A method for dry land green manure and carbon sequestration

Abstract

The application discloses a dry land green manure field returning carbon fixation method and belongs to the technical field of green manure field returning, and the method comprises the steps of soil pretreatment, seeding and field returning, etc., adopts mixed seeding of Changwu Huai beans and sudan grass, carries out field returning treatment, and applies a conditioner during green manure field returning, so that the green manure field returning is effectively accelerated to rot, and the accumulation of the organic carbon stability of farmland soil is promoted, so that long-term carbon pool construction of farmland and carbon sink enhancement of an ecological system are realized.

Description

Technical Field

[0001] This invention relates to the field of green manure return to the field, and in particular to a method for carbon sequestration through green manure return to the field in dry land. Background Technology

[0002] Returning green manure to the field is an important agronomic measure to improve soil fertility in dryland farmland and enhance the carbon sequestration potential of the ecosystem. By supplementing the soil with exogenous organic matter, it can not only improve the physical and chemical properties of the soil and enhance its water and fertilizer retention capacity, but also provide core substrates for the construction of farmland carbon pools. It is a key technical path to promote the sustainable development of dryland agriculture and help achieve the goal of carbon peaking and carbon neutrality.

[0003] Currently, traditional green manure application to the field is mostly done using a single green manure method. While leguminous green manures have strong biological nitrogen fixation capabilities and can effectively increase soil nitrogen levels, their own carbon substrate input is insufficient, making it difficult to meet the needs of soil organic carbon accumulation. Gramineous green manures are rich in carbon substrates but suffer from nitrogen deficiency. During decomposition, they easily trigger nitrogen competition among soil microorganisms, thus inhibiting the stable accumulation of organic carbon. Applying a single green manure can easily lead to severe organic carbon mineralization and loss, making the carbon fixation effect unsustainable. To address this problem, a conventional solution is to use a mixed sowing of leguminous and gramineous green manures. By complementing each other, the carbon-nitrogen ratio of the green manure substrate is optimized, alleviating the inherent shortcomings of single green manures and improving carbon fixation efficiency in the initial stages of application. However, the mixed sowing of legumes and grasses into the field only optimizes the structure of green manure substrates, without specifically intervening in the key links of stable accumulation of organic carbon. It lacks active regulation of long-term carbon fixation mechanisms such as the formation of mineral-organic matter complexes and the retention of carbon in microbial residues. As a result, the organic carbon after returning to the field exists mostly in easily decomposable forms, which are easily mineralized and lost due to environmental factors, making it difficult to achieve long-term stable retention of organic carbon and the construction of a long-term carbon pool in farmland.

[0004] Therefore, there is a need to find a method for carbon sequestration through green manure return to the field to solve the problem of insufficient soil organic carbon stability and easy mineralization loss under the conventional green manure mixed sowing and return to the field model. Summary of the Invention

[0005] Therefore, the purpose of this invention is to provide a method for carbon sequestration by returning green manure to the field in dryland, which solves the problem of insufficient soil organic carbon stability and easy mineralization and loss under the conventional green manure mixed sowing and returning method.

[0006] The present invention solves the above-mentioned technical problems through the following technical means:

[0007] A method for carbon sequestration through returning green manure to the field in dryland areas, the method comprising the following steps:

[0008] (1) Soil pretreatment: In mid-to-late June, after the wheat harvest, the remaining straw in the field is cleared, the soil is plowed to a depth of 10-25cm and then leveled, and then mixed base fertilizer is applied to obtain pretreated soil;

[0009] (2) Sowing: Mix the seeds of Changwu Huai Dou and Sudan grass, and sow by broadcasting at a depth of 2-3 cm;

[0010] (3) Returning to the field: From late August to mid-September, after applying a conditioner to the soil, turn over and return Changwu Huai Dou and Sudan grass to the field. The turning depth is 15-20cm.

[0011] Furthermore, the mixed base fertilizer in (1) is obtained by mixing well-rotted manure and superphosphate in a mass ratio of 1:1, and the amount of mixed base fertilizer applied is 8-12 kg / mu.

[0012] Furthermore, in (2), the total amount of mixed sowing of Changwu Huai Dou and Sudan grass seeds is 3-4 kg / mu, and the mass ratio of Changwu Huai Dou to Sudan grass seeds is 2:1.

