Utilization method of cadmium-polluted cultivated land soil

Abstract

The invention relates to the field of safe utilization of heavy metal polluted cultivated land, and discloses a utilization method of cadmium polluted cultivated land soil. The method comprises the following steps: S1, mixing dolomite, a functional improvement material and cadmium-polluted farmland soil, and soaking in water to submerge the farmland; s2, planting crops; the preparation method of the functional improved material comprises the following steps: inoculating a microbial agent containing bacillus licheniformis into a material containing sweet sorghum residues, and fermenting. According to the utilization method provided by the invention, on the basis of not changing the original planting habit, the content of cadmium in the crops in season can be effectively reduced by applying the dolomite powder and the functional improvement material in combination with water and fertilizer management of the crops, and the improvement effect lasts for a long time.

Description

Technical Field

[0001] The present invention relates to the field of safe utilization of heavy metal-contaminated cultivated land, and in particular to a method for long-term and safe utilization of cadmium-contaminated cultivated land soil. Background Art

[0002] Cadmium (Cd), mercury (Hg), and arsenic (As) are typical heavy metal pollutants in contaminated farmland. Remediation of heavy metal-contaminated farmland requires effectively reducing the activity of heavy metals in the soil, preventing their incorporation into crops and seeds to avoid impacting agricultural product quality and food security, while also minimizing the impact on crop growth and grain yield, and preventing "secondary pollution" that could affect soil environmental quality. Currently, the most common technologies for safe farmland utilization in China are phytoremediation, agronomic manipulation, and in-situ passivation. Phytoremediation offers advantages such as low cost, minimal environmental impact, and environmental beautification. However, its disadvantages include low biomass, slow growth, and a long growth cycle, resulting in low remediation efficiency and a poor fit for mechanized operations. Agronomic manipulation offers simplicity, low cost, and mature technology, but its drawbacks are limited remediation effectiveness and the need for annual adjustments, such as the "VIP+N" technique currently being implemented in Hunan. In-situ passivation is currently one of the most suitable technologies for safe farmland utilization, offering low cost and rapid results. The current mainstream passivation materials include calcium magnesium phosphate fertilizers, clay minerals and biochar. Excessive addition of calcium magnesium phosphate fertilizers and clay minerals can easily cause soil compaction, and the possibility of mass production of biochar is also low. Therefore, in the face of the arduous goal of safe utilization of cultivated land, it is particularly important to screen out materials that are scalable, sustainable, green and efficient.

[0003] Therefore, there is an urgent need for a sustainable and safe method for utilizing cadmium-contaminated farmland that can effectively reduce the cadmium content in crops and the mobility of heavy metal cadmium without changing the original planting habits, and that can have the effect of reducing the cadmium content in crops for many years. Summary of the Invention

[0004] The purpose of the present invention is to overcome the problems of low remediation efficiency, limited remediation effect and the need for annual regulation in the existing technology, and to provide a sustainable and safe utilization method for cadmium-contaminated cultivated land soil. This utilization method can not only effectively reduce the cadmium content in crops, reduce the mobility of heavy metal cadmium, increase soil fertility, and regulate soil pH without changing the original planting habits, but also has the effect of reducing the cadmium content in crops for at least 4 years or more.

[0005] In order to achieve the above object, the present invention provides a method for utilizing cadmium-contaminated cultivated soil, wherein the method comprises the following steps:

[0006] S1. Mixing dolomite, functional improvement materials and cadmium-contaminated farmland soil and flooding the fields;

[0007] S2, planting crops;

[0008] The method for preparing the functional improved material comprises: inoculating a bacterial agent containing Bacillus licheniformis into a material containing sweet sorghum residue for fermentation.

