Development of an experimental variable-rate sprayer for nursery liner applications

Abstract

Sensor-guided application technologies are needed to achieve constant spray deposition for the rapid growth of nursery liner trees during a growing season. An experimental real-time variable-rate sprayer that implemented 20 Hz ultrasonic sensors and pulse width modulation (PWM) solenoid valve-controlled spray nozzles was developed to adjust spray outputs automatically based on the liner canopy size. The developed sprayer consisted of two vertical booms, an ultrasonic sensor detecting system coupled with a spray flow rate controlled unit, a microcontroller and a spray delivery system. Two booms were integrated with five opposing pairs of equally spaced spray nozzles. The sensors were mounted 0.36 m ahead of spray nozzles to ensure sufficient time for processing signals. The accuracy of the sprayer in triggering spray against detected targets moving at 3.2 km/h was evaluated by use of a high-speed camera. A laboratory field consisting of six different sized tree species was used to test the sprayer performance consistency. Test results revealed that spray nozzles were triggered from 4.5 to 12.5 cm ahead of detected targets. Seventy-five percent of test runs for detecting canopy volume of the six tree species produced significant (P < 0.05) Pearson correlation coefficients from 0.43 to 0.88 when the sprayer travel speed was from 3.2 to 6.4 km/h. While the sprayer applied variable output rates from 0 to 20.4 L/min at travel speeds from 3.2 to 8.0 km/h, the mean spray coverage inside canopies of six tree species was from 12.0 to 14.7 % and mean spray deposit was from 0.72 to 0.90 L/cm2. Effects of travel speed on both mean spray deposit and coverage were insignificant (P > 0.05). Therefore, the newly developed sprayer offered a possibility to achieve uniform spray deposition and coverage for nursery liner applications despite variations in liner canopy size and sprayer travel speed.