Preparation method and application of metal-coupled biochar-based coated fertilizer

Abstract

The application belongs to the technical field of agricultural fertilizer, and particularly relates to a preparation method and application of metal-coupled biochar-based coated fertilizer. The application is beneficial to improving the compression resistance of chitosan by adding the metal-modified biochar into the chitosan, and is further beneficial to coping with poor storage and transportation process, and meeting the requirements of industry. Experimental results prove that the metal-coupled biochar-based coated liquid prepared by the application can be expanded to 16.91 times of the original after film formation, and the degradation rate of the biochar-based film is 57.61% after 30 days of soil burying. After the biochar-based film is used for preparing the coated slow-release fertilizer, the cumulative release percentages of nitrogen, phosphorus and potassium of the coated slow-release fertilizer within 33 days are only 8.46%, 17.99% and 77.01% respectively, which are far lower than those of traditional chemical fertilizer, so that the utilization rate of the fertilizer is greatly improved, and the use cost of the fertilizer is reduced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of agricultural fertilizers, and particularly relates to a preparation method and application of a metal-coupled biochar-based coated fertilizer. BACKGROUND

[0002] Agriculture is the foundation of the national economic construction and development of China. With the growth of global population, the demand for food and agricultural products has also increased dramatically. In the process of agricultural production, fertilizers play a crucial role in effectively improving the yield and quality of food. However, traditional fertilizers are often rapidly dissolved and lost in the soil, which not only reduces the production efficiency of agriculture but also exacerbates the damage to the natural environment, which is not conducive to the healthy and sustainable development of agriculture.

[0003] The existing technology research finds that the coated slow-release fertilizer using the coating method is beneficial to slow down the release of fertilizer nutrients, but the preparation method of the coating material and the selection of raw materials have different effects on the subsequent use of the coating material. For example, Chinese patent 201710152234.1 discloses a chitosan-coated slow-release fertilizer and a preparation method thereof, which coats humic acid particles with borax and chitosan as coating materials, greatly improving the water retention effect of the fertilizer. However, this scheme has a high cost, which is not conducive to large-scale agricultural production. For another example, Chinese patent 201110379195.1 discloses a chitosan and sulfur-coated wheat special controlled-release fertilizer and a preparation method thereof. Although this method is low in price, the coating material prepared by this method is prone to rupture due to poor swelling performance, thereby polluting the soil environment and damaging the soil ecological structure. It can be seen that there is no coating material that is low in price, environmentally friendly and high in swelling performance, which seriously restricts the development and use of coated slow-release fertilizers. SUMMARY

[0004] The purpose of the present application is to provide a preparation method and application of a metal-coupled biochar-based coated fertilizer, which has a coating liquid that is easily degradable and has high swelling performance, is low in price and environmentally friendly.

[0005] In order to solve the above technical problems, the technical solutions of the present application are as follows:

[0006] The present application provides a preparation method of a metal-coupled biochar-based coating liquid, comprising the following steps:

[0007] Glycerol and chitosan are added to the metal-modified biochar water suspension and stirred, and acetic acid is added under stirring to obtain the metal-coupled biochar-based coating liquid.

[0008] Preferably, the preparation method of the biochar water suspension comprises: pyrolyzing crop stalks soaked in a metal solution to obtain metal-modified biochar; and mixing the metal-modified biochar with water to obtain the biochar water suspension.

[0009] The metal solution comprises an FeCl3 solution, an MgCl2 solution or a CaCl2 solution.

[0010] Preferably, the concentration of the metal solution is 1 mol / L.

[0011] The volume-mass ratio of the metal solution to the crop stalks is 10 mL:1 g.

[0012] The crop stalks comprise rice stalks.

[0013] Preferably, the soaking is performed under oscillation; the oscillation time is 24 h, the temperature is 25℃, and the speed is 200 rpm.

[0014] Preferably, when mixed, the mass-volume ratio of the biochar to water is 2 g:170 mL.

[0015] Preferably, the pyrolysis treatment comprises: pyrolyzing the soaked crop stalks under an N2 atmosphere and rinsing.

[0016] The rinsing solution comprises water; and after rinsing, the pH value of the solution is 6-8.

[0017] The pyrolysis temperature is 550℃, and the time is 2 h.

[0018] Preferably, the volume of the biochar water suspension, the mass of glycerol and the mass of chitosan are in a ratio of 170 mL:1 g:5 g.

[0019] The volume concentration of the acetic acid is 1% of the total system comprising the biochar water suspension, glycerol and chitosan.

[0020] The stirring speed is 700-900 rpm.

[0021] The application provides an application of the metal-coupled biochar-based coating liquid prepared by the preparation method in a metal-coupled biochar-based coated fertilizer.

[0022] The application provides a preparation method of a metal-coupled biochar-based coated fertilizer, comprising the following steps:

[0023] The fertilizer core is cyclically soaked in the metal-coupled biochar-based coating liquid prepared by the preparation method and a NaOH solution to obtain the metal-coupled biochar-based coated slow-release fertilizer.

