Activated Carbon Reduced Nitrate Loss from Agricultural Soil but Did Not Enhance Wheat Yields
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis article primarily explores the use of activated carbon to reduce nitrate leaching in agricultural soils yet finds it fails to effectively maintain wheat yields; as a reviewer, I believe major revisions are necessary—particularly to clarify activated carbon’s specific impacts on soil nutrient dynamics and wheat physiology, and to provide more rigorous data analysis and discussion for stronger, more practical conclusions.
- Lines 4–6: The abstract mentions that AC failed to maintain wheat yield, but it does not specify the benchmark for “maintain.” Is it compared to a control without any nitrogen fertilizer or to a conventional fertilization treatment?
- Lines 38–40: It mentions “stagnation of wheat yield,” yet the cited literature [2] does not directly confirm this claim, and there is no clear evidence of long-term yield data from France or other European countries.
- Lines 89–91: Some parameters in Table 2 (e.g., SSA, TPV) have only one BET measurement result. Why are repeated data or error ranges not provided? Does this affect the credibility of the material properties?
- Lines 107–109: The experiment mentions “65 columns per soil treatment (five replicates),” but how are different doses (1%, 2%, 5%) combined with four types of AC handled in the specific experimental design? Is the total sample size sufficient to support statistical significance?
- Lines 159–161: In the pot experiment, “ten pots per treatment, divided into vegetated and non-vegetated groups,” but there is no explanation of how environmental variables were controlled, and this omission may introduce bias.
- Lines 222–224: Figure 2 shows that 5K AC significantly reduces nitrate leaching, but Table 4 indicates an increase in nitrification potential in Tournoisis soil. Why is this contradiction (i.e., enhanced nitrification but no significant increase in nitrate leaching) not discussed?
- Lines 292–294: In Table 5, the AC1 treatment in Saugy soil shows nitrate concentrations below 10 mg/L at T191, but there is no clarification of whether this result primarily reflects plant uptake or AC adsorption, and the evidence for separating these contributions is insufficient.
- Lines 354–356: Figure 4 shows that AC significantly reduces yield in Tournoisis soil, but it does not analyze possible reasons (e.g., soil type, climate differences, or chemical interactions between AC and soil). Is further discussion needed?
- Lines 468–470: The discussion states that AC reducing β-glucosidase activity may relate to carbon recalcitrance, without explaining why other enzymes remain unaffected, implying a need to investigate possible selective inhibition by AC.
- Lines 531–533: The authors speculate that the differences between field and pot experiments are due to climatic factors, but they do not provide specific meteorological data (e.g., rainfall, temperature) to support this hypothesis. Should relevant environmental parameters be supplemented?
- Lines 618–620: The conclusion indicates that AC requires improvement to enhance crop benefits, without specifying directions for such improvement, and more concrete proposals would clarify how to optimize AC properties.
- In some charts (e.g., Table 5, Table 6), “significant differences” are marked only with letters, but the chart descriptions do not clarify the letter comparison rules (e.g., p-value thresholds). Should statistical details be added to improve readability?
- Informal expressions are used in multiple places. It is recommended to unify terminology usage and consistently abbreviate “activated carbon” as “AC.”
Author Response
Reviewer 1
This article primarily explores the use of activated carbon to reduce nitrate leaching in agricultural soils yet finds it fails to effectively maintain wheat yields; as a reviewer, I believe major revisions are necessary—particularly to clarify activated carbon’s specific impacts on soil nutrient dynamics and wheat physiology, and to provide more rigorous data analysis and discussion for stronger, more practical conclusions.
We sincerely appreciate the suggestions for improvement and the comments made by the reviewer. Below we have answered the questions posed point by point and made the appropriate changes in the text.
Lines 4–6: The abstract mentions that AC failed to maintain wheat yield, but it does not specify the benchmark for “maintain.” Is it compared to a control without any nitrogen fertilizer or to a conventional fertilization treatment?
We apologize for the lack of clarity; the control used had no any activated carbon amendment and fertilization. Compared to the similar condition without activated carbon, wheat yield did not increase with AC application, regardless nitrogen fertilization.
This clarification has been added to the abstract (lines 24-25).
Lines 38–40: It mentions “stagnation of wheat yield,” yet the cited literature [2] does not directly confirm this claim, and there is no clear evidence of long-term yield data from France or other European countries.
