Magnesium-containing controlled-release urea and preparation method thereof

Abstract

The invention belongs to the technical field of fertilizers, and particularly relates to magnesium-containing controlled-release urea and a preparation method thereof, and the magnesium-containing controlled-release urea is characterized in that magnesium or magnesium-boron, magnesium-zinc and magnesium-boron-zinc medium trace element combinations are added into large-particle urea, and then coating is carried out. According to the controlled-release urea, elements such as magnesium are added into molten urine, then roller granulation and cooling are carried out, and finally coating is carried out. According to the prepared product, urea, magnesium and other elements can be synchronously and slowly released for a long time, nitrogen, magnesium and other nutrients have synergistic benefits, the utilization rate of nitrogen fertilizer, magnesium and other elements can be further increased, robust growth of crops is promoted, the yield is increased, the quality is improved, the stress resistance is enhanced, and labor is saved; and the method is especially suitable for regions with relatively common lack of medium trace elements and high-added-value commercial crops, and has a wide practical application value.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer technology, specifically relating to a magnesium-containing controlled-release urea and its preparation method. Background Technology

[0002] In traditional agricultural planting, due to intensive cultivation, crops continuously remove micronutrients such as magnesium, boron, and zinc from the soil. Based on the fundamental theory of nutrient return, high crop yields require the replenishment of sufficient nutrients removed by crops; this is the theoretical basis of fertilization. Furthermore, excessive application of nitrogen, phosphorus, and potassium fertilizers (especially high-potassium fertilizers, which antagonize the absorption of micronutrients like magnesium and zinc) while neglecting the replenishment of micronutrients can lead to crop deficiencies in certain key nutrients, resulting in reduced yields. The following is an introduction to the functions of these three elements within crops.

[0003] In crops, magnesium is a core element of chlorophyll and directly participates in photosynthesis. Adding magnesium can significantly increase chlorophyll content in leaves, enhance photosynthetic efficiency, and provide more assimilates (carbohydrates) for plant growth. Magnesium acts as an activator or component of enzymes involved in carbohydrate metabolism, respiration (glycolysis), and energy transfer (ATP synthesis), and as an activator of key enzymes involved in nitrogen assimilation (converting inorganic nitrogen into organic nitrogen) (such as glutamine synthase), thus helping to improve nitrogen fertilizer utilization and protein synthesis efficiency. Boron, on the other hand, is crucial for the long-distance transport of sugars within plants, helping to transport photosynthetic products to organs such as grains, fruits, or tubers. It plays a decisive role in pollen tube elongation, fertilization, flowering, fruit setting, and seed formation. It is also related to cell wall synthesis (cross-linked pectin), and the formation of meristematic tissues and new cells such as root tips, shoot tips, and floral organs. Boron deficiency leads to severe problems such as flower and fruit drop, failure to bear fruit (e.g., in rapeseed), and fruit malformation (e.g., in citrus). Zinc is a key element in the synthesis of indoleacetic acid (IAA, the main auxin), which promotes cell elongation and division, and affects tillering, panicle formation, and plant height. It also participates in carbohydrate metabolism (such as sucrose synthesis), nitrogen metabolism, protein synthesis, and protects enzyme systems. Zinc is involved in the synthesis of chlorophyll precursors and the activity of enzymes related to photosynthesis. Zinc deficiency in rice can directly reduce yield by 30-50%.

[0004] Currently, in many agricultural production areas in China (such as acidic soils in the south, calcareous soils in the north, and greenhouse soils), available magnesium (Mg) is low. 2+The levels of magnesium, zinc, and boron are generally low or deficient, and these elements are more easily leached in acidic soils. In sandy soils, where water and fertilizer retention capacity is poor, they are also easily lost. The loss of magnesium, zinc, and boron during crop growth exacerbates the soil's magnesium, zinc, and boron deficiency. Furthermore, in conventional fertilizer production, high-phosphorus fertilizers can easily lead to antagonism between magnesium and zinc. Large amounts of magnesium and zinc applied can easily combine with and be fixed by phosphorus in the soil, affecting the movement of micronutrients and phosphorus. Boron, on the other hand, is highly mobile and extremely easy to lose with water. Therefore, supplementing with micronutrients such as magnesium, zinc, and boron, based on soil conditions and the target crop yield, is crucial for improving crop yield. Summary of the Invention

