Biochar-based slow-release fertilizer for improving acidified soil and preparation method of biochar-based slow-release fertilizer

Abstract

The invention relates to the field of agricultural fertilizer and soil improvement, in particular to a biochar-based slow release fertilizer for improving acidified soil and a preparation method thereof.The biochar-based slow release fertilizer is prepared from, by mass, 60 parts of a biochar system, 5-12 parts of nitrogen fertilizer, 10-18 parts of phosphate fertilizer, 5-12 parts of potash fertilizer, 5-10 parts of an acid soil modifier and 2-5 parts of a slow release film; graded release of nutrients is achieved through a multi-aperture biochar system, the release rhythm is dynamically adjusted according to soil acidity in combination with a three-layer pH response type slow-release film, the problems that existing fertilizer nutrient release is not matched with crop requirements, and the persistence of acidified soil improvement is poor are solved, the pH and buffer capacity of acidified soil can be improved, the nutrient utilization rate is increased, and the soil quality is improved. And most of the raw materials are agricultural and forestry wastes and industrial byproducts, so that the soil conditioner meets agricultural requirements, is suitable for acidified soil, and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of agricultural fertilizer and soil improvement, and particularly relates to a biochar-based slow-release fertilizer for improving acidified soil and a preparation method thereof. BACKGROUND

[0002] In recent years, soil acidification has become a prominent problem restricting the sustainable development of agriculture. Large areas of cultivated land are affected by acidification to varying degrees, especially in regions of red soil, laterite and acid paddy soil. The soil pH value is generally low, and in some plots, it has even dropped to the level of extreme acidity, which seriously threatens the quality of cultivated land and crop growth. There are two main reasons for soil acidification: one is the long-term excessive use of chemical nitrogen fertilizers such as ammonium sulfate and urea in agricultural production, which leads to the continuous production of hydrogen ions in the process of ammoniation and nitrification, thereby destroying the original acid-base balance; the other is external environmental factors such as acid rain deposition and industrial waste gas emission. In some areas, due to the concentration of acid gas emission and frequent rainfall, acid substances enter the soil with precipitation or dry deposition, accelerating the leaching of calcium, magnesium and other base ions, and further accelerating the acidification process.

[0003] The harm of soil acidification is multifaceted: not only can it significantly reduce the buffering capacity of the soil, making it less resistant to changes in acidity and alkalinity, but it can also activate harmful ions such as aluminum and manganese in the soil. High concentrations of exchangeable aluminum ions can damage the root structure of crops, leading to root deformities, lack of lateral roots and root hairs, and the formation of "aluminum toxicity" phenomenon, thereby inhibiting the absorption of water and nutrients by crops. At the same time, acidification also increases the positive charge of soil colloids, reducing their ability to adsorb calcium, magnesium, potassium and other base ions, causing nitrogen, phosphorus, potassium and other essential nutrients to be lost with precipitation or irrigation water, not only causing a decline in fertilizer efficiency, but also causing water eutrophication and other agricultural non-point source pollution problems, forming a vicious cycle of "acidification - lack of fertilizer - pollution".

[0004] Existing improvement methods can alleviate soil acidification to some extent, but still have obvious limitations. The application of limestone and other chemical modifiers can quickly increase the soil pH, but the solubility is low and the movement in the soil profile is slow, and the improvement effect on the subsoil acidification is limited. Long-term and large-scale application can easily lead to soil compaction and damage to the aggregate structure. Increasing the application of organic fertilizer can improve the soil buffering capacity and provide a habitat for microorganisms, but the required amount is large, the transportation and application cost is high, and the nutrient release rate is difficult to control, making it difficult to accurately match the fertilizer demand rhythm of crops. Traditional biochar modifiers have porous structure and strong adsorption capacity, but are designed with single pore size and lack of graded release mechanism. The nutrient release process is either too fast and prone to leaching or too slow and prone to nutrient deficiency. At the same time, the soil improvement function is single, and it is difficult to simultaneously achieve acidification relief and precise fertilizer supply.

[0005] In addition, although the conventional slow-release fertilizer can prolong the nutrient release period, it is usually coated with high-molecular materials such as polyvinyl alcohol and epoxy resin, which is not only high in cost and not conducive to large-scale application, but also lacks pH response characteristics. In acid soil, such coated materials swell slowly, resulting in insufficient early nutrient release and easy occurrence of nutrient deficiency symptoms in crops; when the soil acidity is improved, the coating is difficult to adjust the release rate according to the environmental changes, and there is still a risk of nutrient waste and loss, which cannot meet the phased demand for nutrient supply in the dynamic improvement process of acidified soil.

[0006] Therefore, in view of the above prior art, it is urgent to develop a biochar-based slow-release fertilizer for improving acidified soil and a preparation method thereof. SUMMARY

[0007] Therefore, the purpose of the present application is to provide a biochar-based slow-release fertilizer for improving acidified soil and a preparation method thereof, so as to solve the problems of poor persistence, large dosage, unstable nutrient release, single soil improvement ability, dependence on high-molecular coating, high cost and lack of pH response ability in the prior art.

