A multi-rotor UAV-based oscillating-tube broadcasting device incorporating replaceable material-specific screw metering units was developed for low-rate seed and granular-fertilizer application. The key structural parameters of the oscillating tube were screened through theoretical analysis and single-factor experiments using pre-germinated conventional Huanghuazhan rice. An L16(4³) orthogonal experiment was then conducted solely for exploratory screening of the main effects of flight height, forward speed, and broadcasting material on the single-pass broadcasting-uniformity coefficient of variation (${\mathrm{C}\mathrm{V}}_{\mathrm{b}}$) and effective spreading width (We). Forward speed significantly affected ${\mathrm{C}\mathrm{V}}_{\mathrm{b}}$, whereas all three factors significantly affected We, with flight height showing the strongest effect. Separate two-factor central composite design experiments were subsequently conducted for conventional Huanghuazhan rice, hybrid Yongyou 12 rice, Yangguang 131 rapeseed, and Stanley compound fertilizer. Material-specific quadratic models were established, yielding model-recommended flight height and forward speed combinations of 3.04 m and 2.35 m s⁻¹, 2.79 m and 1.70 m s⁻¹, 3.00 m and 1.80 m s⁻¹, and 3.20 m and 2.25 m s⁻¹, respectively. These combinations represent constrained model-based recommendations rather than global or independently verified optima. In a limited consecutive-pass field demonstration, the field-sample coefficient of variation (${\mathrm{C}\mathrm{V}}_{\mathrm{f}}$) ranged from 13.76% to 20.34%, and the mean absolute pointwise deviation from the target count ranged from 15.11% to 19.05%. The results demonstrate the preliminary mechanical and operational feasibility of the prototype under the tested materials, operating settings, site, and environmental conditions.