Quantitative analysis method for evaluating excitation effect of biochar on soil endogenous organic carbon

Abstract

The invention designs a quantitative analysis method for evaluating the excitation effect of biochar on soil endogenous organic carbon, and the method combines a benzene polyacid molecular marker method and soil particle density grading to distinguish and quantify biochar and soil endogenous carbon. On the basis, a quantitative evaluation method for the excitation effect of biochar addition on the endogenous carbon in the soil is constructed, biochar information can be accurately recognized and quantified from the soil through the method, and the mineralization amount or accumulation amount of nSOC can be quantified. Specifically, according to the method, the biochar and the soil endogenous carbon are distinguished, and the time and economic cost caused by isotope labeling and CO2 detection is avoided.

Description

Technical Field

[0001] The invention belongs to the field of agricultural science and technology, and specifically relates to a quantitative analysis method for evaluating the stimulating effect of biochar on endogenous organic carbon in soil. Background Art

[0002] The soil organic carbon (SOC) pool is the largest terrestrial carbon pool on Earth, with a storage volume 3.2 times that of the atmospheric carbon pool. It plays a vital role in maintaining global carbon balance and stabilizing atmospheric CO2 concentrations. Even small fluctuations in the SOC pool may significantly affect atmospheric CO2 concentrations, thereby triggering huge feedbacks of climate change. Therefore, the dynamic changes of the SOC pool have always been a research hotspot in the fields of environmental science and agricultural science.

[0003] In agricultural soils, tillage activities have a significant impact on the mineralization and depletion of soil organic carbon. Long-term tillage can lead to a large loss of soil organic carbon, reduce soil quality, and affect crop growth and ecosystem functions. In order to improve the quality and quantity of SOC, people have begun to explore various soil improvement methods, among which biochar has attracted much attention due to its unique structure and properties.

[0004] Existing studies have shown that the addition of biochar may have a stimulating effect, that is, it affects the mineralization rate of existing nSOC. However, there is still a lot of controversy about whether the addition of biochar accelerates or reduces the mineralization rate of nSOC (i.e., it produces a positive stimulating effect or a negative stimulating effect). The reason lies in how to accurately identify and quantify biochar information from the soil and quantitatively evaluate the mineralization amount of nSOC.

[0005] At present, the research on soil organic carbon does not distinguish between biochar and soil endogenous carbon. For example, in the prior art, Shang Jie, Geng Zengchao, Chen Xinxiang, Zhao Jun, Geng Rong, Wang Sen. Effects of biochar application on soil organic carbon, nitrogen and its components in dryland farmland[J]. Journal of Agro-Environment Science, 2015, 34(3): 509-517., no distinction is made between biochar and soil endogenous carbon, which will lead to a large error in the final result. At the same time, in the prior art, the detection of radioisotope-labeled 14 CO2 or stable isotope labeled 13 CO2 emissions can be used to distinguish and quantify whether the mineralized organic carbon comes from added biochar or endogenous organic carbon, but this method is cumbersome (continuous monitoring of CO2 emissions is required) and requires isotope labeling; it still has some defects. Summary of the invention

[0006] In order to solve the above technical problems, the present invention designs a quantitative analysis method for evaluating the stimulating effect of biochar on soil endogenous organic carbon. This method uses a combination of benzene polyacid molecular markers and soil particle density classification to distinguish and quantify biochar and soil endogenous carbon. On this basis, a quantitative evaluation method for the stimulating effect of biochar addition on soil endogenous carbon is constructed. This method can accurately identify and quantify biochar information from the soil, and quantify the mineralization amount of nSOC. Specifically, this method not only distinguishes biochar from soil endogenous carbon, but also avoids the time and economic costs caused by the use of isotope labeling and CO2 detection.

