Controlled-Release Urea–Hydroxyapatite Nanohybrid for Foliar Nitrogen and Phosphorus Delivery Enhances Biomass and Grain Yield in Wheat (Triticum aestivum L.)

S. No

Comment

Response

1

Fertilization plays a fundamental role in grain growth and production. In Triticum, in particular, it plays a crucial role in transforming elements into proteins such as albumins and globulins, which are water-soluble proteins. Gliadins and glutenins represent the water-insoluble portion and, when combined, form glutenin. These factors, in turn, are crucial for the grain's characterization and marketability.
Fertilization with nitrogen and potassium is essential for positively influencing the protein content of grain. Nitrogen is directly linked to the formation of proteins and starch, while potassium helps maintain the plant's structure, preventing quality losses such as reduced specific weight.

Phosphorus plays a crucial role, especially in the initial stages of plant development, where it promotes rapid germination, strong root development, and improved water and nutrient absorption.
It is essential for the formation of nucleic acids, proteins, and enzymes, as well as participating in numerous metabolic processes essential for balanced and healthy plant growth, including the formation of nucleic acids (DNA and RNA).
Potassium also plays a key role in fertilizing wheat, influencing various aspects of its growth and development. It promotes photosynthesis, optimizes water use, provides resistance to stress such as cold and drought, and strengthens the plant's structure, making it less susceptible to lodging.
To better evaluate the proposed work, it is believed that the influence of individual elements should be analyzed more carefully in order to provide a greater benefit to growers.

Our scientific work focused specifically on the relevance of n-UHA foliar application in enhancing yield while minimizing nutrient losses and reducing excessive fertilizer use. As such, no Osborne Fractionation Method was conducted to separate and quantify protein types based on their solubility.

Please review the lines (lines 364–393) to address the role of nutrient interactions in protein formation; we have included a dedicated paragraph in the discussion section. This text elaborates on how potassium (K), nitrogen (N), and phosphorus (P), particularly when delivered through nano-urea hydroxyapatite (n-UHA)act synergistically to improve wheat growth, grain protein content, and nitrogen use efficiency, especially in K-rich soils.

Key clarifications included:

Role of High Baseline Potassium (K):
Soils with elevated K levels (~400 mg kg⁻¹) were shown to:

§  Support osmotic regulation and activate over 60 enzymes.

§  Enhance biomass production and grain filling.

§  Indirectly stimulate nitrogen metabolism and protein synthesis.

Nutrient Synergy in High-K Soils:
The controlled release of N and P from n-UHA aligned well with crop nutrient demands:

§  Phosphorus supported ATP generation, root nitrogen uptake, and protein formation.

§  Potassium facilitated enzyme activation, nitrate transport, and amino-N remobilization.

This synergistic effect—high K combined with slow-release N and P—resulted in up to a twofold increase in grain protein compared to conventional urea treatments.

Please check Table 3 (line 239), where support for these findings is provided; the initial soil analysis conducted before sowing was added to the manuscript to substantiate the nutrient status of the experimental site.

S. No

Comment

Response

1

Lines 15-16: Please expand the abbreviations 'SEM', 'EDS', and 'FTIR' the first time they appear in the abstract and in the main text separately.

Thank you. We have now expanded all abbreviations: Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), Zetasizer, and Fourier Transform Infrared Spectroscopy (FTIR) at their first occurrence in both the abstract and the main text. We highlighted the correction and please lines 18-19

2

Line 16: "....formation of sphere-like/spherical n-UHA...". Pick either 'spherical' or 'sphere-like'.

Corrected. We chose the term "spherical" for consistency and clarity. We highlighted the correction, and please line 20

3

Line 39: ".....slow controlled-release fertilizer (CRF)"

We have revised this to: "slow-release controlled fertilizer (CRF)" and expanded the abbreviation on first use.

4

Line 56: "......threatening food security". Add period '.'

A period has been added at the end of the sentence

5

Line 80: ".......remain, to our knowledge, largely unexamined." Add the punctuation ',' as shown.

Corrected. A comma has been inserted as suggested.

6

Line 80: "Kottegoda et al [41] (year).........". Add year in round bracket after each instance of a reference in this format. Please check throughout the manuscript.

All references in the manuscript have been checked, and publication years have been added in parentheses following the author names, as suggested.

7

Line 89: "Present work is aiming at the evaluation ........". Add 'is'

Corrected to: "The present work aims at the evaluation..." please check line 91.

8

Line 156: "......NIR spectroscopy (DS2500, FOSS),......". Please expand 'NIR'

Expanded to "Near-Infrared (NIR) spectroscopy" at first mention.

9

Line 166: "Field capacity (FC)...........". Add the abbreviation, since it is used in the formula following the text.

Abbreviation (FC) has been added upon first use of "field capacity."

10

Line 167-168: Type out the formula for water content at field capacity like the other text. The formula looks copied and pasted.

We have retyped the formula manually and formatted it consistently with the rest of the manuscript.

11

Line 193: ".......physical bounding/bonding." Spell check.

Corrected to "physical bonding."

12

Line 202: ".......aligns with the findings of XYZ et al. (yr) [41]." Add the reference as shown.

