Nitrogen Availability in Biochar-Amended Soils with Excessive Compost Application
Round 1
Reviewer 1 Report
Tsai et al. reported an interesting study on effect of biochar addition as amendments onto 3 contrasted soils subjected to excessive compost application.
The context of the present study was well presented and explained; problematic well posed; as expected, complete bibliographic point based on recent references was added; hypothesis were clearly expressed (in a particular context of agricultural practices (Taiwan)); objectives of the study were well explained in light of important previous work (ref 19) with conclusive results in the interest of adding biochar to agricultural soil, both to retain nutrients and to sequester carbon was clearly . Objectives of the present study were the evaluation of nitrogen regulation in the case of biochar additions at different rates in different soils subject to excessive compost input. The authors did a hard work (many replicates)
In view of the remarks made below, I consider this article to be fine if corrections requested are done.
"Mat & meth" part: what does 3 soils representative of rural soils in Taiwan mean?
Which part of the wood was used to produce the biochar?
Why this choice of 371 incubation days?
Some details are missing on the procedure for the determination of NO3- and NH4+ in the extracts: conditions? standards used? technical repetitions?
Incubation conditions chosen to be better explained
“Results & discussion" part: on the results side, apart from a few remarks, mainly of form (see below), the results are correctly presented; the authors go to the essential, highlighting the strong points of their data.
However, regarding the discussion of the results, this is too often based on hypotheses that are sometimes not very solid!
Conclusion: is correct, highlighting the interest of the present study; with, as expected, a warning regarding the non generalization of the conclusions made since this applies to particular soils (this is clearly a specific context).
Concerning tables and figures:
Table 2: Meaning of "error 48" and "error 1008"?
Figure 1: The inserts are too small and the axes are not filled in.
Figure 2: Same remark as figure 1
Table 3: to be put in appendix (supp data) from my point of view; what is the interest to calculate (last line) an average for the 12 treatments?
Figure 3: to review the way of presenting the different treatments (as they are designated under the horizontal axis, it remains difficult to read); a suggestion: separate the modalities by group!
Figure 4: what is the interest in the form of a graph to represent such data?
Table 4 and table 5: same remark as table 3.
Author Response
Dear reviewer:
The authors have provided a point-by point response to the reviewer's comments.
Please see the attachment.
Sincerely
Chen-Chi Tsai
Author Response File: 
Author Response.docx
Reviewer 2 Report
Some recommendations to improve the manuscript:
- The novelty of this work should be explained in more detail.
- The experimental plan and treatments included in the "Materials and methods" (e.g. as a table) would give more clarity what has been done witin this study as compared to the other studies.
- As for the incubation test it is not clear which compost was used - was it the one that is described in the table (i.e. poultry manure and mushroom compost commercially available) or swine manure?
- What was the protocol for the incubation test? Any references or standards on that? This section describing the incubation test is a little unclear when read for the first time. Perhaps, adding a graphical representation would help the reader to follow.
- Usually, in practice this is a challenge to mix biochar with soil and compost to get a uniform sample. How was this mixture prepared?
- The manuscript should be proof read to remove minor lanugage errors, for example in line 99 it should be corrected to "(...) three studied soils", as the authors studied 3 representatives rural soils.
Author Response
Dear reviewer:
The authors have provided a point-by point response to the reviewer's comments.
Please see the attachment.
Sincerely
Chen-Chi Tsai
Author Response File: Author Response.docx
Reviewer 3 Report
Title define N availability perhaps Plant Available N or Inorganic N
Throughout the manuscript authors do not consistently define/spell out elemental and chemical constituents the first time with the abbreviation then use the abbreviation. Remember this must be done separately in the abstract , text, figures and tables.
page 1 lines 34 to 37 this sentence is very confusing rewrite.
page 2 line 45 authors use the term excessive compost define the term excessive authors give a range in the materials and methods but this needs to be discussed in the intro too.
The hypotheses We hypothesized that the addition of biochar would diminish mixed-soil N mineralization, enhance ammonium (NH4+) retention, and reduce nitrate (NO3-) leaching in excessive compost-applicated soils. The aim of our research was to evaluate the N regulation or enhancement role of different biochar addition rates in three excessive compost-applicated soils over time.
