Method for evaluating carbon sequestration potential of biomass charcoal based on soil aggregate

Abstract

The invention belongs to the technical field of ecological science and soil carbon sequestration, and particularly relates to a method for evaluating the carbon sequestration potential of biomass charcoal based on soil aggregates. According to the method, the change degree of the carbon sequestration capacity of the soil after the biomass charcoal is added is evaluated by measuring the numerical value variation of the soil aggregate with the particle size larger than or equal to 250 microns in the soil, and then the carbon sequestration potential of the biomass charcoal is evaluated. Results show that the content of the soil aggregate with the particle size larger than or equal to 250 micrometers can reflect the carbon sequestration capacity level of the soil, if the content of the soil aggregate with the particle size larger than or equal to 250 micrometers is high, soil background organic carbon is not prone to being mineralized, the carbon sequestration effect of the soil is higher, and it is indicated that the carbon sequestration capacity of the soil is affected after the charcoal is added. The research result can realize simplified evaluation of the carbon sequestration potential of the biomass charcoal, and provides technical support for optimized application of the biomass charcoal in agriculture and ecological restoration. In addition, the method is simple and convenient to operate, low in cost and suitable for evaluating the carbon sequestration potential of different types of soil and biomass charcoal materials.

Description

Technical Field

[0001] The present invention belongs to the technical fields of ecological science and soil carbon sequestration technology. More specifically, it relates to a method for evaluating the carbon sequestration potential of biochar based on soil aggregates. Background Art

[0002] The current global warming caused by the increasing emissions of greenhouse gases dominated by human activities has become a severe challenge faced by the international community and threatens the survival and development of humanity. Human society is responding to its effects. The Sixth Assessment Report of the IPCC shows that the concentrations of the two major greenhouse gases in the current atmosphere, carbon dioxide (CO2) and methane (CH4), have increased by 47% and 156% respectively compared with 1750. Affected by this, the global average surface temperature from 2011 to 2020 has increased by 1.09 °C compared with 1850 - 1900. As a large agricultural and populous country in the world, greenhouse gas emissions related to agricultural activities in the country are approximately 828 million tons of carbon dioxide equivalent (CO2-eq), accounting for about 7.9% of the total national greenhouse gas emissions.

[0003] As a porous carbon-rich material, biochar has been widely used in the fields of soil improvement and carbon sequestration. It forms a stable aromatic carbon structure through the pyrolysis of biomass and can theoretically exist in the soil for hundreds of years. Existing research shows that the addition of biochar can increase the soil organic carbon pool capacity by about 20 - 50%, but the actual carbon sequestration effect is significantly affected by many factors such as raw material type, pyrolysis temperature, and soil texture. The current assessment of soil carbon sequestration capacity mainly relies on Flux monitoring: This method requires complex processes such as the purification, separation, capture, and compression of carbon dioxide; in actual operation, the purchase cost of high-precision gas analysis equipment is high, and the construction and operation and maintenance costs of the monitoring network are difficult to match. Coupled with the strict requirements for supporting infrastructure, this assessment system is difficult to promote and apply on a large scale.

[0004] Therefore, there is an urgent need to establish a method system for evaluating the carbon sequestration efficiency of biochar that does not rely on the direct detection of carbon dioxide. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects and deficiencies in the prior art that the assessment system of the carbon sequestration potential of soil after the addition of biochar mainly relies on the direct detection of carbon dioxide, and to provide a method for evaluating the soil carbon sequestration capacity after the addition of biochar based on soil aggregates.

[0006] The above object of the present invention is achieved by the following technical solutions:

[0007] The present invention protects a method for evaluating the soil carbon sequestration capacity after adding biochar based on soil aggregates, comprising the following steps: determining the soil aggregate composition of the soil sample before applying biochar; determining the soil aggregate composition of the soil after culturing to a set time point after applying biochar, and evaluating the change degree of the soil carbon sequestration capacity after adding biochar by comparing the change amount of the soil aggregate value with a particle size ≥ 250 μm in the soil aggregate composition.

[0008] Further, the soil aggregates with a particle size ≥ 250 μm are soil aggregates with a particle size of 250 - 2000 μm.

[0009] Further, the culturing time is 60 - 80 days.

[0010] Further, the addition amount of the biochar is 1 - 3 wt% of the soil addition amount.

