Biochar-based slow-release fertilizer as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of fertilizer preparation, and particularly relates to a biochar-based slow release fertilizer as well as a preparation method and application thereof. The preparation method of the slow-release fertilizer comprises the following steps: mixing and adsorbing the urea and the biochar, then mixing with the flax gum and the red soil, and granulating and drying to obtain the biochar-based slow-release fertilizer. The preparation process is simple, the cost is low, and the prepared slow-release fertilizer not only can realize the slow-release effect of nutrient substances, remarkably reduce soil nutrient loss, effectively suppress the water eutrophication trend caused by farmland water and fertilizer loss and practically improve the rural water environment quality, but also can improve the soil fertility, improve the soil structure and improve the water quality. And crop yield increase and quality improvement are promoted.

Description

Technical Field

[0001] This invention belongs to the field of fertilizer preparation technology, specifically relating to a biochar-based slow-release fertilizer, its preparation method, and its application. Background Technology

[0002] With the increasing grain output in my country, more and more fertilizers are being used in agricultural production to improve grain yield. Ordinary granular urea dissolves quickly after being applied to the soil. Due to ammonia volatilization, leaching, runoff, nitrification, and denitrification, nitrogen utilization is low, resulting not only in nitrogen fertilizer loss but also in a series of environmental problems such as water pollution. Statistics show that the effective utilization rate of chemical fertilizers is only 30-35%, and that of urea is only 50%, with approximately 2-20% lost due to volatilization, 15-25% reacting with soil organic matter, and 2-10% leaching into water. The main reason for the large-scale loss of fertilizer nutrients is that chemical fertilizers dissolve too quickly, leaving crops insufficient time to absorb them. Pure urea dissolves completely within hours in moist soil, and then, under the action of urease, is completely decomposed into ammonium nitrogen within about a week. Ammonium nitrogen then undergoes nitrification under the action of nitrifying bacteria, becoming nitrate nitrogen, while another portion is converted into nitrogen gas and released into the air through denitrification. In view of the above situation, starting from fertilizer production, innovation in materials and processes is an effective way to improve fertilizer utilization.

[0003] Biochar-based slow-release fertilizer is a long-acting fertilizer produced by mixing or granulating biochar with organic / inorganic fertilizers through different processes. The porosity, large specific surface area, negative surface charge, and charge density of biochar enable it to adsorb and retain nutrients in fertilizers, achieving a slow-release effect, significantly reducing soil erosion, improving soil fertility, promoting crop yield, and maintaining the balance of the soil ecosystem.

[0004] However, existing biochar-coated slow-release fertilizers mostly employ coating processes such as heating and spraying, which are relatively complex, require sophisticated equipment, and often necessitate the use of synthetic adhesives such as polyvinyl alcohol, potentially leading to material degradation residues or high costs. Therefore, providing a simpler, lower-cost, and more environmentally friendly method for preparing biochar-based slow-release fertilizers, while ensuring good slow-release performance and pelleting rate, and making it suitable for large-scale production by small and medium-sized enterprises and cooperatives, has become a pressing technical problem in this field. Summary of the Invention

[0005] Based on the above technical problems, this invention utilizes crop straw to prepare porous biochar with high carbon content, high stability, and a large specific surface area. Using biochar as the main material and urea as the fertilizer core, it produces a highly efficient, inexpensive, and environmentally friendly carbon-based slow-release fertilizer. The preparation process is simple and low-cost. The resulting slow-release fertilizer not only achieves a slow-release effect on nutrients, significantly reducing soil nutrient loss and effectively curbing the eutrophication trend in water bodies caused by farmland water and fertilizer runoff, thus substantially improving the quality of the rural water environment, but also enhances soil fertility, improves soil structure, and promotes increased crop yield and quality.

[0006] The specific technical solution provided by this invention is as follows: In a first aspect, this invention provides a method for preparing a biochar-based slow-release fertilizer, comprising the following steps: Urea is mixed with biochar for adsorption, then mixed with linseed gum and red clay, granulated and dried to obtain biochar-based slow-release fertilizer.

[0007] This invention utilizes high-yield crop straw as a carbon source, opening up a new direction for the resource utilization of straw. Using linseed gum as a binder and modifier, and red clay as a filler, it exhibits good pelleting properties, low urea release, and a high nitrogen content in the finished product. Furthermore, the addition of red clay not only enhances the adsorption and slow-release effects but also strengthens the structure of the slow-release fertilizer, making it less prone to breakage during transportation.

[0008] In a preferred embodiment of the present invention, the biochar-based slow-release fertilizer is prepared according to the following steps: After dissolving urea, biochar is added for adsorption. Then, a mixture of linseed gum and red soil is added, mixed well, water is added, kneaded into a ball, granulated, and dried to obtain a biochar-based slow-release fertilizer.

[0009] More preferably, the mass ratio of biochar to urea is 1:0.5~1.5.

[0010] More preferably, the amount of laterite added is 10-30% of the total weight of the entire system.

[0011] More preferably, the amount of linseed gum added is 1 to 2% of the total weight of the entire system.

[0012] In a preferred embodiment of the present invention, the biochar is obtained by carbonizing straw.

[0013] More preferably, the carbonization is carried out in an inert gas protective environment, with the temperature increased to 400-600°C at a rate of 10-25°C / min, and held at that temperature for 0.5-1h.

[0014] In a second aspect, the present invention provides a biochar-based slow-release fertilizer prepared according to the above method, wherein the biochar-based slow-release fertilizer is a granular composite material comprising urea, biochar, linolenic acid and red clay, wherein the biochar serves as an adsorption carrier for urea, and the linolenic acid and red clay serve as binders and skeleton materials uniformly dispersed in the granules.

[0015] In a third aspect, the present invention provides the application of the biochar-based slow-release fertilizer in promoting crop growth.

[0016] In a preferred embodiment of the present invention, the crop is a chili pepper or a strawberry.

[0017] In a preferred embodiment of the present invention, promoting crop growth means increasing crop yield and quality.

[0018] In a third aspect, the present invention provides the application of the biochar-based slow-release fertilizer in soil improvement.

[0019] As a preferred embodiment of the present invention, the biochar-based slow-release fertilizer is used to improve the physical and chemical properties of soil or increase the organic matter content in soil.

