Change in Land Use Affects Soil Organic Carbon Dynamics and Distribution in Tropical Systems

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Good work! The paper presents useful and pertinent information. However, some important and major changes are suggested:

1. Title can be rephrased. Example: "Change in land-use effects Soil Organic Carbon Dynamics 2 and Distribution in Tropical Systems"

2. Abstract: Simplify the introductory sentence. Line 18: what sort of coarse fractions? Do the authors mean soil coarse fractions? mention it clearly. Line 21-24: The sentence is long and unclear. Suggest simplifying.

3. Line 66: The authors mentioned "several authors" yet only 1 reference is cited. Please check and update.

4. No hypothesis or objectives mentioned in the text, why? Also, what sort of research gaps does this study fill, clearly specify in the Introduction section.

5. Section 2.5: Elaborate the statistical analyses used in the study in detail.

6. Line 122: What type of "systems"? Specify

7.Section 2.3: Elaborate how the soil sampling was done, the methodology is unclear.

8. Line 172: What does this mean, "Something similar happens....."? Please modify the language.

9. The discussion is less throughout the MS. Suggest updating.

10. The conclusion section is not sufficient. Please mention your major findings in bullet form. Also, suggest some future recommendations.

 

 

Comments on the Quality of English Language

Overall, English language is not up to mark. Please check the grammar throughout, especially the use of tense needs correction.

Author Response

Dear review,

We sincerely appreciate your time and your detailed and constructive comments on our manuscript entitled “Effect of Land Use Change on Soil Organic Carbon Dynamics and Distribution in Tropical Systems”. We have revised the paper following your recommendations, and we are confident that the modifications made have significantly improved the quality of the paper. Below, we respond to each of your comments:

1. Title can be rephrased. Example: "Change in land-use effects Soil Organic Carbon Dynamics and Distribution in Tropical Systems"

Thank you very much. We have considered your suggestion, and the title has been modified as indicated.

 

2. Abstract: Simplify the introductory sentence. Line 18: what sort of coarse fractions? Do the authors mean soil coarse fractions? mention it clearly. Line 21-24: The sentence is long and unclear. Suggest simplifying.

Thank you very much. You will find the modification made in blue color inside the Abstract.

 

3. Line 66: The authors mentioned "several authors" yet only 1 reference is cited. Please check and update.

Thank you very much. We proceeded to modify the structure of the paragraph, which you will find in blue color.

 

4. No hypothesis or objectives mentioned in the text, why? Also, what sort of research gaps does this study fill, clearly specify in the Introduction section.

Thank you very much. You will find in the last paragraph of the Introduction in blue color, where the hypothesis and objectives of the research are more clearly explained and detailed.

 

5. Section 2.5: Elaborate the statistical analyses used in the study in detail.

Thank you very much. First, the data obtained did not meet the assumptions of normality and homogeneity of variance, according to the Shapiro-Wilk and Levene tests, respectively. Therefore, we opted to perform a nonparametric analysis, as detailed in the modifications included in the manuscript, specifically section 2.5 of the Materials and Methods section.

 

6. Line 122: What type of "systems"? Specify

Thank you very much. Throughout the study area and between systems there is a texture ranging from loamy to sandy loam.

 

7.Section 2.3: Elaborate how the soil sampling was done, the methodology is unclear.

Thank you very much. You will find in this section a paragraph explaining in more depth the process from the collection of the samples to the methodologies used in the analysis.

 

8. Line 172: What does this mean, "Something similar happens....."? Please modify the language.

Thank you very much. We have proceeded to review and change the deed.

 

9. The discussion is less throughout the MS. Suggest updating.

Thank you very much. In the Results and Discussion section we have considered improving the statistics and the annex of illustrative graphs, as well as strengthening the discussion of the results.

 

10. The conclusion section is not sufficient. Please mention your major findings in bullet form. Also, suggest some future recommendations.

Thank you very much. We have proceeded to review and improve the conclusions and consider recommendations. Finally, we proceeded to a thorough revision of the English language throughout the document.

