Impact of Split-Application Nitrogen Strategies on Maize (Zea mays L.) Yield and Soil Fertility Indices Across Contrastive Soil Types in the Transylvanian Plateau

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Review

Manuscript ID 4275540 "Impact of Split-Application Nitrogen Strategies on Maize (Zea mays L.) Yield and Soil Nitrogen Indices across Contrastive Soil Types in the Transylvanian Plateau"

 

This manuscript investigates the effects of split-application nitrogen fertilization strategies (urea and calcium ammonium nitrate supplementation versus NPK-only control) on maize grain yield and soil chemical properties across three contrasting soil types in Mureș County, Romania, over three cropping seasons (2022–2024). The topic is relevant to regional agronomy in the Transylvanian Plateau, where site-specific fertilization data remain scarce.

The study has a clear applied objective and provides useful field-level data from an under-represented region. The statistical framework (ANOVA/Kruskal–Wallis, Spearman correlations, PCA) is generally appropriate. However, the manuscript suffers from several methodological ambiguities, inconsistencies in data presentation, an insufficiently critical discussion, and numerous language errors that collectively require major revision before the work can be considered for publication.

Major comments:

• The design is described as a "non-randomized 2 × 3 × 3 subdivided plot design" (line 123), but only three factors are identifiable (3 soil types × 3 fertilization variants × 3 years), not a 2 × 3 × 3. What is the factor with two levels? Furthermore, the lack of randomization is a serious limitation that is never discussed. Non-randomized designs are highly vulnerable to confounding spatial gradients. Was there any spatial blocking or arrangement to mitigate this? How many replicate plots existed per treatment × location × year combination? The statement "three repetitions per plot" is ambiguous — does this mean three subsamples within each plot, or three independently established plots per treatment? The distinction is critical because subsampling inflates the effective sample size and leads to pseudoreplication if analyzed as independent replicates. Please provide a clear experimental layout diagram and state the actual number of independent experimental units.

 

• V1 receives 300 kg/ha NPK 20-20-0 (= 60 kg N/ha) + 300 kg/ha urea (= 138 kg N/ha), totaling approximately 198 kg N/ha. V2 receives 300 kg/ha NPK 20-20-0 (= 60 kg N/ha) + 300 kg/ha NAC27 (= 81 kg N/ha), totalling approximately 141 kg N/ha. V3 receives 300 kg/ha NPK 20-20-0 alone (= 60 kg N/ha). Therefore, V1 receives roughly 40% more total nitrogen than V2 and over three times as much as V3. The observed yield differences cannot be attributed to the nitrogen source per se; they are confounded with the total N rate. The claim that urea is "the most effective strategy" (abstract, conclusions) is not supported by this design — a fair source comparison would require equal total N inputs. This confounding must be explicitly stated and the conclusions modulated accordingly.

 

• Table 2 reports "NI" (nitrogen index, calculated as humus% × V / 100), whereas Table 3 reports "N (ppm)" with the column header labelled inconsistently. Are these the same variable? If NI values range from 2.41 to 3.34 (Table 2), how do the values in Table 3 (2.20–3.56) relate? The abstract and correlation sections discuss "nitrogen index," but Table 3 appears to present raw soil nitrogen concentration. This ambiguity undermines the central analytical thread of the paper. Please clarify which variable was used in which analysis and ensure consistent naming throughout.

 

• In Table 1, the precipitation values for 2022 and 2023 are identical across all months (3.05, 70.09, 67.05, 34.54, 50.81, 60.19, 120.9, 36.83). It is highly improbable that two consecutive years had exactly the same monthly rainfall. This appears to be a copy-paste error. Accurate climatic data are essential, especially since the authors claim inter-annual variability influenced yields. Please verify and correct these data.

 

• The Discussion section (lines 329–399) largely restates results or provides textbook-level descriptions of urea and NAC27 properties (lines 336–345) without critically interrogating the data. Several specific deficiencies: (a) The claimed mechanism that urea provides "synchronized nutrient release" during high-demand stages is asserted without evidence — no tissue N analyses, no temporal N uptake curves, and no soil mineral N measurements during the season are presented. (b) The suggestion that mechanical hoeing minimizes volatilization losses (line 358) is reasonable but is presented as fact without supporting measurements.

