Kinetics of C Mineralization of Biochars in Three Excessive Compost-Fertilized Soils: Effects of Feedstocks and Soil Properties
Round 1
Reviewer 1 Report
The authors have improved the manuscript by following the suggestions that were provided during the first round of revision.The work is the result of a massive work of data acquisition.
However, I think that the manuscript would benefit from additional revision taht should valorize more the results obtained.
In some cases I found it too difficult to follow (also due to several tretments under comparison, e.g. studied with a tree-way anova that is difficult to intepret), and clear concluding remarks were not provided. Conclusions are indeed rather a summary.
Despite I am not an English mother tongue, I feel to suggest that a deep revision of tenses, grammar, and sentences construction is required before accepting the paper for publication.
See also the pdf attached for some some revisions.
Comments for author File: 
Comments.pdf
Author Response
Dear reviewer:
Thank referee’s valuable comments. The descriptions of three-way ANOVA and repeated measure multivariate analysis of variance (MANOVA), and Conclusions have corrected and revised in the revised manuscript. We have revised the manuscript carefully and in details based on the valuable comments of reviewers, and have made the presentation and discussion of manuscript more complete.
bestregards
Author Response File: Author Response.pdf
Reviewer 2 Report
The manuscript has been greatly improved based on my previous suggestions and comments. I have no further comments.
Author Response
Dear reviewer:
Thank referee’s valuable comments.
We have revised the manuscript carefully and in details based on the valuable comments of reviewers, and have made the presentation and discussion of manuscript more complete.
bestregards
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript slightly improved. However, there are numerous awkward wordings and statements hard to understand including, at least for me, numerous syntax and grammar issues.
For example:
Lines 36-39: this statement makes no sense at al and contains several grammar issues, which is in light of the proof reading confusing
Lines 39-43: again a statement which is hard to follow
Lines 43-45: what was the proxy for LOM and how was stabilization measured?
Lines 61-65: hard to understand
Lines 78-82: to a large part this is a repetition from the paragraph before
The question about the variability of replicates and, therefore, the validity of statistical tests remains.
Lines 113-115: did you treat the subsamples as independent field replicates or did you mixed the sample to one composite bulk sample, in latter case no field variability is given in your one composite bulk sample
Line 183: independence of replicates, which would allow for ANOVA analyses, is still not clear to me; as of now the five replicates appear not to be independent and lack variability; to analyze the effect of factor ‘soil type’ on CO2 it would require here to take the different biochar types as independent replicates for one soil type, effect of factor biochar would require to take the three soil types per biochar type as independent replicates etc. but all this is not explained or considered
Lines 226-232: from my point of view, such analyses cannot be done given the lacking independence of the laboratory replicates
My main critics still stand given the questions about the independence of replicates and the resulting statistical tests.
Author Response
Dear reviewer:
Thank referee’s valuable comments.
We have revised the manuscript carefully and in details based on the valuable comments of reviewers, and have made the presentation and discussion of manuscript more complete.
sincerely
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The paper was imporved following the reviewer's comments and can now be published.
Author Response
Dear reviewer:
Thanks for reviewer's valuable comments and suggestion.
sincerely
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
General Comments
The paper deals with microbially mediated CO2 release from soils that were mixed with biochar from different feedstock and at different rates. The title suggests that the paper looks specifically into the mineralization of biochar-C but the required isotopic labeling approach for such outcome is not given in this study, please see my specific comments. The study presents a large set of data but the reader gets easily lost within the sheer amount of measurements, which is largely a result of poorly defined hypotheses and research questions and an accordingly aligned structure, please see my specific comments. The variability (field scale and landscape scale) especially within the three analyzed soils is not given based on the information that can be found in this paper and previous publications, which impedes statistical tests for significant differences, please see my specific comments. The manuscript would benefit from being proof read for grammar and syntax by a professional editing service.
