A liquid slow-release nitrogen fertilizer and its preparation method

Abstract

The present invention discloses a liquid slow-release nitrogen fertilizer and a preparation method thereof, relating to the technical field of fertilizer preparation; the liquid slow-release nitrogen fertilizer is composed of a nano-particle synergistic carrier, urea, ammonium bicarbonate, magnesium sulfate heptahydrate, a hybrid gel coating material and water; the nano-particle synergistic carrier is composed of nano biochar, nano humic acid and zero-valent iron; the hybrid gel coating material is composed of sodium carboxymethylcellulose, sodium alginate and aluminum sulfate; the nano-particle synergistic carrier carries nitrogen fertilizers such as urea, and then is coated with the hybrid gel coating material. The prepared liquid slow-release nitrogen fertilizer has excellent slow-release properties, can enhance the complexation and adsorption of nitrogen fertilizers, effectively reduce the volatilization and loss of nitrogen fertilizers, improve the utilization rate of nitrogen fertilizers, and can also improve soil acidification, increase the nutrient absorption of crops, and achieve the effect of increasing production.

Description

Technical Field

[0001] The present invention belongs to the technical field of fertilizer preparation, and specifically refers to a liquid slow-release nitrogen fertilizer and a preparation method thereof. Background Art

[0002] In agricultural production, nitrogen fertilizer is a crucial nutrient that plays a vital role in the growth and development of crops and their yields. With the continuous development of agricultural technology, the types of nitrogen fertilizers are constantly being enriched and innovated. As a new type of nitrogen fertilizer, liquid nitrogen fertilizer has received much attention in recent years; since it is in solution form, liquid nitrogen fertilizer can be quickly absorbed by plant roots after application, accelerating the supply rate of nitrogen, which helps to improve the growth rate and yield of crops; compared with solid nitrogen fertilizer, the application of liquid nitrogen fertilizer is more convenient and can be applied through irrigation systems, spraying, etc., with simple operation and enabling precise fertilization.

[0003] Currently, the existing technologies mainly have the following problems:

[0004] The nitrogen element in liquid nitrogen fertilizer has high mobility and is prone to volatilization and loss. Only a very small part can be absorbed and utilized by crops, resulting in low fertilizer utilization rate. And the nitrogen fertilizer flowing into the soil will be converted into nitrate, releasing hydrogen ions, causing soil acidification, which is not conducive to the nutrient absorption of crops and leads to a reduction in yield. Summary of the Invention

[0005] In view of the above situation, to overcome the defects of the existing technologies, the present invention provides a liquid slow-release nitrogen fertilizer, which comprises the following components in parts by weight: 20 - 30 parts of nano-particle synergistic carrier, 20 - 30 parts of urea, 10 - 20 parts of ammonium bicarbonate, 8 - 10 parts of magnesium sulfate heptahydrate, 8 - 12 parts of hybrid gel coating material, and 40 - 80 parts of water.

[0006] The nano-particle synergistic carrier comprises the following components in parts by weight: 20 - 30 parts of nano-biochar, 5 - 8 parts of nano-humic acid, and 5 - 10 parts of zero-valent iron.

[0007] The hybrid gel coating material comprises the following components in parts by weight: 10 - 15 parts of sodium carboxymethylcellulose, 8 - 12 parts of sodium alginate, and 8 - 10 parts of aluminum sulfate.

[0008] The preparation method of the nano-particle synergistic carrier specifically comprises the following steps:

[0009] (1) After washing the sunflower straw with deionized water, place it in an oven at 55-65°C to dry, crush it, sieve it, and transfer the sunflower straw powder into a muffle furnace. Under anaerobic conditions, the temperature is increased at a rate of 10°C / min, and the high-temperature pyrolysis temperature is 400-600°C for 2-3 hours. There are problems such as livestock not liking to use sunflower straw and slow degradation after returning to the field, resulting in extremely low utilization rate. Using it as a biomass raw material can improve its economic utilization value and realize waste recycling. After pyrolysis, it is naturally cooled to room temperature and ball-milled in a planetary ball mill for 10-12 hours. The ball-milled product is poured into a beaker, 50-100 times the weight of deionized water is added, and it is physically separated by an ultrasonic pulverizer. Centrifugation, freeze-drying, the drying temperature is -20°C to -40°C, and the drying time is 12-24 hours. The sunflower straw biomass can be prepared into a nanoscale, making it appear broken and uneven on the surface, increasing a large number of gaps, thereby enhancing the adsorption sites, allowing more loaded fertilizers to play a role, and obtaining nano-biochar;

[0010] (2) The humic acid is ball-milled for 10-12 hours using a planetary ball mill, and the ball-milled product is poured into a beaker, and 50-100 times the weight of deionized water is added, and the product is physically separated using an ultrasonic pulverizer, centrifuged, and the precipitate is freeze-dried at a drying temperature of -20°C to -40°C for 12-24 hours. The humic acid treated by this process has good dispersibility, a small particle size, a rough and prominent surface, and thus nano-humic acid is obtained;

[0011] (3) The nano humic acid described in step (2) is dissolved in 25 mL of 0.1 mol / L sodium hydroxide solution, and 0.1 mol / L hydrochloric acid solution is added dropwise to adjust the pH to 7.0. The prepared nano humic acid solution is set aside, and then 1.0-1.8 g of ferric sulfate powder is added to 70 mL of ultrapure water and 30 mL of anhydrous ethanol, and stirred until completely dissolved. The nano humic acid solution is added and stirred at a speed of 80-120 rpm for 8-12 h, and then 0.1-0.2 g of the nano biochar described in step (1) is added and stirred at 2.5 mL / min under the protection of nitrogen. 100mL of 0.5mol / L sodium borohydride solution was added dropwise at a speed of 1:1 min, and zero-valent iron was prepared by liquid phase reduction method. The addition of zero-valent iron can effectively increase the specific surface area of nano-biochar, expose more adsorption sites, enhance the adsorption effect, and further enhance the complexation between the carrier and nitrogen fertilizers such as urea, which is conducive to better nitrogen fixation and reduce fertilizer loss. After the addition is completed, stirring is continued for 40-60min, the mixed solution is filtered, and the precipitate is washed with ultrapure water for 3-5 times and dried at a drying temperature of 50-60°C for 24-48h to obtain a nanoparticle synergistic carrier;

[0012] Preferably, in step (3), the dosage of nano-humic acid is 40-50 mg. Nano-humic acid can promote the formation of the porous structure of nano-biochar, improve the dispersion uniformity of zero-valent iron, reduce the adverse effects caused by the blockage of pores by zero-valent iron, and further increase the adsorption capacity.

[0013] The preparation method of the hybrid gel coating material specifically includes the following steps:

[0014] a. Dissolve aluminum sulfate powder in 50 mL of water, stir for 0.5-1 h, then add a mixed solution of sodium hydroxide and succinic acid. In the mixed solution of sodium hydroxide and succinic acid, the weight of sodium hydroxide is 6 g, the weight of succinic acid is 6 g, and the volume of water is 60 mL. Continue to stir for 1-2 h, centrifuge, wash the precipitate with distilled water 2-3 times, and dry. The drying temperature is 40-50 °C, and the drying time is 3-4 h. A metal material is prepared by a green, safe, and economical strategy. As a new type of porous crystal, it has an adjustable pore structure and can be used as a slow-release material to obtain MOF-Al;

[0015] b. Grind and mix the MOF-Al obtained in step a with sodium alginate and sodium carboxymethylcellulose, disperse them in 100 mL of water, and perform ultrasonic homogenization. During the ultrasonic homogenization process, the ultrasonic temperature is 50-60 °C, the ultrasonic frequency is 30-50 KHz, the ultrasonic power is 600-800 W, and the ultrasonic time is 20-30 min. Ultrasonic treatment is beneficial to the dispersion of MOF-Al in sodium alginate and sodium carboxymethylcellulose, and also improves the crosslinking degree of sodium alginate and sodium carboxymethylcellulose. The addition of MOF-Al further enhances the mechanical strength and release stability of the hydrogel to obtain the hybrid gel coating material;

[0016] Preferably, in step a, the mass fraction of the aluminum sulfate solution is 16-17%. The aluminum element provided by aluminum sulfate can promote plant growth and disease resistance, increase crop yield, and is also beneficial to improving soil structure and adjusting the pH environment.

