A Review on Carbon Source and Sink in Arable Land Ecosystems

Round 1

Reviewer 1 Report

This is an interesting and well-structured review of carbon sources and sinks in arable land ecosystems. The methodology used is sound and the paper is also relevant in the context of climate change, which is the greatest global environmental challenge of the 21st century. Therefore, I would recommend its publication, but only after a minor revision in view of the following specific comments.

Abstract

Information about the background is too redundant. At the same time, that authors failed to tell use what conclusions they have drawn from the synthesis review. So I suggest to shorten the background while iterate several results and conclusions. Review paper still need to show us with results and conclusions. In the present form, only content on Lines 27-30 is about the results and conclusions, which is too simple considering the whole manuscript.

The authors should pay more attention to the English language.

L17-18：have strong carbon storage capacity？try to revise this sentence

L17-18: arable land ecosystem is one of the ···

L19: has -> have

Line 76-86, add appropriate references

L99: “carbon sink”

Line 262-271, add appropriate references

L189 change “ecosystem” to ecosystems

Table 1 needs to show the specific study areas and which studies the results come from

Figure 1 Only one figure was shown in the entire manuscript. I suggest to add one or two figures to summarize the current methods or approaches being used for section 2 or 4.

Section 4.1 can be combined with the current background of frequent extreme climate events to appropriately increase the research results of their impact on carbon sources and sinks.

4.2.4 The latest research results are rarely introduced and need to be added

I think the section 5 is too short at the present form. For example, Lines 541-543 is too vague. As a remedy, the authors could give some examples to show us with what kind of high-tech should be used in the future.

The English used is good enough and easy to follow, but it can still be improved.

Author Response

Reviewer: 1

Comments and Suggestions for Authors

This is an interesting and well-structured review of carbon sources and sinks in arable land ecosystems. The methodology used is sound and the paper is also relevant in the context of climate change, which is the greatest global environmental challenge of the 21st century. Therefore, I would recommend its publication, but only after a minor revision in view of the following specific comments.

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 manuscript of marked are detailed below.

Detailed comments

1. Information about the background is too redundant. At the same time, that authors failed to tell use what conclusions they have drawn from the synthesis review. So I suggest to shorten the background while iterate several results and conclusions. Review paper still need to show us with results and conclusions. In the present form, only content on Lines 27-30 is about the results and conclusions, which is too simple considering the whole manuscript.

Reply: Based on your comments, we have revised the abstract. We shortened the background and then added results. L26-34

2. The authors should pay more attention to the English language.

Reply: Based on your comments, we invite native English speaking researchers to revise the full text of the manuscript.

3. L17-18: have strong carbon storage capacity? try to revise this sentence

Reply: Based on your comments, we thought this sentence was redundant, so we removed it. L17

4. L17-18: arable land ecosystem is one ofthe...

Reply: We have changed “Arable land ecosystems are” to “Arable land ecosystem is ”. L17

5. L19: has -> have

Reply: We have changed “has” to “have”. L18

6. Line 76-86.add appropriate references

Reply: Based on your comments, we have added appropriate references. L88-96

7. L99: “carbon sink"

Reply: We have changed “Carbon sink” to “carbon sink”. L108

8. L189change "ecosystem" to ecosystems

Reply: Based on your comments, we have changed “ecosystem’” to “ecosystems”. L200

9. Line 262-271.add appropriate references

Reply: Based on your comment, we have added appropriate references. L289-299

10. Table 1 needs to show the specific study areas and which studies the results come from

Reply: Based on your comment, we have added references and study areas information to better display the information of the table. Table 1, L441-442

11. Figure 1Only one figure was shown in the entire manuscript. I suggest to add one or two figures to summarize the current methods or approaches being used for section 2 or 4.

Reply: Based on your comment, we have added a figure to introduce the current methods more intuitive in Section 3. Figure 1, L210-213

12. Section 4.1 can be combined with the current background of frequent extreme climate events to appropriatelyincrease the research results of their impact on carbon sources and sinks.

