Soil improvement method based on synergism of charcoal-based slow release fertilizer and green manure

Abstract

The invention discloses a soil improvement method based on synergism of a charcoal-based slow release fertilizer and green manure, and belongs to the technical field of agriculture and environment. The method comprises the following steps: granulating biochar, kaolin, zeolite and a phosphate fertilizer according to a specific ratio to prepare a slow release fertilizer, applying the slow release fertilizer to degraded soil in winter, then sowing leguminous green manure vicia villosa, and turning, pressing and returning to the field when the biomass of the green manure reaches the maximum. According to the method, a synergistic system of carrier slow release, green manure activation and microorganism driving is constructed, the exchange capacity of soil organic matter, total nitrogen, available phosphorus and cation is synchronously improved, the diversity of soil microorganisms and the nutrient utilization efficiency are remarkably improved, and rapid and systematic remediation of degraded soil is achieved. The method is simple and convenient in process, low in cost and suitable for soil fertility cultivation of barren farmlands and orchards.

Description

Technical Field

[0001] This invention belongs to the field of agricultural and environmental technology, specifically relating to a soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure. Background Technology

[0002] Soil degradation is a serious challenge facing global agriculture and the environment, typically characterized by depletion of organic matter, nutrient imbalance, soil compaction, and decreased microbial activity. Improving and restoring the fertility of such degraded soils is crucial for achieving sustainable agricultural development.

[0003] In degraded soil ecosystems, the natural restoration of soil organic matter is extremely slow and complex, primarily constrained by the efficiency of chemical transformation of organic matter and the difficulty of rebuilding microbial community function, often requiring decades to achieve effective restoration. Currently, commonly used soil improvement pathways mainly fall into two categories: one relies on rapid nutrient replenishment through chemical fertilizers, and the other uses single organic improvement measures. However, both conventional pathways have inherent drawbacks. While chemical fertilizers are fast-acting, they are easily leached and have low utilization rates; long-term application can also lead to soil acidification, damaging aggregate structure and microbial activity. On the other hand, the application of green manure as a single organic improvement measure, although providing organic carbon and nitrogen simultaneously, has a rapid decomposition rate and high mineralization degree, making it difficult to effectively convert into stable soil organic matter. Its humification process is also often limited by insufficient soil background nutrients, low microbial activity, and adverse external environmental conditions, resulting in a relatively long improvement cycle.

[0004] To further enhance the improvement effect, various compound soil conditioners or specialized fertilizers have emerged in existing technologies. However, these solutions still have significant limitations. In pursuit of comprehensive functionality, they combine multiple minerals, organic matter, and biochemical stimulants, but their complex composition and lack of targeted synergistic design between functional units often result in scattered improvement targets, insufficient effectiveness in addressing the core obstacles to degraded soils, and high costs. For example, patent CN115304420A discloses a technical solution that adds sand, clay, and humic acid to adapt to different soil textures, but this solution has a single function in heavy metal remediation and lacks comprehensive regulation of the long-term ecological health of the soil system. Patent CN102206494A focuses on heavy metal passivation, using a compound of organic materials and potassium polyacrylate to reduce the heavy metal content in vegetables, but its function is specific, with limited synergistic effects on the continuous improvement of soil organic matter and microbial diversity. In addition, some solutions focus on the in-depth development of specific functional materials. Although they can improve a single property, their preparation process is complex and costly, making them difficult to apply to large-scale, low-cost farmland improvement scenarios.

[0005] On the other hand, improved methods for the combined application of organic and mineral materials have gradually developed, but most remain at the level of simple mixing or parallel use, failing to construct a "physical-chemical-biological" synergistic system with a clear time sequence and coupled links. In particular, there is a lack of an integrated solution that can first rapidly optimize the soil microenvironment through specific carrier materials, then precisely introduce high-efficiency green manure varieties and control their return to the field, thereby systematically stimulating the soil's inherent ecological functions. Patent CN110066662A, "A Functional Soil Conditioner and Its Preparation Method," specifically discloses mixing more than ten components, including biochar, kaolin, zeolite, phosphate fertilizer, humic acid, amino acids, and seaweed extract, in a certain proportion, followed by pulverization and granulation to obtain a composite conditioner. This solution attempts to simultaneously achieve multiple objectives such as soil improvement, fertilization, water retention, and stimulation through the physical mixing of various functional materials. However, the combination of multiple components in this scheme focuses more on the aggregation of various individual improvement effects. When addressing the systemic problem of "synergistic degradation of soil physical structure, nutrient cycling, and microbial activity," there is still room for further exploration regarding the synergistic mechanisms between its different components and the precise regulation of specific obstacle factors. In addition, the scheme does not reflect the temporal coordination relationship between its application as an independent product and the specific growth cycle of green manure. Summary of the Invention

