Characteristics of Soil DOM and Its Effect on the Transformation of Potentially Toxic Elements (PTE) Forms under Organic Fertilizer Return Conditions
Round 1
Reviewer 1 Report
Dear,
The manuscript has an interesting research line and brings to light relevant results. However, there are a few concerns that must be highlighted.
1- The term heavy metal is no longer indicated to refer to the metals studied in this research. Currently is correct to replace it with the expression “Potentially Toxic Elements (PTE)”. Also, I would suggest reading the paper published by Pourret and Hursthouse (2019) in MDPI International Journal of Environmental Research and Public Health (doi:10.3390/ijerph16224446).
2- Despite there are limitations to the number of words in the abstract, I would suggest to the authors that they could revisit it to replace a few less important pieces of information with others related to the material and methods.
3- Lines 69-71: Despite this sentence, it is not clear to me why this study is relevant (scientifically). I would suggest to the authors reorganize the introduction’s structure to make it clear. Once the introduction is too short, they would insert two or three paragraphs to explore more the different fractions of the soil organic matter (then they may give the right attention to the DOM) and their relations to the PTE with the use of organic inputs. There are a lot of papers exploring the theme in the literature that the authors could use.
4- I would suggest the authors rewrite the objectives, as I’m not familiar with this format of objectives’ presentation.
5- 2.1 Section: What is the soil classification? What is the parent material of this soil? How is the topography? What is the history of the application of inputs in the study area? Additionally, I would suggest including a figure of the location of the study area with an experiment design showing the treatments’ position.
6- 2.2 Section: What was used for sampling the soil? How would you argue that your experiment has consistent results even without repetition over the years (at least 4)?
7- 2.6 Section: Please insert information on analytical quality control.
8- 2.8 Section: Don’t you think a descriptive statistical analysis could be important? How potential problems with multicollinearity and heteroscedasticity were addressed?
9- I am no longer comfortable with the presentation of results and discussion in the same section. Some results usually are less discussed in this format, as we see between lines 152-160. Then separating the discussion from the results would be very welcome. It would certainly improve this manuscript.
1- The conclusions should be rewritten, once they are more similar to the results than to the conclusions.
Author Response
Response to Reviewer 1 Comments
Point 1: The term heavy metal is no longer indicated to refer to the metals studied in this research. Currently is correct to replace it with the expression “Potentially Toxic Elements (PTE)”. Also, I would suggest reading the paper published by Pourret and Hursthouse (2019) in MDPI International Journal of Environmental Research and Public Health (doi:10.3390/ijerph16224446).
Response 1: We have replaced the term heavy metal according to your suggestion. Thank you for your reminder.
Point 2: Despite there are limitations to the number of words in the abstract, I would suggest to the authors that they could revisit it to replace a few less important pieces of information with others related to the material and methods.
Response 2: We have re-examined the summary according to your requirements, replacing less important information with materials and methods. (Lines 11-19, page 1)
Point 3: Lines 69-71: Despite this sentence, it is not clear to me why this study is relevant (scientifically). I would suggest to the authors reorganize the introduction’s structure to make it clear. Once the introduction is too short, they would insert two or three paragraphs to explore more the different fractions of the soil organic matter (then they may give the right attention to the DOM) and their relations to the PTE with the use of organic inputs. There are a lot of papers exploring the theme in the literature that the authors could use.
Response 3: Thank you for your suggestion. According to your suggestion, we reorganized the structure of the introduction and added more content about different components of soil DOM and its relationship with PTE after organic fertilizer input. (Lines 50-101, page 2-3)
Point 4: I would suggest the authors rewrite the objectives, as I’m not familiar with this format of objectives’ presentation.
Response 4: Based on your suggestions, we have read the relevant literature and have modified the target format. (Lines 102-108, page 3)
Point 5: What is the soil classification? What is the parent material of this soil? How is the topography? What is the history of the application of inputs in the study area? Additionally, I would suggest including a figure of the location of the study area with an experiment design showing the treatments’ position.