[0005] The technical problem this invention aims to solve is to provide a magnesium-containing controlled-release urea and its preparation method. The purpose is to use a molten urea drum granulation process to fuse magnesium and other micronutrients into urea particles, allowing for the simultaneous application of magnesium and other micronutrients in a single fertilization, matching the nutrient requirements of most crops. This enables magnesium to be released synchronously with nitrogen, achieving a synergistic effect. Furthermore, the controlled-release urea preparation process of this invention allows for the slow, prolonged release of magnesium / zinc / boron from urea, effectively avoiding phosphorus antagonism. The gradual release of magnesium / zinc / boron during the release period reduces nutrient loss, promotes more balanced nutrient absorption by crops at different stages, and reduces soil stress such as salinity and alkalinity.

[0006] One aspect of the present invention provides a magnesium-containing controlled-release urea, which is composed of a core and a coating material, wherein the core is a urea particle containing magnesium.

[0007] Furthermore, the fertilizer core also contains one or both of zinc and boron.

[0008] Furthermore, the fertilizer core includes:

[0009] Nitrogen 35-46 wt%

[0010] Magnesium content: 0.001–5 wt%

[0011] Zinc element 0–4.8 wt%

[0012] Boron element 0–2 wt%.

[0013] More preferably, the fertilizer core contains:

[0014] Nitrogen 40-46 wt%

[0015] Magnesium element 0.001~1wt%

[0016] Zinc element 0-0.5 wt%

[0017] Boron content: 0–0.3 wt%.

[0018] Furthermore, the raw materials for preparing the fertilizer core include urea, a zinc source, a boron source, and a magnesium source; the zinc source is selected from one or more combinations of zinc sulfate, zinc nitrate, and zinc chloride; the boron source is selected from one or more combinations of borax, boric acid, sodium octaborate tetrahydrate, and potassium octaborate; and the magnesium source is selected from one or more combinations of magnesium sulfate, magnesium nitrate, and magnesium chloride.

[0019] Furthermore, the coating material is polyurethane.

[0020] Furthermore, the amount of polyurethane used is 1.5 to 3 wt% of the fertilizer core.

[0021] Another aspect of the present invention provides a method for preparing the above-mentioned magnesium-containing controlled-release urea, comprising the following steps: weighing zinc source, boron source, and magnesium source, adding water and stirring until completely dissolved to obtain a near-saturated solution of trace elements, dispersing the near-saturated solution of trace elements in molten urea at 130-145°C in a certain proportion to form a mixed slurry, granulating the mixed slurry twice by roller granulation, cooling and sieving to obtain fertilizer cores; and then coating the fertilizer cores with a coating material to obtain magnesium-containing controlled-release urea.

[0022] Furthermore, by weight, the raw materials for preparing the fertilizer core contain 90-99.99 parts urea, 0.01-10 parts magnesium source, 0-6 parts zinc source, and 0-5 parts boron source.

[0023] The near-saturated solution of trace elements is prepared by gradually adding water to weighed zinc, boron, and magnesium sources, stirring until just completely dissolved, and allowing it to stand for more than 1 hour without precipitation. This step is to reduce the amount of water used, so that the water can completely evaporate when the solution is added to molten urea at a temperature above 137°C.

[0024] Furthermore, the specific steps of the secondary granulation in the drum include: dividing the mixed slurry into two parts; introducing cold air into the drum, first spraying the first part of the mixed slurry into the rotating drum for initial granulation, and after the initial granulation is completed, continuing to introduce cold air for 5-10 minutes to cool the particles; causing the rotating drum to continue rotating the particles obtained from the initial granulation, and continuing to spray the second part of the mixed slurry into the drum for secondary granulation, until all the mixed slurry has been sprayed. Further, the mass ratio of the two parts of the mixed slurry can be 1:0.5-1.

[0025] By using the secondary granulation technology of the drum, the particle size of magnesium-containing urea particles can be further increased, and the uniformity of particle size can be improved, thereby obtaining a fertilizer core suitable for coating.