[0017] The present invention also provides a preparation method of a liquid slow-release nitrogen fertilizer, which specifically includes the following steps:

[0018] S1. First mix urea, ammonium bicarbonate, and magnesium sulfate heptahydrate. After mixing evenly, add a nano-particle synergistic carrier, and continue to mix for the second time. After the mixing is completed, add 1-2 times the amount of water to the mixture, control the temperature at 50-80 °C, and stir to completely dissolve it. The nano-particle synergistic carrier loads nitrogen fertilizers such as urea, effectively fixes the amino groups in urea, gives a certain slow-release property, and thus increases the utilization of fertilizers to obtain a nitrogen fertilizer slurry;

[0019] S2. Add the hybrid gel coating material into the nitrogen fertilizer slurry described in step S1, and perform high-pressure homogenization. The hybrid gel coating material not only coats the nitrogen fertilizer slurry, provides dual protection and adsorption with the nanoparticle synergistic carrier, enhances the slow-release performance of the fertilizer, but also improves the adhesion, reduces the high fluidity of the nitrogen fertilizer, and significantly reduces the volatilization loss of the nitrogen fertilizer, thus obtaining a liquid slow-release nitrogen fertilizer;

[0020] Preferably, in step S1, during the first mixing process, the mixing speed is 60 - 80 rpm and the mixing time is 5 - 10 min. During the second mixing process, the mixing speed is 80 - 100 rpm and the mixing time is 10 - 15 min. Separated mixing is beneficial for a more excellent mixing effect and also beneficial for the nanoparticle synergistic carrier to more fully complex with urea, etc.;

[0021] Preferably, in step S2, during the high-pressure homogenization process, the homogenization pressure is 800 - 1000 bar and the homogenization time is 2 - 3 min. High-pressure homogenization can further enhance the coating effect of the hybrid gel coating material and is beneficial for better exerting the coating slow-release effect.

[0022] The beneficial effects achieved by the present invention are as follows:

[0023] The present invention prepares a liquid slow-release nitrogen fertilizer by carrying nitrogen fertilizers such as urea on a nanoparticle synergistic carrier and then coating it with a hybrid gel coating material. The obtained liquid slow-release nitrogen fertilizer has excellent slow-release properties, can enhance the complexation and adsorption of nitrogen fertilizers, effectively reduce the volatilization and loss of nitrogen fertilizers, improve the utilization rate of nitrogen fertilizers, and can also improve soil acidification, increase the nutrient absorption of crops, and achieve the effect of increasing production; in the nanoparticle synergistic carrier, zero-valent iron increases the specific surface area of nano biochar, nano humic acid promotes the formation of porous structures in nano biochar, and at the same time improves the dispersion and uniformity of zero-valent iron. The combination of the three forms more active groups and a more abundant micro-mesoporous structure, thereby providing more adsorption sites, increasing the adsorption and complexation of nitrogen fertilizers, having a certain slow-release property, thus reducing the volatilization and loss of nitrogen fertilizers, and improving the utilization rate of nitrogen fertilizers. The nanoparticle synergistic carrier can also adsorb nitrates converted from nitrogen fertilizers and inhibit the release of hydrogen ions by nitrates, so it can effectively regulate soil acidity. Among them, nano biochar and nano humic acid provide organic matter and nutrients, improve soil structure, and nano-scale particles complex nutrients, better promoting the absorption of crop roots, so it is beneficial to increase crop production and income; in the hybrid gel coating material, with MOF-Al as the framework, it increases the cross-linking stability of sodium alginate and sodium carboxymethylcellulose, and the formed gel coating liquid has strong adhesion, which can reduce the high fluidity of urea molecules in the liquid slow-release nitrogen fertilizer, and can also adsorb ammonia generated after urea decomposition to form fertilizer, thus effectively reducing fertilizer loss. The gel coating liquid also has a porous structure, further enhancing the slow-release performance. Among them, the ion exchange and hydrogen bond effects of sodium carboxymethylcellulose and sodium alginate can enhance the adsorption of nitrates, and cooperate with the nanoparticle synergistic carrier to play a role in improving soil acidification, thereby enhancing the absorption of nutrients by crop roots and achieving the effect of increasing production; the hybrid gel coating material protects the nanoparticle synergistic carrier, reducing the occurrence of zero-valent iron losing fluidity and reaction activity due to oxidation and aggregation. The addition of sodium carboxymethylcellulose increases the steric resistance effect and electrostatic repulsion, can reduce the aggregation and adhesion of nano biochar, and enhances the adsorption effect; the present invention uses a nanoparticle synergistic carrier, urea, ammonium bicarbonate, magnesium sulfate heptahydrate, a hybrid gel coating material and water to make a liquid slow-release nitrogen fertilizer, slowly releasing nitrogen fertilizer, reducing the volatilization and loss of nitrogen fertilizer, improving the fertilizer utilization rate, effectively improving soil acidification, increasing the nutrient absorption of crops, and having the effect of increasing production and income. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a scanning electron microscope image of the nanoparticle synergistic carrier prepared in Example 1 of the present invention;

[0025] Figure 2 It is a scanning electron microscope image of the hybrid gel coating material prepared in Example 1 of the present invention;

[0026] Figure 3 It is the nitrogen cumulative release amount result graph of Examples 1-4 and Comparative Examples 1-3 of the present invention;

[0027] Figure 4 It is the nitrogen fertilizer utilization rate result graph of Examples 1-4 and Comparative Examples 1-3 of the present invention;

[0028] Figure 5 It is the soil pH and the fresh weight result graph of corn ears and stems of Examples 1-4 and Comparative Examples 1-3 of the present invention. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to the described content can be applied to the present invention. The preferred implementation methods and materials described herein are only for demonstration purposes and cannot limit the content of this application.

[0031] The experimental methods in the following embodiments are all conventional methods unless otherwise specified; the test materials used in the following embodiments are all obtained from commercial channels unless otherwise specified.

[0032] The sources of the reagents used in the examples are as follows:

[0033] Urea CAS No: 57-13-6, brand Innochem, product number A68476;

[0034] Ammonium bicarbonate CAS No: 1066-33-7, brand Innochem, product number A02294;

[0035] Magnesium sulfate heptahydrate CAS No: 10034-99-8, brand Innochem, product number A52643;

[0036] Humic acid CAS No: 1415-93-6, brand Alfa, product number 041747;

[0037] Sodium hydroxide CAS No: 1310-73-2, brand Innochem, product number A36865;

[0038] Hydrochloric acid CAS No: 7647-01-0, brand Innochem, product number A04558;

[0039] Ferric sulfate, CAS No: 10028-22-5, brand Innochem, product number A04263;

[0040] Sodium borohydride, CAS No: 16940-66-2, brand Acros, product number 189300025;

[0041] Aluminum sulfate, CAS No: 10043-01-3, brand Acros, product number 192430050;

[0042] Succinic acid, CAS No: 110-15-6, brand Innochem, product number A00815;

[0043] Sodium alginate, CAS No: 9005-38-3, brand Innochem, product number A02570;

[0044] Sodium carboxymethyl cellulose, CAS No: 9004-32-4, brand Innochem, product number A05925;

[0045] Absolute ethanol, CAS No: 64-17-5, brand Innochem, product number G00004.

[0046] Example 1

[0047] This example presents a liquid slow-release nitrogen fertilizer, which includes the following components in parts by weight: 30 parts of nano-particle synergistic carrier, 30 parts of urea, 20 parts of ammonium bicarbonate, 10 parts of magnesium sulfate heptahydrate, 12 parts of hybrid gel coating material, and 80 parts of water.

[0048] The nano-particle synergistic carrier includes the following components in parts by weight: 30 parts of nano biochar, 8 parts of nano humic acid, and 10 parts of zero-valent iron.

