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Article

Effects of Biochar under Different Preparation Conditions on the Growth of Capsicum

by
Haiwei Xie
*,
Xuan Zhou
and
Yan Zhang
School of Mechanical Engineering, Tianjin University of Commerce, Tianjin 300134, China
*
Author to whom correspondence should be addressed.
Sustainability 2024, 16(16), 6869; https://doi.org/10.3390/su16166869
Submission received: 7 July 2024 / Revised: 2 August 2024 / Accepted: 7 August 2024 / Published: 10 August 2024
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Abstract

:
Biochar return to the field has been widely explored, but there is a problematic disconnect between biochar preparation and biochar return to the field. In this study, soybean straw is used as a raw material and is sieved into two components: 60-mesh (0.250 mm) and 110-mesh (0.130 mm). Four kinds of biochar were obtained by pyrolysis under the condition of no heat preservation and heat preservation for 60 min. The biochar was applied to the soil, and the effects of biochar on soil and capsicum growth were analyzed by Spearman correlation. Compared with the control group, soil pH, soil electrical conductivity, and soil organic matter decomposition were increased by 0.58, 101 μs/cm, and 9.48%, respectively. The fruit quantity, plant height, water, fat, soluble solid, and titrable acidity of capsicum were increased by 1, 0.55, 0.08, 0.62, 0.67, and 0.7 times, respectively. Spearman correlation analysis showed that soil properties and capsicum growth were most affected by biochar’s specific surface area (SSA). Therefore, increasing the biomass mesh number and heat preservation time is beneficial to increasing the SSA of biochar and facilitating the return of biochar to the field and the best preparation conditions are 110-mesh soybean straw biomass pyrolysis and heat preservation for 60 min.

Graphical Abstract

1. Introduction

Agriculture is a basic industry for economic and social development, providing basic living materials for human beings [1,2]. The rational use of agricultural waste can improve the efficiency of resource production. In this regard, straw is an important source of biochar raw materials because of its stability and sustainability [3]. Biochar obtained by the pyrolysis of biomass at a high temperature with limited oxygen has a large porosity [4], stable aromatic carbon skeleton, and polymer layered structure and is not easily degraded by soil microorganisms [5]. Biochar return to the field affects crop growth and development by changing the physical and chemical properties of soil, so it is considered as an agricultural practice with potential value [6].
Biochar is an environmentally friendly carbon-rich product with a rich pore structure, large specific surface area (SSA), and strong adsorption effect on various pollutants [3]. Many scholars have explored that changing the pyrolysis conditions such as biomass mesh numbers, heat preservation time, pyrolysis temperature, and heating rate will affect the physical and chemical properties of biochar. The SSA of biochar increases with an increase in heat preservation time [7]; biochar electric conductivity (EC) also increased with an increase in pyrolysis temperature and heat preservation time [8]; the pH of biochar increases with an increase in final pyrolysis temperature [9]; the yield of biochar decreases with an increase in heat preservation time [10]. In the process of pyrolysis, the heat preservation time affects the pore formation of biochar and the total pore volume and mesopore volume [11]; small-size biochar has a larger SSA, more micropores, and a higher EC [12].
Biochar with a lower final pyrolysis temperature can be used as a better soil amendment [13]. Returning biochar to the field can help increase crop yields, increase soil moisture, effectively reducing soil water evaporation [14] and soil acidity [15], and increase crop yields by improving the effective hydration of root zone plants [16]. In addition, biochar has a good retention effect on soil nutrients, and small-particle biochar shows a higher nutrient retention capacity than large-particle biochar [17]. This increases crop nutrient supply and promotes crop growth [18]. Li et al. [18] used the co-application method of straw and biochar to increase the net photosynthetic rate of rice, thereby increasing crop yield and finding the optimal amount of corn straw and biochar co-application for planting rice; Yanze Zhao et al. [19] co-applied nitrogen fertilizer with corn straw and rice husk biochar to improve and stabilize rice yield. By comparison, corn straw biochar was more suitable for returning to the field in combination with nitrogen fertilizer. Returning biochar to fields can increase the soil’s carbon storage potential, effectively slowing down greenhouse gas emissions, retaining nutrients for plants, and improving soil fertility [20]. Most scholars only explore the changes in soil and crops before and after returning biochar to the fields and do not explore the relationship among the physical and chemical properties of biochar, soil changes, and crop growth.
To sum up, a large number of scholars either focus on the effects of different preparation conditions on the physical and chemical properties of biochar [21,22], or on the different effects of returning it to the field before and after biomass pyrolysis [23,24], or on the effects of different amounts of biochar on crop growth [25,26]. Previously, a large number of scholars have found that applying biochar to the soil does improve the physical and chemical properties of the soil and is beneficial to plant growth [27,28]. But there is a disconnection between the preparation of biochar and the return of biochar to the field. There is a lack of exploration into the effects of different preparation conditions on the effect of biochar returning to the field. Biochar prepared under different conditions will affect its physical and chemical properties, such as functional groups, SSA, pH, and EC, and the essence of affecting the effect of biochar returning to the field is the physical and chemical properties of biochar. In this study, soybean straw biochar prepared with different particle sizes and different heat retention times was applied to the soil to plant hot capsicum in pots. The changes in functional groups, crystal structure, SSA, pH, and EC of soybean straw biochar under pyrolysis conditions and the effects of different physical and chemical properties on pot capsicum planting were studied. The specific aim of the study is to affect the physical and chemical properties of biochar by changing the preparation conditions of biochar, changing the physical and chemical properties of the soil after applying it to the soil, and ultimately affecting the growth of capsicum. With the combination of biochar preparation and biochar returning to the field, the mechanism of biochar returning to the field to promote plant growth was revealed, and the best preparation conditions of biochar returning to the field were found. It is of great significance to study the effects of biochar preparation conditions on crop growth and to provide a theoretical reference for biochar returning to the field.

