Published in Crop Sci. 44:595-599 (2004).
© 2004 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
TURFGRASS SCIENCE
Nitrogen Use in Tifway Bermudagrass, as Affected by Trinexapac-Ethyl
Matthew J. Fagerness*,a,
Daniel C. Bowmanb,
Fred H. Yelvertonb and
Thomas W. Rufty, Jr.b
a Dep. of Horticulture, Forestry, and Recreation Resources, Kansas State Univ., 2021 Throckmorton, Manhattan, KS 66506-5507
b Crop Science Dep., North Carolina State Univ., 100 Derieux St. Box 7620, Raleigh, NC 27695-7620
* Corresponding author (mfagerne{at}oznet.ksu.edu).
 |
ABSTRACT
|
|---|
Nutrient movement from turfgrass systems into surface and ground water is a public concern. Data indicate that actively growing turf rapidly immobilizes applied N, thus restricting nutrient movement. It is possible, however, that growth suppression with plant growth regulators (PGRs) could reduce N demand and thus N uptake, resulting in greater leaching losses. An experiment was conducted with column lysimeters to investigate the effects of trinexapac-ethyl (TE) on nitrate leaching and N-use efficiency in Tifway bermudagrass (Cynodon dactylon x C. transvaalensis). The experiment was conducted in a growth chamber with day/night temperature set at 29/24°C and a 12-h photoperiod. Trinexapac-ethyl was applied twice at 4-wk intervals at 0.11 kg a.i. ha–1. Ammonium nitrate (AN) was applied at 50 kg N ha–1 2 wk after each TE application, and again 6 wk after the second TE application. Separate sets of columns received 15N-labeled AN for the first two applications. Irrigation was scheduled to provide a leaching fraction of 
50%; leachate was collected after each irrigation and analyzed for nitrate and ammonium. Cumulative nitrate leaching was unaffected by TE after the first two N applications, but was reduced 60% by TE following the third N application. Trinexapac-ethyl reduced 15N allocation to clippings by 25% and increased 15N allocation to roots and rhizomes; total recovery of applied 15N in tissues was 65%. Results demonstrate chemical growth suppression with TE does not reduce N uptake or increase nitrate leaching from bermudagrass.
Abbreviations: AN, ammonium nitrate • ET, evapotranspiration • PGR, plant growth regulator • TE, trinexapac-ethyl
|
INTRODUCTION
|
|---|
BERMUDAGRASS [C. dactylon (L.) Pers.] is widely used as a turfgrass in the southern USA, as well as in other subtropical to tropical regions. Maintaining a high-quality bermudagrass turf, typical of golf course fairways, requires fertilizers and pesticides. As a result, public concern about water pollution has often focused on this and other turfgrass systems like urban landscapes.
Previous researchers have examined turfgrass management factors that may affect N leaching, including fertilizer form and rate, soil type, irrigation, and plant selection (Brown et al., 1977; Bowman et al., 1989a, 1998; Geron et al., 1993; Miltner et al., 1996; Liu et al., 1997). Among the primary management practices in turf, irrigation and fertilization most directly affect nitrate losses. High rates and frequencies of applied irrigation or fertilizer N, the use of readily soluble N sources, and coarse-textured soils such as sands may all increase N losses from turfgrass systems (Brown et al., 1977; Snyder et al., 1980; Morton et al., 1988; Geron et al., 1993). Controlled irrigation practices and slow-release fertilizers help reduce N losses (Snyder et al., 1980, 1984) by allowing sufficient opportunity for turf to immobilize applied N.
To perhaps a greater degree, leaching is controlled by turfgrass biology, most notably the development of enhanced N uptake and a very dense root system (Bowman et al., 1989b, 1998; Geron et al., 1993). Rapid N uptake and immobilization serve to limit the period during which fertilizer N is most susceptible to leaching. Applied compounds that affect turfgrass growth and metabolism such as pesticides, biostimulants, and PGRs might affect N uptake, and thus leaching. Of these, PGRs may have the greatest potential to affect nitrate leaching since they reduce shoot growth and may thus reduce plant demand for N.
