Biochar Boosts Pepper Yield and Soil Health in Protected Continuous Cropping Systems in China

Round 1

Reviewer 1 Report (Previous Reviewer 3)

Comments and Suggestions for Authors

I am happy about the modifications

congratulations 

Author Response

We are truly delighted to hear that the reviewer is happy with the modifications. Thank you so much for the encouraging words and for your congratulations. We greatly appreciate the reviewer’s time, expertise, and constructive input throughout the review process, which has significantly improved our manuscript.

Reviewer 2 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

This study investigates the effects of continuous cropping in protected pepper production on acidic red soils in southern China by analyzing yield, soil physicochemical properties, enzyme activities and microbial community structure. Although the data analysis is comprehensive, the manuscript requires improvements in methodology organization and clarity.

The introduction highlights soilborne pathogens and diseases as major challenges in continuous cropping and discusses suppression of pathogen-related microbial taxa. However the results section lacks data on disease incidence or severity. Since disease measurements were not conducted the paper should avoid implying that biochar suppresses disease beyond what microbial data support.

The winter-spring 2021 stubble experiment included four treatment levels (0, 2, 4, and 6%), with the 10% treatment introduced only from the autumn-winter 2021 stubble. This creates an unbalanced dataset for the initial season preventing dose-response modeling across all five treatment levels for the entire period. Thus tables and statistical analyses for the first season should clearly note this limitation.

Section 3.4 appears twice: once for "Composition and Carbon Distribution of Soil Aggregates" (line 368) and again at line 418

The study combined soil from 10 pots into one composite sample, then used three subsamples as replicates, causing pseudo-replication. This invalidates ANOVA degrees of freedom. The authors must justify this or acknowledge it as a limitation.

The authors state that the fourth crop yield decreased by 78% compared to the third crop. However Table 1 shows the third crop (winter-spring stubble 2022) yielded 252–374 g/plant, while the fourth crop (autumn-winter stubble 2022) yielded only 55 g/plant. This large difference likely reflects seasonal factors as autumn-winter stubbles consistently produce lower yields. The authors should distinguish seasonal effects from continuous cropping impacts and or justify  their interpretation.

Author Response

Thank you very much for your handling of our manuscript. We have prepared a point-by-point response to all reviewer comments in the attached file. Please see the attachment. We greatly appreciate your time and effort.

Author Response File: Author Response.pdf

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

The study presents an evaluation of the addition of biochar on pepper growth and soil properties. To this end, it includes two approaches: incubation and pot experiments conducted between 2021 and 2022, from which physicochemical and microbial indicators of soil, as well as plant growth parameters, were obtained. Overall, the manuscript is well structured and the methodological design is appropriate, generating consistent results. However, several aspects need to be strengthened in the introduction and in the interpretation of the results, particularly regarding the articulation of findings under a soil health framework, as well as a deeper discussion of soil processes and microbial functions. Before recommending publication, the following revisions should be addressed:

In the title, the term “synergistically” could be removed, as it is ambiguous and suggests interaction with another amendment or management practice.

Abstract (lines 25–35): Quantitative results should be included, and the abstract should not exceed the word limit recommended by the journal.

Keywords: These should be reconsidered. Avoid repeating terms already included in the title and abstract.

The introduction should cover the key aspects of the research, clearly state the novelty of the study, and present a well-defined hypothesis. The concept of soil health and its relationship with amendments such as biochar and productivity should be developed. The scientific problem must be clearly formulated.

Line 41: Scientific names should be written in italics.

Line 100: Specify the soil type according to USDA Soil Taxonomy or WRB classification.

Lines 102–105 and 118–120: What is the standard deviation of these properties? Were they measured only once? What methods were used? Key properties of the initial soil characterization should be reported, particularly texture and water retention, as they are essential for controlling the incubation experiment.

Lines 133–135: Provide a detailed characterization of the biochar, including point of zero charge and functional groups, to better understand its interaction mechanisms with soil.