[0007] In order to achieve the above technical effects, the present invention discloses a quantitative analysis method for evaluating the stimulating effect of biochar on endogenous organic carbon in soil, comprising the following steps: S1: Collection and pretreatment of soil samples; S2: preparation of biochar; S3: soil-biochar incubation; S4: Soil density component classification, including: S4.1: Add the sieved air-dried soil incubated in S4 to the centrifuge tube, then add the sodium iodide solution, slowly shake the centrifuge tube up and down to moisten the soil, and let it stand for a while; after standing, centrifuge again, and then filter the supernatant with filter paper. The residue is the free light fraction (fLF), which is repeatedly rinsed with ultrapure water to remove excess NaI; S4.2: Add NaI solution to the free light fraction obtained by centrifugation in S4.1 again, shake up and down to disperse the solid residue, and use ultrasonic treatment to destroy the agglomerates; S4.3: After the ultrasonic treatment, let it stand, then centrifuge at 3500r / min and filter to obtain the closed light component (oLF) wrapped in the agglomerates. The remaining particles in the centrifuge tube are the heavy components (HF) combined with the minerals. Rinse repeatedly with ultrapure water until the conductivity of the supernatant is <50μS / cm; all components are dried at 40℃ and weighed; S5: Quantitative analysis of soil biochar, specifically: S5.1: Weigh the final graded sample obtained in S4 and pour it into a reactor, add TFA solution to react; after the reaction is complete, filter it with a glass fiber membrane, and repeatedly rinse it with ultrapure water to obtain a filter residue; S5.2: After drying the filter residue, pour it into a reactor, add HNO3 to react for a period of time, and after the reaction is completed, add ultrapure water to the reactor in multiple times and filter; take the filtrate, add ultrapure water and citric acid in sequence, mix well, and pass it through a cation exchange column; S5.3: After the filtrate is freeze-dried, it is dissolved with methanol and transferred to a liquid phase bottle, dimethyl biphenyl-2,2'-dicarboxylate is added, and nitrogen is blown to dryness; anhydrous pyridine and N,O-bistrimethylsilyltrifluoroacetamide + trimethylchlorosilane are then added in sequence for further reaction; S6: Determination of total soil organic carbon: use an element analyzer to determine the C, H, N, and O contents of the total soil and each component of the soil after density classification; and simultaneously determine the soil pH.

[0008] Further, in S4.1, the density of sodium iodide is 1.8 g / cm 3 , the centrifugal condition was 3500r / min for 30 min; Furthermore, the density of sodium iodide added in S4.2 is 1.8 g / cm 3 , 300 J / cm 3 Ultrasonic treatment; Furthermore, the content of the TFA solution added in S5.1 is 4 mol / L, and the reaction is carried out at 105° C. for 4 h; Furthermore, the percentage of HNO3 added in S5.2 is 65%, and the reaction is carried out at 170°C for 8 h; Furthermore, N, O-bistrimethylsilyltrifluoroacetamide + trimethylchlorosilane are added to S5.3 in a ratio of 99:1, and the reaction is carried out at 80 °C for 2 h; Furthermore, before determining the BPCAs content in the heavy component (HF), the HF needs to be demineralized. The process is as follows: S4.3.1: Add HF to a mixture of 10% hydrofluoric acid / 1 mol / L hydrochloric acid at a ratio of 1:4 (mass ratio) and place in a shaker (room temperature, 120 rpm) for 2 h; S4.3.2: Then centrifuge at 2500 r / min for 30 min to separate the solid and liquid. Repeat the above operation several times, and then wash repeatedly with ultrapure water until no Cl is detected. – Finally, dry at 40 ℃.

[0009] Furthermore, in S1, the mixed sample is collected by the plum blossom point method, 9 sampling points are set at each sampling site, and the collected samples are fully mixed; the visible roots, plant residues and rocks in the fresh soil are removed, and then the soil is sieved and thoroughly mixed and stored for later use; Furthermore, in S2, pine sawdust was selected as the raw material for preparing biochar. After the sample was naturally dried, it was crushed and sieved through a 2 mm sieve, and then placed in an oven and baked at 70 °C for 24 h. The dried raw material was placed in a muffle furnace and pyrolyzed at 300 °C for 4 h in a N2 atmosphere to obtain biochar. The biochar was ground and sieved through a 150 μm sieve and stored in a sample bottle for later use, marked as PW300.

