the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Jan 2025
Physical Protection of Soil Carbon Stocks Under Regenerative Agriculture
Abstract. Regenerative agriculture is emerging as a strategy for carbon sequestration and climate change mitigation. However, for sequestration efforts to be successful, long-term stabilisation of Soil Organic Carbon (SOC) is needed. This can be achieved either through the uplift in recalcitrant carbon stocks, and/or through physical protection and occlusion of carbon within stable soil aggregates. In this research, soils from blackcurrant fields under regenerative management (0 to 7 years) were analysed with respect to: soil bulk density (SBD), aggregate fractionation (water stable aggregates vs. non-water stable aggregates (WSA and NWSA respectively)), soil carbon content, and carbon stability (recalcitrant vs. labile carbon). From this, long term carbon sequestration potential was calculated from both recalcitrant and physically occluded carbon stocks (stabilised carbon). Results indicated favourable shifts in the proportion of NWSA:WSA with time. This ratio increasing from 27.6 % : 5.8 % (control soil) to 12.6 % : 16.0 % (alley soil), and 16.1 % : 14.4 % (bush soil) after 7 years. While no significant (p ≥ 0.05)) changes in recalcitrant carbon stocks were observed after 7 years, labile carbon stocks increased significantly (p ≤ 0.05) from 10.44 t C ha-1 to 13.87 t C ha-1. As a result, total sequesterable carbon (stabilised carbon) increased by 1.7 t C ha-1 over the 7 year period, due to the occlusion and protection of this labile carbon stock within WSA fraction. This research provides valuable insights into the mechanisms of soil carbon stabilisation under regenerative agriculture practices and highlights the importance of soil aggregates in physically protecting carbon net-gains.
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RC1: 'Comment on egusphere-2024-4029', Anonymous Referee #1, 02 Mar 2025
This manuscript aims to determine the effects of regenerative agriculture on soil carbon stocks. The authors found that regenerative agriculture did not increase recalcitrant carbon stocks but did significantly increase labile carbon stocks. A lot of work has been done, and some results are interesting. However, I do not think the current version is suitable for publication in SOIL because of several weaknesses. Please see below for my main concerns:
First, the methods were not introduced clearly in the current manuscript, making it difficult to judge the results. For example, what were the management practices (fertilizer, tillage, and so on) that were used for the conventional farming? What were the grazing cover crops that were planted on the alleyways? What were the amount and nutrient content of the sprays of compost tea and organic fertilizer? Which year was the soil sample collected? There were many different soil carbon types in this manuscript (e.g. labile and recalcitrant carbon, occluded carbon, stabilised carbon, WSA, and NWSA); however, the authors failed to separate them clearly. It is hard for me to digest so many different terminologies.
Second, the main text should be improved seriously. For example, many parts in the Results and Discussion section were not about “results and discussion” but were about “background”, which should be moved to the introduction section. In addition, more information about the field design and methods should be included in the abstract; otherwise, it is difficult for readers to know the meaning of “alley soil and bush soil”.
Third, in the abstract section, the authors stated that “This research provides valuable insights into the mechanisms of soil carbon stabilisation under regenerative agriculture practices.” However, I am not sure if they really unravel the mechanisms because they did not measure other soil variables (e.g. soil nutrient content and soil microbial parameters), which can be used to explain the results. Moreover, the “Results and Discussion” section was mainly introducing background and describing the results. Instead, more deep discussions and measurements should be included to explain the interesting results (e.g. when compared to control treatment, why did total carbon stock decreased in the short term and then increased to the similar level like the control treatment in the long term). Does this mean regenerative agriculture must be conducted for a long time? Otherwise, croplands would lose soil carbon?Citation: https://doi.org/10.5194/egusphere-2024-4029-RC1 -
AC1: 'Reply on RC1', sam keenor, 28 Mar 2025
Dear Reviewer,
We appreciate the time and effort that you have taken in evaluating our manuscript and for your constructive feedback, which we hope will help us improve the clarity and robustness of our work.
Below, we provide responses to each of your comments and outline what potential actions we suggest.
- The methods were not introduced clearly, making it difficult to judge the results.
- What were the management practices (fertiliser, tillage, etc.) used for conventional farming?
- What were the grazing cover crops planted in the alleyways?
- What were the amount and nutrient content of the compost tea and organic fertiliser?
- Which year was the soil sample collected?
This section initially opens with a brief outline of the field experiment, detailing the location and layout of the field sites used in the investigation, including a figure of field history. Broad information as to cultivation and management activities is provided for both the blackcurrant crop and the arable control field. The use of both the diverse grazing cover crop, and summer fallow planted into the fields during the investigation, as standard seed mixes were noted, however the specific species which made up these mixes were not explicitly stated.
Given the soil physical property-centric focus of this investigation, we do not feel that the quantity and nutrient content of the compost tea organic fertilisers are important to the wider story told in this manuscript and would have minimal influence on soil aggregate stability and carbon storage. These additions were infrequent, and their carbon flux contribution would be insignificant when compared with the plant biomass carbon inputs.
Year of soil sampling was omitted as an oversight – this can be clarified.