Reply: Based on your comments, we have added the part in the manuscript. L403-408

13. 2.4 The latest research results are rarely introduced and need to be added

Reply: Based on your comments, we have added the suggested in the manuscript. L544-556 

14. I think the section 5 is too short at the present form.For example, Lines 541-543 is too vague. As a remedy, the authors could give some examples to show us with what kind of high-tech should be used in the future.

Reply: Based on your comments, we have added more examples in the manuscript. L598-602

We thank reviewer`s constructive comments, which significantly help improve our manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors,

I believe the significance of this study is valuable, however, it should be improved before it is published.

Line 4: “Chunlan, Han”

Chunlan Han

Lines 22-23: “Different arable land management measures, research areas and arable land planting strategies will have an important impact on the carbon storage of arable land ecosystems”

I would remove “research areas” from this sentence or explain it better.

Lines 44-46: “After the late 1980s, many scholars found that although the land may retain some carbon, the terrestrial ecosystem has been emitting carbon to the atmosphere all the time from a global perspective, making it in a state of carbon imbalance.”

The word “some” in this sentence is very imprecise.

Why “making it in a state of carbon imbalance”?

Lines 46-47: “According to statistics, more than 70% of the global total greenhouse effect is caused by greenhouse gases released by human activities”

Please, add a reference.

Lines 50-51: “arable land ecosystems had a weaker carbon source or carbon sink”

Had or were?

Lines 53-54. “recent studies have shown that in terms of net ecosystem productivity, arable land ecosystems have the same or even higher level as forest ecosystems”.

Which recent studies? Add references.

Line 55: “Arable land ecosystems account for 37% of the earth's land area”

Please, add the reference. Is number [7]?

Line 99: “carbon sink” instead of “Carbon sink”

Lines 105-107: “Many scholars usually used two indicators-net primary productivity (NPP) and net ecosystem exchange (NEE) of vegetation to describe the carbon source and sink of ecosystem”

Perhaps: Many scholars usually used two indicators, net primary productivity (NPP) and net ecosystem exchange (NEE) of vegetation, to describe the carbon source and sink of ecosystem.

Line 133: “Global terrestrial SOC stocks are about 1400-1500 PgC…”

Please add that it is in the first meter of soil.

Line 148: “satellite images, hyperspectral remote sensing technology”

Suggestion: satellite images and hyperspectral remote sensing technology.

Lines 150-152: “Tommaso et al. [33] considered the whole arable land category, it was estimated that the average SOC stock in the topsoil (30 cm) of Italy was 52.1 ± 17.4 MgC ha-1…”

Rewrite the sentence. Perhaps: Tommaso et al. [33] considering the whole arable land category estimated that …

Lines 153-154: “Sleutel et al. [34] combined SOC data with arable land area data, the SOC stocks of arable land was about 49000 tons in Belgium”

This sentence is not clear.

Line 154: “In French, ….”

In France, …

Line 164: “0.75-1.0PgC yr-1”

As far as I know, the SI prescribes inserting a space between a number and a unit of measurements units. Review the article considering this. (line 252: 77g C cm-2, line 504, 505, …)

Line 169: “Wang et al. [40]predicted”.

Wang et al. [40] predicted

Line 302: Wu et al. [65]also

Wu et al. [65] also

Lines 175-176: “If more incentive policies could be formulated and implemented, China's arable land soil carbon sequestration would be doubled”.

It is imprecise to say that it would be doubled without data that support it.

Lines 179-181: “It can be seen that arable land ecosystem has strong carbon sequestration

capacity, and different land use patterns, different soil types and fertilization methods will affect the soil carbon stocks capacity.”

Review English.

Lines 183-184: “As a subsystem of terrestrial ecosystems, arable land ecosystems are most closely related to human beings”.

It is a very general statement.

Lines 196-197: “This method was currently the most popular technology in small-scale research”

Suggestion: This method is currently the most popular technology in small-scale research

Lines 215-216: “which hindered understanding of the soil depth of gas generation and movement in the soil profile”.