[0013] Furthermore, the conditioning agent in (3) includes the following raw materials;

[0014] Sodium bentonite, white rot fungi, manganese sulfate, cetyltrimethylammonium chloride, propylene glycol alginate, and polyvinyl butyral.

[0015] Furthermore, the preparation method of the conditioner is as follows:

[0016] A: Sodium-based bentonite is added to water and stirred to disperse it according to the mass ratio of sodium-based bentonite to water = 1:10. Then manganese sulfate is added and the temperature is raised to 60-80℃ and stirred for 2-4 hours. After the reaction is completed, the filtrate is removed by suction filtration and washed with water 2-3 times to obtain primary modified bentonite. The primary modified bentonite is added to water and stirred to disperse it. The mass ratio of primary modified bentonite to water is 1:10. Then hexadecyltrimethylammonium chloride is added and the temperature is raised to 60-80℃ and stirred for 2-4 hours. After the reaction is completed, the filtrate is removed by suction filtration and washed with anhydrous ethanol and water in sequence. Then it is dried at 45-60℃ to obtain modified bentonite.

[0017] B: Inoculate the white rot fungus into PDA liquid medium and culture it in a shaker at 26-30℃ for 3-5 days to obtain a bacterial solution. Add modified bentonite to the bacterial solution and stir to disperse it. After standing for 2-4 hours, filter to remove the filtrate. Then granulate it to prepare particles with a particle size of 2-3 mm. Dry it at 40℃ to a moisture content of 10-15% to obtain mixed particles.

[0018] C: Prepare an alginate solution by dissolving propylene glycol alginate in water at a mass ratio of 1:20. Prepare a polyvinyl butyral solution by dissolving polyvinyl butyral in anhydrous ethanol at a mass ratio of 1:10. Then, mix the alginate solution and the polyvinyl butyral solution evenly to obtain a composite solution. Add the mixed particles to the composite solution and stir to disperse. After standing for 2-5 minutes, remove the particles and dry them at 40℃ for 15-20 minutes. Then, add the particles back to the composite solution and stir to disperse. After standing for 5-8 minutes, remove the particles and dry them at 40℃ for 30-60 minutes to obtain the conditioning agent.

[0019] In order to improve the stability of organic carbon generated after Changwu Huai Dou and Sudan grass are returned to the field, this invention prepares a conditioner that is applied during the return process to fix the organic carbon generated by the decomposition of green manure into a mineral-bound organic carbon with high stability, thereby achieving the purpose of enhancing the stability of soil organic carbon.

[0020] Specifically, the conditioner is prepared by loading white-rot fungi onto sodium-based bentonite as the main material. When the conditioner is applied to the soil, the sodium-based bentonite can bind with the organic carbon formed by the decomposition of green manure through interfacial adsorption, cation bridging, and coordination complexation, generating highly stable mineral-bound organic carbon and improving the soil aggregate structure, thus protecting the organic carbon and inhibiting the mineralization and decomposition of organic carbon formed by returning green manure to the field. At the same time, white-rot fungi, as lignocellulose-decomposing fungi, can secrete lignin peroxidase, manganese peroxidase, and laccase to depolymerize plant lignin into small-molecule aromatic compounds, promoting the decomposition of green manure after returning it to the field. They also assimilate some carbon into fungal biomass, and after death, they form fungal residual carbon, which, due to its high chitin / melanin content, readily combines with minerals to form stable mineral-bound organic carbon, further improving the stability of soil organic carbon.

[0021] However, sodium-based bentonite is highly hydrophilic and has a negatively charged surface, resulting in poor affinity for hydrophobic organic compounds such as alkyl chains and aromatic hydrocarbons. Furthermore, in the early stages of white-rot fungi entering the soil, they easily compete with indigenous microorganisms that decompose easily decomposable components such as proteins and sugars, affecting the composting of green manure. Based on these problems, this invention sequentially treats sodium-based bentonite with manganese sulfate and hexadecyltrimethylammonium chloride. Manganese sulfate and hexadecyltrimethylammonium chloride enter the interlayer structure of sodium-based bentonite through ion exchange, introducing manganese ions and hydrophobic sites into the interlayer structure to enhance the sodium-based bentonite's ability to capture and fix alkyl chains and aromatic hydrocarbons. On the other hand, sodium-based bentonite can release manganese ions in the later stages, increasing the decomposition activity of white-rot fungi on difficult-to-decompose components such as lignin in green manure, thus promoting efficient composting of green manure in the field.