[0049] The hybrid gel coating material includes the following components in parts by weight: 15 parts of sodium carboxymethyl cellulose, 12 parts of sodium alginate, and 10 parts of aluminum sulfate.

[0050] The preparation method of the nano-particle synergistic carrier specifically includes the following steps:

[0051] (1) After washing the sunflower straw with deionized water, place it in a 65°C oven to dry, crush it, sieve it, and transfer the sunflower straw powder into a muffle furnace. The anaerobic conditions are carried out at a heating rate of 10°C / min, and the high-temperature pyrolysis temperature is 600°C for 3 hours. There are problems such as livestock not liking to use sunflower straw and slow degradation after returning to the field, resulting in extremely low utilization rate. Using it as a biomass raw material can improve its economic utilization value and realize waste recycling. After pyrolysis, it is naturally cooled to room temperature and ball-milled in a planetary ball mill for 12 hours. The ball-milled product is poured into a beaker, 100 times the weight of deionized water is added, and it is physically separated by an ultrasonic pulverizer. Centrifugation, freeze-drying, drying temperature -40°C, drying time 24 hours, the sunflower straw biomass can be prepared into nanoscale, making it appear broken and uneven on the surface, increasing a large number of gaps, thereby enhancing the adsorption sites, more loaded fertilizers play a role, and obtaining nano biochar;

[0052] (2) The humic acid was ball-milled for 12 hours using a planetary ball mill, and the ball-milled product was poured into a beaker, and 100 times the weight of deionized water was added. The product was physically separated using an ultrasonic pulverizer, centrifuged, and the precipitate was freeze-dried at a drying temperature of -40°C for 24 hours. The humic acid treated by this process had good dispersibility, a small particle size, a rough and prominent surface, and thus nano-humic acid was obtained;

[0053] (3) The nano-humic acid described in step (2) is dissolved in 25 mL of 0.1 mol / L sodium hydroxide solution. The amount of nano-humic acid used is 50 mg. Nano-humic acid can promote the formation of a porous structure of nano-biochar, improve the uniformity of the dispersion of zero-valent iron, reduce the adverse effects of zero-valent iron blocking the pores, and further increase the adsorption capacity. 0.1 mol / L hydrochloric acid solution is added dropwise to adjust the pH to 7.0. The prepared nano-humic acid solution is set aside. Then 1.8 g of ferric sulfate powder is added to 70 mL of ultrapure water and 30 mL of anhydrous ethanol, stirred until completely dissolved, and the nano-humic acid solution is added. Stirring, the stirring speed is 120 rpm, and the stirring time is 12 h. Then, 0.2 g of the nano biochar described in step (1) was added, and 100 mL of 0.5 mol / L sodium borohydride solution was added dropwise at a rate of 2.5 mL / min under the protection of nitrogen, and zero-valent iron was prepared by liquid phase reduction method. The addition of zero-valent iron can effectively increase the specific surface area of the nano biochar, expose more adsorption sites, enhance the adsorption effect, and further enhance the complexation between the carrier and nitrogen fertilizers such as urea, which is conducive to better nitrogen fixation and reduce fertilizer loss. After the addition is completed, stirring is continued for 60 minutes, the mixed solution is filtered, and the precipitate is washed with ultrapure water 5 times and dried at a drying temperature of 60°C and a drying time of 48 hours to obtain a nanoparticle synergistic carrier.

[0054] The preparation method of the hybrid gel coating material specifically comprises the following steps:

[0055] a. Dissolve aluminum sulfate powder in 50 mL of water and stir for 1 h. The mass fraction of the aluminum sulfate solution is 17%. The aluminum element provided by aluminum sulfate can promote plant growth and disease resistance, increase crop yields, and is also beneficial to improving soil structure and regulating the pH environment. Then add a mixed solution of sodium hydroxide and succinic acid. In the mixed solution of sodium hydroxide and succinic acid, the weight of sodium hydroxide is 6 g, the weight of succinic acid is 6 g, and the volume of water is 60 mL. Continue to stir for 2 h, centrifuge, wash the precipitate 3 times with distilled water, and dry it. The drying temperature is 50 °C and the drying time is 4 h. Adopt a green, safe, and economical strategy to prepare a metal material. As a new type of porous crystal, it has an adjustable pore structure and can be used as a slow-release material to obtain MOF-Al;

[0056] b. Grind and mix the MOF-Al described in step a with sodium alginate and sodium carboxymethylcellulose, and disperse them in 100 mL of water. Perform ultrasonic homogenization. During the ultrasonic homogenization process, the ultrasonic temperature is 60 °C, the ultrasonic frequency is 50 KHz, the ultrasonic power is 800 W, and the ultrasonic time is 30 min. Ultrasonic treatment is beneficial to the dispersion of MOF-Al in sodium alginate and sodium carboxymethylcellulose, and also improves the crosslinking degree of sodium alginate and sodium carboxymethylcellulose. The addition of MOF-Al further enhances the mechanical strength and release stability of the hydrogel to obtain a hybrid gel coating material.

[0057] This embodiment provides a preparation method for a liquid slow-release nitrogen fertilizer, which specifically includes the following steps:

[0058] S1. Perform a primary mixing of urea, ammonium bicarbonate, and magnesium sulfate heptahydrate. During the primary mixing process, the mixing speed is 80 rpm and the mixing time is 10 min. After mixing evenly, add a nano-particle synergistic carrier and continue secondary mixing. During the secondary mixing process, the mixing speed is 100 rpm and the mixing time is 15 min. Separated mixing is beneficial for a more excellent mixing effect and also beneficial for the nano-particle synergistic carrier to be more fully complexed with urea, etc. After the mixing is completed, add 2 times the amount of water to the mixture, control the temperature at 80 °C, and stir until it is completely dissolved. The nano-particle synergistic carrier loads nitrogen fertilizers such as urea, effectively fixes the amino groups in urea, confers a certain slow-release property, and thus increases the utilization of the fertilizer to obtain a nitrogen fertilizer slurry;

[0059] S2. Add the hybrid gel coating material into the nitrogen fertilizer slurry described in step S1, and perform high-pressure homogenization. During the high-pressure homogenization process, the homogenization pressure is 1000 bar and the homogenization time is 3 min. High-pressure homogenization can further enhance the coating effect of the hybrid gel coating material, which is beneficial to better exert the slow-release effect of the coating. The hybrid gel coating material not only coats the nitrogen fertilizer slurry, but also provides dual protection and adsorption with the nanoparticle synergistic carrier, enhancing the slow-release performance of the fertilizer. At the same time, it improves the adhesion, reduces the high fluidity of nitrogen fertilizer, and significantly reduces the volatilization loss of nitrogen fertilizer, thus obtaining a liquid slow-release nitrogen fertilizer.

[0060] In this example, scanning electron microscopy was performed on the prepared nanoparticle synergistic carrier and hybrid gel coating material to observe their microtopographies. Figure 1 Figure 5 is an SEM image of the nanoparticle synergistic carrier prepared in Example 1 magnified 1000 times. Figure 2 Figure 7 is an SEM image of the hybrid gel coating material prepared in Example 1 magnified 400 times. As Figure 1 shown, the nanoparticle synergistic carrier prepared in this example presents a rich microporous and mesoporous structure. As Figure 2 shown, the hybrid gel coating material prepared in this example is a porous gel.

[0061] Example 2

[0062] This example presents a liquid slow-release nitrogen fertilizer, which includes the following components in parts by weight: 20 parts of nanoparticle synergistic carrier, 20 parts of urea, 10 parts of ammonium bicarbonate, 8 parts of magnesium sulfate heptahydrate, 8 parts of hybrid gel coating material, and 40 parts of water.

[0063] The nanoparticle synergistic carrier includes the following components in parts by weight: 20 parts of nanobiocarbon, 5 parts of nano-humic acid, and 5 parts of zero-valent iron.

[0064] The hybrid gel coating material includes the following components in parts by weight: 10 parts of sodium carboxymethylcellulose, 8 parts of sodium alginate, and 8 parts of aluminum sulfate.

