Frequent Trinexapac-ethyl Applications Reduce Nitrogen ...tendents manage putting greens and the amounts were credited to the following season’s total annual N fertility rate (Table

1348 WWW.CROPS.ORG CROP SCIENCE, VOL. 52, MAY–JUNE 2012

RESEARCH

Application of N fertilizer is used to enhance turfgrass yield, color, and visual quality as N is often the most limiting

nutrient in a turfgrass system (Christians et al., 1979). However, maximizing yield is rarely, if ever, the goal in turfgrass manage-ment. Bowman (2003) reported that turfgrass yield increased with increasing N rate even when N rates are several times greater than recommendations. Nitrogen requirements for golf course putting greens are often based on the annual N required to maintain turf-grass recuperative potential and visual quality deemed acceptable by the golfi ng public and typically range from 100 to 250 kg ha–1 N annually for creeping bentgrass (Agrostis stolonifera L.) (Carrow et al., 2001).

A primary pathway of N removal on golf putting greens results from mowing and subsequent removal of clippings, which would otherwise disrupt playability. The magnitude of N removal is the product of clipping yield and tissue N content. Heckman et al. (2000) and Kopp and Guillard (2002) found that removing clippings after mowing approximately doubled annual N require-ments of Kentucky bluegrass (Poa pratensis L.) lawns. Most uni-versity recommendations aim to match N fertilization with N removal during mowing (McCarty, 2005). Therefore, manage-ment practices that suppress N removal by mowing may reduce annual N fertilization requirements.

Application of trinexapac-ethyl (TE) is common on turfgrass to increase visual quality, color, and shoot density (Qian and Engelke,

Frequent Trinexapac-ethyl Applications Reduce Nitrogen Requirements of

Creeping Bentgrass Golf Putting Greens

William C. Kreuser* and Douglas J. Soldat

ABSTRACT

The plant growth regulator trinexapac-ethyl

(TE) [4-(cyclopropyl-a-hydroxymethylene)-3,5-

dioxo-cyclohexanecarboxylic acid ethylester]

reduces turfgrass clipping yield and enhances

turfgrass color and density. Typically, such

responses are achieved through alteration of

N application rate, yet few have comprehen-

sively investigated the effect of TE on turfgrass

N requirements. We hypothesized that TE

reduces putting green N requirements with-

out sacrifi cing turfgrass quality. A three year

study was conducted on a creeping bentgrass

(Agrostis stolonifera L.) putting green with treat-

ments consisting of three N application rates

(5, 10, and 20 kg N ha–1 14 d–1) with or without

TE application. To sustain season-long growth

suppression, TE was applied at 0.10 kg a.i. ha–1

every 200 growing degree days (GDD; base

0°C). Turfgrass yield and color were quanti-

fi ed every other week, and clipping tissue N

content was analyzed monthly. Clipping yield,

tissue N content, N removal, and color index

increased with N rate. All attributes responded

linearly to N application rate. Trinexapac-ethyl

enhanced color while suppressing clipping yield

and nutrient removal from mowing. As a result,

TE reduced creeping bentgrass putting green

N requirements by 25% conservatively and on

several occasions by greater than 50%.

W.C. Kreuser, Department of Horticulture, Cornell University, Ithaca,

NY 14853; D.J. Soldat, Department of Soil Science, University of Wis-

consin-Madison, Madison, WI 53706. Received 18 July 2011. *Cor-

responding author ([email protected]).

Abbreviations: GDD, growing degree days; TE, trinexapac-ethyl.

Published in Crop Sci. 52:1348–1357 (2012).doi: 10.2135/cropsci2011.07.0364© Crop Science Society of America | 5585 Guilford Rd., Madison, WI 53711 USA

All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher.

CROP SCIENCE, VOL. 52, MAY–JUNE 2012 WWW.CROPS.ORG 1349

1999; Ervin and Koski, 1998; Beasley and Branham, 2007; Ervin and Zhang, 2008; Kreuser and Soldat, 2011), which is similar to increasing N rate (i.e., Waddington et al., 1972; Christians et al., 1979, 1981; Johnson et al., 2003). These enhancements occur because TE inhibits gibberel-lin synthesis, which results in reduced leaf cell length and increased mesophyll cell density, chlorophyll, and cytoki-nin concentrations (Rademacher, 2000; Ervin and Koski, 2001; Stier and Rodgers, 2001; Bunnell et al., 2005).

Unlike N, however, TE suppresses turfgrass clipping yield. Researchers have noted that TE typically provides 20 to 40% growth suppression on creeping bentgrass put-ting greens for a duration dependent on air temperature but typically less than 4 wk (Beasley and Branham, 2005; McCullough et al., 2006c; Kreuser and Soldat, 2011). Additionally, TE applications have been associated with redistribution or partitioning of nutrients from plant leaves to the roots while N uptake is unaff ected (Fagerness et al., 2004; McCullough et al., 2006b, c). The additive eff ect of reduced clipping yield and foliar N content would sub-stantially reduce N removal during mowing.

We hypothesized that repeat applications of TE to creeping bentgrass putting greens would reduce annual N requirements by both reducing N removal during mow-ing and increasing turfgrass color, which are responses often used to determine N requirements. The objective of this study was to evaluate the eff ect of N application rate and TE on creeping bentgrass putting green yield, color, clipping tissue N content, and N removal. Evalu-ations of these responses were used to assess diff erences in creeping bentgrass N requirements as infl uenced by multiple TE applications.

MATERIALS AND METHODSA fi eld experiment was conducted on a creeping bentgrass (cv.

