Published online 1 January 2005
Published in Crop Sci 45:245-250 (2005)
© 2005 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
Fan and Syringe Application for Cooling Bentgrass Greens
E. A. Guertal*,
Edzard van Santen and
D. Y. Han
Dep. of Agronomy and Soils, Auburn Univ., Auburn, AL 36849-5412
* Corresponding author (eguertal{at}acesag.auburn.edu).
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ABSTRACT
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Creeping bentgrass [Agrostis stolonifera var. palustris (Huds.) Farw.] is only marginally adapted to the southeastern USA, where summer high heat and humidity can cause this cool-season turfgrass to thin and perform poorly. Used solely on southeastern putting greens, management techniques to maintain bentgrass include syringing (cooling via application of a light spray of water) and aboveground cooling fans. There is limited research which has examined separate and combined effects of syringing and fans. The objective of this research was to examine the effects of syringing and fans on creeping bentgrass grown on a southeastern native soil putting green. Conducted for 2 yr during the summer months, the experiment consisted of three replications of fan and syringe treatments. Specific treatments were: (i) fan, or (ii) no fan; and, (i) syringe, or (ii) no syringe. Collected data include soil temperature (1.3-cm depth) and root-length density. The combined use of fans and syringing reduced soil temperatures below that of fans alone, syringing alone, and the no fan–no syringe control. Use of fans and syringing decreased the time that soil temperatures remained at or above levels injurious to bentgrass plants. Use of syringing alone never increased root-length density, and in two cases decreased it. Use of fans increased bentgrass root growth at some samplings.
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INTRODUCTION
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CREEPING BENTGRASS is desirable on southeastern putting greens because it offers a smooth putting surface and winter green color. These attributes have pushed bentgrass into environments to which it is poorly adapted, particularly the humid Southeast. Newer cultivars, which supposedly have improved heat tolerance (Liu and Huang, 2000), will only increase this trend.
Frequent observation of the putting green, proper fungicide scheduling, and moderation of the canopy temperature are keys to successful bentgrass management in the humid South. However, these management strategies may not always prevent stand thinning and summer decline. The detrimental effects of increasing temperatures and high heat have been well documented in growth chamber studies (Beard and Daniel, 1965; Huang and Gao, 2000; Xu and Huang, 2000a, 2000b). The result is always the same; as the air or soil temperature increases above the optimum for cool-season grasses, both shoot and root growth decline.
Two techniques commonly used by superintendents for cooling bentgrass turf are syringing and fans, or a combination of the two. Syringing is a fine spray of water applied in small amounts when close examination of the turf reveals stress, often diagnosed by the applicator as visible footprints left in the turf surface. Fans are large (0.5 to 1 m in diam.) units placed at the edge of putting greens, producing air movement across the surface of the green. Fans are often used when terrain and/or landscape vegetation impede the flow of air across a green.
A fairly new technique for cooling putting greens is subsurface aeration, where a stream of air is either pulled or pushed though the green using a motorized blower. In some cases the air stream is cooled as well. Although some preliminary research has shown that such units are effective for cooling greens and improving turf quality (Bunnell and McCarty, 2000; Feng et al., 2002), subsurface cooling units are expensive, and not as widely used as syringing and/or surface cooling fans.
Use of syringing and fans is not new. As early as 1966 researchers found that air movement reduced turf mat temperatures, and syringing prevented turf from reaching higher temperatures (Duff and Beard, 1966). In that unreplicated 1-yr Michigan study, air movement at 1.8 m s–1 reduced soil temperatures at a 5-cm depth an average of 7°C, while relative humidity above the bentgrass was unaffected. In a separate unreplicated study, the application of 6-mm syringe water reduced soil temperature a smaller amount (4°C). Researchers suspected that air movement reduced turf mat temperatures, and that syringing might prevent turf from reaching higher temperatures (Duff and Beard, 1966). Because air movement and syringing were separate experiments, the interaction of air movement and syringing could not be evaluated in this study.
