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 degrees. Two sets of flat fall nozzles (VMD = 230 and 400 mu m, 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 degrees 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.