10-20 or 20-40.8:10-20:10-20.

[0050] In some embodiments of the present invention, the outer shell 1 and / or even-numbered layers 22 further include additives. Preferably, the additives are selected from one or more minerals, bentonite, and attapulgite.

[0051] In some embodiments of the present invention, the average diameter of the slow-release fertilizer is 2-5 mm.

[0052] In some embodiments of the present invention, the content of each component in the core layer 3 is the same as the content of each component in the odd-numbered layers 21. Here, "content" refers to a mass percentage content.

[0053] In some embodiments of the present invention, the slow-release fertilizer comprises the following raw materials by weight percentage: 8-95% oxamide, 1-35% readily available nitrogen source, 0.5-35% phosphorus source, 0.5-35% potassium source, 2-10% adjuvants, 0.01-5% trace elements, 0.1-1% biological agent, 0.2-7% organic matter, and 0.2-3% polyhydroxy acid.

[0054] In some embodiments of the present invention, the slow-release fertilizer comprises the following raw materials in weight percentages: 8-15% oxamide, 25-35% readily available nitrogen source, 25-35% phosphorus source, 25-35% potassium source, 8-10% adjuvants, 0.01-2% trace elements, 0.1-0.8% biological agent, 0.2-7% organic matter, and 0.2-1% polyhydroxy acid.

[0055] In some embodiments of the present invention, the slow-release fertilizer comprises the following raw materials by weight percentage: 15-95% oxamide, 1-25% readily available nitrogen source, 0.5-25% phosphorus source, 0.5-25% potassium source, 2-8% adjuvants, 0.5-5% trace elements, 0.1-1% biological agent, 0.2-7% organic matter, and 0.2-3% polyhydroxy acid.

[0056] In some embodiments of the present invention, the content ratio of oxalamide in the outer shell 1 to that in the inner layer unit is 0.1:1-3:0.1; specifically, it can be 0.2:1.5-2.8:0.2. Preferably, the content of oxalamide in the outer shell 1 is the same as the content of oxalamide in each even-numbered layer 22.

[0057] In some embodiments of the present invention, the content of each component in each odd-numbered layer 21 is the same; and / or, the content of each component in each even-numbered layer 22 is the same.

[0058] In some embodiments of the present invention, the content ratio of the additive in the outer shell 1 to the additive in the inner layer unit is 0.1:1-3:0.1; preferably, the content of the additive in the outer shell 1 is the same as the content of the additive in each even-numbered layer 22.

[0059] In some embodiments of the present invention, the porosity of the outer shell 1 is ≤20%; preferably, the porosity is ≤15%, and more preferably, the porosity is ≤10%.

[0060] In some embodiments of the present invention, the biological agent is selected from one or more of Bacillus subtilis, Bacillus amyloliquefaciens, Bacillus polymyxa, Trichoderma, or Bacillus mucilaginosus.

[0061] In some embodiments of the present invention, the polyhydroxy acid is selected from one or more of polyglutamic acid or polyhydroxy fatty acid esters.

[0062] In some embodiments of the present invention, the weight-average molecular weight of the polyhydroxy acid is 100-800 kDa; specifically, the weight-average molecular weight of the polyhydroxy acid is selected from one or more of 100-300 kDa, 300-500 kDa, and 500-800 kDa.

[0063] In some embodiments of the present invention, the number of inner layer groups is 0-10. Specifically, it can be 0-2, 2-5, 5-8, or 8-10.

[0064] In some embodiments of the present invention, the nitrogen source is selected from one or more of urea, ammonium sulfate, ammonium chloride, or ammonium nitrate.

[0065] In some embodiments of the present invention, the phosphorus source is selected from one or more of monoammonium phosphate, diammonium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, or superphosphate.

[0066] In some embodiments of the present invention, the potassium source is selected from one or more of potassium sulfate, potassium chloride, or potassium carbonate.

[0067] In some embodiments of the present invention, the trace elements are selected from one or more of magnesium, copper, zinc, boron, calcium, silicon, selenium, iron, and manganese.

[0068] In some embodiments of the present invention, the organic matter is selected from one or more of fulvic acid or humic acid.

