Biochar quality factor comprehensive evaluation method based on saline-alkali soil improvement application potential

Abstract

The invention discloses a biochar quality factor comprehensive evaluation method based on saline-alkali soil improvement application potential, belongs to the technical field of biochar quality factor comprehensive evaluation methods, and aims to solve the problem that the optimal quality of different biochar types is closely related to thermal cracking temperature. Although the livestock and poultry manure biochar has relatively high char yield, water and salt immobilization capability and rich nutritional factors, the contents of salt and toxic factors are also relatively high, so that the comprehensive quality of the livestock and poultry manure biochar is reduced; the special plants in the saline-alkali soil have high water and salt immobilization capacity, the pH value and the salinity are low, toxic factor indexes are low, and therefore the comprehensive quality of the special plants is optimal.

Description

Technical Field

[0001] The present invention relates to a comprehensive evaluation method for the quality factors of biochar, in particular to a comprehensive evaluation method for the quality factors of biochar based on the potential for saline-alkali soil improvement, and belongs to the technical field of comprehensive evaluation methods for the quality factors of biochar. Background Art

[0002] Soil salinization is one of the important problems threatening agricultural production, food security and sustainable development globally.

[0003] In saline-alkali areas, fresh water resources are usually scarce, the terrain is low and the groundwater level is high, and it is difficult to desalinate the soil. Problems such as the decline in soil fertility, poor crop growth and fragile ecological environment caused by soil salinization seriously restrict regional economic development. Applying biochar can directly or indirectly regulate soil nutrients and structure, increase soil organic matter content, cation exchange capacity, permeability and microbial activity, reduce nitrogen and phosphorus loss, increase the formation of soil aggregate structure, and also improve the water conductivity, thereby improving the crop habitat and increasing crop yield.

[0004] However, some biochars produced on a large scale currently contain a large amount of alkali metal salt ions and have a strong alkalinity, which may instead increase the soil pH and salt content, exacerbate the degree of soil salinization, and reduce the ecological function. This has led to the current contradiction and lack of systematicness in biochar technology for saline-alkali soil improvement, which is not conducive to accurately predicting and evaluating the targeted application of biochar in the improvement and treatment of complex types of saline-alkali soils in multiple regions. Therefore, how to comprehensively and systematically evaluate its application value in saline-alkali soil improvement, efficiently quantify its advantages and disadvantages, can correctly plan the wide application of biochar technology in saline-alkali soil improvement in China, and promote the healthy development of saline-alkali soil biochar improvement technology. Based on the specific application scenario of saline-alkali soil improvement, it is necessary to determine the type with the best comprehensive quality potential among various biochars. Therefore, screening out key core evaluation indicators and establishing a scientific and reasonable comprehensive evaluation system are crucial. For this reason, a comprehensive evaluation method for the quality factors of biochar based on the potential for saline-alkali soil improvement is designed to solve the above problems. Summary of the Invention

[0005] The main purpose of the present invention is to provide a comprehensive evaluation method for the quality factors of biochar based on the potential for saline-alkali soil improvement.

[0006] The object of the present invention can be achieved by adopting the following technical solutions:

[0007] A comprehensive evaluation method for the quality factors of biochar based on the potential for saline-alkali soil improvement includes the following steps:

[0008] Step 1: Use Origin 2021Pro software for principal component analysis, and clarify the effects of pyrolysis temperature and biomass source on the quality of biochar by observing the overlapping regions in the results of principal component analysis;

[0009] Step 2: Conduct a comprehensive evaluation using the grey relational analysis method, and rank the core indicators of biochar. Use dimensionless data, and the calculation formula is as follows:

[0010]

[0011] In formulas (1) and (2), Y i (j) is the standardized value of the j-th index of the i-th biochar;

[0012] x i (j) is the measured value of the physical and chemical properties of the j-th index of the i-th biochar;

[0013] maxx(j) and minx(j) are the maximum and minimum values of x i (j) respectively;

[0014] When the larger the index, the better, the standardization of the original data is calculated using formula (1);

[0015] When the smaller the index, the better, the standardization of the original data is calculated using formula (2);

[0016] Step 3: Calculate the correlation coefficient W(j), and the specific calculation formula is as follows:

[0017]

[0018] In formula (3), W(j) is the correlation coefficient;

[0019] Δ i (j) represents the absolute difference between the dimensionless data of the i-th sample and the ideal sample in the j-th index;

[0020] miniminjΔ i (j) and maximaxjΔ i (j) respectively represent the second-level minimum and maximum values of Δ i (j);

[0021] ρ is the resolution coefficient;

[0022] Step 4: Use the independent weight coefficient method to calculate the weights and obtain the comprehensive scores of each biochar. The formula is as follows:

[0023]

[0024] In formula (4), RI is the weighted correlation score;

[0025] B(j) is the weight of the j-th index;

[0026] n is the number of evaluation indicators.