 

• With 3 soil types × 3 treatments × 3 years, and an unclear number of true replicates, the total number of independent experimental units is uncertain. Tables 2 and 3 present what appears to be n = 9 per soil type or fertilization treatment (based on 3 years × 3 replications). For the Kruskal–Wallis test and Dunn's post-hoc, this sample size is at the lower boundary of reliability. The authors should explicitly state the n for each comparison, discuss statistical power, and consider whether the non-significant results (e.g., pH, humus, P, K across fertilization treatments) reflect true absence of effect or insufficient power to detect one.

Minor comments:

• Multiple punctuation errors in the abstract: missing space before "The variant" (line 25); "(ρ=0.93 to 0.97,p<0.001),." has both a comma and a period plus misplaced parenthesis (line 28); "In contrastother" is missing a comma and space (line 28); the abstract ends without a period (line 32). The abstract should be carefully proofread.

 

• The section on potassium (lines 77–82) is particularly tangential since K was not a treatment variable. Consider condensing the introduction to focus on: (a) the importance of N management in maize, (b) the rationale for comparing urea vs. NAC27, (c) the specific knowledge gap regarding Transylvanian soils, and (d) the study objectives. This would improve readability and focus.

 

• Line 149 states "soils from the 0–40 cm depth were sampled at 10 cm intervals," implying four layers (0–10, 10–20, 20–30, 30–40 cm). However, line 152 states only "soils from the 0–10 cm and 10–20 cm layers were removed separately." What happened to the 20–40 cm samples? Were the results averaged across depths, or were only the top two layers analyzed? This must be clarified.

 

• Figure 8 labels the soil groups as "Calcaric Fluvisol," "Luvic Phaeozem," and "Mollic Luvisol." These do not match the soil names used in the text (calcaric fluvisol, stagnic phaeozem, mollic preluvisol). This is confusing and must be corrected to use a single consistent nomenclature throughout.

 

• The manuscript contains numerous grammatical errors, typos, and awkward phrasings that impede readability. Examples include: "yeilding" (line 332), "demostrated" (line 401), "confim" (line 410), "thelowest" (line 250), "lowesin" (line 248), "reord" (line 251), "whithout" (line 343), "maze" instead of "maize" (lines 254, 275, 293. Professional English editing is strongly recommended before resubmission.

 

The manuscript addresses a relevant agronomic question with a multi-year, multi-site field experiment, and the core finding — that soil type is the dominant factor governing N fertilization outcomes — is well supported. However, the fundamental confounding of total N rate with N source, ambiguities in experimental design description, apparent data errors, terminological inconsistencies and a discussion that lacks critical engagement with the data all require substantial revision. The language quality also needs significant improvement.

Sincerely,

Author Response

Dear Academic Editor,

            We sincerely thank you for the time and effort dedicated to proofreading and reviewing our article. All the modifications we made are reflected both in the article and in the attached document. We would like to thank you once again and hope that all the changes we implemented meet your requirements and expectations.

Please see the attachment.

Sincerely,

Vlăduț-Ionuț Șter and co-authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscipt nitrogen-4275540 entitled "Impact of Split-Application Nitrogen Strategies on Maize (Zea mays L.) Yield and Soil Nitrogen Indices across Contrastive Soil Types in the Transylvanian Plateau" presents and discuss the results of a three-year field experiment were the effect of three different fertilization regimes were assessed on corn growth.

Unfortunately, the manuscript has a number of serious shortcomings. In particular, the methodological issues are significant and severely undermine the quality of the experimental results. The experimental design adopted is, in fact, unsuitable for the study, and a number of details are missing from the ‘Materials and Methods’ section. Finally, the manuscript suffers from poor textual development. My comments are included in the attached file

Comments for author File: Comments.pdf

Author Response

Dear Academic Editor,

            We sincerely thank you for the time and effort dedicated to proofreading and reviewing our article. All the modifications we made are reflected in the attached document. We would like to thank you once again and hope that all the changes we implemented meet your requirements and expectations.

Please see the attachment.

Sincerely,

Vlăduț-Ionuț Șter and co-authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The study investigates the effects of different fertilization strategies on soil fertility and crop yield across various soil types. However, the following revisions are required prior to its acceptance for publication:

1. Title

Since the study not only focuses on nitrogen but also determines soil P, K, and other related indices, it is recommended to replace “soil nitrogen indices” with “soil fertility indices”.