Memorial) putting green research plot at the O.J. Noer Turfgrass

Research and Education Facility in Madison, WI, during 2008

to 2010. The green was constructed in 2006 to United States

Golf Association specifi cations for putting green construction

with peat-amended calcareous sand (20% v/v) with a pH of 7.4

(USGA Green Section Staff , 2004). The green was mowed 6

d wk–1 at 3.2 mm with a Toro Greensmaster 1000 (Toro Co.)

and irrigated daily with an overhead irrigation system to 80% of

estimated evapotranspiration as calculated by an on-site weather

station. Chlorothalonil (2,4,5,6-tetrachloroisophthalonitrile)

applications were used to control turfgrass diseases during both

years. Annual soil testing indicated that all essential soil nutri-

ents were suffi cient during all 3 yr of the experiment, although

maintenance applications of P and K were applied periodically

as monopotassium phosphate to off set leaching, immobilization,

and nutrient removal during mowing.

Plots measured 2.4 by 1.8 m and were arranged in a ran-

domized complete block design with six treatments in four

complete blocks. Treatments consisted of a 3×2 factorial of three

liquid urea N rates (5, 10, and 20 kg N ha–1) applied every other

week with or without TE application (Primo Maxx, Syngenta

Co.). Approximately 5 mm of irrigation was applied following

N application. Nitrogen treatments occurred from 5 June until 9

Sept. 2008, 11 May until 2 Sept. 2009, and 30 Mar. until 1 Sept.

2010. Nitrogen treatments were initiated on spring green-up

each year and resulted in diff erent annual N delivery rates over

the course of the study (Table 1). Maintenance N applications

were applied at an equal rate to all treatments during late fall and

early spring, between the active summer research seasons. These

N additions were similar to how Wisconsin golf course superin-

tendents manage putting greens and the amounts were credited

to the following season’s total annual N fertility rate (Table 1).

During 2008, TE was applied to applicable plots every 3

wk at the rate of 0.05 kg a.i. ha–1. Unfortunately, this application

regime did not provide season long clipping yield suppression

(data not shown), which was required to achieve the objective

of this study. The TE application regime was amended for the

2009 and 2010 growing seasons to 0.10 kg a.i. ha–1 applied every

200 growing degree days (GDD), which has been shown to sus-

tain season long clipping yield suppression (Kreuser and Soldat,

2011). Application intervals ranged from 6 to 18 d depending

on air temperature during the 2009 and 2010 growing seasons.

Applications occurred from 21 May to 9 Sept. 2008, 11 May to

17 Aug. 2009, and 1 Apr. to 23 Aug. 2010 for a total of 6, 11,

and 14 applications in 2008, 2009, and 2010, respectively. Both

TE and N fertilizers were applied with a CO2 powered back-

pack sprayer with TeeJet AI 11004 nozzles (TeeJet Technolo-

gies) calibrated to deliver 810 L ha–1 at 276 kPa.

Clipping yield and color index were recorded approximately

twice per month before N fertilization applications; for brevity

and because of modifi cation to the TE treatments, only the 2009

and 2010 data will be presented. Data collection occurred from

26 May to 1 Sept. 2009 and 6 May to 1 Sept. 2010. Clippings

were collected by mowing one 2.4 m pass down the center of

each plot 24 h (±2 h) following the previous mowing. Before

clipping collection, 27-cm buff er alleys were mowed at the top

and bottom of each plot to reduce variation from starting and

stopping the mower. Clippings were then brushed from the

mower collection bucket into paper bags before drying to a con-

stant mass at 60°C. Sand debris was removed with the vibrat-

ing pan method (Kreuser et al., 2011) and clipping mass was

recorded. Ground clippings from one rating day per month were

passed through a Wiley mill (Thomas Scientifi c) and sent to

the University of Wisconsin Soil and Plant Analysis Laboratory

for Kjeldahl digestion and total N analysis (Lachat Instruments).

Nitrogen removal was calculated by multiplying clipping yield

by clipping tissue N content. Due to technical problems with

the mowers in 2009, a diff erent Toro Greensmaster 1000 was

Table 1. Fertility record for all three nitrogen treatments dur-

ing 2009 and 2010. High, medium, and low rates achieved

by application of 20, 10, and 5 kg ha–1 on a 14 d interval from

urea during the active study period. Trinexapac-ethyl was

applied to appropriate plots 11 and 14 times during 2009 and

2010, respectively.

Date

N Treatments

P (all) K (all)High Medium Low

Year ——————————————— kg ha–1 ———————————————

2009 201 112 68 5 6

2010 235 135 85 15 18


Doubling N rate from 5 to 10 and 10 to 20 kg ha–1 increased average clipping yield by 27 and 34% in 2009 and 24 and 28% in 2010, respectively (data not shown). Clipping yields were signifi cantly greater in 2009 com-pared to 2010 and there was a strong date eff ect both years. Increased 2009 clipping yields most likely resulted from use of a diff erent greens mower the day before clip-ping collection. Application of TE reduced clipping yield by an average of 18% across all N rates and rating days.

The TE × rating date interaction resulted from two dates, 14 July 2009 and 21 June 2010, in which clipping yields were not statistically aff ected by TE. On the other 17 rating dates in 2009 and 2010 TE signifi cantly reduced clip-ping yield. There was a signifi cant N rate × TE × rating date interaction resulting from diff erent responses to N rate and TE on specifi c rating dates (Table 3). Although responses fl uctuated, the addition of TE reduced clipping yield by a similar extent as reducing N rate by half on 17 of 22 and 16 of 16 rating occasions in 2009 and 2010, respectively (Table 3).

