Determining Critical Fall Height for Bermudagrass Grown on Sand and Native Soil Root Zones

Surface hardness is typically measured using a Clegg Impact Soil Tester (ASTM F355-D), but recent trends in sports turf are to use the F355-E missile as a potential alternative, because it may provide a more meaningful measurement. Forty traffic events were applied to ‘Tifway’ bermudagrass grown in an ASTM constructed sand root zone and a silt loam soil on the Center for Athletic Field Safety at the University of Tennessee. An F355-E was used to measure head injury criteria (HIC) for both root zones after every eight traffic events. Head injury criteria values were regressed to varying drop heights to calculate critical fall height (CFH) for both root zones. Critical fall height is the maximum height an athlete can fall from where the surface meets the impact attenuation performance criterium (1000 HIC) established by World Rugby for synthetic turf surfaces. Critical fall height for the ASTM constructed sand root zone was 2.3 m, while CFH for the silt loam soil was 2.0 m. The differences in CFH were due to soil compaction. After 40 traffic events, the average soil bulk density of the ASTM constructed sand root zone was 1.3 g/cm³, and the silt loam was 1.4 g/cm³. A 2.3 m CFH of the ASTM root zone occurred during the initial testing, before the loss of green turf cover. A 2.0 m CFH of the silt loam soil was calculated after 40 traffic events. Head injury criteria values for both root zones were significantly influenced as a result of traffic.