[0009] Through the above technical solution, the beneficial effects of the present invention include at least:

[0010] The method for the sustainable and safe utilization of cadmium-contaminated cultivated land soil provided by the present invention is based on not changing the original planting habits. By mixing cadmium-contaminated cultivated land soil with dolomite and functional improvement materials, combined with the water and fertilizer management of crops, the cadmium content in the crops of the season can be effectively reduced, and the improvement effect can last for many years. In a preferred case, the improvement effect can last for at least 4 years. The pH value of the acidified soil can be effectively alleviated by adding dolomite. At the same time, the magnesium hydroxide formed by applying dolomite to the soil can effectively react with heavy metal cadmium ions such as adsorption and complexation. The functional improvement material after fermentation by Bacillus licheniformis can produce a large amount of extracellular secretions and extracellular polymers, such as organic acids, proteins, polypeptides, lipids, amino groups, sulfhydryl groups, hydroxyl groups, carboxyl groups, phosphate groups and amide groups. These secretions can provide a large number of anionic groups to combine with heavy metals through various methods such as complexation and chelation to form precipitates, thereby reducing the biological toxicity of heavy metals. In addition, the functional improvement material after fermentation has a high organic matter content and fertilizer effect, which can effectively improve soil structure and enhance soil fertility. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a flow chart of a method for sustainable and safe utilization of acidified and severely cadmium-contaminated farmland in a preferred embodiment of the present invention;

[0012] Figure 2 Schematic diagram of field distribution during the field trial in Example 3 of the present invention. DETAILED DESCRIPTION

[0013] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0014] The present invention provides a method for utilizing cadmium-contaminated cultivated soil, wherein the method comprises the following steps:

[0015] S1. Mixing dolomite, functional improvement materials and cadmium-contaminated farmland soil and flooding the fields;

[0016] S2, planting crops;

[0017] The method for preparing the functional improved material comprises: inoculating a bacterial agent containing Bacillus licheniformis into a material containing sweet sorghum residue for fermentation.

[0018] In a preferred embodiment of the present invention, the specific implementation time of step S1 is: after the harvest of the previous season's crops and before the planting of the next season's crops, and the straw of the previous season's crops is required to be removed from the field.

[0019] In the present invention, the pH value of acidified soil can be effectively alleviated by adding dolomite powder. At the same time, the magnesium hydroxide formed by dolomite powder in the soil can effectively react with heavy metal cadmium ions by adsorption and complexation. The biological toxicity of heavy metals can be reduced by applying functional improvement materials. The functional improvement materials after fermentation by Bacillus licheniformis can produce a large amount of extracellular secretions and extracellular polymers, such as organic acids, proteins, polypeptides, lipids, amino groups, sulfhydryl groups, hydroxyl groups, carboxyl groups, phosphate groups and amide groups. These secretions can provide a large number of anionic groups to combine with heavy metals through various means such as complexation and chelation to form precipitates, thereby reducing the biological toxicity of heavy metals. In addition, the functional improvement materials after fermentation have a high organic matter content and fertilizer effect, which can effectively improve soil structure and enhance soil fertility. The product obtained by fermenting sweet sorghum residue with Bacillus licheniformis and dolomite powder can play a good synergistic role. By applying dolomite powder and functional improvement materials, combined with reasonable crop water and fertilizer management, the cadmium content in seasonal crops can be effectively reduced, and the improvement effect lasts for a long time.

[0020] The present invention has no particular limitation on the method for mixing dolomite, functional improvement materials and cadmium-contaminated cultivated soil. As long as the soil, dolomite and functional improvement materials can be evenly mixed, conventional methods of mixing additives in the art can be adopted. Preferably, in order to make the dolomite and functional improvement materials play a better role in the cadmium-contaminated cultivated soil, preferably, in S1, the mixing method includes: deep plowing the cadmium-contaminated cultivated soil, sowing dolomite on the deep-plowed soil, performing rotary tillage and leveling, and sowing the functional improvement material.

[0021] In the present invention, a rotary tiller can be used to deep plow the soil.

