Rice soil methane emission reduction method based on mixed application of biochar and kitchen biogas slurry

Abstract

The invention relates to a rice soil methane emission reduction method based on mixed application of biochar and kitchen biogas slurry. The method specifically comprises the following steps: in an inert atmosphere, heating rice straws to obtain straw biochar, oscillating and washing with water, drying and grinding to obtain biochar particles; placing rice soil in a culture vessel, adding the charcoal particles, and mixing and stirring; placing the kitchen waste biogas slurry in an aerobic environment, standing for several days, and uniformly applying the biogas slurry to the surface of the rice soil; adding water into the culture vessel, mixing, and then standing to fully infiltrate the soil until the soil is in a moisture saturation state; and carrying out constant-temperature culture on the culture vessel, and pre-culturing in an aerobic and light-shielding environment, so as to realize methane emission reduction of the rice field soil. According to the technical scheme, the biogas slurry is pretreated, the mixed application proportion of the biochar and the kitchen biogas slurry in the incubation process is regulated and controlled, the methane emission flux generated in the culture period is monitored, and by means of the technical scheme, methane emission can be effectively reduced.

Description

Technical Field

[0001] The invention relates to the technical field of water pollution control and sewage treatment, and in particular to a method for reducing methane emissions from paddy soil based on biochar and kitchen waste slurry. Background Art

[0002] According to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), the increase in global greenhouse gas emissions is expected to cause the global average temperature to rise by about 0.2°C every decade. There is an urgent need to develop and apply innovative technologies to effectively reduce methane emissions from rice fields.

[0003] Biogas slurry is rich in nitrogen (N) required for crop growth and is often used to replace urea. However, a large number of literatures show that biogas slurry alone can increase methane emissions from paddy fields when used instead of urea. Chinese patent CN116472927A discloses a method for reducing greenhouse gas emissions from paddy fields by applying biogas slurry concentrate and wood vinegar. However, there are no reports of reducing methane emissions from paddy soil by treating biogas slurry and mixing it with specific biochar. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for reducing greenhouse gas emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry. Based on the incubation and cultivation of paddy soil, the present invention proposes a technology for the mixed application of kitchen biogas slurry and biochar. By pretreating the biogas slurry to keep its ammonia nitrogen and nitrate nitrogen in an appropriate range, and regulating the mixed application ratio of the two during the incubation process, and monitoring the methane emission flux generated during the cultivation period, this technical solution can effectively reduce methane emissions and provide innovative technical support for agricultural carbon reduction and solid waste resource utilization.

[0005] The object of the present invention is to provide a method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry, comprising the following steps:

[0006] (1) In an inert atmosphere, the rice straw is heated to obtain straw biochar, which is then shaken and washed with water, and then dried and ground to obtain biochar particles;

[0007] (2) placing the food waste biogas slurry in an aerobic environment and leaving it to stand for several days, so that the ammonia nitrogen and nitrate nitrogen and the pH value reach a suitable concentration range, thereby obtaining the treated food waste biogas slurry;

[0008] (3) placing the rice soil in a culture vessel, adding the biochar particles and mixing and stirring; adding the pretreated kitchen biogas slurry and applying it evenly on the surface of the rice soil;

[0009] (4) Add water to the culture vessel and mix, then let it stand to allow the soil to be fully soaked until it is saturated with water;

[0010] (5) The culture vessel is cultured at a constant temperature in an aerobic, light-proof environment for 2-7 days to stimulate the activity of soil microorganisms, and the culture is continued for 40-50 days.

[0011] In some embodiments of the present invention, in step (1), the inert gas in the inert atmosphere is selected from nitrogen and / or argon, and the gas flow rate of the inert gas is 0.5-4 L / min. For example, it can be 0.5 L / min, 1 L / min, 1.5 L / min, 2 L / min, 2.5 L / min, 3 L / min, 3.5 L / min, 4 L / min, etc., or any interval value between any two values.