Clipping Tissue N Content and N RemovalYear, date, and N rate had a statistically signifi cant eff ect on clipping tissue content (Table 2). These sources of variation explain the majority of the model variance although there was also a signifi cant N × date interaction (Table 2). Clipping tissue N content increased linearly with N application rate (Table 2). Doubling N rate increased dry clipping tissue N content by an average of 2 mg g–1 (Fig. 1). During both years, clipping tissue N content increased as the season progressed. Mean clipping tissue N content was greater in 2009 than 2010 and may have contributed to greater clipping yields in 2009. The 5 and 20 kg ha–1 N treatments were statistically

used for daily maintenance than data collection. This problem

was corrected during 2010.

Turfgrass color index was quantifi ed by recording the

mean of 10 random measurements of color index per plot using

a CM-1000 refl ectometer (Spectrum Technologies, Inc.) on

a 0 to 999 scale higher index values correlate with increased

chlorophyll content (Mangiafi co and Guillard, 2005). The

CM-1000 was held one meter from the turfgrass surface with

the incidental light meter pointed in the direction of the sun.

The JMP software was used for statistical analysis (version

8.0.2; SAS Institute, 2010). Clipping yield, color index, N con-

tent, and N removal were subject to repeated measures analysis.

The random term in that model was PLOT [N, TE]. To satisfy

the constant variance assumption, clipping yield and N removal

data were subjected to square root transformation. Means were

separated with Fisher’s protected LSD (α = 0.05) when appro-

priate (Fisher, 1935). Orthogonal contrasts examined linear and

quadric responses to N fertilization rate. To determine how

TE altered average creeping bentgrass putting green N require-

ments, clipping yield, color, N removal during mowing, and

diff erence between N application and N removal were plotted

as function of N fertilizer rate with or without TE and sub-

jected to linear regression analysis.

RESULTSClipping Yield

Year, rating date, N rate, TE, and the N × year interac-tion explain a vast majority of model variability and were statistically signifi cant (Table 2). Additionally, the N × date, TE × date, and N × TE × date interactions were signifi cant although these interactions had less of a role explaining model variability with F ratio values less than 4 (Table 2). Orthogonal contrasts indicate a signifi cant lin-ear response to N application rate (Table 2).

Table 2. Summary of repeated measures ANOVA table of main effects and their interactions on creeping bentgrass putting

green responses during 2009 and 2010.

Sources of variation

Clipping yield Clipping N Nitrogen removal Color

df F ratio df F ratio df F ratio df F ratio

Nitrogen (N) 2 59*** 2 54*** 2 64*** 2 457***

Linear *** *** *** ***

Quadratic NS† NS NS NS

Trinexapac-ethyl (TE) 1 26*** 1 2 NS 1 17*** 1 44***

Year (Yr) 1 1046*** 1 201*** 1 399*** 1 5*

Date [Yr] 17 236*** 10 93*** 8 429*** 18 470***

N × TE 2 3 NS 2 1 NS 2 1 NS 2 1 NS

N × Yr 2 15*** 2 3 NS 2 7*** 2 42***

TE × Yr 1 1 NS 1 0 NS 1 1 NS 1 21***

N × TE × YR 2 3 NS 2 1 NS 2 0 NS 2 5**

N × Date [Yr] 34 4*** 20 3*** 16 7*** 36 7***

TE × Date [Yr] 17 2** 10 1 NS 8 3** 18 3***

N × TE × Date [Yr] 34 3*** 20 1 NS 16 3*** 36 2*

* Signifi cant at the 0.05 probability level.

** Signifi cant at the 0.01 probability level.

*** Signifi cant at the 0.001 probability level.

† NS, not signifi cant at p ≤ 0.05.


Table 3. Effect of N rate (14 d interval) and 200-GDD† trinexapac-ethyl (TE) applications on creeping bentgrass putting green

clipping yield during 2009 and 2010.

N rate TE rate

2009 dry clipping yield‡

26 May 9 June 23 June 1 July 7 July 14 July 28 July 4 Aug. 11 Aug. 17 Aug. 1 Sept. 2009‡

kg ha–1 kg a.i. ha–1 ————————————————————————————————————— g m–2 —————————————————————————————————————

5 0.1 0.77b§ 3.28bc 2.72c 1.41b 2.34c 3.60c 6.03c 4.92d 4.75d 1.98d 4.91d 3.12e

5 0.0 0.94b 4.07b 3.39bc 1.55b 2.61c 4.24c 6.49c 5.73d 5.70cd 2.84c 6.20c 3.73d

10 0.1 1.09b 4.11b 3.72b 1.48b 3.82b 3.51c 6.92c 5.78d 6.74bc 3.34bc 5.64cd 4.19cd

10 0.0 1.20ab 2.81c 4.53b 2.36a 3.42b 3.65c 7.79bc 7.22c 7.46b 4.67ab 7.41b 4.48bc

20 0.1 1.07b 4.17b 3.96b 2.04ab 4.06b 5.90b 8.87b 8.61b 9.24a 3.97b 7.71b 5.02b

20 0.0 1.7a 7.62a 5.81a 2.44a 7.18a 7.46a 11.02a 10.36a 9.84a 5.68a 9.2a 6.73a

N rate TE rate

2010 dry clipping yield¶

6 May 20 May 3 June 21 June 3 July 15 July 17 Aug. 1 Sept. 2010¶

kg ha–1 kg a.i. ha–1 ————————————————————————————————————— g m–2 —————————————————————————————————————

5 0.1 2.25c 1.61c 2.28c 2.97b 1.69c 1.99c 1.78c 1.81b 2.03e

5 0.0 2.94bc 1.84bc 2.96bc 3.26b 1.83c 2.61bc 2.30bc 2.33ab 2.48d

10 0.1 3.16b 2.35b 2.69bc 3.56b 1.79c 2.71b 2.51b 2.22b 2.60cd

10 0.0 3.35b 2.27b 3.20b 3.48b 2.32bc 2.98b 352ab 2.98ab 2.99bc

20 0.1 3.48b 2.88ab 3.40b 3.99ab 2.74ab 3.12b 2.84b 2.72ab 3.13b

20 0.0 4.59a 3.54a 4.40a 4.75a 3.42a 4.33a 4.23a 3.44a 4.07a

† Growing degree day (GDD) was the summation of mean daily air temperature (base 0°C) after TE application.

