A preparation method of a soil carbon sequestration agent for reducing greenhouse gas emission in farmland

Abstract

The application belongs to the technical field of soil improver, and particularly relates to a preparation method of a soil carbon sequestration agent for reducing greenhouse gas emission in farmland; the preparation method of the soil carbon sequestration agent for reducing greenhouse gas emission in farmland provided by the application calcic or sodium-based montmorillonite, non-calcic montmorillonite, and other raw materials are calcined at 1000-1100 DEG C for 0.5-2 hours to obtain the soil carbon sequestration agent; compared with the raw materials, the soil carbon sequestration agent obtained by calcination contains active mineral phases such as calcium silicate and calcium aluminate, improves the solubility of the soil carbon sequestration agent, promotes the release of effective components such as calcium and silicon, can enhance the silicate weathering effect and adjust the microbial community structure such as methanogen and methanotroph in the soil, effectively reduces the emission of greenhouse gases such as methane and carbon dioxide through a composite mechanism, and solves the technical problem that the existing soil improver is difficult to effectively reduce the greenhouse gas emission in the fertilized farmland soil.

Description

Technical Field

[0001] This application belongs to the field of soil conditioner technology, and in particular relates to a method for preparing a soil carbon sequestrant that reduces greenhouse gas emissions from farmland. Background Technology

[0002] Currently, soil conditioners in the agricultural field are mainly mineral-based, such as limestone and zeolite, and biological-based, such as microbial agents and humic acid. Mineral-based conditioners improve acidic soils, saline-alkali lands, and heavy metal-polluted soils by adjusting soil pH and supplementing trace elements through ion exchange and acid-base neutralization. Biological-based conditioners improve soil microecology and restore soil ecological balance.

[0003] In addition, the emission of greenhouse gases such as methane and carbon dioxide from farmland soils cannot be ignored. This is mainly because rice seedlings grown in paddy fields grow better after fertilization, producing more organic matter in the soil. At the same time, paddy fields are in a reducing environment due to long-term flooding, providing organic matter substrates and environment for microorganisms to decompose and produce methane. In contrast, agricultural activities such as fertilizer application and tillage disturbance in dry land accelerate the mineralization of soil organic matter, making it easier for decomposition to lead to the continuous release of carbon dioxide and methane. Therefore, in order to reduce greenhouse gas emissions such as methane and carbon dioxide in agricultural planting and achieve carbon reduction, it is necessary to manage carbon sequestration in fertilized farmland soils. However, conventional soil conditioners cannot sequestrate carbon, so it is necessary to develop new types of soil conditioners as soil carbon sequestrants.

[0004] Calcium-based minerals and silicate minerals are important minerals in the Earth's crust. Calcium-based minerals refer to all minerals rich in calcium, and are mainly divided into two categories based on the form in which calcium exists. One category consists of calcium as a core cation combined with acid ions such as carbonate and sulfate to form non-calcium-based montmorillonite, such as calcium carbonate and calcium sulfate. The other category consists of calcium-based montmorillonite formed by calcium ions loosely adsorbed in the interlayer of clay minerals such as montmorillonite. Geological studies have shown that the silicate weathering effect of silicate minerals is a promising carbon reduction technology, as weathered silicates react with carbon dioxide to form carbonates, thus achieving carbon sequestration. In addition, the mineral elements in silicate minerals are important nutrients required for plant growth and microbial metabolism. They can alter the chemical environment of soil, such as pH, ionic composition, and nutrient availability, regulate the composition and metabolic function of microbial communities, and affect the decomposition and transformation of organic carbon, thereby changing the soil carbon cycle. Therefore, silicate minerals are a potential soil carbon sequestrant. However, the weathering rate of natural silicate minerals is low, and the reaction kinetics are relatively slow, making it difficult to effectively reduce greenhouse gas emissions when applied to agricultural planting. Summary of the Invention

[0005] In view of this, this application provides a method for preparing a soil carbon sequestrant to reduce greenhouse gas emissions from farmland, thereby solving the technical problem that existing soil conditioners are unable to effectively reduce greenhouse gas emissions from fertilized farmland soil.

[0006] The first aspect of this application provides a method for preparing a soil carbon sequestrant to reduce greenhouse gas emissions from farmland, comprising the following steps:

[0007] Pre-treating a mixture of montmorillonite and non-calcium-based montmorillonite calcium-based mineral powders yields a mixed dry powder.

[0008] The mixed dry powder is calcined at 1000~1100℃ for 0.5~2h to obtain a soil carbon sequestration agent;

[0009] The montmorillonite is selected from calcium-based montmorillonite and / or sodium-based montmorillonite.

[0010] Preferably, the pretreatment process includes: grinding, drying, and pulverizing in sequence;

[0011] After roasting for 0.5 to 2 hours, the post-processing includes: cooling to room temperature, pulverizing, and sieving.

[0012] Preferably, the mixed powder of montmorillonite and non-calcium-based montmorillonite calcium-based minerals is composed of montmorillonite powder with a particle size of less than 100 mesh and non-calcium-based montmorillonite calcium-based mineral powder with a particle size of less than 100 mesh.

[0013] Preferably, the calcium-based mineral of the non-calcium-based montmorillonite is selected from at least one of calcium carbonate and calcium sulfate.

[0014] Preferably, the mass ratio of the montmorillonite to the calcium-based minerals in the non-calcium-based montmorillonite is 1:2~3.

[0015] Preferably, the dispersion medium used for grinding is deionized water, and the grinding time is 10-20 minutes.

[0016] Preferably, the drying temperature is 100~110℃.

[0017] Preferably, the sieve used for sieving has a mesh size of 50 to 150.

[0018] Preferably, the heating rate to 1000~1100℃ is 5~10℃ / min.

[0019] The second aspect of this application provides a method for reducing greenhouse gas emissions from farmland, comprising the steps of: adding a soil carbon sequestrant prepared by the preparation method described in the first aspect to the soil of fertilized farmland to reduce greenhouse gas emissions from the fertilized farmland soil.