[0006] To address the limitations of existing soil improvement technologies, such as the easy loss of chemical fertilizers, the rapid decomposition and difficulty in conversion of single green manure, and the lack of synergy in the function of compound conditioners, this invention provides a soil improvement method based on the synergy of biochar-based slow-release fertilizer and green manure. This method constructs a synergistic system of "carrier slow release - green manure activation - microbial drive," which rapidly improves the organic matter content, the availability of key nutrients, the cation exchange capacity, and the function of microbial communities in degraded soils.

[0007] To achieve this objective, the following solution is provided: This invention provides a soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure, comprising the following steps: S1. Preparation of biochar-based slow-release fertilizer: Kaolin, zeolite, biochar and phosphate fertilizer are mixed, crushed and granulated, and dried to obtain biochar-based slow-release fertilizer; S2. During November to December each year, apply the biochar-based slow-release fertilizer prepared in step S1 to the target soil and till it to ensure that the fertilizer is evenly distributed in the 0-20 cm topsoil layer. S3. Evenly disperse hairy vetch seeds; S4. During April to May of the following year, when hairy vetch is in full bloom or pod formation, it should be plowed back into the field.

[0008] Further, in step S1, the biochar-based slow-release fertilizer includes the following raw materials in the following mass percentages: 5%~15% kaolin, 5%~15% zeolite, 35%~45% biochar and 35%~45% phosphate fertilizer.

[0009] Furthermore, the kaolin is one or more of calcined kaolin, washed kaolin, and metakaolin; the zeolite is one or more of green zeolite, yellow zeolite, and white zeolite; and the phosphate fertilizer is one or more of superphosphate, triple superphosphate, and calcium magnesium phosphate.

[0010] Furthermore, the biochar is a powdered or granular material obtained by pyrolysis of one or more raw materials selected from straw, sawdust, bamboo, or rice husks under anaerobic or limited oxygen conditions at 400-600℃.

[0011] Furthermore, the granulation process in step S1 is carried out by a disc granulator or a drum granulator. Water is sprayed in during the granulation process to control the particle size of the biochar-based slow-release fertilizer to be 2-5 mm. The granulated particles are dried at 40-60℃ for 12-24 h until the moisture content is ≤5%.

[0012] Furthermore, in step S2, the application rate of biochar-based slow-release fertilizer is 1000~1800 kg·hm². -2 .

[0013] Furthermore, in step S3, the sowing rate of hairy vetch seeds is 150–200 kg·hm². -2 .

[0014] Furthermore, in step S4, the incorporation depth is 15-20 cm.

[0015] This invention also applies a soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure to the improvement of degraded farmland and non-grain-producing arable land.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention utilizes a specific ratio of biochar, kaolin, and zeolite to synergistically construct a stable multi-level porous structure and ion exchange sites, achieving effective phosphorus loading and long-term slow release without modification. This significantly reduces phosphorus fixation and leaching losses in the soil, significantly improves the utilization rate of phosphate fertilizers in traditional fertilization methods, and substantially reduces raw material and production costs, making the technology feasible for large-scale promotion. Furthermore, this simplified carrier combination not only provides nutrients but, more importantly, rapidly improves the soil's physical structure and chemical environment at the fertilization site.

[0017] 2. This invention employs a strict timing sequence of applying fertilizer before green manure. By pre-applying a special slow-release fertilizer before sowing hairy vetch, a nutrient base is provided for seed germination and seedling growth. This ensures that the green manure receives a sufficient and continuous supply of key phosphorus from the early stages of growth, significantly promoting plant height, biomass accumulation, and nitrogen fixation capacity. High biomass and high nitrogen fixation in green manure form a high-quality material foundation for subsequent soil improvement. Furthermore, this invention strictly stipulates that plowing should be carried out from the peak flowering period to the pod-setting period of hairy vetch. At this time, the plant material returned to the field is most easily decomposed by microorganisms and transformed into stable soil organic matter. This design avoids the problems of insufficient biomass due to early plowing or high lignification and difficulty in decomposition due to late plowing, thus optimizing the efficiency of organic material conversion into soil organic carbon.

