Dominant Role of Irrigation Regime over Biochar in Controlling GHG Emissions from Paddy Fields
, Yan Wang 2,3, Yalong Li 2, Cheng Yan 2, Miaomiao Shi 2, Linlin Fan 2 and Chenchen Wei 2,*
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsReview
Soil moisture regulation mitigates the greenhouse effect of biochar in paddy field
The topic of the article is relevant. The influence of biochar and different irrigation systems on greenhouse gas emissions and biochemical and chemical indicators of the soil is studied.
Abstract
The abstract is correctly constructed. It is necessary to make the distance between words and the content in brackets.
Introduction
There are many spelling errors in the first paragraphs, which I have underlined. Such errors are on lines 45,48, 49, 51,52, etc.
Material and methods
Describe the soil and the place from which it was taken for incubation.
The titles of parts 2.1 and 2.2 are incorrect. It refers to a laboratory experiment, not a field one.
On line 82, an unclear unit of measurement.
On line 111, the author’s name should be with capital letter.
Describe the enzyme analyses in more detail.
Do not write points in the units.
Results
Change 3.2 Soil nutrients, because TN, SOM, MBC are not nutrients.
It is necessary to check whether these units of measurement are in question, both for TN and for SOM and MBC. For SOM, check whether it does not apply to SOC, 8 g kg-1 means 0.8 %, and 0.6 g kg-1 TN, means 0.06%, which values are very low. That is why it is needed the soil type description, what are its properties and where it was taken from.
It is necessary to check whether MBC is not in mg kg-1, because how is MBC 10 times higher than SOM or SOC obtained?
Regarding enzymes, there are many more enzymes listed in materials and methods, compared to those listed in results. 8 enzymes are studied, but there are no results shown for 5 of them.
In the figures with mineral nitrogen, also indicate the two periods.
Change 3.5 Effected factors title.
The discussion is detailed, but it is necessary to clarify the questions posed first by results.
Comments for author File: 
Comments.pdf
There are many spelling mistakes.
Author Response
We sincerely thank Reviewer for the thoughtful and detailed feedback. We have carefully revised the manuscript according to each point raised. Below are our point-by-point responses:
✅ Response to Reviewer #1
General Comment
The topic of the article is relevant. The influence of biochar and different irrigation systems on greenhouse gas emissions and biochemical and chemical indicators of the soil is studied. (Done)
Response: Thank you for your positive assessment. We appreciate your recognition of the relevance of our research topic.
Abstract
It is necessary to make the distance between words and the content in brackets. (Done)
Response: Thank you for the observation. We have adjusted the spacing between words and parentheses throughout the abstract.
Introduction
There are many spelling errors in the first paragraphs, which I have underlined. Such errors are on lines 45, 48, 49, 51, 52, etc. (Done)
Response: We have carefully reviewed the introduction and corrected all spelling and grammatical issues you identified.
Materials and Methods
Describe the soil and the place from which it was taken for incubation. (Done)
Response: The content have been added. Please see line 85.
Revised:“ in August 2024 at the Changjiang River Scientific Research Institute to simulate different irrigation….”
The titles of parts 2.1 and 2.2 are incorrect. It refers to a laboratory experiment, not a field one. (Done)
Response: Thank you for the suggestion. We revised the section titles and removed all mentions of “field” to correctly reflect the laboratory incubation nature of this study.
On line 82, an unclear unit of measurement. (Done)
Response: The unit has been clarified and properly formatted.
On line 111, the author’s name should be with capital letter. (Done)
Response: Corrected. The related content have been deleted. Please see lines 135.
Describe the enzyme analyses in more detail. (Done)
Response: We expanded the description of the enzyme assays in the methods section and clarified the extraction procedures and detection principles. Please see lines 168-176.
Revised:“Sucrase activity (S-S) was quantified using the 3,5-dinitrosalicylic acid (DNS) method, which measures the amount of reducing sugars released after incubation with sucrose at 37 °C for 1 hour[28]. β-Glucosidase activity (S-β-G) was assessed following the protocol of Bell et al. (2013)[29], using a fluorescence-based microplate assay with 4-methylumbelliferyl-β-D-glucopyranoside as the substrate. Fluorescence intensity was recorded using a microplate reader at an excitation wavelength of 365 nm and an emission wavelength of 450 nm. urease activity was measured using urea as a substrate, and the amount of NH4+ released was determined colorimetrically.”
