A method for repairing cyanide-contaminated soil using southern amaranth

Abstract

The invention discloses a method for repairing cyanide-contaminated soil using southern amaranth, and belongs to the field of soil remediation technology. The soil remediation method of the present invention comprises the following steps: (1) applying biomass activated carbon prepared with southern amaranth to cyanide-contaminated soil, applying to topsoil and then rotary tilling and mixing; (2) sowing southern amaranth when the temperature of the soil surface layer 5-10cm rises to more than 20 DEG C; (3) thinning is carried out when the seedlings grow to 8-12cm high after southern amaranth sprouts; spraying cytokinin solution when southern amaranth grows to vigorous growth period; (4) mowing is carried out when southern amaranth grows to the initial flowering period, leaving a recommended height of 8-10cm; and then watering and fertilizing until the next mowing, mowing 2-3 times in each growing season, collecting stems and leaves for cyanide recovery. The present invention significantly improves the remediation effect of cyanide-contaminated soil by applying biochar prepared with southern amaranth, spot planting southern amaranth and spraying appropriate concentration of cytokinin during repair.

Description

Technical Field

[0001] The present invention relates to the technical field of soil remediation, and in particular to a method for remediating cyanide-contaminated soil by utilizing southern amaranth. Background Art

[0002] In recent years, with the rapid development of industries such as metallurgy, cyanide pollution has become increasingly serious, and the problem of soil cyanide contamination has also arisen. Cyanide is highly toxic to biological organisms. It rapidly ionizes into cyanide ions in animals, causing acute poisoning and even death. The lethal dose of potassium cyanide is 1-2 mg / kg. Severe cyanide contamination in soil can lead to reduced crop yields and even complete plant growth. The natural degradation rate of cyanide in soil is much slower than its degradation rate in natural water bodies. The migration behavior of cyanide in soil profiles is similar to that of soluble salts in soil. In arid and semi-arid climates, cyanide can be highly concentrated in the salt crust on the soil surface. The clay layer in the soil profile can partially block the migration of cyanide into the groundwater, resulting in high cyanide concentration in the clay layer. Cyanide in soil has a serious impact on plant growth. Soil contaminated by cyanide becomes a secondary source of pollution in the environment, posing long-term potential hazards to the surface environment, land use, surface water and groundwater. Therefore, there is an urgent need to remediate cyanide-contaminated soil.

[0003] Currently, the main methods reported for remediating cyanide-containing soils include chemical, microbial, and botanical methods. Chemical oxidation is the most common method, but the use of large amounts of oxidants during the treatment process increases material consumption and wastewater treatment costs. Furthermore, the addition of excessive oxidants can negatively impact soil physical and chemical properties and generate harmful byproducts. Consequently, chemical methods have drawbacks such as large engineering workloads, high costs, and complex operational procedures. Microorganisms used in microbial remediation are often obtained through natural selection or enrichment culture. Their cyanide remediation efficiency is weakened by soil heterogeneity or extreme environments (such as high or low pH, high salt concentrations, varying contamination levels, and the presence of other pollutants). Therefore, it is necessary to develop efficient, environmentally friendly, and economical cyanide treatment technologies.

[0004] Phytoremediation, a bioremediation technique, has gained widespread attention due to its low production costs and ability to meet environmental control requirements. It is increasingly considered a key technology for remediating cyanide contamination. Phytoremediation of cyanide-contaminated soils is based on the theory that plants tolerate and directly absorb and metabolize cyanide, or enhance cyanide mineralization in the rhizosphere. It utilizes plants and their coexisting microbial systems to remove cyanide from the soil environment. Phytoremediation utilizes the extraction, degradation, and stabilization properties of plants to remediate contaminated sites. Using plants to remediate cyanide-contaminated soils offers advantages such as ease of operation, low cost, minimal land damage, and environmental friendliness. This technology not only degrades cyanide and heavy metals in the growth layer of cyanide-containing tailings, but also enables in situ control of cyanide-containing tailings beneath the growth layer, reducing the potential environmental risk. Its environmentally friendly, economical, and feasible characteristics hold great promise for the treatment of closed tailings ponds.

