The nozzle is a crucial component in unmanned aerial vehicle (UAV) sprayers. The centrifugal nozzle offers unique advantages; however, there is a scarcity of published research regarding the structural parameters, spraying parameters, and practical applications specifically for UAV spraying. Furthermore, there is a need for UAV-specific nozzles that demonstrate high efficiency and excellent atomization performance. In this present study, a multi-disc centrifugal nozzle (MCN) capable of controlling droplet size was designed and optimized. The droplet size spectra with different atomizing discs were tested, and indoor and field tests were conducted to investigate the atomization and spray deposition characteristics of the MCN. It was found that the MCN with six atomizing discs with a curved groove, a disc angle of 120°, and a disc diameter of 77 mm demonstrated better atomizing performance. The volume median diameter was 96–153 μm, and the relative span was 1.0–1.3. Compared with the conventional hydraulic nozzle, this nozzle increased the effective spray swath width from 2.5–3.0 m to 4.0–5.0 m and promoted the average deposition rate by 132.4% at a flying height of 1.0 m and a flying speed of 3.0 m/s, which tends to raise the operation efficiency by four to five times. This study can provide a reference for the design and optimization of centrifugal nozzles for a UAV sprayer and the selection of operating parameters in aerial spraying operations.

Maize, as a critical crop for China’s food security, is constantly challenged by weed infestations and environmental risks associated with herbicide overuse. Improving herbicide utilization efficiency through equipment optimization and intelligent control during spraying has become an essential strategy for weed management in Chinese maize fields. However, most current sprayers fail to achieve coordinated control of spray volume and nozzle parameters, and their performance is typically evaluated using single indices, such as the coefficient of variation (CV) for spray uniformity and deposition density. In this study, a split-split-plot experiment was conducted in 2022–2023 to assess the feasibility of herbicide reduction using intelligent variable-rate boom sprayers in summer maize fields on the North China Plain (NCP). The key variables included spray volume (225 vs. 180 L/ha), nozzle type (AI11003VS/LECHLER11003 in 2022; TTI11004/LECHLER11004 in 2023), and herbicide dose (recommended, −15%, and −30% reduction). Results showed that the coefficients of variation for droplet coverage and density remained below 12% for all treatments (n = 4), indicating stable spray performance. A higher spray volume (225 L/ha) significantly improved deposition uniformity (p < 0.01). In 2022, herbicide input could be reduced by 15–30% while maintaining efficacy above 90% when applied at the 3–4 leaf stage of dominant weeds. However, in 2023, efficacy dropped to 72.67% when the herbicide was applied at a 30% reduced dose with 180 L/ha and when dominant weeds had reached the 5–6 leaf stage or higher, indicating an agronomic risk. Reduced herbicide input decreased maize injury by 47–53%. Only the 30% reduced-dose treatment significantly increased maize yield by 3.05% in 2022 and 2.62% in 2023 compared to the control (both p < 0.05). Spray volume significantly influenced droplet deposition and weed control efficacy; thus, caution is warranted regarding herbicide reduction for later weed growth stages. This study demonstrates that real-time variable-rate boom sprayers, optimized for spray volume and nozzle type, can reduce herbicide use without compromising weed control efficacy or maize yield, providing both theoretical support and practical guidance for sustainable herbicide management in summer maize fields on the NCP.

The unmanned aerial spraying system (UASS) has emerged as an advanced tool in precision agriculture for applying plant protection products (PPP). The addition of tank-mix adjuvants to PPP solutions is a common practice to enhance aerial spray performance. However, the effects of these adjuvants on spray performance under the downwash airflow fields generated by UASS rotors remain unclear. This study aimed to evaluate the impacts of adjuvant addition (AGE852B, AGE825, AGE809, and CCL846) on droplet size spectrum and spray deposition distribution with various rotor speeds and layouts, using an indoor simulated single-rotor/multi-rotor UASS spraying platform. The results showed that adding AGE809 and AGE825 made the droplet size and distribution much better in the flat fan nozzle LU110-015 under the downwash airflow field. The spray volume fractions made with droplets smaller than 100 µm (V₁₀₀) went down by 48.15% and 21.04%, respectively. Furthermore, rotor speed was found to have a significant impact on volume median diameter, relative span, and V₁₀₀ (p < 0.05). The downwash airflow field was observed to increase the vertical droplet velocity, achieving a more uniform spray distribution in the central airflow area. These results show that choosing the right adjuvants and making the most of the operational parameters can improve spray deposition, coverage uniformity, and drift reduction. This gives us useful information for making PPP applications more efficient and effective in precision agriculture.