Published in Crop Sci. 43:2182-2188 (2003).
© 2003 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
TURFGRASS SCIENCE
Shade and Airflow Restriction Effects on Creeping Bentgrass Golf Greens
K. J. Koha,
G. E. Bell*,a,
D. L. Martina and
N. R. Walkerb
a Dep. Horticulture and Landscape Architecture, Oklahoma State University, Stillwater, OK 74078
b Dep. Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078
* Corresponding author (bgregor{at}okstate.edu).
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ABSTRACT
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Creeping bentgrass (Agrostis stolonifera L.) golf greens are often shaded by trees and surrounded by shrubs or brush that restrict airflow. The objective of this study was to compare and independently evaluate turfgrass responses to light reduction and airflow restriction in ‘L93’ and ‘SR1020’ creeping bentgrass. Artificial structures (122 by 122 cm) were assembled from polyvinyl chloride (PVC), and covered with black, woven polyester shade cloth (80% light reduction) to provide treatment effects. Shade cloth was applied to the structures to reduce irradiance and allow airflow or reduce airflow and allow irradiance. Plots were rated monthly for canopy, soil, and air temperature, visual color, density, and disease, soil moisture, root mass, and root glucose and fructose. Canopy and soil temperatures were lower in shade than in airflow restriction and uncovered, unsurrounded control turf. Canopy temperature was higher in airflow restriction than control but soil temperatures did not differ. Both shade and airflow restriction had a negative effect on turf color in L93. Airflow restriction caused a greater reduction in mean color rating than shade in SR1020 but shade color did not differ from control. Turf density declined in both cultivars due to both airflow restriction and shade compared with control. Air restriction reduced density more than shade in SR1020 but not in L93. The severity of brown patch (caused by Rhizoctonia solani Kühn) and dollar spot (caused by Sclerotinia homoeocarpa F.T. Bennett) in shade was less than in airflow restriction in both cultivars and less than control in SR1020. Soil moisture did not differ among treatments. Root mass was affected by both shade and airflow restriction in both cultivars and declined more rapidly in shade than in airflow restriction. Root glucose and fructose were not significantly affected by treatments.
Abbreviations: HPLC, high performance liquid chromatography • PAR, photosynthetically active radiation • TNC, total nonstructural carbohydrates
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INTRODUCTION
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CREEPING BENTGRASS is the most widely used cool season grass for golf greens, although it may decline because of intense management and environmental stresses during the summer months. A reduction in solar irradiance caused by shade is usually combined with other environmental stresses such as airflow restriction and tree root competition to reduce creeping bentgrass quality in shade. Shade alters several physiological and morphological characteristics of plants. Low irradiance results in increased stem elongation, longer leaf sheaths, higher chlorophyll content, and higher leaf succulence (Dudeck and Peacock, 1992). Plant growth is more vertical in shade because of the inactivation of phytochrome influenced by far-red irradiance, resulting in increased gibberellic acid (Rood et al., 1986). Low radiant flux can increase stem elongation, lengthen leaf sheaths, and reduce tillering in ‘Diamond’ zoysiagrass [Zoysia matrella (L.) Merr.] (Qian and Engelke, 1999); although, under certain conditions, moderate shade may increase tillering in some tropical grasses (Inosaka et al., 1977) and shoot growth in some forage grasses (Eriksen and Whitney, 1981). Low photosynthesis caused by limited photosynthetically active radiation in shade, caused a decrease in available carbohydrates and total nonstructural carbohydrates in ‘Coastal’ bermudagrass [Cynodon dactylon (L.) Pers.; Burton et al., 1959]. Turf in shade is more susceptible to disease caused by fungal pathogens such as R. solani (causal agent of brown patch), S. homoeocarpa (causal agent of dollar spot), Pythium spp. (causal agent of Pythium blight), and Fusarium spp. (causal agent of Fusarium blight) because of high soil moisture and more succulent leaf tissue (Vargas and Beard, 1981).