As such we suggest the following actions:
- Provide further clarity as to cultivation depth and broader management in the arable control field
- If deemed necessary by the editor, include further information regarding diverse grazing and summer fallow mixes
- Include reference to the year and time of sampling within the methods section
- There were many different soil carbon types in this manuscript (e.g. labile and recalcitrant carbon, occluded carbon, stabilised carbon, WSA, and NWSA). The authors failed to separate carbon types clearly, It is hard to digest so many different terminologies.
We recognise that the terminology may be complex. However, we believe we have clearly defined each soil carbon stock and its origin throughout the manuscript. To further improve clarity, we propose including a supplementary table that outlines and defines each type of carbon and its physical associations discussed in the study.
As such we suggest the following action:
- An additional table within the supplementary section can be included which details each type of carbon discussed in the investigation and their origins. A glossary of terms if you will.
- Many parts in the Results and Discussion section were not about “results and discussion” but were about “background”, which should be moved to the introduction section
In addition to adding a level of further interest and value to the manuscript, this content helps to define and delineate the types of carbon pools being discussed (raised as an issue above). While we believe that the background information within the Results and Discussion section is essential to contextualising the findings, we acknowledge the need to better balance content between sections.
In revising the manuscript we will seek to better balance this content between the introduction and discussion sections.
We suggest the following action:
- Balance the content between the introduction and discussion sections, being mindful of content that may be repetitive or inappropriately placed within the discussion section.
- More information about the field design and methods should be included in the abstract, to make it easier for readers to know the meaning of “alley soil and bush soil”.
Due to word count constraints, we were limited in the level of detail provided in the abstract. However, we acknowledge the potential need for greater clarity in this regard and would be willing to add a concise acknowledgement of alley and bush soils.
As such we suggest the following action:
- Following the Editor’s advice regarding word count and section length, we can seek to add a short statement detailing the alley/bush soils and their relevance within the research.
- The authors stated that “This research provides valuable insights into the mechanisms of soil carbon stabilisation under regenerative agriculture practices.” However, I am not sure if they really unravel the mechanisms because they did not measure other soil variables (e.g. soil nutrient content and soil microbial parameters), which can be used to explain the results.
While we appreciate this concern, soil nutrient content and soil biodiversity parameters were not the focus of this investigation. Our research reveals the collective outcome of a switch to regenerative agricultural principles as a soft fruit crop establishes. We feel that the insights regarding labile vs recalcitrant carbon stocks and their association with stable and non-stable aggregates does amount to appreciation of the mechanisms of soil carbon protection.
We acknowledge that there are, of course, a myriad of causal factors at play that may influence the outcome. As such, we highlight that this is a field experiment and control of parameters is challenging. Even if for example nutrient content and soil microbial parameters were elucidated, we do not feel such information would support causality of the outcome.
Additionally, measuring these additional variables such as soil microbiome dynamics would require near-continuous monitoring, which was beyond the scope of our research.
We suggest no further action.
- The “Results and Discussion” section was mainly introducing background and describing the results. Instead, more deep discussions and measurements should be included to explain the interesting results (e.g. when compared to control treatment, why did total carbon stock decrease in the short term and then increase to the similar level like the control treatment in the long term). Does this mean regenerative agriculture must be conducted for a long time? Otherwise, croplands would lose soil carbon?
We feel that the results and discussion section answers adequately these points within the constraints of the experimental investigation that was undertaken. We emphasise that the observed trends suggest that long-term management is required to achieve significant recalcitrant carbon gains.
We feel that the text in its present form already addresses these points, however, we welcome specific guidance from the reviewer on any aspects requiring further clarification.
We suggest no further action, pending a point of clarification from the reviewer.
Once again, we sincerely thank you for your insights and your time.
Kind regards,
Sam G. Keenor, and Brian J. Reid
Citation: https://doi.org/10.5194/egusphere-2024-4029-AC1
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AC1: 'Reply on RC1', sam keenor, 28 Mar 2025
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RC2: 'Comment on egusphere-2024-4029', Anonymous Referee #2, 03 Mar 2025
This paper explores the impact of regenerative management on soil aggregates and carbon pools. The samples originate from blackcurrant fields (bushes and alleys) with duration from 1 to 7 years, and a control plot still under conventional management. Many analyses were conducted (soil bulk density, stable and non-stable aggregate contents, soil carbon contents and stocks, and carbon stability). The main observation is a shift towards more stable aggregates and an increase of the labile carbon pool under regenerative management, with little effect on the recalcitrant pool.
The aim of this research and the results are interesting. Although I think the article is not acceptable at this stage, I would recommend resubmitting the manuscript after signficant changes and thorough proofreading to enhance the work that has been conducted. Some of the elements that should be reconsidered follow.
The article lacks clarity regarding crucial details such as the experimental set-up (number of fields, number of samples and replicates, etc.) and the presentation of results. Figure 1 from the supplement should be included in the article to provide a clearer picture of the set-up; a map of the experiment could also bring some clarity. It would also be interesting to discuss the prior presence of blackcurrant fields in years 5 and even 3: did the introduction of new plants lead to a return to a state of conventional management, thereby 'resetting' the regenerative agriculture counter to 0 years?
