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Published online 18 May 2006
Published in Crop Sci 46:1515-1525 (2006)
© 2006 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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TURFGRASS SCIENCE

Bermudagrass Putting Green Growth, Color, and Nutrient Partitioning Influenced by Nitrogen and Trinexapac-Ethyl

Patrick E. McCullougha, Haibo Liub,*, Lambert B. McCartyb, Ted Whitwellb and Joe E. Tolerc

a Dep. of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901-8520
b Dep. of Horticulture, D-136 Poole Ag. Center, Clemson, SC 29634-0319
c Dep. of Applied Economics and Statistics, Clemson University, Clemson, SC 29634-0319

* Corresponding author (haibol{at}clemson.edu)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Plant growth regulators (PGRs) improve turf color by inhibiting leaf growth and may reduce fertilization requirements of bermudagrass [Cynodon dactylon (L.) Pers. x C. transvaalensis Burtt-Davy] golf greens by reducing nutrients removed through clipping collection. To test this hypothesis, growth, color, and nutrient allocation of ‘TifEagle’ bermudagrass maintained at 3.2 mm were investigated in field experiments conducted in Clemson, SC, from April to August in 2003 and 2004. Ammonium nitrate was applied at 6, 12, 18, or 24 kg N ha–1 wk–1 with a PGR, trinexapac-ethyl {[4-(cyclopropyl-[{alpha}]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester]} (TE), at 0 or 0.05 kg a.i. ha–1 3 wk–1. Turf required 18 to 24 kg N ha–1 wk–1 from May to June and ≤12 kg N ha–1 wk–1 from July to August to maintain acceptable color (≥7, 1–9 scale). Trinexapac-ethyl initially caused discoloration but bermudagrass recovered and had color enhanced 10 to 25% from nontreated. Trinexapac-ethyl reduced clippings 67% from nontreated while clippings, percentage of lateral regrowth, and aerification recovery increased with N rate. Bermudagrass treated with TE had similar root mass to nontreated but 5% greater stolon and rhizome mass, 18% higher chlorophyll concentration, up to 67% reduced lateral regrowth, and up to 38% reduced aerification recovery. Trinexapac-ethyl reduced leaf N, P, K, Mg, S, and Fe concentrations 10 to 25% and increased rhizome concentrations 8 to 36%. Nutrients recovered through clippings were reduced {approx}70% from TE applications while TE-treated turf had increased N, P, K, Ca, Mg, S, Mn, and Fe retention in stolons and rhizomes. Overall, TE enhanced color while reducing nutrient translocation from rhizomes to leaves, thus increasing bermudagrass nutrient retention.

Abbreviations: PGR, plant growth regulator • TE, trinexapac-ethyl • USGA, United States Golf Association • WAA, week after aerification • WAINT, week after initial N treatment


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
HYBRID bermudagrass is widely used in hot and warm humid climatic regions for golf course putting greens. Traditional bermudagrass putting green cultivars like ‘Tifdwarf’ and ‘Tifgreen’ only tolerate long-term mowing heights of 4.8 mm which produce inferior playing surfaces compared to creeping bentgrass greens (Agrostis stolonifera L.) (Beard, 1973; Foy, 1991). Dwarf-type bermudagrasses are improved cultivars that tolerate long-term mowing heights of ≤3.2 mm and produce putting green quality comparable to creeping bentgrass for transition zone golf courses (Hanna and Elsner, 1999; McCarty and Miller, 2002). Finer leaf textures and lower growth habits of dwarf-type cultivars are accredited to genetic and morphological differences from Tifdwarf and Tifgreen bermudagrasses (Burton, 1991; Hanna and Elsner, 1999; Capo-chichi et al., 2005).

Bermudagrass greens are heavily fertilized with annual N ranging from 390 to 1170 kg N ha–1 to meet growth requirements and compensate for nutrient loss through daily clipping removal (McCarty, 2005). Cultural practices, including excessive N fertility and routine close mowing, may further shift turfgrass nutrient allocation from roots to shoots (Hull, 1978). Compared to Tifdwarf bermudagrass, popular dwarf-type cultivars like ‘TifEagle’ have greater thatch production and reduced root growth as a result of closer mowing heights (White, 1998; White et al., 2004). Maintaining sufficient N fertility levels without exacerbating root growth is a major agronomic concern for successful long-term dwarf bermudagrass culture.