 

Finally, we thank you again for your time and effort in reviewing our manuscript. Your suggestions and comments have been invaluable in improving our work.

We remain at your disposal for any further clarification.

Yours sincerely,

Reviewer 2 Report

Comments and Suggestions for Authors

Deforestation, agricultural production, and grazing activities can have significant impacts on the physical, chemical, and biological properties of tropical forest soils, leading to the degradation process of tropical forest soils. The organic matter content in soil not only determines the level of soil fertility, but also has an impact on soil carbon sinks. This paper analyzes the changes in soil bulk density and organic carbon after the transformation of forests in central and eastern Honduras into cultivated land, pastures, and agroforestry land types, using tropical dry forest soil as a control. This is of great significance for understanding the impact of human agricultural activities on the dynamic changes in soil bulk density and organic carbon in tropical forests. This paper has detailed data and a reasonable research approach, but significant modifications are needed in terms of paper structure, analysis methods, and depth of content.

Here are a few revision suggestions for the author to further consider and improve during the paper revision process.

1. The paper only analyzed the changes in soil bulk density and organic carbon content after tropical forests were converted into arable land, grazing and other land types, and the data analysis method was single, resulting in insufficient research depth overall;

2. It is recommended to use statistical analysis methods such as analysis of variance and multiple comparisons on the basis of existing data analysis methods, draw data change charts, further discuss the differences in soil bulk density and organic carbon content under different land use conditions, and explain the reasons for the differences based on the characteristics of land use types;

3. It is suggested that the author further supplement and improve the experiment, increase the determination of relevant soil physical, chemical, and biological indicators, and conduct in-depth comparative research on the impact of agricultural activities on soil bulk density and organic carbon change in tropical forests from the years of conversion from tropical forests to arable land and the intensity of human use;

4. In the "Results and Discussion" section, it is recommended to further optimize the structural hierarchy of the paper by exploring the research results information and providing in-depth discussions on the research results from 3-4 aspects, in order to make the hierarchical structure of the paper clearer and increase the writing depth of this paper;

5. There is also a problem of insufficient analysis depth in the discussion section of the paper. It is suggested to separately list the content of the "Discussion" section, combined with the current research progress on soil bulk density and organic carbon changes caused by human agricultural activities, to further explain the reasons for the changes in soil bulk density and organic carbon after the transformation of forests in the central and eastern regions of Honduras into cultivated land, pastures, and agroforestry land types.

Comments on the Quality of English Language

The overall English writing is good, only requiring appropriate modifications and improvements.

Author Response

Dear review,

We sincerely appreciate your time and your detailed and constructive comments on our manuscript entitled “Effect of Land Use Change on Soil Organic Carbon Dynamics and Distribution in Tropical Systems”. We have revised the paper following your recommendations, and we are confident that the modifications made have significantly improved the quality of the paper. Below, we respond to each of your comments:

1. The paper only analyzed the changes in soil bulk density and organic carbon content after tropical forests were converted into arable land, grazing and other land types, and the data analysis method was single, resulting in insufficient research depth overall;

Thank you very much. The main objective of the research was to evaluate the dynamics and distribution of total soil organic carbon (TOC) in different systems, comparing them with a primary forest in a tropical region. Although bulk density, together with other variables such as soil organic carbon and coarse soil fragments, is part of an integral formula, we were particularly interested in the behavior of bulk density, which is described in detail in the paper. As for TOC, which is the central focus of the research, we worked at three depth levels (0.00-0.10 m, 0.10-0.20 m and 0.20-0.30 m). The analysis presented in the discussion was carried out considering a single average value of 0.00-0.30 m, following IPCC recommendations. On the other hand, for a better understanding of the work, please refer to the supplementary materials section, where the database is provided.

