Sprayer Boom Dynamic Effects on Application Uniformity

Boom acceleration and height effects on spray deposit were determined for distinctly different track conditions,droplet spectra, and sprayer tank loads using an instrumented self-propelled sprayer with a 27 m boom at 12.8 km/h. Trackconfigurations were: smooth, a 20 cm high bump, and a 20 cm high bump and an opposing 20 cm deep dip. Droplet spectraincluded 255 and 588 .m volume median diameters (Dv0.5) as determined by laser diffraction. Sprayer tank loads were eitherhalf capacity or empty. Results indicated three-dimension accelerations ranging from 1.8 to -1.1 g, 14.3 to -6.7 g, and 20.7to -11.0 g and boom end height effects ranging from 2.0 to 1.2 m, 2.6 to 0.5 m, and 3.5 to 0.4 m for smooth, bump, and bumpand dip tracks, respectively. Small droplets of 255 .m (Dv0.5) resulted in a spray coverage range (with maximum coefficientof variation, CV) from 11% to 22% (55%). Small droplets produced Pearson correlation coefficients between coverage andlocalized, instantaneous boom height ranging from -0.40 to -0.58. Large droplets of 588 .m (Dv0.5) resulted in a spraycoverage range (with maximum CV) from 9% to 18% (39%). Large droplet Pearson correlation coefficients between coverageand localized, instantaneous boom height ranged from 0.49 to -0.62. Spray coverage significantly (P < 0.05) correlated withaccelerations in 19% and 11% of acceleration direction-test run combinations for 255 and 588 .m (Dv0.5) droplets,respectively. Similarly, droplet density significantly (P < 0.05) correlated with accelerations in 33% and 26% of combinationsfor 255 and 588 .m (Dv0.5) droplets, respectively. Instantaneous boom heights less than 1.5 m maximized spray coverage andminimized variation in coverage for 255 .m (Dv0.5) droplets. Boom height did not significantly affect spray coverage anddroplet density of the 588 .m (Dv0.5) droplets. Future test standards of field boom testing should consider a lower bump height,especially for high-speed self-propelled sprayers, and take height of the bump and depth of the dip into account to preventboom ends from striking the ground at a nominal boom height, especially for wide booms. Observed correlations suggest thatboom stability is an important element in determining the uniformity of spray application. Lack of complete correlationsuggests that other factors affect droplet transport to the target, other than the spray release trajectory from the boom.Implications are that active sprayer suspensions to stabilize boom movements should improve application uniformity, but fieldambient conditions would likely limit achieving complete uniformity on a day-to-day basis. The study may be useful indetermining future boom test standards, in the design of future sprayers and spray booms, and may assist decisions on sprayersuspensions, operating speeds, boom design length, and use of active boom suspensions.