Nitrous Oxide Emission from Grazing Is Low across a Gradient of Plant Functional Diversity and Soil Conditions
, Carsten S. Malisch 1, Ralf Loges 1, Friedhelm Taube 1,3, Christof Kluß 1, Iris Vogeler 1,4 and Thorsten Reinsch 1Round 1
Reviewer 1 Report
The manuscript atmosphere-1070026, entitled “Nitrous oxide emissions from grazing are low across a gradient of plant functional diversity and soil conditions” by Nyameasem et al. deals about the effect of grazing management on N2O emission from Eutric Luvisol in northern Germany. The manuscript it is composed by collecting data, results and discussion from three different experiments that would assess the effect of grazing on different pasture, animal excreta (urine and dung) and pasture irrigation on N2O field emission.
Taking into consideration the topic investigated and the importance of this kind of study, in order to develop sustainable management in order to minimize N2O emission, I believe that the manuscript is of potential interest for readers of Atmosphere and fall within its scope.
First of all, the manuscript needs a deep style revision regarding many aspects and in particular to image quality and mineral nitrogen form expression.
With regard to the contents, in general, the experiments seem to be well performed, the results are clearly presented and the discussion it is well articulated. Material and methods should be improved because among the different experiment it is difficult to follow the activities carried out. The set-up of the discussion tends to keep the author’s considerations separated between different experiments. Try to add some comprehensive considerations. I suggest to delete the last paragraph in the conclusion.
Some keywords should be reconsidered.
Finally, I suggest to revise some small language issues along the text.
My specific comments, that I hope will help the authors to improve the manuscript, are reported in the attached files.
Comments for author File: 
Comments.pdf
Author Response
xx
University of Kiel,
Grassland And Forage Science/Organic Agriculture Group
Hermann-Rodewald Str. 9
24118 Kiel.
29.01.2021
Dear Sir/Madam,
Responses to review report 15705066
We are grateful for your kind words and fair comments regarding our manuscript titled “Nitrous oxide emissions from grazing are low across a gradient of plant functional diversity and soil conditions”. We have revised the manuscript to correct units in the tables and text, and have also improved the quality of the images (see figures 2, 4, 5), as recommended. The “Material and methods” section has been revised (see table 1) to improve readability and comprehension and the “discussion” section has been revised comprehension. The revised manuscript is attached.
Please find below our response and actions regarding your comments.
27-29. The sentences are corrected (see lines 26-28).
- The correction is made (“greenhouse gas” changed to “N2O”) and “organic N fertilization” is added to the key words (see lines 30-31).
- This correction is made (“Agriculturally used soils” changed to “Agricultural soils”) (see lines 40-41)
- This is corrected (see line 57).
- This has been revised please (see lines 83-84).
92-97. This error is corrected (see lines 88-91).
- This is corrected (see line 92).
- This has been revised (see line 94).
- “Add, according with the particle classification method its soil class”. This point is not clear to us, please. The soil class is already given as “Eutric Luvisol soil class” (see line 98).
- “The unit is missing. 1.65 it seems very high. Please check”. The correct value and unit is 1.56 g/cm3. Thanks for your intervention.
- This section is revised and no more present in the revised paper. Thanks.
- “Did you placed only a collar for each replicate? How many per treatments? “
Response: Please, each treatment had its collar (18 in all). See Table 1.
- Please this paragraph is no more available.
- The table is made larger (see table 2).
- Add some detail regarding WFPS measure (bulk density) and calculation.
Response: This has been added (see line 248-252).
221-222. The sentence has been moved (see 168-169).
- The equation is added (Eq 2, line 252).
- To ensure uniformity, NO3, NH4 has been adopted to mean nitrate of ammonium ion, please.
- This is corrected (see line 264).
- This is corrected (see line 230).
- This is corrected (see line 277).
- “what kind of regression? linear?”.
Response: Both linear and quadratic (see line 291 for the insert).
- Figure 2 has been improved (see figure 2).
- This is corrected (see line 331).
- The figure has been improved (see figure 4).
- “what kind of mode? add more detail in the statistics paragraph and here.