[0020] Preferably, the soil carbon sequestration agent is added to the fertilized farmland soil at an amount of 1-5 wt.%.

[0021] Compared with existing technologies, the method for preparing a soil carbon sequestrant to reduce greenhouse gas emissions from farmland provided in this application has at least the following beneficial effects:

[0022] Compared with soil conditioners such as natural silicate minerals, the method for preparing a soil carbon sequestrant that reduces greenhouse gas emissions from farmland provided in this application involves calcining calcium-based or sodium-based montmorillonite with calcium-based minerals (non-calcium-based montmorillonite) to obtain the soil carbon sequestrant. After calcination, on the one hand, it promotes the activation and decomposition of elements such as calcium, strengthening the mechanism of carbon sequestration through the reaction with carbon dioxide to form carbonates. On the other hand, it converts the main chemical components in the raw materials, such as silicon dioxide and alumina, which are difficult to utilize, into silicates, which can promote the release of mineral elements such as Si in the soil carbon sequestrant. The content of available silicon and its bioavailability are improved, and the structure of microbial communities such as methanogens or methanogens in fertilized farmland soil is regulated, inhibiting the decomposition of organic matter in farmland soil by microorganisms from the source and affecting carbon metabolism pathways. Through a complex mechanism, the emission of greenhouse gases such as methane and carbon dioxide from fertilized farmland soil is effectively reduced. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a graph showing the cumulative methane emissions in experimental group 1 and blank control group 1 obtained by gas chromatography in Experimental Example 1 of this application.

[0025] Figure 2 This is a graph showing the cumulative carbon dioxide emissions in experimental group 1 and blank control group 1 obtained by gas chromatography in Experimental Example 1 of this application.

[0026] Figure 3 This is a graph showing the abundance results of key methanogenic genes in experimental group 1 and blank control group 1 obtained from metagenomic sequencing analysis in Experimental Example 1 of this application.

[0027] Figure 4 This is a graph showing the abundance results of key genes for methane oxidation in experimental group 1 and blank control group 1 obtained from metagenomic sequencing analysis in Experiment Example 1 of this application.

[0028] Figure 5This is a graph showing the abundance results of methanogens in experimental group 1 and blank control group 1 obtained from metagenomic sequencing analysis in Experimental Example 1 of this application.

[0029] Figure 6 The abundance results of methanogenic bacteria in experimental group 1 and blank control group 1 obtained from metagenomic sequencing analysis in Experiment Example 1 of this application are shown in the figure.

[0030] Figure 7 This is a graph showing the cumulative methane emissions in experimental group 2 and blank control group 1 obtained by gas chromatography in Experimental Example 1 of this application.

[0031] Figure 8 This is a graph showing the cumulative carbon dioxide emissions in experimental group 2 and blank control group 1 obtained by gas chromatography in Experimental Example 1 of this application.

[0032] Figure 9 This is a graph showing the abundance results of key methanogenic genes in experimental group 2 and blank control group 1 obtained from metagenomic sequencing analysis in Experiment Example 1 of this application.

[0033] Figure 10 This is a graph showing the abundance results of key genes for methane oxidation in experimental group 2 and blank control group 1 obtained from metagenomic sequencing analysis in Experiment Example 1 of this application.

[0034] Figure 11 The abundance results of methanogens in experimental group 2 and blank control group 1 obtained from metagenomic sequencing analysis in Experiment Example 1 of this application are shown in the figure.

[0035] Figure 12 This is a graph showing the abundance results of methanogenic bacteria in experimental group 2 and blank control group 1 obtained from metagenomic sequencing analysis in Experiment Example 1 of this application;

[0036] Figure 13 This is a graph showing the cumulative methane emissions in experimental group 3 and blank control group 2 obtained by gas chromatography in Experimental Example 2 of this application.

[0037] Figure 14 This is a graph showing the cumulative carbon dioxide emissions in experimental group 3 and blank control group 2 obtained by gas chromatography in Experimental Example 2 of this application.

[0038] Figure 15 This is a graph showing the cumulative methane emissions in experimental groups 4, 5, and 6 and the blank control group 3, obtained by gas chromatography in Experimental Example 3 of this application.

[0039] Figure 16 The graph shows the cumulative carbon dioxide emissions of experimental groups 4, 5, and 6 and the blank control group 3, obtained by gas chromatography in Experimental Example 3 of this application.

[0040] Figure 17 This is the X-ray diffraction pattern of the soil carbon sequestrant provided in Example 1, analyzed by X-ray diffractometer in Experimental Example 4 of this application;

[0041] Figure 18 This is the X-ray diffraction pattern of the soil carbon sequestrant provided in Example 2, analyzed by X-ray diffractometer in Experimental Example 4 of this application;

[0042] Figure 19 This is a graph showing the water solubility and citric acid solubility results of the soil carbon sequestrant and calcium-based montmorillonite provided in Example 1 of Experimental Example 4 of this application;

[0043] Figure 20 This is a graph showing the water solubility and citric acid solubility results of the soil carbon sequestrant and sodium montmorillonite provided in Example 2 of Experimental Example 4 of this application;

[0044] Figure 21 This is a graph showing the water solubility and citric acid solubility of the mineral element Si in the soil carbon fixative and calcium-based montmorillonite provided in Example 1 of Experiment 4 of this application;

[0045] Figure 22 The graph shows the water solubility and citric acid solubility of the soil carbon fixative and sodium montmorillonite mineral element Si provided in Example 2 of Experiment 4 of this application. Detailed Implementation

[0046] This application provides a method for preparing a soil carbon sequestrant that reduces greenhouse gas emissions from farmland, thereby addressing the technical problem that existing soil conditioners are unable to effectively reduce greenhouse gas emissions from fertilized farmland soils.

