Influence of INGER and TORDIS Energetic Willow Clones Planted on Contaminated Soil on the Survival Rates, Yields and Calorific Value

Round 1

Reviewer 1 Report

Production of wood on marginal resp. contaminated land is an important option to avoid the fuel-food debate in bioeconomy. The authors are ambitiously dedicated to this topic and performed an interesting cultivation experiment with willow clones made for the production of energy wood. However, wood production with willow on degraded soil is not new and there is already good information available in literature. Taking this into account, there are some serious problems with this paper and the way of presenting and discussing the results. A thorough revision of the whole paper is recommended before it is suitable for publication. In particular, the following aspects need to be addressed:

-    The title does not reflect the focus of the paper.
-    The whole paper needs to be checked thoroughly regarding English language. There are several sections in the paper, where it was difficult to find out what the authors actually mean.
-    The use of technical terms needs to be checked again, the same terms should be used always for the same items (e.g. energetic willow vs. energy willow; fossil coal vs. natural coal, classic energy sources?, SRC – commonly this abbreviation is used for ‘short rotation coppices’ in agriculture seldomly for ‘short rotation crop’ but not for ‘short rotation cycle’)
-    For basic information about willow cropping/biomass use, there is not need to cite yourself [5, 7] or Wikipedia [10].
-    For many calculations or results it’s not clear, if these are based on dry matter or wet based. But that’s crucial for mass/energy/yield balances of wood chips. Please revise and deliver a consistent definition for the calculation basis used. Furthermore, for yield data it should be made clear if these are on an annual basis or measured after more than one growing seasons.
-    Some figures are not helpful for the understanding of the discussed subjects or results. E.g., Fig. 2 and 4 are not really useful because not properly discussed in the introduction and not containing further interesting information regarding the main focus of the paper. The majority of the statistical prints can be substituted by just the results for the average/median + standard deviations and measures for significance.
-    The introduction gives the impression, that heavy metal contaminated soils are in the focus of the paper. But later on, heavy metals are not playing any role in the presented experiments and results (by the way: Al, Ca, K, and Mg are not heavy metals – see page 4 line 117). In general, the effect of SRC cultivation in the presented work is mainly focused on the soil nutrients. This needs to be made clear in the introduction (with reference to relevant literature) and in the materials and methods chapter.
-    Planting date, fertilization, weather conditions respectively precipitation during the growing season and weed control are essential factors for the survival rate of willow. This information is completely missing in the paper.
-    Many factors in the experimental setup and about the analysis are missing such as precise information about field location, field size, sampling locations in the fields, sample numbers etc.
-    Some of the equations are incorrect resp. incomplete regarding the resulting units (e.g., no. 6) or not all abbreviations used in the equations are defined (e.g., ‘V’ in no. 8)
-    The energetic use of the wood is one of the main subjects of this paper as well as the analysis of bark content. Ash content another very important factor here and is highly influenced by the bark content. Furthermore, ash contents are essential for the incineration behavior of biomass. Therefore, some facts about the ash contents of the willow samples from the experiment and the relevance of ash for energetic use should be added.
-    The use/results of HCV and LCV on page 13 are somehow surprising. LCV is typically used for biomass with a higher moisture content and therefore significantly lower than HCV. 
-    Several references are wrong or missing in the text.
-    The conclusions need a complete revision because some of them are just repeating the results and others are not supported by the presented work (e.g., no 1). The conclusions should focus on the lessons learned from the presented experiments.
-    The conclusion if willow cropping on marginal land is a promising option needs to be discussed on basis of cropping costs and yields as well. This aspect must not go unmentioned in the discussion/conclusions.

Author Response

Reviewer 1

 

 - Reviewer: Production of wood on marginal resp. contaminated land is an important option to avoid the fuel-food debate in bioeconomy. The authors are ambitiously dedicated to this topic and performed an interesting cultivation experiment with willow clones made for the production of energy wood. However, wood production with willow on degraded soil is not new and there is already good information available in literature. Taking this into account, there are some serious problems with this paper and the way of presenting and discussing the results. A thorough revision of the whole paper is recommended before it is suitable for publication.

Author answers: According to the reviewers' recommendations, the entire paper was majorly revised to make it easier for journal readers to understand.

  

• Reviewer: The title does not reflect the focus of the paper.

