Biochar Improves Wax Gourd (Benincasa hispida (Thunb.) Cogn.) Yield and Quality by Regulating the Chemical Properties of Acidic Soil and Promoting Nutrient Uptake

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript describes well the effect of biochar on the growth of wax ground, in terms of plant physiology, nutrient content and soil properties. Some minor comments/clarifications are given below:

1. How did the results correlat to the climatic changes between 2022 and 2023, based on Fig. 1? Is this an important reason for showing this figure? Otherwise, it may be moved to SM, to save some space.

2. In Table S1, you could also add the properties of the soil, to see the differences. Although the primary scope is to compare the different methodologies, data on the control sample could further help in observing the changes in soil after the different applications.

3. Check the syntax in lines 155-156.

4. Can you give more details in the methodology you used in lines 183-184? Add it to SM.

5. Could the differences in yield between 2022 and 2023 (Table 1) be attributed to the longer application time? 

6. In line 362 you say that biochar improved the soil acidity, but the pH remains constantly below 6, in all treatments. So you may also discuss the initial soil pH.

 

Comments on the Quality of English Language

English are fine

Author Response

Thank you very much for taking the time out of your busy schedule to review this manuscript.

Detailed responses can be found below.

Response to Editor and reviewer’s comments (Agronomy-3118132)

Preface: We appreciate the editor and the reviewers’ comments and suggestions concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. We would be glad to respond to any further questions and comments that you may have. The main corrections in the paper and the responds to the editor and the reviewers’ comments are as following:

 

Response to Editor's comments

Response: We appreciate the referee’s positive comments and detailed analysis of the merits and dements. According to reviewer’s comments, we have made earnest modifications. We hoped meet with approval. And a point-by-point response has been listed below.

 

Response to Reviewer's main comments

1. How did the results correlat to the climatic changes between 2022 and 2023, based on Fig. 1? Is this an important reason for showing this figure? Otherwise, it may be moved to SM, to save some space.

Response: We appreciate the referee’s suggestions. After careful consideration, we believe that climate change is an important reason for the difference between the field test results in 2022 and 2023. Therefore, climate change in 2022-2023 may affect the yield difference between the two years, as shown in Table 1, thereby indirectly affecting the yield composition factors and other results. Therefore, it is put in Figure 1 as a foundation.

 

2. In Table S1, you could also add the properties of the soil, to see the differences. Although the primary scope is to compare the different methodologies, data on the control sample could further help in observing the changes in soil after the different applications.

Response: We appreciate the referee’s suggestions. Corresponding additions have been made (Table S1).

 

3. Check the syntax in lines 155-156.

Response: It has been revised accordingly (Page 5/ lines 155-156).

 

4. Can you give more details in the methodology you used in lines 183-184? Add it to SM.

Response: We appreciate the referee’s suggestions. Corresponding supplements have been made in SM.

 

5. Could the differences in yield between 2022 and 2023 (Table 1) be attributed to the longer application time? 

Response: We appreciate the referee’s suggestions. According to the reviewer's suggestion, with the increase of biochar application years, the annual yield of crops will also be different, and the general yield will decrease with the application years [1]; Climate change in 2022-2023 May also be responsible for the difference in production between the two years, as other studies have suggested [2].

1. Aydin, V. Šimanský, J. Horák, D. Igaz. Potential of biochar to alternate soil properties and crop yields 3 and 4 years after the application. Agronomy 2020, 10(6), 889. https://doi.org/10.3390/agronomy10060889
2. Baige Zhang, I. Cakamak, Jianchun Feng, Chaoran Yu, Xiao Chen, Dasen Xie, Liangquan Wu, Zhao Song, Jian Cao, Yuzhi He. Magnesium deficiency reduced the yield and seed germination in wax gourd by affecting the carbohydrate translocation. Front. Plant Sci 2020, 11, 797. https://doi.org/10.3389/fpls.2020.00797.

 

6. In line 362 you say that biochar improved the soil acidity, but the pH remains constantly below 6, in all treatments. So you may also discuss the initial soil pH.

Response: According to reviewer’s suggestions, we improved the discussion of relevant results and carefully analyzed the differences between soil pH and each treatment under biochar input, as well as the initial soil pH. We found that biochar can improve the acidic soil environment in South China, increase the initial soil pH, and improve nutrient availability. , thereby promoting crop nutrient absorption and increasing yield (Page 13/ lines 376-379).

 

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper.

We appreciate for Editors/Referees’ warm work earnestly, and hope that the correction will meet with approval.

Once again, thank you very much for your comments and suggestions.

 

Baige Zhang

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

 

The reviewed work concerns biochar improves wax gourd yield and quality by regulating the physicochemical properties of acidic soil and promoting nutrient uptake

I consider the research topic very interesting, implementation-oriented, and important from the point of view of food security, but the work requires some additions.

 

My comments:

Line 76: ...of 50 t/ha biochar significantly in - Please use the same form of units throughout the manuscript.

Line 79: ...Plaseaand EC. High-yield and high-quality vegetable... - Please explain the abbreviation for electroconductivity used for the first time.

Line 97-98: ...and 2 dosages (12 t ha−1 and 3 t ha−1) of biochar on the basis of optimized fertilization. The objectives of this study - Please use the same form of units throughout the manuscript.

Line 112-113 - as above

Line 125-129 - as above

Line 135-136: ...500 °C, a 135 heating rate of 5–10 °C min−1, and a duration of 4 h. The specific physical and chemical... - Please do not use a space before the Celsius symbol.

