Guava branch biochar as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of biochar materials, and particularly relates to guava branch biochar as well as a preparation method and application thereof. The biochar formed by calcining branches of guava fruit trees is adopted, the surface of the biochar presents more irregular squamous shapes and has a porous structure and a large aperture, more adsorption sites and spaces are provided for survival of soil nutrients and microorganisms, and the biochar contains a crystal structure of quartz, calcite type carbonic acid and calcium magnesium carbonate, so that the physical and chemical properties of soil can be improved; compared with camphor tree biochar and eucalyptus biochar, the psidium guajave branch biochar can significantly improve the pH value, increase the content of alkali-hydrolyzable nitrogen (AN), rapidly available potassium (AK) and dissolved organic carbon (DOC) in soil, and improve the activity of urease, sucrase and cellulase in farmland soil and the bacterial diversity of agriculture and forestry soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of biochar materials, and particularly relates to a guava branch biochar, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, with the breakthrough development of modern agricultural technologies, large-scale production models and intensive management systems have improved agricultural production efficiency. However, the accompanying problem of agricultural waste disposal has become increasingly prominent. Statistics show that as a major agricultural country, the total annual amount of crop straw in China is about 800-900 million tons, and the annual pruning amount of fruit tree branches generated by fruit tree planting is about 65 million tons, but the resource utilization rate is still at a relatively low level. If these neglected biomass resources can be systematically developed, it can not only effectively relieve environmental pressure, but also provide important strategic resource support for new energy development, the construction of ecological agricultural cycle systems, and the research and development of solid waste materials.

[0003] At the same time, although traditional chemical fertilizers can improve soil conditions in the short term, long-term use is likely to cause negative impacts such as deterioration of soil structure, acidification, and environmental pollution. Therefore, it is particularly urgent to explore environmentally friendly and sustainable soil improvement technologies. In this context, biochar shows broad application prospects. Biochar is a solid substance generated by the high-temperature pyrolysis of biomass under oxygen-limited conditions, which can increase the cation exchange capacity of the soil, increase the organic matter content, and effectively retain soil nutrients through its pore structure and surface characteristics. The surface is rich in oxygen-containing functional groups, endowing it with strong ion adsorption and exchange capabilities, and being able to adsorb inorganic nitrogen and soluble nutrients in the soil.

[0004] Current research has shown that the effect of biochar on soil improvement varies with different soil types, biochar raw materials, and preparation processes (such as pyrolysis temperature, heating rate). And the main research focuses on the improvement effect of biochar made from agricultural waste (such as rice and wheat straw) and forestry waste (camphor tree branches, eucalyptus tree branches) on farmland soil. There is still a blank in the research on the improvement mechanism of biochar prepared from guava fruit branches in forest land and farmland ecosystems. In addition, it is also urgent to further explore the differences in physical and chemical properties of biochars prepared from fast- and slow-growing tree species and fruit branch wastes. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a guava branch biochar, a preparation method thereof, and an application thereof.

[0006] The technical content of the present invention is as follows:

[0007] The present invention provides a guava branch biochar, which is a biochar obtained by calcining guava fruit branches, and its preparation method includes the following steps:

[0008] The guava branches (fruit tree branches) were cleaned of surface dust with ultrapure water and then crushed to 1 - 2 cm and placed in an oven at 80 °C until dried to a constant weight and taken out to obtain a biochar raw material sample (original sample). The original sample was compacted in portions and filled into a crucible, nitrogen was filled, and then it was placed in a muffle furnace and heated at 10 °C / min to the final pyrolysis temperature of 500 °C and pyrolyzed at a constant temperature for 2 h to obtain guava branch biochar;

[0009] In the structure of the guava branch biochar, its surface shows many irregular scales and has a porous structure and large pores, and it contains crystal structures of quartz, calcite - type carbonate, and calcium magnesium carbonate.

[0010] The present invention provides an application of guava branch biochar in soil improvement;

[0011] The soil improvement includes improving the pH value of the soil, the content of alkaline hydrolyzable nitrogen (AN), the content of available potassium (AK), the content of dissolved organic carbon (DOC), the activities of soil urease, sucrase, and cellulase, and the bacterial diversity in the soil.

