A biochar-based slow-release improver and its preparation method

Abstract

The present invention discloses a biochar-based slow-release improver and a preparation method thereof. The biochar-based slow-release improver comprises biochar, a chemical fertilizer at least partially formed in the pores of the biochar, and a biodegradable film at least partially wrapped around the surface of the biochar. In the biochar-based slow-release improver provided by the present invention, the biodegradable film at least partially wrapped around the surface of the biochar can form a shielding layer, enclosing the chemical fertilizer formed in the pores of the biochar within the biochar carrier. Under natural conditions, these enclosed pores are gradually opened by the action of microorganisms, achieving a slow-release effect of nutrients. This slow-release effect can further reduce the loss of chemical fertilizers and improve the long-term effectiveness of fertilizers.

Description

Technical Field

[0001] The present invention relates to the technical field of soil improvement, and in particular to a biochar-based slow-release improver and a preparation method thereof. Background Art

[0002] Currently, most rivers and lakes are severely eutrophic. Eutrophication is caused by excessive levels of plant nutrients such as nitrogen and phosphorus. Most water eutrophication is primarily caused by the accumulation of externally imported nutrients in the water. Agricultural non-point source pollution is a major source of pollution. According to statistics, my country is currently the world's largest producer and consumer of fertilizers. Conventional fertilizers have a short shelf life and cannot meet the fertilizer requirements of crops. To increase crop yields, more fertilizer is often applied. Excessive fertilizer application not only wastes resources and causes soil compaction, but also often flows with rainwater into rivers, lakes, and rivers, leading to eutrophication. This, in turn, triggers more serious environmental problems, including algal blooms, red tides, and black and smelly water. Therefore, addressing fertilizer loss and ensuring its long-term effectiveness is crucial to addressing agricultural non-point source pollution in my country. Summary of the Invention

[0003] The main purpose of the present invention is to provide a biochar-based slow-release improver and a preparation method thereof, aiming to solve the problem in the prior art that chemical fertilizers are easily lost and fertilizers cannot achieve long-term effectiveness.

[0004] To achieve the above objectives, the present invention proposes a biochar-based slow-release improver, comprising biochar, a chemical fertilizer at least partially formed in the pores of the biochar, and a biodegradable film at least partially wrapped around the surface of the biochar.

[0005] Optionally, the chemical fertilizer includes at least one of ammonium salt, potassium salt, urea and calcium salt.

[0006] Optionally, the biochar-based slow-release improver includes 60 to 120 parts of biochar, 100 to 400 parts of chemical fertilizers and 5 to 20 parts of biodegradable films.

[0007] Optionally, the material of the biodegradable film includes at least one of sodium alginate, polyvinyl alcohol, polyacrylamide, and potassium polyacrylate.

[0008] Optionally, the average particle size of the biochar-based slow-release modifier is 3 to 5 mm.

[0009] The present invention also provides a method for preparing a biochar-based slow-release improver, comprising the following steps:

[0010] Step S1, adding biochar powder and a chemical fertilizer source to a solution containing a polymer thickener to obtain a first suspension;

[0011] Step S2, adding the first suspension to the aqueous solution containing calcium ions in a dropwise manner, and causing the polymer thickener to undergo a cross-linking reaction with the calcium ions to form a gel wrapped around the surface of the biochar;

[0012] Step S3: drying to obtain the biochar-based slow-release improver.

[0013] Optionally, in step S2:

[0014] The cross-linking reaction temperature is 2-5°C; and / or,

[0015] The cross-linking reaction time is 18 to 36 hours; and / or,

[0016] The first suspension is dripped into the aqueous solution containing calcium ions through a syringe, the distance between the liquid outlet of the syringe and the liquid surface of the aqueous solution containing calcium ions is 10 to 20 cm; the dripping speed is 0.4 ml to 0.6 ml per 10 seconds.

[0017] Optionally, in step S2, the mass proportion of calcium salt in the aqueous solution containing calcium ions is 2.5-5%.

[0018] Optionally, the chemical fertilizer source includes at least one of urea, ammonium salt, and potassium salt; and / or the polymer thickener includes at least one of sodium alginate, polyvinyl alcohol, polyacrylamide, and potassium polyacrylate; and / or the calcium ion-containing aqueous solution includes at least one of calcium hydroxide solution and calcium chloride solution.