‡ Yearly averages result from repeated measures analysis and do not refl ect arithmetic means.

§ Column means followed by different letters are statistically different according to Fisher’s LSD (α = 0.05).

¶ Values back-transformed for ease of interpretation.

Figure 1. Creeping bentgrass clipping tissue N content as affected by N fertilization and rating date during 2009 and 2010 on a sand

green in Madison, WI.


diff erent on all dates except for the last date in 2009 and fi rst date in 2010. Diff erences between the 10 kg ha–1 N rate and the 5 and 20 kg ha–1 N rate varied with date. In contrast to the literature (Fagerness et al., 2004; McCullough et al., 2006b, c), application of TE during 2009 and 2010 did not alter clipping tissue N content (p = 0.16).

For N removal, rating date, year, N rate, and TE were all statistically signifi cant model sources and explained a major-ity of model variability (Table 2). Additionally, there were signifi cant N × year, N × date, TE × date, and N × TE × date interactions although these interactions had less of a role explaining model variability (Table 2). Doubling N rate from 5 to 10 and 10 to 20 kg ha–1 increased average N removal by 24 and 47% in 2009 and 39 and 31% in 2010, respectively (data not shown). Trinexapac-ethyl reduced N removal by 16% regardless of year, likely as a result clipping yield suppres-sion (data not shown). The signifi cant interactions outlined in the ANOVA table (Table 2) occurred for the same reasons identifi ed in the clipping yield section of this manuscript. As with clipping yield, there was a N rate × TE × date interac-tion; TE reduced N removal to a similar extent as reducing N rate by half on seven of the 10 possible occasions in 2009 and on all occasions in 2010 (Table 4).

Turfgrass Color IndexAlthough all main eff ects and interactions except the N × TE interaction were statistically signifi cant, rating date, N rate, TE, and the TE × year and N × year interaction rep-resent a majority of model variance (Table 2). Orthogonal

contrasts revealed a signifi cant linear color response to N application rate (Table 2).

Turfgrass color index responded positively to increased N rate. Turfgrass color increased from May until July both years. The N × date interaction resulted from similar turf-grass color at the 5 and 10 kg ha–1 N rates on the fi rst rating date of each year. Average turfgrass color was statistically lower in 2010 than 2009 at the 5 kg ha–1 N rate while the 20 kg ha–1 N rate enhanced color by a greater extent in 2010 than 2009 (Fig. 2). Average turfgrass color response was unchanged from 2009 to 2010 at the 10 kg ha–1 N rate.

Turfgrass color increased with application of TE in both years. There was a signifi cant N rate × TE × date interaction (Table 5). Color index did not increase immediately follow-ing the initial TE application, which is consistent with the lit-erature (McCullough et al., 2007; Kreuser and Soldat, 2011). The 20 kg ha–1 N application rate always had superior turf-grass color compared to the 5 and 10 kg ha–1 N application rates. There were select dates however, in which the 5 and 10 kg N rates had statistically similar turfgrass color, especially early in 2009. Delayed color enhancement following the initial TE application and variable response to N rate early in 2009 explain a majority of the N rate × TE × date interaction.

DISCUSSIONTurfgrass N RequirementsCarrow et al. (2001) has outlined many of the diverse parameters that need to be considered to accurately deter-mine turfgrass N requirements. Duration of growing

Table 4. Effect of 200-GDD† trinexapac-ethyl (TE) and urea N rate (14 d interval) on N removal from a creeping bentgrass put-

ting green during mowing in 2009 and 2010. Nitrogen removal was calculated as the product of clipping yield and clipping

tissue P content.

N rate TE rate

2009 N removal

26 May 9 June 1 July 11 Aug. 1 Sept. 2009‡

kg ha–1 kg a.i. ha–1 —————————————————————————————— mg g–1 dry wt. ——————————————————————————————

5 0.1 20b§ 74c 42b 169c 186c 85d

5 0.0 24b 98bc 47b 197c 219c 102c

10 0.1 30b 108b 49b 252b 187c 110c

10 0.0 28b 75c 80a 258b 261b 122c

20 0.1 32b 121b 71a 384a 273b 150b

20 0.0 49a 216a 416a 416a 328a 192a

N rate TE rate

2010 N removal

20 May 21 June 15 July 17 Aug. 1 Sept. 2010§

kg ha–1 kg a.i. ha–1 —————————————————————————————— mg g–1 dry wt. ——————————————————————————————

5 0.1 30c 94c 58c 46d 48c 53e

5 0.0 33c 96c 79bc 56cd 68b 64de

10 0.1 51ab 115bc 90b 72c 68b 78cd

10 0.0 43bc 107c 94b 97b 97a 86bc

20 0.1 62ab 142ab 101b 88bc 91ab 95b

20 0.0 64a 161a 141a 136a 106a 119a


‡ Yearly averages result from repeated measures analysis and do not refl ect arithmetic means.

