A method for applying and screening biochar

Abstract

This invention relates to a method for applying and screening biochar, specifically within the field of paddy field emission reduction technology. This method effectively solves the problems of insufficient CH4 emission reduction methods and unstable emission reduction effects in existing technologies by precisely selecting wheat straw biochar from various crop straw biochars and controlling its application rate. Wheat straw biochar, with its well-developed porous structure and abundant oxygen-containing functional groups on its surface, can adsorb easily decomposable organic matter in the soil, reducing the supply of methanogenic substrates. Simultaneously, it regulates the soil redox potential, inhibits the activity of methanogenic bacteria, and promotes the proliferation of methanogenic bacteria, reducing CH4 generation at the source and achieving significant emission reduction. Its loose and porous structure also improves soil aggregate structure and enhances water and fertilizer retention capacity, ensuring stable and increased rice yields. This method is simple to operate and seamlessly integrates with conventional paddy field fertilization management, without requiring additional field operation costs.

Description

Technical Field

[0001] This invention belongs to the field of paddy field emission reduction technology, and relates to a method for applying and screening biochar. Background Technology

[0002] Since the Industrial Revolution, the concentration of greenhouse gases such as methane (CH4) in the atmosphere has been continuously rising. The global warming potential of CH4 over the past century is 28 times that of carbon dioxide (CO2) and 265 times that of CO2. Rice paddies are a significant source of CH4 emissions. Currently, rice cultivation is widespread, therefore, carbon sequestration and emission reduction in rice paddies are of great significance in mitigating the global greenhouse effect.

[0003] However, how to achieve CH4 emission reduction in paddy fields is a problem that needs to be solved. Summary of the Invention

[0004] In view of this, the present invention provides a method for applying and screening biochar in order to solve the above problems.

[0005] To achieve the above objectives, the present invention provides the following technical solution: In the first aspect, a method for applying biochar is provided, comprising: selecting wheat straw biochar as the type of biochar to be applied to paddy fields from a variety of crop straw biochar; applying wheat straw biochar to paddy fields at an application rate of 1.5-2.5 tons per hectare (t / hm²).

[0006] Therefore, by precisely selecting wheat straw biochar from various crop straw biochar sources and controlling its application rate, the problem of insufficient CH4 emission reduction methods and unstable emission reduction effects in existing technologies for paddy fields can be effectively solved. Wheat straw biochar, with its well-developed porous structure and abundant oxygen-containing functional groups on its surface, can adsorb easily decomposable organic matter in the soil, reduce the supply of methanogenic substrates, regulate the soil redox potential, inhibit the activity of methanogenic bacteria, and promote the proliferation of methanogenic bacteria, thereby reducing CH4 generation at the source and achieving significant emission reduction. Its loose and porous structure can also improve soil aggregate structure, enhance water and fertilizer retention capacity, and ensure stable and increased rice yields. This method is simple to operate, seamlessly integrates with conventional paddy field fertilization management, requires no additional field operation costs, and is easy to promote and implement in vast rice-growing areas.

[0007] Optionally, the application rate of wheat straw biochar is 2 t / hm². At this rate, the inhibitory effect of wheat straw biochar on methanogens and the soil improvement effect are optimally balanced.

[0008] Optionally, wheat straw biochar can be applied simultaneously with base fertilizer before rice transplanting in paddy fields. This allows the biochar to fully age in the soil and exert its effects, improving the soil microenvironment in advance and providing a foundation for methane emission reduction and nutrient supply throughout the rice's growth period.

[0009] Optionally, it also includes excluding rice straw biochar and / or corn straw biochar as the type of biochar to be applied to paddy fields. This exclusionary limitation establishes a clear negative list for the selection of biochar materials for paddy fields, which greatly improves the certainty and safety of technology implementation.

