Assessing Nitrogen Cycling in Corncob Biochar Amended Soil Columns for Application in Agricultural Treatment Systems

Round 1

Reviewer 1 Report

Manuscript: Assessment of corncob biochar for amendment in agricultural treatment systems.

Manuscript ID: agronomy-840744

The manuscript entitled “Assessment of corncob biochar for amendment in agricultural treatment systems” is interesting. Although the methods and type of study are not necessarily highly novel, the authors give a reasonable justification for the requirement for this type of study on the soils investigated here and would warrant publication. However, I have a concern about the structure of manuscript particularly for material/method, and result section. Overall, the paper is well presented, adheres to the scientific method, but contains several important deficiencies. My comments are given as under.

Abstract

Need more experimental information for clarification. Treatments description and objectives are not clear in the abstract. Subscript needs to be fixed throughout manuscript.

Introduction

This section provides a good justification for the study. References missing and subscript need to be fixed. Language needs improvement. There are some grammatical and typo mistakes throughout the manuscript.

Line 36: reference missing

Line 77-80: this is part of material method

Materials and Methods:

Not clear, some of the results were presented in the material which should be in the result section.

• Line 83-86 section 2.1 should be in the result part not material method.
• I suggest splitting section 2.1 into soil type/soil classification and biochar processing and characteristics.
• Line 103: was gravels acid washed?
• Line 102-109: methodology not clear and is hard to follow. Need to be rewritten in clear words such as height of column, soil wt and then mixing of treatment at surface or at depth. It will be good to have Table s1 and s2 in text for explanation. Information missing about the water application ie how much and what rainfall.
• Line 165: looks like 50 degree is bit higher, why not air dried.
• Line 166: pH method reference missing
• Line 175: Filtrate stored at what temperature.Results
• Many a statement in the results section are confusing and not clear such as page 236.
•  

• Line 193: soil and biochar basic characterisation missing.
• Line 217-218, 225-226, 241-243: very hard to follow cumulative TN. Need a clarification.
• Line 243: TAN need explanation
• Line 240: mass balance approach needs to discuss in the data analysis.
• Line 253-259: hard to follow results as author saying that NO3-N increased significantly for BC2 compared to other treatments but Figure 5A indicated NO3-N in BC2 is lower than control, BC1 and BC3. Need a clarification.
• Line 265: following application of ?
• Line 265: Please explain XPS
• Line 275: Keep consistency with significant figures.
• Line 265-270: Need a bit more explanation for further clarification. Looks like lot of information in Table2. Need to review paper thoroughly for any missing information before resubmission.
• Line 275: table 2 need explanation for BC, ORG etc in the bottom as note.

Discussion

Discussion should be under same section as results were described to provide a better understanding. Explaining all together make it bit more confusing to understand and is hard to follow.

• Mentioned about C/N ratio but there is no data to support it.
• Similarly, CEC values of BC need to support the retention of TN
• Line 333: It will be good to have fig S1 in text.

Please note I have not checked text reference against the reference list. Check whether the format of all references is according to the journal format.

I would suggest that authors need to spend some time on improving the readability of the manuscript at this stage.

However, this manuscript needs further work before it is ready for submission and a careful check particularly in material and method. Furthermore, I found that the sometime missing information’s and other issues in the manuscript such as significant figures and subscripts within the text needs to be fixed before resubmission.

Author Response

Dear Reviewer,

Thank you for taking the time to review our manuscript. We have made changes in regard to yours and other reviewers comments and hope that they have enhanced the manuscript. Below you will find responses to your individual comments regarding the manuscript.

Sincerely,

Joseph Sanford, PhD

Comments and Suggestions for Authors

The manuscript entitled “Assessment of corncob biochar for amendment in agricultural treatment systems” is interesting. Although the methods and type of study are not necessarily highly novel, the authors give a reasonable justification for the requirement for this type of study on the soils investigated here and would warrant publication. However, I have a concern about the structure of manuscript particularly for material/method, and result section. Overall, the paper is well presented, adheres to the scientific method, but contains several important deficiencies. My comments are given as under.