[0010] The beneficial effects of the present invention are: The present invention uses soil particle density classification and benzene polyacid (BPCAs) molecular biomarker method to distinguish and quantify the biochar content and soil endogenous carbon content in each density component of the soil, and constructs the EA-C method for evaluating the stimulating effect of biochar on soil endogenous organic carbon: the same type of soil has the same carbon mineralization rate without adding biochar. After adding biochar, the total carbon content of each component is subtracted from the carbon content in the blank control soil, and the remaining carbon content is the carbon contributed by biochar and the accumulation or loss of soil endogenous carbon caused by the addition of biochar, which is recorded as EA-C. The part of EA-C content that is higher than the biochar content is considered to be carbon accumulation caused by the negative stimulating effect of soil endogenous carbon induced by biochar addition, and the part that is lower than the biochar carbon content is considered to be carbon mineralization caused by the positive stimulating effect of soil endogenous carbon induced by biochar addition. This method not only distinguishes biochar from soil endogenous carbon, but also avoids the time and economic cost caused by the use of isotope labeling and CO2 detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0012] Figure 1 is a graph of carbon content of different types of total soil after adding different proportions of biochar according to the present invention; Figure 2 is the carbon content in different density components of brown soil after adding different proportions of biochar in the present invention; Figure 3 is the carbon content in different density components of lime soil after adding different proportions of biochar according to the present invention; Figure 4 is the carbon content in different density components of red soil after adding different proportions of biochar of the present invention; Figure 5 is the change of the biochar content in the total soil and the endogenous carbon in the soil after adding different proportions of biochar in the present invention; Figure 6 The changes of biochar content and soil endogenous carbon in different density components of brown soil after adding biochar in different proportions of the present invention; Figure 7The changes of biochar content and soil endogenous carbon in different density components of lime soil after adding biochar in different proportions according to the present invention; Figure 8 It is the change of biochar content and soil endogenous carbon in different density components of red soil after adding biochar in different proportions of the present invention. DETAILED DESCRIPTION Example 1

[0013] The present invention discloses a quantitative analysis method for evaluating the stimulating effect of biochar on endogenous organic carbon in soil, and the specific process is as follows: S1: Collection and pretreatment of soil samples: Three types of soil samples, brown soil, lime soil and red soil, were collected in Yunnan Province. The specific sampling methods are as follows: The soil samples of the cultivated layer (0-20 cm) were mainly collected during the collection. To ensure the representativeness of the samples, the plum blossom point method was adopted to collect mixed samples. Nine sampling points were set up in each sampling site, and the collected samples were fully mixed. The visible roots, plant residues and rocks in the fresh soil were removed, and then the soil was sieved (<2mm) and thoroughly mixed and stored for later use.

[0014] S2: Preparation of biochar: Pine sawdust was selected as the raw material for preparing biochar. After natural drying, the sample was crushed through a 2 mm sieve and then placed in an oven at 70 °C for 24 h. The dried raw material was placed in a muffle furnace and pyrolyzed at 300 °C for 4 h in a N2 atmosphere to obtain biochar. The biochar was ground through a 150 μm sieve and stored in a sample bottle for later use, labeled PW300.

[0015] S3: Soil-biochar incubation; Biochar was mixed with soil at a ratio of 0 (blank control), 1, 3 and 5%, and then poured into pots for cultivation. Three parallel groups were set for each treatment. The soil moisture content was maintained at 60% of the water holding capacity, the temperature in the greenhouse was maintained at around 25°C, and the average sunshine hours were about 8 h. After one year of cultivation, 300 g of soil was evenly taken from each pot, naturally air-dried, ground and sieved through a 2 mm sieve; among them, the brown soil, lime soil and red soil samples were marked as L (brown soil), M (lime soil) and S (red soil), respectively, the blank control with a biochar addition ratio of 0 was marked as LK, MK and SK, the brown soil with a biochar addition ratio of 1, 3 and 5% was marked as L1, L3 and L5, the lime soil was marked as M1, M3 and M5, and the red soil was marked as S1, S3 and S5.

[0016] S4: Soil density fractionation: 7 g of air-dried soil passed through a 2 mm sieve was added to a 50 mL centrifuge tube, followed by 28 mL of a 1.8 g / cm 3Add sodium iodide (NaI) solution, shake the centrifuge tube slowly up and down to moisten the soil, let it stand for 30 minutes, centrifuge at 3500 rpm for 30 minutes, filter the supernatant with 0.45 μm filter paper, the residue on the filter paper is the free light fraction (fLF), rinse repeatedly with ultrapure water to remove excess NaI. Add 28 mL of 1.8 g / cm 3 The NaI solution was shaken up and down to disperse the solid residue and then 300 J / cm 3 Ultrasonic treatment is performed to destroy the agglomerates (an ice water bath is required during ultrasound to ensure that the liquid temperature in the sample is <50°C). After the ultrasound is completed, it is allowed to stand for 30 minutes and centrifuged at 3500 rpm for 30 minutes. The operation steps of the supernatant are the same as fLF, and the filter residue obtained is the closed light component (oLF) wrapped by the agglomerates. The remaining particles in the centrifuge tube are the heavy components (HF) combined with minerals, which are repeatedly rinsed with ultrapure water until the conductivity of the supernatant is <50 μS / cm. All components are dried at 40°C and weighed.