[0012] The beneficial effects of the present invention are as follows:

[0013] The guava branch biochar of the present invention is biochar formed by calcining guava fruit tree branches. Its surface shows many irregular scales and has a porous structure and large pores, providing more adsorption sites and space for soil nutrients and the survival of microorganisms. In addition, it contains crystal structures of quartz, calcite - type carbonate, and calcium magnesium carbonate, which can improve the physical and chemical properties of the soil. Compared with camphor tree biochar and eucalyptus biochar, the guava branch biochar of the present invention can significantly improve the pH value, increase the contents of alkaline hydrolyzable nitrogen (AN), available potassium (AK), and dissolved organic carbon (DOC) in the soil, improve the activities of urease, sucrase, and cellulase in farmland soil, and increase the bacterial diversity in agricultural and forestry soil. Description of the Drawings

[0014] Figure 1 It is a scanning electron microscope image of biochar (a eucalyptus biochar, b guava biochar, c camphor tree biochar);

[0015] Figure 2 It is the change of the pH value of farmland soil in different treatment groups;

[0016] Figure 3 It is the change of the content of alkaline hydrolyzable nitrogen in farmland soil in different treatment groups;

[0017] Figure 4 It is the change of the content of available potassium in farmland soil in different treatment groups;

[0018] Figure 5 It is the change of the content of dissolved organic carbon in farmland soil in different treatment groups;

[0019] Figure 6 are the changes in the urease activity of farmland soil in different treatment groups;

[0020] Figure 7 are the changes in the cellulase activity of farmland soil in different treatment groups;

[0021] Figure 8 are the changes in the sucrase activity of farmland soil in different treatment groups;

[0022] Figure 9 is the Venn diagram (OTU classification level);

[0023] Figure 10 is the principal component analysis diagram (OTU classification level);

[0024] Figure 11 is the relative species abundance diagram (phylum classification level);

[0025] Figure 12 is the species clustering heat map (phylum classification level). Detailed implementation manners

[0026] The present invention will be further described in detail below through specific implementation cases and accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the present invention, various equivalent modifications made by those skilled in the art fall within the scope defined by the appended claims of this application.

[0027] Unless otherwise specified, all raw materials and reagents of the present invention are raw materials and reagents on the conventional market.

[0028] Example 1

[0029] Preparation of guava branch biochar

[0030] The guava fruit tree branches are compacted in batches and filled into a crucible. The lid is covered, nitrogen is filled, and then it is placed in a muffle furnace. It is heated to the final pyrolysis temperature of 500 °C at a rate of 10 °C / min and pyrolyzed at a constant temperature for 2 h to obtain guava branch biochar. After the temperature drops to room temperature, the sample is fully mixed, ground through a 2 mm sieve, and finally sealed for storage.

[0031] The guava branch biochar prepared by the present invention is compared with eucalyptus biochar and camphor tree biochar:

[0032] 1. Biochar characterization and elemental composition

[0033] As Figure 1As shown, the scanning electron microscope images of guava branch biochar, eucalyptus biochar, and camphor tree biochar are presented. It can be seen that there are significant differences in their structures. After high-temperature pyrolysis, all three retain the skeletal structure of the original biomass. The pore structures of eucalyptus biochar and camphor tree biochar are relatively regular, while guava branch biochar exhibits more irregular flaky structures, with larger pores and more prominent porous characteristics, which can provide more adsorption sites for nutrients.

[0034] The elements of guava branch biochar, eucalyptus biochar, and camphor tree biochar were determined:

[0035] Table 1 Elemental composition of biochar

[0036]

[0037] As can be seen from Table 1, the guava branch biochar of the present invention provides more trace elements of H, O, N, and S compared to camphor tree biochar and eucalyptus biochar. The H / C, O / C, and (O+N) / C ratios respectively reflect the aromaticity, hydrophilicity, and polarity of biochar. The lower the ratio, the stronger the aromaticity, and the weaker the hydrophilicity and polarity. The O / C ratio is also positively correlated with the cation exchange capacity (CEC). The O / C and (O+N) / C ratios of the guava branch biochar and camphor tree biochar of the present invention are relatively high, indicating that they have strong hydrophilicity and cation exchange capacity, which is beneficial to improving the adsorption and water retention performance of biochar.

