Effects of Biochar to Excessive Compost-Fertilized Soils on the Nutrient Status

Round 1

Reviewer 1 Report

The paper on the addition of Leucaena leucocephala biochar on different soils is interesting and is backed by a lot of data and by interpretation of results.

However, a few points have to be raised:

• English language has to be carefully and thoroughly checked, examples Line 36 "application charcoal" should be "application of charcoal", Line 37 - "in Australian", Line 104 - "reaches" should be  "reached", Line 114 - "as followed" etc.
• What is the rationale for using this particular species Leucaena leucocephala for biochar production? Is it more suited than other species in terms of chemical composition? IS it economically more feasible?
• The authors attempt to explain the observed values, based on eisting literature, which is a good thing, but a fundamented intepretation should be based on additional analyses, such as IR, Raman, calorimetry, that may indicate the formation of particular complexes and could explain beyond assumptions the variations in mineral contents. Further analyses may allow more adequate conclusions.

Author Response

Dear Reviewer:

Thank referee’s valuable comments and the authors will reply following comments one by one. Please see the attachment.

According to the comments, the title of this manuscript has deleted the “Sustainable”, and the revised title is”Effects of Biochar to Excessively Compost-Fertilized Soils on the Nutrient Status”.

Table 2, Table 4 and Figure 3 were also deleted for avoiding repeat results.

The revised manuscript has added one reference (No. 23), so the numbering of references has revised in the text.

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

Reviewer 2 Report

This is an interesting study, but use of the English is very poor and should be corrected by a person well versed in the English language. I have indicated some areas showing the deficiencies but there are many more areas that need improvement. Further, I find that the authors do not pay sufficient attention to the change of soil properties after incubation without and with biochar. I think this is the really interesting part of the paper, because most studies only show how biochar affected soil properties after a certain amount of time. A question I often have is : ‘how long does it take the biochar to react with the soil to significantly affect soil properties, and does it effect change after a certain amount of time.’ I thought this study would help us answer some of these questions, but the authors don’t discuss this at all. I also find the discussion of Principal Component Analysis needs to be improved. At the moment I cannot make sense of the meaning of the PCA. Considering all this I believe the paper needs significant improvement.  

Title – I think the word ‘Sustainable’ is not needed in the title. It doesn’t anything of value.

L9 remove ‘The’ and start with ‘Positive’

L10 a lot of the groundbreaking work on biochar was done on infertile Oxisols in the Amazon region (Lehmann etc) , these soils are high in clay and located in a very humid area. So this statement cannot be true.

L12-13 this is not a good sentence. Needs to be re-written.

L13-16 this sentence needs to be broken up and re-written. At the moment it is too long and not clear.

L14 do you mean biochar made from woody material? This is also confusing, because Leucaena is also a tree – so you were amending biochar made from wood with biochar made from wood?

L17 You need to supply a rationale for this research. Which positive results of biochar to you expect in over-fertilized soils? Is this a common problem?

L18 ‘resulted in significant values’ – this is not a correct way of communication – you probably mean ‘had a significant effect on’.

L19 remove ‘Soil type is an important factor’ – it doesn’t add any important information.

L20 tell the reader if compost increases or decreases pH. Typically, low pH is a problem in Oxisols, so if compost decreases pH that would be bad. However, compost typically increases and buffers pH so I’d be surprised if this was the case.

L21 ‘decreasing change’  - you don’t need to use the word ‘change’ because decrease is already a change!

L21 you state ‘the’ increase in soil P. This suggests that biochar always results in an increase in soil P availability. Is that really the case?

L24 ‘slightly’ needs to read ‘a slight’

L25 ‘slightly’ needs to be ‘a slight’ ‘obviously’ probably needs to read ‘a large decrease’

L26 it would not make a lot of sense to apply excessive amounts of compost with biochar. This work could show the value of biochar application if soil has a history of excessive compost application and the biochar is used to remediate the situation. Another point is that the words ‘maintaining soil fertility’ suggest the problem is fertility depleted soils, not overfertilized soils. The word ‘down-to-earth’ should not be used in a scientific publication.

