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Title: CARBON DIOXIDE AND TEMPERATURE EFFECTS ON EVAPOTRANSPIRATION AND WATER-USE EFFICIENCY OF SOYBEAN.

Author
item Allen Jr, Leon
item PAN, DEYUN - UNIVERSITY OF FLORIDA
item BOOTE, KENNETH - UNIVERSITY OF FLORIDA
item PICKERING, NIGEL - UNIVERSITY OF FLORIDA
item JONES, JAMES - UNIVERSITY OF FLORIDA

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2002
Publication Date: 8/15/2003
Citation: ALLEN JR, L.H., PAN, D., BOOTE, K.J., PICKERING, N.B., JONES, J.W. CARBON DIOXIDE AND TEMPERATURE EFFECTS ON EVAPOTRANSPIRATION AND WATER-USE EFFICIENCY OF SOYBEAN. AGRONOMY JOURNAL. 2003. v. 95. p. 1071-1081

Interpretive Summary: Rising carbon dioxide (CO2) and global warming will likely cause changes in crop water use (crop transpiration) and thus affect soil water available for producing food. In order to test these effects, ARS scientists and University of Florida research partners at Gainesville, Florida grew soybeans in outdoor, sunlit chambers at controlled levels of ambient CO2 (350 parts per million, PPM) and doubled-ambient CO2 (700 PPM), and at a wide range of five temperatures with daily maximum values of 28 degrees Celsius (a comfortable 82 degrees Fahrenheit) up to 44 degrees Celsius (a sizzling 111 degrees Fahrenheit). Elevated CO2 always decreased crop water use and increased the water-use efficiency, the yield per unit amount of water used, of the soybean plant. However, the water required for transpiration at the highest temperature tested, 44 degrees Celsius, increased 2.5-fold compared to the water required at 28 degrees Celsius, with a corresponding decrease in water-use efficiency. These results show that, in the future, rising CO2 will decrease water use and increase water-use efficiency of crops, but, unfortunately, this benefit will likely be offset or even made worse if temperatures also increase.

Technical Abstract: Rising carbon dioxide (CO2) and potential climate changes will likely cause changes in crop evapotranspiration (ET). The objectives were to determine the impact of both CO2 and temperature on canopy ET and water- use efficiency (WUE) of soybean [Glycine max L. (Merr.)]. Plants were grown in sunlit controlled-environment chambers at sinusoidal daily temperatures ranging from 28/18 to 48/38 degrees Celsius (C) day/night maximum/minimum values at either 700 or 350 micromoles (CO2) per mole air. Elevated CO2 decreased ET and increased WUE. Maximum ET rates at 35 days after planting (DAP) ranged from 7.5 to 19.0 millimole (water) per square meter per second at 28/18 and 44/34 degrees C, respectively. Daily total ET (10-h period) ranged from 260 to 660 mole (water) per square meter during the middle of the season. Maximum WUE occurred early in the daytime (0800 h) and minimum WUE occurred at the end of the daylight period (1800 h). Midday WUE ranged from 5 to 2 micromole (CO2) per millimole (water) for temperature treatments of 28/18 and 44/34 degrees C, respectively. In future conditions, rising CO2 will decrease ET and increase WUE, but this benefit will likely be offset if temperatures also increase.