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a Dep. of Horticulture, Univ. of Wisconsin, Madison, WI 53706-1590
b III, Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824-1325
Corresponding author (jstier{at}facstaff.wisc.edu)
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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-hydroxy-methylene)-3,5-dioxo-cyclohexane-carboxylic acid ethyl ester]} (TE), foliar iron, and simulated athletic traffic inside a covered stadium simulator facility. Analysis of variance showed supina bluegrass was more responsive to TE than Kentucky bluegrass. Trinexapac-ethyl reduced supina bluegrass clipping yields approximately 60%; Kentucky bluegrass yields were reduced by 20% or less. In non-trafficked turf, TE increased supina bluegrass tillers by 50% and leaves by 33% but did not change tillering and leaf number of Kentucky bluegrass. Without traffic, TE-treated supina bluegrass provided an acceptable turf at 10 to 15% solar irradiance for at least 4 to 6 mo, while Kentucky bluegrass and untreated supina bluegrass became unacceptable within 2 to 4 mo. Under traffic, TE-treated supina bluegrass provided acceptable turf for up to 5 wk, while Kentucky bluegrass did not provide acceptable turf for more than 2 to 4 wk. Trinexapac-ethyl enhanced supina bluegrass color and increased chlorophyll levels of both species. Foliar applications of iron had negligible effects on all of the parameters evaluated. Supina bluegrass is a useful turf for reduced irradiance situations but requires more than 5 mol m-2 d-1 to sustain traffic for periods longer than 5 wk.
Abbreviations: CSSF, Covered Stadium Simulator Facility • GA, gibberellic acid • LAI, leaf area index • PAR, photosynthetically active radiation • PGR, plant growth regulator • TE, trinexapac-ethyl
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Supina bluegrass is a cool-season stoloniferous turfgrass capable of forming a dense turf at low mowing heights suitable for athletic and golf course turf (Berner, 1980; Pietsch, 1989). The stolons are significantly more robust and have shorter internodes compared with rough bluegrass. Supina bluegrass is endemic to moist, shaded sites, often subject to high traffic (e.g., human and cattle paths) in the sub-alpine regions of the European Alps (Pietsch, 1989). In Germany, supina bluegrass often encroaches and fills in high-wear areas on sports fields (Köck and Walch, 1977). Berner (1980) demonstrated good wear tolerance of supina bluegrass due in part to a rapid recuperative rate.
The ability to persist in moist, shaded, high-traffic environments makes supina bluegrass a suitable candidate for use as a turf for shaded golf course or athletic field situations (e.g., partially or wholly covered stadia). Limitations for the use of supina bluegrass include light green leaf color and undefined management regimes (Berner, 1980). Leaf color is an adjustable parameter that could increase the acceptability of supina bluegrass if a darker color can be easily obtained.
Flurprimidol {-(1-methylethyl)--[4-(trifluoromethoxy)phenyl]-5-pyrimidine-methanol}, a plant growth regulator that suppresses gibberellic acid (GA) biosynthesis, can significantly enhance turf color and quality in reduced irradiance (<30% full sunlight) (Stier et al., 1999). Trinexapac-ethyl (TE), the most recently labeled GA inhibitor for turf, reduced clipping yields and enhanced creeping bentgrass quality under normal field conditions (Calhoun and Branham, 1995). Its effects on cool-season turf in reduced irradiance have not been reported.
Turf color decreases as chlorophyll content is reduced under extremely low irradiances (Beard, 1973). Foliar applications of iron have been used to darken turf color (Glinski et al., 1992) and to negate the transient phytotoxicity that can result from plant growth regulator (PGR) application under normal irradiance (Carrow and Johnson, 1990). Lee et al. (1996) showed above-normal levels of iron in nutrient culture enhanced granal development in chloroplasts with a commensurate increase of chlorophyll b levels in Kentucky bluegrass, a situation characteristic of shade-adapted plants (Nobel, 1991). The effect of foliar iron applications, and the potential interaction with PGRs, on turf color and chlorophyll in reduced irradiance is unknown.