Plant growth regulators are widely used in routine putting green management for promoting smoother putting surfaces by reducing undesirable top growth (Fagerness et al., 2000). A gibberellic acid inhibitor, TE, is widely used for putting green management and effectively reduces clippings of higher mowed bermudagrasses such as ‘Tifway’ (Johnson, 1994; Fagerness and Yelverton, 2000). Trinexapac-ethyl is a PGR that disrupts 3ß-hydroxilation of GA20 to GA1 in late stages of GA (gibberellic acid) biosynthesis (Rademacher, 2000; Tan and Qian, 2003). Applications of TE often enhance turfgrass color and quality from increased cell density and compacted leaf tissue containing greater chlorophyll per unit leaf area (Qian and Engelke, 1999; Ervin and Koski, 2001; Heckman et al., 2001). Inhibiting leaf growth with TE enhances dwarf bermudagrass color, promotes root growth, and improves ball roll distances (McCullough, 2004). Bunnell et al. (2005) found inhibiting TifEagle bermudagrass leaf growth with TE helped maintain acceptable golf greens under low light intensities by increasing chlorophyll concentrations and improving turf quality. Similar results have been reported when TE was applied to Kentucky bluegrass (Poa pratensis L.), zoysiagrass [Zoysia matrella (L.) Merr.], and creeping bentgrass (Qian and Engelke, 1999; Goss et al., 2002; Steinke and Stier, 2003).

Reducing dwarf-type bermudagrass shoot growth with TE may encourage nutrient allocation for storage in belowground tissues. Fagerness et al. (2004) noted TE applied at 0.11 kg ha–1 4 wk–1 on Tifway bermudagrass reduced 15N allocation to leaf tissue while increasing N retention in rhizomes. It was also noted Tifway bermudagrass receiving TE had NO3–N leaching reduced approximately 60% from nontreated.

Dwarf bermudagrass putting greens require intensive management since closer mowing heights may exacerbate root decline, thatch production, and sensitivity to environmental stresses (Jiang et al., 2004; White et al., 2004; Hollingsworth et al., 2005). Dwarf bermudagrass putting greens generally require greater quantities of applied mineral nutrients than creeping bentgrass greens and higher mowed cultivars, such as Tifway (McCarty and Miller, 2002). Thus, improving nutrient use efficiency would be agronomically and economically beneficial for long-term putting green culture. Furthermore, incorporating TE into fertility programs may allow practitioners to reduce N requirements by enhancing leaf color and minimizing nutrients removed through clipping collection.

To test this hypothesis, field experiments were conducted to investigate (i) physiological responses of TifEagle bermudagrass including nutrient allocation and chlorophyll concentrations from TE integrated into N fertility regimes, and, (ii) growth responses of TifEagle bermudagrass shoots, roots, and rhizomes following N and TE treatments.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Field experiments were conducted from April to August in 2003 and 2004 on a TifEagle bermudagrass putting green constructed approximately to United States Golf Association (USGA) specifications (USGA Green Section Staff, 1993) in July 2002 at the Turf Service Center, Clemson University, Clemson, SC.

Potash was applied according to soil tests at 48 kg K ha–1 to help correct deficiencies on 17 Apr. 2003. Beginning the first week in May, turf was mowed 6 d wk–1 at 3.2 mm and irrigated as needed to prevent plant stress. On 21 June 2003 and 18 June 2004, 12 kg N ha–1 was applied to all plots with a greens-grade granular fertilizer containing 18% N, 1% P, 15% K, 0.6% Mg, 7% S, 1% Fe, 0.5% Mn, and 2% Cl. Bermudagrass was aerified with 1.3-cm-diameter hollow tines with 5-cm spacing and 10-cm lengths on 20 May 2003, 28 July 2003, 26 May 2004, and 28 July 2004. Cores were removed and holes were filled with topdress sand similar to rootzone mix. Bermudagrass aerification recovery was visually rated on a 0 to 100% scale where 0 equaled no recovery and 100 equaled complete aerification recovery. Crabgrass germination following aerifications was rated by counting all plants per plot.

