A composted straw field returning method for carbon-mercury co-regulation of mercury contaminated paddy field

Abstract

The application discloses a kind of for mercury pollution paddy field carbon-mercury synergic regulation and control compost straw field returning method, comprising: applying straw-based organic fertilizer to mercury pollution paddy field;Wherein, the straw-based organic fertilizer is straw compost product and / or straw biochar.By applying straw-based organic fertilizer to mercury pollution paddy field, the problem that straw direct field returning significantly promotes methylmercury generation and accumulation in flooded paddy field is solved, and the exposure risk of soil and rice MeHg is reduced;At the same time, it is beneficial to solve the problem of CH4, CO2 short-term high-intensity release caused by straw input, reduce the carbon mineralization and greenhouse gas emission risk of straw field returning, and give consideration to straw resource utilization and paddy field carbon-mercury synergic regulation and control.

Description

Technical Field

[0001] This invention relates to the field of soil mercury pollution remediation technology, specifically to a compost straw return method for the synergistic regulation of carbon and mercury in mercury-polluted paddy fields. Background Technology

[0002] Mercury (Hg) is a persistent and bioaccumulative global pollutant, among which methylmercury (MeHg) is highly toxic and easily accumulates through the food chain. Long-term flooding of paddy fields creates a reducing environment, which is an important site for the methylation of inorganic mercury by microorganisms. MeHg generated in the soil can be absorbed by rice roots and migrate to the grains, posing an exposure risk to agricultural products.

[0003] Returning straw to the field is an important measure to improve the organic matter of farmland and realize the resource utilization of agricultural waste. However, straw is rich in easily degradable organic carbon. When it enters flooded paddy fields, it will increase the concentration of DOC and the biological activity of DOM, stimulate microbial metabolism, and thus may simultaneously promote the release of CH4 / CO2 and mercury methylation.

[0004] Existing technologies for reducing mercury risk in paddy fields mostly employ biochar, minerals, or chemical passivation materials. While biochar has some mercury-fixing and emission-reduction effects, it requires high-temperature pyrolysis, resulting in high energy consumption and equipment costs. Furthermore, the impact on MeHg varies depending on the raw materials and pyrolysis conditions. Current technologies primarily focus on a single objective of "carbon fixation," "emission reduction," or "mercury control," lacking low-cost treatment methods that simultaneously address straw resource utilization, greenhouse gas emission reduction, and methylmercury risk control, and can be directly integrated into conventional agronomic systems.

[0005] Therefore, a technology is needed to first change the activity and humification level of straw organic matter before returning it to the paddy field, so that the straw can be fully decomposed before entering the flooded environment, thereby reducing the risk of "high active carbon input - microbial activation - CH4 / CO2 emission increase - MeHg accumulation" caused by direct straw return to the field. Summary of the Invention

[0006] In order to at least partially overcome the shortcomings of the prior art, the present invention provides a low-energy-consumption, simple process that can be integrated with the existing paddy field cultivation system for treatment and returning to the field.

[0007] The first aspect of the present invention provides a method for straw return to the field for carbon-mercury synergistic regulation in mercury-contaminated paddy fields, comprising: Applying straw-based organic fertilizer to mercury-contaminated paddy fields; The straw-based organic fertilizer is straw compost product and / or straw biochar; Preferably, the mercury content in the soil of the mercury-contaminated paddy field is greater than or equal to 2 mg / kg.

[0008] According to the method of the first aspect, the straw is rapeseed straw and / or rice straw.

[0009] According to the method of the first aspect, the application rate of the straw-based organic fertilizer is 0.1% to 1.0% of the soil mass, preferably 0.3% to 0.8%; and / or The straw-based organic fertilizer is applied to the topsoil and / or rhizosphere soil of mercury-contaminated paddy fields.

[0010] According to the method of the first aspect, the straw compost product is prepared by the following method: S1 provides straw raw materials and crushes them; S2. The straw raw material is mixed with an optional C / N regulator and optional water to obtain a first material. The first material has a C / N ratio of 25 to 30 and a moisture content of 50% to 70%. S3 The first material is aerobically composted at 35℃~45℃ for 20 to 45 days. During the aerobic composting period, the compost is turned over. When the carbon-nitrogen ratio (C / N) of the compost product is less than or equal to 20, the straw compost product is obtained.

[0011] According to the method of the first aspect, in step S1, the straw raw material is crushed to 1cm~2cm.

[0012] According to the method of the first aspect, in step S2, the C / N regulator is selected from at least one of urea, ammonium nitrogen fertilizer, nitrate nitrogen fertilizer, and organic nitrogen source, preferably urea.

[0013] According to the method of the first aspect, in step S3, ventilation is carried out for 0.5h to 2h per day, preferably 1h; and / or The turning frequency is 4 to 5 days per turn.

[0014] According to the method of the first aspect, the straw biochar is prepared by the following method: The straw raw material is pyrolyzed at 450℃~600℃ under anaerobic conditions for 2h~6h to obtain the straw biochar.

