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Evaluation of turfgrass salt tolerance is a basic strategy for selecting grasses that can be grown in areas with salt-affected water or soils. Our objectives were to determine the relative salinity tolerances of 32 grasses and to evaluate potential shoot-based criteria for assessing salinity tolerance. Shoot growth responses to salinity of 28 seashore paspalums (Paspalum vaginatum Swartz) and four bermudagrass [Cynodon dactylon (L.) × C. transvalensis Burtt-Davy] cultivars were investigated under solution/sand culture in a greenhouse. Turfgrasses were grown in a sea-salt amended nutrient solution. Salinity ranges were 1.1 to 41.1 dS·m^-1 based on electrical conductivity of the solution (EC_w). Selection criteria to assess salt tolerance were absolute growth at 1.1 (EC_w0), 24.8 (EC_w24), 33.1 (EC_w32), and 41.1 dS·m^-1 (EC_w40); threshold EC_w; EC_w for 25% and 50% growth reduction based on EC_w0 growth; and leaf firing (LF) at EC_w0 and EC_w40 (LF0 and LF40, respectively). Significant variations among 32 entries were observed for all shoot responses except threshold EC_w. Ranges of values for shoot parameters were: inherent growth at EC_w0 = 0.10 to 0.98 g dry weight (10-fold difference); growth at 24.8 dS·m^-1 = 0.11 to 0.64 g; growth at 33.1 dS·m^-1 = 0.09 to 0.54 g; growth at 41.4 dS·m^-1 = 0.06 to 0.35 g; threshold EC_W = 3.9 to 12.3 dS·m^-1; EC_w25 % = 14 to 38 dS·m^-1; EC_w50% = 22 to 43 dS·m^-1; and LF40 = 7% to 41%. Results in this study indicated substantial genetic-based variation in salt tolerance within seashore paspalums. When evaluation of salt tolerance based on shoot responses is attempted at wide salinity levels up to 40 dS·m^-1, all seven criteria exhibiting a significant F test can be used. Five entries (SI 92, SI 93-1, SI 91, SI 93-2, SI 89) were ranked in the top statistical grouping for all seven-growth parameters, followed by SI 90 ranked in six out of seven, and three paspalums (SI 94-1, `Sea Isle 1', and `Taliaferro') were ranked in five out of seven categories.

Seashore paspalum (Paspalum vaginatum Swartz) is a warm season turfgrass that survives in sand dunes along coastal sites and around brackish ponds or estuaries. The first exposure to salt stress normally occurs in the rhizosphere for persistent turfgrass. Information on diversity in salinity tolerance of seashore paspalums is limited. From Apr. to Oct. 1997, eight seashore paspalum ecotypes (SI 94-1, SI 92, SI 94-2, `Sea Isle 1', `Excalibur', `Sea Isle 2000', `Salam', `Adalayd') and four bermudagrass (Cynodon dactylon × C. transvaalensis Butt-Davy) cultivars (`Tifgreen', `Tifway', `TifSport', `TifEagle') were investigated for levels of salinity tolerance based on root and verdure responses in nutrient/sand culture under greenhouse conditions. Different salt levels (1.1 to 41.1 dS·m^-1) were created with sea salt. Measurements were taken for absolute growth at 1.1 (EC_w0; electrical conductivity of water), 24.8 (EC_w24), 33.1 (EC_w 32), and 41.1 dS·m^-1 (EC_w40), threshold EC_w, and EC_w for 25% growth reduction from EC_w0 growth (EC_w25%). Varying levels of salinity tolerance among the 12 entries were observed based on root, verdure, and total plant yield. Ranges of root characteristics were inherent growth (EC_w0) = 0.20 to 0.61 g dry weight (DW); growth at EC_w24 = 0.11 to 0.47 g; growth at EC_w32 = 0.13 to 0.50 g; growth at EC_w40 = 0.13 to 0.50 g; threshold EC_w = 3.1 to 9.9 dS·m^-1; and EC_w25% = 23 to 39 dS·m^-1. For verdure, ranges were inherent growth at EC_w0 = 0.40 to 1.07 g DW; growth at EC_w40 = 0.31 to 0.84 g; and ratio of yields at EC_w40 to EC_w0 = 0.54 to 1.03. Ranges for total growth were inherent growth at EC_w0 = 0.72 to 2.66 g DW; growth at EC_w24 = 0.55 to 2.23 g; growth at EC_w32 = 0.54 to 2.08 g; growth at EC_w40 = 0.52 to 1.66 g; threshold EC_w = 2.3 to 12.8 dS·m^-1; and EC_w25% = 16 to 38 dS·m^-1. Significant salinity tolerance differences existed among seashore paspalums and bermudagrasses as demonstrated by root, verdure, and total growth measurements. When grasses were ranked across all criteria exhibiting a significant F test based on root, verdure, and total growth, the most tolerant ecotypes were SI 94-1 and SI 92. Salinity tolerance of bermudagrass cultivars was relatively lower than SI 94-1 and SI 92. For assessing salinity tolerance, minimum evaluation criteria must include absolute growth at EC_w0 and EC_w 40 dS·m^-1 for halophytes, but using all significant parameters of root and total yield is recommended for comprehensive evaluation.

Traffic stresses often cause a decline in turfgrass quality. Analysis of spectral reflectance is valuable for assessing turfgrass canopy status. The objectives of this study were to determine correlations of narrow band canopy reflectance and selected reflectance indices with canopy temperature and turf quality for seashore paspalum exposed to wear and wear plus soil compaction traffic stresses, and to evaluate the effects of the first derivative of reflectance and degree of data smoothing (spectral manipulations) on such correlations. `Sea Isle 1' seashore paspalum (Paspalum vaginatum Swartz) was established on a simulated sports field during 1999 and used for this study. Compared to original reflectance, the first derivative of reflectance increased the correlation coefficient (r) of certain wavelengths with canopy temperature and turf quality under both traffic stresses. Among 217 wavelengths tested between 400 and 1100 nm, the peak correlations of the first derivative of reflectance occurred at 661 nm and 664 nm for both canopy temperature and turf quality under wear stress, respectively, while the highest correlations were found at 667 nm and 820 to 869 nm for both variables under wear plus soil compaction. Collectively, the first derivative of reflectance at 667 nm was the optimum position to determine correlation with canopy temperature (r > 0.62) and turf quality (r < -0.72) under both traffic stresses. All correlations were not sensitive to degrees of smoothing of reflectance from 400 to 1100 nm. A ratio of R936/R661 (IR/R, Infrared/red) and R693/759 (stress index) had the strongest correlations with canopy temperature for wear (r = -0.63) and wear plus soil compaction (r = 0.66), respectively; and a ratio of R693/R759 had the strongest correlation with turf quality for both wear (r = -0.89) and wear plus soil compaction (r = -0.82). The results suggested that the first derivative of reflectance could be used to estimate any single wavelength simultaneously correlated with multiple turf canopy variables such as turf quality and canopy temperature, and that the stress index (R693/R759) was also a good indicator of canopy stress status.

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 treatments 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. Re sults 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.