Ball-Milling-Modified Biochar with Additives Enhances Soil Cd Passivation, Increases Plant Growth and Restrains Cd Uptake by Chinese Cabbage

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I have reviewed the manuscript. The research conducted is up to the mark. However, the Manuscript needs some improvements before publishing in this journal. 

Some recommendations are as follows: 

Title of the paper: See the attached file. 

Abstract: There is a need to add one or two lines for the background/ importance of the study. Mention the treatments you applied during the study. It looks a bit longer with some extra data that doesn't need to be put in the abstract. Focus on your main results/ findings that you think could make a difference to present this study. 

Keywords: It needs to be revised as per the title. Avoid the words that are already used in the title to maximize your work availability. 

Introduction: There is a need to improve the introduction based on the modified biochar you used in your study. Most of the background you provided is based on the simple biochar applied but not/ very less about the modified biochar that needs to be addressed there because biochar and modified biochar are two different things so, their efficiency will also be different. Also, see the attached file for more comments. 

Material and Methods: There is a need to add the soil properties used in the experiment. Also, add biochar properties used in the experiment. I would recommend adding a table for both materials. 

Results and Discussion: There is a need to make extensive changes in this section. I should not recommend doing them together. I recommend doing them separately because they way you are presenting the results and doing the discussion it looks like a parameter to parameter discussion which is not a way to do a discussion. You have to do the discussion separately in this case you can consider all your results and do a discussion and discuss them collectively. In this way, you can present your findings more accurately and more precisely. 

In table 2, double-check the things about the table. Have you done the statistical analysis?

For all tables, you need to put the description of the table in terms of statistical analysis p<0.05, p<0.01, p<0.001. 

Conclusion: There is a need to avoid the results terms like non-significant difference/ significant difference. There is a need to focus on your main results without there statistical results just to highlight the importance of those results and what you missed during your experiment that needs to be considered for future study and future directions based on the results of your experiment. 

References: Follow the MDPI policy for formatting the results. Like placing the year in its proper place. Please also see some other errors as well. 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

Extensive English editing is required throughout the manuscript. 

Author Response

1. Comments: Title of the paper: See the attached file “what is the meaning of this modified biochar? means how you modified this biochar? like by fermentation or by other methods? i recommend to put like acidifed biochar or etc.”

Response: An excellent suggestion. We have revised the title as follows: Ball milling modified biochar with additives enhances soil Cd passivation, increases plant growth and restrains Cd uptake by Chinese cabbage, which may make the topic of this article more clearly.

2. Comments: Abstract:There is a need to add one or two lines for the background/ importance of the study. Mention the treatments you applied during the study. It looks a bit longer with some extra data that doesn't need to be put in the abstract. Focus on your main results/ findings that you think could make a difference to present this study. 

Response: The background/ importance of the study was added in the abstract, such as in line 14-16 “Biochar is a popular amendment in Cd polluted soil. However, the performance of bulk biochar is still less than satisfactory, effective modification are of very important to improve its adsorption capacity for Cd”, line 18-20 “Both batch experiment and pot cultivation were conducted to elucidate the adsorption mechanisms of Cd by modified biochar and their effects on Cd passivation and plant uptake in Cd polluted soil”. Additionally, some extra data about pH, EC, CEC, available potassium, organic matters in soil was removed (line 25-27). Please see the revised MS for details, the changes have been highlighted in red.

3. Comments: Keywords:It needs to be revised as per the title. Avoid the words that are already used in the title to maximize your work availability. 

Response: keywords have been revised to “heavy metals; soil pollution; modification; adsorption; safe production”. The words that are already used in the title has been removed.

4. Comments 3: Introduction: There is a need to improve the introduction based on the modified biochar you used in your study. Most of the background you provided is based on the simple biochar applied but not/ very less about the modified biochar that needs to be addressed there because biochar and modified biochar are two different things so, their efficiency will also be different. Also, see the attached file for more comments. 

Response: The introduction based on the modified biochar used in our study has been intensively and carefully improved according to your constructive suggestion. The changes have been highlighted in red in revised MS as showed in line 59-63 “More importantly, biochar application is expected to decrease the content of bioavailable heavy metals in polluted soil and reduce the transport of heavy metals from soil to plant, perhaps allowing and even promoting the production of valuable products by the plant [10]. However, the performance of bulk biochar is still less than satisfactory, and there is still plenty room for improvement”, line 65-66, and line 68-94. Please see the revised MS for details.

5. Material and Methods: There is a need to add the soil properties used in the experiment. Also, add biochar properties used in the experiment. I would recommend adding a table for both materials. 