Line 138-139: Wax gourd seeds were soaked in deionized water for 8 h, wrapped in wet paper, and later placed in plastic bags for germination. - Please explain what germination conditions were used. Have the requirements of plants been taken into account, i.e. hypo- or epigeic germination?

Line 149-151: as above for Celsius

Line 139, 168 - In the description of distilled water, sometimes the full name is used, sometimes an unexplained abbreviation.

Line 174: ...drainage method and gloss meter. - Please provide device data (company, city, country).

Line 175: ...by anthrone colorimetry and the Caustic Blue method, respectively. - Please provide references to the methods used.

Line 176-177: ...of Vc and titratable acid content of fruits by UV-Vis spectrophotometry and potentiometric titration methods. 177
2.3.5. -  Please explain the abbreviation for vitamin C used for the first time. Please provide device data (company, city, country).

Table 1. - Please use the same form of units throughout the manuscript.

Line 207: ...wax gourd ( Figure... - spacing problem before bracket

Table 3 - Please use the same form of units throughout the manuscript.

Table 3: NH4 + -N - spacing problem

Table 3: It is only for the first time that information about  EC.

Line 382-386 - Please use the same form of units throughout the manuscript.

Discussion section: The discussion is well written.

The presented work is interesting, and correctly written, after supplementation and introduction of explanations it can be considered for publication in a journal.

 

Author Response

Thank you very much for taking the time out of your busy schedule to review this manuscript.

Detailed responses can be found below.

 

Response to Editor and reviewer’s comments (Agronomy-3118132)

Preface: We appreciate the editor and the reviewers’ comments and suggestions concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. We would be glad to respond to any further questions and comments that you may have. The main corrections in the paper and the responds to the editor and the reviewers’ comments are as following:

 

Response to Editor's comments

Response: We appreciate the referee’s positive comments and detailed analysis of the merits and dements. According to reviewer’s comments, we have made earnest modifications. We hoped meet with approval. And a point-by-point response has been listed below.

 

1. Line 76: ...of 50 t/ha biochar significantly in - Please use the same form of units throughout the manuscript.

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Page 2/ lines 77). And the full text has been checked and modified.

 

2. Line 79: ...Plaseaand EC. High-yield and high-quality vegetable... - Please explain the abbreviation for electroconductivity used for the first time.

Response: We appreciate the referee’s suggestions. Corresponding supplements and modifications have been made (Page 2/ lines 80).

 

3. Line 97-98: ...and 2 dosages (12 t ha⁻¹ and 3 t ha⁻¹) of biochar on the basis of optimized fertilization. The objectives of this study - Please use the same form of units throughout the manuscript.

Response: We appreciate the referee’s suggestions. Following the format of the latest published article in the journal, we have modified the unit form to t ha^-1 throughout the manuscript.

 

4. Line 112-113 - as above

Response: We appreciate the referee’s suggestions. It has been revised accordingly.

 

5. Line 125-129 - as above

Response: We appreciate the referee’s suggestions. It has been revised accordingly.

 

6. Line 135-136: ...500 °C, a 135 heating rate of 5–10 °C min−1, and a duration of 4 h. The specific physical and chemical... - Please do not use a space before the Celsius symbol.

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Page 5/ lines 140).

 

1. Line 138-139: Wax gourd seeds were soaked in deionized water for 8 h, wrapped in wet paper, and later placed in plastic bags for germination. - Please explain what germination conditions were used. Have the requirements of plants been taken into account, i.e. hypo- or epigeic germination?

Response: We appreciate the referee’s suggestions. The germination conditions of winter melon are to germinate in a constant temperature and dark environment at 32°C [1]^. It has also been added to Page 5, line 144-146.

 

1. Jingjing Chang, Jiawei Li, Jinlong Li, Xiao Chen, Jiabin Jiao, Jing Li, Zhao Song, Baige Zhang. The GA and ABA signaling is required for hydrogen-mediated seed germination in wax gourd. BMC Plant Biol 2024, 24, 542. https://doi.org/1186/s12870-024-05193-3.

 

2. Line 149-151: as above for Celsius

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Page 5/ lines 155).

 

3. Line 139, 168 - In the description of distilled water, sometimes the full name is used, sometimes an unexplained abbreviation.

Response: We appreciate the referee’s suggestions. We have rewritten this to deionized water, its abbreviation is DI water (Page 5/ lines 144, Page 5/ line 175).

 

4. Line 174: ...drainage method and gloss meter. - Please provide device data (company, city, country).

Response: According to the referee’s suggestion, we have added equipment information on Page 5/lines 181.

 

5. Line 175: ...by anthrone colorimetry and the Caustic Blue method, respectively. - Please provide references to the methods used.

Response: We appreciate the referee’s suggestions. Anthrone colorimetry [1], and the Caustic Blue ^[2]. It has also been added to Page 5-6, line 182-183.

 

1. W. Yemm, A. J. Willis. The estimation of carbohydrates in plant extracts by anthrone. Biochem J 1954, 57 (3), 508-514. https://doi.org/10.1042/bj0570508
2. A. Deans, G. A. Sword, P. A. Lenhart, E. Burkness, W. D. Hutchison, S. T. Behmer. Quantifying plant soluble protein and digestible carbohydrate content, using corn (Zea mays) as an exemplar. Environment 2018. https://doi.org/10.3791/58164

 

 

 

6. Line 176-177: ...of Vc and titratable acid content of fruits by UV-Vis spectrophotometry and potentiometric titration 177

Response: We appreciate the referee’s suggestions. UV-Vis spectrophotometry ^[1], and potentiometric titration ^[2]. It has also been added to Page 5-6, line 182-183.

