General comments

“Digging deeper: assessing soil quality in a diversity of Conservation Agriculture Practices” presents novel data and understanding of the effects of conservation agricultural practices on several metrics of soil quality. Twenty eight farms using Conservation Agriculture in Wallonia, Belgium are sampled and surveyed to document the agricultural practices used and fifteen soil quality outcomes. The agricultural practices and soil properties outcomes are conceptualized within the framework of previous work by the same authors (Ferdinand and Baret, 2024). Correlations are calculated between farming practice and soil quality, indicating that the rotation of temporary grassland substantially improves soil organic carbon content and soil stability. The co-dependence of multiple conservation practices is highlighted, particularly in the case of reduced tillage, which is observed to not be strongly beneficial without other concurrent conservation practices.

Overall, the manuscript is interesting and very high quality. The study is well-conceptualized, the data collection is comprehensive and valuable, and the results are well-presented. The primary strength of the study is the comprehensive dataset which characterizes practices at 28 conservation agriculture farms. The data is clearly carefully collected and has insights to offer. The analysis and discussion effectively address the topic of additive benefits of multiple practices, rather than dichotomous classification based on single practices.

 The manuscript could be strengthened by adding further analysis and discussion on the context-dependent success of various strategies. This important topic is noted in the introduction and the conclusions, but not addressed substantively. The farms included in this study span a climactic gradient and range from permanent cropland to pasture rotation – it would be compelling to understand how practices and outcomes covary with the context in which they are applied.

Specific comments

• The methods section is extremely thorough, but the detailed description of the soil chemical analysis could be edited for brevity or moved partially to the supplement. Additionally, several analyses are introduced that are not discussed – perhaps these could be moved to the supplement as well.
• Permanganate oxidizable carbon is used to measure the labile carbon pool, but this metric is known to be sensitive to soil type to some extent – this should be addressed in the methods or the discussion.
• CA type is used heavily throughout the manuscript, but the motivation is not specifically addressed. Further discussion could help clarify the utility of this classification.
• It is not clear what happened to the seven field not assigned to any CA type. Why were those fields not classified? Were those fields included in the analysis of correlation between practices and outcomes? It seems they would have information about the breadth of CA practices actually in use, and for the analysis in table 2 and figure 3, as well as further analysis of context.
• Gradients in soil and climate are introduced but not used for the analysis or discussion. To interpret the results, it would be useful at minimum to understand the covariation of CA type and climate/geology. This could shed light on to what extent practice or underlying factors are responsible for the observed differences in outcome.

Technical comments

The manuscript is well written and edited, with only a few confusing word choices:

• 38: should be “and also to unsustainable …”
• 47-49: “on the one hand”/“on the other hand” indicates conflicting ideas – different transition words here would make more sense
• 2.3.153: change “combined to a” to “combined with a”
• 3.166: Pie roll = rolling pin?
• 3.3.30: “average per CA type” is not clear what was done
• 2.80: “enrich” => “enriching”

Dear Editor,

These are my comments about the paper 'Digging Deeper: Assessing Soil Quality in a Diversity of Conservation Agriculture Practices', from Ferdinand et al., submitted for publication to EGUsphere.

This is a good and interesting paper, worth to be published after refining a few details. As you will see in my comments, none is drastic, and I am confident that authors can deal with my inquiries without special problems.

GENERAL COMMENT

No relevant criticisms about the paper. I should only make a comment about the 'Discussion' paragraph, which in my view does not emphasize clearly enough which of the studied factors seem most relevant for SOC accumulation (i.e., C sequestration). What agricultural practices seem to give the best results is not emphasized enough, it becomes disperse within the text, thus diluting the impact of your work in the mind of a potential reader. Note that many of your conclusions may become (should become?) recommendations for farmers or land owners. 

One way for solving the problem would be make sub-paragraphs specifically devoted to each of the main considered factors. The 2-3 factors that (according to your results) seem more relevant for SOC sequestration deserve a sub-paragraph focused on each one. Eventually, you could also make a last sub-paragraph devoted to those factors that (perhaps unexpectedly) seem less relevant than 'a priori' supposed.

Alternatively, you could also a small set of lines for this:

'From our data, the studied factors the most relevant for SOC sequestration are (i) presence/absence of a 'grassland' stage in their rotation, (ii) the SOC:Clay ratio, (iii) etc...'. And, perhaps, something such as 'In contrast, other studies factors such as... [add yourself the list] seem less relevant than often tought.'