2. Materials and Methods

2.1. Preparation of Biochar

The soybean straw of Sudou No. 18 (Lianyungang City, China) was selected as the material, crushed by a grinder, and filtered through 60-mesh and 110-mesh sieves (RCZ-PJS). The biomass of soybean straw with different mesh numbers of the same quality was put into the pyrolysis furnace at an initial temperature of 20 °C, a final pyrolysis temperature of 350 °C, and a heating rate of 6 °C/min. Heat preservation time is an important parameter affecting the physical and chemical properties of biochar [29]. In order to explore the effect of heat preservation treatment on the physical and chemical properties of biochar, after the pyrolysis was completed, the 60-mesh and 110-mesh biomasses were treated without heat preservation and with heat preservation for 60 min, respectively, and then cooled to room temperature to obtain biochar under four preparation conditions. Soybean straw biochar was stored in an anti-light container for further characterization to reduce the impact of potential factors on biochar production. The four types of biochar obtained under different preparation conditions were named: BC60-0 min, BC60-60 min, BC110-0 min, and BC110-60 min and represent different biomass meshes; 0 min means no heat preservation, and 60 min means heat preservation for 60 min.

2.2. Pot Experiment

The potted plant experiments used plastic pots with a height of 31 cm and a diameter of 27 cm, which were filled with 7 kg of unfertilized soil. The pot without biochar was used as control group (CK). Other pots were filled with 250 g powdered BC60-0 min, BC60-60 min, BC110-0 min, and BC110-60 min, respectively, and the biochar and soil were fully stirred in advance before being put into pots. Three pots were planted each with the four biochar types and without biochar, for a total of 15 pots in the experiment, with plant Tebaolong varieties of capsicum of similar sizes in each pot. The potted plants were placed outdoors, and no nutrients were added during the planting period, only regular watering. The experimental area is located in the eastern part of the North China Plain in China, which belongs to the warm temperate semi-humid monsoon climate zone. Planting started in April 2023 and ended in September 2023. Different capsicum plants were dug out of the soil and marked after planting; the soil of each pot was fully stirred; the stones and plant root debris in the soil were removed; the soil was ventilated and dried and then stored in a dark container through a 40-purpose screen for further characterization. Soil pH and EC were measured using a model MP522 precision pH/conductivity meter, and soil organic matter was measured using the incineration method.

