Oxamido multi-nitrogen-source core-shell structure long-acting slow-release fertilizer as well as preparation method and application thereof

Abstract

The invention provides an oxamido multi-nitrogen-source core-shell structure long-acting slow release fertilizer as well as a preparation method and application thereof. The slow-release fertilizer is of a core-shell structure, the core-shell structure comprises an inner core area and a shell, the inner core area at least comprises a quick-acting core, and raw materials of the quick-acting core comprise a quick-acting nitrogen source, a medium trace element compound, humus, poly-polyhydroxy acid and a first auxiliary agent; the shell is prepared from the following raw materials: slow-release nitrogen source oxamide, a second auxiliary agent and a biological agent. Controllable slow release within 50-200 days is achieved, the nitrogen utilization rate is increased by 1.25-2 times compared with a conventional compound fertilizer, the nitrogen and carbon utilization rate is remarkably increased, and carbon emission to the atmosphere is reduced. The fertilizer can meet the requirements of the whole growth period after being applied once, is suitable for food crops and commercial crops, and has remarkable economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to a long-acting slow-release fertilizer with a core-shell structure of oxalamide-based multi-nitrogen source, its preparation method, and its application. Background Technology

[0002] Oxalide (CONH2)2-, also known as ethylenediamine, has a molecular weight of 88.1 and contains 31.8% nitrogen. It is a white powder that is non-hygroscopic, non-toxic, and easy to store. It is slightly soluble in water at room temperature. Its nitrogen utilization rate is as high as 65% to 80%, which is about twice that of urea. Its nutrients are mainly decomposed by amidase, releasing ammoniacal nitrogen and oxalic acid. Oxalic acid can be mineralized by soil and partially absorbed by plant roots. Both nitrogen and carbon in oxalamide can be utilized by crops. With proper combination with other nutrients, it can synergistically improve the utilization rate of fast-dissolving fertilizers. It is an important raw material for making high-efficiency slow-release fertilizers. Slow-release / controlled-release fertilizers have the following advantages: (1) Nitrogen fertilizer utilization rate is increased from 20% to over 80%, which can significantly improve the utilization rate and fertilizer efficiency of other nutrients and reduce environmental pollutant emissions; (2) Increase crop yield and regulate soil nutrients and physicochemical properties; (3) Apply once during the crop growth cycle, saving labor and time. (4) Intelligent fertilizer that synchronizes crop nutrient absorption and release (5) Can be seeded at low altitudes.

[0003] Existing slow-release compound fertilizers for crops mostly use urea as a fast-acting nitrogen source, which has problems such as rapid nitrogen release, low utilization rate, need for multiple topdressings, and large ammonia volatilization losses.

[0004] Existing slow-release fertilizers are mainly produced by physical or chemical coating and the addition of urease inhibitors. Some of them have very good slow-release effects, but due to the residues of coating agents and urease inhibitors, they cause secondary pollution to the land. Long-term use has caused soil compaction, which is an indisputable fact.

[0005] Oxamide is a poorly soluble organic nitrogen compound with low water solubility at room temperature. It is a highly efficient slow-release nitrogen fertilizer with high nitrogen utilization and a slow-release nitrogen characteristic, which can match the nutrient requirements of crops throughout their entire growth cycle. Oxamide is expensive and is suitable for high-end applications and food and cash crops when used alone.

[0006] To expand the application scenarios of oxamide and synergistically improve the utilization rate of nutrients in other fast-dissolving fertilizers, developing a new type of fertilizer with synergistic effects of oxamide groups and core is one of the future development directions. Combining the synergistic effects of biological agents and polyhydroxy acids, the goal is to achieve four effects of "reduced dosage, slow release, long-lasting effect, soil nourishment and increased yield", with excellent granular performance and environmentally friendly oxamide-based slow-release fertilizer and its preparation method.

[0007] Patent CN202110301388.9 discloses a slow-release fertilizer produced by spraying ammonium phosphate solution. The process involves simply melting a high-concentration ammonium phosphate emulsion with water-soluble raw materials such as ammonium bicarbonate and urea, then spraying and granulating the mixture. The granules are homogeneous internally, lacking an outer shell. The nitrogen release rate is highly dependent on temperature and humidity, and is essentially completed within 30–60 days, failing to meet the needs of a single basal application throughout the crop's growth cycle. Patent CN102304003A discloses an oxamide-based slow-release nitrogen fertilizer, which simply mixes oxamide and urea. The granules remain homogeneous, lacking both an outer shell and a core for readily available nutrients, resulting in insufficient nitrogen supply in the early stages and nutrient deficiency in the later stages. Patent CN115677409A proposes a double-layer coated compound fertilizer. Although it is nominally "double-layered", its inner layer is a nitrogen, phosphorus and potassium mixed melt, and the outer layer is a sulfur / resin coating. Both layers are continuous phase coatings, lacking the "core-shell" functional partition, and no biological agents are introduced, so it cannot simultaneously achieve nutrient supply and soil micro-ecological restoration.

[0008] Overall, the main problems with current technologies are: 1. Single slow-release system, with nitrogen source mainly being fast-acting. Ammonium phosphate, ammonium bicarbonate, and urea are all highly water-soluble and release rapidly, which does not coincide with the peak fertilizer demand of crops in the middle and late stages, requiring multiple topdressings and resulting in low nitrogen utilization; 2. Lack of biological activity: Current technologies do not combine biological agents with the slow-release system, making it impossible to simultaneously achieve nutrient supply and soil microecological restoration; 3. Fixed slow-release cycle: Traditional slow-release fertilizers cannot dynamically adjust the nutrient release rate according to the needs of crop growth stages.