[0069] A second aspect of this invention is to provide a method for preparing a long-acting slow-release fertilizer with an oxamid-based multinutrient core-shell structure, comprising the following steps:

[0070] (1) Mix some oxalamide and some adjuvants, crush them, and then mix them with water and biological agent to obtain a slurry with a solid content of outer shell layer;

[0071] (2) Mix the remaining oxalamide, the remaining adjuvants, and water to obtain an even-numbered slow-release slurry;

[0072] (3) Mix available nitrogen, available phosphorus, available potassium, trace elements, humic acid, fulvic acid and polyhydroxy acid to obtain a mixture;

[0073] (4) Divide the mixture from step (3) into 1 part of core layer raw material and n parts of odd-numbered layer raw material; divide the even-numbered layer slow-release slurry obtained from step (2) into n parts; where n≥0;

[0074] (5) The core layer raw material is fed into a rotating disc for granulation to obtain spherical material 1;

[0075] (6) Spray the first even-numbered layer of slow-release slurry onto spherical object one, dry it to form a slow-release shell, and obtain spherical object two;

[0076] (7) The first odd-numbered layer of raw material is fed into a turntable and mixed with spherical material two for granulation to obtain spherical material three;

[0077] (8) Repeat steps (6)-(7) to obtain 2n+1 spherical objects;

[0078] (9) Spray the shell layer mixture slurry obtained in step (1) onto the surface of the spherical object 2n+1, dry, cool and sieve to obtain oxalamide-based multinutrient core-shell structure long-acting slow-release fertilizer.

[0079] In step (3) of this invention, the trace elements are added in the form of compounds containing trace elements during the preparation process.

[0080] In some embodiments of the present invention, the granulation in step (5) and / or step (7) is selected from one or more of the following: agglomeration, spray granulation, high tower granulation, extrusion, or roller pressing. Preferably, the agglomeration method is selected from one or more of the following: drum granulation or rotary disc granulation.

[0081] In some embodiments of the present invention, the ratio of oxamide in step (1) to oxamide in step (2) is 1:n, where n≥1. Specifically, when n=2, that is, when there are 2 inner layers, the added oxamide is divided into 3 parts, with oxamide in the outer shell 1 accounting for 1 part, and the remaining 2 parts corresponding to the 2 even-numbered layers 22 of the inner layer unit.

[0082] In some embodiments of the present invention, the ratio of the additive in step (1) to the additive in step (2) is 1:n, where n≥1. Specifically, when n=2, that is, when there are 2 inner layer groups, the added additive is divided into 3 parts, the additive in the outer shell 1 occupies 1 part, and the remaining 2 parts correspond to the 2 even-numbered layers 22 of the inner layer unit.

[0083] In some embodiments of the present invention, the solid content of the outer shell layer mixing slurry in step (1) is 25-30%.

[0084] In some embodiments of the present invention, the solid content of the even-numbered slow-release slurry in step (3) is 25-30%.

[0085] In some embodiments of the present invention, the specific parameters of the rotary granulation are as follows:

[0086] Rotational speed: 10-100 r / min, specifically 60-90 r / min, 70-80 r / min, or 10-20 r / min;

[0087] Feed rate: 50-100 kg / h, preferably 60-90 kg / h, especially preferably 70-80 kg / h;

[0088] Atomization pressure: 0.3~0.5MPa, preferably 0.35~0.45MPa, particularly preferably 0.38~0.42MPa;

[0089] Coating temperature: 30-60℃, preferably 35-55℃, and especially preferably 40-50℃.

[0090] A third aspect of the present invention is to provide the application of slow-release fertilizers prepared by the method of preparing oxalamide-based multinutrient core-shell structured slow-release fertilizers as described in the present invention in food crops and / or cash crops.

[0091] In some embodiments of the present invention, the grain crop is selected from one or more of rice, wheat, corn, sorghum, millet, soybean, red bean, mung bean, sweet potato, potato, and cassava.

[0092] In some embodiments of the present invention, the cash crop is selected from one or more of cotton, sugarcane, sugar beets, black tea, green tea, oolong tea, wolfberry, and honeysuckle.

[0093] The present invention will be further illustrated by the following examples, but these examples do not limit the scope of the invention.