[0024] The circulating soaking includes: soaking the fertilizer core first in a metal-coupled biochar-based coating liquid to obtain a first-soaked fertilizer core;

[0025] Soaking the first-soaked fertilizer core second in a NaOH solution to obtain a second-soaked fertilizer core;

[0026] Soaking the second-soaked fertilizer core third in the metal-coupled biochar-based coating liquid to obtain a third-soaked fertilizer core;

[0027] Soaking the third-soaked fertilizer core fourth in the NaOH solution to obtain the metal-coupled biochar-based coating slow-release fertilizer.

[0028] Preferably, the fertilizer core includes spherical fertilizers with a diameter of 2-4 mm.

[0029] The concentration of the NaOH solution is 1-2 mol / L.

[0030] Beneficial effects:

[0031] The application provides a preparation method of a metal-coupled biochar-based coating liquid, including the following steps: adding glycerol and chitosan into a water suspension of biochar modified by a metal, stirring, and adding acetic acid under the condition of stirring to obtain the metal-coupled biochar-based coating liquid. The application is beneficial to improving the compression resistance of chitosan by adding the biochar modified by the metal into the chitosan, and thus is beneficial to coping with poor storage and transportation processes and meeting the requirements of the industry. Experiments prove that the mass of the metal-coupled biochar-based coating liquid prepared by the application can expand to 16.91 times of the original mass after film formation, and the degradation rate of the biochar-based film is 57.61% after 30 days of soil burial, so the metal-coupled biochar-based coating liquid prepared by the application has high swelling performance and is easy to degrade.

[0032] Based on the above technical advantages, the application also provides application of the metal-coupled biochar-based coating liquid prepared by the preparation method in preparation of a metal-coupled biochar-based coating fertilizer. Experiments prove that after the coating liquid provided by the application is used to prepare a coating slow-release fertilizer, the cumulative release percentages of nitrogen, phosphorus and potassium of the coating slow-release fertilizer within 33 days are only 8.46%, 17.99% and 77.01%, which are much lower than those of traditional chemical fertilizers, greatly improving the utilization rate of the fertilizer and reducing the use cost of the fertilizer. BRIEF DESCRIPTION OF DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed in the embodiments.

[0034] Figure 1 The growth conditions of the peppers in different fertilization treatments in application example 1;

[0035] Figure 2 The coating coverage of the different treated fertilizers in application example 2;

[0036] Figure 3 The swelling property of the different treated fertilizer films in application example 3;

[0037] Figure 4 The water retention of the different treated fertilizers in application example 3;

[0038] Figure 5 The microbial degradability of the different treated fertilizer films in application example 4;

[0039] Figure 6 The nitrogen nutrient release curve of the different treated fertilizers in the soil column leaching test in application example 5;

[0040] Figure 7 The phosphorus nutrient release curve of the different treated fertilizers in the soil column leaching test in application example 5;

[0041] Figure 8 The potassium nutrient release curve of the different treated fertilizers in the soil column leaching test in application example 5;

[0042] Figure 9 The plant height of the pepper after different fertilization treatments in application example 1. DETAILED DESCRIPTION

[0043] The application provides a preparation method of a metal-coupled biochar-based coating liquid, and comprises the following steps: stirring glycerol and chitosan in a water suspension of biochar modified by a metal, and adding acetic acid under the stirring condition to obtain the metal-coupled biochar-based coating liquid.

[0044] In the application, the raw materials and equipment used are conventionally purchased unless otherwise specified.

[0045] The application preferably prepares crop straw powder. In the application, the preparation method of the crop straw powder preferably comprises: cleaning crop straw, and sequentially performing fixation and first homogenization treatment on the cleaned crop straw to obtain the crop straw powder.

[0046] The application preferably cleans the crop straw. The crop straw in the application preferably comprises rice straw; the cleaning method has no special requirements and can use the technology well known in the art.

[0047] After the cleaning, the application preferably performs fixation on the cleaned crop straw. The temperature of the fixation in the application is preferably 105 DEG C; and the time of the fixation is preferably 10-30 min, and more preferably 30 min.

[0048] After the fixation, the application preferably carries out a first homogenization treatment on the fixed crop straw. In the application, the first homogenization treatment preferably includes drying, crushing and sieving the fixed crop straw; the temperature of the drying is preferably 80-100℃, more preferably 80℃; the time of the drying is preferably 24h; the crushing method has no special requirements and can use the technology well known in the art; the mesh number of the sieving is preferably 80-100 mesh, more preferably 100 mesh. Through the above technical solutions, it is beneficial to obtain the crop straw powder suitable for subsequent operations.

[0049] After obtaining the crop straw powder, the application preferably carries out mixed soaking of the crop straw powder and a metal solution, and further preferably carries out the mixed soaking under the condition of oscillation; the speed of the oscillation is preferably 200r / min; the time of the oscillation is preferably 24h; the temperature of the oscillation is preferably 25℃; when the mixed soaking is carried out, the volume-mass ratio of the metal solution to the crop straw is preferably 10mL:1g; the metal solution preferably includes FeCl3 solution, MgCl2 solution or CaCl2 solution, more preferably FeCl3 solution; the concentration of the metal solution is preferably 1mol / L.