[0009] In summary, most existing technologies use single oxamide or simple physical mixtures, which fail to solve problems such as insufficient fast-acting nitrogen in the early stage, low particle strength, and easy inactivation of biological agents, and have not formed a truly meaningful "core-shell" structured slow-release system. Summary of the Invention

[0010] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a long-acting slow-release fertilizer with a core-shell structure based on oxalamide multi-nitrogen source, its preparation method and application, to solve many problems that need to be solved in the practical application of slow-release fertilizer, to achieve a dynamic balance between rapid nitrogen supply and long-acting slow release, and at the same time improve particle strength and maintain biological activity, so as to meet the needs of modern agriculture for efficient, environmentally friendly and intelligent fertilization.

[0011] The technical solution of this invention is:

[0012] This invention provides a long-acting slow-release fertilizer with a core-shell structure based on oxalamide multi-nitrogen source. The slow-release fertilizer has a core-shell structure, which includes a core region and an outer shell. The core region includes at least a fast-acting core. The raw materials of the fast-acting core include a fast-acting nitrogen source, trace element compounds, humic substances, polyhydroxy acids, and a first adjuvant. The raw materials of the outer shell include the slow-release nitrogen source oxalamide, a second adjuvant, and a biological agent.

[0013] In some embodiments of the present invention, the kernel region further includes n kernel fast-acting layers and n kernel slow-release layers, and the core-shell structure includes, from the inside out, a fast-acting core, a first kernel slow-release layer, a first kernel fast-acting layer, ..., an nth kernel slow-release layer, an nth kernel fast-acting layer and a shell; wherein, n≥0.

[0014] Another aspect of the present invention provides a method for preparing a long-acting slow-release fertilizer with a core-shell structure based on oxalamide multi-nitrogen source, the preparation method comprising the following steps:

[0015] 1) Mix the fast-acting nitrogen source, trace element compounds, humic substances, polyhydroxy acids and the first auxiliary agent evenly and then crush them to obtain the raw material of the core region;

[0016] 2) The slow-release nitrogen source oxamide, the second adjuvant, and the biological agent are mixed to obtain the shell material;

[0017] 3) Using the granulation method, the raw material in the core region is formed into the core region, and then the raw material in the outer shell is sprayed into the surface of the core region to obtain a slow-release fertilizer with a core-shell structure.

[0018] In some embodiments of the present invention, in step 1), the fast-acting nitrogen source, trace element compound, humic substance, polyhydroxy acid and first auxiliary agent are mixed evenly and pulverized to obtain fast-acting core material and core fast-acting layer material. The core fast-acting layer material is divided into the first core fast-acting layer material to the nth core fast-acting layer material.

[0019] Step 2) also includes mixing the slow-release nitrogen source oxamide, the second adjuvant and the biological agent to obtain the core slow-release layer raw material, and the core slow-release layer raw material is divided into the first core slow-release layer raw material to the nth core slow-release layer raw material;

[0020] In step 3), the granulation method is used to form a fast-acting core material into a fast-acting core, and then the first core slow-release layer material and the first core fast-acting layer material are sprayed in sequence. This process is repeated, and finally the nth core slow-release layer material and the nth core fast-acting layer material are sprayed in sequence to form a multi-layer fast-acting-slow-release core region. The outer shell material is sprayed on the surface of the core region to obtain a core-shell structured slow-release fertilizer.

[0021] In another aspect, this invention provides the application of the oxamyl-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer according to the present invention and / or the oxamyl-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer prepared by the preparation method of the oxamyl-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer according to the present invention in food crops and cash crops.

[0022] By adopting the aforementioned technical solution, the beneficial effects of the present invention are:

[0023] 1. Through an innovative dual-zone structure design of "core zone-outer shell," a perfect combination of rapid effect and slow release is achieved. The rapid-acting core and / or core rapid-acting layer in the core zone uses a combination of rapidly acting nitrogen and trace element compounds, which can quickly release nutrients within 15 minutes to meet the early growth needs of crops; the outer shell and / or core slow-release layer is composed of oxalamide, biological agents, and polyhydroxy acids, which achieve gradient release through the unique slow-release characteristics of oxalamide (50-200 days), precisely matching the "S"-shaped nutrient requirement curve of crops throughout their entire growth period. This design solves the technical problem of traditional fertilizers' inability to simultaneously achieve rapid effect and slow release.

[0024] 2. Employing a 30-60℃ low-temperature rotary ball rolling process ensures granulation quality while maintaining the activity rate of the biological agent at over 85%. Through the synergistic effect of the biological agent and polyhydroxy acid, not only is slow-release of nutrients achieved, but also soil improvement, root promotion, and disease resistance enhancement are simultaneously realized, significantly improving the functionality of the fertilizer.

[0025] 3. It exhibits outstanding environmental friendliness. Its main raw materials, oxalamide and polyglutamic acid, are completely biodegradable. The production process leaves no sulfur residue in acidic soils and no resin film pollution in acidic or alkaline soils, achieving zero environmental burden. Practical applications show that this fertilizer can increase yields in field crops such as rice, wheat, and corn with reduced application rates, and is particularly suitable for forestry, forage grasses, and flowers—fields requiring long-term nitrogen supply.

[0026] 4. During the slow-release process of oxalamide, microbial activity is promoted, soil activity is enhanced, continuous cropping obstacles are reduced, and the absorption efficiency of other nutrients is improved. Through its unique chemical properties and technological innovation, it achieves the goals of efficient, environmentally friendly, and labor-saving fertilization, making it an ideal substitute for traditional nitrogen fertilizers, especially suitable for the needs of large-scale agriculture and sustainable agricultural development.

[0027] 5. In terms of soil improvement, this invention achieves significant improvement in soil microecology through the synergistic effect of biological agents and polyhydroxy acids. Biological agents effectively improve the rhizosphere microecology of crops, promoting the growth and reproduction of beneficial microorganisms, thereby enhancing soil biological activity. Simultaneously, polyhydroxy acids significantly improve soil aggregate structure, reduce soil compaction, and thus improve soil aeration and permeability, creating a better soil environment for crop root growth. This soil improvement effect not only helps improve crop growth quality and yield but also gradually improves soil quality over long-term use, promoting sustainable agricultural development.