[0015] A second aspect of the present invention provides a straw compost product prepared by the following method: S1 provides straw raw materials and crushes them; S2. The straw raw material is mixed with an optional C / N regulator and an optional water to obtain a first material. The first material has a carbon-to-nitrogen ratio (C / N) of 25-30 and a moisture content of 50%-70%. S3 The first material is aerobically composted at 35℃~45℃ for 20 to 45 days. During the aerobic composting period, the compost is turned over. When the carbon-nitrogen ratio (C / N) of the compost product is less than or equal to 20, the straw compost product is obtained.

[0016] A third aspect of the present invention provides a soil fertilizer comprising the straw compost product of the second aspect.

[0017] The method of the present invention has, but is not limited to, the following beneficial effects: (1) Soil MeHg reduction: Compared with fresh straw input, straw composting treatment can reduce soil MeHg accumulation. The MeHg content of the composted rapeseed straw group (Rape-C) was 20.74% lower than that of the fresh rapeseed straw group (Rape-F), and the composted rice straw group (Rice-C) was 30.08% lower than that of the fresh rice straw group (Rice-F), indicating that composting can significantly alleviate straw-induced mercury methylation.

[0018] (2) Greenhouse gas emission reduction: During the peak stage of the cultivation experiment, compared with fresh rapeseed straw, composted rapeseed straw reduced CH4 and CO2 emissions by approximately 49.47% and 47.05%, respectively. Pot experiments further showed that composting or biochar treatment can avoid the high-intensity CH4 emissions that occur during the tillering and heading stages when fresh straw is directly returned to the field, and significantly reduce the risk of CO2 emissions.

[0019] (3) Reduced MeHg risk in rice: Compared with the corresponding fresh straw, composted rice / rapeseed straw reduced rice MeHg by 18.82%~23.48% and inhibited the migration of MeHg from the roots to the grains.

[0020] (4) Optimization of MeHg accumulation: Under plantless culture conditions, straw promotes the accumulation of MeHg into active POM components; compared with fresh straw, composting or biochar treatment can effectively reduce POM-MeHg and weaken the accumulation of MeHg in unstable organic matter components.

[0021] (5) Advantages of technology and application: Composting only requires medium-temperature aerobic maturation and does not rely on high-temperature pyrolysis equipment. It has low energy consumption and low preparation threshold. It can simultaneously achieve straw resource utilization, mercury pollution risk control and greenhouse gas emission reduction, and is more suitable for integration with existing paddy field cultivation management. Attached Figure Description

[0022] Figure 1 The changes in soil MeHg content after input of the control group (CK), rapeseed biochar (Rape-B), rice biochar (Rice-B), composted rapeseed straw group (Rape-C), composted rice straw group (Rice-C), fresh rapeseed straw group (Rape-F), and fresh rice straw group (Rice-F) in Experiment Example 1 are shown.

[0023] Figure 2The following figures illustrate the headspace CH4 and CO2 concentrations after input of the control group (CK), rapeseed biochar (Rape-B), composted rapeseed straw group (Rape-C), and fresh rapeseed straw group (Rape-F) in Experiment Example 2; Figure 2 A shows the changes in headspace CH4 concentration. Figure 2 B shows the changes in headspace CO2 concentration.

[0024] Figure 3 The following figures illustrate the MeHg content and translocation coefficients of rice roots and grains after input into the control group (CK), rapeseed biochar (Rape-B), rice biochar (Rice-B), composted rapeseed straw group (Rape-C), composted rice straw group (Rice-C), fresh rapeseed straw group (Rape-F), and fresh rice straw group (Rice-F) in Experiment Example 3; among them, Figure 3 A shows the MeHg content in rice roots and grains. Figure 3 B indicates the translocation coefficient.

[0025] Figure 4 The figure shows the changes in soil MeHg at POM and MAOM after input of the control group (CK), rapeseed biochar (Rape-B), composted rapeseed straw group (Rape-C), and fresh rapeseed straw group (Rape-F) in Experiment Example 2. In the figure, lowercase letters a and b indicate significant differences in MAOM-MeHg at the P<0.05 level, and uppercase letters A and B indicate significant differences in POM-MeHg at the P<0.05 level.

[0026] Figure 5 The table shows the headspace CH4 concentrations of the soil gas sampling device after input into the pot experiment in Experiment Example 3 for the following groups: unplanted rice group (B), control group (CK), rapeseed biochar (Rape-B), rice biochar (Rice-B), composted rapeseed straw group (Rape-C), composted rice straw group (Rice-C), fresh rapeseed straw group (Rape-F), and fresh rice straw group (Rice-F).

