A biochar-based slow-release fertilizer made from garden waste and its preparation method

Abstract

This invention provides a biochar-based slow-release fertilizer made from garden waste and its preparation method. The biochar-based slow-release fertilizer uses tree branch charcoal as the slow-release carrier substrate and tree leaf charcoal as the active nutrient substance. The fertilizer comprises the following raw material components by mass percentage: 16-30% tree branch charcoal, 10-20% tree leaf charcoal, 40-45% nitrogen-phosphorus-potassium compound fertilizer, 3-9% binder, and 4-10% moisture, with the sum of the mass percentages of all raw material components being 100%. This invention fully utilizes the compositional characteristics of the pyrolysis products of garden waste, using tree branch charcoal to construct the slow-release carrier framework and tree leaf charcoal to provide active nutrients, achieving high-value utilization of garden waste, improving fertilizer nutrient utilization efficiency, and promoting resource recycling and green, low-carbon development.

Description

Technical Field

[0001] This invention relates to the field of landscaping technology, specifically to a biochar-based slow-release fertilizer made from landscaping waste and its preparation method. Background Technology

[0002] With the acceleration of urbanization and the continuous expansion of green space in my country, the amount of landscaping waste (dead branches, fallen leaves, and pruned branches) is increasing dramatically year by year. This type of waste is characterized by its wide range of sources, large output, seasonal concentration, and natural cleanliness. However, the mainstream disposal methods are still landfill, stockpiling, and simple incineration. These methods not only occupy land, easily breed pests and diseases, and generate carbon emissions, but also waste a large amount of woody biomass resources, which contradicts the concept of green, low-carbon, and circular development in cities.

[0003] Meanwhile, agricultural and horticultural production still heavily relies on conventional fast-acting fertilizers. These fertilizers are highly soluble, suffer significant losses due to volatilization and leaching, and have nitrogen, phosphorus, and potassium utilization rates of only 30%-50%, easily leading to soil compaction, acidification, and eutrophication of water bodies. To improve nutrient utilization, biochar-based slow-release fertilizers have become a research hotspot. Existing technologies mostly use crop straw such as corn and wheat as raw materials, while research on the specialized and high-value utilization of horticultural waste, especially branches and leaves, is limited. Common problems include insufficient utilization of raw material characteristics, poor molding quality, unstable slow-release effects, and insignificant fertilizer reduction effects.

[0004] Against this backdrop, how to efficiently transform garden waste into high-performance, safe, environmentally friendly, and scalable biochar-based slow-release fertilizer has become a key technical problem that urgently needs to be solved in the field of garden waste resource utilization and fertilizer reduction. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing biochar-based slow-release fertilizer from garden waste. Through an innovative structural design that uses tree char as a slow-release carrier substrate and tree char as an active nutrient substance to replace part of the chemical fertilizer, combined with a precisely optimized molding process, the invention achieves the comprehensive goals of high-value raw materials, standardized processes, high particle strength, long-term slow release of nutrients, reduced chemical fertilizer use, and safer products. This overcomes the shortcomings of existing technologies, such as low resource utilization rate, poor molding performance, weak slow-release effect, high dependence on chemical fertilizer, and single function. Ultimately, it yields a high-performance biochar-based slow-release fertilizer suitable for industrial production and applicable to the agricultural and gardening fields.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing biochar-based slow-release fertilizer from garden waste.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: This invention provides a slow-release fertilizer based on garden waste biochar, wherein the slow-release fertilizer uses tree branch char as the slow-release carrier substrate and tree leaf char as the active nutrient substance; the slow-release fertilizer based on garden waste biochar comprises the following raw material components by mass percentage: 16-30% tree branch char, 10-20% tree leaf char, 40-45% nitrogen, phosphorus and potassium compound fertilizer, 3-9% binder, and 4-10% moisture, and the sum of the mass percentages of all raw material components is 100%.

[0008] Furthermore, the charcoal made from tree branches and leaves is obtained by crushing, drying, and then pyrolyzing them.

[0009] Furthermore, the fixed carbon content of the dendritic charcoal is 65-85%, and the specific surface area is 200-250 m². 2 / g.

[0010] Furthermore, the binder is one or more of attapulgite, bentonite, or starch.

[0011] The present invention also provides a method for preparing the above-mentioned garden waste biochar-based slow-release fertilizer, the method comprising: a) crushing and drying garden waste branches and leaves respectively, and then pyrolyzing and carbonizing them under oxygen-limited conditions to obtain branch char and leaf char; b) mixing branch char, leaf char, nitrogen, phosphorus and potassium inorganic fertilizer, binder and water evenly to obtain the garden waste biochar-based slow-release fertilizer.

