Changes in Soil Aggregate Fractions, Stability, and Associated Organic Carbon and Nitrogen in Different Land Use Types in the Loess Plateau, China
Round 1
Reviewer 1 Report
Dear Authors,
I had the opportunity to read and review the manuscript entitled „Changes in soil aggregate fractions, stability and associated organic carbon and nitrogen in different land use types in the Loess Plateau, China” (ID Sustainability-1633379).
This manuscript is aimed at explaining quantitatively the changes in soil aggregate structure for different ecological restoration treatments.
In my opinion, the manuscript is interesting and in line with the journal's scope: this study contributes to the improvement of a scientific basis for soil quality control and rational use of land resources. My review below suggests some improvements.
Title: Informative and consistent with the study's content.
Abstract: The abstract is clear and reasonable.
- Introduction: The overall structure is logical.
- Materials and methods: The collection of data is clearly described. But the presentation research methods need to be improved: for example, which post hoc tests were used to detect significant differences between the means?
In equation 3, the unit of the proportion of the total soil of aggregates remaining on each sieve, is most likely not the % but the decimal. The same applies to the Wi values in formulas 1-2.
- Results: this section needs to be checked carefully.
Please pay more attention to the representation of the results. The use of letters to represent post hoc test (which?) results is inconsistent. E.g. in Table 2 in some cases “a” denotes the lowest mean value (Ammonium nitrogen), in others (Nitrate nitrogen, Sand/%) the highest. Although the mean and SD values for Available phosphorus for grassland and terrace are exactly the same, I am not sure why we have different letters (a, ab) in the column. In the Clay/% column 'c' denotes the lowest mean value, 'b' the highest, and 'a' denotes the mean value higher than 'c' and lower than 'b'. Figures 2, 4, 5, 6, 7, and Table 3 have similar problems.
Table 4: ’p’ or ’p-value’ instead of ’Sig.’, '0.490', '0.223' and '0.508' instead of '<0.490', '＜0.223', and '＜0.508'.
- Discussion: The fundings of the study were compared with the results of previous research. In my opinion, the evaluation of the results is correct.
- Conclusion: Although this section is short, it presents, in my opinion, the most relevant interpretation of results.
Author Response
In my opinion, the manuscript is interesting and in line with the journal's scope: this study contributes to the improvement of a scientific basis for soil quality control and rational use of land resources. My review below suggests some improvements.
Response: Thank you for your summary. We really appreciate your efforts in reviewing our manuscript. We have revised the manuscript accordingly. Our point-by-point responses are detailed below.
Title: Informative and consistent with the study's content.
Abstract: The abstract is clear and reasonable.
- Introduction: The overall structure is logical.
Response: We appreciate the reviewer’s positive evaluation of our work.
- Materials and methods: The collection of data is clearly described. But the presentation research methods need to be improved: for example, which post hoc tests were used to detect significant differences between the means?
Response: Thanks for the comment and we have added the test method for differences detect as ‘One way analysis of variance (ANOVA) a LSD (least-significant difference) test at 0.05 level was performed in SPSS 18.0 to detect significant differences between the means.’ (Line 127-129)
In equation 3, the unit of the proportion of the total soil of aggregates remaining on each sieve, is most likely not the % but the decimal. The same applies to the Wi values in formulas 1-2.
Response: We are grateful for the suggestion. As suggested by the reviewer, we have modified the unit of the proportion of soil aggregates as ‘decimal’ in formulas 1, 2 and 3.
- Results: this section needs to be checked carefully.
Please pay more attention to the representation of the results. The use of letters to represent post hoc test (which?) results is inconsistent. E.g. in Table 2 in some cases “a” denotes the lowest mean value (Ammonium nitrogen), in others (Nitrate nitrogen, Sand/%) the highest. Although the mean and SD values for Available phosphorus for grassland and terrace are exactly the same, I am not sure why we have different letters (a, ab) in the column. In the Clay/% column 'c' denotes the lowest mean value, 'b' the highest, and 'a' denotes the mean value higher than 'c' and lower than 'b'. Figures 2, 4, 5, 6, 7, and Table 3 have similar problems.
Response: We apologize for the alphabetic notation problem in the results. The letters label to represent post hoc test in all the tables and figures have been improved as suggested, while ‘a’ denotes the highest mean value and ‘c’ means the lowest mean value.
Table 4: ’p’ or ’p-value’ instead of ’Sig.’, '0.490', '0.223' and '0.508' instead of '<0.490', '＜0.223', and '＜0.508'.
Response: We are extremely grateful to reviewer for pointing out this problem. We have modified the expression in Table 4.
- Discussion: The fundings of the study were compared with the results of previous research. In my opinion, the evaluation of the results is correct.
Response: Thank you for your careful review and we really appreciate your generous comments.
- Conclusion: Although this section is short, it presents, in my opinion, the most relevant interpretation of results.
