Enhanced Soil Carbon Stability through Alterations in Components of Particulate and Mineral-Associated Organic Matter in Reclaimed Saline–Alkali Drainage Ditches

Round 1

Reviewer 1 Report

The paper deals with a very relevant and topical problem of soil organic matter (SOM) stability and transformation with the use of instrumental methods of analysis and investigation. This problem is very complex as it simultaneously is a problem of soil sciences, chemistry, and has a statistical character due to the diversity of the material. And, on top of this, it should have a distinct practical value. 

However complex, some parts of this problem directly connected with SOM composition is problem, especially if we speak of the structures of SOM with a organomineral particles, especially particulate organic matter, and organomineral substances, at the molecular level, which are represented by mineral-associated organic matter in this paper.

Thus, the topic of the paper is selected correctly, and the results obtained by multiple interconnected instrumental methods and statistical treatment are correct. Therefore, the results obtained are relevant and discussed in due detail.

I believe that this paper can be published in the Journal upon correcting some issues that improve and deepen the material of the paper.

- The introduction is well written but seems to be not fully complete as the instrumental approaches for SOM and existing approaches for statistical treatment should be taken into account, especially those that were devoted to FTIR, which provides much more data that are discussed in the Introduction and Results sections in the paper. Thus, I suggest adding more paragraphs in the introduction and adding some more relevant references, especially papers published in Agronomy.

- The selection of transmission IR with KBr pressing should be briefly discussed mentioning advantages and disadvantages of this approach, especially the possibility of reaction with SOM with KBr as not a fully inert reagent, and a full comparison with diffuse-reflection and ATR FTIR techniques should be given.

- For such a paper, when the statistical treatment is of prime importance, the presentation of the figures of merit is not satisfactory. First of all, the number of significant digits for the data from all the methods used  is strange. In Table 2 some methods (EC, TN) show 5-6 (!) significant digits, which is not possible by the measurement correctness of these methods. In many cases 4 digits is the maximum detail determined by the bias (systematic error) of the method.

- Second, the precision (random error) of the data is not correct as well. The same Table 2 shows 4 to 5 (!) significant digits in the error values, which is incorrect. In rare cases, which should be discussed, ther could be two significant digits in the error; in the majority of cases this is a level of precision, and only 1 significant digits. This should be corrected. And, which is clear from Table 2, all the data values are governed not by the systematic, but the random value of the error. So all the data should be corrected accordingly 

So, as an example,

Instead of

EC (μs cm^-1) 3573.88 ± 366.98 a

there should be

EC (μs cm^-1) 3600 ± 400 a

All Tables in the paper as well as values of the text should be checked and corrected both from the viewpoint of both correctness and precision of data. The supplementary data should be treated as well.

- As well error values should be added to Figure 4 and the uncertainty of these data should be discussed in the text.

- Another questin is both on the FTIR data and precision. First of all, neither main text nor Supplementary contain FTIR spectra, so a reader relies on the summary tables only. This is rather incorrect as the spectra provide much more useful information

- Secondly, at least without spectra, such strict selection of the ranges is not proven. the identification tables should be given for soil samples, especially for objects having mineral parts. All the ranges have other counterparts: hydrogen bonds, SiO₂ vibrations, other mineral and organic constituents. Moreover, on the same page, the authors treat some peaks as SOM and soil water. 

- Next, without much explanation and proving for the subject of this paper "the methodology proposed by Liu et al. [36]", which seems to be a rather narrow approach, and not a wider term 'methodology' cannot be used as is. Much more discussion is needed, why this approach is used and not other more information-bearing and detailed approached.

-Finally, also it is difficult to discuss it without spectra, peak positions with such a precision for the used resolution and complex composition of soil particles in KBr is not correct.

Thus, summing up these last 4 points, the part on FTIR methodology, use, and results requires much more data, illustration, assignment tables, more literature discussion, and explanation of the details that raise too many questions.

Author Response

General comment

I believe that this paper can be published in the Journal upon correcting some issues that improve and deepen the material of the paper.

Response:

Thanks for your positive and insightful comments on our manuscript! These profound comments have greatly enhanced the quality of our manuscript. In the revised version, all issues raised have been addressed. Detailed modifications please see our responses to the following comments and the revised manuscript.

Specific comment (1):

- The introduction is well written but seems to be not fully complete as the instrumental approaches for SOM and existing approaches for statistical treatment should be taken into account, especially those that were devoted to FTIR, which provides much more data that are discussed in the Introduction and Results sections in the paper. Thus, I suggest adding more paragraphs in the introduction and adding some more relevant references, especially papers published in Agronomy.

- The selection of transmission IR with KBr pressing should be briefly discussed mentioning advantages and disadvantages of this approach, especially the possibility of reaction with SOM with KBr as not a fully inert reagent, and a full comparison with diffuse-reflection and ATR FTIR techniques should be given.

Response:

Thanks for your comment! We have added the paragraph in Introduction section for FITR approaches for SOM and making a fully comparison with diffuse-reflection and ATR FTIR techniques (Line 84-102). In addition, we have added the statement that the possibility of reaction with SOM with KBr in Discussion section (Line 416-425). We hope the revised version can be endorsed.