[0019] Optionally, in step S1, the average particle size of the biochar powder is 80-120 meshes; and / or; in step S3, the drying treatment is drying at a temperature of 30-50°C.

[0020] In the technical solution of the present invention, the biodegradable film at least partially wrapped around the surface of the biochar forms a shielding layer, enclosing chemical fertilizers formed in the biochar pores within the biochar carrier. Under natural conditions, these enclosed pores gradually open due to microbial activity, achieving a slow-release effect of nutrients. This slow-release effect, in turn, reduces fertilizer loss and improves the long-term effectiveness of the fertilizer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0022] Figure 1 This is a flow chart of the preparation process of the biochar-based slow-release improver provided in Example 1 of the present invention;

[0023] Figure 2 This is a physical picture of the biochar-based slow-release improver provided in Example 1 of the present invention;

[0024] Figure 3-7 This is a physical picture of the biochar-based slow-release improver provided in Examples 4-8 of the present invention.

[0025] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. Where the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased commercially. In addition, the meaning of "and / or" appearing in the full text includes three parallel schemes. Taking "A and / or B" as an example, it includes scheme A, or scheme B, or schemes that A and B meet at the same time. In addition, the technical solutions between the various embodiments can be combined with each other, but must be based on the ability of ordinary technicians in this field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that the combination of such technical solutions does not exist and is not within the scope of protection required by the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] Conventional chemical fertilizers have a short shelf life and cannot meet the fertilizer requirements of crops. To increase crop yields, more fertilizer is often applied. Excessive fertilizer application not only wastes resources and causes soil compaction, but also often flows with rainwater into rivers and lakes, leading to eutrophication and, in turn, causing more serious environmental problems such as algal blooms, red tides, and black and smelly water. Therefore, addressing fertilizer loss and ensuring its long-term effectiveness is crucial to addressing agricultural non-point source pollution in my country.

[0028] In view of this, the present invention proposes a biochar-based slow-release improver, comprising biochar, a chemical fertilizer at least partially formed in the pores of the biochar, and a biodegradable film at least partially wrapped around the surface of the biochar.

[0029] In the technical solution of the present invention, the biodegradable film at least partially wrapped around the surface of the biochar forms a shielding layer, enclosing chemical fertilizers formed in the biochar pores within the biochar carrier. Under natural conditions, these enclosed pores gradually open due to microbial activity, achieving a slow-release effect of nutrients. This slow-release effect, in turn, reduces fertilizer loss and improves the long-term effectiveness of the fertilizer.

[0030] In one feasible embodiment, the chemical fertilizer includes at least one of ammonium salt, potassium salt, urea, and calcium salt. Among them, the ammonium salt, potassium salt, and calcium salt may contain phosphorus so as to simultaneously meet the soil's demand for phosphorus. For example, the ammonium salt may include at least one of ammonium chloride, ammonium sulfate, monoammonium phosphate, and diammonium phosphate; the potassium salt may include at least one of potassium dihydrogen phosphate, potassium sulfate, and potassium chloride; and the calcium salt may include at least one of calcium hydrogen phosphate and calcium dihydrogen phosphate.

[0031] It should be noted that biochar is a solid product of high-temperature pyrolysis of biomass. It has many excellent properties, such as porosity, high stability, high aromatization, a large number of various functional groups on the surface, and both positive and negative charges. It can adsorb molecules and anions and cations, polar and non-polar substances, and can effectively adsorb various salts to achieve a slow-release function. At the same time, after being applied to the soil, it can also increase the soil organic carbon content, improve the soil's fertilizer and water retention properties, and is beneficial to the habitat and activity of soil microorganisms. It also has a good effect in adsorbing soil salt ions and heavy metal ions.