Author answers: The title of paper was changed in “Influence of INGER and TORDIS clones of energetic willow when woody biomass and remediation of degraded soils are capitalized”. In this way we consider not only that we respond to the reviewer's remarks but we emphasize the two main objectives of the paper, namely that of soil remediation and that of obtaining woody biomass.

-    Reviewer: The whole paper needs to be checked thoroughly regarding English language. There are several sections in the paper, where it was difficult to find out what the authors actually mean.

Author answers: The paper has been completely revised from the point of view of English grammar. Thus, with the help of an English teacher, a few paragraphs were deleted, long sentences were divided and some words were added, in order to make this work better understood by readers.

-    Reviewer: The use of technical terms needs to be checked again, the same terms should be used always for the same items (e.g. energetic willow vs. energy willow; fossil coal vs. natural coal, classic energy sources, SRC – commonly this abbreviation is used for ‘short rotation coppices’ in agriculture seldomly for ‘short rotation crop’ but not for ‘short rotation cycle’)

Author answers: The words in question (energy…, natural…, etc) were changed in whole paper, as the reviewer proposed. See all of these in revised paper. SRC abbreviation was changed on line 76.

-    Reviewer: For basic information about willow cropping/biomass use, there is not need to cite yourself [5, 7] or Wikipedia [10].

Author answers: The reference quoted from Wikipedia has been deleted. The other two self-cited references remained in the paper, considering that out of the total number of over 50 references, two are acceptable, representing under 3.9%. We resorted to this option due to the lack of concrete data in this field, even if the authors do not benefit from that, being known that self-citations are not taken into account on Web of Sciences.

-    Reviewer: For many calculations or results it’s not clear, if these are based on dry matter or wet based. But that’s crucial for mass/energy/yield balances of wood chips. Please revise and deliver a consistent definition for the calculation basis used. Furthermore, for yield data it should be made clear if these are on an annual basis or measured after more than one growing seasons.

Author answers: -Where necessary, details on "dry basis" or "wet basis" were made in the revised paper; - Usually the harvest can be done annually or at an interval of 2-3 years, but in the case of our study we referred to the production obtained after the germination period, respectively after the first year of cultivation. See paragraph 3.2.

-    Reviewer: Some figures are not helpful for the understanding of the discussed subjects or results. E.g., Fig. 2 and 4 are not really useful because not properly discussed in the introduction and not containing further interesting information regarding the main focus of the paper.

The majority of the statistical prints can be substituted by just the results for the average/median + standard deviations and measures for significance.

Author answers: - Figure 4 has been deleted from the paper. Figure 2 has been retained because it refers to the role that wood biomass will play in the coming years in the substitution of fossil fuels. - In the paper we chose to use the facilities offered by the statistical program Minitab, through its graphs, but especially by providing some essential statistical parameters and verifying the normality of the group of values. Of course, all this can be determined directly, with the facilities offered for example by Microsoft Excel, but the parameters will have to be calculated step by step.

-    Reviewer: The introduction gives the impression, that heavy metal contaminated soils are in the focus of the paper. But later on, heavy metals are not playing any role in the presented experiments and results (by the way: Al, Ca, K, and Mg are not heavy metals – see page 4 line 117). In general, the effect of SRC cultivation in the presented work is mainly focused on the soil nutrients. This needs to be made clear in the introduction (with reference to relevant literature) and in the materials and methods chapter.

Author answers: The objectives of paper were completed, in such a way as to clearly show the purpose of the work (See lines 135-138). Two more references were introduced and another one was extracted. The methodology chapter has been completed.

-    Reviewer: Planting date, fertilization, weather conditions respectively precipitation during the growing season and weed control are essential factors for the survival rate of willow. This information is completely missing in the paper.

Author answers: This information was added on line 158. Growth conditions were specific to the plains of Southeast Europe, with a temperate continental climate, with average annual temperatures of 10-11 ⁰C and average annual rainfall of 630 mm / year. No fertilizers or irrigation were administered for this growing period.

-    Reviewer: Many factors in the experimental setup and about the analysis are missing such as precise information about field location, field size, sampling locations in the fields, sample numbers etc.

Author answers: A new paragraph with the requested data has been added in the methodology chapter on lines 158-159, 301, 147, 175.

-    Reviewer: Some of the equations are incorrect resp. incomplete regarding the resulting units (e.g., no. 6) or not all abbreviations used in the equations are defined (e.g., ‘V’ in no. 8)

Author answers: The required elements were introduced in the paper, inside of Eq. 6 and Eq. 8.