2.3. Characterization

Biochar was obtained by pyrolyzing biomass in an electrically heated pyrolysis furnace (BJS-40 electrically heated pyrolysis furnace, Tianjin Xiqing Mechanical and Electrical Equipment Company; Tianjin, China). The SSA and average particle size of biochar were characterized by Bruauer–Emmet–Teller based on N2 adsorption (Type F-Sorb3400 SSA analyzer, Beijing Jinai Pu Technology Company; Beijing, China). The changes in functional groups in biochar of soybean straw were detected by Fourier transform infrared FTIR (Nicolet 380 FT-IR, Thermo Nicolet Corporation; Madison, WI, USA). An elemental analyzer (Zeiss gemini360; Carl Zeiss AG; Oberkochen, Germany) was used to measure the content of each element in soybean straw biochar. A scanning electron microscope (JEOLJSM-6390A; JEOL; Tokyo, Japan) was used to observe the surface pore structure of soybean straw biochar. The pH value and electrical conductivity of soybean straw biochar were measured by pH meter and electrical conductivity meter (Model MP522 precision pH/conductivity meter; SASSIN; Shanghai, China). Analysis of lattice characteristics and crystal phase composition of soybean straw biochar was performed by X-ray diffractometer (Ultima IV X-ray diffractometer; Rigaku Corporation; Tokyo, Japan). Soil organic matter content was measured using a muffle furnace (SX-ES07123; Zhongyi Guoke Technology Company; Beijing, China). The titratable acidity and the content of soluble solids in capsicum fruits were detected by acid and sugar integrated machine (PAL-BX/ACID 1; ATAGO; Guangzhou, China). The hydration and fat content of capsicum fruit were detected by food calorie composition detector (CA-HM food calorie composition detector; IRIE Corporation; Tokyo, Japan).

2.4. Data Analysis

Spearman correlation was used to determine the correlation degree between the physicochemical properties of soybean straw biochar pyrolysis under different preparation conditions and plant growth, so as to find the best preparation conditions suitable for crop growth of biochar. Spearman correlation analysis is the strength of the monotonic relationship between variables. It quantifies the degree of association between two variables by calculating the Spearman correlation coefficient, which has a value between −1 and 1. A value close to 1 indicates a strong positive correlation; a value close to −1 indicates a strong negative correlation, and a value close to 0 indicates no obvious linear relationship. We used version 24 of IBM SPSS Statistics.

3. Results

3.1. Physical and Chemical Properties of Soybean Straw Biochar

The element contents of soybean straw biochar obtained under different preparation conditions are shown in Table 1. Element C decreased with the increase in biomass mesh numbers and heat preservation time from 52.69% to 20.11%. The O, Si, K, and Cl elements increased with the increase in biomass mesh size and heat preservation time from 31.4%, 11.05%, 2.1%, and 0.75% to 51.42%, 23.8%, 3.43%, and 1.17%, respectively. C element provides organic carbon to the soil and allows plants to absorb soil organic matter; Si element helps improve crops’ photosynthesis and resistance to pests and diseases; K element can adjust the balance of crop ions and water and promote enzyme activation.
The physical and chemical properties of soybean straw biochar obtained under different preparation conditions are shown in Table 2. The pH, EC, and SSA of soybean straw biochar increased with the increase in biomass mesh numbers and heat preservation time from 9.82, 8.06 ms/cm and 31.3322 m2/g to 10.29, 7.74 ms/cm and 115.3912 m2/g, respectively.
The surface structure of soybean straw biochar obtained by pyrolysis under different preparation conditions can be observed by scanning electron microscopy, as shown in Figure 1. Comparing Figure 1a,b, it is found that increasing the heat preservation time can reduce the clogging of the holes; comparing Figure 1a,c, it is found that increasing the biomass mesh number increases the number and types of holes; comparing Figure 1a,d, it is found that as the biomass mesh number and the heat preservation time increase simultaneously, not only the number of mesopores and small pores in the pore structure increases, but also more volatiles escape and the clogging phenomenon decreases.
As shown in Figure 2, changing the number of biomass mesh and heat preservation time does not affect the types of biochar functional groups of soybean straw. The peak at 3451 cm−1 is caused by the stretching vibration of oxhydryl (OH) in the carboxyl group (COOH) [30]. The peak at 3132 cm−1 is caused by the stretching vibration of the C-H bond. The peaks at 1638 cm−1 and 1420 cm−1 are caused by the vibration of the aromatic ring skeleton [31]. The peak at 1089 cm−1 is caused by the symmetrical tensile vibration of the aliphatic ether bond (C-O-C) [32]. The peak at 790 cm−1 is caused by the N-H vibration [33]. The peak at 462 cm−1 is caused by the stretching vibration of the C-Br bond in halogen-containing compounds.
Figure 3 shows the XRD of biochar prepared under different conditions. The diffraction peaks of potassium chloride (KCl) at 28.26°, 40.51°, and 51.16° [34] were observed in the XRD of four kinds of biochar, and there was a strong peak at 28.26° for KCl. The surface KCl has a good structure and a high biochar content. The diffraction peaks of silicon dioxide (SiO2) appear at 22.3°, 25.6°, and 40.8° [35]. SiO2 is only present in BC60-0 min and BC110-0 min.

