Distribution of dye deposits from a small-plot track sprayer on biological and artificial targets

Abstract

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 m 2 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 ≈ 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 by 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.