Treatments
The experimental design was a split-block with four replications of 1.5 by 2.1 m plots (Steele et al., 1997). Four N rates were whole plots (1.5 by 4.2 m) with TE applied across N treatments over half of every block (1.5 by 2.1 m). Ammonium nitrate solution was applied with a single-nozzle CO2 spray tank at 6, 12, 18, or 24 kg N ha–1 wk–1 beginning 24 Apr. 2003 and 26 Apr. 2004. Nitrogen treatments were continued for 16 wks thereafter. Trinexapac-ethyl, in emulsifiable concentration (1EC), was applied at 0 or 0.05 kg a.i. ha–1 3 wk–1 with a CO2 sprayer at 700 L ha–1 from 8 May to 9 Aug. 2003 and 4 May to 11 Aug. 2004.

Turf Color and Growth Measurements
Turf color was visually rated weekly on a 1-to-9 scale with 1 equal to brown turf and 9 equal to dark green turf. Color ratings below 7 were considered unacceptable. Seedheads were visually measured as percentage of plot coverage. Clippings were harvested 10, 17, 24 May 2003 and 2004; 10, 14, 22, 24, 28, 22 June 2003 and 2004; 2, 5, 7, 12, 14, 19 July 2003 and 2004; 7 Aug. 2003 and 2004 with a walk behind greensmower (Toro, Bloomington, MN). Clippings were oven dried at 80°C for 48 h and then weighed. Two 600-cm3 (30 by 20 cm2) soil core samples per plot were taken 23 May 2003, 20 June 2003, 19 July 2003, 14 Aug. 2003, 18 May 2004, 17 June 2004, 15 July 2004, and 11 Aug. 2004. Roots and stolons and rhizomes were harvested by thoroughly washing samples to remove soil and organic matter over sieve screens that prevented loss of root fragments. Samples were oven dried as previously noted. After backfilling soil in sample holes, percentage of lateral regrowth was measured with a sampling grid (1-mm2 cells) beginning 2 wk after the first and second root samples. Total cells with plant tissue were calculated as percentage of the 20-cm2 area until complete bermudagrass cover.

Tissue Tests and Chlorophyll Concentration Measurements
Clippings, roots, and stolon and rhizome samples were subjected to tissue analysis conducted at the Clemson Agriculture Service Laboratory. Leaf tissue was collected for subsequent tissue analysis on the same day as roots by collecting clippings. Soil (30-cm depth) was randomly taken from root samples and analyzed for NO3–N concentrations. Nitrogen concentrations were extracted using a LECO FP528 N combustion analyzer (Warrendale, PA) with tissue analysis procedures (Anonymous, 2000). Other plant tissue nutrients were determined using wet ashing procedures (Anonymous, 2000) with HNO3 plus 30% H2O2 on a Digestion Block Magnum Series Block Digester (Martin Machine, Ivesdale, IL) and analyzed with an ICP model TJA-61E autosampler (Thermo Electron-Chromatography, Madison, WI). Soil NO3–N determinations were made with an ISE Electrode (Thermo Electron Corp., Beverly, MA) by dissolving 173.2 g Al2(SO4)3.18H2O, 12.8 g H3BO3, and 0.7222 g KNO3 in 8 L of deionized water (Anonymous, 2000). Chlorophyll concentrations (milligrams per gram of fresh clipping weight) were determined 8 and 16 wk after initial N treatments (WAINT) with a spectrophotometer (Genesys 20 Thermo Spectronic Model 4001/4, Waltham, MA) (Moran and Porath, 1980).

Data Analysis
Data were subjected to analysis of variance with SAS General Linear Model procedure (SAS Institute, 1999). Orthogonal polynomial contrasts examined linear, quadratic, and cubic plant responses to N levels for all parameters and root sampling dates. Cubic responses were not detected for N rates and thus only linear or quadratic relationships are presented. A cubic response was detected for root mass sampling date in 2004 and thus a cubic term is presented for this parameter.