-    Reviewer: The energetic use of the wood is one of the main subjects of this paper as well as the analysis of bark content. Ash content another very important factor here and is highly influenced by the bark content. Furthermore, ash contents are essential for the incineration behaviour of biomass. Therefore, some facts about the ash contents of the willow samples from the experiment and the relevance of ash for energetic use should be added.

Author answers: Lines 431-432 present the contents of the ash for the wood and bark of the energetic willow, only as an informative title. The presentation of its importance, of the determination methodology and of the results in extenso are part of another work of ours that is cited in the bibliography, respectively Scriba et al (2020) [9]. I chose this form of presentation in order not to reach self-citation, a procedure that is very serious.

-    Reviewer: The use/results of HCV and LCV on page 13 are somehow surprising. LCV is typically used for biomass with a higher moisture content and therefore significantly lower than HCV. 

Author answers: Higher calorific value (HCV) values will always be higher than lower calorific value (LCV), regardless of the moisture content value. The values in the paper follow this general rule, as we see on lines 420-421.

-    Reviewer: Several references are wrong or missing in the text.

Author answers: All references have been verified. Moreover, two other new references were added and another one was deleted.

-    Reviewer: The conclusions need a complete revision because some of them are just repeating the results and others are not supported by the presented work (e.g., no 1). The conclusions should focus on the lessons learned from the presented experiments.

Author answers: All conclusions were revised.

-    Reviewer: The conclusion if willow cropping on marginal land is a promising option needs to be discussed on basis of cropping costs and yields as well. This aspect must not go unmentioned in the discussion/conclusions.

Author answers: The chapter of conclusions was redone, by eliminating the results of the tests and bringing them as close as possible to the significance of the conclusion term. See lines 444-458.

 

Reviewer 2 Report

General comments

The purpose of this study was to analyse two energy woody crops established in contaminated/non-contaminated terrains and planted with two different willow clones. The subject of the paper is very interesting since analyse the double role that these woody crops can play: i) biomass production and ii) phytoremediation.  However, I think the paper still have an important room for improving (mainly in data analysis and results presentation).

 

Following the authors “the main purpose of this paper is to plant willow on degraded and un-degraded land, respectively to find out the influence of degraded/undegraded soil on the viability of seedlings, and also on the amount of biomass, energetic value and calorific value of biomass”. Nevertheless, authors only carried out comparisons between contaminated/non-contaminated soils for average values of the mortality rate but not for biomass production or calorific values as was stated in objectives. Also, the evolution of soils parameters before/after planting on contaminated soils should be presented more in detail.

 

I have also some questions related to the data analysis. Why didn´t you analyse the trials as a factorial completely randomized design? Why didn´t you carried out comparison of means (survival rates, biomass, calorific values) between clones y/or terrains? This is the usual way to determine if there are statistically significant differences between the means.

I think also that the results and discussion section must be reorganized and rewritten according to the main goal of the research. Currently the article seems to be a mix of several studies that have been put here together, but in a loosely organized way.

 

 

Specific Comments

 

Introduction

• Figures 1, 2 and 4 are not necessary and can be removed.

Material and methods

• Line 211-213: please provide more details on how total biomass was determined.
• Please be more careful with equations and their symbols.
• Equation line 229: Dew (wood density within the willow) must be bark density?. Explain the meaning of “m”, that it must be “m-mass of pieces bark, in g”. Rename “m” to differentiate it of that of equation 4. E.g., use a subscript “b “for bark and “t” for total mass (total density D_t and bark density D_b)
• Lines 236, 269: Please specify if MC is the biomass moisture content on dry weight basis or on a wet weight basis.
• Line 263: replace “kJ” with “kg”
• Line 267, equation 8: Replace “V” with “CV_MC” where CV_MC is the calorific value at a known moisture content MC. MC is the moisture content (expressed as a fraction on a dry weight basis??). Please include an appropriated reference for this equation.
• Line 269: HCV_MC is wet higher heating value (MJ/wet kg) or dry higher heating value (MJ/dry kg)? Please specify.
• Line 271, equation 9: Replace D with “D_x” (x subscript), being x equal to “t” for total density or “b” for bark density.
• Line 297: replace “Figure 9” with “figure 7,
• Lines 306-307 “the survival rate on contaminated land is better and the Tordis clone is higher from this point of view that clone Inger” and lines 385-386: “it can be concluded that the two clones have the same energy value”. To refer appropriately to this, authors must perform a mean comparison test to determine if there are statistically significant differences between the means of the two groups.
• Lines 249-251: The same comment as mentioned above. A comparison of means test must be performed.