[0012] Furthermore, in step a, the pyrolysis carbonization under oxygen-limited conditions includes: carbonization temperature of 550-650℃, heating rate of 10-20℃ / min, and holding time of 120-180min.

[0013] Furthermore, the preparation method also includes: c. compressing the garden waste biochar-based slow-release fertilizer into tablets.

[0014] Furthermore, in step c, the garden waste biochar-based slow-release fertilizer is thoroughly stirred and then loaded into a cylindrical mold with a radius of 2-4 mm. After pressing with a tablet press for 5-20 seconds at 1.5-3 MPa, the fertilizer is demolded.

[0015] This invention also provides the application of the above-mentioned garden waste biochar-based slow-release fertilizer in the field of garden waste utilization.

[0016] This invention also provides the application of the above-mentioned garden waste biochar-based slow-release fertilizer in the fertilizer field.

[0017] Compared with the prior art, the technical solution provided by the present invention has at least the following advantages: (1) The raw materials are used to achieve high-value utilization of the whole plant: This invention uses tree branch charcoal as a carrier and tree leaf charcoal to provide nutrients, thereby improving the utilization efficiency of fertilizer nutrients and promoting resource recycling and green and low-carbon development.

[0018] (2) Achieve fertilizer reduction: Use leaf charcoal as a nutrient substitute to reduce fertilizer use, reduce non-point source pollution and soil compaction risk, and meet the requirements of green agriculture and landscaping reduction.

[0019] (3) Stable and long-lasting slow-release effect: The high porosity and high specific surface area of ​​the charcoal provide strong adsorption capacity, so that nutrients are not released in the early stage and are continuously supplied in the later stage. It has strong resistance to rain leaching and loss, and the fertilizer utilization rate is significantly improved. Attached Figure Description

[0020] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments, and unless otherwise stated, the figures in the drawings are not to be limited by scale.

[0021] Figure 1 A flowchart of a method for preparing biochar-based fertilizer from garden waste provided in this embodiment of the invention: (a) schematic diagram; (b) physical image; Figure 2 The present invention provides charcoal-based fertilizers with different charcoal contents as embodiments; Figure 3 The nitrogen release rates of the charcoal-based fertilizers with different charcoal contents provided in the embodiments of the present invention are: (a) 0%; (b) 20%; (c) 25%; (d) 30%; (e) 35%. Figure 4 The phosphorus release rates of the charcoal-based fertilizers with different charcoal contents provided in the embodiments of the present invention are: (a) 0%; (b) 20%; (c) 25%; (d) 30%; (e) 35%. Figure 5 These are dendritic carbon-based fertilizers prepared using different processes according to embodiments of the present invention; Figure 6 The hardness of the dendritic charcoal-based fertilizer under different preparation processes provided in the embodiments of the present invention; Figure 7 Trend chart of factors affecting the hardness of the charcoal-based fertilizer provided in the embodiments of the present invention: (a) amount of binder added; (b) amount of moisture added; (c) molding pressure; Figure 8 The fracture resistance of dendritic charcoal-based fertilizers under different preparation processes provided in the embodiments of the present invention; Figure 9 Trend chart of maximum fracture resistance factors for the charcoal-based fertilizer provided in the embodiments of the present invention: (a) amount of binder added; (b) amount of moisture added; (c) molding pressure; Figure 10The residual weight ratio of dendritic charcoal-based fertilizers under different preparation processes; Figure 11 Trend chart of residual weight ratio factors for the charcoal-based fertilizer provided in the embodiments of the present invention: (a) amount of binder added; (b) amount of moisture added; (c) molding pressure; Figure 12 These are samples of garden waste biochar-based slow-release fertilizer with different rates of nitrogen, phosphorus, and potassium inorganic fertilizer substitution provided in the embodiments of the present invention. Figure 13 The following are examples of garden waste biochar-based slow-release fertilizers with different rates of nitrogen, phosphorus, and potassium inorganic fertilizer substitution provided in this invention: (a) hardness; (b) maximum crush resistance; (c) residual weight ratio; Figure 14 The following are the contents of the main components and the heavy metal content of the biochar-based slow-release fertilizer made from garden waste provided in this embodiment of the invention: (a) main component content; (b) heavy metal content. Figure 15 The nitrogen release rate of the garden waste biochar-based slow-release fertilizer provided in the embodiments of the present invention under normal leaching conditions is as follows: (a) single release rate; (b) cumulative release rate. Figure 16 The cumulative nitrogen release rate under continuous leaching of the garden waste biochar-based slow-release fertilizer provided in this embodiment of the invention; Figure 17 Visual representations of soybean seedling growth results provided in this embodiment of the invention: (a) Day 14; (b) Day 21; Figure 18 Growth changes of soybean seedlings provided in the embodiments of the present invention: (a) changes in plant height; (b) changes in leaf area; Figure 19 (a) chlorophyll content; (b) biomass; Growth results of soybean seedlings on day 21 provided for embodiments of the present invention; Figure 20 The growth results of dwarf sunflowers provided in the embodiments of the present invention: intuitive diagram (a) day 14, (b) day 21; (c) changes in plant height and (d) changes in leaf area within 21 days; Figure 21 The growth results of dwarf sunflowers on day 21 provided in this embodiment of the invention are as follows: (a) plant height; (b) leaf area; (c) chlorophyll content; and (d) biomass. Detailed Implementation