   RESULTS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
Turf Color (2003)
Turf color results are presented separately by year since interactions were detected with treatments. Nitrogen x TE interactions were detected on six dates in 2003. Turf color initially increased linearly with N rate 1 WAINT (3 May), but quadratic relationships were observed 2 WAINT (10 May) as higher N rates produced similar turf color (Table 1). On 24 May, 4 d after aerification, turf color was unacceptable across all treatments but a significant N x TE interaction was detected. Turf color was linearly reduced with increased N rate for nontreated bermudagrass while color quadratically increased with N rate for TE-treated bermudagrass. Color of nontreated bermudagrass fertilized with 18 and 24 kg N ha–1 wk–1 recovered from aerification injury by 31 May as color linearly increased with N rate. However, TifEagle bermudagrass fertilized with 6 and 12 kg N ha–1 wk–1 only had acceptable color when treated with TE. Subsequent TE treatments reduced TifEagle bermudagrass color 36, 15, 48, and 21% from nontreated, a week after the first, second, third, and fourth applications in 2003, respectively. The fifth application, however, did not cause discoloration from the nontreated. Bermudagrass color recovered and TE treatments enhanced color from nontreated 10 to 25% by 5, 7, 10, and 16 WAINT (31 May, 14 June, 5 July, 14 August). Color was reduced for bermudagrass fertilized at 18 and 24 kg N ha–1 wk–1 with and without TE by 13 and 15 WAINT (26 July and 9 August), respectively, but TE-treated bermudagrass fertilized at 18 kg N ha–1 wk–1 had acceptable color.


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  		Table 1. Turf color for TifEagle bermudagrass treated with N and trinexapac-ethyl (TE) from May to August, 2003.

 
TE and higher N rates slowed TifEagle bermudagrass dormancy, but interactions were not detected among treatments (Table 2). By 16 Oct. 2003, TifEagle bermudagrass receiving TE applications during the growing season averaged 57% darker color compared to nontreated as turf began to go dormant. Bermudagrass visual color linearly increased with N rate 16 Oct. and 1 Dec. 2003. TifEagle bermudagrass treated with TE retained green color on 1 Dec. 2003 but all plots were completely dormant 1 Jan. 2004.


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  		Table 2. Fall and winter turf color for ‘TifEagle’ bermudagrass treated with N and trinexapac-ethyl (TE) in field experiments, Clemson, SC.

 
Turf Color (2004)
Bermudagrass emerged from dormancy in early March but returned to dormancy with subsequent cooler temperatures which masked treatment influences on spring greenup. Nitrogen x TE interactions were not detected until 11 Aug. 2004. Two WAINT (7 May 2004), TE-treated bermudagrass averaged 5% darker color than nontreated (Table 3). Similar to 2003, turf color initially linearly increased with N rates at 1 and 2 WAINT (1 and 7 May). Beginning 3 WAINT (13 May), quadratic relationships with N rate and turf color were detected as higher N rates (18 and 24 kg N ha–1 wk–1) produced similar color. From 1 May to 18 June 2004, bermudagrass fertilized at 6 and 12 kg N ha–1 wk–1, had unacceptable color. Thereafter, bermudagrass had acceptable color when fertilized with 12 kg N ha–1 wk–1 but color was unacceptable at 6 kg N ha–1 wk–1. On 3 June (1 wk after aerification [WAA]), bermudagrass fertilized with 24 kg N ha–1 wk–1 (with and without TE) had color decline by 17% from 27 May ratings taken before aerification. Bermudagrass color recovered to acceptable levels by 11 June.


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  		Table 3. Turf color for ‘TifEagle’ bermudagrass treated with N and trinexapac-ethyl (TE) from May to August 2004.