[0047] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0048] Example 1

[0049] This embodiment provides a method for preparing a soil carbon sequestrant to reduce greenhouse gas emissions from farmland, comprising the following steps:

[0050] Weigh 100g of calcium-based montmorillonite and 250g of calcium carbonate as raw materials according to a mass ratio of 1:2.5. Crush the calcium-based montmorillonite and calcium carbonate separately and pass them through a 100-mesh sieve. Then place them in a mixing container and mix thoroughly to obtain a mixed powder. The purity of the calcium-based montmorillonite in the raw materials is ≥95%, and its main chemical compositions of SiO2, Al2O3, Fe2O3, MgO, and CaO are 62.48%, 16.32%, 2.14%, 5.60%, and 1.90%, respectively. The loss on ignition (1000℃) is 9.82%.

[0051] Add an appropriate amount of deionized water to the mixed powder to make it grindable. Grind it continuously in a porcelain mortar for 10 minutes until a uniform slurry is formed. Place the slurry at 105℃ to dry to constant weight and then pulverize it to obtain a mixed dry powder.

[0052] The mixed dry powder was placed in a tube furnace and heated to 1100°C at a heating rate of 10°C / min. It was then activated by constant temperature calcination for 0.5 hours. After calcination, the sample was immediately removed from the furnace and rapidly cooled to room temperature. The cooled sample was then pulverized again and passed through a 100-mesh sieve to obtain the soil carbon fixative. It was then sealed and stored in a dry environment with a relative humidity of no more than 40% for later use.

[0053] Application Example 1

[0054] This application example provides a method for reducing greenhouse gas emissions from fertilized farmland soil, the steps of which include:

[0055] The soil carbon sequestration agent provided in Example 1 was added to fertilized paddy soil in Chashan Town, Dongguan City, Guangdong Province, China, at an addition rate of 1 wt.%, i.e., 1 g of soil carbon sequestration agent per 100 g of paddy soil. The mixture was then thoroughly mixed to reduce greenhouse gas emissions from fertilized farmland soil.

[0056] Example 2

[0057] This embodiment provides a method for preparing a soil carbon sequestrant to reduce greenhouse gas emissions from farmland, comprising the following steps:

[0058] According to a mass ratio of 1:2.5:0.08, 100g of sodium montmorillonite, 250g of calcium carbonate, and 8g of calcium sulfate were weighed as raw materials. The weighed sodium montmorillonite and calcium carbonate were crushed separately and passed through a 100-mesh sieve before being placed in a mixing container and thoroughly mixed to obtain a mixed powder. The purity of sodium montmorillonite in the raw materials was ≥95%, and its main chemical compositions of SiO2, Al2O3, Fe2O3, MgO, CaO, and Na2O were 59.66%, 22.14%, 3.17%, 2.22%, 1.33%, and 3.15%, respectively, with a loss on ignition of 7.01% (at 1000℃).

[0059] Add an appropriate amount of deionized water to the mixed powder to make it grindable. Grind it continuously in a porcelain mortar for 10 minutes until a uniform slurry is formed. Place the slurry at 105℃ to dry to constant weight and then pulverize it to obtain a mixed dry powder.

[0060] The mixed dry powder was placed in a tube furnace and heated to 1100°C at a heating rate of 10°C / min. It was then calcined at a constant temperature for 1 hour for activation. After calcination, the sample was immediately removed from the furnace and rapidly cooled to room temperature. The cooled sample was then pulverized again and passed through a 100-mesh sieve to obtain the soil carbon fixative. It was then sealed and stored in a dry environment with a relative humidity of no more than 40% for later use.

[0061] Application Example 2

[0062] This application example provides a method for reducing greenhouse gas emissions from fertilized farmland soil. The steps include: adding 1 wt.% of the soil carbon sequestrant, i.e., 1 g of soil carbon sequestrant per 100 g of paddy soil, to fertilized paddy soil in Chashan Town, Dongguan City, Guangdong Province, China, and mixing it evenly to reduce greenhouse gas emissions from fertilized farmland soil.

[0063] Comparative Example 1

[0064] This comparative example provides a method for preparing a soil carbon sequestrant to reduce greenhouse gas emissions from farmland, the steps of which include:

[0065] Calcium silicate was placed in a tube furnace and heated to 1100°C at a heating rate of 10°C / min. It was then activated by constant-temperature calcination for 0.5 hours. After calcination, the sample was immediately removed from the furnace and rapidly cooled to room temperature. The cooled sample was then pulverized again and passed through a 100-mesh sieve to obtain activated calcium silicate as a soil carbon fixative. It was then sealed and stored in a dry environment with a relative humidity not exceeding 40% for later use.

[0066] Application Example 3

[0067] This application example provides a method for reducing greenhouse gas emissions from fertilized farmland soil, the steps of which include:

[0068] Add 1 wt.% of activated calcium silicate as a soil carbon fixative, that is, add 1 g of activated calcium silicate to every 100 g of paddy soil. Add the activated calcium silicate provided in Comparative Example 1 to the fertilized paddy soil in Chashan Town, Dongguan City, Guangdong Province, China and mix evenly to reduce greenhouse gas emissions from fertilized farmland soil.

[0069] Comparative Example 2

[0070] This comparative example provides a soil carbon sequestrant for reducing greenhouse gas emissions from farmland. The soil carbon sequestrant is selected from commercially available calcium silicate.

[0071] Application Example 4

[0072] This application example provides a method for reducing greenhouse gas emissions from fertilized farmland soil, the steps of which include:

[0073] Add calcium silicate as a soil carbon fixative at an addition rate of 1 wt.%, that is, 1 g of calcium silicate per 100 g of paddy soil sample. Add the calcium silicate provided in Comparative Example 2 to the fertilized paddy soil in Chashan Town, Dongguan City, Guangdong Province, China and mix evenly to reduce greenhouse gas emissions from fertilized farmland soil.