[0005] Phytoremediation, an environmentally friendly, cost-effective, and novel soil remediation method, has rapidly developed over the past two decades. In 2000, the Danish municipality of Rudersdal successfully remediated cyanide contamination at a gas plant site by combining phytoremediation with extraction treatment. Plant species reported for cyanide-contaminated soil remediation include rice, soybeans, corn, willow, and poplar. However, rice and soybeans suffer from low biomass, poor stress tolerance, a narrow adaptability range, and low remediation efficiency. Willow and poplars also suffer from slow growth, inability to rapidly reproduce from seeds, and low remediation efficiency. Therefore, the search for new remediation plants continues.

[0006] Amaranthus australis is an annual C4 herbaceous plant of the genus Amaranth in the family Amaranthaceae. http: / / www.iplant.cn / info / %E5%8D%97%E6%96%B9%E8%8B%8B Amaranthus australis, also known as giant amaranth, is known for its strong stress resistance, rapid growth, and large biomass. Plants can reach up to 8 meters tall, making it the tallest species in the genus Amaranth. While most Amaranth species are diploid, with genomes ranging from 400 to 600 megabytes, Amaranthus australis is an allotetraploid with a genome of approximately 824 megabytes, making it the largest species in the genus (Molecular Phylogenetics and Evolution, 2017, 109:80-92). However, research on Amaranthus australis is relatively limited, and there are no reports on its use in remediating cyanide contamination in soil. Summary of the Invention

[0007] In view of the above-mentioned prior art, the purpose of the present invention is to provide a method for repairing cyanide-contaminated soil using Amaranthus australis.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] The first aspect of the present invention provides the use of Amaranthus australis in the remediation of cyanide-contaminated soil.

[0010] The present invention discovered for the first time that southern amaranth has the advantages of high repair efficiency, fast growth rate, large biomass, good stress resistance, wide adaptability, and rapid seed reproduction, and can be used for the repair of cyanide-contaminated soil.

[0011] A second aspect of the present invention provides a method for remediating cyanide-contaminated soil using Amaranthus australis, comprising the following steps:

[0012] (1) Applying biomass activated carbon prepared from Amaranthus chinensis to cyanide-contaminated soil, applying it to the topsoil and then rotary tilling and mixing;

[0013] (2) When the temperature of the top 5-10 cm of soil rises to above 20°C, sow southern amaranth;

[0014] (3) After the southern amaranth germinates, the seedlings are thinned out when they grow to 8-12 cm in height; when the southern amaranth reaches its vigorous growth stage, the cytokinin solution is sprayed;

[0015] (4) When the southern amaranth grows to the initial flowering stage, it is mowed, leaving a recommended height of 8-10 cm; then watering and fertilizing are carried out until the next mowing. Mowing is carried out 2-3 times per growing season, and the stems and leaves are collected for cyanide recovery.

[0016] Preferably, in step (1), the biomass activated carbon is prepared by the following method:

[0017] The southern amaranth straw is dried and crushed, and then pyrolyzed at high temperature in an oxygen-free state to prepare biochar; the high-temperature pyrolysis conditions are: heating to 440-460°C at a heating rate of -10°C / min, and continuing constant temperature heating for 1-2 hours.

[0018] The biomass activated carbon prepared by the method of the present invention has low hardness, good porosity, is rich in micropores, has good adsorption properties, and has the characteristics of improving soil and promoting plant growth.

[0019] Preferably, in step (1), the amount of biomass activated carbon applied is 2.5-3 t / hm 2 .

[0020] Preferably, in step (2), southern amaranth is sown by seed sowing with a plant spacing of 20 cm×30 cm.

[0021] Preferably, in step (3), when thinning out the seedlings, only one healthy seedling is left for each plant, and weeds are removed at the same time.

[0022] Preferably, in step (3), the cytokinin solution is a 6-BA solution; the concentration of the 6-BA solution is 50-150 μmol / L.

[0023] Preferably, in step (3), foliar spraying is used, spraying once a day, and the spraying amount is 4500L-5500L / hm 2 , spray continuously for 6-8 days.

[0024] Beneficial effects of the present invention:

[0025] (1) The present invention screened and obtained a new C4 plant, Amaranthus australis, which can be used for the remediation of cyanide-contaminated soil. It has a fast growth rate and can grow 3-5 cm per day during the vigorous growth period. It has a large biomass of 30-40 tons per mu, is suitable for planting in a wide area, and has strong stress resistance.

