Long-acting acid-removing conditioner for acidified soil based on aerobic iron reduction and application thereof

Abstract

The application relates to the technical field of soil improvement, and discloses an acidified soil long-acting acid-removing conditioner based on aerobic iron reduction and application thereof. The soil conditioner is alkaline woody peat loaded with aerobic iron reduction microorganisms. The alkaline woody peat has multiple functions of rapidly neutralizing acidity, providing an electron shuttle and a microbial carrier, avoids the problems of short-acting acid return and hardening of traditional lime improvers, provides a stable metabolic environment for aerobic iron reduction microorganisms, and significantly improves the iron reduction activity of the aerobic iron reduction microorganisms in a dry land aerobic condition; the soil conditioner continuously drives Fe(III) reduction to consume protons, realizes long-acting and stable improvement of soil pH, simultaneously promotes the generation of active iron minerals, strengthens the interface holding effect on heavy metals such as Cd, Pb, As, Cr and Hg, and significantly improves the environmental risk threshold of the soil to multiple metals.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology, and in particular to a long-lasting deacidification and conditioning agent for acidified soil based on aerobic iron reduction and its application. Background Technology

[0002] Soil acidification in dryland areas is a prominent farmland quality problem in agricultural regions of southern my country. Long-term excessive application of nitrogen fertilizer and acid deposition have accelerated soil acidification, while the biogeochemical oxidation processes of iron and sulfur in the soil are the key drivers of the continuous decline in pH. In the aerobic environment of dryland, divalent sulfur in iron-sulfur minerals is oxidized to sulfate, and Fe(II) is oxidized to Fe(III). Both processes continuously release protons, leading to the continuous accumulation of soil acidity. Therefore, how to consume protons at the source and inhibit the iron-sulfur oxidation cycle is crucial for achieving long-term deacidification of dryland soils.

[0003] From the perspective of reaction mechanism, Fe(III) reduction is an effective pathway for consuming protons and increasing pH. Furthermore, pH increase can enhance the interfacial binding between polymetals and iron oxide, raising the soil heavy metal risk threshold (the critical content of a certain heavy metal in the soil; below this value, the risks of heavy metal leaching and plant absorption are acceptable; above this value, the risks increase significantly). Theoretically, this can achieve the dual goals of acid removal and risk management. However, under aerobic conditions in dryland, oxygen, as a strong electron acceptor, preferentially captures metabolic electrons from microorganisms, severely inhibiting electron transfer to Fe(III). This significantly limits the microbial iron reduction process, making it difficult to effectively consume protons.

[0004] Existing technologies mainly remove acid by adding traditional chemical neutralizers such as lime or organic materials such as straw. While traditional chemical neutralizers such as lime can quickly raise soil pH, their acid removal effect is short-lived. After the alkaline substances are consumed, the soil is prone to acidification and can also cause soil compaction and nutrient imbalance, failing to achieve long-term acid buffering and regulation. Ordinary organic materials such as straw and peat have weak acid removal capabilities. Even when alkaline woody peat is applied alone, its effect on regulating the form of iron oxide in the soil and raising the risk threshold of multiple metals is limited, and it lacks a synergistic effect mechanism with functional microorganisms.

[0005] Existing research indicates that while some functional microorganisms possess a certain capacity for aerobic iron reduction, their electron transfer efficiency is low, and their individual application has a limited effect on pH improvement, failing to achieve long-term deacidification. Furthermore, most existing microbial iron reduction technologies are only applicable to anaerobic or flooded environments. Under aerobic conditions in drylands, oxygen strongly inhibits microbial iron reduction activity, making it difficult to effectively drive iron oxide conversion and heavy metal fixation. In addition, most existing technologies only target single heavy metal passivation or short-term soil pH increases, lacking technical solutions that can simultaneously achieve long-term soil deacidification and a systematic improvement of multi-metal environmental risk thresholds under aerobic conditions in drylands, thus failing to meet the sustainable improvement needs of acidified dryland soils. Summary of the Invention

[0006] The present invention aims to at least solve one of the aforementioned technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a soil conditioner.