[0027] Preferably, before step one, the preparation of biochar is further included, and its preparation process includes the following steps:

[0028] S11: Collect corn straws, eggplant stalks, apple branches, reeds and sesbania during the harvest season;

[0029] S12: Remove roots, leaves and fruits, only keep the stalk part, after bringing it back to the laboratory, rinse the stalks with tap water and distilled water in sequence, then dry them in the air, cut them into 1 - 2 cm small sections with scissors respectively, and place them in an oven at 60 °C to dry to constant weight;

[0030] S13: For the freshly collected chicken manure, remove chicken feathers and debris, place it in an oven at 60 °C to dry to constant weight, and grind it through a 10 - mesh sieve with a clean mortar;

[0031] S14: Seal all biomass raw materials in a crucible with aluminum foil, place it in a muffle furnace, heat it to the target temperature at a rate of 20 °C / min, keep it for 2 h, and take it out after natural cooling to room temperature;

[0032] S15: Grind the obtained biochar sample thoroughly with an agate mortar and pass it through a 10 - mesh stainless steel sieve, place it in a stoppered brown wide - mouth glass bottle, and store it at room temperature for later use.

[0033] Preferably, in S13, all biomass raw materials are sealed with self - sealing bags and stored in a cool and dry place for later use.

[0034] Preferably, in S14, the pyrolysis temperature gradient is set to 350, 450, 550, 650 °C, and the crucible is subjected to high - temperature dry burning at 750 °C before biomass pyrolysis to remove moisture and organic impurities.

[0035] Preferably, before step one, the establishment of the key action mechanism and ecological effects of biochar in the process of improving saline - alkali soil and the induction of 5 major categories of indicators are further included;

[0036] Specifically, it includes carbon sequestration ability, pH value and salt content, water - salt retention ability, nutrient factors and toxicity factors.

[0037] The beneficial technical effects of the present invention:

[0038] The comprehensive evaluation method of biochar quality factors based on the application potential of saline-alkali land improvement provided by the present invention shows that the optimal quality of different biochar types is closely related to the pyrolysis temperature. Although livestock and poultry manure biochar has a high carbon yield, waterlogging retention ability, and rich nutrient factors, its salt and toxicity factor contents are also relatively high, resulting in a reduction in its comprehensive quality. Saline-alkali land characteristic plants have a high waterlogging retention ability, low simplification degree, and low salt and toxicity factor indicators, so their comprehensive quality is the best.

[0039] It is scientific and reasonable to select five indicators, namely carbon sequestration ability, pH and salinity, water-salt retention ability, nutrient factors, and toxicity factors, as the core evaluation indicators of biochar.

[0040] With the increase of pyrolysis temperature, the optimal comprehensive quality of different types of biochar changes. The grey relational grade index of biochar from saline-alkali land characteristic plants is the highest, indicating greater application potential for saline-alkali land improvement. Description of the Drawings

[0041] Figure 1 Principal component analysis of the quality of 24 biochars in a preferred embodiment of the comprehensive evaluation method of biochar quality factors based on the application potential of saline-alkali land improvement according to the present invention: (A) Principal component analysis of different biomass types; (B) Principal component analysis of different pyrolysis temperatures. Detailed Embodiments

[0042] To make the technical solutions of the present invention clearer and more definite for those skilled in the art, the present invention will be further described in detail below with reference to the embodiments and the drawings. However, the embodiments of the present invention are not limited thereto.

[0043] Preparation of Biochar

[0044] Select crop straw (corn straw), tail vegetables (eggplant stems), fruit tree branches (apple tree branches), livestock and poultry manure (chicken manure), and saline-alkali land characteristic plants (reed and sesbania) as biomass raw materials, and carry out pyrolysis at 350 - 650 °C to prepare biomass charcoal. The main operations are as follows:

[0045] Pretreatment of biomass raw materials:

[0046] Collect corn straw, eggplant stems, apple tree branches, reed, and sesbania during the harvest season, remove roots, leaves, fruits, etc., and only retain the stem part. After bringing them back to the laboratory, rinse the stems with tap water and distilled water in sequence, then dry them in the air, cut them into 1 - 2 cm small sections with scissors, and place them in an oven at 60 °C to dry to constant weight; for the freshly collected chicken manure, remove impurities such as chicken feathers and gravel, dry it in an oven at 60 °C to constant weight, and grind it through a 10-mesh sieve with a clean mortar; seal all the above biomass raw materials with self-sealing bags and store them in a cool and dry place for later use.