[0012] In some embodiments of the present invention, in step (1), the heating temperature is 300-700° C. and the heating time is 2-6 hours.

[0013] In some embodiments of the present invention, in step (1), the solvent for the oscillation water washing of the straw biochar is water, and the charcoal-water ratio for the oscillation water washing is (1:20)-(1:40). Exemplarily, it can be 1:20, 1:25, 1:30, 1:35, 1:40, etc., or any interval value between any two values.

[0014] In some embodiments of the present invention, in step (1), the drying temperature after washing is 100-120° C., and the drying time is 20-30 hours.

[0015] In some embodiments of the present invention, in step (1), the particle size of the biochar particles is 500-1000 μm.

[0016] In some embodiments of the present invention, in step (2), the food digester liquid should be placed in an aerobic environment for 4-8 days to convert part of its ammonia nitrogen into nitrate nitrogen, and the ammonia nitrogen and nitrate nitrogen in the treated food digester liquid account for 70-75% and 0.2-0.5% of the total nitrogen.

[0017] In some embodiments of the present invention, in step (2), the pH of the treated food biogas slurry should be greater than 8 to inhibit the activity of methanogens in the biogas slurry.

[0018] In some embodiments of the present invention, in step (3), the biochar particles account for 0.5-2% of the mass of the paddy soil. Exemplarily, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.5%, 2%, etc., or any interval value between any two values.

[0019] In some embodiments of the present invention, in step (3), the amount of kitchen biogas slurry is 5-20 mL / kg·soil. For example, it can be 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 mL / kg·soil., etc., or any interval value between any two values.

[0020] In some embodiments of the present invention, in step (4), the standing time is 1-2 hours; the soil moisture content after water infiltration is 80-100% of the maximum water holding capacity of field soil;

[0021] The water layer height of the soil is 1-3 cm.

[0022] In some embodiments of the present invention, in step (5), the temperature of the constant temperature culture is 30±2°C.

[0023] The above technical solution of the present invention has the following advantages:

[0024] The present invention takes paddy soil as the research object, sets different ratios of biogas slurry to replace nitrogen, washes the biochar, and pre-treats the biogas slurry before conducting soil incubation experiments. The study evaluated the effects of mixed application of biogas slurry and biochar with different pyrolysis temperatures on methane emissions from paddy soil under equal nitrogen conditions. The results showed that compared with the conventional urea application without biochar addition group, mixed application of biochar and biogas slurry can not only reduce the urea application by 50-100%, but also reduce methane emissions by 16.37%-66.42%. The biochar after water washing has a higher content of C, H, and O elements (Table 1), and its surface exhibits high polarity and hydrophilicity. At the same time, its higher ash content fully exposes the adsorption sites in the porous structure of biochar, thereby increasing the soil's resistance to greenhouse gas CH4. 4 In addition, washed biochar can not only increase the number of methane-oxidizing bacteria by providing a suitable growth environment, but also its rich surface functional groups (such as hydroxyl (-OH), carbonyl (C=O), CO and other oxygen-containing functional groups) ( Figure 2 ) can also cause an increase in its surface negative charge and adsorption potential, thereby increasing CH 4 The mixing of biochar and biogas slurry changed the soil pH and moisture content (Table 3). 4 The production of CH is very sensitive to changes in these two factors. Soil pH can affect the activity of methanogens and methanotrophs, thereby affecting CH 4 The increase in soil moisture content increases the number of collisions between methane molecules and water molecules, increasing CH 4 The friction resistance during the diffusion process causes CH 4 Lower emissions.

