Application of drones in pesticide spraying: A review

Introduction

Pest management is a crucial factor in crop health and productivity, and agricultural chemicals such as fertilizers and pesticides are often required for specific conditions. Pesticides are widely used in most sectors of the agricultural production to prevent or reduce losses by pests and thus can improve yield as well as quality of the produce (Oerke et al., 2004; Cooper et al., 2007). Population growth and climate change contribute mainly to the increasing use of pesticides (Tirado et al., 2010; Hailu et al., 2016; Miraglia et al., 2009) and a higher global pesticide production is estimated in the future. In 2020, the worldwide agricultural sector maintained a stable level of pesticide usage, totaling 2.7 MT of active chemicals. This general trend, however, masks divergent patterns seen across countries (FAO. 2022a, b & c). Notably, India experienced a notable increase in pesticide application, reflecting the growing demands of its expanding agricultural industry. With a strong reliance on pesticides for pest management and crop protection, Indian farmers contributed to the rising consumption of these chemicals within the country. Moreover, the global pesticide trade also witnessed a significant boost, with a remarkable 30% surge in the overall volume of pesticides traded during the same year. This increase in trade activity underscores the escalating global demand for pesticides, as agriculture sectors worldwide seek effective solutions for sustainable and efficient farming practices (WTO, 2020). Although pesticides play a significant role in improving crop yields and the production of affordable and good quality food, the increasing use of pesticides also brings a number of negative effects to the environment and human health (Miraglia et al., 2009). Moreover, pesticide contamination moves away from the target plants, resulting in environmental pollution. Pesticides move in several ways, including to the air, through wind currents, to water, through runoff or leaching, and to plants, animals, and humans (Singh et al., 2012; Fang et al., 2017) However, prolonged exposure to these chemicals can cause health complications, and conventional methods of chemical application can be inefficient for small plot production systems. Scientists and researchers are working towards making the chemical application process more efficient to prevent diseases and pests effectively on a large scale (Zhu et al., 2010). Concurrent with the evolving UAV technology are the demands for correct and safe application of pesticides under challenged environmental and biological conditions (Li et al., 2019). The modernization of agriculture is imperative for increasing production and food supply (Rahman et al., 2021) [6] . Adoption of modern technologies such as unmanned aerial vehicles (UAVs) or drones can significantly enhance risk and damage assessments and revolutionize the way we prepare for and respond to disasters that affect vulnerable farmers and the country's food security (FAO, 2018) A drone is an unmanned aircraft or more formally known as unmanned aerial vehicles (UAVs). Drones are increasingly being used for pesticide spraying in agriculture, offering several advantages over traditional ground-based methods (Rolle et al., 2020; FAO, 2018). Essentially, a drone is a flying robot that can be remotely controlled or fly autonomously through software-controlled flight plans in their embedded systems, working in conjunction with onboard sensors and GPS. In recent years, drones have gained significant attention due to their ability to perform a wide range of tasks, including aerial photography, delivery, inspection, and surveying. One such application is in pesticide spraying (Wang et al., 2022), where drones have been found to be more efficient and effective than traditional methods. Drones are able to cover large areas of farmland quickly and accurately, while minimizing the risks associated with human exposure to pesticides. Furthermore, the use of drones in pesticide spraying has been found to reduce the amount of pesticide needed, resulting in cost savings and decreased environmental impact. Drones can spray chemicals like fertilizers and pesticides based on the spatial variability of crops and fields, and the amount of chemicals can be adjusted depending on the crop conditions or the severity of the pest attack. Heavy lift UAVs are required for large-scale spraying, providing accurate, site-specific application for crop fields (Gopal Dutta and Purba Goswami, 2020). By detecting pest hotspots and enabling variable rate application of pesticides, drones can potentially reduce the amount of pesticide lost to drift and minimize its impact on neighbouring ecosystems and human health.

Methodology

A number of reviewers discuss the application of drones in agriculture, focusing on various applications such as crop monitoring, livestock monitoring, spraying, and seeding (Colwell. 1956; Cisternas et al., 2020; Wang et al., 2016; patel et al., 2013; swain, 2010; Xue, 2020). In this review, we use rigorous bibliometric techniques and quantitative methodology to assess the present status of research at the nexus between drones and pest management. We argue that the current study makes several contributions to the existing literature by examining an emerging drone technology that is highly needed in agriculture as it provides tremendous potential to alter several aspects of this sector. Considering the transformational potential of the technology, we posit that an in-depth network analysis yields novel insights by determining influential works and revealing themes concerning drones' potential for pesticide spraying. We performed a comprehensive search of journal articles to cover the entire research domain of drone applications in pesticide spraying. The first step was data collection, we selected several search engines such as Science Direct, Willey, MDPI and PubMed these are the most comprehensive and trustworthy databases with standardized results. We searched the related work publications (research papers) for 22 years (2000-2023) by applying several keywords and the meta-data of publications related to drone applications in pesticide spraying was retrieved. Further, we analysed the selected articles, by removing off-topic articles from the analysis and identified the most important key words used in the research area. We applied keyword like "Unmanned aerial vehicle", "UAV", "UAS", "Unmanned aircraft system" or "Drone" and "Pesticide" or "Pest Management" and "UAV sprayer" or "UAV Variable precession sprayer" or "Drone pesticide sprayer" or "Drone pesticide deposition". To start, we analysed the developments in publication output in the current literature on drones in pesticide spraying. The temporal distribution of scholarly research is shown in Fig. 1. We see a rapid increase in publications from 2019 onward. We refer to the period between 2018 and 2019 as the build-up stage, which had roughly twenty papers published annually. The post-2019 period has been called the growth stage since research on drone applications in pest spraying witnessed an exponential surge during this period. After 2019, the increasing number of publications confirms the growing interest among researchers, which also reflects that drones have been applied in precision agriculture ( ). Multi-rotor and single-rotor (helicopter) drones do not require specific structures for take-off and landing. Moreover, they can hover and perform agile maneuvering, making them suitable for pesticide applications (Wang et al., 2021) [12] , where precise maneuvering or the ability to maintain a visual of a target for an extended period of time is required (Shuping et al., 2023) [8] . Especially multirotor drones tend to be easy to use [13] ; Spoorthi, 2019 [9] cross (X) model

Hexacopter

The hexacopter featuring a central body frame with six horizontally rotating blades. This configuration provides increased stability, payload capacity, and redundancy compared to quadcopters. The hexacopter is capable of vertical take-off and landing, precise maneuverability in various directions, and the ability to hover at specific locations.