[0026] (2) Amaranthus australis is rich in potassium. Its straw is made into biochar with a high potassium content, which is 50-200% higher than the potassium content in other plant straws. The potassium content is 3.3 times that of corn straw biochar and 1.9 times that of rice straw biochar. Applying this type of high-potassium biochar to the cyanide-contaminated soil where Amaranthus australis is planted can significantly improve the rhizosphere environment and facilitate the root system to absorb and repair cyanide.

[0027] (3) When the present invention utilizes southern amaranth to repair cyanide-contaminated soil, spraying cytokinins at an appropriate concentration can increase transpiration and promote the absorption and repair of cyanide. DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0029] As mentioned above, existing plants that can be used to remediate cyanide-contaminated soil have problems such as small biomass, slow growth, inability to reproduce rapidly through seeds, poor stress resistance, narrow adaptability, and low remediation efficiency. Therefore, there is still a need to develop and find new remediation plants.

[0030] The inventors, who have been deeply involved in the field of soil remediation for many years, unexpectedly discovered a C4 plant, Amaranthus australis, while searching for a method to repair cyanide-contaminated soil. While little research has been conducted on Amaranthus australis, the inventors discovered that Amaranthus australis can be propagated from seeds, grows rapidly, produces a large biomass, is suitable for cultivation in a wide range of areas, and is highly resistant to stress, making it a promising candidate for the remediation of cyanide-contaminated soil.

[0031] Furthermore, the inventors investigated the use of southern amaranth in remediating cyanide-contaminated soil and discovered that southern amaranth is potassium-rich, and its straw, when converted into biochar, contains high levels of potassium, 50-200% higher than the potassium content in the straw of other plants. Applying this high-potassium biochar to cyanide-contaminated soil remediation plants planted with southern amaranth significantly improved the rhizosphere environment, facilitating root absorption and remediation of cyanide. The inventors also discovered that spraying a cytokinin solution at an appropriate concentration during the growth of southern amaranth can increase transpiration, thereby promoting cyanide absorption and remediation.

[0032] Therefore, the present invention proposes a new method for repairing cyanide-contaminated soil using southern amaranth. By applying biochar prepared from southern amaranth, spot-seeding southern amaranth and spraying cytokinins of appropriate concentrations during repair, the repair effect of cyanide-contaminated soil is significantly improved.

[0033] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below with reference to specific embodiments.

[0034] The experimental materials used in the examples of the present invention are all conventional experimental materials in the field and can be purchased through commercial channels. Experimental methods without detailed conditions were performed according to conventional experimental methods or the operating instructions recommended by the supplier. Among them, the southern amaranth variety used in this invention is called Giant Amaranth, and its seeds are obtained from the United States Department of Agriculture Germplasm Resource Bank with the germplasm number PI 553076.

[0035] Example 1: Preparation and performance testing of biomass activated carbon

[0036] 1. Preparation of biomass activated carbon:

[0037] Southern Amaranth straw was naturally air-dried to reduce its moisture content to below 18%, and then crushed into 3-8mm powder particles. Biochar was prepared using an oxygen-limited slow pyrolysis method. The crushed straw was placed in a semi-enclosed biomass carbonization furnace. Nitrogen was introduced into the tubular furnace, and biochar was produced by high-temperature pyrolysis in an oxygen-free environment. The temperature was increased to 450°C at a rate of 8°C / min and the temperature was maintained at a constant temperature for 1 hour. After the processed biomass granular carbon was cooled, it was removed and crushed through a 200-mesh sieve to produce southern Amaranth straw biomass activated carbon.

[0038] Southern Amaranth straw was replaced with rice straw and corn straw, and the same method as above was used to prepare rice straw biomass activated carbon and corn straw biomass activated carbon, respectively.

[0039] 2. Performance testing:

[0040] (1) pH determination:

[0041] The biomass activated carbon and water were stirred and mixed at a weight ratio of 1:25, and the composite electrode method was used for determination.

