Biochar stable coated slow-release urea and preparation method thereof

Abstract

The invention relates to charcoal stable coated slow-release urea and a preparation method thereof, and belongs to the technical field of agricultural chemical fertilizers. The slow-release urea comprises a urea core and a coating layer, wherein the coating layer comprises biochar, a modified binder, a vegetable oil nano-emulsion sealant and a urease inhibitor and / or a nitrification inhibitor. The preparation method comprises the following steps: firstly, preparing the modified binder and the nano-emulsion; uniformly mixing the biochar with an inhibitor; the preparation method comprises the following steps: alternately spraying a binder, adding charcoal-inhibitor mixed powder and spraying a nano emulsion on preheated and rolled urea particles, circularly coating for multiple times, and drying. According to the invention, the biochar is used as a green film material, through a unique coating structure, the slow release of nutrients and the long-acting and stable cooperation of the inhibitor are realized, the nitrogen fertilizer utilization rate is obviously improved, the environmental pollution is reduced, the process is simple, and the cost is relatively low.

Description

Technical Field

[0001] This invention relates to the field of agricultural fertilizer technology, specifically to a biochar-stabilized coated slow-release urea and its preparation method. Background Technology

[0002] Nitrogen fertilizer is a key element for ensuring high grain yields, but its utilization rate in my country is generally low. Statistics show that in 2020, the nitrogen fertilizer utilization rate for my country's three major grain crops was far below the level of developed countries. Nutrient loss from fertilizers not only wastes resources but also leads to environmental problems such as eutrophication of water bodies and greenhouse gas emissions. Improving nitrogen fertilizer utilization has become an urgent need for the green and sustainable development of agriculture.

[0003] Currently, improving nitrogen fertilizer utilization efficiency mainly relies on the development of slow-release and controlled-release fertilizers and stabilized fertilizers. Slow-release and controlled-release fertilizers delay nutrient release through physical coating or chemical synthesis, but their core coating materials (such as polymer resins) are expensive and have degradation residue issues. Stabilized fertilizers, on the other hand, inhibit nitrogen transformation and loss in the soil by adding urease inhibitors (such as NBPT) and nitrification inhibitors (such as DCD). However, the high-temperature environment during the granulation process of traditional stabilized fertilizers easily deactivates the inhibitors, and the inhibitors are easily leached and lost in the soil, resulting in poor persistence.

[0004] Biochar is a porous, carbon-rich material produced by the pyrolysis of biomass, possessing a large specific surface area and excellent adsorption properties. While biochar-based fertilizers, made by simply mixing biochar with fertilizers, can improve soil properties, the excessive adsorption capacity of biochar may "lock in" nutrients, affecting the absorption by crops in the current season, and its protective and slow-release effects on inhibitors are limited.

[0005] Therefore, there is an urgent need to develop a new fertilizer product and its preparation method that is low-cost, environmentally friendly, and can effectively synergistically prolong the action time of nitrogen and inhibitors. Summary of the Invention

[0006] In view of this, the purpose of this invention is to provide a biochar-stabilized coated slow-release urea. This product uses biochar derived from agricultural waste as the main coating material, combined with specific binders and sealants, to construct a novel coating system that can simultaneously achieve slow nitrogen release and long-term stabilizing effect of inhibitors, thereby improving nitrogen fertilizer utilization and reducing environmental pollution. Another object of the present invention is to provide a method for preparing the above-mentioned biochar-stabilized coated sustained-release urea. This method is simple, has low energy consumption, and is suitable for large-scale production.

[0007] This invention is achieved through the following technical solution: In a first aspect, the present invention provides a biochar-stabilized coated slow-release urea, comprising a urea core and a coating layer surrounding the urea core; the coating layer comprises biochar, a modified binder, a vegetable oil nanoemulsion sealant, and a urease inhibitor and / or a nitration inhibitor.

[0008] Furthermore, the modified binder is an aqueous solution of polyvinyl alcohol and sodium alginate.