The objectives of this experiment were to (i) evaluate effects of the commonly used PGR TE on nitrate leaching from established Tifway bermudagrass, and (ii) examine the effects of TE and timing of fertilizer application on N uptake and partitioning in bermudagrass. The experiment was designed to represent a worst-case scenario with a sandy soil, a soluble N source, and heavy irrigation.
|
MATERIALS AND METHODS
|
|---|
The experiment was conducted during a 12-wk period in a controlled-environment growth chamber at the Southeast Plant Environmental Laboratory, Raleigh, NC. The chamber was operated at 29/24°C (day/night) with a 12-h photoperiod and photosynthetically active radiation of 750 µmol photons m–2 s–1.
Bermudagrass was established in 16 randomly arranged PVC column lysimeters (eight replications for each of two TE treatment levels), 37 cm in diameter and 75 cm deep. Three porous ceramic extraction cups, joined with a "T" connector, were placed at the bottom of each column. The cups were connected to 3-L collection bottles which were connected to a vacuum manifold. A 7-cm layer of diatomaceous earth was added to reduce plugging of the ceramic cups, and the columns were then filled with unamended medium sand packed to a final bulk density of 1.6 g cm–3. Tifway bermudagrass was established from sod in June 1998. Columns received 50 kg N ha–1 mo–1 (538 mg N column–1) as AN until 6 Feb. 1999, 4 wk before initiating TE treatments on 6 March.
In addition to a non-TE-treated check, TE was applied at 0.11 kg a.i. ha–1 in 1402 L ha–1 on two occasions, 2 wk before and again 2 wk after the initial 15N application (see Table 1 for timeline). Spray solutions were dispensed from a modified syringe and simultaneously brushed across the canopy to enhance application uniformity. Applications were made at least 12 h before a scheduled irrigation and not within 48 h of mowing.
View this table:
[in this window]
[in a new window]
|
Table 1. Timeline for trinexapac-ethyl (TE) treatments and N applications. Trinexapac-ethyl was applied at 0.11 kg a.i. ha–1 and N was applied at 50 kg N ha–1 as NH4NO3.
|
|
Ammonium nitrate was applied on three occasions at 50 kg N ha–1 and immediately watered in with a scheduled irrigation. The first two applications were timed to follow the TE applications by 2 wk. For the first application, half the columns received AN double-labeled with 15N (10.0% enrichment), the other half with unlabeled AN. The order was reversed for the second application; columns previously fertilized with 15N-AN received reagent-grade AN and vice versa. All columns received a third application of unlabeled AN. The first and second 15N applications were made 12 and 8 wk before final harvest, respectively, allowing comparison of shorter and longer-term 15N partitioning in response to growth inhibition.
Potential ET, as monitored with an atmometer positioned at canopy height, was fairly constant at 3.5 cm wk–1. Columns were irrigated with 2 cm of deionized water three times per week to provide a leaching fraction of 50%. Irrigation was applied through a bucket with holes drilled in the bottom to achieve uniform coverage. Leachate was collected following each irrigation by applying a tension of 0.02 MPa to the columns for 24 h, emulating gravitational effects on water percolation. Leachate volume was recorded and a 20-mL subsample collected and stored at 4°C. Actual ET was calculated by mass balance as the difference between irrigation and leachate volumes.
Ammonium and nitrate in the leachate were determined by the rapid diffusion method (Carlson, 1978, 1986). Columns were mowed at 2.5 cm every 5 to 7 d and clippings were collected. Roots (with rhizomes) and shoots were separately harvested at the end of the experiment. All tissues were dried, weighed, and ground. Tissue N and 15N enrichment were determined by mass spectrometry.
