The Influence of Unmanned Aerial Vehicle Wind Field on the Pesticide Droplet Deposition and Control Effect in Cotton Fields

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The author should explain the meaning of ''moderately fertilized'' experimental field and the type of fertilizer used.

The boom sprayer and its working parameters/adjustments should be characterized in detail. The sprayer has most likely flat-fan nozzles

It is not clear if 11.25 m is the spraying width or the length of the boom. Also, the mounting distance between the 32 nozzles should be brought to the attention.

The author should submit weather data/meteorological variables, such as wind speed and direction, air temperature and relative humidity etc

Author Response

1. The author should explain the meaning of ''moderately fertilized'' experimental field and the type of fertilizer used.

Response: We appreciate the reviewer’s comment regarding the clarification of the term “moderately fertilized” and the type of fertilizer used in our study. To address this, the term “moderately fertilized” refers to the application of fertilizers in amounts that are in line with standard agricultural practices for cotton cultivation in the region, providing sufficient nutrients for healthy plant growth without leading to excessive fertilization or nutrient imbalances. Specifically, a balanced compound fertilizer was used, containing nitrogen (N), phosphorus (P), and potassium (K) in appropriate proportions to meet the needs of the cotton crop throughout the growing season. We have now added this explanation to the revised manuscript to provide further clarity.

 

2. The boom sprayer and its working parameters/adjustments should be characterized in detail. The sprayer has most likely flat-fan nozzles.

Response: We appreciate the instructor’s suggestion to further characterize the boom sprayer and its working parameters, particularly regarding the flat-fan nozzles. To address this, we have expanded the description to include specific details about the nozzle type and adjustable components. The sprayer is equipped with 32 flat-fan nozzles (model 11003, Dongguan Huajue Spray Technology Co., Ltd.), which feature a 110° spray angle and a nominal orifice size designed for medium-to-coarse droplet formation, critical for uniform coverage and reduced drift.

Additionally, we have detailed key working parameters and adjustments: spray pressure (200–300 kPa, adjustable via a hydraulic valve to optimize droplet size), boom height (positioned at 60 cm above cotton plants with a 50–80 cm adjustable range to adapt to crop growth and environmental conditions), tractor speed (4.2–4.5 km/h, calibrated to match nozzle flow rate and spray width for target application rates), and nozzle configuration (90° orientation to the boom for horizontal spray patterns, with replaceable nozzles to accommodate different pest control needs). The self-assembled design includes a lightweight aluminum boom with vibration-damping mounts to ensure stable spray distribution across the 11.25 m width. These details have been integrated into the revised manuscript to provide a comprehensive technical characterization of the equipment and its operational adjustments.

3. It is not clear if 11.25 m is the spraying width or the length of the boom. Also, the mounting distance between the 32 nozzles should be brought to the attention.

Response: We appreciate the reviewer’s comment regarding the clarification of whether 11.25 m refers to the spraying width or the boom length, as well as the mounting distance between the 32 nozzles. To address this, the 11.25 m denotes both the physical length of the boom and the effective spraying width. The nozzles are evenly spaced along the 11.25 m-long boom with a nozzle spacing of 35 cm, meaning each nozzle is 35 cm apart from its adjacent ones. The single spray width of each nozzle is 70 cm, designed with 50% overlap between adjacent nozzles to ensure uniform spray coverage, which results in the effective spraying width matching the boom length of 11.25 m. We have now added this clarification to the revised manuscript to explicitly state that the boom length and effective spraying width are both 11.25 m due to the intentional nozzle spacing and overlap design, and to confirm the consistent 35 cm mounting distance between each of the 32 nozzles.

4. The author should submit weather data/meteorological variables, such as wind speed and direction, air temperature and relative humidity etc.

Response: We appreciate the instructor’s suggestion regarding the inclusion of weather data/meteorological variables in the manuscript. To address this, we have monitored and recorded key meteorological parameters throughout the experiment, including wind speed, wind direction, air temperature, and relative humidity. These data have been systematically organized and are presented in Table 1, which is appended to the relevant section describing the experimental setup.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors reported that the influence of unmanned aerial vehicle (UAV) wind field on the pesticide droplet deposition and control effect in cotton fields.

The results showed that the critical role of wind field intensity in influencing the spraying performance, with UAVs featuring stronger wind fields exhibiting superior droplet penetration and distribution uniformity. These findings provide valuable scientific insights for optimizing UAV spraying in cotton fields. This article does seem to give readers new understandings and knowledge about advantages of valuable scientific insights for optimizing UAV spraying in cotton fields.

I feel that the findings and methodologies from this article will be of much interest to the readers of “Agronomy”.  Therefore, I suggest this manuscript be valuable and acceptable for “Agronomy” after revisions.

 

I would like the authors to address the following issues. Please check thoroughly.

