The Effects of Different Tillage Techniques and N Fertilizer Rates on Nitrogen and Phosphorus in Dry Land Agriculture
Round 1
Reviewer 1 Report
Review Comments for Agronomy manuscript agronomy-1883347, entitled "Phosphorus and nitrogen pools under different tillage techniques and N fertilizer rates in dry land agriculture"
General Comments
This MS investigated the impacts of tillage and fertilizer management practices on soil phosphorus (P) and nitrogen (N) dynamics based on a region-scale dataset. Overall, This paper is a good scientific contribution, the quality of MS is good in terms of subject, statistics, data presentation and discussion of the obtained results. I recommend this MS for publication in Agronomy after the incorporation and consideration of the following comments and suggestions.
Specific Comments
Lines 1：In the title, the study content, phosphorus and nitrogen pools, is vacuous. Please revise it. The object of this study, different tillage techniques and N fertilizer rates, is interesting.
Line 14: Syntax error.
Line 17-21: Please show the treatments clearly. The object of this study is tillage techniques and N fertilizer rates. Hence, it is better to show treatment using the two factors. What’s mean about ‘conventional tillage every 5th season’ ? no-till with crop residue or not?
In addition, is it a common tillage practice for CT-Y5? If not, it is not reasonable considering CT-Y5 practice as conventional tillage in sub-Saharan region, because the practice is not common in most countries.
Line 22-26: what’s the difference between CT-Y5 and CT-ANNUAL. Please add the content.
Line 28: Please add the content about implications for authors.
Line 37-38: it’s incorrect because there is no limitation for P in some soils.
Line 40: [2] found? Revise it.
Line 54: The explanation is one-sided. The main reason is that Nitrate moves with soil water. This relevant content can be found in the paper titled “Negative pressure irrigation increases vegetable water productivity and nitrogen use efficiency by improving soil water and NO3 distributions”
Introduction: Many previous studies have studied the effect of tillage management or nitrogen application on P and N dynamics. What is the new or original content in this study? I can’t find it. It’s better to point it out from the perspective that many studies only study the effect of tillage management on soil N or P rather that the interaction effect of tillage practice and nitrogen application.
Line 94: According to the previous content in this Introduction, NT could have higher N and P in topsoil due to residue. Please check it again.
Line 102-103: Syntax error.
Line 103: Is there residue in NT. If not, why do you explain the results using residue under NT in the Introduction part. In addition, it’s necessary to add detailed information about CT. plough? Depth?
Line 116: Is P application dose the same among different treatments? How about K application?
Line 126: 655 nm
Line 186: Please add letters in figures to represent the difference between treatments.
Line 210: why the standard error is much higher under 20-30 cm layer than 0-20 cm? Please check the date.
Line 261: Is crop residue added in NT?
Line 309-321: It is different about the effect of NT on nitrate among previous studies according to this sentence. However, what’s the contribution to explaining your results? It’s not clear. Please revise the sentence and show a clear reason.
Line 445: This sentence is not supported in this study. Please revise it.
Line 446-462: Simply this results and add main conclusions. In addition, the content about the interaction effect of tillage and nitrogen application should be added in the Discussion and Conclusions parts. It is novel in this study.
Line 463: Does the hypothesis is shown in previous content? This content must be shown according to previous studies.
Line 465: The total nitrogen, nitrate, ammonium-N, total P, and organic P were not higher under 60 kg N ha-1 than other nitrogen fertilizer application rates. How do you get the conclusion?
In addition, it’s interesting that the effect of nitrogen application on yield under different tillage management. Adding the result about yield helps to obtain the conclusion and it can also increase the quality of this study. I look forward to seeing this data.
