Nitrous Oxide from Beef Cattle Manure: Effects of Temperature, Water Addition and Manure Properties on Denitrification and Nitrification^†

Round 1

Reviewer 1 Report

This is a well written paper with clear text that is easy to follow. I recommend publication following minor revisions.

Minor corrections:
Li 9: Remove "Affiliation 2"
Li 14: "Correspondence" is repeated
Li 34: nitrate is repeated (insert nitrite?)
Li 66: and throughout - there is lack of clarity with units, e.g. Li66: mg N2O m–2 h–1, Li68: mg N2O–N m–2 h–1 Table 1 mg m-2 h-1 Please check, standardise and clarify units throughout - suggest as mg N2O–N m–2 h–1

Figure 3: annotations are small and fuzzy, can this be improved?

Figure 5; DEA(l) appears poorly modelled by linear decay, the rationale for modelling as linear is not clear.

Li257: suggested small clarification "where the isotope site preference, which can indicate origin as nitrification or denitrification, showed that surface samples produced N2O via bacterial denitrification."

Li326: this is an interesting phenomenon which has been widely observed with many examples but not fully understood. A bit more discussion would be valuable. e.g. in ag soils, Rudaz et al suggest rapid denitirfication activity is possible
Rudaz, A.O., Davidson, E.A., Firestone, M.K. (1991) Sources of nitrous oxide production following wetting of dry soil. FEMS Microbiology Letters, 85(2): 117-124. doi: 10.1111/j.1574-6968.1991.tb04703.x-i1

Xu et al suggest large degassing fluxes are possible

Xu, J., Wei, Q., Yang, S., Liao, L., Qi, Z., Wang, W. (2018) Soil degassing during watering: An overlooked soil N2O emission process. Environmental Pollution, 242: 257-263. doi: https://doi.org/10.1016/j.envpol.2018.06.103
soil degas displacement

Li 687: The long URL link does not connect to the document. Please update
https://nepis.epa.gov/Exe/ZyNET.exe/30002U3P.TXT?ZyActionD=ZyDocument&Client=EPA&Index=1991+Thru+1994&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5Czyfiles%5CIndex%20Data%5C91thru94%5CTxt%5C00000008%5C30002U3P.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C–&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=1&SeekPage=x&ZyPURL.

Author Response

Please see attachment

Reviewer 2 Report

This manuscript is a continuation of the evaluation of an experiment conducted regarding disturbed cattle manure from a cattle feed lot and subsequent N2O emissions. The N2O emission data has already been published. This paper focuses on detailed analysis using statistical correlation of various manure parameters to the reported N2O flux. Overall the manuscript is well written and detailed in its explanation of the observed data. What should be made evident in the abstract, however, is that the authors are basically reporting results from single observations in an un-replicated experiment. This reviewer appreciates the issue dealing with attempting to measure emissions in situ, and the authors can argue multiple measurements were made from the constructed systems, but Lines 143 – 160 describe an un-replicated experiment in this reviewer’s opinion. This reviewer is merely asking that this fact be made more evident in the abstract.

The abstract is also misleading in that there is repeated reference to feed yards and manure from these feed yards and one sentence talking about measuring emissions using large chambers. The initial impression is that the work was actually done in situ, not from reconstructed manure packs in a highly controlled environment. It is not until reading the Methods section that it becomes evident exactly what the data potentially represent. As noted above, the authors could be a little more honest for the general reader. Drop descriptors like “dynamic” and reference reconstructed manure packs in isolated non-replicated constructed chambers held at different temperatures.

It would also be useful if some information is provided about analytical uncertainty associated with much of the manure extraction data. Looking at Table 1a&b, the relative standard deviation of many of the numbers for all 5 chambers would seem to fall well within analytical uncertainty, especially from such an inhomogeneous material. The reported correlations from the comparisons really are called into question as to whether this is just random chance.

Lastly, the authors keep coming back to making a differentiation about source of the N2O in what is essentially a constructed system. This seems premature at best because the authors acknowledge they did not design the system to really test this fact. They simply added water twice. It is not even clear if they did some sort of water retention curve on the reconstructed manure pack.

Author Response

Please see attachment.

Author Response File: Author Response.docx