HORTSCIENCE, V OL. 38(6), OCTOBER 2003 1218 T URF MANAGEMENT HORTSCIENCE 38(6):1218–1222. 2003. Received for publication 8 July 2002. Accepted for publication 4 Feb. 2003. 1 Postdoctoral Research Associate. E-mail: yjiang@ griffin.uga.edu 2 Professor. Effects of Morning and Afternoon Shade in Combination with Traffic Stress on Seashore Paspalum Yiwei Jiang 1 , Robert N. Carrow 2 , and Ronny R. Duncan 2 Department of Crop and Soil Sciences, Georgia Experiment Station, University of Georgia, Griffin, GA 30223-1797 Additional index words. Paspalum vaginatum, turfgrass, wear, wear plus soil compaction Abstract. Turfgrasses are often exposed to different shade environments in conjunction with traffic stresses (wear and/or compaction) in athletic fields within stadiums. The objective of this study was to assess the effects of morning shade (AMS) and afternoon shade (PMS) alone and in combination with wear and wear plus soil compaction on ‘Sea Isle 1 seashore paspalum (Paspalum vaginatum Swartz). The study was conducted using two consecutive field trials under sports field conditions from 9 July to 10 Sept. 2001 at the Univ. of Georgia Experiment Station at Griffin. “T” shaped structures constructed of plywood on the sports field were used to provide 90% morning and afternoon shade, respectively, and were in place for 1 year prior to data accumulation. A wear device and a studded roller device simulated turfgrass wear (WD) and wear plus soil compaction (WSC), respectively, to the shaded plots. Only minor differences in turf color, density, or canopy spectral reflectance were found between AMS and PMS under no-traffic treat- ments in both trials. Grasses under WD generally recovered faster than those exposed to WSC across all light levels, including full sunlight (FL), AMS, and PMS. AMS combined with WD treatment had an average 9% higher rating of color, 11% higher density, and 28% less tissue injury than that of PMS with WD at 7 days after traffic treatment (DAT). Compared to PMS with WSC treatment at 7 DAT, AMS with WSC had 12% higher rating of color, 9% higher density, and 4% less tissue injury. AMS with WD treatment exhibited 11% higher normalized difference vegetation index (NDVI), 4% higher canopy water band index (CWBI), and 13% lower stress index than that of PMS with WD at 7 DAT. AMS with WSC, relative to PMS with WSC, demonstrated 8% higher NDVI, 3% higher CWBI, and 8% lower stress index at 7 DAT. Results indicated that AMS (i.e., afternoon sunlight) had less detrimental influences than PMS (i.e., morning sunlight) on turfgrass performance after it was subjected to wear stress or wear plus soil compaction. primary stresses on sports fields. It is vital to evaluate turfgrass tolerance to traffic stress due to high use demands placed on recreational grasses. Traffic generally consists of turfgrass wear stress and soil compaction (Carrow and Petrovic, 1992). Several independent studies have been reported on wear tolerance (Can- away et al., 1981; Carrow and Johnson, 1996; Shearman and Beard, 1975; Trenholm et al., 1999b) and soil compaction in turfgrass (Car- row, 1980). Wear and soil compaction stresses usually both occur on athletic fields and result in more severe injury to turfgrass; however, few studies have investigated these two fac- tors simultaneously. More recently, turfgrass traffic simulators have been designed primarily to apply wear only or wear plus soil compac- tion to turfgrass and to evaluate turfgrass performance, including seashore paspalum and bermudagrass (Cynodon sp.) (Carrow et al., 2001), Kentucky bluegrass (Poa pratensis L.) (Shearman et al., 2001), and bermudagrass (Cynodon dactylon L.) with cool-season turf- grass mixtures (Dunn et al., 1994). Turfgrass injury could be greater under the combined stresses of shade and traffic in comparison to either stress alone. The addi- tive effects of these stresses make turfgrass management more difficult, particularly for sports fields. Turfgrass grown under reduced irradiance is easily damaged from traffic (Cock- erham et al., 1994) because