Diagnosing Early Establishment of Hybrid Sorghum in Response to Seeding Rates Using UAV-Based Remote Sensing and Soil ECa Analysis

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Title: Should more highlight used methods as the effect of variable seeding rates on the early development was relatively weak. Moreover – from my point of view you did not tested variable seeding rates, but simply different seeding rates

Abstract: adequate

Introduction: should more focus on effects of variable seeding rates on crop yield and development.

Materials and Methods: used methods are well described. I only recommend to move section on climate and weather data into this chapter. What I find problematic is only one experimental year for field study. It is problematic to analyse biomass production or canopy coverage under field conditions based on data from only one year. What should be the effect of actual weather? Trials were harvested after 33 days – is it enough to see the real effect of intraspecific competition related to different seeding rates? Was there any reason you did not obtain data on final yield?

Results: clearly presented but with the respect to my previous comments I doubt the experiment was properly realised.

Discussion: well structured, detailed.

Conclusions: based on results, limited by used methods.

Author Response

We thank the reviewer for encouraging this new version and hope that the revisions meet the high standards of the journal.

Please, see the responses in the attached PDF.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article, titled "Influence of Variable Seeding Rates on the Initial Development of Hybrid Sorghum," presents an important approach and a significant contribution to defining plant population based on precision agriculture tools. Some suggestions are presented in the appendix to clarify important points of the research.

Comments for author File: Comments.pdf

Author Response

We thank the reviewer for encouraging this new version and hope that the revisions meet the journal's high standards.

Please see the responses in the attached PDF.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

General comments

The subject and research approach are relevant for the progress in crop cultivation in the time of precision farming. Methods are adequate but not innovative. 

The constraint of the study is that the field experiments reveal only the results of one year with a very short cropping period.

Concise explanation of instrumentation and trial design with necessary details and sound but not excessive descriptions. Well defined research goals, except the lack of explanation of the seeding equipment with regard to precise adjustment of seeding rates.

Helpful is the list of abbreviations easing to read the scientific publication.

Key words

Not applicable as too general: nutrition, fertilization, phenotyping, automation, decision support

Materials and methods

Line 94 and 96, 97 Description of experimental device by company names is not scientific sound. Please indicate instrumentation by technical attributes e.g. four-wheel 50 kW and in brackets producer name and type.

Line 97-99 Please explain the precision of the seed rate adjustment. The seed drill has a working space of 3 m, which represents the lateral resolution. What about the longitudinal resolution and please, explain the control of metering device.

Please, explain why the momentum dates are timewise uneven distributed over the entire experimental period.

How about fertilisation (see key words) and weed management. Was there any chemical input following the pre-emergence application? The nutrient supply was uniform in all management zones or plots?

Table 1: figures indicate in each plot one uniform seeding rate. How about the former described management zones?

Results 

Table 3 NP 2-13 results in 80 000 up to 520 000 plants per ha. What were the seeding rates in terms of number of seeds per ha? Is there an information about field emergence rate and relation between seeding rate and emergence rate?

Table 4 Ph looks very like not normal distributed?

Results page 22 line 366 An earlier statement that the sorghum was provided for forage harvest and not for grain is decisive for understanding the short vegetation period.

Figure 5 PH vs Strategy and Ph vs plot optimise strategy is lower and in PH vs plot lower than maximise? The same for NVDI?

Line 370 and fig 10 b Cveg in % 30 – 80% in fig 0.3 to o.8 % ?

Discussion

4.2 line 418 ECa is a driver or more an indicator?  In line 436 is a reliable proxi?

All the statements reflect the state of science concerning EC as an indicator for soil characteristics but the study outlines no results on relationship between  ECa and early growth variables. 

 

Conclusion

What is the conclusion of the VRS management related to nutrient supply in the field/experimental plots?

Under Introduction the research aim “Determine the correlation between EC and early growth metrics” was defined but not commented under conclusion.

Author Response

We thank the reviewer for encouraging this new version and hope that the revisions meet the journal's high standards.