 

1. P. Desai, S. Desai. UV spectroscopic method for determination of Vitamin C (ascorbic acid) content in different fruits in South Gujarat Region. International Journal of Environmental Sciences and Natural Resources 2019, 21, 2. https://doi.org/10.19080/IJESNR.2019.21.556056.
2. A. Volmer, L. Curbani, T. A. Parker, J.Garcia, L. D. Schultz, E. M.Borges. Determination of titratable acidity in wine using potentiometric, conductometric, and photometric methods. Journal of chemical education 2017, 94, 9. https://doi.org/10.1021/acs.jchemed.6b00891.

 

7. Please explain the abbreviation for vitamin C used for the first time. Please provide device data (company, city, country).

Response: According to the referee’s suggestion, we added an explanation for the first use of the Vc abbreviation (Page 5/ lines 183). We have added equipment information on Page 5/lines 181.

 

8. Table 1. - Please use the same form of units throughout the manuscript.

Response: We appreciate the referee’s suggestions. It has been revised accordingly.

 

9. Line 207: ...wax gourd ( Figure... - spacing problem before bracket

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Page 6/ lines 218).

 

10. Table 3 - Please use the same form of units throughout the manuscript.

Response: We appreciate the referee’s suggestions. It has been revised accordingly.

 

11. Table 3: NH4 + -N - spacing problem

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Table 3).

 

12. Table 3: It is only for the first time that information about  EC.

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Table 3).

 

13. Line 382-386 - Please use the same form of units throughout the manuscript.

Response: We appreciate the referee’s suggestions. I have revised the unit form to t ha⁻¹ throughout the manuscript.

 

 

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper.

We appreciate for Editors/Referees’ warm work earnestly, and hope that the correction will meet with approval.

Once again, thank you very much for your comments and suggestions.

 

Baige Zhang

 

Reviewer 3 Report

Comments and Suggestions for Authors

A report for Agronomy-3118132 “Biochar improves wax gourd yield and quality by regulating the physicochemical properties of acidic soil and promoting  nutrient uptake“

 

Title: I don't know if it would be useful to indicate “Benincasa hispida” in addition to the trivial name, since this species is not popular in many countries.

 

Abstract:

In general, I recommend including some additional information to obtain a valid abstract to be read in isolation:

 

More details should be given about the origin of the biochar. Even the particle size would be interesting.

In the Materials and Methods section it is said for the first time that “sawdust biochar” and “rice biochar” are used, but it would be useful to have more data on the characteristics of these products: the origin of the sawdust, the carbon content, the content of nutrient elements. These data are not trivial, since they substantially influence the characteristics of the product.

Knowing the organic matter content of the soil before applying biochar is also of interest when judging the results indicated in the summary.

Some information should also be given on the mineral content of the biochar used: not only the percentage of ash, but also the content of some elements important in plant nutrition.

All of this would allow us to know whether the positive effect of biochar should be attributed fundamentally to the improvement in the physico-chemical properties of the soil and/or to the additional contribution of nutrients.

Biochar application rates to soil should also be indicated (in the summary).

Line 23: I would add more information besides the generic term "acidic soils", for example USDA or FAO classification.

 

Finally: if two types of biochar were used, were differences found in the effect of each of them that deserve to be noted in the summary?.

I recommend carefully reviewing the use of acronyms throughout the paper. Introduce the acronym the first time it is used and do not re-enter it or use the full words in subsequent text.

For example, the acronym OPT is used for the first time on line 24, but is introduced on line 126, and in other lines "optimized fertilization" is used instead of the acronym (lines 98, 204, 263...). (In this last case it would be correct to use the complete words again, since they are the beginning of a paragraph).

Line 33: indicate that the acronym "Vc" corresponds to vitamin C. I would use both capital letters (VC).

 

A generic comment for the entire work--but that must also be taken into account in the summary--is that the effect of the cation exchange capacity of biochar on its ability to improve nutrient availability and retention is frequently invoked.

However, my experience with biochar compared to soil humus is that biochar is often characterized by a low cation exchange capacity. This is largely due to the fact that thermal treatment produces intense decarboxylation and dehydration of the organic matter, and the reactive oxygen-containing functional groups such as carboxyl groups are the first to be removed. Especially when the heat treatment is not carried out in particularly oxidizing conditions.

My theory has always been that the beneficial effect of biochar is closely related to the diffusion processes in the microporous structure of the corresponding material, but not so much to the functional groups supported on the carbonaceous matrix.

In any case, as the paper does not provide data on the cation exchange capacity of the biochar used, nor on the amended soils, but only on electrical conductivity, I always recommend writing with caution so as not to make unsupported statements.

 

Keywords: I recommend not combining independent keywords with the conjunction "and"

 

Introduction

Lines 76, 97, 98…: Many Journals recommend using units of the international system (SI), i.e., Megagram instead of Ton. However, I will not insist on this point because in many cases this can lead to confusion.

Line 85 “(Benincasa hispida (Thunb.) Cogn),”. Add dot after Cogn.

Line 111: as suggested in the case of the Abstact, I recommend presenting some soil classification (USDA, FAO...) in addition to "sandy loam"

 Line 154: Perkin Elmer.

 Line 169: Introduce the acronym in “DI water” (deionized…?). In any case, I think it is not worth introducing any acronym instead of the complete words, since it is only used a couple of times in the entire article.