[0047] Biochar pyrolysis conditions:

[0048] After all biomass raw materials were placed in the crucible, they were sealed with aluminum foil, placed in a muffle furnace, heated to the target temperature at a rate of 20 °C / min, held for 2 h, taken out after natural cooling to room temperature; the pyrolysis temperature gradients were set at 350, 450, 550, and 650 °C. Before the biomass pyrolysis, all crucibles were subjected to high-temperature dry burning at 750 °C to remove moisture and organic impurities. The obtained biochar samples were sufficiently ground in an agate mortar, passed through a 10-mesh stainless steel sieve, placed in a stoppered brown wide-mouth glass bottle, and stored at room temperature for later use.

[0049] Analysis of evaluation indicators

[0050] Based on the key action mechanisms and ecological effects of biochar in the process of improving saline-alkali soil, this study summarized the following five categories of indicators and sorted out the key contents of each indicator: Table 1 Division of core indicators of different biochars and their relationship with the improvement effect of saline-alkali soil;

[0051]

[0052] Referring to relevant standards, the test indicators were analyzed, and the specific implementation was as follows:

[0053] Table 2 Determination items, detection methods, and index requirements for fertilizer carbon

[0054]

[0055]

[0056] Construction of biochar comprehensive evaluation system

[0057] First, the principal component analysis was carried out using Origin 2021Pro software, and the influence of pyrolysis temperature and biomass source on biochar quality was clarified by observing the overlapping regions in the results of principal component analysis.

[0058] Then, to evaluate the comprehensive quality potential of different biochar types, the grey relational analysis method was used for comprehensive evaluation. The core qualities affecting the comprehensive quality of biochar are defined in Table 1, and the core indicators of 24 biochars were ranked as follows:

[0059] First, the data was dimensionless, and the calculation formula is as follows:

[0060]

[0061]

[0062] In formulas (1) and (2), Y i (j) is the standardized value of the jth index of the ith biochar, x i(j) is the measured physical and chemical property value of the j-th index of the i-th biochar, and maxx(j) and minx(j) are the maximum and minimum values of x i (j), respectively.

[0063] When the larger the index, the better, the original data standardization is calculated using Equation (1); when the smaller the index, the better, the original data standardization is calculated using Equation (2).

[0064] Then, calculate the correlation coefficient W(j), and the specific calculation formula is as follows:

[0065]

[0066] In Equation (3), W(j) is the correlation coefficient, and Δ i (j) represents the absolute difference between the dimensionless data of the i-th sample and the ideal sample in the j-th index; miniminjΔ i (j) and maximaxjΔ i (j) represent the second-level minimum and maximum values of Δ i (j), respectively; ρ is the resolution coefficient, generally taken as 0.5.

[0067] Finally, use the independent weight coefficient method to calculate the weight and obtain the comprehensive score of each biochar. The formula is as follows:

[0068]

[0069] In Equation (4), RI is the weighted correlation score, B(j) is the weight of the j-th index, and n is the number of evaluation indicators.

[0070] Research results;

[0071] Physical and chemical indexes of different biochars at different pyrolysis temperatures;

[0072] The quality indexes of all biochars were detected and analyzed according to the corresponding standard methods in Table 2. The specific results are shown as follows:

[0073] Table 3 Carbon sequestration indexes of 24 biochars

[0074]

[0075] Table 4 pH and salinity indexes of 24 biochars;

[0076]

[0077]

[0078] Table 5 Structural indexes of 24 biochars;

[0079]

[0080]

[0081] Table VI Fertility and trace element indexes of 24 kinds of biochars;

[0082]

[0083]

[0084]

[0085] Table VII Toxicity factor indexes of 24 kinds of biochars;

[0086]

[0087]

[0088] Comprehensive effects of different pyrolysis temperatures and biomass sources on biochar quality;

[0089] Principal component analysis of physical and chemical indexes of different biochar types is shown in Figure 1 .

[0090] Analysis shows that the first principal component PC1 and the second principal component PC2 of different biomass types and pyrolysis temperatures explain 50.1% and 12.6% of the total variance respectively, with a total of 62.7%. This indicates that the two principal components can well represent the 25 physical and chemical properties of all tested biochars and reflect most of the information in the original data.

[0091] From Figure 1 it can be seen that biochar types at different pyrolysis temperatures show a certain overlap in principal component analysis, indicating that biochars at different pyrolysis temperatures may have similar characteristics in specific physical and chemical properties.

