Biochar-based phosphorus slow-release fertilizer and preparation method thereof

Abstract

The application discloses a biochar-based phosphorus slow-release fertilizer and a preparation method thereof, and belongs to the technical field of fertilizers.The biochar-based phosphorus slow-release fertilizer is composed of the following raw materials: corn straw charcoal 50-60 parts, slow-release phosphorus source 20-25 parts, plant source functional additive 5-10 parts, activated sepiolite 5-10 parts, dolomite powder 3-6 parts and chelated microelement fertilizer 3-5 parts; the plant source functional additive is compounded by dandelion and extract of million bells for tobacco in proportion.The application realizes that the utilization rate of phosphorus is greater than or equal to 40% by constructing a controlled release mechanism in a multi-component synergistic manner, regulates the nicotine content to 1.8-3.2% at the same time, the extreme difference of nicotine in parts is less than or equal to 0.3%, and the qualified rate of high-quality tobacco is greater than or equal to 96.8%; the raw materials are derived from agricultural wastes and natural minerals, the preparation process is green and scalable, has the functions of fertilizer efficiency and soil improvement, and is suitable for field popularization of flue-cured tobacco.

Description

Technical Field

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

[0002] Phosphorus is an essential nutrient element for the growth and development of flue-cured tobacco, participating in key physiological processes such as photosynthesis, respiration, and nutrient synthesis and transport, and significantly influencing plant architecture and leaf quality. The phosphorus requirement of flue-cured tobacco at different growth stages exhibits a significant stepwise characteristic: the seedling stage requires less phosphorus but is highly sensitive, with insufficient phosphorus easily leading to weak seedlings; the peak phosphorus requirement occurs during the rosette stage to the vigorous growth stage, where sufficient phosphorus supply effectively promotes root development and vegetative growth; phosphorus demand gradually slows down during the maturity stage, and appropriate amounts of phosphorus can promote the synthesis and accumulation of carbohydrates and nicotine in tobacco leaves.

[0003] In existing flue-cured tobacco fertilizers, the phosphorus source is mostly ordinary phosphates (such as potassium phosphate), which have a rapid phosphorus release rate and are easily fixed by the soil, resulting in low phosphorus utilization. Furthermore, the rapid release of phosphorus does not match the phosphorus requirements of flue-cured tobacco. Excessive phosphorus during the seedling stage may cause seedling burn, insufficient phosphorus supply during the vigorous growth stage will affect tobacco growth, and phosphorus deficiency during the maturity stage will reduce the quality of tobacco leaves. In addition, existing flue-cured tobacco fertilizers mostly focus on the basic nitrogen-phosphorus-potassium ratio, and the regulation of nicotine content is achieved through only a single component, resulting in limited regulatory effects. The problems of low nicotine content in tobacco leaves and significant differences in nicotine content among different leaf parts still exist, restricting the industrial utilization value of flue-cured tobacco.

[0004] Biochar, due to its abundant porous structure, is widely used as a carrier for slow-release fertilizers. However, ordinary biochar has limited adsorption capacity, resulting in poor slow-release effects on phosphorus and poor compatibility with other fertilizer components. While there are reports on biochar-based flue-cured tobacco fertilizers in the current technology, these have not modified the biochar to specifically address phosphorus slow-release characteristics, nor have they constructed a composite phosphorus source and slow-release regulation system. Therefore, the mismatch between phosphorus release and the phosphorus requirements of flue-cured tobacco has not been effectively resolved. Furthermore, in terms of nicotine content regulation, existing fertilizers mostly rely on single chemical additives or conventional nutrient regulation, with limited effectiveness, making it difficult to simultaneously achieve precise increases in nicotine content and reduce differences in nicotine content among different leaf parts.

