Thirsty cotton plants call for irrigation
Aug 12, 2008 10:09 AM,
By J.D. Bilbro
Contributing Writer
In decades past, cotton producers on the Texas High Plains believed water in the Ogallala aquifer was continually replenished by underground streams from the Rocky Mountains. Consequently, they irrigated without seriously considering the timing or the amount of water used to produce a crop. However, that theory was wrong and water available for irrigation has declined significantly.
PERIODICALLY, THE HEIGHT and orientation of each infrared sensor must be changed to keep it properly focused on the cotton plants, James Mahan says.
"Today producers are limited in the amount of irrigation they can apply in a given time frame," says James Mahan, plant physiologist, USDA-Agricultural Research Service, Lubbock. "Therefore, (producers need) a technique to enable them to save water by determining when their crop actually needs irrigation.
"About 20 years ago we theorized the cotton plant itself should be the best source of information for telling us when we should apply irrigation. So we began research to prove or disprove this theory."
In a laboratory, Mahan and colleagues studied various metabolic processes of plants and discovered enzymes that were very temperature sensitive and closely associated with water needs. Additional research indicated that for cotton plants to make maximum lint yields they should receive additional water after the plant temperature stayed above 82 degrees F for 5.5 hours.
"We investigated various ways to measure plant temperatures in the field, and found infrared sensors could do the job adequately. Subsequently we developed a biologically-based irrigation scheduling protocol and named it 'BIOTIC' for Biological Identified Optimal Temperature Interactive Console"
The BIOTIC irrigation system works this way:
Infrared sensors are installed in the field and focused on the plants to record canopy temperatures. Periodically, the sensors transmit accumulated data to the base controller located within the field. The controller uses this data to determine if time and temperature thresholds have been reached. If they have, an "irrigate" signal is transmitted to the producer's computer or cell phone.
The controller can also be programmed to transmit detailed temperature data and other information to the producer's computer. Then the producer can, at any time, view in graph form the current and previous six days' data. This enables him to approximate the date he will receive an irrigate signal.
"We found threshold temperatures are very critical in scheduling irrigation. In a three-year study we found if irrigations were initiated when canopy temperatures were three degrees below the optimum temperature of 82, yields were reduced by 33 percent. If irrigation was delayed until canopy temperatures reached 4 degrees above optimum, yields were reduced 35 percent.
"Length of time plants are above the optimum threshold setting is also very critical. We found changing the time threshold from 5.5 hours to 6.5 hours reduced lint yields about 350 pounds of lint per acre.
"The computer program that drives BIOTIC irrigation was designed for 'full' irrigation. That is, the cotton plants would make maximum yields when they got additional water any time their temperature exceeded 82 degrees F for 5.5 hours. Unfortunately, the underground water supply on the Texas High Plains is inadequate for full irrigation," Mahan said. "However, a producer can easily adjust the time/temperature thresholds in the computer so irrigations will be in keeping with his irrigation potential."
The USDA, Agricultural Research Service holds a patent on this technology application known as BIOTIC or Time-Temperature-Threshold. Accent Engineering Inc., licensed the BIOTIC technology and cooperatively developed a hardware and software package currently available commercially.
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