CO Editor

Suggestions for revision or reasons for rejection

GENERAL COMMENTS

The revised version of this manuscript has been very much modified regarding the first version. Several points that were raised by reviewers and editor have been addressed. Thus, organization has been somewhat improved, complementary information has been provided in the material and methods section, new indices have been taken into account and a number of sentences have been rephrased or corrected in all the sections of the manuscript.
However, in my opinion, this manuscript is not acceptable in its present form and therefore I still recommend major revision or rejection. This is mainly because results presented here are only significant for a very particular situation, but in spite of this generalization without experimental support have been made. Subsequently, presentation of results (including results cropped from the literature) is neither clear nor concise; also results are not put in context of the previous existing experimental evidence and text is far from precise.

First, I recognize that the results provided are interesting. However, the intended generalization from experimental results of a particular or “unique” case is one of my main concerns. Therefore, I completely agree with a previous comment of a different reviewer, which stated: “(I have) the feeling that authors overestimated the relevance of their results and reached conclusions that are not sufficiently proved by their data”. In my opinion this statement still remains absolutely valid for the current version of the manuscript. For example, several statements in the Abstract section are too vague, imprecise or even misleading. Also other statements in the Discussion and Conclusions section are too strong or even not supported by results and evidence

Second, preparation of soil surface to obtain a smooth surface in this work could result in an important bias. To the best of my understanding “tamping using a plywood board” for smoothing is an uncommon method. Using such procedure compaction of soil aggregates and structural units should be expected. Compaction intensity should increase with increasing soil water content and strength of tamping. Subsequently, the evolution of small aggregates, resulting mainly from tamping, under simulated rainfall could be far away from that of aggregate beds prepared by methods commonly used in field and laboratory experiments.

SPECIFIC COMMENTS

Please, note that my specific comments are far from exhaustive. Next, I’m only addressing examples of statements where clarification is needed.

Abstract
Page 1, Lines 13 to 17. On the one hand it is stated that roughness of about 2-5 mm is common on agricultural landscapes, but on the other hand the focus of this manuscript is on roughness of 2 mm or less. I don’t understand the discrepancy between the problem to be dressed and the focus of the manuscript.
Page 1, Line l5. What means “long undisturbed exposure to rainfall impact”?.
Page 1, Line 18. “generic extreme conditions” is too vague. Also, it is not clear, here and all over the paper if your focus is in extreme conditions or in conditions that are common in agricultural landscapes.
Page 1, Lines 25 to 27. The statement beginning “this contradicts...” and ending “… roughness conditions” is awkward, as before noted by other reviewer. What is the meaning of “monotonic” in this context?. The “commonly adopted literature” (for examples Zobeck and Onstad, 1987, who analysed 483 data sets and since them several other works) is the result of hundreds, perhaps thousands of experimental evidence in different soils with different roughness magnitude, texture, aggregate stability, soil water content etc. In contrast in the present work results are limited to three soil surfaces from a particular soil, and the results obtained may be biased by the soil preparation procedure.
Etc., etc., etc. Again, my comments are not exhaustive. Altogether, I feel this abstract as awkward.

Introduction
Page 2. Lines 10 to 21. Indeed, random roughness assessment requires correction for both, slope and tillage marks. This is clearly stated in lines 18 and 19, but not in lines 10 and 11. Text in Lines 10 to 21. Also, please consider if Equation 1 should be in the Methods section.
Page 2Lines 28 to 29. Please, note that Kamphorst et al. (2000) analysed 48 seedbeds with a roughness of the order of magnitude that you mention. Again 48 is much higher than 3, and several different soils have been studied by Kamphorst et al. (2000). Therefore, even if your results may be of interest, the should be put in the context of the previous work about the studied topic, and care should be taken to avoid overestimation of their relevance.
Page 2, Lines 29 to 34 and page 3, Lines 1 to 2. Sentences beginning with “Surfaces with microroughness…” are too vague. In addition, please note that in conventional tillage between postharvest and plant growth there is seedbed preparation. In these conditions seedbeds constituted by small aggregates are the best example of real “microroughnees” or smooth soil surface.
Page 3, lines 12 to 16. Again, I don’t understand that if the aim of the work is to address the microrelief in soil surfaces with aggregates of about 2-5 mm you are focusing on “the order of 2 mm o less”.
Page 3, lines 19 and 20. Although “disturbed” nay be an antonym of “smooth”, in the context of this work correct is “rough”. Please, see also Table 1.
Page 3, line 22. “Different intensities” of which?.
Etc., etc., etc. Again, my comments are not exhaustive. Again, tightening up is required.