[0022] According to the present invention, the deep plowing depth is preferably 25-30 cm. When the deep plowing depth falls within this range, it can ensure that the soil within the plant root system is fully mixed with the dolomite dust and functional improvement materials. If the deep plowing depth is too shallow, the lower soil layer will not be fully mixed with the dolomite dust and functional improvement materials. If the deep plowing depth is too deep, the bottom layer of the cultivated land may be damaged.

[0023] In a preferred embodiment of the present invention, the rotary tillage and leveling method includes: using a rotary tiller to perform rotary tillage, and then installing a rotary tillage harrow behind the rotary tiller to continue rotary tillage, ensuring that the soil and dolomite are thoroughly mixed and the land is leveled after rotary tillage. Preferably, the rotary tillage depth is 15-20 cm.

[0024] The method of the present invention can effectively and safely utilize acidified, heavily cadmium-contaminated farmland, preventing cadmium from entering crops and seeds, thus avoiding impacts on agricultural product quality and food security, while also not affecting crop growth and grain yield. In a specific embodiment of the present invention, the pH value of the cadmium-contaminated farmland soil is 4-5.5, more preferably 4.36-5.27; and the cadmium content of 1 kg of cadmium-contaminated farmland soil is 2-5.5 mg, more preferably 2.23-5.25 mg.

[0025] In order to further alleviate the pH value of acidified soil and further reduce the content of heavy metal cadmium ions in the soil, preferably, the dolomite powder includes: CaO, MgO, SiO2 and carbonate; wherein the content of carbonate is calculated as CO2, and based on the total weight of the dolomite powder, the mass percentages of CaO, MgO, SiO2 and carbonate in the dolomite powder are 26-50wt%, 26-31wt%, 2-8wt% and 22-46wt% respectively.

[0026] Preferably, the deposit number of the Bacillus licheniformis is CGMCC No. 20977, which has been disclosed in CN117447270A.

[0027] According to the present invention, preferably, the material containing sweet sorghum residue is a mixture of sweet sorghum residue and agricultural and forestry wastes such as soybean meal.

[0028] According to the present invention, preferably, the average particle size of the sweet sorghum residue and soybean meal in the mixture is less than or equal to 5 mm. Grinding the sweet sorghum residue and soybean meal to less than 5 mm before mixing and then subjecting to microbial fermentation ensures that the materials are fully mixed and is conducive to the growth and fermentation of microorganisms. Otherwise, the fermentation of the materials will be affected, thereby affecting the improvement effect.

[0029] In order to further improve the fermentation effect and further optimize the composition of the extracellular secretions and extracellular polymers of Bacillus licheniformis and the fermentation products, thereby further reducing the biological toxicity of heavy metals and further improving the soil structure and enhancing the soil fertility, preferably, the amount of each component in the material containing sweet sorghum residue is such that the weight ratio of the C element to the N element in the material containing sweet sorghum residue is less than or equal to 25, preferably (23-25):1.

[0030] The present invention has no particular limitation on the water content in the material containing sweet sorghum residue, as long as it can meet the moisture content requirement during microbial growth and fermentation. Preferably, the water content in the mixed material containing sweet sorghum residue is 50-60 wt%.

[0031] In order to further improve the quality of the raw materials and control the pH during the fermentation process, thereby more effectively inhibiting the growth of miscellaneous bacteria and improving the effect of improving the material, preferably, the pH value of the material containing sweet sorghum residue is 3.6-4.5.

[0032] In the present invention, the pH value of the material containing sweet sorghum residue can be adjusted by a pH regulator, such as soda ash (sodium carbonate). In a preferred embodiment of the present invention, the amount of soda ash used is 2-5 wt% based on the total weight of the material containing sweet sorghum residue.

[0033] According to the present invention, preferably, the inoculation amount of the bacterial agent containing Bacillus licheniformis in the material containing sweet sorghum residue is such that the number of viable bacteria of Bacillus licheniformis in 1g of the material containing sweet sorghum residue on a dry weight basis is 10 3 -10 5 indivual.