[0028] 6. In terms of application, the slow-release fertilizer of this invention offers significant ease of use. A single basal application can meet the nutrient requirements of crops throughout their entire growth cycle, effectively reducing the frequency of topdressing required in traditional fertilization (typically 3-4 times). This one-time fertilization method not only saves labor and time costs but also reduces soil disturbance caused by multiple fertilizations, further protecting soil structure and the ecological environment. This invention achieves four benefits: reduced dosage, slow release, long-lasting effect, and soil nourishment and yield increase. It also features excellent granular performance and an environmentally friendly oxalamide-based slow-release fertilizer and its preparation method.

[0029] Oxalide slow-release fertilizer, through its unique chemical properties and innovative processing, achieves the goals of efficient, environmentally friendly, and labor-saving fertilization, making it an ideal substitute for traditional nitrogen fertilizers. During the slow-release process, oxalamide promotes microbial activity, enhances soil activity, reduces continuous cropping obstacles, and improves the absorption efficiency of other nutrients. Its unique chemical properties and innovative processing achieve the goals of efficient, environmentally friendly, and labor-saving fertilization, making it an ideal substitute for traditional nitrogen fertilizers, especially suitable for the needs of large-scale agriculture and sustainable agricultural development. Detailed Implementation

[0030] The following details the implementation methods of the oxamyl-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer, its preparation method, and its applications provided by this invention.

[0031] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0032] Existing slow-release fertilizers suffer from the following technical shortcomings: Firstly, the inadequacy of oxalamide slow-release fertilizers. Most existing oxalamide fertilizers are simply mixed with urea or melt-granulated, resulting in a uniform structure and slow nitrogen release in the early stages, making seedlings prone to nutrient deficiency. Simultaneously, the low particle strength and tendency to pulverize hinder mechanized fertilization. Furthermore, traditional oxalamide fertilizers lack bioactive components, failing to simultaneously improve soil microecology and hindering soil-crop synergistic regulation. Secondly, the compatibility between biological agents and slow-release systems is poor, especially under high-temperature processing conditions, where the activity of biological agents is easily lost, thus failing to fully exert their effects on improving soil microecology and promoting crop growth. Moreover, most existing slow-release fertilizers lack a synergistic effect on improving soil microecology, failing to optimize the soil environment as a whole to better promote crop growth. These problems not only limit the widespread application of slow-release fertilizers in agricultural production but also fail to meet the current requirements for sustainable agricultural development and carbon emission reduction. Therefore, there is an urgent need to develop a novel slow-release fertilizer to overcome the shortcomings of existing technologies and provide a core-shell structured slow-release fertilizer that achieves a dynamic balance between rapid nitrogen supply and long-term slow release, while simultaneously improving particle strength and maintaining biological activity, thus meeting the demands of modern agriculture for efficient, environmentally friendly, and intelligent fertilization. This invention achieves controlled slow release over 50–200 days, with nitrogen utilization 1.25–2 times higher than conventional compound fertilizers, significantly improving nitrogen and carbon utilization and reducing carbon emissions into the atmosphere. 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. Based on this, this application was completed.

[0033] [Oxalide-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer]

[0034] This invention provides a long-acting slow-release fertilizer with a core-shell structure based on oxalamide multi-nitrogen source. The slow-release fertilizer has a core-shell structure, which includes a core region and an outer shell. The core region includes at least a fast-acting core. The raw materials of the fast-acting core include a fast-acting nitrogen source, trace element compounds, humic substances, polyhydroxy acids, and a first adjuvant. The raw materials of the outer shell include the slow-release nitrogen source oxalamide, a second adjuvant, and a biological agent.

[0035] The present invention includes both a two-layer scheme of a fast-acting core and a shell, and a scheme of a fast-acting core, a multi-layered core fast-acting layer, a multi-layered core sustained-release layer, and a shell. Specifically:

[0036] The core region further includes n fast-acting core layers and n slow-release core layers. The core-shell structure, from the inside out, includes a fast-acting core, a first slow-release core layer, a first fast-acting core layer, ..., an nth slow-release core layer, an nth fast-acting core layer, and an outer shell; where n ≥ 1. When n is 1, it includes only one slow-release core layer and one fast-acting core layer. Optionally, n ≥ 1, and further, n can be 1 to 7, 1 to 5, etc. More specifically, n is 1, 2, 3, 4, 5, 6, 7. Taking n = 3 as an example, the core-shell structure, from the inside out, includes a fast-acting core, a first slow-release core layer, a first fast-acting core layer, a second slow-release core layer, a second fast-acting core layer, a third slow-release core layer, a third fast-acting core layer, and an outer shell.

[0037] In this invention, the fast-acting core, the first kernel slow-release layer, the first kernel fast-acting layer, ..., the nth kernel slow-release layer, and the nth kernel fast-acting layer together constitute the kernel region.

[0038] In this invention, the raw materials of the core fast-acting layer are the same as those of the fast-acting core raw materials, including fast-acting nitrogen source, trace element compounds, humic substances, polyhydroxy acids and a first auxiliary agent.

[0039] In this invention, the raw materials of the core slow-release layer are the same as those of the outer shell, including the slow-release nitrogen source oxalamide, a second adjuvant, and a biological agent.

[0040] In the oxamyl-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer provided by this invention, the shell porosity is ≤20%, optionally ≤19%, ≤18%, ≤17%, ≤16%, ≤15%, etc. Preferably ≤15%, more preferably 5% to 15%.

[0041] The oxamid-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer provided by this invention comprises, by weight percentage:

[0042]

[0043] The adjuvants include a first adjuvant and a second adjuvant.