[0026] Furthermore, in the roller granulation step, the roller inclination angle is 2 to 10°, the roller rotation speed is 10 to 25 r / min, and cold air at 0 to 25°C is introduced during the granulation process, with a cold air wind speed of 2 to 5 m / s.

[0027] Furthermore, after the granulation by the drum is cooled, fertilizer cores with a particle size of 3 to 4.75 mm are screened out; the fertilizer cores are then coated with polyester polyol and isocyanate.

[0028] Furthermore, the molar ratio of the hydroxyl groups of the polyester polyol to the NCO groups of the isocyanate is 1 to 1.05; the specific steps of the coating process can be referred to in the prior invention patents CN113512172A and CN114292390A.

[0029] The present invention has the following beneficial effects:

[0030] 1. This invention provides a magnesium-containing controlled-release urea and its preparation method. The urea is prepared using a drum secondary granulation process, in which elements such as magnesium, zinc, and boron are added to molten urea at 130–145°C. The fertilizer granules have uniform composition, with a coating material content of 1.5–3 wt%. The release period is approximately 30–120 days, effectively meeting the early-stage nutrient supply and later-stage nutrient balance of crops. For example, for different varieties of corn, the average growth period is approximately 100–130 days. Within the 120-day release period, it can effectively meet the nitrogen nutrient requirements of corn during the jointing and tasseling stages, as well as the supply of magnesium, boron, and zinc. It regulates nutrient absorption throughout the entire growth cycle, promotes fertilizer utilization, and increases crop yield.

[0031] 2. This invention provides a magnesium-containing controlled-release urea and its preparation method. The formula includes magnesium, boron, and zinc, with urea comprising 90%–99.99% of the total composition, and the total proportion of magnesium, boron, and zinc sources ranging from 0.01% to 10%. This specific combination of core fertilizer elements helps to synergistically enhance the effects of nitrogen, magnesium, zinc, and boron. For example, magnesium drives photosynthesis: chlorophyll contains Mg, and the energy-providing substance ATP requires Mg activation to assimilate nitrogen from urea, providing crops with a carbon skeleton (sugars) and energy (ATP). Magnesium directly activates glutamine synthase (GS), promoting the efficient conversion of nitrogen into protein. Zinc activates nitrogen-metabolizing enzymes such as carbonic anhydrase (CA), which promotes CO2 fixation, providing carbon for nitrogen absorption and amino acid synthesis. Boron participates in the regulation of sugar-nitrogen transport and reproductive differentiation. Magnesium, zinc, and boron are not only essential nutrients; adding these elements to urea and controlling their simultaneous release in appropriate proportions can synergistically enhance nitrogen fertilizer utilization, improve crop quality, and increase farmers' income.

[0032] 3. Typically, agricultural workers apply fertilizers in three or four applications of granular materials such as magnesium sulfate, zinc sulfate, and borax. This method is time-consuming, labor-intensive, and results in low fertilizer uniformity, low fertilizer utilization, and susceptibility to soil effects such as leaching and antagonism, further reducing fertilizer efficiency. This invention provides a magnesium-containing controlled-release urea and its preparation method, suitable for saline-alkali soils, sandy soils, acidic soils in southern regions with high rainfall, and salinized soils in facility agriculture. Its continuous release of magnesium, zinc, and boron helps crops obtain sustained amounts of these elements near their roots, significantly enhancing crop stress resistance. Simultaneously, the long-term release reduces rainwater runoff and fertilizer leaching, decreases soil EC (excessive organic matter), protects crop roots in saline-alkali and salinized soils, and reduces fertilizer-induced stress responses.

[0033] In summary, the magnesium-containing controlled-release urea and its preparation method of the present invention are reliable and practical. In soils with relatively low levels of magnesium, boron, and zinc, it effectively integrates with crop growth patterns, provides uniform nutrient release, reduces salt and alkali stress, and avoids nutrient stress and micronutrient antagonism caused by fertilizers. It is easy to operate, has low usage costs, increases crop yield and income, and improves crop quality. It has high economic and social value and is suitable for large-scale promotion and application. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention, and should not be used to limit the scope of protection of the present invention.

[0035] The polyester polyol used in the embodiments of the present invention was prepared by the method described in Example 5 of patent CN 113512172A. Other commercially available products or other polyester polyols described in the prior applications of the inventors may also be used as substitutes.