Our research objectives were to compare the tolerance of supina bluegrass and Kentucky bluegrass under reduced irradiance, with and without traffic, and to determine the effects of multiple applications of TE and iron on the growth and quality of supina bluegrass and Kentucky bluegrass grown under reduced irradiance.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Daily totals of photosynthetically active radiation (PAR) in the CSSF were determined, based on the percentage of PAR transmitted through the fabric onto the turf canopy inside the CSSF. A spectroradiometer (model LI-1800, Li-Cor, Lincoln, NE) was used to scan irradiance weekly on each plot inside the CSSF within 1 h of the solar zenith using a 300- to 850-nm bandwith at 2-nm intervals. Two scans were collected outside the CSSF with the spectroradiometer immediately before, midway through, and immediately after collecting data inside the CSSF. Data from inside the CSSF were divided by data collected outside to determine the percent transmission. Average daily PAR values were determined by collecting solar radiation data outside the CSSF daily with a pyranometer (model Li-Cor PY 14226, Li-Cor, Lincoln, NE) located approximately 15 m north of the CSSF. Radiometric units from the pyranometer were converted to quantum units using the following equation, which was based on conversion units from Thimijan and Heins (1983):
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The average percentage of light transmitted into the CSSF was used to determine the daily PAR inside the CSSF, based on the data recorded outside with the pyranometer.
Temperature and relative humidity were recorded daily with a sling psychrometer. Temperature inside the CSSF averaged 16.6°C ± 1.5°C with a range of 12 to 24°C. Relative humidity averaged 46% ± 12% with a range of 28 to 63%.
Plot Construction and Maintenance
Portable plots were established as previously described (Stier et al., 1999). The project was conducted twice from December 1994 through June 1996. A first set of plots was sodded 28 Sept. 1994 and a second set was sodded 28 Aug. 1995. Starter fertilizer was applied to the root zone mix surface immediately before sodding (Table 1). Additional fertilizer was applied twice in 1994 and once in 1995 during establishment. The turf was mowed at 3-cm height once to twice weekly, depending on growth rate, and irrigation was applied as necessary to prevent visible drought stress.
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Treatments and Experimental Design
A completely randomized design with three replications was used, since there was no apparent spatial or environmental variability that required blocking. Data were analyzed as a 2 x 2 x 2 factorial using MSTAT analysis of variance procedures (MSTAT, 1988). The factors were turfgrass species, TE, and foliar iron. When appropriate, means for interactions were separated using Fisher's Protected LSD ( = 0.05).
Supina bluegrass cv. Supranova and Kentucky bluegrass cv. Victa/Abbey (50:50 v/v) were used both years. Washed sod was used for establishment except in 1994, when supina bluegrass, produced on a plastic surface in composted bark media, was used. Trinexapac-ethyl at 0.19 kg ha-1 in 896 L of H2O ha-1 was applied on 3 Oct. 1994 and 9 Oct. 1995, using a CO2-powered backpack sprayer equipped with 8002 flat fan nozzles. Additional TE (0.08 kg ha-1 in 896 L of H2O ha-1) was applied on 21 Dec. 1994, 20 Jan. 1995, 18 Feb. 1995, and 16 Mar. 1995 for the first year's testing and on 31 Jan. 1996, 15 Mar. 1996, and 26 Apr. 1996 for the second year's testing. Iron (1.14 kg of Fe ha-1 as FeSO4·7H2O) was applied to foliage using Ferromec AC (PBI Gordon, Kansas City, MO) on 10 Jan. 1995, 14 Feb. 1995, 17 Mar. 1995, 28 Feb. 1996, and 13 May 1996.