[0008] Based on the above purpose, the present application provides a biochar-based slow-release fertilizer for improving acidified soil and a preparation method thereof.

[0009] A biochar-based slow-release fertilizer for improving acidified soil, the biochar-based slow-release fertilizer comprising the following raw materials by mass: a biochar system 60 parts, nitrogen fertilizer 5-12 parts, phosphorus fertilizer 10-18 parts, potassium fertilizer 5-12 parts, acid soil conditioner 5-10 parts and slow-release film 2-5 parts; The biochar system is a mixture of tea dregs carbon and coffee grounds carbon 20 parts, a mixture of tobacco straw carbon and bamboo chip carbon 25 parts, and a mixture of coconut shell carbon and fruit shell carbon 15 parts, the tea dregs carbon and coffee grounds carbon are mixed in a mass ratio of 2:1, the tobacco straw carbon and bamboo chip carbon are mixed in a mass ratio of 3:2, and the coconut shell carbon and fruit shell carbon are mixed in a mass ratio of 1:1; The acid soil conditioner is magnesium-modified biochar or silicon-enriched by-product, the acid soil conditioner is magnesium-modified biochar or silicon-enriched by-product, wherein the magnesium element loading is ≥1.5%, and the silicon dioxide content is ≥40%. The magnesium ions can neutralize soil acidity and increase the cation exchange capacity; and the silicon element can improve the cell wall structure of crops and enhance the stress resistance. This component cooperates with alkaline biochar to improve the soil buffer capacity and significantly reduce the harm of acidification; The slow-release film is a chitosan and sodium alginate compound, the mass ratio of chitosan to sodium alginate in the chitosan and sodium alginate compound is 3:2, and the chitosan and sodium alginate compound comprises three layers of an inner layer (50-100 nm), a middle layer (100-200 nm) and an outer layer (200-300 nm). The compound film has good film-forming property and pH response characteristics, can swell and release rapidly in an acidic environment, and can release slowly in a neutral condition, so that nutrients are supplied in stages. In addition, the film layer can also improve the mechanical strength of the granules, prevent pulverization and early dissolution.

[0010] The specific surface area of the biochar system is 300-500 m² / g, and the total porosity is ≥60%.

[0011] The micropore accounts for 15%-20%, the mesopore accounts for 70%-75%, and the macropore accounts for 5%-10% in the biochar system, and such a porous structure is helpful for adsorbing and loading nutrients, and realizing the graded release of quick-acting, medium-acting and long-acting; The pore diameter of the micropore is <2 nm, the pore diameter of the mesopore is 2-50 nm, and the pore diameter of the macropore is >50 nm.

[0012] Preferably, the preparation process of the biochar system is as follows: Tea dregs carbon and coffee grounds carbon are mixed at a mass ratio of 2:1, pyrolysis is carried out at 450-500°C for 2-5h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, and then the pyrolyzed product is crushed to pass through an 80-100 mesh sieve to obtain a tea dregs carbon and coffee grounds carbon mixture, wherein the pore diameter of the tea dregs carbon and coffee grounds carbon mixture is 2-15 nm, and the pH is 8-9, and the tea dregs carbon and coffee grounds carbon mixture is mainly used for quick-acting nutrient release. The tea dregs carbon is rich in polyphenol residues, which can promote the growth of beneficial bacteria and inhibit harmful bacteria; the coffee grounds carbon contains organic nitrogen sources, which can provide initial fertilizer effect. The part of the carbon has a compact structure and a large specific surface area, and can quickly release the adsorbed nitrogen, phosphorus and potassium nutrients to meet the early fertilizer demand of crops; Tobacco straw carbon and bamboo chip carbon are mixed at a mass ratio of 3:2, pyrolysis is carried out at 500-550°C for 2-5h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, and then the pyrolyzed product is crushed to pass through an 80-100 mesh sieve to obtain a tobacco straw carbon and bamboo chip carbon mixture, wherein the pore diameter of the tobacco straw carbon and bamboo chip carbon mixture is 16-40 nm, and the pH is 9-10.5, and the tobacco straw carbon and bamboo chip carbon mixture can play a core role in medium-term slow release and soil improvement. The tobacco straw carbon is rich in potassium elements, which can supplement the quick-acting potassium source; the bamboo chip carbon has a stable structure, which is helpful for improving the strength of the fertilizer granules. The two together form a carbon-based network mainly composed of mesopores, which can continuously release nutrients and improve the soil pH and the soil buffering performance; The coconut shell charcoal and the nutshell charcoal are mixed in a mass ratio of 1:1, pyrolyzed at 550-600℃ for 2-5h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crushed through an 80-100 mesh sieve after pyrolysis, to obtain a coconut shell charcoal and nutshell charcoal mixture, wherein the coconut shell charcoal and nutshell charcoal mixture has a pore size of 41-50nm and a pH of 9-10.5, and belongs to a macroporous structure, and is mainly used for long-acting nutrient maintenance and deep soil improvement. The coconut shell charcoal has high mechanical strength and stable structure, and can maintain the form in the soil for a long time; the nutshell charcoal has excellent cation exchange performance, and can adsorb and slowly release nutrients such as potassium, calcium and magnesium, and prevent leaching. The component forms a persistent soil improvement layer, so that the fertilizer efficiency is sustained and the soil structure is stable; Preferably, the heating rate of the pyrolysis process is 5-10℃ / min; The tea dreg charcoal and coffee dreg charcoal mixture, the tobacco straw charcoal and bamboo chip charcoal mixture, and the coconut shell charcoal and nutshell charcoal mixture are mixed in a mass ratio of 20:25:15 to obtain a biochar system.