[0022] This invention further employs a mixture of propylene glycol alginate and polyvinyl butyral to coat the conditioner. Polyvinyl butyral reduces the water absorption and swelling of the coating layer. Consequently, under the coating effect, white-rot fungi in the conditioner are not released during the early stages of returning the material to the field, thus addressing the issue of competition with indigenous microorganisms. When easily decomposable components in the green manure, such as proteins and sugars, decompose and release organic acids that attack the acetal bonds of polyvinyl butyral, along with the decomposition of propylene glycol alginate by microorganisms, the membrane stability decreases, allowing water molecules to enter. This leads to the sodium-based bentonite absorbing water and swelling, causing the membrane to rupture. Only then are the white-rot fungi released to efficiently decompose residual lignin and other components. Through the combined action of the conditioner components, efficient decomposition of green manure is promoted, transforming it into highly stable organic carbon fixed in the soil, thereby improving the stability of soil organic carbon.

[0023] Furthermore, the amount of manganese sulfate added in A is 0.4-0.6% of the mass of sodium-based bentonite.

[0024] Furthermore, the amount of hexadecyltrimethylammonium chloride added in A is 2-4% of the mass of the primary modified bentonite.

[0025] Furthermore, the mass ratio of modified bentonite to bacterial solution in B is 1:1.

[0026] Furthermore, the mass ratio of the alginate propylene glycol solution and the polyvinyl butyral solution in C is 7:3.

[0027] Furthermore, the amount of conditioner applied in (3) is 50-80 kg / mu.

[0028] Beneficial effects:

[0029] This invention uses a mixture of Changwu Huai Dou seeds and Sudan grass for green manure return to the field, optimizes the carbon-nitrogen ratio of the green manure substrate, and combines the effects of conditioners to achieve efficient return and decomposition of green manure, promotes the generation of stable organic carbon, and achieves the goal of enhancing the carbon sequestration performance of farmland. Attached Figure Description

[0030] Figure 1 : This is a picture of the soil after the green manure was returned to the field according to the present invention;

[0031] Figure 2 Image of Changwu Huai soybean used for sowing in this invention;

[0032] Figure 3 Image of Sudan grass used for sowing in this invention;

[0033] Figure 4 This image shows the soil during the sowing of *Changwu Huai Dou* and *Sudan Grass* in this invention. Detailed Implementation

[0034] The present invention will now be described in detail with reference to specific embodiments and accompanying drawings:

[0035] This invention discloses a method for carbon sequestration by returning green manure to the field in dryland. Before returning green manure to the field in dryland, it is necessary to prepare a conditioning agent. Specifically, all the raw materials used in this invention can be purchased from the market. The white rot fungus is *Procambarus chrysospora* purchased from Beinachuanglian Biotechnology Co., Ltd.; the manganese sulfate used is manganese sulfate hexahydrate.

[0036] Example 1: Preparation of Conditioner

[0037] A: Sodium-based bentonite was added to water and stirred to disperse it according to the mass ratio of sodium-based bentonite to water = 1:10. Then manganese sulfate was added and the temperature was raised to 70°C and stirred for 3 hours. The amount of manganese sulfate added was 0.5% of the mass of sodium-based bentonite. After the reaction was completed, the filtrate was removed by suction filtration and washed with water 3 times to obtain primary modified bentonite. The primary modified bentonite was added to water and stirred to disperse it. The mass ratio of primary modified bentonite to water was 1:10. Then hexadecyltrimethylammonium chloride was added. The amount of hexadecyltrimethylammonium chloride added was 3% of the mass of primary modified bentonite. The temperature was raised to 70°C and stirred for 3 hours. After the reaction was completed, the filtrate was removed by suction filtration and washed with anhydrous ethanol and water in sequence. Then it was dried at 50°C to obtain modified bentonite.