 

Lines 178 (and 397): Avoid widow lines.

 

Line 181: Throughout the entire work (which is supposed to be a camera-ready document) I get the feeling that the character used (´) as quotation marks is not correct: it seems more like an accent. It would be more correct to use (”) or (').

 

Table 1: To obtain a self-explanatory Table, I would include in the footnote the meaning of the acronyms FP, OPT, T1… etc. I would also italitize the n in "n = 6".

Line 202: The explanation of the acronyms--although it has already been done in the text--would also be convenient in similar situations, as is the case of the caption of Figure 1.

 

Lines 202, 227, 260… I would use “lowercase letters” instead of “small letters”.

 

Line 221: From this line "Dadao" begins to be written as "DaDao".

 

Line 262: 3.4. Soil physical and chemical properties (and Table 3)

In this section the authors indicate "physical and chemical properties of soils" but in the text and in the Table practically no physical properties are mentioned (such as porosity, water retention, bulk density, stability of aggregates, etc.). In any case the Table show exchangeable Ca and Mg (not total cation exchange capacity), but the latter (CEC) should rather be considered a physicochemical property. Therefore, I suggest changing the title of the section and that of the corresponding Table. This also applies to Table 3: “Responses of soil physical and chemical properties to different treatments on two tested varieties”.

 

“Table 3: Avoid broken lines in some headings (Fertilization, Exchangeable…). This also applies to Table 3.

 

In many Journals the decisiemen/meter (dS m-1) is used as the unit for soil electrical conductivity. If the unit indicated in Table 3 is microsiemen, the Greek letter µ should be used and the S should be capitalized. This also applies to Table 3.

 

Discussion

Line 333: “It is worth noting that under the conditions of fertilizer reduction, the combination of biochar can improve the yield and quality of wax gourd by regulating the soil physicochemical properties, increasing nutrient availability, and promoting crop nutrient absorption” -- All this is very logical, but as I have previously indicated, in addition to the three reasons indicated, some justification could be included on the extent to which the possible mineral content of the biochar could represent a supplementary contribution of nutrients that has influenced the success of the treatment.

 

 On the other hand, the concept "regulating the physicochemical properties of soils" seems a bit vague and in the present paper it seems to refer to the cation exchange capacity (which is a variable that has not been determined).

 

From this point of view, the positive effect of biochar may have been due to the reduction in the risk of leaching, with loss of the most soluble elements, as well as its effect in the delayed release (progressive) of nutrients throughout the entire vegetative cycle.

I recommend writing with caution.

For example, an effect of biochar in promoting nutrient absorption is invoked. This may be the case, but it may also be that application of biochar has involved an incorporation of nutrients, or that the biochar has prevented the loss of elements through leaching.

To know exactly the nature of the processes involved in the positive effect of biochar, it would possibly be necessary to compare the results with those of control plots where the same mineral fertilization has been calculated. If this has been the case, it should be emphasized in the text (lines 121 and below). If it is not, I recommend writing with much more caution.

 

Furthermore, throughout the entire work, the water holding capacity of the soil, or the soil moisture in the different plots during the experiment is not discussed at any time. This could have had a great influence in explaining the different availability of nutrients throughout the growing period. For this reason, I once again recommend writing with caution because it would be necessary to have controlled many more variables throughout the experiment.

Line 360: I have a little problem understanding what exactly is meant by "yield composition"

 

Line 386: “This result is consistent with Liu et al. [46], who found that crop yield tended to decrease with increasing biochar application rates. Similarly, Rondon et al. [51] found that biochar over-application reduced soybean yield. Excessive application of biochar can inhibit plant growth, which is associated with nitrogen fixation and reduced microbial activity and nutrient uptake due to high volatility and increased levels of toxic and hazardous substances [52].” -- ((… As expected from the classical Mitscherlich’s Law of Diminishing Returns)).

 

 

Conclusions

 

Line 442: “Biochar application can improve wax gourd yields by improving the soil environment to increase nutrient effectiveness (such as by increasing soil organic carbon, Olsen-P, and exchangeable Ca).” -- As I have mentioned previously, I would recommend writing with much more caution if there is no data on the different effect of biochar as i) external contribution of nutrients or as ii) regulating agent for the retention and mobility of added or pre-existing fertilizers in the soil.

Probably both effects may occur in the system under study, but establishing the quantitative influence of each one is problematic if additional experimental data are not available. If not, the experimental design could be better explained, in a way that allows a quantitative evaluation of the different causes of the increase in crop yield and quality.

 

Line 452: Supplemenary materials:

 

The link https://www.mdpi.com/xxx/s1 does not work from my computer (Error 404 - File not found).

 

References

 

 Improve format. Use “N-dash” for page ranges.

Take care of the format of the references; in some cases, the journals are abbreviated; in other cases, full words are used.

Do not unnecessarily capitalize the main words in the titles of articles published in journals (Refs. 20,30…)

Reference 28: Italicize Latin names and leave blank space before the parenthesis.

Fix typos (line 590: Journal…)

 

Reference 51: Use the same format as in the other references, do not write the authors' given names but rather Rondón M.A, Lehmann J., Ramírez J., Hurtado M. Add blank space between nitrogen and fixation. Italitize the Latin names

Fix small defects in Journal titles like line 607 where the article "the" is capitalized

 

 

Supplementary information

 

Table S1

I insist again on adding more information about the origin of the sawdust used to make biochar. It could be understood that it is wood sawdust, but such  material has very little ash and is extremely poor in nitrogen, and what is shown in the Table is a material much richer in nutrients than rice biochar.