[0036] Example 1

[0037] This embodiment provides a magnesium-containing controlled-release urea, which consists of a core and a coating material. The core is a urea particle containing magnesium, wherein the nitrogen content is 44% and the magnesium content is 1%.

[0038] The raw materials for preparing the fertilizer core are: 95 parts urea and 5 parts magnesium sulfate; the coating material is polyurethane, and the amount of polyurethane used is 2.1 wt% of the fertilizer core mass. The nutrient content in the magnesium-containing controlled-release urea after coating is: nitrogen 43.4% and magnesium 0.98%.

[0039] Another aspect of this embodiment provides a method for preparing the above-mentioned magnesium-containing controlled-release urea, the steps of which include: weighing magnesium sulfate, adding water and stirring until completely dissolved to obtain a nearly saturated magnesium sulfate solution, dispersing it in molten urea at 137°C to prepare a mixed slurry; setting the drum inclination angle to 10° and the rotation speed to 20 r / min, introducing cold air at 0°C into the drum with a wind speed of 2 m / s, dividing the mixed slurry into two equal parts, first spraying the first part into the rotating drum for primary granulation, and maintaining the cold air supply for 5 minutes after the primary granulation to cool the particles; causing the rotating drum to continue rotating the particles obtained from the primary granulation, and continuing to spray the other part of the mixed slurry into the drum for secondary granulation, until all the mixed slurry has been sprayed. After naturally cooling to room temperature, fertilizer cores with a particle size of 3-4.75 mm are sieved out. Then, polyester polyol and isocyanate are sprayed on the surface of the fertilizer cores in a certain ratio (the molar ratio of the hydroxyl groups of polyester polyol and the NCO groups of isocyanate is 1:1) to form a film in situ and obtain magnesium-containing controlled-release urea.

[0040] Example 2

[0041] This embodiment provides a magnesium-containing controlled-release urea, which consists of a core and a coating material. The core is a urea particle containing magnesium, wherein the nitrogen content is 44%, the magnesium content is 0.8%, and the zinc content is 0.4%.

[0042] The raw materials for preparing the fertilizer core are: 95 parts urea, 4 parts magnesium sulfate, and 1 part zinc sulfate; the coating material is polyurethane, and the amount of polyurethane used is 2.1 wt% of the fertilizer core mass. The nutrient content in the magnesium-containing controlled-release urea after coating is: nitrogen 43.4%, magnesium 0.78%, and zinc 0.39%.

[0043] Another aspect of this embodiment provides a method for preparing the above-mentioned magnesium-containing controlled-release urea, the steps of which include: weighing magnesium sulfate and zinc sulfate, adding water and stirring until completely dissolved to obtain a near-saturated solution of trace elements, dispersing it in proportion in molten urea at 140° to prepare a mixed slurry; setting the roller inclination angle to 10° and the rotation speed to 20 r / min, introducing cold air at 10° to the roller with a wind speed of 3 m / s, dividing the mixed slurry into two equal parts, spraying the first part into the rotating roller for primary granulation, and maintaining the cold air supply for 5 minutes after the primary granulation to cool the particles; allowing the rotating roller to continue rotating the particles obtained from the primary granulation, and continuing to spray the other part of the mixed slurry into the roller for secondary granulation, until all the mixed slurry has been sprayed. After naturally cooling to room temperature, fertilizer cores with a particle size of 3-4.75 mm are sieved out. Then, polyester polyol and isocyanate are sprayed on the surface of the fertilizer cores in a certain ratio (the molar ratio of the hydroxyl groups of polyester polyol and the NCO groups of isocyanate is 1:1) to form a film in situ and obtain magnesium-containing controlled-release urea.

[0044] Example 3

[0045] This embodiment provides a magnesium-containing controlled-release urea, which consists of a core and a coating material. The core is a urea particle containing magnesium, wherein the nitrogen content is 44%, the magnesium content is 0.8%, and the boron content is 0.11%.

[0046] The raw materials for preparing the fertilizer core are: 95 parts urea, 4 parts magnesium sulfate, and 1 part borax; the coating material is polyurethane, and the amount of polyurethane used is 2.1 wt% of the fertilizer core mass. The nutrient content in the magnesium-containing controlled-release urea after coating is: nitrogen 43.4%, magnesium 0.78%, and boron 0.108%.