[0065] The preparation method of the nanoparticle synergistic carrier specifically includes the following steps:

[0066] (1) After washing the sunflower straw with deionized water, place it in a 55°C oven to dry, crush it, sieve it, and transfer the sunflower straw powder into a muffle furnace. The anaerobic conditions are carried out at a heating rate of 10°C / min, and the high-temperature pyrolysis temperature is 400°C for 2 hours. There are problems such as livestock not liking to use sunflower straw and slow degradation after returning to the field, resulting in extremely low utilization rate. Using it as a biomass raw material can improve its economic utilization value and realize waste recycling. After pyrolysis, it is naturally cooled to room temperature and ball milled in a planetary ball mill for 10 hours. The ball milled product is poured into a beaker, 50 times the weight of deionized water is added, and it is physically separated by an ultrasonic pulverizer. Centrifugation, freeze-drying, drying temperature -20°C, drying time 12 hours, the sunflower straw biomass can be prepared into nanoscale, making it appear broken and uneven on the surface, increasing a large number of gaps, thereby enhancing the adsorption sites, more loaded fertilizers play a role, and obtaining nano biochar;

[0067] (2) The humic acid was ball-milled for 10 h using a planetary ball mill, and the ball-milled product was poured into a beaker, 50 times the weight of deionized water was added, and the product was physically separated using an ultrasonic pulverizer, centrifuged, and the precipitate was freeze-dried at a drying temperature of -20°C for 12 h. The humic acid treated by this process had good dispersibility, a small particle size, a rough and prominent surface, and thus nano-humic acid was obtained;

[0068] (3) The nano-humic acid described in step (2) is dissolved in 25 mL of 0.1 mol / L sodium hydroxide solution. The amount of nano-humic acid used is 40 mg. Nano-humic acid can promote the formation of a porous structure of nano-biochar, improve the uniformity of the dispersion of zero-valent iron, reduce the adverse effects of zero-valent iron blocking the pores, and further increase the adsorption capacity. 0.1 mol / L hydrochloric acid solution is added dropwise to adjust the pH to 7.0. The prepared nano-humic acid solution is set aside. Then 1.0 g of ferric sulfate powder is added to 70 mL of ultrapure water and 30 mL of anhydrous ethanol, stirred until completely dissolved, and the nano-humic acid solution is added. Stirring, the stirring speed is 80 rpm, the stirring time is 8 hours, and then Then, 0.1 g of the nano biochar described in step (1) was added, and 100 mL of 0.5 mol / L sodium borohydride solution was added dropwise at a rate of 2.5 mL / min under the protection of nitrogen, and zero-valent iron was prepared by liquid phase reduction method. The addition of zero-valent iron can effectively increase the specific surface area of the nano biochar, expose more adsorption sites, enhance the adsorption effect, and further enhance the complexation between the carrier and nitrogen fertilizers such as urea, which is conducive to better nitrogen fixation and reduce fertilizer loss. After the addition is completed, stirring is continued for 40 minutes, the mixed solution is filtered, and the precipitate is washed 3 times with ultrapure water and dried at a drying temperature of 50° C. for a drying time of 24 hours to obtain a nanoparticle synergistic carrier.

[0069] The preparation method of the hybrid gel coating material specifically comprises the following steps:

[0070] a. Dissolve aluminum sulfate powder in 50 mL of water and stir for 0.5 h. The mass fraction of the aluminum sulfate solution is 16%. The aluminum element provided by aluminum sulfate can promote plant growth and disease resistance, increase crop yield, and is also beneficial to improving soil structure and adjusting the pH environment. Then add a mixed solution of sodium hydroxide and succinic acid. In the mixed solution of sodium hydroxide and succinic acid, the weight of sodium hydroxide is 6 g, the weight of succinic acid is 6 g, and the volume of water is 60 mL. Continue to stir for 1 h, centrifuge, wash the precipitate twice with distilled water, and dry. The drying temperature is 40 °C and the drying time is 3 h. Adopt a green, safe, and economical strategy to prepare a metal material. As a new type of porous crystal, it has an adjustable pore structure and can be used as a slow-release material to obtain MOF-Al;

[0071] b. Grind and mix the MOF-Al described in step a with sodium alginate and sodium carboxymethylcellulose, and disperse them in 100 mL of water, and perform ultrasonic homogenization. During the ultrasonic homogenization process, the ultrasonic temperature is 50 °C, the ultrasonic frequency is 30 KHz, the ultrasonic power is 600 W, and the ultrasonic time is 20 min. Ultrasonic treatment is beneficial to the dispersion of MOF-Al in sodium alginate and sodium carboxymethylcellulose, and also improves the crosslinking degree of sodium alginate and sodium carboxymethylcellulose. The addition of MOF-Al further enhances the mechanical strength and release stability of the hydrogel to obtain a hybrid gel coating material.

[0072] This example provides a preparation method of a liquid slow-release nitrogen fertilizer, which specifically includes the following steps:

[0073] S1. First mix urea, ammonium bicarbonate, and magnesium sulfate heptahydrate. During the first mixing process, the mixing speed is 60 rpm and the mixing time is 5 min. After mixing evenly, add a nanoparticle synergistic carrier and continue the second mixing. During the second mixing process, the mixing speed is 80 rpm and the mixing time is 10 min. Separated mixing is beneficial to a more excellent mixing effect and also beneficial to the nanoparticle synergistic carrier to more fully complex with urea, etc. After mixing, add 1 times the amount of water to the mixture, control the temperature at 50 °C, and stir to completely dissolve it. The nanoparticle synergistic carrier loads nitrogen fertilizers such as urea, effectively fixes the amino groups in urea, gives a certain slow-release property, and thus increases the utilization of fertilizers to obtain a nitrogen fertilizer slurry;

[0074] S2. Add the hybrid gel coating material to the nitrogen fertilizer slurry described in step S1, and perform high-pressure homogenization. During the high-pressure homogenization process, the homogenization pressure is 800 bar and the homogenization time is 2 min. High-pressure homogenization can further enhance the coating effect of the hybrid gel coating material, which is beneficial to better play the role of coating and slow release. The hybrid gel coating material not only coats the nitrogen fertilizer slurry, but also provides double protection and adsorption with the nanoparticle synergistic carrier, enhancing the slow-release performance of the fertilizer. At the same time, it improves the adhesion, reduces the high fluidity of nitrogen fertilizer, and significantly reduces the volatilization and loss of nitrogen fertilizer, thus obtaining a liquid slow-release nitrogen fertilizer.

[0075] Example 3

[0076] This example presents a liquid slow-release nitrogen fertilizer, which includes the following components in parts by weight: 25 parts of nanoparticle synergistic carrier, 25 parts of urea, 15 parts of ammonium bicarbonate, 9 parts of magnesium sulfate heptahydrate, 10 parts of hybrid gel coating material, and 60 parts of water.

[0077] The nanoparticle synergistic carrier includes the following components in parts by weight: 25 parts of nanobiochar, 6.5 parts of nano-humic acid, and 7.5 parts of zero-valent iron.

[0078] The hybrid gel coating material includes the following components in parts by weight: 12.5 parts of sodium carboxymethylcellulose, 10 parts of sodium alginate, and 9 parts of aluminum sulfate.