[0038] B: White rot fungus was inoculated into PDA liquid medium and cultured in a shaker at 28°C for 4 days to obtain a bacterial solution. Modified bentonite was added to the bacterial solution and stirred to disperse it. The mass ratio of modified bentonite to bacterial solution was 1:1. After standing for 3 hours, the solution was filtered to remove the filtrate. Then, the solution was granulated to prepare particles with a particle size of 3 mm. The particles were dried at 40°C to a moisture content of about 12% to obtain mixed particles.

[0039] C: A propylene glycol alginate solution was prepared by dissolving propylene glycol alginate in water at a mass ratio of 1:20. A polyvinyl butyral solution was prepared by dissolving polyvinyl butyral in anhydrous ethanol at a mass ratio of 1:10. The propylene glycol alginate solution and the polyvinyl butyral solution were then mixed evenly to obtain a composite solution at a mass ratio of 7:3. The mixed particles were added to the composite solution and stirred to disperse them until they were completely submerged. After standing for 3 minutes, the particles were removed and dried at 40°C for 18 minutes. They were then added back to the composite solution and stirred to disperse them. After standing for 6 minutes, the particles were removed and dried at 40°C for 45 minutes to obtain the conditioning agent.

[0040] Example 2: Preparation of Conditioner II

[0041] A: Sodium-based bentonite was added to water and stirred to disperse it according to the mass ratio of sodium-based bentonite to water = 1:10. Then manganese sulfate was added and the temperature was raised to 60℃ and stirred for 4 hours. The amount of manganese sulfate added was 0.4% of the mass of sodium-based bentonite. After the reaction was completed, the filtrate was removed by suction filtration and washed twice with water to obtain primary modified bentonite. The primary modified bentonite was added to water and stirred to disperse it. The mass ratio of primary modified bentonite to water was 1:10. Then hexadecyltrimethylammonium chloride was added. The amount of hexadecyltrimethylammonium chloride added was 2% of the mass of primary modified bentonite. The temperature was raised to 60℃ and stirred for 4 hours. After the reaction was completed, the filtrate was removed by suction filtration and washed successively with anhydrous ethanol and water and dried at 45℃ to obtain modified bentonite.

[0042] B: White rot fungus was inoculated into PDA liquid medium and cultured in a shaker at 26°C for 5 days to obtain a bacterial solution. Modified bentonite was added to the bacterial solution and stirred to disperse it. The mass ratio of modified bentonite to bacterial solution was 1:1. After standing for 2 hours, the solution was filtered to remove the filtrate. Then, the solution was granulated to prepare particles with a particle size of 2 mm. The particles were dried at 40°C to a moisture content of about 10% to obtain mixed particles.

[0043] C: Prepare an alginate solution by dissolving propylene glycol alginate in water at a mass ratio of 1:20. Prepare a polyvinyl butyral solution by dissolving polyvinyl butyral in anhydrous ethanol at a mass ratio of 1:10. Then, mix the alginate solution and the polyvinyl butyral solution evenly to obtain a composite solution at a mass ratio of 7:3. Add the mixed particles to the composite solution and stir to disperse them until the particles are completely submerged. After standing for 2 minutes, remove the particles and dry them at 40°C for 15 minutes. Then, put the particles back into the composite solution and stir to disperse them. After standing for 8 minutes, remove the particles and dry them at 40°C for 30 minutes to obtain the conditioning agent.

[0044] Example 3: Preparation of Conditioner

[0045] A: Sodium-based bentonite was added to water and stirred to disperse it according to the mass ratio of sodium-based bentonite to water = 1:10. Then manganese sulfate was added and the temperature was raised to 80℃ and stirred for 2 hours. The amount of manganese sulfate added was 0.6% of the mass of sodium-based bentonite. After the reaction was completed, the filtrate was removed by suction filtration and washed with water 3 times to obtain primary modified bentonite. The primary modified bentonite was added to water and stirred to disperse it. The mass ratio of primary modified bentonite to water was 1:10. Then hexadecyltrimethylammonium chloride was added. The amount of hexadecyltrimethylammonium chloride added was 4% of the mass of primary modified bentonite. The temperature was raised to 80℃ and stirred for 2 hours. After the reaction was completed, the filtrate was removed by suction filtration and washed with anhydrous ethanol and water in sequence. Then it was dried at 60℃ to obtain modified bentonite.