[0005] Therefore, it is of great significance to develop a biochar-based slow-release phosphorus fertilizer that can match the phosphorus requirements of flue-cured tobacco at different stages, so as to achieve segmented and controllable release of phosphorus and improve its utilization rate, while synergistically regulating the nicotine content of tobacco leaves and reducing the differences in nicotine content in different parts. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, the technical problem this invention aims to solve is to provide a biochar-based slow-release phosphorus fertilizer. Using corn straw charcoal as a carrier, it achieves segmented and controllable phosphorus release through a scientifically compounded blend of slow-release phosphorus sources, plant-derived functional additives, activated sepiolite, dolomite powder, and chelated micronutrients. This invention also provides a method for preparing the aforementioned biochar-based slow-release phosphorus fertilizer. The preparation process is green and scalable, suitable for large-scale application in flue-cured tobacco fields. Furthermore, this invention provides the application of the aforementioned biochar-based slow-release phosphorus fertilizer in flue-cured tobacco cultivation.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A biochar-based slow-release phosphorus fertilizer, by weight, is composed of the following raw materials: 50-60 parts corn straw charcoal, 20-25 parts slow-release phosphorus source, 5-10 parts plant-derived functional adjuvants, 5-10 parts activated sepiolite, 3-6 parts dolomite powder, and 3-5 parts chelated micronutrients; wherein the plant-derived functional adjuvants are composed of dandelion extract and marigold extract; and the slow-release phosphorus source is composed of potassium dihydrogen phosphate, potassium pyrophosphate, and magnesium polyphosphate.

[0009] Preferably, the corn straw charcoal is 55-58 parts, the slow-release phosphorus source is 20-23 parts, the plant-derived functional adjuvant is 7 parts, the activated sepiolite is 6-8 parts, the dolomite powder is 4-5 parts, and the chelated micro-fertilizer is 4-5 parts.

[0010] Preferably, the corn stalk charcoal is obtained by pyrolysis at 500-600℃ and then passing it through a 100-mesh sieve.

[0011] Preferably, the activated sepiolite is obtained by thermally activating sepiolite at 300~400℃ for 1 hour.

[0012] Preferably, the mass ratio of the dandelion extract to the marigold extract is 6:1.

[0013] Preferably, the dolomite powder has a particle size of 250 mesh, a CaO content of not less than 30%, and a MgO content of not less than 20%; the chelated micro-fertilizer is a compound of EDTA-chelated manganese, iron, zinc, molybdenum and boric acid, with a molar ratio of Mn:Fe:Zn:Mo:B of 2:2:3:1:2.

[0014] As a preferred embodiment, the preparation process of the dandelion extract is as follows: the whole dandelion herb is pulverized and then added to an 85% ethanol aqueous solution at a material-to-liquid ratio of 1:3. After ultrasonic extraction at 30kHz for 20 minutes, the extract is filtered and concentrated under reduced pressure to obtain the dandelion extract.

[0015] The preparation process of the marigold extract for tobacco is as follows: marigold petals are crushed and added to a 70% ethanol aqueous solution at a material-to-liquid ratio of 1:2. After extraction by ultrasonication at 25kHz for 15 minutes, the mixture is filtered and concentrated under reduced pressure to obtain the marigold extract for tobacco.

[0016] Preferably, the mass ratio of potassium dihydrogen phosphate, potassium pyrophosphate, and magnesium polyphosphate is 2:12~15:5~9.

[0017] A method for preparing the biochar-based phosphorus slow-release fertilizer includes the following steps:

[0018] 1) Pretreatment was performed on potassium dihydrogen phosphate, potassium pyrophosphate, and magnesium polyphosphate respectively;

[0019] 2) Add the pretreated potassium pyrophosphate, magnesium polyphosphate, activated sepiolite, and dolomite powder to a high-speed mixer and mix at 1200 r / min for 10 min. Then add the pretreated potassium dihydrogen phosphate and mix at 800 r / min for 5 min to obtain an inorganic component premix.

[0020] 3) Add corn straw charcoal to the inorganic component premix obtained in step 2), stir at 500 r / min for 2 min for initial mixing, then increase to 800 r / min and continue stirring for 10 min to obtain inorganic mixed powder;

[0021] 4) Mix dandelion extract and marigold extract evenly, add deionized water to dilute at a volume ratio of 1:2.5, and spray evenly into the inorganic mixed powder obtained in step 3) using a 0.4MPa high-pressure atomizing nozzle. During the spraying process, the mixer runs at 600r / min for 6min. After the spraying is completed, continue mixing at 600r / min for 5min to obtain the premixed material.