[0020] More preferably, the biochar-based slow-release fertilizer is used to increase the soil pH value.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Simple process and high pelleting rate: This invention employs a room-temperature or low-temperature blending and adsorption process. This process is simple and easy to implement, requires minimal equipment, and produces no environmental pollution from common coating material residues. It is suitable for low-cost production by small and medium-sized enterprises and cooperatives. Furthermore, the raw materials used, such as linoleic acid, are environmentally friendly adhesives, ensuring safety and zero pollution. Through optimized formulation, this invention achieves a 100% pelleting rate for the slow-release fertilizer under optimal conditions, resulting in stable particle structure, good mechanical strength, and easy storage and application.

[0022] 2. Improve fertilizer utilization and reduce environmental pollution: This invention uses biochar as an encapsulation and adsorbent, utilizing its porous structure and high specific surface area to effectively adsorb urea nutrients and achieve slow-release. The initial release rate of the biochar-based slow-release fertilizer prepared by this invention is mostly less than 15%, and the cumulative release rate after 28 days does not exceed 80%, which meets the national slow-release fertilizer standard, effectively prolonging the nutrient release cycle and improving fertilizer utilization.

[0023] 3. Improved Soil Physicochemical Properties: After applying the slow-release fertilizer provided by this invention, soil bulk density is significantly reduced, soil structure is improved, and this is beneficial to crop root development and microbial activity. Specifically, the alkaline properties and abundant base ions of biochar help raise soil pH and regulate acidic soils. After application, soil organic matter content is significantly increased, enhancing soil fertility and water and fertilizer retention capacity.

[0024] 4. Promotes increased crop yield and quality: In experiments on chili peppers and strawberries, the yield of the group treated with the slow-release fertilizer provided by this invention was significantly higher than that of the unfertilized group, and it also showed an increased yield effect compared with the conventional fertilization group (e.g., strawberry yield increased by 4.8%). At the same time, the vitamin C content of chili peppers was significantly increased, and the vitamin C content and water-soluble sugar content of strawberries were also significantly improved, resulting in improved fruit quality and commercial value.

[0025] 5. Resource utilization of agricultural waste: The biochar of this invention uses crop straw (such as rapeseed straw) as raw material and is prepared through carbonization, which realizes the efficient utilization of agricultural waste, reduces production costs, and conforms to the concept of green circular agriculture. Attached Figure Description

[0026] Figure 1 The appearance of the carbon-based slow-release fertilizers prepared in Examples 1-9; Figure 2 These are the infrared absorption spectra of rapeseed straw biochar prepared at different temperatures; Figure 3 These are the infrared spectra of the carbon-based slow-release fertilizers prepared in Examples 1-9; (samples 1-9 represent the slow-release fertilizers obtained in Examples 1-9, respectively). Figure 4 These are the carbon microstructures of rapeseed straw prepared in Examples 1-3; (magnification: ×500, ×1000, ×2000). Figure 5 The microstructure (×1000) of the biochar-based slow-release fertilizers prepared in Examples 1-9. Figure 6 The microstructure of the biochar-based slow-release fertilizer prepared in Examples 2, 6, and 7 (500℃); Figure 7 These are the thermogravimetric curves of rapeseed straw carbon prepared at different temperatures; Figure 8 The thermogravimetric curves are for the rapeseed straw carbon-based slow-release fertilizer prepared in Example 8; the 500℃ curve refers to the thermogravimetric curve of the biochar prepared at 500℃, indicating good aromatication and small mass loss at higher temperatures; sample 8 is the slow-release fertilizer prepared under the 8th process, which will lose weight at higher temperatures due to being a mixture; the urea curve refers to the thermogravimetric changes of urea, which is almost completely decomposed at high temperatures. Figure 9 Thermogravimetric curves of the rapeseed straw carbon-based slow-release fertilizers prepared in Examples 1-9 are shown. Figure 10 It is a standard curve for the determination of urea nitrogen content; Figure 11 shows the leaching and slow-release rates of the slow-release fertilizers prepared in Examples 1-9 on soil columns after 28 days. Figure 12The impact of different fertilization methods on chili pepper yield; Figure 13 The effects of different fertilization methods on the total yield of strawberries; Figure 14 It is the effect of slow-release fertilizer on soil bulk density. Detailed Implementation

[0027] The present invention will be further described in detail through the following embodiments, but the content of the present invention is not limited thereto.

[0028] The straw samples used in this embodiment of the invention are rapeseed straw, collected from the Agricultural Science and Technology Industrial Park of Huangzhong District, Xining City and Datong Shenyin Flax Planting Professional Cooperative. After natural drying, impurities were removed manually, cut into 2-3 cm sections, dried at 105℃, crushed, and passed through a 40-mesh sieve for later use.

[0029] Example 1 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. First, purge the air by introducing argon gas at 1L / min for 10min. Set the carbonization temperature to 400℃ and the heating rate in the furnace to 17℃ / min. After the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 1h. After the carbonization time is reached, allow it to cool naturally and remove it. Record it as YC400, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid for 24h to improve its adsorption performance.

[0030] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating and adsorbent, linseed gum is used as the modifier and binder, and red clay is used as the filler. The specific process is as follows: First, urea is completely dissolved in distilled water, then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, water is added, and then kneaded until the surface is smooth. The mixture is then loaded into a granulator, and the granules are 4-5 mm in diameter. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:1.5, the amount of red clay added is 30% of the total weight of the whole system, and the amount of linseed gum added is 2% of the total weight of the whole mixed system.

[0031] Example 2 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. First, purge the air by introducing argon gas at 1L / min for 10min. Set the carbonization temperature to 400℃ and the heating rate in the furnace to 10℃ / min. After the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 1h. After the carbonization time is reached, allow it to cool naturally and remove it. Record it as YC400, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid to improve its adsorption performance.

[0032] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating agent, linseed gum is used as the modifier and binder, and red clay is used as the filler. The specific process is as follows: First, urea is completely dissolved in distilled water, then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, water is added, and then kneaded until the surface is smooth. The mixture is then put into a granulator, and the granules are 4-5 mm in diameter. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:1, the amount of red clay added is 20% of the total weight of the whole system, and the amount of linseed gum added is 2% of the total weight of the whole mixed system.