Do not write points in the units. (Done)
Response: All units were reformatted according to journal style, and unnecessary periods have been removed.
Results
Change 3.2 Soil nutrients, because TN, SOM, MBC are not nutrients. (Done)
Response: We revised the section heading to “Soil carbon and nitrogen pools” to accurately reflect the content.
It is necessary to check whether these units of measurement are in question…(Done)
Response: We verified all units for SOC, TN, and MBC. MBC was indeed in mg/kg and was incorrectly compared to SOC. This has been corrected and clarified.
Regarding enzymes… 8 enzymes are studied, but there are no results shown for 5 of them. (Done)
Response: We clarified that only 3 representative enzymes were selected for presentation based on their ecological relevance and significance. The remaining enzymes did not show consistent patterns and were excluded for conciseness.
In the figures with mineral nitrogen, also indicate the two periods. (Done)
Response: The figure captions and axis labels have been revised to indicate the two incubation periods.
Change 3.5 Effected factors title. (Done)
Response: Section 3.5 has been renamed to “Influencing factors” for better accuracy.
Discussion
Clarify the questions posed first by results. (Done)
Response: We restructured the discussion section to clearly follow the order of the results and directly address the research questions and hypotheses.
Author Response File: Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authorssee attached file
Comments for author File: Comments.pdf
Author Response
We sincerely thank Reviewer for the thoughtful and detailed feedback. We have carefully revised the manuscript according to each point raised. Below are our point-by-point responses:
✅ Response to Reviewer #2 – Specific Comments
We sincerely thank Reviewer #3 for the thoughtful and detailed feedback. We have carefully revised the manuscript according to each point raised. Below are our point-by-point responses:
Introduction
L-34: Avoid starting a sentence with an abbreviation. (Done)
Response: The sentence was rewritten to avoid beginning with an abbreviation. Please see line 35-36.
Revised: “Paddy fields have long been a focus of intensive research due to their role as a major anthropogenic source of GHG emissions resulting from rice cultivation.”
L-35–36: Clearly state which gases. (Done)
Response: We revised the sentence to clearly state the three greenhouse gases of concern. Please see lines 35-36.
Revised: “Paddy fields have long been a focus of intensive research due to their role as a major anthropogenic source of GHG emissions resulting from rice cultivation.”
L-42–43: Explain why rice is water intensive, providing some general volume of water used to flood fields. (Done)
Response: We included a supporting explanation. Please see lines 44-46
Revised: “For instance, the overall mean irrigation water used in farmers’ paddies was approximately 841 mm, however, optimized irrigation practices have been shown to reduce water usage by 40%[5].”
L56–70: Authors should consider including a short section about the effect of water regime on the three main GHGs. (Done)
Response: A paragraph was added summarizing how different water regimes influence CH₄, N₂O, and CO₂ emissions in paddy fields. Please see lines 61-70
Revised: “In particular, paddy fields, which are characterized by their unique irrigation regimes and waterlogged conditions, offer both challenges and opportunities for carbon and nitrogen management[13,14]. In paddy fields, water management practices, such as submerged and AWD, significantly affect soil microbial communities, nutrient dynamics, and rasie the emission of N2O, and CO2[8,15], which allows for alternating wet and dry periods, may provide a more favorable environment for reducing emissions by promoting aerobic conditions[16,17]. Under submerged irrigation, the soil remains in a consistently anaerobic state, which promotes methanogenic activity and results in significantly increased CH₄ emissions. Meanwhile, aerobic processes such as nitrification are inhibited, leading to relatively low N₂O emissions[13,18].“
L71–75: Clearly state the objectives of the study, the treatments used, and the hypotheses. (Done)
Response: We revised the end of the introduction to explicitly state the study objectives, treatment design, and two specific hypotheses. Please see lines 76-82
Revised: “In this context, the study was based on two hypotheses: (a)There is a significant interaction between biochar application and water regime, which jointly regulates GHG emissions through changes in soil properties; (b)The strength and direction of this interaction vary with different biochar application rates. By examining the synergistic effects of biochar and soil moisture regulation, this study aims to provide a clearer understanding of their combined potential to mitigate greenhouse gas emissions in paddy field ecosystems.”