L83 I yet have to be convinced that compost causes soil acidification. And, the increase in organic matter typically causes an improvement in soil physical and biological properties. That compost would inhibit crop growth is difficult to believe.

L84 ‘and spread them to the environment.’ This part of the sentence needs to be eliminated.

L85 I cannot see that co-application of excessive amounts of compost and biochar would be something of interest. What is the reasoning behind this?

L91 ‘sustaining soil fertility’ this doesn’t make any sense. The problem you are addressing is overfertilization which is the opposite of this.

L94 I am not sure what the positive impact is that you expect. This has to be explained more clearly.

L95 influence on which properties?

L96 This sentence is not useful and doesn’t sound scientific.

L105 some basic characteristics of the compost used in this study should be provided.

L111 I am not sure if this would be a common practice if the farmers have to pay for the compost.

L113-‘examination’  not ‘exanimation’

L159 ‘significant values’ – do you mean significant effects of biochar on pH, TC, TN, C:N ration and K concentration?

L162 this seems to contradict what you said in L159

Table 1 I am not sure I understand this table. There are Asterix placed to indicate p<0.0001. Why do you give the value of the apparently not significant (and therefore less interesting) p values? Also, why is p=0.00 not significant? I think you at least should give four decimal values (like 0.003 etc).

I do not think Table 2 is a particularly interesting table, considering that all properties you show here changed significantly during the 370 days of your experiment. I think you should not show these values that represent an average over this entire period.

L164 I think you should discuss original differences in soil properties before incubation with biochar, and then how they changed without or with biochar, and how the rate of biochar impacted that change. I don’t think it is particularly valuable to discuss values of soil properties that changes so much over the 370 days of incubation.

L 175-176 what is the difference between a gradual increase and an obvious increase? Not clear.

L176 the proper word to use is not difference but increase because you talk about a change over time..

L223 was this increase on average over all biochar rates or for the control? I think you need to discuss how properties changed without biochar first and then how they were affected by biochar.

Figure 1 is useful and should be kept. The authors need to do a better job explaining why many properties changed over time. This was apparently a result of the addition of compost to the soils because the change happened with or without biochar additions. In fact, the impact of biochar on soil properties seems to be dwarfed by the effect of the compost.

Figure 2 is similarly useful but the figure has to be made larger – too difficult to read. Again, the effect of biochar on most properties except OC and C:N ratio is overwhelmed by the effect of the compost as time went on.

Figure 3. The authors need to do a better job discussing the meaning of these figures. For example to say ‘At the end of the incubation, the PC1 had significantly positive correlations with pH, TC and C:N ratio, but showed significantly negative correlations with NO3-N and TIN content. (L294-296)” does not mean anything to the reader who is not familiar with PCA. You need to explain what this means in terms of the effect of biochar on nitrate and TIN content.

L302-320 I think the authors should not discuss these averages over time, because all properties changed so much over time. Instead, they should discuss how biochar affected the changes over time. I suppose the authors expected that with time, the effect of biochar would increase and that, by the end, the effect would be greater than at the beginning. This needs to be discussed.

L319 you need to distinguish between the soil’s buffering capacity and that of the biochar. It seems to me the biochar had a very small effect on the buffering capacity, but you can make your own interpretation.

Table 4. the title of this table needs to be clearer. It is not clear what this table shows from looking at the title. I also think the authors should not use averages over time,0 but for example, after 370 days of incubation.

L330 what do you mean when you say ‘increasing change’ this means the change was increasing I don’t think this is what you want to say.

L332 I don’t think cations were released from biochar because then you would see a difference between with and without biochar and this is not evident. The sorption of cations (L338) seems to be happening, but only in the SAO soil

L339 what do you mean when you say ‘slightly insignificant’? it is either significant or not.

L347 when you say ‘negative effect’ that is a value judgement. What is a negative effect on DOC – is that an increase or decrease of DOC?

L369 ‘at the beginning’ of what?

L404 did biochar help to reduce N-leaching in your study?