Recently, Bell and Danneberger (1999) concluded that there was no significant effect on creeping bentgrass quality between morning shade and afternoon shade. The researchers reported that the duration of shade was more detrimental to turfgrass health than either the density or the temporal period of shade. In that study, perpetual artificial shade averaging 42% of the photosynthetic photon flux available in full sun caused significantly lower turf density and root mass compared with turf in full sun.
Airflow restriction decreases cooling by reducing transpiration rate, increasing soil moisture content, and decreasing carbon dioxide flux. Airflow promotes heat transfer by forced convection across the leaf boundary layer, and wind speed affects boundary layer resistance between the leaf surface and the ambient air (Nobel, 1991). Airflow increases transpiration and contributes to decreases in stomatal and cuticular resistance that promote cooling by redistributing heat. However, excessive wind speed reduced grass growth even in the absence of water stress (Russell and Grace, 1978, 1979). Kitano and Iguchi (1992) reported that a sudden increase in wind speed caused an increase in water absorption, transpiration, and stomatal conductance of cucumber (Cucumis sativus L.) plants in bright light, with decreased responses in low light and no response in darkness. Air movement of 1.79 m s-1 decreased turf canopy temperature in creeping bentgrass a maximum of 7.2°C compared with no air movement. However, the relative humidity at 7.6 cm above the turf surface was not affected by air movement at that rate (Duff and Beard, 1966). Tall fescue (Festuca arundinacea Schreb.) exposed to an average turbulent airflow speed of 0.5 to 1.0 m s-1 had a much higher conductance and lost water at more than twice the rate of tall fescue grown in optimal conditions (Grace and Russell, 1977). Previous research seems to indicate that both high wind and no wind can be detrimental to turf health but little is known about the airflow restriction effects commonly found in a shade environment.
Bell and Danneberger (1999) speculated that it is possible to consider shade and airflow restriction independently to diagnose specific effects from each factor. Managing the detrimental effects of light and airflow restriction independently may improve turf quality management. The objective of this study was to compare and independently evaluate turfgrass response to light reduction and airflow restriction in two creeping bentgrass cultivars.
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MATERIALS AND METHODS
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Experimental Design
This study was conducted at the Oklahoma State University Turfgrass Research Center, Stillwater, OK. An SR1020 creeping bentgrass area, 18 by 31 m and an L-93 creeping bentgrass area, 11 by 49 m were used for the study. The SR1020 research site was located 107 m from the L93 site and at nearly the same elevation (~1.5 cm lower). The SR1020 site was constructed of United States Golf Association (USGA) approved sand amended with 10% (v/v) rice hulls and seeded in 1994. Soil texture at the end of the study was 960 g kg-1 sand, 0 silt, and 20 g kg-1 clay with 20 g kg-1 organic matter and a pH of 7.4. The L93 site was seeded in 1998 on USGA approved sand amended with 15% peat (v/v). The L93 site contained 940 g kg-1 sand, 0 silt, 20 g kg-1 clay, and 40 g kg-1 organic matter at pH 7.3. Each research site was managed as a golf course putting green. Both sites were mowed six times per week at 4 mm with a walk behind mower. Isobutylidenediurea (21-3-16) was applied monthly at a rate of 24 kg N ha-1 during the spring and fall (March, April, May, September, and October) and 12 kg N ha-1 during the summer (June, July, and August). These sites were aerated and topdressed with pure sand each spring and fall in 2000 and 2001. Chlorothalonil (tetrachloroisophthalonitrile) was broadcast applied at a rate of 16 kg a.i. ha-1 preventatively to the research sites every three weeks to help control brown patch and dollar spot disease. The fungicide program was not sufficient to prevent disease completely but did prevent severe injury. A wheel chair CO2-pressurized sprayer (carrier rate = 234 L ha-1) was used for fungicide applications.