[0017] S5: Quantitative analysis of soil biochar: The amount of biochar in soil was determined by the benzene polyacid molecular marker method (BPCAs). The density component sample with an organic carbon content of <5 mg was weighed and poured into a reactor. 10 mL of 4 mol / L TFA solution was added and reacted at 105 °C for 4 h. The filter was filtered with a glass fiber membrane (Whatman GF / A 1.6 μm) and rinsed repeatedly with ultrapure water. The filter residue was dried and poured into a reactor. 2 mL of 65% HNO3 was added and reacted at 170 °C for 8 h. After the reaction was completed, a total of 10 mL of ultrapure water was added to the reactor in multiple times and filtered. Take 2 mL of the filtrate, add 10 mL of ultrapure water and 100 μL of citric acid in turn, mix well, and pass through a cation exchange column (Dowex 50 WX8, 200-400 mesh). After the filtrate was freeze-dried, it was dissolved in methanol and transferred to a liquid phase bottle. 100 μL of dimethyl biphenyl-2,2'-dicarboxylate was added and blown to dryness with nitrogen. Then, 100 μL of anhydrous pyridine and 100 μL of N,O-bis(trimethylsilyl)trifluoroacetamide+trimethylchlorosilane (BSTFA+TMCS, 99:1) were added in sequence and reacted at 80 °C for 2 h. The reaction was analyzed by GC-MS.

[0018] Since inorganic minerals have a significant protective effect on organic matter, HF needs to be demineralized before the BPCAs content in the heavy component (HF) is determined. HF was added to a mixed solution of 10% hydrofluoric acid / 1 mol / L hydrochloric acid at a ratio of 1:4 (mass ratio) and placed in a shaker (room temperature, 120 rpm) for 2 h. Subsequently, centrifuged at 2500 r / min for 30 min to separate the solid and liquid, and the above operation was repeated 5 times, and then washed repeatedly with ultrapure water until no Cl was detected. – Finally, dry at 40℃.

[0019] S6: The C, H, N, and O contents of total soil and soil fractions after density classification were determined using an elemental analyzer (MicroCube, Elementar, Germany). Since the soil pH was low at 5.3-7.0, total carbon and total nitrogen were considered to represent organic carbon and organic nitrogen (Dymov et al., 2021). Soil pH was determined using a pH reagent with a soil: water ratio of 1 (m):2.5 (v) and oscillation for 30 min. Example 2

[0020] In this embodiment, further experiments were conducted to observe the carbon content changes in soil and soil components after adding different proportions of biochar to different types of soil (specifically, blank control, i.e., no addition, 1%, 3%, 5%). Figure 1-Figure 4 As shown, the components in each group of soil were further determined by the above method. It can be seen from the figure that compared with the control soil without adding biochar, after adding 1% biochar, the carbon content of brown soil increased from 20.06 g / kg to 25.82 g / kg, the carbon content of lime soil increased from 30.19 g / kg to 37.28 g / kg, and the carbon content of red soil increased from 13.51 g / kg to 21.22 g / kg. The carbon content in different soil components also showed consistent change characteristics, namely, the carbon content of the light component of brown soil increased from 3.43 g / kg to 6.07 g / kg, the carbon content of the closed-state component increased from 0.49 g / kg to 3.07 g / kg, and the carbon content of the heavy component increased from 18.17 g / kg to 18.61 g / kg; the carbon content of the light component of lime soil increased from 3.02 g / kg to 6.74 g / kg, the carbon content of the closed-state component increased from 1.51 g / kg to 3.96 g / kg, and the carbon content of the heavy component increased from 26.77 g / kg to 28.15 g / kg; the carbon content of the light component of red soil increased from 1.84 g / kg to 6.72 g / kg, the carbon content of the closed-state component increased from 0.51 g / kg to 1.39 g / kg, and the carbon content of the heavy component increased from 13.89 g / kg to 15.16 g / kg.