[0007] The second objective of this invention is to provide a method for preparing such a soil conditioner.

[0008] The third objective of this invention is to provide the application of this soil conditioner.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A first aspect of the present invention provides a soil conditioner, wherein the soil conditioner is alkaline woody peat loaded with oxy-iron-reducing microorganisms.

[0010] In some embodiments of the present invention, the mass ratio of the aerobic iron-reducing microorganisms to the alkaline woody peat is 1:(10-100) on a dry weight basis.

[0011] In some preferred embodiments of the present invention, the mass ratio of the aerobic iron-reducing microorganisms to the alkaline woody peat is 1:(40-60) on a dry weight basis.

[0012] In some embodiments of the present invention, the aerobic iron-reducing microorganism is selected from Bacillus megaterium (Betagenus 1, 1 oz.). Bacillus megaterium Bacillus subtilis ( Bacillus subtilis ), Bacillus licheniformis ( Bacillus licheniformis Colorado pseudomycolic acid bacteria ( Amycolatopsis albidoflavus ), Streptomyces griseus ( Streptomyces griseus ), Enterococcus montelukast ( Enterococcus mundti At least one of the following.

[0013] Specifically, the present invention described Bacillus subtilis and Bacillus licheniformis Both were purchased from the American Type Culture Collection (ATCC) Biological Standards Resource Center, with catalog numbers ATCC 6051 and ATCC12759, respectively; Bacillus megaterium , Amycolatopsis albidoflavus , Streptomyces griseus and Enterococcus mundti All samples were purchased from the Guangdong Provincial Center for Microbial Culture Collection, with accession numbers GDMCC 1.183, GDMCC 4.102, GDMCC 4.19, and GDMCC 1.981, respectively.

[0014] In some embodiments of the present invention, the physicochemical parameters of the alkaline woody peat include at least one of the following: pH value of 7.5-9.0; organic matter content ≥50wt%; free humic acid content ≥20wt%; moisture content ≤20wt%; and particle size of 0.5-5mm.

[0015] In some preferred embodiments of the present invention, the pH value of the alkaline woody peat is 8.0-9.0.

[0016] In some preferred embodiments of the present invention, the organic matter content of the alkaline woody peat is 80wt%-90wt%.

[0017] In some preferred embodiments of the present invention, the alkaline woody peat has a humic acid content of 20wt%-30wt%.

[0018] In some preferred embodiments of the present invention, the alkaline woody peat has a moisture content of 10wt%-20wt%.

[0019] In some preferred embodiments of the present invention, the alkaline woody peat has a particle size of 0.5-3 mm.

[0020] In some preferred embodiments of the present invention, the physicochemical parameters of the alkaline woody peat further include at least one of the following: K2O content of 4wt%-6wt%; As content of 0.8-1.2mg / kg; Pb content of <15mg / kg; Cd content of <0.02mg / kg; Cr content of 3.5-5mg / kg; and Hg content of 0.05-0.09mg / kg.

[0021] A second aspect of the present invention provides a method for preparing the soil conditioner described in the first aspect of the present invention, comprising the following steps: The soil conditioner is obtained by mixing aerobic iron-reducing microorganisms with alkaline woody peat.

[0022] In some embodiments of the present invention, the aerobic iron-reducing microorganisms are mixed with alkaline woody peat in the form of a bacterial solution, the bacterial solution being obtained by a method comprising the following steps: Aerobic iron-reducing microbial strains were inoculated into the culture medium and cultured at a constant temperature with shaking until the logarithmic growth phase to obtain the bacterial solution.

[0023] In some embodiments of the present invention, the concentration of the bacterial solution is 1×10⁻⁶. 7 -1×10 8 CFU / mL.