Artificial structures were designed and constructed to provide either airflow restriction or light reduction treatment effects. They were placed on the research sites at randomly chosen locations and spaced to eliminate light and airflow interference with each other. The structures were assembled from PVC pipe (3.8-cm-inside diameter) and covered with black, woven, polyester shade cloth (Chicopee, Gainesville, GA) rated for 80% light reduction. Structures were constructed to allow rainfall and irrigation to reach the plots evenly and were tested against control plots for that purpose by collecting rainfall and irrigation in the middle of four 61- by 61-cm grids within each plot. Each structure was 30 cm in height, and 122 cm in width and length. The shade cloth covered only the top of the light reduction structures and the sides were left open to allow air movement across the turf. The sides of the airflow restriction structures were covered with shade cloth to limit air movement but the top was open to sunlight. The airflow restriction structures allowed full sunlight to reach the plots except for short periods (~1 h) at the beginning and end of each day. The structures were mounted in PVC sleeves buried into the soil to allow easy removal for mowing, fertilization, and other cultural practices. The control treatments consisted of uncovered, unsurrounded plots (122 by 122 cm). The structures were placed on the research sites on 20 March 2000 through 19 October 2000, and again on 20 April 2001 through 19 Oct. 2001. Solar irradiance, air speed, canopy, soil, and air temperatures, visual color, density, and disease, root mass, and root glucose and fructose were measured monthly to determine treatment effects. Each treatment was replicated three times at each site.
Solar Irradiance and Air Speed
Solar irradiance was measured to determine if the treatments reduced irradiance using a FieldSpec handheld spectroradiometer and cosign receptor (Analytical Spectral Devices Inc., Boulder, CO). Irradiance levels for each plot were determined on the 20th day (±2 d) of each month under clear skies at solar noon. Solar irradiance was recorded in radiant energy (W m-2 nm-1) and converted to photon flux (µmol m-2 s-1) for solar measurements. Photosynthetic photon flux (400–700 nm) was used to estimate and compare the light available for photosynthesis in each treatment.
Air speed (m s-1) was measured to determine if the treatments reduced airflow on the same dates as irradiance using a portable multi-directional impeller anemometer (Skywatch, Yverdon, Switzerland). Air speed was measured three times at different, randomly chosen, locations in each plot at 10 cm above the turf surface. The subsamples from each plot were averaged before statistical analysis.
Canopy Temperature, Soil Temperature, and Air Temperature
Turf canopy temperatures, soil temperature, and air temperature were measured 1 h after solar noon on calm days under clear skies near the 20th day (±2 d) of each month depending on weather conditions. An infrared temperature thermometer (Standard Oil Engineered Materials Co., Solon, OH) was used to assess turf canopy temperature. Three different turf areas in each plot were arbitrarily selected for canopy temperature measurements and means calculated for statistical analysis. A bimetal analog thermometer (Rio Temp, San Diego, CA) was used to measure soil temperature at the same time turf canopy temperatures were recorded. Measurements were observed at a soil depth of 15 cm. Plot temperature measurements were subsampled three times and the mean recorded. General air temperature at the research site was recorded as an average between the air temperature at the beginning and end of the period required to measure turf canopy temperatures.
Color, Density, and Disease Assessment
Each plot was visually rated for turf color, density, and disease on the 20th day of each month (±2 d). Color was rated on a scale from 1 through 9 (1 = brown, 5 = yellow-green, and 9 = blue-green). Density was visually rated on a 1-through-9 scale (1 = widely spaced plants, 9 = closely spaced plants). Brown patch and dollar spot disease incidence was rated visually on a scale of 0 through 5 (0 = no disease, 5 = plots completely blighted).
Soil Moisture
Soil moisture was determined on the 20th day of each month (±2 d) 3 h after solar noon with time domain reflectometry (TDR; Mesa Systems Co., Framingham, MA). Two TDR probes were inserted 16 cm into the soil to measure moisture content. Measurements were made in three random locations in each plot in each month and the average recorded for analysis.
