Application of Infrared Spectroscopy and Thermal Analysis in Explaining the Variability of Soil Water Repellency
Round 1
Reviewer 1 Report
The manuscript, entitled “Application of infrared spectroscopy and thermal analysis in explaining the variability of soil water repellency”, utilized FTRI and thermal analysis to explore the relationship between SWR and related soil properties in a northern Slovakia forest. This research contains some interesting data, and the writing is generally clear. There are, however, areas that could be improved.
1. Line 41, what is “water erosion”? Should it be soil erosion?
2. Line 56, delete “also”.
3. The paragraph starting in Line 69: Is this paragraph necessary? This paragraph is justifying a different model used in other studies and how it is different than the one in this manuscript. If those models are relevant, then I’d expect to see more in-depth discussion in the “Discussion” part of this manuscript. The fact that those models never were mentioned outside of this paragraph led me to doubt the necessity to include this discussion here. I suggest deleting this paragraph to improve the conciseness of this manuscript.
4. The last paragraph in the “Introduction” section could just end in Line 97, and delete the other two sentences to improve the reading.
5. Line 112, delete “in”.
6. Line 128, replace “Because” with “As”.
7. Line 150, replace “because of” with “to avoid”.
8. Fig 1, the photos are helpful.
9. Lines 161-162, are there any references for this method?
10. Table 1, what is the difference between “hydrophilic” and “rather hydrophilic”?
11. Lines 226 to 227, include the standard for SWR classification here. Also, I suggest that you add the category of the SWR in Table 2.
12. Line 245, this sentence is confusing.
13. Table 2, I assume that the reason why the WDPT data presented here are log transformed is due to the normality test results of those sets of data. This is fine for the regression analysis. However, I suggest that the original data in the unit of seconds be included in Table 2 to improve the readability of this set of data.
14. Why didn’t you consider soil texture a factor in the regression analysis with SWR? As the authors pointed out in the “Introduction”, soil texture is a variable that affects the development SWR. I am surprised that the regression analysis didn’t consider this factor, even though such data are collected.
15. Line 295, beyond this section, all the contents afterwards were grouped in “Discussion”. This arrangement is odd, as Table 3, and Figures 3-6 were never mentioned in the “Results” part and only appeared here. As the way it was written, I suggest merging the “Results” and “Discussion” parts together to form a single “Results & Discussion” section.
16. Table 3b, what is the purpose of presenting this set of data here? The part showed the correlation between the FTIR peak areas with soil properties besides SWR measurement. First, those data are not the focus of this manuscript. Second, I didn’t find anywhere in the text where those data were discussed. I suggest deleting this part of the table.
17. Figure 3 legend should include the information of how FTIR A/B ratio is defined, as all titles and legends need to be self-explanatory.
18. Line 479, I am not sure about the conclusion part on the soil pH here. As in this study, the soil pH ranges were narrow between 3 to 4 for the most part. I’ll feel more comfortable about this part of the conclusion if the soil samples in this study represented a wider range of soil pH.
Author Response
Responses to Reviewer #1:
General comments:
The manuscript, entitled “Application of infrared spectroscopy and thermal analysis in explaining the variability of soil water repellency”, utilized FTRI and thermal analysis to explore the relationship between SWR and related soil properties in a northern Slovakia forest. This research contains some interesting data, and the writing is generally clear. There are, however, areas that could be improved.
Response: Thank you for your thoughtful review, comments, and suggestions. Vast majority of comments and suggestions were accepted and implemented in revised version of the manuscript. They are specified in following part.
- Line 41, what is “water erosion”? Should it be soil erosion?
Response: “water erosion” was changed to “soil erosion”
- Line 56, delete “also”.
Response: Deleted.
- The paragraph starting in Line 69: Is this paragraph necessary? This paragraph is justifying a different model used in other studies and how it is different than the one in this manuscript. If those models are relevant, then I’d expect to see more in-depth discussion in the “Discussion” part of this manuscript. The fact that those models never were mentioned outside of this paragraph led me to doubt the necessity to include this discussion here. I suggest deleting this paragraph to improve the conciseness of this manuscript.
Response: The paragraph was deleted.
- The last paragraph in the “Introduction” section could just end in Line 97, and delete the other two sentences to improve the reading.