A more recent study examined the effect of syringing bentgrass greens in North Carolina (DiPaola, 1984). Consisting of two separate experiments, in the first volumes of syringe water (0, 0.05, 0.1, 0.7, 1.4, 2.7, 4.1, or 5.5 mm) were applied at 1100 or 1300 h. In the second experiment, one volume of syringe water (2.7 mm) was applied as single or multiple applications at hourly intervals, from 1200 to 1600 h. In both experiments, regardless of the volume of water applied or timing of the syringe application, moderation of the bentgrass canopy temperature was not observed 1 h after treatment. When canopy temperature was measured within 0.5 h of syringing, the average reduction in temperature was 0.7°C. It was concluded that, in the absence of wilt, bentgrass canopy temperatures were not markedly affected by varying the volume or timing of syringe applications. It was further suggested that the use of syringing in the absence of wilt might merit reevaluation.
Given the widespread use of fans and syringing by golf courses, there are relatively few published research studies that examine the effect of the practices. One published abstract concluded that as wind velocities from fans increased, soil moisture was affected but air temperature was not altered (Taylor et al., 1994). Effects of syringing have been found to produce mixed benefits (Duff and Beard, 1966; DiPaola, 1984; Peacock et al., 1995). Studies that evaluate the combined effects of fans and syringing have not yet been performed, so potential benefits of the combined effects on evaporative cooling have never been studied. Thus, the objective of this study was to evaluate the combined and separate effects of fans and syringing on subsurface temperatures in a bentgrass putting green.
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MATERIALS AND METHODS
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In September 1999, a bentgrass putting green was constructed at the Auburn University Turfgrass Research Unit (TGRU), Auburn, AL. The green was constructed using the native loamy soil (Maryvn fine sandy loam; fine-loamy, kaolinitic, thermic Typic Kanhapludult) and seeded with ‘Crenshaw’ creeping bentgrass at a rate of 8.7 g m–2. The putting green was managed as a typical southeastern bentgrass green through June 2000, after which fan and syringing treatments were initiated. Data were collected in 2000 and 2001.
Mowing height for the duration of the study was 4 mm. Turf cultivation included once-yearly (October) hollow-tine core aerification with 1-cm diam. tines (10-cm depth), twice-yearly (September, May) vertical mowing (1.3-cm depth), and sand topdressing applied after each cultivation event. Nitrogen was applied twice-monthly at a rate of 1.0 g N m–2 using a soluble spray with an analysis of 18–3–12 (N–P–K). Additional P, K, and lime were not applied during the 2-yr period of this test, as quarterly soil tests revealed soil-test P of 35 mg kg–1 (high), K of 84 mg kg–1 (high), and a pH of 6.3. Herbicides were applied as needed to control common weeds and fungicides were not applied during the experiment periods. In addition to syringe treatments described below, irrigation combined with precipitation was applied to the entire plot to provide at least 2.5 cm of water wk–1. Required irrigation was applied on an every-other-day basis at 0600 h.
The study was arranged in a randomized complete block design (r = 3) with a split-plot restriction on randomization. Fan treatments were assigned to main plots, and syringing to subplots. Fan treatments consisted of (i) fan, or (ii) no fan; and syringe treatments consisted of (i) syringe, or (ii) no syringe. Main plots of fan treatments were 3.2 x 6.5 m, with the syringing split subplots measuring 3.2 x 3.2 m. To reduce water mist effects on nonsyringe treatments, there was a 3.2-m alley around each plot. To apply the fan treatment, one 53-cm nonoscillating fan (0.75 kW, 1725 rpm; Tempest Technology, Fresno, CA) was mounted at a 1-m height at the end of each 6.5-m-long fan block, blowing across the entire length of each main plot. To minimize the effect of fan speed at distances close to the fans, the plot area did not start until 3.2-m away from each fan. Average fan speed across each fan main block was 1.7 m s–1, similar to air speeds used in previous research (Taylor et al., 1994). Fans were moved from one end of each main plot to the other in the second year of the study. Everyday the fans ran from 1115 to 1615 h, regardless of background wind speed or other weather conditions. Run time was dictated by the length of time the fans could run on one tank of diesel fuel for the generator. With this fuel limitation, a time was selected that bracketed the hottest part of a typical summer day.