Results and discussion

• Lines 286-288: Figure 7 do not correspond with this assertion. I do not understand the usefulness of this figure.
• Results of figure 8 should be presented using a box-plot because it is much more informative. Also, comparisons of mean test must be carried out in order to determine if there are significant difference between means of the two clones and/or the two terrains, at a given level of confidence.
• Why do the authors use only one equation for biomass estimation for the two clones? Please clarify.
• Point 3.3. “ Soil enrichment”. For a better explanation of this section, it would be useful to include a table with key chemical or physical parameters before and two- years after planting

Conclusions

• Rewrite conclusion 2. You want to say that “Tordis survival rate was 38.4% or 2.7% higher than Inger clone.”

Author Response

Reviewer 2

 

1. Reviewer: The purpose of this study was to analyse two energy woody crops established in contaminated/non-contaminated terrains and planted with two different willow clones. The subject of the paper is very interesting since analyse the double role that these woody crops can play: i) biomass production and ii) phytoremediation.  However, I think the paper still have an important room for improving (mainly in data analysis and results presentation).

Author answers: Several aspects related to the analysis of data and results were introduced in the revised form of the paper.

 

2. Reviewer: Following the authors “the main purpose of this paper is to plant willow on degraded and un-degraded land, respectively to find out the influence of degraded/undegraded soil on the viability of seedlings, and also on the amount of biomass, energetic value and calorific value of biomass”. Nevertheless, authors only carried out comparisons between contaminated/non-contaminated soils for average values of the mortality rate but not for biomass production or calorific values as was stated in objectives. Also, the evolution of soils parameters before/after planting on contaminated soils should be presented more in detail.

Author answers: All aspects notified by the reviewer can be observed in the revised form of the paper on lines 377-397.

 

3. Reviewer: I have also some questions related to the data analysis. Why didn´t you analyse the trials as a factorial completely randomized design? Why didn´t you carried out comparison of means (survival rates, biomass, calorific values) between clones y/or terrains? This is the usual way to determine if there are statistically significant differences between the means.

Author answers: We have chosen a certain way of analysis, by using the Minitab program, which provides us with a series of data simultaneously. Of course, another kind of analysis can be done, but we chose this path considering that it is easier and more understandable for readers to see a figure or graph than to look at some comparative data. In fact, not all features were comparable; for example, the mass and density of the two clones for the twigs was almost similar, which is why we took as a comparison criterion this property for wood and separately for bark.

 

4. Reviewer: I think also that the results and discussion section must be reorganized and rewritten according to the main goal of the research. Currently the article seems to be a mix of several studies that have been put here together, but in a loosely organized way.

Author answers: In the revised form of the paper there are a series of changes, regarding the objectives of the paper, the working method, the results and the conclusions. We believe that all these changes meet the requirements of the reviewer and make our work more appreciated by journal readers.

 

5. Reviewer: Figures 1, 2 and 4 are not necessary and can be removed.

Author answers: Figure 4 has been deleted from the paper. Figure 1 and 2 have been retained because it refers to the role that wood biomass will play in the coming years in the substitution of fossil fuels.

 

6. Reviewer: Line 211-213: please provide more details on how total biomass was determined.

Author answers: On line 221-223 a new paragraph was introduced “Based on the dry mass of a twig, the number of twigs on a row and the number of rows per hectare, the total mass of biomass per hectare could be determined.”

 

7. Reviewer: Please be more careful with equations and their symbols. Equation line 229: Dew (wood density within the willow) must be bark density? Explain the meaning of “m”, that it must be “m-mass of pieces bark, in g”. Rename “m” to differentiate it of that of equation 4. E.g., use a subscript “b “for bark and “t” for total mass (total density D_tand bark density D_b)

Author answers: Based on the reviewer's recommendations, Eq. 4 and Eq. 5 were redone, changing the initial notations. Expression “On the dry basis” was also introduced to show that it was determined at 0% moisture content.

 

8. Reviewer: Lines 236, 269: Please specify if MC is the biomass moisture content on dry weight basis or on a wet weight basis.