[0027] Figure 6 The table shows the headspace CO2 concentrations of the soil gas collection device after input into the pot experiment in Experiment Example 3 for the following groups: unplanted rice group (B), control group (CK), rapeseed biochar (Rape-B), rice biochar (Rice-B), composted rapeseed straw group (Rape-C), composted rice straw group (Rice-C), fresh rapeseed straw group (Rape-F), and fresh rice straw group (Rice-F). Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention in any way.

[0029] The term “exemplary” as used herein means “serving as an example, embodiment, or illustration.” Any embodiment illustrated herein as “exemplary” is not necessarily to be construed as superior to or better than other embodiments.

[0030] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0031] In this invention, "MeHg" refers to methylmercury.

[0032] In this invention, "MAOM" refers to Mineral-Associated Organic Matter.

[0033] In this invention, "POM" refers to Particulate Organic Matter.

[0034] In this invention, the "carbon-nitrogen ratio C / N" refers to the mass ratio of carbon to nitrogen in the material.

[0035] In this invention, "moisture content" refers to the mass fraction of water in the material.

[0036] This invention provides a method for straw return to the field for synergistic regulation of carbon and mercury in mercury-contaminated paddy fields, comprising: Applying straw-based organic fertilizer to mercury-contaminated paddy fields; The straw-based organic fertilizer is straw compost product and / or straw biochar; Preferably, the mercury content in the soil of the mercury-contaminated paddy field is greater than or equal to 2 mg / kg.

[0037] This application addresses the problem of direct straw return to paddy fields significantly promoting the formation and accumulation of methylmercury in flooded paddy fields by applying straw-based organic fertilizer, thereby reducing the risk of MeHg exposure in soil and rice. It also helps to address the problem of short-term high-intensity release of CH4 and CO2 caused by straw input, reducing the carbon mineralization and greenhouse gas emission risks of straw return to the field, and taking into account both the resource utilization of straw and the synergistic regulation of carbon and mercury in paddy fields.

[0038] In some specific embodiments, the mercury content in the soil of the mercury-contaminated paddy field can be, for example, 2 mg / kg, 5 mg / kg, 8 mg / kg, 10 mg / kg, 12 mg / kg, 15 mg / kg, 16 mg / kg, 18 mg / kg, 20 mg / kg, 30 mg / kg, 50 mg / kg, 100 mg / kg, 150 mg / kg, 200 mg / kg, or any combination of the above values.

[0039] The straw-based organic fertilizer of the present invention can improve the occurrence of MeHg in mercury-polluted paddy fields, especially those with high soil mercury content, while taking into account both the resource utilization of straw and the synergistic regulation of carbon and mercury in paddy fields.

[0040] In some preferred embodiments, the straw-based organic fertilizer is a straw compost product. Compared with straw biochar, straw compost products do not require high-temperature pyrolysis, have lower energy consumption, simpler processes, and lower equipment and large-scale production costs.

[0041] In one embodiment, the straw is rapeseed straw and / or rice straw.

[0042] The technical solution of this invention can use different crop straws for the same composting process. As long as the raw materials are fully decomposed and the amount of readily available organic carbon is significantly reduced through controlled aerobic composting before being returned to the field, the same technical objective can be achieved, and the raw material adaptability is strong.

[0043] Compared with the control group without straw, direct return of fresh rapeseed straw and fresh rice straw to the field significantly increased soil MeHg. During the tillering and heading stages of the rice pot cultivation system, CH4 and CO2 emissions from the fresh straw treatment were significantly increased, with fresh rapeseed straw showing a stronger emission-promoting effect. Therefore, direct return of fresh straw to the field carries significant carbon emissions and MeHg risks. The aerobic composting or biochar treatment of this invention can significantly reduce the high CH4 and CO2 emissions caused by rice straw during the tillering and heading stages. After composting, the emissions throughout the entire growth period are stable and significantly lower than those in the fresh straw treatment group, and it can effectively inhibit MeHg root-grain migration.

[0044] In one embodiment, the straw-based organic fertilizer is applied at a rate of 0.1% to 1.0% of the soil mass, preferably 0.3% to 0.8%; and / or The straw-based organic fertilizer is applied to the topsoil and / or rhizosphere soil of mercury-contaminated paddy fields.

[0045] In some specific embodiments, the amount of straw-based organic fertilizer applied may be, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% of the soil mass, or any range of the above values.

[0046] In one embodiment, the straw compost product is prepared by the following method: S1 provides straw raw materials and crushes them; S2. The straw raw material is mixed with an optional C / N regulator and an optional water to obtain a first material. The first material has a carbon-to-nitrogen ratio (C / N) of 25-30 and a moisture content of 50%-70%. S3 The first material is aerobically composted at 35℃~45℃ for 20 to 45 days. During the aerobic composting period, the compost is turned over. When the carbon-nitrogen ratio (C / N) of the compost product is less than or equal to 20, the straw compost product is obtained.

[0047] The composting method of the present invention can use C / N regulators to adjust the differences in the composition of different straws to achieve a set carbon-nitrogen ratio, and can be corrected by ventilation, turning frequency and composting time, degree of composting and effect indicators.

