Review Reports

Round  1

Reviewer 1 Report

This is a well written manuscript evaluating temporal changes in SOC and soil pH over a 3 decade period that attempts to relate soil changes to land management.  Specific Comments are:

1.      Line 152:  How is the thirty year period “precious”?  Do the authors mean the previous thirty years? Is it the thirty year period?  Choice of words?

2.      Line 153:  Connect the two sentences.  Delete “.” After “China”; insert “was obtained from”.

3.      Line 154:  Delete “was obtained”.

4.      Figure 2:  For each graph legend on the horizontal axis (1982 year 2012 year), remove the word year (i.e., 1982 2012), and place the word "Year” below the numbered years.

5.      Lines 287-292:  (a) “Slope gradient had a negative impact on SOC spatial distribution”.  This is a given because of lower vegetable productivity on steeper slopes contribution to less vegetative biomass on more sloping lands.  This is usually due to less precipitation retention (more runoff) on these sloping areas and less moisture available for plant growth.  However, this is also often a result of erosion; both natural and man-made.  A discussion of erosion potential is not clearly mentioned anywhere in the manuscript.  (b) The authors imply changes in land use and land use management during the 30-year period.  However, they have not presented any information of differences in land use over the time period.  This would greatly help explain changes in SOC and ph that are directly impacted by changes in Land use and management.  This should be added to the discussion.  (c)  “Leaching effect is greater in high terrain?  So this leads to higher salinity?  Generally, the opposite is true because runoff on sloping land is higher, thus, reducing leaching.  Is the higher salinity not more likely due to higher erosion on sloping lands removing less saline soil materials and exposing more saline subsurface materials?  This needs to be re-thought and discussed more clearly.

6.      Lines298-306:  Elevation has a negative correlation with MAP and MAT indicating a greater controller of SOC than temperature and precipitation.  However, elevation also influences both natural and man-influenced soil erosion which directly affects SOC and pH.  Land use and management changes amplify these effects.  Again, the authors need to include information of land use and management change to aid in the discussion in this manuscript.  Obviously, these are impacted factors in this modeling effort but have not been included!

7.      Line 299:  Capitalize “mat” and “map”.

8.      Lines 307-327:  If vegetation patterns and composition changes as land use and management changes, show does species change due to cropland replacing natural vegetation change NDVI?  Solid crop canopies cue to crop cover would influence NVDI differently that native vegetation, wouldn’t it?

9.      Lines 345-346:  What about tillage promoting OM oxidation of SOM/SOC apart from vegetation litter entering the soil?

10.  Line 350:  Change “your” to “a”.

11.  Line 365:  Change “physiological acid” to ”acid forming”.

12.  Line 368:  Change “strengthen” to “improve”; Change “improve” to “reduce”.

13.  Line 422:  Insert “promote” between “could” and “ecological”.

Author Response

Reviewer 1

General comments:

This is a well written manuscript evaluating temporal changes in SOC and soil pH over a 3 decade period that attempts to relate soil changes to land management. 

Reply: We appreciate your help and your patience. With this submission, we provided a version (marked) of the revised manuscript. Responses to reviewers’ comments on the marked manuscript are detailed below.

Specific Comments:

1. Line 152:  How is the thirty year period “precious”?  Do the authors mean the previous thirty years? Is it the thirty year period? Choice of words?

Reply: Thank you for your meticulousness and patience. This is the meaning of the previous thirty years. It was a typo before. We have corrected in the revised manuscript. L167

2. Line 153:  Connect the two sentences.  Delete “.” After “China”; insert “was obtained from”.

Reply: Climate data were derived from interpolation of meteorological stations, not from remote sensing data. We have eliminated redundant “Remote sensing data was obtained.”. L169

3. Line 154:  Delete “was obtained”.

Reply: We have deleted “Remote sensing data was obtained” according to your comment. L169

4. Figure 2:  For each graph legend on the horizontal axis (1982 year 2012 year), remove the word year (i.e., 1982 2012), and place the word "Year” below the numbered years.

Reply: Based on your comment, we have revised the Figure 2. See Figure 2

5. Lines 287-292:  (a) “Slope gradient had a negative impact on SOC spatial distribution”.  This is a given because of lower vegetable productivity on steeper slopes contribution to less vegetative biomass on more sloping lands.  This is usually due to less precipitation retention (more runoff) on these sloping areas and less moisture available for plant growth.  However, this is also often a result of erosion; both natural and man-made.  A discussion of erosion potential is not clearly mentioned anywhere in the manuscript.

