Florida citrus growers have been using variable-rate application technology to help spray their groves for several decades. But the newest enhancement to the process enables them to also apply fertilizer more efficiently, resulting in material and cost savings.
The core of the system is a sensor mounted on the application rig—typically at the front of the tractor—and a computer controller, says Arnold Schumann, associate professor at the University of Florida’s Citrus Research and Education Center at Lake Alfred.
The sensor has two functions.
It determines the presence of trees, so the system doesn’t fertilize areas where nothing is growing. And it measures the size of the trees and adjusts the amount of fertilizer applied based on tree size.
“It basically does a very targeted application of fertilizer, rather than applying it whether there’s a tree or not,” Schumann says.
The delivery mechanism is a dual-chain spreader capable of applying fertilizer independently on the left and right sides between two rows of trees.
There are various types of sensors available, including laser, ultrasonic and infrared optical sensors.
“The most reliable and cost-effective ones are infrared optical sensors,” Schumann says.
How sensors work
When the sensor detects the presence and height of the tree, it feeds that information into a controller, which essentially is a dedicated, custom-built computer that interprets information from the sensor and determines the fertilizer application rate, Schumann says.
The spreaders have been around since the 1990s and are used for a variety of crops, including peaches, apples, avocados or anything that is grown in rows, he says.
Spreaders were first used in conjunction with sensors about the year 2000.
The latest embodiment of the system, which Schumann developed with Kevin Hostler, senior laboratory technician at Lake Alfred, over an 18-month project period senses the speed of the tractor as it applies fertilizer and adjusts for it with the help of a global positioning system.
The system, called the CC-Eye-8000 Tree Sense Control System, available from Chemical Containers Inc. of Lake Wales, automatically applies more or less fertilizer as needed or turns off the application when the tractor stops.
The previous system, with no speed reference, was plagued by poor synchronization, causing the wrong tree to be fertilized or applying fertilizer after the tractor had passed the tree.