Hewett, owner of Blair Air Service, Lemoore, Calif., had made that aerial move thousands of times, but this time one thing was different. As he began the first of his 120-mile-per-hour passes just above the plants, he did not reach down to the left of his pilot’s seat to pull a lever, releasing the flow of liquid from nozzles arrayed along the 70-foot spray boom hanging beneath the powerful aircraft’s wing.
A computer loaded with a pest control advisor-generated map of the field and connected to a satellite-guided global positioning system (GPS) regulated the flow from those nozzles, applying a plant growth regulator based on the predetermined, specific needs of the plants in various areas of the field.
Hewett’s demonstration passes at noontime on a sunny and breezy July day were the first in the U.S. for an agricultural aircraft equipped with variable rate technology.
It represented another major step in the rapidly expanding world of precision agriculture.
Variable rate technology for applying fertilizers, defoliants, pesticides, herbicides and plant growth regulators has been limited to ground applications only until now.
The introduction of aerial variable rate technology represents a major breakthrough in Western, irrigated agriculture where optimum ground applications often are stymied by wet ground, irrigation schedules and other field operations.
Aerial variable rate technology’s U.S. debut was supposed to be a secret as well as the climatic conclusion to a precision agriculture field day at the Sheely farm organized by University of California Cooperative Extension Farm Advisor Steve Wright of Tulare County and Bruce Roberts of Kings County.
It was not a surprise.
"When the word got out that we were installing a variable rate computer system in one of our planes, we got calls from farmers and pest control advisers all over the valley wanting us to put Pix on," said Hewett. "I got calls from people I had never done business with before wanting us to fly their fields."
Differential GPS is nothing new to aerial applicators. It has been used on crop dusters since the mid-1990s, and most aircraft operating in California are equipped with it to improve accuracy and efficiency.
Hooking a GPS guidance system to a computer regulating the flow of material from spray booms is brand new. Specifically Hewett’s plane is equipped with a Satloc computer/GPS system from a company with the same name based in Scottsdale, Ariz. Greg Guyette, director air division sales and system instructor, said the computer can change the flow rate of the nozzles literally every second.
A hydraulic motor was added to the plane’s material handling system to control flow rates dictated by the computer. Changing the flow rate from the nozzles changes the chemical application rate.
Guyette said he is continuing to work with Blair Air Service and Hewett in fine-tuning the on-board computer system, but it should be fully operational soon for full scale commercial use.
"Changing flow rates at 120 miles per hour requires that you predict what is coming up," said Guyette. "That is not a problem when you change the flow rate from say five to six gallons, but it presents a challenge with the flow rate change indicated on the aerial imagery is five to 10 gallons."
Aerial imagery in agriculture is becoming more widely used to map crop and soil variations. It is used to evaluate fertilizer requirements; soil salinity levels, or the growth stages of plants. Consultants use these color maps and plant or soil sampling or proofing to break these variations into manageable zones. A computer draws a map of these zones. They resemble amoebas scattered across fields.
Ground application equipment equipped with GPS guidance systems and computers traveling at less than 10 miles per hour can easily change application rates, but it is more difficult for a pilot and his aircraft traveling at more than 100 miles per hour.
"When you have a small finger of one of these zones you can get three dramatic flow rate changes in a matter of a few feet. Those are the challenges with aerial variable rate applications," said Guyette.
Nevertheless, Guyette and Hewett believe those challenges will be met.
Ready for defoliation
"We are at the tail end of the Pix season for cotton this year, but we should be up and running for defoliation," said Hewett.
"Growers and PCAs really want this aerial variable rate technology for things like Pix. It is often difficult to get into a field to make a timely Pix application by ground because of irrigation scheduling," said Hewett. "Aerial applications can be timed better than by ground to maximize the benefits of something like Pix."
Cotton is obviously not the only crop that would benefit from variable rates. "I see this to be a big plus in whitewash for tomatoes. Seldom does an entire field need whitewash to prevent sun burning — only those areas where the leaves break down," said Hewett.
Maps of weedy areas or emerging high insect or disease pressure areas in all crops could be loaded into airborne computer systems for precise spot treatments thanks to GPS.
Reducing costs and maximizing yields are the two key elements driving precision ag. Sheely’s farm has become the focal point of most of the precision ag work in California as part of a project called Ag 20/20, involving NASA, University of California, California State University, the National Cotton Council and others in researching and demonstrating variable rate technology and other precision ag technologies on a working farm.
"The philosophy behind looking at all these things is simple. Whatever we do here must have a cost/benefit ratio component. If we spend a dollar, will it make more than a dollar?" he said. "If it does not, it becomes a research project to maybe look at later. If it is cost effective, it becomes a demonstration project."
Sheely was one of the first in California to install GPS tractor guidance systems. He said the $50,000 units paid for themselves in improved efficiency in just three months. Other projects are showing a payback of up to a year.
One of the most dramatic validations of combining aerial imagery with GPS guided variable rate technology was in a nitrogen management trial where fertilizer cost was reduced by 52 percent on one 150-acre block of cotton that yielded an average of 1,780 pounds of lint per acre.
That represented a cost savings of more than $3,000 on that one field. With that Sheely purchased one of the first variable rate anhydrous ammonia application system. He believes it is the only one in California. It cost $7,000.
"With 28 cotton fields, do the math. It makes pretty good sense to make that kind of investment," said Sheely at the field day that drew more than 200 people to his farm.
"California farm fields are visibly the most uniform you will see, but there is more variability than you can imagine," Roberts said. Mapping and ground proofing that imagery is validating that variability to a level not heretofore seen. And GPS technology coupled with computer-driven variable rate applicators and planters are giving growers cost-effective tools to achieve even greater uniformity.
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