We reviewed Le Gouis et al. (2020) which states that yield increases are slowing down. Figure 2 of this publication even shows yield trends in six countries, including France, where stagnation has been observed since the 2000s.
We have refined our statement accordiongly (lines 55-57).
Lines 89–91: Some parameters in Table 2 (e.g., SSA, TPV) have only one BET measurement result. Why are repeated data or error ranges not provided? Does this affect the credibility of the material properties?
Physical characterization of the materials was conducted without replication due to time-consuming and costly nature of the analyses. However, this does not compromise the results (e.g., Janus et al. 2018, Igalavithana et al. 2019), as the method relies on the Brunauer-Emmet-Teller equation and N2 isotherms to calculate the physical properties of the activated carbon.
Lines 107–109: The experiment mentions “65 columns per soil treatment (five replicates),” but how are different doses (1%, 2%, 5%) combined with four types of AC handled in the specific experimental design? Is the total sample size sufficient to support statistical significance?
In the column experiment, general statistical analysis was performed to evaluate the influence of the type of activated carbon and doses (which gives more replicates). For finer comparisons, data was analyzed per activated carbon type, reducing the number of conditions compared.
Lines 159–161: In the pot experiment, “ten pots per treatment, divided into vegetated and non-vegetated groups,” but there is no explanation of how environmental variables were controlled, and this omission may introduce bias.
The pots were housed in a climatic chamber in which temperature, light intensity, light duration and humidity were tightly controlled.
Those informations have been added in the text (lines 174-176).
Lines 222–224: Figure 2 shows that 5K AC significantly reduces nitrate leaching, but Table 4 indicates an increase in nitrification potential in Tournoisis soil. Why is this contradiction (i.e., enhanced nitrification but no significant increase in nitrate leaching) not discussed?
We acknowledge the contradicting results between nitrification potential and nitrate leaching. The explanation has been expanded for more clarity (lines 506-510).
Lines 292–294: In Table 5, the AC1 treatment in Saugy soil shows nitrate concentrations below 10 mg/L at T191, but there is no clarification of whether this result primarily reflects plant uptake or AC adsorption, and the evidence for separating these contributions is insufficient.
The experimental design included both vegetated and unvegetated pots, allowing us to separate the contribution from the AC sorption and the plant uptake. In the particular case cited by the Review#1, we can see that the conditions contained 1 % of AC and no plant reduced nitrate leaching below the threshold of 10 mg/L. This shows that such reduction is caused by a sorption of nitrate on AC surface, or to an indirect precipitation of nitrate in soil through the modification of the soil properties. In addition, we can see that when plants are added to the system, nitrate leaching further reduced, demonstrating an additional effect related to plants, either through uptake or a modification of the soil properties through their exudates. This has been added to the manuscript (lines 516-519).
Lines 354–356: Figure 4 shows that AC significantly reduces yield in Tournoisis soil, but it does not analyze possible reasons (e.g., soil type, climate differences, or chemical interactions between AC and soil). Is further discussion needed?
It is true, only on Tournoisis site was the wheat yield reduced following activated carbon application. As soils were of the same texture, we cannot allocate it to a difference in soil type between Saugy and Tournoisis. Similarly, both sites are located in the same Region and so are under the influence of a similar climate. Therefore, the main contributor seems to be a chemical interaction between AC and the soil, notably through the sorption of nitrate. Indeed, we can see that when nitrogen was applied to the soil, the wheat yields increased more in the Tournoisis location than in Saugy, showing that on that location, yields are more dependent on nitrogen. Thus, a sorption of nitrate by the AC could have reduced wheat growth and development. This discussion has been incorporated (lines 572-576).
ines 468–470: The discussion states that AC reducing β-glucosidase activity may relate to carbon recalcitrance, without explaining why other enzymes remain unaffected, implying a need to investigate possible selective inhibition by AC.
We apologize for not having discussed this point previously. We believe unaffected enzymes corrsspond to elements not influenced by AC amendment. This discussion has been added (lines 543-552).
Lines 531–533: The authors speculate that the differences between field and pot experiments are due to climatic factors, but they do not provide specific meteorological data (e.g., rainfall, temperature) to support this hypothesis. Should relevant environmental parameters be supplemented?
We apologize if our statement induced confusion. We meant it in the way that contrary to laboratory pot experiments, which are performed under controlled conditions of temperature, light and humidity, those conditions in the field are not controlled and can vary greatly within time, which will affect agronomic yields.