[0079] The preparation method of the nanoparticle synergistic carrier specifically includes the following steps:

[0080] (1) After cleaning the sunflower straw with deionized water, place it in an oven at 60 °C for drying, crushing, and sieving. Transfer the sunflower straw powder into a muffle furnace, and carry out the anaerobic condition at a heating rate of 10 °C / min. The high-temperature pyrolysis temperature is 500 °C, and it is maintained for 2.5 h. Sunflower straw has problems such as being not favored by livestock and slow degradation rate after returning to the field, resulting in extremely low utilization rate. Using it as a biomass raw material can improve the economic utilization value and realize waste recycling. After pyrolysis is completed, it is naturally cooled to room temperature, and ball-milled for 11 h with a planetary ball mill. Pour the ball-milled product into a beaker, add 75 times the weight of deionized water, perform physical separation with an ultrasonic crusher, centrifuge, and take the precipitate for freeze-drying. The drying temperature is -30 °C and the drying time is 18 h. The sunflower straw biomass can be prepared into nanoparticles, making its surface broken and uneven, increasing a large number of voids, thus enhancing the adsorption sites and enabling more loaded fertilizers to play a role, obtaining nanobiochar;

[0081] (2) The humic acid was ball-milled for 11 hours using a planetary ball mill, and the ball-milled product was poured into a beaker, and 75 times the weight of deionized water was added. The product was physically separated using an ultrasonic pulverizer, centrifuged, and the precipitate was freeze-dried at a drying temperature of -30°C for 18 hours. The humic acid treated by this process had good dispersibility, a small particle size, a rough and prominent surface, and thus nano-humic acid was obtained;

[0082] (3) The nano-humic acid described in step (2) is dissolved in 25 mL of 0.1 mol / L sodium hydroxide solution. The amount of nano-humic acid used is 45 mg. Nano-humic acid can promote the formation of a porous structure of nano-biochar, improve the uniformity of the dispersion of zero-valent iron, reduce the adverse effects of zero-valent iron blocking the pores, and further increase the adsorption capacity. 0.1 mol / L hydrochloric acid solution is added dropwise to adjust the pH to 7.0. The prepared nano-humic acid solution is set aside for use. Then 1.4 g of ferric sulfate powder is added to 70 mL of ultrapure water and 30 mL of anhydrous ethanol, stirred until completely dissolved, and the nano-humic acid solution is added and stirred at a stirring speed of 100 rpm for 10 h. Then, 0.15 g of the nano biochar described in step (1) was added, and 100 mL of 0.5 mol / L sodium borohydride solution was added dropwise at a rate of 2.5 mL / min under the protection of nitrogen, and zero-valent iron was prepared by liquid phase reduction method. The addition of zero-valent iron can effectively increase the specific surface area of the nano biochar, expose more adsorption sites, enhance the adsorption effect, and further enhance the complexation between the carrier and nitrogen fertilizers such as urea, which is conducive to better nitrogen fixation and reduce fertilizer loss. After the addition is completed, stirring is continued for 50 minutes, the mixed solution is filtered, and the precipitate is washed 4 times with ultrapure water and dried at a drying temperature of 55° C. and a drying time of 36 hours to obtain a nanoparticle synergistic carrier.

[0083] The preparation method of the hybrid gel coating material specifically comprises the following steps:

[0084] a. Dissolve aluminum sulfate powder in 50 mL of water and stir for 0.75 h. The mass fraction of aluminum sulfate solution is 16.5%. The aluminum element provided by aluminum sulfate can promote plant growth and disease resistance, increase crop yield, and is also beneficial to improve soil structure and adjust pH environment. Then add a mixed solution of sodium hydroxide and succinic acid. In the mixed solution of sodium hydroxide and succinic acid, the weight of sodium hydroxide is 6 g, the weight of succinic acid is 6 g, and the volume of water is 60 mL. Continue stirring for 1-2 h, centrifuge, wash the precipitate with distilled water twice, and dry it at a drying temperature of 45 ° C and a drying time of 3.5 h. A green, safe and economical strategy is used to prepare metal materials. As a new type of porous crystal, it has an adjustable pore structure and can be used for sustained-release materials to obtain MOF-Al.

[0085] b. Grind and mix the MOF-Al described in step a with sodium alginate and sodium carboxymethylcellulose, disperse them in 100 mL of water, and perform ultrasonic homogenization. During the ultrasonic homogenization process, the ultrasonic temperature is 55 °C, the ultrasonic frequency is 40 KHz, the ultrasonic power is 700 W, and the ultrasonic time is 25 min. Ultrasonic treatment is beneficial to the dispersion of MOF-Al in sodium alginate and sodium carboxymethylcellulose, and also improves the crosslinking degree of sodium alginate and sodium carboxymethylcellulose. The addition of MOF-Al further enhances the mechanical strength and release stability of the hydrogel, obtaining a hybrid gel coating material.

[0086] This example provides a preparation method of a liquid slow-release nitrogen fertilizer, which specifically includes the following steps:

[0087] S1. First mix urea, ammonium bicarbonate, and magnesium sulfate heptahydrate. During the first mixing process, the mixing speed is 70 rpm and the mixing time is 7.5 min. After mixing evenly, add a nanoparticle synergistic carrier and continue the second mixing. During the second mixing process, the mixing speed is 90 rpm and the mixing time is 12.5 min. Separated mixing is beneficial for a more excellent mixing effect and also beneficial for the nanoparticle synergistic carrier to more fully complex with urea, etc. After mixing, add 1.5 times the amount of water to the mixture, control the temperature at 65 °C, and stir to completely dissolve it. The nanoparticle synergistic carrier loads nitrogen fertilizers such as urea, effectively fixes the amino groups in urea, confers a certain slow-release property, thereby increasing the utilization of the fertilizer, and obtaining a nitrogen fertilizer slurry;

[0088] S2. Add the hybrid gel coating material to the nitrogen fertilizer slurry described in step S1 and perform high-pressure homogenization. During the high-pressure homogenization process, the homogenization pressure is 900 bar and the homogenization time is 2.5 min. High-pressure homogenization can further enhance the coating effect of the hybrid gel coating material, which is beneficial for better exerting the coating slow-release effect. The hybrid gel coating material not only coats the nitrogen fertilizer slurry, provides dual protection and adsorption with the nanoparticle synergistic carrier, enhances the slow-release performance of the fertilizer, but also improves the adhesion, reduces the high fluidity of the nitrogen fertilizer, and significantly reduces the volatilization and loss of the nitrogen fertilizer, obtaining a liquid slow-release nitrogen fertilizer.

[0089] Example 4

[0090] This example proposes a liquid slow-release nitrogen fertilizer, which includes the following components in parts by weight: 30 parts of nanoparticle synergistic carrier, 30 parts of urea, 20 parts of ammonium bicarbonate, 10 parts of magnesium sulfate heptahydrate, 8 parts of hybrid gel coating material, and 80 parts of water.

[0091] The nanoparticle synergistic carrier includes the following components in parts by weight: 30 parts of nanobiochar, 8 parts of nano-humic acid, and 10 parts of zero-valent iron.

[0092] Hybrid gel coating material, comprising the following components in parts by weight: 10 parts of sodium carboxymethyl cellulose, 8 parts of sodium alginate, and 8 parts of aluminum sulfate.

[0093] Preparation method of nano-particle synergistic carrier, specifically comprising the following steps:

[0094] (1) After cleaning sunflower straw with deionized water, place it in an oven at 65 °C to dry, crush, sieve, transfer the sunflower straw powder into a muffle furnace, and carry out under anaerobic conditions at a heating rate of 10 °C / min. The high-temperature pyrolysis temperature is 600 °C and is maintained for 2 h. Sunflower straw has problems such as being not favored by livestock and slow degradation rate after being returned to the field, resulting in extremely low utilization rate. Using it as a biomass raw material can improve the economic utilization value and achieve waste recycling. After pyrolysis is completed, naturally cool to room temperature, ball mill with a planetary ball mill for 12 h, pour the ball-milled product into a beaker, add 100 times the weight of deionized water, perform physical separation with an ultrasonic crusher, centrifuge, and take the precipitate for freeze-drying. The drying temperature is -40 °C and the drying time is 12 h. The sunflower straw biomass can be prepared into nanoscale, making it show surface fragmentation and unevenness, increasing a large number of voids, thus enhancing the adsorption sites and enabling more loaded fertilizers to play a role, obtaining nano biochar;

[0095] (2) Ball mill humic acid with a planetary ball mill for 12 h, pour the ball-milled product into a beaker, add 100 times the weight of deionized water, perform physical separation with an ultrasonic crusher, centrifuge, and take the precipitate for freeze-drying. The drying temperature is -40 °C and the drying time is 12 h. The humic acid treated by this process has good dispersibility, small particle size, rough and prominent surface, obtaining nano humic acid;