[0022] The method for preparing garden waste biochar-based slow-release fertilizer provided by the present invention includes the following steps: a) crushing and drying garden waste branches and leaves, and then pyrolyzing and carbonizing them under limited oxygen conditions to prepare branch char and leaf char; b) mixing branch char, leaf char, nitrogen, phosphorus and potassium inorganic fertilizer, binder and water in proportion to form a moldable mixture; c) preparing garden waste biochar-based slow-release fertilizer by using a tableting process.

[0023] In step a, the pyrolysis carbonization conditions are: carbonization temperature 550-650℃, heating rate 10-20℃ / min, and holding time 120-180min.

[0024] In step b, the formable mixture is mixed evenly according to the following proportions: 16-30% tree branch charcoal, 10-20% tree leaf charcoal, 40-50% nitrogen, phosphorus and potassium inorganic fertilizer, 3-9% binder, and 4-10% moisture. Under this ratio, nitrogen and phosphorus release are stable, which not only ensures nutrient content but also has a good slow-release effect.

[0025] In step c, after the mixture is thoroughly stirred, it is put into a cylindrical mold with a radius of 2-4 mm, and a tablet press is used to hold the pressure at 1.5-3 MPa for 5-20 seconds. After demolding, the garden waste biochar-based slow-release fertilizer is obtained.

[0026] It should be noted that nitrogen, phosphorus, and potassium inorganic fertilizers can be composed of urea, diammonium hydrogen phosphate, and potassium sulfate. In some embodiments, in garden waste biochar-based slow-release fertilizers, the content of urea is 20%, the content of diammonium hydrogen phosphate is 12%, and the content of potassium sulfate is 12%.

[0027] The present invention will now be described in detail with reference to specific embodiments.

[0028] Example 1 A biochar-based slow-release fertilizer made from garden waste and its preparation method include the following steps (e.g. Figure 1 ): S1. Garden waste branches and leaves are crushed and dried separately, and branch charcoal and leaf charcoal are prepared under the conditions of carbonization temperature of 600℃, heating rate of 15℃ / min, holding time of 120min and oxygen limitation. S2. Mix the formable mixture evenly according to the following proportions: 25% tree branch charcoal, 15% tree leaf charcoal, 45% nitrogen, phosphorus and potassium inorganic fertilizer, 6% attapulgite soil, and 9% water, to obtain a garden waste biochar-based slow-release fertilizer mixture.

[0029] S3. After thoroughly mixing the garden waste biochar-based slow-release fertilizer mixture, put it into a cylindrical mold with a radius of 3mm, and press it with a tablet press at a pressure of 3MPa for 10s. After pressing, demold to obtain the garden waste biochar-based slow-release fertilizer.

[0030] Example 2 A biochar-based slow-release fertilizer made from garden waste and its preparation method include the following steps: S1. Garden waste branches and leaves are crushed and dried separately, and branch charcoal and leaf charcoal are prepared under the conditions of carbonization temperature of 550℃, heating rate of 20℃ / min, holding time of 180min and oxygen limitation. S2. Mix the moldable mixture evenly according to the following proportions: 30% tree branch charcoal, 15% tree leaf charcoal, 44% nitrogen, phosphorus and potassium inorganic fertilizer, 3% bentonite, and 8% water, to obtain a garden waste biochar-based slow-release fertilizer mixture.

[0031] S3. After thoroughly mixing the garden waste biochar-based slow-release fertilizer mixture, put it into a cylindrical mold with a radius of 2mm, and press it for 20s under a pressure of 1.5MPa using a tablet press. After pressing, demold to obtain the garden waste biochar-based slow-release fertilizer.