[0011] Further, the collection of the soil sample comprises the following steps: the soil sample is collected from the 0 - 10 cm surface soil, naturally air-dried, non-soil impurities are removed, and it is sieved to obtain the soil sample.

[0012] Preferably, the aperture of the sieve mesh for sieving is 2 - 3 mm.

[0013] Further, the culturing comprises the following steps:

[0014] sI. Pre-culturing the soil sample in a sealed and light-shielded environment;

[0015] sII. Adding biochar to the pre-cultured soil and mixing evenly, and continuing to culture under the same sealed and light-shielded conditions;

[0016] sIII. Setting a control group, and except for not adding biochar, the remaining operations are the same as those in steps sI and sII;

[0017] The soil obtained after culturing through steps sII and sIII is used for the detection and analysis of the soil aggregate composition.

[0018] Further, the detection and analysis of the soil aggregate composition is determined by the wet sieving method.

[0019] Further, the wet sieving method comprises the following steps:

[0020] S1. Placing the soil sample for detection and analysis on the sieve mesh and adding water to soak it;

[0021] S2. After the soaking ends, sieving the soil into aggregates with different particle sizes;

[0022] S3. Separately collecting the aggregates with different particle sizes obtained in step S2, drying them, recording the weights, and obtaining the proportions of the aggregates with different particle sizes.

[0023] Further, in step S1, the aperture of the sieve is 2 mm.

[0024] Furthermore, in step S2, as an optional implementation manner, the soil screening specifically includes the following steps: after the infiltration ends, move the sieve up and down at a frequency of 25 - 40 times / min and a moving amplitude of 2 - 4 cm, transfer the soil passing through the 2-mm sieve to a 0.25-mm sieve, repeat the above operation, the soil aggregates with a particle size ≥ 250 μm are those remaining on the 0.25-mm sieve, and the soil micro-aggregates with a particle size < 250 μm are those passing through the 0.25-mm sieve;

[0025] Further, in step S3, the drying is to dry to a constant weight.

[0026] Furthermore, in step S3, the drying is drying in an oven, and the drying temperature is 50 - 80 °C (preferably 60 °C).

[0027] Preferably, the soil sample is from farmland soil.

[0028] Further, the non-soil impurities include gravel and plant roots.

[0029] Preferably, the time of pre-cultivation is 6 - 10 days.

[0030] Further, in step sI, when pre-cultivating, water is added to adjust the maximum water holding capacity of the soil to 30% - 40%, preferably 40%.

[0031] Further, in step sII, when continuously culturing, water is added to adjust the maximum water holding capacity of the soil to 60 - 70%, preferably 60%.

[0032] Further, the maximum water holding capacity of the soil refers to the maximum amount of water that the soil can adsorb and hold in a saturated state.

[0033] Further, the determination of the maximum water holding capacity of the soil is measured by the gravimetric method.

[0034] Further, in step sI or step sII, the temperature of the cultivation is 24 - 30 °C, preferably 25 °C.

[0035] Further, before the determination of the soil aggregates, the soil needs to be naturally air-dried and passed through a sieve with an aperture of 5 mm.

[0036] Preferably, the particle size of the biochar ≤ 0.25 mm.

[0037] Further, the biochar is the biochar made from corn straw as raw material.

[0038] Further, the biochar is obtained by a preparation method comprising the following steps: pyrolyzing corn straw powder at 300-600 °C for 1-3 h under anaerobic or anoxic conditions to obtain biochar.

[0039] Preferably, the particle size of the corn straw powder is ≤2 mm.

[0040] Preferably, the heating rate of the pyrolysis is 1-10 °C / min, preferably 5 °C / min.

[0041] Optionally, the anaerobic or anoxic conditions can be formed by using nitrogen gas with a flow rate of 400-800 mL / min (preferably 600 mL / min) as a protective gas.

[0042] The present invention protects the application of any of the above methods in evaluating the soil carbon sequestration capacity of biochar.

[0043] The present invention protects a method for evaluating the carbon sequestration capacity of biochar, and the evaluation is carried out by using the method.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] (1) The present invention evaluates the change degree of the soil carbon sequestration capacity after the addition of biochar by measuring the numerical change of soil aggregates with a particle size ≥250 μm in the soil, so as to evaluate the carbon sequestration capacity of biochar. The increase in soil aggregates with a particle size ≥250 μm after the addition of biochar is positively correlated with the soil carbon sequestration capacity. The change in the soil carbon sequestration capacity before and after the addition of biochar is used to illustrate the influence of biochar addition on the soil carbon sequestration capacity, and thus the carbon sequestration capacity of biochar can be evaluated. This method has a wide range of applications and can be applied to different soil types and biochar types, providing a new reference scheme for agricultural carbon sink management, helping to improve the carbon storage capacity of agricultural soil, and promoting the sustainable development of agriculture.

