Tillage and Urea Fertilizer Application Impacts on Soil C Fractions and Sequestration
Round 1
Reviewer 1 Report
The manuscript agronomy-1734548, entitled “Tillage and urea fertilizer application impacts 2 on soil C fractions and sequestration” submitted by Vilakazi et al. reported and discussed the results of a field study, inside a framework of a long-term experiment related to soil tillage, where the interactive effect of soil management and N fertilization on C pools was assessed. In particular, the effect of no-tillage, plough every 5 years and annual plough with four application rates of N fertilizer (urea), namely 0, 60, 120 and 240 kg N ha-1 was assessed on total soil carbon, total organic carbon, particulate organic carbon, permanganate oxidizable carbon, microbial biomass carbon and microbial quotient.
Considering the importance of comprehensively assessing the effect of conservation agriculture when inserted with other practices in the ordinary crop management, it is important to evaluate the interaction of conservative tillage with fertilization with the aim to increase sequestered soil C. Therefore, I believe that the manuscript is of potential interest to readers of “Agronomy” in order to improve the knowledge about conservation management in Africa, and fall within its scope.
Globally, the general set-up of the experiment, the analysis and the results are quite good. However, several changes are needed to the content and the style of the manuscript before it is published.
First of all, language should be revised and improved. I suggest a revision by a professional copy-editing service.
The abstract should be revised in the content with more complete information that should support the last statement proposed.
Keywords are fine.
Introduction: it is quite fine, but a presentation related to the effects and the interactions of fertilization management on the C sequestration should be implemented.
The materials and methods are well written. However, I do not understand the motivation why you analyzed separately the total carbon and the total organic carbon and analyzed them with two different methods. The soil samples are rich in inorganic C (carbonates)? Why tillage systems or fertilization could affect this parameter compared to organic C?
Results: Results from the statistical analysis were non presented neither in the text, tables or figures. Please add p values and letters in the figure. Results are quite complicated to read please this section should be more discursive. Moreover, add percentage differences among treatments in order to understand the magnitude of the observed effects. Figures must be embedded in the text.
Discussion: it is quite good. Insert some consideration, well written, related to the effect of N fertilization on C input into the soil and its effect on C sequestration.
Conclusion: I suggest to resume adding some large breadth consideration related to the conservation agriculture and C sequestration into the agroecosystems and the role of N fertilization.
References: References are not uniformly and appropriately formatted according to the journal rules.
My specific comments, which I hope will help the authors to improve the manuscript, are reported in the attached files.
Comments for author File: 
Comments.pdf
Author Response
Line 13 was edited to the soil C fractions along the profile.
The POXC was converted to POxC.
Graphs were all embedded in the text.
Soil type was changed from South African classification to WRB classification, which was Hutton to Lixisols.
The interaction between the fertilizer and tillage was explain very well.
Reviewer 2 Report
The manuscript by Bonginkosi S. Vilakazi and co-authors provides information about the labile C fractions in soils of South Africa. I think the manuscript fit aims and scopes of Agronomy. But some corrections should be made.
I suggest a minor revision of abstract.
Line 93. Please, name the soils according to Soil Taxonomy of WRB.
Section 2.1. Please, add information about geology. Typical soils and vegetation should be mentioned, too. Do the soils contain carbonates?
Section 3. Please, reduce using ‘(p < 0.05)’. The text repeats figures. I suggest rewriting this section as it is too boring and hardly readable. You do not need say ‘higher’ or ‘lower’ for all proxies studied. Please, indicate the main processes defining changes observed. Maybe merging Results and Discussion helps. In this case, delete an actual version of Results.
Please, divide Section 4 into some paragraphs. Discussion is too long and descriptive. Please, shorten it.
References. I have just found 7(!) References published after 2014: 2015 – one, 2016 – one, 2017 – three, 2018 – one, 2019 – one. I suppose provide more relevant discussion using recent works published in 2018 – 2022.
Some my specific comments are in the file attached.
Comments for author File: Comments.pdf
Author Response
Section 4 was divided according to the suggestion of the reviewer.
The parent material and WRB soil forms were added as per suggestion.
References were added as suggested.
The referencing style was modified as per suggestion of the reviewer.
Round 2
Reviewer 1 Report
The authors have applied all the revisions suggested improving the manuscript quality and, therefore, I believe that it can be published in Agronomy.
Author Response
There were no comment brought by forward.
Reviewer 2 Report
The authors have corrected just some points. My major comments - especially presented in the manuscript - are not taken into accounts. I have attached the previous version of the manuscript with my comments. Please, follow it and correct the manuscript.
As for author's reply:
Section 4 was divided according to the suggestion of the reviewer. I did not see deep changes that improved the quality of the paper.
The parent material and WRB soil forms were added as per suggestion. Soils - OK. But I did not information about the parent materials or geology.
References were added as suggested. I did not find new works. Based on the references represented, this research is outdating.
The referencing style was modified as per suggestion of the reviewer. OK.
I did not find changes in abstract that were recommended.
Sections 3 and should be shortened. I have mentioned about this last time.
Statistics is inappropriate. Please, use non-arametric methods.
Similar figures should be merged.
Author Response
Abstract.
Line 16-17: It was modified as suggested to include plough depth and years of annual conventional tillage. “The 30 cm depth …..”
M& M
Line 100- 102: The soil and geology was changed as suggested by the reviewers. “The soil was classified …….”
Results
Line 144-163: The total C and SOC results that were suggested to be combined by the reviewers, the authors decided to keep them separate as they better describe the sequestration of C fraction since the Total C and SOC are different and are also analysed different meaning the findings is also different and should be explained in different.
Discussion
Outdated referencing were removed
Line 212-213: Mann , (1986) was replaced by Govers et al., (2006).
Line 300-301: Angers et al., (1993) was replaced by Ho et al., (2015).
Line 407-408: Jenkinson & Lad, (1981) was replaced by Zhang et al., (2017).
Line 416-417: Powlson & Jenkison, (1981) was replaced by Culman et al., (2012).
