Water Use of Perennial Grasses Under Limited to Full Irrigation in a Semi-Arid Climate.

Future ethanol production above the Energy Independence and Security Act/Renewable Fuels Standard (EISA/RFS) cap of 15 billion gallons will require new biofuel materials. The High Plains is a short grass prairie ecosystem that supports both cool season (CS) and warm season (WS) native species. The goal of this experiment was to determine the water use of several CS and WS grasses receiving differing irrigation allocations. Plots were established in 2009 on a Tripp fine sandy loam soil at Scottsbluff, NE and on a Keith silt loam near Sidney, NE. Soil water balance data were collected weekly during the growing seasons of 2010 through 2012 to determine yield-ET relationships and irrigation effects on seasonal distribution of forage production and phenological/physiological changes. Dry matter yields were maximized with 250 to 300 mm of irrigation for both CS and WS grasses during 2010 and 2011 which were normal to above average precipitation years.  In the 2012 drought year, irrigation above 400 mm was required to produce maximum yields of both CS and WS grasses.  Water use for the spring CS harvest showed good crop water productivity but the late summer and fall growth showed much lower crop water productivity.  The total seasonal water use for cool season grasses was near 660 mm ET for CS grasses and 560 mm for WS grasses in 2010 and 2011, but WS yields were also less.  Water use data for 2012 will be calculated after early fall harvest and will be presented.