[0013] Preferably, the tea dreg charcoal and coffee dreg charcoal mixture has a pore size of 2-15nm and a pH of 8-9; the tobacco straw charcoal and bamboo chip charcoal mixture has a pore size of 16-40nm and a pH of 9-10.5; and the coconut shell charcoal and nutshell charcoal mixture has a pore size of 41-50nm and a pH of 9-10.5.

[0014] Preferably, the slow-release film comprises an inner layer, a middle layer and an outer layer. Preferably, the thickness of the inner layer is 50-100nm, the thickness of the middle layer is 100-200nm, and the thickness of the outer layer is 200-300nm.

[0015] Preferably, the magnesium element loading of the magnesium modified biochar is ≥1.5%, and the silicon dioxide content of the silicon enrichment byproduct is ≥40%.

[0016] Preferably, the nitrogen fertilizer is one or more of urea and ammonium bicarbonate, and the phosphorus fertilizer is one or more of diammonium phosphate and calcium superphosphate, which are important sources of nutrients for root development and reproductive growth. The alkaline functional groups on the surface of the biochar can form weak bonds with phosphate ions, reducing the immobilization of phosphorus in acidic environments and extending the fertilizer cycle. This component ensures that crops can obtain stable phosphorus source supply at different growth stages, and the nitrogen fertilizer is urea or ammonium bicarbonate, which provides a source of readily available nitrogen to promote leaf growth and root development of crops. The nitrogen fertilizer is loaded in the pores of the biochar by vacuum temperature-controlled spraying, which can significantly reduce the loss of nitrogen volatilization, improve the utilization rate of nitrogen fertilizer, realize the dual functions of "rapid-acting nitrogen supply + slow-release maintenance", and the potassium fertilizer is one or more of potassium sulfate and potassium chloride, and the potassium fertilizer is selected as potassium sulfate or potassium chloride, which provides readily available potassium to enhance the stress resistance and quality of crops. Part of the potassium ions is fixed in the pores of the carbon body to form a slow-release potassium source, which can continuously supply the rhizosphere of crops. This design effectively prevents the loss of potassium, improves the utilization efficiency of crops.

[0017] Preferably, the preparation method of the biochar-based slow-release fertilizer for improving acidified soil is as follows: Step S1. Mix nitrogen fertilizer, phosphorus fertilizer and potassium fertilizer to form a nutrient solution with a concentration of 20%-30%, and load the nutrient solution into the pores of the biochar system by vacuum temperature-controlled spraying to obtain a biochar-nutrient composite; Step S2. Add an acid soil improver to the biochar-nutrient composite, mix in a double-helix mixer at a speed of 300-400 r / min for 15-20 min to obtain a mixed base material; Step S3. Dissolve chitosan and sodium alginate in a 1% acetic acid solution in a mass ratio of 3:2 to form a film material solution with a concentration of 5%-8%; spray the solution on the surface of the base material in three times, control the inlet air temperature at 80-90°C and the outlet air temperature at ≤40°C, and form a three-layer slow-release film with a thickness of 50-300 nm; Step S4. Dry the coated particles at 35-40°C until the water content is ≤5%, and screen the particles with a size of 2-4 mm to obtain the biochar-based slow-release fertilizer for improving acidified soil.

[0018] Preferably, the experimental conditions of the vacuum temperature-controlled spraying in step S1 are as follows: vacuum degree is 0.08-0.1 MPa, temperature is 50-60°C, and pressure is 0.2-0.3 MPa.

[0019] Preferably, the biochar-based slow-release fertilizer for improving acidified soil is used in acidified soil with a pH value of less than 5.5, and the application amount is 450-750 kg / hm², and the application method is base application or base application + 1 time of topdressing.