Specific Comments
Introduction
Line 53-65: not clear to me, from my point of view, biochar mainly contributes to C sequestration because it is decomposed at a much lower rate than not charred OM and, over time, by interactions with minerals or occlusion in aggregates but not to a relevant extent by co-stabilizing labile OM, which is only a small percentage of SOM, please clarify
Line 59: to the best of my knowledge, low temperature biochar is not mineralized completely, it contains more compounds that decompose rather quickly than high temperature biochar
Line 60: effect of soil type is not described in the following
Line 84: explain and justify “excessive compost-fertilized”
Line 85-87: the paper is overall poorly structured and the reader gets easily lost among all the analyzed parameters, the paper would highly benefit from clearly formulated research questions and clearly outlined hypotheses, right now the hypotheses are only assumptions because no reasoning is given, after having clearly outlined hypotheses the statistical test should be aligned to prove or reject these hypotheses
Materials and Methods
Lines 95-98: please provide the complete texture for the soils
I did not find any description for the sampling design, so I had to find some of this information in another publication. According to the information given in this paper and in - Tsai, C.-C.; Chang, Y.-F. Carbon dynamics and fertility in biochar-amended soils with excessive compost application. Agronomy 2019, 9, 511. - I need to assume that the authors took one composite sample per field/soil and then used laboratory replicates from this one composite sample to perform incubation analyses by mixing with one type of commercial compost and different biochars at different rates. The lacking variability for the soils (one composite sample and no field or landscape replicates) impedes analyses for significant differences for individual soils. This affects mainly the results presented in Figure 3 and 5. To address variability, the authors could use the three soils as field replicates and then analyze for the effect of char amount and/or type, for example.
For Table 2, for large parts the data basis/data structure (replicates, treatments etc.) is not clear to me. To analyze the impact of time is confusing because the entire manuscript is aimed at analyzing cumulative CO2 values calculated for 400 days of incubation, so the temporal fluctuations in CO2 release is only of marginal interest but are here combined with other non-temporal effects. Therefore, I do not understand the reason for these type of analyses. Based on the heading, how can factor ‘time’ have a significant effect on the CO2 release, after 400 days?
Table 1: heading is not self-explaining and standard error or standard deviation is missing
For all other headings and captures: abbreviations need to be explained.
Discussion
Line 332: be consistent carbon is sometimes abbreviated sometimes not
Lines 332-335: to conclude on priming effects you need to perform labeling experiments, based on your approach you can only guess were the CO2 is coming from (i.e. compost, biochar, or native SOM)
Lines 329-339: biochar might also act as habitat for microorganisms or improves the overall conditions for microbial life such as better aeration, improved pH etc. but this is missing from the discussion here
Lines 349-351: in line 338-339 you claimed exactly the opposite, please clarify or does this refer to the REF
Lines 351-353: again what mechanisms in biochar-compost interactions should be quantitatively relevant in OM stabilization, and if excessive compost is a reason, which relevance does this have for our understanding of processes in the field if no farmer would ever apply such excessive amounts
Lines 355-356: what are you comparing here, please clarify
Lines 359-360: this cannot be concluded from the data
Line 362: this is an assumption only, I do not see any evidence in form of data here
Lines 364-366: see comment above, from my point of view, the variability for the different soils that would allow for such statement is not given, and this is redundant as already discussed above
Lines 366-369: this is not clear to me, nitrification and adding sulfate and chloride are different chemical reaction pathways, and if you are adding sulfate you will not change the pH because the sulfate will not release or attract H+
Line 379: only if you have high amount of ammonium and I do not see evidence here for that
Line 389: define “humus”
Conclusions
Lines 505-514: these are no conclusions but a summary of results Lines 517-518: belongs to the discussion
Line 518-520: I do have different opinion, these data reflect the fact that biochar is added which is decomposed at a much slower rate than non-charred native soil OM, this will decrease the decomspotion rate if you consider biochar and native OM together
520-534: the text needs to be reduced to the one or two strong “what does this mean” type of conclusions including implications of the findings for our broader understanding of biochar-soil interactions
Author Response
Dear reviewer:
Thank referee’s valuable comments and the authors will reply following comments one by one. First of all, the current study not used isotopic labelling approach because research on the isotope labeling method is restricted by government regulations. Research must be conducted at a specific location, and the research time is also limited. In Taiwan, research using isotope labeling method is few, and more few in soil. Hope you can understand our current situation. Second, including Table 2, Table 5, and Figure 5 have moved to supplemental material as Table S2, Table S3, and Figure S2 for reducing the large set of datas in the main text and for preventing the reader gets easily lost within the sheer amount of measurements. One more Figure 4 has added in the main text based on reviewer 3’s comment. The poorly defined hypotheses and research questions and an accordingly aligned structure have corrected and revised based on reviewer’s valuable comments. About the third suggestion, the information of the variability of three analyzed soils has corrected and revised in the revised manuscript for not to impeding statistical tests for significant differences. We have revised the manuscript carefully and in details based on the valuable comments of reviewers, and have made the presentation and discussion of manuscript more complete.