[0022] 5) Add chelated micro-fertilizer to the premixed material obtained in step 4), mix at 300 r / min for 8 min, and add deionized water by spraying to adjust the moisture content of the material to 12-15%;

[0023] 6) Feed the material with the moisture content adjusted in step 5) into an extrusion granulator for granulation. Dry the resulting granules with hot air at 40℃ until the final moisture content is ≤4%. After cooling and sieving, obtain biochar-based phosphorus slow-release fertilizer.

[0024] Application of the aforementioned biochar-based phosphorus slow-release fertilizer in flue-cured tobacco cultivation.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0026] 1) This invention constructs a multi-gradient phosphorus slow-release system by compounding potassium dihydrogen phosphate, potassium pyrophosphate, and magnesium polyphosphate in a specific ratio as a slow-release phosphorus source, and combining the adsorption characteristics of corn straw charcoal with the layered structure of activated sepiolite. Among them, potassium dihydrogen phosphate, as a fast-acting phosphorus source, can quickly meet the phosphorus sensitive needs of flue-cured tobacco seedlings; potassium pyrophosphate is gradually hydrolyzed under the action of soil microorganisms and can continuously release phosphorus from the seedling stage to the vigorous growth stage; magnesium polyphosphate has a slow chelated release characteristic, providing a stable phosphorus supply for the maturity stage, thereby achieving precise matching of phosphorus release with the phosphorus requirements of flue-cured tobacco at different growth stages, effectively improving phosphorus utilization rate to over 40%.

[0027] 2) This invention uses dandelion extract and marigold extract for tobacco in a mass ratio of 6:1 as a plant-derived functional adjuvant; the synergistic effect of the two can not only accurately control the nicotine content of tobacco leaves to a suitable range of 1.8~3.2%, but also significantly reduce the difference in nicotine content in different parts of the leaves, so that the range of nicotine content in different parts is controlled within 0.3%, and greatly improve the qualified rate of high-quality tobacco to over 96.8%;

[0028] 3) This invention uses corn stalks, an agricultural waste, to prepare biochar, which not only realizes the recycling of resources, but also enhances the adsorption and slow release capacity of nutrients through its rich pore structure; after the activated sepiolite is thermally activated at 300~400℃, its adsorption performance is enhanced, which can further synergistically delay the release of phosphorus by corn stalk char.

[0029] 4) The preparation process of this invention is green and environmentally friendly and easy to scale up. Through steps such as high-speed mixing, high-pressure atomization spraying of plant-derived functional additives, and extrusion granulation, the uniform mixing and effective combination of each component are achieved. When this fertilizer is applied to flue-cured tobacco fields, it can not only significantly improve the yield and quality of tobacco leaves, but also improve the physical and chemical properties of the soil and enhance the soil's water and fertilizer retention capacity. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is further described below with reference to specific embodiments. Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0031] In the following examples, corn straw charcoal was pyrolyzed at 500-600℃ and then passed through a 100-mesh sieve. Sepiolite was thermally activated at 300-400℃ for 1 hour to obtain activated sepiolite. Dolomite powder had a particle size of 250 mesh, a CaO content ≥30%, and a MgO content ≥20%. The chelated micronutrient fertilizer used was an EDTA-chelated manganese, iron, zinc, molybdenum + boric acid compound system (Mn:Fe:Zn:Mo:B=2:2:3:1:2).

[0032] The preparation process of dandelion extract is as follows: the whole dandelion herb is crushed and added to an 85% ethanol aqueous solution (the material-liquid ratio is 1g:3mL). After extraction by ultrasonication at 30kHz for 20 min, the extract is filtered and the filtrate is concentrated under reduced pressure to 1 / 4 of the original volume to obtain the liquid extract.

[0033] The preparation process of marigold extract for tobacco is as follows: marigold petals are crushed and added to 70% ethanol aqueous solution (material-liquid ratio of 1g:2mL), and extracted by ultrasonication at 25 kHz for 15 min. After filtration, the filtrate is concentrated under reduced pressure to 1 / 3 of the original volume to obtain liquid extract.

