Biochar-Based Fertilizer Enhances the Production Capacity and Economic Benefit of Open-Field Eggplant in the Karst Region of Southwest China

Round 1

Reviewer 1 Report

This manuscript deals with the ameliorative roles of different application rates of biochar-based fertilizer on the fresh yield, quality, fertilizer utilization, and economic benefits of fresh eggplant in the karst region of Southwest China. The work is carefully conducted and provides significant findings regarding the biological and economic benefits of biochar-based fertilizer. The overall contents of the manuscript are well written and structured. Only I found some improvements which should be included as minor revisions. My specific comments are:

1.      In the last paragraph of the introduction: avoid using too much “In this study”.

2.      Avoid using impersonal terms such as we, our, us.

3.      The manuscript should be carefully checked for syntax and grammar errors.

4.      Section 2.3: Rewrite the experimental design. The current form is hard to understand and lacks several intermediate steps.

5.      Section 2.4: Provide reference for all calculations and models.

6.      Figures: Please rewrite the axial title unit scales of all figures. The authors used “X” and not the proper multiplication sign “×”.

7.      Add alpha or p before 0.05.

8.      Some abbreviations are missing their full explanations in several sections.

9.      References: some outdated references can be replaced by the latest ones.

Author Response

First, thank you very much for taking your time to review this manuscript. Your comments make this paper completer and more outstanding! I really appreciate all your comments and suggestions! Please find my itemized responses in below and my revisions/corrections in the re-submitted files. I had highlighted the revisions in red. Thanks again!

1. In the last paragraph of the introduction: avoid using too much “In this study”.

Thank you very much for your suggestion. We have revised the last paragraph of the introduction.

2. Avoid using impersonal terms such as we, our, us.

Thank you very much for your suggestion. We have checked the impersonal terms of the manuscript, and revised them.

3. The manuscript should be carefully checked for syntax and grammar errors.

Thank you very much for your suggestion. We have invited a native English speaker to revise the syntax and grammar errors in the manuscript.

4. Section 2.3: Rewrite the experimental design. The current form is hard to understand and lacks several intermediate steps.

Thank you very much for your suggestion. We have rewritten the the experimental design, and added some several intermediate steps

5. Section 2.4: Provide reference for all calculations and models.

Thank you very much for your suggestion. We have added the reference for all calculations and models.

6. Figures: Please rewrite the axial title unit scales of all figures. The authors used “X” and not the proper multiplication sign “×”.

Thank you very much for your suggestion. We have remade all the figures, and used the proper multiplication sign.

7. Add alpha or p before 0.05.

Thank you very much for your suggestion. We have added the alpha before 0.05 of the manuscript..

8. Some abbreviations are missing their full explanations in several sections.

Thank you very much for your suggestion. We have checked the manuscript and added the full explanations of abbreviations.

9. References: some outdated references can be replaced by the latest ones.

Thank you very much for your suggestion. We have replaced the outdated references with the latest ones.

Author Response File: Author Response.doc

Reviewer 2 Report

Please open the attached file where the comments and inquiries need to reply.

Comments for author File: Comments.docx

Author Response

First, thank you very much for taking your time to review this manuscript. Your comments make this paper completer and more outstanding! I really appreciate all your comments and suggestions! Please find my itemized responses in below and my revisions/corrections in the re-submitted files. I had highlighted the revisions in red. Thanks again!

1. Important notes: The author should add a line number to facilitate the revision process.

Thank you very much for your suggestion. We have added a line number to facilitate the revision in the later stage.

2. Keywords should be in alphabetical order and should not duplicate words appearing in the title of the manuscript.

Thank you very much for your suggestion. We have revised the Keywords of the manuscript.

3. Change the color of the number of references in texts from red to black throughout the manuscript

Thank you very much for your suggestion. We have changed the color of the number of references in texts from red to black throughout the manuscript.

4. The authors should add the chemical analysis of used biochars in supplementary data. (if have been done to understand the amount of nutrient released from used biochars.

Thank you very much for your suggestion. The nutrient content of biochar has been included in the manuscript. In addition, we have added the characteristic structure of the distiller's grains biochar.

5. In the section of statistical analysis, the authors should clarify the type of Experimental design (RCBD, RCD) and kind of ANOVA (One-Way or Two-Way) and how many biological samples have been taken from soil or plants during experimentations. Also, the bars above the column indicate standard Errors or Standard Deviations.

Thank you very much for your suggestion. We have added the type of Experimental design, kind of ANOVA and number of the samples have been taken from soil or plants during experimentations in the section of statistical analysis. Meanwhile, we also have added the data description to the table title.