bestregards
Author Response File: Author Response.pdf
Reviewer 2 Report
The manuscript "Kinetics of Carbon Mineralization of Biochars in 2 Three Excessive Compost-Fertilized Soils: Effects of 3 Feedstocks and Soil Properties" by Tsai and Change provided a potential way to sequester carbon by stabilizing soil organic matter from the perspective of C mineralization. The design has its novelty and merits as it includes and compares three different biochars applied at different rates. This manuscript has its practical meaning and relevant scientific value. My main concerns and suggestions are summarized as follows:
Introduction:
The introduction stated the purpose of this study with a proper hypothesis. However many of the sentences were too long and difficult to understand. The author may want to rephrase such sentences. These have been highlighted in the PDF document.
Methods and Results
These sections were mostly well written with some minor typos and grammatical errors. My few comments are found in the PDF document.
Discussion:
This section was mostly well written. My only issue was with the canonical discriminate analysis (CDA) subsection. It looks interesting but, in my opinion, it does not add any scientific value to the discussion. It looks more like a discussion on statistics than on C mineralization kinetics. Also, although it appears in the discussion section, it is mainly a reporting of results without much interpretation. The manuscript will still be of good quality without the entire CDA section.
Comments for author File: Comments.pdf
Author Response
Dear reviewer:
Thank referee’s valuable comments. We have revised the manuscript carefully and in details based on the valuable comments of reviewers, and have made the presentation and discussion of manuscript more complete.
bestregards
Author Response File: Author Response.pdf
Reviewer 3 Report
The paper entitled "Kinetics of Carbon Mineralization of Biochars in Three Excessive Compost-Fertilized Soils: Effects of 3 Feedstocks and Soil Properties" reports results from a laboratory experiment where three compost-amended soils where treated with three different biochars at two different rate of input, and the mineralization rate was quantified.
One would expect that at the end of the paper the reader will have the idea that one or another biochar, in one or another soil, is suitable (or not) to reduce the C mineralization.
Unfortunately, the impression is that the authors have the potential to provide relevant and scientific-soundness data on the C mineralization dynamics with different biochar and soil types, however the results are in the end poor, and little understanding is provided. The paper is confusing rather than providing neew clear insights.
Major concerns are as follows:
Introduction: too much is related to the territorial context of Taiwan forest, about 1/3 of the introduction, that is far away form the topic of the study. More space should be referred to specific aspects as related to the topic, such as the drawbacks tha may arise by adding biochar into the soil, and which soils. Some suggested references have been added in ther pdf attached.
Material and methods: the statistical analysis looks interesting, but finally the reader do not understand why authors used so many approaches that were difficultly discussed later in the main manuscript. Improvement in the link between what was done with results is necessary. For instance, the MANOVA was reported, but difficult to see were the results were shown since multivariates not reeported (or where?).
Discussion: CDA should be presented in the results first, and discussed later. The quantity of data is important such that the discussion is too complex and does not provide a clear interpretation of what reported in results.
Conclusion: it is just a summary of what reported in Results and discussion. I see it as a symptom of difficulties in reporting some concluding remarks in light of results and discussion.
Additional remarks are in the pdf attached.
Comments for author File: Comments.pdf
Author Response
Dear reviewer:
Thank referee’s valuable comments. According to the comments of three reviewers, we have corrected and revised a lot of text, and the revised manuscript shown many "in red" paragraphs. We have revised the manuscript carefully and in details based on the valuable comments of reviewers, and have made the presentation and discussion of manuscript more complete.
bestregards
Author Response File: Author Response.pdf
