Towards a model of spray–canopy interactions: Interception, shatter, bounce and retention of droplets on horizontal leaves

• Published in: Ecological modelling Vol. 290; pp. 94 - 101
• Main Authors: Dorr, Gary J., Kempthorne, Daryl M., Mayo, Lisa C., Forster, W. Alison, Zabkiewicz, Jerzy A., McCue, Scott W., Belward, John A., Turner, Ian W., Hanan, Jim
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01-10-2014; Elsevier
• Subjects: Agrichemical spray; Animal, plant and microbial ecology; Biological and medical sciences; Chenopodium; Cotton; Droplet impaction; Droplets; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; Horizontal; Interception; Leaf surface model; Mathematical model; Mathematical models; Methods and techniques (sampling, tagging, trapping, modelling...); Pesticide application; Spray retention; Sprayers; Sprays; Surface properties; Triticum aestivum; Spray retention; Droplet impaction; Leaf surface model; Pesticide application; Mathematical model; Agrichemical spray; Agricultural chemical product; Interaction; Pesticides; Plant leaf; Droplet; Retention; Leaf area; Interception; Canopy(vegetation)
• ISSN: 0304-3800; 1872-7026
• DOI: 10.1016/j.ecolmodel.2013.11.002

•Leaf surface models have been developed for chenopodium, wheat and cotton leaves.•Spray droplet trajectories and interception by virtual leaves are modelled.•If a droplet is intercepted a model is used that determines if it shatters or not.•If drop does not shatter another model is used to determine if it adheres or bounces.•Spray retention was predicted on single horizontal leaves for three spray mixtures.
Pesticides used in agricultural systems must be applied in economically viable and environmentally sensitive ways, and this often requires expensive field trials on spray deposition and retention by plant foliage. Computational models to describe whether a spray droplet sticks (adheres), bounces or shatters on impact, and if any rebounding parent or shatter daughter droplets are recaptured, would provide an estimate of spray retention and thereby act as a useful guide prior to any field trials.
Parameter-driven interactive software has been implemented to enable the end-user to study and visualise droplet interception and impaction on a single, horizontal leaf. Living chenopodium, wheat and cotton leaves have been scanned to capture the surface topography and realistic virtual leaf surface models have been generated. Individual leaf models have then been subjected to virtual spray droplets and predictions made of droplet interception with the virtual plant leaf. Thereafter, the impaction behaviour of the droplets and the subsequent behaviour of any daughter droplets, up until re-capture, are simulated to give the predicted total spray retention by the leaf. A series of critical thresholds for the stick, bounce, and shatter elements in the impaction process have been developed for different combinations of formulation, droplet size and velocity, and leaf surface characteristics to provide this output.
The results show that droplet properties, spray formulations and leaf surface characteristics all influence the predicted amount of spray retained on a horizontal leaf surface. Overall the predicted spray retention increases as formulation surface tension, static contact angle, droplet size and velocity decreases. Predicted retention on cotton is much higher than on chenopodium. The average predicted retention on a single horizontal leaf across all droplet size, velocity and formulations scenarios tested, is 18, 30 and 85% for chenopodium, wheat and cotton, respectively.