[0096] (3) The nano-humic acid described in step (2) is dissolved in 25 mL of 0.1 mol / L sodium hydroxide solution. The amount of nano-humic acid used is 50 mg. Nano-humic acid can promote the formation of a porous structure of nano-biochar, improve the uniformity of the dispersion of zero-valent iron, reduce the adverse effects of zero-valent iron blocking the pores, and further increase the adsorption capacity. 0.1 mol / L hydrochloric acid solution is added dropwise to adjust the pH to 7.0. The prepared nano-humic acid solution is set aside. Then 1.8 g of ferric sulfate powder is added to 70 mL of ultrapure water and 30 mL of anhydrous ethanol, stirred until completely dissolved, and the nano-humic acid solution is added. Stirring, the stirring speed is 120 rpm, the stirring time is 8 hours, and then Then, 0.2 g of the nano biochar described in step (1) was added, and 100 mL of 0.5 mol / L sodium borohydride solution was added dropwise at a rate of 2.5 mL / min under the protection of nitrogen, and zero-valent iron was prepared by liquid phase reduction method. The addition of zero-valent iron can effectively increase the specific surface area of the nano biochar, expose more adsorption sites, enhance the adsorption effect, and further enhance the complexation between the carrier and nitrogen fertilizers such as urea, which is conducive to better nitrogen fixation and reduce fertilizer loss. After the addition is completed, stirring is continued for 40 minutes, the mixed solution is filtered, and the precipitate is washed with ultrapure water 5 times and dried at a drying temperature of 60° C. for a drying time of 24 hours to obtain a nanoparticle synergistic carrier.

[0097] The preparation method of the hybrid gel coating material specifically comprises the following steps:

[0098] a. Dissolve aluminum sulfate powder in 50 mL of water and stir for 0.5 h. The mass fraction of aluminum sulfate solution is 16%. The aluminum element provided by aluminum sulfate can promote plant growth and disease resistance, increase crop yield, and is also beneficial to improve soil structure and adjust the pH environment. Then add a mixed solution of sodium hydroxide and succinic acid. In the mixed solution of sodium hydroxide and succinic acid, the weight of sodium hydroxide is 6 g, the weight of succinic acid is 6 g, and the volume of water is 60 mL. Continue stirring for 1 h, centrifuge, wash the precipitate with distilled water 3 times, and dry it at a drying temperature of 50 ° C and a drying time of 3 h. A green, safe and economical strategy is used to prepare metal materials. As a new type of porous crystal, it has an adjustable pore structure and can be used for sustained-release materials to obtain MOF-Al.

[0099] b. The MOF-Al described in step a was ground and mixed with sodium alginate and sodium carboxymethyl cellulose, dispersed in 100 mL of water, and subjected to ultrasonic homogenization. During the ultrasonic homogenization, the ultrasonic temperature was 60° C., the ultrasonic frequency was 50 kHz, the ultrasonic power was 800 W, and the ultrasonic time was 20 min. The ultrasonic treatment was beneficial to the dispersion of MOF-Al in sodium alginate and sodium carboxymethyl cellulose, and also improved the crosslinking degree of sodium alginate and sodium carboxymethyl cellulose. The addition of MOF-Al also further enhanced the mechanical strength and release stability of the hydrogel, thereby obtaining a hybrid gel coating material.

[0100] This embodiment provides a preparation method of a liquid slow-release nitrogen fertilizer, which specifically includes the following steps:

[0101] S1. Urea, ammonium bicarbonate, and magnesium sulfate heptahydrate are mixed for the first time. During the first mixing process, the mixing speed is 80 rpm and the mixing time is 5 min. After mixing evenly, a nano-particle synergistic carrier is added, and then the second mixing is continued. During the second mixing process, the mixing speed is 100 rpm and the mixing time is 10 min. Separated mixing is beneficial to a more excellent mixing effect and also beneficial to the more sufficient complexation of the nano-particle synergistic carrier with urea, etc. After the mixing is completed, the mixture is added to 2 times the amount of water, the temperature is controlled at 80 °C, and it is stirred until completely dissolved. The nano-particle synergistic carrier loads nitrogen fertilizers such as urea, effectively fixes the amino groups in urea, confers a certain slow-release property, thereby increasing the utilization of the fertilizer, and a nitrogen fertilizer slurry is obtained.

[0102] S2. The hybrid gel coating material is added to the nitrogen fertilizer slurry obtained in step S1, and high-pressure homogenization is carried out. During the high-pressure homogenization process, the homogenization pressure is 1000 bar and the homogenization time is 2 min. High-pressure homogenization can further enhance the coating effect of the hybrid gel coating material, which is beneficial to better exerting the coating slow-release effect. The hybrid gel coating material not only coats the nitrogen fertilizer slurry, provides dual protection and adsorption with the nano-particle synergistic carrier, enhances the slow-release performance of the fertilizer, but also improves the adhesion, reduces the high fluidity of the nitrogen fertilizer, and significantly reduces the volatilization and loss of the nitrogen fertilizer, and a liquid slow-release nitrogen fertilizer is obtained.

[0103] Comparative Example 1

[0104] This comparative example provides a liquid slow-release nitrogen fertilizer, which is different from Example 1 in that the liquid slow-release nitrogen fertilizer does not contain a nano-particle synergistic carrier; the preparation method of the hybrid gel coating material is the same as that in Example 1; the preparation method of the liquid slow-release nitrogen fertilizer is the same as that in Example 1.

[0105] Comparative Example 2

[0106] This comparative example provides a liquid slow-release nitrogen fertilizer, which is different from Example 1 in that the liquid slow-release nitrogen fertilizer does not contain a hybrid gel coating material; the preparation method of the nano-particle synergistic carrier is the same as that in Example 1; the preparation method of the liquid slow-release nitrogen fertilizer is the same as that in Example 1.

[0107] Comparative Example 3

[0108] This comparative example provides a liquid slow-release nitrogen fertilizer, which is different from Example 1 in that the liquid slow-release nitrogen fertilizer does not contain a nano-particle synergistic carrier and a hybrid gel coating material; the preparation method of the liquid slow-release nitrogen fertilizer is the same as that in Example 1.

[0109] Experimental Example 1

[0110] Slow-release performance experiment

[0111] Test samples: Liquid slow-release nitrogen fertilizers prepared in Examples 1-4 and Comparative Examples 1-3.

[0112] Test method: Put 200 mL of the test sample solution into a 250 mL plastic bottle, seal it with a cap, and place it in a constant temperature incubator at 25 °C for cultivation. The sampling times are 1 d, 7 d, and 14 d. When sampling, invert the plastic bottle 3 times to make the liquid concentration in the bottle uniform. After sampling, seal it with a cap and put it back into the constant temperature incubator for continued cultivation. Take 20 mL of the taken-out liquid for digestion, and then use an ultraviolet-visible spectrophotometer to measure the nitrogen release amount (%).

[0113] Figure 3 It is the result graph of the nitrogen cumulative release amount of Examples 1-4 and Comparative Examples 1-3; as shown in the figure, the nitrogen cumulative release amounts of Examples 1-4 at 1 d, 7 d, and 14 d are 40.5 - 48.7%, 71.5 - 76.2%, and 72.6 - 77.9% respectively, indicating good slow-release performance; the nitrogen cumulative release amounts of Comparative Examples 1-3 at 1 d, 7 d, and 14 d are 56.0 - 68.6%, 80.1 - 93.2%, and 82.1 - 95.6% respectively, indicating poor slow-release performance; the liquid slow-release nitrogen fertilizer of Comparative Example 1 does not contain a nano-particle synergistic carrier and cannot provide abundant adsorption sites and active groups, and thus cannot undergo adsorption complexation with molecules such as urea. Urea and the like are released through the porous structure of the hybrid gel coating material and cannot synergistically play a slow-release role, resulting in poor slow-release performance; the liquid slow-release nitrogen fertilizer of Comparative Example 2 does not contain a hybrid gel coating material and cannot form a coating protection on the nitrogen fertilizer slurry, increasing the aggregation of zero-valent iron and nano-biochar and having an adverse impact on the adsorption and reaction activity, resulting in poor slow-release performance; the liquid slow-release nitrogen fertilizer of Comparative Example 3 does not contain a nano-particle synergistic carrier and a hybrid gel coating material, neither contains a micro-mesoporous structure inside nor can form a protective layer outside, accelerating the release rate of fertilizers such as urea and resulting in poor slow-release performance.