Reply: According to your comment, we have added this discussion of erosion potential in the manuscript. L355-371

(b) The authors imply changes in land use and land use management during the 30-year period.  However, they have not presented any information of differences in land use over the time period. This would greatly help explain changes in SOC and ph that are directly impacted by changes in Land use and management. This should be added to the discussion. 

Reply: Following your comments and suggestion, we added land use patterns to the RF model to discuss the impact of land use changes on SOC and pH. L173-178, L420-433

(c) “Leaching effect is greater in high terrain?  So this leads to higher salinity?  Generally, the opposite is true because runoff on sloping land is higher, thus, reducing leaching.  Is the higher salinity not more likely due to higher erosion on sloping lands removing less saline soil materials and exposing more saline subsurface materials?  This needs to be re-thought and discussed more clearly.

Reply: In response to your comments, we have revised the manuscript to make it clearer. L3714-376

6. Lines298-306: Elevation has a negative correlation with MAP and MAT indicating a greater controller of SOC than temperature and precipitation.  However, elevation also influences both natural and man-influenced soil erosion which directly affects SOC and pH.  Land use and management changes amplify these effects.  Again, the authors need to include information of land use and management change to aid in the discussion in this manuscript.  Obviously, these are impacted factors in this modeling effort but have not been included!

Reply: Based on your comments, we have added the land-use data of the two periods to the model in order to discuss the impact of land use and management changes on SOC and pH more clearly. L173-178, L420-433, Table 1, and Table 2

7. Line 299:  Capitalize “mat” and “map”.

Reply: We have capitalized “mat” and “map” according to your comment. L384

8. Lines 307-327:  If vegetation patterns and composition changes as land use and management changes, show does species change due to cropland replacing natural vegetation change NDVI?  Solid crop canopies cue to crop cover would influence NVDI differently that native vegetation, wouldn’t it?

Reply: Your statement is correct. We revised it in the manuscript. L396-399

9. Lines 345-346: What about tillage promoting OM oxidation of SOM/SOC apart from vegetation litter entering the soil?

Reply: Your statement is correct. We have added this part to the manuscript. L443

10. Line 350:  Change “your” to “a”.

Reply: Based on your comment, we have changed “your” to “an”. L447

11. Line 365:  Change “physiological acid” to ”acid forming”.

Reply: We have changed “physiological acid” to ”acid forming”. L453

12. Line 368:  Change “strengthen” to “improve”; Change “improve” to “reduce”.

Reply: We have changed “strengthen” to “improve”; Change “improve” to “reduce”. L457

13. Line 422:  Insert “promote” between “could” and “ecological”.

Reply: According to your comment, we have inserted “promote” between “could” and “ecological”. L492

Author Response File: Author Response.pdf

Reviewer 2 Report

GENERAL COMMENTS

The manuscript ID sustainability-533357 shows results from an interesting research focused on the spatial distribution of SOC and pH in Liaoning Province, China. From a scientific point of view this research is valuable for many reasons: a great effort-consuming fieldwork, testing the effectiveness of random forest techniques for soil properties, usefulness of this information for stakeholders, etc. In addition, the article is generally well-written and structured. Nonetheless, it is a pity that authors have only studied SOC and pH. I guess having studied more soil properties meant spending a lot of money in laboratory analysis. Anyway, I have suggested minor revisions because I like this kind of research.

SPECIFIC COMMENTS

Title

English is not my mother tongue but I am not sure if “Temporospatial” is the most appropriated word.

Abstract

The Abstract section must be self-explanatory.

Lines 15-17: Soil quality and fertility are concepts much more complex than the simple study of SOC and pH. Please rewrite the beginning of your Abstract section trying to find a convincing motivation that justifies the necessity of your research.

Line 19: Why from 1982 to 2012? Is there any special reason?

Line 19: covariates? Please provide more details.

Line 21: Cross-validation was used. Please try to use past tense where it is necessary. You are explaining that you did, not that you do, are doing or you will do.

Line 24: elevation and NDVI are not indicators (this concept has a great complexity), they are parameters, variables, etc.

Line 26: factors: TWI and mean annual rainfall are not factors. They are variables. Please use properly each concept. This is crucial in a refined scientific document.

Lines 30-31: I think you should make an effort to find a less generic conclusion of your research.

Keywords

Please do not repeat the same words you have already mentioned in the title.

Introduction

Some paragraphs are too long and there is some superfluous information.

