Effects of Nitrification Inhibitors on Nitrogen Dynamics and Ammonia Oxidizers in Three Black Agricultural Soils
, Dongpo Li 1,*, Zhijie Wu 1, Yan Xue 1, Yuchao Song 1, Furong Xiao 1,2, Lili Zhang 1, Ping Gong 1 and Ke Zhang 1,2Round 1
Reviewer 1 Report
Refers to manuscript ID: agronomy-1544344. Effects of nitrification inhibitors on nitrogen dynamics and ammonia oxidizers in three Black agricultural soils
In the presented manuscript, the authors assessed the effect of nitrification inhibitors (DMPP and DCD) on changes in the concentrations of ammonium and nitrate nitrogen and on changes in the number of ammonia oxidizing nitrifiers (AOA and AOB). Both inhibitors are common fertilizer additives and are designed to reduce nitrogen leaching from the soil by slowing down the nitrification process. In practice, this slowdown lasts from 4 to 10 weeks and is strongly dependent primarily on soil temperature, which the authors did not mention in their work. Therefore, the presented results do not add anything new. It has also been known for a long time that the activity of nitrifiers depends on the pH and the content of organic matter in the soil (both in terms of autotrophic and heterotrophic nitrification). Therefore, I advise against publishing this article in this form. Only the part of the research concerning the use of a combination of both inhibitors deserves attention. In addition, the research was carried out in laboratory conditions, which does not always translate into field conditions. The authors have already carried out similar studies (https://doi.org/10.3390/agronomy11081674) and have stated themselves that: "Further field studies are required to evaluate the effects of these nitrification inhibitors." It may be worthwhile to conduct similar field experiments using different combinations of DMPP and DCD, checking how it affects plants (phosphorus and micronutrient uptake) and soil microorganisms.
Detailed comments:
Check and correct grammar errors and spaces throughout the article.
The names of the chemical compounds should be correctly formatted. Please change from NH4+-N to NH4-N, NO3--N to NO3-N, NH4+ to NH4+, NO3- to NO3-, N2O to N2O, NH2OH to NH2OH, throughout this article.
- Abstract
„The results demonstrated that NIs significantly increased NH4+-N concentrations and decreased NO3--N concentrations in all three tested soils.”
This is obvious and well known. This has been demonstrated by numerous studies conducted over many years.
The Abstract of a good journal article always ends with an outline of the benefits of the research results and recommendations as a solution to the presented problem. Such information is missing in the presented Abstract.
- Keywords
Should correct "achaea" on “archaea”.
The words that are in the title (nitrification inhibitors) should not be used.
- Introduction
The Introduction section should be enhanced with a state-of-the-art overview to clearly show progress beyond the current state of the arts. Lack of proper justification creates the erroneous impression that authors are unaware of recent events. The authors reviewed the literature and presented the work to date. But what innovations will be introduced to the literature in this article? Therefore, the current state of knowledge should be clearly and precisely specified in the introduction. A hypothesis must be made. How is this work different from available literature? What is the current level of knowledge about nitrification inhibitors in the soil system? What are the gaps in knowledge? The final paragraph of the introductory section always emphasizes the novel aspects of the study with a clear purpose and relevance of the results of the study. The article formulates the goal very generally. It is also recommended to discuss and explain what the appropriate policy should be based on the results of this study. In addition, it should be shown how the results can be used in real field applications.
The introduction should be broadened and redrafted to provide a more comprehensive approach.
- Material and methods
It should be presented how the content of organic matter in the tested soils was determined.
- Results
„3.1. Soil inorganic concentrations in three soils”
The title should be corrected to: Soil inorganic nitrogen concentrations in three soils.
„Compared with CK treatment, the soil treated with only (NH4)2SO4 had a significantly higher NH4+-N concentration in all three soils (Figure 1).”
It is obvious and logical that when (NH4)2SO4 is added to the sample, the concentration of ammonium nitrogen will increase.
„The results of two-way ANOVA indicated that the NIs, soils with different pH level and their interaction all had a significant influence on PNR (Table 3, P < 0.01???).”
What was the PRN before starting the experiment? Table 3 shows: *** Significant at p<0.001. These are inaccuracies.
In the Results section, the authors did not present the effect of organic matter content on the rate of nitrification and the number of AOA and AOB, although the abstract states that: „Moreover, soil pH and soil organic matter were considered to be the most important factors influencing the inhibitionefficiency of NIs and the abundance of AOA and AOB.”
On what basis was this conclusion made?
Unfortunately, it is not possible to reliably assess the Results section, because the presented Figures (1, 2 and 3) are illegible. There are no numerical values or explanations for the colored lines. In the text, when presenting the obtained research results, the authors also did not provide numerical values. The data in Table 3 are incomprehensible. What do the symbols DF and F mean, how were the assigned numerical values calculated?