[0114] Experimental Example 2

[0115] Nitrogen fertilizer utilization rate experiment

[0116] Test samples: Liquid slow-release nitrogen fertilizers prepared in Examples 1-4 and Comparative Examples 1-3.

[0117] Test method: Select 8 areas of the same size in the Shaanxi corn demonstration field for experiments. Among them, 1 area is the control area without applying nitrogen fertilizer, and the other 7 experimental areas are irrigated and fertilized with the test samples. The fertilization amount is 30 kg / mu, and fertilization is carried out once every 10 days. Observe and record the growth of the crops, collect the above-ground parts of the corn at maturity, wipe them clean, blanch them in an oven at 105 °C for 30 min, then dry them at 65 °C to a constant weight, and then record the dry weights of each organ of the corn; after crushing the corn plants through a 0.15 mm sieve, use the concentrated H2SO4-H2O2 digestion method to extract the total nitrogen in the corn, and then use a continuous flow analyzer to measure the total nitrogen content. Multiply it by the dry matter weight of the corn to obtain the total nitrogen uptake of the above-ground parts of the corn. Calculate the nitrogen fertilizer utilization rate (%) according to the following formula:

[0118] Nitrogen fertilizer utilization rate (%) = [(Total nitrogen uptake of the above-ground parts of the mature corn in the experimental area - Total nitrogen uptake of the above-ground parts of the mature corn in the control area) / Nitrogen application rate] × 100%

[0119] Figure 4 It is the result chart of the nitrogen fertilizer utilization rate of Examples 1-4 and Comparative Examples 1-3; as shown in the figure, the nitrogen fertilizer utilization rate of Examples 1-4 is 35.8 - 39.2%, indicating a relatively high nitrogen fertilizer utilization rate; the nitrogen fertilizer utilization rate of Comparative Examples 1-3 is 26.3 - 32.1%, indicating a relatively low nitrogen fertilizer utilization rate; the liquid slow-release nitrogen fertilizer in Comparative Example 1 does not contain a nano-particle synergistic carrier, does not contain rich active groups and micro-mesoporous structures, and cannot adsorb and complex the nitrogen fertilizer, thus increasing the loss and volatilization of the nitrogen fertilizer, resulting in a relatively low nitrogen fertilizer utilization rate; the liquid slow-release nitrogen fertilizer in Comparative Example 2 does not contain a hybrid gel coating material, cannot reduce the mobility of molecules such as urea, and cannot adsorb the ammonia gas generated after the decomposition of urea, thus being not conducive to reducing the loss of nitrogen fertilizer, resulting in a relatively low nitrogen fertilizer utilization rate; the liquid slow-release nitrogen fertilizer in Comparative Example 3 does not contain a nano-particle synergistic carrier and a hybrid gel coating material, can neither provide a carrier to adsorb and complex the nitrogen fertilizer nor reduce the adhesiveness of the solution, increasing the volatilization and loss of the nitrogen fertilizer, resulting in a relatively low nitrogen fertilizer utilization rate.

[0120] Experimental Example 3

[0121] Yield increase effect experiment

[0122] Test samples: The liquid slow-release nitrogen fertilizers prepared in Examples 1-4 and Comparative Examples 1-3.

[0123] Test method: Seven areas of the same size in the Shaanxi corn demonstration field were selected for the experiment. The test samples were used for irrigation and fertilization correspondingly. The fertilization amount was 30 kg / mu, and fertilization was carried out once every 10 days. After entering the mature period, the pH of the soil in different areas was detected respectively. At the same time, the above-ground parts of 10 corn plants in the mature period were collected. After wiping them clean, the fresh weights of each organ of the corn were recorded, and the average value was calculated as the fresh weight of the corn ear and stem (g / plant).

[0124] Figure 5 It is the result graph of the soil pH, and the fresh weights of the corn ear and stem for Examples 1-4 and Comparative Examples 1-3; as shown in the figure, the soil pH, and the fresh weights of the corn ear and stem for Examples 1-4 are 6.6-6.8, 157-178 g / plant, and 206-212 g / plant respectively, indicating that soil acidification is effectively improved and the yield increase effect is better; the soil pH, and the fresh weights of the corn ear and stem for Comparative Examples 1-3 are 6.3-6.5, 108-133 g / plant, and 192-202 g / plant respectively, indicating that soil acidification cannot be effectively improved and the yield increase effect is average; the liquid slow-release nitrogen fertilizer in Comparative Example 1 does not contain a nano-particle synergistic carrier and cannot synergistically adsorb nitrates converted from nitrogen fertilizer through multiple pathways with the hybrid gel coating material, affecting soil acidity. Soil acidification is not conducive to the growth of crop roots and further reduces the absorption of nutrients, resulting in an average yield increase effect; the liquid slow-release nitrogen fertilizer in Comparative Example 2 does not contain a hybrid gel coating material and cannot enhance the adsorption of nitrates through ion exchange and hydrogen bond interactions, nor can it reduce the aggregation of nano biochar, which has an adverse effect on its adsorption, so it is not conducive to adjusting soil acidity, thus having a negative impact on the nutrient absorption of crops and resulting in an average yield increase effect; the liquid slow-release nitrogen fertilizer in Comparative Example 3 does not contain a nano-particle synergistic carrier and a hybrid gel coating material, cannot adsorb nitrates multiple times, and cannot inhibit the release of hydrogen ions, causing soil acidification. An acidic environment is not conducive to the growth and nutrient absorption of crops, resulting in an average yield increase effect.

[0125] The above experimental results show that the slow-release performance, nitrogen fertilizer utilization rate and yield increase effect of Examples 1-4 of the present invention are significantly better than those of the samples of Comparative Examples 1-3. Among them, Example 1 using the nano-particle synergistic carrier and the hybrid gel coating material has better slow-release performance, higher nitrogen fertilizer utilization rate and better yield increase effect. The nano-particle synergistic carrier forms more active groups and a more abundant micro-mesoporous structure, has a certain slow-release property, increases the adsorption and complexation of nitrogen fertilizer, thereby reducing the volatilization and loss of nitrogen fertilizer and improving the utilization rate of nitrogen fertilizer. The nano-particle synergistic carrier can also adsorb nitrates converted from nitrogen fertilizer and inhibit the release of hydrogen ions by nitrates, effectively regulating soil acidity, better promoting the absorption of crop roots, and being beneficial to increasing crop yield and income; the hybrid gel coating material has strong adhesion, reduces the high fluidity of urea molecules, etc., adsorbs ammonia generated after urea decomposition to form fertilizer, effectively reducing fertilizer loss. The gel coating liquid also has a porous structure, further enhancing the slow-release performance. The ion exchange and hydrogen bond interaction between sodium carboxymethylcellulose and sodium alginate can enhance the adsorption of nitrates and synergistically play the role of improving soil acidification with the nano-particle synergistic carrier, thereby enhancing the absorption of nutrients by crop roots and achieving the effect of increasing yield.

[0126] Although the embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made in these embodiments without departing from the principles and spirit of the present invention.