[0025] Compared with the biochar and urea group, the mixed application of biochar and biogas slurry can not only reduce urea by 50-100%, but also reduce methane emissions by 10.74%-64.16%. In this technical solution, the biogas slurry is aerobically pretreated to inhibit anaerobic methanogens in the biogas slurry and regulate the proportion of ammonia nitrogen and nitrate nitrogen. Compared with urea, which needs to be converted into ammonium nitrogen (NH 4 + ), which is further converted into nitrate nitrogen (NO 3 - ), the pretreated biogas slurry contains a certain proportion of nitrate nitrogen, which can be used as a nitrogen source for the growth of some microorganisms, stimulate the metabolic activity of methane-oxidizing bacteria (especially aerobic types), promote their proliferation, and thus increase gene abundance ( Figure 4 ) (such as pmoA, mmoX), strengthen the oxidation of methane, and the adsorption effect of biochar and its impact on soil moisture content and pH, jointly achieve a higher intensity of methane emission reduction.

[0026] In general, the present invention proposes a technical means for the coordinated application of biochar and biogas slurry, which effectively reduces the greenhouse gas CH in paddy soil by aerobic pretreatment of biogas slurry to control the ratio of ammonia nitrogen to nitrate nitrogen, and by mixing biochar and kitchen biogas slurry at different pyrolysis temperatures. 4 This technology provides an effective solution for reducing greenhouse gas emissions from paddy soil and the rational application of food biogas slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0028] Figure 1 This is a SEM scanning electron microscope surface morphology image of two types of rice straw biochar obtained in Example 1 and Example 2 of the present invention after magnification 5000 times (left: SBC300 applied to Control Example 2 and Example 1, right: SBC700 applied to Examples 2-3).

[0029] Figure 2 The present invention is applied to Comparative Example 2 and Example 1 (SBC300) and Examples 2-3

[0030] (SBC700) Fourier transform infrared (FTIR) spectrum of rice straw biochar.

[0031] Figure 3 The soil CH of the embodiment of the present invention and the comparative example 4 Statistics chart of cumulative emissions.

[0032] Figure 4It is a comparison diagram of the sum of the abundance of genes involved in methane generation and methane oxidation in the soil of the embodiment of the present invention and the control example. DETAILED DESCRIPTION

[0033] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0034] Embodiment 1:

[0035] This embodiment provides a method for mixing biochar and kitchen biogas slurry for reducing greenhouse gas emissions from paddy soil, and the specific steps are as follows:

[0036] (1) The rice straw was cleaned, cut and filled into a quartz tube, and heated to 300 °C at a heating rate of 10 °C / min in a tube furnace under the protection of 2 L / min high-purity nitrogen. After being kept at a constant temperature for 4 h, it was naturally cooled to obtain low-temperature pyrolysis rice straw biochar SBC300.

[0037] (2) SBC300 was washed with water at a carbon-water ratio of 1:30, and then dried at 105°C for 24 hours to constant weight. Then, the particles with a particle size of 500-1000 μm were ground and screened.

[0038] (3) Place the food waste biogas slurry in an aerobic environment and let it stand for 5 days to convert part of the ammonia nitrogen in the biogas slurry into nitrate nitrogen (ammonia nitrogen and nitrate nitrogen account for 73.48% and 0.28% of the total nitrogen, respectively), and adjust the pH value of the biogas slurry to greater than 8.

[0039] (4) Accurately weigh 150 g of air-dried rice soil that has been sieved through a 2 mm mesh and placed in a 250 mL culture bottle. Then weigh 1.5 g (1% of the soil mass) of SBC300 obtained in step (2) and stir thoroughly with a spatula to ensure that the biochar is evenly distributed in the soil.

[0040] (5) For the treatment with 50% nitrogen replacement rate, accurately weigh 1.31 mL of the pre-treated food biogas slurry in step (3) and mix it with 60 mL of deionized water, slowly add it to the culture bottle and wait for it to slowly infiltrate. The remaining 50% of nitrogen is provided by urea, accurately weigh 0.0159 g of urea (CH 4 N 2 O46.7%), and evenly applied to the soil surface in step (4).

