Particle Transport and Plume Shape Characteristics in a Trellised Agricultural Canopy During Non-row-parallel Winds

Although particle dispersion in canopies, including agricultural ones, has received considerable research interest in recent years, dispersion patterns near the source location have often been neglected. Plume concentrations are typically the highest very near their source and are therefore likely have a greater influence on the local ecosystem than at locations where the concentrations are significantly diminished. Agricultural systems are exposed to and influenced by particles of many types including fungal spores, water droplets, pesticide sprays, and pollen. Understanding the near-source transport of particles of these sizes is of great importance. To that end, a series of field campaigns were conducted in a commercial vineyard near Monmouth, Oregon. These included the emitting and tracking of plumes of inert fluorescent microspheres (10 to 45 μm diameter) in the canopy. During the 2013 campaign specifically, data from 63 independent plumes were collected during 23 release event periods over 14 days. The release events were conducted under a variety of wind conditions ranging from vine-row-parallel to row-perpendicular. The typical characteristics of plume shape during periods with winds roughly aligned with the vine rows was previously studied from events conducted during the 2011 campaign. Investigation of the plumes collected during periods with non-row-parallel winds has proven that these plumes are of higher complexity and shown that simple uni-directional curve fitting techniques are likely insufficient for characterizing the plume shape beyond the first few meters from the source. Rigorous study of the momentum, flux, and turbulence fields within the vineyard demonstrated significant differences in the behavior of the row-aligned and row-orthogonal components of the flow and elucidated the variation of those behaviors with changes in the above canopy wind direction. That research gave insight into the causes of the increased complexity of the plumes collected during periods with winds that were not aligned with the vine rows. Analysis of the data for those plumes has revealed many interesting results in how the microsphere plumes behaved in the canopy. This includes plume shape statistics in the vine rows nearest to the source as well as the rates of decay of the plume both along the rows as well as across rows.