2. Abstract

The full name of the abbreviation "NAC" should be specified upon its first appearance. Also, there is inconsistent use of abbreviations (e.g., alternating between “nitrogen” and “N”); standardization is required.

3. Introduction

1) Lines 45–50: Excessively redundant, these two sentences convey the same meaning and should be condensed.

2) Lines 57–59: Lack logical connection between the preceding and subsequent content; the logical flow needs to be improved.

3) Lines 86–90: Explicit scientific hypotheses should be proposed to guide the study.

4) Line 89: “plan” should be “plant”.

4. Materials and Methods

1) It is recommended to present the fertilization strategies for different treatments in a table for clarity.

2) All work photos should be placed in the appendix; only key information needs to be included in the main text.

5. Results

1) The soil indices and crop yield under different fertilization strategies for each soil type should all be presented, rather than only displaying the average values across different soil types and different fertilization strategies.

2) Figures 5–7 can be merged into a single figure; additionally, there are multiple superscript and subscript errors in the figures that need correction.

6. Discussion

It is suggested that the authors focus on the differences in the responses of soil fertility indices and crop yield to fertilization strategies across different soil types. This is crucial for proposing targeted improvement strategies tailored to specific soil types.

7. Conclusion

The section excessively lists results without sufficient synthesis; further refinement and condensation are required to highlight the core findings.

8. References

Many cited literatures are more than 10 years old. The authors should incorporate and cite the latest published studies.

Author Response

Dear Academic Editor,

            We sincerely thank you for the time and effort dedicated to proofreading and reviewing our article. All the modifications we made are in the attached document. We would like to thank you once again and hope that all the changes we implemented meet your requirements and expectations.

Please see the attachment.

Sincerely,

Vlăduț-Ionuț Șter and co-authors

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Review- round 2

Manuscript ID 4275540 "Impact of Split-Application Nitrogen Strategies on Maize (Zea mays L.) Yield and Soil Fertility Indices across Contrastive Soil Types in the Transylvanian Plateau "

The authors have engaged constructively with several of the Round 1 comments. The duplicated precipitation data, the sampling-depth contradiction, and the tangential potassium material in the Introduction have been corrected, and some of the textbook-level padding in the Discussion has been removed. The responsiveness on these points is appreciated.

However, the two issues that determine whether the manuscript can support its headline claims - (a) the confounding of nitrogen source with total nitrogen rate, and (b) the conflation of the calculated “nitrogen index” with measured soil nitrogen - remain unresolved. In several places the revision has also introduced new errors, including a chemically incorrect identification of the fertilizer in the Abstract, an internally contradictory soil-classification scheme, and citation–claim mismatches.

 

Major comments:

• The N source × N rate confound is unresolved and the conclusions still overclaim: the response acknowledges verbally that “the observed differences in yield cannot be attributed solely to the nitrogen source,” but the manuscript text was not modulated accordingly. The Abstract (lines 30–32) and Conclusions (lines 403–404) still state that urea is “the most effective strategy.” As noted in Round 1, the regimes differ in total nitrogen: V1 ≈ 198 kg N/ha, V2 ≈ 141 kg N/ha, V3 = 60 kg N/ha. V1 received roughly 40% more N than V2 and over three times that of V3. The design therefore compares regimes that differ simultaneously in source and in rate, so no statement about urea as a source can be defended. The Discussion (lines 351–353) makes this worse by attributing V1’s advantage partly to “the higher concentration of nitrogen in Urea” — i.e., conceding a dose effect — while simultaneously claiming a source/synchronization effect. These cannot both be the explanation. Crucially, the claim that urea “maximizes nitrogen use efficiency” is contradicted by the  authors’ own numbers. Computing agronomic efficiency above the control from the reported median yields: V1: (9560 − 7420) / (198 − 60) ≈ 15.5 kg grain per kg N, V2: (9150 − 7420) / (141 − 60) ≈ 21.4 kg grain per kg N

 

• Pseudoreplication and an inappropriate analysis model remain: stating “n = 9 independent experimental units” (line 221) does not make them independent. There is only one site per soil type (Coroisânmărtin / Ogra / Grebenișu), so the soil-type “replicates” are pooled year × fertilization combinations from a single field - the experimental unit for the soil factor is effectively the site (n = 1 per soil). In addition, the plots were “established in 2022” and re-measured over three years, so the 2022/2023/2024 observations are repeated measures on the same plots, not independent draws. Treating all nine as independent in one-way ANOVA / Kruskal–Wallis is not defensible for the soil-type contrasts. A factorial or mixed model (year × soil × fertilization, with year treated as repeated and site acknowledged as the unit for soil) would be the correct framework; at minimum, pseudoreplication must be stated as a limitation and the inferential claims softened. Separately, the post-hoc power analysis promised in Response 6 (≈0.55–0.73) does not appear anywhere in the revised text -please add it if it was performed.

