The Sustainable Management of Nitrogen Fertilizers for Environmental Impact Mitigation by Biochar Applications to Soils: A Review from the Past Decade

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In this paper, the authors statistically analyzed data from selected studies available in the literature and presented the results based on that analysis. However, they did not provide a comprehensive literature review. Therefore, it is unclear whether this paper can be classified as a proper review article.

The abstract could benefit from a stronger concluding statement that synthesizes the overall implications of the review. For instance, a brief remark on how biochar can be applied effectively in agriculture to reduce nitrogen losses and improve sustainability would provide a more conclusive ending to the abstract.

The Introduction part is too detailed in some parts and could be shorter and clearer. The research goal should be explained earlier, and the knowledge gap and references need to be more clearly and consistently presented.

The authors should clearly highlight the novelty of their study and explicitly state the main purpose of the work. Without this, it is difficult to understand what new contribution the paper offers to the existing body of knowledge.

The conclusion provides a good summary but lacks specificity and critical reflection. The authors should clarify the novelty of their findings and how they contribute to existing knowledge. Claims such as “biochar can effectively mitigate N losses” need to be supported by more precise data. Additionally, the suggestion for further research is too vague; more specific recommendations for future studies are needed.

 

 

Author Response

Reviewers’ Comments to Author and response to the comments
(Page and Line numbers [P, L] indicate where changes/additions were made in the revised manuscript)

 [Reviewer: 1]
In this paper, the authors statistically analyzed data from selected studies available in the literature and presented the results based on that analysis. However, they did not provide a comprehensive literature review. Therefore, it is unclear whether this paper can be classified as a proper review article.
Thank you for your time and insightful comments on our manuscript, “Sustainable Management of Nitrogen Fertilizers for Environmental Impact Mitigation by Biochar Application to Soils: A Review from the Past Decade” (environments-3658397). We appreciate the constructive feedback, which has helped us to improve the quality and clarity of our manuscript. We have carefully considered all comments and have revised the manuscript accordingly. Below, we provide a point-by-point response to the issues raised.

 

1. The abstract could benefit from a stronger concluding statement that synthesizes the overall implications of the review. For instance, a brief remark on how biochar can be applied effectively in agriculture to reduce nitrogen losses and improve sustainability would provide a more conclusive ending to the abstract.
   We agree with your suggestion. We have revised the concluding part of the Abstract to better synthesize the overall implications and provide a more conclusive statement on the effective application of biochar.
   We revised the part of ending the Abstract such as “Overall, biochar application demonstrates significant potential to mitigate N losses and improve N use efficiency, thereby supporting sustainable agriculture, however, its effectiveness is optimized when biochar properties (e.g., high SSA, appropriate C/N ratio) and application strategies are tailored to specific soil types and N sources.” in the revised manuscript (P1, L34–38).

 

2. The Introduction part is too detailed in some parts and could be shorter and clearer. The research goal should be explained earlier, and the knowledge gap and references need to be more clearly and consistently presented.
   The Introduction section has been revised as follows:
   Conciseness and Clarity:
   Detailed descriptions regarding the historical background of nitrogen fertilizers (e.g., the Haber-Bosch process) and global fertilizer consumption trends (related to  in the original manuscript) have been significantly condensed to focus on information directly relevant to the problem statement.
   The explanatory section on biochar has been substantially streamlined, retaining only the most essential information.
   
   Earlier presentation of research goals and clearer definition of knowledge gap:
   In the revised 4th paragraph, the limitations of existing reviews (e.g., insufficient data analysis in reviews from a decade ago, recent reviews focusing on individual N loss pathways, lack of comprehensive evaluation) are specifically highlighted to clearly define the knowledge gap.
   The subsequent 5th paragraph now explicitly presents the objective of this study (to fill this gap) and its novelty (quantitative correlation between physicochemical properties and multiple N loss pathways, based on data from the last decade).
   