L410 this explanation is not clear. What do you mean with ‘variability of destructive samples’

L429 Because biochar, if well cured, is so recalcitrant, it may just be inert and not affect mineralization. Therefore, I don’t think you can assume that N-mineralization is reduced just because the C:N ratio is increased by the addition of biochar. C:N ratio is important if the substances in the soil can be attacked by microbes. If this is not the case, the biochar might be more like an inert substance (e.g. quartz). However, its sorptive properties or surface area might still affect N-mineralization but not due to the change in C:N ratio.

L436 ‘negative effect’ – what does it mean? If you are losing nitrogen by leaching due to excessive inorganic N levels in the soil, reduction of mineralization is positive.

L441 is this a finding from your study or from the referenced study (24) not clear.

L457 ‘amount of available P increment increased’ – not clear. How could the increment increase?

 L483 ‘almost’ – since you had only 3 different soil types, you should be able to tell in which soils this was true and in which ones not.

L488-492 I think this discussion of results from another study is excessive. Stick to your own data.

L532 ‘slightly insignificant’ this is not possible, as pointed out before.

L533 ‘insignificantly increased’ – another impossibility.

L535 ‘amount of available P increment’ – what does this mean?

Author Response

Dear Reviewer:

Thank referee’s valuable comments and the authors will reply following comments one by one. Please see the attachment.

According to the comments, the title of this manuscript has deleted the “Sustainable”, and the revised title is”Effects of Biochar to Excessively Compost-Fertilized Soils on the Nutrient Status”.

Table 2, Table 4 and Figure 3 were also deleted for avoiding repeat results.

The revised manuscript has added one reference (No. 23), so the numbering of references has revised in the text.