[0074] Comparative Example 3

[0075] This comparative example provides a soil carbon sequestrant for reducing greenhouse gas emissions from farmland. The soil carbon sequestrant is selected from commercially available calcium-based montmorillonite.

[0076] Application Example 5

[0077] This application example provides a method for reducing greenhouse gas emissions from fertilized farmland soil, the steps of which include:

[0078] Add 1 wt.% of calcium-based montmorillonite as a soil carbon fixative, i.e., add 1 g of calcium-based montmorillonite per 100 g of paddy soil, and mix evenly with the calcium-based montmorillonite provided in Comparative Example 3 in fertilized paddy soil in Chashan Town, Dongguan City, Guangdong Province, China.

[0079] Comparative Example 4

[0080] This comparative example provides a soil carbon sequestrant for reducing greenhouse gas emissions from farmland. The soil carbon sequestrant is selected from commercially available sodium montmorillonite.

[0081] Application Example 6

[0082] This application example provides a method for reducing greenhouse gas emissions from fertilized farmland soil, the steps of which include:

[0083] Add 1 wt.% of sodium montmorillonite as a soil carbon fixative, i.e., add 1 g of sodium montmorillonite per 100 g of paddy soil. The sodium montmorillonite provided in Comparative Example 4 was added to the fertilized paddy soil in Chashan Town, Dongguan City, Guangdong Province, China and mixed evenly.

[0084] Experimental Example 1

[0085] To evaluate the methods for reducing greenhouse gas emissions from fertilized farmland soil provided in Application Examples 1 and 2, the soil carbon sequestrants provided in Examples 1 and 2 were added to the fertilized farmland soil to reduce greenhouse gas emissions. This experimental example first quantitatively assesses the greenhouse gas emission reduction effect by measuring methane and carbon dioxide emissions, and then further analyzes the reasons for greenhouse gas emission reduction from a microbiological mechanism perspective by analyzing the abundance changes of methanogenic bacteria and methanogenic bacteria and their key genes. The experiment includes the following steps:

[0086] The steps for anaerobic culture of soil microcosms in the experimental and control groups are as follows:

[0087] Soil samples were collected from fertilized paddy fields in Chashan Town, Dongguan City, Guangdong Province, China. The soil samples were taken from the top layer (0-20cm). Five soil samples were randomly selected from the sampling location and thoroughly mixed to form a soil sample. After the soil samples were collected, they were air-dried and then sieved through a 0.5mm sieve to obtain air-dried soil. The dried soil samples were stored at 4℃ for later use.

[0088] Add 10g of air-dried soil to a 100ml sterile serum bottle, then add 0.1g of the soil carbon fixation agent provided in Example 1. Mix well and add 20ml of water at a ratio of 2:1 (V / W). Cover with a rubber stopper and an aluminum cap, install the sampling valve, and rinse the top of the experimental container with pure nitrogen for 15 minutes to remove the air in the bottle. Then close the valve to ensure complete anaerobic conditions in the bottle. The soil anaerobic culture process is carried out under dark conditions at 30±1℃ for 30 days as experimental group 1.

[0089] Add 10g of air-dried soil to a 100ml sterile serum bottle, then add 0.3g of the soil carbon fixation agent provided in Example 2. Mix well and add 20ml of water at a ratio of 2:1 (V / W). Cover with a rubber stopper and an aluminum cap, install the sampling valve, rinse the top of the experimental container with pure nitrogen for 15 minutes to remove the air in the bottle, and then close the valve to ensure complete anaerobic conditions in the bottle. The soil anaerobic culture process was carried out under dark conditions at 30±1℃ for 30 days as experimental group 2.

[0090] Add 10g of air-dried soil to a 100ml sterile serum bottle, then add 20ml of water at a ratio of 2:1 (V / W), cover with a rubber stopper and aluminum cap, install the sampling valve, rinse the top of the experimental container with pure nitrogen for 15 minutes to expel the air in the bottle, and then close the valve to ensure complete anaerobic conditions in the bottle. The anaerobic soil culture process was carried out under dark conditions at 30±1℃ for 30 days as a blank control group 1.

[0091] The steps for analyzing greenhouse gas emissions in the experimental and control groups are as follows:

[0092] The process of determining methane and carbon dioxide emissions: The cumulative emissions of methane and carbon dioxide in the headspace gas of the anaerobic bottles of experimental groups 1 and 2 and blank control group 1 were determined by gas chromatography.

[0093] The process of abundance changes of methanogens and methanotrophs and their key genes: Metagenomic sequencing analysis was used to analyze the changes in the abundance of key functional genes and communities of methanogens and methanotrophs. Based on the metagenomic sequencing results and combined with the KEGG (Kyoto Encyclopedia of Genes and Genomes) database, carbon fixation-related KOs and pathways were screened and statistically analyzed to obtain carbon fixation-related pathways. The results are shown in Table 1. Figure 1-6 and Figure 7-12 As shown;

