A method of calcium ion promoting soil carbon sequestration of biochar

Abstract

This invention relates to the fields of ecological science and soil carbon sequestration technology, specifically to a method for promoting soil carbon sequestration using calcium ions and biochar. The method comprises the following steps: pre-culturing soil under sealed, light-protected conditions for 6-10 days; adding biochar and a calcium source to the pre-cultured soil; mixing thoroughly; and then formally culturing under the same conditions as the pre-culture for 50-70 days. This invention introduces calcium ions into biochar. Calcium ions, through cation bridging and inorganic cementation, significantly promote the formation of large soil aggregates and substantially increase the saturated adsorption capacity and affinity of biochar for dissolved organic carbon, thereby effectively reducing the risk of mineralization loss of organic carbon in the soil. This method is simple to operate and low in cost, providing effective technical support for overcoming the bottleneck of soil carbon sequestration using biochar and improving the application benefits of biochar.

Description

Technical Field

[0001] This application relates to the fields of ecological science and soil carbon sequestration technology, and in particular to a method for calcium ion-promoted biochar soil carbon sequestration. Background Technology

[0002] Global warming, driven by human-led greenhouse gas emissions, has become a severe challenge for the international community, seriously threatening human survival and development. The IPCC Sixth Assessment Report shows that compared to 1750, the concentrations of carbon dioxide (CO2) and methane (CH4) in the atmosphere have increased by 47% and 156%, respectively. As a result, the global average surface temperature from 2011 to 2020 has risen by 1.09 °C compared to 1850-1900. Therefore, a systematic study of greenhouse gas emissions from agricultural systems is of great significance for promoting the development of green and low-carbon agriculture in my country.

[0003] Against this backdrop, biochar, as a porous carbon-rich material with carbon sequestration potential, has attracted widespread attention. For example, Chinese patent application CN115746866A discloses that biochar can promote soil carbon sequestration. However, although it can form a relatively stable aromatic carbon structure through pyrolysis, its actual carbon sequestration effect is still limited by its interaction mechanism with the soil environment. On the one hand, both the surface of biochar and dissolved organic carbon (DOC) are usually negatively charged, and the electrostatic repulsion between them limits the adsorption and fixation of active organic carbon by biochar. Moreover, this physical adsorption often has weak binding force, leading to easy desorption of organic carbon and further mineralization by microorganisms. On the other hand, the simple application of biochar often lacks effective cementing materials, making it difficult to induce the formation of stable soil aggregates, thereby weakening the physical protection of organic carbon. These limitations prevent biochar from fully realizing its carbon sequestration benefits in practical applications.

[0004] Therefore, there is an urgent need to develop a method to enhance the carbon sequestration capacity of biochar, thereby improving the adsorption stability and physical protection effect of organic carbon by improving the interaction between biochar and soil components, so as to more effectively serve the goal of agricultural carbon sequestration and carbon neutrality. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the existing technology in which the carbon sequestration effect of applying biochar alone on soil still needs to be improved, and to provide a method for promoting biochar soil carbon sequestration by calcium ions.

[0006] Another object of the present invention is to provide the application of the above-described method in promoting soil carbon sequestration.

[0007] The above-mentioned objective of this invention is achieved through the following technical solution: This invention protects a method for promoting biochar soil carbon sequestration using calcium ions, comprising the following steps: After pre-culturing the soil in a sealed, light-protected environment for 6-10 days, add biochar and calcium source to the pre-cultured soil, mix thoroughly, and then formally culture for 50-70 days under the same conditions as the pre-culture.

[0008] This invention introduces calcium ions into biochar. These calcium ions, through cation bridging and inorganic cementation, significantly promote the formation of large soil aggregates (soil aggregates with a particle size of 250–2000 μm) and substantially enhance the saturated adsorption capacity and affinity of biochar for dissolved organic carbon, thereby effectively reducing the risk of organic carbon mineralization and loss from the soil. This method is simple to operate and low in cost, providing effective technical support for overcoming the bottleneck of carbon sequestration in biochar and improving its application benefits.

[0009] Furthermore, the soil includes farmland soil, wetland soil, forest soil, or grassland soil.

[0010] Furthermore, the soil in question is farmland soil.

[0011] Furthermore, the soil collection includes the following steps: It is obtained by collecting soil from the top 0-20 cm layer, air-drying it naturally, removing non-soil impurities, and sieving it.

