Abstract
Drone based agrochemical application has gained rapid momentum in Indian agriculture, yet spray drift continues to pose a major operational and environmental challenge. This study quantified wind drift from agricultural drone spraying under varying wind speeds, spray fluid concentrations, and drone flying heights over two consecutive years (2023–24 and 2024–25) at the Agro Climate Research Centre, Tamil Nadu Agricultural University, Coimbatore. In 2023–24, nine treatment combinations involving three wind speeds (6, 9, and 12 kmph) and three spray fluid concentrations (30, 60, and 90 per cent) were evaluated using a fixed drone height of 2.0 m. In 2024–25, the experiment was expanded to include four drone heights (1.2, 1.5, 1.8, and 2.1 m), resulting in 36 treatment combinations. Spray drift was measured using water sensitive papers placed at regular intervals downwind of the spray line. Across both years, drift increased consistently with increasing wind speed, spray volume, and drone height. The lowest drift occurred at 6 kmph wind speed, 30 per cent spray fluid, and 1.2 m drone height, where drift was confined to 3–6 m. In contrast, the highest drift was recorded at 12 kmph wind speed, 70–90 per cent spray fluid, and 2.1 m height, extending up to 18.5 m. Strong interaction effects indicated that the levels of the others amplified the influence of any single factor. The study highlights the need for careful operational planning to minimize off target deposition and ensure safe, efficient drone spraying. The findings provide evidence based thresholds for drone height, spray volume, and allowable wind speed, supporting the development of practical guidelines for drift minimized drone application in field conditions.