Response: The soil and biochar properties used in the experiment were added as illustrated in Table 1 in the revised MS “Basic properties of soil and biochar tested in this study”, Please see the revised MS for details.

6. Results and Discussion: There is a need to make extensive changes in this section. I should not recommend doing them together. I recommend doing them separately because they way you are presenting the results and doing the discussion it looks like a parameter to parameter discussion which is not a way to do a discussion. You have to do the discussion separately in this case you can consider all your results and do a discussion and discuss them collectively. In this way, you can present your findings more accurately and more precisely. 

Response: Thank you for your kind consideration and constructive comments. We have made extensive and careful changes in this section as shown in line 257-261, line 271-276, line 281-287, line 290-300 and line 364-368 about discussion on the results of characteristics of modified biochar and kinetics and isotherms of Cd; and line 519-521, line 546-551, line 555-559, line 562-572, etc concerned the Influence of modified biochar on Cd bioavailability in soils. All changes have been highlighted, please see the revised MS for details.

For almost all journals, it is acceptable to separate or combined the results with discussions, as well as in the Instructions for Authors of “horticulturae” which stated “This section of discussion may be combined with Results” that the latest articles published on horticulturae also adopted this way e.g.“Detection of Tomato Leaf Pesticide Residues Based on Fluorescence Spectrum and Hyper-Spectrum” by Gao et al (Horticulturae 2025, 11(2), 121; https://doi.org/10.3390/horticulturae11020121); and “Influence of Habitat Factors on the Yield, Morphological Characteristics, and Total Phenolic/Flavonoid Content of Wild Garlic (Allium ursinum L.) in the Republic of Serbia” by Gordanić et al (Horticulturae 2025, 11(2), 118; https://doi.org/10.3390/horticulturae11020118), etc.

7. In table 2, double-check the things about the table. Have you done the statistical analysis?

Response: Due to the particularity of adsorption kinetics and Adsorption isotherm research field, adsorption data and their fitting curves, parameters are basically averaged and not subjected to statistical analysis, e.g. the article published by Pan et al on “Biochar”: Biochar. 7, 16. https://doi.org/10.1007/s42773-024-00401-7 and Sun et al on “Science of the Total Environment ”: Sci. Total Environ. 851(2), 158252. https://doi.org/10.1016/j.scitotenv.2022.158252, etc.

8. For all tables, you need to put the description of the table in terms of statistical analysis p<0.05, p<0.01, p<0.001. 

Response: The description of the table and figure in terms of statistical analysis p<0.05 has been added below the table and figure, which have been highlighted in red. Please see the revised MS for details.

9. Conclusion: There is a need to avoid the results terms like non-significant difference/ significant difference. There is a need to focus on your main results without there statistical results just to highlight the importance of those results and what you missed during your experiment that needs to be considered for future study and future directions based on the results of your experiment. 

Response: Thank you for your constructive suggestions. The sentence “However, no significant differences were observed between modified biochar (QA/QKA) and unmodified biochar (YC) treatments” has been deleted. In addition, the conclusion has been carefully and intensively revised as seen in line 609-622 of revised MS. All changes have been highlighted, please see the revised MS for details.

10. References: Follow the MDPI policy for formatting the results. Like placing the year in its proper place. Please also see some other errors as well.

Response: Done. In addition, references cited have been extensively expanded, nineteen latest references closely related to this study, please see the revised MS for details.

11. Comments on the Quality of English Language

Extensive English editing is required throughout the manuscript. 

Response: The manuscript has been carefully and extensively edited by an expert in technical English according to your suggestion.

We hope that our revision will meet your satisfaction. Thank you for your consideration

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript is a complete laboratory study and may be of interest to specialists studying the mechanisms of heavy metal sorption in soils. The use of biochar for the sorption of heavy metals from soils is a fairly popular topic and there are already a sufficient number of publications on this topic.

Please specify the novelty of your research.

The result obtained during the vegetative experiment in the laboratory will not always be reproduced in natural field conditions.

The sorption of heavy metals from soils, in addition to pH and organic matter content, will be influenced by the granulomeric composition of the soil (the content of the silty fraction). Also, in addition to the content of organic carbon, it is important to know the content of humic acids. It is humic acids that are able to form stable complexes with divalent metals. The mechanism of soil self-purification is based on this.

If you have such data, it is better to add it to the manuscript.

