The Effect of Different Biochar Characteristics on Soil Nitrogen Transformation Processes: A Review

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript provides a detailed and systematic overview of the effects of different biochar characteristics on soil nitrogen conversion processes. The article is well written, but before receiving it, I suggest that several issues be addressed:

1. The manuscript was requested to undergo a second revision by the author a while ago, and I am very certain of the content to be revised. However, currently, the structure of the article still needs to be improved, especially the numbering of some titles. I believe this will help improve the completeness of the manuscript. There are some obvious issues that I have highlighted, hoping to be helpful to the manuscript: line 104 directly uses 2.1, But I think there should be a corresponding '2' and '1 Introduction'; In addition, I also suggest adding some serial numbers for lines 419 and 503.

2. Since this manuscript is intended to be published on “sustainability”, I believe a series of outlook sections should be added, including but not limited to the impact of biochar application on agricultural sustainability, soil greenhouse gas emissions reduction, and soil remediation.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Minor modifications

Author Response

Thank you so much for taking the time to review our article.  Your comments are very welcome and useful.

1. I have amended the numbering as requested near lines; 104, 149 and 516.
2. Thank you for this comment, we have revised the paragraph from 102 and hope this will suffice?

Reviewer 2 Report

Comments and Suggestions for Authors

Biochar is a type of charcoal that is produced by heating organic material in the absence of oxygen. It is used as a soil amendment to improve soil quality and fertility. Biochar application can influence soil nitrogen (N) cycle through biological and abiotic processes. The effect of different biochar characteristics on soil nitrogen transformation processes has been studied in several studies.

Thus, the aim of this review is to discuss how biochar with different characteristics obtained from different feedstocks and pyrolysis conditions affects each stage of the soil nitrogen cycle, including N2 fixation, assimilation, mineralisation and denitrification.

It can be clearly seen that the additions and changes highlighted in red are appropriate and greatly improve both the content and perception of this review.

However, the authors should note the following three critical comments.

1. Graphic summary and line 109. Please clarify in the box "Potential influences of biochar on fixation" and line 109 that you are talking about atmospheric N2 fixation and not NH4+ ion fixation in soil.

2. Figure 2.1. There are two comments on this figure. Firstly, the microorganisms are found in the rhizosphere of the plants, around the roots or on the root surface, but not in the roots of the plants. Secondly, ammonium ions are just as easily taken up by plant roots as nitrate ions.

Line 132-134. "This process is carried out by heterotrophic microorganisms, with the bacterium Nitrosomonas converting NH3 to NO2- and Nitrobacter converting NO2- to NO3- [42]".

Nitrification can be carried out by heterotrophic microorganisms as well as by archaea, but Nitrosomonas and Nitrobacter are autotrophic aerobic bacteria.

Good luck and success!

Author Response

Thank you so much for reviewing our paper!  Your comments are most welcome and have been extremely constructive.  We answer them as follows; 

1. We have amended the graphic and made the change at 121
2. Amended at 140 and 145
3. Amended at 143 (thank you for picking this up - everybody else missed it! :-)

Reviewer 3 Report

Comments and Suggestions for Authors

Review Comments for Manuscript ID sustainability- 2661979

The manuscript offers an insightful and comprehensive overview of the impact of biochar on soil properties and nitrogen cycling, emphasizing its potential for agricultural sustainability and environmental improvement. The authors have meticulously examined various aspects, including carbon composition, mineral content, surface area, porosity, cation exchange capacity, inhibitory substances, and pH, providing a thorough analysis of how these factors influence nitrogen fixation, assimilation, mineralization, and denitrification in soil.

After careful consideration, I would like to recommend this manuscript for publication in Sustainability (ISSN 2071-1050), provided the authors address a few minor revisions. These suggestions are outlined below:

1.      Keywords: I suggest considering the addition of the keyword "Soil Amendment," as it is highly relevant and reflects the authors' emphasis on soil improvement through biochar, as highlighted in their review work.

 

2.      Graphical Abstract: I would like to commend you on the exceptional Graphical Abstract accompanying your review. It encapsulates the key themes explored in the review. Not only is it aesthetically appealing, but it also serves as an inviting entry point for readers, providing a clear and concise overview of the review's focal points.

 

3.      Lines 53-61: What is the impact of biochar pH on soil properties, and how does this factor influence the effectiveness and functionality of biochar under varying pH levels in both the biochar and the soil? It would be interesting to include a sentence that broadly incorporates this relationship, emphasizing the significance of biochar pH in its interaction with soil.

 

4.      About the sentence in lines 64-67: Could you please provide further details or clarify this point? The current sentence may be a bit complex and could benefit from a clearer and more precise wording to ensure complete understanding. The current relationship between the volatile matter of the biochar and the microorganism growth is not entirely clear.

 

5.      Lines 124-125: Your 'Simplified Nitrogen Cycle' diagram is exceptionally clear and provides a highly descriptive representation of the various phases involved in nitrogen fixation. Well done! It's a great visual aid for understanding the nitrogen cycle.

 

6.      In lines 246-252, what do the authors attribute the difference in the percentage of organic residue decomposition between sandy and sandy loam soils to?

 

Sincerely,

Comments for author File: Comments.pdf

Comments on the Quality of English Language

I have suggested to the authors to enhance or rephrase specific sentences as indicated in the overall reviews.

Author Response

Thank you very much for taking the time to read our paper, your comments are sincerely appreciated.

1. Changed - thank you
2. Thank you!
3. Hopefully this is now addressed at lines around 63?
4. Hopefully this point is clearer now - lines around 70
5. Thank you!
6. This hopefully is address in paragraph beginning 256?

Reviewer 4 Report

Comments and Suggestions for Authors

General comments

-This manuscript, by authors, studied “

“The Effect of Different Biochar Characteristics on Soil Nitrogen Transformation Processes. A Review.”.

Overall, the topic is of interest to Sustainability, readers. However, following are the specific comments on the article concerns, before publication as minor revision.

Specific Comments and Suggestions

-Abstract

 -better to mention feedstock’s details.

-Give quantitative results.

-What amount of biochar? Detail results?

-Introduction

 -Need to summarize and be specific with your concerned study.

- Soil role? Physical properties? Biochar preparation and on application.

-Can add more recent references.

-“Table 1.1 Selected physical and chemical parameters for a range of biochars.” For biochar preparation? What about application?

-Objectives?

-“[45]-[47].” Check journal guidelines.

-“The untreated biochar soil treatment planted with Phaseolus vulgaris resulted in an increase of 2126% in nitrogen fixation over the control average (as well as a 262 % increase in shoot biomass, 164 % increase in root biomass, 3575 % increase in nodule biomass).” Recheck results?

-Revise fig. 2.3 to clear view.

Conclusions

-“The main findings are, dependent on biochar and soil type.” Not explained well about it

-Too general. What is your specific findings?

 

 

Author Response

Thank you very much for taking the time to review our paper.  Your comments were very much appreciated.

1. As this was a review of 150 articles, we didn't feel we could mention the feedstock, any quantative results or the amount of biochar used in the abstract - as there might be over 100 feedstocks to mention.
2. We've further summarised the intention of the study at 103.
3. We feel soil, physical properties, biochar prep have been addressed , throughout the text e.g. 127,133,140,183,204, 210,227,319,492,506.
4. More recent references have been added.
5. Table 1.1 We couldn't squeeze any additional data into this table and, as this is a review only, it was felt that discussion of any pyrolsysis condition or application rates would be best placed in the discussion.
6. Journal guidelines checked - amended throughout - thank you
7. Yes, reference double checked.
8. Moved figure 2.3
9. Conclusions re-written - thank you!