   Presentation of structure (also partially addressing comment by Reviewer 2):
   Finally, a paragraph concisely outlining the overall structure of the manuscript has been added. This also partially addresses Reviewer 2’s comment about clarifying the structure of Section 3 at the end of the Introduction.
   We believe these revisions have made the Introduction more focused, with a clearer presentation of the research objectives and its positioning within existing research (the knowledge gap).

 

3. The authors should clearly highlight the novelty of their study and explicitly state the main purpose of the work. Without this, it is difficult to understand what new contribution the paper offers to the existing body of knowledge.
   We have addressed this by revising the Introduction section to explicitly state the novelty and main purpose of this study.
   Specifically, in the fourth paragraph of the Introduction, the limitations of previous reviews (lack of data analysis, focus on individual N loss pathways) were pointed out, and the knowledge gap of the lack of comprehensive evaluation was clarified in the revised manuscript (P2, L69–80).
   The following fifth paragraph described the specific objectives of this study to fill the above knowledge gap, the novelty of linking with physicochemical properties, and the expected outcome of contributing to sustainable agriculture in the revised manuscript (P2, L81–92).

 

4. The conclusion provides a good summary but lacks specificity and critical reflection. The authors should clarify the novelty of their findings and how they contribute to existing knowledge. Claims such as “biochar can effectively mitigate N losses” need to be supported by more precise data. Additionally, the suggestion for further research is too vague; more specific recommendations for future studies are needed.
   Thank you for your comments regarding the conclusions. We have revised the conclusions to be more specific by incorporating the precise quantitative findings from the review (e.g., biochar properties (pH, SSA, C/N ratio, etc.) and specific mitigation effect for NH₃, NO₃^–, and N₂O) in the conclusions in the revised manuscript (P17, L612–P18, L634).
   Critical discussion was also added to account for the effects of variability, such as increased NH₃ volatilization at higher ash content and increased N₂O in clayey soils in the revised manuscript (P17, L613–615 / P18, L631–632). In addition to that, we mentioned that the mechanism of biochar N loss reduction is not universal in all conditions, and it depends on many factors and conditions in the revised manuscript (P18, L638–642).
   Finally, we replaced vague suggestions for future research with specific recommendations for (i) long-term field studies, (ii) investigation of microbial mechanisms, (iii) development of predictive models, and (iv) consideration of synergistic effects in the revised manuscript (P18, L644–654).

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript aims to evaluate the potential of biochar to mitigate nitrogen losses and, therefore, the resulting environmental impacts.

Even though the work done is evident, some gaps must be filled.

• Too many reviews are cited among the references, rather than the original articles that report the results being discussed. Furthermore, it is claimed that specific roles of biochar functional groups have been examined; however, this analysis has not actually taken place.
• Section 2.1 "Data Collection" mentions the selection criteria for inclusion, but not the exclusion criteria (among these, we generally have reviews or articles that do not clearly report the types of pyrolysis treatments or tests on plants). 
• Section 2.1 "Data Collection" does not report the number of articles examined from the beginning, before proceeding to the selection according to the defined criteria. Furthermore, it is not clear what n=100, 101, or 102 means.
• To enhance readability, I believe the authors should clarify the structure of Section 3, "Results and Discussion," at the end of the Introduction. This section is quite lengthy and contains numerous paragraphs and subparagraphs.

For detailed comments, see the attached file

Comments for author File: Comments.pdf

Author Response

Reviewers’ Comments to Author and response to the comments
(Page and Line numbers [P, L] indicate where changes/additions were made in the revised manuscript)

 [Reviewer 2]
The manuscript aims to evaluate the potential of biochar to mitigate nitrogen losses and, therefore, the resulting environmental impacts.
Even though the work done is evident, some gaps must be filled.
Thank you for your time and insightful comments on our manuscript, “Sustainable Management of Nitrogen Fertilizers for Environmental Impact Mitigation by Biochar Application to Soils: A Review from the Past Decade” (environments-3658397). We appreciate the constructive feedback, which has helped us to improve the quality and clarity of our manuscript. We have carefully considered all comments and have revised the manuscript accordingly. Below, we provide a point-by-point response to the issues raised.