 

2. It is recommended to use statistical analysis methods such as analysis of variance and multiple comparisons on the basis of existing data analysis methods, draw data change charts, further discuss the differences in soil bulk density and organic carbon content under different land use conditions, and explain the reasons for the differences based on the characteristics of land use types;

Thank you very much. First, the data obtained did not meet the assumptions of normality and homogeneity of variance, according to the Shapiro-Wilk and Levene tests, respectively. Therefore, we chose to perform a nonparametric analysis, as detailed in the paper. In addition, the paper includes considerations to improve the statistical analysis, as well as annexes with illustrative and representative figures that further enrich the discussion.

 

3. It is suggested that the author further supplement and improve the experiment, increase the determination of relevant soil physical, chemical, and biological indicators, and conduct in-depth comparative research on the impact of agricultural activities on soil bulk density and organic carbon change in tropical forests from the years of conversion from tropical forests to arable land and the intensity of human use;

Thank you very much. Due to the large number of samples obtained in the field and the complexity of the variables, this study focused specifically on the behavior of total organic carbon in different systems, comparing them with a primary forest. However, this work is part of a macro project, and we are currently developing a second paper related to soil fertility and some biological parameters in these systems.

 

4. In the "Results and Discussion" section, it is recommended to further optimize the structural hierarchy of the paper by exploring the research results information and providing in-depth discussions on the research results from 3-4 aspects, in order to make the hierarchical structure of the paper clearer and increase the writing depth of this paper;
5. There is also a problem of insufficient analysis depth in the discussion section of the paper. It is suggested to separately list the content of the "Discussion" section, combined with the current research progress on soil bulk density and organic carbon changes caused by human agricultural activities, to further explain the reasons for the changes in soil bulk density and organic carbon after the transformation of forests in the central and eastern regions of Honduras into cultivated land, pastures, and agroforestry land types.

 

Thank you very much. We proceeded to improve the structure and discussion of the results. Finally, we proceeded to a thorough revision and improvement of the English language throughout the document.

 

Finally, we thank you again for your time and effort in reviewing our manuscript. Your suggestions and comments have been invaluable in improving our work.

We remain at your disposal for any further clarification.

Yours sincerely,

Reviewer 3 Report

Comments and Suggestions for Authors

Effect of Land-Use Change on Soil Organic Carbon Dynamics and Distribution in Tropical Systems by Selvin Antonio Saravia-Maldonado et al.

Overall

The work describes a field experiment in Honduras to compare the Bulk Density and TOC in soils under a range of land-uses following historical forest clearance.  It would be of moderate interest to readers of SS but I feel requires more focusing on the international significance of the work.  This is not emphasised particularly well in the manuscript as it is currently written.

There are a few specific changes that I think need attention:

I cant help feeling the introduction is a little over done.  Becomes a list of citations most making the same point regarding management and soil degradation.  Could be shorter and more focused.

All ultimately to assess changes to soils under different land-uses.  Which I don’t believe is particularly novel.

The whole manuscript also requires a more detailed proof-read to resolve the numerous grammatical and expression issues.  One particular issue is tense.  All should be past tense throughout.

Experimental design, soil and data collection, land and statistical analysis require more detail.

TOC values should really be corrected for equivalent mass.

Methods

The method of field sampling is not clear.  How large were plots? How many samples per plot?  Arranged how ?

Were Bulk Density and SOC analysis conducted on separate samples ?  Or the same samples ?

Line 146-151  Seems to suggest no correction for equivalent mass.  This is problematic where there is a demonstrable change in Bulk Density between land-uses.

Given the multi-factor nature of the dataset, I am not sure that the Mann-Whitney U test is sufficiently robust.

Results and Discussion

Line 168-171 It is not at all clear how you can have a significant increase in BD yet suggest that soil compaction is not occurring.

There is also a large degree of repetition in the Results and Discussion – e.g. referring back to probable causes of increased BD.

There is a suggestion that there were differences in BD with depth.  The increase in BD with increasing depth is almost universal, so hardly novel.  What would have been interesting is an exploration of how these BD gradients changed with management.  But statistical analysis is probably not sufficiently detailed to do this.