[0046] (2) The present invention solves the problem in the prior art of lacking a systematic method for correlating aggregate indicators with the soil carbon sequestration capacity of biochar, and can simply and quickly evaluate the soil carbon storage capacity and optimize the application effect of biochar. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of soil cultivation in Example 1 of the present invention.

[0048] Figure 2 It is a graph of the content of soil microaggregates in Example 2 of the present invention.

[0049] Figure 3 It is a graph of the content of soil macroaggregates in Example 2 of the present invention.

[0050] Figure 4It is the graph of the cumulative mineralization amount of soil background organic carbon in Example 3 of the present invention.

[0051] Figure 5 It is the graph of the cumulative mineralization amount of soil background organic carbon on the 60th day in Example 3 of the present invention.

[0052] Figure 6 It is the data statistical graph of the correlation between the increase amount of soil aggregates and the decrease amount of the cumulative mineralization amount of soil background organic carbon. Detailed implementation manners

[0053] The present invention will be further described below in conjunction with the specification drawings and specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0054] Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0055] Example 1 Soil collection and cultivation based on biochar

[0056] The cultivation of the soil includes the following steps:

[0057] S1. Collection of soil samples: Select four different types of farmland soils as the test soils. All soil samples are collected from the 0-10 cm surface soil. After natural air drying, remove gravel and plant roots, etc., pass through a 2 mm sieve, and mix well for standby.

[0058] S2. Preparation of biochar: Grind the naturally air-dried corn straw into powder and put it into a crucible. Place the crucible in a muffle furnace. Then, introduce nitrogen into the furnace at a flow rate of 600 mL / min, and then heat it at a rate of 5 °C / min and stay at the target temperature of 450 °C for 2 h. After cooling to room temperature, take it out. The obtained biochar passes through a 0.25 mm sieve and is mixed well for standby.

[0059] S3. Cultivation of the soil: The experiment is divided into two groups: soil collection analysis (the first group of cultivation) and gas collection analysis (the second group of cultivation). First, add four different types of soils (soils with different degrees of heavy metal pollution) into sterilized high borosilicate glass bottles. Among them, the soil amount used in the first group of cultivation experiments is 100 g / bottle, and the soil amount used in the second group of cultivation experiments is 10 g / bottle. Add deionized water to make the soil water content reach 40% of the maximum water holding capacity, and pre-culture in a 25 °C constant temperature and humidity incubator in the dark for 7 days to restore the soil microbial activity.

[0060] Among them, the maximum water holding capacity of the soil was determined by the gravimetric method. Approximately 2.5 g of the experimental soil was added into a 2 mL syringe tube, and this was repeated 3 times. The bottom of the syringe tube containing the soil was completely wrapped with coarse filter paper, and then it was placed in water such that the water surface was level with the middle of the syringe tube. Be sure not to submerge the top end with water to avoid pore sealing and affecting the experimental results. After soaking for 24 h, an appropriate amount of soil was placed in a crucible that had been dried at 105 °C and cooled to room temperature (the weight of the crucible was W0), and the weight W1 was recorded. Then, the crucible containing the soil was placed in an oven and dried at 105 °C to a constant weight, and the weight W2 was recorded. The difference between the two was the saturated water content of the soil, and the maximum water holding capacity of the soil was expressed as a percentage of the dry weight of the soil.

[0061] After the pre-cultivation ended, fresh corn straw biochar was added to the soil at addition amounts of 0 wt% and 2 wt% (by weight of the soil). It was fully stirred to make the biochar evenly distributed in the soil. Then, the soil water content was adjusted to 60% of the maximum water holding capacity (this value is the most suitable water content for microbial respiration). Next, the culture bottles were sealed and placed in a constant temperature and humidity incubator at 25 °C for 60 days of light-shielded cultivation. The schematic diagram of the soil cultivation is as Figure 1 shown. During the cultivation process, soil and gas samples were collected regularly. After each gas sample collection was completed, all the culture bottles were aerated and deionized water was added to ensure a constant soil water content. Subsequently, the culture bottles were sealed again. A total of 8 treatment groups were cultivated, and 3 replicates were set for each treatment.