3.2. Changes in Soil Properties after Application of Biochar from Soybean Straw

Figure 4 shows the changes in soil pH and EC after potting experiments with the addition of biochar prepared under different conditions. Compared with the control soil (CK), Figure 4a shows that the soil pH increased by 0.24, 0.37, 0.41, and 0.57 after the application of BC60-0 min, BC110-0 min, BC60-60 min, and BC110-60 min, respectively. Figure 4b shows that the soil EC increased by 101, 70, 59, and 48 μs/cm after the application of BC60-60 min, BC60-0 min, BC110-60 min, and BC110-0 min, respectively. Biochar prepared by increasing the biomass mesh number and heat preservation time can increase soil pH and EC by up to 0.1 times and 0.21 times.
The soil properties changed after applying soybean straw biochar obtained by pyrolysis under different preparation conditions, and the soil organic matter content was tested after the pot experiment, as shown in Figure 5. Compared with CK, the soil organic matter treated with BC60-0 min, BC110-0 min, BC60-60 min, and BC110-60 min lost 3.82%, 6.01%, 7.275%, and 9.48%, respectively. Biochar promotes further decomposition of soil organic matter, and soil organic matter decreased by 59% with the increase in biomass mesh and heat preservation time.

3.3. Growth of Capsicum after Application of Biochar from Soybean Straw

As shown in Figure 6 and Figure 7, the effects of biochar on fruit number, plant height, and fruit quality of hot capsicum were studied. As shown in Figure 6a, compared with CK, the roots of plants treated with biochar are more developed and the branches and leaves are more luxuriant. As shown in Figure 6b, the number of capsicum fruits applied with BC60-0 min, BC110-0 min, BC60-60 min, and BC110-60 min biochar increased by 7, 9, 12, and 15, respectively. As shown in Figure 6c, the plant height of capsicum fruits applied with BC60-0 min, BC110-0 min, BC60-60 min, and BC110-60 min biochar increased by 7 cm, 14 cm, 16 cm, and 27 cm, respectively. As shown in Figure 7a, the hydration of capsicum fruits applied with BC60-0 min, BC110-0 min, BC60-60 min, and BC110-60 min biochar increased by 2.4%, 3.5%, 4.7%, and 6.2%, respectively. As shown in Figure 7b, the fat of capsicum fruits applied with BC60-0 min, BC110-0 min, BC60-60 min, and BC110-60 min biochar increased by 0.06%, 0.28%, 0.31%, and 0.51%, respectively. As shown in Figure 7c, the soluble solid of capsicum fruits applied with BC60-0 min, BC110-0 min, BC60-60 min, and BC110-60 min biochar increased by 3.4%, 4.3%, 5.2%, and 7.8%, respectively. As shown in Figure 7c, the titrable acid of capsicum fruits applied with BC60-0 min, BC110-0 min, BC60-60 min, and BC110-60 min biochar increased by 3.54%, 4.44%, 5.37%, and 7.94%, respectively. The fruit number, plant height, hydration, fat, soluble solid content, and titrable acidity of capsicum increased by 1, 0.55, 0.08, 0.62, 0.67, and 0.7 times with the increase in biomass mesh numbers and heat preservation time, respectively. Hydration, fat, soluble solid content, and titrable acidity content increased with the increase in biomass mesh numbers and heat preservation time, and the higher the content, the better the ripening of capsicum.

