Dear Lauric Cecillon and co-authors,

First of all I would like to thank both anonymous reviewers for their comments, David Sebag for his comment and you for your reply. I completely agree with you in that you describe an “indirect” method to estimate centennially persistent soil organic carbon and that a method such as this should be simple and straight forward, giving the best possible result. So if adding slow breakdown of this CP soil organic carbon pool makes this estimation much more complicated without significantly improving the results I agree with your comment to reviewer one. Which does not mean you do not have to deal with the comments of reviewer one in the revised manuscript, clarifying your choices to some degree might help readers understand them better. As for the comments of referee two, I agree with his comments, however I do see that to get the best possible result you would basically need a training set consisting of all possible soil types, making an ‘indirect” method useless since everything would have been measured already. However in this case you could try find a better balance in how you discuss these issues, as you already indicated in your reply.

With one “accepted after minor revision” and one “reconsidered after major revisions”, I would like to ask you to prepare a final rebuttal and revised manuscript according to the comments and your response so far focusing on the training set versus application soil issue (see above).

Thanks,

Marcel

Dear Lauric Cecillon and co-authors,

First of all I would like to thank you for your rebuttal and revised version of your manuscript. I have the impression it has become a more balanced manuscript after review than it was before. You adequately addressed the comments from both reviewers and David Sebag. I would like to ask you to carefully go through the manuscript again to make sure the English is correct. I have a few minor textual things I would like to draw your attention to.
Page 2, line 18: carbon input without the s.
Page 4, lines 25-31: I think centuries without the several might be long enough. The sentence starting with as a results seems a long, perhaps you ca rewrite it more concise? (As a result, its decline is minimal at the timescale of this study and we thus considered the centennially persistent SOC pool at each experimental site to be constant. Or something similar.)
Page 10, line 13: ….showed very different even contrasting correlations…
Page 11, Line 1 and 2: do you mean specific as in unique? Different from the others? If so maybe rewrite it a little, otherwise state what is specific about them.
Page 11, line 11: from the calibration set

Other than these I think the manuscript can be accepted for publication.

Best regards,

Marcel