Line 212-218 Tis value of 1.55 seems rather arbitrary to me.  I would have thought that increased BD is an indicator of trajectory toward increased compaction.  That in itself would be alarming enough.

I am a little troubled by the firm conclusion that pasture TOC does not differ from forest TOC when there is a clear difference in Bulk Density yet this has not been accounted for in an equivalent mass calculation. Increased BD will by its very nature increase apparent TOC – so this needs to be corrected to ensure an appropriate outcome.

Comments on the Quality of English Language

Requires some editing to resolve numerous grammatical and expression issues.

Author Response

Dear review,

We sincerely appreciate your time and your detailed and constructive comments on our paper entitled “Effect of Land Use Change on Soil Organic Carbon Dynamics and Distribution in Tropical Systems”. We have revised the paper following your recommendations, and we are confident that the modifications made have significantly improved the quality of the paper. Below, we respond to each of your comments.:

There are a few specific changes that I think need attention:

1. I cant help feeling the introduction is a little over done.  Becomes a list of citations most making the same point regarding management and soil degradation.  Could be shorter and more focused.

Thank you very much. The Introduction was revised and modified according to your suggestions.

 

2. All ultimately to assess changes to soils under different land-uses.  Which I don’t believe is particularly novel.

Thank you very much. We recognize that carbon assessment is not a novel topic. However, in this work we seek to provide information on the impact of land use change on carbon inputs in different systems, especially in little studied tropical environments and with a focus on periods of approximately 40 years.

 

3. The whole manuscript also requires a more detailed proof-read to resolve the numerous grammatical and expression issues.  One particular issue is tense.  All should be past tense throughout.

Thank you very much. The entire manuscript was revised as indicated.

 

4. Experimental design, soil and data collection, land and statistical analysis require more detail. TOC values should really be corrected for equivalent mass.

Thank you very much. The manuscript includes all the modifications and improvements made, specifically from field sampling, analysis methodologies and statistics. Regarding soil organic carbon (COS), pasture areas showed equal or higher values than forest, and this relationship was also observed in total organic carbon (TOC). Scientific literature supports these findings, reporting equal or higher values in pasture areas compared to forest. Therefore, in this research, both results were maintained, and we did not consider it necessary to apply correction processes.

 

Methods

5. The method of field sampling is not clear.  How large were plots? How many samples per plot?  Arranged how ?

Thank you very much. In the Materials and Methods section, you will find the modifications and improvements made, specifically sections 2.3, 2.4 and 2.5.

 

6. Were Bulk Density and SOC analysis conducted on separate samples ?  Or the same samples ?

Thank you very much. For bulk density (BD) and soil organic carbon (SOC) analysis, the same sampling points were used. Both disturbed and undisturbed samples were collected.

 

7. Given the multi-factor nature of the dataset, I am not sure that the Mann-Whitney U test is sufficiently robust.

Thank you very much. With the Mann-Whitney U test, we performed independent comparisons of means, in response to suggestions from other colleagues, who indicated the opportunity to apply this nonparametric statistical test.

Results and Discussion

8. Line 168-171 It is not at all clear how you can have a significant increase in BD yet suggest that soil compaction is not occurring. There is also a large degree of repetition in the Results and Discussion – e.g. referring back to probable causes of increased BD. There is a suggestion that there were differences in BD with depth.  The increase in BD with increasing depth is almost universal, so hardly novel.  What would have been interesting is an exploration of how these BD gradients changed with management.  But statistical analysis is probably not sufficiently detailed to do this.

Thank you very much. Actually, the compaction process is happening as can be seen in the results, what is not presented are limiting thresholds in the bulk density. We also proceeded in the paper to improve the statistics (Tables), added illustrative multifactorial graphs, clarification and modification of paragraphs, as well as in the discussion that is carried out.

 

9. Line 212-218 Tis value of 1.55 seems rather arbitrary to me.  I would have thought that increased BD is an indicator of trajectory toward increased compaction.  That in itself would be alarming enough.