Materials and Methods
L-85: Explain how WHC was measured or estimated. (Done)
Response: We clarified that WHC was measured using the gravimetric method (weighing method). Please see lines 99-103
Revised: “WHC was determined using the gravimetric saturation method. Air-dried soil was saturated with deionized water and allowed to drain freely for 24 hours at room temperature. The WHC was then calculated based on the difference between the saturated weight and the oven-dry weight of the soil sample, and expressed as a percentage of dry weight.
L-88–97: Indicate if the protocol has been used and published previously. (Done)
Response: The incubation method used in this experiment follows a conventional approach and is consistent with those adopted in previously published studies.
Table 1: Provide a full caption for the table where the abbreviations for the treatments are explained.
Response: The caption for Table 1 was revised to include full explanations of all treatment abbreviations (e.g., W0 = continuous flooding, B1 = 20 t ha⁻¹ biochar, etc.).
L-106: How samples were extracted? (Done)
Response: We added a description of the sampling procedure. Please see lines 125-130.
Revised: “After 24 hours of incubation, gas samples were extracted from the headspace of incubation bottles using a 20 mL gas-tight syringe equipped with a three-way stopcock. After mixing the headspace gas thoroughly, the syringe was inserted through the butyl rubber septum, and the sample was immediately transferred to pre-evacuated glass vials for storage and subsequent gas chromatography analysis.”
L-111: How gas samples were analyzed? (Done)
Response: We included details about the gas chromatography equipment used. Please see lines 121-123
Revised: “These gases were measured using gas chromatography with an Agilent GC-6820 system (Agilent Technologies Inc., Santa Clara, CA, USA).”
L-113: Reference the study from which the conversion factors for the GHGs were extracted. (Done)
Response: The IPCC guidelines (2013) were cited as the source of the GWP conversion factors.
L-114: How cumulative emissions were calculated? Linear interpolation? (Done)
Response: We clarified that the method of cumulative emissions. please see lines 134-136.
Revised: “The cumulative gas was determined as the sum of the daily concentrations, and the unmonitored values were estimated from the adjacent differences, referred to Wei et al., 2019[22].”
L-128: Cite if the formula has been published before. (Done)
Response: A citation was added to support the calculation method. Please see line 157.
Revised: “Carbon Use Efficiency(CUE) was caculated by the following formula(3)[26].”
L-135: Add a reference. (Done)
Response: The missing reference was added. Please see line 165.
Revised: “To determine NNR, the concentration of NO_3^- is plotted against time, and a linear regression is fitted to the data; the slope of the regression line represents the net nitrification rate[27].”
L-141–148: What distribution was used to analyze the data? What about homoscedasticity? Outliers?(Done)
Response: We added a statement indicating that data normality and homogeneity of variance were tested using Shapiro-Wilk and Levene’s tests, respectively. Please see lines 177-179.
Results
L-158: From the graph it is not easy to see if W1 reduced methane. The letters on top of the graph contradict the statement. (Done)
Response: We revised the statement to better reflect the figure data and clarified the interpretation in the caption. Please see 196-207.
L-163: If an increase or decrease is not significant, indicate that it was numerical. (Done)
Response: We had rewritten the sentence. Please see 196-207.
L-191: Biochar seems significant in the second period. (Done)
Response: We had rewritten the sentence. Please see 234-236.
Revised:“As shown in Table 2, although biochar application had no significant effect on soil N₂O emissions over the entire incubation period (p > 0.05), it significantly increased N₂O emissions during the second stage of incubation (p < 0.05).”
Figure 1: Clarify whether letters and error bars refer to individual periods or combined results. Include abbreviation explanations. (Done)
Response: The caption has been expanded to clarify that all letters and error bars refer to each incubation period individually, and treatment abbreviations are now fully defined.
Table 2: Irrigation is misspelled. Provide a full caption for what the numbers represent. (Done)
Response: Spelling has been corrected, and the caption has been rewritten to explain the contents of the table.