[0094] From Table 1 and Figure 1-2 As shown in Table 1, the cumulative emissions of methane and carbon dioxide in the fertilized paddy field soil of the blank control group 1 continuously released methane and carbon dioxide per gram of soil over 30 days, with cumulative emissions of 26.74 μmol / g and 21.55 μmol / g, respectively. In contrast, the fertilized paddy field soil of the experimental group 1, due to the addition of the soil carbon sequestrant provided in Example 1, saw its cumulative emissions of methane and carbon dioxide reduced to 4.49 μmol / g and 4.58 μmol / g, respectively, representing reductions of 83.19% and 78.75%. From Table 1 and... Figure 3-4 The results of the changes in the abundance of key functional genes of soil microorganisms show that, compared with the blank control group 1, the relative abundance of the key methanogenic gene mcrA (methyl-CoM reductase) in the anaerobic bottle of experimental group 1 decreased from 0.0097% to 0.0020% due to the addition of the soil carbon fixative provided in Example 1, while the relative abundance of the key methane oxidation gene pmoA (particulate methane monooxygenase) increased from 0.0020% to 0.0030%; and the results also show that, as shown in Table 1 and Figure 5-6The results of the changes in the abundance of soil microbial carbon-fixing and methanogenic microbial communities shown indicate that, compared with the blank control group 1, the total abundance of methanogenic bacteria in the fertilized paddy field soil in the anaerobic bottle of experimental group 1 decreased from 3.53% to 0.76% due to the addition of the soil carbon-fixing agent provided in Example 1. The abundances of the main methanogenic bacteria, Methanosarcina, Methanocella, and Methanobacterium, decreased by 82.17%, 72.29%, and 85.20%, respectively. Simultaneously, the total abundance of methanogenic bacteria increased from 2.84% to 4.45%, with the main methanogenic bacteria, Methyloceanibacterium, showing a significant increase. The abundance of *Methylovirgula* and *Methylobacterium* increased by 66.40% and 62.60%, respectively. These experimental results indicate that after adding the soil carbon fixative agent provided in Example 1 to fertilized paddy soil, the number and abundance of methane-producing microorganisms and their functional genes significantly decreased, and the source of organic matter decomposition in farmland soil was significantly inhibited. Conversely, the abundance of methane oxidation-related microorganisms and their functional genes increased. This is consistent with the results of cumulative methane and carbon dioxide emissions in experimental group 1 and the blank control group 1, where both cumulative methane and carbon dioxide emissions decreased, with the carbon dioxide reduction effect slightly lower than that of methane. Simultaneously, the carbon fixation pathway results showed that the reduced tricarboxylic acid cycle (Reverse...) The total abundances of the Tricarboxylic Acid Cycle, the Wood-Ljungdahl reductive acetyl-CoA pathway, and the 3-hydroxypropionate / 4-hydroxybutyrate cycle increased from 1.70%, 0.21%, and 0.21% to 1.85%, 0.27%, and 0.31%, respectively, indicating an enhanced potential of metabolic pathways related to inorganic carbon assimilation. This is consistent with the results of the cumulative carbon dioxide emissions in experimental group 1 and blank control group 1.

[0095] From Table 1 and Figure 7-8 As shown in Table 1, the cumulative emissions of methane and carbon dioxide in the fertilized paddy field soil in the blank control group 1 anaerobic bottle continuously released methane and carbon dioxide per gram of soil over 30 days, with cumulative emissions of 26.74 μmol / g and 21.55 μmol / g, respectively. In contrast, the fertilized paddy field soil in the experimental group 2 anaerobic bottle, due to the addition of the soil carbon sequestration agent provided in Example 2, saw its cumulative emissions of methane and carbon dioxide reduced to 0.94 μmol / g and 1.17 μmol / g, respectively, representing reductions of 78.95% and 74.39%. From Table 1 and... Figure 9-10The results of the changes in the abundance of key functional genes of soil microorganisms show that, compared with the blank control group 1, the relative abundance of the methane key gene mcrA (methyl-CoM reductase) in the fertilized paddy field soil of the anaerobic bottle in experimental group 2 decreased from 0.0097% to 0.0026% due to the addition of the soil carbon fixative provided in Example 2, while the relative abundance of the methane oxidation key gene pmoA (particulate methane monooxygenase) increased from 0.0020% to 0.0023%; and from Table 1 and Figure 11-12 The results of the changes in the abundance of soil microbial carbon-fixing and methanogenic microbial communities shown indicate that, compared with the blank control group 1, the total abundance of methanogenic bacteria in the fertilized paddy field soil of the anaerobic bottle in experimental group 2 decreased from 3.53% to 0.76% due to the addition of the soil carbon-fixing agent provided in Example 2. The abundance of the main methanogenic bacteria, Methanosarcina, Methanocella, and Methanobacterium, decreased by 70.70%, 78.51%, and 87.62%, respectively. At the same time, the total abundance of methanogenic bacteria increased from 2.84% to 4.47%, and the main methanogenic bacteria, Methyloceanibacterium, increased. The abundance of *Methylobacterium* (Methylobacterium) and *Methylovirgula* (Methylobacterium) increased by 68.96% and 1.29%, respectively. These experimental results indicate that after adding the soil carbon fixative agent provided in Example 2 to fertilized paddy soil, the number and abundance of methane-producing microorganisms and their functional genes in the soil sharply decreased, significantly inhibiting the source of organic matter decomposition in farmland soil. Conversely, the abundance of methane oxidation-related microorganisms and their functional genes increased. This is consistent with the results of cumulative methane and carbon dioxide emissions in experimental group 2 and the blank control group 1, where both cumulative methane and carbon dioxide emissions decreased, with the carbon dioxide reduction effect slightly lower than that of methane. Simultaneously, the carbon fixation pathway results indicate that the reduced tricarboxylic acid cycle (Reverse...) The total abundances of the Tricarboxylic Acid Cycle, the Wood-Ljungdahl reductive acetyl-CoA pathway, and the 3-hydroxypropionate / 4-hydroxybutyrate cycle increased from 1.70%, 0.21%, and 0.21% to 1.71%, 0.22%, and 0.26%, respectively, indicating an enhanced potential of metabolic pathways related to inorganic carbon assimilation. This is consistent with the results of the cumulative carbon dioxide emissions in experimental group 2 and blank control group 1.

[0096] Table 1: Experimental results of experimental groups 1 and 2 and blank control group 1

[0097]

[0098] Experiment Example 2

[0099] To evaluate the method for reducing greenhouse gas emissions from fertilized farmland soil provided in Application Example 3, the effectiveness of using the soil carbon sequestrant provided in Comparative Example 1 in reducing greenhouse gas emissions from fertilized farmland soil includes the following steps:

[0100] The steps for anaerobic culture of soil microcosms in the experimental and control groups are as follows:

[0101] Soil samples were collected from fertilized paddy fields in Chashan Town, Dongguan City, Guangdong Province, China. The soil samples were collected from the top layer (0-20cm). Five soil samples were randomly selected from the sampling site and thoroughly mixed to form a soil sample. After the soil samples were collected, they were air-dried and then sieved through a 0.5mm sieve. The samples were then stored at 4℃ for later use.