[0018] 3. This method constructs an ordered ecological driving chain. Slow-release fertilizer first stimulates the activity of some soil microorganisms; then, the roots of hairy vetch secrete a large amount of organic matter, further enriching and activating the microbial community; finally, the input of high-quality green manure through incorporation provides a large amount of substrate for microbial proliferation. This sequential resource input significantly enhances the diversity and richness of soil microbial biomass carbon, fungi, and bacteria, especially promoting the proliferation of functional microbial communities related to carbon, nitrogen, and phosphorus cycles, thereby fundamentally enhancing the soil's biological fertility and self-sustaining capacity.

[0019] 4. Compared with existing technologies, the integrated synergistic solution provided by this invention produces a significant synergistic amplification effect through the systematic integration of slow-release carriers, biological components, and agronomic timing. It not only simultaneously achieves rapid and synergistic improvement in organic matter, total nitrogen, available phosphorus, and cation exchange capacity in degraded soils and non-grain-producing arable land, as well as improved nitrogen and phosphorus nutrient utilization efficiency, but also fundamentally enhances the stability of soil microbial diversity and ecological functions. At the same time, the entire solution uses readily available raw materials, has a simple process, and is highly operable in agronomy. Attached Figure Description

[0020] Figure 1 This is a bar chart showing the effects of different soil improvement treatments on the growth of hairy vetch in this invention; Figure 2 This is a comparison chart showing the effects of different soil improvement treatments on the physical and chemical properties of soil in this invention. Figure 3 This is a schematic diagram of the Mantel test analysis of the correlation between soil environmental factors and microbial community structure under different soil improvement treatments in this invention. Detailed Implementation

[0021] The present invention will be further described below with reference to preferred embodiments. The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values. These ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed herein.

[0022] Unless otherwise specified, the experimental methods in the following embodiments are conventional methods, performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions.

[0023] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0024] Example 1 This embodiment provides a soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure, including the following steps: S1. Preparation of biochar-based slow-release fertilizer: Calcined kaolin, zeolite, wheat straw biochar, and superphosphate are mixed in the following mass percentages: 10% calcined kaolin, 10% zeolite, 40% wheat straw biochar, and 40% superphosphate; wherein, the biochar is a granular material obtained by pyrolysis of wheat straw at 500℃ under limited oxygen conditions; the above raw materials are pulverized and mixed evenly using a high-speed pulverizer, and then fed into a disc granulator. During the granulation process, an appropriate amount of water is sprayed in as a binder to control the particle size to 2~5 mm; the granulated particles are dried at 50℃ for 18 h until the moisture content is ≤5%, thus obtaining the biochar-based slow-release fertilizer; S2. During November and December each year, apply the biochar-based slow-release fertilizer prepared in step S1 to degraded farmland at an application rate of 1000 kg·hm². -2 Then, the soil is tilled to ensure that the fertilizer is evenly distributed within the 0-20 cm topsoil layer. S3. Sow hairy vetch seeds evenly, with a sowing rate of 180 kg·hm². -2 ; S4. In April or May of the following year, when hairy vetch is in full bloom and its biomass is at its maximum, it should be plowed back into the field to a depth of 15-20 cm.

[0025] The biochar is a granular material obtained by pyrolyzing wheat straw at 500°C under oxygen-limited conditions.

[0026] Example 2 This embodiment provides a soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure, including the following steps: S1. Preparation of biochar-based slow-release fertilizer: Washed kaolin, yellow zeolite, sawdust biochar, and triple superphosphate are mixed in the following mass percentages: 15% washed kaolin, 15% yellow zeolite, 35% sawdust biochar, and 35% triple superphosphate; wherein, the biochar is a granular material obtained by pyrolysis of sawdust at 400℃ under limited oxygen conditions; the above raw materials are pulverized and mixed evenly using a high-speed pulverizer, and then fed into a drum granulator. During the granulation process, an appropriate amount of water is sprayed in as a binder to control the particle size to 2~5 mm; the granulated particles are dried at 40℃ for 24 h until the moisture content is ≤5%, thus obtaining the biochar-based slow-release fertilizer; S2. During November and December each year, apply the biochar-based slow-release fertilizer prepared in step S1 to non-grain farmland at an application rate of 1400 kg·hm². -2 Then, the soil is tilled to ensure that the fertilizer is evenly distributed within the 0-20 cm topsoil layer. S3. Sow hairy vetch seeds evenly, with a sowing rate of 200 kg·hm². -2 ; S4. In April or May of the following year, when hairy vetch is in full bloom and its biomass is at its maximum, it should be plowed back into the field to a depth of 15-20 cm.