Response: This information has been provided (see 407).
- This has been corrected (see line 414).
- This is corrected (see line 417-426)
- This is corrected (see line 424).
Figure 5. has been revised (see figure 6).
- This is maintained for the reason given earlier.
- This is corrected (see line 489)
- This is corrected (see line 479)
- This is no more in the paper, please.
- This is corrected (see line 623)
- This is corrected (see line 734)
763-774. “I suggest to delete this paragraph. It is too general and not well focused.”
Response: This suggestion is accepted and the paragraph is deleted accordingly (see line 755).
We count on your support.
Yours faithfully,
- K. Nyameasem
(Corresponding Author)
Author Response File: Author Response.pdf
Reviewer 2 Report
This study is about the effect of grazing/ cattle excrements and leguminoses on N2O emissions and N balance. The authors did 3 different experiments to answer this question: 1, comparing pastures of different species; 2, comparing urine and dung application in these pastures; 3, comparing irrigated and non-irrigated grazing.
The authors did an outstanding job in setting up and undertaking these experiments, including a lot of field and laboratory measurements. Numbers and proof from field measurements are crucial to allow knowledge-based modelling and policy making. Thank you very much for this hard work!
In general, the paper is written in very good English, however the text is sometimes confusing and "overloaded". The Structure follows the Experiment 1, Experiment 2/3, but a thematic structure would be favourable (effect of leguminoses, effect of application timing,…). In the text, it becomes obvious that the authors know their measurements, treatments and subject very well. However, to make it more understandable for readers, the text should be condensed, there is several repetition.
Line-by-line review:
14-15: This is also true for other (agro-)ecosystems and forests. Rephrase, e.g. “N2O emissions from pastures can vary significantly depending on…”
21-22: change order and state the number for „control“ first
44-45: Reference 3 seems not to be the appropriate reference for the statement “N20 destroys the ozone layer in the troposphere.” Change.
45-46 “has been increasing” or “is increasing”? For the former state the time period
46: please give a more up-to-date number than a number from 2014
49: kg ha-1 per year?
54: A Reference study from South Africa seems not to be perfect. Please change Reference 9.
81: Please define EF
88-91: The detailed description of this treatment should be mentioned in the methods section as it is a bit too detailed for an introduction. Give just a short treatment name here (e.g. irrigation treatment, high soil moisture treatment?)
105: Preferably, you should also state the values for soil NO3- and NH4+, total N.
108ff: Just a comment: Your nomenclature is a bit confusing. why “g” not “pr”?, it is not straight forward what “g” stands for… (I guess “grass”)
118: What landuse was it before? Cropland? Abandoned grassland? Was is ploughed before sowing the pastures? That is crucial for the soil nutrients.
121: In my understanding Experiment 1 is comparing the 3 different swards, all similarly grazed. Thus, it is not an experiment about grazing. Rename.
129: Grazing includes random urine and dung application? Did you observe dung within the collars?
134-135: Do you mean Figure 1? Don’t mention/show Figure 3 before Figure 1 and 2.
Experiment 2: You need to make clear that you apply urine and dung only 1x per year. Either in spring, summer or autumn. From the topic (cattle grazing) and Table 1, you can get the impression that you apply dung and urine 3x to simulate grazing…
158: “are shown”
Table 1: According to your N loading rate, you applied ~ 500 kgN ha-1 year-1. That is very high. Why?
164: once a week for one year
Experiments: A Table on the 3 Experiments would help. Including treatments, hypothesis tested, measurements taken. Maybe a picture of the plots incl. split-plots would help to understand the design and to proof the statistically important set-up. It is always complicated to catch via text description. E.g. your main results Table2 suggests that you have only the following studied treatments: gwc, gwrc, gwrch, no-fertilizer, urine, dung, spring, summer, autumn. But as I understand, there are 27 treatments (gwc+no-fertilizer+spring; gwc+no-fertilizer+summer;…) This must be more obvious.
182: estimate, not estimated
183: “worst” in what perspective? A high soil moisture would be also worse for N leaching… Actually, the following sentence describes that a high soil moisture is beneficial to plant growth. You need to make it more clear.