[0010] Optionally, wheat straw biochar is prepared by the following method: under anaerobic conditions, wheat straw is pyrolyzed and carbonized at a first temperature, and then reacted with water vapor or carbon dioxide at a second temperature to obtain wheat straw biochar. Optionally, the first temperature is 400-700℃, and the second temperature is 750-950℃. This allows the wheat straw biochar to acquire a highly developed pore structure and abundant oxygen-containing functional groups on its surface. This structure endows the biochar with stronger adsorption properties and redox regulation capabilities, which is a key foundation for achieving efficient CH4 emission reduction and soil improvement.

[0011] Optionally, various types of crop straw biochar include: rice straw biochar, wheat straw biochar, corn straw biochar, and rapeseed straw biochar.

[0012] Alternatively, the water management model for paddy fields can be: flooding in the early and middle stages, followed by moderate drying in the later stages. This allows for a synergistic effect between the water management model and wheat straw biochar: during flooding, biochar alleviates the strong reducing environment by regulating the redox potential, reducing CH4 formation; during drying, the porous structure of biochar helps maintain moderate soil permeability, promoting the oxidative decomposition of residual CH4. The combination of these two approaches further enhances emission reduction.

[0013] Secondly, a method for screening biochar is provided, comprising: preparing multiple types of biochar using multiple types of crop straw as raw materials; applying the multiple types of biochar to multiple groups in paddy fields in a one-to-one correspondence, and monitoring the CH4 emissions and rice yield of each group; and selecting the type of biochar from the multiple types of biochar that corresponds to CH4 emission reduction and rice yield increase based on CH4 emissions and rice yield.

[0014] Therefore, by conducting standardized field comparative trials of various types of biochar prepared from different crop straws and systematically monitoring CH4 emissions and rice yields in each treatment, precise screening of biochar types can be achieved. This effectively distinguishes the differentiated effects of biochar from different raw materials, accurately identifies the optimal biochar type that combines CH4 emission reduction and rice yield increase, and eliminates undesirable types that may increase CH4 emissions, thus avoiding the risk of increased emissions due to incorrect biochar selection. The entire screening process is systematic, complete, and the data is objective, reliable, and highly repeatable.

[0015] Optionally, CH4 emissions include CH4 emission flux and / or cumulative CH4 emissions. In other words, by using CH4 emission flux as a monitoring indicator and employing the static chamber method in conjunction with a trace gas analyzer for real-time measurement, high-precision dynamic emission data for each key growth stage of rice can be obtained. This indicator is the most direct and sensitive parameter for evaluating the emission reduction effect of biochar. The standardized calculation formula ensures the comparability of data between different treatments, enabling objective and accurate screening of biochar types.

[0016] Optionally, the CH4 emission flux for each group is monitored in a static chamber located within that group, and the CH4 emission flux is calculated according to the following relationship: ; Where F represents the CH4 emission flux, M represents the molar mass of CH4, dc / dt represents the CH4 concentration change per unit time in the static chamber, T represents the temperature in the static chamber, V represents the volume of the static chamber, A represents the bottom area of ​​the static chamber, and P represents the gas pressure at the measurement point. It is evident that using CH4 emission flux as a monitoring indicator, and employing the static chamber method in conjunction with a trace gas analyzer for real-time measurement, can yield high-precision dynamic emission data for each key growth stage of rice. This indicator is the most direct and sensitive parameter for evaluating the emission reduction effect of biochar. The standardized calculation formula ensures the comparability of data between different treatments, enabling objective and accurate screening of biochar types.

[0017] Optionally, the calculation of cumulative CH4 emissions satisfies the following relationship: ; Where CE represents cumulative CH4 emissions, and F... i and F i+1 The CH4 emission flux was determined for two consecutive adjacent sampling periods, where d is the time interval between the two consecutive adjacent sampling times. It is evident that using cumulative CH4 emissions as a screening indicator can reflect the total emission reduction throughout the entire rice growth period or key stages, compensating for the inability of a single flux monitoring to reflect long-term cumulative effects. Calculating cumulative emissions in days ensures both data continuity and operability, enabling objective and accurate screening of biochar types.