6. Please check the English grammar of the manuscript.

Thank you very much for your suggestion. We have invited a native English speaker to revise the syntax and grammar errors in the manuscript.

7. Abstract:

- Add letter “s” for the word “rate” in the following statement “different application rate” to become “different application rates”

- Change article “the ” to “their ” in the following statement “which will help farmers increase the income”

- Add the article “the “front of the “karst regions” to become “in the karst regions of Southwest”

Thank you very much for your suggestion. We have revised the errors in the section of Abstract.

8. Introduction

- The following both statement are too long,  simplify them : “At the same time, the soil in karst area is easily affected by human activities and natural environment, so that the agricultural production in karst areas is restricted to a great extent [3-4]. Biochar is prepared by pyrolysis of biomass materials under low oxygen or hypoxia conditions. Because of its large specific surface area and rich pore structure, biochar could absorb and hold nitrogen and phosphorus nutrients, and reduce nutrient loss in the soil [5-6]. 

- Remove the letter “a” and add letter “S to word topic” from the following statement “development and application of new high-efficiency fertilizers have become a hot topic in” to become “of new high-efficiency fertilizers have become hot topics in”

- Change the following statement “As a new type of environmental protection fertilizer, biochar-based fertilizer (BF) has been widely concerned in the field of agriculture and environmental protection in recent years [15-16]” To “Biochar-based fertiliser (BF) has received a lot of attention recently in the fields of agriculture and environmental protection as a new type of environmental protection fertilizer [15-16].”

Change the word “carried at “ to “carried out at” in the following statement “a two-year field experiment was carried to evaluate”

Thank you very much for your suggestion. We have simplified some sentences and revised the errors n the section of Introduction.

9. Material and methods

Remove the extra full stop in the following statement “combined with ammonium fluoride and determined by molybdenum antimony anti colorimetry..”

Thank you very much for your suggestion. We have revised the errors n the section of Material and Methods.

 

Author Response File: Author Response.doc

Reviewer 3 Report

The authors attempted to evaluate the impacts of biochar-based fertilizer on the production and economic benefit of eggplants in the Karst region of southwest China. Although the topic is not new and has been severally investigated, it could serve as an incremental knowledge for the use of biochar in agriculture. However, the experiment has major flaws that may not make it suitable for publication in its present form.

 The major shortcoming of the manuscript is the methodology, as highlighted below:

Methods used was not clearly presented and can in no way be used for reference for any future study, especially the production of the BF and its application rate.

Adequate methods for the production of biochar and its detailed characterization are required for biochar studies, so as to fully understand the impact of these conditions on the effect of biochar in the soil system.

Moreover, the treatment pattern used makes it even difficult to actually judge the effects observed and reported. For example, In Table 1, organic fertilizer was applied in the TFP, as well as inorganic fertilizer. This was not stated in the methods. Why was organic fertilizer used and what was the source? Why was organic fertilizer applied in the biochar amended soil, bearing in mind that biochar is an organic amendment?

What are the properties of the organic amendment? Moreover, the organic amendment and its nutrient composition could also influence and mask the effect of biochar in BF. Therefore, the effects of biochar reported in this study is not reliable and cannot be convincingly concluded.

Combining the complete dose of inorganic fertilizer used in TFP gives 3000 kg/ha (Table 1). This rate is unreasonably high and is impractical for any agricultural production, aside the fact that 1500 kg/ha of organic fertilizer was also applied in this same treatment, but no source of the organic fertilizer was mentioned in the materials and methods section.

The rational behind the different BF doses remain unclear. As it is now, it is not clear if the different rates were based on different fertilizer rates along with biochar, or different biochar rates along with inorganic fertilization.

Plant sampling method was not explained.

Moreover, there was no basic soil analysis after harvest in the two seasons to show the effect of BF on soil properties and how these changes in soil properties may have affected the yield of the eggplants, and if biochar was helpful in improving the fertility of the soils. Note that the impact of biochar on crop productivity is tied to the effect of biochar on the nutritional composition of the soil.

The discussion needs additional re-writing while removing unnecessary information presented, especially, in section 4.1.

Title:

Insert “the” before Karst Region

More specific comments could be seen on the annotated attached pdf file.

 

Comments for author File: Comments.pdf

Author Response

First, thank you very much for taking your time to review this manuscript. Your comments make this paper completer and more outstanding! I really appreciate all your comments and suggestions! Please find my itemized responses in below and my revisions/corrections in the re-submitted files. I had highlighted the revisions in red. Thanks again!