[0046] B: White rot fungus was inoculated into PDA liquid culture medium and cultured in a shaker at 30°C for 3 days to obtain a bacterial solution. Modified bentonite was added to the bacterial solution and stirred to disperse it. The mass ratio of modified bentonite to bacterial solution was 1:1. After standing for 4 hours, the filtrate was removed by filtration. Then, granulation was carried out to prepare particles with a particle size of 3 mm. The particles were dried at 40°C to a moisture content of 15% to obtain mixed particles.

[0047] C: Prepare an alginate solution by dissolving propylene glycol alginate in water at a mass ratio of 1:20. Prepare a polyvinyl butyral solution by dissolving polyvinyl butyral in anhydrous ethanol at a mass ratio of 1:10. Then, mix the alginate solution and the polyvinyl butyral solution evenly to obtain a composite solution at a mass ratio of 7:3. Add the mixed particles to the composite solution and stir to disperse them until the particles are completely submerged. After standing for 5 minutes, remove the particles and dry them at 40°C for 20 minutes. Then, put the particles back into the composite solution and stir to disperse them. After standing for 5 minutes, remove the particles and dry them at 40°C for 60 minutes to obtain the conditioning agent.

[0048] Comparative Example 1: Preparation of Conditioner

[0049] Compared with Example 1, the only difference is that manganese sulfate treatment was not used in step A of the preparation of the conditioner in Comparative Example 1. All other steps are the same as in Example 1, as detailed below:

[0050] A: Sodium-based bentonite was added to water and stirred to disperse it according to the mass ratio of sodium-based bentonite to water = 1:10. Then, hexadecyltrimethylammonium chloride was added, with the amount of hexadecyltrimethylammonium chloride being 3% of the mass of sodium-based bentonite. The mixture was then heated to 70°C and stirred for 3 hours. After the reaction was completed, the filtrate was removed by suction filtration. The mixture was washed with anhydrous ethanol and water in sequence and then dried at 50°C to obtain modified bentonite.

[0051] BC: Same as in Example 1.

[0052] Comparative Example 2: Preparation of Conditioner

[0053] Compared with Example 1, the only difference is that in Comparative Example 2, cetyltrimethylammonium chloride treatment was not used in step A of the preparation of the conditioner. All other steps are the same as in Example 1, as detailed below:

[0054] A: Sodium-based bentonite was added to water and stirred to disperse it according to the mass ratio of sodium-based bentonite to water = 1:10. Then manganese sulfate was added and the temperature was raised to 70°C and stirred for 3 hours. The amount of manganese sulfate added was 0.5% of the mass of sodium-based bentonite. After the reaction was completed, the filtrate was removed by suction filtration, washed with water 3 times and dried at 50°C to obtain modified bentonite.

[0055] BC: Same as in Example 1.

[0056] Comparative Example 3: Preparation of Conditioner

[0057] Compared with Example 1, the only difference is that the original step A was omitted in the preparation of the conditioning agent in Comparative Example 3, that is, the sodium-based bentonite was not modified. All other steps are the same as in Example 1.

[0058] Comparative Example 4: Preparation of Conditioner

[0059] Compared with Example 1, the only difference is that in Comparative Example 4, the original step C was missing in the preparation of the conditioner, that is, the mixed particles prepared directly from steps A and B are the conditioner.

[0060] Comparative Example 5: Preparation of Conditioner

[0061] Compared with Example 1, the only difference is that in Comparative Example 5, propylene glycol alginate was not used in step C of the conditioner preparation process; instead, polyvinyl butyral was used for treatment. The remaining steps are the same as in Example 1, as detailed below:

[0062] AB: Same as Example 1;

[0063] C: Polyvinyl butyral was dissolved in anhydrous ethanol to prepare a polyvinyl butyral solution with a mass ratio of 1:10 between polyvinyl butyral and anhydrous ethanol. The mixed particles were added to the polyvinyl butyral solution and stirred to disperse them so that the mixed particles were completely submerged. After standing for 3 minutes, the particles were removed and dried at 40°C for 18 minutes. Then, the particles were added to the polyvinyl butyral solution and stirred to disperse them. After standing for 6 minutes, the particles were removed and dried at 40°C for 45 minutes to obtain the conditioning agent.

