Dear Editor,

These are my comments about the paper 'Shifts in controls and abundance of particulate and mineral associated organic matter fractions among subfield yield stability zones', from Sam J. Leuthold et al., submitted to EGUsphere.

It is a good paper, and actually I did not expect otherwise, owing to the already known experience and scientific profficiency of some of the senior authors. Therefore, as you will see, I have very little to add to the text. I have a few comments, however, that may be of help to authors, or perhaps may suggest some improvements in the paper.

COMMENTS

As I understand, this research is done simultaneously to other ones, namely that of Fowler et al., which is repeatedly cited (as 'in-review': perhaps the term 'submitted' would have been more appropriate?). The fact that this additional information (about the sites, plant production and so on) is not yet available is a pity. However this is a minor drawback in this work.

Line 93. 'Zea mays', not 'Zea maize'.

Line 145. Remove one of the two consecutive 'the'.

Lines 252-255. If I well understood, your results seem contradictory with those of Maestrini & Basso. This is a very interesting result: could you stress it a bit more in the text? It goes almost unnoticed.

Lines 262-263. Extremely interesting finding, even though it has been observed before (as mentioned in line 265). Note, however, that the relationship is very weak, in the very limit of signification (p = 0.048). Please mention this detail.

About the Figure 6. This figure summarizes, to some extent, the results of this experiment. It is nice. Note, however, that at a first glance, it is a bit unconsistent with some of the results mentioned before. For instance: POM-C is, apparently, the most relevant factor in determining Yield stability. Nevertheless, the previous text (lines 274-276, also the following ones) rather suggests that the relationship between POM-C and yield stability is unclear. The key is, perhaps, the sentence(s) 'POM-C content in unstable zones was significantly higher than in all stable zones (p = 0.019), which had the same POM-C content independent of yields (Fig. 2C)' (lines 273-274), which suggest rather a negative relationship: POM-C relates negatively to yield stability. In line 284 you state 'we did not observe evidence that POM-C conferred additional stability to cropping systems'. But perhaps the key is in your further sentences (lines 285 and following) that rather suggest that POM-C relates indirectly to yield stability. The reasons that make unstable the crop yield have, as a secondary result, the accumulation of POM (if I well understood). However the heading of figure 6 ('Relative importance of variables in determining yield stability zones') rather suggests that you see POM-C as a cause of yield stability. May Figure 6 give an inexact view about your results? Is there any way to distinguish between 'likely causes' and 'likely consequences' of yield unstability? An additional detail: because all bars are given in a left-right orientation, it is not possible to distinguish between factors that affect (or are related) positively to yield stability, and those that affect (or are related) negatively to yield stability (which would be the case of POM-C, by the way). Would it be possible to distinguish them? For instance: perhaps the factors that affect negatively could be in the right-left orientation?

   

FIGURES

Figure 2. Just a question. I observed that the several points for a given 'Stability Zone' are not aligned horizontally. Is this deliberate, to facilitate a good view of these points (thus avoiding their superposition), or does this lack of alignment reflect some property of the points' sets?

Figure 5. Should be improved. I noticed that, in the small icons, there is an area in light violet colour, and another in a blue-greenish colour. The relative area of each one changes. I deduce that the blue-greenish means 'unfair condition', but it is not clear. The legend of the figure does not say anything about it: the meaning of these two colours should be added to the legend, otherwise the precise meaning of the figure remains unclear. Besides this problem, these small icons may be impossible to read in a printed version: would it be possible to enlarge them a bit?

Figure 6. Nice figure. That said, please correct 'Mehlic' to 'Mehlich'. See also my previous comments about this figure, which perhaps summarizes the whole results of this paper.

REFERENCES

The following cites are missing from the 'references' section:

Castellano et al 2015

Just et al 2023 

King et al 2023

Prairie et al 2023

Van oost and Six 2023

The paper 'Shifts in controls and abundance of particulate and mineral associated organic matter fractions among subfield yield stability zones' deals with understanding the relationship between SOM and yield heterogeneity.

The repeated citation of a paper under review/submitted is not a minor drawback in this work. The accessibility of the information about the experimental design is lacking, making the paper really hard to understand. This “minor drawback” is even more exacerbated referring to other papers under review. Moreover, the references section is incomplete and, among the citations, too many papers are authored or coauthored by the same authors of this paper.

Another main drawback relates to the analysis performed, whereas organic C has been analyzed in the bulk soil, the fractions have been characterized only for total C content. It would have been useful to have data on the organic C content also in the fractions.

Moreover (Line 116) the authors should explain what the “Shimadzu method” is. The authors put a reference (Shimadzu, 2021) that is not available in the reference list. Are the authors sure this is a reference?

Another analytical concern: how the authors measured the texture in a not direct way? And why?

The figure 5, that should present the core results of the paper, contains a legend that is not informative at all. The authors used different colors, without really clarifying the meanings.

Based on these considerations I cannot suggest publication of this paper in SOIL.