By Brad Haire
University of Georgia
Plants reflect light in unique ways, said Glen Ritchie, a research coordinator with the UGA College of Agricultural and Environmental Sciences.
Infrared info"Most of the visible light plants reflect is green," Ritchie said. "But they also reflect near-infrared light that we can't see with our eyes."
Since the 1960s, scientists have known that how a plant reflects light can say a lot about its health.
This knowledge can be used to properly schedule irrigation, too, Ritchie said. You just have to get a camera high enough to take a good picture of the field.
BlimphotosA 15-foot helium blimp hovers about 300 feet over a 5-acre cotton field at the UGA's C.M. Stripling Irrigation Research Park in Camilla, Ga.
"You have to get permission from your local air traffic controller if you get much higher," Ritchie said. The blimp can get as high as 1,000 feet.
"We chose a blimp for our platform because it seemed less risky to crash than a kite or model airplane," he said.
From the ground, Ritchie presses a button on a radio transmitter, sending a signal to an adapter hooked into the serial ports of two cameras inside a small plastic container hanging 3 feet below the blimp's belly.
The two cameras are off-the-shelf Nikons. One takes a regular image. The other, fitted with a near-infrared filter, takes a near-infrared image.
At 300 feet, the cameras can take a picture of about an acre of land, an area about the size of a football field. Two people can control the blimp using two ropes attached to it. They can cover the 5-acre field in about 10 minutes.
Farmers can also pay to have a satellite or hire a pilot to take pictures of whole fields. But a satellite can only take a picture when it is passing overhead, he said. And it can be limited by cloud coverage. Airplanes work well but are also limited by cloudy days.
And to schedule irrigation, he said, images would need to be taken of a field more often than satellites or airplanes can provide.
Ritchie downloads his images to a computer. Software combines and analyzes the images and compiles the data into spreadsheets that can be used to make irrigation decisions.
Ritchie hopes to establish benchmarks, or triggers, with the data. This could give a farmer a window of a day or more to begin irrigating his crop.
Before damageFarmers irrigate to keep plants healthy for high yields.
When plants don't get enough water, leaves curl and begin to wilt. Damage has already been done at this point, said Craig Bednarz, a cotton physiologist with the UGA CAES.
Any water applied after wilt occurs would first have to restore the plant to its pre-wilt stage, he said. Only after this could the plant begin to use the water to increase yields.
"What we want to do is to tell when the plant may be going into water stress before it begins to show the visible signs," Bednarz said.
Proper irrigation can increase yields by as much as 300 pounds per acre, he said.
This research project is funded by the Georgia Cotton Commission. The same system could be used to schedule irrigation for other crops, such as peanuts and vegetables.
(Brad Haire is the former news editor with the University of Georgia College of Agricultural and Environmental Sciences.)