[0102] Add 10g of air-dried soil to a 100ml sterile serum bottle, then add 0.1g of soil carbon fixation agent provided in Comparative Example 1. Mix well and add 20ml of water at a ratio of 2:1 (V / W). Cover with a rubber stopper and aluminum cap, install the sampling valve, and rinse the top of the experimental container with pure nitrogen for 15 minutes to remove the air in the bottle. Then close the valve to ensure complete anaerobic conditions in the bottle. The soil anaerobic culture process was carried out under dark conditions at 30±1℃ for 30 days as experimental group 3.

[0103] Add 10g of air-dried soil to a 100ml sterile serum bottle, then add 20ml of water at a ratio of 2:1 (V / W), cover with a rubber stopper and aluminum cap, install the sampling valve, rinse the top of the experimental container with pure nitrogen for 15 minutes to expel the air in the bottle, and then close the valve to ensure complete anaerobic conditions in the bottle. The anaerobic soil culture process was carried out under dark conditions at 30±1℃ for 30 days as a blank control group 2.

[0104] The steps for analyzing greenhouse gas emissions in the experimental and control groups are as follows:

[0105] The cumulative emissions of methane and carbon dioxide in the headspace gas of the experimental group and blank control group 2 were determined by gas chromatography, and the results are as follows: Figure 13-14 As shown;

[0106] from Figure 13-14The cumulative methane and carbon dioxide emissions shown indicate that in the blank control group 2, the fertilized paddy field soil continuously released methane and carbon dioxide per gram of soil over 30 days, with cumulative emissions of 27.21 μmol / g and 40.74 μmol / g, respectively. In contrast, the fertilized paddy field soil in the experimental group 3, due to the addition of the soil carbon sequestrant provided in Comparative Example 1, saw its cumulative methane and carbon dioxide emissions reduced to 21.09 μmol / g and 30.63 μmol / g, respectively. μmol / g, respectively, reduced by 22.49% and 24.82%. As can be seen from Experiment 1, adding the soil carbon sequestrant provided in Example 1 can reduce the cumulative emissions of methane and carbon dioxide by 83.19% and 78.75%, respectively. Adding the soil carbon sequestrant provided in Example 2 can reduce the cumulative emissions of methane and carbon dioxide by 78.95% and 74.39%, respectively. This shows that the soil carbon sequestrants provided in Examples 1-2 are more effective than roasted and activated calcium silicate in reducing greenhouse gas emissions from fertilized farmland soil.

[0107] Experimental Example 3

[0108] To evaluate the effectiveness of the method for reducing greenhouse gas emissions from fertilized farmland soils provided in practical application examples 4-6, after using the soil carbon sequestrant provided in comparative examples 2-4, in reducing greenhouse gas emissions from fertilized farmland soils, the method includes the following steps:

[0109] The steps for anaerobic culture of soil microcosms in the experimental and control groups are as follows:

[0110] Soil samples were collected from fertilized paddy fields in Chashan Town, Dongguan City, Guangdong Province, China. The soil samples were collected from the top layer (0-20cm). Five soil samples were randomly selected from the sampling site and thoroughly mixed to form a soil sample. After the soil samples were collected, they were air-dried and then sieved through a 0.5mm sieve. The samples were then stored at 4℃ for later use.

[0111] Add 10g of air-dried soil to a 100ml sterile serum bottle, then add 0.1g of calcium silicate soil carbon fixation agent provided in Comparative Example 2. Mix well and add 20ml of water at a ratio of 2:1 (V / W). Cover with a rubber stopper and aluminum cap, install the sampling valve, rinse the top of the experimental container with pure nitrogen for 15 minutes to remove the air in the bottle, and then close the valve to ensure complete anaerobic conditions in the bottle. The soil anaerobic culture process was carried out under dark conditions at 30±1℃ for 30 days as experimental group 4.

[0112] Add 10g of air-dried soil to a 100ml sterile serum bottle, then add 0.1g of calcium-based montmorillonite soil carbon fixative provided in Comparative Example 3. Mix well and add 20ml of water at a ratio of 2:1 (V / W). Cover with a rubber stopper and aluminum cap, install the sampling valve, and rinse the top of the experimental container with pure nitrogen for 15 minutes to remove the air in the bottle. Then close the valve to ensure complete anaerobic conditions in the bottle. The soil anaerobic culture process was carried out under dark conditions at 30±1℃ for 30 days as experimental group 5.

[0113] Add 10g of air-dried soil to a 100ml sterile serum bottle, then add 0.1g of sodium montmorillonite soil carbon fixative provided in Comparative Example 4. Mix well and add 20ml of water at a ratio of 2:1 (V / W). Cover with a rubber stopper and aluminum cap, install the sampling valve, and rinse the top of the experimental container with pure nitrogen for 15 minutes to remove the air in the bottle. Then close the valve to ensure complete anaerobic conditions in the bottle. The soil anaerobic culture process was carried out under dark conditions at 30±1℃ for 30 days as experimental group 6.

[0114] Add 10g of air-dried soil to a 100ml sterile serum bottle, then add 20ml of water at a ratio of 2:1 (V / W), cover with a rubber stopper and aluminum cap, install the sampling valve, rinse the top of the experimental container with pure nitrogen for 15 minutes to expel the air in the bottle, and then close the valve to ensure complete anaerobic conditions in the bottle. The anaerobic soil culture process was carried out under dark conditions at 30±1℃ for 30 days as a blank control group.