Thank you for your comments. We agree that this is not necessarily high novelty research as there are multiple papers looking at biochar N dynamics. However, we do believe it is important information regarding the impacts of repeated application of N rich runoff, which has not been studied in depth, thus believe it is important for publication. We are glad our justification warranted publication. We have carefully gone through the manuscript as suggested and made edits. Below you will see additional responses to individual comments.

Abstract:

Need more experimental information for clarification. Treatments description and objectives are not clear in the abstract. Subscript needs to be fixed throughout manuscript.

Thank you for your comment regarding the abstract. We have corrected the subscript issues here and throughout the document. We additionally added text to the abstract to better define the objectives of the study for readers.

Introduction:

This section provides a good justification for the study. References missing and subscript need to be fixed. Language needs improvement. There are some grammatical and typo mistakes throughout the manuscript.

Thank you for your comment and are glad the introduction provides justification for the study. We have reviewed the manuscript introduction and corrected missing references and subscripts. We hope changes to the intro have addressed the grammatical and typo errors from the pervious version of the paper.

Line 35-36 - Confuse because N leaching is an emission to the water. Please improve the sentence.

You are correct that leaching is an emission as well. We have edited to sentient to ready “…cropping system soil can reduce nitrogen (N) leaching [4–12] and gaseous emissions..” We hope this change has improved the sentence

Line 36: reference missing

Thank you for catching this error. We have updated the sentence with the references.

Line 77-80: this is part of material method

Thank you for your comment. We agree that this could be moved to the material and methods and have done so. Please see L86-90 for changes made regarding this comment.  

Materials and Methods:

Not clear, some of the results were presented in the material which should be in the result section.

Thank you for your comment regarding some results being presented in the methods section. However, we believe that this is the proper place for this information as it provides baseline results regarding the soil and biochar characteristics. Since they were not influential on the overall results, but needed to be specified for reproducibility, we have left them in the methods section.

Line 83-86 section 2.1 should be in the result part not material method.

Thank you and please reference previous comment response.

I suggest splitting section 2.1 into soil type/soil classification and biochar processing and characteristics.

Thank you for the comment. We have split them into two sections.

Line 103: was gravels acid washed?

We appreciate you catching this detail. The gravel was acid washed prior to experiment and has now been noted.

Line 102-109: methodology not clear and is hard to follow. Need to be rewritten in clear words such as height of column, soil wt and then mixing of treatment at surface or at depth. It will be good to have Table s1 and s2 in text for explanation. Information missing about the water application ie how much and what rainfall.

We apologize that the methodology in this section was difficult to follow in the pervious version. We have made substantial changes to this section to improve readability and hope that it is now easier to follow. We have added information regarding the column height, soil weight, and how biochar was mixed into the text and hope that this aids in the readability and reproducibility of this section. We also agree that moving Table S2 into the main manuscript would be highly beneficial to readers and have not placed it in this section of the text. Regarding rainfall, each weeks application was 150mL which was equivalent to roughly 13.2cm depth, which is now presented later in the section (Line 150).

Line 165: looks like 50 degree is bit higher, why not air dried.

Thank you for your comment. We apologize that we did not include a source for method regarding drying. For soil analysis we followed procedures outlines in “Methods of soil Analysis”, which states for inorganic nitrogen analysis soils be dried at 50C for 48 hours. This is why this temperature was used. We have added the reference method to justify this temperature.

Line 166: pH method reference missing

Thank you for your comment. We have referenced the studied used for pH measurement method.

Line 175: Filtrate stored at what temperature.

Thank you for the comment. We have added the temperature information regarding storage.

Results:

Many a statement in the results section are confusing and not clear such as page 236.

 We apologize for the issues regarding readability of the results section. We have made numerous edits to this section to improve the clarity and readability of it. Hopefully these changes have enhanced the manuscript and please let us know if additional changes are needed.

Line 193: soil and biochar basic characterization missing.

Thank you for your comment. As previously discussed in above comments we feel that the soil and biochar characterization is more appropriate for the methods section, as it is not the main objective of the study, thus we have left it in that location now.

Line 217-218, 225-226, 241-243: very hard to follow cumulative TN. Need a clarification.

We apologize for the confusion regarding the cumulative TN. We have gone through the entire manuscript and tried to address this issue to better clarify the results. Additionally, we have made alterations to the figure captions referenced in your comment and hope they clarify the cumulative TN. If there are additional issue we will try and address them if there is still need for more clarification.