 
Initial TE applications on 4 May 2004 did not cause turf discoloration as in 2003. The second TE application on 25 May reduced color 14% on 3 June but turf recovered and bermudagrass color was enhanced 6 to 10% from 11 June to 24 June. The third TE application reduced bermudagrass color 21% on 1 July but color was enhanced 19% from nontreated by 8 July. Nontreated bermudagrass fertilized with high N rates (18 and 24 kg N ha–1 wk–1) had color decline comparable to bermudagrass fertilized with 6 and 12 kg N ha–1 wk–1 on 4 Aug. and 11 Aug. 2004. However, TE masked these effects and color of TE-treated turf quadratically increased with N rate on 11 Aug. 2004.

TifEagle Bermudagrass Growth
Date x treatment interaction was not detected for clipping yield, and thus results were pooled over all sampling dates. Nitrogen x TE interaction was not detected for clipping yield, as clippings quadratically increased with N rate (Table 4). TifEagle bermudagrass treated with TE had clipping yield reduced 67% from nontreated.


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  		Table 4. Clipping yield root mass, stolon and rhizome mass, chlorophyll concentration, crabgrass cover, and seedhead cover of ‘TifEagle’ bermudagrass treated with N and trinexapac-ethyl (TE) in field experiments, 2003 to 2004, Clemson, SC.

 
Sample x treatment and N x TE interactions were not detected for root mass. Increased N rate linearly reduced root mass while bermudagrass treated with TE had similar root mass to nontreated (Table 4). When averaged over all treatments, bermudagrass root mass was linearly reduced from May to August 2003. In 2004, a cubic relationship was detected with date and root mass. From May to June root mass declined but then increased by 52% in July. From July to August root mass was reduced by 32%.

Treatment x sampling date or N x TE interactions were not detected for stolon and rhizome mass. Stolon and rhizome mass linearly increased from May to August of both years and was 34% greater in 2004 than 2003. TifEagle bermudagrass treated with TE had 5% greater stolon and rhizome mass than nontreated turf. A quadratic relationship was detected with N rate as stolon and rhizome mass increased with N rate from 6 to 12 kg N ha–1 wk–1 but decreased with higher N rates.

Sample date x treatment interaction was detected for percentage of lateral regrowth, and thus results are presented separately by date. Nitrogen x TE interaction was not detected for percentage of lateral regrowth (Table 5, Fig. 1). Increased N rate linearly enhanced lateral regrowth from 6 June to 27 June and 4 July to 11 July from samples removed 23 May and 20 June 2003, respectively. From samples initiated 18 May and 17 June 2004, lateral regrowth initially linearly increased with N rate but quadratic relationships were detected as higher N rates promoted similar growth.


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  		Table 5. Significance of N and trinexapac-ethyl (TE) for ‘TifEagle’ bermudagrass lateral regrowth and aerification recovery.

 

Figure 1
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  		Fig. 1. Percentage of lateral regrowth from two separate 20-cm2 samples of ‘TifEagle’ bermudagrass treated with N (34–0-0) and trinexapac-ethyl (0 or 0.05 kg ha–1 3 wk–1) in field experiments, Clemson, SC.

 
From samples initiated 23 May and 20 June 2003, TifEagle bermudagrass treated with TE had lateral regrowth reduced 4 to 34% and 3 to 67%, respectively, than nontreated. Bermudagrass lateral regrowth was most significantly inhibited by TE 1 wk after sod plugs were removed. From samples initiated 18 May 2004, TE only reduced lateral regrowth 13% after 2 wk but TE reduced lateral regrowth 19 to 32% for up to 4 wk after sample initiation on 17 June 2004.

Year x treatment interactions were detected for aerification recovery and thus years are presented separately. Bermudagrass recovery after aerification on 20 May 2003 quadratically increased with N rates 1 and 2 WAA (26 May and 3 June) (Table 5, Fig. 2). Bermudagrass recovery linearly increased with N rates 1 WAA on 26 May 2004 but recovery quadratically increased with N rates by 2 and 3 WAA. Bermudagrass treated with TE had recovery reduced 13% from nontreated 1 WAA on 20 May 2003; however, recovery was similar to nontreated on other dates. In 2004, TE reduced aerification recovery 13 to 38% from nontreated 1 to 3 WAA which allowed crabgrass (Digitaria spp.) germination in aerification holes by 17 June 2004. Inhibited aerification recovery of TE-treated bermudagrass resulted in {approx}8.5-fold more crabgrass plants per square meter than nontreated but N input had no effects on crabgrass germination (Table 4).