[0048] In some specific embodiments, when the carbon-to-nitrogen ratio (C / N) of the compost product is less than or equal to 20, the compost product is considered to be fully decomposed. Specifically, when the compost product is fully decomposed, the carbon-to-nitrogen ratio of the compost product can be, for example, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or any range of the above values.

[0049] Compared with anaerobic composting methods, the aerobic composting method of the present invention increases the composting time and strictly controls the carbon-nitrogen ratio (C / N) of the compost product at the time of decomposition to be less than or equal to 20, for example, C / N is in the range of 12 to 18, preferably 13 to 17. For example, when C / N=15±2, the compost product at this specific degree of decomposition is particularly beneficial for the synergistic regulation of carbon and mercury in mercury-polluted paddy fields; at the same time, extending the return time to the field further improves the effect of the compost product.

[0050] In one embodiment, in step S1, the straw raw material is crushed to 1cm~2cm.

[0051] In one embodiment, in step S2, the C / N regulator is selected from at least one of urea, ammonium nitrogen fertilizer, nitrate nitrogen fertilizer, and organic nitrogen source, preferably urea.

[0052] Specifically, the ammonium nitrogen fertilizer refers to nitrogen in the form of ammonium ions (NH4+). +Ammonium fertilizers are nitrogen fertilizers that exist in the form of ammonium ions or can directly dissociate into ammonium ions in the soil. Examples of ammonium nitrogen fertilizers include ammonium bicarbonate (NH4HCO3), ammonium sulfate ((NH4)2SO4), ammonium chloride (NH4Cl), ammonia water (NH3·H2O), and ammonium nitrate (NH4NO3).

[0053] Specifically, the nitrate nitrogen fertilizer refers to nitrogen in the form of nitrate ions (NO3). - Nitrogen fertilizers in the form of sodium nitrate (NaNO3), calcium nitrate (Ca(NO3)2), ammonium nitrate (NH4NO3), etc.

[0054] Specifically, the organic nitrogen source refers to nitrogen-containing substances in which nitrogen exists in the molecular structure of organic compounds (such as amino-NH2, amide groups, etc.). The organic nitrogen source can be, for example, manure, compost, oilseed cake (soybean cake, rapeseed cake, etc.), amino acid fertilizer, animal carcass decomposition products, etc.

[0055] In some specific embodiments, in step S2, the carbon-to-nitrogen ratio (C / N) of the first material can be, for example, 25, 26, 27, 28, 29, 30, or any of the above values.

[0056] In some specific implementations, in step S2, the moisture content of the first material can be, for example, 50%, 55%, 60%, 65%, 70%, or any of the above values.

[0057] In some implementations, step S3 further includes ventilating for 0.5h to 2h per day, preferably 1h.

[0058] In some implementations, in step S3, the turning frequency is 4 to 5 days per turn.

[0059] The composting method of the present invention can maintain the aeration and moisture content of the compost pile by adjusting the ventilation frequency and turning frequency, thereby balancing efficiency and quality, and obtaining mature compost products within a cycle of 20 to 45 days.

[0060] In some specific implementations, in step S3, the composting temperature can be, for example, 35°C, 36°C, 37°C, 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, 45°C, or any range of the above values.

[0061] In some specific implementations, in step S3, the aerobic composting time can be, for example, 20 days, 22 days, 25 days, 28 days, 30 days, 32 days, 35 days, 38 days, 40 days, 42 days, 45 days, or any range of the above values.

[0062] In some specific implementations, step S3 further includes forced ventilation every day, and the ventilation time can be, for example, 0.5h, 1h, 1.5h, 2h or any range of the above values.

[0063] In one embodiment, the straw biochar is prepared by the following method: The straw raw material is pyrolyzed at 450℃~600℃ under anaerobic conditions for 2h~6h to obtain the straw biochar.

[0064] In some specific embodiments, the pyrolysis temperature of straw biochar can be, for example, 450°C, 475°C, 500°C, 525°C, 550°C, 575°C, 600°C, or any combination of the above values.

[0065] In some specific implementations, the oxygen-free condition may be, for example, a nitrogen atmosphere.

[0066] In some specific implementations, the pyrolysis time can be, for example, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, or any range of the above values.

[0067] This invention also provides a straw compost product, which is prepared by the following method: S1 provides straw raw materials and crushes them; S2. The straw raw material is mixed with an optional C / N regulator and an optional water to obtain a first material. The first material has a carbon-to-nitrogen ratio (C / N) of 25-30 and a moisture content of 50%-70%. S3 The first material is aerobically composted at 35℃~45℃ for 20 to 45 days. During the aerobic composting period, the compost is turned over. When the carbon-nitrogen ratio (C / N) of the compost product is less than or equal to 20, the straw compost product is obtained.

[0068] The present invention further provides a soil fertilizer comprising the aforementioned straw compost products.