Lines 143–147: Application rates of 6–10% are relatively high for field conditions. Are they technically and economically feasible? The justification should be improved and supported with references. Express doses in units of t/ha to better reflect their real-scale equivalence.

The discussion section is weak and should be reorganized with subsections for each main result. In particular, the analysis of changes in physicochemical properties is presented in a fragmented manner. An integrated discussion is required, linking these changes to soil fertility functions and ensuring consistency with the “soil health” concept stated in the title. It is also necessary to address variability among different types of biochar. Are these results transferable? The role of biochar production processes and feedstock should be discussed to ensure its effectiveness in improving soil functions.

A separate subsection should address enzymatic activity and microbial diversity. Although key microbial groups and their relationships with specific properties are identified, the discussion should be expanded to consider the integrated role of microbial consortia in soil processes over time and their contribution to soil health.

There is no detailed discussion of crop yield. Results should be linked to soil management practices and yield indicators from a practical perspective. A section on practical implications should be added, addressing the scalability and applicability of the findings.

Lines 712–721 are redundant, as they repeat previously stated ideas.

The conclusions should avoid repeating results and discussion. A concise conclusion should be reformulated in alignment with the initial hypothesis of the study.

Author Response

Thank you very much for your handling of our manuscript. We have prepared a point-by-point response to all reviewer comments in the attached file. Please see the attachment. We greatly appreciate your time and effort.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report (Previous Reviewer 2)

Comments and Suggestions for Authors

The manuscript has been substantially improved and may now be considered for publication in the journal

Reviewer 3 Report (New Reviewer)

Comments and Suggestions for Authors

The revisions and clarifications were properly incorporated into the new version of the manuscript.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review of the manuscript entitled "Biochar Application Synergistically Enhances Pepper Yield and Improves Soil Microecology under Protected Continuous Cropping in Red Soil Region of China”

 

Detailed notes:

1. Line 15-25: The abstract needs to be rebuilt, lines 15-25 need to be shortened because they do not contribute anything scientific.
2. Line 26: Explain what the phrase "The optimal increase in yield" means.
3. Line 27: „The increase in application of biochar increased the soil pH and contents of organic matter …” - Is this surprising or revealing?
4. Line 30-34: “The activities of soil soil key enzymes increased significantly. The application of biochar notably changed the rhizosphere soil microbial …” It is not clear what should be understood by the above-mentioned provision "significantly increased";"clearly changed the structure of soil microorganisms".
5. The abstract requires rewriting to reflect key results and findings.Authors should clearly state what growth they are reporting (e.g., % relative to control) and what population changes (e.g., in the number or abundance of a given microorganism) occurred.Currently, the abstract has no scientific value.
6. Line 48: “high-tem perature pyrolysis of biomass” - explain and justify.
7. Line 57-62: The impact of BC on microbial populations is described very generally.In essence, the authors see only positive effects of BC application to soil, and therefore on microbial communities.Are there actually no negative effects of such treatment, or does the relationship between fertilization, soil properties, microorganisms, and plants operate solely within a homeostatic framework?I believe the authors should consult more literature and present the actual relationships occurring in the environment under the influence of changes resulting from BC application.
8. Comparing the very ambitious assumptions and goals of the research “The specific research objectives were as follows: (1) to clarify the effects of adding different rates of biochar on the yield of pepper, physicochemical properties of the soil, and contents of nutrients; (2) to elucidate the impacts of adding different rates of biochar on the structure and stability of soil aggregates and the distribution of soil organic C; and (3) to reveal the characteristics in the variation of soil microorganisms after adding different rates of biochar and their relationships with the physicochemical properties of soil” Conclusions: I regret to say that the authors failed to clarify the issues raised, but only to establish a better or worse effect of the BC supplement.These research assumptions clearly indicate that at least an attempt was made to describe the mechanisms of action, which I did not notice in the reviewed manuscript.
9. Line 97-98: The conditions under which the experiment was conducted should be described in detail.The current format is unacceptable.
10. Line 102-105: Describe BC production precisely: how long was the straw dried, to what size was the straw chopped, and the time it took to reach the proper temperature and the cooling time.Explain what anaerobic conditions mean.
11. Line 116-122: Describe in detail the plant growth and development protocol, what treatments were performed during the growing season, how optimal soil moisture was determined for various BC doses, and what water was used to water the plants. Present the procedure for maintaining soil moisture, explain, and complete the statement "All treatments were managed with identical water and fertilizer conditions."This is a scientific study; all conditions should be described in detail to provide clarity and ease of comparison between different studies.
12. Line 132: I understand that the humidity given referred to the atmosphere in the incubator.So what was the soil mass humidity and how was it maintained?
13. Line 136-142: Were the roots removed from the soil clod?
14. Line 144-160: It is not clear in which samples the ezyme determinations were performed?
15. Line 248-251:The authors demonstrate that pepper yield increases are generally related to the BC dose.The question is, did the authors balance the amount of nutrients introduced into the soil with the BC dose?Please provide a scientific explanation for the pepper yield increase.
16. Line 253-258: note as above.
17. Line 265: Can you scientifically explain such a drastic decline in organic matter content in such a short time?
18. Line 266-272: Is this groundbreaking? Calculate the load of ingredients brought with BC doses - it is presented in the study.
19. Line 286-288: Explain whether such a rapid increase in the number of microorganisms in the soil is appropriate.Furthermore, microorganisms require carbon, nitrogen, and other nutrients.Wouldn't this situation conflict with the limited availability of nutrients like N for plants?
20. Line 294-295: Should we have expected different results?
21. Line 378-383: Explain scientifically what the mechanism of action of BC is in terms of such effective changes in biodiversity - such an explanation is missing in the discussion.