[0018] Optional, duration is in days.

[0019] Optionally, rice yield is obtained through theoretical yield measurement and / or actual yield measurement, wherein; Theoretical yield measurement satisfies the following relationship: Theoretical yield = Effective panicles × Number of grains per panicle × Seed setting rate × 1000-grain weight × 10 -5 ; The actual yield measurement satisfies the following relationship: Actual yield = weight per square meter × 10 × [(1 - moisture content) / (1 - 14.5%)].

[0020] Therefore, it can be seen that the method of combining theoretical yield measurement and actual yield measurement is used to evaluate rice yield. Theoretical yield measurement reveals the influence mechanism of biochar on the yield formation process through component factor analysis, while actual yield measurement directly reflects the true yield level through standard quadrat harvesting and weighing. The two methods verify each other to ensure the accuracy of yield assessment.

[0021] Alternatively, various types of crop straw may be used, including rice straw, wheat straw, corn straw, and rapeseed straw.

[0022] Optionally, the monitoring period for CH4 emission flux includes at least one of the following stages of rice: tillering stage, jointing stage, booting stage, heading stage, grain-filling stage, and maturity stage. This covers the key stages of rice's vegetative and reproductive growth. These periods are the main windows for CH4 emission from paddy fields. With reasonable monitoring time points, the dynamic changes in CH4 emissions under different biochar treatments can be comprehensively captured without significantly increasing the workload.

[0023] The objectives and other advantages of this invention can be realized and obtained through the following description. Attached Figure Description

[0024] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 A flowchart of a biochar application method provided by the present invention; Figure 2 A flowchart of a biochar screening method provided by the present invention; Figures 3-5 This is a schematic diagram illustrating an application scenario of the present invention. Detailed Implementation

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1 This embodiment provides a method for applying biochar. This method precisely selects wheat straw biochar from various types of crop straw biochar as the application target, and, in conjunction with specific application rates, application times, and field management parameters, achieves a synergistic effect of significantly reducing CH4 emissions in paddy fields and ensuring stable and increased rice yields. The following is combined with… Figure 1 The process shown below provides a detailed explanation of the technical solution in this embodiment.

[0027] S101, wheat straw biochar was selected from various types of crop straw biochar for application in paddy fields.

[0028] The core of this step is to accurately determine wheat straw biochar as the optimal application material from various types of biochar prepared from the straw of major crops, based on its CH4 emission reduction effect and rice yield performance.

[0029] The selected crop straw biochar includes various types such as rice straw biochar, wheat straw biochar, corn straw biochar, and rapeseed straw biochar. Rice, wheat, corn, and rapeseed are typically major food and cash crops, and their straw is one of the largest agricultural wastes generated during agricultural production. Selecting these four crop straws as raw materials for biochar preparation not only covers the main straw resource types in rice-producing areas but also fully reflects the differentiated effects of biochar made from different raw materials, ensuring the representativeness and practicality of the screening results.

[0030] The selection criteria for wheat straw biochar were based on the CH4 emissions and rice yield performance of different types of biochar in paddy fields. Specifically: Regarding CH4 emissions, the cumulative CH4 emissions of the wheat straw biochar treatment group were reduced by 73.7% compared to the control group without biochar, demonstrating the best emission reduction effect among the four biochar treatments. The cumulative CH4 emissions of the rapeseed straw biochar treatment group were basically the same as the control group, making it a viable alternative material. However, the cumulative CH4 emissions of the rice straw biochar treatment group increased by 10.3% compared to the control group, and the cumulative CH4 emissions of the corn straw biochar treatment group increased by 26.4% compared to the control group, both showing a significant CH4 emission-enhancing effect.