Line 36: SOC and pH are not indices. Factors, variables, indicators and indices are complex concepts that must not be mixed under any circumstances. Please see Pulido et al. (2017) or Zornoza et al. (2015) if you are experiencing any problem to properly understand the differences between indices, indicators, parameters and factors. Please keep in mind that our language has to be rigorously perfect.

Line 37: Please clarify SOC is usually 58% of SOM.

Line 79: It has been

Line 90: foci? What its meaning is?

Objectives: Please try to write without using bullet points or numbers.

Objective no. 1: Why 1982 and 2012? It must be clarified in the motivation of the article.

Study area

Figure 1 should be placed at the end of this sub-section.

Figure 1: Please remove the label “Legend”. Please replace km instead of kilometers in the graphic scale.

Data collection

This sub-section should be named “Experimental design”. You should explain firstly the global rationale of your study before giving details of each one of your methodological procedures.

You must differentiate clearly what you have done and which information has been extracted from other sources, i.e. the variables were collected by other ones.

Line 130: factors: Please see previous comments.

Soil sampling in 2012

This sub-section should be named “Soil sampling and analysis”.

Environmental variables

MAT: this value is the average of the 12 months or the average of the 365 days?

Line 154: Please check this sentence.

The software packages you used should be mentioned at the end of the sub-section.

Lines 156-157: Please check this sentence.

The formula to calculate NDVI is commonly known.

Results and Discussion

This section should be divided into two new ones: (3) Results and (4) Discussion

Any section or subsection should be started with a figure. They must be placed below the text.

Figure 2: Please delete Year in the x-axis labels.

Table 1: Why you do not use the correlations of both years together (merged as a single dataset)?

Figure 5 is quite ugly. Please improve it!

Author Response

Reviewer 2

General comments:

The manuscript ID sustainability-533357 shows results from an interesting research focused on the spatial distribution of SOC and pH in Liaoning Province, China. From a scientific point of view this research is valuable for many reasons: a great effort-consuming fieldwork, testing the effectiveness of random forest techniques for soil properties, usefulness of this information for stakeholders, etc. In addition, the article is generally well-written and structured. Nonetheless, it is a pity that authors have only studied SOC and pH. I guess having studied more soil properties meant spending a lot of money in laboratory analysis. Anyway, I have suggested minor revisions because I like this kind of research.

Reply: We appreciate your help. With this submission, we provided a version (marked) of the revised manuscript. Responses to reviewers’ comments on the marked manuscript are detailed below.

Specific comments:

Title

1. English is not my mother tongue but I am not sure if “Temporospatial” is the most appropriated word.

Reply: Thanks for the comments. We change to a more proper word “Spatial-temporal”, but with the same meaning, in this revision.

Abstract

2. The Abstract section must be self-explanatory.

Reply: Based on your comments, we have revised the abstract part of the manuscript. L15-36

3. Lines 15-17: Soil quality and fertility are concepts much more complex than the simple study of SOC and pH. Please rewrite the beginning of your Abstract section trying to find a convincing motivation that justifies the necessity of your research.

Reply: Based on your comments, we have revised it to “Quantification of soil organic carbon (SOC) and pH and their spatial variations at regional scales is a foundation to adequately assess agriculture, pollution control or environmental health and ecosystem functioning so as to establish better practices for land use and land management.”. L15-18

4. Line 19: Why from 1982 to 2012? Is there any special reason?

Reply: 1982 was the year when Liaoning began to reform its economy, and 2012 was the year when Liaoning's economy developed rapidly. Similarly, in 1982, small-scale peasant economy was dominant, while agricultural mechanization was relatively low. In 2012, the opposite was true.

5. Line 19: covariates? Please provide more details.

Reply: Based on your comments, we have added a more detailed description of environmental variables. L20-23

6. Line 21: Cross-validation was used. Please try to use past tense where it is necessary. You are explaining that you did, not that you do, are doing or you will do.

Reply: We have changed “Cross-validation is used” to “Cross-validation was used”. L24-25

7. Line 24: elevation and NDVI are not indicators (this concept has a great complexity), they are parameters, variables, etc.

Reply: We have corrected this according to your comment. L27

8. Line 26: factors: TWI and mean annual rainfall are not factors. They are variables. Please use properly each concept. This is crucial in a refined scientific document.