4. Discussion

4.1. Comparison of Soil Properties Applied with Different Biochar Types

Soybean straw biochar obtained from different pyrolysis conditions was applied to the soil to provide trace elements to the soil. The pH value of the soil suitable for growing capsicum is 5.5–7.0 [36]. Compared with CK, biochar itself is alkaline and applied to soil to reduce soil acidity. XRD shows that all four kinds of soybean straw biochar contain KCl, and a potassium ion, as a basic cation, can neutralize soil acidity. K+ acts as an alkaline earth cation in the soil [37]. It is adsorbed on the soil solid surface through electrostatic attraction and exchanges with the negatively charged soil surface to keep the soil electrically neutral. The basic cations that have not been exchanged exist in the soil and maintain balance in the soil. Therefore, the acid–alkaline trend of the improved soil is consistent with that of biochar (Figure 4), and the pH of the soil is BC110-60 min > BC60-60 min > BC110-0 min > BC60-0 min > CK. The dissociation of phenolic hydroxyl, carbonyl, carboxyl, and ester groups in low-temperature biochar directly controls the pH properties of biochar, in which carboxyl is the main ion exchange site for adsorption or desorption of nutrients or heavy metals [38]. FT-IR showed that there were phenolic hydroxyl and carboxyl groups in soybean straw biochar and functional groups combined with soil groups to neutralize soil acidity. Since the O element and pH of soybean straw biochar increased with the increase in biomass mesh numbers and heat preservation time and the content of the basic oxygen-containing functional group increased, soil pH was proportional to the biomass mesh numbers and heat preservation time.
Soil organic matter is the content of various organic compounds containing carbon in soil. Soil treated with biochar can promote the uptake of nutrients by plants. Spearman correlations were used to determine the effects of biochar’s SSA, pH, and EC on soil organic matter content. As shown in Table 3, the Spearman correlations of soybean straw biocarbon SSA, pH, and EC on soil organic matter were −0.971, −0.971, and −0.47, respectively, indicating a negative correlation between soil organic matter and biochar’s SSA, pH, and EC. The correlation degree between the physicochemical properties of biochar and soil organic matter was SSA = pH > EC. By analyzing the significance level, it can be seen that the significances (two-tailed) of SSA and pH are both less than 0.01. There is a very significant correlation between SSA and pH on soil organic matter. However, the significance (two-tailed) of EC is greater than 0.05, meaning there is no correlation between EC and soil organic matter. Biochar can provide long-term fertility for crop growth. The nutrient elements in biochar migrate in the soil, and the available nutrients in the soil and biochar are absorbed and utilized by crops. Among them, a small part of the structurally stable mineral nutrients migrate to the soil; however, most of them remain in the residual biochar, establishing a storage reservoir of soil nutrient elements in the biochar [39]. In general, compared with CK, the content of soil organic matter applied by biochar is significantly lower than that of CK, indicating that biochar promotes the decomposition of soil organic matter. Biochar with a high SSA can not only improve the water retention of soil, but also change the internal pore structure of soil, thus significantly improving the adsorption capacity of soil [40]. The metal ions in the soil combine with the functional groups of biochar itself to achieve the effect of promoting the absorption of nutrients by plants. The SiO2 structure in biochar is beneficial to increasing soil organic carbon and plant absorption [41]. Therefore, the application of biochar to increase the mesh numbers of biomass and heat preservation time is conducive to plant growth.

