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Can Crop Temperature Guide Center-Pivot Irrigation?

By Hank Becker
October 2, 2000

Adding temperature sensors to a site-specific, center-pivot irrigation system showed that it is possible to detect water stress and manage delivery of irrigation water using that information.

Agricultural Research Service scientists in Florence, S.C., are fine-tuning the controls for a modified center pivot. It can independently water and fertilize nearly 700 mini-areas within a 14-acre circle. Each area is about the size of a two-car garage. The amount of water applied depends on the site-specific needs of plants as sensed by infrared thermometers and other state-of-the art sensors.

The modified center pivot consists of 13 30-foot-long segments with infrared thermometers spaced about 15 feet apart. Each segment has three sets of different-sized sprinklers. Using combinations of sprinklers, up to eight different water-application rates can be delivered. A computer controls the system, driven by specialized software and a database containing information about the soil, crops and farming practices.

Researchers added infrared thermometers to the system to see if water stress was detectable, sense the canopy temperature, and prove that it was possible to apply water to precisely address the sensed need. They also showed that the data could be adjusted for known problems like clouds and daily, or diurnal, cycles.

During the 1999 growing season, which had less rainfall than usual, canopy temperature measurements confirmed that corn plants encountered a wide range of crop stress, even within a fairly small area in a field. The computer-driven system delivered variable amounts of irrigation water, adjusted to relieve crop stress measured as plant temperature. Soil water measurements confirmed a wide range of soil water levels throughout the test plots.

1999 data showed the well-watered plots were up to 7 degrees C cooler than unwatered controls on a given day. Corn yields for well-watered plots were about 150 bushels per acre, compared with 60 bushels for the unirrigated.

ARS is the chief research agency of the U.S. Department of Agriculture.

Scientific contact: E. John Sadler, ARS Coastal Plains Soil, Water and Plant Research Center, Florence, S.C., phone (843) 669-5203, ext. 112, fax (843) 669-6970,