Review Reports - Soil Greenhouse Gas Responses to Biomass Removal in the Annual and Perennial Cropping Phases of an Integrated Crop Livestock System

Round 1

Reviewer 1 Report

In the manuscript the authors presented an important point, although the manuscript has some drawbacks.

Main remarks:

1. Intruduction - what is the research gap?

2. Introduction / "Literature review" - the introduction/literature review should write more about the livestock, biomass, gas responses. Suggested publications:

Roman, M.; Roman, K.; Roman, M. Spatial Variation in Particulate Emission Resulting from Animal Farming in Poland. Agriculture 2021, 11, 168. https://doi.org/10.3390/agriculture11020168

Yunes, M.C.; Osório-Santos, Z.; von Keyserlingk, M.A.G.; Hötzel, M.J. Gene Editing for Improved Animal Welfare and Production Traits in Cattle: Will This Technology Be Embraced or Rejected by the Public? Sustainability 2021, 13, 4966. https://doi.org/10.3390/su13094966

3. Conclusions - very short. In your conclusions, please also answer the following questions:
• what are the directions for the future?
• what are the research gaps?
• what is new to this manuscript?

Editorial errors. See editorial requirements.

Author Response

Authors’ Response to Reviewer 1 Manuscript ID: agronomy-1263797

We thank Reviewer 1 for their constructive comments on our manuscript titled “Soil greenhouse gas responses to biomass removal in the annual and perennial cropping phases of an integrated crop livestock system.” We incorporated reviewer suggestions where relevant and provided rebuttals where suggestions were not used. Please find our specific responses to each of their comments (numbered below). For convenience, we refer to line numbers in the revised manuscript version submitted and blue font in the revised manuscript indicates where revisions were made within the resubmitted text.

Sincerely,

Virginia L. Jin (corresponding author)

REVIEWER 1

Comment 1: Intruduction [sic] – what is the research gap?

Response: The research gap was identified in the original manuscript version in L74-77: “Less clear are the impacts of ICL systems on soil emissions of non-CO2 GHGs (i.e. nitrous oxide, N₂O; methane, CH₄), particularly the effect of grazing on crop residues, cover crops, and perennial grasses.” To improve clarity, L54-61 of the original manuscript was moved to Discussion to focus the introduction on addressing research gaps in soil GHG responses to ICL management practices. We also improved the clarity of the sentence quoted above and added a concluding statement in the introduction on the overarching expectations for this work:

L62-65: Less clear are the impacts of ICL systems on soil emissions of non-CO₂ GHGs (i.e. nitrous oxide, N₂O; methane, CH₄), particularly how livestock grazing of crop residues, cover crops, and perennial grasses affects these emissions.

L90-93: These findings are expected to contribute to the growing body of published information to clarify how soil emissions of non-CO₂ GHGs respond to various aspects of agricultural management within the multi-functional context of ICL systems.

Comment 2: Introduction / "Literature review" - the introduction/literature review should write more about the livestock, biomass, gas responses. Suggested publications:

Roman, M.; Roman, K.; Roman, M. Spatial Variation in Particulate Emission Resulting from Animal Farming in Poland. Agriculture 2021, 11, 168. https://doi.org/10.3390/agriculture11020168

Yunes, M.C.; Osório-Santos, Z.; von Keyserlingk, M.A.G.; Hötzel, M.J. Gene Editing for Improved Animal Welfare and Production Traits in Cattle: Will This Technology Be Embraced or Rejected by the Public? Sustainability 2021, 13, 4966. https://doi.org/10.3390/su13094966

Response: The manuscript includes a description of the impacts of livestock grazing, biomass production, and soil GHG responses, emphasizing that published reports are highly variable (L65-75). We did not include the two suggested publications because the Roman et al. paper reports on particulate emissions (not greenhouse gas emissions), and the Yunes et al. paper is a report on a public perception survey of gene-editing use for animal production. Neither topic is relevant to the specific research focus of the submitted manuscript (i.e. non-CO₂ GHG emissions from soils in response to different agricultural management practices utilized in ICL systems).

