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Alexander R. Kowalewski, Brian M. Schwartz, Austin L. Grimshaw, Dana G. Sullivan, and Jason B. Peake

Hybrid bermudagrasses (Cynodon dactylon × C. transvaalensis) typically have excellent wear tolerance when compared with other turfgrass species. This trait should be evaluated during variety development to reduce the risk of failure when new grasses are planted in areas with traffic stress. The objective of this research was to evaluate the wear tolerance of four hybrid bermudagrasses with differing morphological characteristics. Traffic was applied to the hybrid bermudagrass varieties ‘Tifway’, ‘TifSport’, and ‘TifTuf’, as well as an experimental hybrids (04-76) using a traffic simulator for 6 weeks. Leaf morphology (leaf width, length, and angle) and quantitative measure of density and color [normalized difference vegetation index ratio (NDVI), dark green color index (DGCI), and percent green turf color] were characterized before traffic, and then percent green turf color after 6 weeks of traffic was measured to estimate wear tolerance. ‘TifTuf’ hybrid bermudagrass provided the greatest wear tolerance, as well as the narrowest and shortest leaf lengths, greatest NDVI values and percent green color, and lowest DGCI before traffic. Conversely, 04-76 produced the poorest wear tolerance, as well as the widest and longest leaves, lowest NDVI values and percent green color, and highest DGCI values before traffic. Regression analysis determined that DGCI, leaf length, and leaf width were inversely, or negatively, correlated to wear tolerance, whereas percent green turf color before traffic was directly correlated to wear tolerance. For these hybrids, DGCI had the strongest correlation to increased wear tolerance.

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Kenneth B. Marcum and Charles L. Murdoch

Physiological responses to salinity and relative salt tolerance of six C4 turfgrasses were investigated. Grasses were grown in solution culture containing 1, 100, 200, 300, and 400 mm NaCl. Salinity tolerance was assessed according to reduction in relative shoot growth and turf quality with increased salinity. Manilagrass cv. Matrella (FC13521) (Zoysia matrella (L.) Merr.), seashore paspalum (Hawaii selection) (Paspalum vaginatum Swartz), and St. Augustinegrass (Hawaii selection) (Stenotaphrum secundatum Walt.) were tolerant, shoot growth being reduced 50% at ≈400 mm salinity. Bermudagrass cv. Tifway (Cynodon dactylon × C. transvaalensis Burtt-Davey) was intermediate in tolerance, shoot growth being reduced 50% at ≈270 mm salinity. Japanese lawngrass cv. Korean common (Zoysia japonica Steud) was salt-sensitive, while centipedegrass (common) (Eremochloa ophiuroides (Munro) Hack.) was very salt-sensitive, with total shoot mortality occurring at ≈230 and 170 mm salinity, respectively. Salinity tolerance was associated with exclusion of Na+ and Cl- from shoots, a process aided by leaf salt glands in manilagrass and bermudagrass. Shoot Na+ and Cl- levels were high at low (100 to 200 mm) salinity in centipedegrass and Japanese lawngrass resulting in leaf burn and shoot die-back. Levels of glycinebetaine and proline, proposed cytoplasmic compatible solutes, increased with increased salinity in the shoots of all grasses except centipedegrass, with tissue water levels reaching 107 and 96 mm at 400 mm salinity in bermudagrass and manilagrass, respectively. Glycinebetaine and proline may make a significant contribution to cytoplasmic osmotic adjustment under salinity in all grasses except centipedegrass.

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Ian R. Rodriguez, Grady L. Miller, and L.B. McCarty

For drainage, turfgrass is often established on sand-based soils, which are typically nutrient-deficient and require supplemental fertilization. The objective of this study was to determine the optimum N-P-K fertilizer ratio for establishing bermudagrass from sprigs in sand. `FloraDwarf' and `Tifdwarf' bermudagrasses [Cynodon dactylon (L.) Pers. × C. transvaalensis Burt-Davy] were sprigged on a United States Golf Association (USGA) green [85 sand: 15 peat (v/v)] in Aug. 1996 at the Univ. of Florida's Envirogreen in Gainesville, Fla. `TifEagle' bermudagrass was sprigged on a USGA green [85 sand: 15 peat (v/v)] and `Tifway' bermudagrass [C. dactylon (L.) Pers.] was sprigged on native soil at Clemson Univ. in Clemson, S.C. in May 1999. Treatments consisted of fertilizer ratios of 1N-0P-0.8K, 1N-0P-1.7K, 1N-0.4P-0.8K, 1N-0.9P-0.8K, and 1N-1.3P-0.8K applied based on a N rate of 49 kg·ha-1/week for 7 weeks. Growth differences were apparent among cultivars. A 1N-0P-0.8K or 1N-0P-1.7K ratio is insufficient for optimum growth of bermudagrass during establishment, even when planted on a soil high in P. Increased coverage rate with additional P was optimized at a ratio of 1N-0.4P at all four sites. Increased coverage with P was greatest on the sand-based greens, probably due to the very low initial P levels of the soils. On two of the sand-based greens, P in excess of a 1N-0.4P ratio decreased coverage rate.