- Discussion
„In each soil, all N treatments had higher NH4+-N and NO3--N contents than that in the treatments without N fertilizer (CK), indicating that ammonia sulfate application improved the content of soil inorganic nitrogen.”
It is obvious.
„The main reason for this difference is that the tested soils with different pH.”
It has long been known how pH influences the rate of nitrification.
„Additionally, the result of Pearson correlation revealed that soil NH4+-N content had a negative correlation with soil pH (Figure 5, P < 0.05), while had a significantly positive correlation with SOM (Figure 5, P < 0.01).”
This Figure should be number 4. This is another illegible Figure at work.
„The possible explanation is the same experiment environment (laboratory incubation), which had no nitrate leaching and crop uptake.”
Unfortunately, these results do not bring anything new, they only confirm the information contained in numerous publications.
„In addition, the lower AOA and AOB abundance may contribute to the lower potential nitrification in HLJ, which is In line with recent studies.”
This is obvious and does not come from recent research.
„This could be due to AOB preferring high ammonia substrate conditions.”
Rather not, as high concentrations of ammonium nitrogen are toxic to the nitrifiers.
„In HLJ, AOA abundance significantly decreased after the application of (NH4) 2SO4 at day 1. The result is in agreement with a previous study, which reported AOA inhibited in high N treated soils.”
This may be due to the toxic effects of high concentrations of ammonium nitrogen on AOA.
„Additionally, our results are in line with a recent study conducted by Fan et al [51], who reported an increase in AOA abundance with DMPP application. These discrepancies could be due to AOA being promoted by organic compounds. Therefore, NIs might be used as available carbon substrates to stimulate the growth of AOA.”
The process of heterotrophic nitrification is well known, but I believe it is unwise to suggest AOA growth stimulation by NIs.
- Conclusions
„This study demonstrated that NIs treatments could effectively increase soil NH4+-N and NO3--N concentrations by reducing soil nitrification process, regardless of soil type and NI type.”
If nitrification inhibitors increase the concentration of NH4-N in the soil, i.e. inhibit the nitrification process, what is the reason for the increase in NO3-N concentration?
All conclusions must be convincing statements about what was found to be innovative, contributing to a strong support of the results and discussions. They should end up with a greater emphasis on the main results of the work.
- References
In the References section, remove duplicate numbering.
The article submitted for review is almost identical to this one: https://doi.org/10.3390/agronomy11081674, especially the Materials and methods section. Some words need to be changed to reduce the resemblance.
Author Response
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Author Response File: 
Author Response.docx
Reviewer 2 Report
Manuscript under title "Effects of nitrification inhibitors on nitrogen dynamics and ammonia oxidizers in three black agricultural soils" isn't suitable for publication in the version sent for review.
The manuscript has been prepared not very carefully and has many minor errors, which makes it difficult to understand the main manuscript idea.
Additionally the lack of line numbering makes it difficult to read manuscript and indicate places for improvement and correction.
Figures probably past in manuscript as an object of very low quality, not readable. Data isn’t visible and the information in the text cannot be verified.
The manner of presenting chemical formulas and units is inconsistent with the accepted principles. For example NO3- , NH4+and kg-1 not NO3-, NH4+, kg-1.
Chapter 3.3. my opinion should be rewrite. A very detailed description of the AOA and AOB results is tiring and does not make it possible to understand how the nitrification inhibitors influenced on ammonia-oxidizing archaea and ammonia-oxidizing bacterial. I suggest present this result shorten and more generalize.
I suggest to add soil particles composition in table 1.Authors suggested physicochemical soil properties.
Please unify nitrification inhibitors abbreviations. Mostly used NIs but in any places also NI symbol.
Lack of reference to figure 4. No figure 5 in manuscript which cited few times.
Authors used term "weak soil" in discussion part. What parameters are characteristic for weak soil. Additional explanation is needed.
Detailed comments could be made if the text line was numbered.
Author Response
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Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
- The numerical values for the concentrations of ammonium nitrogen and nitrate nitrogen are clearly summarized in Table S1 as supplementary material. However, this Table was not quoted in the text.
- I still believe that the Figures in the manuscript should be formatted in order to improve their quality (they are blurry and illegible).
Author Response
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Author Response File: Author Response.docx
Reviewer 2 Report
Authors accepted most of the manuscript changing proposal and I recommend for publication. Once again, I note the very low quality of the figures. Articles are written for readers and the quality of the presentation should be the basis. Supplementary file didn't change figure presentation quality.
Point 3: Figures probably past in manuscript as an object of very low quality, not readable. Data isn’t visible and the information in the text cannot be verified.
Author Response 3: Thanks for your review. As the data in the figures are too dense with too many sampling times, the figure may not be readable. Therefore, I have provided data in Supplementary Material to verify the information in the text.
Author Response
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Author Response File: Author Response.docx