Comment 3: very short. In your conclusions, please also answer the following questions: what are the directions for the future? what are the research gaps? what is new to this manuscript?

Response: The reviewer’s questions were addressed in the Conclusions section.

L530-533: Future work includes continued evaluation of perennial grass species management, grazing management in both perennial grasses and crop residues, and the incorporation of enteric emissions for a full system-level GHG assessment.

L517-520: As more producers explore options to diversify their farming enterprises by incorporating livestock, there is a growing need for critical information to fill the knowledge gaps on the environmental and economic impacts of perennial grass incorporation and grazing management of crop residues, cover crops, and perennial grasses.

L526-530: Finally, our results showed that although grazing perennial grasslands tended to increase GHG emissions in pastures selected for forage quality, incorporating perennial grasses into the overall ICL system will likely provide the most effective GHG mitigation outcomes, particularly on marginally productive lands where intensive row-crop production practices would exacerbate, not abate, soil GHG emissions.

Comment 4: Editorial errors. See editorial requirements.

Response: Formatting was updated throughout the manuscript to meet journal editorial requirements.

Reviewer 2 Report

Manuscript Title:

Soil greenhouse gas responses to biomass removal in the annual and perennial cropping phases of an integrated crop live-stock system

This manuscript describes the interesting topic of combining crops and livestock systems to help mitigate the environmental impacts of intensive single-commodity production. It is appreciable that the authors attempted to provide detail on the use of pseudo-replicates for design.

However, this manuscript needs a substantive rewrite to clarify the material and methods.

Also, authors need to clean the manuscript for spacing, punctuation, and formatting issues.

Specific comments are provided below:

Authors reported, “The 8-ha 121 continuous corn area consisted of a randomized design in 3 blocks (2.7 ha each) to assess 122 corn stover removal practices (no removal, mechanical baling, or livestock grazing) and 123 winter cover crop use (with or without triticale).”Please clarify the design for continuous corn and cover crop treatment. Was cover crop planted in the 8-ha assigned for continuous corn or the three blocks only used for different practices within continuous corn?
Line 156-157: why was stover grazing duration different in two years (more than double in 2018 than 2019); would it have impacted GHG emissions?
Line 196-204: Provide the details of method (reference) and equipment for laboratory analysis of soil samples such as bulk density, pH, EC, and C and N analysis?
Line 209: What does “original experiment unit” mean? So, no sampling was conducted in pseudo-replicates?
What was the sampling frequency for GHG measurement; were they conducted weekly/bi-weekly?
Why was CO2 data not included in GHG calculation?
How much was the gas aliquot collected for sampling?
Please provide details of GHG sampling frequency details; Calculating cumulative GHG emission with a longer time gap between sampling creates greater uncertainty in the estimates. Studies suggest careful consideration of the sampling frequency throughout the measurement period and interpolating between sampling points (Charteris et al., 2020). For N₂O measurements, the sampling frequency of at least twice per week around the events when higher emissions are likely (e.g., rainfall, fertilization, cultivation) and when conditions are conducive to near-zero N₂O fluxes (e.g., in dry or cold soils), weekly or biweekly sampling are recommended.

Charteris, A. F., Chadwick, D. R., Thorman, R. E., Vallejo, A., de Klein, C. A. M., Rochette, P., & Cardenas, L. M. (2020). Global Research Alliance N2O chamber methodology guidelines: Recommendations for deployment and accounting for sources of variability. Journal of Environmental Quality.

Author Response

Authors’ Response to Reviewer 2 Manuscript ID: agronomy-1263797

We thank Reviewer 2 for their constructive comments on our manuscript titled “Soil greenhouse gas responses to biomass removal in the annual and perennial cropping phases of an integrated crop livestock system.” We incorporated reviewer suggestions where relevant and provided rebuttals where suggestions were not used. Please find our specific responses to each of their comments (numbered below). For convenience, we refer to line numbers in the revised manuscript version submitted and blue font in the revised manuscript indicates where revisions were made within the resubmitted text.