[0042] (2) Ash content determination:

[0043] Weigh 1g of biomass activated carbon (accurate to 0.01g), place it in a muffle furnace at 800℃ and completely ash it for 4 hours. After natural cooling, take it out and weigh it. Calculate the ash content based on the mass change before and after ignition:

[0044] Ash content (%) = (M1 - M2) / M3 × 100% (unit: g)

[0045] Where M1 represents the ash content and crucible mass, M2 represents the mass of the empty crucible, and M3 represents the mass of biochar.

[0046] (3) Determination of total potassium content:

[0047] Weigh 0.5 g of biomass activated carbon into a 150 mL Erlenmeyer flask, add 10 mL of sulfuric acid and let it stand overnight; the next day, add perchloric acid dropwise, place on a digestion table (temperature 350°C), time for about 8 hours, and shake once every hour; after digestion until the liquid is transparent, transfer to a 100 mL volumetric flask, adjust to volume and filter through a membrane, and the liquid is measured using an inductively coupled plasma mass spectrometer.

[0048] The performance test results of biomass activated carbon prepared from different straws are shown in Table 1.

[0049] Table 1: Performance test results of biomass activated carbon prepared from different straws

[0050]

[0051] The results showed that southern amaranth is rich in potassium, and its straw is high in potassium after being made into biochar. Its potassium content is 3.3 times that of corn straw biochar and 1.9 times that of rice straw biochar. Applying this kind of high-potassium biochar to the cyanide-contaminated soil remediation where southern amaranth is planted can significantly improve the rhizosphere environment, which is beneficial for the root system to absorb and repair cyanide.

[0052] Example 2: Potted experiment on remediation of cyanide-contaminated soil by Amaranthus australis

[0053] 1. Test method:

[0054] The potted restoration experiment was designed into four treatments according to whether straw biochar (AmC) was added to the cyanide-contaminated soil and whether the cytokinin 6-BA (6BA) was sprayed on Amaranthus australis for a long time. The experimental design is shown in Table 2.

[0055] Table 2: Potted restoration experiment design

[0056] deal with Addition amount of activated carbon from straw biomass (g / kg) Cytokinin 6-BA (μmol / L) CK 0 0 AmC 0.5 0 6BA 0 100 AmC+6BA 0.5 100

[0057] Activated carbon dosage: The amount of activated carbon added in the field test of the present invention is 2.8t / hm 2 The tillage depth for field planting is generally 20 cm, and the average bulk density of the soil is 2.65 g / cm 3 ; The amount of activated carbon added per kilogram of soil is calculated to be 0.5g, that is, the concentration of activated carbon added to the soil is 0.5g / kg. In order to facilitate the test and obtain reasonable test data, the present invention uses potted plant test. Since the area of ​​potted soil is very small, if the activated carbon is 2.8t / hm 2 It is neither practical nor convenient to calculate the amount of activated carbon added to the potting soil. Therefore, the weight of the potting soil is weighed and the activated carbon is added according to the concentration of activated carbon in the soil of 0.5g / kg.

[0058] Taking AmC+6BA as an example, the specific repair process is as follows:

[0059] (1) Collect cyanide contaminated soil at a depth of 0 to 20 cm. Mix the collected soil samples, dry them in the dark, remove impurities, and crush them. After drying, crush the contaminated soil into soil particles to be repaired. Pass all the soil particles to be repaired through a 20-mesh sieve. The cyanide content is determined by referring to the Determination of soil cyanide and total cyanide spectrophotometrically Method (HJ745-2015)". The survey results showed that the soil pH value was 6.24, the organic matter content was 21.2g / kg, the total nitrogen content was 1.28g / kg, the alkaline-hydrolyzable nitrogen content was 163.3mg / kg, the available phosphorus content was 1.85mg / kg, the available potassium content was 119.71mg / kg, and the total cyanide content was 183.5mg / kg.

[0060] (2) 0.5 g / kg of biomass activated carbon prepared from southern amaranth straw (prepared in Example 1) was added to the sieved cyanide-contaminated soil to be remediated, and then placed in a plastic basin with an upper diameter of 17 cm, a lower diameter of 15 cm, and a height of 17 cm. Each basin was filled with 4.5 kg of sieved cyanide-contaminated soil, containing a total cyanide of 825.75 mg / basin. A total of 2.25 g of biomass activated carbon prepared from southern amaranth straw was added and mixed thoroughly.

