Soil conditioner for synergistically passivating heavy metals based on pH-responsive humic acid-functional bacteria and preparation method of soil conditioner

Abstract

The invention discloses a soil conditioner for synergistically passivating heavy metals based on pH-responsive humic acid-functional bacteria and a preparation method of the soil conditioner, and relates to the technical field of soil remediation. The preparation method comprises the following steps: mixing bacillus megatherium, bacillus mucilaginosus and azotobacter chroococcum to prepare a compound microbial agent, and activating humic acid by using acid or alkali as an activating agent to obtain pretreated humic acid; and preparing the soil conditioner by taking the compound microbial agent, the pretreated humic acid, the porous mineral matrix and the nutrient as raw materials. According to the prepared soil conditioner, passivation of various heavy metals in soil within a larger pH range is achieved through cooperation of three aspects of chemical passivation, biological mineralization and physical adsorption, and the micro-ecology of the soil can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil remediation, in particular to a soil conditioner based on pH-responsive humic acid-functional bacteria for synergistic passivation of heavy metals and a preparation method thereof. BACKGROUND

[0002] With the rapid development of industrialization and agricultural modernization, soil heavy metal pollution problems are becoming increasingly serious, posing a serious threat to the quality and safety of agricultural products and human health. At present, the remediation techniques for heavy metal contaminated soil mainly include physical, chemical and biological methods. Among them, chemical passivation remediation technology is widely used due to its low cost, simple operation and significant remediation effect.

[0003] At present, the materials used for chemical passivation remediation include inorganic materials such as lime, phosphate, silicate, iron and manganese oxides, and organic materials such as biochar and humic acid. Among them, inorganic materials mainly reduce the availability of heavy metals through increasing soil pH, adsorption or precipitation, and organic materials mainly fix heavy metal ions through complexation and chelation. At present, these materials have the following defects: (1) they need to be effective within a specific pH range, and are strongly dependent on pH. For example, lime works well in acidic soils, but can cause excessive alkalization of the soil, affecting the availability of trace elements; while iron and manganese oxides have poor performance under acidic conditions. (2) Single function: inorganic materials mainly passivate heavy metals through adsorption or precipitation, but have poor long-term stability and risk of desorption and reactivation; organic materials can integrate some heavy metals and improve soil fertility, but have limited passivation ability for certain valence states (such as Cr 6+ ), making it difficult to achieve efficient remediation of multiple metal complex pollution. (3) Low biological activity: traditional passivation agents often ignore the remediation of soil microbial ecosystems, and may even inhibit the activity of indigenous microorganisms, leading to degradation of soil ecological functions and difficulty in maintaining remediation effect.

[0004] In the prior art, CN120554657A discloses the activation of humic acid using a mixed acid composed of hydrochloric acid and citric acid. The paper "Research Progress on Activation and Modification of Mineral-Derived Humic Acid" (Sun Bin et al., Fertilizer and Health, June 2023) discloses the activation of humic acid by reacting it with acidic functional groups in humic acid using alkali (sodium hydroxide, potassium hydroxide, ammonia) and by hydrolyzing some fatty chains. CN109534897A discloses a bio-organic fertilizer for adsorbing heavy metals, comprising: animal manure, plant straw, microbial flora, and inorganic heavy metal adsorbent materials, wherein the microbial flora includes Bacillus megaterium, Azotobacter chrysogenum, and Bacillus mucilaginosus. This patent utilizes microbial flora to reduce the content of heavy metal ions in the soil while also improving soil quality and crop growth. However, the patent directly mixes microbial agents with substrate raw materials and ferments them, then mixes the fermentation products with inorganic metal adsorbent materials to make organic fertilizer for adsorbing heavy metals. This does not effectively protect the functional bacteria, resulting in low survival rate and poor colonization ability when facing harsh soil environments under heavy metal stress, thus affecting the immediacy and durability of the remediation effect.