Sincerely,

Virginia L. Jin (corresponding author)

REVIEWER 2

Comment 1: This manuscript describes the interesting topic of combining crops and livestock systems to help mitigate the environmental impacts of intensive single-commodity production. It is appreciable that the authors attempted to provide detail on the use of pseudo-replicates for design.

However, this manuscript needs a substantive rewrite to clarify the material and methods. Also, authors need to clean the manuscript for spacing, punctuation, and formatting issues.

Response: Please see specific comments below on revisions to improve experimental design description. Formatting was updated throughout the manuscript to meet journal editorial requirements.

Comment 2: Authors reported, “The 8-ha 121 continuous corn area consisted of a randomized design in 3 blocks (2.7 ha each) to assess 122 corn stover removal practices (no removal, mechanical baling, or livestock grazing) and 123 winter cover crop use (with or without triticale).”Please clarify the design for continuous corn and cover crop treatment. Was cover crop planted in the 8-ha assigned for continuous corn or the three blocks only used for different practices within continuous corn?

Response: The design description was clarified to specify that the 8-ha of continuous corn was managed in a randomized complete block design (RCBD). The reviewer question here is unclear – the winter cover crop management treatment (two levels) was included in the RCBD along with the crop residue management treatment (3 levels) as described. Every treatment combination of crop residue management and cover crop management would be replicated three times within the 8-ha continuous corn area.

L112-115: The 8-ha continuous corn area consisted of a randomized complete block design in 3 blocks (2.7 ha each) to assess corn stover removal practice (no removal, mechanical baling, or livestock grazing) and winter cover crop use (with or without triticale).

Comment 3: Line 156-157: why was stover grazing duration different in two years (more than double in 2018 than 2019); would it have impacted GHG emissions?

Response: Stover duration was less in 2019 because cattle were put out to graze much later after grain harvest than in 2018. There was less stover material available to support animal grazing, so grazing length was adjusted accordingly. This has been included in the text:

L143-145: Grazing duration was determined by initial cattle weight, grazing date, and corn yield for each year. Differences in grazing duration, across years, were largely the result of corn residue availability differences between 2018 and 2019.

It is unclear how grazing duration would impact soil GHG emissions because of other interacting factors that can change from year-to-year (i.e. soil moisture conditions, precipitation inputs, crop yield). In this study, the impact of grazing stover in the fall of 2019 would have been detected during the following growing season (2020), but this was not assessed because the experiment was terminated in the spring of 2020 prior to the start of the growing season. This was explained in the Statistics section in the original submission. We added additional detail there to clarify:

L259-263: Fall stover grazing occurred only in 2018 and were expected to affect 2019 growing season GHG emissions. Similarly, fall 2019 stover grazing was expected to affect 2020 growing season GHG emissions, but those emissions were not measured because the experiment was terminated in the spring of 2020 prior to the start of the growing season.

Comment 4: • Line 196-204: Provide the details of method (reference) and equipment for laboratory analysis of soil samples such as bulk density, pH, EC, and C and N analysis?

Response: Method references and equipment for analyses were added to the text.

L188-193: Soil bulk density was determined by using the volume and dry weights (dried at 105 °C) from the sample cores [30]. Soil electrical conductivity (dS m-1) and pH were determined in solution after extraction with deionized water (1:1 soil:water ratio) using a combination electrode (Orion Star A215; Thermo Fisher). A subsample of sieved soil was finely ground then analyzed for total carbon and nitrogen (%) using dry combustion (FlashEA 1112 Series NC Soil Analyzer; Thermo Fisher) [31].

L663-664: 30. Blake, G.R.; Hartge, K.H. Bulk density. In Methods of Soil Analysis, Part I Physical and Mineralogical Methods, Klute, A. Ed., 2nd Edition, ASA-SSSA, Madison, 1986; pp. 363-375.