[0033] Example 3 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. Purge the air with argon gas at 1 L / min for 10 min. Set the carbonization temperature to 400℃ and the heating rate in the furnace to 25℃ / min. Once the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 1 h. After the carbonization time is reached, allow it to cool naturally and remove it. Record it as YC400, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid to improve its adsorption performance.

[0034] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating agent, linseed gum is used as the modifier and binder, and red clay is used as the filler. The specific process is as follows: First, urea is completely dissolved in distilled water, then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, water is added, and then kneaded until the surface is smooth. The mixture is then loaded into a granulator, and the granules are 4-5 mm in diameter. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:0.5, the amount of red clay added is 10% of the total weight of the whole system, and the amount of linseed gum added is 2% of the total weight of the whole mixed system.

[0035] Example 4 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. Purge the air with argon gas at 1L / min for 10min. Set the carbonization temperature to 500℃ and the heating rate in the furnace to 17℃ / min. Once the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 1h. After the carbonization time is reached, allow it to cool naturally and remove it. Record it as YC500, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid to improve its adsorption performance.

[0036] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating agent, linseed gum is used as the modifier and binder, and red clay is used as the filler. The specific process is as follows: First, urea is completely dissolved in distilled water, then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, water is added, and then kneaded until the surface is smooth. The mixture is then loaded into a granulator, and the granules are 4-5 mm in diameter. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:1.5, the amount of red clay added is 10% of the total weight of the whole system, and the amount of linseed gum added is 2% of the total weight of the whole mixed system.

[0037] Example 5 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. Purge the air with argon gas at 1L / min for 10min. Set the carbonization temperature to 500℃ and the heating rate in the furnace to 10℃ / min. Once the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 1h. After the carbonization time is reached, allow it to cool naturally and remove it. Record it as YC500, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid to improve its adsorption performance.

[0038] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating agent, linseed gum is used as the modifier and binder, and red clay is used as the filler. The specific process is as follows: First, urea is completely dissolved in distilled water, then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, water is added, and then kneaded until the surface is smooth. The mixture is then put into a granulator, and the granules are 4-5 mm in diameter. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:1, the amount of red clay added is 20% of the total weight of the whole system, and the amount of linseed gum added is 2% of the total weight of the whole mixed system.

[0039] Example 6 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. Purge the air with argon gas at 1L / min for 10min. Set the carbonization temperature to 500℃ and the heating rate in the furnace to 25℃ / min. Once the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 1h. After the carbonization time is reached, allow it to cool naturally and remove it. Record it as YC500, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid to improve its adsorption performance.

[0040] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating agent, linseed gum is used as the modifier and binder, and red clay is used as the filler. The specific process is as follows: First, urea is completely dissolved in distilled water, then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, water is added, and then kneaded until the surface is smooth. The mixture is then loaded into a granulator, and the granules are 4-5 mm in diameter. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:0.5, the amount of red clay added is 30% of the total weight of the whole system, and the amount of linseed gum added is 2% of the total weight of the whole mixed system.

[0041] Example 7 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. Purge the air with argon gas at 1L / min for 10min. Set the carbonization temperature to 600℃ and the heating rate in the furnace to 17℃ / min. Once the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 1h. After the carbonization time is reached, allow it to cool naturally and remove it. Record the sample as YC600, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid to improve its adsorption performance.

[0042] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating agent, linseed gum is used as the modifier and binder, and red clay is used as the filler. The specific process is as follows: First, urea is completely dissolved in distilled water, then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, water is added, and then kneaded until the surface is smooth. The mixture is then loaded into a granulator, and the granules are 4-5 mm in diameter. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:1.5, the amount of red clay added is 20% of the total weight of the whole system, and the amount of linseed gum added is 2% of the total weight of the whole mixed system.

[0043] Example 8 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. Purge the air with argon gas at 1L / min for 10min. Set the carbonization temperature to 600℃ and the heating rate in the furnace to 10℃ / min. Once the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 0.5h. After the carbonization time is reached, allow it to cool naturally and remove it. Record it as YC600, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid to improve its adsorption performance.

[0044] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating agent, linseed gum is used as the modifier and binder, and red clay is used as the filler. The specific process is as follows: First, urea is completely dissolved in distilled water, then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, water is added, and then kneaded until the surface is smooth. The mixture is then loaded into a granulator, and the granules are 4-5 mm in diameter. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:1, the amount of red clay added is 30% of the total weight of the whole system, and the amount of linseed gum added is 1% of the total weight of the whole mixed system.

[0045] Example 9 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. Purge the air with argon gas at 1 L / min for 10 min. Set the carbonization temperature to 600℃ and the heating rate in the furnace to 25℃ / min. Once the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 0.5 h. After the carbonization time is reached, allow it to cool naturally and remove it. Record it as YC600, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid to improve its adsorption performance.

[0046] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating agent, linseed gum is used as the modifier and binder, and red clay is used as the filler. The specific process is as follows: First, urea is completely dissolved in distilled water, then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, water is added, and then kneaded until the surface is smooth. The mixture is then loaded into a granulator, and the granules are 4-5 mm in diameter. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:0.5, the amount of red clay added is 10% of the total weight of the whole system, and the amount of linseed gum added is 2% of the total weight of the whole mixed system.

[0047] Example 10 A biochar-based slow-release fertilizer is prepared according to the following steps: (1) Biochar preparation: Weigh the crushed straw sample and place it in a crucible. Purge the air with argon gas at 1L / min for 10min. Set the carbonization temperature to 500℃ and the heating rate in the furnace to 17℃ / min. Once the furnace temperature reaches the set carbonization temperature, maintain the temperature and continue carbonization for 1h. After the carbonization time is reached, allow it to cool naturally and remove it. Record it as YC500, pass it through a 100-mesh sieve, seal and store it for later use. When using it, activate it with 1% hydrochloric acid to improve its adsorption performance.

[0048] (2) Preparation of biochar-based slow-release fertilizer: Urea is used as the fertilizer core, the prepared biochar is used as the encapsulating agent, 2.0% linseed gum is used as the modifier and binder, and red clay is used as the filler. First, urea is completely dissolved in a certain amount of distilled water, and then the prepared activated biochar is added. After adsorption for 10 minutes, the mixed linseed gum and red clay mixture is added, mixed well, and then an appropriate amount of water is added and kneaded until the surface is smooth. The mixture is then loaded into a granulator and granulated to a diameter of 4-5 mm. After drying or polishing, the biochar-based slow-release fertilizer is obtained. The mass ratio of biochar to urea is 1:1, and the amount of red clay added is 30% of the total weight of the whole system.