 

1. Too many reviews are cited among the references, rather than the original articles that report the results being discussed.
   Thank you for your comment regarding the citation of review articles. We have addressed this by carefully re-examining our references. Review articles not directly relevant to the discussion have been removed. Where appropriate, particularly in the Introduction, citations to review papers have been replaced with references to original research articles that directly support the statements being made. Furthermore, the Introduction was significantly condensed from the initial submission (i.e., previous manuscript), in part to address feedback from Reviewer 1 regarding conciseness, which also resulted in the automatic removal of many review and meta-analysis articles, leading to a greater emphasis on primary sources.

 

2. Furthermore, it is claimed that specific roles of biochar functional groups have been examined; however, this analysis has not actually taken place.
   We appreciate your comment. We have revised the manuscript to more accurately reflect our analytical focus. First, we did not perform any analysis on the specific role of surface functional groups, so we removed that sentence. In the Abstract, “physicochemical properties” has been changed to “measurable physicochemical properties” in the revised manuscript (P1, L22). In the Introduction, now we state that the analysis focuses on “overall physicochemical characteristics”, such as pH, CEC, and SSA in the revised manuscript (P2, L84–87). This approach was adopted because these broader parameters are more commonly and quantitatively reported across the diverse studies included in our compilation, whereas consistent, detailed data on specific surface functional groups were insufficient for a direct, comparative quantitative analysis at this scale.

 

3. Section 2.1 “Data Collection” mentions the selection criteria for inclusion, but not the exclusion criteria (among these, we generally have reviews or articles that do not clearly report the types of pyrolysis treatments or tests on plants).
   Thank you for pointing this out. While our inclusion criteria inherently defined exclusions, we agree that making these explicit enhances clarity. We have added a detailed list of exclusion criteria to Section 2.1, immediately following the inclusion criteria and before stating the number of selected studies in the revised manuscript (P3, L119–127). This newly added explanation specifies that studies were excluded if they were, for example, review articles themselves, lacked quantitative data for both control and biochar treatments, used modified (treated) biochar, or lacked essential experimental details.

 

4. Section 2.1 "Data Collection" does not report the number of articles examined from the beginning, before proceeding to the selection according to the defined criteria. Furthermore, it is not clear what n=100, 101, or 102 means.
   Thank you for your suggestions. We have revised Section 2.1 to enhance clarity by including the initial number of articles identified and screened before applying the detailed inclusion and exclusion criteria in the revised manuscript (P3, L110–113).
   Furthermore, we have explicitly defined “n” (e.g., n=101 for NH₃ volatilization) immediately after listing the selected studies, clarifying that it represents the total number of individual data points (observations or treatment means) extracted for each N loss pathway from the compiled studies in the revised manuscript (P3, L129–131).

 

5. To enhance readability, I believe the authors should clarify the structure of Section 3, “Results and Discussion,” at the end of the Introduction. This section is quite lengthy and contains numerous paragraphs and subparagraphs.
   Thank you for great suggestion. We have added the following sentence to the end of the Introduction to clarify the structure of Section 3 (Results and Discussion) in the revised manuscript (P3, L93–102):
   “The subsequent sections of this review are structured as follows: Section 2 details the methodology for data compilation and analysis. Section 3, ‘Results and Discussion,’ forms the core of the paper. It begins with an analysis of biochar physicochemical properties based on feedstock type (Section 3.1). It then systematically evaluates the mitigation effects of biochar on NH₃ volatilization (Section 3.2), NO₃^–-N leaching (Section 3.3), and N₂O emission (Section 3.4). Each of these subsections is further divided to discuss the in-fluence of biochar’s intrinsic physicochemical properties first, followed by the impact of various experimental conditions. Principal component analyses (PCA) are also presented within these sections to elucidate complex interactions. Finally, Section 4 provides overall conclusions and suggests directions for future research.”

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have accepted the reviewer’s suggestions and revised the manuscript accordingly

Reviewer 2 Report

Comments and Suggestions for Authors

The authors improved a lot their manuscript. Now it is OK!