[0062] Determination of the soil aggregate composition in Example 2

[0063] The determination of the soil aggregate composition included the following steps:

[0064] On the 60th day of cultivation, the soil in the first group of cultivation was collected, air-dried naturally, and passed through a 5 mm sieve. Then, 25 g of the soil was weighed and placed on a 2 mm sieve. Deionized water was added and the liquid level was 3 cm above the soil. After soaking for 5 min, the sieve was manually moved up and down for 2 min, with a moving amplitude of 3 cm and a frequency of 25 times / min. During this process, all the soil samples passed through the 2 mm sieve. Then, the soil passing through the 2 mm sieve was transferred to a 0.25 mm sieve, and the above operation was repeated. What remained on the 0.25 mm sieve was the soil macro-aggregates (particle size 250 - 2000 μm), and what passed through the 0.25 mm sieve was the soil micro-aggregates (particle size less than 250 μm). The aggregates of each particle size were transferred to an aluminum box and dried to a constant weight at 60 °C, and the weight was recorded.

[0065] Collection and determination of gas samples in Example 3

[0066] The collection and determination of gas samples included the following steps:

[0067] S1. Collection of gas samples: Regarding the second group of cultures, gases were collected on the 1st, 3rd, 7th, 15th, 21st, 30th, 40th, 50th, and 60th days of the culture, and the CO2 and 13 CO2 content was measured. The specific operation was as follows: Select a syringe with good sealing performance, insert its needle into the silicone stopper of the culture bottle, push and pull the syringe to mix the gas in the bottle, and immediately collect 15 mL of gas samples and store them in a gas sampling bag in a vacuum state for proper preservation. After each sampling, insert two syringe needles into the silicone stopper of the culture bottle. One end is connected to a pipeline to introduce a dry nitrogen-oxygen mixture for 5 - 8 minutes to remove other gases in the bottle, and the other end is connected to the atmosphere to ensure the pressure in the bottle while discharging the gas, and then seal the culture bottle for the next gas sampling. After the culture bottle is sealed, immediately inject 15 mL of air into the bottle, mix it evenly, and then extract 15 mL of gas as the initial sample for the next collection.

[0068] S2. Measurement of gas samples: The collected approximately 5 mL of gas samples were used to measure the δ 13 C value of CO2 by a Picarro stable isotope analyzer, and the remaining 10 mL of gas samples were used to measure the CO2 concentration by a gas chromatograph equipped with a flame ionization detector.

[0069] Example 4 Composition of soil aggregates based on biochar and measurement results of gas samples

[0070] The composition of aggregates in the soil collected on the 60th day of the culture experiment was as Figure 2 and Figure 3 shown, where NMB and MB were the treatment groups without adding corn straw biochar and adding 2% corn straw biochar respectively, and S1, S2, S3, and S4 were four different types of soil collected.

[0071] From Figure 2 and Figure 3It can be seen that after adding biochar, the content of soil micro-aggregates generally decreases, while the content of soil macro-aggregates generally increases. This situation is particularly obvious in S4 soil, with the increase rate of macro-aggregate content reaching as high as 109%. Given that the particle size of biochar is ≤250μm, its input will not interfere with the measurement results of soil macro-aggregates with a particle size ≥250μm, indicating that biochar can promote the formation of soil macro-aggregates with a particle size ≥250μm in the later stage of the experiment. This may be due to the carbon-rich and porous structural characteristics of biochar itself. After being put into the soil, it can directly act as a cementing agent to adsorb and aggregate smaller-sized aggregates into macro-aggregates, promoting the transformation of micro-aggregates with a particle size <250μm into macro-aggregates with a particle size ≥250μm. The increase in the content of soil macro-aggregates helps to improve the soil structure, enhance stability, and increase its ability to resist mechanical damage and hydraulic erosion. At the same time, the addition of biochar increases the content of soil organic matter, and macro-aggregates are the main carriers for physically protecting soil organic carbon. A high content indicates a stronger soil carbon sequestration potential after adding biochar, that is, it shows that biochar has the ability of carbon sequestration and can further enhance the soil's carbon sequestration ability.