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Yiwei Jiang and Robert N. Carrow

Canopy reflectance has the potential to determine turfgrass shoot status under drought stress conditions. The objective of this study was to describe the relationship of turf quality and leaf firing versus narrow-band canopy spectral reflectance within 400 to 1100 nm for different turfgrass species and cultivars under drought stress. Sods of four bermudagrasses (Cynodon dactylon L. × C. transvaalensis), three seashore paspalums (Paspalum vaginatum Swartz), zoysiagrass (Zoysia japonica), and st. augustinegrass (Stenotaphrum secundatum), and three seeded tall fescues (Festuca arundinacea) were used. Turf quality decreased 12% to 27% and leaf firing increased 12% to 55% in 12 grasses in response to drought stress imposed over three dry-down cycles. The peak correlations occurred at 673 to 693 nm and 667 to 687 nm for turf quality and leaf firing in bermudagrasses, respectively. All three tall fescues had the strongest correlation at 671 nm for both turf quality and leaf firing. The highest correlations in the near-infrared at 750, 775, or 870 nm were found in three seashore paspalums, while at 687 to 693 nm in Zoysiagrass and st. augustinegrass. Although all grasses exhibited some correlations between canopy reflectance and turf quality or leaf firing, significant correlation coefficients (r) were only observed in five grasses. Multiple linear regression models based on selected wavelengths for turf quality and leaf firing were observed for 7 (turf quality) and 9 (leaf firing) grasses. Wavelengths in the photosynthetic region at 658 to 700 nm or/and near-infrared from 700 to 800 nm predominated in models of most grasses. Turf quality and leaf firing could be well predicted in tall fescue by using models, evidenced by a coefficient of determination (R 2) above 0.50. The results indicated that correlations of canopy reflectance versus turf quality and leaf firing varied with turfgrass species and cultivars, and the photosynthetic regions specifically from 664 to 687 nm were relatively important in determining turf quality and leaf firing in selected bermudagrass, tall fescue, zoysiagrass and st. augustinegrass under drought stress.

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Jason J. Goldman, Wayne W. Hanna, and Peggy Ozias-Akins

`TifEagle' (2n = 3x = 27) hybrid bermudagrass [Cynodon dactylon (L.) Pers. (2n = 4x = 36) × Cynodon transvaalensis Burtt-Davy (2n = 2x = 18)] is an ultradwarf cultivar for greens, and `TifSport' (2n = 3x = 27) is a more versatile hybrid used on fairways, athletic fields, and lawns. To develope a transformation system and determine if somaclonal variation was present in regenerated plants, both cultivars were tested for their ability to produce embryogenic callus from which plants could be regenerated. Sliced nodes of both cultivars and immature inflorescences from `TifSport' were used as the explant sources. Cultures were initiated on Murashige and Skoog medium supplemented with 6.79 μm 2,4-D and 0.044 μm BA (`TifSport' and `TifEagle') or 6.79 μm 2,4-D plus 200 mg.L-1 casein hydrolysate (`TifSport'). In total, 51 plants were regenerated from callus of a single node of `TifEagle'. Nodes from `TifSport' did not produce embryogenic callus. In total, 29 plants were regenerated from callus of `TifSport' produced from immature inflorescences. These plants were grown in the field for at least one season, and 5-cm-diameter plugs were harvested, repotted in a greenhouse, and allowed to reestablish. Data on canopy height, leaf width, leaf length, and number of stolons were collected. Seven `TifEagle'-derived entries (14%) were not significantly different (α = 0.05) from `TifEagle' harvested from the breeder plot in Tifton, Ga., for all measured traits, and 41%, 24%, and 22% differed by one, two, or three measurements, respectively. Flow cytometry indicated that 33% (13 plants) of the `TifEagle' regenerants were hexaploid (2n = 6x = 54) and the rest remained triploid. One `TifSport' regenerant was significantly different (α = 0.05) for plant height.