Summary: The manuscript requires significant work to complete. The resulting summary should be consistent with the assumptions.

Reviewer 2 Report

Comments and Suggestions for Authors

The study aims to elucidate the effects of varying biochar rates on pepper yield and soil physicochemical properties, to clarify their impact on soil aggregate structure and to investigate soil microorganism variation and their relationships with soil properties. This research methodologically addresses a critical issue in protected agriculture. The two-year duration and inclusion of multiple cropping cycles substantially enhance the robustness of the findings. Minor revisions are recommended as outlined below:

-The title is too long. It is advisable to shorten it to enhance clarity and conciseness.

-Lines 25–29: The phrase “application of an appropriate amount of biochar” should be clarified by specifying the exact quantity considered appropriate and indicate any significant changes observed as a result of its application.

-Line 32: The phrase “intensive effect” lacks clarity and should be either rephrased or defined.

 

-Provide justification in the Introduction or Materials and Methods section explaining why pot experiments were selected for this study instead of field trials.

-Please provide detailed information concerning the greenhouse environmental conditions, including temperature, humidity, etc.. Furthermore, describe the water management and fertilization protocols implemented during the study.

-Please specify the duration and conditions of the incubation period.

 

-The reported biochar application rates reported, reaching up to 10% w/w, are notably high for field-scale horticultural practices. It is necessary to provide justification for these rates based on relevant literature.

-Biochar characterization of biochar is inadequate. It is recommended to include additional data, such as the C:N ratio and CEC to provide a more comprehensive analysis.

-Lines 110–115: An inconsistency exists between the biochar application rates employed in the pot experiments (2–10%) and those used in the incubation experiments (2.5–10%). Please provide a justification for this discrepancy, with particular emphasis on the rates applied during the initial cropping cycle.

-Clearly describe the number of replications per treatment in the pot experiments, as well as the number of pots allocated to each treatment.

-In the Statistical analysis section  specify the statistical model used (e.g., the type of ANOVA, post-hoc tests applied, and the number of samples per treatment and replicate). Additionally, indicate whether tests for normality and homogeneity of variance were conducted.

-Beneath each table, include a clear explanation of the meaning of the letter symbols.