It is not clear. Perhaps: which hindered understanding of the relation between soil depth and gas generation and movement in the soil profile

Line 216-217: “Granli [49] proposed a gradient method calculated by Fick's law to measure the gas flux”

Review the word “calculated”. I suppose they proposed a gradient method in which they used Fick's law to measure the gas flux.

Lines 247-248: “Wang et al. [55] studied the net carbon budget of winter wheat summer maize…”

winter wheat-summer maize

Lines 250-252: Please review the units. It is not cm-2.

Wheat season was C sink (90 g C m−2); maize season was C source (167 g C m−2).

Line 317: “Figure 1 showed”

Figure 1 shows

Line 321: “a arable system”

an arable system

Line 325: “4.Main factors”    see also line 514

4. Main factors

Lines 336-337: “Climate first controls the NPP above and below the ground, thus the input of organic matter, microbial activities in soils result in carbon loss”

I think it is not well expressed. Are you talking about soil carbon loss? If you have an input of organic matter you do not have a carbon loss.

Line 338: “had confirmed”

have confirmed

Lines 347-348: ”which might be that the increase of soil carbon input may exceed the carbon loss caused by temperature”

Review the English.

Lines 359-360: “water was the basic driver of almost all chemical and biological processes”

water is the basic driver of almost all chemical and biological processes

Lines 387-388: “No tillage and less tillage had significant effects on the increase of SOC stocks and the change of microbial biomass carbon”

If you write “had significant effects” you must show pieces of evidence. Line 393: topsoil(0-30cm) topsoil (0-30cm) Line 395: “covering the residues of crops”???? 

Lines 394-398: Please review the structure of the sentence “In addition, increasing the complexity of crop rotation and covering the residues of crops could also increase SOC and reduce greenhouse gas emissions [87] which was due to the high use of nitrogen fertilizer, and the absorption of crops is usually less than half of the nitrogen application”.

Line 407: Table 1 CARBONSEQUESTRATION POTIENTIAL

CARBON SEQUESTRATION POTENTIAL

 Line 407: Table 1: a) I think you should write the references from where you have obtained the data.b) TG CA-1??? 

Line 415: “had reported” 

have reported 

Line 421: “showed in meta-analysis” 

showed in a  meta-analysis 

Line 454: “SOM accumulated by drought” 

Perhaps: release SOM accumulated during drought periods 

Line 489: “also had focused” 

had also focused 

Line 495: “A study”

In a study….

Author Response

Reviewer: 2

Comments and Suggestions for Authors

I believe the significance of this study is valuable, however, it should be improved before it is published.

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 manuscript of marked are detailed below.

Detailed comments

1. Line4"Chunian，Han” — “Chunian Han”

Reply: We have modified in the manuscript. L4

2. Lines22-23:"Different arable land management measures, research areas and arable land planting strategies will have an important impact on the carbon storage of arable land ecosystems"

I would remove "research areas" from this sentence or explain it better

Reply: Based on your comments, we have removed “research areas”. L21

3. Lines 44-46:"After the late 1980s, many scholars found that although the land may retain some carbon, the terrestrial ecosystem has been emitting carbon to the atmosphere all the time from a global perspective, making it in a state of carbon imbalance.

The word "some" in this sentence is very imprecise

Why "making it in a state of carbon imbalance"?

Reply: After checking the manuscript, we have removed “some”. L48

The reason of "making it in a state of carbon imbalance" is that: the metabolism of the Earth is essentially in dynamic equilibrium, which means the transfer rate of carbon between different pools remains the same over a certain time period, or there is no net change. Since the Industrial Revolution, human activities have released carbon stored in terrestrial ecosystems into the atmosphere in the form of CO2 through cultivation and fossil fuel burning, thus break the original carbon balance.