[0050] After the mixed soaking, the application preferably carries out suction filtration and a second homogenization treatment on the crop straw soaked in the metal solution. The suction filtration method has no special requirements and can realize solid-liquid separation of the metal solution and the soaked crop straw; the second homogenization treatment preferably includes drying, crushing and sieving the crop straw after the suction filtration. In the application, the temperature of the drying is preferably 80-100℃, more preferably 80℃; the time of the drying is preferably 48h; the crushing method has no special requirements and can use the technology well known in the art; the mesh number of the sieving is preferably 80-100 mesh, more preferably 100 mesh. Through the above technical solutions, it is beneficial to maintain the homogeneity of the crop straw and further obtain the crop straw powder soaked in the metal solution.

[0051] After the crushing, the application preferably carries out pyrolysis treatment on the crop straw powder soaked in the metal solution. In the application, the pyrolysis treatment preferably includes pyrolysis, rinsing and a third homogenization treatment of the crop straw powder soaked in the metal solution under N2 atmosphere.

[0052] The temperature of the pyrolysis is preferably 550℃; the time of the pyrolysis is preferably 2h; the pyrolysis equipment has no special requirements and can use the technology well known in the art.

[0053] After the pyrolysis, the pyrolyzed crop straw is preferably rinsed according to the present application. The present application preferably uses pure water for rinsing; the mode and frequency of rinsing are not particularly required, and the pH value of the rinsed solution is required to reach the requirement; the pH value of the solution is preferably 6.0-8.0, further preferably 6.5-7.5, and more preferably 7.0.

[0054] After the rinsing, the rinsed crop straw is preferably subjected to a third homogenization treatment according to the present application, which preferably includes drying, crushing and sieving; the mode of the third homogenization treatment is the same as that of the second homogenization treatment, which has been described in detail above and will not be repeated here. Through the above technical solution, it is beneficial to obtain a metal-modified biochar powder with a particle size of <0.2 mm.

[0055] After obtaining the biochar powder, the biochar powder is preferably mixed with water, and further preferably ultrasonically mixed. In the present application, the mass-to-volume ratio of the biochar powder to water is preferably 2g:170mL; the ultrasonic mixing time is preferably 30min, which is beneficial to form a system-stable biochar water suspension.

[0056] After obtaining the biochar water suspension, glycerol and chitosan are added to the biochar water suspension and stirred according to the present application. In the present application, the volume of the biochar water suspension, the mass of glycerol and the mass of chitosan are preferably more preferably 170mL:1g:5g; the stirring speed is preferably 700-900rpm, more preferably 900rpm; the temperature during stirring is preferably 40-55℃, more preferably 50℃; and the stirring time is preferably 2h.

[0057] At the same time of stirring, acetic acid is added to the biochar water suspension, and more preferably added dropwise to the biochar water suspension. The volume concentration of acetic acid according to the present application is 1% of the total system containing biochar water suspension, glycerol and chitosan; the mode of dropwise addition is not particularly required and can use techniques well known in the art. By dropwise adding acetic acid, it is beneficial to achieve solubilization of chitosan, and further obtain a metal-coupled biochar-based coating liquid, which has high swelling performance and is easy to degrade.

[0058] The present application provides the use of the metal-coupled biochar-based coating liquid prepared by the preparation method of the above technical solution in a metal-coupled biochar-based coated fertilizer, which is beneficial to improve the water retention and utilization rate of the coated fertilizer.

[0059] The application further provides a preparation method of the metal-coupled biochar-based coated fertilizer, comprising the following steps: cyclically immersing a fertilizer core in the metal-coupled biochar-based coating solution and a NaOH solution to obtain the metal-coupled biochar-based coated slow-release fertilizer; the cyclically immersing comprises: immersing the fertilizer core in the metal-coupled biochar-based coating solution for the first time to obtain a first-immersed fertilizer core; immersing the first-immersed fertilizer core in the NaOH solution for the second time to obtain a second-immersed fertilizer core; immersing the second-immersed fertilizer core in the metal-coupled biochar-based coating solution for the third time to obtain a third-immersed fertilizer core; and immersing the third-immersed fertilizer core in the NaOH solution for the fourth time to obtain the metal-coupled biochar-based coated slow-release fertilizer.

[0060] Preferably, the fertilizer core is immersed in the metal-coupled biochar-based coating solution for the first time to obtain a first-immersed fertilizer core; the fertilizer core preferably comprises spherical fertilizers with a diameter of 2-4 mm; the source of the spherical fertilizers is not specifically required, and the actual planting requirements are met; the first-immersion time is preferably 5-10 s, and more preferably 5 s; and the first-immersion mode and amount are not specifically required, and the metal-coupled biochar-based coating solution uniformly coats the fertilizer core, and the fertilizer core does not dissolve in the coating solution.