Figure 2
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  		Fig. 2. ‘TifEagle’ bermudagrass recovery from aerifications with 1.3-cm-diameter hollow tines at 5-cm spacing and 10-cm lengths on 20 May 2003 and 26 May 2004, as influenced by N (34–0-0) and trinexapac-ethyl (0 or 0.05 kg ha–1 3 wk–1) in field experiments, Clemson, SC.

 
Bermudagrass seedheads were present in June of both years but results were pooled since interactions were not detected with treatments. Nitrogen x TE interaction was not detected but TifEagle bermudagrass seedhead coverage was quadratically reduced as N rates increased (Table 4). Nontreated bermudagrass had 10% seedhead coverage in June while bermudagrass treated with TE had <1% coverage.

Increased N rate linearly reduced chlorophyll concentrations 8 WAINT; however, TE-treated TifEagle bermudagrass had 18% higher total chlorophyll concentrations than nontreated (Table 4). Differences in chlorophyll concentration were not detected 16 WAINT (data not shown).

Nutrient Concentrations
Leaf N concentrations linearly increased with N rate 8, 12, and 16 WAINT in 2003 (data not shown). TifEagle bermudagrass treated with TE had reduced leaf N concentrations by {approx}10%, 12 and 16 WAINT (Table 6). Conversely, stolon and rhizome N concentrations of TE-treated bermudagrass were increased 14 and 22% by 12 and 16 WAINT, respectively, as compared to nontreated turf.


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  		Table 6. Nutrient concentrations in ‘TifEagle’ bermudagrass treated with trinexapac-ethyl (TE) in field experiments, 2003–2004, Clemson, SC.

 
Similarly to N levels, leaf P, K, and S concentrations were reduced 9, 14, and 9%, respectively, in TE-treated turf 8 WAINT in 2003 and remained lower than nontreated turf by 16 WAINT. Similarly to stolon and rhizome N levels, P, K, Ca, and Mg concentrations increased 12 WAINT in TE treated and were 21, 30, 86, and 6% greater than nontreated turf by 16 WAINT, respectively.

Leaf Mn concentrations in TE-treated bermudagrass increased 8, 24, and 19% by 8, 12, and 16 WAINT in 2003, respectively. Turf treated with TE had 26% greater leaf Fe concentrations 8 WAINT but concentrations were reduced 12% from nontreated by 12 WAINT. Bermudagrass treated with TE had 11 and 36% higher stolon and rhizome Mn and Fe concentration, 12 WAINT. Stolon/rhizome Cu concentrations were decreased 8% in TE-treated turf 12 WAINT. Leaf and stolon and rhizome micronutrient levels of TE-treated turf were similar to nontreated 16 WAINT.

In 2004, leaf nutrient concentrations of TE-treated bermudagrass were similar to non–TE-treated turf 4 and 8 WAINT (data not shown). Bermudagrass treated with TE had leaf N concentrations reduced 7% from nontreated by 12 and 16 WAINT. Conversely, stolon and rhizome N concentrations of TE-treated bermudagrass were 8% higher than nontreated by 12 and 16 WAINT. Leaf K concentrations of TE-treated turf were reduced 15% by 12 WAINT. With the exception of N, TE-treated bermudagrass in 2004 had similar stolon and rhizome nutrient concentrations to nontreated turf. Leaf P concentrations were reduced in TE-treated turf by 16% 16 WAINT. Root N and soil NO3–N concentrations of TE-treated turf were similar to nontreated on all dates, but concentrations linearly increased with N rates (data not shown).