[0047] Another aspect of this embodiment provides a method for preparing the above-mentioned magnesium-containing controlled-release urea, the steps of which include: weighing magnesium sulfate and borax, adding water and stirring until completely dissolved to obtain a near-saturated solution of trace elements, dispersing it in proportion in molten urea at 140° to prepare a mixed slurry; setting the drum inclination angle to 10° and the rotation speed to 25 r / min, introducing cold air at 20° to the drum with a wind speed of 5 m / s, dividing the mixed slurry into two equal parts, first spraying the first part into the rotating drum for primary granulation, and after the primary granulation is completed, keeping the cold air flowing for 5 minutes to cool the particles; causing the rotating drum to continue rotating the particles obtained from the primary granulation, and continuing to spray the other part of the mixed slurry into the drum for secondary granulation, until all the mixed slurry has been sprayed. After naturally cooling to room temperature, fertilizer cores with a particle size of 3-4.75 mm are sieved out. Then, polyester polyol and isocyanate are sprayed on the surface of the fertilizer cores in a certain ratio (the molar ratio of the hydroxyl groups of polyester polyol and the NCO groups of isocyanate is 1:1) to form a film in situ and obtain magnesium-containing controlled-release urea.

[0048] Example 4

[0049] This embodiment provides a magnesium-containing controlled-release urea, which consists of a core and a coating material. The core is a urea particle containing magnesium, wherein the nitrogen content is 44%, the magnesium content is 0.6%, the zinc content is 0.4%, and the boron content is 0.11%.

[0050] The raw materials for preparing the fertilizer core are 95 parts urea, 3 parts magnesium sulfate, 1 part zinc sulfate, and 1 part borax; the coating material is polyurethane, and the amount of polyurethane used is 2.1 wt% of the fertilizer core mass. The nutrient content in the magnesium-containing controlled-release urea after coating is: nitrogen 43.4%, magnesium 0.59%, zinc 0.39%, and boron 0.108%.

[0051] Another aspect of this embodiment provides a method for preparing the above-mentioned magnesium-containing controlled-release urea, the steps of which include: weighing magnesium sulfate, zinc sulfate and borax, adding water and stirring until completely dissolved to obtain a near-saturated solution of trace elements, dispersing it in proportion in molten urea at 145° to prepare a mixed slurry; setting the drum inclination angle to 10° and the rotation speed to 25 r / min, introducing cold air at 10° to the drum with a wind speed of 4 m / s, dividing the mixed slurry into two equal parts, first spraying the first part into the rotating drum for primary granulation, and after the primary granulation is completed, keeping the cold air in the drum for 5 minutes to cool the particles; causing the rotating drum to continue rotating the particles obtained from the primary granulation, and continuing to spray the other part of the mixed slurry into the drum for secondary granulation, until all the mixed slurry has been sprayed. After naturally cooling to room temperature, fertilizer cores with a particle size of 3-4.75 mm are sieved out. Then, polyester polyol and isocyanate are sprayed on the surface of the fertilizer cores in a certain ratio (the molar ratio of the hydroxyl groups of polyester polyol and the NCO groups of isocyanate is 1:1) to form a film in situ and obtain magnesium-containing controlled-release urea.

[0052] Field Trial 1:

[0053] Crops planted: Corn

[0054] Planting location: Nenjiang City, Heilongjiang Province

[0055] Basic soil conditions: The arable land soil type is a thin layer of loess with a clayey bottom and black soil. The basic physicochemical properties of the topsoil are: pH 6.2, available phosphorus 36.7 mg / kg, available potassium 118 mg / kg, organic matter 40.9 g / kg, total nitrogen 2.09 g / kg, available magnesium 87.8 mg / kg, available zinc 2.6 mg / kg, and available boron 1.26 mg / kg.

[0056] Experimental variety: Huaqing No. 6 maize.

[0057] Experimental protocol: (The controlled-release urea used in the protocol was all controlled-release urea produced by Maoshi Agricultural Technology Co., Ltd. (45% sustained nitrogen, release period of 80 days))

[0058] Blank control group: Base application per mu: controlled-release urea (total nitrogen 10 kg), potassium sulfate 10 kg, and superphosphate 16 kg.