[0034] Example 1

[0035] A biochar-based slow-release phosphorus fertilizer, by weight, is composed of the following raw materials: 56 parts corn straw charcoal, 21 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 13 parts potassium pyrophosphate, 6 parts magnesium polyphosphate), 7 parts plant-derived functional adjuvants (6 parts dandelion extract, 1 part marigold extract), 8 parts activated sepiolite, 4 parts dolomite powder, and 4 parts chelated micro-fertilizer.

[0036] The preparation method of the above-mentioned biochar-based phosphorus slow-release fertilizer includes the following steps:

[0037] 1) Pre-treat potassium dihydrogen phosphate, potassium pyrophosphate, and magnesium polyphosphate separately: dry potassium dihydrogen phosphate at 60℃ for 2 hours; dry potassium pyrophosphate at 80℃ for 1 hour; and dry magnesium polyphosphate at 100℃ for 1 hour.

[0038] 2) Add the pretreated potassium pyrophosphate, magnesium polyphosphate, activated sepiolite, and dolomite powder to a high-speed mixer and mix at 1200 r / min for 10 min. Then add the pretreated potassium dihydrogen phosphate and mix at 800 r / min for 5 min to obtain an inorganic component premix.

[0039] 3) Add corn straw charcoal to the inorganic component premix obtained in step 2), stir at 500 r / min for 2 min to initially mix the materials, then increase to 800 r / min and continue stirring for 10 min to obtain inorganic mixed powder;

[0040] 4) Mix dandelion extract and marigold extract evenly, add deionized water to dilute at a ratio of 1:2.5, stir evenly, and then spray evenly into the inorganic mixed powder obtained in step 3) using a 0.4MPa high-pressure atomizing nozzle. During the spraying process, keep the mixer running at a speed of 600 r / min for 6 minutes. After the spraying is completed, continue mixing for 5 minutes to obtain the premixed material.

[0041] 5) Evenly sprinkle chelated micro-fertilizer into the premixed material obtained in step 4), mix at 300 r / min for 8 min, add deionized water by spraying, and adjust the moisture content of the mixture to 12-15%;

[0042] 6) Feed the material with the moisture content adjusted in step 5) into an extrusion granulator, granulate it using a 3mm die orifice and a roller speed of 22 r / min, dry the resulting granules with hot air at 40℃ until the final moisture content is ≤4%, and then cool and screen them to obtain biochar-based phosphorus slow-release fertilizer.

[0043] Example 2

[0044] A biochar-based slow-release phosphorus fertilizer, by weight, is composed of the following raw materials: 55 parts corn straw charcoal, 22 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 15 parts potassium pyrophosphate, 5 parts magnesium polyphosphate), 7 parts plant-derived functional adjuvants (6 parts dandelion extract, 1 part marigold extract), 7 parts activated sepiolite, 4 parts dolomite powder, and 5 parts chelated micro-fertilizer.

[0045] The preparation method, parameters, and specific preparation process of the above-mentioned biochar-based phosphorus slow-release fertilizer are the same as those in Example 1.

[0046] Example 3

[0047] A biochar-based slow-release phosphorus fertilizer, by weight, is composed of the following raw materials: 57 parts corn straw charcoal, 20 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 12 parts potassium pyrophosphate, 6 parts magnesium polyphosphate), 7 parts plant-derived functional adjuvants (6 parts dandelion extract, 1 part marigold extract), 8 parts activated sepiolite, 4 parts dolomite powder, and 4 parts chelated micro-fertilizer.

[0048] The preparation method, parameters, and specific preparation process of the above-mentioned biochar-based phosphorus slow-release fertilizer are the same as those in Example 1.

[0049] Example 4

[0050] A biochar-based slow-release phosphorus fertilizer, by weight, is composed of the following raw materials: 56 parts corn straw charcoal, 21 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 13 parts potassium pyrophosphate, 6 parts magnesium polyphosphate), 7 parts plant-derived functional adjuvants (6 parts dandelion extract, 1 part marigold extract), 6 parts activated sepiolite, 6 parts dolomite powder, and 4 parts chelated micro-fertilizer.

[0051] The preparation method, parameters, and specific preparation process of the above-mentioned biochar-based phosphorus slow-release fertilizer are the same as those in Example 1.