[0038] 2. Effects of biochar addition on farmland soil environmental factors and microbial diversity

[0039] An indoor culture method was adopted. Before the experiment started, the soil was pre-cultured. The air-dried farmland soil passed through a 2 mm sieve was added with deionized water to adjust the water content to maintain at 40% of the field water holding capacity. At the same time, it was treated with shading and placed in a constant temperature incubator at 25°C for 7 days of pre-culture to activate the microbial activity in the soil.

[0040] First, about 150 g of fresh soil (2 mm sieve, 40% water holding capacity) was placed into 500 mL PVC bottles, and then different biomass-derived biochars were added and mixed thoroughly. A total of ten treatment groups were set up, with three replicates in each group, as shown in Table 2. All bottles were sealed with breathable membranes and incubated in a constant temperature incubator (temperature set at 25°C, humidity set at 40%). During this period, by the method of weighing and replenishing water, water was replenished every 2 days to make the soil field water holding capacity 60%. After culturing for 56 days, samples were taken on the 0th, 14th, 28th, and 56th days of culture to measure the relevant physical and chemical properties of the soil, and samples were taken on the 56th day to measure microbial carbon and nitrogen and microbial diversity.

[0041] At the end of the incubation, transfer the samples to clean 50 mL centrifuge tubes and centrifuge at 8000 rpm for 10 min using a centrifuge. Remove the supernatant to obtain soil samples. The soil samples are stored in three parts. One part of the soil sample is air-dried naturally to determine the soil physical and chemical properties; one part of the soil sample is stored at 4 °C to determine the soil enzyme activity and microbial carbon and nitrogen; in addition, one part of the soil sample is quickly immersed in liquid nitrogen and then stored in a refrigerator (-80 °C) for microbial diversity analysis.

[0042] Table 2 Design of soil incubation experiments

[0043]

[0044]

[0045] 2.1 Effects of biochar addition on pH value and available nutrients in farmland soil

[0046] The dynamic changes in the pH value of farmland soil after biochar application are as Figure 2 shown. During the entire incubation period, the pH value of the control group soil did not show obvious changes, and its pH value was between 5.71 and 5.90. The pH values of each biochar treatment group showed an obvious upward trend with the increase of incubation time. At the initial stage of incubation, the pH values of the biochar treatments ranged from 6.33 to 7.46, which were significantly increased by 7.29% - 26.49% compared with the control group. At the end of incubation, the pH values of the biochar treatment groups were 6.45 - 7.46, and compared with the control group, the pH values were significantly increased by 0.62 - 1.62 units. Among them, at the 4% addition level, the pH values of the FBC3, ZBC3, and ABC3 treatments reached 7.46, 7.33, and 7.23 respectively, which were significantly increased by 20.29% - 23.26% compared with the control group; at the 2% addition level, the pH values of the FBC2, ZBC2, and ABC2 treatments reached 6.97, 6.76, and 6.86 respectively, which were significantly increased by 14.15% - 17.59% compared with the control group; at the 0.5% addition level, the pH values of the FBC2, ZBC2, and ABC2 treatments reached 6.46, 6.52, and 6.45 respectively, which were significantly increased by 8.27% - 10.67% compared with the control group.