[0069] The present application will be further described in detail below through embodiments. Through these descriptions, the features and advantages of the present application will become clearer and more apparent.

[0070] In the following examples, an elemental analyzer was used to determine the carbon and nitrogen content of straw or fertilizer.

[0071] The soils used in the following experimental examples are all topsoil (0~20cm) of cultivated land in the Wanshan Mercury Mine Area of ​​Guizhou Province.

[0072] In the following experimental examples, cold atomic absorption spectrometry was used to determine the content of methylmercury.

[0073] Example 1 This embodiment illustrates the method for preparing composted rapeseed straw (Rape-C).

[0074] Crush rapeseed straw to 1-2 cm, adjust the initial C / N ratio to 25-30 with urea, adjust the moisture content to 60%, and compost aerobically at 40 ℃ for 30 days, ventilating for about 1 hour daily and turning the pile every 4-5 days.

[0075] The C / N ratio of the obtained composted rapeseed straw was 14.98.

[0076] Example 2 This embodiment illustrates the method for preparing composted rice straw (Rice-C).

[0077] Rice straw was composted using the same process as in Example 1, and the resulting composted rice straw had a C / N ratio of 16.54.

[0078] Example 3 This example illustrates a method for preparing biochar.

[0079] Biochar was prepared by pyrolyzing rapeseed straw or rice straw at 500 °C under nitrogen-induced oxygen removal conditions for 4 h, and the resulting rapeseed biochar (Rape-B) or rice biochar (Rice-B) was obtained by passing it through a 60-mesh sieve.

[0080] Comparative Example 1 Fresh rapeseed straw (Rape-F) or fresh rice straw (Rice-F) that has been crushed to 1-2 cm and is not composted were used as a control.

[0081] Experimental Example 1 This experimental example illustrates the use of straw prepared in the examples or comparative examples for soil cultivation experiments.

[0082] This experiment set up 7 groups for soil cultivation, including straw from different treatments in Examples 1-3 and the blank control group (CK) in Comparative Example 1. The specific settings are shown in Table 1: Table 1

[0083] The total mercury content in the soil for the soil culture experiment was 5.20 mg / kg. -1 The pH value is 7.04.

[0084] Soil cultivation experimental method: For each treatment group, 150 g (dry weight) of experimental soil passed through a 60-mesh sieve was weighed and mixed with 0.75 g of straw from groups 1-1 to 1-6 in Table 1 at a ratio of 0.5% (w / w). No exogenous organic materials were added to the control group (CK). After thorough mixing, 150 mL of deionized water was slowly added, and the mixture was allowed to stand for 24 h. Subsequently, deionized water was added to a constant water layer of 5 cm (approximately 250 mL), and the mixture was immediately sealed.

[0085] Soil samples were collected and tested for MeHg after the 29th day of cultivation.

[0086] Changes in soil MeHg content after input of different types and forms of straw in soil culture experiments are as follows: Figure 1 As shown, the soil MeHg content was lowest in the control group (CK), at 22.88 ± 0.08 ng g. -1 After the introduction of fresh straw, the soil MeHg content increased significantly. The soil MeHg in the fresh rapeseed straw group (Rape-F) and the fresh rice straw group (Rice-F) were 72.67 ± 2.71 mg / L, respectively. -1 and 55.09±3.27 ng g -1 Furthermore, the MeHg content of Rape-F was significantly higher than that of Rice-F.

[0087] Compared with fresh straw input, straw composting treatment can reduce soil MeHg accumulation. The MeHg content in the composted rapeseed straw group (Rape-C) was 20.74% lower than that in the fresh rapeseed straw group (Rape-F), and the MeHg content in the composted rice straw group (Rice-C) was 30.08% lower than that in the fresh rice straw group (Rice-F), indicating that composting can significantly alleviate straw-induced mercury methylation.

[0088] After straw was prepared into biochar and applied to the soil, the MeHg content in the rice biochar group (Rice-B) and the rapeseed biochar group (Rape-B) was 23.92 ± 0.53 ng g, respectively. -1 and 25.91±1.56 ng g -1 There was no significant difference compared to the blank control group.

[0089] Experimental Example 2 This experimental example illustrates the impact of different treatments of rapeseed straw on soil CH4 and CO2 emissions.

[0090] This experiment included four groups for soil cultivation: rapeseed straw under different treatments in Example 1, Example 3, and Comparative Example 1, as well as a blank control group (CK). The specific settings are shown in Table 2. Table 2

[0091] The total mercury content in the soil for the soil culture experiment was 5.20 mg / kg. -1 The pH value is 7.04.

[0092] Soil cultivation experimental method: For each treatment, 150 g (dry weight) of experimental soil passed through a 60-mesh sieve was weighed and mixed with 0.75 g of rapeseed straw from groups 2-1 to 2-3 in Table 2 at a ratio of 0.5% (w / w). No exogenous organic materials were added to the control (CK). After thorough mixing, 200 mL of deionized water was slowly added, and the mixture was allowed to stand for 24 hours. Subsequently, deionized water was added to a constant 5 cm water layer, and the container was immediately sealed. To balance the internal and external air pressure and isolate the system from outside air, a latex balloon was attached to the spout, and the remaining gaps were sealed with sealing film to ensure a tight seal.