§ Column means followed by different letters are statistically different according to Fisher’s LSD (α = 0.05).


season, weather conditions, annual clipping production, and soil N mineralization are a few extremely important factors in determining annual N requirements of turfgrass and all are diffi cult to predict. Therefore, exact determi-nation of turfgrass annual N requirements will probably never be accomplished with great certainty. As a result, historical experience is often used to estimate annual N requirements. This method of estimation is fl awed for two reasons: (i) weather patterns vary from month to month

and year to year and (ii) changes to a fertility program may not be obvious for several years because the soil N pool buff ers rapid change of various plant responses (Qian et al., 2003; Frank et al., 2006).

This study illustrates how altering N fertilization slowly aff ects turfgrass color over several growing sea-sons. During establishment in 2006 and 2007, the entire research area was fertilized twice per month with 25 kg ha–1 N. As a result, initial color ratings were similar for

Figure 2. Average creeping bentgrass color as affected by N rate (14 d interval) and trinexapac-ethyl (TE) application within 2009 and

2010 on a sand green in Madison, WI. Letters indicate statistical differences according to Fisher’s LSD (α = 0.05).

Table 5. Effect of N rate (14 d interval) and 200-GDD† trinexapac-ethyl (TE) applications on creeping bentgrass putting green

turfgrass color index during 2009 and 2010.

N rate TE rate

2009 color index‡

26 May 9 June 23 June 1 July 7 July 15 July 28 July 4 Aug. 11 Aug. 17 Aug. 1 Sept. 2009§

kg ha–1 kg a.i. ha–1 —————————————————————————————————————— g m–2 ——————————————————————————————————————

5 0.0 19 2b¶ 178c 176d 204c 202c 231c 279d 276c 276d 233d 232e 225e

5 0.1 192b 177c 189d 207c 217c 229c 292d 288c 296c 253c 253d 235d

10 0.0 171c 183c 184d 217bc 214c 243bc 321c 321b 308bc 280ab 280c 248c

10 0.1 192b 203b 209c 230b 236b 255b 315c 309b 322b 274b 275c 256b

20 0.0 233a 237a 232b 265a 274a 283a 361b 367a 340a 274b 297b 287a

20 0.1 225a 241a 248a 258a 286a 283a 379a 372a 346a 290a 315a 295a

N rate TE rate

2010 color index‡

6 May 20 May 3 June 21 June 3 July 15 July 17 Aug. 1 Sept. 2010¶

kg ha–1 kg a.i. ha–1 ————————————————————————————————————— g m–2 —————————————————————————————————————

5 0.0 177c 155b 197d 208e 223e 217e 240d 255f 211f

5 0.1 179c 154b 205d 234d 230e 230e 246d 274e 222e

10 0.0 201b 175b 226c 233d 254d 250d 271c 300d 240d

10 0.1 206b 179b 240c 265c 272c 278c 301b 338c 264c

20 0.0 237a 216a 278b 282b 315b 294b 318a 359b 289b

20 0.1 249a 220a 302a 309a 332a 313a 329a 384a 307a


‡ Values back-transformed for ease of interpretation.

§ Yearly averages result from repeated measures analysis and do not refl ect arithmetic means.

¶ Column means followed by different letters are statistically different according to Fisher’s LSD (α = 0.05), equal to 15.6 to compare any treatment across all rating dates.


all N treatments during 2008 (data not shown). However, after 3 yr turfgrass color began to diverge among the N treatments (Fig. 2). Average turfgrass color index for the 5 kg ha–1 N treatments declined as the experiment progressed. In contrast, color improved from 2009 to 2010 on the 20 kg ha–1 N treatment. Turfgrass color of the 10 kg ha–1 N treatment was unchanged in 2009 and 2010, suggesting equilibrium.

Use of an anthropogenic input–out-put N budget can help to explain the divergence between the low and high N treatments. This construct has been used to estimate N and P losses from agroecosystems (Watson and Atkinson, 1999; David and Gentry, 2000; Ross et al., 2008). In this study the anthropogenic input–output N budget was calculated as the function of N removal during mow-ing subtracted from N fertilizer applied in 2010 (Fig. 3). Processes of N addition, loss, or transformation (i.e., atmospheric depo-sition, leaching, volatilization, and immo-bilization) were neglected for simplicity but do not refl ect a lack of importance. To estimate daily N fertilizer availability, each N fertilizer rate was divided by 14 d (35, 71, and 143 mg N m–2 d–1 assumed for the 5, 10, and 20 kg ha–1 N treatments, respectively). Although such uniform urea hydrolysis may not be reasonable due to a variety of factors (Torello and Wehner, 1983; Mosdell et al., 1987; Carrow et al., 2001), it is useful to illustrate diff erences in N addition and removal. Addition-ally, Joo et al. (1991) found turfgrass 15N uptake after urea application was similar both 1 and 2 wk after application and sup-ports our estimation of plant available N. This analysis was limited to 2010 because complications with mower confi gurations described in the methods sections led to an overestimation of N removal during mowing in 2009.

On 20 May 2010 the 10 and 20 kg N ha–1 treatments resulted in a surplus of N fertilizer (Fig. 3). Traditional mass balance studies in turfgrass ecosystems found a majority of N fertilizer is immo-bilized within the soil and leaching is typically minimal, especially shortly after turfgrass establishment (Starr and DeRoo, 1981; Petrovic, 1990; Miltner et al., 1996; Hor-gan et al., 2002). From these results we assume that a

majority of spring applied N fertilizer was immobilized in this young sand root zone. Nitrogen removal exceeded potential N fertilizer mineralization on 21 June, 15 July, 17 Aug., and 1 Sept. 2010 for the 5 kg ha–1 N treatments

Figure 3. Anthropogenic input–output N budget. Nitrogen removal during mowing

was subtracted from estimated plant available N. Plant available N was calculated by

dividing N application rate by 14 d (35, 71, and 143 mg N m–2 d–1 for the 5, 10, and

20 kg ha–1 N treatments, respectively). Nitrogen budget is plotted as a function of (A)

14 d interval N fertilizer rate, (B) 200-growing degree days (GDD) trinexapac-ethyl (TE)

application, and (C) the interaction of N rate and TE application. Asterisks indicate

occasions where the N budget is signifi cantly different than zero according to Fisher’s

LSD (α = 0.05).