[0005] Therefore, developing a highly efficient soil conditioner with multi-mechanism synergistic passivation capabilities and the ability to promote the restoration of soil microbial ecology has become an urgent need in the field of soil heavy metal pollution remediation. Summary of the Invention

[0006] To address the aforementioned limitations of existing technologies, the present invention aims to provide a soil conditioner based on pH-responsive humic acid-functional bacteria synergistic passivation of heavy metals and its preparation method. A composite microbial agent is prepared by mixing *Bacillus megaterium*, *Bacillus mucilaginosus*, and *Azotobacter chrysogenum*. Humic acid is activated using acid or alkali as an activating agent to obtain pretreated humic acid. The composite microbial agent, pretreated humic acid carrier, porous mineral matrix, and nutrients are used as raw materials to prepare the soil conditioner. The soil conditioner prepared by this invention achieves passivation of multiple heavy metals in the soil over a wider pH range through the synergistic effects of chemical passivation, biomineralization, and physical adsorption, and also improves the soil microecology.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a soil conditioner comprising the following raw materials in parts by weight: Pretreatment: 50-70 parts humic acid, 5-15 parts compound microbial agent, 20-30 parts porous mineral matrix, and 3-8 parts nutrients; The compound microbial agent is a mixture of Bacillus mucilaginosus, Bacillus megaterium and Azotobacter chrysogenum in a mass ratio of (1.5-2.5):(0.5-1.5):(0.5-1.5).

[0008] Preferably, the pretreated humic acid is prepared by the following method: humic acid is mixed with an activator solution and reacted at 60-80℃ for 2-4 hours. After the reaction is completed, the pH is adjusted to neutral and centrifuged. The solid after centrifugation is collected, dried and pulverized to obtain pretreated humic acid.

[0009] Furthermore, the mass ratio of humic acid to the activation solution is 1:(5-10).

[0010] Furthermore, the activator solution is one or more of citric acid solution, oxalic acid solution, and potassium hydroxide solution, and the concentration of the activator solution is 1-3 mol / L.

[0011] As preferred, the accession numbers for Bacillus mucilaginosus are BNCC 335819, Bacillus megaterium is CGMCC 1.6721, and Azotobacter chrysogenum is CGMCC 1.142.

[0012] Preferably, the viable count of Bacillus subtilis in the compound microbial agent is ≥1.8×10⁻⁶. 9 CFU / mL and viable count of Azotobacter brownii ≥ 2.6 × 10⁻⁶ 9 CFU / mL and viable count of Bacillus megaterium ≥ 2.2 × 10⁻⁶ 9 cfu / mL.

[0013] Preferably, the porous mineral matrix is ​​zeolite powder and / or attapulgite.

[0014] Preferably, the nutrients are prepared by mixing urea, calcium dihydrogen phosphate and chicken manure in a mass ratio of (2.5-3.5):(1.5-2.5):(2.5-3.5).

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned soil conditioner, comprising the following steps: After mixing porous mineral matrix and composite microbial agent, the mixture is cultured and then dried to obtain microbial agent-mineral composite. Then, pretreated humic acid, nutrients, and microbial agent-mineral composite are mixed to obtain soil conditioner.

[0016] As a preferred method, the culture temperature is 35-38℃ and the culture time is 6-10h.

[0017] A third aspect of the present invention provides the application of the above-mentioned soil conditioner in the remediation of heavy metal contaminated soil.

[0018] Preferably, the heavy metals include lead ions, cadmium ions, mercury ions, chromium ions, and arsenic ions.

[0019] A fourth aspect of the present invention provides a method for remediating heavy metal contaminated soil, comprising the following steps: Apply the soil conditioner to the soil surface and then till the soil.

[0020] As a preferred method, the application rate of soil conditioner is 50-200 kg / mu; the tillage depth is 15-20 cm.

[0021] As a preferred option, the heavy metal contaminated soil contains Hg at a concentration of 0.005-0.007 mg / kg, As at a concentration of 0.15-0.16 mg / kg, Cd at a concentration of 0.30-0.32 mg / kg, Pb at a concentration of 0.61-0.62 mg / kg, and Cr at a concentration of 0.30-0.31 mg / kg.

[0022] As a preferred method, after tilling, the soil moisture content should be maintained at 60%-70% of field capacity.

[0023] Preferably, soil conditioners are applied 1-4 times per year.

[0024] As a preferred option, the soil pH should be tested before applying the soil conditioner, and the type of activator should be selected based on the soil pH.

[0025] For acidic soils, choose soil conditioners that pretreat humic acid using alkaline activators (potassium hydroxide); for alkaline soils, choose soil conditioners that pretreat humic acid using acidic activators (citric acid, oxalic acid).