Shoot biomass, ET, and leachate N analyses were all based upon comparisons between nontreated and TE-treated columns. Tissue N and 15N enrichment analyses included 15N application timing as an additional factor. Data were analyzed by ANOVA (SAS Institute, 1995) and means were separated using Fisher's Protected LSD when F tests were significant at 
= 0.05.
|
RESULTS
|
|---|
Clipping Production and Total Biomass
Clipping production was suppressed up to 50% following the two TE applications (Fig. 1)
. Growth suppression was evident for 4 wk after each application, after which growth rate increased to that of the untreated controls. There was no indication of significant post-inhibition-growth enhancement. Shoot density was increased by TE, compared with the controls; this effect became more pronounced as the experiment progressed (data not shown). There was no effect of TE on root or verdure biomass at the end of the experiment. Total biomass per column was 300 g (equivalent to 28 Mg ha–1), of which 65% was belowground biomass, 25% was verdure, and 10% was clippings.
View larger version (17K):
[in this window]
[in a new window]
|
Fig. 1. Clipping production of trinexapac-ethyl (TE) treated Tifway bermudagrass, as a percentage of the nontreated check (indicated by a dashed line). The TE and N applications are indicated by arrows. Significant effects (P = 0.05) of TE for each clipping collection date are indicated by asterisks.
|
|
Water Use
Evapotranspiration averaged 3.0 cm wk–1 during the course of the 12-wk experiment (Fig. 2)
. This compares with potential ET, estimated with an atmometer, of 3.5 cm wk–1. On the basis of weekly irrigation of 6.0 cm, the leaching fraction averaged 50%. Trinexapac-ethyl did not affect ET during the first 6 wk. However, TE-treated turf used significantly more water during 2 wk in Months 2 and 3 (Fig. 2). In spite of these differences, total ET for each month and for the entire experiment was unaffected by TE.
View larger version (20K):
[in this window]
[in a new window]
|
Fig. 2. Bermudagrass weekly evapotranspiration (ET) in nontreated or trinexapac-ethyl (TE) treated Tifway bermudagrass.
|
|
Nitrogen Leaching
Nitrate concentration in the leachate increased following each fertilizer application, with a peak occurring 5 to 7 d after N application (Fig. 3)
. Thereafter, concentrations decreased during the next 7 to 10 d to near zero. The relatively rapid appearance and decline of nitrate is consistent with the porous soil and high leaching fraction. Peak N concentrations from the first two AN applications were <10 mg L–1, and were unaffected by TE (Table 2). Similarly, volume-weighted nitrate concentrations, averaging <2 mg L–1, were also unaffected by TE. Volume-weighted values for a given period are calculated as cumulative N leached divided by cumulative leachate volume, and are used to adjust average concentrations for differences in volume. Ammonium concentrations in the leachate were very low (<0.1 mg L–1) and were unaffected by TE treatment (data not shown).
View larger version (14K):
[in this window]
[in a new window]
|
Fig. 3. Leachate nitrate concentrations following three consecutive applications of NH4NO3 to bermudagrass turf with and without trinexapac-ethyl (TE) treatment. Leaching patterns in nontreated columns are represented by black dots while those for TE-treated columns are represented by white dots.
|
|
The amount of NO3–N leaching from TE-treated columns after the third AN application was similar to losses following the first two AN applications. By contrast, N leached from nontreated columns increased approximately twofold (Table 2). Increased leaching loss from nontreated columns was coincident with higher leachate volumes as compared with those following the first two AN applications.
Nitrogen Partitioning
Partitioning of N among tissues was determined for total N, representing the integrated response to long-term N nutrition, and for 15N as a tracer for recently-absorbed N. Averaged across TE treatments, total N in the mature bermudagrass (verdure plus belowground tissue) was 190 kg N ha–1, with an additional 60 kg N ha–1 being removed in the clippings during the course of the experiment (Table 3). Absorption of applied 15N by the turf totaled 65% and was unaffected by either TE or timing of 15N application (Table 4). By contrast, partitioning of 15N among harvested tissues was affected by both TE and timing. Treatment with TE reduced 15N allocation to clippings by 25%, similar to the average reduction in leaf growth (Fig. 1). Approximately 40% of applied N was retained in the verdure and belowground biomass. This represents two thirds of the absorbed N, and indicates that these tissues were strong sinks for the fertilizer. Trinexapac-ethyl did not affect partitioning to the verdure, but increased N retention in belowground biomass 50% (Table 4).