[0021] In addition, in this embodiment, compared with the control soil without adding biochar, after adding 3% biochar, the carbon content of brown soil increased from 20.06 g / kg to 40.28 g / kg, the carbon content of lime soil increased from 30.19 g / kg to 52.28 g / kg, and the carbon content of red soil increased from 13.51 g / kg to 32.79 g / kg. The carbon content in different soil components also showed the same change characteristics, that is, the carbon content of the light component of brown soil increased from 3.43 g / kg to 17.58 g / kg, the carbon content of the closed-state component increased from 0.49 g / kg to 6.85 g / kg, and the carbon content of the heavy component changed from 18.17 g / kg to 18.10 g / kg; the carbon content of the light component of lime soil increased from 3.02 g / kg to 15.03 g / kg, the carbon content of the closed-state component increased from 1.51 g / kg to 8.77 g / kg, and the carbon content of the heavy component increased from 26.77 g / kg to 28.80 g / kg; the carbon content of the light component of red soil increased from 1.84 g / kg to 6.72 g / kg, the carbon content of the closed-state component increased from 0.51 g / kg to 4.16 g / kg, and the carbon content of the heavy component increased from 13.89 g / kg to 17.31 g / kg. Compared with the control soil without biochar addition, after adding 5% biochar, the carbon content of brown soil increased from 20.06 g / kg to 64.74 g / kg, the carbon content of lime soil increased from 30.19 g / kg to 64.11 g / kg, and the carbon content of red soil increased from 13.51 g / kg to 47.80 g / kg. The carbon content in different soil components also showed the same change characteristics, that is, the carbon content of the light component of brown soil increased from 3.43 g / kg to 32.96 g / kg, the carbon content of the closed-state component increased from 0.49 g / kg to 8.91 g / kg, and the carbon content of the heavy component changed from 18.17 g / kg to 19.47 g / kg; the carbon content of the light component of lime soil increased from 3.02 g / kg to 26.08 g / kg, the carbon content of the closed-state component increased from 1.51 g / kg to 10.99 g / kg, and the carbon content of the heavy component changed from 26.77 g / kg to 26.74 g / kg; the carbon content of the light component of red soil increased from 1.84 g / kg to 26.56 g / kg, the carbon content of the closed-state component increased from 0.51 g / kg to 5.44 g / kg, and the carbon content of the heavy component increased from 13.89 g / kg to 17.13 g / kg.

[0022] From the above specific comparison, it can be concluded that adding biochar to different types of soil increases the total carbon content of the soil. The increase in total carbon content is proportional to the addition of biochar, and the increased soil carbon is mainly distributed in the light components and closed components of the soil. Example 3

[0023] In this example, the main purpose is to explore the change in the biochar content in the soil after the biochar is added to the soil. The control and the corresponding addition ratio are the same as those in Example 2, and no further explanation is given here. The specific results are as follows Figure 5-8 As shown, it can be seen from the figure: Compared with the control soil without biochar addition, after adding 1% biochar, the biochar content of brown soil increased from 0.27 g / kg to 3.87 g / kg, the biochar content of lime soil increased from 0.16 g / kg to 3.54 g / kg, and the biochar content of red soil increased from 0.20 g / kg to 4.13 g / kg. The biochar content in different soil components also showed consistent change characteristics, namely, the biochar content of the light component of brown soil increased from 0.05 g / kg to 1.63 g / kg, the biochar content of the closed-state component increased from 0 g / kg to 1.67 g / kg, and the biochar content of the heavy component increased from 0.22 g / kg to 0.56 g / kg; the biochar content of the light component of lime soil increased from 0.04 g / kg to 1.95 g / kg, the biochar content of the closed-state component increased from 0.01 g / kg to 1.15 g / kg, and the biochar content of the heavy component increased from 0.11 g / kg to 0.44 g / kg; the biochar content of the light component of red soil increased from 0.08 g / kg to 2.84 g / kg, the biochar content of the closed-state component increased from 0 g / kg to 0.62 g / kg, and the biochar content of the heavy component increased from 0.12 g / kg to 1.43 g / kg.