Lines 618–620: The conclusion indicates that AC requires improvement to enhance crop benefits, without specifying directions for such improvement, and more concrete proposals would clarify how to optimize AC properties.
As advised by the reviewer, we have detailed potential AC improvements (lines 656-660).
In some charts (e.g., Table 5, Table 6), “significant differences” are marked only with letters, but the chart descriptions do not clarify the letter comparison rules (e.g., p-value thresholds). Should statistical details be added to improve readability?
Our threshold p-value was 0.05, as stated in the last sentence of the table captions.
Informal expressions are used in multiple places. It is recommended to unify terminology usage and consistently abbreviate “activated carbon” as “AC.”
We apologize for the confusion, we used ACs as a plural of AC. We have corrected it to AC throughout the manuscript for more clarity.
Reviewer 2 Report
Comments and Suggestions for AuthorsSome revisions are required in the article titled "Activated carbon reduced nitrate loss from agricultural soil but failed to maintain wheat yields".
The abstract section contains very general information. The main criteria of the study should be stated. Optimum data should be presented.
Key words should be given in alphabetical order.
What is the contribution of the study to the literature? The novelty of the study and its differences from other studies should be clearly stated. It should be given in the introduction section.
The importance of some data for the modeling section of the study and the reasons for its selection should be stated.
The references section should be checked and revised according to the journal writing rules.
Author Response
Some revisions are required in the article titled "Activated carbon reduced nitrate loss from agricultural soil but failed to maintain wheat yields".
We sincerely appreciate the suggestions for improvement and the comments made by the reviewer. Below we have answered the questions posed point by point and made the appropriate changes in the text.
The abstract section contains very general information. The main criteria of the study should be stated. Optimum data should be presented.
As requested by the reviewer, we have enriched the abstract to add the main criteria of AC selection, as well as some numeric data (lines 17-25).
Key words should be given in alphabetical order.
We apologize for this mistake; the keywords have been reorganized to be in alphabetical order (line 29).
What is the contribution of the study to the literature? The novelty of the study and its differences from other studies should be clearly stated. It should be given in the introduction section.
Our research is novel due to its multiscale approach assessing soil-plant system components together. Unlike previous studies, which focused on leachate, plant growth, or microbial activities separately, we integrated all three. In addition, we have conducted a field validation, which is often lacking in most AC-related studies. We have added that at the end of the introduction (lines 82-87).
The importance of some data for the modeling section of the study and the reasons for its selection should be stated.
Our study did not involve modeling; thus, we are unsure how to address this comment.
The references section should be checked and revised according to the journal writing rules.
We apologize for the mistake; we have revised the reference format.
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsIt can be accepted in present form.
Author Response
Plese make some small final changes in your text
Title First of all, I would change the title into
Activated carbon reduced nitrate loss from agriculture soil but did not enhance wheat yields
Failed to maintain seems strange to me. Of course, activated carbon such as biochar can never replace N fertilizers as it are soil improvers and not fertilizers. The results are not fully clear to me as to which AC might even reduce yield. In table 7 it shows a small increase for location S but a small decrease for location F, while in figure 4 it always seems to show a decline (Note that the figure is hardly readable and text should be made bigger)
Manhattan Lebrun1,2, and Sylvain Bourgerie1,*
We thank you for your suggestion, we have modified the title.
We also modified the 4th figure to be more readable.
Abstract
In the sentence: "The goal was to find an AC which could stabilize nitrate while improving soil health and wheat yields", chnage AC to activated carbon as the abbreviation has nowhere been introduced.
We apologize for the inconvenience, we made the necessary change.
Text
Line 81-84. Change the tense in those sentences to past tense. You have done the experiments and will not do it as you suggest now. So change to:
"Although studies have assessed those parameters separately, we evaluated them altogether in a multiscale approach, which has not been done yet. In this multiscale approach, we performed ......."
We apologize for the mistake we made, we have corrected it.
Section 4.4 The statement that plant growth relies more on fertilization than activated carbon addition is trivial. As mentioned before, AC is never meant to be used as a fertilzier. So I would change to "plant growth is not enhanced by activated carbon addition.
This point should carefully be checked in the whole manuscript.
We thank you for pointing this out, we have made the requested change in section 4.4 and checked also the whole manuscript for similar mistakes.
