BASAL GROWTH TEMPERATURES AND GROWTH-RATE CONSTANTS OF WARM-SEASON TURFGRASS SPECIES

Degree-day modeling applications in turfgrass management have recently seen increased interest. The predictive capacity of any degree-day mo del is dependent on an accurate determination of the basal growth temp eratures for the species under consideration. The objective of this st udy was to determine basal growth temperatures and growth rate constan ts for eight warm season turfgrasses (five species). Sprigs from bermu dagrass [Cynodon dactylon (L.) Pers. cv. Arizona Common and C. dactylo n lc C., transvaalensis Burtt Davey cv. Midiron], buffalograss [Buchlo e dactyloides (Nutt.) Engelm. cv. Kansas Common and Texoka], zoysiagra ss (Zoysia japonica Steudel cv. Meyer), St. Augustinegrass [Stenotaphr um secundatum (Walter) Kuntze cv. Raleigh and Floratam], and centipede grass [Eremochloa ophiuroides (Munro) Hackel, cv. Common] were grown a t temperatures ranging from 5 to 30 degrees C in a controlled environm ent chamber under 14-h photoperiods. Chamber temperature was decreased in a step-wise fashion to the next temperature after two leaves were fully expanded. Leaf growth rates at each temperature were calculated and expressed as millimeters per day. Base temperature and growth rate constants for each turfgrass were calculated with segmented nonlinear regression analysis. Base temperatures for the eight tested cultivars ranged from 0 to 13 degrees C. Interspecific and intraspecific differ ences for basal growth temperature were found, indicating that degree- day model application accuracy is dependent on proper determination of target species and cultivar basal growth temperature.