[0032] Example 3 A biochar-based slow-release fertilizer made from garden waste and its preparation method include the following steps (e.g. Figure 1 ): S1. Garden waste branches and leaves are crushed and dried separately, and branch charcoal and leaf charcoal are prepared under the conditions of carbonization temperature of 650℃, heating rate of 10℃ / min, holding time of 150min and oxygen limitation. S2. Mix the formable mixture evenly according to the following proportions: 16% tree branch charcoal, 20% tree leaf charcoal, 45% nitrogen, phosphorus and potassium inorganic fertilizer, 9% starch, and 10% water, to obtain a garden waste biochar-based slow-release fertilizer mixture.

[0033] S3. After thoroughly mixing the garden waste biochar-based slow-release fertilizer mixture, put it into a cylindrical mold with a radius of 4mm, and press it with a tablet press at a pressure of 2.5MPa for 8s. After pressing, demold to obtain the garden waste biochar-based slow-release fertilizer.

[0034] The following uses Example 1 as an example to verify the effects in various aspects.

[0035] 1) Dendrobium content in garden waste biochar-based slow-release fertilizer This embodiment uses systematic monitoring of the dynamic release of nitrogen and phosphorus elements in tree charcoal-based fertilizers (with only tree charcoal substitution) with different carbon contents to clarify the relationship between the nutrient release rate and carbon content of the tree charcoal-based fertilizer prepared by this invention.

[0036] The example set up four treatment groups: tree charcoal-based fertilizers with carbon contents of 20%, 25%, 30%, and 35%, and a control group with a carbon content of 0%. Figure 2 All the twig charcoal-based fertilizers exhibited good morphological characteristics, appearing as columnar granules with a smooth and flat surface. The twig charcoal-based fertilizer with a 35% twig charcoal content was easily broken after demolding, which was due to the excessively high twig charcoal content and relatively insufficient binder and moisture content.

[0037] Analysis of the nitrogen and phosphorus release effects revealed a close correlation between nutrient release rate and dendritic char content. Figure 3It can be seen that, in the control group of pure nitrogen, phosphorus, and potassium inorganic fertilizers, almost all of the nitrogen element was released after 2-3 leaching cycles. The release rate of the branch charcoal-based fertilizer with a charcoal content of 20% was higher in the early stage and then slowed down. In contrast, the branch charcoal-based fertilizer with a charcoal content of more than 25% showed a lower and more stable release pattern.

[0038] Analysis of the fitting results using the biphasic first-order kinetic model (Table 1) shows that k1 (the rate constant during the rapid release phase) generally decreases with increasing carbon content, indicating that higher carbon content results in slower initial nitrogen release. All carbon-containing treatments R 2 (Coefficient of determination) > 0.98, significantly superior to pure nitrogen, phosphorus, and potassium inorganic fertilizer (R 2 =0.963). The K1 of pure nitrogen, phosphorus, and potassium inorganic fertilizer reaches 5.32h. -1 Nutrients are released completely in the initial stage, while the char-based fertilizer with a char content of 35% has a lower K1 value, indicating a slower initial nutrient release. The char-based fertilizer with a char content of 25% has a K1 value of 3.12h. -1 R 2 The value reached 0.986, achieving a better balance between controlling the initial burst release and ensuring rapid supply.

[0039] Table 1. Parameters of nitrogen release kinetic model for dendritic charcoal-based fertilizers with different carbon contents

[0040] Figure 4 The results showed that, because phosphorus is not easily lost from the soil, the total phosphorus release rate of the control group was 87% after six leaching cycles. In contrast, the total phosphorus release rates of char-based fertilizers with char contents of 20%, 25%, 30%, and 35% were significantly lower, at 53.4%, 44.09%, 51.8%, and 43.59%, respectively.

[0041] This invention investigates the phosphorus release characteristics of dendritic char-based fertilizers using a biphasic first-order kinetic model. Table 2 shows the model fit (R²) for all char-containing treatments. 2 >0.98) were significantly better than the pure nitrogen, phosphorus, and potassium inorganic fertilizer treatment (R 2 =0.978), indicating that fertilizers containing biochar can reduce phosphorus release. Analysis of the results shows that the ideal release rate constants k1 (rate constant during the rapid release phase) and k2 (rate constant during the slow release phase) should be controlled within 1.5–2.5 h, respectively. -1 (Fast release phase) and 0.1~0.2 h -1 Within the (slow release phase) range, charcoal-based fertilizers with 20% and 25% dendrite char content meet this standard. The charcoal-based fertilizer with 20% dendrite char content exhibits stronger rapid-release characteristics (k1 = 2.44 h).-1 While it can quickly provide available phosphorus, its continuous supply capacity is limited. Carbon-based fertilizers with a carbon content of 25% can provide phosphate fertilizer quickly and have a long supply cycle.