[0024] In some embodiments of the present invention, the culture medium includes LB medium, which has the following composition: 8-12 g / L peptone, 4-6 g / L yeast extract, and 8-12 g / L sodium chloride.

[0025] In some embodiments of the present invention, the pH of the culture medium is 7.0 ± 0.2.

[0026] In some embodiments of the present invention, the parameters of the isothermal oscillation culture include: temperature of 25-30℃, oscillation speed of 120-180rpm, and culture time of 18-30h.

[0027] In some embodiments of the present invention, the aerobic iron-reducing microorganisms are mixed with alkaline woody peat in the form of bacterial liquid. After the mixing is completed, the mixture is dried at 35-45°C until the moisture content is ≤20wt%.

[0028] In some embodiments of the present invention, the aerobic iron-reducing microbial powder is mixed with alkaline woody peat, the powder being obtained by a method comprising the following steps: Aerobic iron-reducing microbial strains were inoculated into the culture medium, cultured at a constant temperature with shaking until the logarithmic growth phase, and the bacterial solution was obtained. The bacterial cells were collected by centrifugation, freeze-dried, and the bacterial powder was obtained.

[0029] In some embodiments of the present invention, the bacterial solution is obtained in the same way as above, and the aerobic iron-reducing microorganisms are directly mixed with alkaline woody peat in the form of bacterial powder to obtain the soil conditioner.

[0030] The third aspect of the present invention provides the application of the soil conditioner described in the first aspect of the present invention in soil improvement.

[0031] In some embodiments of the present invention, the soil includes dryland soil, and the physicochemical parameters of the dryland soil include at least one of the following: water content of 50%-70% field holding capacity; pH ​​value < 5.0.

[0032] In some preferred embodiments of the present invention, the physicochemical parameters of the dryland soil further include: organic matter content of 10-15 g / kg; and cation exchange capacity of 6-10 cmol / kg.

[0033] In some embodiments of the present invention, the soil improvement includes at least one of the following: a. Increase soil pH; b. Reduce the content of available heavy metals in the soil; c. Increase the organic carbon content of the soil.

[0034] In some embodiments of the present invention, the heavy metal includes at least one of Cd, Pb, As, Cr, and Hg.

[0035] In some embodiments of the present invention, the soil conditioner is applied at a rate of 0.5%-5% of the soil mass.

[0036] In some preferred embodiments of the present invention, the soil conditioner is applied at an amount of 1%-3% of the soil mass.

[0037] The basic principles of this invention are explained as follows: The soil conditioner provided by this invention uses alkaline woody peat loaded with aerobic iron-reducing microorganisms. The loose and porous structure of the alkaline woody peat provides micro-anaerobic sites and a nutrient substrate for the aerobic iron-reducing bacteria, significantly improving the survival rate and metabolic activity of the microorganisms in the complex environment of dry land. In addition, the alkaline woody peat (pH=7.5-9.0) is rich in alkaline functional groups and mineral components, and can quickly neutralize free H+ after being applied to acidified soil. + It can rapidly increase soil pH; at the same time, the humic acid and other organic matter it contains can build a natural acid-base buffer system, avoiding the short-term pH increase and rapid acidification problem of chemical neutralizers such as lime, and providing a stable pH environment for subsequent microbial activities; alkaline woody peat is also rich in redox active groups such as quinone groups and phenolic hydroxyl groups, which can act as natural electron shuttles, greatly enhancing the extracellular electron transfer efficiency between aerobic iron-reducing microorganisms and soil iron oxide. This solves the core bottleneck that oxygen preferentially captures electrons and the microbial iron reduction process is severely inhibited under aerobic conditions in dry land, allowing the Fe(III) reduction process to proceed efficiently in a non-flooded and well-aerated environment; Aerobic iron-reducing bacteria use soil Fe(III) as an electron acceptor to reduce Fe(III) to Fe(II) via dissimilatory iron reduction. This process continuously consumes H+ in the soil. + This achieves a continuous pH increase, unlike the one-time neutralization of chemical neutralizers. The biologically driven process can continue, fundamentally blocking the inherent feedback loop of soil acidification (iron / sulfur oxidation to produce acid), achieving long-term acid control and inhibiting acid reversion. During the microbial iron reduction process, amorphous iron oxides are reduced to more active secondary iron minerals (such as amorphous iron hydroxide, green rust, etc.). These minerals have a larger specific surface area and stronger adsorption / co-precipitation capacity, which can significantly enhance the interfacial binding capacity for heavy metals such as Cd, Pb, As, Cr, and Hg, reduce the bioavailability and mobility of heavy metals, and increase the risk threshold of heavy metals in the soil.