 

• Abstract line 20 now reads “300 kg/ha N-acetylcysteine (NAC) 27.” N-acetylcysteine is a thiol pharmaceutical/antioxidant, not a nitrogen fertilizer. NAC27 is calcium ammonium nitrate (≈27% N; “nitrocalcar”), as correctly stated in the keywords and Introduction (line 58). This contradiction must be corrected; as written, the central comparison of the paper is described with the wrong compound. The Abstract now states the study investigated impacts “on environment pollution” (line 15). No pollution endpoints were measured — there are no nitrate-leaching, runoff, N₂O, or in-season mineral-N data. This overclaims the study’s scope and should be removed (the phrasing “environment pollution” is also grammatically off).

 

• The revised Introduction (lines 79–83) supports nitrogen-accumulation and N-availability claims with references [38] and [41], both of which are potassium papers (Zhao et al. on K fertilization; Asante-Badu et al. on maize K uptake). These do not support N claims and should be replaced with appropriate N-focused sources. More broadly, these statements are phrased as declarative facts rather than as the study’s hypotheses, while the explicit objectives present in the original (original lines 86–90) have been dropped - clarity has regressed here. Restoring a clear objectives/hypotheses statement is recommended.

 

Minor comments:

• “Foliar fertilization” is a misnomer (Methods, line 154): a broadcast, hoe-incorporated dose of 300 kg/ha urea/nitrocalcite is soil/basal split application, not foliar (foliar feeding uses dilute sprays). This persists from the original and should be corrected.

 

• Table 2 precipitation column: the “Average” header is used for an annual mean in the temperature rows but for an annual total in the precipitation rows (≈569–683 mm), and these totals do not reconcile with the sum of the displayed March–October values. Please relabel (e.g., “Annual total”) and ensure the displayed months and the total are consistent. 

 

• Depth handling: the four sampled layers (0–10, 10–20, 20–30, 30–40 cm) are now listed (line 165), but the manuscript still does not state how the four increments map to the single per-plot value reported (composited, averaged, or top layer only).

 

The descriptive characterization of the three soils is solid; the interpretive layer is not yet supportable. The study’s central narrative - urea as a superior nitrogen source that maximizes NUE - is confounded by unequal N rates and is contradicted by the authors’ own efficiency numbers. The diagnostic centerpiece (the nitrogen index) is conflated with measured soil N in a way that makes the key tables internally inconsistent, and the inferential statistics rest on units that are not independent.

Author Response

Dear Academic Editor,

We sincerely appreciate the time and effort you have dedicated to reviewing and proofreading our article. All the revisions we have made are reflected both in the manuscript and in the attached document. We would like to express our gratitude once again and hope that the changes implemented meet your expectations and requirements.

Please find the attachment enclosed.

Sincerely,
Vlăduț-Ionuț Șter and co-authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

the revised version was significantly improved compared with the previous version of the manuscript. The manuscript is still affected my minor languange and style problems than can be resolved in proofreading process. 

Author Response

Dear Academic Editor,

We would like to express our sincere gratitude for the time and effort you have invested in reviewing and proofreading our manuscript. We truly appreciate your support.

Kind regards,
Vlăduț-Ionuț Șter and co-authors

Reviewer 3 Report

Comments and Suggestions for Authors

The comments have been addressed in the revised manuscript.

I would like to suggest the acceptance of the article.

Author Response

Dear Academic Editor,

We sincerely appreciate the time and effort you have dedicated to reviewing and proofreading our article. Thank you for your decision and would like to express our gratitude once again.

