The National Turfgrass Evaluation Program (NTEP) conducts trials throughout the United States on turfgrass adaptation. This trial was established in September 2010 as a part of the NTEP program. It contains 88 perennial ryegrass cultivars.
Iowa State University
Christians, Nick E.; Strey, Daniel J.; and Alderman, Evan J., "Perennial Ryegrass Cultivar Study" (2014). Iowa State Research Farm Progress Reports. 2003.