[0012] Furthermore, the non-soil impurities include gravel and / or plant roots.

[0013] Furthermore, the sieve mesh size is 2-3 mm.

[0014] Furthermore, the pre-culture time is 7 days.

[0015] Furthermore, the temperature during the pre-culture period is 24~30 ℃.

[0016] Furthermore, the temperature during the pre-culture period is 25 °C.

[0017] Furthermore, during the pre-cultivation process, water is added to adjust the soil's water holding capacity to 30%~50%.

[0018] Furthermore, during the pre-cultivation process, water is added to adjust the soil's water holding capacity to 35%~45%.

[0019] Preferably, during the pre-cultivation process, water is added to adjust the soil's water holding capacity to 40%.

[0020] Furthermore, the maximum water holding capacity of the soil refers to the maximum amount of water that the soil can absorb and retain under saturated conditions.

[0021] In this invention, the maximum water holding capacity of the soil is determined by gravimetric method.

[0022] In this invention, the purpose of pre-culturing is to stabilize and activate the microorganisms in the soil.

[0023] Furthermore, the method for preparing the biochar includes the following steps: Under a protective gas atmosphere, renewable biomass is dried, pulverized, sieved, pyrolyzed at 350~700℃, and then cooled to obtain the final product.

[0024] Furthermore, the protective gas includes one or more of nitrogen, argon, and helium.

[0025] Furthermore, the protective gas is nitrogen.

[0026] Preferably, the flow rate of the protective gas is 400~800 mL / min.

[0027] More preferably, the flow rate of the protective gas is 600 mL / min.

[0028] Furthermore, the renewable biomass includes one or more of straw, branches, and grass.

[0029] Furthermore, the straw includes one or more of corn straw, wheat straw, and rice straw.

[0030] Preferably, the renewable biomass is corn stalks.

[0031] Furthermore, the drying temperature is 400~600 ℃.

[0032] Furthermore, the sieve mesh size of the sieve is 2~3 mm.

[0033] Furthermore, the pyrolysis time is 1 to 3 hours.

[0034] Furthermore, the heating rate of the pyrolysis is 1~10 ℃ / min.

[0035] Furthermore, the average particle size of the biochar is ≤0.25 mm.

[0036] In this invention, the average particle size of biochar can be measured by standard sieving method.

[0037] Furthermore, the amount of biochar added is 1 wt% to 3 wt% based on the dry weight of the soil.

[0038] Furthermore, the amount of calcium ions added to the calcium source is 0.03wt% to 0.5wt% of the amount of biochar added.

[0039] Furthermore, the amount of calcium ions added to the calcium source is 0.05wt% to 0.2wt% of the amount of biochar added.

[0040] Furthermore, the calcium source includes one or more of calcium salts, calcium oxides, and calcium hydroxides.

[0041] Furthermore, the calcium salt includes one or more of calcium chloride, calcium carbonate, and calcium citrate.

[0042] Furthermore, the calcium oxide is calcium oxide.

[0043] Furthermore, the calcium hydroxide is calcium hydroxide.

[0044] Preferably, the calcium source is calcium chloride.

[0045] Furthermore, during the formal cultivation process, water is added to adjust the soil's water holding capacity to 50%–70%.

[0046] Furthermore, during the formal cultivation process, water is added to adjust the soil's water holding capacity to 55%~65%.

[0047] Preferably, during the formal cultivation, water is added to adjust the soil's water holding capacity to 60%. This moisture content is optimal for microbial respiration.

[0048] Furthermore, the formal cultivation period is 60 days.

[0049] Furthermore, the temperature during the formal cultivation period is 24~30 ℃.

[0050] Furthermore, the temperature during the formal cultivation period is 25 °C.

[0051] Furthermore, during the formal cultivation period, the animals are weighed and watered regularly each week.

[0052] Furthermore, no additional nutrients are added during the formal culture period.

[0053] This invention protects the application of the aforementioned method in promoting soil carbon sequestration.

[0054] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a method for promoting biochar-based soil carbon sequestration using calcium ions, comprising the following steps: Pre-culturing soil under sealed, light-protected conditions for 6-10 days; then adding biochar and a calcium source to the pre-cultured soil, mixing thoroughly, and formally culturing under the same conditions as the pre-culture for 50-70 days. This invention introduces calcium ions into biochar. Calcium ions, through cation bridging and inorganic cementation, significantly promote the formation of large soil aggregates and substantially enhance the saturated adsorption capacity and affinity of biochar for dissolved organic carbon, thereby effectively reducing the risk of organic carbon mineralization loss in the soil. This method is simple to operate and low in cost, providing effective technical support for overcoming the bottleneck of biochar carbon sequestration and improving the application benefits of biochar. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of soil cultivation in Example 1 and Comparative Example 1.