[0049] Experimental Example 1 Biochar and slow-release fertilizer performance testing 1. Ash content determination of biochar The ash content of biochar was determined and the carbonization yield was calculated according to GB / T 17664—1999 "Charcoal and Test Methods".

[0050] 2. Structural characterization of carbon-based slow-release fertilizers (1) Fourier Transform Infrared (FTIR) Analysis After drying in an oven, biochar and its compound slow-release fertilizer samples were mixed with anhydrous KBr at a ratio of 1:1000, ground into a fine powder, and pressed into transparent thin sheets. The functional groups on the surface of the biochar and the biochar-based slow-release compound fertilizer were analyzed using a Fourier transform optical spectrometer (Thermo-Nicolet Nexus 670, USA). The sample scanning range was 4000–400 cm⁻¹. -1 The number of scans was 15, and the resolution was 4cm. -1 .

[0051] (2) Scanning electron microscope (SEM) Before testing, the samples were dried at 80 °C for 48 h. A small amount of the sample was then attached to conductive tape and vacuum-plated with gold for 110 s. During the testing, the accelerating voltage was 0.5~30 kV, and the microstructure of the samples was observed at different magnifications using a scanning electron microscope (S4800 model from Hitachi, Japan).

[0052] (3) Specific surface area (SSA) and pore size (PV) analysis The samples were weighed and pretreated, then heated under vacuum at 105 °C for 2 h. The isothermal adsorption and desorption of the samples were measured at a temperature saturated with liquid nitrogen to analyze the SSA and pore size distribution of biochar and slow-release fertilizer.

[0053] (4) Thermogravimetric analysis (TGA) Accurately weigh 6-8 mg of powder sample and place it in a dried alumina crucible. Protect the crucible with N2 as an inert gas and set the flow rate to 10 mL / min. Increase the temperature from room temperature to 800 ℃ at a rate of 10 ℃ / min and perform the determination on a thermogravimetric analyzer (Mettler-Toledo TGA / DSC 1 / 1600).

[0054] 3. Results and Analysis 3.1 Analysis of Biochar Industrial Use Table 1. Industrial Analysis Results of Rapeseed Straw Biochar As shown in Table 1, with the increase of pyrolysis temperature in biochar preparation, the degree of biomass pyrolysis gradually increases. During the process of increasing the pyrolysis temperature from 400℃ to 600℃, the ash content gradually increases from 11.96% to 17.78%, indicating a higher ash content due to the higher ash content of rapeseed straw after pyrolysis. The volatile matter content gradually decreases from 23.4% to 12.85%, while the fixed carbon content gradually increases from 64.64% to 69.37%. Higher pyrolysis temperature facilitates the decomposition of organic matter, thus promoting the decomposition of volatile organic compounds in the semi-coke and correspondingly increasing the proportion of fixed carbon. Ash is the mineral residue after biomass pyrolysis, which generally does not volatilize with increasing pyrolysis temperature; therefore, its proportion in biochar also increases with increasing pyrolysis temperature. Meanwhile, the fixed carbon content increased proportionally with the increase of the preparation temperature during the biochar production process from straw, while the carbon yield of rapeseed straw was basically the same under the three temperatures, with no significant difference.

[0055] 3.2 Analysis of Pelletization Rate and Appearance of Carbon-Based Slow-Release Fertilizer The macroscopic forms of biochar-based fertilizers made by adding different proportions of biochar, urea, and clayey laterite are as follows: Figure 1 As shown. By Figure 1It can be seen that the degree of urea precipitation after drying of the carbon-based slow-release fertilizer granules prepared in the examples varies greatly. Overall, when the carbon-to-fertilizer ratio is 1:0.5, no urea crystals precipitate in any treatment group. The carbon-based fertilizer granules are black, with no visible trace of urea. Under this biochar addition ratio process, the biochar adsorbs the added urea into its pores, acting as a carrier. However, when the carbon-to-fertilizer ratio is 1:1.5, regardless of the amount of red clay added, urea crystals precipitate. Especially at 500℃, with a carbon-to-fertilizer ratio of 1:1.5 and a red clay addition of 10%, urea precipitation is most severe. Most of the carbon-based fertilizer granules are white, completely covered by biochar, and the slow-release fertilizer pelleting rate is the lowest, only 43%. This may be because the proportion of biochar added is too small, and urea molecules do not effectively enter the pores of the biochar for adsorption, resulting in urea being adsorbed onto the surface during drying. This indicates that under this formulation process, a large portion of the urea does not have a slow-release effect, and the resulting slow-release fertilizer granules have a loose structure and low mechanical strength.

[0056] Table 2. Pelletization rate and urea adsorption degree of slow-release fertilizer in different embodiments 3.3 Fourier Transform Infrared Spectroscopy (FTIR) Analysis of Carbon-Based Slow-Release Fertilizer Figure 2 This indicates that the obvious absorption peaks are mainly located at: 3424, 2968, 2852, 1620, 1514, 1450, 1376, 1046, 874, 780, 662, and 3429 cm⁻¹. -1 The broad absorption peak is located in the stretching vibration region of -OH (3650–3200 cm⁻¹). -1 Within this range, the absorption peak gradually weakens with increasing carbonization temperature, almost flattening out at 600℃. (2968cm) -1 2852cm -1 The absorption peak at 1620 cm⁻¹ is caused by the stretching vibrations of -CH₃ and -CH₂ in the alkane structure. The amplitude of these vibrations gradually decreases with increasing temperature, indicating that the aromaticity of rapeseed straw charcoal gradually increases. -1 1514cm -1 1450cm -1 The absorption peak at 780 cm⁻¹ is caused by the vibration of the benzene ring skeleton, and it gradually strengthens, broadens, and shifts to the high-frequency region as the straw carbonization temperature increases. The aromaticity of the charcoal also increases accordingly. -1 The out-of-plane bending vibration of Ar-H aromatic ring carbon further confirms the aromatization of straw carbon. The stretching vibrations of the aliphatic ether bonds (COC) on the hemicellulose and cellulose chains in rapeseed straw lead to the aromatization of straw carbon at 1046 cm⁻¹. -1An absorption peak appears at a certain point, and this peak gradually disappears with increasing temperature. The absorption peak weakens as the pyrolysis temperature increases, indicating that rapeseed straw cellulose mainly undergoes pyrolysis at low temperatures. Functional groups such as -OH, alkane groups, and COC gradually decrease with increasing carbonization temperature, leaving behind a benzene ring skeleton and aromatic functional groups such as CH on the benzene ring. This suggests that biochar exhibits a variety of functional groups as the pyrolysis temperature increases, with the number gradually decreasing and stabilizing.