[0044] Further, the weight percentage of the slow-release nitrogen source oxalamide can be, for example, 8%–25%, 25%–50%, 50%–75%, 75%–95%, etc. The mass ratio of the slow-release nitrogen source oxalamide in the outer shell material to the slow-release nitrogen source oxalamide in each of the core slow-release layers is 1:10–100:1. Options include 1:10–90:1, 1:10–80:1, 1:10–70:1, 1:10–60:1, 1:10–50:1, 1:10–40:1, 1:10–20:1, 1:10–10:1, 1:3–100:1, 1:5–100:1, and 1:8–100:1. The mass percentage of the slow-release nitrogen source oxalamide in each core slow-release layer material is equal.

[0045] Further, the weight percentage of the readily available nitrogen source can be, for example, 1-15%, 15-30%, 30-45%, 45-68%, 68-83%, etc. Optionally, the readily available nitrogen source is selected from at least one of urea, ammonium sulfate, ammonium nitrate, monoammonium phosphate, ammonium carbonate, and ammonium chloride; at least one of these is one or more. In some embodiments, the mass ratio of the readily available nitrogen source in the readily available core material to the readily available nitrogen source in each of the readily available core layer materials is 1:0.7-1.1, optionally 1:0.8-1.1 or 1:0.9-1.1. Optionally, the mass percentage of the readily available nitrogen source in the readily available core material and the readily available nitrogen source in each of the readily available core layer materials is equal.

[0046] Further, the weight percentage of trace elements in the trace element compound can be, for example, 0.01%–1%, 1%–3%, 3%–5%, etc. Optionally, the trace elements are selected from at least one of magnesium, copper, zinc, boron, calcium, silicon, selenium, iron, and manganese. In some embodiments, the mass ratio of the trace element compound in the fast-acting core material to the trace element compound in each of the core fast-acting layer materials is 1:0.7–1.1, optionally 1:0.8–1.1 or 1:0.9–1.1. Optionally, the mass percentage content of the trace element compound in the fast-acting core material and the trace element compound in each of the core fast-acting layer materials is equal.

[0047] Further, the weight percentage of the humic substance can be, for example, 0.2%–1%, 1%–3%, 3%–5%, 5%–6%, etc. Optionally, the humic substance is selected from one or more of humic acid and fulvic acid. In some embodiments, the mass ratio of humic substance in the raw material of the fast-acting core to that in the raw material of each of the core fast-acting layers is 1:0.7–1.1; optionally, it is 1:0.8–1.1 or 1:0.9–1.1. Optionally, the mass percentage of humic substance in the raw material of the fast-acting core and that in the raw material of each of the core fast-acting layers is equal.

[0048] Further, the weight percentage of the polyhydroxy acid can be, for example, 0.2%–1%, 1%–3%, 1%–2%, 2%–3%, etc. Optionally, the polyhydroxy acid is selected from at least one of polyglutamic acid and polyhydroxy fatty acid esters. Polyglutamic acid is preferred. 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. In some embodiments, the mass ratio of the polyhydroxy acid in the fast-acting core material to the polyhydroxy acid in each of the core fast-acting layer materials is 1:0.7–1.1; optionally, it is 1:0.8–1.1 or 1:0.9–1.1. Optionally, the mass percentage of the polyhydroxy acid in the fast-acting core material and the polyhydroxy acid in each of the core fast-acting layer materials is equal.

[0049] Further, the weight percentage of the biological agent can be, for example, 0.1%–0.5%, 0.5%–1%, 0.1%–0.3%, 0.3%–0.5%, 0.5%–0.8%, 0.8%–1%, etc. The biological agent is selected from at least one of Bacillus subtilis, Bacillus mucilaginosus, Bacillus polymyxa, Bacillus amyloliquefaciens, and Trichoderma. A combination of Bacillus subtilis and Bacillus amyloliquefaciens is preferred. The biological agent retains ≥85% activity under processing conditions of 30–60°C, preferably ≥90%. In some embodiments, the mass ratio of the biological agent in the outer shell material to the biological agent in the core slow-release layer is 1:10–100:1. The ratios can be 1:10-90:1, 1:10-80:1, 1:10-70:1, 1:10-60:1, 1:10-50:1, 1:10-40:1, 1:10-20:1, 1:10-10:1, 1:3-100:1, 1:5-100:1, or 1:8-100:1. The percentage of bio-agent in each core slow-release layer raw material is equal.

[0050] Furthermore, the weight percentage of the additive may be, for example, 2%–5%, 5%–8%, 8%–10%, etc. Optionally, the additive may be a mineral, bentonite, attapulgite, or a combination thereof.

[0051] In some embodiments, the mass ratio of the first adjuvant to the second adjuvant is 1:1 to 1:100; alternatively, it can be 1:1 to 1:10, 1:1 to 1:20, 1:1 to 1:30, 1:1 to 1:40, 1:1 to 1:50, 1:1 to 1:60, 1:1 to 1:70, 1:1 to 1:80, or 1:1 to 1:90.

[0052] In some embodiments, the mass ratio of the first auxiliary agent in the fast-acting core material to the first auxiliary agent in each of the core fast-acting layers is 1:0.7 to 1.1; optionally, it is 1:0.8 to 1.1 or 1:0.9 to 1.1. Optionally, the mass percentage content of the first auxiliary agent in the fast-acting core material and the first auxiliary agent used in each of the core fast-acting layers is equal.

[0053] In some embodiments, the mass ratio of the second auxiliary agent in the outer shell material to the second auxiliary agent in each of the core sustained-release layer materials is 1:10-100:1; optionally, it is 1:10-90:1, 1:10-80:1, 1:10-70:1, 1:10-60:1, 1:10-50:1, 1:10-40:1, 1:10-20:1, 1:10-10:1, 1:3-100:1, 1:5-100:1, or 1:8-100:1. The mass percentage of the second auxiliary agent in each core sustained-release layer material is equal.

[0054] The specific choices for the first and second adjuvants are the same: minerals, bentonite, attapulgite, or combinations thereof.