Line 243: TAN need explanation

Thank you for your comment. TAN is defined upon first use in the methods section (L156) in the revised document as total ammoniacal nitrogen.

Line 240: mass balance approach needs to discuss in the data analysis.

Thank you for catching this error. We agree that this should have been discussed previously. To address your comment, we have added in how N2 was estimated in section 2.3 to add clarification regarding this. Additionally, in each mass balance figure (Figure 2 and 4) we have changed the note to better describe how the mass balance approach was taken to determine N2. We hope these changes have clarified the figures.

Line 253-259: hard to follow results as author saying that NO3-N increased significantly for BC2 compared to other treatments but Figure 5A indicated NO3-N in BC2 is lower than control, BC1 and BC3. Need a clarification.

We appreciate your comment regarding this section. We agree that this may not have been well presented. Treatment BC2 REDUCED the mass of NO3 leaching, due to an increase in soil N retention. Figure 5-A is presenting the mass of N leached, thus treatment BC2 is lower than other treatments. We hope changes to the text and figure caption have clarified this section.

Line 265: following application of ?

We apologize for the confusion. There was a change in FTIR spectra for all applications of N. This has been clarified in the text.

Line 265: Please explain XPS

Thank you for your comment. XPS is defined upon first use in the methods section (L206) in the revised document as X-ray photo-electron spectroscopy.

Line 275: Keep consistency with significant figures.

Thank you for catching this issue with Table 2. We have carefully reviewed the table and made sure significant figures are consistent.

Line 265-270: Need a bit more explanation for further clarification. Looks like lot of information in Table2. Need to review paper thoroughly for any missing information before resubmission.

Thank you for this comment. We agree that this section does not have a lot of discussion regarding all the data in this section. However, we decided to present the general change in biochar surface chemistry in this table. We later have a more in depth discussion regarding the impacts of these changes in the discussion section that we hope address this issue. If further changes are needed we will try and alter the formatting of the paper.

Line 275: table 2 need explanation for BC, ORG etc in the bottom as note.

Thank you for the suggestion. Instead of a bottom note we have altered the column headings to aid in better explaining what the data is. We hope these changes have clarified the table. Please let us know if additional changes may be needed.

Discussion:

Discussion should be under same section as results were described to provide a better understanding. Explaining all together make it bit more confusing to understand and is hard to follow.

Thank you for the comment. We have tried many ways to represent the data including the layout you have suggested above but the mass amount of data makes it very difficult to present clearly. We have divided the section into Results and Discussion in an attempt to clarify. This identifies each treatment application type then the discussion integrates them all to draw more conclusions. We have tried other ways that we found less effective. However, if you find this clarification to not be helpful we can reorganize.

Mentioned about C/N ratio but there is no data to support it.

Thank you for this comment. The discussion surrounding the C/N ratio was not based on data but a hypothesis regarding why in the ORG-N high application columns there was no evidence of NH4 present in the leachate, which suggested mineralization was impeded. We have clarified this statement and hope that it now highlights that this is simple a hypothesis.

Similarly, CEC values of BC need to support the retention of TN

Thank you for your comment. In this statement we were referencing for discussion purposes what past studies had theorized. In this study, since NH4 did not appear to be the driving mechanisms for enhanced N retention, it does not appear that CEC was a driving force for improved leaching characteristics. We hope changes help clarify the statement.

Line 333: It will be good to have fig S1 in text.

Thank you for your comment. We agree that figure S1 would be beneficial to have in the main text and have moved it into it.

Please note I have not checked text reference against the reference list. Check whether the format of all references is according to the journal format.

Thank you for your comment. We have used Mendeley with the Agronomy journal plug in to ensure we are following the correct formatting. We have additionally reviewed to ensure they are following formatting specifications of the journal.

I would suggest that authors need to spend some time on improving the readability of the manuscript at this stage. However, this manuscript needs further work before it is ready for submission and a careful check particularly in material and method. Furthermore, I found that the sometime missing information’s and other issues in the manuscript such as significant figures and subscripts within the text needs to be fixed before resubmission.