[0052] Example 5

[0053] A biochar-based slow-release phosphorus fertilizer, by weight, is composed of the following raw materials: 57 parts corn straw charcoal, 20 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 12 parts potassium pyrophosphate, 6 parts magnesium polyphosphate), 7 parts plant-derived functional adjuvants (6 parts dandelion extract, 1 part marigold extract), 7 parts activated sepiolite, 4 parts dolomite powder, and 5 parts chelated micro-fertilizer.

[0054] The preparation method, parameters, and specific preparation process of the above-mentioned biochar-based phosphorus slow-release fertilizer are the same as those in Example 1.

[0055] Example 6

[0056] A biochar-based slow-release phosphorus fertilizer, by weight, is composed of the following raw materials: 58 parts corn straw charcoal, 20 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 12 parts potassium pyrophosphate, 6 parts magnesium polyphosphate), 7 parts plant-derived functional adjuvants (6 parts dandelion extract, 1 part marigold extract), 6 parts activated sepiolite, 4 parts dolomite powder, and 5 parts chelated micro-fertilizer.

[0057] The preparation method, parameters, and specific preparation process of the above-mentioned biochar-based phosphorus slow-release fertilizer are the same as those in Example 1.

[0058] Example 7

[0059] A biochar-based slow-release phosphorus fertilizer, by weight, is composed of the following raw materials: 56 parts corn straw charcoal, 22 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 13 parts potassium pyrophosphate, 7 parts magnesium polyphosphate), 7 parts plant-derived functional adjuvants (6 parts dandelion extract, 1 part marigold extract), 7 parts activated sepiolite, 4 parts dolomite powder, and 4 parts chelated micro-fertilizer.

[0060] The preparation method, parameters, and specific preparation process of the above-mentioned biochar-based phosphorus slow-release fertilizer are the same as those in Example 1.

[0061] Example 8

[0062] A biochar-based slow-release phosphorus fertilizer, by weight, is composed of the following raw materials: 55 parts corn straw charcoal, 23 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 12 parts potassium pyrophosphate, 9 parts magnesium polyphosphate), 7 parts plant-derived functional adjuvants (6 parts dandelion extract, 1 part marigold extract), 7 parts activated sepiolite, 5 parts dolomite powder, and 3 parts chelated micronutrient fertilizer.

[0063] The preparation method, parameters, and specific preparation process of the above-mentioned biochar-based phosphorus slow-release fertilizer are the same as those in Example 1.

[0064] Comparative Example 1

[0065] A slow-release fertilizer, by weight, is composed of the following raw materials: 56 parts corn straw charcoal, 21 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 13 parts potassium pyrophosphate, 6 parts magnesium polyphosphate), 7 parts dandelion extract, 8 parts activated sepiolite, 4 parts dolomite powder, and 4 parts chelated micronutrient fertilizer.

[0066] The preparation method, parameters, and specific preparation process of the above-mentioned slow-release fertilizer are the same as those in Example 1.

[0067] Comparative Example 2

[0068] A slow-release fertilizer, by weight, is composed of the following raw materials: 56 parts corn straw charcoal, 2 parts potassium dihydrogen phosphate, 19 parts potassium pyrophosphate, 7 parts plant-derived functional adjuvants (6 parts dandelion extract and 1 part marigold extract), 8 parts activated sepiolite, 4 parts dolomite powder, and 4 parts chelated micronutrient fertilizer.

[0069] The preparation method, parameters, and specific preparation process of the above-mentioned slow-release fertilizer are the same as those in Example 1.

[0070] Comparative Example 3

[0071] A slow-release fertilizer, by weight, comprises the following raw materials: 56 parts corn straw charcoal, 21 parts slow-release phosphorus source (2 parts potassium dihydrogen phosphate, 13 parts potassium pyrophosphate, and 6 parts magnesium polyphosphate), 7 parts plant-derived functional adjuvants (6 parts dandelion extract and 1 part marigold extract), 8 parts unactivated sepiolite, 4 parts dolomite powder, and 4 parts chelated micronutrients. The unactivated sepiolite is pulverized to only 100 mesh and has not undergone thermal activation treatment.

[0072] The preparation method, parameters, and specific preparation process of the above-mentioned slow-release fertilizer are the same as those in Example 1.