[0064] Comparative Example 6: Preparation of Conditioner

[0065] Compared with Example 1, the only difference is that in Comparative Example 6, the conditioner preparation step C does not use polyvinyl butyral treatment, but only propylene glycol alginate. The remaining steps are the same as in Example 1, as detailed below:

[0066] AB: Same as Example 1;

[0067] C: Prepare an alginate solution by dissolving propylene glycol alginate in water. The mass ratio of propylene glycol alginate to water is 1:20. Add the mixed particles to the propylene glycol alginate solution and stir to disperse them so that the mixed particles are completely submerged. After standing for 3 minutes, remove the particles and dry them at 40°C for 18 minutes. Then, put the particles back into the propylene glycol alginate solution and stir to disperse them. After standing for 6 minutes, remove the particles and dry them at 40°C for 45 minutes to obtain the conditioning agent.

[0068] Comparative Example 7: Preparation of Conditioner

[0069] Compared with Example 1, the only difference is that sodium alginate was used instead of propylene glycol alginate in step C of the preparation of the conditioner in Comparative Example 7. All other steps are the same as in Example 1, as detailed below:

[0070] AB: Same as Example 1;

[0071] C: Sodium alginate was dissolved in water to prepare a sodium alginate solution with a mass ratio of sodium alginate to water of 1:20. Polyvinyl butyral was dissolved in anhydrous ethanol to prepare a polyvinyl butyral solution with a mass ratio of polyvinyl butyral to anhydrous ethanol of 1:10. The sodium alginate solution and the polyvinyl butyral solution were then mixed evenly to obtain a composite solution with a mass ratio of sodium alginate solution to polyvinyl butyral solution of 7:3. The mixed particles were added to the composite solution and stirred to disperse them so that the mixed particles were completely submerged. After standing for 3 minutes, the particles were removed and dried at 40°C for 18 minutes. They were then added back to the composite solution and stirred to disperse them. After standing for 6 minutes, the particles were removed and dried at 40°C for 45 minutes to obtain the conditioning agent.

[0072] Comparative Example 8: Preparation of Conditioner

[0073] In contrast to Example 1, the only difference is that the conditioner in Comparative Example 8 was prepared using conventional methods, as detailed below:

[0074] White rot fungi were inoculated into PDA liquid culture medium and cultured in a shaker at 28°C for 4 days to obtain a bacterial solution. Sodium bentonite was added to the bacterial solution and stirred to disperse it. The mass ratio of sodium bentonite to bacterial solution was 1:1. After standing for 3 hours, the solution was filtered to remove the filtrate. Then, the solution was granulated to prepare particles with a diameter of 3 mm and dried at 40°C to a moisture content of about 12% to obtain the modifier.

[0075] Example 4: Green Manure Return to Field for Carbon Sequestration in Dry Land

[0076] (1) Soil pretreatment: In late June, after the wheat harvest, the remaining straw in the field was cleared, and the soil was plowed to a depth of about 20cm and then leveled. Well-rotted cow manure and superphosphate were mixed in a mass ratio of 1:1 to obtain mixed base fertilizer. The mixed base fertilizer was applied at a rate of 10kg / mu to obtain pretreated soil.

[0077] (2) Sowing: Select plump seeds of Changwu Huai Dou and Sudan grass without pests and diseases. Sun-dry the seeds for 2 days in the sun and soak them in water for 1 day. Then sow them together by broadcasting. The total amount of Changwu Huai Dou and Sudan grass seeds mixed together is 3.5 kg / mu, and the mass ratio of Changwu Huai Dou to Sudan grass seeds is 2:1. After broadcasting, till the soil at a depth of about 3 cm so that the seeds enter the soil layer at a depth of about 3 cm.

[0078] (3) Returning to the field: In early September, apply the conditioner in Example 3 evenly to the soil at a rate of 60 kg / mu. After application, turn over and return the Changwu Huai Dou and Sudan grass to the field. The turning depth is about 20 cm.

[0079] Experiment: Green manure return to the field for carbon sequestration

[0080] The conditioners prepared in Example 1 and Comparative Examples 1-8 were used in a green manure return experiment. The experiment was conducted at the Shuitou Experimental Base of the Cotton Research Institute of Shanxi Agricultural University. The experiment was divided into 10 groups: experimental group 1, control group 1-8, and blank control.