15Nitrogen accounted for 50 to 60% of the total N incorporated into new leaves during the 4 wk following labeled AN application (Fig. 4)
. The remaining N was contributed from other pools, with root and verdure being the most likely sources. There was an abrupt step decrease in relative 15N allocation to new leaves coincident with subsequent unlabeled AN applications. Approximately 30 d after each 15N application, enrichment declined from roughly 50 to 20% (Fig. 4a, 4b), with a further reduction to 10% at 60 d (Fig. 4a). This pattern is partly because of reduced influx of 15N into new leaves across time, but mostly to increased dilution with 14N from the subsequent fertilizer applications. It is intriguing that significant transport of 15N to new leaf tissue continued during the 12-wk period, suggesting relatively dynamic N pools in the verdure and roots.
View larger version (41K):
[in this window]
[in a new window]
|
Fig. 4. Allocation of 15N to bermudagrass leaf growth following (A) the first and (B) second applications of 15N-NH4NO3. Significant effects (P = 0.05) of trinexapac-ethyl (TE) for each clipping collection date are indicated by asterisks.
|
|
|
DISCUSSION
|
|---|
Plant growth regulators are effective agents in controlling the growth of bermudagrass (Johnson, 1992a, 1992b; Johnson, 1997; Wiecko, 1997), with TE being a common choice among professionals. There are two phases of growth in response to a TE application: a 4- to 5-wk period of inhibition, followed by a recovery to untreated growth rates (Fagerness and Yelverton, 2000). Growth rates in the present study were suppressed for 60 d, reflecting the two TE applications.
Conditions in this experiment were designed to maximize leaching potential. In general, very low amounts of N were leached, ranging from 2.2 to 8.5% of applied N (Table 2). This is consistent with previous data on nitrate leaching from properly managed turf (Rieke and Ellis, 1974; Starr and DeRoo, 1981; Gold et al., 1990; Mancino and Troll, 1990; Miltner et al., 1996; Bowman et al., 2002). Nitrate leaching was either unaffected (N Applications 1 and 2) or reduced by TE (N Application 3; Table 2). This may be because of promotive effects of TE on shoot density (Fagerness and Yelverton, 2000), changes in root density or depth, or to reduced water flux through the TE-treated columns. While PGRs reportedly reduce the water requirements of warm-season turfgrasses (Borden and Campbell, 1987; Devitt and Morris, 1988; Fry and Jiang, 1998), TE actually increased ET on several occasions during the second half of this experiment (Fig. 2). Greater ET may be the result of a denser canopy and greater leaf surface area in the +TE bermudagrass.
Recovery of applied 15N from all tissues combined was 65% (Table 4), considerably greater than 15N recovery by turfgrasses in other studies (Starr and DeRoo, 1981; Miltner et al., 1996) but comparable with recent data on 15N recovery by several warm season turfgrasses (Bowman et al., 2002). This relatively high recovery may have been because of the deep root system characteristic of bermudagrass as compared with cool season grasses. Roots had reached the bottom of the 75-cm-deep soil column by the end of this study. Rooting depth may also partly explain why leaching losses were low, since efficient and rapid N uptake will minimize the resident time of inorganic N in the rootzone. Plant tissue and leaching accounted for 70% of the applied N, with the remaining 30% likely immobilized by soil microorganisms or, to a lesser extent, lost to the atmosphere.
Turfgrass biomass represents a significant component of the N cycle not so much because of pool size but because tissue N is relatively labile. Turfgrass N is most often expressed as a concentration, although it may be informative to consider the total amount, or the total number of fertilizer applications present in the biomass. As noted above, the turf (roots, verdure, and clippings) in this study contained 250 kg N ha–1. On the basis of a value of 65% for fertilizer N absorption efficiency (15N data), this is equivalent to roughly eight applications of 50 kg N ha–1 and represents at least two seasons worth of fertilizer for established bermudagrass in the transition zone. These data indicate considerable N storage capacity within bermudagrass and promote the importance of returning clippings, since the equivalent of a full N application was removed as clippings during the 12-wk experimental period (Table 3).