 

1. Introduction Section: The introduction lacks an accurate and comprehensive literature review. The citations in this paper are limited to papers from within China, but there are many spray comparisons of UAVs spray deposition tests were also reported in other countries.

 

Page 4, line 147 to 149: It is difficult to image “having six rows per film with a spacing of 66 + 10 cm. During the entire growth period, drip irrigation was applied with one film and two tubes”. Further explanation is needed, such as adding information regarding the film width and a schematic figure.

 

Page 5, line 175: “Aphis gossypii Glover” to “Aphis gossypii Glover”.

“Aphis gossypii” is italic.

 

Page 5, line 182 to 183: I the text “a 40% ethephon solution (900 g/ha for UAV and 1800 mL/ha for boom sprayer, Jiangsu Anpon Electrochemical Co., Ltd., Huaian, China)”, it is necessary to confirm whether the g/ha or ml/ha of Goura is correct.

 

Page 5, line 188: In “40% ethephon solution (900 g/ha)”, is the unit of g/ha correct?

 

Page 6, line 211 to 212: “ρis the planting density (plant・m²)” to “ρis the planting density (plant/m²)”.

 

Page 7, line 247 and 252: “aphis gossypii” to “Aphis gossypii”.

 

Page 7, line 252: “Tetranychus urticae” to “Tetranychus urticae”.

 

Page 14, 5. Conclusions Section: Based on the results of this study, how about you also describe your future prospects for research into pesticide spraying using UAVs?

Author Response

1. Introduction Section: The introduction lacks an accurate and comprehensive literature review. The citations in this paper are limited to papers from within China, but there are many spray comparisons of UAVs spray deposition tests were also reported in other countries.

Response: Thank you for the constructive feedback. We acknowledge the importance of incorporating global research perspectives into the literature review. To address this, we have significantly expanded the introduction by integrating recent international studies on UAV spray deposition dynamics and operational parameter optimization, and it has been added to the article. These additions enhance the global relevance of our literature review while maintaining coherence with the original framework. We have ensured balanced citations from both Chinese and international journals to reflect advancements in UAV spray technology worldwide.

2. Page 4, line 147 to 149: It is difficult to image “having six rows per film with a spacing of 66 + 10 cm. During the entire growth period, drip irrigation was applied with one film and two tubes”. Further explanation is needed, such as adding information regarding the film width and a schematic figure.

Response: Thank you for your valuable suggestion regarding the clarification of the planting pattern. To address the difficulty in visualizing the configuration, we have added specific information about the mulch film width (2.05 m) to the paragraph. This detail, combined with the explanation of row spacing and drip tube arrangement, helps readers better understand how six rows and two drip tubes are integrated within each film. The revision enhances the technical accuracy and readability of the description, ensuring clarity for those unfamiliar with the specific agricultural practices mentioned.

3. Page 5, line 175: “Aphis gossypii Glover” to “Aphis gossypii Glover”. “Aphis gossypii” is italic.

Response: Thank you for your valuable feedback regarding the formatting of scientific names. We have revised the text to italicize "Aphis gossypii" while keeping "Glover" in regular font, in accordance with the standard formatting for binomial nomenclature. This change ensures proper taxonomic notation and adherence to scientific writing conventions.

4. Page 5, line 182 to 183: I the text “a 40% ethephon solution (900 g/ha for UAV and 1800 mL/ha for boom sprayer, Jiangsu Anpon Electrochemical Co., Ltd., Huaian, China)”, it is necessary to confirm whether the g/ha or ml/ha of Goura is correct.

Response: Thank you for your valuable feedback regarding the unit notation for the ethephon solution. We appreciate your careful review of the manuscript. On text, we have revised “900 g/ha” (for UAV application) to “900 mL/ha” to align with the correct unit for liquid solution application rates. Since the solution is specified as a 40% concentration (volume-based), the unit should reflect volume per hectare (mL/ha) rather than mass (g/ha). The existing “1800 mL/ha” for the boom sprayer was already correct, and we have ensured consistency across both application methods. This change adheres to standard practices in agricultural research for expressing liquid chemical dosages, ensuring accuracy and clarity in reporting the application rates.

5. Page 5, line 188: In “40% ethephon solution (900 g/ha)”, is the unit of g/ha correct?

Response: Thank you for your valuable feedback regarding the unit notation. We sincerely appreciate your careful review and correction. On Page 5, line 188, we have revised “900 g/ha” to “900 mL/ha” for the 40% ethephon solution. Since “40% ethephon solution” refers to a volume-based concentration, the unit should correctly reflect volume per hectare (mL/ha) rather than mass (g/ha). This change aligns with standard practices for expressing liquid pesticide or chemical solution application rates in agricultural contexts, ensuring accuracy and consistency with industry conventions.

6. line 211 to 212: “ρ is the planting density (plant・m²)” to “ρ is the planting density (plant/m²)”.