184: How did you irrigate? Checking WFPS every day and fill it? Every week? Just before or after your measurements? Did you wet the dung itself, thus simulating rain? This is important for mineralisation.
Figure 1: Usually in climate graphs temperature is shown at the left-hand side, and precipitation at the right-hand side.
2.3 Environmental conditions should be 2.2.
209-210: As 2019 is generally known as a drought year as well, did you also compare the distribution of rain within the year? Was the growing season also higher in precipitation or was it more dry compared to LTA?
247: add reference [number]
248: Did you consider to fit a quadratic regression to the measurements?
260: what means EF1?
261: what means BFN? You should not use the abbreviations before it was explained.
275: please explain P_transanimal after P_transsoil
282-283: Use the term “N2O” to refer to the study subject.
301: Last sentence should be first sentence of the paragraph, as you are mentioning “Packages” within the text.
305ff: You always need to make clear in the unit if you talk about N or N2O.
305ff: [gN ha-1] is an unusual unit for N2O emissions. Choose [kgN ha-1] or [mgN m-2]. Please check the unit as your measured emissions seem very low. ( 1 g ha-1 = 0.1 mg m-2)
305-306: In 2018, you were measuring only 8 months. Thus “annual” mean values are hard to compare with 2019. You need to make it clear. Or you give mean values for May – December for 2018 and 2019.
Figure 2: The graph is hard to read. Please try to improve, e.g. by removing symbols (just lines) or to split into 2 graphs (2018, 2019).
329: What is the control? You don’t use and explain the term “control” very often, even that it is a crucial term in simulation experiments. Here, I understand, you mean “no additional fertilizer”.
331: What do you mean by “for gwc than gwrc of gwrch.”
343: In my understanding, legume proportion is driving BFN and N input accordingly. Thus, the expression “like legume proportion and BFN” is a bit misleading. Maybe “Like legume proportion and resulting BFN” does the job.
355: “immediately” suggests an increase within minutes/ hours after application, but as far as understood from Figure 3, this increase is taking place within the next days/ weeks. Please rephrase.
365: unit not complete
Figure 3: Instead of “experimental days”, you could use “days after application”.
Table 2: Split Table 2 in 2 different tables: Experiment 1 and Experiment 2/3. It is very hard to read and to compare and to keep track. Do lines between Grassland / Treatment/ Season.
Table 2: Please explain the unit of NO3- and NH4+ (mg kg-1 soil d-1). Why d-1? Add yr-1 where appropriate, e.g. N20-N. Add a row “alpha_ N2O-N (kg N ha-1 100d-1)” for Experiment 2 as EF1 is based on this.
Table 2: How did you consider the 2 different number of months in 2018 and 2019 when averaging?
412-419, Figure 4: Do a new paragraph with this topic as all the other results are looking at treatments.
437-440, Figure 5c: No need to say/ show. The increase in EF with length of sampling is due to the equation Nemissions/Ninput – the longer you measure, the larger gets Nemission, the larger gets EF. As the main N emissions are usually taking place soon after application, 30 days is a compromise and as stated it is the minimum, not a recommendation. A statement that your calculation is based on 100 days of sampling should be enough.
443ff, Figure 6: New paragraph “Drivers of EF”
Results paragraph:
You have to check the units. In Figures and Tables it is not clear, if you mean “per application”, “per year”, “per day”. As the “default” unit in talking about N budgets [kgN ha-1 yr-1], people reading the paper will generally think in this “default” unit, e.g. reading Table 2.
The paragraph is not easy to read as you are presenting a lot of variables and comparisons. As you are presenting everything in figures and tables as well, concentrate in the text on the main results and shorten the text. No need to say what was higher or lower as one can see the numbers or graphs. Just point out the most important things that you will discuss later and give a broad summary on the others.
474-476: According to Table 2, gwrch showed the highest annual N2O emissions in 2019. Why? Does plant diversity maybe just change the pattern of release (peaks are lower, but background fluxes higher?