[0056] Figure 2 Figures show the content of soil aggregates in the soil of Example 1 and Comparative Example 1; wherein, (a) is a figure showing the content of soil micro-aggregates, and (b) is a figure showing the content of soil macro-aggregates.

[0057] Figure 3 The graph shows the isothermal adsorption fitting curves of dissolved organic carbon in the soil in Example 1 and Comparative Example 1. Detailed Implementation

[0058] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0059] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0060] Figure 2 (a) indicates Figure 2 Figure (a) in the middle, Figure 2 (b) indicates Figure 2 Figure (b) in the middle.

[0061] The soil samples were collected from farmland in Shaoguan City, Guangdong Province, at a depth of 0–20 cm. After collection, the soil was air-dried, and impurities such as plant roots and stones were removed. The soil was then ground and passed through a 10-mesh sieve and mixed thoroughly before use. The physicochemical properties of the soil samples were as follows: pH 5.3, 49.5% sandy soil, 30.1% silty soil, and 20.4% clay, with an organic carbon content of 27 g·kg⁻¹. -1 Total nitrogen 16 g·kg -1 Available phosphorus 22.2 mg·kg -1 160 mg / kg of readily available potassium -1 .

[0062] Example 1: A method for promoting soil carbon sequestration using calcium ions in biochar 1. Preparation of biochar Corn stalks were washed, air-dried to constant weight, crushed, ground, and sieved to obtain stalk powder. The obtained stalk powder was placed in a muffle furnace, and nitrogen gas was introduced into the furnace at a flow rate of 600 mL / min. The temperature was raised to 450℃ at a rate of 5℃ / min and reacted for 2 h. After naturally cooling to room temperature, the stalks were removed to obtain corn stalk biochar. The biochar was then ground, sieved through a 0.25 mm sieve, and mixed thoroughly for later use.

[0063] 2. Soil culture experiment First, 100 g of air-dried test soil was weighed and placed in a 1 L glass bottle. The water was adjusted to 40% of the soil's maximum water holding capacity with deionized water, the bottle was sealed, and pre-cultured at 25 °C in the dark for 7 days to stabilize and activate the microorganisms in the soil. Then, the previously prepared biochar was added to the soil at a ratio of 2 wt% of the soil dry weight, followed by calcium chloride powder, ensuring the calcium ion addition was 0.1 wt% of the biochar addition. After thorough mixing, the mixture was cultured, and the resulting solution was labeled as 2% biochar (BC) + 0.1% calcium ions (2% BC + 0.1% Ca). 2+ The treatment group consisted of three replicates. Soil was adjusted to 60% of its maximum water holding capacity with deionized water and then cultured in the dark at 25 °C. Weighing and watering were performed weekly, and no additional nutrients were added during the culture period. After 60 days of culture, soil samples were collected and stored at 4 °C for further analysis and testing.

[0064] The maximum water holding capacity of the soil was determined using a gravimetric method: approximately 2.5 g of experimental soil was added to a 2 mL syringe tube, repeated three times. The bottom of the syringe tube containing the soil was completely wrapped with coarse filter paper, and then placed in water until the water level was flush with the middle of the syringe tube. The top of the syringe tube should not be submerged to avoid sealing the pores and affecting the experimental results. After soaking for 24 hours, an appropriate amount of soil was placed in a crucible that had been dried at 105 ℃ and cooled to room temperature (crucible weight W0), and the weight W1 was recorded. The crucible containing the soil was then placed in an oven and dried at 105 ℃ until constant weight, and the weight W2 was recorded. The difference between the two weights is the saturated water content of the soil, expressed as a percentage of the dry weight of the soil.

[0065] The above 2% BC + 0.1% Ca 2+ A schematic diagram of the soil culture experiment for the treatment group is shown below. Figure 1 As shown.

[0066] Example 2: A method for promoting biochar soil carbon sequestration using calcium ions The difference from Example 1 is that in the soil culture experiment, the amount of calcium ions added was adjusted from 0.1 wt% of the biochar addition to 0.05 wt%.