[0009] Furthermore, the vegetable oil nanoemulsion sealant is prepared by emulsifying and homogenizing an emulsifier, vegetable oil, or liquid paraffin. Preferably, the emulsifier includes Span20 and Tween20.

[0010] Furthermore, the urease inhibitor is N-butylthiophosphoric triamine (NBPT), and the nitration inhibitor is dicyandiamide (DCD).

[0011] Furthermore, based on the mass of the urea core, the amount of biochar added is 8%-15%, and the amount of urease inhibitor and / or nitrification inhibitor added is 0.1%-2%.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned biochar-stabilized coated sustained-release urea, comprising the following steps: (1) Preparation of modified adhesive aqueous solution and vegetable oil nanoemulsion sealant; (2) Mix biochar with urease inhibitor and / or nitrification inhibitor evenly to obtain biochar-inhibitor mixed powder; (3) Preheat the urea particles and place them in a coating equipment to roll them, and spray the modified binder obtained in step (1) onto the surface of the rolling urea particles. (4) Add a portion of the biochar-inhibitor mixture powder obtained in step (2) to the surface of the urea particles coated with the modified binder, and after drying, spray the vegetable oil nanoemulsion sealant obtained in step (1). (5) Repeat steps (3) and (4) at least once until the biochar-inhibitor mixture powder is completely coated on the surface of the urea particles, and finally spray a layer of the vegetable oil nanoemulsion sealant. (6) Dry and cool the coated urea particles to obtain the biochar-stabilized coated slow-release urea.

[0013] Further, in step (1), the modified adhesive is prepared by dissolving polyvinyl alcohol and sodium alginate in hot water at 50℃-60℃, stirring until completely dissolved, and then mixing evenly.

[0014] Further, in step (1), the preparation method of the vegetable oil nanoemulsion sealant is as follows: dissolve the emulsifier in water, then add vegetable oil or liquid paraffin of the same volume as the water, and perform preliminary emulsification by stirring and high-pressure homogenization or ultrasonic treatment to obtain the nanoemulsion.

[0015] Furthermore, in step (3), the preheating temperature is 35℃-45℃, and the rotation speed of the coating equipment is 30-50r / min.

[0016] The beneficial effects of this invention are as follows: Environmental and economic benefits: Biochar is used as the main membrane material. The raw material is derived from agricultural waste, which is inexpensive and realizes the resource utilization of waste. In addition, biochar itself has the function of improving soil, avoiding the environmental burden of traditional polymer coating.

[0017] Synergistic effect of slow release and stability: An innovative dual slow release mechanism of "biochar adsorption + physical coating". The huge specific surface area of ​​biochar can effectively adsorb nitrogen and inhibitors, preventing rapid leaching of inhibitors; the physical barrier formed by the outer binder and nanoemulsion sealant further regulates the nutrient release rate, allowing inhibitors and nitrogen to maintain a longer contact and interaction time in the soil.

[0018] The process is simple and effective: the alternating spray coating process requires minimal equipment, is easy to operate, produces a uniform and strong coating, and has a high yield. By controlling the number of coating cycles, the coating thickness and slow-release period can be flexibly adjusted.

[0019] Significantly improved fertilizer efficiency: Data from the examples show that the product of this invention can significantly reduce ammonia volatilization (inhibition rate 12.11%-66.26%) and nitrogen leaching loss, increasing the nitrogen fertilizer utilization rate of corn by 20.56%-28.92% and biomass by 10.24%-14.76% compared with ordinary urea.

[0020] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0021] Figure 1 This is a process flow diagram of the present invention; Figure 2 Photographs of the product; Figure 3 Electron micrograph of the product; Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0025] In the above description of the present invention, it should be noted that the terms "one side," "the other side," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is conventionally placed during use. These terms are used only for the convenience of describing the present invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0026] Furthermore, terms such as "identical" do not imply that components must be absolutely identical; minor differences are permissible. The term "perpendicular" simply means that the positional relationship between components is more perpendicular than "parallel," not that the structure must be perfectly perpendicular; a slight tilt is acceptable.

