Hydrochars Derived from Spent Coffee Grounds as Zn Bio-Chelates for Agronomic Biofortification

Round 1

Reviewer 1 Report

The authors tried to explore Spent Coffee Ground and hydrochars for agronomic biofortication, a very excellent work in attempts to contribute to managing malnutrition problem. The piece is interesting and innovative. However, I have major concerns on the current form of the manuscript. The authors would better distil the manuscript further to tease out an excellent article from the enormous data they have. Below are some of my specific concerns:

Abstract:

The introductory sentence of the abstract supposed to give a background on Hydrochars and their perceived importance in ameliorating micronutrient deficiency problem.

Introduction:

·       Nothing on other agronomic biofortication approaches stated as the phrase is a key word in the title of the manuscript.

·       “Limit” in line 57, better to replace with “reduce”. Sentence in line 58 -59 needs rewriting for clarity especially of the abbreviated elements. Who posit the hypothesis? Line 61

·       I suggest text in Line 69 – 73 to be moved to the section of materials and methods.

Materials and methods

This section is the core of the manuscript novelty but currently is confusing. For example materials preparation, the treatments and experimental set up are mixed up. The section need rewriting for clarity and logical flow of the sentences for easy reproducibility. Some of my specific concerns are:

·       Samples in line 78 refer to soil or Spent Coffee Grounds? Results of soil analysis given and preprocessing came after.(Line 81 – 83). Phrase “N₂ gas (12Mpa)” line 88 means what?

·       Hydrochar preparation does not requires drying of feedstock unlike biochar preparation. Why the authors dried the SCG (Line 78)

·       What is the logic of having control chelate (Line 102), moreover how many controls in this study and what is S.A.U?

·       What are the logic and differences of soil properties stated in sub-section2.1 line 81 – 85 and those in in sub-section 2.5 line 134 – 138?

·       Is this study an In vitro experiment (line 64) or a Greenhouse Pot experiment or both? I could not figure out the In vitro experiment here?

·       This was transplanted with the 30-day-old lettuce and the same substrate of origin so as not to mistreat the roots (Line 117 – 118). This sentence need rewriting for clarity.

·       In general the experimental procedures are not clearly stated and the logical flow is missing

Results and discussion

·       Previously, no pattern was identified for fixed carbon (Line 166) and later, another parameter that is positively affected by HTC temperature is carbon content (Line 172), very confusing or contradictory phrases. These need clarification.

·       Hydrochars showed severe decrease in chelating capacity (line 185 – 186) is this the correct way of reporting statistical outcomes? I suggest the sentence would read “ Hydrochars showed significant decrease in chelation capacity of Zn (94.5%).

·       What follow up experiment the authors alluding to in line 186 – 187?

·       “Hence, it can be hypothesized that the chelating capacity of SCG might be linked more to melanoidins rather than polyphenol content” (Line 194 – 195). I suggest better to change to “This might be due to the chelating capacity of more melanoidins rather than polyphenol content”.

·       Sentence in line 212 – 213 not clear, please rewrite for clarity.

·       Text in line 235 – 244 just synthesis work by other authors, what are exactly the key findings of this study in regard to soil fertility and subsequent potential effect on biofortification of lettuce? There is need to clearly outline these.

·       In general, in this section, there is need to clearly state the main findings of this study, and discuss their implications on biofortification of lettuce. At current form, these are mixed up and unclear.

For the overall manuscript, there is need for language correction, improving the experimental procedures and logical flow; clear stating of the key findings and their probable implications on Lettuce biofortification.

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

The response document and the modified manuscript are attached to this email.

Kind Regards,

The authors

Author Response File: Author Response.pdf

Reviewer 2 Report

This study attempts to use hydrochar made from spent coffee grounds to regulate soil available Zn for Zn biofortification. Below are some major flaws in the manuscript, for which I cannot accept it for publication.

1) Misleading conclusions. One of the major findings of the study was that hydrochar could be used to enhance vegetable Zn nutrition value. Based on Table 3, however, only the original material SCG with Zn (basically equivalent to a fertilizer bringing external Zn to soils) increased plant Zn uptake significantly. Even though the Zn input of SCG-Zn-2 was 3 times higher than Control B (Table S1), the increase of SCG-Zn was still much lower than that upon applying commercial Zn chelates.

2) Weird results. Table 3 shows soil available Zn significantly increased upon Zn-functionalized SCG and hydrochar application. Why did plant Zn uptake not increase with soil Zn availability? If the fortification effect was not significant in the first crop cycle, how could we expect an effect in subsequent cycles?

3) Improperly applied significance tests. At least 2 factors (Zn input and bioproduct input) were mixed to conduct a one-way (i.e. one factor) ANOVA and Tukey post hoc multiple comparisons.

4) Foggy wording. Here are some examples: L34 What is "extractable Zn"? L54-55 What is "agronimic effect"? What is "interesting macronutrient composition"?

Author Response

Dear reviewer,

The response document is attached to this email.

Kind Regards,

The authors

Author Response File: Author Response.pdf

Reviewer 3 Report

This was a well-written paper with the data clearly presented. The authors are attempting to find a way to biofortify a plant product with Zn. I think that consideration of cost should be mentioned in the article. For most farmers, purchasing chelated zinc is prohibitively expensive for the value added to the crop. Would use of any of the created additives reduced this cost so that farmers might consider it? 

I suggest splitting Figure 1 into two panels. FW doesn't accurately show growth, while DW does. However, lettuce is normally sold by FW so both panels are needed. The decrease in FW for most treatments are 20% or greater; This is too much for growers to consider implementing. I think a reason for this needs to be uncovered.