[0026] The beneficial effects of this invention are: 1. This invention uses a mixture of Bacillus megaterium, Bacillus mucilaginosus, and Azotobacter chrysogenum to prepare a composite microbial agent. Humic acid is activated using acid or alkali as an activating agent to obtain pretreated humic acid. The composite microbial agent, pretreated humic acid carrier, porous mineral matrix, and nutrients are used as raw materials to prepare a soil conditioner. The soil conditioner prepared by this invention, based on pH-responsive humic acid-functional bacteria synergistic passivation of heavy metals, achieves passivation of multiple heavy metals in the soil over a wider pH range through the synergistic effects of chemical passivation, biomineralization, and physical adsorption, and also improves the soil microecology.

[0027] Specifically, pretreated humic acid can immobilize heavy metal ions (Pb) through complexation, chelation, and ion exchange. 2+ Cd 2+ Compound microbial agents can specifically reduce and fix heavy metal toxicity, and microbial metabolites can also promote the formation of heavy metal precipitates to fix them. In addition, the use of mineral matrices can physically adsorb and fix heavy metal ions.

[0028] 2. Using acid / alkali as activators to pretreat humic acid not only activates the functional groups in humic acid, giving it excellent pH buffering capacity, but also allows it to be used as a component of soil conditioners. Applying it to the soil can regulate soil pH, overcoming the dependence of traditional soil conditioners on the initial soil pH, thus broadening its applicability.

[0029] 3. This invention employs an "in-situ adsorption culture method," pre-loading the composite microbial agent into a porous mineral matrix. This provides a physical protective barrier for the microbial agent, significantly improving its survival rate, colonization ability, and functional durability after application to heavy metal stress environments. Furthermore, the composite microbial agent used in this invention not only repairs the soil but also enhances soil fertility and promotes plant growth, forming a virtuous cycle of "repair-fertilization-growth promotion." Detailed Implementation

[0030] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0031] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0032] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0033] In this invention, the Bacillus mucilaginosus, with accession number BNCC 335819, was purchased from Beijing Beina Chuanglian Biotechnology Co., Ltd.; the Azotobacter chrysogenum, with accession number CGMCC 1.142 and the Bacillus megaterium, with accession number CGMCC 1.6721, were both purchased from the China General Microbiological Culture Collection Center.

[0034] Example 1: 1. Composition: In this embodiment, the soil conditioner is prepared from pretreated humic acid, compound microbial inoculant, porous mineral matrix, and nutrients in a mass ratio of 60:10:25:5. The preparation method of humic acid is as follows: humic acid and citric acid solution with a concentration of 2 mol / L are mixed at a mass ratio of 1:8 and reacted at 70℃ for 3 hours. After the reaction is completed, the pH is adjusted to neutral, centrifuged, the solid after centrifugation is collected, dried and pulverized to obtain pretreated humic acid. The compound microbial agent is prepared by mixing Bacillus mucilaginosus, Bacillus megaterium, and Azotobacter chrysogenum in a mass ratio of 2:1:1, with the viable count of Bacillus mucilaginosus in the compound microbial agent adjusted to 1.8 × 10⁻⁶. 9 The cfu / mL concentration and the viable count of Azotobacter brownii were 2.6 × 10⁻⁶. 9 The cfu / mL concentration and viable count of Bacillus megaterium were 2.2 × 10⁻⁶. 9 cfu / mL; The porous mineral matrix is ​​zeolite powder; the nutrients are prepared by mixing urea, calcium dihydrogen phosphate and chicken manure in a mass ratio of 3:2:3.

[0035] 2. Preparation method: After mixing porous mineral matrix and composite microbial agent, fermentation was carried out at 37℃ for 8 hours. After cultivation, the microbial agent-mineral complex was obtained by low-temperature drying. Then, pretreated humic acid, nutrients and microbial agent-mineral complex were mixed in proportion to obtain soil conditioner.