[0047] The dynamic changes in the content of alkali-hydrolyzable nitrogen (AN) in farmland soil after biochar application are as Figure 3As shown in the figure. During the entire cultivation period, the AN content in the biochar treatment group was higher than that in the control group, and it showed a downward trend after reaching the peak in the initial stage of cultivation. In the initial stage of cultivation, the AN content in the biochar treatment group was 239.40 - 392.62%, which was significantly increased by 2.74 - 68.49% compared with the control group. Among them, the AN content in the ZBC1 treatment was the highest, which was significantly increased by 68.49% compared with the control group. Secondly, the ABC1 treatment was significantly increased by 52% compared with the control group. At the end of cultivation, the AN content in each biochar treatment group increased by 4.67 - 61.60 mg·kg -1 , with an increase range of 2.99% - 39.52%. Among them, the AN content in the FBC3 treatment was the highest, which was significantly increased by 39.52% compared with the control group. Secondly, the ZBC2 treatment was significantly increased by 17.37% compared with the control group. With the increase of biochar addition level, the AN content increased. In the FBC treatment group, the FBC3 treatment was significantly increased by 20.73% and 35.47% compared with the FBC2 and FBC1 treatments respectively; in the ZBC treatment group, the ZBC3 treatment was significantly increased by 9.67% and 18.49% compared with the ZBC2 and ZBC1 treatments respectively; in the ABC treatment group, the ABC3 treatment was significantly increased by 10.21% compared with the ABC1 treatment and 4.86% compared with the ABC2 treatment (p > 0.05).

[0048] The dynamic changes of the available potassium (AK) content in farmland soil after biochar application are as follows Figure 4 As shown in the figure. During the entire cultivation period, the soil AK content at each time point in the biochar treatment group was significantly higher than that in the control group. In the initial stage of cultivation, the AK content in the biochar treatment group was 97.13 - 455.02 mg·kg –1 , which was significantly increased by 16.30% - 438.88% compared with the control group. The AK content in the biochar treatment group increased with the increase of addition level. At the end of cultivation, the AK content in the biochar treatment group was significantly increased by 40.01 - 506.84 mg·kg -1 , with an increase range of 76.47% - 968.83%. Among them, the AK content at each addition level in the FBC treatment group was the highest. The FBC3 treatment was significantly increased by 68.89% and 66.77% compared with the ZBC3 and ABC3 treatments respectively; the FBC2 treatment was significantly increased by 194.71% and 158.25% compared with the ZBC2 and ABC2 treatments respectively; the FBC1 treatment was significantly increased by 96.53% and 141.55% compared with the ZBC1 and ABC1 treatments respectively; however, in the biochar treatment group, there was no significant difference between the 4% addition level ZBC and ABC treatment groups. Elemental analysis showed that guava fruit branch biochar exhibited stronger cation exchange capacity and adsorption performance, which helped to improve the availability of nitrogen and potassium in the soil, providing a theoretical basis for reducing the input of nitrogen fertilizer and potassium fertilizer and improving soil sustainable productivity.

[0049] 2.2 Effects of Biochar Addition on Farmland Soil Environmental Factors

[0050] As Figure 5 shown, the content of dissolved organic carbon (DOC) in the biochar treatment group showed an upward trend during the incubation period, while the DOC content in the control group showed a downward trend after the 14th day of incubation. At the initial stage of incubation, the DOC content at the 0.5% addition level was significantly lower than that of the control group. Among them, the FBC1 treatment decreased by 17.01%, the ZBC1 treatment decreased by 4.54%, the ABC1 treatment group decreased by 2.93%, while the FBC2 treatment did not show significant differences. From the 28th day to the end of incubation, the DOC content in the biochar treatment group was higher than that of the control group. At the end of incubation, the DOC content in the biochar treatment was significantly increased by 32.41% - 119.19% compared with the control group. Among them, at the 4% addition level, the DOC content of the FBC3 treatment was 0.88% higher than that of the ZBC3 treatment and was significantly increased by 31.58% compared with the ABC3 treatment. Soil dissolved organic carbon (DOC) is the most active substance in the farmland ecosystem. The biogeochemical cycle of soil carbon has been greatly affected. At the same time, it also plays a very important role in the turnover, renewal of the soil organic carbon pool and the realization of the source-sink function. The increase in DOC concentration at the 4% FBC biochar addition rate indicates that the input of organic materials such as biochar provides sufficient carbon sources for the growth of soil microorganisms, which is conducive to enhancing microbial activity, thereby increasing the concentration of carbon components.

