...From the pages of Agricultural Research magazine
Hot Cotton: New System Senses Water Stress
Water stress in crops is caused by drought or poor irrigation. Traditional
methods of identifying water stress use sensors to measure water pressure
in individual, removed leaves, or the flow of sap through the plant
stem. Monitoring soil moisture is also commonly used to determine crop
water use and to schedule irrigation.
While these methods are reasonably reliable, they are time consuming
and costly and give information only for the immediate area in which
they are used.
"It can be very difficult to quantify the stress of the entire
crop canopy," says Gretchen F. Sassenrath-Cole, a plant physiologist
at the Jamie Whitten Delta States Research Center in Stoneville, Mississippi.
"Using measurements from one leaf from the top of a plant to characterize
the entire plant canopy could lead to a false conclusion."
Many environmental factors influence plants' loss of water. Sunlight,
air temperature, humidity, and wind speed all affect plant temperature.
Physiological factors affect a plant's ability to transport water to
cool its leaves through evapotranspiration.
Because inadequate water supply increases canopy temperature, scientists
in the ARS Application and Production
Technology Research Unit at the Stoneville center, in collaboration
with H. C. (Lyle) Pringle, a Mississippi State University scientist,
are exploring canopy temperature change as a more reliable indicator
of crop water status. They developed a movable field-tracking system
that uses thermal sensors to capture images of the canopy and measure
The system can be rapidly deployed and positioned at various levels
above the canopy, measuring individual leaves or entire canopy elements.
The sensors are located at the end of a boom attached to a yoke that
rotates 360 degrees in the horizontal plane. The entire pivoting system
is attached to a tower mounted on the front rack of an all-terrain vehicle.
The boom, engineered by Sassenrath-Cole and technician Ray Adams, is
positioned over the canopy by a hydraulic cylinder that raises and lowers
it to the desired height, focusing the sensors on a specific canopy
Various remote-sensing devices can be attached to the boom, including
infrared thermometers and spectroradiometers, which record reflected
light wavelengths. As incoming radiation and ambient air temperature
are registered, the specific location is recorded with a geographic
positioning system. The data is downloaded into an on-board computer,
along with images from a video camera, allowing the operator to see
the canopy element that's being measured.
"At this time, no standard method to monitor soil moisture or
crop water stress for irrigation purposes has been adopted by producers
in the Mississippi Delta," Sassenrath-Cole says. "Systems
based on thermal detection have been used successfully in arid regions;
but the humid conditions of the Mid-South limit a plant's ability to
Researchers anticipate that managers could make better decisions about
irrigation scheduling by using this technology. Sassenrath-Cole says
one day the system could evolve into a robotic device for continuous
monitoring of crop canopies in a production setting. ARS is interested
in cooperating with a commercial partner to further develop and commercialize
this technology.By Jim
Core, Agricultural Research Service Information Staff.
This research is part of Integrated Agricultural Systems, an ARS
National Program (#207) described on the World Wide Web at http://www.nps.ars.usda.gov.
Gretchen F. Sassenrath-Cole
is with the Application and Production Technology Research Unit, Jamie
Whitten Delta States Research Center, 141 Experiment Station Road,
P.O. Box 36, Stoneville, MS 38776; phone (662) 686-5289, fax (662) 686-5372.
"Hot Cotton: New System Senses Water Stress" was published in the July 2002 issue of Agricultural Research magazine.