 It could happen that the sawdust was not made of wood but of green parts, such as pruning residues or other lignocellulosic wastes, and that would explain the richness in ash (although the ash content ought to be indicated in the Table).

Regarding the nutrient poverty of rice biochar, it could be due to the fact that it has little straw and a greater amount of husk (which mainly contains silica). But all this information should be clarified because it is substantial when it comes to explaining the effect of biochar on crop growth.

 

In table S1 I also recommend including a footnote indicating again the meaning of the acronyms EC, TC..., as well as indicating with a capital letter the S of Siemen in the EC column

 

Table S2

Please consider my previous recommendations regarding the acronyms and footnote in the Tables.

 

 

 

 

 

Author Response

Thank you very much for taking the time out of your busy schedule to review this manuscript.

Detailed responses can be found below.

Response to Editor and reviewer’s comments (Agronomy-3118132)

Preface: We appreciate the editor and the reviewers’ comments and suggestions concerning our manuscript. Those comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied comments carefully and have made correction which we hope meet with approval. We would be glad to respond to any further questions and comments that you may have. The main corrections in the paper and the responds to the editor and the reviewers’ comments are as following:

 

Response to Editor's comments

Response: We appreciate the referee’s positive comments and detailed analysis of the merits and dements. According to reviewer’s comments, we have made earnest modifications. We hoped meet with approval. And a point-by-point response has been listed below.

 

1. Title: I don't know if it would be useful to indicate “Benincasa hispida” in addition to the trivial name, since this species is not popular in many countries.

Response: We appreciate the referee’s suggestions. As suggested by the reviewers, the scientific name (Benincasa hispida (Thunb.) Cogn.) should be added to the title after the wax gourd.

 

2. More details should be given about the origin of the biochar. Even the particle size would be interesting.

In the Materials and Methods section it is said for the first time that “sawdust biochar” and “rice biochar” are used, but it would be useful to have more data on the characteristics of these products: the origin of the sawdust, the carbon content, the content of nutrient elements. These data are not trivial, since they substantially influence the characteristics of the product.

Some information should also be given on the mineral content of the biochar used: not only the percentage of ash, but also the content of some elements important in plant nutrition.

All of this would allow us to know whether the positive effect of biochar should be attributed fundamentally to the improvement in the physico-chemical properties of the soil and/or to the additional contribution of nutrients.

Response: We appreciate the referee’s suggestions. As the reviewers said, the difference in the source and preparation process of biochar, such as pyrolysis temperature, will affect the characteristics of biochar itself, and thus affect the application effect of biochar ^[1]. The element content and carbon content of biochar will affect the organic carbon content and nutrient loss of soil, and the pore structure of biochar will affect the structure and nutrient of soil ^[2]. Therefore, we have supplemented the relevant information of the two biochar in the relevant trial. (Table S2).

1. B. Ahmed, John L. Zhou, Huu Hao Ngo, Wenshan Guo. Insight into biochar properties and its cost analysis. . 2016, 84, 76-86. https://doi.org/10.1016/j.biombioe.2015.11.002
2. Al‐Wabel MI, Hussain Q, Usman AR, Ahmad M, Abduljabbar A, Sallam AS, Ok Impact of biochar properties on soil conditions and agricultural sustainability: A review. Land degradation and development. 2018, 29,7. https://doi.org/10.1002/ldr.2829

 

3. Knowing the organic matter content of the soil before applying biochar is also of interest when judging the results indicated in the summary.

Response: We appreciate the referee’s suggestions. As suggested by the reviewers, we provide the content of the soil's original organic matter in our materials and methods.

 

4. Biochar application rates to soil should also be indicated (in the summary).

Response: We appreciate the referee’s suggestions. In the abstract, we have added the amount of 2 kinds of biochar to the soil (3 t ha⁻¹ and 12 t ha⁻¹) (Page 1/ line 21-24).

 

5. Line 23: I would add more information besides the generic term "acidic soils", for example USDA or FAO classification.

Response: We appreciate the referee’s suggestions. According to the soil classification system of the United States Department of Agriculture (USDA), the soils in South China are acid oxidized soils ^[1]. We have also added relevant points in the article.

1. I Baillie. Soil survey staff 1999, soil taxonomy. Soil use and management. 2001, 17 (1), 57-60. https://doi.org/10.1111/j.1475-2743.2001.tb00008.x.

 

6. Finally: if two types of biochar were used, were differences found in the effect of each of them that deserve to be noted in the summary?

Response: We appreciate the referee’s suggestions. As the reviewers said, different types of biochar have differences in the yield, soil nutrients and nutrient absorption of winter melon. Specifically, under the same dosage, rice biochar has a more significant effect on increasing the yield of wax groud, and has a better effect on the improvement of soil physical and chemical properties, while sawdust biochar has a more significant effect on nutrient absorption. We also added in the summary section.

 

7. I recommend carefully reviewing the use of acronyms throughout the paper. Introduce the acronym the first time it is used and do not re-enter it or use the full words in subsequent text.

For example, the acronym OPT is used for the first time on line 24, but is introduced on line 126, and in other lines "optimized fertilization" is used instead of the acronym (lines 98, 204, 263...). (In this last case it would be correct to use the complete words again, since they are the beginning of a paragraph).

Response: We appreciate the referee’s suggestions. As reviewers say, introduce the acronym the first time you use it, and don't retype or use full words in subsequent texts. We have therefore carefully reviewed the full text and made changes.

