Changes in a crop canopy's temperature may give scientists the most complete picture of how much water stress the plants are experiencing during drought, according to Agricultural Research Service scientists.

Previously, researchers have gauged drought stress using sensors to measure the water pressure of individual leaves removed from the plant, or the sap flow through the plant stem. They've also monitored soil moisture to determine crop water use and to schedule irrigation. While these methods are reasonably reliable, they are time consuming and costly.

Now scientists at the ARS Application and Production Technology Research Unit in Stoneville, Miss., report that changes in canopy temperature may be a more reliable indicator of water stress because canopy temperature rises as water stress increases.

Evaluating the entire plant canopy gives a more complete picture of a crop's health than one gets from measuring a single leaf from the top of a plant, according to Plant Physiologist Gretchen Sassenrath-Cole. She and her colleagues are collaborating with H. C. "Lyle" Pringle, a Mississippi State University scientist located at the Delta Research and Extension Center in Stoneville.

They developed an unobtrusive tracking system that uses thermal sensors to remotely monitor canopy water stress and temperature. The system can be rapidly deployed and positioned at various levels, measuring individual leaves or entire canopy elements.

Sensors are located at the end of a boom attached to a rotating yoke. The entire pivoting system is connected to a tower mounted on the front rack of an all-terrain vehicle. The boom, engineered by Sassenrath-Cole and technician Ray Adams, is raised or lowered over the canopy by a hydraulic cylinder to focus the sensors on a specific area. Data and images from a video camera are simultaneously downloaded to an on-board computer.

Read more about this research in the July issue of Agricultural Research magazine, available on the web at: http://www.ars.usda.gov/is/AR/archive/jul02/water0702.htm