[0036] Example 2: 1. Composition: In this embodiment, the soil conditioner is prepared from pretreated humic acid, compound microbial inoculant, porous mineral matrix, and nutrients in a mass ratio of 60:10:25:5. The preparation method of humic acid is as follows: humic acid and potassium hydroxide solution with a concentration of 2 mol / L are mixed at a mass ratio of 1:8 and reacted at 70℃ for 3 hours. After the reaction is completed, the pH is adjusted to neutral, centrifuged, the solid after centrifugation is collected, dried and pulverized to obtain pretreated humic acid. The compound microbial agent is prepared by mixing Bacillus mucilaginosus, Bacillus megaterium, and Azotobacter chrysogenum in a mass ratio of 2:1:1. The viable count of Bacillus mucilaginosus in the compound microbial agent is adjusted to 1.8 × 10⁻⁶. 9 The cfu / mL concentration and the viable count of Azotobacter brownii were 2.6 × 10⁻⁶. 9 The cfu / mL concentration and viable count of Bacillus megaterium were 2.2 × 10⁻⁶. 9 cfu / mL; The porous mineral matrix is ​​zeolite powder; the nutrients are prepared by mixing urea, calcium dihydrogen phosphate and chicken manure in a mass ratio of 3:2:3.

[0037] 2. Preparation method: After mixing porous mineral matrix and composite microbial agent, fermentation was carried out at 37℃ for 8 hours. After cultivation, the microbial agent-mineral complex was obtained by low-temperature drying. Then, pretreated humic acid, nutrients and microbial agent-mineral complex were mixed in proportion to obtain soil conditioner.

[0038] Example 3: 1. Composition: In this embodiment, the soil conditioner is prepared from pretreated humic acid, compound microbial inoculant, porous mineral matrix, and nutrients in a mass ratio of 50:5:20:3. The preparation method of humic acid is as follows: humic acid and oxalic acid solution with a concentration of 1 mol / L are mixed at a mass ratio of 1:5 and reacted at 60℃ for 2 hours. After the reaction is completed, the pH is adjusted to neutral, centrifuged, the solid after centrifugation is collected, dried and pulverized to obtain pretreated humic acid. The compound microbial agent is prepared by mixing Bacillus mucilaginosus, Bacillus megaterium, and Azotobacter chrysogenum in a mass ratio of 1.5:0.5:0.5. The viable count of Bacillus mucilaginosus in the compound microbial agent is adjusted to 1.8 × 10⁻⁶. 9 The cfu / mL concentration and the viable count of Azotobacter brownii were 2.6 × 10⁻⁶. 9 The cfu / mL concentration and viable count of Bacillus megaterium were 2.2 × 10⁻⁶. 9 cfu / mL; The porous mineral matrix is ​​zeolite powder; the nutrients are prepared by mixing urea, calcium dihydrogen phosphate and chicken manure in a mass ratio of 2.5:1.5:2.5.

[0039] 2. Preparation method: After mixing porous mineral matrix and composite microbial agent, fermentation was carried out at 35℃ for 6 hours. After cultivation, the microbial agent-mineral complex was obtained by low-temperature drying. Then, pretreated humic acid, nutrients and microbial agent-mineral complex were mixed in proportion to obtain soil conditioner.

[0040] Example 4: 1. Composition: In this embodiment, the soil conditioner is prepared from pretreated humic acid, compound microbial inoculant, porous mineral matrix, and nutrients in a mass ratio of 70:15:30:8. The preparation method of humic acid is as follows: humic acid and potassium hydroxide solution with a concentration of 2 mol / L are mixed at a mass ratio of 1:10 and reacted at 80℃ for 4 hours. After the reaction is completed, the pH is adjusted to neutral, centrifuged, the solid after centrifugation is collected, dried and pulverized to obtain pretreated humic acid. The compound microbial agent is prepared by mixing Bacillus mucilaginosus, Bacillus megaterium, and Azotobacter chrysogenum in a mass ratio of 2.5:1.5:1.5. The viable count of Bacillus mucilaginosus in the compound microbial agent is adjusted to 1.8 × 10⁻⁶. 9 The cfu / mL concentration and the viable count of Azotobacter brownii were 2.6 × 10⁻⁶. 9 The cfu / mL concentration and viable count of Bacillus megaterium were 2.2 × 10⁻⁶. 9 cfu / mL; The porous mineral matrix is ​​zeolite powder; the nutrients are prepared by mixing urea, calcium dihydrogen phosphate and chicken manure in a mass ratio of 3.5:2.5:3.5.