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

Reviewer 3 Report

Manuscript Number: Agronomy-777283
Title:
Sustainable effects of biochar to excessively compost-fertilized soils on the nutrient status.
General comments
This manuscript deals with the effect of adding biochar to soils to which an excessive amount of compost
has been added. This has been studied for a little over a year. This study is of great interest because of its
contribution to the knowledge of the sustainability of intensive production agricultural ecosystems. The
methodology used is correct and the results are sound. However, some aspects of the methodology
description, the results presentation and the discussion should be improved or clarified.
Therefore, I recommend to accept the manuscript but after a major revision.
Particular comments
- As my mother tongue is not English, I don't dare to give a consistent opinion, but I get the impression
that the text needs some English edition. For example, on lines 14-15, 84-86, 90-94, 126, ...
- Line 18: “… treatments resulted in significant values for pH, total carbon…” Significant values?
significant increase or decrease? Please, clarify.
- Lines 36-46: This paragraph shows a list of specific cases or studies. Since they were not made on soil
with excess compost, they are not part of the core of this study. Therefore, the paragraph should be
reduced by grouping the references, for example favorable cases on the one hand, unfavorable cases
on the other and indifferent ones.
- This paragraph summarizes in detail the results of the study carried out by Berek et al. There is no
need to supply as much numerical data. This paragraph could be shortened. However, the information
provided by the study by Berek et al. it can be exploited to a greater extent in the discussion section,
and yet it is only slightly cited twice (lines 332 and 447).
- Lines 75-92: These sentences describe the core of this study. For this reason, the previous paragraphs
should be shortened and the authors should pay more attention here. Added after line 85, it would
greatly improve the manuscript if the magnitude of the problem is exposed, which answers questions
such as:
o How much agricultural area is affected in Taiwan?
o Does it affect other countries? How much?
o How much is the soil degraded?
o To what extent is water eutrophication?
o etc.
- Lines 86-96: Review the letter format.
- Lines 99-106: Also, in this paragraph it would be necessary to briefly include the justification of:
o Why those three types of soil and not others? Are they the most widespread in the
agricultural area? Are they the most problematic? Were they chosen at random? ...
o Why Lechaena biochart and not another type? ...
The authors have previously studied these soils, but this manuscript must be self-sufficient,
without having to read previous publications to search for the justification of this selection.
Please clarify.
- Lines 109-111: Also should be clarified why “…5% commercially available poultry-livestock manure
compost was added…” if it is economically unviability to apply 5% compost for most farmers.
- Line 109: Please clarify what are the units of 5%? v/v, w/w, t/ha…?
- Lines 113-114: Please provide details of the incubation conditions: open air or under cover,
temperature, humidity, if leachate was allowed, ... In the Inroduction section the importance of
reducing nutrient losses has been highlighted, but in the Discussion it has hardly been commented, nor
have results been presented.
- Line 115: Please, clarify that 0% biochart treatment is the Control treatment.
- Lines 145-150: It is unclear whether MANOVA or one-way ANOVA was used. The results tables show
MANOVA. Please clarify.
- Lines 159-253 and 276-299 (Results): Most of the information the text offers is redundant, it is already
included in the tables and figures. It does not provide additional information to that offered by tables
and figures. So much data on the text make reading very tedious. Please shorten the text considerably.
- Table 2: It can be removed. There is no point in showing the average value of each parameter, when
the annual evolution has been studied. Furthermore, Table 2 does not offer significant differences
within each soil (except for TC, K and C/N). The information contained in Figures 1 and 2 and Table 1
makes that Table 2 can be eliminated.
- Table 4: It can be also removed. The information contained in Figures 1 and 2 and Table 1 means that
Table 4 can be eliminated. The differences with respect to the control treatment (0%) are very small
(generally <10%, except for TC and C/N). This can be commented in the text in 4-5 sentences and
remove the table.
- Discussion, general comment: Throughout the Discussion section, on many occasions too much text is
used to repeat what has already been stated in the results. Therefore, too much text is used in this. It
is advisable to focus on the most relevant results and increase the discussion about them.
- Fig. 1: What happened to DOC between days 100 and 150 should be commented and discussed.
- Fig. 2: What happened to TN between days 20 and 30 should be commented and discussed.
- Lines 318-319, 330-331, 336-338,…: When showing and discussing differences between soil types, it is
preferable to discuss what soil properties make the differences possible. It is not enough to mention
that one type of soil was different from another. For example, why was the pH lower more in SAO than
in SAI or MAI? What properties of the soil made this possible? Examples of good discussion are lines
362-363, 466-480. Please do the same in the rest of the discussion section.
- Lines 316-320: In these sentences the effects of biochar and compost are differentiated. It is
recommended to do the same for the rest of the variables and parameters discussed.
- The principal component analysis has been widely shown in the Results section, including Figure 3 and
Table 3. However, a discussion of these results is not explicitly appreciated in the discussion section, is
it? Please, if the results of the PC analysis are relevant, they should be highlighted in the discussion
section; but if they are not relevant, better shorten or remove their presence in the Results section.

Author Response

Dear Reviewer:

Thank referee’s valuable comments and the authors will reply following comments one by one. Please see the attachment.

According to the comments, the title of this manuscript has deleted the “Sustainable”, and the revised title is”Effects of Biochar to Excessively Compost-Fertilized Soils on the Nutrient Status”.

Table 2, Table 4 and Figure 3 were also deleted for avoiding repeat results.

The revised manuscript has added one reference (No. 23), so the numbering of references has revised in the text.

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

Round 2

Reviewer 1 Report

The paper was revised, comparing to the first version, however I suggest that the description of the plant specie used - lines 100 - 110 - in the study is much more suited in the Introduction part than in the Methods section.

Author Response

Dear reviewer:

Thank referee’s valuable comments. Based on the valuable comments of reviewers, we revised the manuscript carefully and in details and made the presentation and discussion of manuscript more complete.

Please see the attachment.

sincerely

Author Response File: Author Response.pdf

Reviewer 3 Report

This is a revised and improved version of an earlier version. The authors have taken into all of the comments of the reviewers. Therefore, I have no problem to recommend this manuscript for publication.

Author Response

Dear reviewer:

Thank referee’s valuable comments.

Based on the valuable comments of reviewers, we revised the manuscript carefully and in details and made the presentation and discussion of manuscript more complete.

Please see the attachment.

sincerely

Author Response File: Author Response.pdf