Two experiments were designed to determine treatment effects in both non-trafficked (Exp. I) and trafficked (Exp. II) conditions. Traffic was applied by having a person (approximately 70–75 kg) jog 50 passes at 7-d intervals while wearing molded soccer cleats. Traffic was applied 28 Dec. 1994 through 16 Mar. 1995 (600 passes) and 26 Jan. 1995 through 26 Apr. 1996 (700 passes).
Data Collection
Clippings were collected from a 41- by 117-cm strip through the center of each trafficked and non-trafficked plot, dried in a forced-air oven at 60°C for 48 h, then weighed. Clippings were collected from the remainder of the plot area and discarded. Turf color and quality were evaluated visually on a one-to-nine scale at approximately 14- to 21-d intervals. A rating of one represented 100% necrotic turf/bare soil; a rating of nine represented dark green or ideal turf. A rating of five was considered the minimum acceptable value. Turf rooting and strength were evaluated periodically using an Eijkelkamp shear vane apparatus (Eijkelkamp, Giesbeek, the Netherlands). The torque required to tear the turf with the shear vane was recorded as an average of two measurements per plot (Rogers and Waddington, 1990). On 24 March 1995 and 30 May 1996, plant densities were determined by counting the number of plants in eight random squares (32.7 cm2 each) of a 0.4-m2 quadrat (Skogley and Sawyer, 1992). On 12 Apr. 1995 and 31 May 1996, samples of 10 randomly selected plants were collected from each plot for biomass assessments. Average leaf number shoot-1, average shoot number plant-1, and average oven-dry weight plant-1 (specific weight) were determined for each sample.
Leaf samples from 10 randomly selected plants were collected from each non-trafficked plot for chlorophyll analysis on 4 Apr. 1995 and 29 May 1996 (trafficked plots were not sampled because adequate plant material was often not available). A 10-mm segment from the youngest fully expanded leaf of each plant was excised, starting 5 mm above the leaf collar. Chlorophyll was extracted by placing 10 leaf segments in 3 mL of N,N-dimethlyformamide and incubating them in the dark at 4°C for 48 h (Moran and Porath, 1980). A double-beam spectrophotometer was used to determine absorbances, and the extinction coefficients described by Inskeep and Bloom (1985) were used to calculate levels of chlorophyll a, b, and total chlorophyll.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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Turf Quality
Experiment I: Turf Not Subjected to Traffic
The main effects of both species and TE were significant on most rating dates, but their individual importance was overridden by interaction between the two factors (Table 3). The species x TE interaction significantly affected turf quality on 5 of 7 dates in 1994–1995 and on 9 of 10 dates in 1995–1996 (Table 3). The species effect was inconsistent between years due to differences in disease susceptibility and reaction to TE. Although TE affected the turf quality of both species, supina bluegrass was more responsive than Kentucky bluegrass. Supina bluegrass treated with TE was the only species treatment combination to provide acceptable turf quality for the duration of the test periods (16 wk in 1994–1995 and 27 wk in 1995–1996) (Fig. 1)
. Unlike previous reports of TE-induced phytotoxicity on turf subjected to stress (Quian and Engelke, 1999), no phytotoxicity was observed due to TE applications. This was probably due to the relatively low rates of TE.
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These data indicate that untreated supina bluegrass is not necessarily more tolerant of reduced irradiance than Kentucky bluegrass at 
5 mol m-2 d-1. A companion study in the CSSF during 1995–1996 using supplemental irradiance (5–9 mol m-2 d-1) showed untreated supina bluegrass was superior to untreated Kentucky bluegrass (unpublished data, 1996). Previous reports of supina bluegrass' superior shade tolerance did not indicate the amount of irradiation (Berner, 1980; Pietsch, 1989).