Root Mass and Carbohydrates Analysis
Three soil plugs were collected on the 20th day of each month (±2 d) from each plot with a 2.54-cm diameter soil probe to determine root mass. Root mass was evaluated to a depth of 15 cm. Soil was washed from the roots with mild water on a 24-mesh screen and the samples were oven-dried at 55°C for 48 h. Dry root mass (mg) of three combined samples from each plot was measured with a balance (Ohaus Corp., Florham Park, NJ), and stored in a freezer at –20°C for future carbohydrate analysis. Carbohydrate concentrations were extracted by a modified Weinmann (1947) procedure consistent with Smith (1981) except that a mixture of 
-amylase (Sigma No.2643, Sigma Chemical Co., St. Louis, MO) and amyloglucosidase (Sigma No.7420, Sigma Chemical Co., St. Louis, MO) was used in place of Mylase 100 enzyme (Bell and Danneberger, 1999). Root samples were ground in a Wiley Mill (Arthur H. Thomas Co., Philadelphia, PA), weighed to 30 mg, boiled for 5 min in double-distilled, demineralized water, and incubated in a mixture of -amylase and amyloglucosidase solution for 24 h at 45°C to degrade starch to glucose. Solutions were filtered through Whatman No.1 paper before fructosans were hydrolyzed in 0.5 M sulfuric acid. High performance liquid chromatography (HPLC) was used to measure the glucose and fructose extracted from the root tissue. Sample extract (50 µL) was automatically injected with an automated sampler into a DX500 HPLC (Dionex Co., Sunnyvale, CA) unit equipped with the GP40 gradient pump, and ED40 electronic detector. A Carbonapac PA-1 column (4 by 250 mm; Dionex Co.) was used for separations under isocratic conditions of 92% (v/v) water and 8% (v/v) 0.5 M NaOH over a duration of 25 min. Total glucose, fructose, and sucrose were calculated by means of area units developed by the PeakNet Chromatography Workstation (Dionex Co.). Tissue glucose, fructose, and sucrose were determined by comparing area units of unknown samples with area units of known standards and subtracting area units of enzyme blank extractions. The tissue sucrose content was not considered accurate because a portion of the sucrose present in the turfgrass tissue was probably hydrolyzed during extraction. Therefore, for each molecule of sucrose present, one molecule of glucose and one molecule of fructose were added to the amount of glucose and fructose detected before data analysis.
Statistical Analysis
Data were analyzed by analysis of variance (ANOVA) for a completely randomized design by the Statistical Analysis System (SAS Institute, Cary, NC) and mean separations were determined by Fisher's protected least significant difference (LSD) at P = 0.05. Rating date was used as a blocking criterion to assess overall (full study) observations by ANOVA. Regression and correlation were calculated by means of the simple equation function in Table Curve software (SPSS, Chicago, IL).
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RESULTS AND DISCUSSION
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Simulated artificial shade structures covered with 80% light reduction cloth received an average of 40% of the photosynthetically active radiation (PAR) available in full sun measured monthly at solar noon for two growing seasons. The overall PAR in airflow restriction plots was not significantly different (95% of full sun) from PAR in full sun. The average air speed in airflow restriction structures covered on four sides with cloth material to limit air movement was 0.3 m s – 1 measured monthly near solar noon over two seasons. The structures used to provide shade did not affect airflow across the plots (4.5 m s-1) compared with control (4.6 m s-1).
Canopy, Soil, and Air Temperature
Turf canopy temperatures in full sun and in airflow restriction were significantly higher than in shade for both growing seasons and both cultivars (Table 1). Canopy temperatures in airflow restriction (overall study mean = 32°C) and control (overall study mean = 31°C) differed significantly in both cultivars (Table 1). Soil temperatures in shade were also consistently lower than in full sun and airflow restriction. Therefore, turf in shade was subjected to less heat stress during the summer than turf in full sun and airflow restriction but less PAR was available for photosynthesis.
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Table 1. Turf canopy, soil, and air temperatures recorded for SR1020 and L93 creeping bentgrass putting greens under treatments of air restriction, shade, and control in 2000 and 2001.
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Color, Density, and Disease
For the first two months of 2000, the SR1020 turf in shade maintained a darker green color than turf in control and airflow restriction as the full sun adapted plants acclimated to the new shade environment (Table 2). A similar acclimation period occurred in 2001 during the first month when shade color was statistically the same as control. Following acclimation, SR1020 turf color in shade was consistently the same or lower than control. Turf color was not significantly different in the overall study analysis because the acclimation periods in both years were included in the analysis. Turf color in the SR1020 control exceeded turf color in air restriction significantly on eight of 13 rating dates in 2000 and 2001 and in the overall study results. Compared with shaded turf, color was negatively affected by airflow restriction in SR1020 on four of 13 rating dates during the study and differed significantly in the overall study analysis. In the L93 turf, shade caused a significantly lower color rating than airflow restriction in October 2001 but did not differ on other dates following acclimation or in the overall study analysis (Table 2). Both shade and airflow restriction caused a significant reduction of turf color in L93 compared with control in September and October in both years, in June 2001, and in the overall study results.
