Daily Light Integral Requirements for Twelve Warm-Season Turfgrasses.

When required inputs of turfgrass growth and development (water, temperature, nutrition) are met, light interception becomes a growth-limiting factor.  Most warm-season turfgrasses grown in the southeastern United States require full sun to reach light saturation – the point at which the plant has achieved photosynthetic capacity.  Shade or reduced light conditions, have been estimated to affect 20-25% of all managed turfgrass causing sub-optimal growing conditions for periods of time.  Daily light integral (mol m^-2 d^-1) is a measure that quantifies total light intensity accumulated during the course of a day.  Because incoming solar radiation changes periodically due to sun movement and atmospheric screening, DLI may be a better parameter to evaluate available light in a given environment.  Greenhouse trials were conducted to evaluate minimum DLI requirements to maintain acceptable turfgrass quality for twelve warm-season turfgrasses.  Four shade treatments (0, 30, 60, and 90% shade) were used.  All treatments were performed in a setting that simulated winter temperatures in south Florida (23⁰C average temperature).  Minimum DLI levels required to maintain acceptable turfgrass quality ranged from 11.5 to 6.3 mol m^-2 d^-1.  Species/cultivars ranked from highest to lowest DLI requirements are: ‘Tifway’ and ‘TifGrand’ bermudagrass (Cynodon dactylon X C. transvaalensis), ‘Floratam’  St. Augustinegrass (Stenotaphrum secondatum), ‘TifBlair’ centipedegrass (Eremochloa ophiuroides), ‘Captiva’ St. Augustinegrass (S. secondatum),  ‘Celebration’ bermudagrass (C. dactylon), ‘Palisades’ zoysiagrass (Zoysia japonica), ‘SeaDwarf’ seashore paspalum (Paspalum vaginatum),  ‘PristineFlora’ and ‘Diamond’ zoysiagrass (Z. matrella), ‘JaMur’ zoysiagrass (Z. japonica), and  ‘Argentine’ bahiagrass (Paspalum notatum).  By monitoring DLI requirements in reduced light environments over time, these levels could be used to improve turfgrass selection for a particular site.