[0041] 2. Preparation method: After mixing porous mineral matrix and composite microbial agent, fermentation was carried out at 38℃ for 10 hours. After cultivation, the mixture was dried at low temperature to obtain microbial agent-mineral complex. Then, pretreated humic acid, nutrients and microbial agent-mineral complex were mixed in proportion to obtain soil conditioner.

[0042] Comparative Example 1: The soil conditioner in this comparative example was prepared by mixing pretreated humic acid and nutrients in a mass ratio of 60:5. The pretreated humic acid and nutrients were the same as in Example 2.

[0043] The preparation method is as follows: pretreated humic acid and humic acid are mixed evenly to obtain a soil conditioner.

[0044] Comparative Example 2: The soil conditioner in this comparative example was prepared from a compound microbial inoculant, a porous mineral matrix, and nutrients in a mass ratio of 10:25:5. The compound microbial inoculant, porous mineral matrix, and nutrients were the same as in Example 2.

[0045] Its preparation method is as follows: After mixing porous mineral matrix and composite microbial agent, fermentation was carried out at 37℃ for 8 hours. After cultivation, the mixture was dried at low temperature to obtain microbial agent-mineral complex. Then, nutrients and microbial agent-mineral complex were mixed in proportion to obtain soil conditioner.

[0046] Experimental Example 1: The components of the soil conditioner prepared in Example 1 were analyzed, and the specific analysis method was as follows: Moisture content was determined according to GB / T 8576-2010 "Determination of Free Water Content in Compound Fertilizers - Vacuum Drying Oven Method"; pH was tested according to NY / T 1973-2021 "Determination of Water-Insoluble Matter Content and pH of Water-Soluble Fertilizers"; Humic acid was determined according to GB / T 11957-2001 "Method for Determination of Humic Acid Yield in Coal"; The total viable count was determined according to GB 20287-2006 "Agricultural Microbial Inoculants"; The heavy metal content was determined according to GB / T 23964-2009 "Determination of Heavy Metal Elements in Soil Conditioners"; Porosity was determined according to GB / T 21650.2-2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Method"; The activated humic acid content was determined according to HG / T 5046-2016 "Humic Acid Compound Fertilizer"; Calcium, magnesium and silicon content were tested according to NY / T 2272-2012 "Determination of calcium, magnesium and silicon content in soil conditioners"; The test results are shown in Table 1.

[0047] Table 1. Composition and content of soil conditioners As shown in Table 1, the soil conditioner prepared by this invention has a high number of viable bacteria, abundant humic acid content, excellent physical structure, and is rich in various mineral nutrients. The composition and content of its core functional components provide a solid material basis for its synergistic remediation of heavy metal-contaminated soil through physical adsorption, chemical passivation, and biomineralization. At the same time, the product itself is safe and will not introduce new pollution risks.

[0048] Experiment Example 2: Pot Experiment (1) Collect soil samples from farmland at a depth of 0-20 cm without heavy metal contamination. Add CdCl2·5H2O and Pb(NO3)2 solution to the soil and allow it to age and stabilize for 30 days to construct heavy metal contaminated soil. In heavy metal contaminated soil, Cd... 2+ The concentration was 2.2 mg / kg, Pb 2+ The concentration is 520 mg / kg.

[0049] The pH of the heavy metal contaminated soil prepared above was adjusted to 5.0 and 8.0 by adding 5% sulfuric acid solution and 0.15% calcium hydroxide solution, respectively. After stabilizing for 7 days, acidic heavy metal contaminated soil and alkaline heavy metal contaminated soil were obtained.

