Impacts of Nitrogen Fertilizer Application Timing and Rate on Sweet Corn Production Under Subtropical Environmental Conditions

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Research is relevant and interesting.

1. No research hypothesis is presented in the introduction;

2. The introduction does not provide a relationship between weather conditions, nitrogen fertilization, and sweet corn productivity;

3. I suggest providing more information about sweet corn growing technology;

4. I suggest moving the section 3.1. „Weather data and growing degree days“ and figure No.1 to the section 2.2. „Weather conditions“;

5. I advise splitting the discussion into smaller chapters;

6. I recommend not to use old literature sources.

Author Response

Comment 1: No research hypothesis is presented in the introduction;

Response 1: Authors appreciate the reviewer comment and have added the study hypothesis as requested. The sentence reads as:

“Despite these findings, growers often overapply N fertilizer rates in an effort to maximize yields, leading to increase input costs and environmental degradation [2,14]. However, balancing nutrient management practices is essential to benefit both growers and the environment. Therefore, this study hypothesizes that a reduction on N fertilizer rates can reduce soil N loss while increase sweet corn nitrogen use efficacy and maximize yield and quality, once compared to the current growers’ standard practices. Conse-quently, the study objectives were to evaluate the effects of N fertilizer rates and ap-plication timing on sweet corn growth and yield under the subtropical environmental conditions of southeastern U.S., emphasizing the need for balanced nutrient management to improve yield and quality, minimize risks, and protecting the environmental.”

 

Comment 2: The introduction does not provide a relationship between weather conditions, nitrogen fertilization, and sweet corn productivity;

Response 2: Authors appreciate the reviewer comment. We have added additional information on weather conditions and its impact on soil nitrogen availability on the introduction section as recommended.

 

Comment 3: I suggest providing more information about sweet corn growing technology.

Response 3: Authors appreciate the reviewer comment, but we are not sure what the reviewer means with growing technology. In addition, we see no meaning to add more information to the manuscript as it will only create verbose to our paper, we already have a well described material and method that was highlighted by all reviewers.

 

Comment 4: I suggest moving the section 3.1. „Weather data and growing degree days“ and figure No.1 to the section 2.2. „Weather conditions“;

Response 4: Authors appreciate the reviewer comment but disagreed with the suggestion. Section 2.1 and 2.2 are describing weather conditions of the region, meaning it is characterizing our region as a subtropical environment, as well as describing methodology of weather parameters collected during our experiments, respectively. Contrarily, section 3.1 is reporting results of our study, meaning it is presenting weather parameters that were measured during the research period. No changes were made.

 

Comment 5: I advise splitting the discussion into smaller chapters;

Response 5: Authors appreciate the reviewer comment but see no reason for splitting out discussion. It would just increase the manuscript length and make it exhaustive for readers. No changes were made.

 

Comment 6: I recommend not to use old literature sources.

Response 6: Authors appreciate the reviewer comment and tried to update the literature cited as much as possible.

Reviewer 2 Report

Comments and Suggestions for Authors

The study explores optimal nitrogen management strategies to enhance yield while reducing environmental impact, taking into account the region’s sandy soils and unpredictable rainfall. This research adds value by focusing on sweet corn in subtropical conditions and emphasizing region- and season-specific strategies. Despite being a well-researched topic, nitrogen management remains crucial for sustainable agriculture. The methodology is comprehensively outlined, the research results are thoroughly described. The tables and figures are clearly presented. The references are appropriate. The conclusions are supported by the evidence, highlighting the study’s significance in enhancing nitrogen management for sustainable sweet corn production.

Author Response

Comment 1: The study explores optimal nitrogen management strategies to enhance yield while reducing environmental impact, taking into account the region’s sandy soils and unpredictable rainfall. This research adds value by focusing on sweet corn in subtropical conditions and emphasizing region- and season-specific strategies. Despite being a well-researched topic, nitrogen management remains crucial for sustainable agriculture. The methodology is comprehensively outlined, the research results are thoroughly described. The tables and figures are clearly presented. The references are appropriate. The conclusions are supported by the evidence, highlighting the study’s significance in enhancing nitrogen management for sustainable sweet corn production.