4.2. Comparison of Capsicum Growth Applied with Different Biochar Types

The effects of biochar’s SSA, pH, and EC on fruit number, plant length, and qualitative parameters (water content, fat content, titrable acidity, and soluble solids) of capsicum were determined by the Spearman correlation method. As can be seen from Table 4, the Spearman correlations between biochar EC and fruit number, plant length, and qualitative parameters were less than 0.6 and the significance (two-tailed) of all parameters is greater than 0.05, indicating that biochar EC had no effect on capsicum. Compared with the Spearman correlation coefficient, it was found that the effects of biochar’s physicochemical properties on plant length, hydration, fat, titrable acidity, and soluble solids were as follows: SSA > pH. The effects of biochar’s physicochemical properties on the number of capsicum fruit were as follows: pH < SSA. However, the effects of biochar’s SSA and pH on all capsicum’s qualitative parameters were compared. Only biochar’s SSA had a Spearman correlation greater than 0.9, so biochar’s SSA had the greatest effect on capsicum. The Spearman correlation of biochar’s pH value was between 0.897 and 0.946, indicating that biochar’s pH also influenced capsicum, but the effect was lower than that of biochar’s SSA. Therefore, the number of capsicum fruit, plant length, and qualitative parameters are directly proportional to the mesh numbers of soybean straw biomass and the heat preservation time.
Soybean straw biochar contains potassium salt, which can promote plant photosynthesis and plant growth. SiO2 can be used as a soil amendment to improve crop yield. The oxygen-containing functional group of biochar can increase the available nutrients of plants in the soil [42], significantly increasing the height of plants. Biochar prepared under different conditions has different physical and chemical properties. Mixing biochar with soil with a large SSA can reduce soil bulk density, increase total pore volume, and improve soil water residence capacity [43]. Increasing the heat preservation time makes the volatiles blocked in the pore structure escape. Smaller-diameter biochar may have more broken internal large pores, which increases the amount of water that can be stored [44], which is beneficial for plant growth. Soybean straw biochar is alkaline. Under the same mass, the smaller the particle size of biochar, the higher the number of biochar particles which can be mixed with soil more fully and the carbonate formed by biochar has a longer heat preservation time, which can improve the soil pH value and promote the growth of capsicum crops. Biochar with a high pH can alleviate soil acidification [45]. Through the action of biochar EC in the soil, the ion exchange ability is enhanced and thus plant growth is affected. Biochar’s initiation effects of different ash contents were different, but the difference was not significant [46], indicating that soybean straw biochar EC had little effect on plant growth.
Based on the above analysis, the impact level of biochar’s physicochemical properties on fruit quantity, plant height, and qualitative parameters of capsicum were as follows: SSA > pH. Since the SSA and pH of biochar increase with the biomass mesh numbers and heat preservation time, the number of capsicum fruit, plant length, and qualitative parameters of capsicum are proportional to the biomass mesh numbers and heat preservation time applied to the soil biochar. Among the four kinds of biochar, the biochar with the highest SSA and pH values had the best return effect. Therefore, the best preparation condition of applying soybean straw biochar into soil to affect the growth of capsicum is 110-mesh soybean straw biomass thermal retention for 60 min.

5. Conclusions

Different preparation conditions affect the physical and chemical properties of biochar and then affect the physical and chemical properties of soil and the growth of capsicum. Different plants are suitable for planting in different soil pH, but acid rain can cause soil acidification. Applying biochar to the soil can weaken or eliminate the adverse effects of acid rain. Biochar is fully mixed with soil to increase soil nutrients and water retention capacity, and soybean straw biochar is suitable for crops growing in alkaline soils. It improve soil pH and EC, because the soybean straw biocarbon contains potassium salt and SiO2, so the application of biochar can promote the absorption of soil organic matter by plants, which is conducive to the growth and development of capsicum crops. The pH of soil applied with biochar increased with the increase in biomass mesh numbers and heat preservation time. Soil EC decreased with the increase in biomass mesh numbers and increased with the increase in heat preservation time. The correlation degree between the physicochemical properties of biochar and soil organic matter was as follows: SSA > pH > EC, but only the correlation between the SSA of biochar and soil organic matter was significant, and soil organic matter decreased with the increase in biomass mesh numbers and heat preservation time. All parameters of capsicum increased with the increase in biomass mesh numbers and heat preservation time. Therefore, increasing the biomass mesh numbers and heat preservation time is conducive to crop growth, and the best preparation condition is 110-mesh soybean straw biomass pyrolysis heat preservation for 60 min.
The study only focused on soybean straw biocarbon; however, the properties vary between different biomasses. In the future, it is also necessary to explore the effects of different types of biochar applied to soil under different pyrolysis conditions on crops.

Author Contributions

Conceptualization, H.X.; Methodology, X.Z.; Funding acquisition, H.X.; Investigation, H.X.; Writing—original draft, X.Z.; Writing—review and editing, H.X., X.Z. and Y.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the Tianjin Graduate Science and Technology Innovation Project (2022SKY328).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

All data are available upon request.

