Agronomic Effectiveness of Biochar–KCl Composites for Corn Cultivation in Tropical Soils

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors

My comments on your article are stated below.

Abstract Part:

Why is it important to optimize their use as full or partial substitutes for KCl in Brazilian agriculture? The first sentence of the abstract can begin by explaining why it is important.

Introduction Part:

The introduction section provides detailed information on the sources of potassium, potassium chloride, biochar and composed used. However, there is no explanation of the product corn grown. Why were corn chosen as plant material? What is the importance of corn for Brazil? It should be explained in a paragraph.

Although corn is generally used in the article, maize is used in some sentences. Either maize or corn should be used throughout the article.

Materials and Methods Part:

Authors reported that "The K contents found in the raw material were as follows: BP 6.2%, CH 2.6% and CM 3.0%. The potash contents of the biochar BP, CH and CM should also be stated.

The data of each feature in the formulas used in the calculation of parameters such as 𝐵𝑖𝑜𝑐ℎ𝑎𝑟 𝐾 𝑅𝑒𝑡𝑒𝑛𝑡𝑖𝑜n, 𝐾 𝑟𝑒𝑡𝑒𝑛𝑡𝑖𝑜n can be given as a supplementary table.

Why weren't BCM650 and CCM300 used as potassium sources?

What are the environmental conditions such as temperature and humidity in a green-house study?

Is there repetition in the pot study? What is the trial design? Were all applications carried out in only one pot?

The soil properties given in Table 2 would be more understandable if they were given horizontally.

Results Discussion Part

The results and discussion sections are too complex. There is too much data loading. These two sections can be given separately or divided into more subheadings.

Also, all figures should be more understandable.

Best regards,

Author Response

Comments and Suggestions for Authors

We appreciate the time and effort invested by the reviewer in evaluating our work and providing constructive feedback that contributed significantly to the revision of this manuscript.

Comments 1: Abstract Part: Why is it important to optimize their use as full or partial substitutes for KCl in Brazilian agriculture? The first sentence of the abstract can begin by explaining why it is important.

Response 1: Thank you for the suggestion. To clarify the relevance of optimizing KCl substitution in Brazilian agriculture, we added the following sentence at the beginning of the abstract: "Potassium chloride (KCl) is the main source of potassium (K) in Brazilian agriculture, but its high import dependency and the need for split applications increase costs and expose the system to supply and efficiency risks."

This change was made on page 1, line 8 of the revised manuscript.

 

Comments 2: Introduction Part: The introduction section provides detailed information on the sources of potassium, potassium chloride, biochar and composed used. However, there is no explanation of the product corn grown. Why were corn chosen as plant material? What is the importance of corn for Brazil? It should be explained in a paragraph.

Although corn is generally used in the article, maize is used in some sentences. Either maize or corn should be used throughout the article.

Response 2: Thank you for the comment. We agree with the suggestion and have added a paragraph in the introduction explaining the choice of corn as the model crop, highlighting its agricultural relevance in Brazil and its high potassium demand.

This change was made on page 3, line 107 of the revised manuscript.

Also, all occurrences of “maize” were changed to “corn” for consistency.

 

Comments 3: Materials and Methods Part:

Authors reported that "The K contents found in the raw material were as follows: BP 6.2%, CH 2.6% and CM 3.0%. The potash contents of the biochar BP, CH and CM should also be stated.

Response 3: Thank you for the comment. The potassium (K) content of the biochars is reported and discussed as one of the first results in the Results and Discussion section. This information is presented in Figure 1, located on line 441 of the manuscript.

 

Comments 4: The data of each feature in the formulas used in the calculation of parameters such as ????ℎ?? ? ????????n, ? ????????n can be given as a supplementary table.

Response 4: Thank you for the suggestion. The values related to Biochar K Retention and K Retention are already presented in Figure 1 and discussed in section 3.1.6 (lines 467–470).

 

Comments 5: Why weren't BCM650 and CCM300 used as potassium sources?

Response 5: Thank you for the question. The other biochars from the same feedstocks (BCM300 and CCM650) exhibited very similar chemical characteristics to BCM650 and CCM300, respectively, such as pH, electrical conductivity, carbon content, and potassium release profile. Therefore, we chose not to include them in the greenhouse experiment to avoid redundancy and to maintain a manageable number of treatments, ensuring experimental feasibility and statistical robustness.