[0072] The cumulative emissions of CO2 released from the soil background organic carbon in the gas collected on the 1st, 3rd, 7th, 15th, 21st, 30th, 40th, 50th, and 60th days of cultivation are as Figure 4 shown, where S1, S2, S3, and S4 respectively represent four different types of soil treatment groups without adding biochar, and S1+MB, S2+MB, S3+MB, and S4+MB respectively represent four different types of soil treatment groups with added biochar. The results of the cumulative mineralization amount of soil background organic carbon on the 60th day are as Figure 5 shown.

[0073] It can be Figure 4 seen that the trend of the cumulative emissions of CO2 from the soil background organic carbon changing with time under different treatment conditions is obvious and tends to be stable in the later stage of cultivation. After adding biochar to the four soils, the cumulative emissions of CO2 released from the soil background organic carbon all decrease. Especially in S3 soil, the inhibitory effect of adding biochar is the most significant ( Figure 4 , Figure 5 ), which indicates that the addition of biochar can effectively inhibit the release of CO2 from the soil background organic carbon and achieve the effect of carbon sequestration.

[0074] It can be Figure 6It can be seen that there is a significant positive correlation between the increase in the amount of macroaggregates with a particle size ≥ 250 μm and the decrease in the amount of CO2 released from the background organic carbon after biochar is added to the soil. This indicates that the increase in macroaggregates caused by biochar can effectively explain the enhanced soil carbon sequestration ability after biochar addition. Therefore, this method can illustrate the impact of biochar addition on the soil carbon sequestration ability through the change in the soil carbon sequestration ability before and after biochar addition, and further evaluate the carbon sequestration ability of biochar.

[0075] In summary, a method for evaluating the soil carbon sequestration ability after biochar addition based on soil aggregates provided by the present invention evaluates the change degree of the soil carbon sequestration ability after biochar addition by comparing the change amount of the value of soil macroaggregates with a particle size ≥ 250 μm (especially soil aggregates with a particle size of 250 - 2000 μm) in the soil aggregate composition, so as to evaluate the carbon sequestration ability of biochar. The results show that compared with the soil with a low content of macroaggregates with a particle size ≥ 250 μm, the addition of biochar further increases the content of soil macroaggregates, and the organic carbon mineralization rate of the soil is lower, and its carbon fixation effect is better.

[0076] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for evaluating the soil carbon sequestration capacity after adding biochar based on soil aggregates, characterized in that, Comprising the following steps: Determine the soil aggregate composition of the soil sample before applying biochar; determine the soil aggregate composition of the soil after culturing to a set time point after applying biochar, and evaluate the change degree of the soil carbon sequestration ability after adding biochar by comparing the change amount of the soil aggregate value with a particle size ≥ 250 μm in the soil aggregate composition.

2. The method according to claim 1, wherein The soil aggregate with a particle size ≥ 250 μm is a soil aggregate with a particle size of 250 - 2000 μm.

3. The method according to claim 1, wherein The culturing time is 60 - 80 days.

4. The method according to claim 1, characterized in that, The addition amount of the biochar is 1 - 3 wt% of the soil addition amount.

5. The method according to claim 1, characterized in that The collection of the soil sample comprises the following steps: The soil sample is taken from the 0 - 10 cm surface soil, naturally air-dried, non-soil impurities are removed, and it is sieved to obtain the sample.

6. The method according to claim 1, wherein The culturing comprises the following steps: sI. Place the soil sample in a sealed and light-proof environment for pre-culturing; sII. Add biochar to the pre-cultured soil and mix evenly, and continue culturing under the same sealed and light-proof conditions; sIII. Set a control group, and except for not adding biochar, the other operations are the same as those in steps sI and sII; The soil obtained after culturing through steps sII and sIII is used for the detection and analysis of the soil aggregate composition.

7. The method according to claim 1, characterized in that The detection and analysis of the soil aggregate composition is determined by the wet sieving method.

8. The method according to claim 7, wherein The wet sieving method comprises the following steps: S1. Place the soil sample for detection and analysis on a sieve mesh and moisten it with water; S2. After the moistening is completed, sieve the soil into aggregates with different particle sizes; S3. Respectively collect the aggregates with different particle sizes obtained in step S2, dry them, record the weights, and obtain the proportions of the aggregates with different particle sizes.

9. The application of the method according to any one of claims 1 to 8 in evaluating the soil carbon sequestration ability of biochar.

10. A method for evaluating the carbon sequestration capacity of biochar, characterized in that, Evaluate by using the method according to any one of claims 1 to 9.

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