New Insights into the Enhancement Effect of Exogenous Calcium on Biochar Stability during Its Aging in Farmland Soil
Round 1
Reviewer 1 Report
The manuscript entitled ‘’ New insights into the enhancement effect of exogenous calcium on biochar stability during its aging in farmland soil’’ is very interesting work, innovative and significant findings. Actually, studies like this are passing the era of usual biochar experiments that are running out similarly for two decades. So, this is the big point for this work. However, there are some points that could be helpful for improvement of the manuscript.
-Please make the abstract shorter than the current version. Method and results can be reduced a bit!
Line 45: which is closely related to biochar stability -> Is this statemnet your opinion? If YES, its kind of hypothesis and here is not the currct place for it, but at th eend of introduction would be ok. If NOT, please bring a reference for this and introduce one study at least that mentioned this point before.
Lines 72-73: many researchers found that adding exogenous minerals (K, Na, Ca, 72 Mg, Fe, Al, P, Si, etc.) in feedstock before pyrolysis could improve C stability by changing 73 the compositions and structure of biochar. -> Before this please give readers a background of biochar modification in all. Then specify it with your idea about adding mineral. Here are two about that fit here, you can add them: https://doi.org/10.1002/ldr.4464 and https://doi.org/10.3390/su15097158
Good luck!
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
General Comments:
The study explores the influence of exogenous calcium on the stability of biochar during aging processes in farmland soil. The results provide valuable insights into the role of calcium in enhancing the stability of biochar and its potential for carbon sequestration. Overall, the study is well-conducted and provides significant contributions to the field. However, there are a few areas that need clarification and further improvement. I recommend addressing the following points before it can be considered for publication:
Abstract:
a. The abstract provides a concise overview of the study; however, it would be helpful to highlight only the key findings and implications in a few sentences.
b. It is unclear how the CaCl2 additive was used with sewage sludge and bone dreg. Please provide more details regarding the experimental setup and the rationale behind the choice of additives.
Introduction:
a. Provide a clearer justification for studying the stability of biochar during aging processes in farmland soil. What are the potential implications or applications of this research?
b. The introduction should provide more background information on the significance of calcium in biochar stability with literature published in the recent three years (i.e., since 2020). Include relevant references and explain why the focus is on calcium as an exogenous additive.
c. The literature review must be improved by adding more up-to-date references. Many of the articles cited in this review are published more than five years ago.
Methods:
a. Provide more detailed information on the specific procedures and parameters used for dry-wet aging, freeze-thaw aging, and natural aging in farmland soil. This will help readers understand the experimental setup and ensure reproducibility.
b. Clarify the selection criteria for the farmland soils used in the study. How representative are these soils in terms of their properties and characteristics?
c. Include information on the analytical techniques used to quantify surface C and bulk C stability in the biochar samples. Provide references or additional details to support the chosen methods.
Results and Discussion:
a. The results presented in terms of oxidized surface C and oxidized bulk C are important for understanding the stability of biochar during aging. However, it is not clear how these measurements were obtained or calculated. Please provide more information on the analytical techniques used for these measurements.
b. The discussion should include a more thorough analysis and interpretation of the results. Discuss the implications of the findings and relate them to the existing literature on biochar stability and carbon sequestration.
c. Consider presenting the results and discussion in a more structured manner, grouping them according to the different aging processes and the influence of exogenous calcium.
Conclusion:
a. The conclusion should provide a concise summary of the key findings and their implications. Highlight the main contributions of the study and suggest avenues for future research.
Minor Comments:
a. Check for grammatical errors and ensure consistent use of terminology throughout the manuscript.
b. Consider providing more specific details regarding the Ca-containing crystals identified on the biochar surface, including their composition and morphology.
Overall, this study provides valuable insights into the role of exogenous calcium in enhancing the stability of biochar during aging in farmland soil. Addressing the above-mentioned points will strengthen the manuscript and improve its clarity.
The English language in the manuscript is generally clear and understandable. However, there are a few areas where moderate editing can improve the clarity and flow of the text. Here are some examples.
1. Consider rephrasing the sentence: "Converting biowaste into biochar and subsequently putting it into the soil are considered to be an effective approach to sequestrate carbon (C)." to: "Converting biowaste into biochar and incorporating it into soil is recognized as an effective method for carbon sequestration."
2. Break down the sentence starting with "This study selected CaCl2 as exogenous additive..." into two sentences for better readability.
General suggestion:
1. Review the manuscript for grammatical errors and ensure consistent use of terminology throughout.
2. Consider adding more specific details when appropriate and beneficial.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
