Reply to comments made by reviewer 1:

We wish to thank the reviewer for his kind word and insightful comments.

Comment 1: Please correct minor typos as marked on the attached pdf.

Reply: Thank you for noticing the typos. All were corrected.

Comment 2: Consider expressing fluxes in units more familiar to readers e.g g/m²/d even as a one off comparison.

Reply: The units were changed to g m^-2 d^-1 in all the graphs and text as suggested.

Comment 3: - L236 check text and caption for Fig. 3 align

Reply: Indeed the caption had a typo where NO₃ and NH₄ were mixed. It was corrected.

Comment 4: L266-267 Add text to indicae why higher WFPS or higher N concentrations favour higher N₂O. See pdf.

Reply: As requested, an explanation was added to the text “Suggests N₂O_In results from conditions more conducive to denitrification (e.g., higher WFPS) or nitrification (e.g., higher NH₄⁺ concentrations) (Lines 313-314 in the revised text).

Comment 5: L319-333 is this in the results? Shift to results section.

Reply: As suggested, some of the text was transferred to the results section. The revised section now reads ”Comparison of cumulative N₂O emission measured in 2018, 2019, and 2020 and the simulated cumulative emissions (over 60 days) showed the N₂O_In flux to be 40% – 70% higher than the N₂O_Adjecent (Fig. 7B)”. 

Comment 6: P10 a lot of this text reads as results or methods. Suggest some is shifted to appropriate sections and discussion revised.

Reply: As suggested the text on page 10 was modified. A substantial portion of the text was moved to the Methods section, under a new subsection titled “2.2.4 Recommendation on the diameter of the chamber's base” . Another part was moved to the results section.    

Comment 7: For the conclusion suggest "...we concluded that static chamber methodology, which requires the insertion of bases into the soil, underestimates N₂O emissions when used in drip irrigation........This effect can be mitigated through optimizing chamber design. A nomogram is proposed..."

Reply: We adopted the suggested edits to the text and modified it to “ … we concluded that static chamber methodology, which requires the insertion of bases into the soil, underestimates N₂O emissions when used in drip irrigation. “These effects can be mitigated through optimizing the chamber design. A nomogram is proposed…” .

Reply to comments made by Reviewer #2

We thank the reviewer for the comments and concerns.

Please find below our detailed replies to all the comments.

Comment 1: Calculating cumulative emissions – why don’t you use linear interpolation? I do not think that your results will change, but I think that use of arbitrary Q10 is not any better than to estimate cumulative/daily flux using linear interpolation. Calculation of daily emissions can be done by dividing annual accumulative emissions by number of included in cumulative flux estimation days.

Reply: We thank the reviewer for raising this point. All calculations were modified as suggested using linear interpolation and numerical integration between sampling times. The text was modified accordingly: “…by linear interpolation and numerical integration between sampling times. Cumulative N₂O flux estimates for N₂O_In and N₂O_Adjacent were taken as the average of the cumulative fluxes of the 12 individual chambers, each”.

Comment 2: Why do you think that your modeled emissions are better than observed? I think that for real answer if static chamber methods under- or overestimate real fluxes a comparison between static chambers and eddy-covariance based measurements is needed. And, Comment 3: You are using 3D flow model and some simple assumptions, you may model the water flow well, but I doubt that you can model N₂O emissions. At least DayCent model, after ~30 years of development cannot.You are using 3D flow modeld and some simple assumptions, you may model the water flow well, but I doubt that you can model N₂O emissions. At least DayCent model, after ~30 years of development cannot.

Reply: Our field measurements show that the measured N₂O flux is highly affected by the location of the chamber’s base relative to the drip line. We agree that eddy-covariance based measurements may provide a good tool to validate our field measurement on a larger scale. Nevertheless, in the discussed emitter-spacing scale eddy-covariance could not be used.

Please note, that we do not think that our modeled emissions are better than the measured/observed emissions. Further, we do not think that the simple assumptions used by us to model N₂O fluxes accurately capture the “true” N₂O flux, as rightfully commented by the reviewer. Yet, our results raise a question as to what is the “correct” or the most representative way to capture the true ambient N₂O emissions around a single dripper, part of a drip line, when using static chambers.

N₂O fluxes are mainly driven by N availability and form (i.e., nitrate vs. ammonium), oxygen availability, and soil water content [readily expressed as the ratio between the volumetric water content and the porosity (WFPS)]. Thus, we decided to use a robust 3D flow model to study the effect that a chamber base may have on water and N distribution in the top soil. The main assumption for both the 3D flow model and the DIDAS model simulations/computations was that the ambient N₂O emissions (i.e., not affected by the base) will be those emitted from a location with minimal perturbation by the base. That is, places where the N-form concentrations and distributions, and the water content are not affected by the base.   

With this assumption in mind, the model was used to:

1. Evaluate the impact of the dripper location relative to a base (i.e., inside, adjacent, few cm away, etc.);
2. Find the optimal base diameter;

Comment 4: I am wondering if your proposed method to calculate optimal chamber (base) size for field measurements of soil N₂O emissions (monogram) will provide better flux estimation. I think that few weeks of additional measurements comparing the proposed “optimal base size” with bases used to acquire data for the manuscript under discussion will improve the manuscript. If you are claiming that using modeled flow of water and nutrients, you can determine the optimal chamber – prove it.

Reply: In continuation to the reply to comments 2 and 3, to date, the standard method for static chambers calls for the use of basses. Hence, there is no way to get the “true” ambient N₂O emissions from a single dripper. With that in mind and the model’s limitation in predicting N₂O emissions (simplified assumptions), we do not see how few weeks of additional measurements comparing the proposed “optimal base size” with bases used to acquire data will benefit the manuscript.

Our intention was to merely raise the problem of the systematic, 3D heterogeneities around a dripper, to present relevant, simulated results, and to propose relevant methodologies assisting in deciding regarding the size and placement of the base. It will take many users in many conditions (soil types, wetting patterns, variable N carbon (C) and O regimes), rather than a single study, to tell whether these methodologies are constructive or not.