And we have explained the reason why the ecosystem was in a state of carbon imbalance in the manuscript. L42-45

4. Lines 46-47:"According to statistics, more than 70% of the global total greenhouse effect is caused by greenhouse gases released by human activities.  add a reference

Reply: Based on your comments, we have added appropriate references. L50-52

5. Lines 50-51:"arable land ecosystems had a weaker carbon source or carbon sink". Had or were?

Reply: After checking the manuscript, we have changed “had” to “were”. L56

6. Lines 53-54"recent studies have shown that in terms of net ecosystem productivity arable land ecosystems have the same or even higher level as forest ecosystems". Which recent studies? Add references

Reply: Based on your comments, we have added appropriate references. L59-62

7. Line 55:"Arable land ecosystems account for 37% of the earths land area. Please, add the reference. Is number [7]?

Reply: After checking the manuscript, we have added the reference and the number is [13]. L64

8. Line 99:"carbon sink" instead of Carbon sink

Reply: We have changed “Carbon sink” to “carbon sink”. L108

9. Lines 105-107:Many scholars usually used two indicators-net primary productivity (NPP) and net ecosystem exchange (NEE) of vegetation to describe the carbon source and sink of ecosystem. Perhaps: Many scholars usually used two indicators, net primary productivity (NPP) and net ecosystem exchange (NEE) of vegetation, to describe the carbon source and sink of ecosystem

Reply: Based on your comments, we have modified this sentence into “Many scholars usually used two indicators, net primary productivity (NPP) and net ecosystem exchange (NEE) of vegetation, to describe the carbon source and sink of ecosystem”. L114-116

10. Line 133:"Global terrestrial SOC stocks are about 1400-1500 PgC " Please add that it is in the first meter of soil.

Reply: Based on your comments, we have added the suggested in the manuscript. L153

11. Line 148:"satellite images, hyperspectral remote sensing technology. Suggestion: satellite images and hyperspectral remote sensing technology

Reply: Based on your comments, we have revised in the manuscript. L166

12. Lines 150-152:"Tommaso et al. [33] considered the whole arable land category, it was estimated that the average SOC stock in the topsoil (30cm) of Italy was 52.1±17.4MgCha^-1…" Rewrite the sentence. Perhaps Tommaso et al. [33] considering the whole arable land category estimated that...

Reply: Based on your comments, we have modified this sentence into “Considering the whole arable land category, Tommaso et al. [50] estimated that”. L168-169

13. Lines 153-154:"Sleutel et al. [34] combined SOC data with arable land area data, the SOC stocks of arable land was about 49000 tons in Belgium” This sentence is not clear

Reply: Based on your comments, we have modified this sentence into "Sleutel et al. [51], combining SOC data with arable land area data, estimated that the SOC stocks of arable land was about 49000 tons in Belgium”. L171-172

14. Line 154:"In French...."→In France,.

Reply: Based on your comments, we have revised the manuscript. L172

15. Line 164: 0.75-1.0PgCyr^-1. As far as I know,the SI prescribes inserting a space between a number and a unit of measurements units. Review the article considering this (line 252: 77gC cm^-2, line 504, …)

Reply: Based on your comments, we have revised the manuscript. L182, L278, L540, L541, L542

16. Line 169:"Wang et al.[40]predicted.→Wang et al [40] predicted

Reply: Based on your comments, we have revised the manuscript. L187

17. Line 302: Wuet al.[65]also →“Wu et al. [65] also”

Reply: Based on your comments, we have revised the manuscript. L329

18. Lines 175-176:"If more incentive policies could be formulated and implemented, China’s arable land soil carbon sequestration would be doubled.

It is imprecise to say that it would be doubled without data that support it

Reply: We have added appropriate reference. L194

19. Lines 179-181:" It can be seen that arable land ecosystem has strong carbon Sequestration capacity, and different land use patterns, different soil types and fertilization methods will affect the soil carbon stocks capacity. Review English.