[0055] The oxamyl-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer provided by this invention has a nitrogen content of 30-41%. Optionally, the nitrogen content of the slow-release fertilizer can be, for example, 30-35%, 35-41%, etc.

[0056] Preparation method of oxalamide-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer

[0057] This invention also provides a method for preparing a long-acting slow-release fertilizer with a core-shell structure based on oxalamide multi-nitrogen source, the preparation method comprising the following steps:

[0058] 1) Mix the fast-acting nitrogen source, trace element compounds, humic substances, polyhydroxy acids and the first auxiliary agent evenly and then crush them to obtain the raw material of the core region;

[0059] 2) The slow-release nitrogen source oxamide, the second adjuvant, and the biological agent are mixed to obtain the shell material;

[0060] 3) Using the granulation method, the raw material in the core region is formed into the core region, and then the outer shell raw material is sprayed into the surface of the core region to obtain a slow-release fertilizer with a core-shell structure.

[0061] When the core contains a fast-acting layer, in step 1), the fast-acting nitrogen source, trace element compounds, humic substances, polyhydroxy acids, and the first adjuvant are mixed evenly and pulverized to obtain fast-acting core raw materials and core fast-acting layer raw materials. The core fast-acting layer raw materials are divided into the first core fast-acting layer raw materials to the nth core fast-acting layer raw materials. In step 2), the slow-release nitrogen source oxalamide, the second adjuvant, and the biological agent are mixed to obtain core slow-release layer raw materials. The core slow-release layer raw materials are divided into the first core slow-release layer raw materials to the nth core slow-release layer raw materials. In step 3), the fast-acting core raw materials are formed into fast-acting cores using a granulation method. Then, the first core slow-release layer raw materials and the first core fast-acting layer raw materials are sprayed in sequentially. This process is repeated. Finally, the nth core slow-release layer raw materials and the nth core fast-acting layer raw materials are sprayed in sequentially to form a multi-layered fast-acting-slow-release core region. The outer shell raw materials are sprayed onto the surface of the core region to obtain a core-shell structured slow-release fertilizer.

[0062] In step 1) of this invention, the mixture is uniformly mixed and pulverized to 40-80 mesh, which can be selected as 40-50 mesh, 50-70 mesh or 70-80 mesh, etc.

[0063] In step 2) of this invention, the slow-release nitrogen source oxamide, the second adjuvant, and the biological agent are added to a rotary ball mill at a rotation speed of 10–100 r / min, preferably 21–90 r / min; a feed rate of 50–100 kg / h, optionally 50–70 kg / h or 70–100 kg / h; and a coating temperature of 30–60°C, preferably 35–50°C, to form the core slow-release layer raw material and / or the outer shell raw material, i.e., the core slow-release layer slurry and / or the outer shell slurry. The biological agent is added during the low-temperature atomization stage at 30–40°C, preferably 35–38°C.

[0064] In step 3) of this invention, the outer shell accounts for 10% to 50% of the total weight of the slow-release fertilizer granules, and can be selected as 10% to 15%, 15% to 40%, 40% to 50%, etc. Preferably, it is 15% to 40%.

[0065] In step 3) of this invention, the porosity of the outer shell is ≤20%. Optionally, the porosity is ≤19%, ≤18%, ≤17%, ≤16%, ≤15%, etc. Preferably, it is ≤15%.

[0066] In step 3) of this invention, the granulation method is selected from one of rotary disc granulation and rotary drum granulation, preferably rotary disc granulation.

[0067] In step 3) of this invention, after the outer shell material is sprayed in, drying and sieving are also included: drying at a low temperature of 30-60°C until the water content is ≤2%, preferably ≤1.5%, and after cooling, sieving by 2-5mm, preferably 2.5-3.5mm, to obtain the core-shell structured slow-release fertilizer product.

[0068]

application

[0069] The present invention also provides the application of the oxamid-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer according to the present invention and / or the oxamid-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer prepared by the preparation method of the oxamid-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer according to the present invention in food crops and cash crops.

[0070] Slow-release fertilizers are suitable for single application to grain crops and cash crops.

[0071] The beneficial effects of the present invention will be further illustrated below with reference to the embodiments.

[0072] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention is further described in detail below with reference to embodiments. However, it should be understood that the embodiments of this invention are merely for illustrative purposes and not for limiting the invention, and the embodiments are not limited to those given in the specification. Unless otherwise specified, specific experimental or operational conditions in the embodiments were prepared under conventional conditions or according to the conditions recommended by the material supplier.

[0073] Furthermore, it should be understood that the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, does not preclude the existence of other method steps before or after the combined steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. It should also be understood that the combined connection relationship between one or more devices / apparatus mentioned in this invention does not preclude the existence of other devices / apparatus before or after the combined devices / apparatus, or the insertion of other devices / apparatus between these explicitly mentioned devices / apparatus, unless otherwise stated. Moreover, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and not for limiting the order of the method steps or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0074] In the following embodiments, unless otherwise specified, all the raw materials of the present invention are commercially available or prepared according to conventional methods in the art.

[0075] Example 1

[0076] This embodiment provides a long-acting slow-release fertilizer with a core-shell structure based on oxalamide multi-nitrogen source. The core-shell structure includes a core region and an outer shell. The core region includes a fast-acting core, a core fast-acting layer, and a core slow-release layer. The core fast-acting layer includes three core fast-acting layers (1-3), and the core slow-release layer includes three core slow-release layers (1-3). The slow-release fertilizer, from the inside out, includes a fast-acting core, a first core slow-release layer, a first core fast-acting layer, a second core slow-release layer, a second core fast-acting layer, a third core slow-release layer, a third core fast-acting layer, and an outer shell.

[0077] The preparation method includes the following steps:

[0078] 1) Mix urea, compounds containing trace elements (magnesium sulfate), humic acid, fulvic acid, polyhydroxy acid, and a portion of clay according to Table 2. After crushing, pass the mixture through a 60-mesh sieve to obtain the core region raw material. Divide the raw material into 4 equal portions to obtain the fast-acting core raw material, the first core fast-acting layer raw material to the third core fast-acting layer raw material.