[0059] Experimental control group: Base application per acre: controlled-release urea (total nitrogen 10 kg), potassium sulfate 10 kg, 16 kg superphosphate, 0.3 kg magnesium sulfate, 0.1 kg zinc sulfate, 0.1 kg borax.

[0060] Experimental groups 1-4: Base application per mu: magnesium-containing controlled-release urea (total nitrogen 10 kg), potassium sulfate 18 kg, and superphosphate 16 kg of the present invention in Examples 1-4.

[0061] The experiment consisted of 6 treatments, each with 3 replicates, and the plot area was 46m². 2 The plots were randomly divided into blocks. Ditches were constructed between each plot to prevent water and fertilizer cross-contamination. Protective rows were established within each plot, with a row spacing of 60cm and a plant spacing of 40cm. Other field management practices followed local farmer customs. Sowing was carried out on May 18, 2024; seedlings emerged on June 4; and irrigation (sprinkler irrigation) was applied to a 15m² area on July 15. 3 / mu, and topdress with 10kg / mu of granulated urea. On August 10th, a sampling survey was conducted to investigate plant characteristics. In each plot, a five-point random sampling method was used to measure the plant height of five consecutive corn plants and the length*width (length: from leaf tip to leaf top; width: the widest part of the leaf) of the third leaf from the top. Actual yield was calculated on September 24th.

[0062] Table 1

[0063]

[0064] The results are as follows:

[0065] The actual yield results of maize under each fertilization treatment are shown in Table 1. The addition of magnesium, zinc, and boron promoted photosynthesis and synergistically improved nitrogen utilization, thereby increasing crop yield. The highest maize yield was achieved in the magnesium-containing controlled-release urea area, reaching 585.84 kg / mu, an increase of 39.39 kg / mu (7.2%) compared to the conventional fertilization area. Using the magnesium-containing controlled-release urea of ​​this invention, magnesium, zinc, boron, and urea are released simultaneously, aligning with the nutrient requirements of maize growth. In contrast, conventional fertilization methods easily lead to the loss of magnesium and other elements, failing to achieve a synergistic effect with urea in the mid-to-late stages of maize growth, resulting in low fertilizer utilization and impacting maize yield. The magnesium-containing controlled-release urea of ​​this invention also significantly improves maize quality, increasing the 100-kernel weight by 2.23 g (8.2%), resulting in fuller kernels and higher market value. Simultaneously, plant height increased, leaf area significantly enlarged, and photosynthetic efficiency was further enhanced. In terms of nitrogen fertilizer utilization rate, the magnesium-containing controlled-release urea achieved the highest rate of 69.7%, an increase of 8.5 percentage points compared to the control group. This fully demonstrates the advantages of this invention in improving fertilizer utilization efficiency. The significant increase in yield and the remarkable improvement in quality can significantly enhance the final profit, resulting in considerable economic benefits.

[0066] Field Trial 2

[0067] Crops planted: Corn

[0068] Planting location: Qingzhou, Shandong.

[0069] Soil basic conditions: The soil type is brown soil, with a medium loam texture and moderate fertility in the topsoil. The physicochemical properties of the 0-20cm topsoil layer before the experiment were: pH 7.5, organic matter 15.4 g / kg, total nitrogen 1.17 g / kg, available phosphorus 138 mg / kg, available potassium 239 mg / kg, exchangeable magnesium 513.6 mg / kg, available zinc 0.56 mg / kg, and available boron 0.4 mg / kg.

[0070] Experimental variety: Jinnonghua 803 corn

[0071] Experimental protocol: (The controlled-release urea used in the protocol was all controlled-release urea produced by Maoshi Agricultural Technology Co., Ltd. (45% sustained nitrogen, release period of 80 days))

[0072] Blank control group: Base application per mu: controlled-release urea (total nitrogen 10 kg), superphosphate 10 kg, potassium chloride 5 kg;

[0073] Experimental control group: Base application per mu: controlled-release urea (total nitrogen 10 kg), superphosphate 10 kg, potassium chloride 5 kg, magnesium sulfate 0.6 kg, zinc sulfate 0.2 kg, borax 0.2 kg.

