Effects of Biochar and Dicyandiamide on Root Traits, Yield, and Soil N₂O Emissions of Greenhouse Tomato Under a Biogas Slurry Hole Irrigation System

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript ID: nitrogen-3828264 

Type of manuscript: Article

Title: Effects of Biochar and Dicyandiamide on Root Traits, Yield, and Soil N2O Emissions of Greenhouse Tomato under a Biogas Slurry Hole Irrigation System

 

The authors presented a valuable contribution to sustainable agriculture, effectively balancing yield optimization and emission reduction in greenhouse tomato systems. The experimental design is rigorous, and the AHP model studies were presented with detailed analysis.

There are some comments that the authors may consider in revising their manuscript as can be seen below:

 

• Soil pH and C/N ratio dynamics are mentioned but not quantified post-treatment; these are critical for interpreting nutrient retention and N₂O pathways, suitable discussion may be included.
• Though biochar plays a vital role, what will happen beyond 2% concentration, also biochar will alter the soil property over time, a discussion on long-term usage may be included.
• Discussion on results with other nitrification inhibitors (https://doi.org/10.1016/j.apsoil.2021.104295) will give merit and more insight into the process.
• In the introduction section, recent studies (published within the last 3-5 years) should be included to emphasize novelty and recent developments.
• Statistical analysis/error of the data is to be included in the materials and methods.
• The Error bar is to be included in the graph (Table 2, Fig 1).

Author Response

Thank you very much for taking the time to review our manuscript entitled “Effects of Biochar and Dicyandiamide on Root Traits, Yield, and Soil N₂O Emissions of Greenhouse Tomato under a Biogas Slurry Hole Irrigation System”. We sincerely appreciate your careful and conscientious evaluation. Your insightful suggestions are highly valuable and have been extremely helpful in improving our manuscript. We have carefully considered all the comments and have made the necessary revisions, which we hope meet your approval. The revised portions are highlighted using tracked changes in the document titled nitrogen-3828264 (text with changes Marked), where all modifications are clearly indicated. Below, we provide a summary of the main corrections made to the manuscript and our responses to the reviewer’s comments.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

General Comments

This manuscript presents a well-designed and timely study investigating the synergistic effects of biochar, dicyandiamide (DCD), and biogas slurry on greenhouse tomato production. The topic is of high relevance to the readership of Nitrogen, as it addresses the critical challenge of balancing crop productivity with environmental sustainability. The authors have done a commendable job in collecting a comprehensive dataset that spans crop physiology (root traits), yield metrics, and greenhouse gas emissions (N₂O). The experimental design is robust, and the primary conclusion—that the T5 treatment (2% biochar + DCD + slurry) offers the optimal balance of benefits—is well-supported by the data.

The study's primary strength lies in its holistic approach and the use of the Analytic Hierarchy Process (AHP) to integrate multiple, competing objectives into a single evaluation framework. This is a sophisticated approach that adds significant weight to the findings.

However, the manuscript's impact could be substantially enhanced. While the AHP provides a comprehensive ranking, the direct statistical results from the ANOVA offer a powerful, yet currently untapped, opportunity. I strongly encourage the authors to translate these statistical findings into a practical, tiered evaluation scheme for end-users (e.g., farmers, consultants). This would elevate the paper from a descriptive scientific report to a prescriptive, decision-making tool, greatly increasing its value to the agricultural community. By creating "performance clusters" based on ANOVA results and introducing secondary criteria like cost, the authors can provide a much more nuanced and actionable set of recommendations.

Overall, this is a valuable piece of research. The manuscript is well on its way to being suitable for publication. My recommendation is Accept with Minor Revisions, contingent on the authors addressing the specific points detailed below, with special attention to the suggestion of creating a practical evaluation framework.

 

Specific Comments

1. Abstract (Page 2)

The abstract, while accurate, lacks the quantitative "punch" to immediately convey the study's most significant findings. Revise the concluding sentence of the abstract to include key quantitative results. For example: "Compared to conventional fertilization, the T5 treatment significantly increased tomato yield by up to 8.13% and 10.19% across two seasons, respectively, while simultaneously reducing cumulative N₂O emissions by as much as 16.16%.

 

2. Materials and Methods (Page 3, Section 2.2)

The term 'hole irrigation', a method not standard in international literature, should be clearly defined upon its first use.

 

3. Discussion (Page 11-12) - Major Recommendation

The manuscript presents excellent statistical data but stops short of translating it into practical, easy-to-use advice. I strongly recommend adding a new subsection within the Discussion titled something like "From Statistical Significance to a Practical Evaluation Framework." In this section, the authors should: Use the ANOVA letter markings to group treatments into "performance clusters" (e.g., treatments with no significant difference in a key metric like IWUE).

Propose a tiered recommendation list:

Tier 1 (Integrated high performance): T5

Tier 2 (Efficient alternatives): T2, T3

Tier 3 (Intermediate / transitional): T1, T4 (if supported)

Reference conventional benchmarks: CK1, CK2

Optionally add a second layer incorporating amendment cost, operational complexity, and emission reduction priority for farm-level decision scenarios.

This framework will make the research far more impactful and directly useful for farmers and advisors.

 

4. Discussion (Page 11-12) - Methodological Limitations

The manuscript would be strengthened by explicitly acknowledging its methodological limitations. Please add a brief paragraph on "Limitations of the study" at the end of the Discussion. Acknowledge that sampling only at maturity captures the final outcome but not the dynamic process of root development, and suggest that future studies could benefit from sampling at Key stages of plant growth.

 

5. Results and Discussion (Page 8-9, Figure 1 & Table 4)

Please clarify if emissions are reported as N₂O or N₂O-N mass. Standardize the unit throughout the manuscript, for example, to 'Cumulative N₂O-N emissions (kg N-N₂O ha^-1)'.

 

6. Conclusion (Page 12)

The conclusion is solid but could be more forward-looking. Please add a final sentence to suggest future research directions or practical considerations. For example, mentioning the need for a "comprehensive cost-benefit analysis" to assess the economic viability of the T5 treatment would be an excellent addition.

 

7. “Introdution” → “Introduction”

Use lowercase “root traits” in running text (retain capitalization only in headings).

Correct the AHP formula: “CI = (λₘₐₓ − n)/(n − 1).” After recalculating, confirm CR < 0.10.

Standardize chemical notation: NH₄⁺-N, NO₃^--N; define PFPN once (PFPN = Yield/Applied N).

Units: adopt consistent superscript formatting (e.g., kg ha^-1 mm^-1).

Author Response

Thank you very much for taking the time to review our manuscript entitled “Effects of Biochar and Dicyandiamide on Root Traits, Yield, and Soil N₂O Emissions of Greenhouse Tomato under a Biogas Slurry Hole Irrigation System”. We sincerely appreciate your careful and conscientious evaluation. Your insightful suggestions are highly valuable and have been extremely helpful in improving our manuscript. We have carefully considered all the comments and have made the necessary revisions, which we hope meet your approval. The revised portions are highlighted using tracked changes in the document titled nitrogen-3828264 (text with changes Marked), where all modifications are clearly indicated. Below, we provide a summary of the main corrections made to the manuscript and our responses to the reviewer’s comments.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have answered the questions proposed by the reviewers. The revised manuscript can be accepted for publication in its present form.