[0051] 2.3 Effects of Biochar Addition on Farmland Soil Enzyme Activity

[0052] As Figure 6 shown, the urease (UA) activity in the biochar treatment group showed an upward trend followed by a downward trend in the first 28 days of incubation, and the UA activity in the biochar treatment group was always higher than that of the control group. At the initial stage of incubation, the UA activity in the biochar treatment group was 243.65 - 364.59 U·g- 1 -1. Compared with the control group, the UA activity at the 4% addition level of biochar treatment was significantly increased by 21.74% - 52.15%. Among them, the UA activities of the ZBC3 and ABC3 treatments were significantly increased by 20.73% and 24.98% respectively compared with the FBC3 treatment, while the FBC1 and FBC2 treatments did not show significant differences compared with the control group. On the 28th day, the UA activity of the biochar treatment reached the peak, which was significantly increased by 21.65% - 68.17% compared with the control group. At the end of incubation, the UA activity in the biochar treatment group was significantly increased by 6.07 - 110.94 U·g -1In particular, at the 4% addition level, the UA activity of the biochar treatment group reached the highest value, showing a significant increase of 2.52% - 45.99% compared with the control group. Among them, the UA activity of the ZBC3 treatment was the highest, showing significant increases of 20.02% and 25.09% compared with the FBC3 and ABC3 treatments respectively. In the ZBC treatment group, the UA activity at each addition level was significantly increased by 4.42% - 45.99% compared with the control group. Among them, the UA activity of ZBC3 was significantly increased by 20.44% and 39.82% compared with the ZBC2 and ZBC1 treatments respectively. At the 2% addition level, the UA activity of the ZBC2 treatment was significantly increased by 6.67% and 14.66% compared with the ABC2 and FBC2 treatments respectively; while at the 0.5% addition level, there were no significant differences among the biochar treatments.

[0053] As Figure 7 shown, during the cultivation period, the cellulase (CL) activity of the biochar treatments was higher than that of the control group, while the CL activity of the control group did not show obvious changes. At the initial stage of cultivation, the CL activity of the biochar treatments was 14.35 - 16.60 U·g -1 , showing a significant increase of 11.70% - 29.26% compared with the control group, but there were no significant differences among the treatment groups. On the 28th day, the CL activity of the ZBC2 treatment was the highest, showing a significant increase of 43.18% compared with the control group. Followed by the FBC2 and FBC1 treatments, showing significant increases of 33.99% and 30.15% compared with the control group, but there were no significant differences between the FBC3 treatment of the biochar treatment group and the ABC treatment group. At the end of cultivation, except that the ZBC1 treatment did not show a significant difference compared with the control group, the CL activities of the other biochar treatment groups were significantly increased by 8.98% - 25.99%. Among them, the CL activity of each biochar treatment was the highest at the 2% addition level, showing FBC2 (16.03 U·g -1 ) > ZBC2 (15.78 U·g -1 ) > ABC2 (13.99 U·g -1 ), showing an increase of 9.92% - 25.99% compared with the control group.

[0054] As Figure 8 shown, at the initial stage of cultivation, when the biochar addition level was 4%, there were significant differences compared with the control group. The sucrase activity (SA) of the FBC3 treatment was significantly increased by 57.57% compared with the control group. As the cultivation progressed, the SA activity of the biochar treatments reached the peak on the 28th day. Among them, the SA activity of the FBC2 treatment was significantly increased by 68.57% compared with the control group; secondly, the SA activity of the FBC3 treatment was significantly increased by 131.41% compared with the control group. At the end of cultivation, the SA activities of the biochar treatment groups were 7.86 - 16.63 U·g -1, among which the FBC biochar treatment significantly increased by 49.07% - 56.76% compared with the control group at the 2% and 4% addition levels.

[0055] 2.4 Effects of Biochar Addition on the Diversity of Bacterial Communities in Farmland Soils