[0038] Compared with the prior art, the beneficial effects of the present invention are: 1) The soil conditioner provided by this invention, alkaline woody peat, has multiple functions, including rapid acid neutralization, providing electron shuttles and microbial carriers. It avoids the short-term acidification and compaction problems of traditional lime amendments, and provides a stable metabolic environment for aerobic iron-reducing microorganisms, significantly improving their iron reduction activity under aerobic conditions in dry land. This soil conditioner continuously drives Fe(III) reduction to consume protons, achieving a long-term stable increase in soil pH. At the same time, it promotes the formation of active iron minerals, strengthens the interfacial fixation of heavy metals such as Cd, Pb, As, Cr, and Hg, and significantly improves the environmental risk threshold of soil for multiple metals. 2) The method for preparing the soil conditioner provided by this invention is simple, low-cost, environmentally friendly, and suitable for industrial use; 3) The soil conditioner provided by this invention, when applied to acidified dryland soil, effectively increases the soil organic carbon content and enhances the soil's acid-base buffering capacity and structural stability. Attached Figure Description

[0039] Figure 1 The image shows the FTIR spectrum of the alkaline woody peat in Example 1. Figure 2 Here is a SEM image of the soil conditioner in Example 1; Figure 3 The graph shows the changes in Fe(II) content in different groups of Experiment Example 1; Figure 4 The curves showing the change in pH of different groups of dryland soil with incubation time are shown in Example 1. Figure 5 The soil organic carbon content after 60 days of reaction for different groups in Example 1; Figure 6 The interfacial binding energy between soil particles and heavy metal ions after 60 days of reaction in control group 1 and experimental group 1 of Example 1; Figure 7 The risk thresholds for soil Cd(a), As(b), Pb(c), and Hg(d) after 60 days of reaction for different groups in Example 1 were used. Detailed Implementation

[0040] The present invention will be further described in detail below through specific embodiments. Unless otherwise specified, the raw materials, reagents, or apparatus used in the embodiments can be obtained from conventional commercial sources or by existing technical methods. Unless otherwise specified, the experimental or testing methods are conventional methods in the art.

[0041] Note: The bacterial strain used in the following examples is Bacillus megaterium (Betaminaria). Bacillus megaterium The sample was purchased from the Guangdong Provincial Center for Microbial Culture Collection, with accession number GDMCC 1.183.

[0042] Example 1 This embodiment prepares a soil conditioner, and the steps are as follows: Bacillus megaterium was inoculated into LB medium and cultured at 30°C in a constant temperature shaking incubator at a shaking speed of 150 rpm for 24 hours to allow the bacteria to grow to the logarithmic growth phase, obtaining a bacterial suspension with a concentration of approximately 1 × 10⁻⁶. 8 CFU / mL; wherein, the composition of LB medium is: peptone 10g / L, yeast extract 5g / L, sodium chloride 10g / L, pH=7.0±0.2; Alkaline woody peat with pH=8.2 was selected, naturally air-dried, crushed and sieved, and the particle size was controlled within the range of 0.5-2mm. Its physicochemical parameters are shown in Table 1. The bacterial culture was centrifuged to collect the bacterial cells, which were then freeze-dried to obtain bacterial powder. The bacterial powder was mixed with alkaline woody peat at a dry weight ratio of 1:50 and stirred thoroughly to obtain a soil conditioner, which was then sealed and stored for later use.