[0034] In the present invention, the form of the inoculum containing Bacillus licheniformis can be any conventional form in the art, such as solid, liquid or semi-solid form. The present invention has no particular limitation on the number of viable bacteria in the inoculum, as long as it can meet the application requirements. In a preferred embodiment of the present invention, the inoculum containing Bacillus licheniformis is a liquid inoculum, and the total number of viable bacteria in the inoculum is (5-10)×10 8 cfu / ml, and the addition amount is 2-5wt% of the total weight of the material containing sweet sorghum residue.

[0035] To further control the growth of contaminants and provide a more suitable temperature for the growth and fermentation of Bacillus licheniformis, the fermentation temperature is preferably 25-50°C and the fermentation time is 10-15 days. The fermentation is performed in piles, and the pile thickness can be 45-55 cm. During the fermentation process, the fermentation temperature can be controlled by turning the material. Fermentation is complete when the temperature stabilizes and is below 50°C. This process generally takes 10-15 days.

[0036] According to the present invention, before spreading dolomite powder, the pH value, heavy metal cadmium content, available cadmium content and soil fertility of the cultivated soil are tested to determine the degree of soil acidification and heavy metal pollution, thereby determining the application amount of the dolomite powder and functional improvement materials.

[0037] In order to further enhance the synergistic effect of dolomite powder and functional improvement materials, preferably, in S2, the amount of dolomite powder added is 500-1000 kg / mu of cultivated land, and the amount of functional improvement materials added is 500-1000 kg / mu of cultivated land.

[0038] Preferably, the weight ratio of the dolomite powder to the functional improvement material is 1:(0.5-1).

[0039] In a specific embodiment of the present invention, the method for sustainable and safe utilization of cadmium-contaminated cultivated land soil includes: S1. First, remove the crop straw from the previous season from the field, deep-plow the field to be improved by deep-plowing machinery, apply the dolomite powder to the field, and then perform rotary tillage and leveling (rotating, harrowing, and leveling); then, evenly sow the functional improvement material in the field, and then soak the field in water, and do not add running water to prevent material loss; S2. After the soaking is completed, pulping and transplanting are carried out; the field management after planting is consistent with daily field management.

[0040] Preferably, the time for flooding the fields is 5-7 days.

[0041] According to the present invention, preferably, the crop is a cereal crop, more preferably rice, and most preferably Nanjing 5055.

[0042] The inventors have found that the method for utilizing cadmium-contaminated cultivated soil provided by the present invention has a significant effect on reducing the cadmium content in cereal crops, especially in reducing the cadmium content in rice, and particularly in reducing the cadmium content in Nanjing 5055 rice.

[0043] In order to make the dolomite and functional improvement materials play a more full role in the cultivated soil, in a preferred embodiment of the present invention, when the crops are cereal crops, agronomic measures are carried out after the crops are planted. The method of agronomic measures management includes: maintaining a 2-5 cm water layer in the field from 20 days before heading to 20 days after heading, so as to avoid alternating dry and wet soil.

[0044] The inventors have found that the utilization method provided by the present invention has a good effect on the cultivation of cereal crops, especially rice. Combined with reasonable water and fertilizer management, it can effectively reduce the cadmium content in the current season's crops, and the improvement effect lasts for at least 4 years.