[0061] After obtaining the first-immersed fertilizer core, the first-immersed fertilizer core is preferably immersed in the NaOH solution for the second time to obtain a second-immersed fertilizer core; in the application, the second-immersion time is preferably 1 min; and the concentration of the NaOH solution is preferably 1-2 mol / L, and more preferably 2 mol / L.

[0062] After obtaining the second-immersed fertilizer core, the second-immersed fertilizer core is preferably immersed in the metal-coupled biochar-based coating solution for the third time to obtain a third-immersed fertilizer core; in the application, the third-immersion method is the same as the first-immersion method, and the first-immersion method has been described in detail above, and will not be described herein again.

[0063] After obtaining the third-immersed fertilizer core, the third-immersed fertilizer core is preferably immersed in the NaOH solution for the fourth time; in the application, the fourth-immersion method is the same as the second-immersion method, and the second-immersion method has been described in detail above, and will not be described herein again. The cyclically immersing of the fertilizer core is conducive to forming a crosslinked network of the coating solution on the surface of the fertilizer core.

[0064] After the fourth immersion, the fourth-immersed fertilizer core is preferably dried; in the application, the drying temperature is preferably 30-40℃, and more preferably 30℃; and the drying time is preferably 18-36 h, and more preferably 24 h, which is conducive to removing acetic acid, water and excess NaOH used in the preparation process.

[0065] Experiments prove that the metal-coupled biochar-based film prepared by the application can expand to 16.91 times of the original after film formation, and the degradation rate of the biochar-based film is only 57.61% after being buried in soil for 30 days. After the biochar-based film is used to prepare the coated slow-release fertilizer, the cumulative release percentages of nitrogen, phosphorus and potassium of the coated slow-release fertilizer within 33 days are only 8.46%, 17.99% and 77.01% respectively, which are much lower than those of traditional fertilizers, thereby greatly improving the utilization rate of the fertilizer and reducing the use cost of the fertilizer.

[0066] In order to further illustrate the application, the preparation method and application of the metal-coupled biochar-based coated fertilizer provided by the application are described in detail below in combination with the drawings and examples, but they should not be understood as limiting the protection scope of the application.

[0067] Example 1

[0068] A preparation method of a metal-coupled biochar-based coated fertilizer, comprising the following steps:

[0069] 1) Taking rice straw as raw material, after cleaning and 105℃ blanching for 30min, the blanched straw is placed in an 80℃ oven, and the straw is completely dried after 24h. The dried straw is crushed and sieved through a 100 mesh sieve to obtain straw powder;

[0070] 2) 10g of the straw powder in step 1) is soaked in 100mL of FeCl3 solution with a concentration of 1mol / L, and oscillated in a constant temperature water bath shaker at 25℃ with a vibration speed of 200rpm for 24h to obtain metal-modified rice straw;

[0071] 3) The rice straw in step 2) is filtered, and then dried in an 80℃ oven for 48h, ground and sieved through a 100 mesh sieve to obtain metal-modified rice straw powder;

[0072] 4) The metal-modified rice straw powder in step 3) is placed in a tube furnace, pyrolyzed at 550℃ for 2h under the condition of being filled with nitrogen, and cooled to room temperature to obtain pyrolyzed rice straw powder;

[0073] 5) The pyrolyzed rice straw powder in step 4) is washed with pure water, and when the pH value of the washing solution is 6-8, the washed rice straw is dried at 80℃ for 48h, ground and sieved through a 100 mesh sieve to obtain iron-modified biochar, and the particle size of the iron-modified biochar is <0.2mm at this time;

[0074] 6) Take 2 g of iron modified biochar in step 5) into 170 mL of pure water, and form a biochar suspension after 30 min of ultrasonic; add 5 g of chitosan and 1 g of glycerol to the biochar suspension and stir, and add acetic acid at 50℃ while stirring (stirring speed is 900 rpm) until the concentration of acetic acid is 1% (1.695 mL of acetic acid is added dropwise according to calculation), to achieve complete solubilization of chitosan, and obtain a coating liquid;

[0075] 7) Select nitrogen, phosphorus and potassium compound fertilizer with particle size of 2-4 mm, immerse the fertilizer in the coating liquid prepared in step 6) for 5 s through the process of immersion, and discharge it through the filtration system, then immerse the discharged fertilizer in 2 mol / L NaOH solution for 1 min, and discharge it through the filtration system again, then immerse the discharged fertilizer in the coating liquid prepared in step 6) for 5 s, and discharge it through the filtration system, then immerse the discharged fertilizer in 2 mol / L NaOH solution for 1 min, and discharge it through the filtration system, then place the coated fertilizer in a 30℃ oven and dry for 24 h until the solvent evaporates, to form iron modified biochar based coated slow-release fertilizer.