481ff – Why do you bring up so detailed Lancelot plantain results, if it is just 5% of your pastures? Why would you expect an effect on N2O emission mitigation from Lancelot plantain? How does it relate to your pastures? What do these results mean for your pastures?
505ff: New paragraph as you start a methodological discussion. Maybe put it at the end or in the beginning of the “Discussions” section.
532: “, but had … period.” Delete as it was said just before.
540-546: shorten this part. The main point is that legume yield is known to decrease with high mineral N availability what might be the reason for your observed reduced yields.
562: Your N2O emission values seem really low, considering that you measured the high-concentrated urine and dung patches. Please provide values from other grazed grassland, e.g. [Rafique, R., Hennessy, D. & Kiely, G. Nitrous Oxide Emission from Grazed Grassland Under Different Management Systems. Ecosystems 14, 563–582 (2011). https://doi.org/10.1007/s10021-011-9434-x]
575: In dry years, the dung would stay dry as well, slowing down the mineralisation even further. Did you observe this in the collars?
589: Why is the N balance low if you state that leaching is high with high soil N in summer/ autumn. The N balance includes leaching, isn’t it?
591ff: As this paragraph is mainly about the effect of species composition, you should put it at the beginning of 4.2.2, as you always start with this topic.
606: change order of numbers, as it looks like that irrigated have the number 0.143.
613-614. This is a very important question, thus, please explain in a bit more detail, why dry climate may cause low EF.
653-654: How does N balance drive N2O emissions/ EF?
674-694: N balance: ~100kg N ha-1 yr-1 is high and high NO3 leaching might be the result. You should further discuss what problems can occur when the grassland is “over-fertilized”.
690-692: Plant N uptake/ productivity depends also on the availability of other nutrients and has a physiological maximum. Please add a comment in the discussion.
702: “)”
740 – 742: This first sentence is not clear. Species richness does not imply high N uptake.
743: Was this N uptake really extraordinary high to explain such low N2O emissions? Please provide other studies (in the Discussion section) proving that your site was more productive than other systems.
750: Your study is using high amounts of N and cannot represent a “low-input system”.
754: A N balance of 100 kgN ha-1 yr-1 is not low, actually, it is high and not worth pursuing. Please keep in mind that each agroecosystem should be well-balanced, thus should have a N balance value of ideally 0. In Germany, the law also follows this principle to avoid “over-fertilizing”, as at the end, plants’ growth has a physiological maximum and the excess in N will be leached or emitted.
“Conclusions” section: You should point out ones more that, especially, 2018 was an drought year and results might be/ probably are effected by this. Actually, the experiment or at least parts of it should be continued to see the difference to “normal” years.
Formal:
1, stay consistent in the writing of references. Sometimes you only use numbers, sometimes both.
2, be consistent in writing NO3 or NO3-, NH4 or NH4+
3, there were several errors in the format of the text. Additional dots, text shifts,.. The equation has a very confusing format and is hard to read. That might be because of the upload to the journal. Please check this.
Author Response
University of Kiel,
Grassland And Forage Science/Organic Agriculture Group
Hermann-Rodewald Str. 9
24118 Kiel.
29.01.2021
Dear Sir/Madam,
Responses to review report 15854140
We are grateful for your kind words and fair comments regarding our manuscript titled “Nitrous oxide emissions from grazing are low across a gradient of plant functional diversity and soil conditions”. We have taken note of all concerns raised in this report and wish to thank the reviewer for a great job done. We have taken steps to condense aspects of the manuscript (especially the materials and methods and results sections). We hope it becomes more interesting to readers.
The revised manuscript is attached.
Please find below our response and actions regarding your comments.
Line-by-line review:
14-15: This is also true for other (agro-) ecosystems and forests. Rephrase, e.g. “N2O emissions from pastures can vary significantly depending on…”
Response: This is revised (see lines 14-15).
21-22: change order and state the number for „control“ first
Response: This is revised (see line 21).
44-45: Reference 3 seems not to be the appropriate reference for the statement “N20 destroys the ozone layer in the troposphere.” Change.
Response: The reference is changed to Portmann et al. (2012).
45-46 “has been increasing” or “is increasing”? For the former state the time period
Response: This is corrected (see line 39).