[0057] Figure 3 This indicates that the prepared slow-release fertilizer exhibits a significant 3500-3300 cm⁻¹ concentration of -NH₂ in urea. -1 Primary amines exhibit bimodal absorption, but some absorption peaks overlap with the -OH absorption peak at 1680 cm⁻¹. -1 The absorption peak corresponds to the stretching vibration of the urea amide carbonyl group, indicating that urea is well adsorbed into the straw biochar. Infrared spectroscopy analysis shows that the char obtained from low-temperature pyrolysis contains a richer variety of functional groups; as the temperature increases, the types of functional groups gradually decrease. When selecting biochar materials for carbon-based fertilizer carriers, it is necessary to comprehensively consider factors such as resource utilization, manufacturing costs, and economic benefits. In summary, when the carbonization temperature is 500℃, the carbonization of rapeseed straw is basically complete, meeting the standards for high-quality biochar as a carbon-based fertilizer carrier material. Excessively high temperatures may reduce the content of some functional groups, potentially leading to a decrease in adsorption capacity.

[0058] 3.4 Specific Surface Area (SSA) and Pore Size (PV) Analysis As shown in Table 3, the surface characteristics of rapeseed straw carbon analyzed using the BET multi-point method and the BJH method revealed that the carbonization temperature of biochar significantly affects its specific surface area, pore volume, and pore size. With increasing carbonization temperature, the specific surface area, micropore volume, total pore volume, and mesopore volume gradually increase, showing a clear upward trend, while the average pore size decreases in the opposite direction. The data indicates that biochar prepared at carbonization temperatures of 500℃ and 600℃ shows little difference in parameters such as carbon stability, specific surface area, pore volume, and average pore size. Considering manufacturing costs and environmental protection, 500℃ should be chosen as the carbonization temperature for biochar preparation, rather than 600℃.

[0059] Table 3. Specific surface area, pore volume, and pore size analysis of rapeseed straw charcoal. 3.5 Scanning Electron Microscopy (SEM) Analysis from Figure 4It can be seen that the straw is well carbonized at 400℃, but the pore structure is not rich; at the carbonization temperature of 500℃, the pore structure is rich and the ashing is minimal, making it a more ideal adsorbent material; however, at 600℃, although the pores are rich, some ashing occurs.

[0060] from Figure 5 It can be seen that under all carbon-based slow-release fertilizer preparation conditions, the surface of the slow-release fertilizer was loaded with a large number of urea crystal particles. In the slow-release fertilizers prepared by biochar at 500 and 600℃, more urea crystals were loaded in the pores of the biochar, but at 400℃, due to the lack of pores, more urea crystals were adsorbed on the surface of the biochar, and the degree of urea loading increased significantly with the increase of the carbon-to-fertilizer ratio. In addition, with the increase of the clay ratio, the pores on the surface of the biochar were blocked by urea and laterite particles, which played a good role in slow release. However... Figure 6 This also indicates that as the carbon-to-fertilizer ratio increases, the amount of urea particles loaded on the surface of biochar particles gradually increases, and it can be clearly seen that the urea loaded on the biochar has blurred the microscopic morphology of the carbon material. However, even with a red soil ratio of 20% in the slow-release fertilizer prepared from biochar at 500℃, a large number of voids still exist. This indicates that some of the voids in the biochar are not fully utilized. Therefore, in the process of preparing slow-release fertilizer, urea can be completely dissolved first and then mixed with straw carbon. After standing for a few minutes until the biochar is saturated and the urea molecules completely occupy the carbon voids, it can be mixed with other components and then granulated.

[0061] 3.6 Thermogravimetric Analysis (TGA) Weight loss analysis (TG) is a key technique for conveniently and quickly obtaining kinetic information on the thermochemical reaction stages of materials. The results are as follows... Figure 7 As shown, in the prepared rapeseed straw char, the biochar prepared at 400℃ experienced mass loss above 100℃, with the mass loss accelerating at 400℃, reaching nearly 25% at 800℃. Conversely, the biochar prepared at 500℃ and 600℃ showed almost no mass loss before 550℃, and the mass loss was less than 10% even with increased temperature. This indicates that carbonization was very effective at temperatures above 500℃, and the rapeseed straw char achieved good aromatization transformation, which indirectly confirms the results of infrared spectroscopy.

[0062] from Figure 8It can be seen that the pyrolysis process of slow-release fertilizer mainly goes through three stages: In the first stage, from room temperature to 220℃, the first stage of weight loss occurs, during which the sample loses its moisture and volatile groups. Before 100℃, adsorbed water is lost; after 100℃ to 220℃, internal bound water is lost, and urea undergoes de-NH2 removal and the formation of a complex HN-CO mixture, resulting in a mass reduction of approximately 40%. The second stage of weight loss occurs between 220℃ and 340℃, mainly involving the further carbonization and decomposition of the complex HN-CO mixture. After 340℃, the third stage of biomass pyrolysis begins. In this stage, the sample mass does not change significantly; it mainly involves the decomposition of uncarbonized components of the biomass over a relatively long period.

[0063] from Figure 9 It can be seen that the pyrolysis process of the carbon-based slow-release fertilizers prepared in different embodiments all includes three stages, but the overall trend of the weight loss curves is basically the same, and similar to that of urea, while differing significantly from that of pure biochar. The different preparation processes of the slow-release fertilizers result in significant differences in pyrolysis temperature and rate due to the inconsistent content of urea and laterite. In particular, the process route of Example 4 has the largest mass loss due to the high urea ratio (1:1.5) and low laterite ratio (10%). Therefore, the slow-release fertilizers of Examples 1, 4, and 7 all have large mass losses, while the slow-release fertilizers of Examples 5, 6, and 9 have low urea and high laterite ratios, resulting in minimal mass loss before 550℃. The other groups fall between these two extremes.

