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Effects of Elevated CO2 and Soil Nitrogen on Wheat
Hunsaker, D.J., Kimball. B.A., Pinter, P.J., Jr., Wall, G.W., LaMorte, R.L., Adamsen, F.J., Leavitt, S.W., Thompson, T.L., Matthias, A.D. and Brooks, T.J.  2000.  CO2 enrichment and soil nitrogen effects on wheat evapotranspiration and water use efficiency.  Agricultural and Forest Meteorology 104: 85-105.

What was done
Spring wheat (Triticum aestivum) was grown for two seasons at atmospheric CO2 concentrations of 370 and 570 ppm in FACE plots located in Arizona, USA.  Additionally, at each CO2 concentration, one-half of each experimental plot received high soil nitrogen supplies, while the other received low soil nitrogen supplies.  Thus, the authors studied the interactive effects of elevated CO2 and soil nitrogen supply on the growth, physiology and water use of spring wheat.  This particular paper reports the data associated with water use in this species.

What was learned
Although elevated CO2 did not significantly impact seasonal evapotranspiration, it did reduce it by about 4 and 1% under conditions of high and low soil nitrogen, respectively.  However, elevated CO2 significantly enhanced water-use efficiency (grain yield per seasonal evapotranspiration) by approximately 20 and 10% in the high and low soil nitrogen regimes, respectively.

What it means
As the CO2 content of the air rises, it is likely that spring wheat yields will rise substantially, with little or no change in irrigation inputs.  In addition, with future increases in the air's CO2 content, farmers may be able to grow and harvest spring wheat in areas where they currently cannot, due to limited soil water availability.

Reviewed 20 September 2000