 

8. Line 33: indicate that the acronym "Vc" corresponds to vitamin C. I would use both capital letters (VC).

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Page 1/ lines 34).

 

9. A generic comment for the entire work--but that must also be taken into account in the summary--is that the effect of the cation exchange capacity of biochar on its ability to improve nutrient availability and retention is frequently invoked.

However, my experience with biochar compared to soil humus is that biochar is often characterized by a low cation exchange capacity. This is largely due to the fact that thermal treatment produces intense decarboxylation and dehydration of the organic matter, and the reactive oxygen-containing functional groups such as carboxyl groups are the first to be removed. Especially when the heat treatment is not carried out in particularly oxidizing conditions.

My theory has always been that the beneficial effect of biochar is closely related to the diffusion processes in the microporous structure of the corresponding material, but not so much to the functional groups supported on the carbonaceous matrix.

In any case, as the paper does not provide data on the cation exchange capacity of the biochar used, nor on the amended soils, but only on electrical conductivity, I always recommend writing with caution so as not to make unsupported statements.

Response: We appreciate the referee’s suggestions. As the reviewers said, the cation exchange capacity of biochar plays an important role in soil nutrients, which can exchange nutrients from soil minerals, thereby increasing soil nutrients. However, biochar may have low cation exchange capacity due to the preparation process [1], so it is more likely to adsorb nutrients in soil through microporous structure and increase the availability of nutrients in soil [2]. In our study, firstly, soil nutrients can be increased by increasing the pH of acidic soil, thus increasing the contents of exchangeable calcium and Olsen-P in soil [3]; secondly, the content of organic carbon in soil is increased by the rich carbon content of biochar itself [4]. 

1. B. Ahmed, John L. Zhou, Huu Hao Ngo, Wenshan Guo. Insight into biochar properties and its cost analysis. 2016, 84, 76-86. https://doi.org/10.1016/j.biombioe.2015.11.002.
2. Al‐Wabel MI, Hussain Q, Usman AR, Ahmad M, Abduljabbar A, Sallam AS, Ok Impact of biochar properties on soil conditions and agricultural sustainability: A review. Land degradation and development 2018, 29,7. https://doi.org/10.1002/ldr.2829.
3. Yang Ding, Yunguo Liu, Shaobo Liu, Zhongwu Li, Xiaofei Tan, Xixian Huang, Guangming Zeng, Lu Zhou, Bohong Zheng. Biochar to improve soil fertility. A review. Agronomy for Sustainable Development.2016, 36, 36. https://doi.org/10.1007/s13593-016-0372-z.
4. W. Gaskin, R. A. Speir, K. Harris, K. C. Das, R. D. Lee, L. A. Morris, D. S. Fisher. Effect of Peanut Hull and Pine Chip Biochar on Soil Nutrients, Corn Nutrient Status, and Yield. Agronomy journal. 2010, 102(2), 623-633. https://doi.org/10.2134/agronj2009.0083.

 

10. Keywords: I recommend not combining independent keywords with the conjunction "and"

Response: We appreciate the referee’s suggestions. The keywords have been modified to Biochar; Chemical properties of soil; Nutrient uptake; Wax gourd; Yield; Quality (keywords).

 

Introduction

11. Lines 76, 97, 98…: Many Journals recommend using units of the international system (SI), i.e., Megagram instead of Ton. However, I will not insist on this point because in many cases this can lead to confusion.

Response: We appreciate the referee’s suggestions. We also Megagram in many cases there is confusion.

 

12. Line 85 “(Benincasa hispida (Thunb.) Cogn),”. Add dot after Cogn.

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Page 2/ lines 87).

 

13. Line 111: as suggested in the case of the Abstact, I recommend presenting some soil classification (USDA, FAO...) in addition to "sandy loam"

Response: We appreciate the referee’s suggestions. According to the soil classification system of the United States Department of Agriculture (USDA), the soils in South China are acid oxidized soils [1]. We have also added relevant points in the article.

1. I Baillie. Soil survey staff 1999, soil taxonomy. Soil use and management. 2001, 17 (1), 57-60. https://doi.org/10.1111/j.1475-2743.2001.tb00008.x.

 

14. Line 154: Perkin Elmer.

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Page 2/ lines 182).

 

15. Line 169: Introduce the acronym in “DI water” (deionized…?). In any case, I think it is not worth introducing any acronym instead of the complete words, since it is only used a couple of times in the entire article.

Response: We appreciate the referee’s suggestions. It has been modified to deionized water (Page 5/ lines 176).

 

16. Lines 178 (and 397): Avoid widow lines.

Response: We appreciate the referee’s suggestions. It has been revised accordingly.

 

17. Line 181: Throughout the entire work (which is supposed to be a camera-ready document) I get the feeling that the character used (´) as quotation marks is not correct: it seems more like an accent. It would be more correct to use (”) or (').

Response: We appreciate the referee’s suggestions. It has been revised accordingly(Page 6/ lines 194).

 

18. Table 1: To obtain a self-explanatory Table, I would include in the footnote the meaning of the acronyms FP, OPT, T1… etc. I would also italitize the n in "n = 6".

Response: We appreciate the referee’s suggestions. It has been added to the meaning of those abbreviations and to italicize the n in "n = 6" (Page 6/ lines 213-215).

 

19. Line 202: The explanation of the acronyms--although it has already been done in the text--would also be convenient in similar situations, as is the case of the caption of Figure 1.

Response: We appreciate the referee’s suggestions. It has been supplemented accordingly.

