Response of Plant Root Growth to Biochar Amendment: A Meta-Analysis

Round 1

Reviewer 1 Report

Dear colleges,

I have read your articel and I feel, that due to the mega-analysis the effects of biochar on soil fertility was not clear foccused. You des

We (Haider et al.) have studied the effects of biochar ( 0- 15-, 30 t/ha) on a sandy soil in Europe and we did not observe a positive effect on the yields of corn , wheat, barley and corn.

However, why did you focus only to the roots?

You have not considered that with biochar black carbon ist applied! This is not organic carbon! This C resulted from the biochar fertilization!

You have not discussed the mechanisms why biochar application resulted to a soil pH increase?

However, when you select a site poor in nutrient availability and with a low pH, you will have a positice effect of a biochar fertilization on plant growth, since you have increased available soil K, soil P and pH!

The main positive effect of biochar-application to our soils is the effect on C sequestration ! This you have not mentioned!

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear author. Your study has scientific relevance, but it needs to improve the quality of writing and approach to data.

Biochar responses are related to initial nutrient content and soil parameters. Thus, a lack of response from Biochar may not be related to the plant or the type of biochar, but rather the quality of the soil. How do the authors get around this problem? Thus, a greater response in forest, for example, may be related to low levels in the soil and not to the forest species. From this, the conclusions may not be true.

The introduction needs to better justify its study. The authors address a lot the issue that one author found results and others did not. Better justify why evaluating these parameters that have been evaluated is important. You need to improve the keywords and not use the same words that are in the title.
Line 101 – Why weren't more assessment scales carried out?. For example, if you have 83 data sets with doses less than 20 t ha. You could divide this scale (maybe less than 10 t ha, and another 10-20 t ha-1.
Provide more details on materials and methods. Improve all figures. The y-axis can use the evaluated parameter instead of “content”. For example, P availability... Figure 6 should come before the other figures. In my opinion, figure 6 presents the characteristic of biochar. And the rest results on the ground. Figure titles need to be clearer.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The authors have attempted to unravel inconsistencies in scientific literature on root biomass response to biochar application through a Meta-Data Analysis.  This is a very useful study particularly when designing agro-management practices such as water and fertilizer placement and rates in different cropping systems. They studied how different factors, particularly biochar type and rate, and their subsequent effects on soil chemical properties could affect root response to biochar amendment.  However, this reviewer suggest following revisions to the manuscript

1. acknowledge that biological as well as physical properties changes in soil as a result of biochar amendment could also affect root response. This could be bring into the discussion with some review of literature.
2. On of your major finding, that is tree roots respond better than other plant types to biochar amendment, needs to be discussed in detail. In doing so authors must explain (or suggest) possible reasons, as it was in your second objective as well. Over all the discussion should be further improved, particularly on whether the observed results could be affected by interaction effects of the factors studied. You relate =ve root growth response to plant nutrients. But this discussion should be further extended to explain mechanisms how SOC, P(?) and N improves root growth.
3. Part of the first objective was to quantify the effect of biochar amendment on soil properties. This reviewer believe that there is ample publication on this aspect (please see some references quoted in the pdf file).  Therefore suggest it to be dropped from the first objective but use such data to explain your results.
4. It is difficult to follow the results and discussion according to the way you have presented. It would have been better properties of biochar (Fig 6) and soils (Fig. 7) were presented after Fig. 2.  Then Fig. 3 modified to relative response of soil properties to biochar types and rates (similar to Fig.4).  There could be 8 figures in that. Then use Fig 5 in the discussion.
5. Improve the language use in scientific writing. suggest to obtain the service of a qualified English language editor

Please go through other comments/revisions suggested given in detail in the pdf file attached.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Most suggestions were made by the authors.

Reviewer 3 Report

Abstract must include how rate of biochar affect root growth (e.g. on the average 18 to 48% increase when biochar rates were increased from <20 to 40 t/ha).

In the discussion explain why tree plants respond more to biochar application and also why biochar made from grasses have increased root biomass more than other biochar types.  

Comments for author File: Comments.pdf