Wang et al., 2021 [12] ; Wang et al., 2022; Biglia et al., 2022 [1] ; Yallappa et al., 2017; Primicerio et al., 2017;

Octacopter

The octacopter distinguished by a central body frame supplemented by eight horizontally rotating blades. This distinctive configuration imparts exceptional stability, augmented payload capacity, and heightened redundancy, surpassing the capabilities of both quadcopters and hexacopters. With its vertical take-off and landing proficiency, precise maneuverability across various axes, and the capacity to maintain a stable hover, the octacopter epitomizes versatility and reliability.

Wang et al., 2021 [12] ; The pesticide application using drones offers a new hightech tool for crop protection (Giles, 2016; Li et al., 2021) [5] . Drone sprayers featured with autonomous flight control to deliver pesticides to an array of crops is now a common substitute for traditional apsack application. The drone pesticide spraying has become increasingly popular due to their higher work efficiency, lower operator exposure, and improved ability to apply chemicals in a timely and highly spatially resolved manner (Wang et al., 2018). The process typically involves several steps as shown in Fig. 3 Working of drone in pesticide spraying application

Fig 3: Flow chart of working of drone in pesticide application

The first step is mapping the area to be sprayed. This is done using GPS, and software generates a flight path based on the field's size and shape. The drone is programmed to fly autonomously, covering the entire field in a predetermined pattern. This ensures that the entire field is covered evenly, and no areas are missed (Faical et al., 2014; Wang et al., 2020) [13] . Once the field is mapped, the sprayer is calibrated to ensure that the correct amount of chemical is applied per unit area. Calibration involves adjusting the spray volume and flow rate to ensure that the desired coverage and droplet size are achieved. Over or under-application can lead to crop damage or reduced efficacy of the chemicals (Guanter et al., 2019; Ali et al., 2019). The drone is then loaded with the chemical to be sprayed. The amount of chemical loaded onto the drone depends on the size of the field to be sprayed and the desired coverage. The chemicals can be stored in tanks on the drone itself or in a separate ground station, which is connected to the drone through hoses (Zhan et al., 2019). Once the drone is loaded and calibrated, it takes off and flies over the field, spraying the chemical in a controlled manner. The drone follows the predetermined flight path, which is set up to ensure that the entire field is covered evenly (Shuping et al., 2023) [8] . The drone's speed, altitude, and spraying rate are all predetermined and can be adjusted by the operator if necessary. During the flight, the drone's sensors and cameras monitor the spraying process to ensure that the correct amount of chemical is being applied and that the spray is evenly distributed. The drone's sensors can detect changes in wind speed and direction, as well as changes in terrain, and can adjust the spraying accordingly to ensure that the chemicals are applied accurately (Ali et al., 2019). Once the spraying is complete, the drone lands and the operator can inspect the results. The operator can review data collected by the drone's sensors and cameras to evaluate the effectiveness of the spraying and make any necessary adjustments for future flights. The flowchart of pesticide spraying is given in Fig. 4. ). In addition to the basic drone components, the spraying system is a crucial part of pesticide application. It comprises the pump and its controlling system, tank and nozzle. The pump is responsible for delivering the pesticide or fertilizer from the tank to the nozzle, while the controlling system ensures precise control and regulation of the spraying process (Rahman et al., 2021) [6] . To design a drone specifically for pesticide application, several factors need to be considered. The first step is to estimate the payload, which determines the weight and capacity requirements of the drone. Based on this estimation, appropriate components are selected. The selection of batteries depends on the current and voltage requirements of the drone's modules. Finally, the drone frame is designed, taking into account the number of arms and the payload it needs to carry (Hafeez et al., 2021).

When it comes to spraying pesticides or fertilizers, a sprayer is connected to the tank of the UAV. The substance to be sprayed is dispensed through a nozzle, which is controlled by the flight controller. The sprayer incorporates a pumpdriven spray motor that generates the necessary pressure to effectively distribute the fluid (Rahman et al., 2021) [6] . These components and systems work in conjunction to ensure accurate and efficient pesticide application from the drone, allowing for targeted and controlled distribution of pesticides or fertilizers on agricultural fields. The algorithm for spraying is given in Fig. 5. The summary of various research work on pesticide application using drone is given in Table . 2.

Conclusions

In conclusion, the use of drones for pesticide application offers significant advantages for modern agriculture. By providing more precise and targeted spraying, drones help reduce pesticide usage, minimize environmental impact, and improve overall efficiency. This technology allows farmers to address pest issues with greater accuracy, ensuring that only the necessary areas are treated, which also reduces the risk of chemical runoff and exposure. Additionally, drones can lead to cost savings and improve safety by reducing direct contact with pesticides. While there are still challenges, such as regulatory concerns and the need for proper training, the continued development of drone technology holds great potential to enhance the sustainability and productivity of farming practices, making them more efficient and environmentally friendly in the long term.

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