[0045] Figure 1This is a flow chart of a method for the sustainable and safe utilization of acidified and severely cadmium-contaminated farmland in a preferred embodiment of the present invention. Figure 1 The process of using this method to plant rice for multiple seasons is described. First, investigate the contaminated arable land, test the pH value, heavy metal cadmium content, cadmium available content and soil fertility of the arable land, and determine the degree of soil acidification and heavy metal pollution; deep plow the acidified and heavily cadmium-contaminated arable land, with a deep plowing depth of 25-30cm; spread dolomite powder on the deep-plowed soil and perform rotary plowing, harrowing and leveling (i.e. rotary plowing and leveling) to evenly mix the dolomite powder and the deep-plowed soil and level the land; spread functional improvement materials on the mixed soil and soak the field, and then perform Beat the rice and transplant the rice seedlings; carry out agronomic management before and after rice heading, maintain a 2-5 cm water layer in the field from 20 days before to 20 days after heading, and prevent alternating dry and wet soil; harvest the rice; conduct a safety utilization effect evaluation and determine the cadmium content in polished rice; before planting the next crop, remove the straw from the previous crop field, and plant the next rice after the straw is removed from the field; after planting the next rice, carry out agronomic management before and after rice heading, harvest, and safety utilization effect evaluation according to the methods of the previous season.

[0046] The present invention will be described in detail below through examples and comparative examples. In the following examples, unless otherwise specified, conventional methods are used; and the reagents and materials used, unless otherwise specified, can be obtained from commercial sources.

[0047] Example 1

[0048] This example is used to illustrate a method for preparing a functional improved material for a sustainable and safe utilization method of acidified and severely cadmium-contaminated farmland, comprising the following steps:

[0049] Sweet sorghum residue and agricultural and forestry waste such as soybean meal were crushed to less than 5 mm and then mixed to obtain a mixture with a C / N ratio of 25 / 1. The moisture content of the mixture was adjusted to 55 wt%, and 5 wt% of the weight of the mixture was added with soda ash. A liquid inoculum of Bacillus licheniformis (Bacillus licheniformis deposit number is CGMCC No. 20977, and the total viable count in the inoculum is 6×10 8 cfu / ml) at a rate of 2 wt% of the total weight of the mixture. Culture and fermentation were carried out at 35°C for 15 days in a pile with a thickness of 50 cm. During the fermentation process, the mixture was stirred according to the fermentation temperature and stirred when the fermentation temperature exceeded 50°C. Fermentation was completed when the fermentation temperature stabilized and remained below 50°C.

[0050] Through testing and analysis by a third-party testing agency, it can be seen from elemental detection and analysis that the elemental composition of the functional improved material obtained in this embodiment is shown in Table 1.

[0051] Table 1

[0052]

[0053] Note: ND is within the detection capability of the detection instrument and is below the minimum scale or resolution.

[0054] Example 2

[0055] This embodiment relates to a potted plant experiment:

[0056] The functional improvement material obtained by Example 1 was used to carry out a safe utilization pot test of cadmium-contaminated soil in Yixing. The average pH value of the test soil was 5.04, the soil was slightly acidic, and the cadmium content in the soil was 2.98 mg / kg, which was a heavy cadmium-contaminated farmland. The test crop was rice (Nanjing 5055). The test set up a control group (CK) and 5 treatment groups and 2 comparison groups, and each group was repeated three times. The soil was pre-treated to turn large pieces of soil into fine particles, and large stones and residual roots were sorted out at the same time, and the soil was fully mixed. The soil after pre-treatment was weighed into 24 equal parts of 5 kg, and each test pot had 5 kg of soil.

[0057] In the control group CK, no white cloud powder and functional improvement materials were applied, and the rest of the operations were the same as those of the control group.

[0058] Treatment group 1, added dolomite powder (the carbonate content is calculated as CO2, based on the total weight of dolomite powder, the mass percentages of CaO, MgO, SiO2 and carbonate in dolomite are 48wt%, 31wt%, 5wt% and 41wt% respectively) at 1wt% of the soil weight, mixed evenly and placed into a potting bucket, then 1wt% of the functional improvement material by weight of the soil was evenly spread on the surface and then soaked in water.

[0059] Treatment Group 2 was operated according to the method of Treatment Group 1, except that the fermentation time was different when preparing the functional improved material. Specifically, the 15-day pile fermentation was replaced by a 7-day pile fermentation.