[0027] 1. Preparation and selection of core raw materials Biochar: The biochar used in this invention is preferably produced by the pyrolysis of agricultural waste (such as rice husks, straw, sawdust, fruit shells, etc.) or livestock and poultry manure under limited oxygen conditions at 400-700℃. Its specific surface area should be greater than 100 m² / g, preferably between 200-400 m² / g, and the pore size distribution should be mainly mesoporous (2-50 nm). Before use, it needs to be pulverized and sieved, with a particle size preferably of 150-300 mesh (approximately 48-100 micrometers). This specification of biochar powder has optimal flowability and adhesion, and its rich pore structure is conducive to the adsorption of inhibitor molecules.

[0028] Modified binder: The core components are polyvinyl alcohol (PVA) and sodium alginate. The degree of polymerization of PVA is preferably 1700-1800, and the degree of hydrolysis ≥88%. The viscosity of sodium alginate (1% aqueous solution, 20℃) is preferably 200-800 mPa·s. The aqueous solution concentration of both is 0.5%-2% (w / v), and the mixing ratio (volume ratio) is 1:0.5 to 1:2. This composite binder combines the strong adhesiveness of PVA with the film-forming properties and biocompatibility of sodium alginate. During the subsequent drying process, it can form a micro-permeable initial film that firmly holds the biochar powder.

[0029] Vegetable oil nanoemulsion sealant: Suitable vegetable oils include soybean oil, rapeseed oil, and palm oil; liquid paraffin is an alternative. A blend of emulsifiers Span20 (strong lipophilicity) and Tween20 (strong hydrophilicity) (typically in a 1:1 to 2:1 mass ratio) forms a stable oil-in-water (O / W) nanoemulsion. After homogenization, the droplet size of the emulsion should be less than 500 nm, preferably less than 200 nm. This nanoemulsion effectively penetrates and fills the surface pores and interlayer gaps of the biochar coating layer, forming a hydrophobic and dense secondary membrane. This allows for precise control of the nutrient (mainly water molecules) inflow and outflow rates, which is crucial for achieving the "controlled release" function.

[0030] Inhibitors: N-butylthiophosphoric triamine (NBPT) is used as the urease inhibitor, and dicyandiamide (DCD) is used as the nitration inhibitor. Both can be used alone or in any proportion. Before mixing with biochar, the inhibitors can be dissolved in a small amount of water or an organic solvent (such as methanol) to achieve a more uniform loading.

[0031] 2. Detailed Description of Implementation Examples Example 1 (Single urease inhibitor type) This example details the preparation of biochar-stabilized coated sustained-release urea with added urease inhibitor (NBPT). (1) Raw material pretreatment: Biochar: Take rice husk biochar (pyrolyzed at 600℃), crush it and pass it through a 200-mesh sieve.

[0032] Urea: Select large-particle urea with a particle size of 2-4mm.

[0033] (2) Preparation of modified binder: Accurately weigh 10.0 g of PVA particles with a degree of polymerization of 1750 and a degree of hydrolysis of 99%, and add them to 1.0 L of deionized water. Place the container in a 60℃ constant temperature water bath and mechanically stir at 500 rpm for 2 hours until completely dissolved to obtain a 1% PVA solution. Cool to room temperature for later use. Separately weigh 10.0 g of medium viscosity sodium alginate and add it to 1.0 L of deionized water. Similarly, stir in a 60℃ water bath until completely dissolved to obtain a 1% sodium alginate solution. Mix the two solutions at a volume ratio of 1:1 and stir with a magnetic stirrer for 30 minutes to ensure uniform mixing to obtain the modified binder. Seal and store.