Author Response

1. Please specify the novelty of your research.

Response: The novelty of our research has been added in line 86-94 as follows “In this study, a novel integration of mechanically ball milling in combined with either KOH alone or with attapulgite as additives for biochar modification was investigated which is expected to provide advanced materials for eco-friendly applications. The objectives of this study were to (1) investigate the characteristics of ball milling modified biochars with addition of either KOH alone or combined with attapulgite, (2) the adsorption mechanisms of Cd by ball milling modified biochar and (3) their performance on soil Cd passivation, plant growth promotion and Cd uptake reduction by Chinese cabbage in the Cd polluted soil.”

2. The result obtained during the vegetative experiment in the laboratory will not always be reproduced in natural field conditions.

Response: Thank you for your kind consideration and constructive comments. As showed in line 637-642, we stated “It should be noted that the performance of QK/QKA on the remediation effects and vegetable production may not be consistent across all soils, as they were highly dependent on the physicochemical characteristics of the biochar and soil properties[68], especially the granulomeric composition of the soil and the organic matter composition (in particular the content of humic acid).” and future researched needed to be considered and future directions based on our present experiment were also proposed as shown in line 617-622 of the revised MS.

3. The sorption of heavy metals from soils, in addition to pH and organic matter content, will be influenced by the granulomeric composition of the soil (the content of the silty fraction). Also, in addition to the content of organic carbon, it is important to know the content of humic acids. It is humic acids that are able to form stable complexes with divalent metals. The mechanism of soil self-purification is based on this.

If you have such data, it is better to add it to the manuscript.

Response: Thank you for your constructive suggestions. The granulomeric composition of the soil and the organic matter composition (in particular the content of humic acid) will be taken into consideration in our future studies to validate the feasibility and stability of modified biochar in different types of soil under different Cd pollution.

We hope that our revision will meet your satisfaction. Thank you for your consideration.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript entitled: “Modified Biochar enhances soil Cd passivation, increases plant 2 growth and restrains Cd uptake by Chinese cabbage” deals with an important issue, which is attracting the interest of the scientific community.

However, there are some points that need to be clarified and improved.

The manuscript needs improvements and a stronger theoretical background enhanced with more and up-to-date articles. Both the Introduction and the Discussion do not provide a thorough discussion of biochar’s use, which is kind of soil remediation that needs to be highlighted, as indeed metal contaminants are retained within the soil, yet the metals are not moved into the plant, perhaps allowing and even promoting the production of valuable products by the plant.

The novelty of the paper should be highlighted and shown at key points in the manuscript, such as at the end of the Introduction chapter or even at the end of the Discussion chapter.

In the Materials and Methods chapter:

The chemical analyses need to be reported in more detail. Method names, a brief description of the reagents, instrumentation and limits of detection of the elements determined should be given.

It is important that below each Figure there is more clarification and explanation of each symbol used.

The size of the manuscript is small. The Introduction, the discussion and the bibliographic references need to be expanded.

Author Response

1. The manuscript needs improvements and a stronger theoretical background enhanced with more and up-to-date articles. Both the Introduction and the Discussion do not provide a thorough discussion of biochar’s use, which is kind of soil remediation that needs to be highlighted, as indeed metal contaminants are retained within the soil, yet the metals are not moved into the plant, perhaps allowing and even promoting the production of valuable products by the plant.

Response: The introduction based on the modified biochar used in our study has been intensively and carefully improved according to your constructive suggestion. The changes have been highlighted in red in revised MS as showed in line 59-63 “More importantly, biochar application is expected to decrease the content of bioavaila-ble heavy metals in polluted soil and reduce the transport of heavy metals from soil to plant, perhaps allowing and even promoting the production of valuable products by the plant [10]. However, the performance of bulk biochar is still less than satisfactory, and there is still plenty room for improvement”, and other revisions in line 65-66, and line 68-94, Please see the revised MS for details.

In addition, we have been made extensive and carefully changes in the Discussion as shown in line 257-261, line 271-276, line 281-287, line 290-300 and line 364-368 about discussion on the results of Characteristics of modified biochar and Kinetics and isotherms of Cd; and line 519-521, line 546-551, line 555-559, line 562-572, etc concerned the Influence of modified biochar on Cd bioavailability in soils. All changes have been highlighted, please see the revised MS for details.

2. The novelty of the paper should be highlighted and shown at key points in the manuscript, such as at the end of the Introduction chapter or even at the end of the Discussion chapter.

Response: The novelty of our research has been added in line 84-87 as follows “In this study, a novel integration of mechanically ball milling in combined with either KOH alone or with attapulgite as additives for biochar modification was investigated which is expected to provide advanced materials for eco-friendly applications. The objectives of this study were to (1) investigate the characteristics of ball milling modified biochars with addition of either KOH alone or combined with attapulgite, (2) the adsorption mechanisms of Cd by ball milling modified biochar and (3) their performance on soil Cd passivation, plant growth promotion and Cd uptake reduction by Chinese cabbage in the Cd polluted soil.”