Author answers: Expression “dry basis” was introduced, meaning that in the moisture formula the denominator is given by the absolutely dry mass of the specimen.

 

9. Reviewer: Line 263: replace “kJ” with “kg”

Author answers: This issue has been corrected on line 274 of revision paper.  

 

• Reviewer: Line 267, equation 8: Replace “V” with “CV_MC” where CV_MCis the calorific value at a known moisture content MC. MC is the moisture content (expressed as a fraction on a dry weight basis??). Please include an appropriated reference for this equation.

Author answers: All the notified aspects were corrected in the revised form of the paper.

 

• Reviewer: Line 269: HCV_MC is wet higher heating value (MJ/wet kg) or dry higher heating value (MJ/dry kg)? Please specify.

Author answers: A few additions were made with the words dry and moist, to clarify this issue in the lines 281-282.

 

• Reviewer: Line 271, equation 9: Replace D with “D_x” (x subscript), being x equal to “t” for total density or “b” for bark density.

Author answers: The required change to equation 9 has been made and is visible on line 285.

 

• Reviewer: Line 297: replace “Figure 9” with “figure 7,

Author answers: This change was made on line 311 of new revision paper.

  

• Reviewer: Lines 306-307 “the survival rate on contaminated land is better and the Tordis clone is higher from this point of view that clone Inger” and lines 385-386: “it can be concluded that the two clones have the same energy value”. To refer appropriately to this, authors must perform a mean comparison test to determine if there are statistically significant differences between the means of the two groups.

Author answers: This check was performed and the result was added to lines 321-323.

 

• Reviewer: Lines 249-251: The same comment as mentioned above. A comparison of means test must be performed.

Author answers: Idem item 14, see lines 405-407.

 

• Reviewer: Lines 286-288: Figure 7 do not correspond with this assertion. I do not understand the usefulness of this figure.

Author answers: Like other graphs of the Minitab 18 program, it shows the normality of the experimental values obtained and identifies the moment when the data collection process got out of control. The Individual range diagram automatically shows us the arithmetic mean and the value limits for a 95% confidence interval. Other new explanation was introduced inside of revised paper on lines 312-315, in order to be more understand for all readers.

 

• Reviewer: Results of figure 8 should be presented using a box-plot because it is much more informative. Also, comparisons of mean test must be carried out in order to determine if there are significant difference between means of the two clones and/or the two terrains, at a given level of confidence.

Author answers: We considered that the graph in figure 8 could remain in the paper, for a certain diversity of figures. This diagram is the only one of its kind made in Excel, it is simple and shows us the difference between the two clones and between the two types of fields. We could use the Minitab 18 program to make a box plot diagram, but then the vast majority of the figures would have been made with the same program and would have created a feeling of monotony. It is added a new sentence on lines 321-323.

 

• Reviewer: Why do the authors use only one equation for biomass estimation for the two clones? Please clarify.

Author answers: The methodology for determining the amount of biomass for the two clones is extensive and laborious and is presented in detail on lines 218-247. The methodology is common to the two clones, so that the values obtained for the two clones can be compared with each other. In the sense described above, I have added a new sentence on line 218: Methodology for biomass estimation for the two clones was unitary.

 

• Reviewer: Point 3.3. “Soil enrichment”. For a better explanation of this section, it would be useful to include a table with key chemical or physical parameters before and two- years after planting

Author answers: In order for the presented results not to be redundant, and for the content of the paper to be exaggeratedly loaded, we preferred to keep this chapter in its initial form. In this way the discussions on this issue could be extended enough for a good understanding of the problem, without duplicating the results.

 

• Reviewer: Rewrite conclusion 2. You want to say that “Tordis survival rate was 38.4% or 2.7% higher than Inger clone.”

Author answers: Conclusion number 2 was adapted to the requirements of the reviewer keeping only the first part of the growth value.

 

Reviewer 3 Report

The introduction can be enriched with information on substances present or likely to be present in the biomass analyzed. Which can potentially be used in other industries contributing to a more profitable biomass energy process, such an example is presented in the article: 

1. Roman, K.; Barwicki, J.; Hryniewicz, M.; Szadkowska, D.; Szadkowski, J. Production of Electricity and Heat from Biomass Wastes Using a Converted Aircraft Turbine AI-20. Processes 2021, 9, 364. https://doi.org/10.3390/pr9020364

2.Stocker, M.; Biofuels and biomass- to- liquid fuels in biorefinery: Catalytic conversion of lignocellulosic biomass using porous materials, Angewandte Chemie International Edition 2008, Vol. 47, Issues 48, pp. 9200-9211, DOI: https://doi.org/10.1002/anie.200801476

 

Conclusions should be short conclusions presented as a result of the research. They should not include the data contained in the results, but should be a generalization of them - so that they can be applied, for example, to the cultivation of genome-altered trees specifically for energy crops or other species applicable to this industry.  

