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