Using Fluorescence Spectroscopy to Assess Compost Maturity Degree during Composting
Round 1
Reviewer 1 Report
The authors suggest that the analysing parameters, namely: Moisture and temperature, EC, pH, Carbon and nitrogen, Humic acid (HA) and fulvic acid (FA) are more about compost quality rather than its maturity. In the title and the conclusion section the authors deduct that fluorescence spectroscopy is a powerful tool for obtaining detailed information about the maturity of compost. Taking into consideration that authors denial most of the analysing parameters as proper compost maturity indicators so how the authors conclude that fluorescence spectroscopy can be a good tool for indication of compost maturity? This issue needs to be clarified in the text.
The title and conclusions should be more precise and strongly related with the scope of the research.
More comments are in the attached file.
Comments for author File: 
Comments.pdf
English is good. Some minor corrections are necessary.
Author Response
Response to Reviewer 1’s Comments
The authors have carefully revised the comments based on reviewers point by point as follows:
Point 1: The authors suggest that the analysing parameters, namely: Moisture and temperature, EC, pH, Carbon and nitrogen, Humic acid (HA) and fulvic acid (FA) are more about compost quality rather than its maturity. In the title and the conclusion section the authors deduct that fluorescence spectroscopy is a powerful tool for obtaining detailed information about the maturity of compost. Taking into consideration that authors denial most of the analyzing parameters as proper compost maturity indicators so how the authors conclude that fluorescence spectroscopy can be a good tool for indication of compost maturity? This issue needs to be clarified in the text.
Response 1: Thanks for the reviewer’s comments and we have rewritten in section of “Introduction” in Page 1 and 2 and section of “Results and discussion” in Page 5-8.
Point 2: Need references in Line 57-62.
Response 2: Thanks for the reviewer’s comments and we have deleted unsuitable sentences and have rewritten in Line 58-62.
Point 3: It is not clear for this reviewer where in the text the results of this statistical analysis are shown (Line 141-162).
Response 3: Thanks for the reviewer’s comment and we have rewritten this paragraph here in Line 166-169.
Point 4: What whiskers mean here in Figure 2?
Response 4: We have added the description in Figure 2 and 3.
Point 5: This sentence (Line 273-274) is not clear for this reviewer.
Response 5: We have corrected the sentences here in Line 298-300.
Point 6: Reference needed in Line 348-349.
Response 6: Thanks for the reviewer’s comment, and we have rephrased this paragraph into in Line 83-89 in Introduction, and Line 250-253 in Results and discussion.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Dear authors,
In this manuscript, you have employed various indicators to understand the maturity of three types of composts. The idea is interesting and well-established, however, the presentation still needs to be improved.
1- The introduction does not follow a proper structure. What was the reason that caused the authors for this study? Is it a comparison that has not been done before? If so, it should be clearly stated.
2- The spectral and biological analysis have not been introduced properly, as well as their advantages and disadvantages.
3- Lines 161-164: "Theoretically, the moisture and temperature of composts could keep decreasing until reaching a changing balance with atmospheric conditions, leading to the difficulty of being reliable indicators for compost maturity". Why changing to reach a balance causes those indicators to be unreliable?
4- Table 2 is complicated and difficult to understand. Better to bring in a horizontal page.
5- Line 229: What is the difference between quality and maturity? Authors should elaborate more on their difference.
6- Line 339 to 354: Why the authors have put this paragraph here? The first sentence is a statement about the objective of the study, which should be removed or moved to the introduction or conclusion. The rest of the paragraph is a report on the results of the other studies, which should be compared with the results obtained by this study. I suggest making a comparison between the result of each indicator obtained in the current study with those obtained in other literature in an appropriate part of the results section.
Author Response
Response to Reviewer 2’s Comments
The authors have carefully revised the comments based on reviewers point by point as follows:
In this manuscript, you have employed various indicators to understand the maturity of three types of composts. The idea is interesting and well-established, however, the presentation still needs to be improved.
Point 1: The introduction does not follow a proper structure. What was the reason that caused the authors for this study? Is it a comparison that has not been done before? If so, it should be clearly stated.
Response 1: Thanks for the reviewer’s comments and we have rephrased and added some paragraph in “Introduction” in Page 1-2, and marked in red color.
Point 2: The spectral and biological analysis have not been introduced properly, as well as their advantages and disadvantages.
Response 2: We have added some illustrations “Introduction” in Page 1-2, and marked in red color.
Point 3: Lines 161-164: "Theoretically, the moisture and temperature of composts could keep decreasing until reaching a changing balance with atmospheric conditions, leading to the difficulty of being reliable indicators for compost maturity". Why changing to reach a balance causes those indicators to be unreliable?