[0041] (6) Slowly add 38 mL of deionized water to the culture bottle, use a spatula to thoroughly mix all the ingredients in the culture bottle, and let it stand for 1.5 hours to allow the soil to be fully soaked to a saturated state, maintaining the soil moisture content at 80% of the maximum field water holding capacity, and finally maintaining a static water layer height of about 1 cm. After adding water, weigh the entire culture bottle.

[0042] (7) Place the culture bottle in an incubator at 30±2℃ and pre-cultivate in an aerobic, light-proof environment for 3 days to stimulate soil microbial activity.

[0043] (8) Gas collection and analysis were performed on the 1st, 3rd, 6th, 9th, 13th, 17th, 22nd, 27th, 36th and 45th days of the incubation experiment. During the 45-day incubation period, deionized water was added by weighing every week to maintain the soil moisture content.

[0044] Embodiment 2:

[0045] This embodiment provides a method for mixing biochar and kitchen biogas slurry for reducing greenhouse gas emissions from paddy soil, and the specific steps are as follows:

[0046] (1) The rice straw was cleaned, cut and filled into a quartz tube, and heated to 700 °C in a tube furnace at a heating rate of 10 °C / min under the protection of 2 L / min high-purity nitrogen. After being kept at a constant temperature for 4 h, it was naturally cooled to obtain high-temperature pyrolysis rice straw biochar SBC700.

[0047] (2) The SBC700 obtained in step (1) was washed with water at a carbon-water ratio of 1:30, and then dried at 105°C for 24 hours to a constant weight. Then, the particles with a particle size of 500-1000 μm were ground and screened.

[0048] (3) Place the food waste biogas slurry in an aerobic environment and let it stand for 5 days to convert part of the ammonia nitrogen in the biogas slurry into nitrate nitrogen (ammonia nitrogen and nitrate nitrogen account for 73.48% and 0.28% of the total nitrogen, respectively), and adjust the pH value of the biogas slurry to greater than 8.

[0049] (4) Accurately weigh 150 g of air-dried rice soil that has been sieved through a 2 mm mesh and placed in a 250 mL culture bottle. Then weigh 1.5 g (1% of the soil mass) of SBC700 obtained in step (2) and stir thoroughly with a spatula to ensure that the biochar is evenly distributed in the soil.

[0050] (5) For the treatment with 50% nitrogen replacement rate, accurately weigh 1.31 mL of the pre-treated food biogas slurry in step (3) and mix it with 60 mL of deionized water, slowly add it to the culture bottle and wait for it to slowly infiltrate. The remaining 50% of nitrogen is provided by urea, accurately weigh 0.0159 g of urea (CH 4 N 2 O46.7%), and evenly applied to the soil surface in step (4).

[0051] (6) Slowly add 38 mL of deionized water to the culture bottle, use a spatula to thoroughly mix all the ingredients in the culture bottle, and let it stand for 1.5 hours to allow the soil to be fully soaked to a saturated state, maintaining the soil moisture content at 80% of the maximum field water holding capacity, and finally maintaining a static water layer height of about 1 cm. After adding water, weigh the entire culture bottle.

[0052] (7) Place the culture bottle in an incubator at 30±2℃ and pre-cultivate in an aerobic, light-proof environment for 3 days to stimulate soil microbial activity.

[0053] (8) Gas collection and analysis were performed on the 1st, 3rd, 6th, 9th, 13th, 17th, 22nd, 27th, 36th and 45th days of the incubation experiment. During the 45-day incubation period, deionized water was added by weighing every week to maintain the soil moisture content.

[0054] Embodiment 3:

[0055] This embodiment provides a method for mixing biochar and kitchen biogas slurry for reducing greenhouse gas emissions from paddy soil, and the specific steps are as follows:

[0056] (1) The rice straw was cleaned, cut and filled into a quartz tube, and heated to 700 °C in a tube furnace at a heating rate of 10 °C / min under the protection of 2 L / min high-purity nitrogen. After being kept at a constant temperature for 4 h, it was naturally cooled to obtain high-temperature pyrolysis rice straw biochar SBC700.