-Line 249 states that “the yield of the fourth crop decreased by 77.88% compared with that of the third crop.” This significant decline necessitates further elucidation. It is recommended to discuss potential factors contributing to this substantial reduction in yield.

-The Conclusions section or in a separate section before the Conclusions should include a discussion of the study's limitations and future research.

 

Comments on the Quality of English Language

The study aims to elucidate the effects of varying biochar rates on pepper yield and soil physicochemical properties, to clarify their impact on soil aggregate structure and to investigate soil microorganism variation and their relationships with soil properties. This research methodologically addresses a critical issue in protected agriculture. The two-year duration and inclusion of multiple cropping cycles substantially enhance the robustness of the findings. Minor revisions are recommended as outlined below:

-The title is too long. It is advisable to shorten it to enhance clarity and conciseness.

-Lines 25–29: The phrase “application of an appropriate amount of biochar” should be clarified by specifying the exact quantity considered appropriate and indicate any significant changes observed as a result of its application.

-Line 32: The phrase “intensive effect” lacks clarity and should be either rephrased or defined.

 

-Provide justification in the Introduction or Materials and Methods section explaining why pot experiments were selected for this study instead of field trials.

-Please provide detailed information concerning the greenhouse environmental conditions, including temperature, humidity, etc.. Furthermore, describe the water management and fertilization protocols implemented during the study.

-Please specify the duration and conditions of the incubation period.

 

-The reported biochar application rates reported, reaching up to 10% w/w, are notably high for field-scale horticultural practices. It is necessary to provide justification for these rates based on relevant literature.

-Biochar characterization of biochar is inadequate. It is recommended to include additional data, such as the C:N ratio and CEC to provide a more comprehensive analysis.

-Lines 110–115: An inconsistency exists between the biochar application rates employed in the pot experiments (2–10%) and those used in the incubation experiments (2.5–10%). Please provide a justification for this discrepancy, with particular emphasis on the rates applied during the initial cropping cycle.

-Clearly describe the number of replications per treatment in the pot experiments, as well as the number of pots allocated to each treatment.

-In the Statistical analysis section  specify the statistical model used (e.g., the type of ANOVA, post-hoc tests applied, and the number of samples per treatment and replicate). Additionally, indicate whether tests for normality and homogeneity of variance were conducted.

-Beneath each table, include a clear explanation of the meaning of the letter symbols.

-Line 249 states that “the yield of the fourth crop decreased by 77.88% compared with that of the third crop.” This significant decline necessitates further elucidation. It is recommended to discuss potential factors contributing to this substantial reduction in yield.

-The Conclusions section or in a separate section before the Conclusions should include a discussion of the study's limitations and future research.

 

Reviewer 3 Report

Comments and Suggestions for Authors

i am very interested by this subject and off course i have some comments.

INTRODUCTION

Very good introduction which explains the objectives of this research but why biochar? why you did not choose compost? you did not said any word on compost which is also soil amendment.

you did not tell us also which kind of organic amendment or fertilizer the farmers are using currently for pepper crop.

 

MATERIAL & METHODS

Even the period march 21 to december 22 is quite big it is not enough for such studies. 

Do you think the soil you used can be representative of the soil used in China for pepper crop?

I also noticed that the soil used is not poor in organic matter. This may affect the response to biochar application.

You did not explained the choice of varieties. Are they mostly used by the farmers?

You also did not explained the choice of this biochar. you know that results may be different if you take another biochar.

Three replicates are not enough for such studies!!

 

RESULTS

I see the improvement in yields but what is the normal yield obtained by the farmers in China. Furthemore, concerning the impact on physico chemical properties of soil it will be more interesting and more realistic if you select soils from different farms  because the impact of rain, temperature, wind, animals...is very important.

Very interesting results in table 5.

I think there is big mass of results in this study and the discussion was very good. However as you said by yourself in the conclusion, this greenhouse experiment and the results are not necessary the same in the field conditions. Therefore you should try to explain us how the chineese farmers can improve their pepper crop by using your results and what is the cost of using biochar comparatively with the current cost.