Syringe treatments were automatically applied by low-volume misting irrigation heads (Rain Bird, Azusa, CA) placed at each corner of syringe plots. Syringe applications were applied three d–1 (1200, 1400, and 1600 h) for a period of 2 min syringe cycle–1. This run time applied 1.3 mm of water to each plot at each syringing. Typical temperature of the mist water was 22°C.
In 2000 and 2001, treatments began when daytime afternoon temperatures consistently reached 29 to 32°C. These are typical air temperatures at which local golf course superintendents would initiate syringing or start fan cooling. The study was stopped each year when air temperatures dropped out of this range. In 2000, data collection occurred from 23 June until 7 Aug., and in 2001 from 9 July until 5 September. Collected data included soil temperature at a 1.3-cm depth, using continuously measuring (every 5 min) temperature probes (Onset Computer, Bourne, MA) placed in each plot. One probe was placed near the center of each plot, with each sensor attached directly via a 5-m cable to a logging unit buried in the alley outside each plot. Since the probe, attached cable, and logging unit were all buried, there was no need to remove units during mowing. All other cultural management that could damage the probes was performed outside the data collection period, when the probes had been removed. Data were downloaded onto a laptop computer each week and stored for future analysis.
Each week, core samples (0- to 15-cm depth) were removed for root length analysis. To collect samples, a 2.2-cm diam. soil sampler was inserted at random 10 times in each plot. Collected cores were composited and treated as one sample per plot. Aboveground growth and thatch were discarded and roots from each core were hand washed over a 0.5-mm sieve. Rinsed roots were stained with Congo red dye and analyzed for root length index. Root length index was measured with a Comair root length scanner via a high power light image (Comair Rootlength Scanner, Hawker de Havilland, VIC, Australia).
Data Analysis
The main response variable of interest was the maximum temperature recorded. To make the data set a manageable size, weekly averages were calculated. Mixed model methodology for repeated measures was used to analyze the data (Littell et al., 1996). The temporal correlation structure was modeled and the best-fitting model selected using the Residual Log Likelihood criterion (Littell et al., 1996).
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RESULTS AND DISCUSSION
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The 2000 season was warmer than 2001, with an extended period of drought in June and July (Fig. 1)
. Minimum and maximum air temperatures in both years were often more extreme compared with those applied or observed in other bentgrass heat stress research, which to date has often been conducted in controlled growth chambers. For example, the maximum air temperature observed in 2000 (37°C) was greater than that used as a high air temperature (35°C) in growth chamber studies (Huang et al., 1998a, 1998b, 2001; Xu and Huang, 2000a, 2000b). Minimum summer air temperatures (24°C in 2000; 21°C in 2001) in our study rarely dropped to an optimum nighttime level (15°C), as defined in previous research (Huang et al., 1998a, 1998b).
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Fig. 1. (A) Average weekly maximum and minimum air temperatures and (B) total weekly precipitation during the 2000 and 2001 study periods.
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Figure 2
illustrates soil temperatures for the days in 2000 and 2001 in which the lowest and highest maximum air temperatures for the experiment period were recorded. Thus, in 2000, the coolest day (25.5°C maximum) was on 3 August (Fig. 2A), and the hottest day occurred on 18 August (Fig. 2B). In 2001, the coolest and hottest days occurred on 9 September (Fig. 2C) and 26 August (Fig. 2D), respectively. Effects of fan and syringing treatments on soil temperatures were more pronounced in 2000 (Fig. 2A and 2B), when the experiment period was hotter and drier than in 2001. In the period 1 July to 15 Aug. 2000, there were a total of 35 d with maximum air temperatures that exceeded 32.2°C, and one day that exceeded 37.7°C. In comparison, from 1 July to 28 Aug. 2001, only 23 d had maximum air temperatures that exceeded 32.2°C.