[0093] Headspace gas was collected from each group using a 10 mL airtight syringe on days 1, 2, 3, 4, 6, 8, 12, and 14 of the culture. Soil samples were collected after the culture was completed.

[0094] (1) The impact of different forms of rapeseed straw on soil CH4 and CO2 emissions Headspace gas was collected using an airtight syringe and the concentrations of CH4 and CO2 were determined by gas chromatography.

[0095] The changes in CH4 and CO2 concentrations in the headspace of the apparatus after rapeseed straw was introduced into the soil under different treatments are as follows: Figure 2 A and Figure 2 As shown in B. From Figure 2 As can be seen from A, the CH4 concentration in each group during the early stage of culture (0-8 days) ranged from 2.29 to 2.85 mg / L. -1 After 8 days, CH4 concentration began to rise significantly. By day 12 of cultivation, CH4 emissions from all straw-added treatments reached their peak, with the CH4 concentration in the fresh rapeseed straw group (Rape-F) being 6.61 ± 0.64 mg / L. -1 The CH4 concentration increased significantly by 131.12% compared to day 8. The CH4 concentrations in the composted rapeseed straw group (Rape-C) and the rapeseed biochar group (Rape-B) increased by only 24.72% and 32.58% respectively compared to day 8. This was consistent with the control group (2.55 ± 0.02 mg / L). -1Compared to the control group (CK), the peak CH4 emissions of Rape-F, Rape-C, and Rape-B increased by 159.21%, 30.98%, and 37.25%, respectively. By day 14 of cultivation, the CH4 concentrations in all treatment groups began to decrease, with CH4 emissions from Rape-F, Rape-C, and Rape-B increasing by 114.12%, 13.73%, and 17.25%, respectively, compared to the control group (CK). These results indicate that there is a significant lag effect on soil CH4 emissions after straw input, and composting and biochar treatments can effectively alleviate the enhanced CH4 emissions caused by direct straw application.

[0096] from Figure 2 As shown in Figure B, during the early stage of cultivation (0-8 days), the CO2 concentration in each group increased slowly. When CO2 emissions reached their peak on day 12, the CO2 concentration in the fresh rapeseed straw group (Rape-F) was 2306.15 ± 219.15 mg / L. -1 The CO2 emissions were significantly higher than the control (CK) group (Rape-C and Rape-B) by 15.41%, while the CO2 emissions from the composted rapeseed straw group (Rape-C) and the rapeseed biochar group (Rape-B) were lower than the CK group by 29.49% and 23.15%, respectively. By day 14, the CO2 concentrations in all groups showed a decreasing trend. These results indicate that soil CO2 emissions increase over time after straw input, and composting and biochar treatments can effectively suppress soil CO2 emissions.

[0097] (2) Changes in the occurrence of methylmercury in soil organic carbon component caused by rapeseed straw under different treatments Separation of soil MAOM and POM components: Soil samples were passed through a 2 mm sieve to remove stones and plant debris, which was used to separate the particulate matter (POM) and mineral-bound matter (MAOM) components in the organic matter. Soil samples were then passed through a 53 µm sieve, and the portion that passed through (<53 µm) was collected as MAOM, while the portion remaining on the sieve was collected as POM.

[0098] Soil samples were collected from each group, and the MAOM and POM components were separated, and the MeHg content was tested. The changes in MeHg distribution in POM and MAOM after rapeseed straw input into the soil under different treatments are shown in the figure below. Figure 4 As shown, where: Compared with the blank control group (CK), the MAOM-MeHg level in the fresh rapeseed straw group (Rape-F) was 3.67±0.67 mg / L. -1 The content was lower than that of CK (6.71±1.35 ng g). -1 )45.31%, while POM-MeHg (9.13±1.10 ng g -1 The level was significantly higher than that of the control group (CK) (6.30 ± 0.81 ng g). -1The MAOM-MeHg of the composted rapeseed straw group (Rape-C) and the rapeseed biochar group (Rape-B) decreased by 21.31% and 17.44% respectively compared with the control group, while their POM-MeHg increased by only 3.49% and 7.78% respectively compared with the control group.

[0099] The above results indicate that direct input of fresh rapeseed straw alters the component distribution pattern of MeHg, causing MeHg to accumulate more in the unstable POM component and decrease in the less active MAOM component. This invention, through composting or biochar treatment, can reduce the proportion of MeHg in POM and promote the distribution of methylmercury to the less active MAOM component, thereby inhibiting the accumulation and transfer of MAOM-MeHg to POM-MeHg, and consequently reducing the bioavailability of mercury.