Response 1: Authors appreciate the reviewer comment and have made minor changes to improve even more the quality of the manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

The article presents the effect of nitrogen (dose, application date) on sweet corn yield. However, I have a few questions:

1. The key words include the word kernel quality - was this feature studied
2. Why was nitrogen applied on the same day as corn sowing, what was the emergence dynamics? were there any interference?
3. Why was LAI studied only on two plants?
4. Why was a synthesis not performed for two years of research for Alabama?
5. The paper confused LAI with the assimilation area of ​​a single plant. LAI for corn is 3.5-5.0. The article calculates the assimilation area of ​​a single plant
6. Why was the plant density per hectare only 26,684 plants. This gives only 2.4 plants per square meter. The cast is too small to draw conclusions
7. What variety of sweet corn was used in the study
8. How were P and K supplemented (balanced)?
9. Sweet corn is very damaged by pests. How were they combated
10. How were weeds eliminated

The article requires a very thorough re-editing

Comments on the Quality of English Language

The article presents the effect of nitrogen (dose, application date) on sweet corn yield. However, I have a few questions:

1. The key words include the word kernel quality - was this feature studied
2. Why was nitrogen applied on the same day as corn sowing, what was the emergence dynamics? were there any interference?
3. Why was LAI studied only on two plants?
4. Why was a synthesis not performed for two years of research for Alabama?
5. The paper confused LAI with the assimilation area of ​​a single plant. LAI for corn is 3.5-5.0. The article calculates the assimilation area of ​​a single plant
6. Why was the plant density per hectare only 26,684 plants. This gives only 2.4 plants per square meter. The cast is too small to draw conclusions
7. What variety of sweet corn was used in the study
8. How were P and K supplemented (balanced)?
9. Sweet corn is very damaged by pests. How were they combated
10. How were weeds eliminated

The article requires a very thorough re-editing

Author Response

The article presents the effect of nitrogen (dose, application date) on sweet corn yield. However, I have a few questions:

Comment 1: The key words include the word kernel quality - was this feature studied

Response 1: Yes. Kernel qualities, number of kernels per row (KR), number of kernels in an ear row (KIR), and total number of kernels per ear (KTG), were evaluated in our study and measurement described in the material and methods section.

 

Comment 2: Why was nitrogen applied on the same day as corn sowing, what was the emergence dynamics? were there any interference?

Response 2: Fertilizer nitrogen application on the same day as planting is a common grower practice in the region. Literature has proven that soil nitrogen availability during germination increase root development; however, the nitrogen requirement at planting is minimal; therefore, only about 20% of total nitrogen fertilizer is applied at this point. In our study, nitrogen fertilizer application at planting was a practice used but not evaluated, in which we have used the same nitrogen fertilizer rate for all treatment.

 

Comment 3: Why was LAI studied only on two plants?

Response 3: Leaf area index (LAI) was measured several times during the growing season in our study. As described in the material and methods, we have used destructive methods to evaluate LAI, and to avoid impacting plant population on plots and minimize errors, authors opted to evaluate only two plants per plot on each sampling timing. This approach allowed us to evaluate the LAI on 40 plants per treatment (2 plants per plot, with 4 replications, and 5 sampling times).

 

Comment 4: Why was a synthesis not performed for two years of research for Alabama?

Response 4: Authors are not sure what the reviewer means with synthesis. We assume it is related to the statistical analysis of comparing nitrogen treatment only within the Alabama location. In that case, nitrogen treatments were not evaluated only in Alabama because our objective was to compare treatment among different weather conditions that represented the sub-tropical climate of the region. Therefore, we have used location (e.g., Georgia 2020, Alabama 2021, and Alabama 2022) as single factor. This approach did not impact our statistical model; contrarily, it increased our degrees of freedom, reduced our errors, and allowed us to achieve the objective of the study.

 

Comment 5: The paper confused LAI with the assimilation area of ​​a single plant. LAI for corn is 3.5-5.0. The article calculates the assimilation area of ​​a single plant.

Response 5: Authors appreciate the reviewer comment but disagree that we have measured the assimilation area. As explained in the material and methods, we have used an optical-electronic area meter (LI-3100, LI-COR Inc., Lincoln, NE, USA) that measures the area of the leaf portion of the plant and not area of light assimilation by the plant. Authors have several other publications using and describing this methodology and data presentation. No changes were made.

 

Comment 6: Why was the plant density per hectare only 26,684 plants. This gives only 2.4 plants per square meter. The cast is too small to draw conclusions

Response 6: Authors appreciate the reviewer comment. The 26,684 represent plants/acre, authors have fixed this typo and the converted the number to the correct population of 61,813 plants/ha.

 

Comment 7: What variety of sweet corn was used in the study

Response 7: Authors appreciate the reviewer comment. Information on sweet corn cultivar used in our study was added to the material and methods section. The new sentence reads:

“Planting occurred on August 26, 2020, August 16, 2021, and August 17, 2022, the sweet corn cultivar Remedy (Syngenta Seeds, Minneapolis, MN, US) was used and harvests took place in early November each year (Table 1).”