[0094] When numerical ranges are given in the embodiments, it should be understood that, unless otherwise stated in the present invention, both endpoints of each numerical range and any value between the two endpoints may be selected. Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. All reagents or instruments whose manufacturers are not specified are conventional products that can be purchased commercially. In addition to the specific methods, equipment, and materials used in the embodiments, based on the knowledge of the prior art possessed by one of ordinary skill in the art and the description of this invention, any prior art methods, equipment, and materials similar to or equivalent to those described, used, and materials in the embodiments of this invention may be used to implement this invention.

[0095] The commercially available compound fertilizers of the present invention, models 16-16-16, 18-8-16 (chlorine-free), and 22-8-12 (chlorine-free) (free of oxamyl and uncoated), are all commercially available ordinary fertilizers. The numbers 16-16-16 represent the nitrogen, phosphorus, and potassium content in the compound fertilizer, respectively. The manufacturer is Shaanxi Shanken Fuxing Agricultural Development Co., Ltd. The manufacturers of the 18-8-16 (chlorine-free) and 22-8-12 (chlorine-free) compound fertilizers are Qingdao Suofeng Biotechnology Co., Ltd.

[0096] Table 1. Main parameters of biological agents, polyhydroxy acids, and core-shell structures in Examples 1-5

[0097]

[0098] Table 2. Raw material composition and percentage content (wt%) of each component in Examples 1-6

[0099]

[0100]

[0101] Table 3 Comparative Examples 1-5 using compound fertilizer

[0102]

[0103] Example

[0104] Example 1

[0105] This embodiment provides a oxamide-based multinutrient core-shell structured long-acting slow-release fertilizer. The slow-release fertilizer has a core-shell structure, including an outer shell 1, an inner layer unit, and a core layer 3. The inner layer unit includes two inner layer groups, each inner layer group including an odd-numbered layer 21 and an even-numbered layer 22. The odd-numbered layer 21 in the inner layer group closest to the outer shell 1 is adjacent to the outer shell layer 1, and the even-numbered layer 22 in the inner layer group closest to the core layer 3 is adjacent to the core layer 3. The odd-numbered layers 21 and even-numbered layers 22 in the inner layer unit are arranged alternately. The outer shell 1 includes the following raw materials: oxamide, biological agent, and adjuvants. The even-numbered layer 22 is made of oxamide and adjuvants. The odd-numbered layer 21 includes the following raw materials: nitrogen source, phosphorus source, potassium source, organic matter, trace elements, and polyhydroxy acid. The content of each component in the core layer 3 is the same as that in the odd-numbered layers 21; the content of each component in each odd-numbered layer 21 is the same; the content of each component in each even-numbered layer 22 is the same; the content ratio of oxamide in the outer shell 1 to that in the inner layer unit is 1:3; the content ratio of oxamide in the outer shell 1 to that in the even-numbered layers 22 is 1:1; the adjuvant is clay, and the content ratio of the adjuvant in the outer shell 1 to that in the inner layer unit is 1:3; the content ratio of the adjuvant in the outer shell 1 to that in the even-numbered layers 22 is 1:1; the type and activity retention rate of the biological agent are shown in Table 1, the type and weight-average molecular weight of the polyhydroxy acid are shown in Table 1, and the raw material composition of the slow-release fertilizer is shown in Table 2. The porosity of the outer shell of the slow-release fertilizer is shown in Table 1.

[0106] This embodiment provides a method for preparing a long-acting slow-release fertilizer with an oxamid-based multinutrient core-shell structure. The method employs a slurry method combined with a rotary ball rolling process. The rotary ball rotation speed is 18 r / min, the tilt angle is 50°, the feed rate is 60 kg / h, and the coating temperature is 45°C. The specific steps include:

[0107] (1) Divide oxamide into three parts and attapulgite into three parts. Mix one part of oxamide and one part of the additive, crush them and pass them through a 60-mesh sieve. Then mix them with water and biological agent to obtain a shell layer mixed slurry with a solid content of 30%.

[0108] (2) Mix the remaining two parts of oxamide, two parts of attapulgite, and water to obtain an even-numbered layer slow-release grout with a solid content of 30%.

[0109] (3) Mix available nitrogen, available phosphorus, available potassium, compounds containing trace elements, humic acid, fulvic acid, and polyhydroxy acid, pulverize and pass through a 60-mesh sieve to obtain a mixture;

[0110] (4) Divide the mixture from step (3) into three equal parts, one part being the core layer material and two parts being the odd-numbered layer material; divide the even-numbered layer slow-release slurry obtained in step (2) into two equal parts.