[0034] (3) Preparation of soybean oil nanoemulsion: Add 25.0g Span20 and 25.0g Tween20 to a beaker, then add 1.0L of distilled water at 60℃ and stir until completely dissolved to obtain a 5% composite emulsifier aqueous solution. Measure 1.0L of commercially available Grade 1 soybean oil and slowly add the emulsifier aqueous solution dropwise to the soybean oil under stirring in a high-speed shear press (10000rpm). After the addition is complete, continue shearing and stirring for 15 minutes to obtain a crude emulsion. Transfer the crude emulsion to a high-pressure homogenizer and homogenize it 5 times under a pressure of 60MPa to obtain a milky white, semi-transparent soybean oil nanoemulsion with a particle size distribution of 80-150nm. Store it in a sealed container at room temperature.

[0035] (4) Preparation of biochar-inhibitor mixed powder: Weigh 120.0g of biochar powder, which is 12% of the total mass of urea (1kg). Weigh 5.0g of NBPT, which is 0.5% of the total mass of urea. Dissolve NBPT in 10mL of anhydrous ethanol, then spray the solution evenly onto the biochar powder. Place the powder in a fume hood to allow the ethanol to evaporate completely. Then mix in a mixer for 30 minutes to ensure that NBPT is evenly loaded into the pores and surface of the biochar.

[0036] (5) Coating process: A. Preheating and Equipment Preparation: Weigh 1,000 kg of dry, large-particle urea and pour it into a rotary drum coating machine (or disc granulator) with an adjustable tilt angle. Start the equipment, set the rotation speed to 40 r / min, and adjust the tilt angle to approximately 45 degrees to ensure good rolling fluidization of the urea particles within the drum. Turn on the electric heating system of the coating machine's jacket and simultaneously blow hot air at 50-60°C into the drum to uniformly raise the temperature of the urea particle bed to (40±2)°C. This step aims to reduce the surface moisture of the urea and enhance the wetting effect of the binder.

[0037] B. First Coating Cycle: Start the high-pressure airless spray gun (nozzle diameter 0.8mm, atomization pressure 0.3MPa), and evenly and atomize about 10mL (1 / 4 of the total amount) of modified binder onto the surface of the turbulent urea particles for about 30 seconds. Immediately afterward, quickly and evenly sprinkle 1 / 4 of the total amount of biochar-NBPT mixed powder prepared in step (4), i.e., 30.0g, into the machine through the solid powder feeder. Under the action of rolling friction and binder, the biochar powder quickly adheres to the surface of the urea particles, forming a preliminary coating layer. Keep the equipment running for 5-8 minutes, and use hot air to dry the binder layer to a basically dry state until it is no longer sticky.

[0038] C. Sealing and Circulation: After the initial layer has dried, use another spray gun to evenly spray approximately 5 mL (1 / 4 of the total volume) of soybean oil nanoemulsion onto the surface of the coating layer. This step can quickly fill the micropores on the surface of the biochar layer.

[0039] D. Repeated Coating: Repeat steps B and C three times. That is: second application of adhesive -> addition of 30.0g of mixed powder -> drying -> application of nanoemulsion; third operation as above; fourth operation as above. In total, a total of 120.0g of biochar-NBPT mixed powder was used.

[0040] E. Final sealing: After completing four cycles of coating, an additional layer of approximately 10 mL of nano-emulsion is sprayed on as the outermost layer for enhanced sealing and waterproofing.

[0041] (6) Post-processing and finished product: The coated fertilizer granules are removed from the coating machine, spread evenly on a stainless steel tray, and transferred to a circulating hot air drying oven. They are dried at (50±2)℃ for 2 hours. Then the heat source is turned off, and the mixture is allowed to cool naturally to room temperature. A small amount of agglomerated powder is removed by sieving to obtain a black granular finished product with good flowability.

[0042] (7) Product performance characterization: Physicochemical indicators: determined according to relevant national standard methods. Total nitrogen content (Kjeldahl method) is 43.93%, which meets the high-nitrogen fertilizer standard. Biochar content (loss on ignition method) is 10.93%, which meets the NY / T3041-2016 standard (>6%).

[0043] Sustained-release performance (water dissolution rate method): 10.00 g of sample was weighed and placed in a 100-mesh nylon mesh bag, then immersed in 100 mL of deionized water at 25℃. The sample was removed on days 1, 3, 7, 14, and 28, and the nitrogen content in the water was measured. The cumulative nitrogen dissolution rate was calculated. The results showed that the dissolution rate was <15% on day 1, <50% on day 7, and reached over 80% on day 28, exhibiting good initial sustained-release and sustained-release characteristics.

