Two reviewers thoroughly evaluated the manuscript. Below, I briefly summarize the main comments:

(i) The reviewers very much liked the study approach and emphasized that the data set is great. At the same time, however, it was pointed out that the study is rather descriptive and little quantitative information is given.

(ii) Both reviewers indicated to refine some statements (in the abstract, objectives and conclusions) about the novelty of the study compared to the authors’ own and other previous studies.

(iii) The interpretation of ambient air measurements is not clear. For this statement and other findings, conclusions are presented with little or without further prove of evidence.

(iv) Results are presented but a discussion of results is largely missing.

(v) It was recommended to restructure the results and discussion chapters and to improve the writing (i.e. structure, grammar, “isotopic” instead of “isotope”).

The authors answered in detail to the reviewers’ comments. Most of the answers are sufficient and should be included in the revised manuscript. Therefore, I only emphasize some of the comments that need more attention for revising the manuscript. Additionally, I have some important points that need to be addressed in a revised version:

1) The reviewers pointed out that comparison to other studies is missing in the discussion. As no answer was provided by the authors, I want to emphasize that the authors need to address it when revising their manuscript.

2) I disagree to combine the results and discussion chapter. However, I recommend moving chapter 4.2 into the results chapter. Here, measured data are presented just in a different way and not discussed. Still, an explanation and discussion of the d2H-d18O relationship needs to be included in a revised version of the manuscript.

3) As already indicated in the answers, kinetic fractionation factors will be presented in the revised version. To my opinion, the manuscript would benefit from some theoretical calculations similar to the zero infiltration conditions in Singleton et al. (2004; cited in the manuscript).

4) As already indicated by the reviewers, the interpretation of the ambient air measurements is highly speculative in the current version of the manuscript. Even though the authors stated that the air condition did not exchange the air in the lab, it is not a closed system. There can be other reason why the slopes are changing (other water sources, opening the door etc.). More evidence needs to be provided e.g. by adding some theoretical calculations of evaporation and mixing lines. Further, is there a correlation between the atmospheric d-Excess and the evaporation flux? Or the d-Excess of the upper soil layers and evaporation flux? The evaporation is highest at the beginning of your experiment. However, (i) slopes are not impacted here and (ii) the humidity did not change indicating that the contribution of water vapor to the lab atmosphere is negligible.

Minor comments:
Abstract, ln 8-9: the long-term application is new, not the method itself
3895, ln 20: according to Fick’s law
3895, ln 24: HYDRUS not Hydrus
3896, ln 2-3: For water samples, also suction cups are none destructive methods which have been frequently used (e.g. in combination with lysimeters). However, the great benefit of the study is that you get "continuous" (high temporal resolution) information and high spatial resolution.
3896, ln 5: see simliar approach of Gaj et al. 2015, HESSD
3897: Did you check the water at the end of your experiment to verify that there were no fractionation effects over time? Are these closed vessels. Even when looking at Rothfuss et al. 2013, I have difficulties to understand your internal standard system.
3898, ln 7: how was lab air sampled?
3898, ln 17: in situ (italic)
3900, ln 16-19: It is actually difficult to see the changes in the raw data of Figure 2
3903, chapter 4.1: the word "very" is often used; this is a rather subjective word and can be deleted (e.g. there is no difference between "very tightly" and "tightly" bound water - as long as you do not use it in a quantitative way).
3904, ln 6: Why not splitting the observation period into the same days like in Figure 5? These three groups represent the three phases of your experiment: (i) evaporation, (ii) water-atmospheric vapor equilibration (iii) irrigation.
Figure 2: stick to SI units like in the text and report depths in meter (not centimeter)
Figure 4, caption: soil temperature is not shown; delete in caption
Figure 5: just an idea: is d-Excess giving you any additional information?


Due to the comments requiring detailed rewriting of the manuscript including the addition of more quantitative aspects and discussion of results, I will reconsider the manuscript after major revisions have been done.

Both referees appreciated the revisions of the manuscript. Still, there are some specific comment that certainly should be addressed. They help make your story even stronger and explain your findings in more detail.

Please see the reports for details.

I am looking forward receiving your revised version.