Contribution of Arbuscular Mycorrhizal Fungi to Sustainable Maize Production in the Low-Fertility Ultisols of Thailand

Comments 1: The manuscript is devoted to increasing soil fertility and plant yields using mycorrhizal fungi of the genus Glomus. The authors obtained interesting and practically significant results. The article is interesting, and the research was conducted at a high methodological level.

As a comment, I would note that the author worked with only one strain of Glomus sp., KUSoil5. However, for some reason, they always refer to it as AMF, without discussing the specific characteristics of the fungus at all. This needs to be corrected.

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have discussed the specific characteristics of Glomus sp. KUSoil5 in paragraph 4 of the discussion section (page 12).

Comments 1: While the work is relevant, AMF–maize interactions in low-fertility soils have been extensively studied. The introduction briefly references previous studies, but the specific novelty of this research is not sufficiently highlighted. A stronger justification of the scientific novelty would increase reader’s interest.

Response 1: Thank you for pointing this out. We agree with this comment. This research examined low-fertility soils that require chemical fertilisers for maize cultivation to increase the limited soil nutrients. Therefore, the challenge of this research is to evaluate the tolerance of arbuscular mycorrhizal fungi to high rates of chemical fertiliser application and to determine whether they can improve the growth and yield of maize in low-fertility soils. We hope that the results of this research will be practically applied in plant cultivation. Therefore, we have given more explanation about this point in the introduction section (page 2).

Comments 2: The authors state that AMF efficiency becomes low under 100% CF, which is reasonable; however: very low RMD at 100% CF (as low as 5.38% in Korat) indicates almost no benefit. Yet the Discussion still emphasizes advantages at all CF levels.

The authors should address the diminishing returns more critically: at what fertiliser threshold does AMF inoculation no longer provide economic/agronomic value? Are AMF treatments cost-effective at full fertilization rates?

Response 2: Thank you for pointing this out. We agree with this comment. The combination of AMF with high levels of chemical fertilisers seems to result in low economic efficiency. Consequently, we've included a discussion on this topic in the discussion and conclusion section for further consideration (Page 13, 14).

Comments 3: The study claims the results will benefit maize cultivation in Thailand, yet there is no economic analysis of fertilizer savings vs. AMF cost.

Response 3: Thank you for pointing this out. We agree with this comment. The combination of AMF with high levels of chemical fertilisers seems to result in low economic efficiency. Consequently, we've included a discussion on this topic in the discussion and conclusion section for further consideration (Page 13, 14).

Comments 4: The Introduction cites many general AMF references but needs more region-specific information and clearer statement of how this work differs from previous studies.

Response 4: Thank you for pointing this out. We agree with this comment. This research examined low-fertility soils that require chemical fertilisers for maize cultivation to increase the limited soil nutrients. Therefore, the challenge of this research is to evaluate the tolerance of arbuscular mycorrhizal fungi to high rates of chemical fertiliser application and to determine whether they can improve the growth and yield of maize in low-fertility soils. We have given more explanation about this point in the introduction section (page 2).

Comments 5: In material and methos clarify if plants received uniform irrigation (drip, hand-watering, volume?)

Response 5: Thank you for pointing this out. We agree with this comment. The plants were watered using pot weighing to maintain uniform irrigation (page 4).

Comments 6: The manuscript contains grammatical errors that should be corrected

Response 6: Thank you for pointing this out. We agree with this comment. Therefore, the re-submitted manuscript's English-language accuracy has been improved by MDPI author services.

Comments 7: “AMF can play a role in enhance nutrient availability for plants.” change to “AMF can play a role in enhancing nutrient availability for plants.”

Response 7: Thank you for pointing this out. We agree with this comment. “AMF can play a role in enhancing nutrient availability for plants.” has been changed to “AMF can play a role in enhancing nutrient availability for plants.” (Abstract, Page 1)

Comments 8: “AMF are outstanding at increasing nutrient absorption in plants.” could be “AMF are highly effective at increasing nutrient absorption in plants.”

Response 8: Thank you for pointing this out. We agree with this comment. “AMF are outstanding at increasing nutrient absorption in plants.” has been changed to “AMF are highly effective at increasing nutrient absorption in plants.” (Introdution, Page 2)

Comments 9: “The soils were homogenised and sterilised using an autoclave… before their use in the experiment.” would be better if “The soils were homogenised and sterilised using an autoclave… before being used in the experiment.”

Response 9: Thank you for pointing this out. We agree with this comment. “The soils were homogenised and sterilised using an autoclave… before their use in the experiment.” has been changed to “The soils were homogenised and sterilised using an autoclave… before being used in the experiment.” (Materials and method, Page 3)

Comments 10: “Using AMF in combination with high levels of chemical fertilisers can potentially hinder plant growth by fostering a parasitic relationship.” is redundant, use instead “Using AMF with high levels of chemical fertilisers may hinder plant growth by fostering a parasitic relationship.”