[0056] A Venn diagram was used to visually show the differences and overlaps in the OTU composition of the soil bacterial communities in the biochar treatment groups ( Figure 9 ). In this study, a total of 1,863,706 effective sequences were obtained through high-throughput sequencing. After clustering analysis with 97% similarity, a total of 34,034 OTUs were divided in the soil samples of each treatment, among which 135 OTUs were common taxa. Among them, the proportion of OTUs in the FBC1 treatment was the largest, reaching 19.83%, followed by the ZBC2, ABC1, and ABC2 treatments, accounting for 9.35%, 11.87%, and 10.81% of the total number of OTUs, respectively. The changes in the Alpha diversity indices of the soil bacterial communities in different biochar treatment groups are shown in Table 3. The coverage indices of all samples with biochar addition were greater than 99%, indicating that the probability of detecting gene sequences in the samples was extremely high, and the true situation of the soil bacterial communities could be better reflected. The Chao1 index represents the abundance of the bacterial community, and the Shannon and Simpson indices evaluate the diversity of the bacterial community. In terms of the Chao1 index, the FBC1, ZBC2, ABC1, and ABC2 treatments significantly increased by 42.06%, 19.78%, 25.19%, and 22.89% respectively compared with the control group; while the FBC2, ZBC1, ZBC3, and ABC3 showed no significant differences compared with the control group. In the Shannon index, except for the FBC3 treatment, the Shannon indices of other treatments were significantly higher than the control group by 2.69% - 7.04%. There were no significant differences in the Simpson index among the biochar treatments. Thus, it can be seen that adding biochars from different sources changed the Alpha diversity of the soil bacterial communities to varying degrees.

[0057] Principal component analysis (PCA) was used to evaluate the Beta diversity of the soil bacterial communities. PCA analysis can extract two coordinate axes that can best reflect the differences between samples to the greatest extent, so as to reflect the differences in multi-dimensional data on a two-dimensional coordinate diagram, such as Figure 10As shown in the figure, the explanatory degrees of PC1 and PC2 for the differences in each processed sample were 58.11% and 25.17% respectively, and their cumulative contribution rate reached 83.28%. It can be seen from the figure that there was an obvious separation between the control group (CK) and the treatments of ABC3, ZBC3, FBC1, FBC2, and ZBC2 on the PC2 axis of the principal component, indicating that the biochar treatment changed the structure of the farmland soil bacterial community. The ZBC2 treatment was concentrated on the positive semi-axis of the PC1 axis, and the ABC3 and ZBC3 treatments were concentrated on the negative semi-axis of the PC1 axis, indicating that the addition of biochar changed the soil bacterial structure as the biochar addition amount increased.

[0058] 2.5 Influence of Biochar Addition on the Structure of Farmland Soil Bacterial Community

[0059] As Figure 11As shown in the figure, after adding biochar from different sources, the relative abundances of the top 10 species in the soil bacterial community structure at the phylum level were: Acidobacteriota, Proteobacteria, Firmicutes, Chloroflexi, Myxococcota, Cyanobacteria, Bacteroidota, Patescibacteria, and Gemmatimonadota. Among them, the relative abundance of Acidobacteriota in the control group was the highest, reaching 26.26%. Compared with the control group, the abundances of Acidobacteriota in all biochar treatment groups decreased significantly by 11.71% - 48.02%, and the abundances of Acidobacteriota in the FBC1, ZBC2, and ABC3 treatments were the lowest. In terms of Proteobacteria, except for the ABC1 treatment, the abundances of this phylum in other biochar treatment groups increased significantly, with an increase range of 1.41% - 103.18%, especially in the FBC2 treatment group. In contrast, the abundances of Firmicutes in all biochar treatment groups decreased significantly by 13.60% - 260.62% compared with the control group. The FBC1 and FBC3 treatments significantly reduced the abundances of Chloroflexi, with the decrease ranges being 41.87% and 33.77% respectively, while the abundances in the remaining treatment groups increased significantly by 20.95% - 53.95%. In Myxococcota, the abundances in the FBC1, FBC3, and ABC1 treatment groups decreased significantly by 20.31%, 38.77%, and 6.63% respectively compared with the control group, while the abundances in other treatments increased significantly by 17.67% - 39.05%. The FBC and ABC at the 4% addition level significantly increased the abundances of Cyanobacteria, while the abundances of this phylum in the FBC1, FBC2, ZBC3, and ABC2 treatment groups decreased significantly, with the decrease ranges being 19.53% - 125.48%. In addition, the relative abundance of Bacteroidota in the ZBC1 treatment decreased significantly by 22.21% compared with the control group, while the abundances in other biochar treatments increased significantly by 14.69% - 78.96%. The study also found that the abundances of Patescibacteria in the FBC1 and FBC3 treatment groups decreased significantly by 42.76% and 30.11% respectively compared with the control group, but at the 4% addition level, the abundances of Patescibacteria increased significantly, showing ABC3 > ZBC3 > FBC3. In addition, for the relative abundance of Gemmatimonadota, only the FBC1 treatment decreased significantly by 9.67% compared with the control group, while at the 2% addition level, the relative abundance of Gemmatimonadota was the highest, showing FBC2 > ZBC2 > ABC2.