(Fig. 3a). Soil N mineralization likely sustained the clip-ping productivity during these times at a likely cost to soil N reserves; previous research has shown a signifi cant portion of turfgrass N uptake results from soil mineraliza-tion (Starr and DeRoo, 1981; Petrovic, 1990). Meanwhile, the 20 kg ha–1 N treatment provided a N surplus dur-ing all rating days except 21 June 2010. This treatment likely increased soil N reserves and has the greatest poten-tial for N leaching (Qian et al., 2003; Frank et al., 2006), especially after organic soil N level approaches a satura-tion point. The season average input–output N budget was plotted as a function of fertilizer application rate and subjected to linear regression (Fig. 4b). The break-even point where fertilizer input equaled clipping N removal for this particular putting green was 14.7 kg ha–1 when TE was not applied. Therefore, the 20 kg ha–1 N treat-ment likely caused a net increase in soil N while the 5 kg ha–1 N treatment would cause a net reduction in soil N reserves. The 10 kg ha–1 N treatment was the closest treat-ment to the modeled break-even point and is refl ected in unchanged color ratings between 2009 and 2010. Because soil N mineralization accounts for a large portion of total

plant N uptake, changes in soil N due to under- and over-application of N likely caused color divergence between the N treatments in 2009 and 2010.

This conceptual framework has several implications for determination and management of annual N fertil-ization requirements. First, changing N fertilization pro-grams slowly alters turfgrass attributes because soil N buff ers rapid change. When a N fertilization program is altered, turfgrass attributes such as color, density, and visual quality need to be assessed over a period of sev-eral years rather than several weeks. Second, matching N fertilizer application to N removal during mowing maintained consistent color from year to year, presum-ably by sustaining soil N levels. Lastly, basing annual N rates on historical data alone is ill-advised because changes in growing season duration, weather patterns, and soil N reserves occur year to year.

Trinexapac-ethyl Reduces N RequirementsTrinexapac-ethyl altered putting green performance in a similar fashion as altering N application rate when reap-plied on a growing degree day schedule (Fig. 4). Within

Figure 4. Creeping bentgrass putting green dry clipping yield (A), anthropogenic input–output N budget (B), N removal during mowing (C),

and color (D) when averaged across 2009 and 2010 and plotted as a function of N fertilizer application rate (14 d interval) with or without

trinexapac-ethyl (TE) application. Nitrogen budget was only calculated in 2010.


the creeping bentgrass fertilization range of 10 to 40 kg N ha–1 mo–1, results show that TE can maintain color and canopy density while simultaneously reducing N require-ments by as much as 50%. For example, doubling N rate enhanced clipping yield 0.7 and 1.1 g m–2 on average while TE reduced clipping yield by an average of 0.7 g m–2. The signifi cance here is twofold. First, doubling N rate on a creeping bentgrass putting green did not double clipping yield, a common yet unfounded (Schlossberg and Schmidt, 2007) concern of many golf course superinten-dents. Second, 200-GDD TE applications reduced clip-ping yield by the same amount as reducing N fertilization by half on 31 of the 38 rating occasions in 2009 and 2010 (Table 3). By reducing clipping yield and not altering clip-ping tissue N content, TE reduced N removal by a similar magnitude as reducing N fertilization by half on 15 of the 20 ratings occasions (Table 4).

Large reductions in N removal with 200-GDD TE applications altered the N budget, which is evident by dif-ferences in color response between years (Fig. 2 and 4). On 4 of the 5 d in which the N budget was calculated, TE likely enhanced or sustained soil N supply by reducing N removal during mowing (Fig. 3). When the N budget data was averaged across 2010 and plotted as a function of N rate (Fig. 4b) it became clear how TE reduced N removal by shifting the break-even N rate from 14.7 to 11.0 kg ha–1 N, a 25% decrease.

Changes in the input–output N budget with TE appli-cations were apparent when the eff ect of 200-GDD TE applications on color index was analyzed by year (Fig. 2). Plots that received TE maintained the same turfgrass color index from 2009 to 2010. Nontreated plots had a statis-tically signifi cant decrease in color index from 2009 to 2010. This likely occurred because TE-treated plots had greater soil N reserves because of decreased N removal during mowing. Accumulation of soil N may also explain why tissue N levels were unchanged with application of TE. Additionally, N may be partitioned to basal parts of the plant and protected from removal during mowing. Others have found that TE partitions N from clipping tis-sue to the turfgrass roots, which supports this hypothesis (Fagerness et al., 2004; McCullough et al., 2006b, c).

Turfgrass color is typically used by turfgrass managers to determine rate and frequency of N fertilization. Appli-cation of TE every 200-GDD enhanced turfgrass color similarly to doubling N rate on several occasions (Table 5). More typically, however, TE treatments increased color compared to the nontreated control within a fertil-izer level but not to the level of the next fertilizer treat-ment. Comparison of the regression indicates that TE has a similar eff ect as increasing N application rate by 2.5 kg ha–1 every 2 wk (Fig. 4).