46: please give a more up-to-date number than a number from 2014
Response: This is provided (see lines 40-43).
49: kg ha-1 per year?
Response: This is corrected (see line 43).
54: A Reference study from South Africa seems not to be perfect. Please change Reference 9.
Response: This reference is removed completely. We think the two references are enough (line 49). Thanks.
81: Please define EF
Response: This is defined (see lines 77-78).
88-91: The detailed description of this treatment should be mentioned in the methods section as it is a bit too detailed for an introduction. Give just a short treatment name here (e.g. irrigation treatment, high soil moisture treatment?)
Response: This is has been revised (check lines 84-85).
105: Preferably, you should also state the values for soil NO3- and NH4+, total N.
Response: The information is added (see the values on line 98).
108ff: Just a comment: Your nomenclature is a bit confusing. why “g” not “pr”?, it is not straight forward what “g” stands for… (I guess “grass”)
Response: This has been revised throughout the manuscript (eg. Lines 102-111).
118: What landuse was it before? Cropland? Abandoned grassland? Was is ploughed before sowing the pastures? That is crucial for the soil nutrients.
Response: This information has been added (see lines 112-118).
121: In my understanding Experiment 1 is comparing the 3 different swards, all similarly grazed. Thus, it is not an experiment about grazing. Rename.
Response: This section has been revised into Table 1.
129: Grazing includes random urine and dung application? Did you observe dung within the collars?
Response: Yes. This is one of the setbacks with the static chamber method. This is briefly discussed in lines 491-499.
134-135: Do you mean Figure 1? Don’t mention/show Figure 3 before Figure 1 and 2.
Experiment 2: You need to make clear that you apply urine and dung only 1x per year.
Either in spring, summer or autumn. From the topic (cattle grazing) and Table 1, you can get the impression that you apply dung and urine 3x to simulate grazing…
Response: This has been revised (see tables 2 and lines 170-173).
158: “are shown”
Response: This is corrected (see line 176).
Table 1: According to your N loading rate, you applied ~ 500 kgN ha-1 year-1. That is very high. Why?
Response: Indeed, we wanted to mimic the average urine and dung volumes from a dairy cow to ensure similar wetting by urine or coverage by dung. In doing so, we could not control the N load. However, pasture N loading by grazing cows range from 200-2000 kg ha-1 yr-1 (Selbie et al. 2015) and previous authors have applied similar, lower or higher N rates in simulated grazing experiments:
(eg. doi:10.1016/j.agee.2011.04.007;
http://dx.doi.org/10.1016/j.scitotenv.2017.08.186; http://dx.doi.org/10.1016/j.scitotenv.2016.06.016).
164: once a week for one year
Response: This is corrected (see Table 1 under Experiment 2 )
Experiments: A Table on the 3 Experiments would help. Including treatments, hypothesis tested, measurements taken. Maybe a picture of the plots incl. split-plots would help to understand the design and to proof the statistically important set-up. It is always complicated to catch via text description. E.g. your main results Table2 suggests that you have only the following studied treatments: gwc, gwrc, gwrch, no-fertilizer, urine, dung, spring, summer, autumn. But as I understand, there are 27 treatments (gwc+nofertilizer+ spring; gwc+no-fertilizer+summer;…) This must be more obvious.
Response. We found this advice very useful since it helped to reduce the narrative and provided a clearer picture of the experimental design. Accordingly, we have revised this section (Table 1).
182: estimate, not estimated
Response: This is no more in the text.
183: “worst” in what perspective? A high soil moisture would be also worse for N leaching… Actually, the following sentence describes that a high soil moisture is beneficial to plant growth. You need to make it clearer.
Response: This has been revised (see lines 152-154).
184: How did you irrigate? Checking WFPS every day and fill it? Every week? Just before or after your measurements? Did you wet the dung itself, thus simulating rain? This is important for mineralisation.
Response: This information has been added in lines 155-158. Thank you.
Figure 1: Usually in climate graphs temperature is shown at the left-hand side, and precipitation at the right-hand side.
Response: This has been corrected (see figure 1). Thanks.