[0100] The results of this experiment demonstrate that composting or biochar treatment of rapeseed straw can effectively alleviate the enhanced CH4 emissions caused by direct straw application, suppress soil CO2 emissions, and optimize the occurrence of MeHg in the soil.

[0101] Experimental Example 3 This experimental example is used to illustrate the use of straw prepared in the examples or comparative examples for pot experiment verification.

[0102] This experiment set up 8 groups for pot experiments, including straw from different treatments in Examples 1-3 and Comparative Example 1, a blank control group (CK), and a group without rice (B). The specific settings are shown in Table 3: Table 3

[0103] The total mercury content in the soil of the rice pot experiment was 16.00 mg / kg. -1 The pH value is 7.18.

[0104] Pot experiment method: Each pot contains 7 kg of mercury-contaminated soil. Straw from different treatments 3-1 to 3-6 in Table 3 is mixed in at a ratio of 0.5% (w / w) and thoroughly mixed with the soil. No exogenous organic materials are added to the control group (CK). A water layer of about 5 cm is maintained on top. Rice seedlings with uniform growth are transplanted in each group. No rice is transplanted in the non-rice group (B).

[0105] Plant sample collection and processing: Plant samples were collected during the rice maturity period, and root and aboveground tissues were obtained.

[0106] Headspace gas was collected using an airtight syringe and the concentrations of CH4 and CO2 were determined by gas chromatography.

[0107] (1) Effects of straw input on the enrichment of methylmercury in rice and its roots The MeHg content and translocation coefficient of rice and its roots after the input of straw-derived organic matter are as follows: Figure 3 As shown, where: The MeHg content in rice of the blank control group (CK) was 280.55 ± 33.85 ng g. -1 The MeHg of rice in the fresh straw treatment groups (Rape-F, Rice-F) showed an increasing trend. The MeHg range of rice in the compost treatment groups (Rape-C, Rice-C) and the biochar treatment groups (Rape-B, Rice-B) was 224.90–251.82 ng g. -1 It is 10.24%~19.84% lower than CK.

[0108] The root MeHg content in the CK group was 40.41 ± 4.01 ng g. -1 The MeHg levels in the roots of the fresh straw treatment groups (Rape-F, Rice-F), compost treatment groups (Rape-C, Rice-C), and rice biochar group (Rice-B) increased significantly by 145.85%–226.90%, while the rapeseed biochar group (Rape-B) showed no significant difference from the control group (CK). Furthermore, compared to the control group, all groups except Rape-B significantly reduced the MeHg translocation coefficient to rice, with reduction rates ranging from 54.14% to 71.86%.

[0109] The results above show that, compared with the corresponding fresh straw treatment group, the MeHg of rice decreased by 18.82% to 23.48% after composting treatment, and the MeHg root-grain migration was inhibited.

[0110] (2) Impact of straw input on soil CH4 emissions Figure 5 The following figures show the headspace CH4 concentrations of the soil gas sampling device in the pot experiment after each set of inputs: Soil CH4 emissions during tillering stage, such as Figure 5 As shown in Figure A, the CH4 concentrations in the gas sampling devices of the non-rice-planted group (B), the blank control group (CK), the compost treatment groups (Rape-C, Rice-C), and the biochar treatment groups (Rape-B, Rice-B) ranged from 2.18 to 3.45 mg / L. -1 There were no differences between the groups. The fresh rice straw treatment group (Rice-F: 356.99±47.03 mg / L) -1 The control group treated with fresh rapeseed straw (Rape-F: 2116.72±213.12 mg / L) was compared with the control group treated with fresh rapeseed straw (Rape-F: 2116.72±213.12 mg / L). -1 The soil CH4 emissions of the Rape-F group were significantly higher than those of the Rice-F group. The CH4 concentration of Rape-F was 5.93 times that of Rice-F.

[0111] Soil CH4 emissions during the heading stage Figure 5 As shown in Figure B, the overall trend of soil CH4 emissions was consistent with that during the tillering stage. The CH4 concentrations in the unplanted rice group (B), the blank control group (CK), the compost treatment groups (Rape-C, Rice-C), and the biochar treatment groups (Rape-B, Rice-B) ranged from 1.98 to 3.83 mg / L. -1 There were no differences between groups. Rape-F (739.65±185.71 mg L) -1 The CH4 concentration of Rice-F was 278.22 ± 66.80 mg / L. -1 2.66 times that of ).

[0112] Soil CH4 emissions during grouting period Figure 5 As shown in C, there were no differences in soil CH4 emissions among groups, with an overall range of 2.06–3.45 mg / L. -1 .

[0113] The results above indicate that the type and form of straw affect soil CH4 emissions. The CH4 emissions from soil after rapeseed straw input are higher than those after rice straw input. However, composting or biochar treatment of straw before applying it to the soil can effectively reduce CH4 emissions.