[0092] While Figure 1 (A) shows that the overlapping area of different biomass types in principal component analysis is less, indicating that different biomass types have a significant impact on the physical and chemical properties of biochars compared with pyrolysis temperatures. Specifically, biochars from livestock and poultry manure show higher nutrient factors (Mn, B, Zn, Mo, Cu) and toxicity factors (Cu, Cr, Cd, Pb) in principal component analysis; saline-alkali land characteristic plants mainly composed of reed and sesbania show higher specific surface area and oxygen-containing functional groups; tail vegetable biochar shows higher acidity and alkalinity and salts (Na, K).

[0093] In addition, Figure 1(B) shows that when the pyrolysis temperature rises to 650 °C, the specific surface area and the content of oxygen-containing functional groups of biochar are relatively high; when the pyrolysis temperature is 350 - 550 °C, the conductivity, Na, K and pore size of biochar are relatively high, and the carbon yield is higher.

[0094] Screening of core indicators for evaluating the application potential of biochar in the field of saline-alkali land improvement;

[0095] When a certain index of biochar has no significant correlation with other physical and chemical indexes and reaches 1 / 3 (≥9) of the total indexes, it is directly screened as the core quality index of biochar, and other indexes are screened as the core quality index according to the principle of significance strength.

[0096] As can be seen from Table VIII, all indexes of carbon sequestration ability, pH and salinity, water and salt retention ability, nutrient factors and toxicity factors meet the above screening conditions and can be used as the core indexes for evaluating the quality of biochar for saline-alkali land improvement potential.

[0097] Table VIII Correlation coefficient matrix of 22 quality indexes of 24 biochars;

[0098]

[0099]

[0100] Table VIII Correlation coefficient matrix of 22 quality indexes of 24 biochars (continued table 1);

[0101] P K Na Ca Mg Fe Mn K -0.013 Na -0.056 .478* Ca .947** 0.049 .0.067 Mg .627** .625** 0.186 .717** Fe 0.386 .473* 0.403 0342 0.278 Mn .845** -0.121 -0.166 .761** 0.328 .480* B .962** 0.054 -0.027 .984** .723** 0.315 .764** zn .712** .554** 0.078 .811** .939** 0.394 .474* Mo 0.081 .466* .805** 0.128 .445* 0.2 -0.27 Cu .785** 0.13 0.305 .839** .688** 0.321 .469* Cr 0.203 0.135 0.297 0.179 0.176 .477* 0.369 Cd 0.28 0.148 0.096 <![CDATA[.431 * > <![CDATA[.422 * > 0.084 0.203 Pb .503* 0.132 -0.012 .422* 0.404 0.172 .628** <![CDATA[I D / I G > 0.371 -0.292 0.008 0397 0.139 -0.113 0.273 Oxygen-containing functional group -.626** .0.021 0.247 -.656** -.510* -0.106 -.460*

[0102] Table VIII Correlation coefficient matrix of 22 quality indexes of 24 biochars (continued table 2);

[0103] B zn Mo Cu Cr Cd Pb <![CDATA[I D / I G > Zn .798** <![CDATA[M o > 0.17 0.281 Cu .855** .673** .568** Cr 0.174 0.112 0.136 0.241 Cd 0.379 .447* 0.219 .446* 0.326 Pb .437* 0354 -0.016 0.285 0.355 0.288 <![CDATA[I D / I G > 0.358 0.166 0.177 0.426 -0.14 -0.016 0.339 Oxygen-containing functional group -.660** -.478* -0.043 -.588** -0.097 -0.315 -0.319 -0.078

[0104] Comprehensive quality evaluation of the application potential of different types of biochar in the field of saline-alkali land improvement;

[0105] The comprehensive quality evaluation results of 24 biochars obtained from 6 biomasses at 4 different pyrolysis temperatures are shown in Table IX.

[0106] The results show that the grey relational coefficients of 24 different types of biochar are in the range of 0.5315 - 0.6169. When the pyrolysis temperature is 650 °C, the quality of reed and sesbania biomass char is the best, and their comprehensive evaluation indices (RI) are 0.6169 and 0.6113 respectively; when the pyrolysis temperature is 550 °C, the quality of sesbania biochar is the best, with an RI of 0.5920; when the pyrolysis temperature is 450 °C, the quality of reed, apple branch and sesbania biochar is the best, and their RIs are 0.5963, 0.5933 and 0.5810 respectively; when the pyrolysis temperature is 350 °C, the comprehensive quality of chicken manure biochar is the best, with an RI of 0.5864. Based on the numerical analysis of the total average correlation degree, the quality of biochar at the four pyrolysis temperature gradients from high to low is 650 °C, 450 °C, 550 °C and 350 °C respectively.