Author Response

Reviewer 3

1. Reviewer remarks: The introduction can be enriched with information on substances present or likely to be present in the biomass analyzed. Which can potentially be used in other industries contributing to a more profitable biomass energy process, such an example is presented in the article: 

-Roman, K.; Barwicki, J.; Hryniewicz, M.; Szadkowska, D.; Szadkowski, J. Production of Electricity and Heat from Biomass Wastes Using a Converted Aircraft Turbine AI-20. Processes 2021, 9, 364. https://doi.org/10.3390/pr9020364

-Stocker, M.; Biofuels and biomass- to- liquid fuels in biorefinery: Catalytic conversion of lignocellulosic biomass using porous materials, Angewandte Chemie International Edition 2008, Vol. 47, Issues 48, pp. 9200-9211, https://doi.org/10.1002/anie.200801476

Author answers: The two references proposed by the reviewer were inserted in the paper in the References chapter and cited accordingly in the paper. Also, all citations in the paper have been renumbered.

 

2. Conclusions should be short conclusions presented as a result of the research. They should not include the data contained in the results, but should be a generalization of them - so that they can be applied, for example, to the cultivation of genome-altered trees specifically for energy crops or other species applicable to this industry.

Author answers: Conclusions with numbers 4 and 5 have been simplified, eliminating the data resulting from research, and thus increasing their degree of generalization. This took into account the reviewer's proposal.

 

Round 2

Reviewer 1 Report

Unfortunately, the questions from the last review have not been answered completely. Please check them very careful again and complete the missing points. In some cases, the answers are incomplete. If in a review is written, that technical terms are not consistently used in the paper and some examples are given, it’s not sufficient to correct the given examples only! Check the whole manuscript again please. 
Further most important points to revise (the list is not complete – see last review too):
-    Figure 4 is still in the paper, why do you write it has been deleted?
-    I disagree that Fig 2 is required. There is neither a reference in the text to this figure (or did I missed it?) nor any number from this figure is used in the text. It looks like just nice illustration but this is not appropriate for a scientific article.
-    The title still doesn’t fit. There is no information in the paper how such soils are ‘capitalized’ – because here someone could expect economic figures or a least a general statement in this direction. From my point of view the focus is on survival rates and yields for these willow clones on degraded soils.
-    Regarding capitalization: In the introduction the authors cite Swedish references with yields of 30 – 50 t/ha. That’s probably not on dry matter bases as well as not on annual basis. The yields measured by the authors are lower than 1 t/ha. Please check again and make the calculation basis clear. If the yield is that low, why it’s suitable for cropping? Planting willow need high input of labour and costs. Please elaborate this a bit more in the discussion and conclusion. Could this crop be recommended in general or only for phytoremediation?
-    Check the units again, use SI units only (e.g. no kcal)
-    Growing conditions during the trial: It’s a must regarding results for survival rates that the rainfall in the respective growing season is given. The averages of rainfall from the last 5 … 20 years can be used only for a further a statement if the weather conditions during the year of the experiment have been typical for the region.
-    Check the equations again. An equation should always result in the correct unit by itself. If there are e.g. percentage values used in an equation, check if an additional %-multiplicator is required to result in a balanced equation.
-    The use of the terms for the calorific values seems still to be incorrect resp. not according to the way of common use. Let me go back to basics: the definition of HHV(HCV) or GCV is the heat liberated in the combustion of dry material typically with the product water condensed and the condensation energy included. Important for presentation of the result is mainly, if the condensation energy of the water produced by the chemical reaction of the elements is included or not. LHV or LCV / NCV is more complicated in that the material does not have to be dry when it is combusted. Secondly the LHV measurement assumes that the water vapour after combustion is not condensed -so the latent heat of condensation is not realised. The LCV is normally given on basis of a raw material as received – consequently without any drying before. For freshly harvested willow typical moisture contents are in dependence to intermediate storage between 30% and 55%. Please check your equations and results again accordingly. 
-    It’s sometimes unclear or a bit hidden in the text how many samples/repetitions have been used during the measurements. Well, if the authors insist on keeping plots from the statistical analysis in the manuscript, then information about the population of a sample and interdependencies are essential. I would suggest to add a table here, showing the measured values, number of samples/repetitions and the reference to standards used for the measurements.