Thank you for your comment. We hope that the changes to the manuscript in this revised document improves the readability of the manuscript. We have gone through carefully and attempted to address all concerns mentioned and hope they have enhanced the manuscript to your standard.

Reviewer 2 Report

Comments on manuscript agronomy- 840744:

This manuscript aims to evaluate the impacts of biochar and nitrogen applications on N flows and losses. I have carefully read the manuscript and the aims of the study in not new. Anyway, a strong revision will be needed on this manuscript. Please find below my comments:

Line 26 – The keywords “nitrogen leaching” and “nitrate leaching” are quite similar. Replace nitrogen leaching by another keyword.

Line 35-36 - Confuse because N leaching is an emission to the water. Please improve the sentence.

Line 83 – Please add more information about the location (name, coordinates). Add more details about the soil characteristics (WRB soil classification, OM, …).

Line 101 – Climate conditions of the experiments like soil temperatures and humidity? The duration of each experiment event? Please add to the manuscript.

Line 155-158 - Authors referred that were measured N2O, CO2 and CH4 concentrations and describe the equipment and methods used. However, I missed the CO2 and CH4 data in Results section. These data could help to explain your results. Please add to the manuscript.

Line 193 – The presentation of the results is a bit confuse for me. Please consider the following subsections: soil N dynamics, gas emissions, nitrate leaching, N balance.

Line 206 – Please clarify the units of the Fig. 1. mg N per kg of dry soil, mg N per kg of wet soil? Please add to the manuscript.

Line 211 – Please improve the clarity of the Fig. 2B. The value 8.7% appear in an incorrect position.

Line 213 - Please clarify the units of the Table 1. mg N per kg of dry soil, mg N per kg of wet soil? How do you explain the negative values of organic and inorganic N and below of your detection limits given in Table S3? Are you sure about your data? Please carefully see your raw data. Please add to the manuscript.

Line 224, 252 – “ammonium(nitrate) nitrogen application” does not sound well. The sections 3.1-3.3 could be presented together as soil N dynamics.

Line 260 – Please clarify the units of the Fig. 5A-B (also Fig. S2). mg N per kg of dry soil, mg N per kg of wet soil? Please add to the manuscript.

Line 272 – Missed the comparison of means among treatments presented in Table 2. Please add letters for a proper comparison.

Line 193-276 – The structure of this manuscript needs a strong revision. Missed data apparently collected during the experiments, such as NH3, N2O, CO2 and CH4 fluxes, nitrate leaching, and a nitrogen balance for each treatment. Please add to the manuscript.

Also, gas fluxes and nitrate leaching events were not presented in Figs or Tables (including supplementary material). Please add to the manuscript.

Line 276-384 - Authors should focus in the aim of the study, comparing the treatments evaluated, but such results are presented and discussed very briefly.

Authors referred that mineralization and nitrification could explain the results of the study. Please estimate the mineralization/immobilization and nitrification rates for these experiments, using the soil mineral N dynamics, and add to the manuscript.

Authors referred that soil pH is an important parameter to explain the results of the experiment. Please add the values of soil pH at the beginning and at the end of each experiment and for each treatment. Please add to the manuscript.

The treatments C1, C2, C3 and C3 are presented and discussed very briefly. A deeper discussion is needed.

This experiment was made under laboratory conditions and during a short period, being different of field conditions. A sentence regarding this point should be added to the discussion section.

Author Response

Dear reviewer,

Thank you for taking the time to review our manuscript for publication in Agronomy . We have reviewed your comments and made changes to the manuscript to address yours and the other reviewers concerns. We agree that a strong revision was needed before publication and hope that the changes to the manuscript have enhanced the paper. We appreciate you pointing out some of the issues regarding the figures, as we agree some of them were a little difficult to understand in terms of units. We hope that by making clarifications in the text and in figure and table captions these are now easier to understand and address a few of your concerns. Below you will find individual responses to your comments. We hope that the new revision has enhanced the manuscript, but please let us know of any further concerns so that we may address them to provide further clarification on issues.