The results should be discussed further and the text should be better organized between what is general introduction of the topic, results, and discussion. Even if results and discussion can be addressed altogether, they should be clarified and strengthened.
Overall, the article is not easily readable. Check for typos, missing verbs or parts (abrupt end L.631 for example). Indications regarding p-values appear repeatedly throughout the text (as you defined two levels of confidence) without really bringing relevant information; the p-values could appear on your graphs but not in text for instance, with only mentions to 'significant' or 'not significant'. Also, a genuine thought: could some results be non significant due to the small numbers of samples? Would other tests be better at handling this issue?
Citation: https://doi.org/10.5194/egusphere-2024-4029-RC2 -
AC2: 'Reply on RC2', sam keenor, 28 Mar 2025
Dear Reviewer,
We appreciate the time and effort that you have taken in evaluating our manuscript and for your constructive feedback, which we hope will help us improve the clarity and robustness of our work.
Below, we provide responses to each of your comments and outline what potential actions we suggest.
- The article lacks clarity regarding crucial details such as the experimental set-up (number of fields, number of samples and replicates, etc.) and the presentation of results.
This section initially opens with a brief outline of the field experiment, detailing the location and layout of the field sites used in the investigation, including a figure of field history. As such, the number of fields sampled during this investigation in addition to the number of samples are explicitly stated within the methodology sections.
However, in line with comments from both reviewers, we accept that there could be increased clarity regarding some aspects of the methodology section of the manuscript.
As such we suggest the following actions:
- Provide additional clarity and changes to the methodology, with focus placed specifically on clarifying the number of replicates and total samples taken.
- Provide further clarity as to cultivation depth and broader management in the arable control field
- If deemed necessary by the editor, include further information regarding diverse grazing and summer fallow mixes
- Include reference to the year and time of sampling within the methods section
- Figure 1 from the supplement should be included in the article to provide a clearer picture of the set-up; a map of the experiment could also bring some clarity.
We agree that Figure 1 could be made as part of the main article, a map of the experiment can also be produced if required by the editor.
We suggest the following actions:
- Move Figure 1 to an appropriate place within the main article
- Pending the Editors judgement, produce a map as required
- It would also be interesting to discuss the prior presence of blackcurrant fields in years 5 and even 3: did the introduction of new plants lead to a return to a state of conventional management, thereby 'resetting' the regenerative agriculture counter to 0 years?
We agree that there is a point of interest here. Given the methods of establishment – between the cultivation of a new crop of blackcurrant bushes (i.e. field Y5) the field undergoes a total cultivation essentially ‘resetting’ the field as the reviewer identifies. The methodology can be updated to clarify that total cultivation between plantings effectively resets the soil conditions.
We suggest the following actions:
- Clarify the ‘reset’ of the soil following total cultivation between plantings of blackcurrants.
- Results should be discussed further, and the text should be better organised between what is general introduction of the topic, results, and discussion. Even if results and discussion can be addressed altogether, they should be clarified and strengthened
While we believe that the background information within the Results and Discussion section is essential to contextualising the findings, we acknowledge the need to better balance content between sections.
In revising the manuscript, we will seek to better balance this content between the introduction and discussion sections.
We suggest the following action:
- Balance the content between the introduction and discussion sections, being mindful of content that may be repetitive or inappropriately placed within the discussion section.
- Overall, the article is not easily readable. Check for typos, missing verbs or parts, abrupt end L.631 for example
We will provide additional grammar and spell checks when reviewing potential changes to the article. We agree there is an error in L631.
As such we suggest the following action:
- Review grammar, spelling and readability of the text.
- Indications regarding p-values appear repeatedly throughout the text (as you defined two levels of confidence) without really bringing relevant information; the p-values could appear on your graphs but not in text for instance, with only mentions to 'significant' or 'not significant'.
We would be happy to make this amendment and move the p-values to figures instead of being repeatedly stated in the text. We highlight that such an approach in the case of the stacked histograms may be too confusing, to be included on the figure itself alongside the other statistical notations, however accommodation of P-values could be made within figure legends for clarity. We will act as advised by the editor.
We suggest the following action
- Follow advice of the editor and make the necessary alterations to statistics reporting in the text and on the Figures.
- Could some results be non-significant due to the small numbers of samples? Would other tests be better at handling this issue?
For statistical analysis, a one way ANOVA with post-hoc testing was used to determine significance at a 95% confidence level, alongside 2-tailed T-tests – both are robust and standard statistical tests for analysis of this type of data. We do not believe that altering the statistical testing methodology would provide any benefit to the analysis. Furthermore, the sample numbers are, as they are. There is no prospect to generate more measurements.
We suggest no further action.
Once again, we sincerely thank you for your insights and your time.
Kind regards,
Sam G Keenor, and Brian J. Reid
Citation: https://doi.org/10.5194/egusphere-2024-4029-AC2
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AC2: 'Reply on RC2', sam keenor, 28 Mar 2025
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