Reply: Based on your comments, we have revised this sentence into “Therefore, adopting the optimal management practices will provide more opportunities to improve soil carbon sequestration”. L197-199

20. Lines 183-184: As a subsystem of terrestrial ecosystems, arable land ecosystems are most closely related to human beings.” It is a very general statement

Reply: Based on your comments, we have added appropriate references and revised this sentence to “As a subsystem of terrestrial ecosystems, arable land ecosystem is most closely related to human beings, because it not only provides food, fiber, fuel and other products continuously for human beings, but also supports and maintains the natural environment on which human beings depend for survival [26]". L201-204

21. Lines 196-197:This method was currently the most popular technology in small scale research” Suggestion: This method is currently the most popular technology in small-scale research

Reply: Based on your comments, we have revised in the manuscript. L222

22. Lines 215-216:"which hindered understanding of the soil depth of gas generation and movement in the soil profile”. It is not clear Perhaps which hindered understanding of the relation between soil depth and gas generation and movement in the soil profile.

Reply: Based on your comments, we have revised it into “which hindered understanding of the relation between soil depth and gas generation and movement in the soil profile”. L240-242

23. Line 216-217"Granli[49] proposed a gradient method calculated by Fick's law to measure the gas flux" Review the word" calculated I suppose they proposed a gradient method in which they used Fick's law to measure the gas flux.

Reply: Based on your comments, we have revised it into “Granli [66] proposed a gradient method in which they used Fick's law to measure the gas flux in the soil profile based on the gas concentration gradient in the soil profile” in the manuscript. L242-244

24. Lines247-248:"Wanget al. [55] studied the net carbon budget of winter wheat summer maize.

Winter wheat-summer maize

Reply: Based on your comments, we have revised in the manuscript. L274

25. Lines 250-252: Pleasereview the units. It is not cm-2

Wheat season was C sink (90gCm^-2); maize season was C source (167gCm^-2).

Reply: Based on your comments, we have revised in the manuscript. L276-277

26. Line 317:"Figure 1 showed→Figure1shows

Reply: Based on your comments, we have revised in the manuscript. L347

27. Line 321:"a arable system→an arable system

Reply: Based on your comments, we have revised in the manuscript. L350

28. Line 325:"4.Main factors" seealso line 514→Main factors

Reply: Based on your comments, we have revised in the manuscript. L354, L560

29. Lines 336-337: Climate first controls the NPPabove and below the ground. thus the input of organic matter, microbial activities in soils result in carbon loss. I think it is not well expressed. Are you talking about soil carbon loss? If you have an input of organic matter you do not have a carbon loss.

Reply: Based on your comments, we have revised this sentence into “Climate controls NPP above and below the ground and thus the input of organic matter, also climate contributes to carbon loss by driving the output of organic matter through microbial activity in the soil”. L365-367

30. Line 338:"hadconfirmed"→have confirmed

Reply: Based on your comments, we have revised in the manuscript. L368

31. Lines 347-348:"which might be that the increase of soil carbon input may exceed the carbon loss caused bytemperature". Review the English.

Reply: Based on your comments, we have revised it to “which might ascribe to the increase of soil carbon input exceeded the carbon loss caused by elevated temperature”. L377-378

32. Lines 359-360:"water was the basic driver of almost all chemical and biological processes

water is the basic driver of almost all chemical and biological processes

Reply: Based on your comments, we have revised in the manuscript. L389-390

33. Lines 387-388:"No tillage and less tillage had significant effects on the increase ofSOC stocks and the change of microbial biomass carbon”. If you write" had significant effects " you must show pieces of evidence.

Reply: Based on your comments, we have added appropriate references. L423

34. Line 393: topsoil(0-30cm)→topsoil (0-30cm)

Reply: Based on your comments, we have revised in the manuscript. L428 

35. Line 395: covering the residues of crops"????

Reply: Based on your comments, we have revised it into “straw return”. L430

36. Lines394-398: Please review the structure of the sentence" In addition, increasing the complexity of crop rotation and covering the residues of crops could also increase soc and reduce greenhouse gas emissions [87]which was due to the high use of nitrogen fertilizer, and the absorption of crops is usually less than half of the nitrogen application".

