Evaluation of a flow control system for site-specific herbicide applications

An electronic flow control system for site-specific herbicide applications was tested for steady state performance. The control system used spray nozzles coupled with solenoid valves, regulated using pulse-width modulation at 10 Hz and duty cycles of 10 to 100% to control the flow rate. The controller could vary the nozzle flow rate in the ratio of up to 9.5 to 1 without a significant change in the spray pattern. Droplet size distribution of the variable rate system was fairly constant at duty cycles of 25 to 100%. The Volume Median Diameter (VMD) at a duty cycle of 10% was significantly different from the rest. Response delay was small and suitable for high-speed herbicide applications. The uniformity of spray deposition along the orthogonal direction (along travel direction) decreased dramatically as the duty cycle decreased and travel speed increased. The variable flow nozzle could be used on existing sprayers for maintaining the application rate as the speed changes by controlling the flow rate. For local sensor based site-specific herbicide application, the controller has to be modified to overcome banded spray deposition at high travel speed and low duty cycle combinations.