I don't have the raw data to evaluate, but I am very surprised that more of the treatments don't show a significant difference. In table 3, there are 50-100% increases in Zn levels and the variances are small. Why aren't these differences significant? Were your sample sizes too small? You might want to repeat these data and increase n. This seems like a promising start, but a statistically significant outcome was not observed.

Line 45: What does revalorized mean? I would consider finding another term.

 

Author Response

Dear reviewer,

The response document is attached to this email.

Kind Regards,

The authors

Reviewer 4 Report

Dear Authors,

I reviewed the article " Hydrochars derived from spent coffee grounds as Zn bio-chelates for agronomic biofortification" and I found it interesting and overall nicely prepared. Research conducted are comprehensible and interesting to read. Conceptualisation was done accordingly to proper manners in agronomy sciences. Presentation of the results is on a sufficiently high level. Moreover, the topic can considered as an innovative one, which I find very significant. The background was nicely introduced in pinpointing crucial problems that need to be solved making it reasonable to follow this kind of research. Methods selected have been reasonably chosen according to the actual state of knowledge but the description needs some corrections. As for the result section, it is worth mentioning that obtained results are indeed scientifically valuable. Descriptive presentation of obtained outcomes is pleasant to read and easy to understand. Altogether, there are some corrections that must be implemented before recommending the manuscript to be published, but I find them minor. Please see the detailed review below:

I Introduction
The research background and aims were presented clearly and transparently. It is clear which topics had to be broadened in order to enrich scientific knowledge. Given reasoning is easy to follow which makes the perception of the introduction very positive.
In my opinion this section doesn’t need any corrections besides one:

[53] “The use of SCG as an organic soil amendment.. “ – this is the first time you are mentioning SCG term (excluding abstract) Therefore, It has to be explained properly. Especially, since this is in an introduction section. Make sure to explain each abbreviation at the first moment you are using in the paper. It is crucial for the comprehensive readability.

 
II Materials and Methods

This section was written nicely but need some corrections.

[77-78]-  “They were spread into a thin layer and dried at room temperature to remove residual moisture” I strongly advice to be more precise in this description to ensure repeatability of your study. Please do mention the time and temperature of airdrying here.

[78] “Samples were taken..” please be more precise. I recommend changing term “samples” into “soil for the study”. As it is now it is not very clear what kind of samples you do mean.

[83] Term “assays” in this context is unclear for me. Please precisely indicate what did you mean here.  Please do precisely describe what and how was produced.

[91] “The solid by-products produced by the HTC (hydrochars) were..” I strongly recommend to change this statement into “Hydrochars produced by HTC were..” to not confuce the HTC meaning.

[113] “For each soil microcosm..” There is no description of the mesocosm that you have used. It is essential to describe it in the most detailed way to ensure the repeatability. That have to be corrected. Please do ensure you provide the information on shape, surface area, volume used etc. . 300ml PVC is not even close to description which is needed.  As it is now, there is no way to know how dense soil has to be compacted, or how wet the soil in each phase of the study and study preparation. Please do correct the study setup description.

[153-156]  There is no information about the normal distribution assessment crucial to use parametric tests. Please do correct that. Moreover, please od include the information on how the data was standardized for principal component analysis. It is essential to check and repeat your analysis.  

 

III Results and discussion

 I have positive feelings after reading the results and discussion section. No amendments are needed in my opinion. Presenting the outcomes was done nicely. The descriptive part of the section completes presented tables and figures. Everything is nice to read and comprehend here. It is worth mentioning that the presented statements follow the sequential reasoning making it nice and easy to read. It is also understandable why and what authors wanted to explain here. The chance to enrich the scientific knowledge with critical discussion using properly chosen references was used properly.

 

 V Conclusions

 The conclusions are supported by both results and discussion sections. It is proper. The opportunity to inform about the future research demands was stated which I find well-needed.  Good job!

 

 

 authors should make suitable corrections to the manuscript according to mentioned issues

Author Response

Dear reviewer,

The response document is attached to this email.

Kind Regards,

The authors

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The responses of the authors to my concerns are acknowledged and accepted. I hope the points stated are fully implemented in the text of the manuscript. Having said so, it is likely the form of the revised manuscript is improved.

Below are some additional points to further improve the manuscript.

 

Response 4. The last sentence of the response must be included in the main text of the manuscript and not just in the response.

Response 5. It is better to only state the explanation of what is crucial to the manuscript and exclude what is not relevant and the later add no value. Nobody is interested in what you intent to do afterward with some of your materials

Response 7. The authors’ better quote IFAPA rather than presenting the results of IFAPA as this can confuse the reader.

Response 11 and 17

I hope all the responses are integrated in the main text of the manuscript as the manuscript is meant for wider readers or scientific community and not a disputation between me and the authors.

Author Response

Dear reviewer,

We send attached to this message the document of the response to your comment. 

 

Kind regards,

Leslie Lara-Ramos

Corresponding author

Author Response File: Author Response.pdf

Reviewer 2 Report

Thank you for responding to my last comments. My concern remains regarding the main message presented by the manuscript that hydrochars can potentially be used for Zn biofortification. As the data show, only hydrochars functionalized with Zn improved soil Zn availability (but not plant Zn nutrition), while both soil available Zn and plant Zn can be increased upon Zn-EDTA application. In this case, why should we consider Zn-fortified hydrochars with a higher cost instead of cheaper Zn-EDTA? Therefore, compared to Zn-EDTA, hydrochars have no application potential for Zn biofortification. Overall, I still think the message the authors deliver to readers is misleading and not convincing.

Author Response

Dear reviewer,

We send attached to this message the document of the response to your comment. 

Kind regards,

Leslie Lara-Ramos

Corresponding author

Author Response File: Author Response.pdf