Carbon dioxide enrichment and irrigation effects on wheat evapotranspiration and water use efficiency
Evapotranspiration (ET) and water use efficiency were evaluated for two spring wheat crops, grown in a drip-irrigated field under ambient (about 370 mmol mol–1) and enriched (550 mmol mol–1) carbon dioxide (CO2) concentrations during the 1992-1993, and 1993-1994, Free-Air CO2 Enrichment (FACE) experiments in central Arizona. CO2-enriched (FACE) and ambient CO2 (CONTROL) treatments were replicated in four circular plots, 25 m in diameter, and well-watered (WET) and water-stressed (DRY) irrigation treatments were imposed on one-half of each plot. Wheat ET, measured over discrete time periods of several days by a soil water balance, was significantly higher for WET than DRY irrigation treatments after the first week in March in both years. Differences in ET between CO2 treatments during the season were generally small, although there was a consistent trend towards decreased ET for the FACE over CONTROL under the well-watered irrigation regime.