Wind tunnel experiments and a mathematical model of electrostatic spray deposition in barley

This paper reports experiments aimed at measuring deposits on vertical and horizontal targets located between rows of barley. The variables investigated were nozzle size, nozzle height, charge and wind speed. The results showed that charging increased deposits on vertical targets and tended to lecrease deposits on the upper surfaces of horizontal targets. Both effects were greatest with the smallest nozzels, and were independent of nozzle height. In wind the increase in deposits on vertical targets was less. This was because wind tended to increase deposits from uncharged spray on vertical targets and decrease deposits from charged spray. There was no effect of charging on deposits on the upper surfaces of horizontal targets in wind. Deposits on the lower surfaces of horizontal targets were always low and none of the variables produced significant effects. A simple mathematical model was developed and used to explain some of the effects found in the experiments, for example those of nozzle size and wind. The practical implications of the work are discussed in relation to the control of weeds within a cereal canopy. It was concluded that charging may increase deposits on vertical targets such as grass weeds but more work needs to be done, especially on the uniformity of deposits, before the full effects of charging sprays from hydraulic nozzles can be assessed.