DISTRIBUTION OF DYE DEPOSITS FROM A SMALL-PLOT TRACK SPRAYER ON BIOLOGICAL AND ARTIFICIAL TARGETS

The design and operation of a portable track sprayer for small-plot deposition evaluations are described. Boom movement was regulated through an electrostatic clutch that provided rapid acceleration then constant speed. The drive mechanism together with a fixed boom path provided consistent deposits over a defined 6.4 m2 sampling area. When nozzles were orientated downward and operated at selected pressures or heights, volumes of deposits on wheat heads were 37-45% of those on paper strips. Total variability in deposits was higher on wheat heads [coefficient of variation (CV) 36.4-39.3] than on paper strips (CV 11.3-13.8). Heterogeneity indices, derived from variance components, identified important sources of variation. Random variation and across-boom variation were almost-equal-to 15-20% higher on wheat heads than on paper strips. Volumes of deposits on both target surfaces fluctuated in a cyclic pattern between (d(b)) and below d(n)) nozzles. Fluctuations were more pronounced on wheat heads (d(b)/d(n) = 1.5-1.9) than on paper strips (d(b)/d(n) = 1.1-1.2) when nozzles were orientated downward. When nozzles were orientated forward rather than downward, volume and uniformity of deposits on paper strips declined 3% and 9%, respectively. In contrast, volumes of deposits on wheat heads increased by 51-57%, CV values declined by 9-23% and across-boom variation declined by 17-28%. Fluctuations in deposits were reduced markedly (d(b)/d(n) = 0.9-1.1). Deposits were most uniform at 200 kPa and 0.40 m spray path. These conditions also would reduce potential drift. Findings indicated that droplet trajectories were the most important factor influencing deposits on wheat heads, especially those positioned directly below nozzles.