The impact of canopy geometry on particle dispersion gradients in sparse agricultural canopies

Turbulent dispersion is one of the most important transport mechanisms in the life cycle of many fungal plant pathogens. Without turbulent dispersion both inoculum spread beyond leaves adjacent to infection sites and epidemics would be limited in severity. Thus, understanding the mechanisms that influence and control dispersion gradients from disease foci are of primary importance towards improving our ability to prevent and respond to disease outbreaks. In sparse canopy environments, the influence of canopy geometry (row spacing, canopy height, and plant density) on turbulent fluxes results in highly intermittent transport. This can be problematic for traditional dispersion modeling techniques that rely on assumptions of steady or horizontally homogeneous velocity fields. Here, the link between canopy geometry, turbulent fluxes and particle dispersion gradients in sparse agricultural canopies is explored using a Lagrangian particle dispersion model linked to velocity fields from large-eddy simulations. In particular, particle dispersion from point and line sources in plant canopies with geometry characteristic of grape vineyards are examined. Simulations are performed with varying row spacing, canopy height and particle source height to characterize the length and velocity scales associated with turbulent fluxes and particle dispersion gradients within the canopy.