[0044] Ammonia volatilization inhibition effect (indoor simulation): determined using the aeration method. A sample equivalent to 50 mg of pure nitrogen was uniformly mixed with 100 g of air-dried soil and placed in a sealed container. The mixture was incubated at 25°C and a soil moisture content of 60% of field capacity. Released ammonia gas was absorbed with a 2% boric acid solution, and titrations were performed periodically. After 7 days of incubation, the cumulative ammonia volatilization was calculated. Compared to treatment with the same nitrogen content of ordinary urea, the cumulative ammonia volatilization of the product in this example was reduced by 48.08%.

[0045] Example 2 (Single nitrification inhibitor type) The main difference between this example and Example 1 is the type and dosage of the inhibitor.

[0046] Steps (1)-(3) are the same as in Example 1.

[0047] (4) Preparation of biochar-inhibitor mixed powder: Weigh 120.0g of biochar powder and 10.0g (1% of urea mass) of DCD nitrification inhibitor. Grind the DCD into fine powder and then dry mix it directly with the biochar powder in a mixer for 60 minutes to ensure uniform mixing.

[0048] (5) Coating process: The coating process and parameters are exactly the same as step (5) in Example 1, that is, four cycles of coating are used.

[0049] (6) Post-processing: Same as in Example 1.

[0050] (7) Product performance characterization: Total nitrogen content: 42.54%; biochar content: 8.31%.

[0051] Ammonia volatilization inhibition rate: 25.67%. Since DCD mainly inhibits nitrification, its contribution to directly reducing ammonia volatilization is relatively smaller than that of NBPT, hence the inhibition rate is lower but still significant.

[0052] Nitrification inhibition effect (soil incubation): The sample was applied to the soil for incubation, and the NH4+ in the soil was measured periodically. 4+ -N and NO 3- -N content. The results showed that, after 28 days of cultivation, the NO content in the soil in this example was significantly reduced. 3- The amount of -N generated was reduced by about 40% compared with ordinary urea treatment, indicating that DCD maintained its activity in the soil for a longer period of time under the protection of biochar coating, effectively delaying the conversion of ammonium nitrogen to nitrate nitrogen.

[0053] Example 3 (Combination Inhibitor Type) The main difference between this embodiment and Embodiment 1 is that two inhibitors are used simultaneously.

[0054] (1) - (3) are the same as in Example 1.

[0055] (4) Preparation of biochar-inhibitor mixed powder: Weigh 120.0g of biochar powder. Weigh 5.0g of NBPT and 10.0g of DCD. First, dissolve NBPT in ethanol and load it onto part of the biochar. Then, mix the DCD powder with the remaining biochar and the aforementioned NBPT-loaded biochar for 60 minutes.

[0056] (5) Coating process: Same as in Example 1, using four-cycle coating. (6) Post-processing: Same as in Example 1. (7) Product performance characterization: Total nitrogen content: 41.58%; biochar content: 11.22%.

[0057] Ammonia volatilization inhibition rate: up to 66.26%, showing the synergistic effect of NBPT and DCD.

[0058] Overall results: In the leaching test, it had the lowest cumulative nitrogen leaching loss; in the pot experiment, it had the highest nitrogen fertilizer utilization rate and biomass yield increase in maize.

[0059] Example 4 (Process Parameter Adjustment: The Influence of Coating Times) This embodiment aims to illustrate the controllability of the number of coating cycles on product performance.

[0060] Steps (1)-(4) are the same as in Example 1 (using NBPT).

[0061] (5) Coating process: Sample A: Only two cycles of coating were performed (i.e., the total amount of biochar added was 6% of the urea quality), and then it was sealed.