Please see the responses in the attached PDF.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Editor and Author,

After evaluating the manuscript “Influence of Variable Seeding Rates on the Early Development of Hybrid Sorghum”, my decision is: Major revision.

Overview: The study evaluated the effect of different variable seeding rate strategies, defined by soil apparent electrical conductivity, on the early development of hybrid sorghum in a Mediterranean environment. The research compares the “Uniformise”, “Optimise”, and “Maximise” strategies, using UAV imagery and field measurements to analyze crop establishment and vegetative vigor. However, a major revision is recommended due to the short experimental period (only 33 days), which prevents linking the results to final productivity, and the absence of statistically significant differences in biomass among the tested strategies, which weakens the practical strength of the conclusions. Other inconsistencies were also identified. Therefore, specific comments on each section of the manuscript that requires revision are provided below:

Title: The title should include the use of remote sensing/UAV and soil variability, as these are central elements of the study. The phrase “Early Development” should be removed.

Abstract: It is already clear from the abstract that there were no statistically significant variations in final biomass among the strategies. This raises doubts about the actual effectiveness of the tested VRS prescriptions in the short term. The names of the strategies (“Uniformise”, “Optimise”, “Maximise”) are not self-explanatory, and the abstract does not objectively clarify how they differ.

Keywords: Some terms such as "Nutrition" and "Fertilisation" are not the central focus of the study and therefore should not appear in this section. Essential terms are missing, such as: variable rate seeding, remote sensing, or UAV.

Introduction: The justification does not provide sufficient grounds to convince the reader of the relevance of the research. The problem is not clearly presented, which makes it difficult to understand the importance of the study, and overall, the section does not adequately clarify its objective. In addition, there is no justification for adopting such a short experimental period (33 days) without monitoring the crop cycle until physiological maturity or final grain/forage harvest. The text is also excessively generic, beginning with broad arguments about sorghum and precision agriculture without clearly identifying the scientific gap. The reasoning relies mainly on theoretical relationships, particularly regarding the use of soil electrical conductivity, without considering its limitations, and the topics are presented with little logical integration, indicating excessive dependence on ECa as a productivity indicator. Finally, the introduction does not present any explicit hypothesis, leaving the reader without a clear expectation of what the authors intend to demonstrate.

Materials and Methods: The methodology is incomplete and requires further clarification regarding the proposed procedures. Many basic details are missing, and in its current form, the reader would not be able to replicate the experiment. In fact, it is difficult to determine whether the methodology aligns with the study objectives, and some of the described procedures are questionable. The experimental period of only 33 days is insufficient to evaluate the productive potential of the crop under variable seeding rate strategies, making interpretations related to system efficiency weak. The manuscript describes methodological procedures whose results are not presented, such as nitrogen analysis using the Kjeldahl method, rendering this information irrelevant in the current version. Some methods are insufficiently described, such as the classification of low and high ECa zones, with no indication of the statistical criteria or threshold values adopted. The lack of more rigorous radiometric calibration for UAV flights compromises the comparability of spectral indices over time. Similarly, soil moisture monitoring does not specify the location of the probes or the number of devices used, making it difficult to assess the representativeness of the measurements. Essential information is also missing, including the physicochemical characterization of the soil to support the use of ECa as an indicator of productive potential. Details on irrigation volumes and the method used to determine field capacity are absent, as are the field history and soil preparation system. The experimental design is not explicitly defined, preventing validation of the statistical analyses. Additional inconsistencies include the lack of explanation of how continuous ECa values were converted into categorical factors for analysis and the low sampling density, with only 33 points for seven plots, which may be insufficient given the high variability observed. Finally, the declared use of Google Gemini 3 in drafting the text requires careful verification of technical and conceptual accuracy to avoid scientific imprecision.

