An experimental study of momentum and heavy particle transport in a trellised agricultural canopy

• Near source particle dispersion in a sparse agricultural canopy was quantified.
• 3D canopy particle dispersion was measured using a high-density impaction trap array.
• The particle plume shape was strongly impacted by canopy element flow channeling.
• Spanwise concentration profiles were skewed towards the above canopy wind direction.

Turbulent particle dispersion in plant canopies plays an important role in many agricultural and forestry ecosystems. Most research on dispersion in plant canopies has focused on dispersal patterns in homogeneous dense canopies and/or on patterns far from the source. To study near-source particle dispersion in a sparse agricultural canopy, a series of point-source particle release events was conducted in a commercial vineyard. Analysis of the wind velocity data indicated that the majority of the flow in the open spaces between the vine rows was channeled parallel to the vine rows regardless of the direction of the mean wind above the canopy. Although this channeling led to significant turning of the mean velocity, profiles of turbulent statistics taken at times when the above-canopy winds were nearly parallel to the vine rows showed similar behavior to canopy flow profiles in previous studies. The particle release events were conducted using fluorescent microspheres with similar physical characteristics to the spores of multiple airborne fungal pathogens of grapes (diameter = 10–45 μm, density = 1.0 g/cm3). Microspheres were released from two vertical positions within the canopy and monitored using a dense three dimensional impaction trap array in the near-source region (1–5 canopy heights downwind). The shape of the microsphere plumes was strongly impacted by the flow channeling within the canopy. Specifically, the plumes’ maximum concentrations were typically channelled down the aisle in which they originated. The spanwise concentration profile also tended to be skewed from the release aisle toward the mean wind direction above the canopy. This was believed to be caused by the wind directional shear created by the difference between the mean wind direction above the canopy and the vine row direction as well as the filtering effects of the plants themselves.