[0060] Treatment Group 3 was operated according to the method of Treatment Group 1, except that the fermentation temperature was different when preparing the functional improved material. Specifically, the difference was that the culture temperature was changed from 35°C to 60°C.

[0061] Treatment group 4: 1 wt% of the functional improvement material was added to the soil, mixed evenly, and then placed in a potting bucket. Then, 1 wt% of the white cloud powder was evenly sprinkled on the surface, and then soaked in water.

[0062] Treatment group 5 was operated according to the method of treatment group 1, except that the experimental crop rice variety was different, specifically, Nanjing 5055 was replaced by Dao 2845.

[0063] In comparison group 1, only 1 wt% of the functional improvement material was added to the soil, mixed evenly, and then placed in a potting bucket, which was then soaked in water without adding white cloud powder.

[0064] Comparative Group 2 was operated according to the method of Treatment Group 1, except that a different bacterial agent was used in the preparation of the functionally improved material. Specifically, Bacillus licheniformis with a deposit number of CGMCC No. 20977 was replaced with Bacillus cereus with a strain number of ACCC10604.

[0065] The potted plant test process was managed according to the principles of optimality and consistency. The final seed material was sent to a third party for testing. The results are shown in Table 2.

[0066] Table 2

[0067]

[0068]

[0069] Example 3

[0070] This embodiment relates to the first year field trial:

[0071] The functional improved material obtained in Example 1 and dolomite (the composition is the same as that of dolomite in Example 2) were used to conduct a field test for safe utilization in Yixing, Jiangsu. The soil pH value of the test area was 4.36, the soil was acidic, and the heavy metal cadmium content in the soil was 3.74 mg / kg, which was considered to be severely cadmium-contaminated arable land. In the first year, the test crop in the test area was rice, and the rice variety was unified (Nanjing 5055). The test area was about 10,600 square meters, divided into 7 natural plots. The safe utilization plan is shown in Table 3, and the plot distribution is as follows: Figure 2 shown.

[0072] Table 3

[0073]

[0074] The amount of remediation material to be applied is determined based on the design and field size. Before applying dolomite, the soil should be tilled to a depth of 25 cm using a rotary tiller. A fertilizer spreader should then be used to evenly distribute the dolomite. To ensure uniform mixing of the remediation material and the contaminated soil, the soil should be tilled 2-3 times with a rotary tiller to a depth of 15 cm. For the final tillage, a harrow should be installed behind the rotary tiller to ensure a level field. After the materials have been spread and the soil has been leveled, the functional remediation material should be evenly applied to the surface. The field should then be soaked for 5 days (no running water allowed). After soaking, rice seedlings should be beaten and transplanted. During rice management, a 3 cm water layer should be maintained in the field from 20 days before to 20 days after heading to prevent alternating periods of wetting and drying. At harvest, random samples from each field were sent to a third party for inspection. The results are shown in Table 4.

[0075] Table 4

[0076]

[0077]

[0078] Example 4

[0079] This embodiment relates to the second year field test:

[0080] On the basis of Example 3, after the crop straw of the previous season was removed from the field, the fields were rotary tilled to a depth of 15 cm. In the second year, the test crop in the experimental area was rice, and the rice variety was uniform (Nanjing 5055). Rice planting and management were consistent with conventional methods. During the rice management process, a 3 cm water layer was maintained in the field from 20 days before heading to 20 days after heading to prevent alternating dry and wet soil. At the time of rice harvest, random samples were taken from each field and sent to a third party for inspection. The test results are shown in Table 5.

[0081] Table 5

[0082]

[0083] Example 5

[0084] This example relates to the third and fourth year field trials:

[0085] On the basis of Example 4, after the crop straw of the previous season was removed from the field, the fields were rotary tilled to a depth of 15 cm. In the third year, the test crop in the experimental area was rice, and the rice variety was uniform (Nanjing 5055). Rice planting and management were consistent with conventional methods. During the rice management process, a 3 cm water layer was maintained in the field from 20 days before heading to 20 days after heading to prevent alternating dry and wet soil. At the time of rice harvest, random samples were taken from each field and sent to a third party for inspection. The test results are shown in Table 6.