Results: This section contains several passages with interpretations, deductions, and causal explanations that go beyond the objective description of the data. At multiple points, the authors assign biological meaning to the findings, such as stating that plant height is a more robust indicator of biomass than spectral indices or that validating these correlations is essential for interpreting strategy performance. This type of analysis should be moved to the Discussion, keeping the Results focused strictly on presenting evidence. A similar issue appears in the presentation of meteorological and soil moisture data, where maintaining adequate water levels is described as a determining factor for successful crop establishment, representing a cause-and-effect relationship that exceeds the descriptive role of this section. Likewise, when presenting UAV-derived maps and indices, the text explains the reasons for the observed values and directly links spatial heterogeneity to seeding strategies, which also constitutes interpretation. Evaluative language is also used when biomass indicators are described as essential for assessing the efficiency of variable rate applications, a judgment that should be reserved for the Discussion or Conclusions. Furthermore, the statistical analysis indicates that the strategy factor had no significant effect on fresh or dry plant matter, reducing evidence of practical treatment impact. High coefficients of variation for important variables, such as plant number and canopy cover, also suggest substantial experimental heterogeneity that may have masked treatment effects and compromised analytical sensitivity.

Discussion: The discussion presents some limitations in the interpretation of the results. The greater initial vegetative vigor observed in the “Uniformise” strategy did not translate into increased biomass, which weakens the evidence of agronomic benefit. Even so, the text suggests potential management advantages based mainly on theoretical economic benefits from the literature, without demonstrating this viability using the experiment’s own data. There is also repetition of interpretations already presented in the Results section, making the text redundant and less objective, indicating organizational problems that reduce argumentative clarity. Although study limitations are mentioned, they are treated superficially, particularly considering the short experimental period and the absence of statistical differences in final biomass, both of which reduce the strength of the conclusions. Additionally, the discussion tends to attribute agronomic relevance to the strategies despite limited experimental evidence, suggesting impacts that are not consistently supported by the data. Finally, the numerous suggestions for future research reinforce the still exploratory nature of the study and highlight gaps that weaken the inferences presented.

Conclusion: This section should be rewritten. The conclusion in its current version presents stronger claims than the results can support. Even without statistical differences in productivity, the “Uniformise” strategy is identified as the most effective, which constitutes an excessive generalization. There is also an overemphasis on initial vigor and spectral indices that did not result in productive gains, reducing the agronomic relevance of the conclusions. The text adopts an inflated tone by classifying remote sensing as a robust tool and by suggesting practical applications for management without this having been demonstrated in the experiment. Furthermore, there are extrapolations regarding decision-making support and sustainable intensification that are not fully supported by the data. Finally, the main limitations of the study, such as the short experimental period and the lack of a productivity response, are not given due emphasis.

References: The authors should consult recent articles from the journal to ensure that the references are organized and formatted according to MDPI requirements. Additionally, some listed references are outdated, and others come from sources that did not undergo ad hoc peer review. Whenever possible, these should be replaced with more current references from high-impact journals.

Given the above, some inconsistencies are evident, and my recommendation is “Major revision”.

I encourage the authors to submit a new version of the manuscript and, if they agree, I would like to receive responses to all comments they disagree with or choose not to address.

Best regards,

Reviewer

Author Response

We thank the reviewer for encouraging this new version and hope that the revisions meet the journal's high standards.

Please see the responses in the attached PDF.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

All my comments to the previous version were accepted or clarified by authors.

Author Response

Dear Reviewer,

We would like to express our sincere gratitude to you for the time and significant effort dedicated to providing such a comprehensive and rigorous critique of our manuscript.

Kind regards

Reviewer 2 Report

Comments and Suggestions for Authors

The authors addressed all the points raised; therefore, I accept the article.

Author Response

Dear reviewer,

We would like to express our sincere gratitude to you for the time and significant effort dedicated to providing such a comprehensive and rigorous critique of our manuscript.

Kind regards

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Authors and Editor,

After a new evaluation of the manuscript “Assessing Hybrid Sorghum Response to Seeding Rates Using UAV-Based Remote Sensing and Soil Variability Analysis”, my recommendation is: Minor revision.