[0076] Example 2

[0077] A method for preparing a metal-coupled biochar-based coated fertilizer, the steps are:

[0078] 1) Take rice straw as raw material, wash and kill green at 105℃ for 30 min, then put the killed green straw into an 80℃ oven and dry completely for 24 h, then crush and pass through a 100 mesh sieve to obtain straw powder;

[0079] 2) Take 10 g of straw powder in step 1) and immerse it in 100 mL of 1 mol / L CaCl2 solution, and oscillate at 25℃ and 200 rpm for 24 h in a constant temperature water bath shaker to obtain metal modified rice straw;

[0080] 3) Filter the rice straw in step 2), then dry it in an 80℃ oven for 48 h, grind and pass through a 100 mesh sieve to obtain metal modified rice straw powder;

[0081] 4) Put the metal modified rice straw powder in step 3) into a tube furnace, pyrolyze it at 550℃ under nitrogen atmosphere for 2 h, and cool it to room temperature to obtain pyrolyzed rice straw powder;

[0082] 5) Rinse the pyrolyzed rice straw powder in step 4) with pure water, and when the pH value of the rinsed solution is 6-8, dry the rinsed rice straw at 80℃ for 48 h, grind and pass through a 100 mesh sieve to obtain calcium modified biochar; at this time, the particle size of the calcium modified biochar is <0.2 mm;

[0083] 6) Take 2 g of calcium modified biochar from step 5) into 170 mL of pure water, and form a biochar suspension after 30 min of ultrasonic; add 5 g of chitosan and 1 g of glycerol to the suspension, and add acetic acid at 50°C while stirring (stirring speed is 900 rpm) until the acetic acid concentration is 1% (1.695 mL of acetic acid is added by calculation), so that the chitosan is completely solubilized, and a coating solution is obtained;

[0084] 7) Select nitrogen, phosphorus and potassium compound fertilizer with particle size of 2-4 mm, immerse the fertilizer in the coating solution prepared in step 6) for 5 s by the process of immersion, and discharge it through the filtration system, then immerse the discharged fertilizer in 2 mol / L NaOH solution for 1 min, and discharge it through the filtration system again, then immerse the discharged fertilizer in the coating solution prepared in step 6) for 5 s, and discharge it through the filtration system, then immerse the discharged fertilizer in 2 mol / L NaOH solution for 1 min, and discharge it through the filtration system, then place the coated fertilizer in a 30°C oven and dry for 24 h until the solvent evaporates, to form calcium modified biochar based coated slow-release fertilizer.

[0085] Example 3

[0086] A method for preparing a metal-coupled biochar-based coated fertilizer, the steps are as follows:

[0087] 1) Using rice straw as raw material, after washing and 105°C blanching for 30 min, the blanched straw is placed in an 80°C oven and dried for 24 h until the straw is completely dried, then the dried straw is crushed and sieved through a 100 mesh sieve to obtain straw powder;

[0088] 2) Take 10 g of straw powder in step 1) and soak it in 100 mL of 1 mol / L MgC2 solution, and oscillate it in a constant temperature water bath shaker at 25°C and 200 rpm for 24 h to obtain metal modified rice straw;

[0089] 3) Filter the rice straw in step 2), then dry it in an 80°C oven for 48 h, grind it and sieve it through a 100 mesh sieve to obtain metal modified rice straw powder;

[0090] 4) Place the metal modified rice straw powder in step 3) in a tube furnace, pyrolyze it at 550°C under nitrogen atmosphere for 2 h, and cool it to room temperature to obtain pyrolyzed rice straw powder;

[0091] 5) Rinse the pyrolyzed rice straw powder in step 4) with pure water, and when the pH value of the rinsed solution is 6-8, dry the rinsed rice straw at 80°C for 48 h, grind it, and sieve it through a 100 mesh sieve to obtain magnesium modified biochar; At this time, the particle size of the magnesium modified biochar is <0.2 mm;

[0092] 6) Take 2g of magnesium modified biochar from step 5) and put it into 170mL of pure water, form a biochar suspension by ultrasonic for 30min, add 5g of chitosan and 1g of glycerol into the suspension, and add acetic acid to the suspension by stirring (stirring speed is 900rpm) at 50℃ until the concentration of acetic acid reaches 1% (calculated, add 1.695mL of acetic acid), to achieve complete solubilization of chitosan, to obtain a coating liquid;

[0093] 7) Select nitrogen, phosphorus and potassium compound fertilizer with particle size of 2-4mm, immerse the fertilizer in the coating liquid prepared in step 6) for 5s by impregnation process, and discharge it through the filtration system, then immerse the discharged fertilizer in 2mol / L NaOH solution for 1min, and discharge it through the filtration system again, then immerse the discharged fertilizer in the coating liquid prepared in step 6) for 5s, and discharge it through the filtration system, then immerse the discharged fertilizer in 2mol / L NaOH solution for 1min, and discharge it through the filtration system, then put the coated fertilizer in a 30℃ oven to dry for 24h until the solvent evaporates, to form calcium modified biochar based coated slow-release fertilizer.

