Formation and Characteristics of Secondary Droplets from Agricultural Spray Impingement

During crop protection spray application, droplets inevitably impact crop or weed leaf surfaces. After impact, these droplets may spread, bounce, or splash, and bouncing and splashing can reduce overall spray coverage and the retained foliar dosage, thereby diminishing efficacy. Previous studies have mainly identified the threshold conditions that separate these impact regimes, but systematic measurements of the size and behavior of the resulting secondary droplets, particularly on real crop leaves with agronomically relevant droplet diameters and impact velocities, are still lacking. To address this gap, this study employs Digital Inline Holography (DIH) combined with a machine learning based processing method to analyze secondary droplet generation resulting from agricultural spray impingement on real soybean leaves, quantifying their size, number, and velocity distributions. The impingement dynamics were further investigated through a series of well-controlled single droplet impact experiments on various plant surfaces. Collectively, these results deepen the mechanistic understanding of impingement and splashing and provide guidance for optimizing spray systems and application parameters across agricultural use cases.