[0050] (2) Acidic heavy metal contaminated soil: This experiment consisted of 3 treatment groups, with 3 replicates in each treatment group, as detailed below: Acidic control group: No soil conditioner applied; Acid treatment 1: Apply the soil conditioner prepared in Example 2; Acid treatment 2: Apply silicon-calcium-potassium-magnesium alkaline soil conditioner, purchased from Shandong Agricultural University Fertilizer Technology Co., Ltd. The amount of soil conditioner added to each treatment group was 30g / 2kg of soil; (3) Alkaline heavy metal contaminated soil: This experiment consisted of 3 treatment groups, with 3 replicates in each treatment group, as detailed below: Alkaline control group: No soil conditioner was applied; Alkaline treatment 1: Apply the soil conditioner prepared in Example 1; Alkaline treatment 2: Apply silicon-calcium-potassium-magnesium acidic soil conditioner, purchased from Shandong Agricultural University Fertilizer Technology Co., Ltd. The amount of soil conditioner added to each treatment group was 30g / 2kg of soil; (4) “Shanghai green” was used as the test plant. Pots with an upper diameter of 20cm and a height of 15cm were selected. Each pot contained 2.0kg of acidic heavy metal contaminated soil / alkaline heavy metal contaminated soil. Soil conditioner was added to the acidic heavy metal contaminated soil / alkaline heavy metal contaminated soil and mixed well before sowing. After emergence, thinning was carried out. Three seedlings with uniform growth were retained in each pot. The soil moisture content was kept at 60%-70% of the field water holding capacity. After 60 days of cultivation, the aboveground parts were harvested at ground level. Soil physicochemical properties, heavy metal content and plant quality indicators were measured. The results are shown in Table 2.

[0051] The detection methods are as follows: soil bulk density is determined according to NY / T 1121.4-2006 "Soil Testing Part 4: Determination of Soil Bulk Density"; soil organic matter is determined according to NY / T 1121.6-2006 "Soil Testing Part 6: Determination of Soil Organic Matter"; soil pH is determined according to NY / T 1377-2007 "Determination of Soil pH"; soil cation exchange capacity is determined according to NY / T 1121.5-2006 "Soil Testing Part 5: Determination of Cation Exchange Capacity in Calcareous Soils"; vitamin C content in Chinese cabbage is determined according to GB / T 6195-1986 "Determination of Vitamin C Content in Fruits and Vegetables"; and soil Pb and Cd contents are determined according to DB65 / T 3974-2017 "Determination of Heavy Metal Elements in Soil by Inductively Coupled Plasma Mass Spectrometry".

[0052] Table 2 Physicochemical properties of acidic heavy metal contaminated soil / alkaline heavy metal contaminated soil As shown in Table 2, compared with the control group, the soil conditioner prepared in this invention can significantly reduce the heavy metal content in the soil, improve the physical and chemical properties of the soil, and improve the quality of Chinese cabbage.

[0053] Experimental Example 3: Field Experiment A field experiment was conducted at the taro planting base in Hetian Town, Changting County, Fujian Province, using gray-yellow clay soil.

[0054] The physicochemical properties, types, and contents of heavy metals in the soil were tested. The results showed that organic matter was 53.6 g / kg, hydrolyzable nitrogen was 147 mg / kg, available phosphorus was 78.1 mg / kg, available potassium was 175.4 mg / kg, and the pH was 5.21. The contents of toxic and harmful heavy metals were as follows: available Hg 0.006 mg / kg, available As 0.156 mg / kg, available Cd 0.31 mg / kg, available Pb 0.614 mg / kg, and available Cr 0.304 mg / kg.

[0055] This experiment consisted of four treatment groups: Control group: Conventional fertilization treatment + application of nutrients as soil conditioner, wherein the preparation method of the nutrients is the same as in Example 2; Treatment 1: Conventional fertilization + application of the soil conditioner prepared in Example 2; Treatment 2: Conventional fertilization + application of the soil conditioner prepared in Comparative Example 1; Treatment 3: Conventional fertilization + application of the soil conditioner prepared in Comparative Example 2; The plant variety tested was: Tufang taro.

[0056] The specific experimental steps are as follows: On March 4, 2024, soil conditioner was applied during land preparation at a rate of 1500 kg / hm². 2 After thoroughly mixing the soil conditioner with the topsoil, the seedbeds were prepared and planted with taro seedlings. On October 30, 2024, samples of taro and topsoil were collected from each plot, followed by harvesting and yield measurement. Each experimental plot covered an area of ​​20 m². 2 Each treatment was repeated three times, and each experimental plot was randomly arranged into blocks.

[0057] The contents of Pb, Cd, Hg, Cr and As in the soil were determined according to DB65 / T 3974-2017 "Determination of Heavy Metal Elements in Soil by Inductively Coupled Plasma Mass Spectrometry". The results are shown in Table 3.