[0042] Table 2. Phosphorus release kinetic model parameters of dendritic charcoal-based fertilizers with different carbon contents

[0043] 2) Preparation of charcoal-based fertilizer and the influence of preparation process on hardness, maximum breakage resistance, and residual weight ratio. This embodiment systematically analyzes the influence of the preparation process of dendritic charcoal-based fertilizer on its mechanical properties by measuring the hardness, maximum crush resistance, and residual weight ratio of the fertilizer under different preparation processes.

[0044] like Figure 5 The paper showcases dendritic charcoal-based fertilizers prepared using different processes. Samples A through F exhibited fragile edges and poor surface smoothness under external force, displaying obvious roughness and unevenness. This may be due to insufficient binder addition and low molding pressure, failing to form a dense, well-shaped charcoal-based fertilizer.

[0045] Table 3 shows the mechanical properties of the dendritic charcoal-based fertilizer under different preparation process parameters, including three indicators: hardness, maximum crush resistance, and residual weight ratio. The data shows that the hardness of the prepared dendritic charcoal-based fertilizer ranges from 20 to 64.4 H. D Within this range, the maximum fracture resistance is 75.90~317.40 N, and the residual weight ratio is between 80% and 99.6%. Performance analysis of samples A to F shows that their hardness is all below 40H. D The surface strength of the samples was low; the maximum fracture resistance of none of them reached 180N. Except for sample D, the remaining weight ratio of the other samples was less than 90%, indicating poor wear resistance. Samples G to P exhibited superior mechanical properties, with their hardness generally greater than 50H. D Most of the samples had a maximum breaking strength exceeding 200N and a residual weight ratio of over 90%.

[0046] When the preparation process parameters meet the requirements of binder addition ≥5%, moisture addition ≥6%, and molding pressure ≥2MPa, the mechanical properties of the obtained samples are significantly improved. Among them, samples G and O exhibit the best comprehensive performance: sample G has a maximum fracture resistance of 317.40N and a weight ratio as high as 99.6%; sample O has a hardness of 64.6HD and a weight ratio of 99.6%.

[0047] Table 3 Mechanical properties of dendritic charcoal-based fertilizers prepared by different processes

[0048] Figure 6The hardness test results showed that the hardness of the dendritic charcoal-based fertilizers varied significantly under different preparation processes. The hardness ranged from 20 to 64.6 HD, with sample O exhibiting the highest hardness at 64.6 HD. D The fertilizer surface exhibits excellent compressive strength. Figure 7 Factor trend analysis further revealed the relationship between hardness and key process parameters. Within a certain range, hardness increased with increasing binder content, moisture content, and molding pressure. When the binder content exceeded 5% and the moisture content exceeded 8%, the change in hardness tended to level off, and the increase decreased. The variance analysis results in Table 4 further verified the correlation between hardness and various process parameters. The results showed that hardness was highly significantly correlated with the amount of binder added (p<0.01) and significantly correlated with the amount of moisture added and molding pressure (p<0.05).

[0049] Table 4. Results of Hardness Variance Analysis

[0050] Figure 8 The maximum breakage resistance test results show that the maximum breakage resistance of the dendritic charcoal-based fertilizer prepared in this invention reaches 317.4 N. Figure 9 The factor trend analysis further revealed the relationship between the fracture resistance and key process parameters. Table 5 shows that the maximum fracture resistance of the charcoal-based fertilizer is significantly correlated with the amount of binder added.

[0051] Table 5. Results of variance analysis of maximum fracture resistance

[0052] Figure 10 The results of the residual weight ratio test showed that the residual weight ratio of the tree branch carbon-based fertilizer was between 80% and 99.6%. Since the tree branch has a relatively complete carbon structure after carbonization, it has the potential to improve the wear resistance of the carbon-based fertilizer as a raw material. Figure 11 Factor trend analysis results show that the residual weight ratio of charcoal-based fertilizer increases with the increase of binder, moisture, and pressure, while the change trend is smaller after the binder addition reaches 5%. The residual weight ratio increases steadily with the increase of moisture and molding pressure. Table 6 shows the variance analysis results of the residual weight ratio, indicating a significant correlation between the residual weight ratio and the amount of binder added, and a highly significant correlation with the amount of moisture added.

