From the journal Environmental Science: Atmospheres Peer review history

25-Apr-2022

Dear Dr Abdalla:

Manuscript ID: EA-CRV-03-2022-000033
TITLE: Impacts of crop type, management and soil quality indicators on background nitrous oxide emissions (BNE) from Chinese croplands: a quantitative review and analysis

Thank you for your submission to Environmental Science: Atmospheres, published by the Royal Society of Chemistry. I sent your manuscript to reviewers and I have now received their reports which are copied below.

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Environmental Science: Atmospheres
Royal Society of Chemistry

************

Reviewer 1

This manuscript assessed the impacts of crop type, management and soil quality indicators on Chinese cropland background N2O emissions. The results show crop type has significant impact on the background N2O emissions with identification of its controlling factors, which provides implications for N2O emission inventory for different crop type. In general, this manuscript was well-organized and easy to follow. However, there are some aspects can be considered and improved as follows:

Introduction: Since crop type is an important part of this study (i.e., results are presented by crop type), there should be more introduction of the effect of crop type on Chinese cropland background N2O emissions, see references such as https://doi.org/10.1111/gcb.15847 and https://doi.org/10.1111/gcb.14741.
Discussion: I strongly suggest to compare the results shown in previous studies which, however, focused on fertilized-induced N2O emissions, e.g., https://doi.org/10.1038/s43016-021-00384-9, https://doi.org/10.1093/nsr/nwz087.
Line 70-81: The authors mentioned that other countries have higher/lower background N2O emissions than IPCC default values, but state the advances in Chinese background N2O emissions without clarification of current gap. Please indicate what is the gap of Chinese cropland background N2O emissions.

Line 83: “Return of residue” is described in the next paragraph. Here it should be removed.

Line 90-91: This does not belong to nitrogen fertilization and field management practices, which are the topics of this paragraph as indicated in the first sentence.

Line 137-141: These sentences do not belong to data collection. They are about how to estimate total Chinese background N2O emissions, which is an important part of this study.

Line 183-185: Please explain what the values of MIC and MIC-R2 mean. Do larger values represent more related relationship?

Table 1: Lowercase letters were mislabelled, especially in the raw of National BNE in Table 1. It is normal to use letter a to indicate the largest value, followed by b, c, d etc. in descending order.

Figure 3: What does crop mean in Figure 3? There is a sub-group called crop in the category crop.

Reviewer 2

Comments:

General comments:
This is a very interesting manuscript that estimates the background N2O emissions from Chinese cropland soils and assesses impacts of crop type, management and soil quality indicators on background N2O emissions. This quantitative review and analysis can reduce uncertainty in the total N2O emissions, support decision-makers to advise on the best possible management strategies for mitigating N2O emissions and reducing the impact of croplands on climate change. Some detailed comments are as follows.

Specific comments:
Line 83: In China, livestock manure application also can greatly impact the BNE.

Line 85: “farmers often overuse N fertiliser by 30 to 40%, (Norse, 2011)” should update this data.

Line 134: Please give the details description of the environmental and management factors in the main text.

Line 164: Please assess the possibility of publication bias.


The environmental and management factors how to impact the BNE and crop yields, please add one paragraph to discuss this in China. In addition, please add the discussion this study findings how to guide the 4Rs in China.

Responses to Referees’ comments on Abdalla et al.: Manuscript ID EA-CRV-03-2022-000033. Title: “Impacts of crop type, management and soil quality indicators on background nitrous oxide emissions (BNE) from Chinese croplands: a quantitative review and analysis”.

The authors would like to thank the associate editor and reviewers for their valuable comments and suggestions, which we have used to improve our manuscript. Below we provide our responses to referees’ comments - referee comments are shown in italics, our responses in normal text.

REVIEWER REPORT(S):
Referee: 1
Comments to the Author
This manuscript assessed the impacts of crop type, management and soil quality indicators on Chinese cropland background N2O emissions. The results show crop type has significant impact on the background N2O emissions with identification of its controlling factors, which provides implications for N2O emission inventory for different crop type. In general, this manuscript was well-organized and easy to follow. However, there are some aspects can be considered and improved as follows:
Introduction: Since crop type is an important part of this study (i.e., results are presented by crop type), there should be more introduction of the effect of crop type on Chinese cropland background N2O emissions, see references such as
as https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1111%2Fgcb.15847&data=05%7C01%7Cmabdalla%40abdn.ac.uk%7C8f0222404a9348aaa8a208da265f5721%7C8c2b19ad5f9c49d490773ec3cfc52b3f%7C0%7C0%7C637864488335722958%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=5Whp4Ib4nkj6CDtr9dB9UONkISpDZyaEeQeDSVgmho0%3D&reserved=0
and https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1111%2Fgcb.14741&data=05%7C01%7Cmabdalla%40abdn.ac.uk%7C8f0222404a9348aaa8a208da265f5721%7C8c2b19ad5f9c49d490773ec3cfc52b3f%7C0%7C0%7C637864488335722958%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=7%2BPXjptFtd3m0NK3XXxJ30pwz4yLDEXHc9tT9X36Wz4%3D&reserved=0.

