Spray chamber evaluation of air-assisted spraying on potato plants.
This article reports on a study of air-assisted spraying where the effects of air speed, airflow rate, and air jet 
orientation were isolated. The study was carried out in a spray chamber. A carriage supporting a standard spray boom 
was moved at 6 km/h over micro-plots of greenhouse grown potato plants. Air was delivered slightly behind the nozzles 
from a variable width slot producing a uniform two-dimensional air jet that was adjustable in tilt in the direction of 
travel. Experiments were carried out using a central composite design (CCD). Compared to a full factorial design, this 
design required fewer experiments and allowed one to find the optimum operating conditions. The range of the 
independent variables was: air speed, 0 to 36 m/s; airflow, 0 to 1.3 m 3 /s/m, and air jet angle, –10.2 to 40.2°. Two sets of 
flat fan nozzles (VMD = 230 and 400 µm, both delivering 250 L/ha at 6 km/h) were used to carry out two full sets of 
experiments. Results showed that air speed had the larger impact on leaf coverage. Higher air speeds (> 25 m/s) increase 
the coverage on the underside of the leaves at all levels within the canopy and on the top side of the leaves in the lower 
third of the canopy. However, lower air speeds (< 20 m/s) are desirable for a better coverage on the top side of the leaves 
in the higher two-thirds of the canopy. Based on data presented here, the use of an air speed higher than 25 m/s coupled 
with an air jet angle of 20° forward and a fine spray increase both the coverage of hidden parts of the plants and the 
spray penetration towards the bottom of the canopy. Airflow rate affected coverage significantly only in conjunction with 
finer spray.