Response 3: The temperature might be a rough index for identifying maturity of composts and these physical indices could not elucidate changing of humic substances during composting. We have rewritten the sentence in Line 185-187.
Point 4: Table 2 is complicated and difficult to understand. Better to bring in a horizontal page.
Response 4: The Table 2 has been turned into Figure 2 in Line 204.
Point 5: Line 229: What is the difference between quality and maturity? Authors should elaborate more on their difference.
Response 5: Thanks for the reviewer’s comment and we have deleted the unsuitable sentence here.
Point 6: Line 339 to 354: Why the authors have put this paragraph here? The first sentence is a statement about the objective of the study, which should be removed or moved to the introduction or conclusion. The rest of the paragraph is a report on the results of the other studies, which should be compared with the results obtained by this study. I suggest making a comparison between the result of each indicator obtained in the current study with those obtained in other literature in an appropriate part of the results section.
Response 6: Thanks for the reviewer’s comment, and we have rephrased this paragraph into in Line 83-89 in Introduction, and Line 250-253 in Results and discussion.
Author Response File: Author Response.docx
Reviewer 3 Report
Dear authors of agronomy-2495066,
This paper analyzed the changes in eight indicators of three commercial composts during composting and investigated the changes in compost components such as total organic carbon, dissolved organic carbon, humic acid, fulvic acid, and total nitrogen during composting. Finally, this paper recommended the E4/E6 ratio as the indicator of early-stage maturity and HIX as the indicator of organic material maturity, which embodied the practical value of this study.
This is a wonderful study, however, some questions need improvement and revision. Therefore, the paper can be considered for acceptance after the necessary major revision.
1. FIX appeared on Line 26 and Line 367, but I don’t know what FIX is.
2. Lines 68-70, this paper indicated that “However, the fact still revealed that no absolute quantitative criterion of the decrease in the absorbance by sugars at 50-112 ppm could assure compost maturity.”
What does this mean? This study seemed to not analyze the sugar change during composting.
3. In the introduction, this paper emphasized the importance of accurate determination of compost maturity and indicated that spectral analysis, 3D-EEM, and absorbance of DOM could be used to determine compost maturity.
However, this paper failed to point out the current questions in detecting compost maturity, and this study could solve these questions efficiently.
4. This paper did not show how to extract humic acid and fulvic acid and how to determine the concentrations of humic acid and fulvic acid.
5. Are total carbon, DOM, TOC, EC, pH, HIX, and E4/E6 measurements performed on the compost or compost leachate?
If leachate, please clearly state how the compost leachate was obtained.
6. Please provide the detailed operation and parameters for 3D-EEM measurements.
7. Line 169, EC of the compost extracts reflects…,
Lines 104-106, In this study, we used… and monitoring probes to continuously monitor the temperature, moisture, and EC during the composting process….
If EC is measured on compost extracts, how do you achieve the continuous monitoring of EC during composting?
8. Table 2 has too much data and information, which is inconvenient for readers to read. Please change it to a graph. The vertical axis is the detection index, and the horizontal axis is the composting time. Differences (e.g., a, ab) can also be marked on the graph.
9. Line 187, “Table 2 shows that the pH values of CMC and GC significantly increased during…”. It should be HMC, not CMC.
10. Lines 244-245, 2b), “…, probably because FA is lower in molecular weight, simpler in chemical structure, and more decomposable than HA.” Please cite references about this conclusion (e.g., https://doi.org/10.1016/j.eti.2023.103232).
11. Lines 255-256, “It is generally adapted that compost matures when the HA/FA ratio reaches 1.7.” This conclusion should have a citation.
12. Line 279, “…, and that of CMC exceeded 80% after 60 days.”. This is different from Figure 2f.
13. Lines 291-294, “…has been introduced to divide the EEM spectra into five excitation-emission regions (Region I: tyrosine-like organic compounds; Region II: tryptophan-like organic compounds; Region III: fulvic acid-like materials; Region IV: soluble microbial byproduct-like materials; Region V: humic acid-like materials).” Please cite references for that (e.g., https://doi.org/10.1016/j.envpol.2022.120420).
14. For Figure 3, the 0 value of the pseudo-color map is red and the maximum value (500) is also red, which is not convenient for readers to read. Please modify it by referencing Figure 7 in the paper https://doi.org/10.1016/j.envpol.2022.120420.
15. For Figure 14, it is recommended to modify the gray graph to a color graph.
16. The paragraph (Lines 339-354) briefly discusses the results and conclusions of previous studies but does not summarize the results of this study and emphasize the meaning of this study.
17. The reference section lacks research literature on recent years.
Author Response
Response to Reviewer 3’s Comments
The authors have carefully revised the comments based on reviewers point by point as follows:
Point 1: FIX appeared on Line 26 and Line 367, but I don’t know what FIX is.