Response 5: The soil is composed of clay (0.002mm), silt (0.002~0.02mm) and sand (0.02~2mm). The particle size of silt loam is: clay 25%, silt 50% and sand 24.88%. The study area belongs to residual parent material. In the past few years, the study area has applied pig manure, chicken manure and other organic fertilizers and organic fertilizer combined with chemical fertilizers on soil fertility and crop growth. Located in the north-central part of Henan Province, the middle and lower reaches of the Yellow River, the terrain is flat. The study area location map has been supplemented according to your suggestion (see Figure 1). (Lines 111-119, page 3)
Point 6: 2.2 Section: What was used for sampling the soil? How would you argue that your experiment has consistent results even without repetition over the years (at least 4)?
Response 6: In this study, earth auger was used for sampling for chemical analysis. Although we did not repeat it for many years, we set up four replicates in the experiment to verify the reproducibility of the results. (Lines 129-130, page 4)
Point 7: 2.6 Section: Please insert information on analytical quality control.
Response 7: Each sample was repeated four times to control experimental errors. (Lines 172-173-174, page 5)
Point 8: 2.8 Section: Don’t you think a descriptive statistical analysis could be important? How potential problems with multicollinearity and heteroscedasticity were addressed?
Response 8: Thanks to the reviewer’s questions, we also think descriptive statistical analysis is very important. Because it meets the requirements, it is ignored to add in the text. It has been added in Section 2.8. (Lines 182-185, page 5)
Point 9: I am no longer comfortable with the presentation of results and discussion in the same section. Some results usually are less discussed in this format, as we see between lines 152-160. Then separating the discussion from the results would be very welcome. It would certainly improve this manuscript.
Response 9: We are extremely grateful to reviewer for pointing out this problem. According to your suggestion, we have written the results and discussion separately. (Lines 189-373, page 5-12)
Point 10: The conclusions should be rewritten, once they are more similar to the results than to the conclusions.
Response 10: We modify the conclusions of this paper based on the recommendations, avoiding the problem of similar results and conclusions. (Lines 375-383, page 12)
Author Response File: 
Author Response.docx
Reviewer 2 Report
Lines 41-44: It is kind of obvious that an aplication of organic fertilizer will change the DOM composition, but why is it "an important way"? I guess that sentences starting with "Zhou et al..." explains that. Maybe you shoud not start the sentence with :therefore...that would change a bit the meaning of that part.
Lines 45-58: Does the biological activity of hevy metals have influence only on crop yeal or also on crop quality? If yes, it should be mentioned here.
Line 63: If in your opinion names of elements should be explained, you shoul explaine them also in the abstract part.
Line 88: Why did you choose silk loam soil for the experimental study? Is it main type of China agricultural land?
Line 91:
Why did you choose pig manure for the experiment? Is it most commonly used?
Lines 128: Please write the spectrum scaning operating steps.
Lines 145-149: Please add Matlab 2018b.
Line 152: "...analyzed in(with use of) PARAFAC..."
Please write the total number of samples. It is important especialy for PARAFAC results.
Lines 198-199: If C4 is negatively correlated with ETC it is obvious that the trends changes were opposite. no reson to mention that.
Lines 254-164: What does it mean? Does it mean that your study was too short? or that the longlasting fertilizing does more bad than good? or that there should be longer breaks between fertilizing considered? How that can be checked?
Line 274: what does it mean that component C4 was improved?
Lines 278-279: It is enough if you use tyrosine-like and tryptophan-like, without protein-like, at the same place.
Lines 270-184: What other conclusions can we take from your study? How the results should influence the usage of organic fertilizer? Is it better or worse to use it?
Table 3: Please specify after who you are using peak nomencalture, e.g. Coble, 1996.
Figure 1: Please ad:"components derived by PARAFAC" to the caption.
Figure 2: Please change sampling time into sampling state/sampling state of cultivation. What did you mean by Fmax? Shouldnt you use fluorescence intensity? What were the units? What do you present on this graph? are those averages? How many samples did you collect during each state of growth? Cant find it in the text. Please ad:"components derived by PARAFAC" to the caption.
Figure 3: Please ad:"components derived by PARAFAC" to the caption. Is that proportion of components or components fluorescence?
Figure 4. Please change sampling time into sampling state/sampling state of cultivation.What those small nested graphs show? It should be explained in the caption.
