Impacts of Low Disturbance Liquid Dairy Manure Incorporation on Alfalfa Yield and Fluxes of Ammonia, Nitrous Oxide, and Methane

Round 1

Reviewer 1 Report

The authors address a timely and important issue.  Managing manures in ways that protect the environment, while optimizing crop production, is an issue of interest in countries around the world.  The design of the experiment, methods used, and interpretation of the results are good. However, I thought some expansion of the Discussions would be helpful.  The authors do a good job of explaining the results and suggesting possible reasons for differences among treatments, but I felt it would be good to say more about the implications and applications of the findings.  In the Conclusions, you summarize the findings but don’t say much about what the results mean for ag production in your region.  Also in the Introduction, it would be good to expand the reason for wanting to apply manures on alfalfa.  I think a lot of readers would just think that the practice wastes nitrogen.  You mention increasing acreage available for manure application in the first sentence of the Introduction, but it would be helpful to expand why the additional acreage is needed.  Many readers probably understand the additional acreage is needed for proper nutrient management, but others may not be familiar with current nutrient management requirements in your region. The paper is generally clearly written and easy to understand, but I’ve noted a few points that could benefit from minor revision.

L72: The formation of favorable conditions for denitrification within the manure injection slot probably also causes greater N2O emissions, along with retaining more N as NH4.

L80: “be” should be “are”

L118-124: Was there any offset angle for the Aerway?

L163-166:  A closing bracket is needed.  Does the parenetical material go all the way to the end of the sentence?

L226-227:  This sentence doesn’t seem to be consistent with Table 2.

L248 -252:  Is the lower NH3 loss for Aerator/Band relative to broadcast?  That should be clarified. Also, First and second sentences have somewhat different topics, so some addition transition would help avoid confusion.

L348-350: Sentence is a bit hard to follow.

L359:  Would the result have been different if you had used measured N2O flux for each treatment rather the general emission factor?

L371: Wording is awkward.  I think you need a ‘’were” before “triggered.”

Author Response

Reviewer 1:  Thank you for your comments. We added to the Conclusion and Introduction to clarify the need to better understand the impacts of manure application on alfalfa and the relevance of our findings to regional producers. We accept all of your recommendations and replied to your comments in the notes below.

We have added a sentence to the conclusions clearly summarizing the implications of our findings to field applications in our area.

We have added to the Introduction to explain the reasoning behind manure application to alfalfa.

The first paragraph was rewritten to improve clarity and justification for the research (lines 34-42).

Line 72: This point has been clarified in the text.

Line 80: This been corrected.

Lines 118-124: The offset angle for the aerator unit was clarified.

Lines 163-166: Parentheses were closed.

Lines 226-227: This concern was addressed

Lines 248-252: We revised the paragraph to clarify this transition.

Lines 348-350: We tried to better clarify the intent of this sentence.

Lines 359: If CO₂ is omitted from the GWP calculation the pattern of treatment differences and significant differences mirror what is seen in the “Manure Application Effects on Nitrous Oxide Fluxes” section lines 278-321 and particularly in Figure 5.

Lines 371: This was revised.

Author Response File: Author Response.pdf

Reviewer 2 Report

This article deals with impacts of low disturbance liquid dairy manure application on alfalfa yield and flux of significant gases (ammonia, nitrous oxide, and methane). Ammonia is an important alkali gas, affecting PM generation, and NOx, methane are famous GHG. This manuscript is well made to introduce significant manure application method in agricultural soil. 

 

There are some comments.

 

line 34. Change scientific names to italics.

line 34-37. Alfalfa is a legume plant. Therefore, nitrogen utilization efficiency may be high. It would be nice to add this.

line 53.  Ammonia can be a precursor to a secondary aerosol, PM2.5, in the atmosphere. It would be good to mention this.

line 110. Correct the superscript of the unit

line 114-130. For the readers, it would be good to add the four methods by simply modeling them in figure, if possible. 

line 139. Enter all types of minerals analyzed.

Table 2. What is the unit of DM? please input this information in the Table.

Why was the inorganic nitrogen content (NH4, NO2, NO3) not analyzed in the soil?

Figure 2-6. It is difficult to check the difference according to the liquid manure spraying method not only in the part where the gas emission is increased, but also in the whole.

line 358. change the format of reference style, IPCC 2014 to [15]

 

 

Author Response

Reviewer 2:  Thank you for your comments. We accept all of your suggestions and replied to your comments in the notes below.

Lines 34: scientific names are now all in italics

Lines 34-37: We have added to this part of the text to reflect this point.

Lines 53: We have made this addition to the text.

Lines 110: Corrected superscript

Lines 114-130: We added a supplementary figure showing surface physical differences among treatments after manure application (Figure S1)

Lines 139: The macronutrients analyzed were added.

Table 2: These units are stated in the table itself (all columns have same units)

Soil NO₃ and NH₄ concentrations were measured monthly (0-10 cm and 10-20 cm depths); there were no NH₄ and few NO₃ differences among treatments. Aerator/Band and Inject tended to have greater NO₃ immediately after manure application but this was not consistent. We therefore we did not emphasize these data given the high inherent variability in the data and felt it did not add much to the overall significance of the NH₃ discussion. 

We created several versions of these graphs and found this particular combination of lines and symbols easiest to read and that differences among treatments at manure application for N₂O can be discerned.  where there are not differences (which is prominent before and after manure application for N₂O and throughout the sampling period for CH₄) they are harder to discern but the small differences among treatments are not important in these timeframes and so the graphs support our main interests for displaying this data showing where differences occur for N₂O and showing there are no differences for CH₄.

Line 358: This was corrected.

Author Response File: Author Response.pdf

Reviewer 3 Report

The manuscript entitled- “Impacts of Low Disturbance Liquid Dairy Manure Incorporation on Alfalfa Yield and Fluxes of Ammonia, Nitrous Oxide, and Methane” has the potential to be an important contribution. Manuscript covers an interesting topic, Low Liquid Manure Incorporation (LDMI) and fits in the aim and scope of the journal. I recommend the following suggestion before final consideration of the manuscript.

 

General Comment: Proofreading is required (looks for subscript and superscript in manuscript).

 

Introduction: Well organized

 

Material and Methods: Need to re-arrange in following subsections

2.1 Study site

2.2 Treatment details and crop management practice

2.3  Ammonia and GHG sampling and analysis

 

 

Author Response

Reviewer 3:  Thank you for your comments.  We carefully reviewed and edited the paper accordingly for subscript, superscript, and other errors and added the subheadings requested in the Materials and Methods section.  

Author Response File: Author Response.pdf