Modeling Nitrogen Migration Characteristics in Cool-Season Turf Grass Soils via HYDRUS-2D

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study by Li et al. used the HYDRUS-2D model to simulate nitrogen migration in turfgrass soils under different slope gradients and nitrogen application rates. Results showed that increased slope gradients led to greater horizontal nitrogen disparities but reduced vertical differences, with nitrate nitrogen exhibiting greater mobility than ammonium nitrogen. The study concluded that optimizing nitrogen management can help minimize nitrogen leaching and groundwater contamination in urban green spaces. Below are some comments the author can use to improve their manuscript.

The abstract does not clearly establish the significance of studying nitrogen migration in turfgrass soils. While it mentions "green space management and maintenance," it does not explain why nitrogen transport in these ecosystems is an issue. The abstract states that the study uses HYDRUS-2D to model nitrogen transport but does not explain what makes this approach novel. Many studies have used HYDRUS-2D for nitrogen transport modeling; therefore, the abstract should clarify how this study differs from or improves upon previous work. The abstract concludes with a vague reference to "management and maintenance" but does not provide a clear takeaway message.

Lines 34–41 The introduction begins by providing statistics on urban green space expansion in China but does not sufficiently establish why nitrogen transport in these areas is a pressing concern. While it mentions that intensive lawn management increases nonpoint source pollution, it does not clearly differentiate this study from prior research. The introduction should explicitly state what previous studies have done on nitrogen migration in urban landscapes and identify the knowledge gap this study aims to fill.

While the introduction discusses the role of nitrogen in turfgrass growth and mentions its low utilization rate (lines 42–57), it does not thoroughly explain how excess nitrogen contributes to environmental problems.

The introduction discusses numerical modeling as a tool for nitrogen transport studies, but much of this discussion focuses on agriculture (e.g., maize and wheat fields) rather than urban landscapes. Since the study examines nitrogen transport in turfgrass ecosystems within urban green spaces, the introduction should better explain the unique challenges of nitrogen application in urban environments (lines 58–69).

 

The introduction states that HYDRUS-2D has been widely used to model water and solute transport but does not clarify why this model is particularly suitable for studying nitrogen migration in turfgrass soils (lines 70–76).

The selection of three slope gradients (5.09%, 14%, and 27.53%) is not justified.

The time period (40 days) for nitrogen monitoring needs justification—why this duration?

It is unclear why five levels of nitrogen application (N1–N5) were chosen instead of a different range or incremental levels.

While HYDRUS-2D is a powerful model, there is no discussion of its limitations in the study.

Key processes such as organic nitrogen mineralization and microbial interactions may affect nitrogen transformation but are not addressed.

Lines 295–303 introduce the model results and validation. However, there is redundancy in explaining sensitivity analysis (lines 298–304) and its classification (Table 5). Instead, the discussion should focus more on how sensitivity impacts the model outcomes rather than reiterating the classification methodology.

Lines 340–363 discuss model validation but do not explicitly compare the observed and simulated values beyond general trends. Figures 4 and 5 are mentioned, but numerical comparisons of simulated vs. observed values should be included to quantify model performance beyond just RMSE and R².

Lines 366–375 discuss trends in nitrogen distribution, but the rationale for the negative correlation between slope and vertical nitrogen differences is not well explained.

 

Minor comments

The manuscript feels rushed, as evidenced by incomplete figure titles and occasional awkward phrasing.

The Results and Discussion section lacks a smooth flow, with some areas repeating concepts already introduced in the Methods section, making the paper harder to follow.

Some sentences are overly long and difficult to read.

Comments on the Quality of English Language

Some sentences are overly long and difficult to read.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript reported the results of modeling nitrogen leaching characteristics in simulated grass soil boxes using HYDRUS-2D. The results contained some useful message which deserves to be published. The authors should make some revisions by fully refining the expression of the text. Some special comments are shown at the bottom.

1) In abstract, it is not clear. This section needs to be rewritten. What is the meaning of N5 treatment here?

 

2) In the introduction, the reasons why the authors selected grass soil samples as tested soils to perform the related modeling should be fully explained. 