[0027] Example 3 This embodiment provides a soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure, including the following steps: S1. Preparation of biochar-based slow-release fertilizer: Metakaolin, white zeolite, bamboo biochar, and calcium magnesium phosphate fertilizer are mixed in the following mass percentages: metakaolin 5%, white zeolite 5%, bamboo biochar 45%, and calcium magnesium phosphate fertilizer 45%; wherein, the biochar is a granular material obtained by pyrolysis of bamboo at 600℃ under limited oxygen conditions; the above raw materials are pulverized and mixed evenly using a high-speed pulverizer, and then fed into a disc granulator. During the granulation process, an appropriate amount of water is sprayed in as a binder to control the particle size to 2~5mm; the granulated particles are dried at 60℃ for 12 h until the moisture content is ≤5%, thus obtaining the biochar-based slow-release fertilizer; S2. During November and December each year, apply the biochar-based slow-release fertilizer prepared in step S1 to degraded farmland at an application rate of 1800 kg·hm². -2 Then, the soil is tilled to ensure that the fertilizer is evenly distributed within the 0-20 cm topsoil layer. S3. Sow hairy vetch seeds evenly, with a sowing rate of 150 kg·hm². -2 ; S4. In April or May of the following year, when hairy vetch is in full bloom and its biomass is at its maximum, it should be plowed back into the field to a depth of 15-20 cm.

[0028] Example 4 This embodiment provides a soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure, including the following steps: S1. Preparation of biochar-based slow-release fertilizer: 10% kaolin, 10% zeolite, 40% biochar and 40% phosphate fertilizer are mixed according to the following mass percentages: kaolin is a mixture of washed kaolin and metakaolin in any proportion; zeolite is a mixture of green zeolite and yellow zeolite in any proportion; biochar is a granular mixture obtained by pyrolysis of bamboo and rice husks under oxygen-limited conditions at 600℃; and phosphate fertilizer is a mixture of superphosphate and triple superphosphate in any proportion. The above raw materials are pulverized and mixed evenly using a high-speed pulverizer, and then fed into a disc granulator. During the granulation process, an appropriate amount of water is sprayed in as a binder to control the particle size to 2~5 mm. The granulated particles are dried at 50℃ for 18 h until the moisture content is ≤5%, thus obtaining the biochar-based slow-release fertilizer. S2. During November and December each year, apply the biochar-based slow-release fertilizer prepared in step S1 to degraded farmland at an application rate of 1000 kg·hm². -2 Then, the soil is tilled to ensure that the fertilizer is evenly distributed within the 0-20 cm topsoil layer. S3. Sow hairy vetch seeds evenly, with a sowing rate of 180 kg·hm². -2 ; S4. In April or May of the following year, when hairy vetch is in full bloom and its biomass is at its maximum, it should be plowed back into the field to a depth of 15-20 cm.

[0029] Comparative Example 1 This comparative example provides a soil improvement method using green manure, comprising the following steps: S1. During November and December each year, degraded farmland is plowed to ensure the normal growth of green manure; S2. Sow hairy vetch seeds evenly, with a sowing rate of 180 kg·hm². -2 ; S3. In April and May of the following year, when the hairy vetch is in full bloom and its biomass is at its maximum, it should be plowed back into the field to a depth of 15-20 cm.

[0030] Comparative Example 2 This comparative example provides a soil amendment method using biochar-based slow-release fertilizer, comprising the following steps: S1. A biochar-based slow-release fertilizer was prepared using calcined kaolin, green zeolite, rice straw biochar, and superphosphate, wherein the mass percentages were 10% calcined kaolin, 10% green zeolite, 40% wheat straw biochar, and 40% superphosphate. S2. During November and December each year, the prepared biochar-based slow-release fertilizer is applied to the degraded farmland at a rate of 1400 kg·hm². -2 Then, the soil is tilled to ensure that the fertilizer is evenly distributed within the 0-20 cm topsoil layer. S3. In April and May of the following year, the degraded farmland was plowed again, with a plowing depth of 15-20 cm.

