Evapotranspiration of Corn and Forage Sorghum for Silage T. A. Howell 1 , S. R. Evett 2 , J. A. Tolk 3 , K. S. Copeland 4 , P. D. Colaizzi 5 , and P. H. Gowda 6 1 Research Leader, PH (806) 356-5746; FAX (806) 356-5750; email: terry.howell@ars.usda.gov 2 Research Soil Scientist, PH (806) 356-5775; FAX (806) 356-5750; email: steve.evett@ars.usda.gov 2 Research Plant Physiologist, PH (806) 356-5736; FAX (806) 356-5750; email: judy.tolk@ars.usda.gov 4 Soil Scientist, PH (806) 356-5735; FAX (806) 356-5750; email: karen.copeland@ars.usda.gov 5 Agricultural Engineer, PH (806) 356-5763; FAX (806) 356-5750; email: paul.colaizzi@ars.usda.gov 6 Agricultural Engineer, PH (806) 356-5730; FAX (806) 356-5750; email: prasanna.gowda@ars.usda.gov *USDA-ARS, Conservation & Production Research Laboratory, P.O. Drawer 10, Bushland, Texas 79012-0010. Abstract In the U.S. Southern High Plains, dairies have expanded and have increased the regional demand for forage and silage. The objectives were to measure water use and determine crop coefficients for corn (Zea mays L.) and forage sorghum (Sorghum bicolor (L.) Moench) produced for silage on the Southern High Plains. Water use was measured with large, precision weighing lysimeters in 2006 and 2007. Both growing seasons had normal to above normal rainfall. The 2006 season was more advective with greater mean daily reference evapotranspiration (ET) rates. Seasonal ET was 671 mm for forage sorghum with a yield of 1.48 kg m -2 in 2006 and 489 mm in 2007 with a yield of 1.70 kg m -2 ; water productivity was 2.21 kg m -3 in 2006 and 3.47 kg m -3 in 2007. Seasonal ET was 418 mm for corn for silage with a yield of 1.52 kg m -2 in 2006 and 671 mm in 2007 with a yield of 2.44 kg m -2 ; water productivity was 3.63 kg m -3 in 2006 and 3.64 kg m -3 in 2007. Using the 2007 season as a better species comparison, forage sorghum can achieve comparable water productivity as corn with less ET (~73% of corn ET) and irrigation requirement although with a reduced yield (~62% of corn dry matter). 1 World Environmental and Water Resources Congress 2008 Ahupua'a © 2008 ASCE