Design, Construction and Evaluation of Variable Rate Spraying System for Weed Controlling

  In the past decades, herbicides were generally applied at a uniform rate to the entire field. But uniform application causes environmental problems such as soil and groundwater pollution and economic problems. General concern about the negative effects of using herbicide was resulted to the development of a new herbicide application system. Variable flow rate technology is being used extensively in precision agriculture. But, it is not developed sufficiently in our country. In this study two types of systems were designed to achieve a suitable variable rate spraying system. For the first step, motorized valve was utilized. Laboratory tests were conducted  with TeeJet nozzle at three different operating pressure levels (2 to 4 bar) and four rotational positions of a servo motor ( 30 , 45, 60, 80 degrees). The performance reduction of the machine due to the pressure variations is one of the disadvantages of this system. The pressure variations caused the spray pattern to be non-uniformed and it also affected the droplet size. For the second tests, a solenoid valve was used which was controlled by pulse width modulation. The duty cycle and operating pressure as effective factors were examined on the spraying angel. The experiments were performed in the form of factorial based on completely randomized design in three replications. The spraying angel measured at five levels in the combined treatment of the duty cycle (20%,30%,50%,70%,90%) and operating pressure at three levels (2,3,4 bar).The duty cycle and pressure had a positive effect on spraying angel and flow rate as well. The spraying angle variation was just 3% when the duty cycle was changed from 20% to 90%.