[0114] (3) Impact of straw input on soil CO2 emissions Figure 6 The above figures show the headspace CO2 concentrations of the soil gas sampling device in the pot experiment after each set of inputs, where: CO2 emissions from the soil during the tillering stage, such as Figure 6 As shown in Figure A, the CO2 concentration in the group without rice (B) was 470.36 ± 51.93 mg / L. -1 The CO2 concentrations in the blank control group (CK), compost treatment groups (Rape-C, Rice-C), and biochar treatment groups (Rape-B, Rice-B) ranged from 501.36 to 531.86 mg / L. -1 Overall CO2 emissions were 6.59%–13.08% higher than group B. The CO2 concentrations in the fresh straw treatment groups Rape-F and Rice-F were significantly higher than the control (CK) (509.57 ± 61.78 mg / L). -1 The CO2 emissions of Rape-F increased by 220.99% and 39.85% respectively. Rape-F's CO2 emissions were significantly higher than Rice-F's by approximately 129.53%.

[0115] Soil CO2 emissions during the heading stage Figure 6 As shown in Figure B, the lowest CO2 concentration was observed in the group without rice (B), at 239.81 ± 78.99 mg / L. -1The CO2 concentrations of Rice-F and Rape-F increased significantly by 131.74% and 193.70% compared to the control (CK), respectively. The CO2 emissions of Rape-F were 28.03% higher than those of Rice-F.

[0116] Soil CO2 emissions during grouting period Figure 6 As shown in Figure C, the CO2 concentration in the unplanted rice group (B) was the lowest. The CO2 concentrations in the blank control group (CK), compost treatment groups (Rape-C, Rice-C), and biochar treatment groups (Rape-B, Rice-B) increased by 24.36% to 56.43% compared to group B.

[0117] The results above demonstrate that composting or biochar treatment of straw before its input can effectively reduce soil CO2 emissions caused by direct straw input.

[0118] The results of the rice pot experiment in this example show that CH4 and CO2 levels were significantly increased during the tillering and heading stages in the fresh straw treatment group, indicating that direct return of fresh straw to the field poses a significant risk of carbon emissions and MeHg. However, the aerobic composting or biochar treatment in this embodiment of the invention can significantly reduce the high CH4 and CO2 emissions caused by rice straw during the tillering and heading stages. After composting, the emissions throughout the entire growth period are stable and significantly lower than those in the fresh straw treatment group, and it can effectively inhibit MeHg root-grain migration.

[0119] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for straw return to the field for synergistic regulation of carbon and mercury in mercury-contaminated paddy fields, comprising: Applying straw-based organic fertilizer to mercury-contaminated paddy fields; The straw-based organic fertilizer is straw compost product and / or straw biochar; Preferably, the mercury content in the soil of the mercury-contaminated paddy field is greater than or equal to 2 mg / kg.

2. The method according to claim 1, wherein, The straw is rapeseed straw and / or rice straw.

3. The method according to claim 1, wherein, The application rate of the straw-based organic fertilizer is 0.1% to 1.0% of the soil mass, preferably 0.3% to 0.8%; and / or The straw-based organic fertilizer is applied to the topsoil and / or rhizosphere soil of mercury-contaminated paddy fields.

4. The method according to claim 1, wherein, The straw compost product is prepared by the following method: S1 provides straw raw materials and crushes them; S2. The straw raw material is mixed with an optional C / N regulator and optional water to obtain a first material. The first material has a C / N ratio of 25 to 30 and a moisture content of 50% to 70%. S3 The first material is aerobically composted at 35℃~45℃ for 20 to 45 days. During the aerobic composting period, the compost is turned over. When the carbon-nitrogen ratio (C / N) of the compost product is less than or equal to 20, the straw compost product is obtained.

5. The method according to claim 4, wherein, In step S1, the straw raw material is crushed to 1cm~2cm.

6. The method according to claim 4, wherein, In step S2, the C / N regulator is selected from at least one of urea, ammonium nitrogen fertilizer, nitrate nitrogen fertilizer, and organic nitrogen source, preferably urea.

7. The method according to claim 4, wherein, In step S3, ventilation is performed for 0.5 to 2 hours per day, preferably 1 hour; and / or The turning frequency is 4 to 5 days per turn.

8. The method according to claim 1, wherein, The straw biochar is prepared by the following method: The straw raw material is pyrolyzed at 450℃~600℃ under anaerobic conditions for 2h~6h to obtain the straw biochar.

9. A straw compost product, prepared by the following method: S1 provides straw raw materials and crushes them; S2. The straw raw material is mixed with an optional C / N regulator and optional water to obtain a first material. The first material has a C / N ratio of 25 to 30 and a moisture content of 50% to 70%. S3 The first material is aerobically composted at 35℃~45℃ for 20 to 45 days. During the aerobic composting period, the compost is turned over. When the carbon-nitrogen ratio (C / N) of the compost product is less than or equal to 20, the straw compost product is obtained.

10. A soil fertilizer comprising the straw compost product as described in claim 9.

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