 

    

SPECIFIC COMMENTS

Line 37. Just a style detail: do not start a sentence with a number. Say 'About 62% of European soils are affected...', or 'In Europe, 62% of soils are affected...', or something similar. That said: do you mean the whole of european continent, or the European Union? Norway and Switzerland, for instance, are included? Sorry, I know it is not a crucial detail for your explanation, but a small detail to make clear.

Lines 45-46. '...at the soil surface and in the topsoil'. Is'nt redundant? Should not be enough to mention 'the topsoil' (without specifying which depth you are refering to)?

Lines 94 and 96. Do you refer to 'catch-crops', instead of 'cash-crops'?

Lines 130-150. The description of the CA practices to be taken into account is impressive, both by its extension and by the precision authors put on them. I sincerely congratulate authors for their effort in ordering and classifying the agricultural practices to be studied here. That said, an important detail is that the terms 'inversion tillage' (or 'non-inversion tillage') are not mentioned here. Taking into account the importance this matter has further in the discussion, I think it should be specifically mentioned in this paragraph; particularly in the lines 133-136.

Lines 157-164 (paragraph 2.2.4). I understand that a single depth was considered (0-30 cm), for the study of chemical soil properties. Now the work is done, but such a gross sampling is not ideal in my view. Splitting the soil in at least two depths (say, 0-15 and 15-30 cm, to sepparate the very topsoil from the middle soil) would have added a lot of additional information. I understand the need of keeping the number of samples within reasonable limits; but the loss of information as a consequence of considering a single depth is a pity.

Lines 170-171. Accept that you mention an ISO protocol instead of a scientific reference for CEC and exchangeable base cations. But it would be nice to mention the main fatures of the method. What is the extractive solution? BaCl2? NH4 acetate? The cations were analyzed by Atomic absorption, ICP... what? How was it measured the exchangeable acidity? Etc.

Actually much of this information is given in further lines (paragraph 2.3.1, lines 179-186), so the continuous mention of ISO or other norms (without explaining clearly what are they doing) is a bit annoying for a scientific reading the paper. The text of the paragraph 2.3.1 should be refined to make both compatible. Thus, the method for CEC and exchangeable cations, given in lines 180-186, is the 'NF X31-130 standard', mentioned a bit before (lines 179-180)? Or potential CEC has nothing to do with the following lines? Note that I do not doubt about the correctness of the methods, I just ask for explaining them properly. If a method matches a standard method (ISO or similar) mention it; but say something about the method, not just the identificative standard number. If a method was not taken from any standard or ISO method, then mention the source (usually, a scientific paper, or a book of methods).

In contrast, the method for soil structural stability (lines 220 and following) is very well explained. It seems a good approach. I understand that you name 'Wend' the proportion of soil sample collected in the mesh basket. Why 'Wend'? Is there any reason? The abbreviation of... what? 

Additionally, you should mention the units in which 'Wend' is given. I deduce that it is a simple proportion of retained soil to total soil (i.e., from 0 to 1), but this should be said explicitly.

Line 245. 'Wend values ranged from 0.01 to 1.00'. It must be noted that the units for Wend were not mentioned in paragraph 2.3.3. From this line I assume that units were g/g (i.e., proportion, from 0 to 1). Or is it %? Even though it can be deduced, I ask authors to mention specifically the units in which 'Wend' is given, here or (prefereably) in paragraph 2.3.3.

[NOTE: apparently, in page 13 line numbers re-start from zero. In our following comments, we made reference to the lines number as they are in the file]

Lines 30-34. I disagree with the way authors expose the relationship between the SOC:Clay ratio and the structural stability (measured by the 'Wend' ratio). Figure 4 is well built, but not very attractive, in spite of the colours used. Rather I would expect a figure showing how both parameters are correlated. Note that both SOC:Clay ratio and Wend ratio are quantitative parameters: a figure joining both, similar to Figure 3, would be possible.

Line 51. '...farming (e.g. Mamedov et al. 2021).' Not necessary a two-level parentheses. This problem appears at other places in the text (e.g., lines 68, 86).

Line 53. '... non-inversion tillage practices'. I assume authors refer to tillage devices that do not result in rolling the topsoil and inversing it (top to bottom, bottom to top). Mention this detail more clearly. See also my previous comments, in the sense that the presence/absence of non-inversion tillage is not mentioned in paragraph 2.2.2. Actually paragraph 2.2.2 was the ideal place to mention explicitly the non-inversion tillage, and how was it included in the list of CA practices.