Herein, we experimentally study the role of boom height in the downwind deposition of agricultural sprays using a boom-scale, low speed, recirculating wind tunnel. A section of a John Deere spray boom fitted with 4 nozzles was mounted at 0.5 m and 1 m heights in the tunnel. Water was sprayed with both fine and extra coarse nozzles, and a drift reduction adjuvant (DRA) was tested with the fine nozzle. The spray solution contained a fluorescent tracer, disodium fluorescein, and both passive and active samplers were used to capture droplets downwind of the boom. These samples were then analyzed to quantify the mass flux of drifting droplets. Passive sampling was performed with mylar cards placed along the length of the wind tunnel as well as a series of monofilament lines. Further downwind, a rotational impactor was used to actively sample entrained droplets. The results of these measurements indicate that maintaining boom height is important for reducing downwind spray drift, as halving the boom height in this study resulted in an average 68.6% reduction in downwind spray flux. However, appropriate nozzle selection had a comparable or larger impact on drift; switching from a fine to extra coarse nozzle resulted in an 84.9% average reduction in spray flux 2 m and farther downwind of the spray boom, while dropping the boom height resulted in a 69.8% average reduction in the same region. The combination of a DRA alongside reduced boom height produced a 79.6% reduction in spray flux across all samplers.
