Review Reports - Optimizing Carbon Sequestration in Croplands: A Synthesis

Round 1

Reviewer 1 Report

Please see the attached for comments and suggestions

Comments for author File: Comments.pdf

Author Response

We would like to thank the anonymous reviewer for her/his critical comments, which will help to improve the quality of our manuscript. Our response to each of the reviewers comments are given in the attachement (word file).

Author Response File: Author Response.pdf

Reviewer 2 Report

This work was obviously the result of a extensive amount of reading and research. Other than figure 1, however, it tends to be a bit convoluted in how it is written/presented. While I understand that there are a lot of contradictory findings/postulates when it comes to SOC, the paper is a bit difficult to follow as is. I suggest that the introduction be rewritten to be more targeted and/or outline how the rest of the paper will be presented and why (I believe the idea is that there are a lot of work out there but when it comes to recommending policy, the way forward is murky because that work is not synthesized in one place, but also that there is no consensus in the research. If that is the authors' point, then please state that more forcefully and concisely). More figures/tables need to be utilized in the text to make the takeaway message from each section easier to read and help with the flow. I found figure 1 to be compelling, but didn't feel like it was the focal point of the paper that I assume, as the only figure, it was meant to be.

Author Response

Author Response File: Author Response.pdf

Reviewer 3 Report

Improving soil C storage is considered a valuable mitigation strategy to fight climate change with positive feedback on soil fertility and the long-term sustainability of agriculture. This manuscript reviews the available agricultural management practices (AMP) capable to sequester Carbon into the soil, analyzing the sequestration potential as well as existing gaps in knowledge and trade-offs emerging from the analysis of a relevant number of scientific papers. In general, I found the proposed synthesis quite informative, well written, and structured, with a relevant potential interest on a wide audience.

The more relevant concern I have regards the opportunity of including organic agriculture in the list of AMPs. Organic agriculture is indeed a general production protocol that may foresee the simultaneous application of several of the previously described AMP with a different degree of intensity and combination, depending on the type of crop and farmers' decisions. I thus disagree to list it among the AMPs. I would rather prefer to add it in chapter 4.5 as a suggestion to practically implement best practices in a productive system without impairing (or in certain cases improving) crop profitability. I would expand that section (4.5) also reporting briefly about the ongoing debate on ecological intensification/ sustainable intensification of agriculture, as a need to achieve a higher degree of efficiency in the use of external resources to maintain or increase yield production standards without the need to further convert other natural areas for agricultural purposes to meet the food demand of an increasing global population.

Besides this “conceptual” change in the manuscript I have some minor comments:

Line 18 (abstract): I would modify indicating respiration as a primary source of C loss: “… reducing SOC losses (reducing soil erosion, managing soil respiration)”
Line 18-21 (abstract): writing that AMP can sequester from -20 to 740 kg C ha^-1y^-1, without defining what do you mean for carbon sequestration, can be quite confusing for the reader. Moreover in other fields (like micro-meteorology), negative fluxes are associated conventionally to C uptake from the atmosphere and positive fluxes are considered net emission. Starting from L 18 I would re-phrase as following: “… - AMP can either sequester, up to 714 kg C (compost)…, having no distinct impact (mineral fertilization, no-tillage), or even reduce SOC stocks in the topsoil (bare fallow or business-as-usual)”.
L 83 (Introduction): in the list of AMPs at lines 83-92, Irrigation is missing, while it is described as AMP n.7 in the text. As said above I would delete n. 6 (organic agriculture) from this list, and also from the text. You could consider leaving it in figure 1 but I would place it at the end of the plot, highlighting the fact that it represents a possible mixture of AMPs that could tendentially provide some SOC sequestration.
L 123 (2.2 Carbon sequestration): In this section, I advise to state clearly that negative carbon sequestration means a net loss of C storage, while positive C sequestration corresponds to an increase of SOC stock.
L137 (2.3 Carbon storage): I would expand a bit this definition to avoid misunderstanding. This could be achieved for instance by adding a clarifying example after [33] at line 141, starting with “ in other words, if C sequestration is…
L 156: check the appropriateness of citation [42], I think the correct number here is [40].
L 183 (Figure 1): In the figure caption I suggest adding again the statement that negative C sequestration potential causes net SOC stock losses, and the opposite for C sequestration potential > 0, as figures should be self-explaining. I then would highlight a bit (with a dotted line) the horizontal zero-line, to help the reader understand which AMP is virtuous and which one is not. As mentioned before, I suggest deleting organic farming or putting it in the last place, to highlight its anomaly with respect to single practices. Why biochar is missing here?
L 209 (3.2 Organic amendments): from line 213, in addition to what already mentioned, it has to be noted that also organic amendments, similarly to what happens for fertilizers (as stated in section 3.1) may stimulate SOC biodegradation.
L 315: better add “carbon emissions” in the phrase “plants assimilate more than 10% of the atmospheric carbon”
L 576 (3.7.2 trade-offs): most of the negative impacts of irrigation could be mitigated (pumping cost) or avoided (leaching and runoff) when irrigation water management aimed at improving water use efficiency (or water productivity) are carried out. Deficit irrigation strategies of precise irrigation methods can sustain crop productivity while limiting the negative externalities, thus improving the capability of this AMP to help increasing SOC stock.
L 605: please check the unit for carbon sequestration potential of biochar (Mt looks too big…)

Author Response

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Thank you for the additional table. While I am saying accept in the current form, I do recommend that the authors have a writing specialist read over the document and improve the flow just for ease of reading. I believe the readability of a paper is incredibly important to maximize the accessibility of the information and impact of the research.