[0079] 2) Prepare the core slow-release layer raw material and the outer shell slurry by mixing oxamide, residual clay and biological agent according to the metering ratio in Table 2. The mass ratio of the core slow-release layer raw material and the outer shell slurry is 2:1. Divide the core slow-release layer raw material into 3 equal parts to obtain the first core slow-release layer raw material to the third core slow-release layer raw material.

[0080] The mass ratio of a portion of the soil to the remaining soil is 1:60. The specific selection and activity of the biological agent are shown in Table 1.

[0081] 3) Rotary ball-rolling process: Rotary speed 21 r / min, inclination angle 46°, feed rate 80 kg / h, coating temperature 45℃. First, fast-acting core material is added to form the fast-acting core. Then, the first core slow-release layer material is sprayed in sequentially, followed by the first core fast-acting layer material, then the second core slow-release layer material is sprayed in sequentially, followed by the second core fast-acting layer material, and so on, alternating between these steps. The third core slow-release layer material is then sprayed in, followed by the third core fast-acting layer material, and finally, the outer shell slurry is sprayed in. The outer shell porosity is 18%. After drying to a moisture content of 1.8%, the product is cooled and sieved to obtain particles with a diameter of 2–5 mm.

[0082] Example 2

[0083] This embodiment provides a long-acting slow-release fertilizer with a core-shell structure based on oxalamide multi-nitrogen source. The core-shell structure includes a core region and an outer shell. The core region includes a fast-acting core, a core fast-acting layer, and a core slow-release layer. The core fast-acting layer includes three core fast-acting layers (1-3), and the core slow-release layer includes three core slow-release layers (1-3). The slow-release fertilizer, from the inside out, includes a fast-acting core, a first core slow-release layer, a first core fast-acting layer, a second core slow-release layer, a second core fast-acting layer, a third core slow-release layer, a third core fast-acting layer, and an outer shell.

[0084] The preparation method includes the following steps:

[0085] 1) Mix urea, compounds containing trace elements (magnesium sulfate), humic acid, fulvic acid, polyhydroxy acid, and a portion of clay according to Table 2. After crushing, pass the mixture through a 60-mesh sieve to obtain the core region raw material. Divide the raw material into 4 equal portions to obtain the fast-acting core raw material, the first core fast-acting layer raw material to the third core fast-acting layer raw material.

[0086] 2) Prepare the core slow-release layer raw material and the outer shell slurry by mixing oxamide, residual clay and biological agent according to the metering ratio in Table 2. The mass ratio of the core slow-release layer raw material and the outer shell slurry is 1.5:1. Divide the core slow-release layer raw material into 3 equal parts to obtain the first core slow-release layer raw material to the third core slow-release layer raw material.

[0087] The mass ratio of a portion of the soil to the remaining soil is 1:60. The specific selection and activity of the biological agent are shown in Table 1.

[0088] 3) Rotary ball coating process: Rotary speed 21 r / min, inclination angle 46°, feed rate 80 kg / h, coating temperature 45℃. First, fast-acting core material is added to form the fast-acting core. Then, the first core slow-release layer material is sprayed in sequentially, followed by the first core fast-acting layer material, then the second core slow-release layer material is sprayed in sequentially, followed by the second core fast-acting layer material, and so on, alternating between these steps. The third core slow-release layer material is then sprayed in, and finally, the outer shell slurry is sprayed in. The outer shell porosity is 15%. The product is dried to a moisture content of 1.8%, cooled, and sieved to obtain a particle diameter of 2–5 mm.

[0089] Example 3

[0090] This embodiment provides a long-acting slow-release fertilizer with a core-shell structure based on oxalamide multi-nitrogen source. The core-shell structure includes a core region and an outer shell. The core region includes a fast-acting core, a core fast-acting layer, and a core slow-release layer. The core fast-acting layer includes three core fast-acting layers (1-3), and the core slow-release layer includes three core slow-release layers (1-3). The slow-release fertilizer, from the inside out, includes a fast-acting core, a first core slow-release layer, a first core fast-acting layer, a second core slow-release layer, a second core fast-acting layer, a third core slow-release layer, a third core fast-acting layer, and an outer shell.

[0091] The preparation method includes the following steps:

[0092] 1) Mix urea, compounds containing trace elements (magnesium sulfate), humic acid, fulvic acid, polyhydroxy acid, and a portion of clay according to Table 2. After crushing, pass the mixture through a 60-mesh sieve to obtain the core region raw material. Divide the raw material into 4 equal portions to obtain the fast-acting core raw material, the first core fast-acting layer raw material to the third core fast-acting layer raw material.

[0093] 2) Prepare the core slow-release layer raw material and the outer shell slurry by mixing oxamide, residual clay and biological agent according to the metering ratio in Table 2. The mass ratio of the core slow-release layer raw material and the outer shell slurry is 1:1. Divide the core slow-release layer raw material into 3 equal parts to obtain the first core slow-release layer raw material to the third core slow-release layer raw material.

[0094] The mass ratio of a portion of the soil to the remaining soil is 1:60. The specific selection and activity of the biological agent are shown in Table 1.

[0095] 3) Rotary ball coating process: Rotary speed 21 r / min, inclination angle 46°, feed rate 80 kg / h, coating temperature 45℃. First, fast-acting core material is added to form the fast-acting core. Then, the first core slow-release layer material is sprayed in sequentially, followed by the first core fast-acting layer material, then the second core slow-release layer material is sprayed in sequentially, followed by the second core fast-acting layer material, and so on, alternating between these steps. The third core slow-release layer material is then sprayed in, and finally, the outer shell slurry is sprayed in. The outer shell porosity is 12%. The product is dried to a moisture content of 1.8%, cooled, and sieved to obtain a particle diameter of 2–5 mm.