 

1. Lines 202, 227, 260… I would use “lowercase letters” instead of “small letters”.

Response: We appreciate the referee’s suggestions. It has been revised accordingly.

 

2. Line 221: From this line "Dadao" begins to be written as "DaDao".

Response: We appreciate the referee’s suggestions. I have changed the whole text to "Dadao".

 

3. Line 262: 3.4. Soil physical and chemical properties (and Table 3)

Response: We appreciate the referee’s suggestions. It has been added (Page 9/ lines 277).

 

4. In this section the authors indicate "physical and chemical properties of soils" but in the text and in the Table practically no physical properties are mentioned (such as porosity, water retention, bulk density, stability of aggregates, etc.). In any case the Table show exchangeable Ca and Mg (not total cation exchange capacity), but the latter (CEC) should rather be considered a physico chemical property. Therefore, I suggest changing the title of the section and that of the corresponding Table. This also applies to Table 3: “Responses of soil physical and chemical properties to different treatments on two tested varieties”.

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Page 10/ lines 281 and Table 3).

 

5. “Table 3: Avoid broken lines in some headings (Fertilization, Exchangeable…). This also applies to Table 3.

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Table 3).

 

 

6. In many Journals the decisiemen/meter (dS m-1) is used as the unit for soil electrical conductivity. If the unit indicated in Table 3 is microsiemen, the Greek letter µ should be used and the S should be capitalized. This also applies to Table 3.

Response: We appreciate the referee’s suggestions. It has been revised accordingly (Table 3).

 

Discussion

7. Line 333: “It is worth noting that under the conditions of fertilizer reduction, the combination of biochar can improve the yield and quality of wax gourd by regulating the soil physicochemical properties, increasing nutrient availability, and promoting crop nutrient absorption” -- All this is very logical, but as I have previously indicated, in addition to the three reasons indicated, some justification could be included on the extent to which the possible mineral content of the biochar could represent a supplementary contribution of nutrients that has influenced the success of the treatment.

Response: We appreciate the referee’s suggestions. As the reviewer said, we have added information about the mineral elements of biochar in the supplementary material.

 

8. On the other hand, the concept "regulating the physicochemical properties of soils" seems a bit vague and in the present paper it seems to refer to the cation exchange capacity (which is a variable that has not been determined).

Response: We appreciate the referee’s suggestions. As the reviewer said, the concept of regulating the physical and chemical properties of soil is vague. Therefore, Let's rewrite this part of the discussion as: It is worth noting that under the conditions of fertilizer reduction, biochar combined application can improve the yield and quality of wax groud by increasing soil organic carbon, increasing nutrient availability and promoting crop nutrient absorption.

 

9. From this point of view, the positive effect of biochar may have been due to the reduction in the risk of leaching, with loss of the most soluble elements, as well as its effect in the delayed release (progressive) of nutrients throughout the entire vegetative cycle. I recommend writing with caution.

For example, an effect of biochar in promoting nutrient absorption is invoked. This may be the case, but it may also be that application of biochar has involved an incorporation of nutrients, or that the biochar has prevented the loss of elements through leaching.

To know exactly the nature of the processes involved in the positive effect of biochar, it would possibly be necessary to compare the results with those of control plots where the same mineral fertilization has been calculated. If this has been the case, it should be emphasized in the text (lines 121 and below). If it is not, I recommend writing with much more caution.

 Furthermore, throughout the entire work, the water holding capacity of the soil, or the soil moisture in the different plots during the experiment is not discussed at any time. This could have had a great influence in explaining the different availability of nutrients throughout the growing period. For this reason, I once again recommend writing with caution because it would be necessary to have controlled many more variables throughout the experiment.

Response: We appreciate the referee’s suggestions. As suggested by the reviewers, the positive effect of biochar from this perspective may be to reduce the leaching of nutrients [1], or biochar may play a role in delaying the release of nutrients throughout the plant growth cycle [2]. In this study, optimized fertilization followed by biochar application significantly increased soil EC, Organic C, NH₄⁺-N, NO₃^--N, and Olsen-P content compared to FP treatment. This may be a manifestation of the role of biochar as a whole [3]. In addition, it is true that soil moisture was not monitored in our study, but the water-retaining effect of biochar is a key influence on the availability of soil nutrients [4]. Therefore, in this part of the discussion, we have modified and supplemented, adding the description of biochar's water retention capacity of soil.

1. Lu Yang, Yunchao Wu, Yichu Wang, Weiqi An, Jie Jin, ,Ke Sun, Xiangke Wang. Effects ofbiochar addition on the abundance, speciation, availability, and leaching loss of soil phosphorus. Science of the total environment.2021, 785. https://doi.org/10.1016/j.scitotenv.2020.143657.
2. M. Alkharabsheh, M. F. Seleima, M. L. Battaglia, A. Shami, R. S. Jalal, B. A. Alhammad, K. F. Almutairi, A. M. Al-Saif. Biochar and Its Broad Impacts in Soil Quality and Fertility, Nutrient Leaching and Crop Productivity: A Review. Agronomy. 2021, 11(5), 993. https://doi.org/10.3390/agronomy11050993.
3. Xu, L. L.Wei, J. N.Sun, H. B.Shao, S. X.Chang. What is more important for enhancing nutrient bioavailability with biochar application into a sandy soil: Direct or indirect mechanism? Ecological Engineering. 2013, 52,119-124. https://doi.org/10.1016/j.ecoleng.2012.12.091.
4. Ling Li, YongJiang Zhang, A. Novak, Yingchao Yang, Jinwu Wang. Role of Biochar in Improving Sandy Soil Water Retention and Resilience to Drought. Water. 2021, 13(4), 407. https://doi.org/10.3390/w13040407.