[0043] Table 1 Physicochemical parameters of alkaline woody peat in Example 1

[0044] The test methods / reference standards for each test item are as follows: 1. Total organic matter: The determination was carried out in accordance with HJ 761-2015 "Determination of organic matter in solid waste by loss on ignition method". The sample was ignited at 550-600℃ to constant weight and the loss on ignition was calculated. 2. Free humic acid content: The content of free humic acid from mineral sources was determined by the sodium pyrophosphate-sodium hydroxide alkaline extraction method, referring to GB / T 35106-2017 "Determination of free humic acid content from mineral sources". 3. Moisture (H2O): The determination was performed according to ASTM D2974-25e1, "Standard Test Method for Determination of Moisture (Humidity), Ash Content and Organic Matter Content in Peat and Other Organic Soils", using the constant weight method at 105℃ (normal pressure drying method). 4. pH: pH was determined according to DIN EN ISO 10390: 2022-08 "Soil, treated biological waste and sludge - Determination of pH", using the water extraction potentiometric method, with a mass ratio of alkaline woody peat to water of 1:2.5. 5. K content (K2O): Referring to PD CEN / TS 17770: 2022 "Determination of total content of specific elements by ICP-AES after digestion of organic and organic mineral fertilizers with aqua regia", ICP-OES (inductively coupled plasma optical emission spectrometry) was used to determine potassium content after digestion and convert it to K2O for determination. 6. As content: The content of mercury, arsenic, cadmium, lead, chromium and nickel in fertilizers was determined by hydride generation-atomic fluorescence spectrometry (HG-AFS) in accordance with NY / T 1978-2022 "Determination of mercury, arsenic, cadmium, lead, chromium and nickel content". 7. Pb content: According to NY / T 1978-2022 "Determination of mercury, arsenic, cadmium, lead, chromium and nickel content in fertilizers", the sample was digested by microwave and then determined by graphite furnace atomic absorption spectrometry. 8. Cd content: According to NY / T 1978-2022 "Determination of mercury, arsenic, cadmium, lead, chromium and nickel content in fertilizers", the sample was digested by microwave and then measured by graphite furnace atomic absorption spectrometry (wavelength 228.8nm). 9. Cr content: According to NY / T 1978-2022 "Determination of Mercury, Arsenic, Cadmium, Lead, Chromium and Nickel Content in Fertilizers", the sample was digested by microwave and then measured by atomic absorption spectrophotometer (wavelength 357.9nm). 10. Hg content: Refer to NY / T 1978-2022 "Determination of mercury, arsenic, cadmium, lead, chromium and nickel content in fertilizers", cold atomic absorption spectrometry (CVAAS) is used. After the sample is digested with aqua regia, it is reduced with potassium borohydride to generate mercury vapor for determination.

[0045] Figure 1 The image shown is the FTIR spectrum of the alkaline woody peat in Example 1. Figure 1 It is known that alkaline woody peat contains a large number of oxygen-containing groups, indicating that it contains a large number of redox active sites, possessing the material basis to act as an electron shuttle. This allows it to effectively mediate extracellular electron transfer between microorganisms and iron oxides, providing structural support for enhancing the aerobic iron reduction process. Specifically, approximately 3400 cm³... -1 The broad peak at approximately 2920 cm⁻¹ corresponds to the OH (hydroxyl) stretching vibration, mainly originating from alcohols, phenols, and adsorbed water; -1 and 2850 cm -1 The peak at approximately 1710 cm⁻¹ represents the CH (saturated alkyl) stretching vibration, indicating an aliphatic structure (such as waxes and lipids). -1 The peak at approximately 1630-1600 cm⁻¹ is attributed to the C=O (carboxyl, ketone, aldehyde) stretching vibration. -1 The peak at approximately 1030 cm⁻¹ mainly corresponds to C=C (aromatic skeleton) and some C=O or amide groups; -1 The strong peak at that point represents the stretching vibration of CO (polysaccharides, alcohols, ethers).