Response: Proposal was accepted. The paragraph ends with the sentence: ”This work further elaborates on the subject by focusing more on plot-scale variability of SOM properties and its effect on SWR”, that was at the line 97 in previous version of the manuscript. We moved the reference [22] upwards and it is now marked as [14].
- Line 112, delete “in”.
Response: Deleted.
- Line 128, replace “Because” with “As”.
Response: Replaced.
- Line 150, replace “because of” with “to avoid”.
Response: Replaced.
- Fig 1, the photos are helpful.
Response: The photos are included.
- Lines 161-162, are there any references for this method?
Response: The reference [21] was added Madejová and Komadel (2001). https://doi.org/10.1346/CCMN.2001.0490508
- Table 1, what is the difference between “hydrophilic” and “rather hydrophilic”?
Response: In the bands assigned as “hydrophilic” vibrations of polar functional groups are detected, whereas in the bands labelled as “rather hydrophilic” mainly vibrations of polar functional groups are detected, however with smaller contribution of nonpolar groups. This is indicated in the “Assignment” row of the table. For example, in band No. 4 (1560–1505 cm-1) various vibrations of polar amide groups are detected, such as NH, C-O, COO-, but there may be contribution from aromatic C, which is nonpolar group. So, the overall (net) effect of the groups detected in the band is rather (mostly) hydrophilic.
- Lines 226 to 227, include the standard for SWR classification here. Also, I suggest that you add the category of the SWR in Table 2.
Response: We added a SWR classification with new (better) reference [35] Bisdom et al., 1993, https://doi.org/10.1016/0016-7061(93)90103-R.
Additionally, we revised Table 2 and added new column with the SWR category.
- Line 245, this sentence is confusing.
Response: The sentence was deleted.
- Table 2, I assume that the reason why the WDPT data presented here are log transformed is due to the normality test results of those sets of data. This is fine for the regression analysis. However, I suggest that the original data in the unit of seconds be included in Table 2 to improve the readability of this set of data.
Response: Yes, the logarithms of WDPT data were in the statistical analysis. In revised manuscript we replaced the Log WDPT values in Table 2 with the time intervals in seconds.
- Why didn’t you consider soil texture a factor in the regression analysis with SWR? As the authors pointed out in the “Introduction”, soil texture is a variable that affects the development SWR. I am surprised that the regression analysis didn’t consider this factor, even though such data are collected.
Response: The relation between contents of textural fractions (sand, silt and clay) SWR data was assessed in correlation and regression analysis. The results of both suggest that the effect of either sand, silt, or clay content on SWR was insignificant. This finding can be attributed to low variability of particle size distribution of studied soils. As it is mentioned in the beginning of “Results and discussion” section, 41 samples out of 45 were classified as sandy loam and remaining 4 as loamy sand according to FAO-USDA texture triangle.
- Line 295, beyond this section, all the contents afterwards were grouped in “Discussion”. This arrangement is odd, as Table 3, and Figures 3-6 were never mentioned in the “Results” part and only appeared here. As the way it was written, I suggest merging the “Results” and “Discussion” parts together to form a single “Results & Discussion” section.
Response: We merged “Results” and “Discussion” parts into one “Results and Discussion” section.
- Table 3b, what is the purpose of presenting this set of data here? The part showed the correlation between the FTIR peak areas with soil properties besides SWR measurement. First, those data are not the focus of this manuscript. Second, I didn’t find anywhere in the text where those data were discussed. I suggest deleting this part of the table.
Response: Table 3 was modified. Letters “a” and “b” were deleted, and the two parts of the table were merged into one. We decided not to delete part “b” of Table 3, as the correlations between the peak areas and selected soil properties are discussed in the 3.4. section “Functional composition of SOM”. For example, correlation between 3020 and 2800 cm-1 peak area and SOM content, or 1505-1560 cm-1 peak area and content of soil N, or correlation between 1740-1710 cm-1 peak area and soil pH values are discussed in 3.4. section.
- Figure 3 legend should include the information of how FTIR A/B ratio is defined, as all titles and legends need to be self-explanatory.
Response: Explanatory text was added into the caption of Figure 3 to clarify the meaning of FTIR A/B ratio.
- Line 479, I am not sure about the conclusion part on the soil pH here. As in this study, the soil pH ranges were narrow between 3 to 4 for the most part. I’ll feel more comfortable about this part of the conclusion if the soil samples in this study represented a wider range of soil pH.