[0111] (5) The core layer raw material is fed into a rotating disc for granulation to obtain spherical material 1;

[0112] (6) Spray the first even-numbered layer of slow-release slurry onto spherical object one, dry it to form a slow-release shell, and obtain spherical object two;

[0113] (7) The first odd-numbered layer of raw material is fed into a turntable and mixed with spherical material two for granulation to obtain spherical material three;

[0114] (8) Spray the second even-numbered layer of slow-release slurry onto spherical object three, dry it to form a slow-release shell, and obtain spherical object four;

[0115] (9) The second odd-numbered layer of raw material is fed into the turntable and mixed with spherical material four for granulation to obtain spherical material five;

[0116] (10) Spray the outer shell layer mixture slurry obtained in step (1) onto the surface of the spherical particles, with an outer shell porosity ≤20%. Dry the particles to a moisture content ≤2%, cool, and sieve to obtain a finished product with a diameter of 2–5 mm. Figure 1 As shown.

[0117] Example 2

[0118] This embodiment provides a oxamyl-based multinutrient core-shell structured long-acting slow-release fertilizer. The type and activity retention rate of the biological agent are shown in Table 1, the type and weight-average molecular weight of the polyhydroxy acid are shown in Table 1, and the raw material composition of the slow-release fertilizer is shown in Table 2. The porosity of the outer shell of the slow-release fertilizer is shown in Table 1. The difference from Example 1 is that the raw material components and their composition ratios are different, and the porosity of the outer shell of the resulting slow-release fertilizer is different.

[0119] Example 3

[0120] This embodiment provides a oxamyl-based multinutrient core-shell structured long-acting slow-release fertilizer. The type and activity retention rate of the biological agent are shown in Table 1, the type and weight-average molecular weight of the polyhydroxy acid are shown in Table 1, and the raw material composition of the slow-release fertilizer is shown in Table 2. The porosity of the outer shell of the slow-release fertilizer is shown in Table 1. The difference from Example 1 is that the raw material components and their composition ratios are different, and the porosity of the outer shell of the resulting slow-release fertilizer is different.

[0121] Example 4

[0122] This embodiment provides a oxamyl-based multinutrient core-shell structured long-acting slow-release fertilizer. The type and activity retention rate of the biological agent are shown in Table 1, the type and weight-average molecular weight of the polyhydroxy acid are shown in Table 1, and the raw material composition of the slow-release fertilizer is shown in Table 2. The porosity of the outer shell of the slow-release fertilizer is shown in Table 1. The difference from Example 1 is that the raw material components and their composition ratios are different, and the porosity of the outer shell of the resulting slow-release fertilizer is different.

[0123] Example 5

[0124] This embodiment provides a oxamyl-based multinutrient core-shell structured long-acting slow-release fertilizer. The type and activity retention rate of the biological agent are shown in Table 1, the type and weight-average molecular weight of the polyhydroxy acid are shown in Table 1, and the raw material composition of the slow-release fertilizer is shown in Table 2. The porosity of the outer shell of the slow-release fertilizer is shown in Table 1. The difference from Example 1 is that the raw material components and their composition ratios are different, and the porosity of the outer shell of the resulting slow-release fertilizer is different.

[0125] Example 6

[0126] This comparative example provides a compound fertilizer, which differs from Example 2 in that it does not have odd-numbered layers 21 and even-numbered layers 22; it only has inner and outer layers. Specifically, the raw material composition and formulation of the compound fertilizer are shown in Table 2, and the preparation method of the compound fertilizer is as follows:

[0127] (1) Mix oxamide and attapulgite, crush them, and then mix them with water and biological agent to obtain a shell layer mixed slurry with a solid content of 30%.

[0128] (2) Mix available nitrogen, available phosphorus, available potassium, trace elements, humic acid, fulvic acid and polyhydroxy acid, granulate to obtain spherical material;

[0129] (3) Spray the mixed slurry of the outer shell layer obtained in step (1) onto the surface of the spherical object, dry, cool and screen to obtain compound fertilizer with a particle size of 2-5 mm.

[0130] Comparative Example

[0131] The compound fertilizers used in Comparative Examples 1-5 are shown in Table 3.

