Spray deposition and distribution on the targets and losses to the ground as affected by application volume rate, airflow rate and target position

Greenhouse crop production in China has in the recent years expanded widely. To minimize compromised pesticide use and adverse environmental impact in these structures, it is essential to optimize the working parameters and settings of sprayers. Experiments using an air assisted greenhouse sprayer and artificial plants with attached fruits were conducted to investigate the effects of volume rate, target location, and airflow rate on spray deposition and distribution uniformity on leaves, fruits and losses to the ground. Three spray volume rates (530, 368 and 220 l ha⁻¹) and three nozzle's outlet volumetric airflow rates (374.4, 289.4 and 234.7 m³ h⁻¹) were evaluated. Ground speeds were set at 0.36 and 0.31 m s⁻¹ for volume rate and airflow rate trials, respectively. Artificial targets (filter-paper collectors) were attached on either sides of leaves, fruits and the ground to collect deposits of a food colourant used as a tracer (Spray solution). Deposition was quantified through UV-VIS spectroscopy at a wavelength of 508 nm. Results indicated that volume rate significantly influenced deposition and distribution uniformity. Reducing the volume rate reduced deposition but improved distribution homogeneity. Quantified absolute deposits on upper leaf surfaces declined by 27.4% (MV) and 43.3% (LV). Normalized deposition displayed under-leaf to upper-leaf deposition ratios of between 16.1% (HV) to 20.0% (LV). Ground deposits were reduced by roughly 37.3% (MV) and 54.7% (LV). Similar to volume rate, airflow rate influenced spray deposition on leaves but followed an opposite trend. Reducing airflow rate improved deposition although the effect attained a threshold at medium airflow rate beyond which further reduction the deposition decreased though the reduction was not statistically significant (P = 0.069). Airflow rate did not significantly affect ground deposits (P = 0.315) it reduced the quantity of spray lost by 7% (MF) and 8.4% (HF).