Chapter 34

Precision Viticulture

Variable-Rate Application Technology

There are numerous areas in the vineyard that differ from one another with respect to soil type, topography, microclimate, and other factors that influence crop yields. Variable-rate application (VRA) has been widely heralded as a means of applying crop inputs (e.g., pesticides, fertilizer, etc.) in a non-uniform manner based on varying needs throughout a vineyard with advantages including higher average yields, lower input costs, and environmental benefits from applying fewer inputs. There are two ways in which automated variable-rate technology (VRT) can be utilized for site-specific crop management (SSCM) systems. These are sensor-based and map-based systems. There are advantages and drawbacks to both application systems. Generally, map-based variable-rate applicators will require more components than a sensor-based applicator, however, this is offset by the fact that these components can be used for multiple inputs. The hardware and sensors that make automated variable rate application possible include the controller, the microprocessor, actuators, pressure sensors, flow sensors, speed sensors, and differential global positioning system (DGPS) technology.

Variable-Rate Application Technologies

There are a variety of variable-rate application (VRA) technologies available that can be used with or without a global positioning system (GPS) system. The two basic technologies for VRA are: map-based and sensor-based.

Map-Based Variable-Rate Application

The map-based method consists of a controller, sensors, and actuators (devices that responds to signals from controllers) to adjust inputs based on a pre-made electronic map of the input using a differentially corrected positioning system to determine the applicator position in the vineyard. Application maps may be constructed from yield, topography, soil, plant, or weed data. Map-based systems allows the grower to make decisions based on knowledge of the vineyard before they are in the vineyard.

Sensor-Based Variable-Rate Application

The sensor-based method provides the capability to vary the application rate of inputs with no prior mapping or data collection involved. Real-time sensors measure the desired properties—usually soil properties or crop characteristics—while on the go.

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