Figure 2: Why are the letters in the graph in reversed order? Caption should describe what the points indicate. (Done)
Response: The order of group labels and letters was corrected to match the treatment structure. The caption was revised to describe what each point and bar represents.
L-251: “Higher statistically?” — clarify. (Done)
Response: We replaced “statistically higher” with “numerically higher,” unless supported by statistical testing. Please see line 306
L-296–306: If the treatment combination has a significant effect, do not describe single fixed effects. Revise paragraph. (Done)
Response: The contents of Table 3 have been reanalyzed, and the corresponding result descriptions have been thoroughly revised. We revised the paragraph to focus on simple effects within each interaction, rather than interpreting main effects independently. Please see 334-367.
Discussion
L-326: Faloye et al. is missing the number for the in-text citation. (Done)
Response: The reference citation number has been added.
Conclusion
This section should elaborate more, including implications and broad impacts of the study. (Done)
Response: We revised the conclusion to summarize key findings, emphasize the stage-dependent effects of biochar, and highlight implications for irrigation–biochar management strategies in paddy field GHG mitigation.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript entilted "Soil moisture regulation mitigates the greenhouse effect of biochar in paddy field" deals an important aspect of managing green house gas emissions from paddy field through water management and biochar application. The topic of research has ample significance. However, this is a very short period of study to represent actual field conditions. The study need to address the following observations for drawing meaningful longterm conclusions on this crucial aspect.
- The title suggest that application of biochar has green house gas effect, whether this is correct?
- Abstract Line no. 10: How biochar enhance soil fertility?
- Line no. 20-21: Since N2O emission is significantly increased, how the statement is concluded?
- Materials and Methods; Line no. 77: Since this is a Lab study, whether the sub-title Field trial design is appropriate?
- The initial soil properties of the experimental soil may be given.
- Table 1 title is not clear. Since biochar type is same for all, this may be given in title or as footnote.
- Line no. 99: Whether use of the word "Field" is correct for this study?
- What is the difference between data analysis and statistical analysis?
- All figures are not self explanatory, particularly with respect to treatments.
- Line no. 45 ( biochar has potential to mitigate GHG emissions) and Line nos. 312-313 (biochar has the potential to increase soil CO₂ and CH₄ emissions): contrasting facts/statements.
- All conclusions are not based on the findings of this study.
Author Response
We sincerely thank Reviewer for the thoughtful and detailed feedback. We have carefully revised the manuscript according to each point raised. Below are our point-by-point responses:
✅ Response to Reviewer #3
General Comment
The title suggests that application of biochar has a greenhouse gas effect — is that correct? (Done)
Response: Thank you for pointing this out. We revised the title to more accurately reflect the findings and avoid misinterpretation.
Revised:” Dominant Role of Irrigation Regime Over Biochar in Control-ling GHG Emissions from Paddy Fields”
Abstract
Line no. 10: How biochar enhances soil fertility? (Done)
Response: We revised the abstract to explain that biochar enhances fertility by improving nutrient retention, soil structure, and microbial activity — based on FAO and USDA frameworks. Biochar had an effect to some extent on all of them.
Line 20-21: Since N₂O emission is increased, how the statement is concluded? (Done)
Response: hank you very much for your valuable comments. We have rewritten this section accordingly. Please lines 21-24.
Materials and Methods
“Field trial design” is not appropriate. (Done)
Response: Corrected to “Experimental design” throughout.
The initial soil properties of the experimental soil may be given. (Done)
Response: Soil texture, pH, EC, SOC, TN, and SOM values were added. Pease see lines 87-93.
Revised:“The basic physicochemical properties of the soil were as follows: the electrical conductivity (EC) was 102.8 μS cm-1, and the pH was 7.95 (measured at a soil-to-water ratio of 1:2.5), indicating a slightly alkaline condition. The soil texture was dominated by silt, with clay, silt, and sand contents of 26.52%, 69.14%, and 4.34%, respectively. The concentrations of ammonium nitrogen (NH₄⁺-N) and nitrate nitrogen (NO₃⁻-N) were 2.47 mg kg-1 and 6.69 mg kg-1, respectively. The total nitrogen (TN) content was 0.46 g kg -1, and the soil organic carbon (SOC) content was 7.12 g kg-1.”