[0086] The fourth year of the field trial was conducted based on the third year's field trial. The rice varieties and test methods were the same as those used in the third year. At harvest, random samples were taken from each plot and sent to a third party for inspection. The results are shown in Table 6.

[0087] Table 6

[0088]

[0089] Through four years of follow-up monitoring of the one-time improvement shown in Tables 4, 5 and 6, it was found that a sustainable and safe utilization method for acidified and severely cadmium-contaminated farmland can reduce the cadmium content in rice to the limit of the "Food National Safety Standard" (0.2 mg / kg) or below at one time after adding appropriate amounts and proportions of dolomite and functional improvement materials, and the safe utilization effect can be maintained for at least 4 years.

[0090] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for utilizing cadmium-contaminated cultivated soil, characterized in that: The method comprises the following steps: S1. Mixing dolomite, functional improvement materials and cadmium-contaminated farmland soil and flooding the fields; S2, planting crops; The method for preparing the functional improved material comprises: inoculating a bacterial agent containing Bacillus licheniformis into a material containing sweet sorghum residue for fermentation.

2. The method according to claim 1, characterized in that In S1, the mixing method includes: deep plowing the cadmium-contaminated cultivated soil, spreading dolomite on the deep-plowed soil, performing rotary tillage and leveling, and spreading functional improvement materials; Preferably, the depth of deep plowing is 25-30 cm; Preferably, the pH value of the cadmium-contaminated cultivated soil is 4-5.5, more preferably 4.36-5.27; the cadmium content in 1 kg of cadmium-contaminated cultivated soil is 2-5.5 mg, more preferably 2.23-5.25 mg.

3. The method according to claim 2, characterized in that The depth of the rotary tillage is 15-20 cm; Preferably, the dolomite powder includes: CaO, MgO, SiO2 and carbonate; wherein the content of carbonate is calculated as CO2, and based on the total weight of the dolomite powder, the mass percentages of CaO, MgO, SiO2 and carbonate in the dolomite powder are 26-50wt%, 26-31wt%, 2-8wt% and 22-46wt% respectively.

4. The method according to any one of claims 1 to 3, characterized in that The deposit number of the Bacillus licheniformis is CGMCC No.20977.

5. The method according to any one of claims 1 to 4, characterized in that The material containing sweet sorghum residue is a mixture of sweet sorghum residue and soybean meal; Preferably, the average particle size of the sweet sorghum residue and soybean meal in the mixture is less than or equal to 5 mm; Preferably, the weight ratio of the C element to the N element in the material containing sweet sorghum residue is less than or equal to 25, preferably (23-25):1; Preferably, the water content in the material containing sweet sorghum residue is 50-60wt%; Preferably, the pH value of the material containing sweet sorghum residue is 3.6-4.

5.

6. The method according to any one of claims 1 to 5, characterized in that The inoculation amount of the bacterial agent containing Bacillus licheniformis in the material containing sweet sorghum residue is such that the number of viable bacteria of Bacillus licheniformis in 1g of the material containing sweet sorghum residue on a dry weight basis is 10 3 -10 5 indivual.

7. The method according to any one of claims 1 to 6, characterized in that The fermentation temperature is 25-50° C. and the fermentation time is 10-15 days.

8. The method according to any one of claims 1 to 7, characterized in that In S1, the amount of the dolomite added is 500-1000 kg / mu of arable land, and the amount of the functional improvement material added is 500-1000 kg / mu of arable land; Preferably, the weight ratio of the dolomite powder to the functional improvement material is 1:(0.5-1).

9. The method according to any one of claims 1 to 8, characterized in that In S2, the time for flooding the fields is 5-7 days.

10. The method according to any one of claims 1 to 9, characterized in that The crops are cereal crops, preferably rice.

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