Response: Additional two references were added into the text [39] and [40] (at the end of section 3.3. “Effect of basic soil properties on WDPT and MED values”). In cited works the authors reported inverse relation between soil pH and SWR data. From published data it follows that negative correlation between SWR data and soil pH was reported not only for acidic soils, but for neutral and slightly alkaline as well (Mataix-Solera et al., 2007; https://doi.org/10.1002/hyp.6750).
Author Response File: 
Author Response.docx
Reviewer 2 Report
This is a very interesting article that evaluates soil water repellency (SWR) and others soil properties in mountain forest area of Slovakia. The paper’s title match its content. The issue presented in the paper have practical applications. The research topic presented clearly, aim of article clearly specified and realized. The article have a logical layout. The language of article correct. The paper’s conclusions follow logically from the development of the argument. The text adequately illustrated (tables and figures). Statistical analysis is sufficient and appropriate.
Author Response
Responses to Reviewer #2:
General comments:
This is a very interesting article that evaluates soil water repellency (SWR) and others soil properties in mountain forest area of Slovakia. The paper’s title match its content. The issue presented in the paper have practical applications. The research topic presented clearly, aim of article clearly specified and realized. The article have a logical layout. The language of article correct. The paper’s conclusions follow logically from the development of the argument. The text adequately illustrated (tables and figures). Statistical analysis is sufficient and appropriate.
Response: Thank you for the review. We appreciate the kind words.
Author Response File: Author Response.docx
Reviewer 3 Report
Dear Authors!
Excellence paper, certainly relevant and interesting for a wide range of specialists from soil scientists and forest ecologists to organic chemists, biochemists and physicists of surface phenomena. Both classic soil physics methods for assessing water repellency and modern instrumental methods of IR spectroscopy and thermal analysis were used. The most interesting is the statistically confirmed conclusion about the determining role of water content and accumulations of aliphatic structural units on water repellency in forest soils. The most debatable, it seems to me, is the conclusion about the mechanism of hydrophobization of the soil surface after heating. There may be alternative physical explanations, but separate studies are needed. I believe that the paper can be published in its present form.
Just one small note about the statement on lines 387-389 "As it was indicated in the previous part, water evaporation from the samples proceeded approximately up to 150°C and thermal degradation of SOM started between 150 and 180 °C." I found no clear evidence in the paper that at 150°C all water is removed from the soil. Moreover, as shown in DOI: 10.1134/S1061933X16030170, complete dehydration of soil colloids requires higher temperatures up to 400-500 °C. Therefore, I advise you to correct this phrase by removing " As it was indicated in the previous part…" and strengthening the hypothetical meaning, for example, "Supposedly bound water evaporates almost completely at 150 ° C ...."
I hope to see your article published in Applied Sciences soon.
Best Wishes, Your Reviewer.
Author Response
Responses to Reviewer #3:
General comments:
Dear Authors!
Excellence paper, certainly relevant and interesting for a wide range of specialists from soil scientists and forest ecologists to organic chemists, biochemists and physicists of surface phenomena. Both classic soil physics methods for assessing water repellency and modern instrumental methods of IR spectroscopy and thermal analysis were used. The most interesting is the statistically confirmed conclusion about the determining role of water content and accumulations of aliphatic structural units on water repellency in forest soils. The most debatable, it seems to me, is the conclusion about the mechanism of hydrophobization of the soil surface after heating. There may be alternative physical explanations, but separate studies are needed. I believe that the paper can be published in its present form.
Response: Thank you for the review. We appreciate the kind words.
Just one small note about the statement on lines 387-389 "As it was indicated in the previous part, water evaporation from the samples proceeded approximately up to 150°C and thermal degradation of SOM started between 150 and 180 °C." I found no clear evidence in the paper that at 150°C all water is removed from the soil. Moreover, as shown in DOI: 10.1134/S1061933X16030170, complete dehydration of soil colloids requires higher temperatures up to 400-500 °C. Therefore, I advise you to correct this phrase by removing " As it was indicated in the previous part…" and strengthening the hypothetical meaning, for example, "Supposedly bound water evaporates almost completely at 150 ° C ...."
Response: We slightly modified the sentence at the beginning of 3.5. section “Thermal stability of SOM”. Currently it states that: “Below 150°C, the evaporation of residual water takes place, and the thermal degradation of SOM started between 150 and 180 °C”. The term residual water refers mainly to water adsorbed on soil particles.
Author Response File: Author Response.docx