[0064] Experimental Example 2 Nutrient release and slow-release performance of biochar-based slow-release fertilizer 1. Initial release rate test Initial nutrient release rate refers to the percentage of nutrients released prematurely during the slow-release fertilizer production process, without achieving the desired slow-release effect. This percentage represents the mass fraction of the total nutrient content. It is expressed as the mass fraction of the nutrient released after 24 hours of extraction in still water at 25°C, calculated using the following formula: V1 = W1 / W * 100%. Where W1 is the amount of urea released after 24 hours of extraction at 25°C, and W is the mass of the total urea measured.

[0065] Clean and dry 150 mL PET bottles and set aside. Weigh 0.5 g of carbon-based slow-release fertilizer (9 types of fertilizer) into each bottle, and set up three replicates for each experiment. Add 100 mL of deionized water, shake well, and let stand for 24 h. Use a syringe to draw 4 mL of the extract and filter it through a 0.45 mm organic filter membrane. Determine the urea content by spectrophotometry. This experiment uses the p-dimethylbenzaldehyde method in GB / T23348-2009 to evaluate the release of urea nitrogen nutrients. This method is based on the quantitative reaction of dimethylbenzaldehyde solution with urea nitrogen in an acidic environment, and the analysis is performed by measuring the absorbance of the solution at a wavelength of 430 nm using a spectrophotometer.

[0066] 2. Soil column leaching experiment The soil column leaching apparatus was made by removing the bottom of a 550 mL mineral water bottle. It had a diameter of 5.8 cm and a height of 21.5 cm, with the leaching outlet at the bottle mouth. Three small holes (approximately 1 mm in diameter) were punched in the bottle cap. The cap was tightened, and a small amount of cotton was added to the outlet. Two layers of gauze were then placed on top, followed by a 1-2 cm layer of clean quartz sand (soaked in 2.0 mol / L concentrated sulfuric acid for 24 h and washed with distilled water). On top of this, a 10 cm layer of crushed, air-dried, and sieved experimental soil was laid. 1.0 g of slow-release fertilizer was weighed and evenly spread on the soil surface, covered with a 3 cm thick layer of soil. Then, a 2 cm thick layer of treated quartz sand (soaked in 2.0 mol / L concentrated sulfuric acid for 24 h and washed with distilled water) was laid on top to prevent disturbance when water was added. The soil layer was then compacted. The control group (CK blank) did not receive slow-release fertilizer; all other steps were the same.

[0067] Quartz sand, carbon-based slow-release fertilizer, and soil samples were sequentially loaded into a mineral water bottle chromatography column. A leachate collection bottle was placed at the bottom of the column. The flow rate of distilled water was controlled using an infusion tube, and distilled water was slowly added to the column to simulate rainfall, ensuring uniform penetration into the soil. After the soil column was filled, distilled water was slowly injected until leachate flowed out, at which point the injection was stopped to ensure complete soil saturation. Subsequently, 50 mL of distilled water (equivalent to 7.5 mm of rainfall) was slowly injected into the soil column daily for 1 hour, with the flow rate controlled. The leachate was collected, and the absorbance of the leachate was measured at 430 nm using a spectrophotometer to calculate the urea release on days 1, 3, 5, 9, 15, 20, 25, and 28, thus calculating the urea release rate of the slow-release fertilizer prepared under the corresponding process conditions. The formula for calculating the urea release rate on day n is as follows: Vn = W1 / W * 100%. Wherein, Vn: urea release rate on day n; Wn: urea release amount measured on day n; W: total urea mass in the slow-release fertilizer.

[0068] 3. Spectrophotometric determination of urea content (1) Test principle: Urea nitrogen in the test solution reacts quantitatively with p-dimethylaminobenzaldehyde. The absorbance is measured at a wavelength of 430 nm by spectrophotometry, and the content of urea nitrogen is calculated.

[0069] (2) Test method Urea standard solution: Accurately weigh 1.0719 g of the national standard urea sample and dissolve it in a 1 L volumetric flask. Each milliliter of this solution contains 0.5 mg of urea nitrogen.

[0070] p-Dimethylaminobenzaldehyde solution: Weigh 20g of p-dimethylaminobenzaldehyde, dissolve it in 1000 mL of 95% ethanol, then add 100 mL of concentrated hydrochloric acid and mix. Store in a brown bottle, protected from light.

[0071] (3) Measurement Plotting the standard curve and measuring the samples: As shown in Table 4, the urea standard solution was sequentially injected into six 100 mL volumetric flasks. Each flask was diluted with water to approximately 50 mL, gently shaken, and 20.0 mL of p-diaminobenzaldehyde solution was added. The solution was then diluted to the mark with water, thoroughly shaken, and allowed to stand for 10 min. The absorbance of each solution was measured at 430 nm, using the solution with zero urea nitrogen as the reference solution. A standard curve was plotted with the mass (mg) of urea nitrogen in 100 mL of the standard colorimetric solution on the x-axis and the corresponding absorbance value on the y-axis. The absorbance of the slow-release fertilizer extract or leachate was measured under the same experimental conditions as those used to plot the standard curve. The mass of urea nitrogen in the extract was calculated using a linear regression equation, and the nutrient release rate was calculated.

[0072] Table 4. Amount of urea solution added 4. Results and Analysis 4.1 Initial Release Rate like Figure 10 As shown, at a wavelength of 430 nm, the urea content and light absorption have a good linear relationship, which can be used for sample analysis.

[0073] Table 5 Initial release rate of carbon-based slow-release fertilizer in different embodiments The initial release rate study after 24 hours (Table 5) showed that all nine slow-release fertilizers exhibited significant slow-release performance within 24 hours. The slow-release rate was lowest in Example 6 (7.5%), while the dissolution rate was highest in Example 4 (21.3%). This indicates that the initial release rates of carbon-based slow-release fertilizers prepared under different processing conditions vary significantly after 24 hours. Except for Example 4, which had a higher slow-release rate, the other examples all met the national standard requirement for slow-release fertilizers of ≤15% initial release rate. It was also found that the most significant factor affecting the initial release rate of slow-release fertilizers was the carbon-to-fertilizer ratio, followed by the biochar preparation temperature, with the least impact from the amount of red clay added. Although the red clay addition ratio had a relatively small impact on the initial release rate, it had a significant impact on the pelleting rate of the slow-release fertilizer. Therefore, a red clay addition ratio of 30% was optimal in the preparation of slow-release fertilizers.