[0074] Experimental groups 1-4: Base application dosage per mu: Magnesium-containing controlled-release urea (total nitrogen 10 kg), superphosphate 10 kg, and potassium chloride 5 kg of the present invention were applied respectively in Examples 1-4 of this invention.

[0075] On June 15, 2024, land preparation and fertilization were carried out. Manual sowing was conducted on June 16, and seedlings emerged on June 22. The row spacing was 60cm x 25cm, with two seeds sown per hole, resulting in 400 holes per plot. On August 8, a plant trait survey was conducted. In each plot, a five-point random sampling method was used to measure the plant height of five consecutive corn plants and the length * width (length: from leaf tip to leaf apex; width: the widest part of the leaf) of the third leaf from the top. The survey revealed an excessively long period of high temperature and drought; therefore, irrigation (sprinkler irrigation) was applied to a 15m area on August 10. 3 / mu, and apply 12kg / mu of large granular urea as top dressing. Other field management is the same as in local fields. No obvious diseases, pests and weeds appeared during the growing season. The actual yield was calculated on October 9.

[0076] Table 2

[0077]

[0078] The results are as follows:

[0079] The actual yield results of maize under each fertilization treatment are shown in Table 2. The addition of magnesium, zinc, and boron promoted photosynthesis and synergistically improved nitrogen utilization, thereby increasing crop yield. The maize yield in the magnesium-containing controlled-release urea area was the highest at 794.8 kg / mu, an increase of 54.5 kg / mu (7.36%) compared to the conventional fertilization area; nitrogen fertilizer utilization also increased significantly from 62.2% to 72.4%, achieving fertilizer saving and efficiency improvement. The quality of maize treated with the magnesium-containing controlled-release fertilizer of this invention was improved, with a thousand-grain weight of 294.9 g, an increase of 6.39% compared to the conventional fertilization area. Meanwhile, field survey results showed that the maize plant height in experimental group 4 was 1.4 cm greater than that in the conventional fertilization group, with thicker stems, indicating more balanced nutrient absorption; and the leaves were significantly larger, with a more rational plant structure, which is conducive to improving light energy utilization efficiency. This further verifies the significant advantages of the controlled-release fertilizer of this invention in improving soil nutrient supply and promoting crop growth.

Claims

1. A magnesium-containing controlled-release urea, characterized in that, It consists of a fertilizer core and a coating material, wherein the fertilizer core is a urea particle containing magnesium.

2. The magnesium-containing controlled-release urea according to claim 1, characterized in that, The fertilizer core contains: Nitrogen 35-46 wt% Magnesium content: 0.001–5 wt% Zinc element 0–4.8 wt% Boron element 0–2 wt%.

3. The magnesium-containing controlled-release urea according to claim 2, characterized in that, The raw materials for preparing the fertilizer core include urea, a zinc source, a boron source, and a magnesium source; the zinc source is selected from one or more combinations of zinc sulfate, zinc nitrate, and zinc chloride; the boron source is selected from one or more combinations of borax, boric acid, sodium octaborate tetrahydrate, and potassium octaborate; and the magnesium source is selected from one or more combinations of magnesium sulfate, magnesium nitrate, and magnesium chloride.

4. The magnesium-containing controlled-release urea according to claim 1, characterized in that, The coating material is polyurethane; the amount of polyurethane used is 1.5 to 3 wt% of the fertilizer core.

5. A method for preparing magnesium-containing controlled-release urea according to any one of claims 1-4, characterized in that the step... include: Weigh the zinc source, boron source, and magnesium source, add water and stir until completely dissolved to obtain a near-saturated solution of trace elements. Disperse the near-saturated solution of trace elements in molten urea at 130-145℃ in a certain proportion to make a mixed slurry. After the mixed slurry is granulated twice by a drum, it is cooled and sieved to obtain fertilizer cores. Then, the fertilizer cores are coated with a coating material to obtain magnesium-containing controlled-release urea.

6. The method for preparing magnesium-containing controlled-release urea according to claim 5, characterized in that, After being cooled, the granules from the drum granulation process are screened to obtain fertilizer cores with a particle size of 3 to 4.75 mm. The fertilizer cores are then coated with polyester polyol and isocyanate to obtain magnesium-containing controlled-release urea.

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