 

Comments 6: What are the environmental conditions such as temperature and humidity in a green-house study?

Response 6: Thank you for the comment. The environmental conditions in the greenhouse have now been included in the Materials and Methods section. The following sentence was added: “The average daytime temperature in the greenhouse during the experiment was 35 °C, the nighttime temperature was 20 °C, and the mean relative humidity was 60%.”

This change was made on page 5, line 210 of the revised manuscript.

 

Comments 7: Is there repetition in the pot study? What is the trial design? Were all applications carried out in only one pot?

Response 7: Thank you for your comment. The information regarding the experimental design and repetition has now been included in the Materials and Methods section. The following sentence was added: “All treatments were arranged in a randomized block design in a greenhouse, with three replicates per treatment in each of two contrasting tropical soils, totaling 72 pots.”

This change was made on page 6, line 223 of the revised manuscript.

 

Comments 8: The soil properties given in Table 2 would be more understandable if they were given horizontally.

Response 8: Thank you for the suggestion. We opted to keep the vertical layout of Table 2 because it allows for a clearer grouping of related soil attributes (chemical, physical, and micronutrients), improving readability without segmenting the table into too many parts. However, we are open to adapting the format if the editorial team considers it necessary.

 

Comments 9: Results Discussion Part The results and discussion sections are too complex. There is too much data loading. These two sections can be given separately or divided into more subheadings.

Response 9: Thank you for the suggestion. We have reorganized the Results and Discussion section by introducing subheadings to enhance clarity and improve overall readability.

This change was made throughout section 3 (pages 8 to 23).

 

Comments 10: Also, all figures should be more understandable.

Response 10: Thank you for the comment. We have improved the figures by adjusting their visual design, increasing font size for better readability, and including statistical test results to enhance clarity and interpretability.

These changes were applied to all figures throughout the manuscript (Figures 1 to A3), starting from page 11.

 

We sincerely thank the reviewer’s insightful comments and remain at the journal’s and reviewers’ disposal for any additional modifications required to improve the manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript titled "Biochar-Based Potassium Fertilizers as an Alternative to KCl: Corn Growth in Contrasting Tropical Soils" focuses on the evaluation of different biochars produced from different biomasses for the production of potassium fertilizers with high agronomic value.
The main objective of this research work was to partially or completely replace the need for KCl in the supply of K to corn crops grown in two soils with contrasting textures and organic matter content. The topic addressed by authors is very interesting not only because very abundant by-products in Brazil are used for the production of biochar but also because they try to replace the use of KCl with innovative biochars.
The paper is well written and the data presented attracts the attention of the readers.
It needs some minor revisions before being ready for publication.
Title:
- It could be made more attractive considering the results obtained. The authors could remove the colon.
Abstrct:
- This part is clear and interesting.
Introduction:
- Some dated bibliographic references should be updated;
- Report some examples of effects in the use of biochar produced with the same raw materials under study;
- The paragraph regarding hypotheses and objectives is too long. It should be more concise.
Materials and methods:
- A bibliographic reference regarding the method used for the production of bichar is missing ;
- Why was only the value of total carbon presented? The analyzer used for the analysis allows to read also the organic and inorganic ones. These two data could be useful;
- A complete characterization of the experimental soils and related bibliographic references are needed. 
Results and discussions:
- Each parameter reported in table 3 must be provided with statistical analysis;
- In this section more references to similar paper are needed when discussing the results obtained;
- Figure 5: insert the statistical analysis.
Conclusions:
- This section should be rewritten. Authors should avoid re-presenting the results obtained by providing useful suggestions to Brazilian farmers to solve the problem of low K availability in soils.

Author Response

We would like to thank the reviewer for their careful reading of the manuscript and their thoughtful comments, which helped us improve the overall quality and clarity of the work.

Comments 1: Title: - It could be made more attractive considering the results obtained. The authors could remove the colon.