[0031] In terms of rice yield, the actual yield of the wheat straw biochar treatment group increased by 4.14% compared to the control group, and the theoretical yield increased by 3.29%. All other biochar treatment groups also showed stable or increased yields, and no yield reduction occurred due to emission reduction. However, considering both the emission reduction effect and the yield increase, wheat straw biochar is the optimal choice that simultaneously achieves significant emission reduction and stable yield increase.

[0032] Based on the above comparison results, this step clearly selects wheat straw biochar as the biochar type to be applied to paddy fields, and rapeseed straw biochar as a candidate material; at the same time, rice straw biochar and corn straw biochar are excluded as biochar types to be applied to paddy fields. This selection mechanism effectively avoids the risk of increased CH4 emissions due to the incorrect selection of biochar type, and solves the prominent problems of blind biochar screening and unstable emission reduction effects in existing technologies.

[0033] It should be understood that specific choices can be found in the relevant description of Example 2, and will not be repeated here.

[0034] Furthermore, in this step, wheat straw biochar is prepared by the following method: under anaerobic conditions, wheat straw is pyrolyzed and carbonized at a first temperature, and then reacted with an oxidizing gas at a second temperature to obtain wheat straw biochar. The oxidizing gas is water vapor, carbon dioxide, or a mixture thereof. For example, the first temperature is 400-700℃, and the second temperature is 750-950℃. This two-step preparation process—anaerobic pyrolysis carbonization followed by high-temperature oxidation activation—enables wheat straw biochar to possess a highly developed pore structure, a large specific surface area, and abundant surface oxygen-containing functional groups. For example, in a specific and non-limiting embodiment, using water vapor as the oxidizing gas, the biomass raw material is heated to 550℃ under a nitrogen atmosphere for anaerobic pyrolysis carbonization and held at this temperature for 2 hours to obtain a carbonization precursor; subsequently, the precursor is subjected to high-temperature oxidation activation at 850℃ using water vapor as an activator and held at this temperature for 1.5 hours, and then cooled to obtain biochar. These physicochemical properties endow wheat straw biochar with the following key functions: its well-developed porous structure provides strong adsorption capacity, enabling it to adsorb easily decomposable organic matter in the soil and reduce the supply of methanogenic substrates; its abundant surface oxygen-containing functional groups can regulate the soil redox potential, inhibiting the activity and proliferation of methanogenic bacteria while simultaneously promoting the activity of methanogenic bacteria and accelerating CH4 oxidation and decomposition. This is the material basis for wheat straw biochar to distinguish itself from other straw biochars and achieve efficient CH4 emission reduction.

[0035] S102, apply wheat straw biochar to paddy fields at a rate of 1.5-2.5 t / hm².

[0036] Field trials have verified that an application rate of 2 t / hm² of wheat straw biochar achieves the optimal balance between CH4 emission reduction and rice yield increase. This rate serves as the baseline application rate for this embodiment. Based on this, the application rate can be fine-tuned to other values ​​within the range of 1.5-2.5 t / hm², depending on the soil fertility conditions of the paddy field, such as soil organic matter content and pH value.

[0037] Regarding the application timing, wheat straw biochar was applied simultaneously with basal fertilizer before rice transplanting in paddy fields. The specific field operation method was as follows: wheat straw biochar was applied to the paddy field once, along with nitrogen, phosphorus, and potassium basal fertilizer, before rice transplanting, with the basal fertilizer accounting for 60% of the total fertilizer application. Each treatment group received equal amounts of pure nitrogen (12 kg / mu), pure phosphorus (9 kg / mu), and pure potassium (10 kg / mu); tillering fertilizer accounted for 30% of the total fertilizer application and was applied during the rice tillering stage; panicle fertilizer accounted for 10% of the total fertilizer application and was applied during the rice heading stage. Simultaneous application of biochar and basal fertilizer allows biochar to fully exert its soil-improving and greenhouse gas-regulating effects throughout the entire rice growth period.

