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

Authors: BAILEY, BRIAN - Utah State University; STOLL, ROB - Utah State University; Mahaffee, Walter - Walt; PARDYJAK, ERIC - Utah State University

Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/29/2010
Publication Date: 8/6/2010
Citation: Bailey, B., Stoll, R., Mahaffee, W.F., Pardyjak, E. 2010. The impact of canopy geometry on particle dispersion gradients in sparse agricultural canopies. Agricultural and Forest Meteorology Conference Proceedings. Available: http://ams.confex.com/ams/19Ag19BLT9Urban/techprogram/MEETING.HTM.

Interpretive Summary: We are building a new Pathogen Transport and Response-tool for Agricultural Canopies (P-TRAC) to predict the spread of a pathogen from internal and external inoculum sources at region to sub-block scales. This system will combine detailed pathogen and host biology models with state-of-the-art, fast response models for the canopy and soil environments and the dispersion of airborne particles. Its main purpose will be to aid in targeting disease, monitoring, and mitigation efforts to areas within vineyards that have the highest probability for deposition and disease development. P-TRAC will also be useful for predicting plant growth phenology, evapotranspiration, and pesticide drift in real time. Particle dispersion data from the past two years indicate that traditional dispersion modeling approaches do not adequately predict dispersion in vineyards, and a new approach is required. We used Large-Eddy Simulation to create state-of-the-art small-scale turbulence models that adjust to local flow conditions dynamically. The models allow for 3D simulation of airflow and particle dispersion and deposition in vineyards. The simulations will provide high-resolution time resolved 3D distributions of momentum, heat, moisture, and spore concentration that will be used to develop a better understanding of the relationship between canopy architecture, weather and disease development. Models indicate that as spores move from one row to the next, the majority are either deflected up and out of the canopy or down under the canopy or to ground with few being deposited in or passing through the canopy. They also indicate that spore dispersion decreases with increasing leaf area and reducing row spacing. Further development and testing of these models will continue.

Technical Abstract: 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.