L665-669: 31. Nelson, D.W.; Sommers, L.E. Total carbon, organic carbon, and organic matter. In Methods of Soil Analysis Part 3: Chemical Methods, Sparks, D.L., Page, A.L., Helmke, P.A., Loeppert, R.H., Soluanpour, P.N., Tabatabai, M.A., Johnston, C.T., Sumner, M.E., Eds. Soil Science Society of America, Inc. and American Society of Agronomy, Inc., Madison, Wisconsin, USA, 1996; pp. 961–1010.

Comment 5: Line 209: What does “original experiment unit” mean? So, no sampling was conducted in pseudo-replicates?

Response: This statement in the manuscript was worded poorly. Soil GHG sampling was conducted in all treatments in both the corn system (RCBD) and perennial grass system (pseudo-replicates). The text has been revised for clarity.

L202-203: Soil GHG emissions were sampled in all treatments in the continuous corn system (RCBD) and perennial grass system (pseudo-replicates) throughout the 2017 to 2019 growing seasons…

Comment 6: What was the sampling frequency for GHG measurement; were they conducted weekly/bi-weekly?

Response: The total number of sampling events was reported in the “Soil GHG Emissions” subsection of the Materials and Methods. The text was revised for clarity.

L225-226: Eight sampling events occurred during the 2017 growing season, 5 events in the 2018 growing season, and 9 events in the 2019 growing season.

Comment 7: Why was CO2 data not included in GHG calculation?

Response: Although soil CO₂ emissions were also measured here, we did not present this data in the context of GHG mitigation potential because chamber-based CO₂ represents only CO₂ outputs, not net ecosystem CO₂ exchange (Cavigelli and Parkin 2012). This text was included in the revised manuscript:

L376-379: Although soil CO₂ emissions were also measured here, we did not present this data in the context of system GHG mitigation potential because chamber-based CO₂ represents only CO₂ outputs, not net ecosystem CO₂ exchange [41].

L695-699: 41. Cavigelli, M.A.; Parkin, T. Cropland management contributions to greenhouse gas flux. In Managing Agricultural Greenhouse Gases: Coordinated Agricultural Research through GRACEnet to Address Our Changing Climate, Liebig, M., Franzluebbers, A., Follett, R.F. Eds., Academic Press, Waltham, MA, 2012; pp. 129–165.

Comment 8: How much was the gas aliquot collected for sampling?

Response: Details were added to describe the GHG sampling procedure:

L219-222: Headspace gas samples (25 mL) were collected via syringes and then injected into 12 mL evacuated vials at time 0-, 10-, 20-, and 30-min for each sampling event. Over-pressurization of vials ensured that sufficient sample would be available for automated GHG analysis in the laboratory (described below).

Comment 9: Please provide details of GHG sampling frequency details; Calculating cumulative GHG emission with a longer time gap between sampling creates greater uncertainty in the estimates. Studies suggest careful consideration of the sampling frequency throughout the measurement period and interpolating between sampling points (Charteris et al., 2020). For N2O measurements, the sampling frequency of at least twice per week around the events when higher emissions are likely (e.g., rainfall, fertilization, cultivation) and when conditions are conducive to near-zero N2O fluxes (e.g., in dry or cold soils), weekly or biweekly sampling are recommended.

Response: We agree with this important caveat. Text was included to acknowledge this as a limitation of our study, and we cite the reviewer’s suggested reference here.

L379-382: We also note that the limited GHG sampling frequency used in this study introduces substantial uncertainty in the calculation of total growing season GHG emissions (Parkin 2008; Charteris et al 2020). To reduce this uncertainty, we limited comparisons of total GHG emissions between treatments within growing seasons instead of across seasons and our results are discussed below.

Round 2

Reviewer 1 Report

Accept in present form.

Reviewer 2 Report

The authors' effort to thoroughly revised the manuscript based on the given suggestions and comments is appreciable. This study's findings will provide valuable information on the impacts of ICL systems on soil emissions of non-CO₂ GHGs.