[0038] In this embodiment, the paddy field water management model is: flooding in the early and middle stages, and moderate drying in the later stages. Specifically, after rice transplanting, the field is kept flooded until the early grain-filling stage, and moderate drainage and drying are carried out from the late grain-filling stage to maturity. "Moderate drying" specifically means: when the rice enters the late grain-filling stage, irrigation is stopped and the field is allowed to drain naturally until the surface water layer completely disappears, the soil surface is moist and fine cracks appear, and the soil water potential at a depth of 15cm is maintained between -15 kPa and -30 kPa; when the soil develops cracks wider than 1cm or the plants show signs of water shortage and leaf curling, a quick irrigation is performed until the field surface is moist, then immediately drained, and the drying process is repeated. This alternating wet and dry cycle is performed 2-3 times until the field is completely drained 7-10 days before harvest. This water management model and wheat straw biochar have a synergistic effect: during the early and middle stages of flooding, wheat straw biochar regulates the soil redox potential through its oxygen-containing functional groups on its surface, alleviating the strong reducing anaerobic environment formed by long-term flooding, improving soil micro-oxygen conditions, and reducing CH4 generation from the source; during the later stages of field drying, the loose and porous structure of wheat straw biochar helps maintain moderate soil permeability, promotes the oxidative decomposition of residual CH4, and further enhances the emission reduction effect throughout the entire growth period.

[0039] The method provided in this embodiment transforms low-value agricultural waste, namely wheat straw, into high-value environmentally friendly materials through a controlled pyrolysis activation process. These materials offer benefits such as greenhouse gas emission reduction in paddy fields, soil improvement, and increased crop yield, achieving the efficient utilization of agricultural waste through harmlessness, reduction, and resource recovery. This technological approach replaces straw burning at the source, significantly reducing environmental pollution and carbon emissions caused by straw burning. It forms a green cycle of "straw—biochar—paddy field emission reduction and yield increase," achieving the triple goals of agricultural waste resource recovery, paddy field carbon sequestration and emission reduction, and stable and increased rice yield. Compared to existing technologies where biochar raw materials are scattered and do not address the needs of agricultural waste resource recovery, the raw materials in this embodiment are widely available, readily accessible, and inexpensive, making it more scalable and practical.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0041] Example 2 This embodiment provides a method for screening biochar. This method involves standardized field comparative experiments on various types of biochar prepared from different crop straws, systematically monitoring CH4 emissions and rice yield in each treatment group, thereby scientifically and accurately screening for the optimal biochar type that combines both CH4 emission reduction and rice yield increase. The following is combined with… Figure 2 The process shown below provides a detailed explanation of the technical solution in this embodiment.

[0042] S201 uses various types of crop straw as raw materials to prepare various types of biochar.

[0043] The various types of crop straw included were rice straw, wheat straw, corn straw, and rapeseed straw. Rice, wheat, corn, and rapeseed are major food and cash crops, and their straw is one of the largest agricultural wastes generated in agricultural production. Selecting these four types of crop straw as candidate raw materials not only covers the main straw resource types in rice-producing areas but also fully reflects the differentiated effects of different raw materials for biochar, ensuring the representativeness and comprehensiveness of the screening scope and avoiding the omission of potentially high-quality raw materials.

[0044] The preparation method for various types of biochar is as follows: under anaerobic conditions, crop straw is pyrolyzed and carbonized at a first temperature, and then reacted with an oxidizing gas at a second temperature to obtain powdered biochar. The oxidizing gas is water vapor, carbon dioxide, or a mixture thereof. For example, the first temperature is 400-700℃, and the second temperature is 750-950℃. This two-step preparation process, namely anaerobic pyrolysis carbonization followed by high-temperature oxidation activation, endows the biochar with a porous structure and surface functional groups, providing structurally stable and consistent candidate materials for subsequent field screening trials.

[0045] S202 involves applying various types of biochar to multiple groups in paddy fields and monitoring the CH4 emissions and rice yield of each group.