[0081] After the wheat harvest, an area was designated as an experimental zone, which was then divided into 10 smaller zones, each with an area of ​​30m². 2 These correspond to experimental group 1, control group 1-8, and blank control group, respectively.

[0082] First, the soil in each group was pretreated and sown according to the methods in steps (1) and (2) of Example 4. The sown Changwu Huai Dou and Sudan grass were managed in the same way.

[0083] In early September, conditioners were applied to the soil in each group. Experimental group 1 was treated with the conditioner from Example 1; Comparative Examples 1-8 were treated with the conditioners from Comparative Examples 1-8 respectively; and the blank control group was not treated with any conditioner. The amount of conditioner applied to each group was 3 kg. Before the experiment, the initial soil organic carbon (SOC) and mineral-bound organic carbon (MAOC) content (0-20 cm soil layer) were measured using a five-point sampling method. Then, after 90 days, the soil organic carbon content and mineral-bound organic carbon content (0-20 cm soil layer) were measured again in each group. Three replicate experiments were conducted, and the average data are shown in Table 1.

[0084] Table 1

[0085]

[0086] Based on the data analysis in Table 1, we can conclude that:

[0087] (1) The soil organic carbon content after returning the soil to the field in experimental group 1 was 10.2 g / kg, of which the mineral-bound organic carbon content reached 8.4 g / kg; while the organic carbon content after returning the soil to the field in the blank control group was 9.1 g / kg, and the mineral-bound organic carbon content was 6.7 g / kg. This indicates that the method of the present invention of mixing Changwu Huai Dou and Sudan grass, and preparing a conditioner for application and then turning it back to the field can effectively increase the soil organic carbon content, promote the generation of stable organic carbon, and enhance the carbon sequestration capacity of farmland.

[0088] (2) In control group 1, the conditioner was not treated with manganese sulfate during preparation, which failed to provide manganese ions in a slow-release manner, resulting in a decrease in the effect of white rot fungi and a decrease in the content of soil mineral-bound organic carbon. In control group 2, the conditioner was not treated with hexadecyltrimethylammonium chloride during preparation, which resulted in a decrease in the ability to capture and fix hydrophobic organic matter, and a significant decrease in both soil organic carbon content and mineral-bound organic carbon content. In control group 4, step C was missing during the preparation of the conditioner, which was not coated. The conditioner quickly absorbed water and swelled in the soil, releasing white rot fungi, which competed with the indigenous microorganisms in the early stage of green manure return to the field, resulting in a decrease in the effect of both the indigenous microorganisms and the conditioner.

[0089] (3) In control group 5, the conditioner was prepared using only polyvinyl butyral coating. The single polyvinyl butyral coating layer had too strong water-resistant capacity, which limited the release of white-rot bacteria from the bentonite in the conditioner during the mid-term water absorption and swelling, thus affecting the generation of mineral-bound organic carbon. In control group 6, the conditioner was prepared using only propylene glycol alginate coating. The poor stability of the coating layer led to the premature release of white-rot bacteria, which competed with indigenous microorganisms and reduced the composting effect of green manure. In control group 7, the conditioner was prepared using sodium alginate coating. Sodium alginate... Sodium is sensitive to calcium and magnesium ions in the soil, causing the membrane layer to break down rapidly and release white rot fungi prematurely, thus reducing the effectiveness of the conditioner. However, the conditioner used in experimental group 1, propylene glycol alginate, is not sensitive to calcium and magnesium ions in the soil. Therefore, it can form a stable coating layer with polyvinyl butyral. Only after being attacked by organic acids from the decomposition of green manure and the cumulative decomposition by microorganisms will the membrane layer stability be effectively destroyed, allowing water molecules to enter and causing the sodium-based bentonite to absorb water, expand, and break through the membrane layer structure. This enables the controlled release of white rot fungi and ensures the effectiveness of the conditioner.

[0090] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications and substitutions should be covered within the scope of the claims of the present invention. Technical aspects, shapes, and structures not described in detail in this invention are all well-known technologies.