Response 10: Thank you for pointing this out. We agree with this comment. “Using AMF in combination with high levels of chemical fertilisers can potentially hinder plant growth by fostering a parasitic relationship.” has been changed to “Using AMF with high levels of chemical fertilisers may hinder plant growth by fostering a parasitic relationship.” (Discussion, Page 13)

Comments 1: Major comments: It should have at least one photo to show how maize plant growth with different treatments; There are only Tables, no figures

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have added the photos of maize growth at 30DAP, which were compared between non-AMF and AMF treatments at 0% CF of Korat (a), Mabbon (b) and Pakthongchai (c) soil series in Figure 1 (Page 6).

Comments 2: Minor comments: The key words are only three, it should increase to 4 or 5 key words; The first letter of each key word should be capital;

Response 2: Thank you for pointing this out. We agree with this comment. Therefore, we have added keywords from 3 to 5 and use the capital of the first letter of each keyword (Page 1).

Comments 3: Minor comments: In the material part, why 100-25-60 kg N-P₂O₅-K₂O/ha and 100-25-50 kg N-P₂O₅-K₂O/ha were chosen, it should have some explanation.

Response 3: Thank you for pointing this out. We agree with this comment. The rate of chemical fertiliser was applied according to site-specific soil analysis for maize cultivation (Page 3), which was reported by Attanandana, T.; Yost, R.S. A site-specific nutrient management approach for maize: Thailand’s experience. Better Crops Int. 2003, 17, 3–7. (Page 15).

Abstract:

Comments 1: Some scored key data regarding the effect of AMF on growth, yield, nutrients, and P-value of maize plant should be added. This is important to provide concise results.

Response 1: Thank you for pointing this out. We agree with this comment. Therefore, we have added p-value for the effect of AMF (Abstract, Page 1). 

Comments 2: Key words: This section's content should be changed since the words used to create the title should not be utilized as the keyword, then rearrange alphabetically.

Response 2: Thank you for pointing this out. We agree with this comment. Therefore, keywords have been changed (page 1).

Introduction:

Comments 3: Using the most recent references (those published after 2020) is advised.

Response 3: Thank you for pointing this out. We agree with this comment. Therefore, we have included the articles published after 2020 in the introduction (References no. 11, 15, 16).

Comments 4: Detailed information about beneficial impacts of AMF in maize cultivation should be defined. This paper will help you https://doi.org/10.3390/microorganisms13061345

Response 4: Thank you for pointing this out. We agree with this comment. Therefore, we have included this articles in the introduction (Page 2).

Comments 5: The gaps in the study must be succinctly defined by the researchers, and the authors must show the originality of the study.

Response 5: Thank you for pointing this out. We agree with this comment. This research examined low-fertility soils that require chemical fertilisers for maize cultivation to increase the limited soil nutrients. Therefore, the challenge of this research is to evaluate the tolerance of arbuscular mycorrhizal fungi to high rates of chemical fertiliser application and to determine whether they can improve the growth and yield of maize in low-fertility soils. We hope that the results of this research will be practically applied in plant cultivation. Therefore, we have given more explanation about this point in the introduction section (page 2).

M&M:

Comments 6: How did the authors sterilize so large amounts of soil???

Response 6: We faced a shortage of large sterilisers, which forced us to rely on autoclaves as a substitute, and this occurred on several occasions.

Comments 7: Is “KUSoil5” the accession number in the GenBanK???

Response 7: Thank you for pointing this out. We agree with this comment. This AMF was isolated from maize-associated soils at the National Corn and Sorghum Research Centre (Pakchong soil series, Rhodic Kandiustox, 14.64227° N, 101.31517° E) and identified based on morphological characteristics and 18S rDNA sequence analysis by Na Bhadalung et al. 2005 and Na Bhadalung 2005. (Page 3)

Comments 8: Please add some details about the pots such as height, diameter, etc….

Response 8: Thank you for pointing this out. We agree with this comment. Therefore, we have added the details of the pots in the materials and methods section (page 4).

Comments 9: Please supplement the basis for the application rate and method of AMF under different treatments.

Response 9: Thank you for pointing this out. We agree with this comment. Therefore, we have given the details about the application rate and method of AMF under different treatments in the materials and methods section (page 4).

Comments 10: Why was not the method of Vierheilig with ink instead of toxic trypanblue used? Vierheilig H., Coughlan A. P., Wyss U., Piché Y. (1998). Ink and vinegar, a simple staining technique for arbuscular-mycorrhizal fungi. Applied and Environmental Microbiology 64, 5004-5007.

Response 10: Thank you for pointing this out. We agree with this comment. We appreciate this helpful advice. Trypan blue can be dangerous, but we use it with caution. However, we will try the method you suggested.

Results:

Comments 11: The significant status should be mentioned at the beginning of the text for each measurement.

Response 11: Thank you for pointing this out. We agree with this comment. 

We have highlighted the significance of each issue.

Comments 12: For better understanding, creating a PCA plot is necessary.

Response 12: Thank you for pointing this out. We agree with this comment. The amount of data may not be sufficient for a PCA plot.

Discussion

Comments 13: I really appreciate the well-written discussion, however I suggest citing tables to make the readers in contact with the results.

Response 13: Thank you for pointing this out. We agree with this comment. Therefore, We have included citing tables in the discussion section ( pages 11 to 13).