[0046] This step involves setting up a standard field comparison experiment that includes multiple types of biochar treatment groups and control groups to systematically monitor CH4 emissions and rice yield for each treatment group. A specific example is provided below for illustration.

[0047] Example of test setup: like Figure 3 As shown, five treatment groups were set up, with the following correspondence between treatment groups and the type of biochar applied: T1 treatment group applied rice straw biochar; T2 treatment group applied wheat straw biochar; T3 treatment group applied corn straw biochar; T4 treatment group applied rapeseed straw biochar; and the CK group did not receive any biochar and served as a control group. Each treatment group was replicated three times, for a total of 15 plots, which were randomly arranged. Each plot area was 3 meters (m) × 7 meters, separated by 0.5-meter field ridges covered with film. Each treatment group was applied with equal amounts of pure nitrogen (12 kg / mu), pure phosphorus (9 kg / mu), and pure potassium (10 kg / mu), and the biochar application rate was 2 t / hm². The nitrogen, phosphorus, and potassium fertilizers in each treatment group were applied according to the ratio of 60% basal fertilizer, 30% tillering fertilizer, and 10% heading fertilizer. Biochar and basal fertilizer were applied together before rice transplanting, while tillering fertilizer and heading fertilizer were applied at the tillering stage and heading stage, respectively. After rice transplanting, follow conventional field management practices, maintaining a water management pattern of flooding in the early and middle stages and moderate drying in the later stages.

[0048] CH4 emission monitoring: CH4 emissions include CH4 emission flux and CH4 cumulative emissions.

[0049] CH4 emission flux was monitored using the static chamber method. Specifically, a trace gas analyzer (such as the LI-7810 CH4 / CO2 / H2O, or any other feasible model, without specific limitations) was used in conjunction with the static chamber for measurement. The CH4 emission flux for each group was monitored in the static chamber set up for that group. The static chamber consisted of a stainless steel base and a top. The base was 50cm long, 50cm wide, and 10cm deep, with a 5cm groove along the upper edge to facilitate placing the top chamber on it and sealing it with water. The lower part had evenly spaced round holes to allow for the flow of water and nutrients. The top chamber was 50cm long, 50cm wide, and 50cm high. The outside of the chamber was covered with an insulating film, with two holes on the side for gas collection; one hole on the top for mounting a thermometer to measure the internal temperature; and a small fan was installed inside the chamber to thoroughly mix the gases.

[0050] The CH4 emission flux for each group is calculated according to the following relationship: ; Where F is the CH4 emission flux (mg / m² / h); M is the molar mass of CH4; 22.4 is the volume of 1 mole of air under standard conditions (L / mol); dc / dt is the change in CH4 concentration in the static chamber per unit time (μL / L / h); T is the temperature in the static chamber (°C); V is the volume of the static chamber (m³); A is the bottom area of ​​the static chamber (m²); P is the air pressure at the measured point (kPa); and 101.32 is 1 standard atmosphere (kPa).

[0051] The calculation of CH4 cumulative emissions for each group satisfies the following relationship: ; Wherein, CE represents the cumulative CH4 emissions (in kilograms per hectare (kg / hm)). - ²); Fi and Fi+1 are the CH4 emission fluxes (in mg / m² / h) determined for two consecutive adjacent sampling periods; d is the duration between two consecutive adjacent sampling times. For example, this duration is in days.

[0052] The monitoring period for CH4 emission flux includes at least one of the following stages of rice: tillering stage, jointing stage, booting stage, heading stage, grain-filling stage, and maturity stage. These six stages cover the key stages of vegetative and reproductive growth in rice and represent the main window for CH4 emission from paddy fields. By monitoring during these periods, the dynamic changes in CH4 emissions under different biochar treatments can be comprehensively captured without significantly increasing the workload.

[0053] Rice yield measurement: Rice yield is obtained through theoretical yield measurement and / or actual yield measurement.