[0094] Comparative Example 1

[0095] A method for preparing an unmodified biochar based coated fertilizer, the steps are as follows:

[0096] 1) Take rice straw as raw material, wash it, and then kill the greenness at 105℃ for 30min, then put the killed straw into an 80℃ oven, and dry the straw completely for 24h, then crush and sieve the dried straw through a 100 mesh sieve to obtain straw powder;

[0097] 2) Put the straw powder in step 1) into a tube furnace, introduce nitrogen into the reaction system, and pyrolyze at 550℃ for 2h, then cool to room temperature to obtain pyrolyzed biochar;

[0098] 3) Wash the pyrolyzed rice straw powder in step 2) with pure water, and when the pH value of the washing solution is 6-8, dry the washed rice straw at 80℃ for 48h, grind and sieve through a 100 mesh sieve to obtain biochar;

[0099] 4) Take 2g of biochar from step 3) and put it into 170mL of pure water, form a biochar suspension by ultrasonic for 30min, add 5g of chitosan and 1g of glycerol into the biochar suspension, and add acetic acid to the suspension by stirring (stirring speed is 900rpm) at 50℃ until the concentration of acetic acid reaches 1% (calculated, add 1.695mL of acetic acid), to achieve complete solubilization of chitosan, to obtain a coating liquid;

[0100] 5) Selecting the nitrogen, phosphorus and potassium compound fertilizer with the particle size of 2-4 mm, immersing the fertilizer in the coating liquid prepared in step 4) through the process of immersion, discharging through the filtering system, immersing the discharged fertilizer in the 2 mol / L NaOH solution for 1 min, discharging through the filtering system, then immersing the discharged fertilizer in the coating liquid prepared in step 4) again, discharging through the filtering system, immersing the discharged fertilizer in the 2 mol / L NaOH solution for 1 min again, discharging through the filtering system, and then placing the coated fertilizer in a 30℃ oven for drying for 24 h until the solvent is evaporated to form the biochar-based coated slow-release fertilizer.

[0101] Comparative Example 2

[0102] A preparation method of a conventional coated fertilizer, the steps of which are as follows:

[0103] 1) Placing 5 g of chitosan and 1 g of glycerol in 170 mL of pure water, adding acetic acid at 50℃ while stirring (stirring speed: 900 rpm) until the concentration of acetic acid is 1% (1.695 mL of acetic acid is added according to calculation), achieving complete solubilization of chitosan to obtain a coating liquid;

[0104] 2) Selecting the nitrogen, phosphorus and potassium compound fertilizer with the particle size of 2-4 mm, immersing the fertilizer in the coating liquid prepared in step 1) through the process of immersion, discharging through the filtering system, immersing the discharged fertilizer in the 2 mol / L NaOH solution for 1 min, discharging through the filtering system, then immersing the discharged fertilizer in the coating liquid prepared in step 1) again, discharging through the filtering system, immersing the discharged fertilizer in the 2 mol / L NaOH solution for 1 min again, discharging through the filtering system, and then placing the coated fertilizer in a 30℃ oven for drying for 24 h until the solvent is evaporated to form the coated slow-release fertilizer.

[0105] Comparative Example 3

[0106] Common fertilizer: the fertilizer core in Examples 1-3 and Comparative Examples 1-2, i.e. the nitrogen, phosphorus and potassium compound fertilizer, the mass ratio of NPK in the compound fertilizer is 4:2:1, and the brand is Lüpan.

[0107] Application Example 1

[0108] Effects of different fertilization treatments on the height and growth of pepper plants

[0109] The coated fertilizers prepared in Examples 1-3 and Comparative Examples 1-2 were respectively applied to pots in which peppers were planted (pepper variety was Supeiqi No. 5), and the application amount was 1 g per pot. During the experiment, the peppers were first grown, and the peppers with basically the same growth conditions were selected and transplanted in flowerpots, and routine management was performed. Among them, the potting was set as follows: 1 kg of soil was contained in each pot, 1 pepper was planted in each pot, each pot was a treatment, and 3 repeated parallel experiments were performed for each treatment. A treatment without applying any fertilizer was used as a blank control, and a treatment applying the ordinary fertilizer in Comparative Example 3 was used as a control treatment.

[0110] Results and analysis:

[0111] After 30 days of planting, the pepper plant heights in different treatments were counted and analyzed, and the results are shown in Table 1 and Figure 9 ; the growth conditions of the peppers were observed, and the results are shown in Figure 1 (As shown in Figure 1 , the upper graph is a side view of the growth conditions of the peppers, and in the side view, Fe represents the treatment results of Example 1, Ca represents the treatment results of Example 2, Mg represents the treatment results of Example 3, BC represents the treatment results of Comparative Example 1, NO-BC represents the treatment results of Comparative Example 2, NPK represents the treatment results of Comparative Example 3, and CK represents the treatment results of the blank control; the lower graph is a plan view of the growth conditions of the peppers)

[0112] Table 1 Influence of different fertilizer treatments on the plant height of peppers (unit: cm)

[0113] Replicate 1 Replicate 2 Replicate 3 Average Example 1 20 18.5 16 18.7 Example 2 21.8 18.6 11 17.13 Example 3 14.5 14 12.5 13.67 Comparative Example 1 14.5 13.5 10.3 12.77 Comparative Example 2 13.8 13.4 11.7 12.97 Comparative Example 3 16.5 13.5 12.1 14.03 Blank Control 12.5 12.4 12.3 12.4