Sincerely,
Vlăduț-Ionuț Șter and co-authors

 

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

Review- round 3

Manuscript ID 4275540 "Impact of Split-Application Nitrogen Strategies on Maize (Zea mays L.) Yield and Soil Fertility Indices across Contrastive Soil Types in the Transylvanian Plateau"

The authors have made substantial and welcome progress in this third round. The statistical pseudoreplication issue has been properly addressed through a re-analysis using linear models with soil type, fertilization, and year as fixed factors and post-hoc comparisons via estimated marginal means with Tukey adjustment. The site = soil-type confounding is now explicitly acknowledged as a limitation (lines 232–235 and 402–406). The NAC27 misidentification, the “environmental pollution” overclaim, the “foliar” vs split-application misnomer, the Table 2 column-header issue, and the citation–claim mismatches in the Introduction have all been corrected. The new Methods/Results presentation is markedly clearer than in Round 2, and the authors deserve credit for genuinely engaging with what was a demanding review cycle.

However, a few items still prevent immediate acceptance - and importantly, they are now all textual or editorial, not methodological.

Major comments:

• The one-sentence caveat added to the Conclusions is correct, but it now sits inside a manuscript whose Abstract still ends with “These findings indicate that a split-fertilization regime combining NPK with urea is the most effective strategy for maximizing N use efficiency and maize output in the Transylvanian Plateau” (lines 31-33), and whose final Conclusions paragraph (lines 425–428) still asserts that “split urea application (V1) offers the best balance between productivity and cost-effectiveness.” The Abstract and the final Conclusions paragraph therefore directly contradict the caveat added two paragraphs above. Suggestions: delete “is the most effective strategy for maximizing N use efficiency” from the Abstract and replace with neutral wording consistent with the Conclusions caveat; (b) revise the Discussion paragraph at lines 356–360 so that the source-vs-dose confound is acknowledged at the point where V1 vs V2 is interpreted, not only at the end of the Conclusions or (c) remove or reframe the “best balance between productivity and cost-effectiveness” sentence at lines 425–428

 

• Figure 4 The figure legend still reads “Calcaric Fluvisol / Luvic Phaeozem / Mollic Luvisol,” whereas the body text and Tables 4–5 use “calcaric fluvisol / luvic phaeozem / stagnic phaeozem.” The third label in particular is wrong: there is no “Mollic Luvisol” in the study — it is the Grebenișu de Câmpie site, which the text and Table 1 classify as a Stagnic Phaeozem. Response 9 states the symbols were removed to avoid confusion, but the underlying figure does not appear to have been regenerated. My suggestion: regenerate Figure 4 (or simply edit the legend keys on the existing figure) so the three group names exactly match those used in Tables 4 and 5 and in the body text.

• Response 7 explained clearly that the four 10-cm depth increments were combined into a single composite sample per plot. This is exactly the information needed — but it lives only in the response letter, not in the Methods. Please add one sentence to 2.3 (e.g., “The four 10-cm depth increments were combined into a single composite sample per plot prior to laboratory analysis.”).

Minor comments:

• The Results description in 3.1 (lines 253–256) is doubled. Two consecutive sentences say almost the same thing about the three experimental sites and the seven variables. One should be removed.
• Please read carefully the whole manuscript for typography errors (for example: line 23, line 165)
• Check the Reference list and style (some journals are abbreviated, others are not).

 

The data and analytical framework are now sound. The remaining weaknesses are internal consistency: the Conclusions correctly disavow what the Abstract still claims; the Discussion attributes V1’s advantage to two mutually exclusive mechanisms; the diagnostic centrepiece variable (NI) is still labelled inconsistently across tables; and Figure 4 - flagged three rounds in a row - still shows wrong soil names. After corrections the Manuscript will be suitable for publication.

Sincerely,

Author Response

Dear Academic Editor,

We would like to extend our sincere appreciation for the time and attention devoted to the review and proofreading of our manuscript. We are grateful for the valuable feedback provided, which has contributed to further improving the quality and clarity of our work.

All revisions undertaken in response to the comments and suggestions have been carefully incorporated into the revised manuscript and are detailed in the accompanying document. We trust that the modifications made adequately address the issues raised and fulfill the journal’s requirements.

Thank you once again for your consideration and support throughout the editorial process. We hope that the revised version of the manuscript will meet your expectations.

Please find the revised manuscript and the accompanying response document attached.

Yours sincerely,

Vlăduț-Ionuț Șter and co-authors

Author Response File: Author Response.pdf