[0054] The theoretical yield measurement procedure is as follows: Three rice plants with uniform growth are selected from each experimental plot, bundled together, and the number of panicles, number of grains per panicle, seed setting rate, thousand-grain weight, and moisture content of each bundle are recorded. Each treatment group is replicated three times. The theoretical yield satisfies the following relationship: Theoretical yield (t / hm²) = Effective panicles (panicles / m²) × Number of grains per panicle (grains / panicle) × Seed setting rate (%) × Thousand-grain weight (g / 1000 grains) × 10 -5 .

[0055] The actual yield measurement was conducted as follows: Rice was harvested manually, with 1 square meter of rice collected from each experimental plot as a test plot. Each treatment was replicated three times. The rice was threshed using a traditional threshing machine, dried, and winnowed. The dry weight was then measured, and the moisture content of the dried rice was determined. The yield of rice with a moisture content of 14.5% (japonica rice) was then calculated. The actual yield satisfies the following relationship: Actual yield (t / hm²) = weight per square meter (kg) × 10 × [(1 - moisture content) / (1 - 14.5%)].

[0056] Rice yield was assessed by combining theoretical and actual yield measurements. Theoretical yield measurement revealed the influence mechanism of biochar on the yield formation process through yield components, while actual yield measurement directly reflected the true yield level through standard quadrat harvesting and weighing. The two methods mutually verified each other to ensure accuracy.

[0057] S203, based on CH4 emissions and rice yield, selects the biochar type that corresponds to CH4 emission reduction and rice yield increase from a variety of biochar types.

[0058] This step involves comparative analysis of CH4 emission and rice yield data for each treatment group obtained in S202 to make a selection decision.

[0059] CH4 emission comparative analysis: like Figure 4As shown, the CH4 emission flux variation characteristics of each biochar treatment group and the control group showed that the CH4 emission flux of the wheat straw biochar treatment group (T2) was significantly lower than that of the control group (CK) at all growth stages, with a significant emission reduction effect; the CH4 emission flux of the rapeseed straw biochar treatment group (T4) was basically the same as that of the control group; while the rice straw biochar treatment group (T1) and the corn straw biochar treatment group (T3) showed higher CH4 emission fluxes than the control group at multiple growth stages.

[0060] like Figure 5 As shown, the cumulative CH4 emissions of each treatment group were as follows: the cumulative CH4 emissions of the rice straw biochar treatment group (T1) increased by 10.3% compared with the control group; the cumulative CH4 emissions of the wheat straw biochar treatment group (T2) decreased by 73.7% compared with the control group; the cumulative CH4 emissions of the corn straw biochar treatment group (T3) increased by 26.4% compared with the control group; and the cumulative CH4 emissions of the rapeseed straw biochar treatment group (T4) were basically the same as those of the control group.

[0061] The above results indicate that biochar from different straw sources has significantly different, and even opposite, effects on CH4 emissions from paddy fields; some types of biochar can substantially reduce emissions, while others can actually increase them. Therefore, systematic screening before application is necessary and crucial.

[0062] Comparative analysis of rice yield: The rice yield and yield components of each treatment group are shown in Table 1.

[0063] Table 1 As can be seen, the actual yield of the wheat straw biochar treatment group (T2) was 11.81 t / hm², an increase of 4.14% compared with the control group (11.34 t / hm²), and the theoretical yield was 11.94 t / hm², an increase of 3.29% compared with the control group (11.56 t / hm²). The actual yields of the rice straw biochar treatment group (T1) and the corn straw biochar treatment group (T3) were 12.05 t / hm² and 12.08 t / hm², respectively, also showing a certain yield increase effect. The yield components such as effective panicles, number of grains per panicle, seed setting rate, and thousand-grain weight of each biochar treatment group remained at a stable level, and no significant yield decrease was observed due to emission reduction.