Response 1: Thank you for the suggestion. The title has been revised to make it more concise and attractive, reflecting the results obtained. The new title is: Biochar-Based Potassium Fertilizers as an Alternative to KCl for Corn Growth in Contrasting Tropical Soils.

Comments 2: Introduction: - Some dated bibliographic references should be updated;

Response 2: Thank you for the suggestion. While we agree on the importance of including recent literature, some of the references cited, particularly those regarding potassium essentiality and chloride toxicity, are classical works that remain scientifically valid and widely referenced in current studies. Nonetheless, we reviewed the introduction and ensured that more recent references were added where appropriate to complement the foundational ones.

 

Comments 3: Report some examples of effects in the use of biochar produced with the same raw materials under study;

Response 3: Thank you for the suggestion. Studies involving biochars produced from the same raw materials were cited throughout the manuscript to support the discussion of their properties and agronomic performance. However, it is important to note that, in most of these studies, the biochars were not evaluated specifically as potassium (K) sources. As a result, K content was often not reported or discussed in detail.

 

Comments 4: The paragraph regarding hypotheses and objectives is too long. It should be more concise.

Response 4: Thank you for the suggestion. We have revised the paragraph to make the presentation of the hypotheses and objectives more concise and easier to follow.

This change was made on page 3, lines 113 to 122 of the revised manuscript.

 

Comments 5: Materials and methods: - A bibliographic reference regarding the method used for the production of bichar is missing

Response 5: Thank you for the observation. A bibliographic reference has now been added at the end of the paragraph describing the biochar production method, as suggested.

This change was made on page 3, line 137 of the revised manuscript.

 

Comments 6: Why was only the value of total carbon presented? The analyzer used for the analysis allows to read also the organic and inorganic ones. These two data could be useful;

Response 6: Thank you for the comment. In this study, only total carbon was measured, as the vast majority of carbon in biochars is considered to be in the organic form. Therefore, separating the carbon fractions was not prioritized, since our objective was to assess the overall carbon content rather than distinguish between organic and inorganic forms. We agree that this information may be useful in other contexts and will consider it for future investigations.

 

Comments 7: A complete characterization of the experimental soils and related bibliographic references are needed. 

Response 7: Thank you for your suggestion. A complete characterization of the experimental soils was already included in Table 2 (page 6, line 252), along with methodological details and footnotes referencing the analytical procedures.

 

Comments 8: Results and discussions: - Each parameter reported in table 3 must be provided with statistical analysis;

Response 8: Thank you for the observation. Statistical analyses were applied to all parameters for which experimental replicates were available. However, for some parameters, such as biochar yield, only a single value was obtained per treatment due to the nature of the procedure and equipment used. Therefore, statistical comparisons were not possible for these specific cases, and the values are reported as single-point measurements.

 

Comments 9: In this section more references to similar paper are needed when discussing the results obtained;

Response 9: Thank you for the suggestion. We have added additional references to similar studies in the discussion section to strengthen the contextualization and support the interpretation of our results.

 

Comments 10: Figure 5: insert the statistical analysis.

Response 10: Thank you for the suggestion. Statistical analysis has been added to Figure 5 to improve the interpretation and comparison of the results.

This change was made on pages 19 and 20, line 681 of the revised manuscript.

 

Comments 11: Conclusions: - This section should be rewritten. Authors should avoid re-presenting the results obtained by providing useful suggestions to Brazilian farmers to solve the problem of low K availability in soils.

Response 11: Thank you for the comment. The Conclusions section has been rewritten to make it more concise and to focus on practical suggestions for Brazilian farmers regarding strategies to address low potassium availability in soils, as recommended.

This change was made on page 24, line 821 of the revised manuscript.

 

We are grateful for the reviewer’s insightful comments and remain at the journal’s and reviewers’ disposal for any additional modifications required to improve the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

I managed to read the manuscript Biochar-Based Potassium Fertilizers as an Alternative to KCl: Corn Growth in Contrasting Tropical Soils and I apologize for the delay in responding.
The paper presents a comprehensive study on biochar-based fertilizers as an alternative for corn cultivation. For biochar production, three different sources were used: banana peel, coffee husk and chicken manure. Each was used pure or as composite, and for each 2 different pyrolysis temperature were used, resulting in a high number of experimental factors. The analysis on two soil types and a larger number of analyzed aspects (eg. ash, C, pH, EC, CEC, Potassium release in 24 and 672 hours, agronomic effectiveness of the biochar) adds considerable value to the work.

