|Overall, the articles has been much improved in terms of clarity and the authors should be commended for the revisions. There are nevertheless a few minor issues left to address.|
“The QuantiSlakeTest, measuring soil structural stability by dynamic underwater weighing” : strictly speaking, the weighing is not done underwater. The sample is underwater. What about “The QuantiSlakeTest, measuring soil structural stability by dynamic weighing of undisturbed samples immersed in water”?
I greatly appreciated the changes brought by the authors. The reading is now more fluid, and the text more focused. Nevertheless, there are some mostly minor issues that need to be addressed. See also the annotated manuscript for typos and corrections of English language.
L24 : please add a reference
L25-26 : remove ‘of Belgium’, because this is equally true across all of the western European loess belt; add a reference supporting the fact that structure is particularly relevant for Luvisols (I don’t think it is true, but what the authors probably mean is that structure of Luvisols is particularly sensitive to management (due to their texture) and therefore even more attention has to be paid to structure for these soils)
L34 ‘structural stability’ would probably be more relevant, as ‘aggregate stability’ does not relate to compaction.
L44 : I didn’t check the publication of Meersmans et al. 2011, but I don’t think these authors are actually at the source of this threshold value. It is good practice to cite original papers rather than citing authors which cited other authors. Though I’ve also read about the 1.2% SOC threshold for luvisols, a recent paper has reported that this threshold may be closer to 2% SOC (Shi et al., 2020; https://www.sciencedirect.com/science/article/pii/S0016706119310298)
L51-53 : rephrase sentence, because climate and soils are all part of environmental factors (not just topography), while ‘soil cover’ is more of a management factor (and not an environmental factor).
L59 significant presence of Al only in soils with pH < 5 (strongly acidic). Even though base saturation will progressively decrease with decreasing pH, Ca and Mg will thus remain important in weakly acidic soils
L75 : sounds intuitive, but has this been studied ? A reference would be nice. Compaction most strongly affects macroporosity, which is typically not the porosity found inside small aggregates. Macroporosity corresponds more to pores in-between aggregates + macropores resulting from biological activity (roots, worms, etc.)
L75 “differential swelling occurs under wet conditions” : actually, it happens during the process of wetting. In the presence of swelling clays, as soon as free water is added, swelling will occur as a result of water moving in-between the clay platelets.
I’m surprised by the statement that differential swelling mainly plays a role at macroscopic scales. I could not find this in the paper of Le Bissonnais 1996 (which is cited here by the authors). On the contrary, it says in that paper
To my understanding, differential swelling is a microscopic mechanism (separation of clay platelet) inside clay domains. Because the orientation of the platelets of different domains is more or less random, the swelling generates mechanical stresses inside the macroscopic aggregates.
L82-89 : I would have expected a few words about the ‘scale’ of the units being subjected to aggregate stability measurements : from aggregates of a few mm to … (cores) ?
L98 : what do you mean by ‘delay’ ? ‘labour requirement’ ?
L100 : throughout the introduction, ‘aggregate stability’ has been used (almost) exclusively. Here, the authors switch to ‘structural stability’. As mentioned in the previous review, I believe this is an adequate use of terms, but for the reader this switch happens insidiously. It would be good to explicitly express this conscious change in terminology. This is also related to the ‘scale’ issue raised in relation to L82-89.
L109-113 : these lines should be moved to the beginning of the M&M section.
Materials and methods
L127 I believe plots must always be aligned in rows in a Latin square design
L141 : please specify whether the means are followed by standard deviation or standard error
L158 ‘repeated three times in … two blocks’ ? ‘three blocks’, I suppose? Please check or explain (I assume 1 block = 1 rep)
L177-L178 : It was initially not clear to me that these oven dried samples were used ONLY for bulk density determination.
L212 change to ‘namely slaking, mechanical breakdown and differential swelling – clay dispersion …’
L216-219 : this should be moved to the introduction (see earlier comment regarding aggregate / structural stability)
L223 ‘timestep’ (units = time), and not ‘frequency’ (units = 1/time)
L245-246 : the nota bene is unclear to me. Please rephrase
L249 : 900 sec. sounds arbitrary, but probably based on the authors experience of when the mass loss becomes negligible for a majority of samples. Please justify briefly the origin of these ‘900 sec’.
L251 how were roots separated from soil ? by sieving ? on what mesh size?
L259-260 and L265-266 : the authors explain on L259-260 that they used a linear mixed model approach to evaluate whether soil management affects QST indicators, and on L265-266, they say they used ANOVA for the same purpose. Please clarify.
L291: besides slope 0-max, slope 60-300 and slope 300-600 are also NOT positively correlated to MWD1 according to the table.
L324 : how could slope affect structural stability (at plot scale) ?
L330-333 : this sentence is not very clear (‘:’ is used twice in the same sentence), and seems to repeat what has been said on L288-289. Repeating the info is useful, but the sentence can be simplified (see annotated manuscript)
Fig. 5 : please indicate on the graphs the results of the pairwise comparisons between treatments (using for instance small cap letters) to better highlight which treatment is different from which other treatment.
L340 : ‘discordant’ doesn’t sound right in English, but can’t think of the proper word. ‘Antagonistic results’ ?
L349 : please express root biomass in terms of root mass density (mg/cm³ or g/dm³ or …) for easier comparison with the literature
L350 name of the variable is misspelled
Isn’t Fig. 6b the same as Fig. 7d ? I suggest removing 6b.
In Fig. 7, please indicate on the graphs the results of the pairwise comparisons between treatments
L372 ‘advocate’ means ‘publicly recommend’. This is probably not what the authors had in mind, since the sentence is not a ‘recommendation’. Please check
L392 : what does a ‘field gradient’ mean ? ‘field’ is not a property (temperature gradient, concentration gradient, …)
L402 : I don’t understand the statement ‘with an average complexation potential of 1 g of SOM for 10 g of clay’, especially given the first part of the sentence. The next sentence seems to imply that 1 g SOM for 10 g clay is a threshold value. Please explain and rephrase this sentence.
L417-418 : not sure why the authors advocate the use of the 0.1 SOM/clay threshold value, even though their results do not support the existence of such a threshold, and the results of Johannes et al. (2017) and Prout et al. (2020) also do not support the existence of a “threshold” (but rather a linear relationship, as stated by the authors on L405). It may still be that the 0.1 threshold value coincides with a change in structural quality class according to VESS (class boundaries being often more or less arbitrary), but there is nothing in this paper to support the existence of a threshold.
L455 replace ‘advocate’ by a more suitable word
L459-462 : did the authors check the composition of the exchange complex ? Is the proportion of K significantly (and substantially) higher in K2 than K0 treatment, for instance ? As stated by the authors, it may well be that the exchange complex has had time to reequilibrate since 2016, and looking at the relative importance of Ca, Mg and K should give a clue.
L473 ‘crumbled’ ? (rather than crambled)
L475 : sampling stony soils with a kopecki ring is very tricky …!
L488 ‘…but curve modelling is another perspective of curve interpretation’ : replace by ‘…but curve modeling may offer further perspective for curve interpretation’
L496-497 : summing up before a conclusion seems redundant
Some sentences are almost exact copies of sentences used in the discussion, which should be avoided.
L511 : ‘is closely related to the SOM status of soil, well-captured by the SOC:clay ratio’ : sounds a bit contradictory. So it’s not just the ‘SOM status’, but the concentration of SOM relative to the clay content.