I pulled this from the
University of Tennessee's PDF about Irrigation.
How Much Water?
Turfgrass water use can be estimated using local weather-pan evaporation and crop coefficient information (Kopec, D. M. and C. Throssell. 1995. Irrigation Scheduling Techniques. Golf Course Superintendents ssociation of America Seminar Manual).
Turfgrass ET = crop coefficient x pan evaporation
The crop coefficient, with a value most often less than 1, varies among turfgrasses and geographic locations.
If, for example, the pan evaporation rate is a reported 1.9 inches / week and the tall fescue crop coefficient is an estimated 0.8, the weekly water requirement of a tall fescue turf is 1.9 inches x 0.8 or 1.52 inches. One and one-half inches (41,000 gallons per acre) of irrigation or rainfall are required to replace the amount of water lost through evapotranspiration during the week.
So, if an acre of fescue takes ~41,000 gallons of water to replace the amount of moisture lost due to evapotranspiration per week, that's more than the (roughly) 24.5 thousand gallons corn evapotranspirates per week (3,500 gallons per day x 7 days per week).
I would not have suspected that. I would have suspected that corn, being taller and having more surface area, would transpirate more.