Author Response

Answers to reviewer 1

We would like to thank the reviewer for the recommendations and observations made to improve the paper. We consider that all these will contribute to raising the scientific level of the paper and to increasing the attractiveness of the paper towards the readers of the journal.

 

• Unfortunately, the questions from the last review have not been answered completely. Please check them very careful again and complete the missing points. In some cases, the answers are incomplete. If in a review is written, that technical terms are not consistently used in the paper and some examples are given, it’s not sufficient to correct the given examples only! Check the whole manuscript again please. Further most important points to revise (the list is not complete – see last review too):
• Author answer: The entire work was carefully checked and the necessary changes were made.
• 
  -   Figure 4 is still in the paper, why do you write it has been deleted?

Author answer: The old Fig 1, Fig 2 and Fig 4 were erased definitively from paper.

-    I disagree that Fig 2 is required. There is neither a reference in the text to this figure (or did I missed it?) nor any number from this figure is used in the text. It looks like just nice illustration but this is not appropriate for a scientific article.

Author answer: As a main recommendation of reviewer, the old Fig 1, Fig 2 and Fig 4 were erased definitively from paper.

-    The title still doesn’t fit. There is no information in the paper how such soils are ‘capitalized’ – because here someone could expect economic figures or a least a general statement in this direction. From my point of view the focus is on survival rates and yields for these willow clones on degraded soils.

 Author answer: Respecting the reviewer's point of view, new title is proposed: Influence of INGER and TORDIS energetic willow clones planted on contaminated soil on the survival rates, yields and calorific value

-    Regarding capitalization: In the introduction the authors cite Swedish references with yields of 30 – 50 t/ha. That’s probably not on dry matter bases as well as not on annual basis. The yields measured by the authors are lower than 1 t/ha. Please check again and make the calculation basis clear. If the yield is that low, why it’s suitable for cropping? Planting willow need high input of labour and costs. Please elaborate this a bit more in the discussion and conclusion. Could this crop be recommended in general or only for phytoremediation?

Author answer: The Swedish reference thought an approximate value at the maturity of the energetic willow, somewhere at 7-10 years old. It was also a value of biomass at 50% moisture content, and in the paper, we referred to dry biomass. Also, another important thing, in the paper we referred to the biomass obtained in the first year of vegetation, respectively the sprouting period of the energetic willow in which the shoots are small and non-vigorous and the amount of biomass is 8-10 times lower than that obtained at maturity. See additional sentences on line 361.

-    Check the units again, use SI units only (e.g. no kcal)

Author answer: Whole paper was checked.  “kcal” was deleted from paper and replaced by “kJ”. The initial values have been transformed accordingly.

-    Growing conditions during the trial: It’s a must regarding results for survival rates that the rainfall in the respective growing season is given. The averages of rainfall from the last 5 … 20 years can be used only for a further a statement if the weather conditions during the year of the experiment have been typical for the region.

 Author answer: A short sentence referring to the meteorological characteristics for the analysed period, respectively 2014-2015, was completed in the paper.

-    Check the equations again. An equation should always result in the correct unit by itself. If there are e.g. percentage values used in an equation, check if an additional %-multiplicator is required to result in a balanced equation.

Author answer: The nine calculation relations in the paper were verified.

-    The use of the terms for the calorific values seems still to be incorrect resp. not according to the way of common use. Let me go back to basics: the definition of HHV(HCV) or GCV is the heat liberated in the combustion of dry material typically with the product water condensed and the condensation energy included. Important for presentation of the result is mainly, if the condensation energy of the water produced by the chemical reaction of the elements is included or not. LHV or LCV / NCV is more complicated in that the material does not have to be dry when it is combusted. Secondly the LHV measurement assumes that the water vapour after combustion is not condensed -so the latent heat of condensation is not realised. The LCV is normally given on basis of a raw material as received – consequently without any drying before. For freshly harvested willow typical moisture contents are in dependence to intermediate storage between 30% and 55%. Please check your equations and results again accordingly. 