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Table 2. Turf color measured visually for SR1020 and L93 creeping bentgrass putting greens under treatments of air restriction, shade, and control in 2000 and 2001.
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Turf density started to decline because of shade and airflow restriction in both cultivars during the summer of 2000. Monthly visual ratings for density in control were significantly higher than in shade and airflow restriction on most rating dates during and after that period. The SR1020 turf in shade had greater density in April, May, June, and September 2000 and in August, September, and October 2001 than in airflow restriction (Table 3). The same result did not occur in L93. Shade and airflow restriction caused lower density ratings compared with control on six of thirteen rating dates but did not differ significantly from each other until the final month of the study (October 2001). Overall study analysis indicated that airflow restriction and shade significantly affected density in both cultivars and airflow restriction affected density more severely than shade in SR1020.
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Table 3. Turf density measured visually for SR1020 and L93 creeping bentgrass putting greens under treatments of air restriction, shade, and control in 2000 and 2001.
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Disease damage contributed to the difference in turf density between shade and airflow restriction in SR1020 (Table 4). Less disease occurred in shaded SR1020 than in airflow restriction and control. Disease did occur in shade in September 2000 and May, September, and October 2001, but disease damage was always significantly less than both airflow restriction and control. No disease was observed in L93 shade or control throughout the study but was observed in air restriction in May (dollar spot), August (brown patch), and September 2001 (dollar spot; data not shown). Less dew was visually observed on the turf under shade canopies than in air restriction or control, a condition also common under tree canopies or overcast skies. Air movement under the shade canopies encouraged dew to dry quickly reducing the period conducive for disease compared with other treatments in SR1020. The same effect occurred on L93 but control was not affected probably because of lower innoculum levels or greater genetic resistance compared with SR1020. Air restriction encouraged disease on both cultivars compared with shade and control.
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Table 4. Brown patch and dollar spot severity measured visually for an SR1020 creeping bentgrass putting green under treatments of air restriction, shade, and control in 2000 and 2001.
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Soil Moisture
There was no significant difference in soil moisture content among treatments except in June 2001 in SR1020 when the moisture content in airflow restriction exceeded that in shade (data not shown). Soil moisture in airflow restriction did not differ from shade and control in L93. Irrigation and rainwater reaching the turf was thoroughly tested and was found to be uniform among treatments and not a factor affecting soil moisture.
Root Mass
Root mass was consistently less in shade than in control on rating dates following about one month of treatment on L93 and about 3 mo of treatment on SR1020 (Table 5). Overall, shade had significantly less root mass than airflow restriction and airflow restriction had significantly less root mass than control in both cultivars. Xu and Huang (2000a) found that soil temperature was more detrimental than air temperature to plant growth and lower soil temperature promoted shoot and root growth even when air temperature was supraoptimal. Even though soil temperatures were cooler in shade (Table 1), the advantage of cooler soil was overcome by reduced photosynthesis in shade resulting in poor root growth. Regression (root mass = 12.69 + 0.01 soil temperature3) and correlation (r2 = 0.29) of soil temperature and root mass over time and treatments indicated a significant (P < 0.001) but weak, positive relationship in this case.
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Table 5. Dry root mass of samples collected on SR1020 and L93 creeping bentgrass putting greens under treatments of air restriction, shade, and control in 2000 and 2001.