Revised and inserted the appropriate reference with author name and publication year in the required format.

13

Line 206: With relation  to Figure 3, please give a chemical structure for n-UHA so that one can relate all the descriptions here with the chemical groups in the structure.

n-UHA (nano-urea hydroxyapatite) does not have a single, well-defined molecular structure like small organic molecules (e.g., urea or glucose) because it is a nano-hybrid composite, not a discrete chemical compound. It consists of hydroxyapatite (HA) nanoparticles coated or associated with urea molecules through surface adsorption, hydrogen bonding, or weak electrostatic interactions, rather than covalent bonds. Therefore, I included the chemical formula of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂) ( line 227)  to reflect its structured crystalline component.

14

Line 210: "......in particular at 5000 ppm (Tables 3 and 4)." 'Tables' instead of 'Table' suggested here.

We correct this point: Foliar application of n-UHA significantly improved spike length compared to traditional urea, in particular at 5000 ppm (Table 4).

15

Line 221: ".....given to the soil 2 times; once .........". Suggested 'times' instead of 'time'.

Revised to: "two times" for grammatical correctness.

16

Line 285: "Wheat...........". Check the capitalization.

The term has been checked and corrected to "wheat" (lowercase) unless used at the beginning of a sentence.

17

Line 313 and line 318: Add year after the reference. Check throughout the manuscript.

Publication years have been added after all relevant references throughout the manuscript.

18

Line 327: "......in local acidity throw through the production ........". Spell check

Corrected to: "through the production of acidic compounds that contribute to local acidity."

19

Line 336-340: "This slow and steady .................. leaf P concentration (from <2000 to >6000 ppm)." Please break into two sentences for simplifying ideas.

We have revised the sentence and split it into two for better clarity and flow.

20

Line 337-338: "......., such essay is in agreement........". Please check (essay?).

Corrected

21

Line 340: ".....near plant root leaded led to a significant ........".

Corrected to: "near the plant root led to a significant..." Please check line 438

S. No

Comment

Response

1

-The abstract should begin with a couple of sentences about the relevance of the topic;

Thank you for the suggestion. We have revised the opening of the abstract to emphasize the global relevance of efficient nitrogen and phosphorus use, particularly in the context of increasing agricultural sustainability and minimizing environmental impact. The revised abstract now begins as follows:Efficient use of nitrogen and phosphorus is crucial for achieving sustainable wheat pro-duction. Slow-release nanofertilizers offer a targeted strategy to minimize nutrient losses, reduce excessive fertilizer application, and improve crop yield.

2

-Lines 88 - 97 are a bit confusing. It's hard to understand what exactly the purpose of this work is, some parts describe the purpose of this manuscript, other parts describe the purpose of a previous experiment. Please edit to make it clearer.

We appreciate this observation and agree that clarification was necessary. The paragraph has been restructured to clearly distinguish between background information from previous studies and the objectives of the present work. Specifically, we revised lines 91–97 by omitting the sentence “our research aligns with…”, which may have confused. The updated text now focuses solely on the aims and scope of the current study, which include evaluating the agronomic performance and physicochemical properties of the nano–urea hydroxyapatite (n-UHA) formulation under foliar application in wheat.

3

-How is the maturity of wheat determined?

This was clarified by including a parenthetical explanation in the text (lines 150–152). At physiological maturity (24 June 2024)—the stage when grain filling is complete and the crop has reached its maximum dry weight—plants were harvested manually at the soil surface to avoid soil contamination.

4

Data dispersion data, such as standard error, should be added to the presentation of results.

Thanks for your comment: Standard errors have been incorporated into Tables 4–9 to reflect data variability and enhance statistical interpretation. Additionally, the table numbering has been updated to account for the insertion of a new table presenting the initial soil analysis (now Table 3; see lines 240.

5

--Figure 5 need corrections: lack of clarity, treatments marked differently than in the manuscript, text cut out (probably unnecessary, but part of it remains). High-quality and clear presentation is required.

Thanks for your comment: Figure 5 has been updated and is now presented as Figure 7 (a) and (b)  following a restructuring of the manuscript to separate results and discussion for improved clarity.

6

-I suggest separating the results section from the discussion. The description is now presented in a similar way, with the results presented first and then the discussion, so I suggest doing this as separate sections.

Thank you for this valuable suggestion. In response, we have restructured the manuscript by clearly separating the Results and Discussion into two distinct sections. This revision enhances clarity and allows the reader to differentiate between the empirical findings and their scientific interpretation.

7

-Present the conclusions in 2-3 sentences, emphasizing the most important results.

We appreciate the reviewer’s suggestion. Upon review, we confirm that the conclusion section (lines 456–463) already consists of three concise and informative sentences that clearly summarize the core findings of the study. These statements highlight the effectiveness of n-UHA as a controlled-release nano-fertilizer, its impact on wheat growth and yield, and its potential as a sustainable alternative to conventional fertilizers. We believe this aligns well with the reviewer’s recommendation.

8

Review references, the style of the citation must be consistent and meet the journal's requirements for authors.

Thank you for highlighting this important point. We have thoroughly reviewed and revised the entire reference list to ensure full compliance with the citation format required by the Nitrogen journal.