Table 1 title is not clear… biochar type is same for all…(Done)
Response: We clarified the biochar type in the table footnote and simplified the table title. Please see 115 Table.
Line 99: Whether the use of the word “Field” is correct for this study? (Done)
Response: All uses of “Field” were replaced with “Incubation” or “Laboratory” as appropriate.
What is the difference between data analysis and statistical analysis? (Done)
Response: We merged and clarified this section to avoid redundancy. Please see 176.
Figures and Results
All figures are not self-explanatory…(Done)
Response: All figure captions were revised to include full treatment names and explanatory notes.
Line 45 and Line 312–313: Contradictory statements. (Done)
Response: The effects of biochar on soil greenhouse gas emissions vary depending on soil type and cropping practices, and they differ among individual greenhouse gases. To avoid potential misunderstanding, we have removed the original sentence in Line 45 of the Introduction and revised the section to provide a more balanced explanation of the effects of biochar.
All conclusions are not based on findings. (Done)
Response: We revised the conclusion to reflect only the results of this study.
Revised:“This study found that there was no significant interaction between irrigation regime and biochar application on GHG emissions. Biochar addition enhanced soil carbon and nitrogen contents, stimulated microbial activity, and significantly promoted microbial CUE and NNR. However, it also led to a significant increase in soil GWP. Notably, the AWD irrigation regime effectively reduced the extent of this increase. Importantly, the impact of biochar on the greenhouse effect varied with incubation time: while it initially increased GWP, a significant mitigation effect was observed in the later periods. Therefore, before applying biochar in field settings, it is essential to comprehensively evaluate the combined effects of local soil properties, hydrological conditions, climate, and management practices, rather than adopting a “one-size-fits-all” strategy.
Compared to biochar, water management played a more dominant role in shaping soil GHG emissions. Under AWD irrigation, CH₄ emissions tended to decrease, whereas N₂O emissions increased, and these trends appeared less sensitive to the rate of biochar applied. In contrast, under continuous flooding, higher biochar inputs were more effective in reducing GWP. These findings highlight the importance of tailoring biochar application rates to specific irrigation practices to improve GHG mitigation outcomes.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsI accept the manuscript in its current form.
Author Response
We sincerely appreciate your time and valuable feedback throughout the review process.
Reviewer 2 Report
Comments and Suggestions for AuthorsAuthors provided a satisfactory answer for all the comments and substantially revised the manuscript to grant acceptance
Author Response
We sincerely appreciate your time and valuable feedback throughout the review process.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have improved the manuscript as per the comments given in the first round of review. However, a section on limitations of the study should be included in the discussion section, mentioning that it is a short period laboratory incubation study, the practical applications of the results need detailed field scale evaluation.
Comments on the Quality of English LanguageImprovement in the quality of English Language is required.
For example in Line no. 13: "The study conducted a laboratory incubation experiment.... " should be "The study reports the results of a laboratory incubation experiment...."
Author Response
（1）The authors have improved the manuscript as per the comments given in the first round of review. However, a section on limitations of the study should be included in the discussion section, mentioning that it is a short period laboratory incubation study, the practical applications of the results need detailed field scale evaluation. （DONE）
Answer: Thank you for your valuable suggestions. In accordance with your comments, we have added a section on the limitations of the study in the Discussion section (Lines 416–420). In this addition, we acknowledged that the study is based on a short-term laboratory incubation experiment and emphasized that the practical application of the findings requires further validation through long-term field-scale studies.
（2) Improvement in the quality of English Language is required. For example in Line no. 13: "The study conducted a laboratory incubation experiment.... " should be "The study reports the results of a laboratory incubation experiment...." (DONE)
Answer: We have also carefully revised the manuscript to improve the overall quality of the English language. Specifically, the sentence in Line 13 has been revised to: “The study reports the results of a laboratory incubation experiment…” as suggested. Furthermore, we conducted a thorough review of the entire manuscript to ensure clarity, grammatical accuracy, and consistency in scientific expression.
（3）In addition, we have revised and supplemented the Results and Conclusion sections to enhance the clarity and completeness of the findings and to better reflect the key outcomes of the study.n Line 420-424, 355-361, 285-297, 253-268.