Reply: Based on your comments, we have revised into “In addition, increasing the complexity of crop rotation and straw return could also increase SOC and reduce greenhouse gas emissions [99]. In monoculture system, crops uptake less than half the amount of nitrogen fertilizers normally, through crop rotation, other types of crops could absorb nitrogen during the fallow period of bare land, also straw might lead to the richness and diversity of plant litter and increase the acquisition of carbon”. L429-434

37. Line 407: Table1 CARBONSEQUESTRATION POTIENTIAL. CARBON SEQUESTRATION POTENTIAL. Line 407: Table 1: a) I think you should write the references from where you have obtained the data. b) TG CA-1??? 

Reply: Based on your comment, we have added references to better display the information of the table. Table 1, L441-442

And we have revised “CARBON SEQUESTRATION POTENTIAL” into “Carbon Sequestration Potential”. Table 1, L441-442

We have revised “TG CA-1” into “Tg C year^-1”. Table 1, L441-442

38. Line 415: "hadreported→have reported

Reply: Based on your comments, we have revised in the manuscript. L449

39. Line421: "showed in meta-analysis→showed in a meta-analysis

Reply: Based on your comments, we have revised in the manuscript. L454

40. Line 454: “SOM accumulated by drought→Perhaps: release SOMaccumulated during drought periods

Reply: Based on your comments, we have revised this part into “Wetting the soil with irrigation after drought could release the accumulated SOM during drought periods and produce a large amount of nutrients and organic carbon”. L488-489

41. Line 489:"also had focused"→had also focused

Reply: Based on your comments, we have revised in the manuscript. L523

42. Line 495:“A study”→In a study....

Reply: Based on your comments, we have revised in the manuscript. L529

We thank reviewer`s constructive comments, which significantly help improve our manuscript.

Reviewer 3 Report

The paper " A review on carbon source and sink in arable land ecosystems" is a review for better understanding of carbon source and sink in arable land ecosystems and enhancing carbon sink capacity as well as guiding low-carbon agriculture in arable lands. The paper is well written and easily read.

At current state, the manuscript is suitable for publication after minor revisions.

Minor comments/suggestions follow.

Line 46: “According to statistics…”, Please, explain which statistics

Line 52: Please, explain which recent studies

Line 71: Please, enter the other two “major systems of terrestrial ecosystems”

Line 405: I didn't understand where the data in table 1 comes from

Table 1: Wouldn't it be better to also put a variability indicator or a range?

Page 13: There are not Appendix A and B as supplementary materials. I suppose lines 563-573 are to be deleted

Author Response

Reviewer:3

Comments and Suggestions for Authors

The paper " A review on carbon source and sink in arable land ecosystems" is a review for better understanding of carbon source and sink in arable land ecosystems and enhancing carbon sink capacity as well as guiding low-carbon agriculture in arable lands. The paper is well written and easily read. At current state, the manuscript is suitable for publication after minor revisions.

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 manuscript of marked are detailed below.

Detailed comments

Introduction

1. Line 46: “According to statistics…”, Please, explain which statistics

Reply: Based on your comments, we have completed this part of the missing statistical information. L50-52

2. Line 52: Please, explain which recent studies

Reply: Based on your comments, we have added appropriate references. L59-62

3. Line 71: Please, enter the other two “major systems of terrestrial ecosystems”

Reply: Based on your comments, we have added the other two major systems of terrestrial ecosystems: “wetland ecosystem and forest ecosystem” in our manuscript, and have revised this part into “Arable land ecosystem is one of the three major terrestrial ecosystems (including wetland ecosystem, forest ecosystem and arable land ecosystem)”. L80-81

4. Line 405: I didn't understand where the data in table 1 comes from

Table 1: Wouldn't it be better to also put a variability indicator or a range?

