Evaluation of a variable rate controller for aldicarb application around buffer zones in citrus groves

Advances in precision farming technologies have facilitated controlled application of agrochemicals and documentation procedures to follow environmental regulations. This paper details evaluation of a commercial variable rate (VR) controller for preventing aldicarb applications in the buffer zones around potable water wells of citrus groves. The controller was coupled to two common drive mechanisms, a ground-driven electric clutch-engaged (GDEC) and pulse-width-modulation motor-driven (PWMM). The evaluation involved determination of dynamic performance of the VR application system through quantification of reaction times and rate transition distances and determination of appropriate ''look-ahead'' times for each of the drive mechanisms. Without a look-ahead (zero) setting, the mean midpoint reaction distances were about 1.8 and 3.6m for the GDEC and PWMM mechanisms, respectively, at 7.0-km/h ground speed. For the GDEC, a look-ahead time of 1s gave the mean midpoint reaction distances of -0.06 and 0.04m during step-up and step-down of the rate, respectively. For PWMM, the best look-ahead times were 1 and 2s during step-up and step-down of the rate, respectively. However, since the prototype unit could not accommodate two look-ahead times, the compromise look-ahead time for both step-up and -down was 2s. Validation in the actual buffer zone showed that, at 95% confidence level, the buffer zone should be increased by 2.5 or 3.3m in commercial applications using GDEC or PWMM systems, respectively.