shade environments alter turfgrass morphological, physiological, and anatomical responses, causing excessive shoot elongation and reduced shoot density (Beard, 1997). Under low irradiance, appli- cation of trinexapac-ethyl [4-(cyclopropyl- -hydroxy-methylene)-3,5-dioxo-cyclohex- ane-carboxylic acid ethyl ester] enhanced turf quality by decreasing traf fic effects (Stier and Rogers, 2001). However, the combined effects of morning and afternoon shade with different traffic stresses on turfgrass quality and recover- ability from injury have not been examined. Influences of shade with wear or wear plus soil compaction will have an impact on successful management of sports fields. Seashore paspalum is an environmentally compatible warm-season turfgrass that has be- come adapted to a wide range of environmental conditions (Duncan, 1999). Wear tolerance of different seashore paspalum ecotypes has also been evaluated (Trenholm et al., 1999b), but not under shade conditions. ‘Sea Isle 1 seashore paspalum is adapted to sports-related uses, and knowledge of temporal shade combined with traffic stresses on this grass would benefit sports turf management. Therefore, the objective of this study was to assess the effects of morning and afternoon shade alone and in combination with wear and wear plus soil compaction on ‘Sea Isle 1 seashore paspalum. Materials and Methods Plant growth. This research consisted of two studies conducted at the Univ. of Georgia Experiment Station in Griffin. Study 1 was conducted from 9 July to 30 July 2001, and Study 2 was conducted from 20 Aug. to 10 Sept. 2001. ‘Sea Isle 1 seashore paspalum was fully established on a simulated sports field since 1999 and was used in this experiment. The soil profile was an Appling sandy clay loam (clayey, kaolinitic, thermic Typic Kan- hapludult) capped with a 10-cm mixture of 90% sand and 10% peat. The plots were mowed to 1.7 cm three times weekly using a reel mower with clippings removed. The grasses were ir- rigated to 2.4 cm weekly. Fertilization applied to the site in terms of N kg·ha –1 in 2001 was: 5.8 N on 13 Apr. (12N–24P–14K); 16 N on 30 Apr. and 18 May (34N–0P–0K); 6.6 N on 23 May (Milorganite, 6.75N–2.65P–0.46K, Milwaukee Metropolitan Sewerage District, Milwaukee); 9.8 N on 25 May, 1 June, and 10 July (GreenEdge, 10N–0P–18K, GreenTech- nologies, Gainesville, Fla.); 7.3 N on 25 July (15N–0P–15K). Shade environment. The shade environment was created using a “T” shaped structure con- structed of plywood on the simulated sports field. Each of the three structures was 4.9 m long, 1.4 m high, had a 6.0-m 2 area covered horizontally with plywood on the top, and was oriented north to south. The vertical plywood under the top cover could be moved out of the structure to allow operation of the traffic devices and mowers. The “T” structure could provide an area of 15 m 2 AMS and 15 m 2 PMS from July to September. Plots of 3.2 m 2 within the 15-m 2 shade area, receiving up to 5 h AMS Turfgrasses are often exposed to shade environments, and shade stress is one of the major problems limiting turfgrass growth. Physiological and growth responses associated with shade tolerance have been investigated in a number of turfgrass species (Bell and Danneberger, 1999; Qian and Engelke, 1999; Stier and Rogers, 2001; Van Huylenbroeck and Van Blockstaele, 2001). In many recreational sites, light is available for turfgrass only during morning or afternoon hours because of restricted light intensities from trees or stadium structures. However, no variations in growth of creeping bentgrass (Agrostis palustris Huds.) was found between morning and afternoon shade or between plots in 80% or 100% shade under shadecloth (Bell and Dan- neberger, 1999). Their results also showed that turf color and density did not vary between creeping bentgrass exposed to morning shade, afternoon shade, or full sunlight, but continu- ous shade caused severe decline in turfgrass growth and development. Along with shade, traffic is another fac- tor that is often considered to be one of the