[0057] (2) The SBC700 obtained in step (1) was washed with water at a carbon-water ratio of 1:30, and then dried at 105°C for 24 hours to a constant weight. Then, the particles with a particle size of 500-1000 μm were ground and screened.

[0058] (3) Place the food waste biogas slurry in an aerobic environment and let it stand for 5 days to convert part of the ammonia nitrogen in the biogas slurry into nitrate nitrogen (ammonia nitrogen and nitrate nitrogen account for 73.48% and 0.28% of the total nitrogen, respectively), and adjust the pH value of the biogas slurry to greater than 8.

[0059] (4) Accurately weigh 150 g of air-dried rice soil that has been sieved through a 2 mm mesh and placed in a 250 mL culture bottle. Then weigh 1.5 g (1% of the soil mass) of SBC700 and stir thoroughly with a spatula to ensure that the biochar is evenly distributed in the soil.

[0060] (5) For the treatment with 100% nitrogen replacement rate, accurately weigh 2.62 mL of the pretreated food biogas slurry in step (3), mix it with 60 mL of deionized water, slowly add it to the culture bottle, and wait for it to slowly infiltrate.

[0061] (5) Slowly add 38 mL of deionized water to the culture bottle, use a spatula to thoroughly mix all the ingredients in the culture bottle, and let it stand for 1.5 hours to allow the soil to be fully soaked to a saturated state, maintaining the soil moisture content at 80% of the maximum field water holding capacity, and finally maintaining a static water layer height of about 1 cm. After adding water, weigh the entire culture bottle.

[0062] (6) Place the culture bottle in an incubator at 30±2℃ and pre-culture for 3 days in an aerobic, light-proof environment to stimulate soil microbial activity.

[0063] (7) Gas collection and analysis were performed on the 1st, 3rd, 6th, 9th, 13th, 17th, 22nd, 27th, 36th and 45th days of the incubation experiment. During the 45-day incubation period, deionized water was added by weighing every week to maintain the soil moisture content.

[0064] Control Example 1 (without any biochar and biogas slurry):

[0065] (1) Accurately weigh 150 g of air-dried rice soil that has been passed through a 2 mm sieve and place it in a 250 mL culture bottle.

[0066] (2) All nitrogen is provided by urea. Accurately weigh 0.03188 g urea (CH 4 N 2 O46.7%), evenly applied on the soil surface.

[0067] (3) Slowly add 98 mL of deionized water to the culture bottle, use a spatula to thoroughly mix all the ingredients in the culture bottle, and let it stand for 1.5 hours to allow the soil to be fully soaked to a saturated state, maintaining the soil moisture content at 80% of the maximum field water holding capacity, and finally maintaining a static water layer height of about 1 cm. After adding water, weigh the entire culture bottle.

[0068] (4) Pre-culture: Place the culture bottle in an incubator at 30±2℃ and pre-culture in an aerobic, light-proof environment for 3 days to stimulate soil microbial activity.

[0069] (5) Gas collection and analysis: Gas collection and analysis were performed on days 1, 3, 6, 9, 13, 17, 22, 27, 36, and 45 of the incubation experiment. During the 45-day incubation period, deionized water was added by weighing every week to maintain the soil moisture content.

[0070] Control Example 2 (adding only biochar, without adding biogas slurry)

[0071] (1) The rice straw was cleaned, cut and filled into a quartz tube, and heated to 300 °C at a heating rate of 10 °C / min in a tube furnace under the protection of 2 L / min high-purity nitrogen. After being kept at a constant temperature for 4 h, it was naturally cooled to obtain low-temperature pyrolysis rice straw biochar SBC300.

[0072] (2) SBC300 was washed with water at a carbon-water ratio of 1:30, and then dried at 105°C for 24 hours to constant weight. Then, the particles with a particle size of 500-1000 μm were ground and screened.