[0046] Figure 2 Here is a SEM image of the soil conditioner in Example 1, from... Figure 2 It can be seen that aerobic iron-reducing microorganisms are uniformly loaded, adsorbed and fixed on the surface and inside the pores of alkaline woody peat, forming a stable microbial-peat composite system.

[0047] Experimental Example 1 This experimental example verifies the potential of the soil conditioner in Example 1 to promote iron reduction under aerobic conditions. The steps are as follows: Experimental Group 1: Weigh the solid hydrated iron ore and add deionized water to prepare a mineral suspension with a concentration of 1 g / L. Take 100 mL and place it in a 250 mL Erlenmeyer flask. Add the Bacillus megaterium powder and alkaline woody peat prepared in Example 1 to the mineral suspension. The final concentration of Bacillus megaterium is 1 × 10⁻⁶ g / L. 7 CFU / mL, the final concentration of alkaline woody peat is 2 g / L; Control group 1: Weigh out the solid ferrohydrate, add deionized water to prepare a mineral suspension with a concentration of 1 g / L, and take 100 mL and put it into a 250 mL conical flask; Control Group 2: Weigh out the solid ferrohydrate and add deionized water to prepare a mineral suspension with a concentration of 1 g / L. Take 100 mL of the suspension and place it in a 250 mL Erlenmeyer flask. Add the Bacillus megaterium powder prepared in Example 1 to the mineral suspension. The final concentration of Bacillus megaterium is 1 × 10⁻⁶ g / L. 7 CFU / mL; Glucose was added as an electron donor to experimental group 1, control group 1, and control group 2, with a final concentration of 5 mmol / L. All systems were then sealed with a breathable sealing film to ensure contact with air and maintain an aerobic environment. The systems were placed in a constant-temperature shaking incubator and cultured at 30°C with a shaking speed of 150 rpm for 7 days. Samples were taken every 24 hours to analyze the content of hydrochloric acid-extractable Fe(II), using the following method: Take the sample of the mixture from the conical flask and mix it with 6 mol / L hydrochloric acid at a volume ratio of 1:1. Soak the sample in hydrochloric acid for 2 days until it is completely dissolved, then filter and collect the filtrate. Dilute the filtrate with an acetate-sodium acetate buffer solution at pH 5.0 to ensure that the iron concentration falls within the linear range of 0-20 mg / L of the Fe(II) standard curve. Determine the Fe(II) content using the o-phenanthroline colorimetric method with a sample to colorimetric reagent volume ratio of 4:1. Finally, calculate the original concentration of hydrochloric acid-extracted Fe(II) in the system based on the dilution factor. Figure 3 The graph shows the changes in Fe(II) content in different groups of Experiment Example 1. Figure 3 It can be seen that almost no Fe(II) was generated in control group 1, the Fe(II) concentration in control group 2 was low, and it was less than 10 mg / L after 5 days of reaction. The Fe(II) concentration in experimental group 1 was significantly increased, reaching more than 30 mg / L after 5 days of reaction. This proves that alkaline woody peat can enhance the iron reduction of aerobic iron-reducing microorganisms and greatly enhance the iron reduction efficiency under aerobic conditions.