[0032] In the technical solution of the present invention, the chemical fertilizer formed in the pores of the biochar includes inorganic salts adsorbed in the pores of the biochar by electrostatic action, such as ammonium salts, potassium salts, etc. The chemical fertilizer also includes urea molecules and urea crystalline particles that are physically adsorbed or chemically adsorbed in the pores of the biochar. For example, urea can be adsorbed on the surface of the biochar by physical adsorption, and at the same time, the oxygen-containing functional groups on the surface of the biochar form hydrogen bonds with the urea molecules to undergo chemical adsorption; urea can also exist in the pores of the biochar in the form of crystalline particles. The chemical fertilizer also includes inorganic salt particles. For example, calcium salts such as calcium hydrogen phosphate can exist in the pores of the biochar in the form of precipitated particles, and ammonium salts can exist in the pores of the biochar in the form of inorganic salt particles. Chemical fertilizers can be formed in the pores of the biochar, or they can be formed on the surface of the biochar at the same time.

[0033] In this way, when the chemical fertilizers in the biochar pores include urea crystal particles and inorganic salt particles, the biochar-based slow-release modifier provided by the present invention has multiple slow-release effects. On the one hand, the biodegradable film at least partially wrapped on the surface of the biochar can form a shielding layer to seal the chemical fertilizers formed in the biochar pores in the biochar carrier. Under natural conditions, these closed pores will gradually be opened due to the action of microorganisms, thereby achieving the slow-release effect of nutrients. On the other hand, the urea crystal particles and inorganic salt particles present in the biochar pores require a longer time to be released into the soil than other forms of chemical fertilizers, such as urea molecules through physical adsorption, thereby achieving another slow-release effect of nutrients.

[0034] In one feasible method, the biochar-based slow-release agent comprises 60-120 parts biochar, 100-400 parts chemical fertilizer, and 5-20 parts biodegradable film. The biochar content influences the morphology of the biochar-based slow-release agent, while the biodegradable film content influences its coating effect. The above ratio allows the biochar-based slow-release agent to form a spherical shape with good coating effect.

[0035] In order to achieve the coating of biochar with a biodegradable film, in the present invention, the material of the biodegradable film includes at least one of sodium alginate, polyvinyl alcohol, polyacrylamide, and potassium polyacrylate.

[0036] In one feasible embodiment, the average particle size of the biochar-based slow-release amendment is 3 to 5 mm, which helps the biochar-based slow-release amendment to be evenly dispersed in the soil particles.

[0037] The present invention also provides a method for preparing a biochar-based slow-release improver, comprising the following steps:

[0038] Step S1: adding biochar powder and a chemical fertilizer source into a solution containing a polymer thickener to obtain a first suspension.

[0039] The polymer thickener includes at least one of sodium alginate, polyvinyl alcohol, polyacrylamide, and potassium polyacrylate. The biochar powder has an average particle size of 80 to 120 mesh. The polymer thickener solution is used to evenly disperse the biochar powder and prevent it from agglomerating, thereby facilitating the incorporation of chemical fertilizers into the pores of the biochar.

[0040] The chemical fertilizer source includes at least one of urea, ammonium salts, and potassium salts. The ammonium salts and potassium salts may contain phosphorus to simultaneously meet the soil's phosphorus requirements. For example, the ammonium salt may include at least one of ammonium chloride, ammonium sulfate, monoammonium phosphate, and diammonium phosphate; and the potassium salt may include at least one of potassium dihydrogen phosphate, potassium sulfate, and potassium chloride.

[0041] In the process of adding biochar powder and chemical fertilizer source to a solution containing a polymer thickener, at least part of the urea, ammonium salt, and potassium salt can be adsorbed in the pores of the biochar. For example, due to the two charges on the biochar, ammonium salt and potassium salt can be adsorbed in the pores of the biochar through electrostatic action, while urea can be adsorbed in the pores of the biochar by physical adsorption or chemical adsorption.

[0042] Step S2: adding the first suspension to the aqueous solution containing calcium ions in a dropwise manner, and causing the polymer thickener to undergo a cross-linking reaction with the calcium ions to form a gel wrapped around the surface of the biochar.