The sensitivity of supina bluegrass to TE had both negative and positive impacts. For example the turf, which was semi-dormant when brought into the CSSF in both years, recovered within 2 wk except in year two when greenup of the TE-treated supina bluegrass took 4 wk. Daytime temperatures, which dropped to near 0°C, and the occurrence of snow cover within 1 mo after the first application of TE in the second season (during October) seemed to delay the metabolism of TE in the supina bluegrass. The delayed greenup in the second year is important because turf brought into a covered stadium for repair of damaged areas will need to be able to quickly recover from winter dormancy. Thus PGR applications made during the autumn should be applied well in advance of potential winter dormancy so as not to inhibit recovery. Additional work is needed to determine metabolic rates of TE during hardening and de-hardening periods.
Experiment II: Turf Subjected to Traffic
As in the non-trafficked turf, the interaction between species and TE had significant impact on most rating dates with TE-treated supina bluegrass providing the best turf on 7 of 13 dates during both years of the study. On a practical basis, during both years, approximately 5 wk after initiating traffic (200 jogging passes), turf quality was reduced to unacceptable levels for all treatments (Fig. 2)
. Supina bluegrass treated with TE provided higher quality turf for the first 4 wk after traffic was started in 1994. Similar differences were not statistically significant during the second year, perhaps because traffic was initiated 7 wk (instead of 2 wk) after installation in the CSSF to allow TE-treated supina bluegrass to recover from dormancy. Supina bluegrass treated with TE recovered more quickly than Kentucky bluegrass or untreated supina within 3 wk after traffic ceased in 1996 (Fig. 2b). Although turf quality did not reach acceptable levels 8 wk after traffic ceased, under greater irradiances supina bluegrass treated with TE could be expected to recover to acceptable levels faster than untreated supina bluegrass or Kentucky bluegrass.
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Chlorophyll Content
Trinexapac-ethyl increased the amount of chlorophyll on a leaf-area basis from 26.7 to 36.7 µg cm-2 (Table 5). Kentucky bluegrass averaged 35.9 µg of total chlorophyll cm-2 leaf area vs. 27.4 µg cm-2 in supina bluegrass. Unlike the results seen for color, there was no species x TE interaction on chlorophyll content.
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Clipping Yields
Species, TE, and species x TE interaction resulted in significant differences in clipping yields on more than half the dates (Tables 3 and 4). Trinexapac-ethyl reduced yields of both turfgrasses in the first year but reduced yields of only supina bluegrass in the second year (data not shown). Averaged over both years, TE reduced supina bluegrass yields 61% in non-trafficked turf (99.7 g cm-2 total yield for untreated turf vs. 38.7 g cm-2 for TE-treated turf) and 56% in trafficked turf (39.1 g m-2 total yield for untreated turf vs. 17.4 g cm-2 for TE-treated turf). Kentucky bluegrass yields were reduced 20% (105.2 g m-2 total yield for untreated turf vs. 83.9 g cm-2 for TE-treated turf) and 14% (50.1 g m-2 total yield for untreated turf vs. 38.0 g cm-2 for TE-treated turf) for non-trafficked and trafficked turf, respectively. Some of the difference between species yields was due to the prostrate growth habit of supina bluegrass, which was enhanced by TE.
During the first year, TE decreased supina bluegrass yields to zero (data not shown) approximately 10 wk after installation in the CSSF when irradiance ranged from approximately 1 mol m-2 d-1 during December and January to 2.6 mol m-2 d-1 in March. In the trafficked plots, supina bluegrass yields declined to zero within 4 wk after traffic began (approximately 6 wk after installation in the CSSF). Although acceptable turf quality was maintained on the non-trafficked plots during the period of non-yield, quality of the trafficked plots plummeted due partly to excessively suppressed growth. During the second year when irradiance was greater, a reasonable amount of growth was maintained even in the trafficked plots, with oven-dry weights ranging from approximately 0.5 to 4.3 g m-2.
Plant Density and Biomass
Experiment I: Turf Not Subjected to Traffic
The two-way interaction between species and TE was significant for plant density, tillering, leaf number, and specific weight (Table 6). Trinexapac-ethyl significantly enhanced plant density, tillering, leaf number, and specific weight of supina bluegrass but not of Kentucky bluegrass. Even without TE, supina bluegrass had approximately two to three times the number of tillers and leaves per plant compared with Kentucky bluegrass (Table 6). In 1996 supina bluegrass had significantly greater plant density.