[0115] The steps for analyzing greenhouse gas emissions in the experimental and control groups are as follows:

[0116] The cumulative emissions of methane and carbon dioxide in the headspace gas of the experimental group and blank control group 3 were determined by gas chromatography, and the results are as follows: Figure 15-16 As shown;

[0117] from Figure 15-16The cumulative emissions of methane and carbon dioxide shown in the figures indicate that in the blank control group 3, the fertilized paddy field soil in the anaerobic bottle continuously released methane and carbon dioxide per gram of soil over 30 days, with cumulative emissions of 30.71 μmol / g and 88.54 μmol / g, respectively. In contrast, the fertilized paddy field soil in the experimental group 4, which incorporated the soil carbon sequestration agent calcium silicate provided in Comparative Example 2, saw its cumulative methane and carbon dioxide emissions reduced to 30.08 μmol / g and 71.54 μmol / g, respectively, representing reductions of 2.1% and 19.2% compared to the blank control. Furthermore, the results of Experiment 2 show that adding calcined calcium silicate to the fertilized farmland soil in Experiment 3 reduced the cumulative emissions of methane and carbon dioxide by 22.49% and 24.8%, respectively. The 2% reduction indicates that roasting can enhance the weathering effect of silicates, promoting the reaction of calcium and other metal ions in silicates with carbon dioxide to form carbonates, thus achieving better carbon sequestration and emission reduction effects. Furthermore, in experimental groups 5-6, the fertilized paddy field soils, with the addition of calcium-based and sodium-based montmorillonite provided in comparative examples 3-4, showed cumulative methane and carbon dioxide emissions similar to the blank control group 3. This suggests that calcium-based and sodium-based montmorillonite are insufficient to effectively reduce greenhouse gas emissions from fertilized paddy field soils. However, the results of Experiment Example 1 show that in experimental groups 1 or 2, adding calcium-based or sodium-based montmorillonite mixed with non-calcium-based montmorillonite calcium-based minerals and roasting it to the fertilized farmland soil reduced cumulative methane and carbon dioxide emissions by 78.95%–83.19% and 74.39%–78.75%, respectively.

[0118] Such a high carbon sequestration and emission reduction effect is significantly better than that of the calcined calcium silicate in Experiment Example 2. This indicates that the calcium-based or sodium-based montmorillonite provided in this application, which is mixed with non-calcium-based montmorillonite calcium-based minerals and calcined, serves as a soil carbon sequestrant. In addition to utilizing the reaction of non-calcium-based montmorillonite calcium-based minerals with carbon dioxide to generate carbonates for carbon sequestration, it also promotes the release of mineral elements in calcium-based or sodium-based montmorillonite through calcination, regulates the microbial community structure of methanogens, methanogens, and other microorganisms in the soil, inhibits the decomposition of organic matter in farmland soil by microorganisms from the source, and achieves excellent carbon sequestration and emission reduction effects through a complex mechanism.

[0119] Experiment Example 4

[0120] To investigate the mechanism by which the soil carbon fixatives obtained in Examples 1-2, which are obtained by calcining calcium-based or sodium-based montmorillonite mixed with non-calcium-based montmorillonite, promote the release of mineral elements and reduce greenhouse gas emissions such as methane and carbon dioxide, this experiment first used X-ray diffraction to analyze the compounds in the soil carbon fixatives provided in Examples 1-2, and then analyzed the water solubility and citric acid solubility (2% citric acid) of the soil carbon fixative as a whole and its mineral element Si. The results were compared with those of the raw materials, including non-calcium-based montmorillonite calcium-based minerals, calcium-based or sodium-based montmorillonite. Figure 17-18 , Figures 19-20 as well as Figure 21-22 As shown.

[0121] X-ray diffraction analysis of the soil carbon sequestration agents provided in Examples 1-2 yielded the following results: Figure 17-18 As shown, from Figure 17 and Figure 18 It can be seen that the soil carbon sequestrant provided in Example 1 has the main chemical composition of Ca2SiO4 and Ca3Al2O6, while the soil carbon sequestrant provided in Example 2 has the main chemical composition of Ca2SiO4, Na2Ca3Si2O8, and Ca3Al2O6. The difference in phase composition between the soil carbon sequestrants provided in Examples 1 and 2 is mainly due to the fact that the non-calcium-based montmorillonite calcium-based minerals were calcined with either calcium-based montmorillonite or sodium-based montmorillonite, respectively. Furthermore, compared to the calcium-based montmorillonite (with the main chemical composition of SiO2 and Al2O6) used in the soil carbon sequestrant provided in Example 1 before calcination and activation, the difference is also significant. Compared to the raw materials used in the soil carbon fixation agent provided in Example 2, such as sodium montmorillonite (main chemical composition is SiO2, Al2O3, Fe2O3, MgO, CaO, Na2O), calcium carbonate (CaCO3), and calcium sulfate (CaSO4), the main chemical composition of the soil carbon fixation agent after calcination and activation has changed. The chemical composition of the raw materials before calcination and activation, such as SiO2, is transformed into simple silicate chemical composition after calcination and activation, and the effective components are more easily released.