[0043] The aqueous solution containing calcium ions includes at least one of a calcium hydroxide solution and a calcium chloride solution. The mass ratio of the calcium salt in the aqueous solution containing calcium ions is 2.5 to 5%. When the first suspension is added dropwise to the aqueous solution containing calcium ions, the polymer thickener has not yet undergone a cross-linking reaction with the calcium ions. At this time, the calcium ions react with the acid radical ions in the first suspension (for example, hydrogen phosphate ions formed by the hydrolysis of monoammonium phosphate) to generate calcium salts with lower solubility. Due to the decrease in solubility, the precipitated calcium salts adhere to and settle on the surface of the biochar micropores. When the chemical fertilizer source contains urea and / or ammonium salts, and the aqueous solution containing calcium ions is a calcium hydroxide solution, the solubility of urea and / or ammonium salts decreases under weakly alkaline conditions, and the precipitated ammonium salts and / or urea crystals adhere to the surface of the biochar micropores.

[0044] The cross-linking reaction temperature is 2 to 5° C., and the cross-linking reaction time is 18 to 36 hours. Under these conditions, the polymer thickener and calcium ions undergo a cross-linking reaction, and the generated gel wraps the biochar.

[0045] It should be noted that, in the present invention, the first suspension is dripped into the aqueous solution containing calcium ions through a syringe, and the distance between the liquid outlet of the syringe and the liquid surface of the aqueous solution containing calcium ions is 10 to 20 cm; the dripping speed is 0.4 ml to 0.6 ml per 10 seconds. The dripping process affects the particle size of the modifier. If the distance between the liquid outlet of the syringe and the liquid surface of the aqueous solution containing calcium ions is too small and the dripping speed is too fast, it will cause too much dripping at one time, making the particle size of the modifier exceed 5 mm, which can easily cause the acid radical ions ionized by the chemical fertilizer source in the water to react unevenly with the calcium ions in the solution added subsequently. The particle size of the modifier can be controlled to 3-5 mm by the dripping distance and dripping speed, so that the biochar powder is evenly distributed without excessive deposition, and the adsorbed ammonium salt particles and urea crystals are also more evenly distributed in the entire reaction system.

[0046] Step S3: drying to obtain the biochar-based slow-release improver.

[0047] The drying process is drying at a temperature of 30 to 50° C., and the product is washed with deionized water 2 to 3 times before the drying process.

[0048] It should be noted that, in the technical solution of the present invention, before step S1, step S0 may also be included: drying, grinding, and sieving the agricultural and forestry waste, and then placing it in a tubular furnace. Under a nitrogen atmosphere, the temperature is raised to 300-700°C and maintained at a constant temperature for 4-8 hours, and then naturally cooled to room temperature to obtain biochar.

[0049] Among them, agricultural and forestry wastes include crop straws, garden plant branches and leaves, and other unused waste resources rich in organic matter such as cellulose. The present invention fully utilizes common wastes such as agricultural and forestry wastes to achieve the effect of recycling waste resources.

[0050] In a feasible method, the constant temperature in step S0 is maintained at 400-600°C. If the temperature is too low, the biochar will be easily decomposed after being applied to the soil, affecting the slow-release effect of the amendment. If the temperature is too high, the nutrients in the biochar will not be easily released.

[0051] In the preparation method proposed in the present invention, biochar powder and a chemical fertilizer source are first added to a solution containing a polymer thickener. This is then added dropwise to an aqueous solution containing calcium ions, and dried to obtain the desired biochar-based slow-release modifier. This preparation method is simple and highly efficient. Furthermore, the method for preparing a biochar-based slow-release modifier proposed in the present invention produces a biochar-based slow-release modifier with excellent slow-release properties, which possesses all the beneficial effects of the aforementioned biochar-based slow-release modifiers with excellent slow-release properties, and therefore will not be further elaborated here.

[0052] The technical solutions of the present invention are further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0053] Example 1

[0054] (1) Preparation of biochar from crop straw

[0055] Crop straw was dried at 105°C, ground into powder using a pulverizer, and passed through a 100-mesh (<0.15mm) sieve to obtain crop straw powder. The crop straw powder was placed in a quartz boat and placed in a tube furnace. N2 was introduced into the furnace at a flow rate of 40mL / min. After 1 hour, the temperature was increased at a rate of 5°C / min to 400°C. Once the target temperature was reached, the temperature was maintained constant for 8 hours before naturally cooling to room temperature. During this process, N2 was continuously introduced into the tube furnace at a flow rate of 40mL / min to maintain an anaerobic state. Biochar powder with an average particle size of 80 mesh (0.178mm) was obtained.