[0062] Sample B: Six cycles of coating were performed (i.e., the total biochar addition was 18% of the urea quality), followed by sealing. Other process parameters (binder, emulsion dosage ratio, temperature, rotation speed, etc.) remained consistent with those in Example 1.

[0063] (6) Post-processing: Same as in Example 1.

[0064] (7) Performance comparison: Film thickness and weight gain: Scanning electron microscopy (SEM) showed that the coating layer of sample A was thin and uneven, and the product weight gain was about 8%; the coating layer of sample B was thick and dense, and the product weight gain was about 22%; the product weight gain of Example 1 (4 cycles) was about 15%, and the film layer was uniform.

[0065] Slow-release cycle: Through water dissolution rate tests, Sample A's cumulative nitrogen dissolution rate exceeded 80% by day 14 (relatively fast release); Sample B's dissolution rate was only about 60% by day 28 (too slow release); the product of Example 1 had a dissolution rate of about 80% by day 28 (ideal release curve). This indicates that by adjusting the number of coating cycles (i.e., the total amount of biochar used), the nutrient release cycle of the product can be flexibly designed to meet the needs of different crop growth stages.

[0066] Example 5 (Raw Material Substitution Example) This embodiment aims to illustrate the substitutability of core raw materials.

[0067] (1) Biochar: Wood chip biochar (pyrolyzed at 500℃) was used and passed through a 180-mesh sieve.

[0068] (2) Adhesive: The concentration of PVA solution was changed to 1.5%, the concentration of sodium alginate solution was changed to 0.8%, and the mixing volume ratio was PVA solution: sodium alginate solution = 2:1.

[0069] (3) Nanoemulsion: Rapeseed oil is used instead of soybean oil. The emulsifier is a mixture of glyceryl monostearate and sucrose fatty acid ester (mass ratio 3:2). The total amount added is 10% of the oil phase mass. It is emulsified by an ultrasonic cell disruptor (power 600W, working time 20min, on / off cycle 2s / 1s).

[0070] (4) Inhibitor: Only DCD is used, at a dosage of 1.5% of urine quality.

[0071] (5) Coating process: The total amount of biochar used is 10% of the urea quality, and it is added in 5 cycles. The preheating temperature is 45℃ and the drum speed is 35r / min.

[0072] (6) The test results showed that the obtained product had a nitrogen content of 40.12% and a biochar content of 9.05%, and still exhibited good slow-release and nitrification inhibition effects. This indicates that within the technical framework provided by this invention, those skilled in the art can reasonably select and adjust the specific raw material types and some process parameters according to resource availability to achieve the purpose of this invention.

[0073] 3. Application effect verification (comprehensive experimental data) To systematically evaluate the effects of the product of this invention, standardized pot and field micro-plot experiments were conducted.

[0074] Soil samples were taken from the same cultivated land at the same depth, and then the samples were mixed and prepared for use.

[0075] Test crop: summer maize (variety: Zhengdan 958).

[0076] Experimental treatments: (1) No nitrogen fertilizer (CK0); (2) Ordinary urea (CKU); (3) Product of Example 1 (T1); (4) Product of Example 2 (T2); (5) Product of Example 3 (T3).

[0077] All treatments used the same amount of nitrogen, phosphorus, and potassium (N:P2O5:K2O=200:100:150kg / ha), and all were applied as a single basal fertilizer.

[0078] Main results: Nitrogen loss: Compared with CKU, the cumulative ammonia volatilization of T1, T2 and T3 treatments decreased by 48.1%, 25.7% and 66.3% respectively; in the leaching experiment of 30cm soil column, the cumulative nitrogen leaching loss decreased by 35.2%, 28.5% and 52.8% respectively.

[0079] Soil nitrogen forms: 30 days after fertilization, the NH3 content in soil treated with T1 and T3 was... 4+ -N content was significantly higher than CKU, indicating that NBPT effectively delayed urea hydrolysis; NO in soil treated with T2 and T3 was significantly higher than CKU. 3- The -N content was significantly lower than that of CKU, indicating that DCD effectively inhibited nitrification.