[0020] The beneficial effects of the present application are as follows: The application provides a biochar-based slow-release fertilizer for improving acidified soil, which realizes accurate matching of nutrient release and crop nutrient requirement regulation through synergistic effect of porous biochar and three-layer pH response film, can quickly release nutrients to relieve crop nutrient deficiency when soil acidity is high, and is converted to slow release to reduce loss after soil acidity is improved, so as to significantly improve nitrogen utilization rate, and meanwhile, biochar and improver in the product can effectively improve soil pH value and buffer capacity, reduce aluminum ion activity and relieve aluminum toxicity. In application in acid soil, the fertilizer can promote yield increase and quality improvement of crops such as rice, flue-cured tobacco and vegetables, such as optimizing flue-cured tobacco components and reducing nitrate content in vegetables. In addition, raw materials are derived from agricultural and forestry waste and industrial by-products, the production process is environmentally friendly, and the fertilizer has economic and ecological benefits.

[0021] The application provides a biochar-based slow-release fertilizer for improving acidified soil and a preparation method thereof, which realizes nutrient graded release and effectively improves acidified soil through synergistic effect of porous and multi-pH biochar and pH response type slow-release film, can significantly improve soil pH and buffer capacity, improve nitrogen, phosphorus and potassium utilization rate, prolong fertilizer effect period, and has wide application prospect in fields such as acid farmland, orchard, tea garden and tobacco planting. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below with reference to specific examples.

[0023] Part of the properties of part of the raw materials used in the examples of the application are as follows: The pore size of the mixture of tea dreg charcoal and coffee dreg charcoal is 2-15 nm, the pH is 8-9, and the mixture is food grade; The pore size of the mixture of tobacco straw charcoal and bamboo charcoal is 16-40 nm, the pH is 9-10.5, and the mixture is food grade; The pore size of the mixture of coconut shell charcoal and fruit shell charcoal is 41-50 nm, the pH is 9-10.5, and the mixture is food grade; The magnesium element loading of the magnesium modified biochar is greater than or equal to 1.5%, and the biochar is industrial grade; The silicon dioxide content of the silicon-rich by-product is greater than or equal to 40%, and the by-product is industrial grade; Example 1: A preparation method of a biochar-based slow-release fertilizer for improving acidified soil, comprising the following steps: S1. Mix tea dregs charcoal and coffee dregs charcoal at a mass ratio of 2:1, pyrolyze at 450℃ for 2h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crush through an 80-100 mesh sieve after pyrolysis, to obtain a tea dregs charcoal and coffee dregs charcoal mixture, mix tobacco stem charcoal and bamboo chip charcoal at a mass ratio of 3:2, pyrolyze at 500℃ for 2h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crush through an 80-100 mesh sieve after pyrolysis, to obtain a tobacco stem charcoal and bamboo chip charcoal mixture, mix coconut shell charcoal and fruit shell charcoal at a mass ratio of 1:1, pyrolyze at 550℃ for 2h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crush through an 80-100 mesh sieve after pyrolysis, to obtain a coconut shell charcoal and fruit shell charcoal mixture, the heating rate during the pyrolysis process is 5℃ / min, mix the tea dregs charcoal and coffee dregs charcoal mixture, the tobacco stem charcoal and bamboo chip charcoal mixture, and the coconut shell charcoal and fruit shell charcoal mixture at a mass ratio of 20:25:15, to obtain a biochar system; S2. Mix nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer to form a 20% nutrient solution, load the nutrient solution into the pores of the biochar system by vacuum temperature-controlled spraying, to obtain a biochar-nutrient compound; S3. Add an acid soil conditioner to the biochar-nutrient compound, mix in a double helix mixer at a rotation speed of 300r / min for 15min, to obtain a mixed base material; S4. Dissolve chitosan and sodium alginate in a 1% acetic acid solution at a mass ratio of 3:2, to form a 5% film material solution; spray the solution onto the surface of the base material in three times, control the air inlet temperature at 80℃ and the air outlet temperature at ≤40℃, to form a three-layer slow-release film with a thickness of 50nm; S5. Dry the coated particles at 35℃ until the water content is ≤5%, screen the particles with a size of 2-4mm, to obtain the biochar-based slow-release fertilizer for improving acidified soil.

[0024] Example 2: A preparation method of a biochar-based slow-release fertilizer for improving acidified soil, comprising the following steps: S1. Mix tea dregs charcoal and coffee dregs charcoal at a mass ratio of 2:1, pyrolyze at 475℃ for 3h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crush through an 80-100 mesh sieve after pyrolysis, to obtain a tea dregs charcoal and coffee dregs charcoal mixture, mix tobacco stem charcoal and bamboo chip charcoal at a mass ratio of 3:2, pyrolyze at 525℃ for 3h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crush through an 80-100 mesh sieve after pyrolysis, to obtain a tobacco stem charcoal and bamboo chip charcoal mixture, mix coconut shell charcoal and fruit shell charcoal at a mass ratio of 1:1, pyrolyze at 575℃ for 3h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crush through an 80-100 mesh sieve after pyrolysis, to obtain a coconut shell charcoal and fruit shell charcoal mixture, the heating rate during the pyrolysis process is 7℃ / min, mix the tea dregs charcoal and coffee dregs charcoal mixture, the tobacco stem charcoal and bamboo chip charcoal mixture, and the coconut shell charcoal and fruit shell charcoal mixture at a mass ratio of 20:25:15, to obtain a biochar system; S2. The nitrogen fertilizer, phosphorus fertilizer and potassium fertilizer are mixed into a nutrient solution with a concentration of 23%, and the nutrient solution is loaded into the pores of the biochar system by vacuum temperature control spraying to obtain a biochar-nutrient compound; S3. An acid soil conditioner is added to the biochar-nutrient compound, and the mixture is mixed in a double helix mixer at a speed of 330 r / min for 17 min to obtain a mixed base material; S4. Chitosan and sodium alginate are dissolved in a 1% acetic acid solution at a mass ratio of 3:2 to prepare a 6% membrane material solution; the solution is sprayed on the surface of the base material in three times, and the air inlet temperature is controlled at 83°C and the air outlet temperature is ≤40°C to form a three-layer slow-release film with a thickness of 140 nm; S5. The coated particles are dried at 37°C until the water content is ≤5%, and the 2-4 mm particles are screened to obtain the biochar-based slow-release fertilizer for improving acidified soil.