The pattern of 15N partitioning indicates that, at least under the conditions of this experiment, new leaves, verdure, and roots were all relatively strong sinks for recently absorbed N. By contrast, recent work, also with bermudagrass, found that root sink strength for N was considerably less than that for leaf or verdure (Bowman et al., 2002). One possible explanation for this difference is that the prior study was conducted in the greenhouse under high natural light, and leaf growth rate (and thus, sink strength) was approximately twice that in the present growth chamber study. It is noteworthy that TE reduced N allocated to new leaves while increasing retention in the roots (Table 3). From a practical standpoint, this might reduce N lost from the system when clippings are removed, and thus increase the efficiency of applied N. It is unclear if increased N storage in belowground tissue in response to TE has any benefit, although conceivably it might improve early spring regrowth.
New leaf growth requires relatively large amounts of N, which is supplied both from coincident absorption of soil N and transport of previously absorbed tissue N. The use of 15N allows the relative contribution of each source to be determined. Because turfgrasses are mowed frequently, clippings can be analyzed to produce a fairly detailed time course of 14N and 15N allocation to new leaf growth, allowing researchers to construct a balance sheet for leaf N (Fig. 4). With N applied monthly, assuming little contribution from soil organic N, 50% of leaf N is derived from the most recent N application, 20% from the previous application, 10% from 8 wk previous, and the remaining 20% from 
12 wk prior. While recent applications of N are often associated with increased color and growth, these data indicate that antecedent N contributes significantly to leaf N budgets.
These results demonstrate that suppression of bermudagrass growth with TE does not negatively impact N absorption by the turf nor increase NO3 leaching, but does slightly affect N allocation within the plant. Nitrate concentrations and total N loss in the leachate were low despite conditions favoring high leaching, and fertilizer recovery by the turf was relatively high. Conservative fertility management and growth regulation with TE are common in bermudagrass turf and, based upon the results from this experiment, may represent components of a program to maximize turfgrass N-use efficiency.
Received for publication July 5, 2002.
|
REFERENCES
|
|---|
- Borden, P., and R.W. Campbell. 1987. Growth and water use of ‘Meyer’ zoysiagrass as influenced by five chemical growth regulators. HortScience 22:63.
- Bowman, D.C., C.T. Cherney, and T.W. Rufty, Jr. 2002. Fate and transport of nitrogen applied to six warm-season turfgrasses. Crop Sci. 42:833–841.[Abstract/Free Full Text]
- Bowman, D.C., D.A. Devitt, M.C. Engelke, and T.W. Rufty, Jr. 1998. Root architecture affects nitrate leaching from bentgrass turf. Crop Sci. 38:1633–1639.[Abstract/Free Full Text]
- Bowman, D.C., J.L. Paul, and W.B. Davis. 1989a. Rapid depletion of nitrogen applied to Kentucky bluegrass turf. J. Am. Soc. Hortic. Sci. 114:229–233.
- Bowman, D.C., J.L. Paul, and W.B. Davis. 1989b. Nitrate and ammonium uptake by N-deficient perennial ryegrass and Kentucky bluegrass turf. J. Am. Soc. Hortic. Sci. 114:421–426.
- Brown, K.W., R.L. Duble, and J.C. Thomas. 1977. Influence of management and season on fate of N applied to golf greens. Agron. J. 69:667–671.[Abstract/Free Full Text]
- Carlson, R.M. 1978. Automated separation and conductimetric determination of ammonia and dissolved carbon dioxide. Anal. Chem. 50:1528–1531.
- Carlson, R.M. 1986. Continuous flow reduction of nitrate to ammonia with granular zinc. Anal. Chem. 58:1590–1591.
- Devitt, D.A., and R.L. Morris. 1988. Growth and water consumption of common bermudagrass as influenced by plant growth regulators, soil type and nitrogen fertility. HortScience 23:30.
- Fagerness, M.J., and F.H. Yelverton. 2000. Tissue production and quality of ‘Tifway’ bermudagrass, as affected by seasonal application patterns of trinexapac-ethyl. Crop Sci. 40:493–497.[Abstract/Free Full Text]
- Fry, J., and H. Jiang. 1998. Plant growth regulators may help reduce water use. Golf Course Manage. 66:58–61.