[0056] (2) Preparation of biochar-based slow-release modifier

[0057] In this example, the components were weighed in the following amounts (parts, 1 part is 1 g): 5 parts of sodium alginate; 120 parts of biochar powder; 50 parts of ammonium chloride; 50 parts of potassium dihydrogen phosphate;

[0058] (201) Sodium alginate was dissolved in 1000 parts of water, heated in a water bath to dissolve, and then biochar powder, ammonium chloride, and potassium dihydrogen phosphate were added and stirred for 5 minutes to obtain a first suspension;

[0059] (202) The first suspension was injected into a disposable syringe with a total capacity of 10 ml, and the distance between the liquid outlet of the syringe and the liquid surface of the aqueous solution containing calcium ions was adjusted to 10 cm. The dripping speed was controlled to 0.4 ml per 10 seconds, and the first suspension was dripped into a 2.5% calcium hydroxide solution while shaking the container containing the calcium hydroxide solution; the polymer thickener was allowed to cross-link with the calcium ions at 2°C to form a gel wrapped on the surface of the biochar. The cross-linking reaction time was 36 hours to obtain immobilized particles;

[0060] (203) The immobilized particles were washed twice with deionized water and dried at 50 °C to obtain the biochar-based slow-release improver.

[0061] Example 2

[0062] (1) Preparation of biochar from branches and leaves of garden plants

[0063] Garden plant branches and leaves were dried at 105°C, ground into a powder using a pulverizer, and passed through a 100-mesh (<0.15 mm) sieve to obtain a powder. The powder was placed in a quartz boat and placed in a tube furnace. N2 was introduced into the furnace at a flow rate of 60 mL / min. After 1 hour, the temperature was increased at a rate of 5°C / min to 600°C. Once the target temperature was reached, the temperature was maintained constant for 4 hours before being naturally cooled to room temperature. During this process, N2 was continuously introduced into the tube furnace at a flow rate of 60 mL / min to maintain an anaerobic state. The resulting biochar powder had an average particle size of 120 mesh (0.125 mm).

[0064] (2) Preparation of biochar-based slow-release modifier

[0065] In this embodiment, the components are weighed according to the following addition amounts (parts, 1 part is 1 g): 10 parts of potassium polyacrylate, 10 parts of polyvinyl alcohol; 90 parts of biochar powder; 100 parts of urea, 200 parts of diammonium phosphate, and 100 parts of potassium chloride;

[0066] (201) Potassium polyacrylate was dissolved in 1000 parts of water, heated in a water bath to dissolve, and then biochar powder, urea, diammonium phosphate, and potassium chloride were added and stirred for 10 min to obtain a first suspension;

[0067] (202) The first suspension was injected into a disposable syringe with a total capacity of 10 ml, and the distance between the liquid outlet of the syringe and the liquid surface of the aqueous solution containing calcium ions was adjusted to 20 cm. The dripping speed was controlled to 0.4 ml per 10 seconds, and the first suspension was dripped into a 2.5% calcium chloride solution while shaking the container containing the calcium hydroxide solution; the polymer thickener was allowed to cross-link with the calcium ions at 5°C to form a gel wrapped on the surface of the biochar. The cross-linking reaction time was 18 hours to obtain immobilized particles;

[0068] (203) The immobilized particles were washed three times with deionized water and dried at 30 °C to obtain the biochar-based slow-release improver.

[0069] Example 3

[0070] (1) Preparation of biochar mixed with crop straw and garden plant branches and leaves

[0071] Crop straw and garden plant branches and leaves were mixed in a 1:1 ratio by weight, dried at 105°C, ground into a powder using a pulverizer, and passed through a 100-mesh (<0.15 mm) sieve to obtain a powder. The powder was placed in a quartz boat in a tube furnace. N₂ was introduced into the furnace at a flow rate of 50 mL / min. After 1 hour, the temperature was raised to 500°C at a rate of 5°C / min. Once the target temperature was reached, the temperature was maintained constant for 6 hours before being naturally cooled to room temperature. During this process, N₂ was continuously introduced into the tube furnace at a flow rate of 50 mL / min to maintain an anaerobic state. Biochar powder with an average particle size of 100 mesh (0.150 mm) was obtained.