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Donald M. Vietor, Ronnie W. Schnell, Tony L. Provin, Richard H. White, and Clyde L. Munster

Incorporation or top-dressing of composted biosolids (CB) can enhance turfgrass establishment and sod properties at harvest, but soil phosphorus (P) and nitrogen must be managed to protect water quality. Alum treatment of CB could reduce soluble P concentrations in amended soil and limit runoff loss of P. The objective was to evaluate CB and Alum effects on turfgrass coverage of soil and runoff losses during ‘Tifway’ bermudagrass [Cynodon dactylon (L.) Pers. var. dactylon × C. transvaalensis Burtt-Davey] establishment from sprigs or transplanted sod. Three replications of eight treatments comprised a complete randomized design. Four treatments were composed of ‘Tifway’ sprigged in soil with and without incorporation of CB and Alum. Four remaining treatments were sods harvested from ‘Tifway’ grown with and without top-dressed CB that were transplanted with and without a surface spray of Alum. Surface coverage of ‘Tifway’ sprigged in soil mixed with inorganic fertilizer or CB was comparable to transplanted sod 25 days after planting. In contrast, Alum incorporation acidulated soil, slowed coverage rates of sprigged ‘Tifway’, and increased NH4-N runoff loss during early establishment in treatments without CB. Incorporation of Alum with CB or inorganic fertilizer in soil before sprigging reduced soil water-extractable P (WEP) more than 38% and reduced runoff loss of soluble reactive P (SRP) in three of four establishment treatments. Although SRP runoff loss from CB-amended sod was greatest among treatments, the Alum spray minimized SRP loss after transplanting. Alum effectively reduced runoff loss of SRP from CB, soil, and turfgrass sources during establishment from sprigs or sod. Additional field research is needed, but incorporated or surface sprays of Alum offer a potential new practice for mitigating runoff loss of SRP from establishing turfgrass.

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Jordan M. Craft, Christian M. Baldwin, Wayne H. Philley, James D. McCurdy, Barry R. Stewart, Maria Tomaso-Peterson, and Eugene K. Blythe

Traditional hollow-tine (HT) aerification programs can cause substantial damage to the putting green surface resulting in prolonged recovery. Despite the growing interest in new and alternative aerification technology, there is a lack of information in the literature comparing new or alternative technology with traditional methods on ultradwarf bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis (Burtt-Davy)] putting greens. Therefore, the objective of this research was to determine the best combination of dry-injection (DI) cultivation technology with modified traditional HT aerification programs to achieve minimal surface disruption without a compromise in soil physical properties. Research was conducted at the Mississippi State University golf course practice putting green from 1 June to 31 Aug. 2014 and 2015. Treatments included two HT sizes (0.6 and 1.3 cm diameter), various DI cultivation frequencies applied with a DryJect 4800, and a noncultivated control. The HT 1.3 cm diameter tine size had 76% greater water infiltration (7.6 cm depth) compared with the DI + HT 0.6 cm diameter tine size treatment. However, DI + HT 0.6 cm diameter tine size had greater water infiltration at the 10.1 cm depth than the noncultivated control. Results suggest a need for an annual HT aerification event due to reduced water infiltration and increased volumetric water content (VWC) in the noncultivated control treatment. It can be concluded that DI would be best used in combination with HT 1.3 or 0.6 cm diameter tine sizes to improve soil physical properties; however, the DI + HT 0.6 cm diameter tine size treatment resulted in minimum surface disruption while still improving soil physical properties compared with the noncultivated control.

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Maria P. Fuentealba, Jing Zhang, Kevin E. Kenworthy, John E. Erickson, Jason Kruse, and Laurie E. Trenholm