[0132] Comparative Example 2A

[0133] This comparative example provides a compound fertilizer, which differs from Example 2 in that it is not made into a core-shell structure but is directly mixed. Specifically, the raw material composition and proportions of the compound fertilizer are shown in Table 2, and the preparation method of the compound fertilizer is as follows: the above raw materials are mixed and granulated to obtain the final product.

[0134] Performance testing

[0135] Apply the above-mentioned compound fertilizer evenly during land preparation before sowing. After application, rotary tillage or harrowing is recommended, or a fertilizer spreader can be used to sow it into the soil. The application rate per acre should be adjusted according to the specific compound fertilizer and crop. This fertilizer is a one-time basal application; no further topdressing is required. All other planting conditions are the same for the same crop. The performance test results of the compound fertilizer are shown in Table 4.

[0136] Table 4. Performance test results of compound fertilizer in Examples 1-6 and Comparative Examples 1-5, 2A

[0137]

[0138]

[0139] Table 5. Performance test results of compound fertilizer in Examples 2, 6, and Comparative Example 2A.

[0140]

[0141] As can be seen from the data in Table 4, the slow-release fertilizer prepared in this application is suitable for various crops. In addition, it is superior in terms of nitrogen utilization rate, phosphorus oxide utilization rate, and potassium oxide utilization rate. Moreover, the amount of fertilizer required to produce the same crop yield is less than that of commercially available compound fertilizers.

[0142] Combining the data in Tables 4 and 5, it can be seen that Comparative Example 2A (coreless, whole particles) dissolves slightly faster in the initial stage due to the lack of an outer shell barrier, shortening the cycle by about 20–30 days and reducing the utilization rate by 7–9 percentage points.

[0143] Combining the data in Tables 4 and 5, it can be seen that although Example 6 (only inner and outer layers) has an outer shell, compared with Example 2, it does not have an odd-even multilayer distribution, the nutrient gradient driving force is weakened, the cycle is shortened by 10-20 days, and the utilization rate decreases by 4-6 percentage points.

[0144] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An oxalyl amido multi-nutrient core-shell structure long-acting slow-release fertilizer, characterized in that, The slow-release fertilizer is a core-shell structure, comprising an outer shell (1), an inner layer unit and a core layer (3), the inner layer unit comprises n inner layer groups (n≥0), each of the inner layer groups comprises an odd layer (21) and an even layer (22), the outer shell (1) comprises the following raw materials: oxamide, biological bacteria, the even layer (22) is made of oxamide; the odd layer (21) comprises the following raw materials: nitrogen source, phosphorus source, potassium source, organic matter, trace elements, polyhydroxy acid; the core layer (3) has the same components as the odd layer (21); when n≥1, the odd layer (21) in the inner layer group closest to the outer shell (1) is adjacent to the outer shell layer (1), the even layer (22) in the inner layer group closest to the core layer (3) is adjacent to the core layer (3), and the odd layer (21) and the even layer (22) in the inner layer unit are arranged alternately.

2. The oxamide-based polynutrient core-shell structure long-acting slow-release fertilizer according to claim 1, characterized in that: Further comprising one or more of the following features: a1) the outer shell (1) and / or even layer (22) further comprises an auxiliary agent; preferably, the auxiliary agent is selected from one or more of mineral substances, bentonite, attapulgite; a2) the mass percentage of N:P2O5:K2O in the slow-release fertilizer ranges from 3.0-40.8%:0.3-20%:0.3-20%; a3) the average diameter of the slow-release fertilizer is 2-5mm; a4) the content of each component of the core layer (3) is the same as that of the odd layer (21).

3. The oxamide-based polynutrient core-shell structure long-acting slow-release fertilizer according to claim 2, characterized in that: The slow-release fertilizer comprises the following raw materials by weight percentage: oxamide 8-95%, readily available nitrogen source 1-35%, phosphorus source 0.5-35%, potassium source 0.5-35%, auxiliary agent 2-10%, trace elements 0.01-5%, biological bacteria 0.1-1%, organic matter 0.2-7%, polyhydroxy acid 0.2-3%.

