Design and Field Evaluation of an Air-assistance Unit for Spraying Pesticide on a Vertical Crop Canopy

Aims: Determination of theoretical requirements of an air assistance unit suitable for coconut palm sprayers Study Design: The principles of displacement of air volume and terminal velocity for calculating air volume requirement and flow velocity respectively. Place and Duration of Study: Kelappaji College of Agricultural Engineering and Technology, Kerala Agricultural University, Tavanur Malappuram, Kerala and 3 to 6 months. Methodology: Based on the theoretical calculation of air volume and flow requirements, an Electric Ducted Fan (EDF) was selected for the air-assistance unit. The EDF offers an effective solution to meet the high air velocity requirements while addressing size concerns. Field trials were conducted to optimise the performance parameters of the EDF, including the air velocity at the fan outlet (10, 15 and 17 m‧s-1) and its position relative to the canopy (1, 1.5, and 2 m below the canopy). Results: The airflow from the EDF effectively reached the top of the canopy, overcoming the challenge of delivering spray droplets to elevated heights in a vertical crop canopy. The adoption of EDF as air assistance unit, addresses the size and weight limitations by providing a higher weight-to-thrust ratio. However, droplet deposition and coverage were found to decrease with increasing spray distance. Operating the sprayer too close to the canopy cause the droplet coalescence, leading to the formation of larger droplets that dripped onto the ground. Over-spraying was more likely when the EDF was positioned too close to the canopy (1 m) at high speed (17 m‧s⁻¹), whereas under-spraying occurred when the EDF was placed too far away (2 m). Further studies are recommended to provide a more comprehensive understanding of airflow velocity trajectories within the canopy when spraying in vertical direction against gravity. Conclusion: Optimal spray deposition and coverage were achieved when the EDF operated at an airflow velocity of 17 m‧s⁻¹ and was positioned 1.5 m below the crop canopy.