Reply: Based on your comment, we have corrected this. L29

9. Lines 30-31: I think you should make an effort to find a less generic conclusion of your research.

Reply: Based on your comments, we have revised it to “This study provided important information of spatial variations in SOC and pH to agencies and communities in this region to evaluate soil quality and make decisions on remediation and prevention of soil acidification and salinization.”. L33-36

Keywords

10. Please do not repeat the same words you have already mentioned in the title.

Reply: We changed the keyword to "spatial variability; environmental variables; digital soil mapping; random forest ". L37

Introduction

11. Some paragraphs are too long and there is some superfluous information.

Reply: We have eliminated the redundancy to make it more compact. L40-101

12. Line 36: SOC and pH are not indices. Factors, variables, indicators and indices are complex concepts that must not be mixed under any circumstances. Please see Pulido et al. (2017) or Zornoza et al. (2015) if you are experiencing any problem to properly understand the differences between indices, indicators, parameters and factors. Please keep in mind that our language has to be rigorously perfect.

Reply: According to your comment, we have changed “indices” to “indicators”. L41

13. Line 37: Please clarify SOC is usually 58% of SOM.

Reply: Based on your suggestion, we have added “However, SOC is usually 58% of SOM” to the manuscript. L44

15. Line 79: It has been

Reply: We have changed it to “It has been”. L84

16. Line 90: foci? What its meaning is?

Reply: To avoid this ambiguity, we revised it to “the specific objectives were”. L98

17. Objectives: Please try to write without using bullet points or numbers.

Reply: Based on your comments, we have revised it. L94-101

18. Objective no. 1: Why 1982 and 2012? It must be clarified in the motivation of the article.

Reply: 1982 was the year when Liaoning began to reform its economy, and 2012 was the year when Liaoning's economy developed rapidly. Similarly, in 1982, small-scale peasant economy was dominant, while agricultural mechanization was relatively low. In 2012, the opposite was true. In addition, we supplemented it in the manuscript. L94-98

Study area

19. Figure 1 should be placed at the end of this sub-section.

Reply: We have moved the Figure to the end of this section. L121

20. Figure 1: Please remove the label “Legend”. Please replace km instead of kilometers in the graphic scale.

Reply: Based on your comment, we have revised Figure 1. L121

Data collection

21. This sub-section should be named “Experimental design”. You should explain firstly the global rationale of your study before giving details of each one of your methodological procedures.

Reply: We have the sub section name to “Experimental design”. In addition, we have revised this part according to your comment. L123-130

22. You must differentiate clearly what you have done and which information has been extracted from other sources, i.e. the variables were collected by other ones.

Reply: We have revised those parts according to your comment. L124-130,173-178

23. Line 130: factors: Please see previous comments.

Reply: We have changed “factors” to “variables” according to your comment. L144

Soil sampling in 2012

24. This sub-section should be named “Soil sampling and analysis”.

Reply: We have changed this sub-section name to “Soil sampling and analysis”. L137

Environmental variables

25. MAT: this value is the average of the 12 months or the average of the 365 days?

Reply: This value is the average of the 12 months.

26. Line 154: Please check this sentence.

Reply: We have revised this wrong sentence. L168

27. The software packages you used should be mentioned at the end of the sub-section.

Reply: According to your comment, we have mentioned the software packages at the end of the sub-section. L167-168

28. Lines 156-157: Please check this sentence.

Reply: Based on your comment, we have revised this sentence. L170-171

29. The formula to calculate NDVI is commonly known.

Reply: We deleted this unnecessary formula. L172

Results and Discussion

30. This section should be divided into two new ones: (3) Results and (4) Discussion

Reply: Based on your comments, we separated Results from Discussion section. See 3. Results and 4. Discussion.

31. Any section or subsection should be started with a figure. They must be placed below the text.

Reply:  We have revised the whole manuscript so that all the figures are under the text.

32. Figure 2: Please delete Year in the x-axis labels.

Reply: We have deleted “Year” in the x-axis labels according to your comment. See Figure 2.

33. Table 1: Why you do not use the correlations of both years together (merged as a single dataset)?

Reply: The environment variables such as B3, B4, B5 and NDVI in the two periods are different, so the data of the two periods cannot be merged together.

34. Figure 5 is quite ugly. Please improve it!

Reply: Based on your comments, we have revised Figure 5. See Figure 5.

Author Response File: Author Response.pdf

Round  2

Reviewer 1 Report

The authors have addressed most of the concerns of this reviewer.  However, there is still need for significant editing of English grammar and usage, especially in the newly revised sections.  Addition of land use as a study factor greatly improved the manuscript.  Specific comments are: 

1.      Line 356:  Change “vegetable” to “vegetative”.

2.      Line 360:  Change “migrated” to “displaced”.

3.      Line 362-363:  “Water erosion and wind erosion…” sentence is awkward and disrupts the flow of ideas.  English grammar and usage editing.