Thank you very much. Modifications and improvements have been included in the wording and in the Results and Discussion section.

 

10. I am a little troubled by the firm conclusion that pasture TOC does not differ from forest TOC when there is a clear difference in Bulk Density yet this has not been accounted for in an equivalent mass calculation. Increased BD will by its very nature increase apparent TOC – so this needs to be corrected to ensure an appropriate outcome.

Thank you very much. Again, we agree with your opinion. We also emphasize that before the conversion from SOC to TOC, the values in managed pasture areas were equal or higher, and statistically equal to the forest. In this sense, we do not consider this assessment. Likewise, the scientific literature reports findings of pasture areas with higher TOC values when compared to forest or vice versa. We believe that a correct management of pastures can be beneficial in carbon sequestration.

 

Finally, we proceeded to a thorough revision and improvement of the English language throughout the document.

Finally, we thank you again for your time and effort in reviewing our paper. Your suggestions and comments have been invaluable in improving our work.

We remain at your disposal for any further clarification.

Yours sincerely,

Reviewer 4 Report

Comments and Suggestions for Authors

This research shows how different management practices affect soil organic carbon after deforestation in a tropical forest. Several areas with different land management practices are reviewed to see how SOC and bulk density changed as compared to an intact forest. Interestingly, grazing pastures showed greater SOC and bulk density than intact forest, indicating that
adequate grazing practices can help the system to store carbon. However,
the increase in bulk density might indicate that something else is going on.

The research is simple but properly conducted and provides important and useful information about land management and historical disturbance.

I would recommend to do some minor revisions, particularly to the abstract to make it more clear as some sentences are confusing.
 
14. SOC assessments by themselves do not reduce greenhouse gas emissions, or mitigate climate change... The assessments are needed to understand the effects from anthropogenic activities on soil carbon,
so we can do management practices that can effectively reduce emissions or sequester carbon (such as grazing, overseeding, reducing stocking rates, tree planting).


18 and 144. What was the purpose of the coarse fragments? They were part of the formula to estimate SOC and bulk density? The way is described right now in the abstract makes it sound as it is another evaluated parameter. Could you please provide more details on this?

21. "deforestation has caused a decrease of 44%, from a decrease of 17% in agricultural 21 soils to 48% in agroforestry soils" This sentence is confusing, please reword it, it is not clear what is reduced by 44% and why.

25. Bulk density could be associated to the machinery used in the pasture (as mentioned in the discussion), is there data about the machinery being constantly used? It would be important to know to advise land managers about options to reduce soil compaction, if needed.
 
Line 100: This is the objective. What is the hypothesis of the study? Since you are comparing different groups with the "baseline" (DTF), I would assume that the hypothesis is that your groups (GC, HG, ASP, AFC, CP, GP) are different from the baseline as a result of the disturbance.

Methods:
What was the process to estimate bulk density? What type of equipment was used to dig the metal ring into the soil?

Statistical analysis
Could you please provide mode details on the statistics? Did you use the current method because there was not a normal distribution? What did you used to test for normality?

Results and discussion

Is very interesting that TOC is slightly greater in the pastures used for livestock, suggesting that adequate livestock grazing of forages, over time, helps to increase soil organic carbon faster as compared to the other management practices. However, it would be important to know more about the possible reasons for the bulk density to increase.

Was soil texture analyzed in the study? It could be useful to know if soil texture varied around the experimental area too.

Comments on the Quality of English Language

Overall the English is good, it is not difficult to read and understand. I just recommend some minor adjustments to the grammar, particularly to the abstract.

Author Response

Dear review,

We sincerely appreciate your time and your detailed and constructive comments on our paper entitled “Effect of Land Use Change on Soil Organic Carbon Dynamics and Distribution in Tropical Systems”. We have revised the paper following your recommendations, and we are confident that the modifications made have significantly improved the quality of the paper. Below, we respond to each of your comments:

14. SOC assessments by themselves do not reduce greenhouse gas emissions, or mitigate climate change... The assessments are needed to understand the effects from anthropogenic activities on soil carbon, so we can do management practices that can effectively reduce emissions or sequester carbon (such as grazing, overseeding, reducing stocking rates, tree planting).