[0122] The water solubility and citric acid solubility (2% citric acid) of the soil carbon fixatives provided in Examples 1-2 were determined using the mass difference subtraction method. First, the initial masses of sodium-based montmorillonite, calcium-based montmorillonite, and the soil carbon fixatives provided in Examples 1-2 were weighed. Then, they were extracted with deionized water and 2% citric acid solution, respectively. After shaking and filtration, the filter residue was collected and dried to constant weight. The mass of the residual solids after extraction was recorded. Based on the difference between the initial mass of the sample before extraction and the mass of the residual solids after extraction, the dissolution mass of the sample in deionized water and 2% citric acid solution was calculated. This mass was then divided by the initial mass of the sample before extraction to calculate the solubility of the sample. The water solubility and citric acid solubility results were expressed as mass percentages. Water solubility reflects the overall dissolution degree of the material in water, while citric acid solubility reflects the overall dissolution degree of the material under weakly acidic conditions of 2% citric acid. These results can be used to evaluate the effectiveness of potentially releaseable components in the material. The water solubility and citric acid solubility (2% citric acid) results of sodium-based montmorillonite, calcium-based montmorillonite, and the soil carbon fixatives provided in Examples 1-2 are as follows: Figures 19-20 As shown; from Figure 19 and Figure 20 It can be seen that, compared with the water solubility of the raw calcium-based or sodium-based montmorillonite being close to 0% and its citric acid solubility being 25-30%, after calcination and activation with non-calcium-based montmorillonite calcium-based minerals, the difficult-to-use chemical components such as SiO2 in the raw calcium-based or sodium-based montmorillonite are transformed into chemical components such as anhydrous silicates, and its water solubility is improved to a certain extent. At the same time, its citric acid solubility (2% citric acid) is significantly improved. The water solubility and citric acid solubility of the soil carbon fixative provided in Example 1 reached 14.96% and 94.09%, respectively, and the water solubility and citric acid solubility of the soil carbon fixative provided in Example 2 reached 16.38% and 97.82%, respectively. This indicates that the soil carbon fixative provided in Examples 1-2, due to constant temperature calcination and activation at 1000-1100℃, has changed the types and structures of its compounds, enhanced the solubility of the soil carbon fixative, and facilitated the release of various mineral elements.

[0123] To further investigate the effect of calcination activation on the release of mineral elements from soil carbon sequestrants, this experiment analyzed the water solubility and citric acid solubility (2% citric acid) of the mineral element Si in sodium-based montmorillonite, calcium-based montmorillonite, and the soil carbon sequestrants provided in Examples 1-2; referring to the national standard GB / T 36207-2018 "Silicon-Magnesium-Calcium-Potassium Fertilizer" and NY / T Standard 2272-2012, "Determination of Calcium, Magnesium, and Silicon Content in Soil Conditioners," determined the water-soluble and plant-available forms of silicon in sodium-based montmorillonite, calcium-based montmorillonite, and the soil carbon fixatives provided in Examples 1-2. Extraction was performed using deionized water and 2% citric acid solution, followed by shaking and filtration. Atomic absorption spectrophotometry was used for quantitative analysis of the extracts. The water-soluble silicon release ratio and citric acid-soluble silicon release ratio (based on total silicon) were calculated based on the ratio of silicon released from the extract to the total silicon content of the sample. Water-soluble silicon reflects the supply capacity of readily soluble silicon in the material, while citric acid-soluble silicon reflects the level of available silicon that can be released and absorbed by plants under weakly acidic rhizosphere conditions. Results are as follows: Figure 21-22 As shown; from Figure 21 and Figure 22 It can be seen that, compared with the water solubility of calcium-based or sodium-based montmorillonite (approximately 0%) and citric acid solubility (less than 5%), the water solubility and citric acid solubility (2% citric acid) of Si are improved due to the calcination activation process, allowing for the effective release of the mineral element Si. The water solubility and citric acid solubility of silicon in the soil carbon fixative provided in Example 1 reached 12.40% and 75.78%, respectively, while those in the soil carbon fixative provided in Example 2 reached 15.40% and 86.94%, respectively. This indicates that the soil carbon fixatives provided in Examples 1-2 of this application, through the calcination activation of calcium-based minerals such as montmorillonite and non-calcium-based montmorillonite... The soil carbon sequestrant is activated by constant-temperature roasting at 1000~1100℃, which transforms chemical components such as SiO2 and Al2O3 into anhydrous silicates and aluminates. This changes the main chemical composition of the soil carbon sequestrant, enhances its solubility, promotes the release of mineral elements such as Si, and improves the content and bioavailability of available silicon. It also regulates the microbial community structure of methanogenic bacteria or methanogenic bacteria in fertilized farmland soil, affects carbon metabolism pathways, and inhibits the decomposition of organic matter in farmland soil by microorganisms at the source. This effectively suppresses the emission of greenhouse gases such as methane and carbon dioxide from fertilized farmland soil, achieving excellent carbon sequestration and emission reduction effects.

[0124] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for reducing greenhouse gas emissions from farmland, characterized in that the steps include... include: Adding soil carbon sequestrants to fertilized farmland soil reduces greenhouse gas emissions from fertilized farmland soil; The method for preparing the soil carbon sequestration agent includes the following steps: Pre-treating a mixture of montmorillonite and non-calcium-based montmorillonite calcium-based mineral powders yields a mixed dry powder. The mixed dry powder is calcined at 1000~1100℃ for 0.5~2h to obtain a soil carbon sequestration agent; The montmorillonite is sodium-based montmorillonite; The calcium-based minerals of the non-calcium-based montmorillonite are calcium carbonate and calcium sulfate; The mass ratio of the montmorillonite, the calcium carbonate, and the calcium sulfate is 1:2.5:0.

08.

2. The method for reducing greenhouse gas emissions from farmland according to claim 1, characterized in that, The pretreatment process includes: grinding, drying, and pulverizing in sequence; After roasting for 0.5 to 2 hours, the post-processing includes: cooling to room temperature, pulverizing, and sieving.

3. The method for reducing greenhouse gas emissions from farmland according to claim 1, characterized in that, The montmorillonite and non-calcium-based montmorillonite calcium-based mineral mixed powder is composed of montmorillonite powder with a particle size of less than 100 mesh and non-calcium-based montmorillonite calcium-based mineral powder with a particle size of less than 100 mesh.

4. The method for reducing greenhouse gas emissions from farmland according to claim 2, characterized in that, The dispersion medium used in the grinding is deionized water, and the grinding time is 10-20 minutes.

5. A method for reducing greenhouse gas emissions from farmland according to claim 2, characterized in that, The drying temperature is 100~110℃.

6. A method for reducing greenhouse gas emissions from farmland according to claim 2, characterized in that, The sieve used for sieving has a mesh size of 50-150.

7. The method for reducing greenhouse gas emissions from farmland according to claim 1, characterized in that, The amount of soil carbon sequestrant added is 1~5 wt.%.

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