3. In the Materials and Methods chapter:

The chemical analyses need to be reported in more detail. Method names, a brief description of the reagents, instrumentation and limits of detection of the elements determined should be given.

Response: Thank you for your kind suggestion. The measurement of C, H, O, N, S in biochar (in line 128-129), the analysis of Cd in plant tissues, soil and basic properties of soil and biochar have been reported in more detail (line 204-208, line 212-230, and detection limits of Cd were given.

4. It is important that below each Figure there is more clarification and explanation of each symbol used.

Response: More clarification and explanation of each symbol used were given below each Figure or table. Please more details in the revised MS.

5. The size of the manuscript is small. The Introduction, the discussion and the bibliographic references need to be expanded.

Response: Thank you for your constructive suggestion. The Introduction, the discussion and the bibliographic references have been extensively expanded.

The introduction based on the modified biochar used in our study has been intensively and carefully improved according to your constructive suggestion. The changes have been highlighted in red in revised MS as showed in line 59-63 “More importantly, biochar application is expected to decrease the content of bioavailable heavy metals in polluted soil and reduce the transport of heavy metals from soil to plant, perhaps allowing and even promoting the production of valuable products by the plant [10]. However, the performance of bulk biochar is still less than satisfactory, and there is still plenty room for improvement”, and other revisions in line 65-66, and line 68-94, Please see the revised MS for details.

In addition, we have made extensive and careful changes in the Discussion as shown in line 257-261, line 271-276, line 281-287, line 290-300 and line 364-368 about discussion on the results of Characteristics of modified biochar and Kinetics and isotherms of Cd; and line 519-521, line 546-551, line 555-559, line 562-572, etc concerned the Influence of modified biochar on Cd bioavailability in soils. All changes have been highlighted, please see the revised MS for details.

And bibliographic references have been extensively expanded, nineteen latest references closely related to this study were included as follows:

Pan, X., Kuang, S.P., Wang, X., Ullah, H., Rao, Z.P., Ali, E.F., Abbas, Q., Lee, S.S., Shaheen, S.M., 2025. Functionalization of sawdust biochar using Mg-Fe-LDH and sodium dodecyl sulfonate enhanced its stability and immobilization capacity for Cd and Pb in contaminated water and soil. Biochar. 7, 16. https://doi.org/10.1007/s42773-024-00401-7.

Fakhar, A., Snowie, J.C.G., Ronley, C.C., Mazhar, R., Rubab, S., Aitazaz, A.F., Muhammad, I.K., 2025. Advancing modifed biochar for sustainable agriculture: a comprehensive review on characterization, analysis, and soil performance. Biochar. 7, 8. https://doi.org/10.1007/s42773-024-00397-0.

Zhang, P., Xue, B., Jiao, L., Meng, X., Zhang, L., Li, B., Sun, H., 2022. Preparation of ball-milled phosphorus-loaded biochar and its highly efective remediation for Cd- and Pb-contaminated alkaline soil. Sci. Total Environ. 813,152648. https://doi.org/10.1016/j.scitotenv.2021.152648.

Montinaro, S.,  Concas, A., Pisu, M., Cao, G., 2008. Immobilization of heavy metals in contaminated soils through ball milling with and without additives. Chem. Eng. J. 142(3), 271-284.

Muñoz-Batista, M.J., Rodriguez-Padron, D., Puente-Santiago, A.R., Luque, R., 2018. Mechanochemistry: toward sustainable design of advanced nanomaterials for electrochemical energy storage and catalytic applications. ACS Sustainable Chem. Eng. 6, 9530–9544. https://doi.org/10.1021/acssuschemeng.8b01716.

Jiang, M.Y., He, L.Z., Niazi, N.K., Wang, H.L., Gustave. W., Vithanage, M., Geng, K., Shang, H., Zhang, X.L., Wang, Z.Y., 2023. Nanobiochar for the remediation of contaminated soil and water: challenges and opportunitie. Biochar. 5, 2. https://doi.org/10.1007/s42773-022-00201-x.

Vuong, X., Vu. L., Duong, A., Duong, H., Hoang, T., Luu, M., Nguyen, T., Nguyen, V., Nguyen, T., Van, T., 2023. Speciation and environmental risk assessment of heavy metals in soil from a lead/zinc mining site in Vietnam. Int. J. Environ. Sc.i Technol. 20(5), 5295–5310.