[0061] (3) Sow southern amaranth seeds in plastic pots, sow 3-5 seeds per pot, and place the pots in a greenhouse at a temperature of 25-32℃ with natural light. When the seeds germinate and grow to 10 cm in height, thin out the seedlings and leave one healthy seedling in each pot. When the seedlings reach the vigorous growth period (generally about one and a half months after sowing), prepare 100μmol / L cytokinin 6-BA solution and spray it on the leaves. The spraying lasts for 7 days, spraying once a day, and the spraying amount is 10ml / pot.

[0062] (4) When the southern amaranth reaches the initial flowering stage, it is mowed, leaving a recommended height of 8-10 cm. The remaining part continues to be watered and fertilized until the next mowing. A total of three mowings are performed during the growing season. The stems and leaves are collected for cyanide recovery.

[0063] Measurement and analysis: Plant height and dry weight were measured and analyzed when the plants were mowed at the early flowering stage. At the same time, the rhizosphere soil of the southern amaranth plants with different treatments was measured and analyzed for cyanide content to evaluate the remediation effect of cyanide-contaminated soil.

[0064] Removal rate (%) = cyanide content absorbed and enriched by plants / cyanide content in soil before treatment × 100%;

[0065] Enrichment coefficient = cyanide concentration in plants / cyanide concentration in soil;

[0066] Transfer coefficient = cyanide concentration in the aboveground part of the plant / cyanide concentration in the underground part of the plant.

[0067] 2. Test results:

[0068] The test results are shown in Table 3.

[0069] Table 3: Results of potted restoration test

[0070]

[0071] Results showed that applying biochar from southern amaranth straw significantly promoted the growth of southern amaranth plants, increasing their plant height and dry weight per plant. Application of biochar from southern amaranth straw or spraying with the cytokinin 6BA significantly increased cyanide content in the aboveground parts of southern amaranth plants. The combined application of biochar from southern amaranth straw and 6BA was even more effective, increasing the removal rate by 35.7 and 51.6 mg / pot, respectively, compared to either application alone, and by 63.8 mg / pot compared to the control. Both the transfer coefficient and the enrichment coefficient were significantly improved. Under control conditions, the total cyanide removal rate per pot of southern amaranth plants was 8.2%. Application of biochar from southern amaranth straw and spraying with 6BA significantly increased the removal rate to 11.6% and 9.7%, respectively. The combined application of biochar from southern amaranth straw and 6BA spraying resulted in a total cyanide removal rate of 15.9%.

[0072] Example 3: Field trial of using southern amaranth to repair cyanide-contaminated soil

[0073] 1. Test method:

[0074] The field remediation experiment was designed into four treatments according to whether straw biochar (AmC) was added to the cyanide-contaminated soil and whether the cytokinin 6-BA (6BA) was sprayed long-term on Amaranthus australis. The experimental design is shown in Table 4.

[0075] Table 4: Field restoration trial design

[0076] deal with Straw biomass carbon addition (t / hm2) Cytokinin 6-BA (μmol / L) CK 0 0 AmC 2.8 0 6BA 0 100 AmC+6BA 2.8 100

[0077] Taking AmC+6BA as an example, the specific repair process is as follows:

[0078] (1) Land preparation and fertilization: The cultivated land to be repaired (the cyanide content in the cultivated land is between 170-190 mg / kg, and the average cyanide content using the five-point sampling method is 183.0 mg / kg) is leveled and plowed to a depth of 20 cm, and 50 t / hm2 of organic fertilizer is applied. 2 , apply potassium dihydrogen phosphate 450kg / hm 2 , ammonium nitrate 600kg / hm 2 .

[0079] (2) Biochar application: 2.8 t / hm2 of biomass activated carbon prepared from Amaranthus chinensis (prepared in Example 1) was applied to the soil. 2 After applying it to the topsoil, use a rotary tiller to mix it evenly with the topsoil.