[0073] (3) Accurately weigh 150 g of air-dried rice soil that has been sieved through a 2 mm mesh and placed in a 250 mL culture bottle. Then weigh 1.5 g (1% of the soil mass) of SBC300 obtained in step (2) and stir thoroughly with a spatula to ensure that the biochar is evenly distributed in the soil.

[0074] (4) All nitrogen is provided by urea. Accurately weigh 0.03188 g urea (CH 4 N 2 O46.7%), and evenly applied to the soil surface in step (3).

[0075] (5) Slowly add 98 mL of deionized water to the culture bottle, use a spatula to thoroughly mix all the ingredients in the culture bottle, and let it stand for 1.5 hours to allow the soil to be fully soaked to a saturated state, maintaining the soil moisture content at 80% of the maximum field water holding capacity, and finally maintaining a static water layer height of about 1 cm. After adding water, weigh the entire culture bottle.

[0076] (6) Pre-culture: Place the culture bottle in an incubator at 30±2℃ and pre-culture in an aerobic, light-proof environment for 3 days to stimulate soil microbial activity.

[0077] (7) Gas collection and analysis: Gas collection and analysis were performed on days 1, 3, 6, 9, 13, 17, 22, 27, 36, and 45 of the incubation experiment. During the 45-day incubation period, deionized water was added by weighing every week to maintain the soil moisture content.

[0078] Test Example 1:

[0079] The performance of the soil in the above embodiments and comparative examples was tested in the following specific steps:

[0080] (1) The experiment was conducted in a culture bottle equipped with a double-pass cap. The double-pass cap was designed with an interface for connecting a hose, and the hose was equipped with a water stop clamp to control gas flow. The culture bottle was kept in an aerobic environment through the double-pass cap and placed in an incubator at 30°C and dark conditions. The gas was taken three times each time, with an interval of 30 minutes in between.

[0081] (2) At 0 min, use a 60 mL syringe to inject 10 mL of high-purity nitrogen (99.999%) into the culture bottle, ensuring that the bottle body and the syringe remain airtight when connected. After the gas in the bottle is fully mixed, use a syringe to extract 10 mL of gas and inject it into a 50 mL air bag for storage.

[0082] (3) At the 30th minute, under the same culture conditions, the sealed culture was cultured for 30 minutes and then sampled again: 10 mL of high-purity nitrogen was injected and 10 mL of gas was extracted into the air bag at the same time.

[0083] (4) At the 60th minute, repeat the same operation as at the 30th minute to perform the third sampling.

[0084] (5) Within 24 hours after sampling, the CH in the gas sample was measured using a gas chromatograph GC2014C (Shimadzu). 4 Concentration. 4 The measurement was performed using an FID detector at a detection temperature of 250°C.

[0085] (6) CH 4 The calculation formula of emission flux is as follows:

[0086]

[0087] Where: F is the CH per unit mass of soil 4 Emission flux, μg·kg -1 ·h -1 ; dc / dt is the detected CH 4 The rate of change of concentration over time, in mol·10 -6 mol -1 ·h -1 ; V is the effective volume of the culture bottle, in L; M is the molar mass of the gas, in g·mol -1 ; m is the mass of soil in the culture bottle, in kg; T is the thermodynamic temperature of the culture, in K; T 0 It is the thermodynamic temperature under standard conditions, and its unit is 273K.

[0088] (7) CH 4 The cumulative emissions are calculated as follows:

[0089]

[0090] Where: E is CH 4 Cumulative gas emissions, in mg kg -1 ; F is CH per unit mass of soil 4 Emission flux, in μg kg -1 ·h -1 ;t i+1 -t i is the time interval between two samplings, d; i is the number of samplings.