Response: Thank you for your valuable feedback regarding the unit notation. We have revised lines 211 to 212 to replace “plant・m²” with “plant/m²” for the planting density (ρ). This change aligns with standard scientific notation for unit expressions, using a forward slash to denote "per" in measurement units, which enhances clarity and consistency with conventions in technical literature.

7. Page 7, line 247 and 252: “aphis gossypii” to “Aphis gossypii”.

Response: Thank you for your valuable feedback regarding the formatting of scientific names. We have revised Page 7, lines 247 and 252 to correct the capitalization of "aphis gossypii" to "Aphis gossypii" and italicized the binomial name ("Aphis gossypii"), as required by standard taxonomic conventions. This ensures proper adherence to scientific naming rules for clarity and consistency.

8. Page 7, line 252: “Tetranychus urticae” to “Tetranychus urticae”.

Response: Thank you for your feedback on the scientific name formatting. We have updated Page 7, line 252 to italicize "Tetranychus urticae" as "Tetranychus urticae", in accordance with the standard practice for binomial nomenclature. This change aligns the manuscript with scientific writing guidelines for taxonomic accuracy.

9. Page 14, 5. Conclusions Section: Based on the results of this study, how about you also describe your future prospects for research into pesticide spraying using UAVs?

Response: Thank you for your insightful suggestion. In the Conclusions section on Page 14, we have now incorporated future research prospects for pesticide spraying using UAVs. Building on the findings of this study, future research could focus on exploring the application of UAV - based pesticide spraying in a wider variety of crops, beyond just cotton. This would help to understand the adaptability of UAV - generated wind fields in different canopy structures. Additionally, research could be conducted to develop more intelligent UAV systems that can automatically adjust their flight parameters and spraying strategies in real - time according to changing environmental conditions and crop growth status. Another important area for future work is to study the long - term environmental and ecological impacts of UAV - based pesticide spraying, including effects on soil, water, and non - target organisms, to ensure the sustainable development of this technology in agriculture.

Reviewer 3 Report

Comments and Suggestions for Authors

Review Agronomy 3611894 - The influence of Unmanned Aerial Vehicle wind field on the 2 pesticide droplet deposition and control effect in cotton fields

This paper aims at studying the influence of the downwash air flow (called downwash wind field) from different UAV design on the deposition in a cotton canopy for different purpose :, aphids control and defoliant at two different crop stages. Although this topic is not totally new, this paper has potential interest since it concern the lastest generations of UAV available on the market.  

Globally the paper is well written, and authors show a correct use of protocols and data analysis.

However, there is a permanent confusion in this paper that is related to the air downwash. Although this parameter can be logically evoked in order to interprete the results, the paper does not contain any formal information from air speed measurements nor from manufacturer to validate this simple hypothesis. As a consequence, the title (and most of figures captions as well the text itself) might be changed accordingly (for example : “The influence of UAV design on pesticide….”)

The introduction mostly gives general information but does not really details the differences between the different designs of T30, T40, T50 and T60 (number of nozzles, number of impellers / rotor, etc…) Information about the air velocity at the height of the crop in the different systems would probably help to better analyse the results.

At least a precise description of impeller  number, size and revolution speed may help to characterize differences between drones. In particular, double impeller present in the T50 may require comparison in terms of downwash airflow. 

Detailed comments

Material and methods : what were the atmospheric conditions (T°C, RH, wind direction and velocity). There is a possibility of cross contamination from one plot to another when 4m buffer distance are used in teh wind direction...

Page 9 Fig 4 : does the PPP and/or the formulation modify the droplet size explaining slight differences between the two products? But Fig 5 Page 10 shows that the density of impacts is also higher for the defoliant

Page 11 Fig 6 : I believe these data are from the red dye analysis?  

Why data from Fig 6 are a bit different from Fig 4 (case of the defoliant?)

Globally, results are mostly described but tehy are not really analyzed : differences between products , between WSP and dye tracer, wwhat are the impact size distributions on WSP ?

 

Detailed comments

Material and methods : what were the atmospheric conditions (T°C, RH, wind direction and velocity)

Page 9 Fig 4 : does the PPP and/or the formulation modify the droplet size explaining slight differences between the two products? But Fig 5 Page 10 shows that the density of impacts is also higher for the defoliant

Page 11 Fig 6 : I believe these data are from the red dye analysis?  

Why data from Fig 6 are a bit different from Fig 4 (case of the defoliant?)

 

Author Response

1. Material and methods: what were the atmospheric conditions (T°C, RH, wind direction and velocity). There is a possibility of cross contamination from one plot to another when 4m buffer distance are used in the wind direction...