[0067] The other steps and conditions are the same as in Example 1.

[0068] Example 3: A method for promoting biochar soil carbon sequestration using calcium ions The difference from Example 1 is that in the soil culture experiment, the amount of calcium ions added was adjusted from 0.1 wt% of the biochar addition to 0.2 wt%.

[0069] The other steps and conditions are the same as in Example 1.

[0070] Comparative Example 1: A method for promoting soil carbon sequestration using biochar The difference from Example 1 is that no calcium chloride powder was added in the soil incubation experiment, and the resulting soil was the 2% biochar (2% BC) treatment group; a schematic diagram of the soil incubation experiment of the 2% BC treatment group is shown below. Figure 1 As shown.

[0071] The other steps and conditions are the same as in Example 1.

[0072] Experimental Example 1: Determination of Soil Aggregate Content 1. Experimental Methods The soil aggregate content was determined using the wet sieving method, which included the following steps: On day 60 of soil incubation, soil samples from Example 1 and Comparative Example 1 were collected, air-dried, and then passed through a 5 mm sieve. 25 g of soil was then weighed and placed on a 2 mm sieve. Deionized water was added until the water level was 3 cm above the soil surface. After soaking for 5 minutes, the sieve was manually moved up and down 3 cm at a frequency of 25 times / min for 2 minutes, ensuring all soil samples passed through the 2 mm sieve. The sieved soil was then transferred to a 0.25 mm sieve, and the above operation was repeated. Large soil aggregates (particle size 250–2000 μm) remained on the 0.25 mm sieve, while micro-aggregates (particle size <250 μm) passed through. All aggregate sizes were transferred to an aluminum box and dried at 60 °C to constant weight. The weights were recorded.

[0073] 2. Experimental Results After soil incubation, the soil aggregate content results for Example 1 and Comparative Example 1 are as follows: Figure 2 As shown. Compared to Comparative Example 1 (biochar alone, 2% BC group), Example 1 showed improvement with the synergistic application of calcium ions (2% BC + 0.1% Ca). 2+ After group 1), the content of soil micro-aggregates (particle size <250 μm) showed a significant decreasing trend.Figure 2 (a)), while the content of large aggregates (particle size ≥250 μm) increased significantly ( Figure 2 (b) According to statistical data, the average proportion of large aggregates in Example 1 increased by approximately 75% compared to Comparative Example 1. Since the biochar particle size is ≤0.25 mm, its input does not directly increase the sieve weight of components with a particle size ≥250 μm, indicating that the introduction of calcium ions significantly promoted the transformation of microaggregates into large aggregates during cultivation. The inventors speculate that the main mechanism is that calcium ions (Ca... 2+ As a cation, it acts as an inorganic cementing agent in the soil, binding and adsorbing dispersed micro-aggregates and biochar particles through electrostatic attraction and flocculation, agglomerating them into larger, more stable aggregates. The significant increase in the content of these large soil aggregates contributes to the formation of a favorable soil pore structure and provides physical isolation and protection for organic carbon, thereby hindering microbial contact and decomposition of the encapsulated carbon. This demonstrates that the method of this application can significantly enhance the soil's carbon sequestration potential through a physical cementation mechanism.

[0074] Experimental Example 2: Determination of the Adsorption Performance of Dissolved Organic Carbon in Soil 1. Experimental Methods The adsorption capacity of dissolved organic carbon in soil was determined using a batch equilibrium adsorption method, which includes the following steps: S1. Preparation of adsorption standard solution Using commercially available humic acid as a solute, a series of dissolved organic carbon (DOC) solutions with different initial concentrations were prepared, with concentration gradients of 0, 1, 3, 7, 10, and 15 mg / L, as standard working solutions for adsorption experiments.

[0075] S2. Preparation of soil samples Soil samples were collected from Example 1 and Comparative Example 1 after the 60th day of cultivation. The soil samples were air-dried and sieved before use.

[0076] S3. Adsorption test Accurately weigh 2.0 g of soil samples from each of the above treatment groups and place them into 50 mL polypropylene centrifuge tubes. Add 20 mL of DOC adsorption standard solutions of different concentrations to each centrifuge tube at a solid-liquid ratio of 1:10 (g / mL). After tightening the caps, place the tubes in a 25℃ constant temperature shaker and shake continuously at 220 r / min for 24 h under light-protected conditions to allow the dissolved organic carbon in the soil and solution to reach adsorption equilibrium.