[0080] Crop response and nitrogen fertilizer utilization: At harvest, compared with CKU, the corn grain yield of T1, T2 and T3 treatments increased by 8.7%, 5.2% and 12.5% ​​respectively; the apparent nitrogen fertilizer utilization rates (difference method) were 61.3%, 56.8% and 65.9% respectively, which were 20.8, 16.3 and 25.4 percentage points higher than CKU (40.5%).

[0081] Economic and environmental benefits: Although the cost of the product of this invention is slightly higher than that of ordinary urea, its high fertilizer efficiency and low loss result in a significant increase in crop yield per unit of nutrients. At the same time, it significantly reduces nitrogen emissions into the atmosphere and water bodies, resulting in significant environmental benefits.

[0082] In summary, the biochar-stabilized coated slow-release urea and its preparation method provided by this invention, through innovative material combination and process design, successfully integrate the adsorption properties of biochar, the biochemical activity of inhibitors, and the barrier effect of physical coating, creating a new type of fertilizer product that is highly efficient, green, and controllable. This is of great significance for promoting the reduction of fertilizer use and the increase of efficiency and the sustainable development of agriculture.

[0083] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A biochar-stabilized coated sustained-release urea, characterized in that, It includes a urea core and a coating layer surrounding the urea core; the coating layer contains biochar, a modified binder, a vegetable oil nanoemulsion sealant, and urease inhibitors and / or nitration inhibitors.

2. The biochar-stabilized coated sustained-release urea according to claim 1, characterized in that, The modified binder is an aqueous solution of polyvinyl alcohol and sodium alginate.

3. The biochar-stabilized coated sustained-release urea according to claim 1, characterized in that, The plant oil nanoemulsion sealant is made by emulsifying and homogenizing emulsifiers, plant oils, or liquid paraffin.

4. The biochar-stabilized coated sustained-release urea according to claim 3, characterized in that, The emulsifiers include Span20 and Tween20.

5. The biochar-stabilized coated sustained-release urea according to claim 1, characterized in that, The urease inhibitor is N-butylthiophosphoric triamine (NBPT), and the nitration inhibitor is dicyandiamide (DCD).

6. The biochar-stabilized coated sustained-release urea according to claim 1, characterized in that, Based on the mass of the urea core, the amount of biochar added is 8%-15%, and the amount of urease inhibitor and / or nitrification inhibitor added is 0.1%-2%.

7. A method for preparing biochar-stabilized coated sustained-release urea as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) Preparation of modified adhesive aqueous solution and vegetable oil nanoemulsion sealant; (2) Mix biochar with urease inhibitor and / or nitrification inhibitor evenly to obtain biochar-inhibitor mixed powder; (3) Preheat the urea particles and place them in a coating equipment to roll them, and spray the modified binder obtained in step (1) onto the surface of the rolling urea particles. (4) Add a portion of the biochar-inhibitor mixture powder obtained in step (2) to the surface of the urea particles coated with the modified binder, and after drying, spray the vegetable oil nanoemulsion sealant obtained in step (1). (5) Repeat steps (3) and (4) at least once until the biochar-inhibitor mixture powder is completely coated on the surface of the urea particles, and finally spray a layer of the vegetable oil nanoemulsion sealant. (6) Dry and cool the coated urea particles to obtain the biochar-stabilized coated slow-release urea.

8. The method according to claim 7, characterized in that, In step (1), the modified adhesive is prepared by dissolving polyvinyl alcohol and sodium alginate in hot water at 50℃-60℃, stirring until completely dissolved, and then mixing evenly.

9. The method according to claim 7, characterized in that, In step (1), the preparation method of the vegetable oil nanoemulsion sealant is as follows: dissolve the emulsifier in water, then add vegetable oil or liquid paraffin of the same volume as the water, and perform preliminary emulsification by stirring and high-pressure homogenization or ultrasonic treatment to obtain the nanoemulsion.

10. The method according to claim 7, characterized in that, In step (3), the preheating temperature is 35℃-45℃, and the rotation speed of the coating equipment is 30-50r / min.

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