Author Response
Response to Reviewer 2 Comments
Point 1: Lines 41-44: It is kind of obvious that an aplication of organic fertilizer will change the DOM composition, but why is it "an important way"? I guess that sentences starting with "Zhou et al..." explains that. Maybe you shoud not start the sentence with: therefore...that would change a bit the meaning of that part.
Response 1: Thank you for your valuable suggestions. We have made changes according to your suggestions. (Lines 59-60, page 2)
Point 2: Lines 45-58: Does the biological activity of hevy metals have influence only on crop yeal or also on crop quality? If yes, it should be mentioned here.
Response 2: The effects of PTE bioavailability on crop quality have been supplemented according to your suggestions. (Lines 68-70, page 2)
Point 3: Line 63: If in your opinion names of elements should be explained, you shoul explaine them also in the abstract part.
Response 3: Thanks for your reminder, we have added the full names of Cr, Pb and Cd in the abstract. (Lines 13, page 1)
Point 4: Line 88: Why did you choose silk loam soil for the experimental study? Is it main type of China agricultural land?
Response 4: This is because different soil types may affect the experimental results. Sandy loam is one of the typical soils in central China. We choose it because it is one of the representative soils in our region. Of course, other types of soil are also necessary to study. Perhaps we will carry out relevant research in the future.
Point 5: Line 91: Why did you choose pig manure for the experiment? Is it most commonly used?
Response 5: Pig manure is the most productive manure of livestock and poultry in China. It is rich in nutrients such as organic matter and nitrogen, and it is widely used in the production of compost products and for arable land. In the introduction, we added the reasons for choosing pig manure compost products to carry out the experiment. (Lines 40-49, page1-2)
Point 6: Lines 128: Please write the spectrum scaning operating steps.
Response 6: We have added spectral scanning steps in Section 2.5. (Lines 156-161, page 4)
Point 7: Lines 145-149: Please add Matlab 2018b.
Response 7: Thanks for your reminder, we added Matlab 2018b in Section 2.8. (Lines 185-186, page 4)
Point 8: Line 152: "...analyzed in(with use of) PARAFAC..."
Please write the total number of samples. It is important especialy for PARAFAC results.
Response 8: The fluorescence spectra of 56 samples were obtained in this study. (Lines 190, page 5)
Point 9: Lines 198-199: If C4 is negatively correlated with ETC it is obvious that the trends changes were opposite. no reson to mention that.
Response 9: Thanks to the reviewer 's reminder, we have deleted the unnecessary part. (Lines 242, page 9)
Point 10: Lines 254-264: What does it mean? Does it mean that your study was too short? or that the longlasting fertilizing does more bad than good? or that there should be longer breaks between fertilizing considered? How that can be checked?
Response 10: Thank you for your question. From this study, short-term application of organic fertilizer reduced the biological effectiveness of PTE in soil. In addition, from other related studies, long-term application of organic fertilizer may increase the biological effectiveness of PTE, probably because the content of PTE in organic fertilizer is relatively high. After long-term accumulation, the biological effectiveness of PTE increased. In this study, the effect of applying organic fertilizer on reducing the biological effectiveness of PTE in soil came from the electron transfer between D0M and PTE in organic fertilizer. From the perspective of DOM, the application of organic fertilizer was beneficial to reduce the biological effectiveness of PTE in soil. Therefore, reasonable control of PTE content and relative content of DOM in organic fertilizer is beneficial to effectively control the biological effectiveness of PTE in soil. (Lines 352-362, page 12)
Point 11: Line 274: what does it mean that component C4 was improved?
Response 11: Thank you for your question, here we want to express the relative content of C4 fluorescent components is increased, and it has been revised in the manuscript.
Point 12: Lines 278-279: It is enough if you use tyrosine-like and tryptophan-like, without protein-like, at the same place.
Response 12: Thank you for your suggestion, we have modified.
Point 13: Lines 270-284: What other conclusions can we take from your study? How the results should influence the usage of organic fertilizer? Is it better or worse to use it?