4.      Line 363:  Change “severe erosion” to “moderate erosion”. (Editing).

5.      Line 364:  Change “moderate erosion” to “severe erosion”. (Editing).

6.      Lines 369-370:  Another awkward sentence.  Was SOC loss “in farmland” or “from farmland”?  What do the authors mean by “reclaimed farmland”? It seems that the farmland needs to be reclaimed after erosion.  Is this a task that needs to be done or has it already been done?  Also, the farmland is either in Mississippi (the state) of near the Mississippi River.  I think that it is in Mississippi (the state).  There is a floodplain near the Mississippi River which has soils likely high in SOC due to erosion sediments being deposited here. Again, English editing.

7.      Line 426:  Change “changes” to “changed”.

8.      Line 428:  What are production and living activities?  Do you mean cultivation/farming/crop production activities and human activities (building houses roads etc.)?

9.      Lines 430-431:  Could surface soil acidification be due to the use of acid forming fertilizers as land is converted to crop production?

10.  Line 433:  What are soil salt segregates? Explain. (Editing).

The authors need to address the above remaining concerns, especially, the English editing before the manuscript is accepted for publication.

Author Response

Reviewer 1

General comments:

The authors have addressed most of the concerns of this reviewer.  However, there is still need for significant editing of English grammar and usage, especially in the newly revised sections. Addition of land use as a study factor greatly improved the manuscript. 

Reply: We appreciate your help and your patience. With this submission, we provided a version (Track Changes) of the revised manuscript. Responses to reviewers’ comments on the manuscript of marked are detailed below.

Specific Comments:

1. Line 356:  Change “vegetable” to “vegetative”.

Reply：According to your comment, we have changed “vegetable” to “vegetative”. L356

2. Line 360:  Change “migrated” to “displaced”.

Reply: We have changed “migrated” to “displaced”. L360

3. Line 362-363:  “Water erosion and wind erosion…” sentence is awkward and disrupts the flow of ideas.  English grammar and usage editing.

Reply: In order to keep the passage fluent, we remove this embarrassing sentence. L362-363

4. Line 363:  Change “severe erosion” to “moderate erosion”. (Editing).

Reply: We have changed“severe erosion” to “moderate erosion”. L364

5. Line 364:  Change “moderate erosion” to “severe erosion”. (Editing).

Reply: We have changed“moderate erosion” to “severe erosion”. L364

6. Lines 369-370:  Another awkward sentence.  Was SOC loss “in farmland” or “from farmland”?

Reply: SOC loss from farmland. In order to avoid this confusion, we have this sentence. L369-371

What do the authors mean by “reclaimed farmland”? It seems that the farmland needs to be reclaimed after erosion.  Is this a task that needs to be done or has it already been done?

Reply: This sentence means that after 100 years of farmland reclamation, it is not“reclaimed farmland”. To avoid this ambiguity, we revised the manuscript to “Harden et al. [40] found that nearly 100% of the SOC had been lost after nearly 100 years of farmland cultivation near the Mississippi State, USA.”. L369-371

Also, the farmland is either in Mississippi (the state) of near the Mississippi River.  I think that it is in Mississippi (the state).  There is a floodplain near the Mississippi River which has soils likely high in SOC due to erosion sediments being deposited here. Again, English editing.

Reply: Yes, this is the Mississippi State. In the manuscript, we made corresponding amendments. L369-371

7. Line 426:  Change “changes” to “changed”.

Reply: Based on your comment, we have changed “changes” to “changed”. L429

8. Line 428: What are production and living activities?  Do you mean cultivation/farming/crop production activities and human activities (building houses roads etc.)?

Reply: In order to avoid ambiguity, we revised it to “crop production activities and human activities (building houses roads etc.)”. L431-432

9. Lines 430-431: Could surface soil acidification be due to the use of acid forming fertilizers as land is converted to crop production?

Reply: Your analysis is correct. In response to the questions you mentioned, we have supplemented them in the manuscript. L436-437

10. Line 433: What are soil salt segregates? Explain. (Editing).

Reply: Here should be“ soil salt ions” (Cl^-、SO₂^-4、CO₂^-3、HCO^-3、Na⁺、K⁺、Mg₂⁺、Ca₂⁺). L438-439

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.