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Root Carbohydrates
Measurement of root carbohydrates indicated that fructose levels exceeded glucose levels in the SR1020 control by a factor of 4.0 during the months of April, May, and June averaged over treatments, months, and years. Results were similar in L93 where fructose exceeded glucose by a factor of 3.9 in those months (data not shown). During July, August, and September, root fructose and glucose levels declined sharply then increased in October in both cultivars in both years. Fructose content in SR1020 exceeded glucose by a factor of 1.6 in July, August, and September averaged over treatments, months, and years and by a factor of 2.0 in October averaged over treatments and years. Similar results occurred in L93. These seasonal trends were also evident in both the shade and airflow restriction treatments. This seasonal carbohydrate production and decline in the field supports the information reported by Xu and Huang (2000b) who found that total nonstructural carbohydrates in both roots and shoots under controlled conditions decreased with increasing soil and air temperatures.
The carbohydrate results, however, did not provide meaningful data for comparison of the treatments. The results were ambiguous with no consistent trends or patterns. Root carbohydrate levels were a good indicator of plant seasonal health in both years but did not elucidate the differences among treatments that were apparent when color, density, disease, and root mass were compared. This research supports the findings of Bell and Danneberger (1999) who concluded that carbohydrate to tissue ratios were maintained even in severe shade (42% of full sun). Plant density and root mass in both that study and this one indicated that low photosynthesis in shade affected creeping bentgrass spread and root growth but did not affect carbohydrate to tissue ratios.
Cultivar Comparison
Cultivar–site differences were compared over time and treatments. It is not clear whether differences occurred because of growing conditions or genetic constitution but the similarity of environmental conditions suggested that cultivar had the greatest influence. The SR1020 site was four years older than the L93 site but pH, soil texture, location, and elevation were basically the same. There was a difference, however, in soil organic matter (SR1020 = 2.1%; L93 = 3.9%) that may have affected the results. There was no significant difference between solar radiation, airspeed, canopy temperature, soil temperature, root mass, root glucose, or root fructose between sites. Significant differences did occur in color, density, disease, and soil moisture. The L93 turf had significantly better color (8.0 > 6.7), greater density (8.1 > 7.6), less disease (0.3 < 1.6), and the site had higher soil moisture (161 > 145 g kg-1) than SR1020.
Comparisons of cultivars within treatments over time indicated that color was higher and disease lower in L93 compared with SR1020 regardless of treatment. Density was higher in L93 under airflow restriction and control. However, no difference occurred in shade between the two cultivars suggesting that shade had a greater effect on L93 density than it did on SR1020. Soil moisture was higher at the L93 site under shade and control but no difference occurred under airflow restriction suggesting that airflow restriction reduced evapotranspiration more in SR1020.
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SUMMARY
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Canopy and soil temperatures were lower in shade than in airflow restriction and control. Canopy temperatures were slightly higher in airflow restriction compared with control but no difference occurred between soil temperatures in airflow restriction and control. Shade and airflow restriction caused a loss in turf color in L93 during both years. In SR1020, color was more severely reduced by airflow restriction compared with shade and shade color did not differ from control. Both shade and airflow restriction caused losses in turf density in both cultivars but airflow restriction caused greater density reductions than shade. More disease occurred in airflow restriction plots than shade or control in both cultivars. In L93, disease was not reported in control or shade but in SR1020 disease in control was greater than in shade. Soil moisture did not differ significantly among treatments. Root mass was lowest in shade, higher in airflow restriction, and highest in control. Root glucose and fructose followed seasonal patterns in all treatments but were not a good indicator of plant health among treatments.
Airflow restriction was a greater stress on the creeping bentgrass turf causing greater losses in turf density and more disease than shade. Shade, however, caused a greater loss in root mass that would require careful management of nutrients and water to maintain plant health. Increasing airflow on shaded sites or removing shade from sites with low air movement should improve turf health, decrease management expenditures, and lower the incidence of turf loss on golf course putting greens and other turfgrass.
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ACKNOWLEDGMENTS
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Approved for publication by the Director, Oklahoma Agricultural Experiment Station. Funding provided by the Oklahoma Turfgrass Research Foundation, grant number AG-89-RS-140 and The Oklahoma Agricultural Experiment Station, project number OKLO 2392.
Received for publication November 13, 2002.
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REFERENCES
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ABSTRACT
INTRODUCTION