[0048] Application Example 1 This application example uses the soil conditioner from Example 1 to improve soil conditions. The soil used is a typical acidified dryland soil in southern China, with an initial pH of 4.8, an organic matter content of 12 g / kg, and a cation exchange capacity of 8 cmol / kg. Experimental Group 1: 2 wt% of the soil conditioner from Example 1 was added to acidified dryland soil; Control group 1: No conditioning agents added; Control group 2: 2 wt% lime (calculated as CaO) was added to acidified dryland soil. Control group 3: 2 wt% of alkaline woody peat from Example 1 was added to acidified dryland soil; Control group 4: Add Bacillus megaterium powder from Example 1 to acidified dryland soil to make the bacterial content the same as that of test group 1; Each group was set up with 3 replicates. The soil moisture content was adjusted to 60% of field capacity, and the soil was placed in a constant temperature incubator at 25℃ for 60 days. The soil was turned over every 5 days to ensure aerobic conditions. After the culture was completed, the following tests were performed: (1) Soil pH: According to DIN EN ISO 10390: 2022-08 "Soil, treated biological waste and sludge - Determination of pH", the water extraction potentiometric method was used to determine the pH value at a soil to water mass ratio of 1:2.5. (2) Soil organic carbon content: The determination was carried out by potassium dichromate oxidation method according to HJ 615-2011 "Determination of Soil Organic Carbon by Potassium Dichromate Oxidation-Spectrophotometry".

[0049] (3) Interfacial binding energy between soil particles and heavy metal ions: The interfacial binding energy between soil particles and heavy metal ions was quantitatively determined by atomic force microscopy single-molecule force spectroscopy (AFM-SMFS). Different metals were modified onto the atomic force microscopy probe, and the interfacial binding energy was subsequently determined by kinetic force spectroscopy (Reference: Chi et al., Cadmium Immobilization on Fe Oxyhydroxides Enhanced by DOM Using Single-Molecule Determinations. Environ. Sci. Technol. 2025, 59, 7, 3771-3779). (4) Calculate the heavy metal risk threshold: ; ; ; ; ; In the formula, OC represents the organic carbon content, in g / kg.

[0050] Figure 4 To apply the pH change curves of different groups of dryland soils in Example 1 over time, from... Figure 4 It can be seen that in control group 2, after the addition of lime, the pH rose rapidly in the early stage, but dropped significantly in the later stage, resulting in acidification. This indicates that the effect of traditional chemical neutralizing agents is concentrated in the early stage. Once the alkaline substances are consumed, the iron-sulfur oxidation process in the soil continues, and protons are continuously produced, leading to a rapid pH rebound. In control groups 2 and 3, the addition of alkaline woody peat and Bacillus megaterium powder alone had limited effect on increasing soil pH. However, the effect of alkaline woody peat on increasing soil pH was significantly better than that of Bacillus megaterium. This is because alkaline woody peat is an organic material rich in humus and with a high cation exchange capacity. It can slowly release alkaline substances and quickly neutralize free H+ in the soil. + This resulted in an early increase in soil pH. In experimental group 1, the soil pH increased significantly and remained stable over a long period after the addition of the soil conditioner from Example 1, maintaining a high level (pH=6.3) even after 60 days. This was attributed to the dual function of alkaline woody peat: in the early stages, the alkaline woody peat itself can slowly release alkaline substances, rapidly neutralizing free H+ in the soil. + This invention enables early improvement of soil pH. In the later stage, its rich quinone and other redox active groups can act as natural electron shuttles, mediating extracellular electron transfer between microorganisms and iron oxide, significantly enhancing iron reduction efficiency under aerobic conditions, and continuously consuming protons, thereby maintaining long-term stability of soil pH. The above results indicate that the soil conditioner provided by this invention can achieve early and rapid pH improvement and long-term non-acidification, overcoming the shortcomings of traditional soil conditioners.

[0051] Figure 5 To determine the soil organic carbon content of different groups after 60 days of reaction in Example 1, the data was obtained from... Figure 5 It can be seen that, compared with control group 1, the soil organic carbon content of control group 2 decreased slightly after the addition of lime; the soil organic carbon content of control group 3 did not increase significantly after the addition of Bacillus megaterium powder; the soil organic carbon content of control group 2 increased significantly after the addition of alkaline woody peat; and the soil organic carbon content of experimental group 1 increased more significantly after the addition of the soil conditioner in Example 1. This indicates that the soil conditioner provided by the present invention can increase the soil organic carbon content while increasing the pH of acidic soil. The increase in organic carbon can enhance the soil buffering capacity, improve the aggregate structure, and strengthen the fixation of heavy metals, providing a material basis for long-term acid control and risk threshold improvement.