[0114] As shown in Table 1, Figure 1 Table 2 and Figure 9 , the plant growth of the Fe modified biochar-based coated slow-release fertilizer is better than that of the Ca modified biochar-based coated slow-release fertilizer, which is better than that of the Mg modified biochar-based coated slow-release fertilizer, and the growth conditions of the nano metal modified biochar-based coated slow-release fertilizer are obviously better than those of the biochar-based coated slow-release fertilizer and the chitosan-based coated slow-release fertilizer. It can be seen that the nano metal modified biochar-based coated slow-release fertilizer has a good effect of promoting plant growth, can be better absorbed and utilized by plants, can provide the required nutrients for plants, can save the cost of fertilization, can reduce environmental hazards, can achieve environmental friendliness, can achieve good slow-release effect, and can promote plant growth.

[0115] Application Example 2

[0116] After the coated fertilizers in Examples 1-3, Comparative Examples 1-2 and the ordinary fertilizer in Comparative Example 3 were subjected to routine digestion and cooking treatment, each fertilizer corresponded to a treatment, and each treatment was repeated three times.

[0117] The coating rates of the fertilizers in different treatments were counted and analyzed, and the results are shown in Table 2 and Figure 2 (As shown inFigure 2 In Table 2, Fe represents the treatment result of Example 1, Ca represents the treatment result of Example 2, Mg represents the treatment result of Example 3, BC represents the treatment result of Comparative Example 1, and NO-BC represents the treatment result of Comparative Example 2.

[0118] Table 2 Coating rate of different treated fertilizers (unit: %)

[0119] Replicate 1 Replicate 2 Replicate 3 Average Example 1 94.0838 90.6448 84.7189 89.82 Example 2 87.81523 75.1522 83.6105 82.19 Example 3 95.6417 82.3527 86.3816 88.13 Comparative Example 1 92.2292 90.9316 81.9477 88.37 Comparative Example 2 96.4206 73.3769 84.2043 84.67 Comparative Example 3 100 100 100 100

[0120] From Table 2 and Figure 2 It can be seen that the coating rate of the fertilizers after different treatments is all above 82%, which has good consistency and is conducive to subsequent slow-release experiments at the same level. In addition, since the fertilizers have a high coating rate, they are conducive to providing sufficient nutrients to plants.

[0121] Application Example 3

[0122] 1) The swelling properties of the films in Examples 1-3 and Comparative Example 2 were verified respectively, with one treatment corresponding to each fertilizer, and each treatment was performed twice in parallel. The results are shown in Table 3 and Figure 3 (At Figure 3 In Table 2, Fe represents the treatment result of Example 1, Ca represents the treatment result of Example 2, Mg represents the treatment result of Example 3, BC represents the treatment result of Comparative Example 1, and NO-BC represents the treatment result of Comparative Example 2.

[0123] Table 3 Swelling properties of coating materials in different treatments (unit: %)

[0124] Replicate 1 Replicate 2 Average Example 1 1689 1693.21 1691.10 Example 2 659.29 737.44 698.36 Example 3 1663.99 1783.27 1723.63 Comparative Example 2 659.68 705.85 682.77

[0125] From Table 3 and Figure 3 It can be seen that the iron-modified biochar-based film can expand to 16.91 times the original size at most, and the swelling properties of each metal-modified biochar-based film are greater than that of the pure chitosan-based film. This indicates that with the addition of metal-modified biochar, the swelling properties of the film are improved, which can effectively improve the water retention capacity of the soil and make the fertilizer suitable for the fertilization environment under dry conditions. Better swelling properties indicate that the film material has better flexibility and is not easily broken by water, and it also has good mechanical properties.

[0126] 2) The water retention properties of each fertilizer used in Application Example 1 were verified respectively, and the water retention properties at 0d, 5d, 10d, 15d, 21d and 23d were statistically analyzed. The results are shown in Table 4 and Figure 4 (At Figure 4In this table, Fe represents the processing result of Example 1, Ca represents the processing result of Example 2, Mg represents the processing result of Example 3, BC represents the processing result of Comparative Example 1, NO-BC represents the processing result of Comparative Example 2, NPK represents the processing result of Comparative Example 3, and CK represents the processing result of the blank control.

[0127] Table 4. Effects of different fertilizers on water retention (unit: %)

[0128]

[0129]

[0130] From Table 4 and Figure 4 It can be seen that the Fe-modified biochar-based membrane has better water retention performance, while the metal-modified biochar-based membrane has relatively better water retention performance. The water retention performance of the biochar-based membrane is better than that of pure chitosan-based, ordinary compound fertilizer, and untreated samples. This indicates that the fertilizer we prepared can effectively improve soil water retention.