 

3) Regarding Table 1, the titles 1 to 3 are not indeed clear.

 

4) Lines 116-118, the authors mentioned the five treatments, without any explanations. However, in later contents, five nitrogen treatments were set up. These contents should be combined into one paragraph.

 

5) In the line 125, the authors mentioned slope groups. But there is no message about the four slope groups in the M&M section.

 

6) line 166, I cannot understand the transport and transformation process of fertilizer in soil.

 

7) For the equation 6, what is the meaning of θ?

 

8)  the layout of Figures and the text is not nice for peer-review. The authors should refine the text to improve the readability.

 

9) The subtitle of some sections is too long. For example, the section 3.2.1.  

Comments on the Quality of English Language

The text is not good for scientific review. The authors should refine the text for the readability.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

I ask that the comments be respected.

 You can also find comments, recommendations, questions at the edge of the article in the notes (in bubbles).

Line

27         The abstract should be written in such a way that the reader can understand its meaning without having to read the entire article. Describe Treatment 5.

28         So if there are such large differences with the actual data, what does this mean for the application of this model in practice? Insert the answer to this question. This will be key information.

34         In agronomy, the designation hm² is not used to express area. Use the standard notation. For example, just m².

43         Please provide the years this information was published. Include these authors in the references. Alternatively, delete the authors because this information is generally known

46         The sentence starting in line 46 is valid in European conditions at most on 50%. In at least  50% of cases, nitrogen fertilization increases the susceptibility of plants to disease. Also state such – contradictory findings. Change the style (change the style of the sentence). Formulate your ideas carefully.

49         In Central Europe, this number is absolutely not valid. For example, in Slovakia it is 40-80%. Your statements must be more careful.

54         In Slovakia, an average of 8-10 kg/ha of N is leached from agricultural soils annually. Your statements must be more careful. They must respect global knowledge.

88         Two notes:

1/ Create the table according to the recommendations (see the author's manual, instructions for authors). Missing numbering, title, etc.

2/ The table in this form is useless.

113       In agriculture and the environment, slope is usually expressed in degrees. Express it in degrees - as the angle of inclination.

119       At what time intervals was the leachate collected?

124 – table      Instead of a slash /, use square brackets. The term fertilizer means that you used, say, 6.6 kg of fertilizer. Is this true information, or did you use 6.6 kg of nitrogen? If it is a fertilizer, instead of the word fertilizer, state its name - urea.

124 – table      Justify why they apply less water in the warm season than in the cold season. Also, why is less (fertilizer? nitrogen?) applied in the warm season?

127       Please indicate the amount of soil (kg) to which you applied the given amount of nitrogen, or indicate the area in m2 to which the given amount of nitrogen was applied. The information in line 137 indicates that the given amount of N was applied more than once. Provide information on the total doses of N. The chapter Material and methods is not clearly written.

131       Use only one volume designation. Either liters (line 131) or milliliters (line 137).

156       Is that spelled correctly?

237       Non-standard source citation used for a journal.

345       It is customary for the letter used to have its own meaning. Why did you use the letters T and B?

374       The figures listed in lines 350, 374 and 382, ​​​​​​​​425, 478 (but also elsewhere) do not have a number. They also do not have a title. The units on the X and Y axes are also missing.

542       Why are there no pictures in this chapter, while a similar chapter (3.2.2.1 Changes in soil NO3-N content at different slope inclinations) has pictures? Please add them.

626       Describe - explain tratment 5.

634       Complete what follows from the above findings. You should draw general conclusions from the results obtained. This also applies to the following conclusions. Do this.

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The idea presented in the article is interesting, but the formal execution of the article and its interpretation have certain (significant) shortcomings.

Authors should also pay attention to the formal aspect of the article.

There is no mention of the practical applicability of the acquired knowledge in agronomy, i.e. in areas where nitrogen fertilizers are regularly applied.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed the reviewers' concerns, and the manuscript is now ready for publication.

Reviewer 2 Report

Comments and Suggestions for Authors

This is a piece of nice work. At present the authors have made substantial revisions by considering the reviewers' comments, and it can be considered for acceptance. 

Comments on the Quality of English Language

The text needs to be edited for publication.