[0053] Table 6 Results of Analysis of Variance on Residual Weight Ratio

[0054] 3) Optimized process for tree charcoal-based fertilizer In this embodiment, the mechanical properties of the charcoal-based fertilizer prepared with 5% binder, 8% moisture, and 2 MPa molding pressure were tested. As shown in Table 7, the average hardness of the charcoal-based fertilizer was 64.5 H. D It has an average maximum crushing resistance of 309.77N and an average residual weight ratio of 99.5%, demonstrating excellent mechanical properties.

[0055] Table 7 Mechanical Properties of Tree Charcoal-Based Fertilizer

[0056] 4) Preparation of biochar-based slow-release fertilizer from garden waste This embodiment prepared a biochar-based slow-release fertilizer from garden waste with different replacement rates of nitrogen, phosphorus, and potassium inorganic fertilizers using leaf char. For example... Figure 12 The biochar-based fertilizers TBF (leafless charcoal replacing nitrogen, phosphorus, and potassium inorganic fertilizer) and WBF-15% (leaf charcoal replacing 15% of nitrogen, phosphorus, and potassium inorganic fertilizer) have relatively smooth surfaces, while WBF-25% (leaf charcoal replacing 25% of nitrogen, phosphorus, and potassium inorganic fertilizer) and WBF-35% (leaf charcoal replacing 35% of nitrogen, phosphorus, and potassium inorganic fertilizer) show obvious unevenness on their surfaces and the phenomenon of biochar breaking off at the edges of the particles.

[0057] Figure 13 Mechanical performance results showed that the hardness of the garden waste biochar-based slow-release fertilizer ranged from 18.5HD to 64.5HD, the maximum breakage resistance ranged from 85.47N to 309.77N, and the residual weight ratio ranged from 79.5% to 99.5%. With the increase of leaf char content, the hardness, maximum breakage resistance, and residual weight ratio of the garden waste biochar-based slow-release fertilizer all showed a decreasing trend. Figure 13 a, b, and c show that the hardness and maximum breakage resistance of garden waste biochar-based slow-release fertilizer decrease significantly when the leaf biochar content is 25% and 35%, respectively, while the decrease in the residual weight ratio is slightly smaller.

[0058] Table 8 shows the mechanical properties of two types of garden waste biochar-based slow-release fertilizers. Both fertilizers exhibit excellent compressive strength and abrasion resistance. Their hardness is 64.5H. D and 49.6H D The maximum crushing resistance is 307.99N and 206.64N, respectively, and the remaining weight ratio is 99.5% and 95.9%, respectively.

[0059] Table 8 Mechanical properties of biochar-based slow-release fertilizer from garden waste

[0060] 5) Basic physicochemical properties of carbon-based fertilizers This embodiment analyzed and determined the main components and basic physicochemical properties of biochar-based slow-release fertilizer made from garden waste. For example... Figure 14a. The total biochar content of the garden waste biochar-based slow-release fertilizer is 23.63% - 57.32%. The contents of total nitrogen (10.95% - 19.56%), available phosphorus (3.8% - 8.14%), and total potassium (5.27% - 8.79%) gradually decrease with the increase in the leaf charcoal substitution rate. The chloride ion content is controlled at a low level (1.19% - 1.3%), significantly lower than the standard limit value, and has less negative impact on the soil and plants. Heavy metal contents such as Figure 14 As shown in b, no As, Cd, and Hg elements were detected in the garden waste biochar-based slow-release fertilizer, and the contents of Pb and Cr elements are both lower than the relevant standard limit values (0.05%). As shown in Table 9, the total nutrient content is between 20.92% and 36.49%, and the pH value ranges from 7.04 to 7.95, showing a weak alkaline overall and having little impact on the soil pH value.

[0061] Table 9 Physical and chemical indexes of garden waste biochar-based slow-release fertilizer

[0062] Figure 15 a and Figure 15 b respectively show the dynamic change characteristics of the single-release rate and cumulative release rate of nitrogen in the garden waste biochar-based slow-release fertilizer under normal leaching. From the single-release rate curve ( Figure 15 a), it can be seen that the overall trend is to first decrease and then fluctuate steadily. In the early stage, the fertilizer on the surface of the garden waste biochar-based slow-release fertilizer quickly dissolves and releases under the leaching of water. In the middle and later stages, the nutrients are leached out regularly under the adsorption of biochar, forming a stable slow-release mechanism. The WBF-35% treatment maintains a relatively high single-release rate throughout the observation period, and the nitrogen release rate within 24 hours is between 16.35% and 21.06%. The garden waste biochar-based slow-release fertilizer has excellent initial nutrient control and release performance. From Figure 15 b, it can be seen that the nitrogen cumulative release rates of the TBF, WBF-15%, and WBF-25% treatments are between 40.53% and 41.85% in the first three days, significantly lower than that of the pure nitrogen fertilizer treatment (70.06%). After 7 days of leaching, the nitrogen cumulative release rate of the garden waste biochar-based slow-release fertilizer reaches 58.36% - 79.25%.