[0025] Example 3: A preparation method of a biochar-based slow-release fertilizer for improving acidified soil, comprising the following steps: S1. Tea dregs charcoal and coffee grounds charcoal are mixed at a mass ratio of 2:1, pyrolyzed at 490°C for 4h under an anaerobic atmosphere with an oxygen volume fraction of ≤5%, and then crushed through an 80-100 mesh sieve to obtain a tea dregs charcoal and coffee grounds charcoal mixture; tobacco straw charcoal and bamboo chip charcoal are mixed at a mass ratio of 3:2, pyrolyzed at 540°C for 4h under an anaerobic atmosphere with an oxygen volume fraction of ≤5%, and then crushed through an 80-100 mesh sieve to obtain a tobacco straw charcoal and bamboo chip charcoal mixture; coconut shell charcoal and fruit shell charcoal are mixed at a mass ratio of 1:1, pyrolyzed at 590°C for 4h under an anaerobic atmosphere with an oxygen volume fraction of ≤5%, and then crushed through an 80-100 mesh sieve to obtain a coconut shell charcoal and fruit shell charcoal mixture; the pyrolysis process has a heating rate of 9°C / min; and the tea dregs charcoal and coffee grounds charcoal mixture, the tobacco straw charcoal and bamboo chip charcoal mixture, and the coconut shell charcoal and fruit shell charcoal mixture are mixed at a mass ratio of 20:25:15 to obtain a biochar system; S2. The nitrogen fertilizer, phosphorus fertilizer and potassium fertilizer are mixed into a nutrient solution with a concentration of 26%, and the nutrient solution is loaded into the pores of the biochar system by vacuum temperature control spraying to obtain a biochar-nutrient compound; S3. An acid soil conditioner is added to the biochar-nutrient compound, and the mixture is mixed in a double helix mixer at a speed of 360 r / min for 19 min to obtain a mixed base material; S4. Chitosan and sodium alginate are dissolved in a 1% acetic acid solution at a mass ratio of 3:2 to prepare a 7% membrane material solution; the solution is sprayed on the surface of the base material in three times, and the air inlet temperature is controlled at 86°C and the air outlet temperature is ≤40°C to form a three-layer slow-release film with a thickness of 230 nm; S5. The coated particles are dried at 39°C until the water content is ≤5%, and the 2-4 mm particles are screened to obtain the biochar-based slow-release fertilizer for improving acidified soil.

[0026] Example 4: A preparation method of a biochar-based slow-release fertilizer for improving acidified soil, comprising the following steps: S1. Mix tea dregs carbon and coffee grounds carbon at a mass ratio of 2:1, pyrolyze at 500℃ for 5h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crush to pass through an 80-100 mesh sieve after pyrolysis, to obtain a tea dregs carbon and coffee grounds carbon mixture, mix tobacco straw carbon and bamboo chip carbon at a mass ratio of 3:2, pyrolyze at 550℃ for 5h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crush to pass through an 80-100 mesh sieve after pyrolysis, to obtain a tobacco straw carbon and bamboo chip carbon mixture, mix coconut shell carbon and fruit shell carbon at a mass ratio of 1:1, pyrolyze at 600℃ for 5h under an anaerobic atmosphere with an oxygen volume fraction ≤5%, crush to pass through an 80-100 mesh sieve after pyrolysis, to obtain a coconut shell carbon and fruit shell carbon mixture, the heating rate of the pyrolysis process is 10℃ / min, mix the tea dregs carbon and coffee grounds carbon mixture, the tobacco straw carbon and bamboo chip carbon mixture, and the coconut shell carbon and fruit shell carbon mixture at a mass ratio of 20:25:15, to obtain a biochar system; S2. Prepare a 30% nutrient solution by mixing nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer, load the nutrient solution in the pores of the biochar system by vacuum temperature-controlled spraying, to obtain a biochar-nutrient composite; S3. Add an acid soil improver to the biochar-nutrient composite, mix in a double helix mixer at a rotation speed of 400r / min for 20min, to obtain a mixed base material; S4. Dissolve chitosan and sodium alginate in a 1% acetic acid solution at a mass ratio of 3:2, to prepare an 8% film material solution; spray the solution on the surface of the base material in three times, control the air inlet temperature at 90℃ and the air outlet temperature at ≤40℃, to form a three-layer slow-release film with a thickness of 300nm; S5. Dry the coated particles at 40℃ until the water content is ≤5%, screen the particles with a size of 2-4mm, to obtain the biochar-based slow-release fertilizer for improving acidified soil.