[0074] 4.2, Cumulative release rate over 28 days A 28-day cumulative leaching rate experiment was conducted on nine types of carbon-based fertilizers using soil column leaching. The results are as follows: Figure 11 As shown, the carbon-based slow-release fertilizers prepared in different embodiments all exhibited certain slow-release performance. The results showed that the slow-release fertilizer in Example 4 had the highest dissolution rate of 88.4% after 28 days and 90.4% after 35 days. Examples 2, 3, 5, 6, 7, 8, and 9 all met the national standard that the slow-release rate of slow-release fertilizers should not exceed 80% after 28 days. Under optimal conditions, such as in Example 8, the cumulative nutrient release rate during the nutrient release period was greater than 80%, and the total nutrient concentration of the fertilizer was 37.9%, meeting the requirements for slow-release rate and total nutrient content in the national standard for slow-release fertilizers.

[0075] Experimental Example 3 The effects of carbon-based slow-release fertilizer on crop growth and soil physicochemical properties The experimental site was located in the deep winter greenhouse of Qinghai Kayue Chuhe Ecological Agriculture Technology Co., Ltd. in the Agricultural Science and Technology Industrial Park of Huangzhong District, Xining City. The basic conditions of the planting soil were as follows: the previous crop was solanaceous crops, with organic matter of 15.8 g / kg, total nitrogen of 0.46 g / kg, available nitrogen of 21.25 mg / kg, total phosphorus of 9.16 mg / kg, available phosphorus of 14.46 mg / kg, and pH of 7.23.

[0076] Two representative crops, chili peppers and strawberries, were selected as experimental materials. The effects of slow-release fertilizer on the yield and quality of chili peppers and strawberries were studied using the chili pepper variety Hangjiao No. 8 and the strawberry variety Miaoxiang No. 7.

[0077] 1. Experimental Design Chili peppers: The experiment used a randomized block design with three treatments. Treatment 1 (P1) received no fertilizer; Treatment 2 (P2) received conventional fertilization (100 kg / mu of compound fertilizer as basal fertilizer); Treatment 3 (P3) received 100 kg / mu of compound fertilizer plus 100 kg / mu of controlled-release fertilizer as basal fertilizer (Example 10 is used as an example). Each treatment was replicated three times in a randomized block design, with each experimental plot measuring 30 m². 2 (5m×6m) During this period, all treatment groups were top-dressed with special fertilizer twice. The planting method was to raise low ridges and cover them with black film, with a plant spacing of 25cm×110cm. Other field production management followed the park's routine management measures, including timely weeding and prevention of pests and diseases.

[0078] Strawberries: Cultivated in greenhouses for two consecutive years, the greenhouses were treated with a 20-day fumigation treatment using methamidophos in July. The experiment employed a randomized block design with three treatments. 1500 kg / mu of fermented and decomposed farmyard manure was used as base fertilizer. Treatment 1 (B1) received no fertilizer; Treatment 2 (B2) received conventional fertilization (120 kg / mu of compound fertilizer); Treatment 3 (B3) received 120 kg / mu of compound fertilizer plus 120 kg / mu of controlled-release fertilizer (Example 10 is used as an example). During the strawberry growth process, all treatments received two additional applications of strawberry-specific fertilizer. Field management followed the usual practices of the orchard, including timely pesticide spraying. White mulch was applied after the strawberries began to bud in mid-October. Each treatment was replicated three times in a randomized block design, with each experimental plot measuring 30 m². 2 (5 m × 6 m) Strawberries are planted in double rows on a single ridge, with a plant spacing of 20-30 cm.

[0079] 2. Yield Measurement and Quality Analysis Methods During the peak fruiting period, three pepper fruits were randomly collected from each plot to investigate the weight of each fruit and conduct quality analysis. Total yield was recorded by month for each experimental plot and converted to yield per 667m². 2 Yield. Vitamin C (Vc) was determined by titration with 2,6-dichlorophenolindophenol; water-soluble sugars were determined by anthrone colorimetric method; and total acidity (organic acids) was determined by standard alkaline titration.

[0080] The total yield of strawberries was calculated by recording the fruit yield of each plot in batches during December, January, February, and March. Mature fruits at their peak fruiting period were analyzed for soluble sugar, free acid, and vitamin C content, and the average values ​​were statistically analyzed and compared. Soluble sugar content in strawberry fruits was determined using a TD-45 digital saccharimeter, while free acid and vitamin C content were determined using alkaline titration and 2,6-dichlorophenolindophenol titration methods, respectively. For soluble sugars, five strawberries of uniform ripeness were juiced, filtered, and mixed thoroughly. Approximately 1 mL of the mixture was pipetted into the induction chamber, and the reading was recorded. The vitamin C content of the fruit was determined by extraction with 2% oxalic acid and titration with 2,6-dichlorophenolindophenol. 100 g of fresh sample was weighed, and an equal volume of 2% oxalic acid solution was added. The mixture was homogenized, and 10–30 g was placed in a 100 mL volumetric flask. The solution was diluted to volume with oxalic acid, filtered, and 5 mL of the filtrate was placed in a 50 mL Erlenmeyer flask. Titration with 2,6-dichlorophenolindophenol solution was performed, with the endpoint determined by the pink color not disappearing within 15 seconds.

[0081] 3. Analysis of the impact of slow-release fertilizer on soil physicochemical properties Soil organic matter content and other indicators were determined according to the methods described in Bao Shidan's "Soil Agrochemical Analysis". Soil samples were taken from the experimental field at crop transplanting time (0 days), 30 days, 50 days, and 70 days to determine soil bulk density, organic matter, and pH. Soil bulk density was determined using the ring sampler method, soil organic matter was determined using the potassium dichromate method, and pH was determined using the potentiometry method.