[0031] Comparative Example 3 This comparative example provides a soil management method for use as a control, comprising the following steps: S1. During November to December each year, degraded farmland shall be plowed to a depth of 0-20 cm. S2. In April and May of the following year, the degraded farmland was plowed again to a depth of 15-20 cm.

[0032] This invention systematically tests and compares the soil improvement methods provided in Examples 1-3 and the methods provided in Comparative Examples 1-3 through standardized field trials.

[0033] A field experiment was conducted on non-grain-grade farmland in a village (119°41′E, 30°10′N) in Lin'an District, Hangzhou City, Zhejiang Province. The experimental area consisted of quadrats measuring 10 m in length and 6 m in width. The soil had low basic fertility and low organic matter content. Four treatments were set up: the soil improvement methods described in Examples 1-3 and Comparative Example 1 were used for treatment, with three replicates for each treatment arranged in a randomized block design.

[0034] (1) Analysis of the growth performance of hairy vetch This implementation follows the steps and parameters described above, performing all agronomic operations synchronously. When the biomass of *Vigna pubescens* reaches its maximum (i.e., from full bloom to pod formation), the entire plant is turned over. A final plant sample is collected before turning over, and a final soil sample is collected one month after turning over to systematically evaluate the effects of green manure decomposition on soil physicochemical properties, microbial characteristics, and carbon and nitrogen transformation processes. As shown in Table 1, in Examples 1-3 where the biochar-based slow-release fertilizer of this invention was applied, the plant height and dry matter accumulation of *Vigna pubescens* throughout the entire growth period were significantly higher than in Comparative Example 1, which did not use biochar-based slow-release fertilizer. The soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure provided in Example 2 was used to study the effects on green manure growth and soil properties. The results are as follows: Figure 1As shown in Figure a, compared to Comparative Example 1 which only used green manure, Example 2 significantly promoted plant height and biomass accumulation of green manure throughout the entire growing season. Specifically, plant heights reached 8.94 cm, 21.90 cm, and 56.36 cm in March, April, and May, respectively. Figure 1 As shown in b, the dry weights of individual plants were 0.07 g, 0.80 g, and 1.39 g, respectively, all significantly higher than those in Comparative Example 1, indicating that this combined treatment continuously promoted the growth and biomass formation of green manure plants; regarding nutrient absorption, such as Figure 1 As shown in cd, the soil improvement method provided in Example 2 resulted in total nitrogen and total phosphorus content of hairy vetch in March of 127.48 g / kg and 4.49 g / kg, respectively, which was significantly better than that in Comparative Example 1. This indicates that the treatment effectively improved the absorption efficiency of nitrogen and phosphorus nutrients by green manure, providing sufficient organic materials and nutrient basis for subsequent soil improvement.

[0035] Table 1

[0036] (2) Analysis of soil physicochemical property improvement Starting in January 2025, soil samples from the 0-20 cm soil layer were collected monthly to determine physicochemical indicators such as total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), available phosphorus (AP), organic matter (SOM), cation exchange capacity (CEC), pH, and water content. Soil microbial biomass carbon (MBC) and soluble organic carbon (DOC) content were also analyzed. Results are as follows: Figure 2 As shown in c, after the green manure decomposed and matured, the soil organic matter (SOM) content treated by the soil improvement method provided in Example 2 was 16.27 g / kg, which was 3.58% higher than that of Comparative Example 3 and Comparative Example 1, while the SOM in Comparative Example 1 decreased to 13.35 g / kg. This indicates that returning green manure alone may lead to soil carbon depletion, while the addition of biochar effectively alleviated this trend and promoted soil carbon accumulation; at the same time, as Figure 2 As shown in a and 2d, the total nitrogen (TN) and available nitrogen (AN) in the soil treated by the soil improvement method provided in Example 2 were 6.50 g / kg and 35.92 mg / kg, respectively, both significantly higher than other treatments, indicating that the synergistic effect of biochar and green manure can help retain and transform nitrogen; regarding phosphorus, such as Figure 2 Compared to control 1, the total phosphorus (TP) and available phosphorus (AP) in soil samples b and 2e were 0.98 g / kg and 2.59 mg / kg, respectively, significantly better than control 1, demonstrating the advantages of biochar-based slow-release fertilizer in slow-release phosphorus and reducing fixation and loss. Furthermore, as... Figure 2 As shown in f, the soil cation exchange capacity (CEC) can be significantly increased to 8.66 cmol. + / kg, further verifying its synergistic effect in improving soil fertility and microenvironment.