Irrigation for commercial and residential turf is becoming limiting, and water scarcity is one of the long-term challenges facing the turfgrass industry. Potential root development and profile characteristics of turfgrass provide important information regarding their drought resistance mechanisms and developing drought-resistant cultivars. The objective of this study was to determine the potential root development and root profile characteristics of two bermudagrass species and two zoysiagrass species using experimental lines and commercial cultivars. The species evaluated in the study were: African bermudagrass (Cynodon transvaalensis Burtt-Davy), common bermudagrass (CB) [Cynodon dactylon (L.) Pers. var. dactylon], Zoysia japonica (ZJ) (Steud), and Zoysia matrella (ZM) L. Plants were grown outdoors in clear acrylic tubes encased in poly vinyl chloride (PVC) sleeves. The experimental design was randomized complete block design with four replications. Rates of root depth development (RRDD) during the first 30 days were obtained. Root length density (RLD) in four different horizons (0–30, 30–60, 60–90, and 90–120 cm) was determined 60 days after planting. Specific root length (SRL, m·g−1) was also calculated dividing total root length by total root dry weight (RDW). The root depth in four turfgrass species increased linearly during the first 30 days after planting. Common bermudagrass (CB) had high RRDD and uniform RLD in different horizons, while ZM accumulated the majority of its roots in the upper 30 cm. Z. matrella had higher RLD than CB in the upper 30 cm. African bermudagrass had higher SRL than CB. There was limited variation within the two African bermudagrass genotypes studied except at the lowest horizon (90–120 cm). Two genotypes in CB and ZJ, respectively, including ‘UF182’ (ZJ), which consistently ranked in the top statistical group for RRDD, and RLD for every horizon, and ‘UFCD347’ (CB) demonstrated greater RLDs in the lower horizons in comparison with the commercial cultivars.

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Brian J. Tucker, Lambert B. McCarty, Haibo Liu, Christina E. Wells, and James R. Rieck

As golfers demand higher quality golf green putting surfaces, researchers continue to seek improved turfgrass cultivars. One such improved cultivar is `TifEagle' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy], which is an improvement over traditional bermudagrass cultivars such as `Tifgreen' and `Tifdwarf' due to its ability to tolerate mowing heights of ≤3.2 mm for extended periods. One observed disadvantage of `TifEagle' is its lack of a deep, dense root system compared to previous bermudagrass cultivars. This field study measured mowing height, N rate, and biostimulant product effects on `TifEagle' rooting. Three mowing heights (3.2, 4.0, and 4.8 mm), three N rates (12, 24, and 48 kg N/ha/week), and two cytokinin-containing commercial biostimulant products (BIO1 and BIO2) were examined. Plant responses measured were root length density (RLD), root surface area (RSA), thatch layer depth (TLD), and turf quality (TQ). Increasing mowing height from 3.2 to 4.0 mm increased RLD by >11%, RSA by >11%, and TQ by >17%. Increasing N rates from 12 to 24 kg N ha-1 week-1 increased RLD by >17%, RSA by >26% and TQ by >16%. No effect on RLD was observed after the first year of biostimulant use, however, after the second year, BIO1 increased RLD by >11% when applied with the lowest rate of N (12 kg N/ha/week). Higher mowing heights (4.8 and 4.0 mm) increased TLD >6% compared to the lowest mowing height (3.2 mm), and higher N rates (48 and 24 kg N/ha/week) increased TLD >3% compared to the lowest N rate (12 kg N/ha/week). Overall, a mowing heights ≥4.0 mm, N rates ≥24 kg N/ha/week, and long-term use of a cytokinins-containing biostimulant had a positive effect on `TifEagle' rooting.

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Glenn R. Wehtje, Joey N. Shaw, Robert H. Walker, and Walker Williams

Various inorganic soil amendments have been promoted as a means of improving the chemical and physical properties of certain soils. To test this hypothesis, a marginally productive soil was supplemented with 20%, 40%, 60%, and 80% (v/v) of either selected inorganic amendments or sand. Amendments consisted of commercially available diatomaceous earth, calcined clay, zeolite, and crystalline SiO2. The soil material was extracted from the argillic horizon of a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults). Ability of these soil-amendment mixtures to promote `Tifway' bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt Davy] growth was evaluated under greenhouse conditions, and contrasted to that obtained in nonamended soil. Selected chemical and physical properties that are pertinent to plant growth were also evaluated. The experiment, which was conducted 3×, began with a §60-day period in which both water and nutrients were optimum. This was followed by a 30-day drought. During optimum water and nutrients, no soil-amendment treatment(s) consistently resulted in superior bermudagrass growth compared to soil alone. However, <2% of the bermudagrass tissue that was produced during the drought became green and succulent with the resumption of irrigation in nonamended soil. This percentage was exceeded by all treatments that contained either ≥60% diatomaceous earth (Axis), or ≥40% calcined clay (Profile); and by 100% zeolite (Clinolite) and 100% silica (Green's Choice). Drought-sustaining ability of soil-amendment mixtures was significantly (P < 0.05) correlated with water-holding ability, soil strength, bulk density, and oxygen diffusion rate, but not correlated with either pH or cation exchange capacity (CEC). While certain inorganic amendments did improve the drought-sustaining ability of soil, the amount required was generally ≥40%.