This manuscript reports a study that simulated organic C accrual over 25 years in eight soils with contrasting properties of North-eastern France. The authors compared the Hassink equation and a novel data-driven approach to estimate soil organic C stocks and maximum soil organic C additional storage capacity. They found that the Hassink approach leads to unrealistic estimates and that the simulated soil organic C accrual over 25 years was five times lower than the maximum storage capacity.

The study has interest, and to the best of my knowledge, well conducted, although some assumptions need to be validated or better justified (see below). Also to the best of my knowledge, the results are well discussed and the conclusion are well supported. However, the study needs to be better introduced and some aspects of the approach need clarification.

My specific comments:

l. 46. This sentence is unclear. What do you mean by “the upper percentiles of the total carbon content in a large dataset”?

l. 50 The Hassink method needs to be introduced.

l. 50. It is unclear what data-driven approach the authors are referring to. This should be better introduced and explained.

l. 64. Additional to what? Please clarify.

l. 75. The last sentence seems to be disconnected from the rest of the paragraph.

l. 78. The model needs to be briefly introduced here.

l. 81-84. This text is unclear.

l. 107. What do the authors mean by data points?

l. 109. Sampling was conducted between and 2019. Do different starting points affect modeling results?

l. 130. The use of this pedotransfer function to estimate bulk density would need to be validated with data from this study.

l. 178-180. These estimates need justification and validation.

l. 307. “for reasons that will be detailed further in the Discussion section” can be removed.

1. More clearly present the logic and reasoning behind comparing two approaches (Hassink vs. Chen et al.) for estimating potential SOC storage. First, there needs to be clearer description of and distinction between the idea of fine fraction saturation vs. maximum SOC accrual, which are two very different concepts (though saturation may be a constraint on maximum SOC accrual), and which relate directly to the conclusions and the implications of the work. I have several specific comments on this below. Second, how do these ideas and assumptions relate to the conclusions drawn from them (see #4)? It is critical to be careful in how one presents and interprets these "maximum values".
2. Provide better rationale of the approach in terms of the scenarios modeled. The input rates were chosen based on what the model requires to maintain the theoretical upper limits of SOC accrual by land use at steady state, and then those input rates were simulated to see how much SOC accrued after 25 years. Why not instead use the accrual rates necessary to achieve theoretical maximum SOC storage to inform ideal inputs and see if they are achievable, or use more realistic input rates (perhaps ranges) and see how far from the maximum SOC accrual those are after 25 years?
3. Provide more detail on the AGM model, especially whether/how it represents saturation and temperature sensitivity of carbon pools and how those relate to the concepts of MAOM and POM mentioned early in the manuscript. Why is this an appropriate model for this use, and what are the implications of the model structure (and perhaps its limitations) for the results and conclusions?
4. The discussion can be much clearer about the implications of the approaches used and dig more into how different assumptions end up informing potential strategies for climate mitigation. How does considering depth change our understanding of how we might manage soils for climate? What about methods of determining maximum potential C storage (and trajectories for reaching it)? Should we even base management ideas around these maxima, or are they infeasible to reach on relevant timescales?