Droplet deposition density of organic liquid fertilizer at low altitude UAV aerial spraying in rice cultivation

•Droplet deposition density increase with the increment of UAV aerial spraying rates.•Droplet deposition density decrease as the UAV flying speeds increase.•The smaller of the CV values the better the uniformity of the droplet deposition.•Accurate and less drift were observed at low flying speeds and high spraying rates. Currently, unmanned aerial vehicles (UAVs) are widely used to ease agricultural activities and has been progressed with recent technology development to perform aerial spraying in the rice cultivation. In fact, UAV aerial spraying ability is not just limited to crop protection but it can be extended for crop fertilization activities. However, off-target and insufficient amount of droplet deposition density during the spraying operation has always been a major concern in research area for UAV aerial spraying. The study aimed to evaluate the optimal operating parameters such as UAV flying speeds, and spraying rate on the droplet deposition density of the targeted surface for a standard UAV spraying system available in the market. Field trials were performed by using UAV that flew at the different flying speeds (2, 4 & 6 m/s), at the constant height of 2 m above the rice canopy to spray the organic liquid fertilizer at the different spraying rate (0.75, 1.5, 2.25 & 3.00 L/min). The water-sensitive paper was used as a sampler to collect droplets and droplet deposition density was statistically analysed. The experimental results showed that the droplet uniformity and droplet deposition density was higher when the UAV flying speed was maintained at the lower speed (2 m/s) compared to the higher flying speed (4 and 6 m/s). Hence, the droplet uniformity and droplet deposition density show the highest count with better droplet pattern when spraying the organic liquid fertilizer at 3.00 L/min spray-rate compared to other sprayer rates. Results from the study could provide technical support for UAV aerial spraying within the rice cultivation field.