[0131] 3) The degradation rates of each fertilizer film in Examples 1-3 and Comparative Examples 1-2 were measured (the degradation rate determination method can be found in the literature: El Assimi T, Lakbita O, El Meziane A, et al. Sustainable coating material based on chitosan-clay composite and paraffin wax for slow-release DAP fertilizer[J]. International journal of biological macromolecules, 2020, 161: 492-502.), and statistical analysis was performed. Each fertilizer corresponded to one treatment, and each treatment was repeated 3 times. The results are shown in Table 5 and Figure 5 (exist Figure 5 In this text, Fe represents the processing result of Example 1, Ca represents the processing result of Example 2, Mg represents the processing result of Example 3, BC represents the processing result of Comparative Example 1, and NO-BC represents the processing result of Comparative Example 2.

[0132] Table 5. Membrane degradability under different treatments (unit: %)

[0133]

[0134] Note: In Figure 5 In the process, values ​​with large errors need to be discarded.

[0135] From Table 5 and Figure 5It can be seen that the degradation rates of the nano-metal modified biochar-based film are 54.65%, 46.52%, and 57.61% respectively after 30 days of soil burial, which are much higher than those of the unmodified coated fertilizer, and the biodegradation performance is better, which is beneficial to the environment and belongs to an environmentally friendly material.

[0136] Application Example 4

[0137] The coated fertilizers obtained in Examples 1-3 and Comparative Examples 1-2 and the ordinary chemical fertilizer in Comparative Example 3 are subjected to soil column leaching tests, and the release amounts of nutrient nitrogen, nutrient phosphorus, and nutrient potassium of different fertilizers within 33 days (the first day is counted when the fertilizer is placed in the soil column and the first leaching water is added) are respectively counted, wherein the release amounts of nutrient nitrogen, nutrient phosphorus, and nutrient potassium in different treatments are shown in Tables 6-8, and the release curves of nitrogen nutrient, phosphorus nutrient, and potassium nutrient are shown in Figures 1-3 respectively. Figure 6-8 (At Figure 6-8 In the figures, Fe represents the treatment results of Example 1, Ca represents the treatment results of Example 2, Mg represents the treatment results of Example 3, BC represents the treatment results of Comparative Example 1, NO-BC represents the treatment results of Comparative Example 2, and NPK represents the treatment results of Comparative Example 3.

[0138] Table 6 Release amount of nutrient nitrogen in different fertilizers (unit: %)

[0139]

[0140] Table 7 Release amount of nutrient phosphorus in different fertilizers (unit: %)

[0141]

[0142]

[0143] Table 8 Release amount of nutrient potassium in different fertilizers (unit: %)

[0144]

[0145] From Tables 6-8 and Figure 6-8 It can be seen that, compared with traditional chemical fertilizers, the coated slow-release fertilizer has advantages in slow-release performance of nitrogen, phosphorus, and potassium nutrients. According to the soil column leaching test, the cumulative release percentages of nitrogen, phosphorus, and potassium of the coated slow-release fertilizer developed in Example 1 within 33 days are 8.457%, 17.988%, and 77.010% respectively, which are about 8.46%, 17.99%, and 77.01% respectively, and are much lower than those of traditional chemical fertilizers. The excellent slow-release effect can balance the supply of nutrients necessary for plant growth, reduce nutrient loss, improve fertilizer utilization rate, and reduce cost.

[0146] Although the above embodiments have been described in detail, it should be understood that these are only some embodiments of the present application, but not all embodiments. Other embodiments can be obtained on the basis of the above embodiments without creativity, and these embodiments all belong to the protection scope of the present application.

Claims

1. A method for preparing a metal-coupled biochar-based encapsulated liquid, characterized in that, The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The metal solution comprises FeCl3 solution, MgCl2 solution or CaCl2 solution; The mass / volume ratio of the biochar and water is 2g:170mL; The volume of the biochar water suspension, the mass of glycerol and the mass of chitosan are 170mL:1g:5g; The volume concentration of the acetic acid is 1% of the total system containing the biochar water suspension, glycerol and chitosan; The stirring speed is 700-900rpm.

2. The production method according to claim 1, characterized by, The concentration of the metal solution is 1mol / L; The volume / mass ratio of the metal solution and the crop straw is 10mL:1g; The crop straw comprises rice straw.

3. The preparation method according to claim 1, characterized in that, The soaking is performed under oscillation; the oscillation time is 24h, the temperature is 25℃ and the speed is 200rpm.

4. The method of claim 1, wherein, The pyrolysis treatment comprises pyrolyzing and rinsing the soaked crop straw under N2 atmosphere; The rinsing solution comprises water; after rinsing, the pH value of the solution is 6-8; The pyrolysis temperature is 550℃ and the time is 2h.

5. Application of the metal-coupled biochar-based coating liquid prepared by the method of any one of claims 1-4 in metal-coupled biochar-based coating fertilizer.

6. A method for preparing a metal-coupled biochar-based coated fertilizer, characterized in that, The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The method comprises the following steps: The fertilizer core comprises spherical fertilizer with a diameter of 2-4mm; 7. The production method according to claim 6, wherein The concentration of the NaOH solution is 1-2mol / L. ​

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