Determining Base Temperatures for Warm- and Cool-Season Turfgrass Species.

Base temperature has been described in many ways, but it is essentially the point at which a plant is physiologically inactive.  Currently, in the turfgrass industry, the base temperature for recommended growing degree day models have been arbitrarily assigned.  Therefore, the objective of this research was to determine and compare the base temperatures of industry standards vs. newly available cultivars of warm- and cool-season species.  This study was conducted in SPAR (Soil-Plant-Atmosphere-Research) units.  Each SPAR chamber consists of a steel soil bin (1 m deep by 2 m long by 0.5 m wide) and a 1.27 cm thick Plexiglas chamber (2.5 m tall by 2.0 m long by 1.5 m wide) to accommodate root and aerial plant parts. The Plexiglas transmits 97% of the visible solar radiation to pass without spectral variability in absorption (wavelength 400–700 nm).  Turfgrass species included bermudagrass, zoysiagrass, seashore paspalum, creeping bentgrass, Kentucky bluegrass, perennial ryegrass, and tall fescue.  Warm-season species were subjected to a day/night temperature (^oC) regime of 20/12, 25/17, 30/22, 35/27, and 40/32.  Cultivars included TifEagle, MSB-285, Tifway, and Latitude 36 bermudagrass, and Meyer zoysiagrass.  Cool-season species were subjected to a day/night temperature (^oC) regime of 13/5, 18/10, 23/15, 28/20, and 33/25.  Cultivars included Penncross, L-93, and Penn-A4 creeping bentgrass, Midnight Kentucky bluegrass, Fiesta 4 perennial ryegrass, and Falcon V tall fescue.  Shoot biomass was collected every three days and root biomass was harvested at the end of the study.