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A powdery mildew epidemic greatly reduced Kentucky bluegrass turf density the second year of the study. Turf density of both species was much lower the second year compared with the first year since plant counts were conducted 24 wk after installation of the plots in the CSSF; in the first year, counts were conducted at 15 wk. The decline in plant population over the longer time period indicates a lack of sufficient irradiance for long-term growth of either species.
Experiment II: Turf Subjected to Traffic
Similar to non-trafficked turf, the main species effect showed supina bluegrass had more tillers, leaves, and a greater specific plant weight compared with Kentucky bluegrass (Table 7). Unlike the results seen in non-trafficked turf, the main effects of TE did not affect tillering, leaf number, and specific plant weights of either species when turf was subjected to traffic. Trinexapac-ethyl did increase plant density. The only species x TE interaction was an increase in the density of TE-treated supina bluegrass in 1996 but not in Kentucky bluegrass turf.
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Turf Shear Resistance
There were significant main effects on shear resistance due both to species and TE but no meaningful interactions (Table 8). Kentucky bluegrass exhibited greater shear resistance than supina bluegrass during the first year; supina bluegrass had greater resistance the second year, although the shear resistance of Kentucky bluegrass was comparable in January and March of both years. Trinexapac-ethyl significantly enhanced shear resistance on three of seven test dates but the magnitude of response was much less than that observed between species.
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Adequate shear strength is important to minimize the amount of tearing and size of divots removed during play. Appropriate shear strength is critical for maximum playability and player safety since too little shear strength can cause athletes to slip and perhaps injure muscles; too much shear strength can result in turf toe. Unfortunately, only anecdotal data are available to indicate acceptable and unacceptable shear values, and these can depend on the type of shear vane used to measure the turf. In our trials, we designated a value of 10 Nm as the minimum acceptable value since the turf was easily torn from the soil at values <10 Nm. Values between 10 to 15 were considered fair, values 15 to 20 were considered good, and values >20 were exceptional. With these criteria we can make the following observations. In the first year when transmission of solar irradiance was restricted to approximately 10%, supina bluegrass provided only acceptable shear strength for approximately 30 d. Kentucky bluegrass' shear strength was acceptable for at least 90 d the first year, although turf quality was not acceptable for more than 30 d (20 d when trafficked). In the second year, when the fabric transmitted approximately 15% of solar irradiance, supina bluegrass provided acceptable shear strength for at least 90 d, which was similar on a practical basis to Kentucky bluegrass.
Effects of Iron and Interactions with Species and Trinexapac-Ethyl
Interactions between iron and species, iron and TE, and three-way interactions were rare and deemed insignificant, based on their relative effect in each situation. The response due to iron was significant with respect to quality, color, and yield on only a few dates (Tables 3 and 4). Iron did not affect turf density, growth, or development. Contrary to expectations and results obtained under normal irradiance, iron did not affect total chlorophyll level. Iron treatment did increase chlorophyll b from 6.7 to 7.3 µg cm-2 in the non-trafficked experiment on 29 May 1996, but the lack of effect on chlorophyll a:b and chlorophyll b levels of both the non-trafficked and trafficked (data not shown) turf in 1995 suggest iron had negligible effect. The lack of iron effect on chlorophyll and the chlorophyll a:b was unexpected since previous work under normal irradiance showed iron was capable of increasing chlorophyll and decreasing chlorophyll a:b in turf (Lee et al., 1996). The lack of effect on chlorophyll content indicates either the iron did not enter the foliage or was not utilized by the turf for chlorophyll production. The extremely low irradiance in the current study may have compromised the ability of the turf to utilize the foliar iron.
Received for publication September 21, 1999.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENCES |
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