Response: We are very grateful to your comments and this give us great encouragement
Author Response File: 
Author Response.docx
Reviewer 2 Report
The matter of the manuscript ‘Changes in soil aggregate fractions, stability and associated organic carbon and nitrogen in different land use types in the Loess Plateau, China’ is vital and fits into the scope of the Sustainability journal. The results presented are relevant and thought-provoking, which deserves publication. The study procedure and analysis are generally correct. Some changes and amendments are desirable, though.
It will be interesting to know, what are the implementation prospects of the obtained data? Do any of the existing state programs in the loess hilly region of China give a chance to scale up the best available practices of the SOC and TN studies? Can it be a basis for cost-effective soil protection?
So, my key question is rather simple: what are the implementation prospects of your findings? If the results are of core value for basic research of SOC and TN properties, it should be emphasized in the conclusion too.
My last major remark is somehow related to the previous one. When explaining the soil processes, it is compulsory to mention the background natural conditions. So please provide more data on a) soil types of the study area; b) soil types and parent material of undisturbed adjoining areas. Considering the Author’s affiliation, I suggest using the FAO soil classification. By understanding mother rocks and natural soils, we will be able to judge, whether the SAS are human-related, or rise from the natural conditions. That will be important for understanding the local transformation processes.
I sincerely hope you will find my suggestions helpful.
Kind regards,
Reviewer
Author Response
Response: Thank you for your comments concerning our manuscript. These comments are valuable and very helpful. We have read through comments carefully and have made corrections based on the instructions provided in your comment.
1 It is indeed important to clarifying the implementation prospects of the obtained data and we added the relative discussion in line 286-293 and emphasized it in the conclusion (line 299). We hope this could satisfy the requirement for publishing and if there is any problem, please contact us anytime.
2 We have added the information about soil types and parent material as ‘The soil types in the study area and the undisturbed adjoining areas are all loessial soils cultivated from loess parent material.’ (Line 79-80). The consistency of soil background could be helpful for confirming that the SAS is human-related.
Author Response File: Author Response.docx
Reviewer 3 Report
This paper presented some valuable data on the improvement of soil physical structures (aggregate size and stability) and chemical properties (SOC and total nitrogen) following on the land conversion from cultivated land to other alternatives, including grassland, terrace, forest and shrubland more than 20 years ago. Appropriate statistical methods were employed to detect differences and infer contributions. The change of soil properties will affect soil erosion and soil conservation. So the paper is relevant to the remit of targeted special issue. But there are some issues need to be addressed and they are outlined below.
1) introduction: please provide the information on the overall adoption of various land conversion on the loess plateau, e.g. slope land to grassland. This will demonstrate how significant is the current studies.
2) Terminologies: Authors have grouped the land use into several categories but some of the terms are not appropriate. Please consider the following changes: forest to woodland; terrace to orchard; slope land to cultivated land. Why the so called 'forest' has such low crown coverage at 0.6%? It would be helpful to include some images to show site conditions. They could be shown in a supplement document if necessary.
3) Sampling methodology: Only 3 samples from each land conversion category was taken. Authors should acknowledge the limitations with this small samples somewhere. Please also explain why samples to 60 cm depth and why 3 equal intervals (0-20; 20-40; 40-60cm)? Should it based on the profile distribution, i.e. short interval near surface?
4) Methodologies: More details should be given about lab analysis and statistical procedures. It is more important to present analysis accuracy and resolutions in addition to the instrument brands used. It is also useful to present more details on the statistical methods, functions used in addition to software package.
5) Assumptions and result interpretations: Authors have attributed all the differences among treatments to the land conversion. Some comments on the land use, management and soil condition on these sites before the conversion should be made, i.e. how variable they are before the change.
6) Wider implications: Some more discussion could be made to explore the wider implication of the results.
7) References: most recent papers are at 2019. Are there any more updated work? Some references are either not complete or not format properly. I have highlighted this in the annotated version of the paper provided.
7) English writing could be improved. I have highlighted some phrases (e.g. aritificial cultivation'), sentences in the annotated version of the paper for your references.
Figures:
Figure 1: please consider re-draw the overview map for loess plateau. No need to show road as it is not relevant to current study
Legend: if multiple diagrams share same legend, please consider show one legend only instead of repeating the legend in each one of them.
Tables: Please insert the unit for a column inside a pair of brackets, e.g. change depth / cm to depth (cm)
Comments for author File: 
Comments.pdf
Author Response
- introduction: please provide the information on the overall adoption of various land conversion on the loess plateau, e.g. slope land to grassland. This will demonstrate how significant is the current studies.
Response: We deeply appreciate the reviewer’s suggestion. According to the reviewer’s comment, we have added a more detailed information about the vegetation conversion on the Loess Plateau in line 52-56.