[0027] Comparative Example 1: This comparative example is compared with Example 1 only by replacing the “porous biochar system of the tea dregs carbon and coffee grounds carbon mixture (20 parts), the tobacco straw carbon and bamboo chip carbon mixture (25 parts), and the coconut shell carbon and fruit shell carbon mixture (15 parts)” with “single-pore ordinary wood chip carbon 60 parts (pore size 10-20nm, pH 7.5-8.0, pyrolyzed at 500℃ for 3h under an air atmosphere, crushed to pass through an 80-100 mesh sieve)”, and the rest of the steps and parameters are the same. This comparative example will not be repeated here. Finally, a biochar-based slow-release fertilizer for improving acidified soil is obtained.

[0028] Comparative Example 2: The comparative example is compared with example 1 only by replacing "three-layer slow-release film of chitosan and sodium alginate 3:2 mass ratio (inner layer 50-100 nm, middle layer 100-200 nm, outer layer 200-300 nm)" with "single-layer 5% polyvinyl alcohol (PVA) film (thickness 250 nm)", using room temperature immersion coating process (non-three times spraying), and the rest of the steps and parameters are the same, the comparative example will not be repeated, and finally the improved acidified soil biochar-based slow-release fertilizer is obtained.

[0029] Comparative example 3: The comparative example is compared with example 1 only by replacing "magnesium modified biochar with magnesium element loading ≥1.5%" with "ordinary quicklime 5 parts (CaO content ≥90%, industrial grade)", and the rest of the steps and parameters are the same, the comparative example will not be repeated, and finally the improved acidified soil biochar-based slow-release fertilizer is obtained.

[0030] Comparative example 4: The comparative example is compared with example 1 only by replacing "vacuum temperature control spraying (vacuum degree 0.08-0.1 MPa, temperature 50-60℃, pressure 0.2-0.3 MPa)" with "room temperature conventional stirring mixing (stirring 20% nutrient solution and biochar system at 200 r / min for 30 min at 25℃)", and the rest of the steps and parameters are the same, the comparative example will not be repeated, and finally the improved acidified soil biochar-based slow-release fertilizer is obtained.

[0031] Comparative example 5: The comparative example is compared with example 1 only by replacing "vacuum temperature control spraying (vacuum degree 0.08-0.1 MPa, temperature 50-60℃, pressure 0.2-0.3 MPa)" with "room temperature conventional stirring mixing (stirring 20% nutrient solution and biochar system at 200 r / min for 30 min at 25℃)", and the rest of the steps and parameters are the same, the comparative example will not be repeated, and finally the improved acidified soil biochar-based slow-release fertilizer is obtained.

[0032] Comparative example 6: The comparative example is compared with example 1 only by replacing "the mass ratio of chitosan to sodium alginate in the slow-release film raw material is 3:2" with "the mass ratio of chitosan to sodium alginate in the slow-release film raw material is 1:1", and the rest of the steps and parameters are the same, the comparative example will not be repeated, and finally the improved acidified soil biochar-based slow-release fertilizer is obtained.

[0033] Performance test: Test basis: Test soil: acidic red soil (initial pH 4.5, exchangeable Al³⁺ concentration 1.45 cmol / kg, organic matter content 12.8 g / kg, cation exchange capacity (CEC) 8.2 cmol / kg).

[0034] Test crop: rice (variety "Xiangzaoxian No. 45") and flue-cured tobacco (variety "K326"), both using pot experiment (pot volume 15 L, each pot containing 10 kg of soil).

[0035] Fertilization method: 450 kg / hm2 converted to pot application (0.675 g per pot), 1 d before transplanting base application and mixed with soil.

[0036] Test period: 120 d of whole growth period of rice, 60 d of vigorous growth period of flue-cured tobacco; each treatment is set with 3 repetitions, and the results are averaged, and the related test methods and instruments are shown in Tables 1-2: Table 1 Test items and methods Table 2 Test items and test instruments The performance test results are shown in Tables 3-4: Table 3 Performance test example summary table Table 4 Performance test comparative example summary table Data analysis: As can be seen from the test results in the table, the improved acidified soil biochar-based slow-release fertilizer prepared by the application is excellent in soil improvement effect, nutrient utilization efficiency, crop growth quality and fertilizer physical properties, and with the increase of pyrolysis temperature, nutrient solution concentration and optimization of slow-release film thickness, the performances are all optimal.