1. Methods used was not clearly presented and can in no way be used for reference for any future study, especially the production of the BF and its application rate.

Thank you very much for your suggestion. We have supplemented the production methods of biochar and BF in the section of Method, and also added some other relevant information.

2. Adequate methods for the production of biochar and its detailed characterization are required for biochar studies, so as to fully understand the impact of these conditions on the effect of biochar in the soil system.

Thank you very much for your suggestion. We have supplemented the method for the production of biochar and its detailed characterization.

3. Moreover, the treatment pattern used makes it even difficult to actually judge the effects observed and reported. For example, In Table 1, organic fertilizer was applied in the TFP, as well as inorganic fertilizer. This was not stated in the methods. Why was organic fertilizer used and what was the source? Why was organic fertilizer applied in the biochar amended soil, bearing in mind that biochar is an organic amendment?

Thank you very much for your suggestion. We have supplemented the amount of chemical fertilizer and nutrient content of all treatments in the section of experimental design. The reason why organic fertilizer was applied in the experiment was determined according to the traditional methods of local farmers. The purpose of this study was to evaluate the difference between traditional compound fertilizer and biochar-based fertilizer. Therefore, the same organic fertilizer varieties and amounts were applied to all treatments except CK treatment in the experiment, which can ensure the reliability of the test results.

4. What are the properties of the organic amendment? Moreover, the organic amendment and its nutrient composition could also influence and mask the effect of biochar in BF. Therefore, the effects of biochar reported in this study is not reliable and cannot be convincingly concluded.

Thank you very much for your suggestion. We have supplemented the detailed information of organic fertilizer, including source, nutrient content and production information. In the present experiment, the management measures of all treatments were consistent except for the difference of inorganic fertilizer. Therefore, we firmly believe that the effect of biochar-based fertilizer in this study is reliable and the test conclusion is convincingly.

5. Combining the complete dose of inorganic fertilizer used in TFP gives 3000 kg/ha (Table 1). This rate is unreasonably high and is impractical for any agricultural production, aside the fact that 1500 kg/ha of organic fertilizer was also applied in this same treatment, but no source of the organic fertilizer was mentioned in the materials and methods section.

Thank you very much for your suggestion. Before the implementation of the experiment, we have investigated the local planting mode of open field eggplant, including the fertilizer type and application amount. The findings of investigation showed that farmers used a large amount of inorganic fertilizer (about 3750-6000 kg ha^-1) in traditional planting methods. At the same time, in order to ensure the long-term planting of crops, they also apply a large amount of inorganic fertilizer (about 750-3000 kg ha^-1). Therefore, the TFP treatment in the experiment can reflect the true traditional fertilization mode. In addition, we have supplemented the detailed information of organic fertilizer, including source, nutrient content and production information.

6. The rational behind the different BF doses remain unclear. As it is now, it is not clear if the different rates were based on different fertilizer rates along with biochar, or different biochar rates along with inorganic fertilization.

Thank you very much for your suggestions. The effect of biochar-based fertilizer on improving crop productivity may be closely related to the combined application of biochar and inorganic fertilizer, and the effect is far greater than that of biochar or inorganic fertilizer alone. For example, Phares et al. found that significant interaction effect was observed between biochar and inorganic fertilizer application which could be related to positive soil conditioning of biochar and biochar surface charges which enhanced retention and steady release of nutrient supplied by inorganic fertilizer for crop use (Phares, C.A., Emmanuel, A., Andrews, D., et al. Improved soil physicochemical, biological properties and net income following the application of inorganic NPK fertilizer and biochar for maize production. (2022). Acta Ecologica Sinica. 42, 289-295. https://doi.org/10.1016/j.chnaes.2021.12.002). Liu et al. Found that the application of biochar together with inorganic and organic fertilizers escalated the plant growth of soybean. Meanwhile, there was no significant difference between high rate and low rate of biochar on plant growth, while the combination of biochar with half rate of inorganic and organic fertilizers improved plant growth more significantly than the treatments of full rate of inorganic fertilizer without organic fertilizer or biochar (Liu, M., Linna, C., Ma, S., et al. (2022). Effects of biochar with inorganic and organic fertilizers on agronomic traits and nutrient absorption of soybean and fertility and microbes in purple soil. Frontiers in Plant Science. 13, 871021. https://doi.10.3389/fpls.2022.871021). Therefore, we can conclude that the effect of biochar-based fertilizer on improving crop productivity may be based on the combined effect of biochar and inorganic fertilizer.