[0127] The above description of the present invention and its embodiments is not restrictive. What is shown in the drawings is only one of the embodiments of the present invention, and the actual application is not limited thereto. Generally speaking, if those of ordinary skill in the art are inspired by it and design similar ways and embodiments to this technical solution without creative efforts without departing from the purpose of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A liquid slow-release nitrogen fertilizer, characterized in that: The liquid slow-release nitrogen fertilizer comprises the following components in parts by weight: 20-30 parts of nano-particle synergistic carrier, 20-30 parts of urea, 10-20 parts of ammonium bicarbonate, 8-10 parts of magnesium sulfate heptahydrate, 8-12 parts of hybrid gel coating material, and 40-80 parts of water; the nano-particle synergistic carrier comprises the following components in parts by weight: 20-30 parts of nano biochar, 5-8 parts of nano humic acid, and 5-10 parts of zero-valent iron; the hybrid gel coating material comprises the following components in parts by weight: 10-15 parts of sodium carboxymethylcellulose, 8-12 parts of sodium alginate, and 8-10 parts of aluminum sulfate; The preparation method of the nano-particle synergistic carrier specifically comprises the following steps: (1) Clean the sunflower straw with deionized water, place it in an oven at 55-65 °C for drying, crush it, sieve it, transfer the sunflower straw powder into a muffle furnace, carry out under anaerobic conditions at a heating rate of 10 °C / min, the high-temperature pyrolysis temperature is 400-600 °C, maintain for 2-3 h, after pyrolysis is completed, naturally cool to room temperature, ball mill with a planetary ball mill for 10-12 h, pour the ball-milled product into a beaker, add 50-100 times the weight of deionized water, carry out physical separation with an ultrasonic crusher, centrifuge, take the precipitate for freeze-drying, the drying temperature is -20 °C to -40 °C, and the drying time is 12-24 h to obtain nano biochar; (2) Ball mill the humic acid with a planetary ball mill for 10-12 h, pour the ball-milled product into a beaker, add 50-100 times the weight of deionized water, carry out physical separation with an ultrasonic crusher, centrifuge, take the precipitate for freeze-drying, the drying temperature is -20 °C to -40 °C, and the drying time is 12-24 h to obtain nano humic acid; (3) Dissolve the nano humic acid described in step (2) in 25 mL of 0.1 mol / L sodium hydroxide solution, add 0.1 mol / L hydrochloric acid solution to adjust the pH to 7.0, and keep the prepared nano humic acid solution for use. Then add 1.0-1.8 g of ferric sulfate powder to 70 mL of ultrapure water and 30 mL of absolute ethanol, stir until completely dissolved, add the nano humic acid solution, stir, the stirring speed is 80-120 rpm, the stirring time is 8-12 h, then add 0.1-0.2 g of the nano biochar described in step (1), and dropwise add 100 mL of 0.5 mol / L sodium borohydride solution at a speed of 2.5 mL / min under the protection of nitrogen. After dropping is completed, continue to stir for 40-60 min, filter the mixed solution by suction, wash the precipitate with ultrapure water for 3-5 times, and dry it, the drying temperature is 50-60 °C, and the drying time is 24-48 h to obtain the nano-particle synergistic carrier; The preparation method of the hybrid gel coating material specifically comprises the following steps: a. Dissolve aluminum sulfate powder in 50 mL of water, stir for 0.5 - 1 h, then add a mixed solution of sodium hydroxide and succinic acid. In the mixed solution of sodium hydroxide and succinic acid, the weight of sodium hydroxide is 6 g, the weight of succinic acid is 6 g, and the volume of water is 60 mL. Continue to stir for 1 - 2 h, centrifuge, wash the precipitate with distilled water 2 - 3 times, and dry at a drying temperature of 40 - 50 °C for 3 - 4 h to obtain MOF - Al; b. Grind and mix the MOF - Al described in step a with sodium alginate and sodium carboxymethylcellulose, disperse in 100 mL of water, and perform ultrasonic homogenization. During the ultrasonic homogenization process, the ultrasonic temperature is 50 - 60 °C, the ultrasonic frequency is 30 - 50 KHz, the ultrasonic power is 600 - 800 W, and the ultrasonic time is 20 - 30 min to obtain a hybrid gel coating material.

2. A preparation method of the liquid slow-release nitrogen fertilizer according to claim 1, characterized in that: Specifically, it includes the following steps: S1. First mix urea, ammonium bicarbonate, and magnesium sulfate heptahydrate. After mixing evenly, add a nanoparticle synergistic carrier, and continue to mix for the second time. After the mixing is completed, add 1 - 2 times the amount of water to the mixture, control the temperature at 50 - 80 °C, and stir to completely dissolve it to obtain a nitrogen fertilizer slurry; S2. Add the hybrid gel coating material to the nitrogen fertilizer slurry described in step S1 and perform high - pressure homogenization to obtain a liquid slow - release nitrogen fertilizer; The preparation method of the nanoparticle synergistic carrier specifically includes the following steps: (1) After cleaning sunflower straw with deionized water, place it in an oven at 55 - 65 °C for drying, crush it, and sieve it. Transfer the sunflower straw powder into a muffle furnace. Under anaerobic conditions, heat it at a heating rate of 10 °C / min, with a high - temperature pyrolysis temperature of 400 - 600 °C, and maintain for 2 - 3 h. After pyrolysis is completed, naturally cool it to room temperature, ball - mill it with a planetary ball mill for 10 - 12 h. Pour the ball - milled product into a beaker, add 50 - 100 times the weight of deionized water, perform physical separation with an ultrasonic crusher, centrifuge, and take the precipitate for freeze - drying at a drying temperature of - 20 °C to - 40 °C for 12 - 24 h to obtain nano - biochar; (2) Ball - mill humic acid with a planetary ball mill for 10 - 12 h. Pour the ball - milled product into a beaker, add 50 - 100 times the weight of deionized water, perform physical separation with an ultrasonic crusher, centrifuge, and take the precipitate for freeze - drying at a drying temperature of - 20 °C to - 40 °C for 12 - 24 h to obtain nano - humic acid; (3) Dissolve the nano-humic acid described in step (2) in 25 mL of 0.1 mol / L sodium hydroxide solution, add 0.1 mol / L hydrochloric acid solution dropwise to adjust the pH to 7.0, and set aside the prepared nano-humic acid solution. Then, add 1.0 - 1.8 g of ferric sulfate powder into 70 mL of ultrapure water and 30 mL of absolute ethanol, stir until completely dissolved, add the nano-humic acid solution, stir, with a stirring speed of 80 - 120 rpm and a stirring time of 8 - 12 h. Then, add 0.1 - 0.2 g of the nano-biochar described in step (1), and dropwise add 100 mL of 0.5 mol / L sodium borohydride solution at a rate of 2.5 mL / min under the protection of nitrogen. After the addition is completed, continue to stir for 40 - 60 min. Filter the mixture by suction, wash the precipitate with ultrapure water for 3 - 5 times, and dry it at a drying temperature of 50 - 60 °C for 24 - 48 h to obtain a nano-particle synergistic carrier; The preparation method of the hybrid gel coating material specifically includes the following steps: a. Dissolve aluminum sulfate powder in 50 mL of water, stir for 0.5 - 1 h, then add a mixed solution of sodium hydroxide and succinic acid. In the mixed solution of sodium hydroxide and succinic acid, the weight of sodium hydroxide is 6 g, the weight of succinic acid is 6 g, and the volume of water is 60 mL. Continue to stir for 1 - 2 h, centrifuge, wash the precipitate with distilled water for 2 - 3 times, and dry it at a drying temperature of 40 - 50 °C for 3 - 4 h to obtain MOF-Al; b. Grind and mix the MOF-Al described in step a with sodium alginate and sodium carboxymethylcellulose, disperse it in 100 mL of water, and perform ultrasonic homogenization. During the ultrasonic homogenization process, the ultrasonic temperature is 50 - 60 °C, the ultrasonic frequency is 30 - 50 KHz, the ultrasonic power is 600 - 800 W, and the ultrasonic time is 20 - 30 min to obtain a hybrid gel coating material.

3. The preparation method of the liquid slow-release nitrogen fertilizer according to claim 2, characterized in that: In step S1, during the primary mixing process, the mixing speed is 60 - 80 rpm and the mixing time is 5 - 10 min. During the secondary mixing process, the mixing speed is 80 - 100 rpm and the mixing time is 10 - 15 min.

4. The preparation method of the liquid slow-release nitrogen fertilizer according to claim 3, characterized in that: In step S2, during the high-pressure homogenization process, the homogenization pressure is 800 - 1000 bar and the homogenization time is 2 - 3 min.

5. The preparation method of the liquid slow-release nitrogen fertilizer according to claim 4, characterized in that: In step (3), the dosage of the nano-humic acid is 40 - 50 mg.

6. The preparation method of the liquid slow-release nitrogen fertilizer according to claim 5, characterized in that: In step a, the mass fraction of the aluminum sulfate solution is 16 - 17%.

Images