[0063] The present invention systematically analyzed the nitrogen release characteristics of the garden waste biochar-based slow-release fertilizer through the Korsmeyer-Peppas model. As shown in Table 10, the n values of the four biochar-based fertilizers are similar, indicating that they all exhibit a typical non-Fickian diffusion mechanism (0.45 < n < 0.89), that is, the release process is controlled by both diffusion and erosion. The k value reflects the release rate, and the smaller the value, the slower and more persistent the release. The release rates from low to high are WBF-15%, WBF-25%, TBF, WBF-35%. The R of all garden waste biochar-based slow-release fertilizers2 All values ​​are above 0.96, indicating that the model fits well, with TBF showing the best fit (R²). 2 =0.975), followed by WBF-15% (R 2 =0.971), WBF-25% and WBF-35% are slightly lower (R 2 ≈0.961).

[0064] Table 10. Nitrogen release kinetic model parameters of garden waste biochar-based slow-release fertilizer in soil

[0065] Figure 16 This study presents the nitrogen cumulative release curves of garden waste biochar-based slow-release fertilizer under different formulation conditions. The results show that the WBF-35% treatment group consistently exhibited the highest nitrogen release rate during continuous leaching. Different formulations of garden waste biochar-based slow-release fertilizer showed significant differences in release characteristics: the TBF and WBF-15% treatment groups released all nitrogen after 450 minutes of continuous leaching; the WBF-25% treatment group had a slightly shorter nitrogen release period of 420 minutes; while the WBF-35% treatment group showed the fastest release rate, completing the release of all nitrogen in 390 minutes. The TBF and WBF-15% formulations of garden waste biochar-based slow-release fertilizer exhibit superior slow-release performance and anti-leaching characteristics. Their slower nutrient release rate and longer residual effect indicate that these two formulations can achieve a more controllable slow-release effect, demonstrating significant advantages in reducing nutrient loss and improving fertilizer utilization, making them suitable for promotion and application in areas with frequent rainfall.

[0066] 6) Carbon-based fertilizer application experiment This embodiment compares the effects of three treatments—CK (no fertilizer), CF (conventional fertilizer), and TBF (tree charcoal fertilizer)—on the growth of soybean seedlings through a pot experiment. Figure 17 As shown in figure a, on day 14, the seedlings treated with TBF showed significantly better growth than the other two treatments. By day 21 ( Figure 17 (b) The soybean plants treated with TBF showed a more significant growth advantage, fully demonstrating the long-term growth-promoting effect of TBF compared to other treatments. Dynamic monitoring of plant height and leaf area over 21 days ( Figure 18 a and Figure 18(b) Seedlings treated with TBF showed significantly better growth performance than those in the CK and CF groups across all growth indicators. On day 7, soybean seedlings in the CK treatment had the smallest plant height; by day 14, the growth trends of the CF and CK treatments converged. This rapid release pattern promotes early plant growth but accelerates soil nutrient depletion, making it difficult to sustain continuous plant growth. By day 21, soybean plants treated with TBF reached a height of 37 cm, representing increases of 27.6% and 34.5% compared to the CF and CK treatments, respectively. Furthermore, the leaf area of ​​the TBF-treated plants was 18.6 cm². 2 Compared with the control treatment, the increase was 18.8% to 21.2%.

[0067] like Figure 19 a. On the 21st day after sowing, the chlorophyll content of soybean seedlings treated with TBF reached 54.2 mg / g, indicating that twig charcoal-based fertilizer significantly increased the chlorophyll content of soybeans. Figure 19 As shown in b, compared with the CK and CF treatments, the total fresh weight and dry weight of soybean seedlings treated with TBF were significantly higher. This result highlights the effectiveness of TBF in promoting biomass accumulation. In conclusion, twig charcoal-based fertilizer can achieve reduced utilization of nitrogen, phosphorus, and potassium inorganic fertilizers, and the application of twig charcoal-based fertilizer promotes the growth of soybean seedlings.