7. Plant sampling method was not explained.

Thank you very much for your suggestion. We have added the type of Experimental design, the number and method of plant sampling have been taken from soil or plants during experimentations in the section of statistical analysis.

8. Moreover, there was no basic soil analysis after harvest in the two seasons to show the effect of BF on soil properties and how these changes in soil properties may have affected the yield of the eggplants, and if biochar was helpful in improving the fertility of the soils. Note that the impact of biochar on crop productivity is tied to the effect of biochar on the nutritional composition of the soil.

Thank you very much for your suggestion. We agree with you very much that the impact of biochar on crop productivity is related to the impact of biochar on soil nutrients. However, we only observed the effect of biochar-based fertilizer on crop yield, quality, fertilizer utilization and economic benefits in this study. We ignored the impact of biochar-based fertilizer on soil properties and fertility, so we did not pay attention to collecting relevant data. Thank you again for your questions, we will add the collection and analysis of this part of data in future research.

9. The discussion needs additional re-writing while removing unnecessary information presented, especially, in section 4.1.

Thank you very much for your suggestion. We have rewritten the section of Discussion and removed unnecessary information presented, especially in section 4.1. 

10 .Title: Insert “the” before Karst Region

Thank you very much for your suggestion. We have revised the title of the manuscript.

11. More specific comments could be seen on the annotated attached pdf file.

Thank you very much for your suggestion. We have revised the relevant issues in the PDF file.

Author Response File: Author Response.doc

Round 2

Reviewer 2 Report

The authors addressed all the comments. therefore, I recommend publishing this manuscript

Author Response

Thank you very much.

Reviewer 3 Report

The authors took their time to improve the content and structure of the manuscript according to the review comments. The treatments presentation, design and methods presentation have been reasonably improved. However, the fertilizer application rate seems unreasonably high (up to 450 kg N/ha) unlike the average of 60-100 kg N/ha that is commonly used. Biochar is used to avoid overfertilization because of its positive impact on nutrient retention and use efficiency. Therefore lower rates, including the commonly applied rates are often used to evaluate its impacts.

The author must note that the effects of biochar are tied to its impact on soil fertility, hence discussing improved crop productivity without associating it with the changes in soil fertility parameters would be more of speculation. This is even more important because the impacts of biochar-fertilizer-organic manure on soil properties need to be adequately understood to provide a more comprehensive conclusion

However, the work has been reasonably improved and can be considered for publication if the additional suggestions are incorporated.

Minor comments

Line 70: The citation [34] is not appropriate. The citation numbers cannot jump from [26] to [34]. This may have altered you entire citation numbering pattern. Please check to ensure that the citations are properly arranged  in the text and that they correspond in the reference section.

Line 242: The title of Table 2: The second sentence " Different lowercase letters denote significant differences among treatment means at the α= 0.05 level by the Duncan’s MRT method. Results were presented as mean value ± standard error" should be moved below the table as a foot note. Do the same for Table 3 and 4

Line 299: Section 4.2: This section should contain adequate discussions on the comparative impacts of the different treatments on the yield of the eggplant, it nutritional composition and the related mechanisms and literature supporting these observations. I believe this section forms the most important part of the work and should be discussed reasonably.

Author Response

Thank you again for taking your time to review this manuscript. Your comments make this paper completer and more outstanding. I really appreciate all your comments and suggestions! Please find my itemized responses in below and my revisions/corrections in the re-submitted files. I had highlighted the revisions in red. Thanks again.

1. Line 70: The citation [34] is not appropriate. The citation numbers cannot jump from [26] to [34]. This may have altered you entire citation numbering pattern. Please check to ensure that the citations are properly arranged in the text and that they correspond in the reference section.

Thank you very much for your suggestion. We have checked the revised the references and numbers, and modified the citation numbers.

2. Line 242: The title of Table 2: The second sentence " Different lowercase letters denote significant differences among treatment means at the α= 0.05 level by the Duncan’s MRT method. Results were presented as mean value ± standard error" should be moved below the table as a foot note. Do the same for Table 3 and 4

Thank you very much for your suggestion. We have revised the titles of table 2-4, and transferred other information to footnotes.

3. Line 299: Section 4.2: This section should contain adequate discussions on the comparative impacts of the different treatments on the yield of the eggplant, it nutritional composition and the related mechanisms and literature supporting these observations. I believe this section forms the most important part of the work and should be discussed reasonably.

Thank you very much for your suggestion. We have supplemented the discussion on the effects of BF on the yield, nutritional composition and related mechanisms, and added the relevant references.

Author Response File: Author Response.docx