[0107] The average comprehensive evaluation results of 5 types of biochar are shown in Table 10.

[0108] The results show that the average comprehensive evaluation value of the grey correlation degree of different types of biochar will change with temperature.

[0109] Specifically, the best quality of crop straw biochar appears at a pyrolysis temperature of 350 °C, with an RI of 0.5594; the best quality of tail vegetable and fruit branch biochar both appears at 450 °C, with RIs of 0.5551 and 0.5933 respectively; the best quality of livestock and poultry manure biochar appears at a pyrolysis temperature of 350 °C, with an RI of 0.5894; the best quality of biochar from special plants in saline-alkali land appears at a pyrolysis temperature of 650 °C, with an RI of 0.6141.

[0110] Moreover, the correlation degree of biochar from special plants in saline-alkali land is much higher than that of other types of biomass.

[0111] Table 9 Comprehensive quality evaluation results of 24 kinds of biochar at different pyrolysis temperatures;

[0112]

[0113]

[0114] Table 10 Average comprehensive evaluation results of 5 types of biochar at different pyrolysis temperatures;

[0115]

[0116] The above is only a further embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the scope disclosed by the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, all belong to the protection scope of the present invention.

Claims

1. A comprehensive evaluation method for biochar quality factors based on the potential for application in saline-alkali land improvement, characterized by: The steps include: Step 1: Conduct principal component analysis to clarify the effects of pyrolysis temperature and biomass source on biochar quality by observing the overlapping areas in the principal component analysis results; Step 2: Use the grey correlation method to conduct a comprehensive evaluation and rank the core indicators of biochar. Use dimensionless data and the calculation formula is as follows: In formula (1) and (2), Y i (j) is the standardized value of the jth index of the i-th biochar; x i (j) is the measured value of the physical and chemical properties of the jth index of the i-th biochar; maxx(j) and minx(j) are x i (j) maximum and minimum values; When the index is larger, the better, the original data standardization is calculated using formula (1); When the index is as small as possible, the original data standardization is calculated using formula (2); Step 3: Calculate the correlation coefficient W(j). The specific calculation formula is as follows: In formula (3), W(j) is the correlation coefficient; Δ i (j) represents the absolute difference between the dimensionless data of the i-th sample and the ideal sample in the j-th index; miniminjΔ i (j) and maximaxjΔ i (j) respectively represent Δ i (j) Secondary minimum and maximum values; ρ is the resolution coefficient; Step 4: Use the independence weight coefficient method to calculate the weight and obtain the comprehensive score of each biochar. The formula is as follows: Formula (4), RI is the weighted relevance score; W(j) is the correlation coefficient of the jth indicator; B(j) is the weight of the jth indicator; n is the number of evaluation indicators.

2. The comprehensive evaluation method of biochar quality factor based on saline-alkali land improvement application potential according to claim 1 is characterized by: Before step 1, the process also includes the preparation of biochar, and the preparation process includes the following steps: S11: Collect corn stalks, eggplant stalks, apple branches, reeds and sesbania during the harvest season; S12: Remove roots, leaves, and fruits, and keep only the stems. Take them back to the laboratory, rinse them with tap water and distilled water, and dry them. Cut them into 1-2 cm small pieces with scissors, and dry them in a 60℃ oven until constant weight. S13: Remove the chicken feathers and debris from the collected fresh chicken manure, dry it in a 60°C oven to a constant weight, and grind it with a clean mortar to pass through a 10-mesh sieve; S14: All biomass raw materials are placed in a crucible and sealed with aluminum foil, placed in a muffle furnace, heated to the target temperature at 20°C / min, maintained for 2 hours, and taken out after naturally cooling to room temperature; S15: The obtained biochar sample was fully ground with an agate mortar and passed through a 10-mesh stainless steel sieve, placed in a brown wide-mouth glass bottle with a stopper, and stored at room temperature for later use.

3. The comprehensive evaluation method of biochar quality factor based on saline-alkali land improvement application potential according to claim 2 is characterized by: In S14, the thermal cracking temperature gradient was set to 350, 450, 550, and 650°C, and the crucibles were dry-burned at 750°C before the biomass thermal cracking to remove moisture and organic impurities.

4. The comprehensive evaluation method of biochar quality factor based on saline-alkali land improvement application potential according to claim 3 is characterized by: Before step one, it also includes establishing the key mechanism and ecological effect of biochar in improving saline-alkali soil and summarizing five major indicators; Specifically, they include carbon fixation capacity, pH and salinity, water-salt retention capacity, nutritional factors and toxicity factors.

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