CONCLUSIONSFrequently reapplied TE reduces creeping bentgrass putting green N fertility requirements by reducing N removal, which likely shifts the input–output N bud-get to the left, and by enhancing turfgrass color. These results did not occur when TE was applied every 3 wk in 2008 because clipping yield suppression was not sustained. For this particular putting green, TE use allowed for the reduction of N application by 15 to 11 kg ha–1 every 2 wk without negatively aff ecting turfgrass color or the input–output N budget. Furthermore, ball roll distances may likely benefi t from the cumulative eff ect of reducing N fertilization rate and application of TE by reducing clip-ping yield (McCullough et al., 2006a; Pease et al., 2011). A reduction of N fertilizer rate from 15 to 11 kg N ha–1 in conjunction with TE would reduce clipping yields from 4.5 to 3.2 g m–2 (Fig. 4). Nitrogen application rate would need to be reduced to 6 kg N ha–1 every 2 wk to achieve a similar yield without frequently applied TE, a level that would severely reduce putting green color, result in an unsustainable N budget, and likely lead to collapse of the putting surface during stressful conditions.

AcknowledgmentsSpecial thanks to Dr. Wayne Kussow for help with the develop-

ment of this project and expertise in fi eld research methodology

and for his continuous support. We would also like to thank

Drs. Phillip Barak, James Kerns, John Stier, and William Bland

for serving on William Kreuser’s M.S. committee. Additional

thanks to Mr. Bradley DeBels, Shane Griffi th, Josh Horman,

John Kreuser, Daniel Lloyd, Eric Melby, Tim Opsal, Ryan

Orlovsky, and Peter Pfaller for their many hours of assistance

with sample collection and processing, treatment application,

and plot maintenance. Finally, thanks to the Wisconsin Turf-

grass Association for providing the Wayne R. Kussow Distin-

guished Turfgrass Fellowship, which supported of this research.

ReferencesBeasley, J.S., and B.E. Branham. 2005. Analysis of paclobutrazol

and trinexapac acid in turfgrass clippings. Int. Turfgrass Soc.

Res. J. 10:1170–1175.

Beasley, J.S., and B.E. Branham. 2007. Trinexapac-ethyl and

paclobutrazol aff ect Kentucky bluegrass single-leaf carbon

exchange rates and plant growth. Crop Sci. 47:132–138.

Bowman, D.C. 2003. Daily vs. periodic nitrogen addition aff ects

growth and tissue nitrogen in perennial ryegrass turf. Crop

Sci. 43:631–638.

Bunnell, B.T., L.B. McCarty, and W.C. Bridges. 2005. ‘TifEagle’

bermudagrass response to growth factors and mowing height

when grown at various hours of sunlight. Crop Sci. 45:575–581.

Carrow, R.N., D.V. Waddington, and P.E. Rieke. 2001. Turfgrass

soil fertility and chemical problems: Assessment and manage-

ment. Ann Arbor Press, Chelsea, NY.

Christians, N.E., D.P. Martin, and K.J. Karnok. 1981. The inter-

relationship among nutrient elements applied to calcareous

sand greens. Agron. J. 73:929–933.


Christians, N.E., D.P. Martin, and J.F. Wilkinson. 1979. Nitro-

gen, phosphorus, and potassium eff ects on quality and growth

of Kentucky bluegrass and creeping bentgrass. Agron. J.

71:564–567.

David, M.B., and L.E. Gentry. 2000. Anthropogenic inputs of

nitrogen and phosphorus and riverine export for Illinois,

USA. J. Environ. Qual. 29:494–508.

Ervin, E.H., and A.J. Koski. 1998. Growth responses of Lolium

perenne to trinexapac-ethyl. HortScience 33:1200–1202.

Ervin, E.H., and A.J. Koski. 2001. Trinexapac-ethyl increases

Kentucky bluegrass leaf cell density and chlorophyll concen-

tration. HortScience 36:787–789.

Ervin, E.H., and X. Zhang. 2008. Applied physiology of natural

and synthetic plant growth regulators on turfgrasses. In: M.

Pessarakli, editor, Handbook of turfgrass management and

physiology. CRC Press, Boca Raton, FL. p. 171–200.

Fagerness, M.J., D.C. Bowman, F.H. Yelverton, and T.W. Rufty

Jr. 2004. Nitrogen use in Tifway bermudagrass, as aff ected by

trinexapac-ethyl. Crop Sci. 44:595–599.

Fisher, R.A. 1935. Design of experiments. Oliver & Boyd, London.

Frank, K.W., K.M. O’Reilly, J.R. Crum, and R.N. Calhoun.

2006. The fate of nitrogen applied to a mature Kentucky

bluegrass turf. Crop Sci. 46:209–215.

Heckman, J.R., H. Liu, W. Hill, M. DeMilia, and W.L. Anastasia.

2000. Kentucky bluegrass responses to mowing practice and

nitrogen fertility management. J. Sustain. Agric. 15:25–33.

Horgan, B.P., B.E. Branham, and R.L. Mulvaney. 2002. Mass bal-

ance of 15N applied to Kentucky bluegrass including direct

measurement of denitrifi cation. Crop Sci. 42:1595–1601.

Johnson, P.G., R.T. Koenig, and K.L. Kopp. 2003. Nitrogen,

phosphorus, and potassium responses and requirements in

calcareous sand greens. Agron. J. 95:697–702.

Joo, Y.K., N.E. Christians, and A.M. Blackmer. 1991. Kentucky

bluegrass recovery of urea derived nitrogen-15 amended with

a urease inhibitor. Soil Sci. Soc. Am. J. 55:528–530.