The introductory part is clearly structured, the materials and working methods are presented in detail. The results clearly show the differences between the variants, so that conclusions can be drawn and recommendations can be offered for the two soil types analyzed. In table 3, the ±SE values could be checked, but in rest I did not notice any major problems. The references are consistent with the topic studied.

Author Response

We appreciate the time and effort invested by the reviewer in evaluating our work and for the thoughtful and encouraging comments on our manuscript.

Comments: The introductory part is clearly structured, the materials and working methods are presented in detail. The results clearly show the differences between the variants, so that conclusions can be drawn and recommendations can be offered for the two soil types analyzed. In table 3, the ±SE values could be checked, but in rest I did not notice any major problems. The references are consistent with the topic studied.

Response: We appreciate the recognition of the structure, experimental design, and the depth of analysis presented in the study. Regarding Table 3, statistical analyses were applied to all parameters for which experimental replicates were available. However, for some parameters, such as biochar yield, only a single value was obtained per treatment due to the nature of the procedure and equipment used. Therefore, statistical comparisons were not possible for these specific cases, and the values are reported as single-point measurements. No further major changes were necessary based on this feedback, but we remain available for any additional clarification the reviewer or editorial team may require.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors

Your article is more suitable for publication in its current form. I wish you good work.

Best regards,

Author Response

Thank you very much for your kind words and for the positive evaluation of our revised manuscript. We greatly appreciate your time and constructive feedback throughout the review process.

Reviewer 2 Report

Comments and Suggestions for Authors

After the authors' revision, the paper is significantly improved. Before it is ready for publication, the authors should pay attention to some suggestions.
Considering the submitted version, it is difficult to appreciate some changes such as the updated references in the introduction and references to similar studies in the discussion section. Therefore, it is suggested to submit a version with track change. Also, the title seems not to have been changed. I look forward to the new version of the paper.

Author Response

We sincerely thank the reviewer for the thorough and constructive feedback, which has contributed meaningfully to the improvement of our manuscript.

In response to the latest suggestions, we carefully reviewed the points raised and made the necessary adjustments to ensure the manuscript is clearer and more aligned with the expectations. We also acknowledge that certain revisions, such as the updated title and the inclusion of new references, were more thoroughly addressed in this latest version. We apologize for any lack of clarity in the previous submission and appreciate the opportunity to correct and expand these points. As requested, we have now submitted a revised version with all changes clearly marked using comments in the manuscript.

Regarding the title, it was previously only adjusted through punctuation. Following the reviewer’s suggestion to make it more attractive and reflective of the results, we have now revised it to: "Agronomic Effectiveness of Biochar-KCl Composites for Corn Cultivation in Tropical Soils." This version better captures the scope and findings of the research, highlighting the role of biochar-KCl composites as potassium sources and their agronomic performance in tropical soils, while remaining concise and technically appropriate.

In addition, several new references have been included throughout the Introduction and Discussion sections, particularly studies involving biochars produced from banana peel, coffee husk, and chicken manure, the same feedstocks used in this study. These references reinforce discussions related to yield, potassium content and FTIR characteristics. Although studies focused specifically on potassium release kinetics and greenhouse trials using these exact feedstocks remain limited in the literature, we discussed our results in light of similar studies that address comparable nutrient release mechanisms and agronomic applications.

Specifically, updated or newly added references appear in the manuscript at:

Lines 38, 39, 42-47, 101-105, 316, 321-323, 456-458, 499, 504-506, 693-695, 786-791, and 799-801.

We truly appreciate the reviewer’s detailed reading and helpful suggestions, and we remain at your disposal for any further clarification or revision that may be required.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors reply to the requested clarifications and improved the manuscript. I suggest accepting it for publication.

Author Response

We sincerely thank you for your thoughtful comments and support. Your feedback was essential to improving the clarity and quality of our manuscript.

Round 3

Reviewer 2 Report

Comments and Suggestions for Authors

After further revisions, the paper is ready for publication.