Nutrient Recovery
Total nutrients recovered through clippings increased with N rate (Table 7). However, inhibiting bermudagrass leaf growth with TE reduced total clipping nutrients recovered by 70 to 75% from nontreated. As nutrient removal through clippings was decreased from growth suppression by TE, greater amounts of nutrients were retained in belowground plant tissues relative to the nontreated. TifEagle bermudagrass treated with TE had 7 to 21% higher Ca, Mg, S, Mn, and Fe retention in stolons and rhizomes 8 WAINT (20 June) in 2003 (Table 8). By 14 Aug. 2003, TE-treated turf averaged 23, 19, 30, 88, and 8% higher N, P, K, Ca, and Mg retention in stolons and rhizomes, respectively. In 2004, TifEagle bermudagrass treated with TE had similar nutrient retention in stolons and rhizomes 4 and 8 WAINT (data not shown). By 12 WAINT (15 July), TE-treated bermudagrass had {approx}10% higher N and P retention in stolons and rhizomes. Bermudagrass treated with TE averaged 23% higher N retention in stolon and rhizomes than nontreated by 11 Aug. 2004. Root N recovery was similar across all treatments (data not shown).


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  		Table 7. Total clipping nutrient recovery from four sampling dates for ‘TifEagle’ bermudagrass treated with N and trinexapac-ethyl (TE) in two combined field experiments.

 

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  		Table 8. Nutrient retention of stolons and rhizomes of ‘TifEagle’ bermudagrass treated with trinexapac-ethyl (TE) in field experiments, 2003 to 2004, Clemson, SC.

 

   DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
The presence of clippings after mowing interferes with the direction and velocity of ball roll on golf greens and thus their removal is necessary. However, substantial amounts of essential plant nutrients are removed and not recycled to putting greens from routine clipping collection. Heavy fertilizations of dwarf-type bermudagrass greens may deplete nutrients stored in rhizomes as shoots compete for plant reserves. Inhibiting bermudagrass shoot growth with TE reduces nutrients removed through clippings and minimizes nutrient partitioning required for leaf growth.

Throughout two growing seasons, TifEagle bermudagrass color improved with increased N rate but color declined with higher N rates in July and August likely from mower scalping and possibly excessive N levels for dwarf-type bermudagrass. Fertilizing TifEagle bermudagrass at 12 kg N ha–1 wk–1 provided the most consistent turf color from April to August 2003. In 2004, bermudagrass fertilized with 12 kg N ha–1 wk–1 did not have acceptable turf color until 9 WAINT (24 June). TifEagle bermudagrass grown in the transition zone may require higher N input (18 to 24 kg N ha–1 wk–1) during spring and early summer months but these rates appear to be excessive when continually applied throughout the summer.

Trinexapac-ethyl treatments in both years caused discoloration but bermudagrass color recovered and was enhanced from nontreated turf. Discoloration following initial TE applications did not occur in 2004 likely due to higher May temperatures than 2003. Fagerness et al. (2002) noted that applications of TE to Tifway bermudagrass when temperatures were <20°C caused leaf chlorosis and reduced turf density. Similar discoloration with TE applications has been reported on Tifway bermudagrass in late spring and early summer but turf recovered to acceptable levels within 1 or 2 wk (Johnson, 1994; Fagerness and Yelverton 2000). In plots adjacent to this experiment, TifEagle bermudagrass discoloration was minimized by applying TE at 0.017 kg ha–1 wk–1 from April to August in 2003 and 2004 (McCullough, 2004). Short-term discoloration of bermudagrass greens in early summer from TE likely results from temperature, nutrient status, and adaptation to GA inhibition which warrants further investigations with bermudagrass putting green cultivars, maturity, and fertility levels.

TifEagle bermudagrass chlorophyll concentrations declined with increased N fertility likely from less chlorophyll per unit leaf area with enhanced growth. Conversely, reduced leaf growth from TE increased chlorophyll concentration per unit leaf area. This has been previously attributed to increased cell density and compacted leaf tissue in cool season turfgrasses (Ervin and Koski, 2001; Heckman et al., 2001).