Response 13: Combined with your suggestions, we have adjusted the structure of the conclusion appropriately. This study showed that short-term application of organic fertilizer or increased the electron transfer capacity of organic fertilizer (increased DOM content) were two feasible ways to safely utilize organic fertilizer. (Lines 378-380, page 12)
Point 14: Please specify after who you are using peak nomencalture, e. g. Coble, 1996.
Response 14: Based on your suggestion, we have included the source of the peak term in the text, as shown in Table 3. (Lines 200, page 5)
Point 15: Figure 1: Please ad:"components derived by PARAFAC" to the caption.
Response 15: Thank you for your suggestion, the title of Figure 2 has been perfected. (Lines 201, page 7)
Point 16: Figure 2: Please change sampling time into sampling state/sampling state of cultivation. What did you mean by Fmax? Shouldnt you use fluorescence intensity? What were the units? What do you present on this graph? are those averages? How many samples did you collect during each state of growth? Cant find it in the text. Please ad:"components derived by PARAFAC" to the caption.
Response 16: Thank you for your suggestions and questions. According to your suggestion, we have modified the sampling time in Figs. 3,4,5 to the sampling state (Line 227-230, page 8 - Line 260-261, page 9). The maximum fluorescence intensity (Fmax) is usually used to reflect the relative content of DOM (Lines 202-204, page7). The unit is a.u. (Lines 228, page8). Figure 3 represents the change in relative DOM content at each growth stage. These numbers are the average of parallel samples at each stage. Eight samples were collected in each growth state (Lines 129, page4). The title has been perfected.
Point 17: Figure 3: Please ad: "components derived by PARAFAC" to the caption. Is that proportion of components or components fluorescence?
Response 17: The title of Figure 4 has been improved (Lines 227-228, page8). Fig.4 represents the proportion of fluorescent components.
Point 18: Figure 4. Please change sampling time into sampling state/sampling state of cultivation. What those small nested graphs show? It should be explained in the caption.
Response 18: The sampling time in Fig.5 has been modified to the sampling state. The nested diagrams represent the chronoamperometric plots of EAC and EDC, respectively. (Lines 260-261, page9)
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
Dear
The authors did great work in the major review. However, I would recommend checking the following issues:
1- I discourage the use of words from the title in the keywords.
2- The soil classification is still missing in the manuscript. As well as the soil parent material. You mentioned that the study area belongs to the residual parent material. Which one? Also, you did not include the history of land use in the manuscript. It should be done. This is important.
3- Please check the sentence “…depth of 0-20cm, Soil samples were collected by earth auger…”. There is a mistake there.
4- Please check the sentence “…and tested.Each sample was repeated four times to avoid…”. It is missing a space between a point and the word Each.
5- In the section on “Results and analysis”, I would suggest modifying it to just “Results”.
6- I would suggest checking figure 5. It seems a little disarranged.
Author Response
Q1. I discourage the use of words from the title in the keywords.
Response：Thank you for your suggestion. We have modified it according to your suggestion. (Lines 35-36, page1)
Q2. The soil classification is still missing in the manuscript. As well as the soil parent material. You mentioned that the study area belongs to the residual parent material. Which one? Also, you did not include the history of land use in the manuscript. It should be done. This is important.
Response：According to your suggestions, we have supplemented and modified the soil classification, soil parent material and land use history by referring to relevant materials. (Lines 113-121, page3)
Q3.Please check the sentence “…depth of 0-20cm, Soil samples were collected by earth auger…”. There is a mistake there.
Response: Thank you for the reviewer 's reminder, we have modified it according to your reminder. (Lines 135, page4)
Q4. Please check the sentence “…and tested.Each sample was repeated four times to avoid…”. It is missing a space between a point and the word Each.
Response: Thank you for the reviewer 's reminder, we have modified it according to your reminder. (Lines 179, page5)
Q5. In the section on “Results and analysis”, I would suggest modifying it to just “Results”.
Response: Thank you for the reviewer 's reminder, we have modified it according to your reminder. (Lines 194, page5)
Q6. I would suggest checking figure 5. It seems a little disarranged.
Response: Thank you for your reminder, according to your reminder we modified Figure 5. (Lines 265, page10)
Author Response File: Author Response.docx
