Heavy particle transport in a trellised agricultural canopy during non-row-aligned winds

Authors: MILLER, NATHAN - University Of Utah; STOLL, ROB - University Of Utah; Mahaffee, Walter - Walt; Neill, Tara

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2018
Publication Date: 3/20/2018
Citation: Miller, N., Stoll, R., Mahaffee, W.F., Neill, T.M. 2018. Heavy particle transport in a trellised agricultural canopy during non-row-aligned winds. Agricultural and Forest Meteorology. 256-257:125-136. https://doi.org/10.1016/j.agrformet.2018.02.032.
DOI: https://doi.org/10.1016/j.agrformet.2018.02.032

Interpretive Summary: The influence of grapevine row orientation on pathogen dispersion was examined using fluorescent microspheres as surrogate fungal spores. A novel analysis approach was developed that allowed for a more accurate characterization of the influence canopy architecture on particle dispersion. The spacing between rows caused the air to follow row orientation below row height which caused particles to be transported two times further than expected when wind directions was perpendicular to row orientation. This turning of the air also increased particle plum height indicating that the potential dispersion longer distances is increased when wind direction differs more than 20 degrees from row orientation. These results will aid in the development of models that more accurately predict the spatial and temporal risk of disease development while including the influence of canopy architecture and terrain.

Technical Abstract: Agricultural systems are exposed to and influenced by particles of many types (e.g., pathogens, pollen, pests), the concentrations of which are typically highest in the regions immediately surrounding their sources. The intermittent nature of trellised canopies creates an unique canopy architecture that directly affects the shape of particulate plumes and tends to alter their transport patterns in the near-source region. To investigate the behavior of particle plumes near their sources in a trellised canopy, a set of particle release experiments was conducted during a field campaign in an Oregon vineyard in 2013. Specifically, plumes of inert fluorescent microspheres (10 to 45 um diameter) were released into the canopy during periods when the mean wind direction was significantly different from the vine-row direction. Plume concentrations were collected at over 100 separate locations in a three-dimensional space < 10 canopy heights downwind of the source during each release period. These plumes were more complex than those released during periods of row-aligned winds. A novel analysis approach using the superposition of two orthogonal Gaussian plume equations was developed to quantitatively assess the plumes’ shape behavior. Basic plume shape parameters, as determined by integrating the superposed Gaussian equation, varied significantly as a function of the mean wind direction. As the wind direction changed from roughly row diagonal to directly row-normal, the rate at which the spanwise plume width increased with downwind distance increased by a factor of two. Similarly, the rate at which the plume height increased with downwind distance was higher for row-perpendicular plumes than for row-diagonal plumes. Row-diagonal plumes exhibited a much higher spanwise skewness than did the row-normal plumes, but for all plumes the skewnesses tended towards zero (symmetric) with increasing downwind distance.