Biochar Functions in Soil Depending on Feedstock and Pyrolyzation Properties with Particular Emphasis on Biological Properties

Round 1

Reviewer 1 Report

Biochar functions in soil depending on feedstock and pyrolyzation properties

The manuscript is well written and changes/improvements in almost all aspects of soil chemistry and biology due to application of biochar have been covered. The following ponts might be considered before publishing:

·         The manuscript is very long by adding some very basic information about biochar production and application which can be curtailed to reduce the content.

·         Chemical activation method of char is employed for activated carbon not for the purpose of soil application and should be beyond the scope of this manuscript.

·         In some places there are grammatical mistakes which may be corrected.

English needs minor corrections. 

Author Response

Thank you very much for your valuable comments, the correction of which led to an improvement of the manuscript.
1. According to the reviewer's comments, the introductory section on the definition of biochar was shortened, but additional sections were added according to the comments of another reviewer, which led to the preservation of the length of the manuscript.
2. The section dedicated to "Chemical activation method" has been removed
3. The latest version of the article will definitely be sent for proofreading

Reviewer 2 Report

A review article's plot should be captivating and introduce the subject with an attention-grabbing problem statement. The issue needs to be examined from an entirely new perspective. Each subheadline must include a critical analysis of the data and critically address any potential points of contention. Lots of improvements are needed. Please find the attached file.

Comments for author File: Comments.pdf

Difficult to understand the sentences and many spelling mistakes.

Author Response

Thank you very much for your valuable comments, the correction of which led to an improvement of the manuscript.
1. According to the reviewer's comments, technical errors in the text were corrected, the sentence was rewritten to be harmful, and points were added.
2. Sections in the introduction have been swapped
3. The text dedicated to the number of publications on the subject of biochar has been removed
4. Table 1 redone
5. Section 3.1, 3.5 rewritten
6. Figure 6 converted into a table

Reviewer 3 Report

The titles below  in my view would be more appropriate:

Biochar functions in soil depending on feedstock and pyrolyzation properties with particular emphasis on biological properties or

Biochar functions in soil with particular emphasis on biological properties depending on feedstock and pyrolyzation  properties

It  is a comprehensive and useful review.

It is well organised and referenced, and covers all of the important aspects.

It is a very good review article, very comprehensive and in my opinion it would be great interest to other researchers of biochar. It is well organised and referenced, and covers all of the important aspects.

There is a dearth of good review article on biochar as regards biological properties and the authors have done an excellent job.

However there are certain weaknesses and if added/corrected it would make the paper more interesting and more  effective.

The areas that could be improved I my opinion would be:

·        No discussion or information on the cost of biochar. The authors mention rates of biochar e.g. 50t/ha. With the present cost of biochar in Europe hundreds of euro per tonne, if not thousands of euro, what type of crop and environmental benefits would justify these rates of application? However in certain parts of the world the price of biochar can be much lower. A bit of discussion on this is warranted and make the paper more interesting.

·        The authors mention the benefits of biochar application e.g. improvement in physical properties such as decrease in bulk density, increase in water holding properties, decrease in soil borne disease, increase in plant nutrient supply e.g. K, and  increase in pH. But such benefits also accrue with the application of composted greenwaste/ composted biowaste at a fraction of the price of biochar.A brief discussion of this, in this  paper would make the paper more interesting.

·        Discussion on carbon sequestration is minimal. Perhaps this could enlarged, e.g.mechanism of carbon sequestration. Sequestration  is an  important aspect when biochar is applied to soil in relation of  getting carbon credits when this becomes a reality Carbon credits could be defining on the use of biochar as soil improver.

·        I found the discussion on the use of biochar as peat replacement rather simplistic/superficial .There more recent publications, e.g. a review article should be included. In addition many of the papers mentioned in  this manuscript re biochar as growing media, the effect of biochar on crop growth was restricted to fresh weight( e.g. Ref. 235) and not on  crop quality( refences 230 and 232 were exception to some extent) or  in the publication they made no attempt   to separate the effect of biochar per se from the effect nutrients in the biochar. In other words they did not equalise the nutrients as far as possible. They just added a standard rate of fertilizer N,P,K even when there were adequate K and P. When plants are grown in limited volume everything has to be right more so than in mineral soil in  the open. One of the reference( Ref.233) used fine brown peat( mostly < 2mm) and amended it with coarser biochar and found a positive effect on plant growth. I would say that any other coarse growing media constituent would have given similar results. In addition in many cases  the biochar were not sufficiently characterized e.g specfic surface area. To some extent this is  understandable as they were early days of biochar research as a growing media constituents  but since last 5 years there has been exponential growth in publication.

·         May be the authors  could consider including some publication give below  in the section on biochar as a replacement of peat.

 Alleviate environmental concerns with biochar as a container substrate: a review

P Yu, K Qin, G Niu, M Gu - Frontiers in Plant Science, 2023 - ncbi.nlm.nih.gov

This is the latest comprehensive review on the use of biochar in growing media

This paper shows effect of biochar on crop yield and quality in contrast to indirect effect of nutrients. Nutrients were equalised in the growing media as far as practicable.

 Here are specific points the  author’s attention is needed.

Line 65:: Chair , I think it should be char

Line 108: Table 2 maybe a reference should be given.

Line 145: “organic fertilizer and as  a constituent of growing media”.

Line 219:250⁰ C rather than 250 oC .

Line 305: FeCl_3, not FeCl3

Line 364: a sentence or two   re differences in the chemical composition of different fractions in the same biochar should be included in discussion on chemical properties, in my opinion. See publications below:

Particle size dependence of the physicochemical properties of biochar. He,et al., Chemosphere 2018, 212, 385–392.

Plant Nutrient Availability and pH of Biochars and Their Fractions, with the Possible Use as a Component in a Growing Media, Agronomy, 2019•mdpi.com

Line 562 silt “masses” what is “masses”

Fig 6. load g/ha ??

Line 1027: 4g/ha

In Table 10 the authors have given very useful information !

Author Response

Thank you very much for your valuable comments, the corrections of which improved the manuscript.
1. The title of the article has been corrected to what was suggested by the reviewer.
2. Added a section dedicated to estimating the cost of biochar
3. Added comparison of biochar with compost, including comparison of their carbon footprints
4. The amount of information devoted to sequestration potential has been increased
5. A comparison of peat with biochar is given
6. Technical errors corrected
7. Added information about the composition of different biochar fractions

Round 2

Reviewer 2 Report

Good improvement compared to previous version. Congratulations.