The authors have improved the manuscript. They included the physicochemical characterization of the soil, justified the 33-day period based on cyanogenic toxicity, clarified the research hypotheses, and removed nitrogen data that were not relevant. However, some points still need adjustment before acceptance.

The issue of low sampling density remains a concern. Only 33 sampling points were used across 7 fields in an area with high variability and elevated coefficients of variation. The authors justify this as common in on-farm experiments, but they do not explain how this limitation may have affected the statistical power to detect real differences among the seeding strategies.

There is still some mixing between the Results and Discussion sections. Even after the revisions, the Results section includes interpretations, such as statements that certain strategies influenced canopy density and vigor. This type of interpretation should be presented in the Discussion, while the Results section should remain limited to the objective description of the data.

Another point concerns the interpretation of the absence of statistical differences. The authors state that the “Optimise” strategy was efficient in resource use because it did not differ from “Maximise” in terms of biomass. However, turning a lack of statistical difference into proof of equivalence is risky, especially in an experiment with high variability, which may have limited the ability to detect real effects.

The declaration of AI use (Google Gemini 3) also requires caution. In some sections, particularly in the Conclusion, the text seems slightly overstated when describing remote sensing as “essential”, even though the results did not demonstrate clear productivity gains. I recommend revising the text to avoid terms that overemphasize the impact of the findings.

Finally, with the justification for harvesting at 33 days for safety reasons, the study now has a stronger focus on diagnosing early establishment rather than final productivity. This should be made clearer in the title and abstract to avoid creating the expectation that the study demonstrated productivity gains in grazing systems.

The study has merit in integrating ECa and UAV data, but the conclusions need to be more balanced and aligned with what the data actually showed.

In light of the above, I recommend “Minor Revision”. I encourage the authors to submit a revised version of the manuscript and, if they disagree with or choose not to address any of the comments, I would appreciate receiving a response explaining their position.

Best regards,

Reviewer

Author Response

Dear reviewer,

We thank you for encouraging this new version and hope that the minor revisions meet the journal's high standards.

Please see the responses in the attached PDF.

Kind regards

Author Response File: Author Response.pdf

Round 3

Reviewer 4 Report

Comments and Suggestions for Authors

Dear Authors and Editor,

After a new evaluation of the manuscript “Diagnosing Early Establishment of Hybrid Sorghum in Response to Seeding Rates Using UAV-Based Remote Sensing and Soil ECa Analysis”, my recommendation is: Accept the manuscript for publication.

The authors have made a significant effort to address the previous comments, modifying the title to focus on “early establishment” rather than final productivity gains. In addition, the manuscript structure has improved, with a clearer separation between Results and Discussion and a moderation of exaggerated terms previously introduced by AI assistance. Although I agree that the manuscript can be published in its current form, the authors could still make minor adjustments to further improve it:

The Results section still contains passages that approach interpretation. For example, by stating that the indicators represent the final biological response, the authors are already assigning functional meaning to the data, which would be more appropriately presented in the Discussion section.

Section 4.5 acknowledges that variability may have limited the statistical power. In this regard, the authors could clarify whether the absence of differences in biomass truly reflects a biological outcome or is merely a consequence of the reduced sample size (n = 33) combined with the high coefficient of variation.

In the Abstract, the language is cautious, referring only to the potential for resource optimization. However, in the Conclusion, the statement that the “Optimise” strategy may provide more efficient resource use is slightly more assertive than what the absence of statistical difference allows. It is important to maintain the same cautious tone consistently across all final sections of the manuscript.

In the Conclusion, the authors also mention that the impact of ECa may have been reduced due to the field’s history of high fertility. This is a new and relevant point that was not as clearly presented in the previous version as a limitation of the study. Therefore, it should be discussed carefully to avoid sounding like an ad hoc justification for the lack of significant differences in biomass.

Congratulations to the authors on their work.

Best regards,

Reviewer

Author Response

Dear reviewer,

We thank you for encouraging this new version and hope that the minor revisions meet the journal's high standards.

Please see the responses in the attached PDF.

Kind regards

Author Response File: Author Response.pdf