[0024] Compared with the control soil without biochar addition, after adding 3% biochar, the biochar content of brown soil increased from 0.27 g / kg to 14.61 g / kg, the biochar content of lime soil increased from 0.16 g / kg to 11.52 g / kg, and the biochar content of red soil increased from 0.20 g / kg to 14.56 g / kg. The biochar content in different soil components also showed consistent change characteristics, namely, the biochar content of the light component of brown soil increased from 0.05 g / kg to 8.62 g / kg, the biochar content of the closed-state component increased from 0 g / kg to 4.45 g / kg, and the biochar content of the heavy component increased from 0.22 g / kg to 1.55 g / kg; the biochar content of the light component of lime soil increased from 0.04 g / kg to 6.92 g / kg, the biochar content of the closed-state component increased from 0.01 g / kg to 4.08 g / kg, and the biochar content of the heavy component increased from 0.11 g / kg to 0.53 g / kg; the biochar content of the light component of red soil increased from 0.08 g / kg to 9.22 g / kg, the biochar content of the closed-state component increased from 0 g / kg to 2.35 g / kg, and the biochar content of the heavy component increased from 0.12 g / kg to 3.85 g / kg.

[0025] Compared with the control soil without biochar addition, after adding 5% biochar, the biochar content of brown soil increased from 0.27 g / kg to 28.16 g / kg, the biochar content of lime soil increased from 0.16 g / kg to 22.16 g / kg, and the biochar content of red soil increased from 0.20 g / kg to 20.38 g / kg. The biochar content in different soil components also showed consistent change characteristics, namely, the biochar content of the light component of brown soil increased from 0.05 g / kg to 19.35 g / kg, the biochar content of the closed-state component increased from 0 g / kg to 5.47 g / kg, and the biochar content of the heavy component increased from 0.22 g / kg to 3.34 g / kg; the biochar content of the light component of lime soil increased from 0.04 g / kg to 15.22 g / kg, the biochar content of the closed-state component increased from 0.01 g / kg to 6.14 g / kg, and the biochar content of the heavy component increased from 0.11 g / kg to 0.82 g / kg; the biochar content of the light component of red soil increased from 0.08 g / kg to 13.61 g / kg, the biochar content of the closed-state component increased from 0 g / kg to 3.42 g / kg, and the biochar content of the heavy component increased from 0.12 g / kg to 4.11 g / kg.

[0026] From the above experimental results, it can be concluded that the addition of biochar to the same type of soil increases the soil biocarbon content, the increase in biochar content is proportional to the addition of biochar, and the increased biochar is distributed in the three soil components. The inconsistent changes in biochar and total carbon content in soil components are caused by the stimulating effect of biochar on endogenous carbon in the soil. Example 4

[0027] In this example, biochar added to soil will produce a stimulating effect on soil endogenous organic carbon. In order to distinguish the direction of the stimulating effect and the amount of carbon mineralization / carbon accumulation, we conducted a quantitative analysis. The results are as follows: Figure 5-8 As shown in the figure: the same type of soil has the same carbon mineralization rate without the addition of biochar. After adding biochar, the total carbon content of each component minus the carbon content in the blank control soil, the remaining carbon content is the carbon contributed by biochar and the accumulation or loss of endogenous carbon in the soil caused by the addition of biochar, recorded as EA-C. The part of EA-C that exceeds the biochar content is considered to be carbon accumulation caused by the negative excitation effect of endogenous carbon in the soil induced by the addition of biochar, and the part that is lower than the biochar carbon content is considered to be carbon mineralization caused by the positive excitation effect of endogenous carbon in the soil induced by the addition of biochar.

[0028] After adding 1% biochar, the EA-C of all types of overall soil was higher than the amount of biochar, indicating that the addition of 1% biochar had a negative excitation effect on the endogenous carbon in all soil types. These negative excitation effects were also reflected in all soil density components. The carbon accumulation caused by the negative excitation effect reached 2.03 C mg / g soil in brown soil, of which the accumulation of endogenous carbon in light component, closed component and heavy component was 1.04, 0.91 and 0.08 C mg / g soil, respectively; the carbon accumulation reached 4.35 C mg / g soil in lime soil, of which the accumulation of endogenous carbon in light component, closed component and heavy component was 1.80, 1.32 and 1.23 C mg / g soil, respectively; the carbon accumulation reached 3.08 C mg / g soil in red soil, of which the accumulation of endogenous carbon in light component, closed component and heavy component was 2.06, 0.27 and 0.76 C mg / g soil, respectively.