[0096] Example 4

[0097] This embodiment provides a long-acting slow-release fertilizer with a core-shell structure based on oxalamide multi-nitrogen source. The core-shell structure includes a core region and an outer shell. The core region includes a fast-acting core, a core fast-acting layer, and a core slow-release layer. The core fast-acting layer includes three core fast-acting layers (1-3), and the core slow-release layer includes three core slow-release layers (1-3). The slow-release fertilizer, from the inside out, includes a fast-acting core, a first core slow-release layer, a first core fast-acting layer, a second core slow-release layer, a second core fast-acting layer, a third core slow-release layer, a third core fast-acting layer, and an outer shell.

[0098] The preparation method includes the following steps:

[0099] 1) Mix urea, compounds containing trace elements (magnesium sulfate), humic acid, fulvic acid, polyhydroxy acid, and a portion of clay according to Table 2. After crushing, pass the mixture through a 60-mesh sieve to obtain the core region raw material. Divide the raw material into 4 equal portions to obtain the fast-acting core raw material, the first core fast-acting layer raw material to the third core fast-acting layer raw material.

[0100] 2) Prepare the core slow-release layer raw material and the outer shell slurry by mixing the oxamide, residual clay and biological agent according to the metering ratio in Table 2. The mass ratio of the core slow-release layer raw material and the outer shell slurry is 1:1.5. Divide the core slow-release layer raw material into 3 equal parts to obtain the first core slow-release layer raw material to the third core slow-release layer raw material.

[0101] The mass ratio of a portion of the soil to the remaining soil is 1:60. The specific selection and activity of the biological agent are shown in Table 1.

[0102] 3) Rotary ball-rolling process: Rotary speed 21 r / min, inclination angle 46°, feed rate 80 kg / h, coating temperature 45℃. First, fast-acting core material is added to form the fast-acting core. Then, the first core slow-release layer material is sprayed in sequentially, followed by the first core fast-acting layer material, then the second core slow-release layer material is sprayed in sequentially, followed by the second core fast-acting layer material, and so on, alternating between these steps. The third core slow-release layer material is then sprayed in, and finally, the outer shell slurry is sprayed in. The outer shell porosity is 10%. The product is dried to a moisture content of 1.8%, cooled, and sieved to obtain a particle diameter of 2–5 mm.

[0103] Example 5

[0104] This embodiment provides a oxamyl-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer, which differs from Embodiment 1 in that it does not have a core fast-acting layer and a core slow-release layer; it only has a fast-acting core and a shell. Specifically, the raw material composition and formulation of the compound fertilizer are shown in Table 2. Oxalide is divided into two parts, and attapulgite is divided into two parts. The preparation method of the compound fertilizer is as follows:

[0105] 1) Mix urea, compounds containing trace elements (magnesium sulfate), humic acid, fulvic acid, polyhydroxy acid, and a portion of clay according to Table 2, crush them, and pass them through a 60-mesh sieve to obtain fast-acting nuclear raw materials.

[0106] 2) Prepare the shell slurry by mixing oxamide, residual clay, and biological agent according to the metering ratio in Table 2.

[0107] The mass ratio of a portion of the soil to the remaining soil is 1:60. The specific selection and activity of the biological agent are shown in Table 1.

[0108] The process employs a rotary ball-rolling process: rotary table speed 21 r / min, inclination angle 46°, feed rate 80 kg / h, and coating temperature 45℃. First, fast-acting nucleus material is added to form the core, then the outer shell slurry is sprayed in, with an outer shell porosity of 18%. After drying to a moisture content of 1.8%, the product is cooled and sieved to obtain particles with a diameter of 2–5 mm.

[0109] Comparative Examples 1-4: Commercially available agricultural urea, specifically Hubei Saning Chemical Agricultural Urea (nitrogen content: ≥46%, particle diameter 3-4.5mm), was used.

[0110] The urea used in the examples is also commercially available agricultural urea, specifically Hubei Saning Chemical's agricultural urea.

[0111] Table 1. Selection of adjuvants and core-shell parameters in the formulation.

[0112]

[0113] Table 2 Content of each embodiment and comparative example formulation

[0114]

[0115] The urea from Examples 1-5 and the comparative examples were used in different test sites and on different crops. The performance of the urea in different test sites and on different crops is shown in Table 3.

[0116] Table 3. Fertilizer performance of each embodiment and comparative example.

[0117]

[0118] In summary, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0119] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any form or substance. It should be noted that those skilled in the art can make various improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention. Any modifications, alterations, and equivalent changes made by those skilled in the art based on the above-disclosed technical content without departing from the spirit and scope of the present invention are equivalent embodiments of the present invention. Furthermore, any modifications, alterations, and evolutions made to the above embodiments based on the essential technology of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A long-acting slow-release fertilizer with a core-shell structure of oxalamide-based multi-nitrogen source, characterized in that, The slow-release fertilizer has a core-shell structure, which includes a core region and an outer shell. The core region includes at least a fast-acting core, and the raw materials of the fast-acting core include a fast-acting nitrogen source, trace element compounds, humic substances, polyhydroxy acids, and a first adjuvant. The raw materials of the outer shell include a slow-release nitrogen source, oxalamide, a second adjuvant, and a biological agent.

2. The oxamyl-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer according to claim 1, characterized in that, The kernel region further includes n kernel fast-acting layers and n kernel slow-release layers. The core-shell structure, from the inside out, includes a fast-acting core, a first kernel slow-release layer, a first kernel fast-acting layer, ..., an nth kernel slow-release layer, an nth kernel fast-acting layer, and an outer shell; where n ≥ 1.

3. The oxamyl-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer according to claim 2, characterized in that, It also includes one or more of the following conditions: A1) The raw material of the fast-acting core layer is the same as the raw material of the fast-acting core; A2) The raw material of the core slow-release layer is the same as that of the outer shell; A3) n is 1 to 7, preferably 1 to 5.