[0072] (2) Preparation of biochar-based slow-release modifier

[0073] In this example, the components were weighed in the following amounts (parts, 1 part is 1 g): 10 parts of polyacrylamide; 120 parts of biochar; 50 parts of ammonium sulfate, 100 parts of monoammonium phosphate, and 50 parts of potassium sulfate;

[0074] (201) Potassium polyacrylate was dissolved in 1000 parts of water, heated in a water bath to dissolve, and then biochar powder, ammonium sulfate, monoammonium phosphate, and potassium sulfate were added and stirred for 8 minutes to obtain a first suspension;

[0075] (202) The first suspension was injected into a disposable syringe with a total capacity of 10 ml, and the distance between the liquid outlet of the syringe and the liquid surface of the aqueous solution containing calcium ions was adjusted to 15 cm. The dripping speed was controlled to 0.4 ml per 10 seconds, and the first suspension was dripped into a 4% calcium chloride solution while shaking the container containing the calcium hydroxide solution; the polymer thickener was allowed to cross-link with the calcium ions at 4°C to form a gel wrapped around the surface of the biochar. The cross-linking reaction time was 24 hours to obtain immobilized particles;

[0076] (203) The immobilized particles were washed three times with deionized water and dried at 40 °C to obtain the biochar-based slow-release improver.

[0077] Example 4

[0078] The difference from Example 1 is that in (202), the distance between the liquid outlet of the syringe and the liquid surface of the aqueous solution containing calcium ions is adjusted to 5 cm.

[0079] Example 5

[0080] The difference from Example 1 is that in (202), the distance between the liquid outlet of the syringe and the liquid surface of the aqueous solution containing calcium ions is adjusted to 25 cm.

[0081] Example 6

[0082] The difference from Example 1 is that the dripping speed in (202) is controlled to be 0.6 ml per 10 seconds.

[0083] Example 7

[0084] The difference from Example 1 is that the dripping speed in (202) is controlled to be 0.7 ml per 10 seconds.

[0085] Example 8

[0086] The difference from Example 1 is that the dripping speed in (202) is controlled to be 0.3 ml per 10 seconds.

[0087] Example 9

[0088] The difference from Example 1 is that the components in (2) are weighed according to the following addition amounts (parts, 1 part is 1 g): 5 parts of sodium alginate; 60 parts of biochar powder; 50 parts of ammonium chloride, and 50 parts of potassium dihydrogen phosphate.

[0089] Example 10

[0090] The difference from Example 1 is that the components in (2) are weighed according to the following addition amounts (parts, 1 part is 1 g): 5 parts of sodium alginate; 50 parts of biochar powder; 50 parts of ammonium chloride, and 50 parts of potassium dihydrogen phosphate.

[0091] Example 11

[0092] The difference from Example 1 is that the components in (2) are weighed according to the following addition amounts (parts, 1 part is 1 g): 5 parts of sodium alginate; 130 parts of biochar powder; 50 parts of ammonium chloride, and 50 parts of potassium dihydrogen phosphate.

[0093] Comparative Example 1

[0094] The difference from Example 1 is that no polymer thickener is added and no biodegradable film is coated. 120 parts of biochar powder, 50 parts of ammonium chloride, and 50 parts of potassium dihydrogen phosphate are mixed in 1000 parts of water and soaked for 24 hours to obtain a compound fertilizer.

[0095] Comparative Example 2

[0096] The difference from Example 1 is that biochar is not used. 50 parts of ammonium chloride and 50 parts of potassium dihydrogen phosphate are mixed into 1000 parts of water to obtain a compound fertilizer.

[0097] Comparative Example 3

[0098] The difference from Example 1 is that the polymer thickener does not undergo a cross-linking reaction and cannot form a biodegradable film covering the surface of the biochar. (2) Dissolve 5 parts of sodium alginate in 1000 parts of water, heat in a water bath to dissolve, then add 120 parts of biochar powder, 50 parts of ammonium chloride, and 50 parts of potassium dihydrogen phosphate and stir for 5 minutes to obtain a compound fertilizer.

