Building canopy retention into AGDISP: Preliminary models and results

AGDISP (a spray application simulation model with a primary focus on aerial applications) uses canopy structure and collection efficiency to model canopy interception but assumes droplets that intercept a leaf surface are retained at that point. This is not the case for many plant species, particularly moderate through to very difficult to wet species, where canopy deposition would currently be overestimated. This paper summarizes the initial implementation of process-based models for spray droplet bounce and shatter within an experimental build of AGDISP in order to predict spray retention within plant canopies. Spray simulations were run for formulations ranging in surface tension, applied to three species (wheat, canola and capsicum) with different wettabilities and leaf orientations, and using the AGDISP ground model with and without the retention model, to evaluate the impact the retention model has on canopy deposition within AGDISP. The 7odel outputs were also compared to previously determined tracksprayer results. The current AGDISP canopy deposition (interception) model was unable to fully account for differences in retention due to the spray formulation used or species studied. The incorporation of the process-driven models for bounce and shatter has allowed these differences to be predicted, with excellent agreement in relation to experimentally determined retention. There is considerable work still required to make this approach practical. However this paper illustrates that the difference between interception and retention is an important distinction for many crops (and weeds) and that the approach outlined is an effective adjunct to the current AGDISP interception model.