[0073] Effect verification:

[0074] A field experiment was conducted using yellow-brown soil with a pH of 5.8 and an available phosphorus content of 12.5 mg / kg. The experimental area was divided into 11 groups (8 specific examples and 3 comparative examples), each 0.5 mu (approximately 0.067 hectares). The fertilizer application rate for each group was 90 kg / mu (approximately 150 kg / hectare), with 80% applied as basal fertilizer in furrows and 20% applied in holes during the early vigorous growth period. All field management was consistent (routine management for flue-cured tobacco, with no additional fertilization). Tobacco seedlings were transplanted in mid-April and harvested in mid-August. The test indicators included nicotine content (YC / Z240-2008), available phosphorus in the soil (NY / T1121.7-2014), phosphorus utilization rate (subtraction method), qualified rate of high-quality tobacco (nicotine 1.5~3.5% with a range of ≤0.3% in different parts), phosphorus cumulative release rate (28 days), and soil organic matter improvement rate. The results are shown in Tables 1 and 2.

[0075] Table 1. Nicotine content in different parts of the tobacco planted in Examples 1-8 and Comparative Examples 1-3

[0076] Upper leaves nicotine content (%) Middle leaves nicotine content (%) Lower leaves nicotine content (%) Nicotine range (%) Example 1 2.95 2.78 2.74 0.21 Example 2 2.92 2.75 2.71 0.21 Example 3 3.05 2.88 2.84 0.21 Example 4 2.88 2.72 2.69 0.19 Example 5 3.10 2.92 2.89 0.21 Example 6 2.90 2.75 2.70 0.20 Example 7 3.02 2.85 2.81 0.21 Example 8 2.85 2.70 2.68 0.17 Comparative Example 1 2.40 2.08 1.83 0.57 Comparative Example 2 2.32 2.05 1.79 0.53 Comparative Example 3 2.52 2.26 2.07 0.45

[0077] Table 2. Actual field test results of Examples 1-8 and Comparative Examples 1-3

[0078] Soil available phosphorus retention rate (%) Phosphorus utilization rate (%) Phosphorus cumulative release rate in 28 days (%) High-quality tobacco qualified rate (%) Example 1 80.2 41.5 68.5 97.5 Example 2 79.8 40.8 70.2 97.0 Example 3 82.5 42.8 65.8 98.2 Example 4 81.3 41.2 67.3 97.8 Example 5 83.1 43.5 64.5 98.5 Example 6 81.8 42.0 66.7 97.6 Example 7 82.7 43.2 65.2 98.3 Example 8 80.5 41.0 63.8 97.3 Comparative Example 1 79.5 40.2 66.5 58.2 Comparative Example 2 65.5 26.5 81.5 63.0 Comparative Example 3 59.3 27.8 78.8 68.7

[0079] As shown in Tables 1 and 2, under a uniform application rate (90 kg / mu) and the same application process, the fertilizer prepared by this invention through the scientific compounding of slow-release phosphorus source, plant-derived functional adjuvants, and activated mineral materials exhibits a nicotine range ≤0.21%, a soil available phosphorus retention rate ≥78.5%, and a high-quality tobacco qualification rate ≥96.8% after application, demonstrating a significant slow-release effect of phosphorus and an improvement in the quality of flue-cured tobacco. Specifically, the compounding of marigold extract and dandelion extract effectively coordinates the nicotine content in different parts of flue-cured tobacco, reduces the range, and significantly increases the proportion of high-quality tobacco. The introduction of magnesium polyphosphate effectively slows down the phosphorus release rate, improves phosphorus retention in the soil, and enhances crop absorption efficiency. Furthermore, sepiolite, after thermal activation treatment, has enhanced adsorption performance and structural stability, enabling it to better synergize with biochar and other components to exert a slow-release effect of phosphorus.

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A biochar-based slow-release phosphorus fertilizer, characterized in that, The product is composed of the following raw materials by weight: 50-60 parts corn straw charcoal, 20-25 parts slow-release phosphorus source, 5-10 parts plant-derived functional adjuvant, 5-10 parts activated sepiolite, 3-6 parts dolomite powder, and 3-5 parts chelated micro-fertilizer; wherein the plant-derived functional adjuvant is composed of dandelion extract and marigold extract; and the slow-release phosphorus source is composed of potassium dihydrogen phosphate, potassium pyrophosphate, and magnesium polyphosphate.

