The Precision Decision
As inputs become more costly, site-specific crop management (precision agriculture) is slowly becoming more widely adopted in Florida citrus production. Used properly, precision agriculture can contribute to reduced waste, increased profits, and protection of the environment.
“Precision agriculture is not a single technology, but rather a set of many components from which growers can select to form a system that meets their unique needs and operation size,” says Reza Ehsani, assistant professor of agricultural and biological engineering at the UF/IFAS Citrus Research and Education Center (CREC). “In citrus production, a small change in increasing the efficiency of the input materials or yield could significantly affect the bottom line.”
Esa Ontermaa, precision agriculture coordinator at Lykes Citrus Management Division, says that precision agriculture includes many technologies, but that they don’t always fit every operation. He cautions growers to have a well-defined purpose and to thoroughly investigate and evaluate the options prior to implementation.
According to Ehsani, collecting yield data is the first step in precision agriculture. Yield monitoring is the process of measuring fruit yield for a given location and integrating it with GPS-obtained information.
“Yield monitors can provide and document the amount of yield variability at a smaller scale and can lead the way to manage the needs of each individual tree rather than treating the entire block of trees uniformly,” Ehsani says.
Several commercially available software packages can read yield data and create a yield map. Most can:
• Provide detailed statistical information regarding the collected data
• Use several years of collected data to categorize it and create different management zones
• Overlay the yield variability maps on aerial images of the grove to provide an enhanced visualization of the data
• Create profitability maps that show where grove profit was maximum or minimum, or which areas lost money
• Create application maps based on different management zones for different crop inputs
• Extract machinery-management information such as field efficiency, machine operator performance, total downtime, and actual harvest time
Remote sensing refers to the multi-band images that are taken from an airplane, helicopter, or satellites. These images contain spectral reflectance data from the tree canopy and soil.
Laser map of a citrus tree canopy. The map can help determine fertility needs by tree size. “Analyzing these images can provide cost effective and timely information about tree health and soil conditions,” says Ehsani. “For example, it can help in spotting drainage problems in the field or detecting moisture stress. Large citrus growers can use this technology for counting trees and canopy-covered area, and eventually use the information for forecasting crop quality and yield.”
Variable Rate Technology
Variable rate technology (VRT) of inputs is another key component of precision ag, providing economic benefits to growers in the form of reduced use of fertilizer, agrochemicals, and irrigation water, while having a positive environmental impact. A system can be as simple as a variable rate fertilizer spreader with a couple of canopy sensors that can apply the fertilizer based on the tree size.
“The idea of variable rate application of inputs is to save resources, thereby lowering production costs and increasing profits,” says Ehsani. “It also helps to reduce ground water contamination and environmental degradation.”
A University of Florida study found that a VRT spreader costs approximately $29,000. A 15% reduction in fertilizer would save $21 per acre, so 1,380 acres of use would pay for the spreader.
Joby Sherrod, R&D/technical services manager of Duda Products Inc., says he has seen major monetary benefits through the use of VRT. For example, phosphorus has been eliminated from Duda’s standard fertilizer mix. Now, phosphorous is only applied, via VRT, to areas in which soil and leaf tissue tests indicate it is needed.
“We’re using much less phosphorus than when we blanket-applied a maintenance rate to everything. And we’re being more sustainable. By cutting the amount we apply, we cut the dollars spent, and we’re also addressing the needs of the trees better,” says Sherrod.
Ontermaa agrees. “We’ve seen significant savings and reduction of inputs as a result of our soil sampling program and VRT,” he says.
Ehsani says other precision agriculture technologies that are currently under development at CREC include yield monitoring systems for mechanical harvesters and sensors that detect disease and tree stress atearly stages of development.