[0037] Comparative Example 1 cannot realize the release of nutrients with “quick-acting, medium-acting and long-acting” due to the lack of porous diameter gradient cooperation, the nutrient release period is only 50% of Example 1, the nitrogen utilization rate is 16.2 percentage points lower than that of Example 1, and the rice yield is reduced by 19.4%; at the same time, the pH of ordinary wood chip carbon is low, the soil pH is only increased to 4.9, the exchangeable Al³⁺ concentration is 1.88 times of Example 1, and the aluminum toxicity relief effect is significantly insufficient; Comparative Example 2 uses a conventional polymer film without pH response and without a three-layer structure, and the film layer swells slowly in acid soil, resulting in insufficient nutrient supply in the early stage (the root dry weight of flue-cured tobacco is 19.6% lower than that of Example 1); in the later stage, it cannot be accurately controlled, the nutrient leaching is serious, the nitrogen utilization rate is 12.9 percentage points lower, and the mechanical properties of PVA film are poor, the particle compressive strength is 24% lower than that of Example 1, highlighting the necessity of a three-layer pH-responsive composite film; In Comparative Example 3, although ordinary quicklime can short-term increase the soil pH, it lacks the effect of magnesium element on the improvement of cation exchange capacity and the effect of silicon element on the relief of aluminum toxicity, the soil buffer capacity is 20% lower than that of Example 1, and the exchangeable Al³⁺ concentration is 38.5% higher; and quicklime can easily cause soil compaction, and the root dry weight of flue-cured tobacco is reduced by 12.7%, which proves that the synergistic soil improvement effect of functional acid soil improver and biochar cannot be replaced. In Comparative Example 4, since the vacuum temperature control spraying process is not used, the nutrients cannot be fully embedded in the pores of the biochar, and are easy to be lost with irrigation, the nitrogen utilization rate is 8.4 percentage points lower than that of Example 1, and the nutrient release period is shortened by 22.2%; but because the other core design is retained, the performance is better than that of Comparative Examples 1-3, which shows that the preparation process plays a role in improving the efficiency of nutrient loading; In Comparative Example 5, the pore structure of biochar collapses under air atmosphere, the degree of aromatization decreases, the specific surface area decreases significantly, the nutrient adsorption capacity decreases, the nitrogen utilization rate is 14 percentage points lower, and the nutrient release period is shortened by 38.9%; and the air pyrolysis produces acidic functional groups, the pH of biochar decreases, and the soil improvement effect is weakened (the soil pH is 0.4 lower than that of Example 1), which proves that anaerobic pyrolysis is a key process to ensure the performance of biochar; In Comparative Example 6, the ratio of chitosan to sodium alginate deviates from the optimal value (3:2), which leads to a decrease in the pH response sensitivity of the membrane layer, a swelling rate that is 30% slower than that of Example 1 in an acidic environment, a nutrient release period that is shortened by 16.7%, and a nitrogen utilization rate that is 6.3 percentage points lower, which shows that the ratio of 3:2 of the membrane material is an important parameter for realizing targeted release of nutrients; Those skilled in the art will understand that the discussion of any of the above examples is merely exemplary and is not intended to suggest that the scope of the application is limited to these examples; under the idea of the application, the technical features of the above examples or different examples can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the application as described above. In order to be brief, they are not provided in details.

[0038] The present application is intended to cover all such alternatives, modifications and variations as fall within the broad scope of the appended claims. Accordingly, any and all such modifications, variations or equivalents that fall within the spirit and scope of the application are intended to be included within the scope of the application.

Claims

1. A biochar-based slow-release fertilizer for improving acidified soil, characterized in that, The biochar-based slow-release fertilizer comprises the following raw materials in parts by weight: 60 parts biochar system, 5-12 parts nitrogen fertilizer, 10-18 parts phosphate fertilizer, 5-12 parts potassium fertilizer, 5-10 parts acid soil conditioner, and 2-5 parts slow-release membrane. The biochar system is composed of 20 parts of a mixture of tea residue charcoal and coffee residue charcoal, 25 parts of a mixture of tobacco straw charcoal and bamboo shavings charcoal, 15 parts of a mixture of coconut shell charcoal and fruit shell charcoal, tea residue charcoal and coffee residue charcoal are mixed at a mass ratio of 2:1, tobacco straw charcoal and bamboo shavings charcoal are mixed at a mass ratio of 3:2, and coconut shell charcoal and fruit shell charcoal are mixed at a mass ratio of 1:

1. The acid soil conditioner is magnesium-modified biochar or silicon enrichment byproduct. The sustained-release membrane is a chitosan and sodium alginate complex, wherein the mass ratio of chitosan to sodium alginate complex in the chitosan and sodium alginate complex is 3:

2.

2. The biochar-based slow-release fertilizer for improving acidified soil according to claim 1, characterized in that, The biochar system has a specific surface area of ​​300-500 m² / g and a total porosity of ≥60%.