[0068] This embodiment compared the effects of six treatments (CK, CF, TBF, WBF-15%, WBF-25%, and WBF-35%) on the growth of dwarf sunflower seedlings through a pot experiment. The results showed that on the 14th day of plant growth (…),… Figure 20 a) Seedlings treated with TBF, WBF-15%, and WBF-25% showed better growth. By day 21 ( Figure 20 (b) Seedlings treated with TBF showed significantly better growth than those treated with other methods, followed by those treated with WBF-15% and WBF-25%. Changes in plant height and leaf area of ​​dwarf sunflower seedlings over 21 days ( Figure 20 c and Figure 20 d) indicates that on day 7, the CF-treated seedlings had the tallest plant height and largest leaf area. By day 14, the growth trend of the CF-treated seedlings was similar to that of the WBF-35%. On day 21, the plant heights of the dwarf sunflowers in the TBF, WBF-15%, and WBF-25% treatments were 13.8 cm, 13.5 cm, and 13.3 cm, respectively.

[0069] like Figure 21 a, 21b, and 21c show the significant correlations between different treatments for plant height, leaf area, and chlorophyll content on day 21. Figure 21As shown in d, different treatments had a significant impact on the biomass of dwarf sunflowers. On the 21st day after sowing, the treatments with the highest and lowest total fresh weight and dry weight of the plants were TBF, WBF-15%, WBF-25%, WBF-35%, CF, and CK. Tree branch charcoal-based fertilizer and garden waste biochar-based slow-release fertilizer using tree leaf charcoal to replace chemical fertilizers could promote biomass accumulation.

[0070] Those skilled in the art will understand that the above embodiments are specific examples of implementing the present invention, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of the present invention. Any person skilled in the art can make their own modifications and alterations without departing from the spirit and scope of the present invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A biochar-based slow-release fertilizer made from garden waste, characterized in that, The aforementioned garden waste biochar-based slow-release fertilizer uses tree branch charcoal as the slow-release carrier substrate and tree leaf charcoal as the active nutrient substance; the garden waste biochar-based slow-release fertilizer comprises the following raw material components by mass percentage: 16-30% tree branch charcoal, 10-20% tree leaf charcoal, 40-45% nitrogen, phosphorus and potassium compound fertilizer, 3-9% binder, and 4-10% moisture, and the sum of the mass percentages of all raw material components is 100%.

2. The garden waste biochar-based slow-release fertilizer according to claim 1, characterized in that, The charcoal made from tree branches and leaves is obtained by crushing, drying, and then pyrolyzing them.

3. The garden waste biochar-based slow-release fertilizer according to claim 1, characterized in that, The fixed carbon content of the dendritic charcoal is 65-85%, and the specific surface area is 200-250 m². 2 / g.

4. The garden waste biochar-based slow-release fertilizer according to claim 1, characterized in that, The binder is one or more of attapulgite, bentonite, or starch.

5. A method for preparing a biochar-based slow-release fertilizer from garden waste according to any one of claims 1 to 4, characterized in that, The preparation method includes: a. Garden waste branches and garden waste leaves are crushed and dried separately, and then pyrolyzed and carbonized under limited oxygen conditions to obtain branch charcoal and leaf charcoal; b. Mix the charcoal branches, charcoal leaves, nitrogen, phosphorus, and potassium inorganic fertilizers, binder, and water evenly to obtain the garden waste biochar-based slow-release fertilizer.

6. The method for preparing biochar-based slow-release fertilizer from garden waste according to claim 5, characterized in that, In step a, the pyrolysis carbonization under oxygen-limited conditions includes: carbonization temperature of 550-650℃, heating rate of 10-20℃ / min, and holding time of 120-180min.

7. The method for preparing biochar-based slow-release fertilizer from garden waste according to claim 5, characterized in that, The preparation method also includes: c) compressing the garden waste biochar-based slow-release fertilizer into tablets.

8. The method for preparing biochar-based slow-release fertilizer from garden waste according to claim 7, characterized in that, In step c, the garden waste biochar-based slow-release fertilizer is thoroughly stirred and then loaded into a cylindrical mold with a radius of 2-4 mm. After pressing with a tablet press for 5-20 seconds at 1.5-3 MPa, the fertilizer is demolded.

9. The application of a biochar-based slow-release fertilizer made from garden waste according to any one of claims 1 to 4 in the field of garden waste utilization.

10. The application of a garden waste biochar-based slow-release fertilizer according to any one of claims 1 to 4 in the field of fertilizers.

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