Specific comment (2):

- For such a paper, when the statistical treatment is of prime importance, the presentation of the figures of merit is not satisfactory. First of all, the number of significant digits for the data from all the methods used is strange. In Table 2 some methods (EC, TN) show 5-6 (!) significant digits, which is not possible by the measurement correctness of these methods. In many cases 4 digits is the maximum detail determined by the bias (systematic error) of the method.

- Second, the precision (random error) of the data is not correct as well. The same Table 2 shows 4 to 5 (!) significant digits in the error values, which is incorrect. In rare cases, which should be discussed, their could be two significant digits in the error; in the majority of cases this is a level of precision, and only 1 significant digits. This should be corrected. And, which is clear from Table 2, all the data values are governed not by the systematic, but the random value of the error. So all the data should be corrected accordingly

So, as an example,

Instead of

EC (μs cm-1) 3573.88 ± 366.98 a

there should be

EC (μs cm-1) 3600 ± 400 a

All Tables in the paper as well as values of the text should be checked and corrected both from the viewpoint of both correctness and precision of data. The supplementary data should be treated as well.

- As well error values should be added to Figure 4 and the uncertainty of these data should be discussed in the text.

Response:

Thanks for your comment! We have carefully reviewed all the data for precision and correctness. Both the tables in the manuscript and the supplement have been thoroughly checked and corrected. In addition, we have added the error values in Figure 4 and discussed the uncertainty of these data in Discussion section (Line 410-425). We hope the revised version can be endorsed.

Specific comment (3):

- Another question is both on the FTIR data and precision. First of all, neither main text nor Supplementary contain FTIR spectra, so a reader relies on the summary tables only. This is rather incorrect as the spectra provide much more useful information.

- Secondly, at least without spectra, such strict selection of the ranges is not proven. the identification tables should be given for soil samples, especially for objects having mineral parts. All the ranges have other counterparts: hydrogen bonds, SiO2 vibrations, other mineral and organic constituents. Moreover, on the same page, the authors treat some peaks as SOM and soil water.

- Next, without much explanation and proving for the subject of this paper "the methodology proposed by Liu et al. [36]", which seems to be a rather narrow approach, and not a wider term 'methodology' cannot be used as is. Much more discussion is needed, why this approach is used and not other more information-bearing and detailed approached.

-Finally, also it is difficult to discuss it without spectra, peak positions with such a precision for the used resolution and complex composition of soil particles in KBr is not correct.

Response:

Thanks for your insightful comments! Firstly, we have added the FTIR spectra as the Figure S1 in the supplement to provide the useful information. Secondly, we agree with your point that to improve the precision and reliability of the FTIR spectra, the identification tables about soil mineral parts should be given to prove the selection of the ranges in FITR spectra. This statement has been added in the Discussion section and will be the focus of the following studies (Lines 414-416). Next, we have added the reasons for choosing this method in the Materials and Methods section (Line 191-195). Finally, the pellets of POM and MAOM fraction soils separated by physical grouping method may affect the precision of peak positions in terms of particle compositions. We agree with your point and have added this statement in the Discussion section (Line 410-425), which will be the focus of the following studies. We hope the revised version can be endorsed. Thanks again!

Reviewer 2 Report

This study presents a case study investigating the processes underlying the stability of soil carbon components.

The manuscript is presented in a very good condition. The introduction explains well the scenario and the questions that motivated this study. The statements are very clear and always linked to an appropriate bibliography.

The methodology is described in detail and allows the repeatability of the tests carried out. The materials used are also explained.

The results are presented in tables, adequately accompanied by statistical analysis, and the conditions for carrying it out are verified. The choice of graphs is very appropriate and greatly facilitates the understanding of the results and also accompanies the discussion.

The discussion of the results is relevant and critically explains the scenario indicated by the results.

The results contribute to a deeper understanding of soil dynamics and its components and the influence of environmental factors, thus providing a theoretical basis for effective improvement of soil carbon content and stability in saline alkaline soils.

Overall, therefore, the manuscript is already in the form to be published, except for two very minor comments:

- In Fig.1 enter the direction of north.

- Thank you for your attention in providing the supplementary material. However, in the tables in this document (S1,S2,S3,S4) you can see that there is no statistically significant difference between the values, in fact the letters indicating group membership are always the same (a). I would advise in such cases to avoid writing the letter and to state in the note that no statistical significance was found for any of the conditions compared.

Otherwise, I can only congratulate the authors on this long and well-conducted study. Kudos also for writing it in such a clear way and for choosing to present the results in a way that helps the reader to understand the research that has been done.

Author Response

General comment

Overall, therefore, the manuscript is already in the form to be published, except for two very minor comments.

Response:

We are grateful to you for the positive comments on our manuscript! In the revised version, all issues raised in the review process have been addressed point by point. Detailed modifications please see our responses to the following comments and the revised manuscript.

Specific comment (1):

- In Fig.1 enter the direction of north.

Response:

Thanks for your comment! We have added the direction of north in Figure 1.

Specific comment (2):

- Thank you for your attention in providing the supplementary material. However, in the tables in this document (S1,S2,S3,S4) you can see that there is no statistically significant difference between the values, in fact the letters indicating group membership are always the same (a). I would advise in such cases to avoid writing the letter and to state in the note that no statistical significance was found for any of the conditions compared.

Response:

Done as suggested. In the Table S1, S2, S3 and S4 of the supplement, we have deleted the letters and added the note that no statistical significance was found for any of the conditions compared.