Higher N fertility generally promotes shoot growth giving leaf tissue competitive priority for available root carbohydrates (Hull, 1978). Increasing N rate enhanced TifEagle bermudagrass shoot growth but reduced root mass. Furthermore, increased N rate from 6 to 12 kg N ha–1 wk–1 increased TifEagle bermudagrass stolon and rhizome mass but reductions were noted when N rates were increased to 18 and 24 kg N ha–1 wk–1. Reduced TifEagle bermudagrass stolon and rhizome mass may have resulted from prolific shoot production with higher N rates, thus decreasing thatch accumulation. TifEagle bermudagrass treated with TE had greater stolon and rhizome accumulation than nontreated turf which was exacerbated by reduced lateral growth. Reduced lateral growth of TE-treated bermudagrass delayed aerification recovery which may concern practitioners since dwarf bermudagrass requires routine aerification, topdressing, and vertical mowing to manage prolific thatch accumulation (White et al., 2004). Dwarf bermudagrass managers will need to withhold TE treatments before aerification or enhance N levels to promote quicker recovery. However, increased N to 24 kg N ha–1 wk–1 caused substantial discoloration following aerifications in both years but bermudagrass color generally recovered to acceptable levels within 7 d.

TifEagle bermudagrass root growth was linearly reduced from May to August 2003, likely from persistent shoot growth and routine maintenance at 3.2-mm mowing height. Low cutting height and frequent mowing are directly correlated with decreases in root growth and carbohydrate reserves (Fagerness and Yelverton, 2001; Liu and Huang, 2002). However, an increase in root mass was observed in July 2004 which was also noted in plots adjacent to this experiment (McCullough, 2004). Applications of TE did not affect bermudagrass putting green root mass which agrees with previous research on ‘Penncross’ creeping bentgrass greens (Fagerness and Yelverton, 2001).

Under the influence of TE, TifEagle bermudagrass allocated greater amounts of plant nutrients to belowground tissues. These are the first comprehensive reports for bermudagrass putting green nutrient use as influenced by N fertility and TE. Fagerness et al. (2004) noted less N translocated to Tifway bermudagrass leaves and greater N storage in verdure following TE applications. TifEagle bermudagrass fertilized with 18 and 24 kg N ha–1 wk–1 had acceptable color in May of both years but less N was allocated to leaf tissue when TE was applied. Furthermore, bermudagrass fertilized with 18 and 24 kg N ha–1 wk–1 plus TE had lower leaf N concentrations and higher N concentrations in stolons and rhizomes by May of both years from nontreated. Results suggest fertilizing TifEagle bermudagrass early in the growing season with higher N rates (18 and 24 kg ha–1 wk–1) may increase nutrient storage in rhizomes when using TE to better prepare bermudagrass for active growth later in the season. Since greater amounts of nutrients are stored early in the growing season, continually fertilizing with 18 and 24 kg N ha–1 wk–1 may not be necessary to provide acceptable turf when using TE.

Enhanced turf color in late summer and early fall from repeated use of TE delayed TifEagle bermudagrass winter dormancy in 2003. Similar results were noted when applying TE throughout the growing season to Tifway bermudagrass maintained at fairway mowing heights (Fagerness and Yelverton, 2000; Richardson, 2002). In this experiment, TE-treated TifEagle bermudagrass in 2003 had similar nutrient concentrations to nontreated turf in spring of 2004. Delayed winter dormancy may have resulted from increased nutrient allocation from rhizomes to leaves which prevented leaf chlorosis during cooler temperatures.

Results from these experiments suggest dwarf bermudagrass managers in the transition zone may be able to reduce yearly N requirements when consistently using TE to inhibit shoot growth. Reducing leaf growth of dwarf bermudagrass greens reduces nutrient removal through clippings and favors nutrient storage in rhizomes. Applications of TE appear not to adversely affect dwarf bermudagrass rooting but may increase thatch production from greater stolon and rhizome mass with reduced lateral growth. Although TifEagle is a widely used bermudagrass putting green cultivar, other dwarf bermudagrass cultivars may perform differently from maintenance with various fertilizer formulations, disease control strategies, or cultivation practices which warrant further investigations in the transition zone.


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ABSTRACT
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Technical contribution of the South Carolina Agricultural Experiment Station, Clemson, SC.

Received for publication September 1, 2005.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 




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