Acknowledgments

We are grateful to all laboratory colleagues and researchers for their constructive comments and help.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The scanning electron microscope pictures of (a) BC60-0 min; (b) BC60-60 min; (c) BC110-0 min; (d) BC110-60 min.
Figure 1. The scanning electron microscope pictures of (a) BC60-0 min; (b) BC60-60 min; (c) BC110-0 min; (d) BC110-60 min.
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Figure 2. FT-IR spectra with different preparation conditions.
Figure 2. FT-IR spectra with different preparation conditions.
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Figure 3. Biochar X-ray diffraction (XRD) under preparation conditions.
Figure 3. Biochar X-ray diffraction (XRD) under preparation conditions.
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Figure 4. Soil pH (a) and EC (b) after application of biochar prepared under different conditions and without biochar application.
Figure 4. Soil pH (a) and EC (b) after application of biochar prepared under different conditions and without biochar application.
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Figure 5. Impact of biochar application on soil organic matter of soil generated at different preparation conditions.
Figure 5. Impact of biochar application on soil organic matter of soil generated at different preparation conditions.
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Figure 6. (a) Growth of plants in 5 treatments; (b) Number of fruits during planting; (c) Plant length.
Figure 6. (a) Growth of plants in 5 treatments; (b) Number of fruits during planting; (c) Plant length.
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Figure 7. Effects of biochar under different preparation conditions on the (a) hydration, (b) fat, (c) soluble solid, and (d) titrable acid of capsicum fruit.
Figure 7. Effects of biochar under different preparation conditions on the (a) hydration, (b) fat, (c) soluble solid, and (d) titrable acid of capsicum fruit.
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Table 1. Element contents of soybean straw biochar obtained by pyrolysis under different preparation conditions.
Table 1. Element contents of soybean straw biochar obtained by pyrolysis under different preparation conditions.
Carbon
(C)		Oxygen
(O)		Silicon
(Si)		Potassium
(K)		Chlorine
(Cl)		Other
Elements
wt%
BC-60-0 min52.6931.411.052.10.752.01
BC-110-0 min34.4343.216.972.720.881.8
BC-60-60 min26.5347.3820.293.230.981.59
BC-110-60 min20.1151.4223.83.431.171.24
Table 2. Physical and chemical properties of soybean straw biochar obtained by pyrolysis under different preparation conditions.
Table 2. Physical and chemical properties of soybean straw biochar obtained by pyrolysis under different preparation conditions.
pHECSSA
ms/cmm2/g
BC-60-0 min9.828.0631.3322
BC-110-0 min10.17.0145.6193
BC-60-60 min10.168.8279.6448
BC-110-60 min10.297.74115.3912
Table 3. Spearman correlation between soil organic matter and biochar’s SSA, pH, and EC.
Table 3. Spearman correlation between soil organic matter and biochar’s SSA, pH, and EC.
SSApHEC
Soil organic matterSpearman correlation−0.971 **−0.971 **−0.47
Significance (two-tailed)0.0000.0000.077
** indicates that the significance (two-tailed) is less than 0.01 and the correlation is very significant.
Table 4. Spearman correlation between fruit number, plant length, qualitative parameters, and biochar’s SSA, pH, and EC in capsicum.
Table 4. Spearman correlation between fruit number, plant length, qualitative parameters, and biochar’s SSA, pH, and EC in capsicum.
SSApHEC
The number of capsicum fruitSpearman correlation0.920 **0.943 **0.503
Significance (two-tailed)0.0000.0000.056
Capsicum plant lengthSpearman correlation0.910 **0.946 **0.394
Significance (two-tailed)0.0000.0000.146
HydrationSpearman correlation0.982 **0.925 **0.509
Significance (two-tailed)0.0000.0000.053
FatSpearman correlation0.944 **0.897 **0.393
Significance (two-tailed)0.0000.0000.148
Titrable aciditySpearman correlation0.982 **0.939 **0.480
Significance (two-tailed)0.0000.0000.070
Soluble solidsSpearman correlation0.944 **0.922 **0.477
Significance (two-tailed)0.0000.0000.072
** indicates that the significance (two-tailed) is less than 0.01 and the correlation is very significant.
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Xie, H.; Zhou, X.; Zhang, Y. Effects of Biochar under Different Preparation Conditions on the Growth of Capsicum. Sustainability 2024, 16, 6869. https://doi.org/10.3390/su16166869

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Xie H, Zhou X, Zhang Y. Effects of Biochar under Different Preparation Conditions on the Growth of Capsicum. Sustainability. 2024; 16(16):6869. https://doi.org/10.3390/su16166869

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Xie, Haiwei, Xuan Zhou, and Yan Zhang. 2024. "Effects of Biochar under Different Preparation Conditions on the Growth of Capsicum" Sustainability 16, no. 16: 6869. https://doi.org/10.3390/su16166869

APA Style

Xie, H., Zhou, X., & Zhang, Y. (2024). Effects of Biochar under Different Preparation Conditions on the Growth of Capsicum. Sustainability, 16(16), 6869. https://doi.org/10.3390/su16166869

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