Carbon Accumulation in Arable Soils: Mechanisms and the Effect of Cultivation Practices and Organic Fertilizers

Round 1

Reviewer 1 Report

I consider this paper  makes a very pertinent contribution to awareness of Soil  Humic Substances (HSs). Treatment of the controversial approach by Lehmann and Kleber (Nature 2015) is good, and it politely shows the nonsence of the awareness they have promoted.. That paper in the views of established scientists in the field is highly misleading, and clearly has influenced the FAO Soil Organic Carbon treatise (2017) referenced. The author might have a look at the paper on Vindication of Humic substances (cited in ref ca.77) which shows that (in references therein) extraction with base does not when used appropriately, give rise to artefacts. That misconception of damage is a major pseudo-proof provided by those who attempt to refute the concept of HSs, I like the way in which  reference PAH components in HSs can arise from transformations of lignin, and not just from  pyrolysis processes. I would like to see differentiation between humin and HSs, and the author's view about the clay fraction /humin associations, and if humin will influence how HSs may associate withclays/hydroxides. 

For the most part the article is intelligibly written. I would consider that the author means Section rather than chapter, and consideration given to spelling of such terms as those ending in icity.

Such considerations can be resolved by the desk editor.

Author Response

I am grateful for the comments of reviewer 1.

The following changes within the manuscript were made:

1. Chapter was substituted by section as recooended.
2. On page 15, line 428 reference 75, Hayes, 2006 was also included in the discussion of artifacts during the alkaline extraction.
3.  Reviewer 1 pointed to the lack of a seperate discussion of the role humins for soil carbon storage. The work of Hayes, Swift and coworkers show in detail that most of the humins are aliphatic. The principles of C accumulation as affected by cations such as Al(III) and Fe(III) may also apply for the aliphatic and probably amphphilic humin fraction in soil as shown in figure 2. And the main focus in this manuscript is to reject the statement that a de novo formation of organic matter in soil called humic matter does not exist and to show that the de novo formation has strong implications for the accumulation of soil organic carbon. The questions on humins are important and should be addressed in future research.  

Reviewer 2 Report

Line 200: The chapter title is underlined. The Author need to change the format.

Line 226: The cations should be presented in the same format, as in line 283. The Ca⁺² probably should be changed to Ca(II)

Line 338: I understand  the author’s need to emphasize, however the word “is” should not be underlined

Line 356: “not” should not be underlined

Line 337-338: The “majority” of scientists several times were wrong or at least not absolutely correct in the past. In this matter the Author is right in his words, suggesting that the FAO report could have included the point of view of the “minority “in the report. However, the way the Author express his criticism against Schmidt may be slightly over the line. The Author should probably rephrase (see line 338).

Line 389: (unproven, 19). It’s not easy to understand the meaning, and probably the Author needs to rephrase.

Line 390: (wrong, 81). same as the previous comment.

In general, it’s a well stated review, although in some lines looks more like a scientific letter, or discussion or perhaps to some others scientific criticism.

Such kind of scientific papers, need to be published. Scientific discussion, productive criticism etc. create challenges and enhance scientific knowledge.

Author Response

I am grateful for the comments of reviewer 2.

1. The cations inccluding Ca are now all in the same format.
2.  Underlining within the text was omitted.
3. Line 337/338 This sentence has been changed to indicate that the view of Schmidt et al., 2011 is not the exclusive view of scientific knowledge which is a more liberal formulation. 
4. Line 389, 390: during revision the argument of the FAO paper that the assumed role of biochar in soil on carbon accumulation  is unproven (Gerke, 2019) is explained in more detail. It is also explained in more detail citing Jeffery et al. (2017) why the assumed positive effect of biochar on plant yield in the FAO paper is not supported by experimental results.