[0052] Figure 6Table 2 shows the interfacial binding energy between soil particles and heavy metal ions after 60 days of reaction in control group 1 and experimental group 1 of Application Example 1. Figure 6 As shown in Table 2, compared with control group 1, the absolute value of the binding energy between heavy metals and soil was significantly increased after adding the soil conditioner in Example 1 to experimental group 1. The higher the binding energy, the stronger the heavy metal adsorption, the more difficult it is to desorb, and the more difficult it is to be absorbed by plants. This proves at the molecular level that the soil conditioner provided by the present invention can significantly enhance the fixation of heavy metals.

[0053] Table 2. Data on the interfacial binding energy between soil particles and heavy metal ions after 60 days of reaction in Application Example 1 (Control Group 1 and Experimental Group 1).

[0054] Table 3 shows the soil heavy metal risk thresholds after 60 days of reaction for control group 1 and experimental group 1 in Application Example 1. As can be seen from Table 3, compared with control group 1, the risk thresholds of heavy metals Cd, Pb, As, Cr and Hg in experimental group 1 were significantly increased after the addition of the soil conditioner in Example 1. This proves that the soil conditioner provided by the present invention can simultaneously achieve long-term soil deacidification and soil heavy metal solidification and stabilization, thereby systematically improving the multi-metal risk thresholds and achieving the goal of safe utilization of farmland.

[0055] Table 3. Soil heavy metal risk thresholds after 60 days of reaction for different groups in Application Example 1

[0056] Figure 7 To apply the risk thresholds of soil Cd(a), As(b), Pb(c), and Hg(d) after 60 days of reaction for different groups in Example 1, from... Figure 7 It can be seen that after adding the soil conditioner in Example 1 to experimental group 1, the effect of improving the risk threshold of soil heavy metals Cd, Pb, As and Hg was significantly better than that of control group 1, control group 2, control group 3 and control group 4.

[0057] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A soil conditioner, characterized in that, The soil conditioner is alkaline woody peat loaded with oxygen-reducing microorganisms.

2. The soil conditioner according to claim 1, characterized in that, On a dry weight basis, the mass ratio of the aerobic iron-reducing microorganisms to the alkaline woody peat is 1:(10-100).

3. The soil conditioner according to claim 1 or 2, characterized in that, The aerobic iron-reducing microorganisms are selected from at least one of Bacillus megaterium, Bacillus subtilis, Bacillus licheniformis, Amycosis discolor, Streptomyces griseus, and Enterococcus montelukastii.

4. The soil conditioner according to claim 1 or 2, characterized in that, The physicochemical parameters of the alkaline woody peat include at least one of the following: pH value of 7.5-9.0; organic matter content ≥50wt%; free humic acid content ≥20wt%; moisture content ≤20wt%; and particle size of 0.5-5mm.

5. The method for preparing the soil conditioner according to any one of claims 1-4, characterized in that, Includes the following steps: The soil conditioner is obtained by mixing aerobic iron-reducing microorganisms with alkaline woody peat.

6. The application of the soil conditioner according to any one of claims 1-4 in soil improvement.

7. The application according to claim 6, characterized in that, The soil includes dryland soil, and the physicochemical parameters of the dryland soil include at least one of the following: water content of 50%-70% field holding capacity; pH ​​value < 5.

0.

8. The application according to claim 7, characterized in that, The soil improvement includes at least one of the following: a. Increase soil pH; b. Reduce the content of available heavy metals in the soil; c. Increase the organic carbon content of the soil.

9. The application according to claim 8, characterized in that, The heavy metals include at least one of Cd, Pb, As, Cr, and Hg.

10. The application according to claim 8, characterized in that, The application rate of the soil conditioner is 0.5%-5% of the soil mass.

Images