[0029] After adding 3% biochar, the EA-C of all types of overall soil was higher than the amount of biochar, but the performance was inconsistent in different components. In the heavy component of brown soil, EA-C was lower than the amount of biochar, indicating that although the addition of 3% biochar had a negative excitation effect on endogenous carbon in all types of overall soil, there was a positive excitation effect in the component soil. The carbon accumulation caused by the negative excitation effect in brown soil reached 6.46 C mg / g soil, of which the accumulation of endogenous carbon in the light component and the closed-state component were 5.62 and 1.92 C mg / g soil, respectively, and the endogenous carbon mineralization caused by the positive excitation effect in the heavy component was 1.09 C mg / g soil; the carbon accumulation in lime soil reached 10.92 C mg / g soil, of which the accumulation of endogenous carbon in the light component, the closed-state component and the heavy component were 5.20, 3.24 and 2.48 C mg / g soil, respectively; the carbon accumulation in red soil reached 6.17 C mg / g soil, of which the accumulation of endogenous carbon in the light component, the closed-state component and the heavy component were 4.00, 1.31 and 0.86 C mg / g soil, respectively.

[0030] After adding 5% biochar, the EA-C of all types of overall soil was higher than the amount of biochar, but the performance was inconsistent in different components. In the heavy component of brown soil, EA-C was lower than the amount of biochar, indicating that although the addition of 5% biochar had a negative excitation effect on the endogenous carbon in all types of overall soil, there was a positive excitation effect in the component soil. The carbon accumulation caused by the negative excitation effect in brown soil reached 12.19 C mg / g soil, of which the accumulation of endogenous carbon in the light component and the occluded component were 10.35 and 2.98 C mg / g soil, respectively, and the endogenous carbon mineralization caused by the positive excitation effect in the heavy component was 1.14 C mg / g soil; the carbon accumulation in lime soil reached 12.10 C mg / g soil, of which the accumulation of endogenous carbon in the light component, the occluded component and the heavy component were 8.01, 3.43 and 0.64 C mg / g soil, respectively; the carbon accumulation in red soil reached 13.54 C mg / g soil, of which the accumulation of endogenous carbon in the light component, the occluded component and the heavy component were 11.23, 1.55 and 0.76 C mg / g soil, respectively.

[0031] It can be seen from the above examples that the addition of biochar can increase the carbon content in the soil and each density component of the soil. The combined density grading and benzene molecular markers further distinguish and quantify whether these increased carbon contents are directly derived from biochar or changes in endogenous organic carbon in the soil caused by the addition of biochar, that is, the excitation effect: the addition of biochar in this example obviously caused a negative excitation effect on endogenous carbon in the soil, resulting in endogenous carbon accumulation; however, in individual soil density components, the addition of biochar will also have a positive excitation effect on endogenous carbon in the soil, that is, accelerate the mineralization of endogenous carbon in the soil. The accumulation and mineralization of endogenous carbon were quantitatively evaluated by the constructed EA-C method. This evaluation method not only distinguishes between biochar and endogenous carbon in the soil, but also avoids the time and economic costs caused by the use of isotope labeling and CO2 detection.

[0032] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only the specific implementation methods described.