[0080] (3) Sowing: When the temperature of the top 5-10 cm of soil rises steadily to above 20°C, sow southern amaranth using the spot sowing method with a plant spacing of 20 cm × 30 cm;

[0081] (3) Field management: After the southern amaranth germinates, the seedlings are thinned out when they grow to 10 cm in height, leaving only one healthy seedling per plant; at the same time, workers are responsible for weed control. When the southern amaranth reaches its vigorous growth stage, a 100 μmol / L cytokinin 6-BA solution is prepared and sprayed on the leaves. The spraying time is 8 days, spraying once a day, and the spraying volume is 5000 L / hm2. 2 .

[0082] (4) Harvesting: When the southern amaranth grows to the initial flowering stage, it is mowed, leaving a recommended height of 8-10 cm, and then watered and fertilized until the next mowing. Mowing is done three times in each growing season, and the stems and leaves are collected for cyanide recovery.

[0083] Measurement and analysis: Plant height and dry weight were measured and analyzed when the plants were mowed at the early flowering stage. At the same time, the rhizosphere soil of Amaranthus australis in different treatment plots was measured and analyzed for cyanide content to evaluate the remediation effect of cyanide-contaminated soil.

[0084] The test results are shown in Table 5.

[0085] Table 5: Field restoration test results

[0086]

[0087] As shown in Table 5, the application of southern amaranth straw biochar significantly increased plant height and dry weight per plant, indicating that southern amaranth straw biochar improves the rhizosphere microenvironment, thereby enhancing the root system's ability to absorb water and fertilizer. Application of southern amaranth straw biochar or spraying the cytokinin 6BA alone increased cyanide content in the aboveground parts of southern amaranth plants, but had little effect on cyanide content in the belowground parts. However, the combined application of southern amaranth straw biochar and 6BA significantly increased cyanide content in the aboveground parts of the plants by 34% compared to the control. The transfer coefficient and enrichment coefficient increased by 37% and 47%, respectively, compared to the control. Furthermore, the cyanide content in the rhizosphere soil was significantly reduced by 19.4% compared to the control. These results indicate that the combined application of 6BA and southern amaranth straw biochar significantly enhanced the cyanide remediation efficiency of southern amaranth plants.

[0088] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A method for repairing cyanide-contaminated soil using southern amaranth, characterized in that: The following steps are involved: (1) Applying biomass activated carbon prepared from Amaranthus chinensis to cyanide-contaminated soil, applying it to the topsoil and then rotary tilling and mixing; (2) When the temperature of the top 5-10 cm of soil rises to above 20°C, sow southern amaranth; (3) After the southern amaranth germinates, the seedlings are thinned out when they grow to 8-12 cm in height; when the southern amaranth reaches its vigorous growth stage, the cytokinin solution is sprayed; (4) When the southern amaranth grows to the initial flowering stage, it is mowed, leaving a recommended height of 8-10 cm; then watering and fertilizing are carried out until the next mowing. Mowing is carried out 2-3 times per growing season, and the stems and leaves are collected for cyanide recovery; In step (1), the biomass activated carbon is prepared by the following method: Southern Amaranth straw was naturally air-dried to reduce its moisture content to below 18%, and then crushed into powder particles of 3-8 mm in size; biochar was prepared using an oxygen-limited slow pyrolysis method, the crushed straw was placed in a semi-enclosed biomass carbonization furnace, nitrogen was introduced into the tubular furnace, and biochar was prepared by high-temperature pyrolysis under an oxygen-free state, and the temperature was increased to 450°C at a heating rate of 8°C / min and the constant temperature was maintained for 1 hour. After the processed biomass granular carbon was cooled, it was taken out and crushed through a 200-mesh sieve to prepare biomass activated carbon; the total potassium content of the biomass activated carbon was 85.3g / kg; In step (3), the cytokinin solution is a 6-BA solution; The concentration of 6-BA solution was 100 μmol / L.

2. The method according to claim 1, characterized in that In step (1), the amount of biomass activated carbon applied is 2.5-3 t / hm 2 .

3. The method according to claim 1, characterized in that In step (2), southern amaranth is sown by seed sowing with a plant spacing of 20 cm × 30 cm.

4. The method according to claim 1, wherein In step (3), when thinning out, only one healthy seedling is left for each plant, and weeds are removed at the same time.

5. The method according to claim 1, wherein In step (3), foliar spraying is used, spraying once a day, and the spraying amount is 4500L-5500L / hm 2 , spray continuously for 6-8 days.

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