Response: Thanks for your valuable comments. This problem has already been addressed as per the comments of reviewer 1 and the response has been added into updated manuscript. And thank you for raising this important concern. We acknowledge the potential risk of cross-contamination between plots and have rigorously addressed it through experimental design and data validation:

(1) Immediate Sampling Protocol: Water-sensitive papers and cotton plants for Allura Red AC elution were replaced and collected immediately after each flight, ensuring that measurements reflect only the deposition from the current spraying event.

(2) Spatial Isolation: Five-point sampling for efficacy assessment was strictly conducted within the central zone of each plot, maintaining a 2-meter distance from buffer edges to avoid edge effects.

 

2. Page 9 Fig 4: does the PPP and/or the formulation modify the droplet size explaining slight differences between the two products? But Fig 5 Page 10 shows that the density of impacts is also higher for the defoliant.

Response: Thank you for highlighting this important point. The slight differences in droplet size between the insecticide and defoliant (Fig 4) and the higher impact density of the defoliant (Fig 5) are probably attributed to formulation-specific physicochemical properties rather than intentional changes in PPP (pesticide application parameters), Their changes are not too great on the whole, change that is relatively obvious is T30, It uses fan-shaped nozzles. Centrifugal nozzles are more suitable for low-viscosity defoliants containing surfactants, which can produce finer droplets, while fan-shaped nozzles are more likely to form coarse droplets for high-viscosity insecticides. This response have been incorporated in the manuscript to enhance clarity and interest to the readers.

 

Page 11 Fig 6: I believe these data are from the red dye analysis?

Response: Thank you for your review! The data in Page 11 Fig 6 originate from the Water Sensitive Paper (WSP) analysis, not the allure red dye tracer used for pesticide utilization rate calculations. As detailed in Section 2.4.2 of the Materials and Methods, WSP was deployed at different canopy heights to capture spray droplets during both insecticide and harvest-aid applications. After spraying, the WSPs were scanned at 600 dpi, and ImageJ software was used to analyze droplet deposits, including coverage, density, and deposition (μL/cm²). This method specifically targets droplet deposition characteristics in the cotton canopy, while the allure red dye was employed separately in Section 2.4.1 to quantify pesticide utilization rates via absorbance measurements. The distinction between these two techniques is crucial: WSP data visualize immediate spray distribution, whereas the dye tracer assesses overall pesticide retention efficiency. We appreciate your attention to this detail, which ensures the accuracy of our methodological description and results presentation.

 

3. Why data from Fig 6 are a bit different from Fig 4 (case of the defoliant?).

Response: We appreciate the reviewer’s observation regarding the differences between Figures 4 and 6. The key reason for this discrepancy lies in the distinct parameters being measured. Figure 4 presents droplet coverage, which reflects the percentage of leaf surface area stained by spray droplets, whereas Figure 6 reports droplet deposition, which quantifies the actual liquid volume per unit area (μL/cm²). We have clarified this point in the manuscript to aid reader interpretation. Specifically, we added the following explanation: "UAV models with stronger wind fields, such as T60, facilitated better penetration and deposition into the lower canopy layers, which is more directly reflected in deposition data (Figure 6), whereas coverage may not fully capture this benefit due to non-uniform leaf surface exposure."

4. Globally, results are mostly described but they are not really analyzed: differences between products, between WSP and dye tracer, what are the impact size distributions on WSP?

Response: Thanks for highlighting the need for a more comprehensive analysis. We have addressed this concern by providing a more detailed analysis of the differences. Specifically: the divergent trends between the insecticide and defoliant such as the defoliant’s higher impact density (Fig 5B) stem primarily from formulation-specific properties: defoliants contain surfactants that reduce surface tension, promoting finer atomization and smaller droplets via centrifugal nozzles (T40/T50/T60), which increase impact numbers on WSP.  In contrast, the insecticide’s higher viscosity leads to coarser droplets from fan-shaped nozzles (T30), resulting in fewer but larger impacts. We have made a clear distinction between Water Sensitive Paper (WSP) and dye tracers (Allura Red). WSP is used for visualizing droplet coverage and distribution uniformity but does not provide precise quantification of liquid volume. Dye tracers, on the other hand, allow for accurate quantification of droplet deposition by measuring the amount of dye deposited, which is directly linked to the liquid volume. This distinction has been added to the Materials and Methods section, and the roles of each method in evaluating the UAV spraying performance have been clarified. The impact size distributions on WSP are a critical metric linking droplet atomization, formulation properties, and canopy deposition.  Fine droplets (defoliants) yield dense, small impacts that enhance coverage and penetration, while coarse droplets (insecticides) produce sparse, large impacts that prioritize retention on exposed leaves.  This distribution is pivotal for optimizing UAV spraying, as it balances key objectives like pest control (requiring deep penetration) and efficiency (requiring uniform retention), guided by nozzle selection and formulation chemistry.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript was significantly improved and authors have considered the comments and suggestions from reviewers