Thank you very much. You will find in the Abstract a blue paragraph with the modifications made according to the indications.

 

18 and 144. What was the purpose of the coarse fragments? They were part of the formula to estimate SOC and bulk density? The way is described right now in the abstract makes it sound as it is another evaluated parameter. Could you please provide more details on this?

Thank you very much. Coarse fragments refer to soil mineral particles > 2 mm and are only an integral part of the formula for calculating total organic carbon (TOC). When evaluated as a variable in isolation, it has more importance when the study refers to soil taxonomy.

 

21. "deforestation has caused a decrease of 44%, from a decrease of 17% in agricultural 21 soils to 48% in agroforestry soils" This sentence is confusing, please reword it, it is not clear what is reduced by 44% and why.

Thank you very much. This sentence has been reviewed and modified, as indicated in the abstract and conclusions sections.

 

25. Bulk density could be associated to the machinery used in the pasture (as mentioned in the discussion), is there data about the machinery being constantly used? It would be important to know to advise land managers about options to reduce soil compaction, if needed.

Thank you very much. We agree with your comment. Over time, the same type of machinery and the same soil preparation practices have been used. Specifically, a heavy traction tractor, with irregular wheels, and a moldboard plow are used to rototill and turn the soil, followed by disk plow passes. So far, some improvements have been proposed, such as the use of subsoiler plows, the incorporation of organic matter, and the implementation of rest periods with the establishment of leguminous plants, among others.

 

Line 100: This is the objective. What is the hypothesis of the study? Since you are comparing different groups with the "baseline" (DTF), I would assume that the hypothesis is that your groups (GC, HG, ASP, AFC, CP, GP) are different from the baseline as a result of the disturbance.

Thank you very much. We have proceeded to modify the Introduction section, adding a new paragraph (in blue color), where our hypothesis and the objectives of the work are explained in greater detail.

 

Methods:

What was the process to estimate bulk density? What type of equipment was used to dig the metal ring into the soil?

Thank you very much. In the manuscript, the Materials and Methods section has been revised and restructured, specifically sections 2.3 and 2.4, with the objective of detailing more clearly the whole process, from the soil sampling stage to the methodologies used in each analysis.

 

Statistical analysis:

Could you please provide mode details on the statistics? Did you use the current method because there was not a normal distribution? What did you used to test for normality?

Thank you very much. The data obtained did not meet the assumptions of normality and homogeneity of variance, according to the Shapiro-Wilk and Levene tests, respectively. Therefore, it was decided to perform a nonparametric analysis, as detailed in the modifications included in the manuscript, specifically in section 2.5 of the Materials and Methods section.

 

Results and discussion

Is very interesting that TOC is slightly greater in the pastures used for livestock, suggesting that adequate livestock grazing of forages, over time, helps to increase soil organic carbon faster as compared to the other management practices. However, it would be important to know more about the possible reasons for the bulk density to increase.

Thank you very much. We agree with your comment and suggestion. Therefore, we have improved the statistical analysis and added images to clarify and enrich the Results and Discussion section.

 

Was soil texture analyzed in the study? It could be useful to know if soil texture varied around the experimental area too.

Thank you very much. The study area is, in general terms, homogeneous in terms of its formation and edaphoclimatic characteristics. Textural analyses were carried out in the different systems studied without observing significant variations, with results ranging from loamy to sandy loam texture (see section 2.1 in Materials and Methods). For this reason, we did not consider texture as a determining variable and focused on soil uses. Finally, we proceeded to a thorough revision and improvement of the English language throughout the manuscript.

 

Finally, we thank you again for your time and effort in reviewing our manuscript. Your suggestions and comments have been invaluable in improving our work.

We remain at your disposal for any further clarification.

Yours sincerely,

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Good job!