[0099] Performance Testing

[0100] (1) The morphology of the biochar-based slow-release modifiers prepared in Examples 1 and 4-8 was observed and the particle size was measured. The morphology results are shown in Figure 2-7 .

[0101] from Figure 2-7 It can be seen that the morphology of the biochar-based slow-release modifier can be controlled by adjusting the distance between the syringe outlet and the surface of the calcium ion-containing aqueous solution. If the distance is too close or too far, a "tailing" phenomenon will easily occur, causing the prepared biochar-based slow-release modifier to have a tadpole-like shape. By controlling the dripping speed, the particle size of the biochar-based slow-release modifier can be adjusted. When the dripping speed is slowed down, the particle size of the obtained biochar-based slow-release modifier also decreases.

[0102] The particle size of the biochar-based slow-release modifiers prepared in Examples 1 and 4-8 was measured, and the average particle size of Example 1 was 4.1 mm, and the average particle sizes of the biochar-based slow-release modifiers prepared in Examples 6-8 were 4.5 mm, 5.2 mm, and 2.3 mm, respectively.

[0103] (2) The slow-release effect of the biochar-based slow-release improvers prepared in Examples 1-11 and the biochar-based slow-release improvers prepared in Comparative Examples 1-3 was measured using the method in GB23348-2003 Slow-release Fertilizers. The results are shown in Table 1:

[0104] Table 1 Slow-release effect of biochar-based slow-release modifier

[0105]

[0106] As shown in Table 1, the biochar-based slow-release improvers provided in Examples 1-11 of the present invention far exceeded national standards for both 24-hour and 28-day nutrient release rates, demonstrating significant nutrient slow-release effects. However, the 24-hour and 28-day nutrient release rates of Comparative Examples 1-3 exceeded national standards for slow-release fertilizers, but their effectiveness was significantly inferior to that of the biochar-based slow-release improvers provided in Examples 1-11 of the present invention.

[0107] (3) The soil improvement effect of the biochar-based slow-release improver prepared in Examples 1-11 and the biochar-based slow-release improver prepared in Comparative Examples 1-3 was measured, and compared with a blank group to which no fertilizer was applied. Specifically, 5% of the biochar-based slow-release improver of different embodiments was added to the soil by mass, and pakchoy was planted conventionally after mixing. After 3 months, various soil indicators were measured. The determination was carried out using the methods of HJ802-2016 (electrode method for measuring soil conductivity), HJ962-2018 (potential method for measuring soil pH value), and NY / T 85-1988 (soil organic matter determination method). The determination results are shown in Table 2:

[0108] Table 2 Soil improvement effect of biochar-based slow-release amendments

[0109] pH EC((us / cm)) Organic matter (g / kg) <![CDATA[Bulk density (g / cm 3 )]]> No fertilizer blank group 8.26 236 10.8 1.26 Example 1 7.87 487 13.6 1.18 Example 2 7.63 563 14.1 1.16 Example 3 7.72 538 13.3 1.20 Example 4 7.93 411 12.6 1.21 Example 5 7.91 420 12.4 1.19 Example 6 7.89 480 13.4 1.17 Example 7 7.92 436 12.8 1.19 Example 8 7.94 442 11.6 1.20 Example 9 7.86 482 13.3 1.17 Example 10 7.95 443 12.4 1.19 Example 11 8.51 639 12.0 1.20 Comparative Example 1 8.01 375 11.3 1.24 Comparative Example 2 8.10 336 11.2 1.25 Comparative Example 3 8.03 368 11.2 1.23

[0110] As shown in Table 2, after applying the biochar-based slow-release improver provided by Examples 1-11 of the present invention, the soil pH value decreased, the soil slowly changed from alkaline to neutral, and the EC value and organic matter content increased to varying degrees, indicating that the organic and inorganic nutrients in the soil increased, the soil's fertilizer retention capacity increased, and the soil's bulk density also decreased, indicating that the soil voids increased and the soil became loose. In summary, the biochar-based slow-release improver provided by the present invention can effectively improve soil compaction, repair salinized soil, and improve the soil's water and fertilizer retention capacity. However, after applying the compound fertilizer provided by Comparative Example 1-3, the improvement effect on the soil was far less than that of the biochar-based slow-release improver provided by Examples 1-10 of the present invention. The improvement effect of Example 1-10 on the soil was better than that of Example 11, because the amount of biochar powder added in Example 11 was too much, and potassium salt was easily released too much, which easily led to soil salinization.