This article does not address nitrate leaching or leaching in anyway. There is published research in microcosms that do measure leaching of nitrate but this one does not.
Materials and methods
I am not sure mineralization is the correct term for what you are measuring as some mineralized material may be trapped in or on biochar surfaces and may even be exchanged and or diffused from the biochar so it would be safer to say you measured net inorganic N or just inorganic N.
The abbreviations for the soils are hard to remember what is the difference between slight and mild define these terms in pH units. I would use Oxi and Incept in the abbreviation and possibly the pH in the abbreviation. At least define the terms slight and mild in the text of materials and methods and tables and figures that need to stand alone.
on page 3 lines 96 to 97 compost is described as poultry manure and mushroom waste but lines 133to134 say the compost is cmmercially available swine manure compost??
Results & Discussion
page 4
Same issue mineralization is not the right term to use as previously discussed.
Are the increased discussed statistically significant? on page 5 192 to 193 authors state no?
I suggest the others discuss the data in greater depth equating the mineral N with the biochar, compost and soil chemical properties and discuss how these effects influence the biological process of nitrification. If authors included a separate graph of nitrates readers could see the conversion of NH4 to NO3 and see NO3 increase while NH4 decreases with time. Figure 4 shows the effect of soil type but not timing of conversion of NH4 to NO3 or the desorption and release of these N species. In general the scale of the graphs make them hard to read and interpret.
The text should better discuss and develop the data in tables and figures. Lead the reader through the tables more.
The conclusions do not flow from the results and discussion they are good but are not connected to what was said in the results and discussion.
I did not check the references
Author Response
Dear reviewer:
The authors have provided a point-by point response to the reviewer's comments.
Please see the attachment.
Sincerely
Chen-Chi Tsai
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
Reviewers have not sufficiently addressed the first set of revisions that I and reviewer 2 provided. It is my opinion that the MS in it's current form is not sufficient. I believe it will take more time for me to continue to detail than the authors spent revising the paper . Therefore, I am providing only a few comments to support my re-review.
The hypotheses is still not clearly written although it is improved.
In addition, technical solutions have become obligatory in Taiwan to reduce inorganic N (NO3− and NH4+) loss from agricultural soils and to improve compost utilization efficiency for sustainable crop production. In the present study, in vitro inorganic N mineralization kinetics are examined further.
Define mandatory is required by law or not?
We hypothesized that the addition of biochar would diminish mixed-soil inorganic N mineralization, Authors is mixed soil refereeing to the soil compost mixture?
enhance ammonium (NH4+) and nitrate (NO3-) retention in excessive compost applicated soils. Because biochar effects on inorganic N availability could have a substantial impact on biochar value and the propensity of producers to apply biochar to their soils, in this study we focused on the inorganic N loss and retention in a biochar-amended soil. The aim of our research was to evaluate the potential of different biochar addition rates for reducing inorganic N loss in three excessive compost-applicated soils over time. From our results, farmers could gradually reduce the addition of compost over the next few years by adding biochar to reduce inorganic N loss, as well as maintaining appropriate soil organic carbon (SOC) in Taiwan.
Again provide a range to define excess which authors have nicely provided later in the MS what does appropriate mean in the context of organic carbon? Provide a % range of each in parentheses in the objective
Reviewer 2 commented about the incubation temperature and the authors suggested it was based on the annual mean temperature. This is not true most incubations and enzyme assays are run near the temperature authors used in order to optimize reaction kinetics for C and N.
Also both reviewer 2 and I asked about what animal manure was contained in the compost substituting livestock does not address our concerns or answer our questions.
Authors need to work further on the results and discussion. Their response that it will be further developed in another paper is an insufficient rebuttal with respect to my concerns.
Author Response
Dear Reviewer:
Thank referee’s valuable comments. All the rewritten words or revised sentences based on reviewer’s comments are shown in red in the revised manuscript (new manuscript), and indicated point by point.
We must emphasize again noted that we pay much times in collecting, analyzing and aggregating data, and are sincerely writing this article. The authors did not intentionally not respond to the reviewer's comments, nor intentionally proposed an insufficient rebuttal with respect to reviewer concerns. We hope to get the understanding of the reviewer.
Please see the attachment.
Sincerely
Chen-Chi Tsai
Author Response File: 
Author Response.pdf