- Geron, C.A., T.K. Danneberger, S.J. Traina, T.J. Logan, and J.R. Street. 1993. The effects of establishment methods and fertilization practices on nitrate leaching from turfgrass. J. Environ. Qual. 22:119–125.[Abstract/Free Full Text]
- Gold, A.J., W.R. DeRagon, W.M. Sullivan, and J.L. Lemunyon. 1990. Nitrate-nitrogen losses to groundwater from rural and suburban land uses. J. Soil Water Conserv. 45:305–310.
- Johnson, B.J. 1992a. Response of ‘Tifway’ bermudagrass to rate and frequency of flurprimidol and paclobutrazol application. HortScience 27(3):230–233.
- Johnson, B.J. 1992b. Response of bermudagrass (Cynodon spp.) to CGA 163935. Weed Technol. 6:577–582.
- Johnson, B.J. 1997. Growth of ‘Tifway’ bermudagrass following application of nitrogen and iron with trinexapac-ethyl. HortScience 32(2):241–242.
- Liu, H., R.J. Hull, and D.T. Duff. 1997. Comparing cultivars of three cool-season turfgrasses for soil water nitrate concentration and leaching potential. Crop Sci. 37:526–534.[Abstract/Free Full Text]
- Mancino, C.F., and J. Troll. 1990. Nitrate and ammonium leaching losses from N fertilizers applied to ‘Penncross’ creeping bentgrass. HortScience 25:194–196.[Abstract/Free Full Text]
- 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.[Abstract/Free Full Text]
- Morton, T.G., A.J. Gold, and W.M. Sullivan. 1988. Influence of overwatering and fertilization on nitrogen losses from home lawns. J. Environ. Qual. 17:124–129.[Abstract/Free Full Text]
- Rieke, P.E., and B.G. Ellis. 1974. Effects of nitrogen fertilization on nitrate movements under turfgrass. p. 121–130. In E.C. Roberts (ed.) Proc. 2nd Int. Turfgrass Res. Conf., Blacksburg, VA. ASA and CSSA, Madison, WI.
- SAS Institute. 1995. The SAS system for Windows. v. 7.0. SAS Inst., Cary, NC.
- Snyder, G.H., B.J. Augustin, and J.M. Davidson. 1984. Moisture sensor-controlled irrigation for reducing N leaching in bermudagrass turf. Agron. J. 76:964–969.[Abstract/Free Full Text]
- Snyder, G.H., E.O. Burt, and J.M. Davidson. 1980. Nitrogen leaching in bermudagrass turf: Daily fertigation vs. tri-weekly conventional fertilization. p. 185–193. In J.B. Beard (ed.) Proc. 3rd Int. Turf Conf., Munich, Germany. 11–13 July 1977. ASA, CSSA, SSSA, and Int. Turfgrass Soc., Madison, WI.
- Starr, J.L., and H.C. DeRoo. 1981. The fate of nitrogen fertilizer applied to turfgrass. Crop Sci. 21:531–536.[Abstract/Free Full Text]
- Wiecko, G. 1997. Response of ‘Tifway’ bermudagrass to trinexapac-ethyl. J. Turfgrass Manage. 2(2):29–36.
This article has been cited by other articles:
|
|
|
|
 
E. H. Ervin and X. Zhang
Influence of Sequential Trinexapac-Ethyl Applications on Cytokinin Content in Creeping Bentgrass, Kentucky Bluegrass, and Hybrid Bermudagrass
Crop Sci.,
September 1, 2007;
47(5):
2145 - 2151.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. C. Knight, E. A. Guertal, and C. W. Wood
Mowing and Nitrogen Source Effects on Ammonia Volatilization from Turfgrass
Crop Sci.,
July 30, 2007;
47(4):
1628 - 1634.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
P. E. McCullough, H. Liu, L. B. McCarty, T. Whitwell, and J. E. Toler
Bermudagrass Putting Green Growth, Color, and Nutrient Partitioning Influenced by Nitrogen and Trinexapac-Ethyl
Crop Sci.,
May 18, 2006;
46(4):
1515 - 1525.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