Author answer: Necessary adding was put on line 278. This addition was based on the fact that although the wood material was dried in the oven, both HCV and LCV were obtained in the experiments. This was also determined by the fact that the working procedure at the calorimetric installation provides for the introduction of a quantity of 3 ml of distilled water for the absorption of some acids during combustion. We considered that briquettes and pellets obtained from energetic willow are delivered wrapped at a constant moisture content of 6-8%.

- It’s sometimes unclear or a bit hidden in the text how many samples/repetitions have been used during the measurements. Well, if the authors insist on keeping plots from the statistical analysis in the manuscript, then information about the population of a sample and interdependencies are essential. I would suggest to add a table here, showing the measured values, number of samples/repetitions and the reference to standards used for the measurements.

 

Author answer: The necessary elements have been added in the chapter on methodology and materials, for each method/test.

Reviewer 2 Report

Authors have taken into account most of my suggestion/correction. I have only some minor suggestion/corrections.

I insist again that figure 1 is totally unnecessary. If you add After (9700 TWh “and natural gas (6500 Twh??)) you already have all the information of the figure in the paragraph.

The same consideration for Figure 2. Moreover, this figure is not currently cited in the manuscript. You can explain the expected role for biomass into the future by saying (i.e. “Biomass is expected to contribute by 9% of the total global renewable energy generation for 2025 [5]” or even some more data and remove the figure. Also, the figure caption it is not correct. It should be “Global renewable energy generation...???”

The same consideration for Figure 2. Moreover, this figure is not currently cited in the manuscript. You can explain the expected role for biomass into the future by saying (i.e. “Biomass is expected to contribute by 9% of the total global renewable energy generation for 2025 [5]” or even some more data and remove the figure. Also, the figure caption it is not correct. It should be “Global renewable energy generation...???”

You insist presenting these figures (help in contextualization although redundant) but do not present a table with the soils parameters before/after planting on contaminated soils and not contaminated soils. It would be useful for result presentation and discussion

Also, for a comparison purposes (they use Inger clone), you can also use this reference for North Spain: Castaño-Díaz et al. 2018. Willow Short Rotation Coppice Trial in a Former Mining Area in Northern Spain: Effects of Clone, Fertilization and Planting Density on Yield after Five Years. Forests 2018, 9, 154; doi:10.3390/f9030154

Line 133: Please replace “paper” with “research”

 Line 239: Please change position of “Db- density of twig bark, in kg/m3”. Put it first.

Line 248: please insert “dry basis” after biomass

Author Response

Answers to reviewer 2

We would like to thank the reviewer for the recommendations and observations made to improve the paper. We also consider that all these will contribute to raising the scientific level of the paper and to increasing the attractiveness of the paper towards the readers of the journal.

 

• Reviewer: I insist again that figure 1 is totally unnecessary. If you add After (9700 TWh “and natural gas (6500 Twh??)) you already have all the information of the figure in the paragraph. The same consideration for Figure 2. Moreover, this figure is not currently cited in the manuscript. You can explain the expected role for biomass into the future by saying (i.e. “Biomass is expected to contribute by 9% of the total global renewable energy generation for 2025 [5]” or even some more data and remove the figure. Also, the figure caption it is not correct. It should be “Global renewable energy generation...???”

Author answer: At the recommendation of the reviewers, the three figures that supported the introductory part of the paper (Fig 1, Fig 2 and Fig 4) were permanently deleted from the paper. Also, that paragraph was completed with the proposal sentences.

• You insist presenting these figures (help in contextualization although redundant) but do not present a table with the soils parameters before/after planting on contaminated soils and not contaminated soils. It would be useful for result presentation and discussion Also, for a comparison purposes (they use Inger clone), you can also use this reference for North Spain: Castaño-Díaz et al. 2018. Willow Short Rotation Coppice Trial in a Former Mining Area in Northern Spain: Effects of Clone, Fertilization and Planting Density on Yield after Five Years. Forests 2018, 9, 154; doi:10.3390/f9030154.

Authors: A table with features of soil before and after two year of planting was introduced.

• Line 133: Please replace “paper” with “research”.

Authors: This change was made.

• Line 239: Please change position of “Db- density of twig bark, in kg/m3”. Put it first.

Authors: This expression position was changed.

• Line 248: please insert “dry basis” after biomass.

Authors: This expression was introduced.

Authors