Response 1: Thanks for reviewer’s comment and we have deleted the term of “FIX” in manuscript.
Point 2: Lines 68-70, this paper indicated that “However, the fact still revealed that no absolute quantitative criterion of the decrease in the absorbance by sugars at 50-112 ppm could assure compost maturity.”
What does this mean? This study seemed to not analyze the sugar change during composting.
Response 2: Thanks for the reviewer’s comment, and we have deleted the sentences and rewritten the sentences in Introduction in Page 1-2, and marked in red color.
Point 3: In the introduction, this paper emphasized the importance of accurate determination of compost maturity and indicated that spectral analysis, 3D-EEM, and absorbance of DOM could be used to determine compost maturity.
However, this paper failed to point out the current questions in detecting compost maturity, and this study could solve these questions efficiently.
Response 3: Thanks for the reviewer’s comment, and we have rewritten and rephrased some sentences in Introduction in Page 1-2, and marked in red color.
Point 4: This paper did not show how to extract humic acid and fulvic acid and how to determine the concentrations of humic acid and fulvic acid.
Response 4: We have added the description in Line 124-133 based on the reviewer’s comment.
Point 5: Are total carbon, DOM, TOC, EC, pH, HIX, and E4/E6 measurements performed on the compost or compost leachate?
If leachate, please clearly state how the compost leachate was obtained.
Response 5: Thanks for the reviewer’s comment, and we have added the explanation in Line 137-143.
Point 6: Please provide the detailed operation and parameters for 3D-EEM measurements.
Response 6: Thanks for the reviewer’s comment, and we have added the operation and parameters for 3D-EEM measurements in Line 137-143.
Point 7: Line 169, EC of the compost extracts reflects…,
Lines 104-106, In this study, we used… and monitoring probes to continuously monitor the temperature, moisture, and EC during the composting process….
If EC is measured on compost extracts, how do you achieve the continuous monitoring of EC during composting?
Response 7: Thanks for the reviewer’s comment and we have deleted wrong sentence here.
Point 8: Table 2 has too much data and information, which is inconvenient for readers to read. Please change it to a graph. The vertical axis is the detection index, and the horizontal axis is the composting time. Differences (e.g., a, ab) can also be marked on the graph.
Response 8: Thanks for the reviewer’s comment, and we have corrected it. The Table 2 has been turned into Figure 2 in Line 204.
Point 9: Line 187, “Table 2 shows that the pH values of CMC and GC significantly increased during…”. It should be HMC, not CMC.
Response 9: Thanks for the reviewer’s comment, and we have corrected it.
Point 10: Lines 244-245, 2b), “…, probably because FA is lower in molecular weight, simpler in chemical structure, and more decomposable than HA.” Please cite references about this conclusion (e.g., https://doi.org/10.1016/j.eti.2023.103232).
Response 10: We have cited the new reference based on the suggestion in Line 270.
Point 11: Lines 255-256, “It is generally adapted that compost matures when the HA/FA ratio reaches 1.7.” This conclusion should have a citation.
Response 11: We have cited the new reference based on reviewer’s suggestion in Line 280-281.
Point 12: Line 279, “…, and that of CMC exceeded 80% after 60 days.”. This is different from Figure 2f.
Response 12: The wrong Fig. 3f has been corrected!
Point 13: Lines 291-294, “…has been introduced to divide the EEM spectra into five excitation-emission regions (Region I: tyrosine-like organic compounds; Region II: tryptophan-like organic compounds; Region III: fulvic acid-like materials; Region IV: soluble microbial byproduct-like materials; Region V: humic acid-like materials).” Please cite references for that (e.g., https://doi.org/10.1016/j.envpol.2022.120420).
Response 13: We have cited the new reference based on reviewer’s suggestion in Line 318.
Point 14: For Figure 3, the 0 value of the pseudo-color map is red and the maximum value (500) is also red, which is not convenient for readers to read. Please modify it by referencing Figure 7 in the paper https://doi.org/10.1016/j.envpol.2022.120420.
Response 14: Thanks for the reviewer’s comment, and we have corrected it.
Point 15: For Figure 14, it is recommended to modify the gray graph to a color graph.
Response 15: Thanks for the reviewer’s comment, and we have corrected it.
Point 16: The paragraph (Lines 339-354) briefly discusses the results and conclusions of previous studies but does not summarize the results of this study and emphasize the meaning of this study.
Response 16: Thanks for the reviewer’s comment, and we have rephrased this paragraph into in Line 83-89 in Introduction, and Line 250-253 in Results and discussion.
Point 17: The reference section lacks research literature on recent years.
Response 17: We have added several new references in the manuscript and in reference list.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The new version was prepared in sufficient way.
Reviewer 3 Report
The questions I proposed have all been solved. I think this paper can be accepted for publication.
