Soil N2O Emissions under Different N Rates in an Oil Palm Plantation on Tropical Peatland
Round 1
Reviewer 1 Report
Review for Manuscript ID: agriculture-548280
“Soil N2O Emissions under Different N rates in an Oil 2 Palm Plantation on Tropical Peatland” by Auldry Chaddy, Lulie Melling, Kiwamu Ishikura and Ryusuke Hatano
This manuscript attempts to find the main factors which control N2O emissions from oil palm located on Peatlands in the tropics. The study describes results from many years of monthly field measurements, and the authors should be praised for all their effort. This set of data is in need for bettering our understanding of global trends in GHG emissions. Four levels of N were tested. GHG fluxes were monitored along with groundwater level and WFPS. The manuscript is well written. However, I feel further work is needed in order to put through the take-home message in a more coherent and robust way.
My main concerns regard the following points:
1. How did the rain affect the WFPS reading? How did you separate the effect of the rain from the effect of the groundwater level? Did the groundwater N contribute to the N2O emission? How can you tell if so or not?
2. Further discussion is needed on the differences between the years. Why was there such big difference between years? The data set presented makes it hard to come with strong conclusions.
3. There are redundant tables and figures.
Some comments:
· Why will there be a difference in soil temp between treatments? Based on the figure there were no differences between 0-5 and 5-10 cm, and between the treatments. Unite all the data to one graph with error bars. You don’t discuss the differences in soil temp between treatments so this data is not relevant to the manuscript. Show just the general trend.
· Not sure what table 5 add to the manuscript. There are no statistical differences between treatments, except for T4 in 2010. This can be noted in the text and the table removed.
· Remove the yield data from table 6. There are no statistical differences between the treatments
· Fig 5. And Fig 7 - Not informative. It can be removed. R2 and the regression equation values can be added to the text instead.
· Consider uniting WFPS, GWL NO3, NH4 and N2O in one graph it makes more sense and follows most of your descriptions.
Please see the attached file for more comments.
I wish you all the best and I admire the effort you put into this work.
Comments for author File: 
Comments.pdf
Author Response
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Author Response File: 
Author Response.doc
Reviewer 2 Report
This manuscript describes an N-manipulation experiment in a peatland in Malaysia. N was added from 2010 to 2013 and then again in 2016-2017, in four levels: 0, 31.9, 63.8, and 127.7 kg/ha/yr. The authors measured N2O fluxes to determine the effect of N addition.
1. The authors found that annual N2O emissions increased in the N-addition soils and were highest for the T4 soils in certain years.
2. The N-addition did not alter oil palm yield.
3. The authors reported fluctuating ground water level (GWL) and found that nitrification increased under low GWL conditions and N2O fluxes increased under high GWL.
4. DN and NO3 were positively correlated at higher water contents.
5. Both nitrification and denitrification increased with N additions.
General comments:
This manuscript is well written and provides good insight on denitrification fluxes in peatland soils. Agricultural (especially peatland) soils are known to have high DN fluxes, and this manuscript examines the influence of N availability on this critical process.
Field experimental design: I am unclear on the field design. Were multiple treatments included within the same block? It sounds like the treatment areas planned around the trees. How far were the trees spaced, and was there a buffer between treatment zones? Could there be potential overlap among treatments? It would be helpful if the authors could provide distances and numbers, as well as a diagram of the experimental layout.
Specific comments:
Line 96: Please provide more detailed classification of the soils
Table 2: Please provide full forms of the fertilizers in the caption
Line 154: Is there a reference for the equations and calculations?
Figure 1: The graphs are very noisy, it would help if the authors plotted lines only, without points.
Figure 1c: Combine 5 and 10 cm data on the same axis and increase the distance among tick marks (ticks of 2C make the axis very busy). Combining both depths on the same axis allows the users to compare depth differences.
Author Response
Please see the attachment.
Author Response File: Author Response.doc
Round 2
Reviewer 1 Report
The manuscript was greatly improved.
Some minor revisions are still needed especially in all the aspects of the N use efficiency and mass balance. that part of the discussion is weak.
Good luck
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