[0060] As Figure 12As shown in the figure, the heatmap of the relative abundances of the top 10 species in the bacterial community structure at the phylum level. Compared with the control group, the addition of biochar significantly changed the abundances of different bacterial phyla. The addition of biochar treatment significantly reduced the relative abundance of Acidobacteria compared with the control group. Except for the ABC1 treatment, the biochar treatments also reduced the relative abundance of Firmicutes; all addition levels of FBC significantly increased the relative abundance of Proteobacteria, while other treatment groups reduced the relative abundance of this phylum; the FBC and ZBC treatment groups significantly increased the relative abundance of Chloroflexi; the ABC and ZBC treatment groups significantly increased the relative abundance of Myxococcota at the 4% addition level. In addition, the FBC treatment group also significantly increased the relative abundance of Cyanobacteria at the 4% addition level. The study also found that ZBC and FBC significantly increased the relative abundance of Gemmatimonadota at addition levels greater than or equal to 2%.

[0061] In summary, taking the typical continuous cropping acidic farmland soil as the research object, three kinds of biochars were prepared by high-temperature pyrolysis of eucalyptus branches, camphor tree branches and guava fruit branches. By systematically comparing the differences in the physical and chemical properties of the biochars from camphor tree, eucalyptus and guava branches, the advantages of guava branch biochar in improving soil in the present invention were revealed; through soil incubation experiments, the dynamic regulation mechanisms of the three biochars on farmland soil environmental factors, available nutrients and soil enzyme activities were explored; through the analysis of the microbial community structure diversity, the effects of the three biochars on the bacterial community and diversity and the relationship between the soil bacterial community structure and environmental factors were explored. The analysis results are as follows:

[0062] (1) FBC has higher pH value and ash content than ABC and ZBC; ABC has higher aromaticity and stability than FBC and ZBC, but relatively weaker hydrophilicity and cation exchange capacity. The surface of FBC presents more irregular scales and has a porous structure and large pore size, providing more adsorption sites and space for nutrients; all three biochars contain crystal structures of quartz and calcite-type carbonates, and only FBC contains calcium magnesium carbonate crystal structure. When biochar is added to acidic soil, a large amount of Ca 2+ can replace exchangeable Al 3+ , thereby reducing the toxic effect of Al 3+ in the soil and increasing the soil base content.

[0063] (2) The three biochars significantly increased the pH value of the farmland soil, and the pH value of the farmland soil increased from 5.71 to 6.45 - 7.46. In addition, the three biochars significantly increased the contents of alkali-hydrolyzable nitrogen (AN) and available potassium (AK) in the farmland soil, which were 2.99 - 35.52% and 76.47 - 968.83% respectively, and increased with the increase of the addition amount. Among them, the improvement effect of FBC was relatively significant.

[0064] (3) Compared with the control group, the dissolved organic carbon (DOC) content in farmland soil increased significantly by 32.41% - 119.19% with the addition of three types of biochar. Among them, at the 4% addition level, the FBC had the best improvement effect. The DOC content in the FBC3 treatment was 0.88% higher than that in the ZBC3 treatment and significantly 31.58% higher than that in the ABC3 treatment. Mechanism: Organic materials such as guava branch biochar provided sufficient carbon sources for soil microorganisms, thus promoting microbial activity and increasing the concentration of relatively stable active carbon components. The increase in DOC concentration indicated that soil microorganisms utilized easily degradable DOC for growth, thereby increasing the concentration of carbon components.