2.3 Environmental conditions should be 2.2.
Response: This is corrected (see line 119).
209-210: As 2019 is generally known as a drought year as well, did you also compare the distribution of rain within the year? Was the growing season also higher in precipitation or was it more dry compared to LTA?
Response: This information has been provided (see line 129-133).
247: add reference [number]
Response: The reference is added (see line 259).
248: Did you consider to fit a quadratic regression to the measurements?
Response: We did not fit a quadratic regression to the measurements. This is because the chambers were large enough to ensure linear N2O emission rate. This was corroborated by the consistent linearity of CO2 fluxes measured from same sampled gases. You may see this article some details, please. (Hutchinson, G. L., and A. R. Mosier 1981. Improved Soil Cover Method for Field Measurement of Nitrous Oxide Fluxes. Soil Sci Society Am J 45, 2: 311. 10.2136/sssaj1981.03615995004500020017x)
260: what means EF1?
Response: As defined in line 269-275, this is another method of estimating N2O-N emission factor to account for the contribution of legumes. Currently, there is no “official” method of accounting for the contribution of legumes to N2O emission. You may check how the concept was used by Reinsch, T.; Malisch, C.; Loges, R.; Taube, F. Nitrous Oxide Emissions from Grass–Clover Swards as Influenced by Sward Age and Biological Nitrogen Fixation. Grass and Forage Science 2020, 1–13, doi:10.1111/gfs.12496.
261: what means BFN? You should not use the abbreviations before it was explained.
Response: Biologically fixed nitrogen. This has been rectified (line 229). Thanks.
275: please explain P_transanimal after P_transsoil
Response: This has been explained (lines 239-241).
282-283: Use the term “N2O” to refer to the study subject.
Response: This has been corrected throughout the paper. Thanks.
301: Last sentence should be first sentence of the paragraph, as you are mentioning “Packages” within the text.
Response: This has been revised (see line 278).
305ff: You always need to make clear in the unit if you talk about N or N2O.
Response: This has been corrected throughout the paper. Thanks.
305ff: [gN ha-1] is an unusual unit for N2O emissions. Choose [kgN ha-1] or [mgN m-2].
Please check the unit as your measured emissions seem very low. ( 1 g ha-1 = 0.1 mg m-2)
Response: This has been corrected throughout the paper (eg. Lines 333-344, figures 2,4).
305-306: In 2018, you were measuring only 8 months. Thus “annual” mean values are hard to compare with 2019. You need to make it clear. Or you give mean values for May –December for 2018 and 2019.
Response: This has been rectified (see figure 3, lines 342-345).
Figure 2: The graph is hard to read. Please try to improve, e.g. by removing symbols (just lines) or to split into 2 graphs (2018, 2019).
Response: We have revised figure 2. We hope is clear to understand. Thank you.
329: What is the control? You don’t use and explain the term “control” very often, even that it is a crucial term in simulation experiments. Here, I understand, you mean “no additional fertilizer”.
Response: The control refers to plots that were not fertilized. However, this paragraph discusses the effects (grassland, the season of excreta application and source of N). Thus, the control cut across pasture types and seasons of excreta application). We have tried to make that clearer in the manuscript (see lines 318-345).
331: What do you mean by “for gwc than gwrc of gwrch.”
Response: This section has been revised (see lines 305-307)
343: In my understanding, legume proportion is driving BFN and N input accordingly.
Thus, the expression “like legume proportion and BFN” is a bit misleading. Maybe “Like
legume proportion and resulting BFN” does the job.
Response: Thanks for this intervention. It is rectified (see line 310-311)
355: “immediately” suggests an increase within minutes/ hours after application, but as
far as understood from Figure 3, this increase is taking place within the next days/ weeks. Please rephrase.
Response: This statement is rephrased (see lines 351-353).
365: unit not complete
Response: This is corrected (line 360).
Figure 3: Instead of “experimental days”, you could use “days after application”.
Response: This is corrected (see figure 4).
Table 2: Split Table 2 in 2 different tables: Experiment 1 and Experiment 2/3. It is very hard to read and to compare and to keep track. Do lines between Grassland / Treatment/Season.