Author Response
Please see the attachment
Author Response File: 
Author Response.docx
Reviewer 2 Report
Review comments:
The authors reported an experimental study of how different tillage and nitrogen fertilizer management practices impact the phosphorus (P) and nitrogen (N) dynamics in dry-land agriculture soils in the sub-Saharan region. They found that no tillage (NT) practice clearly increased the soil Total N, ammonium N, total P, organic P and extractable P relative to scenarios of conventional tillage every 5th season (CT-Y5) and annual tillage (CT-ANNUAL), which was attributed to the accumulation of crop residues on the surface soil and less soil disturbance. The authors further speculated that ploughing during the CT-ANNUAL practice could improve soil aeration and thereby accelerated the decomposition of organic materials as well as the mineralization processes of organic N and P. Finally, they concluded that NT together with 60 kg N ha^-1 application in surface soil (0-10 cm) would benefit soil fertility for the dry-land agriculture in the sub-Saharan region, with optimized soil total N, nitrate, ammonium N, total P and organic P.
The findings are useful towards understanding the soil P and N dynamics in the dry-land agriculture in sub-Saharan region, and would be helpful for the sustainable agriculture practices in this region. The paper was clearly presented, and I have only a few comments as bellow,
1. Abstract: The abstract was not well written, e.g., ‘Under NT, ammonium-N was higher (p < 0.05) compared to CT-Y5 and CT-ANNUAL in surface.’ is a repeat from the last sentence. The authors need to re-organize it more concisely.
2. Lines 40, 45, …: The authors used a special way on citing literatures, for example, ‘[2] found …’, ‘[4] explained …’, and more in the text. I would suggest to revise it into a normal format.
3. Line 67th: ‘bound’ should be ‘bounded’. There are more similar typos, and the authors need to revise the entire manuscript thoroughly.
4. Material and Methods: The experimental site was located at Loskop, KwaZulu Natal Province, South Africa. The authors mentioned that ‘However, in sub-Saharan region limited work has been done on SOM dynamics, therefore was an imperative need for this study’, which confused me. What is the relation between the two regions?
5. I am afraid that equations 2 and 3 will give the same value, and equation 4 likely equals to zero. Please clarify.
6. Lines 255-258: No SOC/SOM result was shown. Please provide detailed data.
Author Response
See the attachement
Author Response File: Author Response.docx
Reviewer 3 Report
Dear authors,
The article presents a very interesting idea when evaluating different soil management systems and N doses. However, there are serious problems in the material and methods, where important information about the conduct of the work is lacking, for example, when and how the samples of soil were collected. How were the samples prepared for the analyses? In addition, the statistical analysis used for the data is not adequate, because when working with increasing doses, it is recommended to use regression analysis.
The experiment was carried out with the corn crop, but the authors did not present yield data. This information is essential to support the results of soil analyses.
In the results, the authors did not present the statistical analysis in the figures, which I suggest that the authors modify (as per the comments in the attached file). In addition, the authors must follow a hierarchy in the presentation of the data, the main factor is the soil management systems, so this is the first factor that the authors must present the results, after the doses of N.
The conclusions are a summary of the results, where the authors do not send a clear message to the reader.
More details and observations can be found in the attached file.
Comments for author File: 
Comments.pdf
Author Response
See the attached
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The result about ANOVA test should be added into all figures using different letters.
Author Response
The authors note the reviewer’s recommendation with great appreciation and welcome the reviewer’s suggestion. However, adding the letter to the graphs makes the work clumsy and losses its scientific appeal. The authors believe that having error bars serve the great purpose of the work and they are enough to explicitly explain and differences within the treatments. Therefore, the authors so wish that the Figures remain without letters which still sustain scientific message to the global platform.
Reviewer 3 Report
Thear authors,
Only minor suggestions were accepted, they did not work on the main suggestions that were made in the "results" item, such as the insertion of statistical analysis in the graphs and the performance of regression analysis to evaluate the effects of N doses.
Furthermore, I suggested that the presentation of the results be simplified, with the presentation of the main results and not so many details that make the text difficult to read. None of these suggestions were accepted.
Comments for author File: Comments.pdf