[0065] (4) The three biochar treatments significantly enhanced the activities of urease and sucrase at a 4% addition rate. While at a 2% addition rate, the biochar treatment group significantly increased the cellulase activity. Mechanism: After biochar is applied to the soil, it can improve the soil nutrient content and pore structure, thereby increasing the microbial biomass and soil enzyme content, and further enhancing the soil enzyme activity. However, there is significant variability in the impact of biochar on soil enzyme activity, and its structure, application rate, and land use pattern all have varying degrees of influence on soil enzyme activity. Urease and nitrate reductase are key enzymes in the conversion of soil organic nitrogen to inorganic nitrogen, participating in the soil nitrogen transformation process. Their activities reflect the intensity of soil nitrogen transformation and nitrogen supply capacity. In this study, the urease activity was significantly enhanced at the 4% addition level because the biochar surface is rich in a large number of oxygen-containing functional groups, which can promote its adsorption of urease, thus enhancing the urease activity. While the nitrate reductase activity decreased to varying degrees because biochar protected the binding sites of enzymatic reactions by adsorbing enzyme molecules, thereby reducing the activity of nitrate reductase. In addition, nitrate reductase promotes the denitrification process. With the increase in biochar application rate, the denitrification effect weakens, and the reduction and loss rate of nitrate nitrogen in the soil slow down, achieving a nitrogen fixation effect. The main enzymes involved in carbon transformation include cellulase, sucrase, and β-glucosidase, etc., which provide carbon sources for the soil. Cellulase hydrolyzes cellulose to generate glucose, providing a carbon source for microorganisms; sucrase catalyzes the degradation of sucrose to produce reducing sugars, providing a carbon source and energy for the soil, reflecting the utilization of soluble substances in the soil and the accumulation and transformation of organic matter. In this study, the 4% addition rate significantly increased the sucrase and cellulase activities because biochar provided a suitable microhabitat for microorganisms through its high specific surface area and pore structure, and significantly promoted the growth and reproduction of microorganisms. At the same time, due to its porous structure and excellent adsorption capacity, biochar can adsorb the substrates participating in enzymatic reactions, providing more binding sites for soil enzymes, thereby enhancing the activities of sucrase and cellulase. In addition, this study also found that there was no significant difference in the sucrase activity between the ABC treatment group and the control group in farmland soil, which may be related to the relatively strong aromaticity of biochar. Biochar itself contains high molecular weight aromatic substances (such as dioxins and furans), which may be toxic to soil microorganisms, thereby inhibiting the activity of soil sucrase;

[0066] (5) The three biochar treatments increased the bacterial diversity of farmland soil. Among them, the FBC1, ZBC2, ABC1, and ABC2 treatments significantly enhanced the Chao index of soil bacteria. In addition, adding biochar from different sources indirectly changed the soil bacterial community by altering the soil physical and chemical properties. In the farmland soil bacterial community, Acidobacteria, Proteobacteria, and Firmicutes are the dominant phyla. AN, AK, NH 4+ -N are the main environmental factors in farmland soil.

Claims

1. A guava branch biochar, characterized in that, It is biochar obtained by calcining guava fruit branches, and its preparation method includes the following steps: Use ultrapure water to remove surface dust from guava branches (fruit tree branches), crush them to 1-2 cm, place them in an 80°C oven and dry to constant weight, then take them out to obtain a biochar raw material sample. Gradually compact and fill the biochar raw material sample into a crucible, fill it with nitrogen, and then place it in a muffle furnace. Heat it at a rate of 10°C / min to the final pyrolysis temperature of 500°C and keep it pyrolyzed at a constant temperature for 2 hours to obtain guava branch biochar.

2. The guava branch biochar according to claim 1, characterized in that, In the structure of the guava branch biochar, its surface presents many irregular scales and has a porous structure and large pores, and it contains crystal structures of quartz, calcite-type carbonate, and calcium magnesium carbonate.

3. Application of a kind of guava branch biochar in soil improvement.

4. The application of the guava branch biochar according to claim 3 in soil improvement, characterized in that, The soil improvement includes the improvement of the pH value of the soil, the content of alkali-hydrolyzable nitrogen, the content of available potassium, the content of dissolved organic carbon, the content of soil urease, the activities of sucrase and cellulase, and the bacterial diversity in the soil.

Images