 

10. Line 360: I have a little problem understanding what exactly is meant by "yield composition"

Response: We appreciate the referee’s suggestions. The yield composition of wax gourd is that the vertical stem length of each wax gourd, the upper middle and lower transverse stem length determines the single fruit weight of each wax gourd, and the product of each wax gourd single fruit weight and planting density is the yield of wax gourd.

 

11. Line 386: “This result is consistent with Liu et al. [46], who found that crop yield tended to decrease with increasing biochar application rates. Similarly, Rondon et al. [51] found that biochar over-application reduced soybean yield. Excessive application of biochar can inhibit plant growth, which is associated with nitrogen fixation and reduced microbial activity and nutrient uptake due to high volatility and increased levels of toxic and hazardous substances [52].” -- ((… As expected from the classical Mitscherlich’s Law of Diminishing Returns)).

Response: We appreciate the referee’s suggestions. As the reviewer said, the higher the amount of biochar input, the higher the planting cost. However, crop yield did not increase with the increase of biochar input, and even decreased, so did economic and benefits, as expected from the classical Mitscherlich’s Law of Diminishing Returns.

 

Conclusions

12. Line 442: “Biochar application can improve wax gourd yields by improving the soil environment to increase nutrient effectiveness (such as by increasing soil organic carbon, Olsen-P, and exchangeable Ca).” -- As I have mentioned previously, I would recommend writing with much more caution if there is no data on the different effect of biochar as i) external contribution of nutrients or as ii) regulating agent for the retention and mobility of added or pre-existing fertilizers in the soil.

Response: We appreciate the referee’s suggestions. As the reviewer said, we have no more description of the nutrients that biochar directly brings into the soil and the characteristics of biochar, and the term soil environment is more vague. Therefore, we rewrote this part of the conclusion to say that the application of biochar can increase winter melon yield by increasing soil pH and improving nutrient availability (such as increasing soil organic carbon, Olsen-P, and exchangeable calcium) compared to pre-planting. (Page 14/ lines 464-467).

 

13. Probably both effects may occur in the system under study, but establishing the quantitative influence of each one is problematic if additional experimental data are not available. If not, the experimental design could be better explained, in a way that allows a quantitative evaluation of the different causes of the increase in crop yield and quality.

Response: We appreciate the referee’s suggestions. As mentioned by the reviewers, it is possible that both effects may occur in this study. 1) Biochar may reduce the leaching of nutrients and 2) it may play a role in delaying the release of nutrients during the whole growth cycle of plants. In this experiment, it was found that the increase of soil nutrients and crop yield after biochar application may be attributed to the overall role of biochar in this system, which not only brings nutrients into the system itself, but also reduces leaching. These two effects are inseparable.

 

14. Line 452: Supplemenary materials:

The link https://www.mdpi.com/xxx/s1 does not work from my computer (Error 404 - File not found).

Response: We appreciate the referee’s suggestions. This problem may be due to the fact that there is no official journal, the journal is temporarily replaced by www.mdpi.com/xxx/s1, so you can not directly open this website on the computer.

 

References

 Improve format. Use “N-dash” for page ranges.

Take care of the format of the references; in some cases, the journals are abbreviated; in other cases, full words are used.

Do not unnecessarily capitalize the main words in the titles of articles published in journals (Refs. 20,30…)

Reference 28: Italicize Latin names and leave blank space before the parenthesis.

Fix typos (line 590: Journal…)

 

Reference 51: Use the same format as in the other references, do not write the authors' given names but rather Rondón M.A, Lehmann J., Ramírez J., Hurtado M. Add blank space between nitrogen and fixation. Italitize the Latin names

Fix small defects in Journal titles like line 607 where the article "the" is capitalized

Response: We appreciate the referee’s suggestions. The format and spelling of the references have been carefully checked and revised.

 

Supplementary information

Table S1

I insist again on adding more information about the origin of the sawdust used to make biochar. It could be understood that it is wood sawdust, but such  material has very little ash and is extremely poor in nitrogen, and what is shown in the Table is a material much richer in nutrients than rice biochar.

It could happen that the sawdust was not made of wood but of green parts, such as pruning residues or other lignocellulosic wastes, and that would explain the richness in ash (although the ash content ought to be indicated in the Table).

Regarding the nutrient poverty of rice biochar, it could be due to the fact that it has little straw and a greater amount of husk (which mainly contains silica). But all this information should be clarified because it is substantial when it comes to explaining the effect of biochar on crop growth.

Response: We appreciate the referee’s suggestions. We have supplemented the elemental content and surface area parameters of the two biochars in the supplementary material (Table S2).

 

In table S1 I also recommend including a footnote indicating again the meaning of the acronyms EC, TC..., as well as indicating with a capital letter the S of Siemen in the EC column

Response: We appreciate the referee’s suggestions. We have already added footnotes to it and modified it.

 

Table S2

Please consider my previous recommendations regarding the acronyms and footnote in the Tables.

Response: We appreciate the referee’s suggestions. It has been added to the meaning of those abbreviations and to italicize the n in "n = 6" (Table S3).

 

We tried our best to improve the manuscript and made some changes in the manuscript. These changes will not influence the content and framework of the paper.

We appreciate for Editors/Referees’ warm work earnestly, and hope that the correction will meet with approval.

Once again, thank you very much for your comments and suggestions.

 

Baige Zhang