Material and Methods
Page 4, line 4. What about aggregate size distribution after tamping?. What about soil compaction before and after tamping?. What about aggregate stability before and after tamping?. Aggregate stability is a very important issue in this particular soil, prepared with a particular procedure before laser scanning. This is because of the strong relationship between processes responsible for roughness and aggregate stability.
Page 5, Line 11. Average hydraulic conductivity was rather low compared to simulated rain intensity. This is very important, since in these conditions in a flat surface should be expected. What about water ponding in your experiment, given that your plots had a slope?. Ponding is known to interfere with roughness decay.
Page 5, Lines 15 to 18. The difference in initial roughness between experiment 1 and experiment 2 and 3, demonstrate roughness decay in your soil under natural rainfall. This is against your main hypothesis, which postulate roughness increase with increasing rainfall.
Page 5, Lines 25. You stated that “no rill formation ever took place”. But, what above “micro rills”?. I’m not sure above the absence of micro rills in your experimental conditions. Indeed, “traditional” works about soil surface roughness decay absolutely exclude the presence of soil erosion.
Page 3, Lines 3 to 24. I wonder if semivariograms, Hurst exponent, etc, have been calculated after removal of oriented roughness, i.e. tillage marks and also slope.
Etc., etc., etc. Again, my comments are not exhaustive. Again, tightening up is required.

Results
I’m very concerned by the procedure used to compare results obtained in this work have with those of previous works. Results shown in Table 1 and in Figure 5 are misleading.
First, as before stated, hundreds of soil surfaces have been analysed for roughness decay in very different experimental conditions and this work only provide results for three soil surfaces measured under “unique” experimental conditions, which perhaps lead to biased results. Moreover, you should include also the data you obtained showing roughness decay under natural rain conditions; this is given by the difference between initial roughness in Experiment 1, performed in earlier August (1.17 mm) and in Experiment 2 and 3, performed in late September (0.42 mm and 0.32 mm). This clearly show roughness decay in your soil with increasing natural rainfall isn’t it?.
Second, I don´t understand the criteria for selecting data from previous authors. In your answers to reviver’s you stated that you only provide data for one simulation in order to focus on the analysis of raindrop impact. However, most experiments quoted in Table 1 and Figure 5 includes several successive events of natural or simulated rainfall. In addition, the selected data sets correspond to very heterogeneous initial conditions, texture, organic matter content, rainfall application, etc.
Third, I don’t understand the way in which calculations of RR ratio have been performed. For example, Vazquez et al (2007, 2008) quoted several measurements of RR for a given surface and you selected only one of them, apparently the last one. Why?.
Summarizing, I’m sorry, but I have no evidence showing an effect of initial RR condition on the RR ratio. The interesting apparent exception found in your work may be the result of experimental biases and may be rather the result of an “artefact”.

On the other hand, I have positive comment regarding subsection 3.2 (pages 8 and 9). Points raised here are important to further assess RR.

Discussion and Conclusions
I can’t review this section before the above mentioned points are addressed.
However, please let me comment that the expected hydrological impact of a soil surface roughness in the order of 0.5 to 1 or 2 mm would be rather scarce. This is because of the expected digressional storage would be less than 1mm per quadrat meter (Kamphost et al., 2000)

Interactive discussion

Peer-review completion