Claims

1. A method for carbon sequestration through returning green manure to the field in dryland areas, characterized in that, The method includes the following steps: (1) Soil pretreatment: In mid-to-late June, after the wheat harvest, the remaining straw in the field is cleared, the soil is plowed to a depth of 10-25cm and then leveled, and then mixed base fertilizer is applied to obtain pretreated soil; (2) Sowing: Mix the seeds of Changwu Huai Dou and Sudan grass, and sow by broadcasting at a depth of 2-3 cm; (3) Returning to the field: From late August to mid-September, after applying a conditioner to the soil, turn over and return Changwu Huai Dou and Sudan grass to the field. The turning depth is 15-20cm.

2. The method for carbon sequestration by returning green manure to the field in dryland according to claim 1, characterized in that, The mixed base fertilizer in (1) is obtained by mixing well-rotted manure and superphosphate in a mass ratio of 1:1, and the amount of mixed base fertilizer applied is 8-12 kg / mu.

3. A method for carbon sequestration by returning green manure to the field in dryland areas according to claim 2, characterized in that, In (2), the total amount of mixed sowing of Changwu Huai Dou and Sudan Grass seeds is 3-4 kg / mu, and the mass ratio of Changwu Huai Dou to Sudan Grass seeds is 2:

1.

4. A method for carbon sequestration by returning green manure to the field in dryland according to claim 3, characterized in that, The conditioning agent in (3) includes the following raw materials; Sodium bentonite, white rot fungi, manganese sulfate, cetyltrimethylammonium chloride, propylene glycol alginate, and polyvinyl butyral.

5. A method for carbon sequestration by returning green manure to the field in dryland areas according to claim 4, characterized in that, The conditioner is prepared as follows: A: Sodium-based bentonite is added to water and stirred to disperse it according to the mass ratio of sodium-based bentonite to water = 1:

10. Then manganese sulfate is added and the temperature is raised to 60-80℃ and stirred for 2-4 hours. After the reaction is completed, the filtrate is removed by suction filtration and washed with water 2-3 times to obtain primary modified bentonite. The primary modified bentonite is added to water and stirred to disperse it. The mass ratio of primary modified bentonite to water is 1:

10. Then hexadecyltrimethylammonium chloride is added and the temperature is raised to 60-80℃ and stirred for 2-4 hours. After the reaction is completed, the filtrate is removed by suction filtration and washed with anhydrous ethanol and water in sequence. Then it is dried at 45-60℃ to obtain modified bentonite. B: Inoculate the white rot fungus into PDA liquid medium and culture it in a shaker at 26-30℃ for 3-5 days to obtain a bacterial solution. Add modified bentonite to the bacterial solution and stir to disperse it. After standing for 2-4 hours, filter to remove the filtrate. Then granulate it to prepare particles with a particle size of 2-3 mm. Dry it at 40℃ to a moisture content of 10-15% to obtain mixed particles. C: Prepare an alginate solution by dissolving propylene glycol alginate in water at a mass ratio of 1:

20. Prepare a polyvinyl butyral solution by dissolving polyvinyl butyral in anhydrous ethanol at a mass ratio of 1:

10. Then, mix the alginate solution and the polyvinyl butyral solution evenly to obtain a composite solution. Add the mixed particles to the composite solution and stir to disperse. After standing for 2-5 minutes, remove the particles and dry them at 40℃ for 15-20 minutes. Then, add the particles back to the composite solution and stir to disperse. After standing for 5-8 minutes, remove the particles and dry them at 40℃ for 30-60 minutes to obtain the conditioning agent.

6. A method for carbon sequestration by returning green manure to the field in dryland areas according to claim 5, characterized in that, The amount of manganese sulfate added in A is 0.4-0.6% of the mass of sodium bentonite.

7. A method for carbon sequestration by returning green manure to the field in dryland areas according to claim 6, characterized in that, The amount of hexadecyltrimethylammonium chloride added in A is 2-4% of the mass of the primary modified bentonite.

8. A method for carbon sequestration by returning green manure to the field in dryland areas according to claim 7, characterized in that, The mass ratio of modified bentonite to bacterial solution in B is 1:

1.

9. A method for carbon sequestration by returning green manure to the field in dryland areas according to claim 8, characterized in that, The mass ratio of alginate propylene glycol ester solution and polyvinyl butyral solution in C is 7:

3.

10. A method for carbon sequestration by returning green manure to the field in dryland areas according to claim 9, characterized in that, The amount of conditioner applied in (3) is 50-80 kg / mu.

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