2. The biochar-based slow-release phosphorus fertilizer according to claim 1, characterized in that, The corn straw charcoal comprises 55-58 parts, the slow-release phosphorus source comprises 20-23 parts, the plant-derived functional adjuvant comprises 7 parts, the activated sepiolite comprises 6-8 parts, the dolomite powder comprises 4-5 parts, and the chelated micro-fertilizer comprises 4-5 parts.

3. The biochar-based slow-release phosphorus fertilizer according to claim 1 or 2, characterized in that, The corn stalk charcoal is obtained by pyrolysis at 500-600℃ and then passing it through a 100-mesh sieve.

4. The biochar-based slow-release phosphorus fertilizer according to claim 1 or 2, characterized in that, The activated sepiolite is obtained by thermally activating sepiolite at 300~400℃ for 1 hour.

5. The biochar-based slow-release phosphorus fertilizer according to claim 1, characterized in that, The mass ratio of the dandelion extract to the marigold extract is 6:

1.

6. The biochar-based slow-release phosphorus fertilizer according to claim 1 or 2, characterized in that, The dolomite powder has a particle size of 250 mesh, a CaO content of not less than 30%, and a MgO content of not less than 20%. The chelated micro-fertilizer is a compound of EDTA-chelated manganese, iron, zinc, molybdenum and boric acid, with a molar ratio of Mn:Fe:Zn:Mo:B of 2:2:3:1:

2.

7. The biochar-based slow-release phosphorus fertilizer according to claim 1, characterized in that, The preparation process of the dandelion extract is as follows: the whole dandelion herb is crushed and then added to an 85% ethanol aqueous solution with a material-to-liquid ratio of 1:

3. After ultrasonic extraction at 30kHz for 20 minutes, the extract is filtered and concentrated under reduced pressure to obtain the dandelion extract. The preparation process of the marigold extract for tobacco is as follows: marigold petals are crushed and added to a 70% ethanol aqueous solution at a material-to-liquid ratio of 1:

2. After extraction by ultrasonication at 25kHz for 15 minutes, the mixture is filtered and concentrated under reduced pressure to obtain the marigold extract for tobacco.

8. The biochar-based slow-release phosphorus fertilizer according to claim 1, characterized in that, The mass ratio of potassium dihydrogen phosphate, potassium pyrophosphate, and magnesium polyphosphate is 2:12~15:5~9.

9. A method for preparing a biochar-based phosphorus slow-release fertilizer according to any one of claims 1-8, characterized in that, Includes the following steps: 1) Pretreatment was performed on potassium dihydrogen phosphate, potassium pyrophosphate, and magnesium polyphosphate respectively; 2) Add the pretreated potassium pyrophosphate, magnesium polyphosphate, activated sepiolite, and dolomite powder to a high-speed mixer and mix at 1200 r / min for 10 min. Then add the pretreated potassium dihydrogen phosphate and mix at 800 r / min for 5 min to obtain an inorganic component premix. 3) Add corn straw charcoal to the inorganic component premix obtained in step 2), stir at 500 r / min for 2 min for initial mixing, then increase to 800 r / min and continue stirring for 10 min to obtain inorganic mixed powder; 4) Mix dandelion extract and marigold extract evenly, add deionized water to dilute at a volume ratio of 1:2.5, and spray evenly into the inorganic mixed powder obtained in step 3) using a 0.4MPa high-pressure atomizing nozzle. During the spraying process, the mixer runs at 600r / min for 6min. After the spraying is completed, continue mixing at 600r / min for 5min to obtain the premixed material. 5) Add chelated micro-fertilizer to the premixed material obtained in step 4), mix at 300 r / min for 8 min, and add deionized water by spraying to adjust the moisture content of the material to 12-15%; 6) Feed the material with the moisture content adjusted in step 5) into an extrusion granulator for granulation. Dry the resulting granules with hot air at 40℃ until the final moisture content is ≤4%. After cooling and sieving, obtain biochar-based phosphorus slow-release fertilizer.

10. The application of the biochar-based phosphorus slow-release fertilizer according to any one of claims 1-8 in flue-cured tobacco cultivation.