[0082] 4. Results and Analysis 4.1 Effects of slow-release fertilizer on chili pepper yield and quality Figure 12 The experimental results showed that the yield of the no-fertilizer treatment (P1) was lower. The conventional fertilization (P2) and the treatments with additional slow-release fertilizer (P3) increased the yield by at least 22.1% to 26.7% compared with the no-fertilizer treatment, indicating that the basic soil fertility was not bad, but the application of compound fertilizer and slow-release fertilizer could significantly increase the yield of chili peppers. The application of slow-release fertilizer (P3) increased the yield by 3.70% compared with conventional fertilization (P2), but the difference was not statistically significant.

[0083] Chili peppers are one of the solanaceous vegetable varieties rich in vitamin C. Water-soluble sugars and total acidity are important indicators for evaluating chili pepper quality. Table 6 shows that the vitamin C content of chili peppers varies considerably, with the P3 treatment having the highest vitamin C content. Compared to the P2, P3, and P1 treatments, the vitamin C content increased by 18.9%–30.5%. There were no significant differences in water-soluble sugar content and total acidity among the treatments.

[0084] Table 6 shows the effects of different fertilization treatments on chili pepper quality. Note: Compared with P1, p < 0.05 is *significant, p < 0.001 is **highly significant, n = 3 In summary, chili peppers require a large amount of fertilizer, and high-yield and high-quality cultivation techniques emphasize multiple fertilizations. Generally, fertilizer needs to be applied once after 1-2 harvests of chili peppers, which is labor-intensive. The slow-release fertilizer in this study can slow down the nutrient release rate and improve fertilizer utilization, while also increasing the yield and quality of chili peppers.

[0085] 4.2 Effects of slow-release fertilizer on strawberry yield and quality Depend on Figure 13 It was found that the yield of the fruit at each of the four harvest periods (December, January, February, and March) was consistently higher than that of the control group (B1) without fertilizer. The total yield of groups B3 and B2 was significantly higher than that of group B1. Under the condition of two late-stage fertigation, the yield increase of groups B2 and B3 compared with the B1 treatment was at least 21.57% to 27.44%. The application of slow-release fertilizer (B3) increased the average yield of strawberries by 4.8% compared with conventional fertilization (B2), but this was not statistically significant. Therefore, the application of fertilizer in the early stages of strawberry cultivation has a significant impact on the final yield, and it is necessary to strengthen the nutrient supply in the early stages of strawberry cultivation.

[0086] Table 7 shows that the supply of nutrients in the early stages of strawberry cultivation has a highly significant impact on the average yield per strawberry plant, the average number of fruits per plant, and the average weight of a single fruit. The effect is most pronounced after the application of slow-release fertilizer (B3), reaching a highly significant level compared to B1 in terms of average yield per plant. It has the greatest impact on both yield per plant and fruit weight, both of which are crucial for strawberry quality and commercial value. High-quality strawberries can significantly improve the economic benefits of strawberry cultivation.

[0087] Table 7. Effects of different fertilization methods on strawberry yield in February. Note: Compared with B1, p<0.05, *significant, p<0.001**highly significant, n=10 Table 8. Effects of different fertilization treatments on strawberry quality Note: p < 0.05 compared to B1, *significant. Table 8 shows the effects of different fertilization treatments on strawberry V C The content has the most significant impact; B2 and B3 treatments affect the vitamin C content of strawberries. C The content increased by at least 6.6% and 15.3%, respectively. After applying slow-release fertilizer (B3), the content of water-soluble sugars was significantly higher than that of B2 and B1, but the total acidity remained almost unchanged. This indicates that applying slow-release fertilizer not only increased yield but also significantly improved the quality of strawberries, resulting in better marketability and increased economic value.

[0088] 4.3 Effects of slow-release fertilizer on soil physicochemical properties Table 9. Changes in pH and organic matter content for each treatment. Note: p < 0.05 compared to P1 and B1. Figure 14 Experimental results showed that applying biochar-based slow-release fertilizer significantly reduced soil bulk density for both chili peppers and strawberries. Besides the low density of biochar itself, this was also due to its ability to enhance soil aggregation and influence soil microbial activity, thereby improving soil structure and impacting other physical properties. Biochar's stable structure resulted in minimal fluctuations in soil bulk density during the crop's growth period, maintaining it within a stable range. This reduction in bulk density and improved structure greatly promoted root development. Compared to the other two treatments, soil bulk density increased continuously after transplanting, reaching its maximum at 50 days, and then gradually decreased. The low bulk density treatment saw an increase due to watering and soil compaction, while the high bulk density treatment experienced a decrease over time due to the soil's inherent expansion and contraction properties.

[0089] As shown in Table 9, the application of biochar-based slow-release fertilizer to the soil can increase the soil pH. This is partly due to the alkalinity of biochar, and partly due to the rich content of base ions in biochar, which reduces the level of exchangeable cations in the soil, thereby increasing the saturation of soil base ions and thus raising the soil pH.

[0090] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A method for preparing a biochar-based slow-release fertilizer, characterized in that, Includes the following steps: Urea is mixed with biochar for adsorption, then mixed with linseed gum and red clay, granulated and dried to obtain biochar-based slow-release fertilizer.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the biochar to the urea is 1:0.5~1.5; The amount of laterite added is 10-30% of the total weight of the entire system; The amount of linolenic acid added is 1 to 2% of the total weight of the entire system.

3. The preparation method according to claim 1, characterized in that, The biochar is obtained by carbonizing straw as raw material; The carbonization is carried out in an inert gas protected environment, with the temperature increased to 400-600℃ at a rate of 10-25℃ / min, and held at that temperature for 0.5-1h.

4. A biochar-based slow-release fertilizer prepared according to any one of claims 1 to 3, characterized in that, The biochar-based slow-release fertilizer is a granular composite material containing urea, biochar, linolenic acid and red clay. Biochar serves as the adsorption carrier for urea, while linolenic acid and red clay are uniformly dispersed in the granules as binders and skeleton materials.

5. The application of the biochar-based slow-release fertilizer of claim 4 in promoting crop growth.

6. The application according to claim 5, characterized in that, The crop in question is either a chili pepper or a strawberry.

7. The application according to claim 5, characterized in that, Promoting crop growth means increasing crop yield and quality.

8. The application of the biochar-based slow-release fertilizer of claim 4 in soil improvement.

9. The application according to claim 8, characterized in that, The biochar-based slow-release fertilizer is used to improve the physical and chemical properties of soil, increase the organic matter content in soil, or raise the soil pH value.

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