Investigating an Efficient Method to Determine Daily Light Integral Requirements of Various Warm Season Turfgrass Cultivars.

Determining daily light integral requirements (DLI) for various turfgrass systems has been an effective method for quantifying the amount of photosynthetically active radiation (PAR) necessary to maintain acceptable quality turfgrass in a controlled research setting. However, shaded areas in the landscape often vary in quantity and duration of available PAR to turfgrasses. The objective of this research is to determine and compare the DLI requirements of four warm season turfgrasses in areas of shade at local golf courses and in a standardized research setting to establish an efficient method for determining minimum DLI thresholds in the turfgrass landscape. Two zoysiagrass and two bermudagrass cultivars were evaluated for visual quality on golf courses in areas of shade and in a standardized research setting under continuous 22, 40, 60, and 90% shade. In areas where shade was suspected to be the cause of turfgrass decline at local golf courses, quantum sensors measuring PAR were installed along a line transect at different points where turfgrass had no visible turfgrass decline, was visibly declining, and where significant decline had already occurred to determine minimum DLI requirements of each cultivar. Quantum sensors were also installed under each shade treatment to establish DLI thresholds for each cultivar in the research setting. In the standardized research setting, the estimated minimum DLI requirements for 'Astro-DLM' bermudagrass, common bermudagrass, 'Cavalier' zoysiagrass, and 'Meyer' zoysiagrass were 22.8, 26.8, 18.5, and 27.8 mol m^-1 d^-1, respectively. In golf course sites, the estimated minimum DLI requirements for 'Astro-DLM' bermudagrass, common bermudagrass, 'Cavalier' zoysiagrass, and 'Meyer' zoysiagrass were 21.6, 11.5, 24.6, and 22.6 mol m^-1 d^-1, respectively. Critical DLI requirements observed in the golf course setting were not consistent to what was observed in the standardized research setting. Additional work is needed to accurately estimate minimum DLI requirements in the established turfgrass landscape.