[0111] (4) The yield-increasing effects of the biochar-based slow-release improvers prepared in Examples 1-11 and the biochar-based slow-release improvers prepared in Comparative Examples 1-3 were measured and compared with a blank group to which no fertilizer was applied. Specifically, 5% of the biochar-based slow-release improver of each example was added to the soil, mixed well, and then pakchoy was planted as usual. The various indicators of the pakchoy were measured 5 days before each harvest. The measurements were performed using the weighing method. The results are shown in Table 3:

[0112] Table 3 Growth status of Chinese cabbage after application of biochar-based slow-release improver

[0113] Above-ground fresh weight (g / plant) Fresh root weight (g / plant) No fertilizer blank group 10.31 2.19 Example 1 12.87 2.87 Example 2 14.10 2.75 Example 3 13.28 2.58 Example 4 12.55 2.67 Example 5 12.54 2.65 Example 6 12.88 2.85 Example 7 12.45 2.55 Example 8 12.50 2.67 Example 9 12.85 2.86 Example 10 12.48 2.57 Example 11 12.44 2.56 Comparative Example 1 11.41 2.41 Comparative Example 2 11.12 2.36 Comparative Example 3 11.48 2.42

[0114] As shown in Table 3, the aboveground fresh weight of pakchoy grown with the biochar-based slow-release improver provided in Examples 1-11 of the present invention increased by 36.76%, and the root fresh weight increased by 31.05%, compared to pakchoy grown without the improver, demonstrating significant growth and yield enhancement. Furthermore, the aboveground fresh weight of pakchoy grown with the compound fertilizer provided in Comparative Examples 1-3 increased by up to 11.35%, and the root fresh weight by up to 10.5%, compared to pakchoy grown without the improver.

[0115] The above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of the present invention.

Claims

1. A biochar-based slow-release modifier, characterized in that: The biochar-based slow-release improver comprises 60 to 120 parts of biochar, 100 to 400 parts of chemical fertilizers, and 5 to 20 parts of a polymer thickener; wherein: The average particle size of the biochar-based slow-release modifier is 3 to 5 mm, and the polymer thickener includes at least one of sodium alginate, polyvinyl alcohol, polyacrylamide, and potassium polyacrylate; The preparation method of the biochar-based slow-release modifier comprises the following steps: Step S1, adding biochar powder and a chemical fertilizer source to a solution containing a polymer thickener to obtain a first suspension; Step S2, adding the first suspension to the aqueous solution containing calcium ions in a dropwise manner, and causing the polymer thickener to undergo a cross-linking reaction with the calcium ions to form a gel wrapped around the surface of the biochar; wherein the first suspension is dripped into the aqueous solution containing calcium ions via a syringe, the distance between the liquid outlet of the syringe and the liquid surface of the aqueous solution containing calcium ions being 10 to 20 cm; and the dripping rate is 0.4 ml to 0.6 ml per 10 seconds; Step S3: drying to obtain the biochar-based slow-release improver.

2. The biochar-based slow-release improver according to claim 1, characterized in that In step S2: The temperature of the cross-linking reaction is 2 to 5°C; The reaction time of the cross-linking reaction is 18 to 36 hours.

3. The biochar-based slow-release improver according to claim 1, characterized in that In step S2, the calcium salt in the aqueous solution containing calcium ions accounts for 2.5-5% by mass.

4. The biochar-based slow-release improver according to claim 1 or 2, characterized in that The chemical fertilizer source includes at least one of urea, ammonium salt, and potassium salt; the aqueous solution containing calcium ions includes at least one of calcium hydroxide solution and calcium chloride solution.

5. The biochar-based slow-release improver according to claim 1 or 2, characterized in that: In step S1, the average particle size of the biochar powder is 80-120 mesh; In step S3, the drying process is drying at a temperature of 30 to 50°C.

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