[0077] S4. Measurement and Calculation After shaking, the suspension was centrifuged at 4200 r / min for 20 min. The supernatant was filtered through a 0.45 μm PTFE aqueous microporous membrane, and the filtrate was collected in a clean sample vial. The equilibrium concentration of DOC in the filtrate was determined using a total organic carbon analyzer (TOC-L, equipped with an autosampler). e ), and calculate the DOC adsorption capacity per unit soil (Q) based on the initial concentration. e The calculation formula is: Q e =[(C0-C e )×V] / m; Where C0 is the initial concentration of the DOC solution (mg / L), C e V is the concentration after adsorption equilibrium (mg / L), V is the solution volume (L), and m is the soil sample mass (kg).

[0078] 2. Experimental Results The results of DOC content in the soil of Example 1 and Comparative Example 1 are as follows: Figure 3 As shown. The equilibrium adsorption capacity (Q) of biochar for DOC under different treatment conditions. e All of these vary with equilibrium concentration (C) e The adsorption rate increases with the increase of ), eventually leveling off and reaching adsorption saturation. However, at the same equilibrium concentration, the adsorption rate of the biochar and calcium ion synergistic group in Example 1 (2% BC + 0.1% Ca) increased. 2+ The adsorption isotherm of the synergistic group (group A) was consistently above that of the biochar-only group (2% BC group) in Comparative Example 1, indicating stronger adsorption capacity. When saturation was reached, the maximum adsorption capacity of the synergistic group was also significantly higher than that of the biochar-only group. These results suggest that the addition of calcium ions is not a simple physical mixing process, but rather a synergistic effect at the chemical level. The inventors hypothesize that the mechanism of action is: Ca... 2+ Through "cation bridging," the negative charge on the biochar surface and DOC molecules is effectively neutralized, reducing electrostatic repulsion. At the same time, new adsorption sites are formed on the biochar surface, thereby significantly enhancing the binding strength and retention capacity of biochar to DOC, effectively inhibiting DOC loss, and achieving chemical carbon fixation.

[0079] The soil aggregate content and dissolved organic carbon adsorption performance of Examples 2 and 3 are basically the same as those of Example 1, and will not be repeated here.

[0080] In summary, this invention provides a method for promoting biochar soil carbon sequestration using calcium ions. Experimental results show that, compared to applying biochar alone, the synergistic application of calcium ions and biochar significantly increases the content of large soil aggregates, achieving physical protection of organic carbon. Simultaneously, it greatly enhances the adsorption and fixation capacity of biochar for active organic carbon, effectively reducing the risk of organic carbon mineralization. Under the synergistic effect of these two mechanisms, the carbon sequestration effect between biochar and soil is significantly enhanced, and the soil's carbon sequestration potential is significantly improved, demonstrating significant agricultural application value.

[0081] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for promoting soil carbon sequestration using calcium ions through biochar, characterized in that, Includes the following steps: After pre-culturing the soil in a sealed, light-protected environment for 6-10 days, add biochar and calcium source to the pre-cultured soil, mix thoroughly, and then formally culture for 50-70 days under the same conditions as the pre-culture.

2. The method according to claim 1, characterized in that, The amount of calcium ions added to the calcium source is 0.03wt% to 0.5wt% of the amount of biochar added.

3. The method according to claim 1, characterized in that, The amount of biochar added is 1 wt% to 3 wt% based on the dry weight of the soil.

4. The method according to claim 1, characterized in that, The calcium source includes one or more of calcium salts, calcium oxides, and calcium hydroxides.

5. The method according to claim 1, characterized in that, The method for preparing the biochar includes the following steps: Under a protective gas atmosphere, renewable biomass is dried, pulverized, sieved, pyrolyzed at 350~700 ℃, and then cooled to obtain the final product.

6. The method according to claim 5, characterized in that, The renewable biomass includes one or more of straw, branches, and grass.

7. The method according to claim 1, characterized in that, The temperature during the pre-culture period is 24~30 ℃.

8. The method according to claim 1, characterized in that, During the pre-cultivation process, water is added to adjust the soil's water holding capacity to 30%~50%.

9. The method according to claim 1, characterized in that, During the formal cultivation process, water is added to adjust the soil's water holding capacity to 50%–70%.

10. The application of the method according to any one of claims 1 to 9 in promoting soil carbon sequestration.

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