Chapter 12

Variable-Rate Technology in Precision Agriculture

Components of Variable-Rate Application

Variable-rate application (VRA) is a core feature of precision agriculture, allowing inputs (like fertilizer, seed, lime, or pesticides) to be applied at different rates across a field based on spatial variability. This process relies on a system of integrated hardware and software components.

GPS Antenna and Receiver

Variable-rate application relies on GPS to maintain constant equipment positions, allowing the in-cab computer to signal rate changes as the equipment moves from one field management zone to the next. If the GPS receiver antenna is not mounted directly on the applicator, the in-cab controller needs to be programmed to account for the separation distance between the GPS antenna and applicator to ensure the fertilizer rate is changed at the correct location as equipment moves into a new management zone.

ISOBUS-Compatible Controllers

The central component of variable-rate application equipment is the ISOBUS-controller, normally mounted in the vehicle cab. ISOBUS (ISO 11783) is an international communication standard that allows tractors, implements, sensors, and computers from different manufacturers to "speak the same language." It simplifies connections between machines, controllers, and software in precision agriculture. The controller performs several functions, including (1) operating a software program to display the product application map, (2) recording the GPS signal to recognize the vehicle’s real-time position on the map, (3) communicating signals with the rate control device to alter the fertilizer rate, (4) monitoring vehicle speed, and (5) recording the product application map.

Software

VRT software solutions are necessary to evaluate the data that sensors gather. These tools process data and generate information that may be utilized using models and algorithms. John Deere Operations Center, Ag Leader, and Trimble are well-known VRT software solutions.

Sensors

Sensors are widely used in digital agriculture. They equip monitoring systems and integrate automated systems for the distribution of inputs, which are generally called variable-rate application machines. Sensors are devices that interact with the physical environment and are capable of producing a signal that is related to the variable to be measured.

Actuators

Variable-rate application (VRA) technology in agriculture uses actuators to apply agricultural inputs, like fertilizers, seeds, and water, at different rates in different field areas. The actuators receive the signal from the controller and vary the regulation of the input metering. There are different types of actuators, and the choice of type is made according to the input to be applied and the metering/distribution mechanism adopted.

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