Response: we thank the reviewer for his/her comment and suggested papers. We have added the following paragraph to the introduction.
“Previous studies found that crop types have great impacts on BNE due to different crop management, quantities and qualities of yield and crop residues (Dobbie et al., 1999). Higher annual BNE rates from Chinese field vegetables, compared to other crop systems, were reported by many studies, e.g. by Wang et al. (2011), Chen et al. (2015) and Aliyu et al. (2018). However, Min et al. (2012) reported seven times greater N2O emissions from greenhouse vegetables compared to a rice-wheat system in the same area and on the same soil type. Moreover, Shang et al. (2019) and Wang et al. (2020) noted the need for detailed high resolution N2O emission data by crop type, land use and technology development to clarify the change in the emissions and inform the progress towards realistic and cost-effective mitigation pathways”.

Discussion: I strongly suggest to compare the results shown in previous studies which, however, focused on fertilized-induced N2O emissions, e.g., https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1038%2Fs43016-021-00384-9&data=05%7C01%7Cmabdalla%40abdn.ac.uk%7C8f0222404a9348aaa8a208da265f5721%7C8c2b19ad5f9c49d490773ec3cfc52b3f%7C0%7C0%7C637864488335722958%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=xj3CsVXXt5gvP6167TwjC8aRkSkwgxosNAA%2BvE%2FngzA%3D&reserved=0,
https://eur03.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1093%2Fnsr%2Fnwz087&data=05%7C01%7Cmabdalla%40abdn.ac.uk%7C8f0222404a9348aaa8a208da265f5721%7C8c2b19ad5f9c49d490773ec3cfc52b3f%7C0%7C0%7C637864488335722958%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=ExEAw0r7iwbjyOu%2FZEdA2cVGiQ90zF%2BoNeNfhUxYE24%3D&reserved=0.
Response: we thank the reviewer for his/her comment and suggested papers. We have added the following text to the discussion:
“Furthermore, Wang et al. (2020) re-assessed global fertilised cropland-N2O emissions from 1961 to 2014 using EFs upscaled from field measurements. Their results agreed with the IPCC Tier 1 default EFs for upland crops in 1990-2014, but gave ∼15% lower EF for the period 1961-1989. However, they calculated a ∼67% larger EF for paddy rice over the period 1961-2014. The global crop-specific N2O mitigation potential from the decrease in N application rate without compromising crop production of maize, wheat, rice or other crops was investigated by Cui et al. (2021). They found that the N2O mitigation potential for maize, wheat, rice and other crops were 54%, 43%, 69% and 65%, respectively”.

Line 70-81: The authors mentioned that other countries have higher/lower background N2O emissions than IPCC default values, but state the advances in Chinese background N2O emissions without clarification of current gap. Please indicate what is the gap of Chinese cropland background N2O emissions.
Response: we thank the reviewer for his/her comment. We have added the following text to the Introduction: “Further, to avoid uncertainty, the BNE from Chinese croplands should be estimated for each crop type separately and proportion of planting areas should be considered when BNE is calculated nationally.”

Line 83: “Return of residue” is described in the next paragraph. Here it should be removed.
Response: this sentence was deleted.

Line 90-91: This does not belong to nitrogen fertilization and field management practices, which are the topics of this paragraph as indicated in the first sentence.
Response: this sentence was deleted.

Line 137-141: These sentences do not belong to data collection. They are about how to estimate total Chinese background N2O emissions, which is an important part of this study.
Response: we thank the reviewer and agree with him/her. A sub heading with a title “Estimation of total BNE” was created.

Line 183-185: Please explain what the values of MIC and MIC-R2 mean. Do larger values represent more related relationship?
Response: we thank the reviewer for the comment. Sure, it is good to add definitions of these parameters in the Methods (at present, the definitions can only be found in the caption of Table 2). These kinds of computer science techniques are expanding and extensively used in the science and statistics for different environmental studies.
We have added the following text to Section 2.5:
“MIC captures relationship strength, and the higher MIC-R2 is, the more non-linear is the relationship”.

