Introduction: In recent years, agricultural UAV spraying has emerged as one of the most promising technologies in precision agriculture and has gained significant attention for crop protection applications. These systems offer several advantages, including the elimination of runway requirements, reduced pesticide and water consumption, higher operational efficiency, improved spray penetration into crop canopies, minimized operator exposure to agrochemicals, and lower environmental contamination. Consequently, UAV sprayers have been increasingly adopted for a wide range of crops, including rice, wheat, maize, soybean, sugarcane, and cotton. Despite the rapid growth of research in this field, existing knowledge remains fragmented, and a comprehensive framework for identifying optimal operational parameters and evaluating spraying performance has not yet been established. Therefore, the present study aimed to systematically review the global literature on agricultural UAV spraying, identify the key factors influencing their performance, determine the optimal ranges of operational parameters, and highlight current challenges and research gaps.

Materials and Methods: This study was conducted using a systematic literature review approach. In the first stage, scientific publications available up to July 13, 2025, were identified through comprehensive searches of major academic databases, including Scopus, Web of Science, ScienceDirect, ResearchGate, Google Scholar, and the Directory of Open Access Journals (DOAJ), using keywords related to agricultural UAV spraying. During the screening process, studies focusing on the design, development, or field evaluation of UAV spraying were retained, while duplicate and irrelevant publications were excluded. Ultimately, 91 articles published between 2009 and 2025 were selected for detailed analysis. The extracted information included UAV type, tank capacity, nozzle type and number, effective spray width, flight height and speed, crop type, target pest or disease, and reported performance indicators. The collected data were organized using Microsoft Excel and analyzed through descriptive statistical methods to identify research trends, characterize the ranges of technical and operational parameters, and evaluate performance indicators. Furthermore, limitations, challenges, and future research directions were identified through a critical synthesis of the reviewed studies.

Results and Discussion: The results revealed a continuous increase in publications related to UAV spraying since 2009, with a compound annual growth rate of approximately 20%. More than 83% of the reviewed studies were conducted in Asia, with China, India, the United States, and Iran accounting for the largest share of research output in this field. Regarding UAV configuration, more than 77% of the studies employed rotary-wing platforms, among which quadcopters were the most frequently used, representing 30.4% of all reported systems. China was identified as the leading manufacturer, supplying approximately 61% of the UAV used in the reviewed studies.

Analysis of technical characteristics showed that most UAV spraying were equipped with tanks ranging from 10 to 20 L, while the effective spray width of the majority of systems was approximately 4–5 m. Standard flat-fan nozzles and centrifugal nozzles were the most commonly used spray devices, accounting for 47% and 21% of applications, respectively. In addition, spray drift was reported to be below 20% in most studies, indicating the potential of UAV-based spraying systems to reduce pesticide losses.

Flight height and flight speed were identified as the most influential operational factors affecting spray quality. The findings indicated that a flight height of 1–2.5 m above the crop canopy and a flight speed of 1–3 m s⁻¹ provided the most favorable conditions for achieving uniform spray distribution, effective canopy penetration, and reduced spray drift. Increasing flight height and speed generally resulted in lower droplet density, reduced spray coverage, and greater drift potential. Furthermore, meteorological conditions, including wind speed, air temperature, and relative humidity, significantly affected spraying performance. Optimal operating conditions were found to include air temperatures below 30°C, wind speeds below 2 m s⁻¹, and relative humidity above 60%.

Despite their numerous advantages, several important challenges were identified. The major limitations included the strong dependence of spraying performance on environmental conditions, restricted tank and battery capacities, the aerodynamic complexity of rotor-induced airflow, insufficient reporting of droplet size and spray drift data, the absence of comprehensive operational guidelines, the concentration of studies on a limited number of crops such as rice and wheat, limited generalizability of existing findings, and inadequate technical knowledge among UAV operators. Moreover, the lack of intelligent and multi-objective optimization models capable of simultaneously improving spray quality, reducing energy consumption, and minimizing environmental impacts was recognized as a major research gap.

Conclusion: This systematic review demonstrated that agricultural UAVspraying have substantial potential to enhance crop protection efficiency, reduce pesticide and water consumption, improve spray uniformity, and mitigate environmental risks. The findings indicate that UAV type, tank capacity, nozzle configuration, flight height and speed, droplet size, and environmental conditions are among the most critical factors determining spraying performance. Rotary-wing UAVs equipped with 10–20 L tanks, operating at an effective spray width of 4–5 m, a flight height of 1–2.5 m above the canopy, and a flight speed of 1–3 m s⁻¹ exhibited the most favorable performance under most conditions.

Nevertheless, the broader adoption and advancement of this technology require the development of standardized operational protocols, intelligent spray control systems, large-scale field evaluations across diverse crops, improved nozzle designs, and enhanced technical training for operators. Implementing these measures will contribute to the more sustainable and efficient utilization of UAV spraying in future agricultural systems.