The paper is very well written, the trial is comprehensive, and methods were explained in detail. The high level of detail in the data presented is a rare find, and valuable insight in the understanding around SOC dynamics in CA systems.  I was unable to find any problems in the manuscript, as far as I can tell the trial layout, sampling and analysis are correct, and the manuscript is written in clear language, that convey the message effectively.  

An overall relevant contribution on use of conservation agriculture practices to improve maize crop productivity and raise carbon stocks (and in turn fertility) in Zimbabwe. The study relies on two well-established field trials and standard yet well executed assessments were used to reveal how tillage, mulching and crop rotation in isolation or jointly influence SOC in these understudied systems. While the approach is overall robust – aside from limited attention to crop C inputs – at times the interpretation remains rather superficial. I have listed a number of comments below:

L103 & 108 One aspect of the hypotheses is best elaborated a bit more: while it is clear that crop residue retention and adoption of no-tillage are likely to improve SOC stocks, this is less obvious so for crop rotation. Crop rotation as such rather seems like a means to combat pests, but why should there necessarily be any beneficial effect onto SOC? Indirectly perhaps, via enhanced crop growth?

L300 Why carry out statistical comparisons for each individual date? This does not provide an overall view on the treatment effects and complicates drawing conclusions.  

In the UFZ site, Fig 3 reveals a rather conspicuous treatment effect of including a rotation 90cm depth (and to a lesser extent at 60cm as well). Perhaps relevant to discuss as well, even though these trends were apparently not (yet) significant. Maybe the introduction of peas particularly led to deeper root proliferation and derived C-inputs at depth… perhaps the authors could try using contrasts in the ANOVA to pool the three ‘rotation’ treatments vs. the other treatments and demonstrate such effect?           

The discussion section requires improvement:

The second half of 4.1 does not make much of a connection with own observations (L476-483) – it is not clear what message the authors wanted to bring here.

Section 4.2 is lengthy - Perhaps this section could benefit from further subdivision into subparts that deal with the various treatment aspects (tillage, mulching, crop rotation).

4.2 lacks a clear calculation of conversion efficiency of C-inputs into SOC. There have been ample studies on removal or incorporation of maize residues (in light of research into the value of root vs. shoot C inputs) – such studies have generally revealed that aboveground biomass C inputs are far less effective in sustaining SOC – and this body of literature should be used to complement the discussion here. Even though much of the C-inputs are just derived from yield data, it would still be relevant to see some estimates of the efficiency by which these C-inputs formed or sustained SOC.

The discussion lacks considerations on the potential mechanisms through which the inclusion of peas in the crop rotation might influence maize C inputs. With a legume introduced there may well be more N-available for the maize crop – not trivial given the very low doses of mineral N-supplied. If so, we may expect this to hold an effect on the soil C balance not only through an overall stimulation of maize productivity (and that is currently not clearly explained in the current discussion) but possibly also by effects onto the maize rooting pattern. These aspects should at least be commented upon, especially in light of the rather conspicuous difference in SOC at 75 or 90cm depth when a rotation is included (at least such would seem so from Fig 3, but unfortunately no comparison is given of the 75-100cm SOC stocks).

Towards the end of the discussion and in the conclusion clearly the specificity of the here established crop rotation needs to be stipulated. By no means could we simply extrapolate found results to other ‘crop rotations’ – with different crops and plant C-inputs.

L497: what about the whole idea that reduction of tillage would promote physical protection of OM inside microaggregates – should be commented on here as well.

L510 SOC storage does not seem very site specific but rather rotation-specific + ‘the differences in the response to SOC changes’ makes little sense -> rephrase

L518 ‘the net SOC loss in CTR was due to seasonal exposure to oxidative losses (SOC mineralization) through disruption of soil macroaggregates by tillage’ this makes little sense since these numbers are actually obtained by comparison with the CT treatment in which there is an equally intensive disruption of soil structure.

L547 what about other SOC stabilization mechanisms?

4.4 as it is stands alone and really does not bring a clear message. It may be better to integrate this section into 4.2 (which then gets even lengthier and is therefore best split).

The conclusion section is fine.