[0091] Table 1 Elemental composition and hydrophilicity / polarity properties of washed biochar

[0092]

[0093]

[0094] *SBC300 and SBC700 represent rice straw biochar pyrolyzed at 300°C and 700°C, respectively;

[0095] Table 2 Specific surface area and porosity (Bet) of washed biochar

[0096]

[0097] Table 3 Time series weighted average values ​​of soil pH and moisture content

[0098]

[0099] like Figure 3 As shown, in the 45-day soil incubation experiment, Examples 1-3 using the technical solution of the present invention showed significant methane emission reduction effects. Compared with the traditional urea single application mode (Control Example 1), the cumulative methane emissions after biochar-biogas slurry mixed application treatment decreased by 16.37%-66.42%. Among them: Example 1 (SBC300+50% biogas slurry replaces urea): the methane emission reduction rate reached 33.46%; Example 2 (SBC700+50% biogas slurry replaces urea): the methane emission reduction rate reached 16.37%; Example 3 (SBC700+100% biogas slurry replaces urea in full): the methane emission reduction rate was as high as 66.42%. Compared with the biochar-urea combination application mode (Control Example 2), the scheme of the present invention further achieved a methane emission reduction increase of 10.74%-64.16%, proving the inhibitory effect of biogas slurry aerobic pretreatment and biochar synergistic regulation on methane generation.

[0100] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry, characterized in that: The following steps are involved: (1) In an inert atmosphere, the rice straw is heated to obtain straw biochar, which is then shaken and washed with water, and then dried and ground to obtain biochar particles; (2) placing the food waste biogas slurry in an aerobic environment and leaving it to stand for several days to obtain treated food waste biogas slurry; (3) placing paddy soil in a culture vessel, adding the biochar particles and mixing and stirring; and applying the treated food biogas slurry evenly on the surface of the paddy soil; (4) Add water to the culture vessel and mix, then let it stand to allow the soil to be fully soaked until it is saturated with water; (5) The culture vessel is cultured at a constant temperature in an aerobic, light-proof environment for 2-7 days to stimulate the activity of soil microorganisms, and the culture is continued for 40-50 days.

2. The method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry according to claim 1, characterized in that: In step (1), the inert gas in the inert atmosphere is selected from nitrogen and / or argon, and the gas flow rate of the inert gas is 0.5-4 L / min.

3. The method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry according to claim 1, characterized in that: In step (1), the heating temperature is 300-700° C. and the heating time is 2-6 hours.

4. The method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry according to claim 1, characterized in that: In step (1), the solvent for oscillating and washing the straw biochar is water, and the charcoal-to-water ratio for oscillating and washing is (1:20)-(1:40); The drying temperature after washing is 100-120°C and the drying time is 20-30 hours.

5. The method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry according to claim 1, characterized in that: In step (1), the particle size of the biochar particles is 500-1000 μm.

6. The method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry according to claim 1, characterized in that: In step (2), the number of days the kitchen biogas slurry is placed in an aerobic environment is 4-8 days; The ammonia nitrogen and nitrate nitrogen in the treated kitchen biogas slurry account for 70-75% and 0.2-0.5% of the total nitrogen respectively.

7. The method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry according to claim 1, characterized in that: In step (2), the pH of the treated food biogas slurry should be greater than 8 to inhibit the activity of methanogens in the biogas slurry.

8. The method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry according to claim 1, characterized in that: In step (3), the biochar particles account for 0.5-2% of the mass of the paddy soil; and the amount of kitchen biogas slurry is 5-20 mL / kg·soil.

9. The method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry according to claim 1, characterized in that: In step (4), the standing time is 1-2 hours; The soil moisture content after water infiltration is 80-100% of the maximum water holding capacity of field soil; The water layer height of the soil is 1-3 cm.

10. The method for reducing methane emissions from paddy soil based on the mixed application of biochar and kitchen biogas slurry according to claim 1, characterized in that: In step (5), the constant temperature culture temperature is 30±2°C.

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