Response: Thanks for this advice. See Figure 3 and Table 3 for the revisions.
Table 2: Please explain the unit of NO3- and NH4+ (mg kg-1 soil d-1). Why d-1? Add yr-1 where appropriate, e.g. N20-N. Add a row “alpha_ N2O-N (kg N ha-1 100d-1)” for
Experiment 2 as EF1 is based on this.
Response: These were errors. Thanks for your intervention. See Table 3 for the revised version.
Table 2: How did you consider the 2 different number of months in 2018 and 2019 when averaging?
Response: to compare 2018 and 2019, we have now calculated means based on 8 months (May–December) measurements of each year (see figure 3).
412-419, Figure 4: Do a new paragraph with this topic as all the other results are looking at treatments.
Response: This section has been revised (see lines 406–414).
437-440, Figure 5c: No need to say/ show. The increase in EF with length of sampling is
due to the equation Nemissions/Ninput – the longer you measure, the larger gets
N emission, the larger gets EF. As the main N emissions are usually taking place soon after application, 30 days is a compromise and as stated it is the minimum, not a
recommendation. A statement that your calculation is based on 100 days of sampling
should be enough.
Response: This suggestion is well taken. We have accordingly revised the paragraph (lines 416-426)
443ff, Figure 6: New paragraph “Drivers of EF”
Response: This paragraph is revised (see line 428)
Results paragraph:
You have to check the units. In Figures and Tables it is not clear, if you mean “per
application”, “per year”, “per day”. As the “default” unit in talking about N budgets [kgN
ha-1 yr-1], people reading the paper will generally think in this “default” unit, e.g. reading
Response: All units throughout the paper have been re-checked. Thanks.
Table 2.
The paragraph is not easy to read as you are presenting a lot of variables and
comparisons. As you are presenting everything in figures and tables as well, concentrate
in the text on the main results and shorten the text. No need to say what was higher or
lower as one can see the numbers or graphs. Just point out the most important things that you will discuss later and give a broad summary on the others.
Response: This suggestion is well taken. We have revised the narratives regarding table 2 (now table 3) to shorten the text (see lines 299-329).
474-476: According to Table 2, gwrch showed the highest annual N2O emissions in 2019. Why? Does plant diversity maybe just change the pattern of release (peaks are lower, but background fluxes higher?
Response: We have recalculated the yearly emissions by considering 8 months (May-December) as shown in figure 3. Based on this, the gwrch (now prwrch) had the lowest N2O emissions, though the differences were not significant (P>0.05). It appears the relatively higher precipitation in 2019 enhanced the ability of the more diverse swards to utilize N more efficiently (lines 549-564).
481ff – Why do you bring up so detailed Lancelot plantain results, if it is just 5% of your
pastures? Why would you expect an effect on N2O emission mitigation from Lancelot plantain? How does it relate to your pastures? What do these results mean for your
pastures?
Response: Thank you for the questions. Upon reflecting on the questions, and considering previous literature, we agree that the proportion of Lancelot plantain in prwrch was too low to influence nitrification. We have accordingly revised the paragraph (see lines 566-577).
505ff: New paragraph as you start a methodological discussion. Maybe put it at the end or in the beginning of the “Discussions” section.
Response: See lines 490-500 for the revision.
532: “, but had … period.” Delete as it was said just before.
Response: See line 464 for the correction. Thanks
540-546: shorten this part. The main point is that legume yield is known to decrease with
high mineral N availability what might be the reason for your observed reduced yields.
Response: This section has been revised (see lines 472-476).
562: Your N2O emission values seem really low, considering that you measured the high concentrated urine and dung patches. Please provide values from other grazed grassland,
e.g. [Rafique, R., Hennessy, D. & Kiely, G. Nitrous Oxide Emission from Grazed Grassland
Under Different Management Systems. Ecosystems 14, 563–582 (2011).
https://doi.org/10.1007/s10021-011-9434-x]
Response: Yes, our emissions are low, but not too different from reports by Bowatte et al. 2018 and Luo et al 2018, who used mono-species swards in their study. We have duly provided some values from the literature. See lines 502-526 for the revisions.