4. The oxamide-based polynutrient core-shell structure long-acting slow-release fertilizer according to any one of claims 1 or 2, characterized in that: Further comprising one or more of the following features: b1) the content ratio of oxamide in the outer shell (3) to that in the inner layer unit is 0.1:1-3:0.1; preferably, the content of oxamide in the outer shell (3) is the same as that in each even layer (22); b2) each of the odd layers (21) has the same content of each component; and / or, each of the even layers (22) has the same content of each component; b3) the content ratio of auxiliary agent in the outer shell (3) to that in the inner layer unit is 0.1:1-3:0.1; preferably, the content of auxiliary agent in the outer shell (3) is the same as that in each even layer (22); b4) the biological bacteria are selected from one or more of Bacillus subtilis, Bacillus amyloliquefaciens, Paenibacillus polymyxa, Trichoderma or Bacillus mucilaginosus; b5) the polyhydroxy acid is selected from one or more of polyglutamic acid or polyhydroxyalkanoate; b6) the weight average molecular weight of the polyhydroxy acid is 100-800kDa; preferably, the weight average molecular weight of the polyhydroxy acid is selected from one or more of 100-300kDa, 300-500kDa, 500-800kDa; b7) the number of the inner layer groups is 0-10; b8) the porosity of the outer shell (1) is ≤20%.

5. The oxamide-based polynutrient core-shell structure long-acting slow-release fertilizer according to claim 1, characterized in that: The nitrogen source is selected from one or more of urea, ammonium sulfate, ammonium chloride, or ammonium nitrate; and / or, the phosphorus source is selected from one or more of monoammonium phosphate, diammonium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, or superphosphate.

6. The oxamide-based polynutrient core-shell structure long-acting slow-release fertilizer according to claim 1, characterized in that: The potassium source is selected from one or more of potassium sulfate, potassium chloride, or potassium carbonate; and / or, the microelement is selected from one or more of magnesium, copper, zinc, boron, calcium, silicon, selenium, iron, and manganese; and / or, the organic matter is selected from one or more of fulvic acid or humic acid.

7. A method for preparing the oxamide-based multi-nutrient core-shell structure long-acting slow-release fertilizer according to any one of claims 1-6, characterized in that, The method comprises the following steps: (1) mixing part of the oxamide and part of the auxiliary agent, crushing, and then mixing with water and biological agents to obtain a shell layer mixed slurry; (2) mixing the remaining oxamide, the remaining auxiliary agent, and water to obtain an even-numbered layer slow-release slurry; (3) mixing the readily available nitrogen, the readily available phosphorus, the readily available potassium, the microelement, the humic acid, the fulvic acid, and the polyhydroxy acid to obtain a mixture; (4) dividing the mixture of step (3) into one core layer raw material and n odd-numbered layer raw materials, and dividing the even-numbered layer slow-release slurry obtained in step (2) into n parts; wherein n≥0; (5) putting the core layer raw material into a rotating disc for granulation to obtain spherical objects one; (6) spraying the first part of the even-numbered layer slow-release slurry onto the spherical objects one, drying to form a slow-release shell, and obtaining spherical objects two; (7) putting the first part of the odd-numbered layer raw material into a rotating disc to mix and granulate with the spherical objects two, and obtaining spherical objects three; (8) repeating steps (6)-(7) to obtain spherical objects 2n+1; (9) spraying the shell layer mixed slurry obtained in step (1) onto the surface of the spherical objects 2n+1, drying, cooling, and sieving to obtain the oxamide-based multi-nutrient core-shell structure long-acting slow-release fertilizer.

8. The oxamide-based polynutrient core-shell structure long-acting slow-release fertilizer according to claim 7, characterized in that: The granulation in step (5) and / or step (7) is selected from one or more of the group consisting of a banding method, a spray granulation method, a high-tower granulation method, an extrusion method, and a roller method; and / or, the ratio of the oxamide in step (1) to the oxamide in step (2) is 1:n, wherein n≥1; and / or, the ratio of the auxiliary agent in step (1) to the auxiliary agent in step (2) is 1:n, wherein n≥1.

9. The application of the slow-release fertilizer prepared by the method of any one of claims 1-6 and / or the method of any one of claims 7-8 in grain crops and / or economic crops.

10. Use according to claim 9, characterized in that: The grain crops are selected from one or more of rice, wheat, corn, sorghum, millet, soybean, red bean, mung bean, sweet potato, potato, and cassava; and / or, the economic crops are selected from one or more of cotton, sugarcane, sugar beet, black tea, green tea, oolong tea, Chinese wolfberry, and honeysuckle.

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