Sincerely,

Joseph R Sanford, PhD

Comments and Suggestions for Authors

This manuscript aims to evaluate the impacts of biochar and nitrogen applications on N flows and losses. I have carefully read the manuscript and the aims of the study in not new. Anyway, a strong revision will be needed on this manuscript. Please find below my comments:

Line 26 – The keywords “nitrogen leaching” and “nitrate leaching” are quite similar. Replace nitrogen leaching by another keyword.

Thank you for the comment. We have removed nitrogen leaching as suggested.

Line 35-36 - Confuse because N leaching is an emission to the water. Please improve the sentence.

You are correct that leaching is an emission as well. We have edited to sentient to ready “…cropping system soil can reduce nitrogen (N) leaching [4–12] and gaseous emissions...” We hope this change has improved the sentence

Line 83 – Please add more information about the location (name, coordinates). Add more details about the soil characteristics (WRB soil classification, OM, …).

Thank you for the comment. We have added some clarification regarding the soil. The soil used in the experiment was an engineered sandy loam. We have added some geographical information from where it was collected form. Because it is an engineered soil there is no WRB class, but we have classified based on % and added USDA reference method. Soil data that we have obtained includes pH, N, P, and K. If more analysis is needed we can evaluate if we have the resources to do so.  

Line 101 – Climate conditions of the experiments like soil temperatures and humidity? The duration of each experiment event? Please add to the manuscript.

Thank you for your observation. We agree that climate data regarding the study was missing from the manuscript. We have added the climate conditions of the room to the text. Additional we have clarified the experiment duration later in the text. Please see L152-154 of all markup version.

Line 155-158 - Authors referred that were measured N2O, CO2 and CH4 concentrations and describe the equipment and methods used. However, I missed the CO2 and CH4 data in Results section. These data could help to explain your results. Please add to the manuscript.

Thank you for the comment regarding gaseous emissions measured. Our main focus was on the N2O emissions. The statement here was provided by the lab that ran this analysis for use. Since we solely used N2O for our analysis purposes, we have removed the reference to the CH4 and CO2 detection sensors to remove any confusion regarding those emissions.

Line 193 – The presentation of the results is a bit confuse for me. Please consider the following subsections: soil N dynamics, gas emissions, nitrate leaching, N balance.

Thank you for the comment. We have tried many ways to represent the data including the layout you have suggested above but the mass amount of data makes it very difficult to present clearly. We have divided the section into Results and Discussion in an attempt to clarify. This identifies each treatment application type then the discussion integrates them all to draw more conclusions. We have tried other ways that we found less effective. However, if you find this clarification to not be helpful we can reorganize.

 Line 206 – Please clarify the units of the Fig. 1. mg N per kg of dry soil, mg N per kg of wet soil? Please add to the manuscript.

Thank you for your comment regarding the units in the figure. We have updated the figure caption to address your concern. The units used in the figure is the cumulative mass of N that was applied and leached through the columns, thus is in just mg N and not mg per kg soil. Additionally, we have added clarification of the bars used in this figure in relation to influent TN and effluent, and hope they have improved the understanding of the figure.

 Line 211 – Please improve the clarity of the Fig. 2B. The value 8.7% appear in an incorrect position.

Thank you for catching this issue. We have updated the figure.

Line 213 - Please clarify the units of the Table 1. mg N per kg of dry soil, mg N per kg of wet soil? How do you explain the negative values of organic and inorganic N and below of your detection limits given in Table S3? Are you sure about your data? Please carefully see your raw data. Please add to the manuscript.

Thank you for your comment and we are sorry that the data was not clearly defined. The values in this table represent the change in cumulative soil N content in mg N total (so not in mg/kg). There are negative values, because over the course of the study period some of the soil N in a specific form was lost either through conversion or leaching, thus the change was negative as the initial soil had a higher N content than the final soil. We have added a footer to the table to clarify this and hopefully address your concern regarding the negative values.

 Line 224, 252 – “ammonium(nitrate) nitrogen application” does not sound well. The sections 3.1-3.3 could be presented together as soil N dynamics.

Thank you for your comment. As discussed previously we wanted to present each of the individual nitrogen applications separately and then discuss the soil N dynamics in the discussion section. Thus we have left the general format as previously stated when addressing previous comment. We have changed the headings in the results to define the treatment groups being discussed in that results section and hope this makes following the results easier.  However, as previously mentioned, if you find this clarification to not be helpful we can reorganize.