575: In dry years, the dung would stay dry as well, slowing down the mineralisation even
further. Did you observe this in the collars?
Response: Yes, this was the situation; lines 590-595 have been revised accordingly.
589: Why is the N balance low if you state that leaching is high with high soil N in
summer/ autumn. The N balance includes leaching, isn’t it?
Response: The N balance (now patch residual N (PRN) only accounted for N uptake by plants as explained in lines 246-248.
591ff: As this paragraph is mainly about the effect of species composition, you should put
it at the beginning of 4.2.2, as you always start with this topic.
Response: Thank you. See lines 548-576 for the revision.
606: change order of numbers, as it looks like that irrigated have the number 0.143.
Response: This is corrected (see line 617)
613-614. This is a very important question, thus, please explain in a bit more detail, why dry climate may cause low EF.
Response: Thank you. See lines 617-619 for the explanation
653-654: How does N balance drive N2O emissions/ EF?
Response: High N balance (now PRN) will potentially result in higher N2O emission as N becomes available for nitrifies and denitrifies to act on. Also, the high surplus N might be leached to pollute underground water or become a secondary source of N2O emissions ( see lines 668-673).
674-694: N balance: ~100kg N ha-1 yr-1 is high and high NO3 leaching might be the result. You should further discuss what problems can occur when the grassland is “overfertilized”.
Response: As we indicated in an earlier response, we have changed the term “N balance” to “patch residual N (PRN)” to avoid a situation where readers would consider “N balance” in our case to mean system N balance. Meanwhile, the problems associated with high PRN are briefly discussed in lines 668-673.
690-692: Plant N uptake/ productivity depends also on the availability of other nutrients and has a physiological maximum. Please add a comment in the discussion.
Response: This is very true. See lines 689-692.
702: “)”
Response: Please see line 622.
740 – 742: This first sentence is not clear. Species richness does not imply high N uptake.
Response: Thanks. This is revised (see lines 733-735).
743: Was this N uptake really extraordinary high to explain such low N2O emissions?
Please provide other studies (in the Discussion section) proving that your site was more productive than other systems.
Response: See lines 677-683 for some discussion regarding this.
750: Your study is using high amounts of N and cannot represent a “low-input system”.
Response: We said this because we felt the systems does not import N from external sources. However, to avoid any misunderstanding, the statement has been revised (see line 744).
754: A N balance of 100 kgN ha-1 yr-1 is not low, actually, it is high and not worth pursuing. Please keep in mind that each agroecosystem should be well-balanced, thus should have a N balance value of ideally 0. In Germany, the law also follows this principle to avoid “over-fertilizing”, as at the end, plants’ growth has a physiological maximum and the excess in N will be leached or emitted.
Response: We agree with these concerns. Like we stated in an earlier response, the idea of n balance has been revised to avoid the impression that we were referring to system N balance. Thanks.
“Conclusions” section: You should point out ones more that, especially, 2018 was an
drought year and results might be/ probably are effected by this. Actually, the experiment
or at least parts of it should be continued to see the difference to “normal” years.
Response: Thank you for this point. See lines 753-755 for the revision. Note also that, the “conclusion” has been shortened based on the advice from a second reviewer.
Formal:
1, stay consistent in the writing of references. Sometimes you only use numbers,
sometimes both.
Response: Thank you. This has been corrected.
2, be consistent in writing NO3 or NO3-, NH4 or NH4+
Response: We are grateful for this. This has been corrected throughout the paper.
3, there were several errors in the format of the text. Additional dots, text shifts,.. The
equation has a very confusing format and is hard to read. That might be because of the
upload to the journal. Please check this.
Response: We have corrected these errors throughout the paper. Thanks.
We count on your support.
Yours faithfully,
- K. Nyameasem
(Corresponding Author)
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Dear authors,
thank you very much for considering my comments and suggestions. You did an amazing job, especially keeping in mind the short time you had. Thank you very much!
The manuscript and graphs significantly improved and it is really pleasant to read.
I am looking forward to see it published!