Kopp, K.L., and K. Guillard. 2002. Clipping management and

nitrogen fertilization of turfgrass: Growth, nitrogen utiliza-

tion, and quality. Crop Sci. 42:1225–1231.

Kreuser, W.C., M.P. Fish, D.J. Soldat, and S. Bauer. 2011. Remov-

ing sand from putting green clipping samples substantially

reduces clipping weight measurement error. Crop Sci.

51:1268–1273.

Kreuser, W.C., and D.J. Soldat. 2011. A growing degree day model

to schedule trinexapac-ethyl applications on Agrostis stolonifera

golf putting greens. Crop Sci. 51:2228–2236.

Mangiafi co, S.S., and K. Guillard. 2005. Turfgrass refl ectance

measurements, chlorophyll, and soil nitrate desorbed from

anion exchange membranes. Crop Sci. 45:259–265.

McCarty, L.B. 2005. Best golf course management practices.

Prentice Hall, New Saddle River, NJ.

McCullough, P.E., H. Liu, L.B. McCarty, and J.E. Toler. 2006c.

Ethephon and trinexapac-ethyl infl uence creeping bentgrass

growth, quality, and putting green performance. Appl. Turf-

grass Sci. doi:10.1094/ATS-2006-0324-01-RS

McCullough, P.E., H. Liu, L.B. McCarty, and J.E. Toler. 2007.

Trinexapac-ethyl application regimens infl uence growth,

quality, and performance of bermudagrass and creeping bent-

grass putting greens. Crop Sci. 47:2138–2144.

McCullough, P.E., H. Liu, L.B. McCarty, T. Whitwell, and J.E.

Toler. 2006a. Growth and nutrient partitioning of ‘TifEagle’

bermudagrass as infl uenced by nitrogen and trinexapac-ethyl.

HortScience 41:453–458.

McCullough, P.E., H. Liu, L.B. McCarty, T. Whitwell, and J.E.

Toler. 2006b. Bermudagrass putting green growth, color, and

nutrient partitioning infl uenced by nitrogen and trinexapac-

ethyl. Crop Sci. 46:1515–1525.

Miltner, E.D., B.E. Branham, E.A. Paul, and P.E. Rieke. 1996.

Leaching and mass balance of 15N-labeled urea applied to a

Kentucky bluegrass turf. Crop Sci. 36:1427–1433.

Mosdell, D.K, W.H. Daniel, and R.P. Freeborg. 1987. Melamine

and ammeline as nitrogen-sources for turfgrass. Fert. Res.

11:79-86.

Pease, B.W., E.J. Koeritz, D.J. Soldat, and J.C. Stier. 2011. Nitro-

gen source and rate eff ects on velvet bentgrass putting green

turf. Crop Sci. 51:342–352.

Petrovic, A.M. 1990. The fate of nitrogenous fertilizers applied to

turfgrass. J. Environ. Qual. 19:1–14.

Qian, Y.L., W. Bandaranayake, W.J. Parton, B. Mecham, M.A.

Harivandi, and A.R. Mosier. 2003. Long-term eff ects of clip-

ping and nitrogen management in turfgrass on soil organic

carbon and nitrogen dynamics: The CENTURY model stim-

ulation. J. Environ. Qual. 32:1694–1700.

Qian, Y.L., and M.C. Engelke. 1999. Infl uence of trinexapac-ethyl

on diamond zoysiagrass in a shade environment. Crop Sci.

39:202–208.

Rademacher, W. 2000. Growth retardants: Eff ects on gibberellin

biosynthesis and other metabolic pathways. Annu. Rev. Plant

Physiol. Plant Mol. Biol. 51:501–531.

Ross, S.M., R.C. Izaurralde, H.H. Janzen, J.A. Robertson, and

W.B. McGill. 2008. The nitrogen balance of three long-term

agroecosystems on a boreal soil in western Canada. Agric.

Ecosyst. Environ. 127:241–250.

SAS Institute. 2010. JMP user guide. Release 8.02. SAS Inst.,

Cary, NC.

Schlossberg, M.J., and J.P. Schmidt. 2007. Infl uence of nitrogen

rate and form on quality of putting greens cohabited by creep-

ing bentgrass and annual bluegrass. Agron. J. 99:99–106.

Starr, J.L., and H.C. DeRoo. 1981. The fate of nitrogen fertilizer

applied to turfgrass. Crop Sci. 21:531–535.

Stier, J.C., and J.N. Rodgers III. 2001. Trinexapac-ethyl and iron

eff ects on supina and Kentucky bluegrasses under low irradi-

ance. Crop Sci. 41:457–465.

Torello, W.A., and D.J. Wehner. 1983. Urease activity in a Ken-

tucky bluegrass turf. Agron. J. 75:654–656.

United States Golf Association (USGA) Green Section Staff .

2004. USGA recommendations for a method of putting green

construction. United States Golf Association, Far Hills, NJ.

http://www.usga.org/Content.aspx?id=26124 (accessed 23

Jan. 2012).

Waddington, D.V., E.L. Moberg, and J.M. Duich. 1972. Eff ect of

N source, K source, and K rate on soil nutrient levels and

the growth and elemental composition of Penncross creeping

bentgrass, Agrostis palustris Huds. Agron. J. 64:562–566.

Watson, C.A., and D. Atkinson. 1999. Using nitrogen budgets to

indicate nitrogen use effi ciency and losses from whole farm

systems: A comparison of three methodological approaches.

Nutr. Cycl. Agroecosyst. 53:259–267.

Documents

Frequent Trinexapac-ethyl Applications Reduce Nitrogen ...tendents manage putting greens and the amounts were credited to the following season’s total annual N fertility rate (Table