Abstract
In this study, the performance of a backpack sprayer equipped with a T-jet nozzle was evaluated under laboratory conditions. To investigate the amount of liquid droplet deposition on each pot, water-sensitive papers were used. The water-sensitive papers were then analyzed using image processing techniques with ImageJ software. This research was conducted based on a factorial experiment arranged in a completely randomized design, including the factors of forward speed at three levels (2, 3.5, and 5 km h⁻¹), spraying pressure at three levels (2, 3, and 4 bar), and distance of the pots from the fan at three levels (1, 2, and 3 m), with three replications. In all measurements, the nozzle height above the ground was maintained at 90 cm. The results showed that with increasing forward speed, the volumetric diameters of 10%, 50%, and 90% and the surface coverage decreased by approximately 11% and 31%, respectively. However, this decreasing trend was not statistically significant at all speed levels, such that no significant difference was observed between the speeds of 3.5 and 5 km h⁻¹ at the 5% probability level. The minimum and maximum solution deposition were obtained at pressures of 4 bar (19.37%) and 3 bar (28.53%), respectively. The highest surface coverage percentage was observed in pots located at the farthest distance from the fan. Ultimately, the highest surface coverage percentage was achieved in the treatment with a forward speed of 2 km h⁻¹ and a spraying pressure of 3 bar.
Introduction
In recent decades, the extensive use of pesticides and herbicides in agriculture has raised significant environmental and health concerns. Excessive and improper application can lead to adverse effects, including water contamination, biodiversity loss, and risks to human health. Consequently, enhancing the efficiency of pesticide application has become a critical priority for sustainable agriculture. One of the most effective approaches to improving pesticide application is to ensure uniform spray distribution and producing droplets of appropriate size, as droplet size directly influences spray coverage, drift, and pesticide effectiveness.
Previous research has shown that spraying performance is significantly affected by factors such as nozzle type, spray pressure, travel speed, and the physicochemical properties of the spray liquid. key indicators for evaluating spray quality include surface coverage percentage, volume median diameter, and spray uniformity, which are typically assessed using image analysis and water-sensitive papers. While many studies have addressed large-scale field spraying, relatively limited research has focused on potted plants under controlled environments such as greenhouses. This study investigates the influence of operational parameters, specifically forward speed, spray pressure, and distance of the fan from the pots on spray deposition characteristics in eggplant plants grown in pots. The goal is to evaluate droplet distribution and spray uniformity in relation to plant surface coverage. By applying cost-efficient image processing methods, the research aims to provide practical insights for improving pesticide application in greenhouses and small-scale farming systems.
Material and Methods 
This study was conducted using a mobile-frame system at the Department of Biosystems Engineering, Shiraz University, to evaluate spraying performance under controlled conditions. A backpack sprayer (METEC SPRAYER) equipped with a TJ60-11004 nozzle was mounted on a galvanized steel frame designed for a 3 m spray width. The system was powered by a 1.1 kW electric motor (Motogen, Tabriz), and its speed was regulated using an inverter (Hyundai N50, South Korea). An axial fan generated a 3 m/s airflow parallel to the spray path, calibrated using an anemometer (Lutron YK-2001 AL). Eggplant seedlings were cultivated in pots, and water-sensitive papers were placed around plants to assess spray coverage and drift. After spraying, cards were scanned (HP Scanjet 3770, 2400 dpi) and analyzed with ImageJ 1.46r. A factorial design in a completely randomized layout was employed, with three levels of pressure (2, 3, 4 bar), speed (2, 3.5, 5 km/h), and fan distance from the pots (1, 2, 3 m). Data were analyzed using Duncan’s test at the 5% significance level with SPSS (version 26).
Results and Discussion 
The results of the variance analysis indicated that forward speed had a significant effect on the volumetric diameter parameters (DV0.1, DV0.5, and DV0.9) and surface coverage percentage at the 5% probability level. Additionally, spray pressure, fan distance from the pots, and the interaction between forward speed and pressure on surface coverage demonstrated statistically significant differences. Increasing the forward speed from 2 to 5 km/h led to a decrease of approximately 11% in volumetric droplet diameters, attributed to reduced droplet deposition on target surfaces due to shorter residence time. Surface coverage also decreased by nearly 31% as forward speed increased, due to the nozzle's shorter exposure time over the plants. At forward speeds of 2, 3.5, and 5 km/h, the average surface coverage was 29.07%, 23.94%, and 20.06%, respectively. Spray pressure significantly influenced surface coverage. The highest surface coverage of 28.53% was observed at 3 bar pressure, while the lowest coverage of 19.37% was observed at 4 bar pressure. The distance of the fan from the pots affected spray deposition; pots located farther from the fan received greater coverage due to droplet drift. No significant difference was observed between those pots positioned closer to the fan. The interaction between spray pressure and forward speed was significant at the 5% probability level. The highest surface coverage was observed at 3 bar and 2 km/h, while the lowest was recorded at 4 bar and 5 km/h. Overall, higher forward speeds and pressures led to smaller droplets and greater drift, reducing overall spray deposition efficiency on target surfaces.
Conclusions 
This study investigated the spray performance of a backpack sprayer equipped with a TeeJet nozzle under varying operational conditions. The results demonstrated that forward speed and spray pressure significantly affect both droplet size and surface coverage. Specifically, increased forward speed led to a reduction in volumetric droplet diameters (DV0.1, DV0.5, DV0.9) and a notable decline in surface coverage, primarily due to reduced nozzle residence time over the target area. Among the evaluated spray pressures, 3 bar provided better overall coverage than 2 and 4 bar, likely due to lower droplet drift at lower pressures. Fan distance also played a critical role in deposition patterns, with pots farther from the fan receiving greater coverage due to the redistribution of airborne droplets. Optimal spraying performance was achieved at a spray pressure of 3 bar, forward speed of 2 km/h, and fan distance of 3 m. These findings offer practical insights for improving pesticide application efficiency in greenhouse or semi-controlled environments. Further research is recommended to validate these results under field conditions and to explore the influence of additional environmental factors, such as wind direction, humidity, and canopy structure, on spray dynamics.
Acknowledgements
The authors gratefully acknowledge Shiraz University for its financial support. 
Author Contributions
Author1: Writing – review & editing, Writing – original draft, Visualization, Validation, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Conceptualization. 
Author2: Visualization, Validation, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Conceptualization. 
Author3: Visualization, Validation, Software, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. 
Author4: Writing – review & editing, Visualization, Validation, Software, Methodology, Investigation, Formal analysis. Author5: Writing – review & editing, Visualization, Validation, Software, Methodology, Investigation, Formal analysis. Author6: Writing – review & editing, Visualization, Validation, Investigation. Author7: Writing – review & editing, Visualization, Validation.
Data Availability Statement
Data will be made available on request. 
Ethical Considerations
The authors confirm that research ethics were considered throughout the research methodology, including data definition, data collection, data analysis, data interpretation, and plagiarism, to provide the final report.
Conflict of Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper
Funding Statement
This work was supported by grant number 148321 from Shiraz University.