 

Comment 8: How were P and K supplemented (balanced)?

Response 8: P and K were supplement only at planting, when the same nitrogen fertilizer rates were used. The fertilizer use had a N-P-K of 10-10-10. Therefore, the same rates of P and K were applied in all plots. At emergence and side dress, treatments were applied and the only fertilizer source used had a N-P-K of 34.4-0-0. All information is presentended in the material and methods and reads as:

“N fertilizer was applied in three stages: pre-planting (Npl), at emergence (Neme), and at side-dress (Nsd). The fertilizer source at Npl was 10-10-10 (N-P-K), while at Neme and Nsd, the source was 34-0-0 (N-P-K). At Npl, a rate of 34 kg N ha⁻¹ was applied across all treatments. At Neme, either 56 or 112 kg N ha⁻¹ was applied, followed by Nsd applications of 134, 162, or 190 kg N ha⁻¹, resulting in six treatment combinations (T1 - T6), as detailed in Table 2.”

 

Comment 9: Sweet corn is very damaged by pests. How were they combated.

Response 9: We follow the growers standard practices for the region, which most use recommendations from the Southeastern US Vegetable Crop Handbook (Kemble et al, 2024 - https://www.aces.edu/wp-content/uploads/2023/02/2024_SEVEG_final_web.pdf). This information was provided in the material and methods section. Particularly, fall armyworm is the most detrimental pest for sweet corn production in the region; therefore, authors used the cultivar Remedy, which has this insect resistance through the Attribute II trait stack from Syngenta.

 

Comment 10: How were weeds eliminated

Response 10: The sweet corn cultivar Remedy holds resistance for the Liberty herbicide (glufosinate-ammonium*: 2-amino-4-(hydroxymethylphosphinyl) butanoic acid-monoammonium salt) throughout the Attribute II trait stack from Syngenta. Therefore, weeds were controlled with two applications of Liberty, one at emergence and other at side dress. Overall, the IPM used in all sites follow growers standard practices for the region, as aforementioned, and most use recommendations from the Southeastern US Vegetable Crop Handbook (Kemble et al, 2024 - https://www.aces.edu/wp-content/uploads/2023/02/2024_SEVEG_final_web.pdf).

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I do not agree with the authors' answers to questions 1 and 9. Question 1. The number of grains in the cob, grains in a row is not the quality of the grain, but the structure of the grain yield. Grain quality is, for example, the content of protein, fiber, etc. Question 9. In a scientific article, it is not allowed to write in accordance with good agricultural practice. This should be corrected. I require that these two deficiencies be corrected

Comments on the Quality of English Language

I do not agree with the authors' answers to questions 1 and 9. Question 1. The number of grains in the cob, grains in a row is not the quality of the grain, but the structure of the grain yield. Grain quality is, for example, the content of protein, fiber, etc. Question 9. In a scientific article, it is not allowed to write in accordance with good agricultural practice. This should be corrected. I require that these two deficiencies be corrected

Author Response

Comment: I do not agree with the authors' answers to questions 1 and 9. Question 1. The number of grains in the cob, grains in a row is not the quality of the grain, but the structure of the grain yield. Grain quality is, for example, the content of protein, fiber, etc. Question 9. In a scientific article, it is not allowed to write in accordance with good agricultural practice. This should be corrected. I require that these two deficiencies be corrected

Response: Authors appreciate the reviewer time and expertise in reviewing our manuscript. We incorporated the suggestion recommended on the manuscript and replaced the term “kernel quality” by “kernel structure” along the entire manuscript. However, authors have not added each single product of our spraying program in the manuscript. We have conducted weekly spraying applications, that accounts with several products (i.e., herbicides, insecticides, and fungicides), the addition of all products for 3 growing seasons would be difficult for the reading and let the manuscript with verbose. Furthermore, our manuscript is not focused on spraying programs or any integrated pest management, but it is on best management practices for nitrogen management. Nevertheless, we agree with the reviewer that saying good agricultural practices is not scientifically, and we did improve the spraying program description in the material and methods, which can be seen below:

“Crop management practices, including soil preparation, irrigation, and the man-agement of pests, weeds, and diseases, were conducted in accordance with established protocols for sweet corn production in the southeastern United States [17]. The integrated pest management strategy employed varied field to field but included the use of bio-logical control agents and selective pesticides to minimize pest populations. Weed control was achieved through a combination of mechanical cultivation and herbicide application. Disease management included regular monitoring of the crop, and the application of fungicides as needed. The weekly scouting performed ensured fields remained free of weeds, insects, and diseases.”