Line 260 – Please clarify the units of the Fig. 5A-B (also Fig. S2). mg N per kg of dry soil, mg N per kg of wet soil? Please add to the manuscript.

Thank you for your comment again. As mentioned in response to your pervious comment we have updated the figure caption to address your concern. The units used in the figure is the cumulative mass of N that was applied and leached through the columns, thus is in just mg N and not mg per kg soil. Additionally, we have added clarification of the bars used in this figure in relation to influent TN and effluent, and hope they have improved the understanding of the figure.

Line 272 – Missed the comparison of means among treatments presented in Table 2. Please add letters for a proper comparison.

Thank you for your comment. We have added asterisk to denote significant differences between initial and final biochar composition for each treatment group. We additionally realized we did not include the initial biochar standard deviation values and have added that to the table.

Line 193-276 – The structure of this manuscript needs a strong revision. Missed data apparently collected during the experiments, such as NH3, N2O, CO2 and CH4 fluxes, nitrate leaching, and a nitrogen balance for each treatment. Please add to the manuscript. Also, gas fluxes and nitrate leaching events were not presented in Figs or Tables (including supplementary material). Please add to the manuscript.

Thank you for your comment regarding data presented in the manuscript. We have presented nitrate leaching data in Figures 1, 3, and 5. The green in the bar graphs represent the cumulative mass of nitrate lost from the columns as leachate. We hope we have clarified these figures as you had previously pointed out. Additional, we updated Figuse S1 in the supplemental to present the cumulative NO3 leaching and have added references to these figures in the text. We think that the changes in the text and figure captions may have clarified the issue. As previously discussed in another comment, we have removed the text regarding CO2 and CH4 fluxes from the methods to avoid confusion. The losses from the columns as NH3 and N2O were very small portions of the losses form the columns, as outlined in figures 2 and 4, thus we decided not to present the fluxes as we did not want to deviate from our main message regarding nitrogen, specifically nitrate, leaching. We hope this is satisfactory, but if needed we can add a supplemental figure regarding the fluxes.

 Line 276-384 - Authors should focus in the aim of the study, comparing the treatments evaluated, but such results are presented and discussed very briefly.

Thank you for your comment regarding the discussion section of the paper. We have made changes to the discussion section to enhance the manuscript to focus more on comparing treatments. We hope these changes are satisfactory but can make additional changes if needed. We believe it was important to make comparison of our data to past studies as well, and those parts remained in the discussion section.

Authors referred that mineralization and nitrification could explain the results of the study. Please estimate the mineralization/immobilization and nitrification rates for these experiments, using the soil mineral N dynamics, and add to the manuscript.

Thank you for the comment regarding calculating mineralization and nitrification rates. However, while we agree that these would be interesting to estimate, we are missing some critical components to make accurate estimations. Thus have decided to leave this out of the manuscript.

Authors referred that soil pH is an important parameter to explain the results of the experiment. Please add the values of soil pH at the beginning and at the end of each experiment and for each treatment. Please add to the manuscript.

Thank you for your comment. We agree that this information should be included. We have added a new supplemental table (Table S5) that contains the soil pH data requested.

The treatments C1, C2, C3 and C3 are presented and discussed very briefly. A deeper discussion is needed.

We appreciate the comment regarding the treatments. We have included a discussion regarding the different treatments. We note that BC1 did not results in significant difference from the control soils, while BC2 and BC3 did. It was hypothesized that this was due to retention time and that BC 2 may have bound NO3 due to additional of functional groups present on the biochar. We also noted that while change in functional groups appears to occur in the soil, leading to enhanced NO3 binding, it did not appear that pre oxidation treatments were a substitute for soil aging. We hope these comparisons are now clear in the discussion section regarding the nitrate application and biochar treatments.  

This experiment was made under laboratory conditions and during a short period, being different of field conditions. A sentence regarding this point should be added to the discussion section.

We agree that this is an important thing that should be noted. We have added in the conclusion section following discussion of performance results that it is important to note that this was a study done under controlled conditions in the laboratory, and that field studies are necessary in the future.

Round 2

Reviewer 2 Report

My concerns about the last version of the present manuscript were explained by the authors and/or included in the revised manuscript.