Table 1: Lowercase letters were mislabelled, especially in the raw of National BNE in Table 1. It is normal to use letter a to indicate the largest value, followed by b, c, d etc. in descending order.
Response: we thank the reviewer and agree with him/her. The lower case letters in Table 1 were corrected.

Figure 3: What does crop mean in Figure 3? There is a sub-group called crop in the category crop.
Response: we thank the reviewer for the comment. We have improved these terms on the Fig. “Crop” in the sub-group means “crop type”.

Referee: 2
Comments: General comments: This is a very interesting manuscript that estimates the background N2O emissions from Chinese cropland soils and assesses impacts of crop type, management and soil quality indicators on background N2O emissions. This quantitative review and analysis can reduce uncertainty in the total N2O emissions, support decision-makers to advise on the best possible management strategies for mitigating N2O emissions and reducing the impact of croplands on climate change. Some detailed comments are as follows.
Specific comments: Line 83: In China, livestock manure application also can greatly impact the BNE.
Response: we thank the reviewer and agree with him/her. We have added the following text to this Section:
“Moreover, application of animal manure in croplands can significantly increase BNE. In a long-term experiment using compost, Ding et al. (2013) observed an increase of 106% in the BNE values from croplands.”

Line 85: “farmers often overuse N fertiliser by 30 to 40%, (Norse, 2011)” should update this data.
Response: we thank the reviewer and agree with him/her. The following text was added to Introduction:
“However, this overuse of N fertilizer has recently declined due to the government policy of zero growth in N fertilizer and pesticide and widespread use of nationwide technological applications (Powlson et al., 2018; Shang et al., 2019).”

Line 134: Please give the details description of the environmental and management factors in the main text.
Response: we thank the reviewer and agree with him/ her. This Section was improved as follows:
“The environmental (average temperature and precipitation) and management (previous N fertiliser rate, tillage, irrigation, liming and drainage) factors for each crop were also analysed separately.

Line 164: Please assess the possibility of publication bias.
Response: we thank the reviewer for the comment. We have added the following text to the materials and methods:
“To assess publication bias we searched for any unpublished or grey literature data”.
We have also adapted the rest of the Section accordingly.
Additionally we have discussed publication bias in the limitation Section:
“Further, no publication bias had been assessed. Here, we found it challenging to access unpublished or grey literature data due to scarcity of these data. However, unlike other research disciplines such as medicine, there is no evidence that publication bias is a significant issue in climate change science (Harlos et al., 2017), although, Michaels (2008) and Reckova and Irsova (2015) reported some publication bias when using a small set of pre-defined journals or a small sample size of only 16 studies, respectively. Additionally, we have used data from a range of Journals some of them have low impact factors such as Journal of Plant Nutrition and Soil Science (2.083) whilst others have high impact factors such as National Science Review (17.275)”

The environmental and management factors how to impact the BNE and crop yields, please add one paragraph to discuss this in China.
Response: we thank the reviewer for the comment. This is already fully discussed under the sub title “Factors controlling the BNE” however, we have improved the sub title to be: “Impacts of environmental and management factors on BNE”. We have also further improved the discussion and added the following text:
“Abdalla et al. (2022) and Zhao et al. (2020) found that Chinese optimized and alternative management cropping systems in which less N fertiliser is used, can decrease total N2O emissions and increase grain yield compared to the conventional cropping management.”

In addition, please add the discussion this study findings how to guide the 4Rs in China
Response: we thank the reviewer for the comment. We have added the following text to the discussion:
“This study findings confirm that to mitigate BNE from Chinese croplands, it is important to follow the nutrients management guidelines (4Rs: right source, right rate, right time, and right place). Adoption by farmers of a suitable fertiliser source and amount that matches crop needs and soil properties would increase nutrient use efficiency and decrease the total N2O emissions. Moreover, application of fertilisers at the right time in the crop root zone and considering crop demands, weather and seasonal conditions would allow the crop to successfully access the nutrients, improve yields and benefit the environment (He et al., 2022).

21-May-2022

Dear Dr Abdalla:

Manuscript ID: EA-CRV-03-2022-000033.R1
TITLE: Impacts of crop type, management and soil quality indicators on background nitrous oxide emissions (BNE) from Chinese croplands: a quantitative review and analysis

Thank you for submitting your revised manuscript to Environmental Science: Atmospheres. I am pleased to accept your manuscript for publication in its current form. I have copied any final comments from the reviewer(s) below.

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Dr Tzung-May Fu
Associate Editor
Environmental Science: Atmospheres
Royal Society of Chemistry

Reviewer 1

All comments have been reasonably addressed, I therefore suggest to accept the manuscript.

Reviewer 2

no more comments, thank you for improving the draft.