2) Terminologies: Authors have grouped the land use into several categories but some of the terms are not appropriate. Please consider the following changes: forest to woodland; terrace to orchard; slope land to cultivated land. Why the so called 'forest' has such low crown coverage at 0.6%? It would be helpful to include some images to show site conditions. They could be shown in a supplement document if necessary.
Response: We are very grateful to your comments for the manuscript. According to your advice, we changed ‘forest’ to ‘woodland’, ‘slope land’ to ‘cultivated land’ throughout the manuscript. But in our manuscript, ‘terrace’ is a level shelf of land interrupting a declivity where could plant crops, economic forest or any vegetations people wanted. And we tried to explore the difference of soil properties when the slope land was turned into this kind of ecological project. ‘Orchard’, in our opinion, is a special land use types for planting fruit trees. Therefore, we wonder if it is appropriate to change ‘terrace’ as ‘orchard’. For now, we keep it as ‘terrace’ and if there is any problem, please contact us anytime.
We apologize for the mistake of crown coverage data of ‘forest’ and we modified it as ‘60’.
3) Sampling methodology: Only 3 samples from each land conversion category was taken. Authors should acknowledge the limitations with this small samples somewhere. Please also explain why samples to 60 cm depth and why 3 equal intervals (0-20; 20-40; 40-60cm)? Should it based on the profile distribution, i.e. short interval near surface?
Response: Thank you for underlining the deficiency. 3 samples from each land conversion category was indeed not enough, due to the limited experiment condition. In the following research, we will try our best to increase the number of sample duplicates and we have added the limitation acknowledgement in line 294-296. In addition, 3 equal intervals were chosen based on the profile distribution and we have added the relevant reference in line 88.
4) Methodologies: More details should be given about lab analysis and statistical procedures. It is more important to present analysis accuracy and resolutions in addition to the instrument brands used. It is also useful to present more details on the statistical methods, functions used in addition to software package.
Response: Thank you for your precious comments and advice. We apologize for not describing the methodologies criteria clearer. We have added more details in line 127-132.
5) Assumptions and result interpretations: Authors have attributed all the differences among treatments to the land conversion. Some comments on the land use, management and soil condition on these sites before the conversion should be made, i.e. how variable they are before the change.
Response: We agree with the comment and have added the comments on the land use/management and soil condition before the conversion (Line 77-80).
6) Wider implications: Some more discussion could be made to explore the wider implication of the results.
Response: We are grateful for the suggestion. As suggested by the reviewer, we have added the wider implication in the discussion (Line 286-296)
- References: most recent papers are at 2019. Are there any more updated work? Some references are either not complete or not format properly. I have highlighted this in the annotated version of the paper provided.
Response: We deeply appreciate the reviewer’s suggestion. According to the reviewer’s annotation, we modified the references that are not complete or format properly. Also, we updated (marked in red in out manuscript) some old references
7) English writing could be improved. I have highlighted some phrases (e.g. aritificial cultivation'), sentences in the annotated version of the paper for your references.
Response: We have carefully revised the language issue again based on the reviewer’s comments.
Figures:
Figure 1: please consider re-draw the overview map for loess plateau. No need to show road as it is not relevant to current study
Response: Thank you for your careful review. We have re-draw the overview map according to the suggestion by removing the ‘road’ legend.
Legend: if multiple diagrams share same legend, please consider show one legend only instead of repeating the legend in each one of them.
Response: Thank you for your precious advice. We have modified the figure by showing one legend only.
Tables: Please insert the unit for a column inside a pair of brackets, e.g. change depth / cm to depth (cm)
Response: We are grateful for the comment and we have modified it as suggested.
Round 2
Reviewer 3 Report
Authors have made efforts to address the issues that have raised by the reviewers and there are more details on the study background and methodologies involved, specially the statistical analysis. The quality of paper has improved. But the revision also introduce some new issues. They are not major but worth improving further.
1) A few errors were reported for a few references.
2) Please report the Shapiro-Wilk test and the Levene test results.
3) There are still some issues in English writing. I have made some suggestions in the annotated paper provided. Please also rephrase the sentence between line 344 to 346 as its meaning is not clear to me.
Comments for author File: Comments.pdf
Author Response
Comments and Suggestions for Authors Authors have made efforts to address the issues that have raised by the reviewers and there are more details on the study background and methodologies involved, specially the statistical analysis. The quality of paper has improved. But the revision also introduce some new issues. They are not major but worth improving further. 1) A few errors were reported for a few references. Response: We had modified the quotation (citation 1 and 24 ). 2) Please report the Shapiro-Wilk test and the Levene test results. Response: We had added the report of the Shapiro-Wilk test and the Levene test results in line 147-148. 3) There are still some issues in English writing. I have made some suggestions in the annotated paper provided. Please also rephrase the sentence between line 344 to 346 as its meaning is not clear to me. Response: We had modified our manuscript accordingly (marked in red).
Author Response File: Author Response.pdf