Reply: Based on your comment, we have added references to better display the information of the table and also put a variability indicator of a range. Table 1, L441-442

5. Page 13: There are not Appendix A and B as supplementary materials. I suppose lines 563-573 are to be deleted

Reply: According to your comments, we have deleted the redundant parts. L609--619

We thank reviewer`s constructive comments, which significantly help improve our manuscript.

Author Response File: Author Response.docx

Reviewer 4 Report

This is an interesting paper dealing with the problem of carbon sequestration in agricultural systems.  The authors analyse the components of carbon inputs and outputs in land ecosystems. The problem is under discussion all over the world as a mean to mitigate climate change.  The paper can be a source of data for studying the potential of different cropping practices. The paper has problem with language and accuracy of terms. Some part are difficult to follow. A thorough editing will improve it and make it easier   for the reader to go through.

I have below some suggestions for improvement but overall editing is required.

L211 “manual management and control”  What do you mean? Without machinery? Or only hand work?

L244  Please remove     of the corn/soybean no tillage ecosystem    It is double

L249-252 Please check the numbers.  They do not make sense.  90 g C per square cm is a huge figure.

L251-253 Please explain better the following:

Therefore, the double cropping system in this area was a carbon source 252 of 77g C cm-2 on an annual basis, which was equivalent to the annual average loss rate of 253 topsoil SOC stocks from 2003 to 2008.

L272-273 What do you mean  by         agricultural  film ?

L294     236.32 TgC yr-1   This figure is for an area. Some estimation of the size of the area? To help the reader.

L301 What is     dry crops? Do you mean not irrigated?  Or non-flooded like rice?

L302   the SOC content of rice   I suppose you mean SOC of fields of rice crop. It is better to make ti clear.

L309   The SOC of soybean was higher than that of other dry crops, which might be because legumes could improve soil structure and reduce soil erosion. I think this needs a better analysis. Legumes produce without N fertilization but compared to corn how soybean reduce   erosion? Corn produce much higher biomass yield than soybean which is the input for SOC.

Figure 1  What do you mean with agricultural practices? Tillage, spraying?  What is decomposition of straw and litter? Do you mean crop residues and root ?

L 351-258 It is difficult to understand.

Table 1 is difficult to read. In management practices there are two No tillage,   Rational fertilization refers to Nitrogen or to all elements?  What does it mean  Protective tillage and crop return ?  Straw return, do you mean only straw or crop residues? Is there a unit in C sequestration?

 L456 infiltration twice

Author Response

Reviewer: 4

Comments and Suggestions for Authors

This is an interesting paper dealing with the problem of carbon sequestration in agricultural systems.  The authors analyse the components of carbon inputs and outputs in land ecosystems. The problem is under discussion all over the world as a mean to mitigate climate change.  The paper can be a source of data for studying the potential of different cropping practices. The paper has problem with language and accuracy of terms. Some part are difficult to follow. A thorough editing will improve it and make it easier for the reader to go through.

I have below some suggestions for improvement but overall editing is required

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 manuscript of marked are detailed below.

We invited native English speakers to revise the whole manuscript.

Detailed comments

1. L211 “manual management and control” What do you mean? Without machinery? Or only hand work?

Reply: Here we wanted to emphasize that the arable land system is heavily influenced by human activities, but the previous expressions “manual management and control” was imprecise obviously. In response to your comments, we have revised this part into “for arable land ecosystems under anthropogenic management, there was evidence that …”. L235-236

2. L244 Please remove  “of the corn/soybean no tillage ecosystem”.It is double.

Reply: Based on your comments, we have deleted “of the corn/soybean no tillage ecosystem”.  L270

3. L249-252 Please check the numbers.  They do not make sense. 90 g C per square cm is a huge figure.

Reply: Based on your comments, we have revised the numbers into “90 g C m^-2_, 167 g C m^-2 and 77 g C m^-2 ” in the manuscript. L276-278

4. L251-253 Please explain better the following:

Therefore, the double cropping system in this area was a carbon source 252 of 77g C cm-2 on an annual basis, which was equivalent to the annual average loss rate of 253 topsoil SOC stocks from 2003 to 2008.