[0037] (3) Analysis of changes in soil microbial community Soil bacterial and fungal community structure was analyzed using 16S rRNA and ITS high-throughput sequencing technologies. Soil cellulase, alkaline phosphatase, and dehydrogenase activities were measured, and the Mantel test was used to explore the correlation between environmental factors and microbial community diversity. Results are as follows: Figure 3 As shown, the Mantel test results indicated that total nitrogen (TN), available nitrogen (AN), soil organic carbon (SOC), microbial biomass carbon (MBC), dissolved organic carbon (DOC), dehydrogenase activity (DHA), soil moisture content (SWC), and cation exchange capacity (CEC) were all significantly positively correlated with bacterial diversity and abundance (p<0.05). Among them, the Mantel's r value for TN and bacterial diversity was 0.42, and the r value for AN and bacterial abundance was 0.38, indicating that the combined treatment significantly promoted bacterial community diversity and abundance by improving the availability of soil nitrogen and carbon components. At the same time, TN, AN, DOC, DHA, total phosphorus (TP), and CEC were also significantly positively correlated with fungal diversity. The r value for AN and fungal diversity was 0.36, and the r value for TP and fungal diversity was 0.41, indicating that the treatment optimized the structure and function of the fungal community while improving soil phosphorus status and enzyme activity. Furthermore, the significant positive correlation between SOC, MBC, DOC, TP, and SWC and fungal abundance (r values ​​ranging from 0.32 to 0.45) further validates that the synergistic application of biochar and green manure enhances the structure and function of soil microbial communities by comprehensively improving soil nutrient and moisture conditions.

[0038] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure, characterized in that, Includes the following steps: S1. Preparation of biochar-based slow-release fertilizer: Kaolin, zeolite, biochar and phosphate fertilizer are mixed, crushed and granulated, and dried to obtain biochar-based slow-release fertilizer; S2. During November to December each year, apply the biochar-based slow-release fertilizer prepared in step S1 to the target soil and till it to ensure that the fertilizer is evenly distributed in the 0-20 cm topsoil layer. S3. Evenly disperse hairy vetch seeds; S4. During April to May of the following year, when hairy vetch is in full bloom or pod formation, it should be plowed back into the field.

2. The soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure according to claim 1, characterized in that, In step S1, the biochar-based slow-release fertilizer includes the following raw materials by mass percentage: 5%~15% kaolin, 5%~15% zeolite, 35%~45% biochar and 35%~45% phosphate fertilizer.

3. A soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure according to claim 2, characterized in that, The kaolin is one or more of calcined kaolin, washed kaolin, and metakaolin; the zeolite is one or more of green zeolite, yellow zeolite, and white zeolite; and the phosphate fertilizer is one or more of superphosphate, triple superphosphate, and calcium magnesium phosphate.

4. A soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure according to claim 2, characterized in that, The biochar is a powdered or granular material obtained by pyrolysis of one or more raw materials, such as straw, sawdust, bamboo, or rice husks, under anaerobic or limited oxygen conditions at 400-600℃.

5. A soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure according to claim 1, characterized in that, The granulation process in step S1 is carried out by a disc granulator or a drum granulator. Water is sprayed in during the granulation process to control the particle size of the biochar-based slow-release fertilizer to be 2-5 mm. The granulated particles are dried at 40-60℃ for 12-24 h until the moisture content is ≤5%.

6. A soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure according to claim 1, characterized in that, In step S2, the application rate of biochar-based slow-release fertilizer is 1000~1800 kg·hm. -2 .

7. A soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure according to claim 1, characterized in that, In step S3, the sowing rate of hairy vetch seeds is 150-200 kg·hm. -2 .

8. A soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure according to claim 1, characterized in that, In step S4, the plowing depth is 15-20 cm.

9. The soil improvement method based on the synergistic effect of biochar-based slow-release fertilizer and green manure as described in any one of claims 1-8 is used for the improvement of degraded farmland and non-grain-producing arable land.

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