[0058] The physicochemical properties, types, and contents of heavy metals in the soil were tested. The results showed that organic matter was 53.6 g / kg, hydrolyzable nitrogen was 147 mg / kg, available phosphorus was 78.1 mg / kg, available potassium was 175.4 mg / kg, and the pH was 5.21. The contents of toxic and harmful heavy metals were Hg 0.006 mg / kg, As 0.156 mg / kg, Cd 0.31 mg / kg, Pb 0.614 mg / kg, and Cr 0.304 mg / kg.

[0059] Table 3. Heavy metal content and taro yield in soils of different treatment groups As shown in Table 3, the application of the soil conditioner prepared according to this invention significantly increased the yield of Areca nut taro and reduced the heavy metal content in the soil. Furthermore, the reduction in heavy metal content was significantly higher than that of the soil conditioners prepared in Comparative Examples 1 and 2. Specifically, compared to the control group, the soil Pb content decreased by 0.386 mg / kg, Cd content decreased by 0.07 mg / kg, Hg content decreased by 0.003 mg / kg, Cr content decreased by 0.087 mg / kg, and As content decreased by 0.103 mg / kg.

[0060] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A soil conditioner, characterized in that, The ingredients include the following parts by weight: Pretreatment: 50-70 parts humic acid, 5-15 parts compound microbial agent, 20-30 parts porous mineral matrix, and 3-8 parts nutrients; The compound microbial agent is a mixture of Bacillus mucilaginosus, Bacillus megaterium and Azotobacter chrysogenum in a mass ratio of (1.5-2.5):(0.5-1.5):(0.5-1.5).

2. The soil conditioner as described in claim 1, characterized in that, The pretreated humic acid is prepared by the following method: After mixing humic acid with an activator solution, the mixture is placed at 60-80℃ for 2-4 hours. After the reaction is complete, the pH is adjusted to neutral and the mixture is centrifuged. The solid after centrifugation is collected, dried, and pulverized to obtain pretreated humic acid.

3. The soil conditioner as described in claim 2, characterized in that, The mass ratio of humic acid to activating solution is 1:(5-10); the activator solution is one or more of citric acid solution, oxalic acid solution, and potassium hydroxide solution, and the concentration of the activator solution is 1-3 mol / L.

4. The soil conditioner as described in claim 1, characterized in that, The accession number for Bacillus mucilaginosus is BNCC335819, the accession number for Bacillus megaterium is CGMCC 1.6721, and the accession number for Azotobacter chrysogenum is CGMCC1.

142. In compound microbial agents, the viable count of Bacillus mucilaginosus is ≥1.8×10⁻⁶. 9 CFU / mL and viable count of Azotobacter brownii ≥ 2.6 × 10⁻⁶ 9 CFU / mL and viable count of Bacillus megaterium ≥ 2.2 × 10⁻⁶ 9 cfu / mL.

5. The soil conditioner as described in claim 1, characterized in that, The porous mineral matrix is ​​zeolite powder and / or attapulgite; the nutrients are made by mixing urea, calcium dihydrogen phosphate and chicken manure in a mass ratio of (2.5-3.5):(1.5-2.5):(2.5-3.5).

6. The method for preparing the soil conditioner according to any one of claims 1-5, characterized in that, Includes the following steps: After mixing porous mineral matrix and composite microbial agent, the mixture is cultured at 35-38℃ for 6-10 hours and then dried to obtain microbial agent-mineral complex. Then, pretreated humic acid, nutrients and microbial agent-mineral complex are mixed to obtain soil conditioner.

7. The application of the soil conditioner as described in any one of claims 1-5 in the remediation of heavy metal contaminated soil.

8. A method for remediating heavy metal-contaminated soil, characterized in that, Includes the following steps: The soil conditioner according to any one of claims 1-5 is applied to the surface of heavy metal contaminated soil and then tilled. The application rate of soil conditioner is 50-200 kg / mu; the tillage depth is 15-20 cm.

9. The method for remediating heavy metal contaminated soil as described in claim 8, characterized in that, After tillage, ensure the soil moisture content is 60%-70% of field capacity, and apply soil conditioner 1-4 times per year.

10. The method for remediating heavy metal contaminated soil as described in claim 8, characterized in that, In soil contaminated with heavy metals, the content of Hg is 0.005-0.007 mg / kg, the content of As is 0.15-0.16 mg / kg, the content of Cd is 0.30-0.32 mg / kg, the content of Pb is 0.61-0.62 mg / kg, and the content of Cr is 0.30-0.31 mg / kg.

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