Gujre, N., Rangan, L., Mitra, S., 2021. Occurrence, geochemical fraction, ecological and health risk assessment of cadmium, copper and nickel in soils contaminated with municipal solid wastes. Chemosphere. 271, 129573. https://doi.org/10.1016/j.chemosphere.2021.129573.

Dong, M.Y.,  Jiang, M.Y.,  He, L.Z., Zhang, Z.R., Gustave, W.,  Vithanage, M.,  Niazi, N.K., Chen, Bo., Zhang, X.K., Wang, H.L., He, F., 2025. Challenges in safe environmental applications of biochar: identifying risks and unintended consequence. Biochar, 7, 12. https://doi.org/10.1007/s42773-024-00412-4.

Yuan, C., Gao, B., Peng, Y., Gao, X., Fan, B., Chen, Q., 2021. A meta-analysis of heavy metal bioavailability response to biochar aging: importance of soil and biochar properties. Sci. Total Environ. 756, 144058. https://doi.org/10.1016/j.scitotenv.2020.144058.

Gong, H.B., Zhao, L., Rui, X., Hu, J.W., Zhu, N., 2022. A review of pristine and modifed biochar immobilizing typical heavy metals in soil: applications and challenges. J. Hazard. Mater. 432, 128668. https://doi.org/10.1016/j.jhazmat.2022.128668.

Liang, X., Su, Y., Wang, X., Liang, C., Tang, C., Wei, J., Liu, K., Ma, J., Yu, F., Li, Y., 2023. Insights into the heavy metal adsorption and immobilization mechanisms of CaFelayered double hydroxide corn straw biochar: synthesis and application in a combined heavy metal-contaminated environment. Chemosphere. 313, 137467. https://doi.org/10.1016/j.chemosphere.2022.137467.

Liu, G.F.,  Dai, Z.M., Tang, C.X., Xu, J.M., 2022. The immobilization, plant uptake and translocation of cadmium in a soil-pakchoi (Brassica chinensis L.) system amended with various sugarcane bagasse-based materials. Environ. Pollut. 311, 119946.

Pathak, H.K., Seth, C.S., Chauhan, P.K., Dubey, G., Singh, G., Jain, D., Upadhyay, S.K., Dwivedi, P., Khoo, K.S., 2024. Recent advancement of nano-biochar for the remediation of heavy metals and emerging contaminants: Mechanism, adsorption kinetic model, plant growth and development. Environ. Res. 255, 119136.

Su, J.Z., Zhang, M.Y, Xu, W.H., Xu, W.M., Liu, C., Rui, S., Tuo, Y.F., He, X.H., Xiang, P., 2024. Preparation and applications of iron/biochar composites in remediation of heavy metal contaminated soils: Current status and further perspectives. Environ. Technol. Inno. 35, 10367.

Khaliq, H., Anwar, S., Shafiq, F., Ashraf, M., Zhang, L., Haider, I., Khan, S., 2023. Interactive effects of soil and foliar-applied nanobiochar on growth, metabolites, and nutrient composition in Daucus carota. J. Plant Growth Regul. 42(6),3715-3729. https://doi.org/10.1007/s00344-022-10832-w.

Mariyam, S., Upadhyay, S.K., Chakraborty, K., Verma, K.K., Duhan, J.S., Muneer, S., Meena, M., Sharma, R.K., Ghodake, G., Seth, S.C., 2024. Nanotechnology, a frontier in agricultural science, a novel approach in abiotic stress management and convergence with new age medicine-A review. Sci. Total Environ. 912, 169097. https://doi.org/10.1016/j.scitotenv.2023.169097.

Chen, W., Kang, Z., Yang, Y., Li, Y., Qiu, R., Qin, J., Li, H., 2022. Interplanting of rice cultivars with high and low Cd accumulation can achieve the goal of “repairing while producing” in Cd-contaminated soil. Sci. Total Environ. 851, 158229. https://doi.org/10.1016/j.scitotenv.2022.158229.

Yan, M.F., Li, H.J., Si. B.C., Xu, C.Y., Li, M., 2024. Parameters Optimization and Physicochemical Properties Characterization of Nanobiochar Prepared from Apple Branches by Ball Milling. Nano. 19 (05), 2450031. https://doi.org/10.1142/S1793292024500310.

 

please see more details in the revised MS.

We hope that our revision will meet your satisfaction. Thank you for your consideration.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have done a great job. I'm happy with the revised version and have no further comments. 

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript was modified according to the recommendations, which significantly improved it. It is advisable to continue the study and add information on the granulometric composition and content of humic acids in soils to assess the mechanism of fixation of heavy metals in soils.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors followed the instructions and suggestions of the reviewers to the letter and now the revised manuscript meets the requirements for publication in the journal.