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Fig. 2. Diurnal soil temperatures at 1.3-cm depth for four dates in 2000 and 2001. Dates indicate the days with the (B, D) highest and (A, C) lowest maximum air temperatures measured each year at the Auburn University weather station during the study period.
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Although the fan x syringing x week (year) interaction for maximum soil temperature was significant (P = 0.01), the pattern was quite consistent (Fig. 3)
. In both 2000 and 2001, the combination of fans and syringing had a greater effect on lowering maximum soil temperature than did syringe only, fan only, or control plots. This interaction of fans and syringing resulted in a lower maximum temperature for every week of the year in both years. In general, reductions in the maximum observed temperature occurred in the following order: fan plus syringing, fan only, syringe only, and, no fan/no syringe (control) (Fig. 3).
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Fig. 3. Fan x syringing interaction means on a weekly basis for study years 2000 and 2001. Vertical bars represent the LSD (0.05).
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In previous research, reduction in canopy (not soil, as measured in our study) temperatures due to syringing were small, averaging only 0.7°C, and lasting only 0.5 h at best (DiPaola, 1984). Syringe applications were made in the absence of wilt, a condition which typically results in lower canopy temperatures than observed in plots with noticeable wilt (DiPaola, 1984). Wilt was not observed in our study, and a similar syringe effect was observed (Fig. 4)
. Without a fan, syringing reduced average maximum soil temperatures an average of 0.5°C in 2000 (NS at P = 0.05) and 0.25°C in 2001 (NS at P = 0.05). When a fan was added the combined effect of fan plus syringing significantly cooled the soil, lowering maximum soil temperatures 2.6°C in 2000 and 1.0°C in 2001, compared with the control (Fig. 4).
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Fig. 4. Fan x syringing interaction means for maximum soil temperature during study years 2000 and 2001. Vertical bars represent the LSD (0.05).
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Not only was the maximum soil temperature reduced significantly when fans and syringing were both applied, but the plants were exposed to these higher stress-inducing temperatures for a shorter period of time. Plots treated with a fan and syringing spent an average of 2 h d–1 less at soil temperatures exceeding 27°C (Fig. 5)
as compared with any other treatment. In growth chamber studies, air temperatures 
30°C caused decreased quality, root viability, and root dry matter production in three bentgrass cultivars (Huang and Gao, 2000). It has also been shown that high soil temperatures (35°C) are more detrimental to bentgrass than high air temperatures (Xu and Huang, 2000a), and when soil temperatures increase from 20°C to 35°C, root number and turf quality decreased (Xu and Huang, 2000a). When soil temperatures were reduced from 35 or 32 to 29°C, root/shoot ratios equal to those of the control plots (20°C) were observed (Xu and Huang, 2001). It was concluded that reducing root zone temperatures, as we did in our study, could help maintain quality creeping bentgrass in high-heat-stress environments.
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Fig. 5. Fan x syringing interaction means for hours above the critical temperature of 27°C. Vertical bars represent the LSD (0.05).
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There was never a significant fan x syringe interaction in either year of the study for root-length density. In both years, root-length differences due to fan or syringing were slight (Fig. 6)
. The use of fans increased root-length density slightly in 2000, especially in August, with significant increases measured on 7, 14, and 21 August. In 2001, bentgrass receiving the fan treatment had longer roots on 17 and 24 July. Except for June and July 2000, there was a consistent, if not always significant, trend for the use of fans to cause increases in bentgrass root-length density. The use of syringing never increased root-length density, and in some cases (17 and 31 July 2001) actually decreased root-length density.
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CONCLUSIONS
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The combined use of fans and syringing reduced soil temperatures in a native soil putting green. Although the separate treatments of fan only and syringe only also reduced soil temperatures below that of the control plots, the reduction in temperature was less than that observed with fans and syringing combined. Use of fans and syringing decreased the time that soil temperatures remained at or above levels injurious to bentgrass plants. For example, the use of fans and syringing kept soil temperatures below 27°C for 2 h longer than without. Root-length density of bentgrass from plots receiving the fan treatment increased at 5 of 17 sampling dates. In comparison, the use of syringing never increased root-length density, and in two cases decreased it. In our study, the combined use of fans and syringing lowered soil temperatures, and the use of fans increased bentgrass root growth at some samplings.