3. The biochar-based slow-release fertilizer for improving acidified soil according to claim 1, characterized in that, The biochar system comprises 15%-20% micropores, 70%-75% mesopores, and 5%-10% macropores. The micropores have a diameter of <2nm, the mesopores have a diameter of 2-50nm, and the macropores have a diameter of >50nm.

4. The biochar-based slow-release fertilizer for improving acidified soil according to claim 1, characterized in that, The preparation process of the biochar system is as follows: Tea residue charcoal and coffee residue charcoal are mixed in a mass ratio of 2:1 and pyrolyzed at 450-500℃ for 2-5 hours in an oxygen-free atmosphere with an oxygen volume fraction of ≤5%. After pyrolysis, the mixture is pulverized and passed through an 80-100 mesh sieve to obtain a mixture of tea residue charcoal and coffee residue charcoal. Tobacco straw charcoal and bamboo charcoal were mixed at a mass ratio of 3:2 and pyrolyzed at 500-550℃ for 2-5 hours in an oxygen-free atmosphere with an oxygen volume fraction of ≤5%. After pyrolysis, the mixture was pulverized and passed through an 80-100 mesh sieve to obtain a mixture of tobacco straw charcoal and bamboo charcoal. Coconut shell charcoal and fruit shell charcoal are mixed in a mass ratio of 1:1 and pyrolyzed at 550-600℃ for 2-5 hours in an oxygen-free atmosphere with an oxygen volume fraction of ≤5%. After pyrolysis, the mixture is pulverized and passed through an 80-100 mesh sieve to obtain a mixture of coconut shell charcoal and fruit shell charcoal. The heating rate of the pyrolysis process is 5-10℃ / min; A biochar system was obtained by mixing tea residue charcoal with coffee residue charcoal, tobacco straw charcoal with bamboo shavings charcoal, and coconut shell charcoal with fruit shell charcoal in a mass ratio of 20:25:

15.

5. The biochar-based slow-release fertilizer for improving acidified soil according to claim 2, characterized in that, The mixture of tea residue charcoal and coffee residue charcoal has a pore size of 2-15 nm and a pH of 8-9; the mixture of tobacco straw charcoal and bamboo shavings charcoal has a pore size of 16-40 nm and a pH of 9-10.5; and the mixture of coconut shell charcoal and fruit shell charcoal has a pore size of 41-50 nm and a pH of 9-10.

5.

6. The biochar-based slow-release fertilizer for improving acidified soil according to claim 1, characterized in that, The sustained-release membrane comprises an inner layer, a middle layer, and an outer layer; The thickness of the inner layer is 50-100nm, the thickness of the middle layer is 100-200nm, and the thickness of the outer layer is 200-300nm.

7. The biochar-based slow-release fertilizer for improving acidified soil according to claim 1, characterized in that, The magnesium-modified biochar has a magnesium loading of ≥1.5%, and the silicon dioxide content of the silicon enrichment byproduct is ≥40%.

8. The biochar-based slow-release fertilizer for improving acidified soil according to claim 1, characterized in that, The nitrogen fertilizer is one or more of urea and ammonium bicarbonate, the phosphate fertilizer is one or more of diammonium phosphate and superphosphate, and the potassium fertilizer is one or more of potassium sulfate and potassium chloride.

9. The method for preparing biochar-based slow-release fertilizer for improving acidified soil according to any one of claims 1-8, characterized in that, Includes the following steps: Step S1. Prepare a 20%-30% nutrient solution by mixing nitrogen fertilizer, phosphorus fertilizer, and potassium fertilizer. Use vacuum temperature-controlled spraying to load the nutrient solution into the pores of the biochar system to obtain a biochar-nutrient complex. Step S2. Add acid soil conditioner to biochar-nutrient complex and mix in a twin-helix mixer at 300-400 r / min for 15-20 min to obtain mixed substrate; Step S3. Dissolve chitosan and sodium alginate in 1% acetic acid solution at a mass ratio of 3:2 to prepare a 5%-8% membrane material solution; spray it onto the substrate surface in three stages, controlling the inlet air temperature to 80-90℃ and the outlet air temperature to ≤40℃, to form a three-layer slow-release membrane with a thickness of 50-300nm. Step S4. Dry the coated granules at 35-40℃ until the moisture content is ≤5%, and screen the 2-4mm granules to obtain the biochar-based slow-release fertilizer for improving acidified soil. The experimental conditions for vacuum temperature-controlled spraying in step S1 are: vacuum degree of 0.08-0.1MPa, temperature of 50-60℃, and pressure of 0.2-0.3MPa.

10. The method for preparing biochar-based slow-release fertilizer for improving acidified soil according to claim 9, characterized in that, The biochar-based slow-release fertilizer for improving acidified soil is used for acidified soil with pH < 5.

5. The application rate is 450-750 kg / hm², and the application method is basal application or basal application + 1 top dressing.

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