4. The oxamyl-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer according to claim 1, characterized in that, The porosity of the outer shell is ≤20%, preferably ≤15%.

5. The oxamyl-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer according to any one of claims 1 to 4, characterized in that, The raw materials of the slow-release fertilizer, by weight percentage, include: The adjuvants include a first adjuvant and a second adjuvant.

6. The oxamyl-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer according to claim 5, characterized in that, It also includes one or more of the following conditions: C1) The fast-acting nitrogen source is selected from at least one of urea, ammonium sulfate, ammonium nitrate, monoammonium phosphate, ammonium carbonate, and ammonium chloride; C2) The trace elements in the trace element compound are selected from at least one of magnesium, copper, zinc, boron, calcium, silicon, selenium, iron, and manganese; C3) The humic substance is selected from at least one of humic acid and fulvic acid; C4) The polyhydroxy acid is selected from at least one of polyglutamic acid and polyhydroxy fatty acid esters; preferably polyglutamic acid; C5) Both the first and second additives are selected from minerals, bentonite, attapulgite or combinations thereof; C6) The mass ratio of the first auxiliary agent to the second auxiliary agent is 1:1 to 1:100; The mass ratio of the fast-acting nitrogen source in the fast-acting core material to the fast-acting nitrogen source in each of the core fast-acting layer materials is 1:0.7 to 1.1; The mass ratio of trace element compounds in the fast-acting core material and trace element compounds in each of the core fast-acting layer materials is 1:0.7 to 1.1; The mass ratio of humic substances in the fast-acting core material to humic substances in each of the fast-acting core layer materials is 1:0.7 to 1.1; The mass ratio of polyhydroxy acid in the fast-acting core material (C10) to polyhydroxy acid in each of the core fast-acting layer materials is 1:0.7 to 1.

1. The mass ratio of the first auxiliary agent in the fast-acting core material and the first auxiliary agent in each of the core fast-acting layer materials is 1:0.7 to 1.1; C12) The mass ratio of the second auxiliary agent in the outer shell material to the sum of the second auxiliary agents in each of the core sustained-release layer materials is 1:10-100:1; the mass percentage of the second auxiliary agent in each core sustained-release layer material is equal; C13) The mass ratio of the slow-release nitrogen source oxalamide in the outer shell material to the sum of the slow-release nitrogen source oxalamide in each core slow-release layer material is 1:10-100:1; the mass percentage of slow-release nitrogen source oxalamide in each core slow-release layer material is equal; C14) The mass ratio of the biological agent in the outer shell material to the sum of the biological agents in each core slow-release layer material is 1:10-100:1; the mass percentage of biological agent in each core slow-release layer material is equal; C15) The biological agent is selected from at least one of Bacillus subtilis, Bacillus mucilaginosus, Bacillus polymyxa, Bacillus amyloliquefaciens, and Trichoderma; preferably a combination of Bacillus subtilis and Bacillus amyloliquefaciens; The biological agent described in C16 retains ≥85% of its activity under process conditions of 30–60°C; The slow-release fertilizer nitrogen content described in C17 is 30-41%.

7. The method for preparing the oxamyl-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer according to any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: 1) Mix the fast-acting nitrogen source, trace element compounds, humic substances, polyhydroxy acids and the first auxiliary agent evenly and then crush them to obtain the raw material of the core region; 2) The slow-release nitrogen source oxamide, the second adjuvant, and the biological agent are mixed to obtain the shell material; 3) Using the granulation method, the raw material in the core region is formed into the core region, and then the raw material in the outer shell is sprayed into the surface of the core region to obtain a slow-release fertilizer with a core-shell structure.

8. The method for preparing the oxamyl-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer according to claim 7, characterized in that, Also includes: In step 1), the fast-acting nitrogen source, trace element compound, humic substance, polyhydroxy acid and the first auxiliary agent are mixed evenly and crushed to obtain fast-acting core material and core fast-acting layer material. The core fast-acting layer material is divided into the first core fast-acting layer material to the nth core fast-acting layer material. Step 2) also includes mixing the slow-release nitrogen source oxamide, the second adjuvant and the biological agent to obtain the core slow-release layer raw material, and the core slow-release layer raw material is divided into the first core slow-release layer raw material to the nth core slow-release layer raw material; In step 3), the granulation method is used to form a fast-acting core material into a fast-acting core, and then the first core slow-release layer material and the first core fast-acting layer material are sprayed in sequence. This process is repeated, and finally the nth core slow-release layer material and the nth core fast-acting layer material are sprayed in sequence to form a multi-layer fast-acting-slow-release core region. The outer shell material is sprayed on the surface of the core region to obtain a core-shell structured slow-release fertilizer.

9. The method for preparing the oxamyl-based multi-nitrogen source core-shell structured long-acting slow-release fertilizer according to claim 7 or 8, characterized in that, It also includes one or more of the following conditions: In step 1) of D1), mix thoroughly and grind to 40-80 mesh; In step 2) of D2), the slow-release nitrogen source oxalamide, the second adjuvant and the biological agent are added to the rotary ball mill at a speed of 10-100 r / min, a feeding rate of 50-100 kg / h and a coating temperature of 30-60℃ to form the outer shell material and / or the core slow-release layer material. In step 3), the granulation method is selected from either rotary disc granulation or rotary drum granulation. In step 3) of D4), the outer shell accounts for 10%–50% of the total weight of the slow-release fertilizer granules; In step 3) of D5, after the outer shell material is sprayed in, drying and sieving are also included to obtain a slow-release fertilizer with a core-shell structure.

10. The application of the oxamid-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer prepared according to any one of claims 1 to 6 and / or the oxamid-based multi-nitrogen source core-shell structure long-acting slow-release fertilizer prepared according to any one of claims 7 to 9 in food crops and cash crops.

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