Received for publication November 24, 2003.
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REFERENCES
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- Beard, J.B., and W.H. Daniel. 1965. Effects of temperature and cutting on the growth of creeping bentgrass (Agrostis palustris Huds.) roots. Agron. J. 57:249–250.[Abstract/Free Full Text]
- Bunnell, B.T., and B. McCarty. 2000. Subsurface air movement: Timing, intervals and direction. TurfGrass Trends 9:1–5.
- DiPaola, J.M. 1984. Syringing effects on the canopy temperature of bentgrass greens. Agron. J. 76:951–953.[Abstract/Free Full Text]
- Duff, D.T., and J.B. Beard. 1966. Effects of air movement and syringing on the microclimate of bentgrass turf. Agron. J. 58:495–497.[Abstract/Free Full Text]
- Feng, Y., D.M. Stoeckel, E. van Santen, and R.H. Walker. 2002. Effects of subsurface aeration and trinexapac-ethyl application on soil microbial communities in a creeping bentgrass putting green. Biol. Fertil. Soils 36:456–460.
- Huang, B., X. Liu, and J.D. Fry. 1998a. Shoot physiological responses of two bentgrass cultivars to high temperature and poor soil aeration. Crop Sci. 38:1219–1224.[Abstract/Free Full Text]
- Huang, B., and H. Gao. 2000. Growth and carbohydrate metabolism of creeping bentgrass cultivars in response to increasing temperatures. Crop Sci. 40:1115–1120.[Abstract/Free Full Text]
- Huang, B., X. Liu, and J.D. Fry. 1998b. Effects of high temperature and poor soil aeration on root growth and viability of creeping bentgrass. Crop Sci. 38:1618–1622.[Abstract/Free Full Text]
- Huang, B., X. Liu, and Q. Xu. 2001. Supraoptimal soil temperatures induced oxidative stress in leaves of creeping bentgrass cultivars differing in heat tolerance. Crop Sci. 41:430–435.[Abstract/Free Full Text]
- Littell, R.C., G. Milliken, W.W. Stroup, and R.D. Wolfinger. 1996. SAS system for mixed models. SAS Inst., Cary, NC.
- Liu, X., and B. Huang. 2000. Carbohydrate accumulation in relation to heat stress tolerance in two creeping bentgrass cultivars. J. Am. Soc. Hortic. Sci. 125:442–447.[Abstract/Free Full Text]
- Peacock, C.H., D.C. Bowman, L.T. Lucas, and R.P. Patterson. 1995. The effects of syringing and handwatering on the leaf water potential of creeping bentgrass greens. p. 147. In 1995 Agronomy abstracts. ASA, Madison, WI.
- Taylor, G.R., C.H. Peacock, J.M. DiPaola, L.T. Lucas, and U. Blum. 1994. Influence of wind velocity on temperature, leaf water potential and soil moisture percentage of creeping bentgrass golf greens. p. 187. In 1995 Agronomy abstracts. ASA, Madison, WI.
- Xu, Q., and B. Huang. 2000a. Growth and physiological responses of creeping bentgrass to changes in air and soil temperatures. Crop Sci. 40:1363–1368.[Abstract/Free Full Text]
- Xu, Q., and B. Huang. 2000b. Effects of differential air and soil temperature on carbohydrate metabolism in creeping bentgrass. Crop Sci. 40:1368–1374.[Abstract/Free Full Text]
- Xu, Q., and B. Huang. 2001. Lowering soil temperatures improves creeping bentgrass growth under heat stress. Crop Sci. 41:1878–1883.[Abstract/Free Full Text]
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ABSTRACT
INTRODUCTION
