Volume 4, Issue 5 (May 2007)
Managing Aldicarb Application with GPS/GIS Systems
Aldicarb is a soil-applied pesticide that is widely used to control certain insects, mites, and nematodes of citrus and other crops. However, due to its high toxicity and leaching potential into groundwater, many states regulate its application. In Florida, aldicarb applications require a 91.4-m buffer zone around all drinking water wells and 304.8 m around wells located in certain sandy soils. To positively control and monitor the discharge of aldicarb in field conditions, the feasibility of using several electronic control systems on the granular applicator was investigated. The project involved fabricating a prototype machine that featured both ground- and motor-driven mechanisms commonly used in commercial aldicarb applications. A ground-driven power train operated one-half of the metering wheel through an electric clutch and a pulse-width modulation (PWM) motor powered the other half. The machine was equipped with various controllers and electronic circuits. Three DGPS-based approaches were considered. The first level consisted of a DGPS antenna and a low-cost data logger. It could provide records including position information (latitude and longitude) and status of the PWM controller and electric clutch (ON/OFF of the discharge system) for monitoring purposes. The second system (mid-range cost) utilized a hand-held computer and variable-rate-application (VRA) software to input prescription maps and provide an operator real-time screen interface. With this system, it was possible to provide ON/OFF control of both discharge drives and generate as-applied maps. The third level (highest-cost) involved the use of a more sophisticated VRA controller comprising modular components and CAN bus system. It allowed detailed operator-machine interface and could input variable rate maps and output information on application rate, acreage, and total material usage. The paper elaborates on the above technology solutions and provides test results of their evaluation under simulated field conditions. Each system had certain merits and limitations but all were capable of providing useful temporal and spatial information for aldicarb application.