[0064] Screening decision: A comparative analysis of CH4 emissions and rice yield: The wheat straw biochar treatment group (T2) reduced cumulative CH4 emissions by 73.7%, demonstrating the best emission reduction effect among the four biochar treatments. Simultaneously, it increased actual yield by 4.14% and theoretical yield by 3.29%, making it the only treatment group to simultaneously achieve significant emission reduction and stable yield increase. Therefore, wheat straw biochar was selected as the optimal biochar type for application in paddy fields.

[0065] The cumulative CH4 emissions of the rapeseed straw biochar treatment group (T4) were comparable to those of the control group, with no increase in emissions, and the actual yield reached 11.02 t / hm², achieving stable production. Therefore, rapeseed straw biochar can be selected as an alternative biochar type in the event of a wheat straw shortage.

[0066] The cumulative CH4 emissions in the rice straw biochar treatment group (T1) increased by 10.3% compared to the control group, and the cumulative CH4 emissions in the corn straw biochar treatment group (T3) increased by 26.4% compared to the control group, both leading to increased CH4 emissions. Therefore, rice straw biochar and corn straw biochar were excluded as biochar types to be applied to paddy fields.

[0067] The method provided in this embodiment, through standardized field comparison trials and a systematic monitoring and evaluation system, scientifically and accurately achieves differentiated screening of various types of biochar, breaking the technical bias of the existing technology of "one-size-fits-all" biochar application and lack of screening standards. This method can effectively distinguish the differentiated effects of biochar from different raw materials, accurately identify the optimal biochar type that has both CH4 emission reduction and rice yield increase functions, and simultaneously exclude undesirable types that will lead to increased CH4 emissions, avoiding the emission increase risk caused by incorrect biochar selection. The entire screening process is systematic, reliable, and highly repeatable, providing a standardized and scalable technical decision-making tool for the field of carbon sequestration and emission reduction in paddy fields.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0069] It should be understood that the term "and / or" in this article is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. Additionally, the character " / " in this article generally indicates an "or" relationship between the preceding and following related objects, but it can also represent an "and / or" relationship. Please refer to the context for a more accurate understanding.

[0070] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, at least one of a, b, or c can mean: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0071] It should be understood that in the various embodiments of this application, the order of the above-mentioned processes does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0072] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method of applying biochar, characterized by, include: Wheat straw biochar was selected as the biochar type to be applied to paddy fields from various types of crop straw biochar. The wheat straw biochar is applied to the paddy field at an application rate of 1.5-2.5 t / hm².

2. The method of claim 1, wherein, The application rate of wheat straw biochar is 2 t / hm².

3. The method of claim 1, wherein, The wheat straw biochar was applied simultaneously with the base fertilizer before rice transplanting in the paddy field.

4. The method of claim 1, wherein, Also includes: Rice straw biochar and / or corn straw biochar are excluded as biochar types applied to the paddy fields.

5. The method of claim 1, wherein, The wheat straw biochar is prepared by the following method: Under anaerobic conditions, wheat straw is pyrolyzed and carbonized at a first temperature, and then reacted with water vapor or carbon dioxide at a second temperature to obtain the wheat straw biochar.

6. The method of claim 5, wherein, The first temperature is 400-700℃, and the second temperature is 750-950℃.

7. The method according to any one of claims 1 to 6, characterized in that, The various types of crop straw biochar include: rice straw biochar, wheat straw biochar, corn straw biochar, and rapeseed straw biochar.

8. The method according to any one of claims 1-6, characterized in that, The water management model for the paddy fields is as follows: Flooding occurred in the early and middle stages, followed by moderate drying of the fields in the later stages.

9. A method for screening biochar, characterized in that, include: Various types of biochar were prepared using various types of crop straw as raw materials; The various types of biochar were applied one-to-one to multiple groups in paddy fields, and the CH4 emissions and rice yield of each group were monitored. Based on the CH4 emissions and the rice yield, select the biochar type that corresponds to CH4 emission reduction and rice yield increase from the various types of biochar.

10. The method according to claim 9, characterized in that, The CH4 emissions include CH4 emission flux and / or CH4 cumulative emissions.

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