Reply: Based on your comments, we have added detailed explanation ,and revised this part into “ the double cropping system in this area was a carbon source of 77 g C m^-2 on an annual basis, which was equivalent to the annual average loss rate of topsoil SOC stocks from 2003-2008 by comparing the measured SOC data from 1998-2008” in the manuscript. L277-280

5. L272-273 What do you mean by  agricultural film ?

Reply: Based on your comments, we have revised it into “plastic film ” in the manuscript. L300

5. L294  236.32 TgC yr^-1 This figure is for an area. Some estimation of the size of the area? To help the reader.

Reply: The figure “236.32 TgC yr^-1” was from She et al. [26], and the study region is China. We have revised this part into “She et al. [26] divided China into six typical regions, namely northeast, north china, northwest, middle-lower reaches of Yangtze River, southwest and south china, collected and analyzed the carbon cost data of main crops, estimated the carbon sink and source effects of arable land and quantitatively evaluated the carbon inputs and outputs of crop production systems. The results showed that the major crops production was a net carbon sink of 236.32 Tg C yr^-1” in the manuscript. L316-321

6. L301 What is  dry crops? Do you mean not irrigated?  Or non-flooded like rice?

Reply: The dry crops in the manuscript refers to rain-fed crops which mainly rely on natural precipitation. And we have added the explanation in our manuscript. L327-328

7. L302   “the SOC content of rice  ”I suppose you mean SOC of fields of rice crop. It is better to make it clear.

Reply: Based on your comments, we have revised “the SOC content of rice” into “SOC of fields of rice crop”. L329

8. L309   The SOC of soybean was higher than that of other dry crops, which might be because legumes could improve soil structure and reduce soil erosion. I think this needs a better analysis. Legumes produce without N fertilization but compared to corn how soybean reduce   erosion? Corn produce much higher biomass yield than soybean which is the input for SOC.

Reply: Based on your comments, we have explained this part in the manuscript “The SOC of soybean is higher than that of other dry crops, which may be because legumes have a large number of rhizobium bacteria attached to their roots, during the growth, nitrogen in the air will be fixed to the roots, which can not only increase soil nitrogen, but also increase soil organic matter, which further improve soil structure and reduce soil erosion”. L336-340

9. Figure 1 What do you mean with agricultural practices? Tillage, spraying?  What is decomposition of straw and litter? Do you mean crop residues and root?

Reply: We believe that agricultural practices including tillage, fertilizer, irrigation and so on. To avoid the misunderstanding, we have deleted agricultural practices in the Figure. And we have revised “decomposition of straw and litter” into “crop residues and root” in the figure. L351-353

10. L 351-258 It is difficult to understand.

Reply: Based on your comments, we have revised this part into “In the research of Wang et al. [72], although the season length of maize (113 days) was 52% shorter than that of wheat (235 days), more than 55% of CO₂ emissions come from maize season, and the interaction of soil temperature and moisture better explained the variations of the ecosystem respiration and soil respiration from the relatively colder and drier wheat growing season to the warmer and wetter maize growing season. L383-388

11. Table 1 is difficult to read. In management practices there are two No tillage, Rational fertilization refers to Nitrogen or to all elements?  What does it mean  Protective tillage and crop return ?  Straw return, do you mean only straw or crop residues? Is there a unit in C sequestration?

Reply: Based on your comment, we have added references to better display the information of the table. We have also added the information that Organic fertilizer refers to nitrogen fertilizer; and Conservation tillage minimizes soil disturbance and increases soil organic carbon content by returning some straw to the fields; Straw return including return straw and crop residues to the land. The figure in this table mean carbon sequestration potential with units of (Tg C year^-1). Table 1, L441-442

13. L456 infiltration twice

Reply: Based on your comments, we have deleted “infiltration”.  L490

We thank reviewer`s constructive comments, which significantly help improve our manuscript.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The article has been improved by incorporating the suggestions and comments of the reviewers.