Contact: Dr. Clint Hoffmann, Agricultural Engineer, USDA-ARS, 2771 F&B Road, College Station, TX 77845 email: choffmann@tamu.edu

Abstract. Researchers use a variety of techniques for measuring spray droplet deposition and movement.  Techniques range from passive samplers such as water sensitive paper or mylar cards to active samplers such as rotary rods and high-volume air samplers.  In most field studies, researchers use one or two different types of samplers but rarely more than three.  In this collaborative study, three types of horizontal collectors were placed in the field at the same time.  The objective was to investigate correlations in deposition and drift data that these different sampling devices collected.  Five sets of ASAE reference nozzles from ASAE Standard S572 AUG99, which produce droplets from Very Fine to Extremely Course, were fitted to a Cessna Ag Husky. 

At 0-25 m (0 – 82 ft) from the downwind edge of the spray swath, there were highly significant correlations between the three samplers for the two nozzles that produced the largest droplet spectra.  As the droplet spectra became smaller, a greater portion of the spray volume was subject to entrainment in the air and resulted in inconsistent and mostly non-significant correlations between the samplers for the three sets of nozzles that generated the smaller droplet spectra.   There was a highly significant correlation for the water-sensitive paper and mylar card samplers that were placed under the aircraft (i.e., in-swath).  The droplet spectra data from the water-sensitive paper samplers placed in-swath separated out along the droplet classification lines in ASAE Standard S572.  The monofilament line samplers at 50 m (164 ft) showed that nozzles that produced smaller droplet spectra generate more airborne spray material downwind than nozzles with larger droplet spectra. 

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