Claims

1. A quantitative analysis method for evaluating the stimulating effect of biochar on soil endogenous organic carbon, characterized in that: The following steps are involved: S1: Collection and pretreatment of soil samples; S2: preparation of biochar; S3: soil-biochar incubation; S4: Soil density component classification, including: S4.1: Add the sieved air-dried soil incubated in S4 to the centrifuge tube, then add the sodium iodide solution, slowly shake the centrifuge tube up and down to moisten the soil, and let it stand for a while; after standing, centrifuge again, and then filter the supernatant with filter paper. The residue is the free light fraction (fLF), which is repeatedly rinsed with ultrapure water to remove excess NaI; S4.2: Add NaI solution to the free light fraction obtained by centrifugation in S4.1 again, shake up and down to disperse the solid residue, and use ultrasonic treatment to destroy the agglomerates; S4.3: After the ultrasonic treatment, let it stand, then centrifuge at 3500r / min and filter to obtain the closed light component (oLF) wrapped in the agglomerates. The remaining particles in the centrifuge tube are the heavy components (HF) combined with the minerals. Rinse repeatedly with ultrapure water until the conductivity of the supernatant is <50μS / cm; all components are dried at 40℃ and weighed; S5: Quantitative analysis of soil biochar, specifically: S5.1: Weigh the final graded sample obtained in S4 and pour it into a reactor, add TFA solution to react; after the reaction is complete, filter it with a glass fiber membrane, and repeatedly rinse it with ultrapure water to obtain a filter residue; S5.2: After drying the filter residue, pour it into a reactor, add HNO3 to react for a period of time, and after the reaction is completed, add ultrapure water to the reactor in multiple times and filter; take the filtrate, add ultrapure water and citric acid in sequence, mix well, and pass it through a cation exchange column; S5.3: After the filtrate is freeze-dried, it is dissolved with methanol and transferred to a liquid phase bottle, dimethyl biphenyl-2,2'-dicarboxylate is added, and nitrogen is blown to dryness; anhydrous pyridine and N,O-bistrimethylsilyltrifluoroacetamide + trimethylchlorosilane are then added in sequence for further reaction; S6: Determination of total soil organic carbon: use an element analyzer to determine the C, H, N, and O contents of the total soil and each component of the soil after density classification; and simultaneously determine the soil pH.

2. A quantitative analysis method for evaluating the stimulating effect of biochar on endogenous organic carbon in soil according to claim 1, characterized in that: In S4.1, the density of sodium iodide is 1.8 g / cm 3 The centrifugal conditions were 3500 r / min for 30 min.

3. A quantitative analysis method for evaluating the stimulating effect of biochar on endogenous organic carbon in soil according to claim 1, characterized in that: The density of sodium iodide added in S4.2 is 1.8 g / cm 3 , 300 J / cm 3 Ultrasonic treatment.

4. A quantitative analysis method for evaluating the stimulating effect of biochar on soil endogenous organic carbon according to claim 1, characterized in that: The content of the TFA solution added in S5.1 is 4 mol / L, and the reaction is carried out at 105° C. for 4 hours.

5. A quantitative analysis method for evaluating the stimulating effect of biochar on soil endogenous organic carbon according to claim 1, characterized in that: The percentage of HNO3 added in S5.2 is 65%, and the reaction is carried out at 170°C for 8 h.

6. A quantitative analysis method for evaluating the stimulating effect of biochar on endogenous organic carbon in soil according to claim 1, characterized in that: N, O-bistrimethylsilyltrifluoroacetamide + trimethylchlorosilane were added to S5.3 in a ratio of 99:1, and the reaction was carried out at 80°C for 2 h.

7. A quantitative analysis method for evaluating the stimulating effect of biochar on endogenous organic carbon in soil according to claim 1, characterized in that: Before determining the BPCAs content in the heavy component (HF), the HF needs to be demineralized. The process is as follows: S4.3.1: Add HF to a mixture of 10% hydrofluoric acid / 1 mol / L hydrochloric acid in a ratio of 1:4 and place in a shaker at room temperature for 2 h; S4.3.2: Then centrifuge at 2500 r / min for 30 min to separate the solid and liquid. Repeat the above operation several times, and then wash repeatedly with ultrapure water until no Cl is detected. – Finally, dry at 40 ℃.

8. A quantitative analysis method for evaluating the stimulating effect of biochar on endogenous organic carbon in soil according to claim 1, characterized in that: In S1, the mixed sample is collected by the plum blossom method, and multiple sampling points are set at each sampling site to fully mix the collected samples; the visible roots, plant residues and rocks in the fresh soil are removed, and then the soil is sieved and thoroughly mixed and stored for later use.

9. A quantitative analysis method for evaluating the stimulating effect of biochar on endogenous organic carbon in soil according to claim 1, characterized in that: In S2, pine sawdust was selected as the raw material for preparing biochar. After the sample was naturally dried, it was crushed and passed through a 2 mm sieve, and then placed in an oven and baked at 70 °C for 24 h. The dried raw material was placed in a muffle furnace and pyrolyzed at 300 °C for 4 h in a N2 atmosphere to obtain biochar. The biochar was ground and passed through a 150 μm sieve and stored in a sample bottle for later use, marked as PW300.

Images