| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a Crop and Soil Environmental Sciences, Virginia Polytechnic Inst. and State Univ., Blacksburg, VA 24061
b Dep. of Horticulture and Landscape Architecture, Colorado State Univ., Fort Collins, CO 80523
* Corresponding author (EErvin{at}vt.edu)
 |
ABSTRACT |
|---|
 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
-hydroxy-methylene)-3,5-dioxo-cyclohexane-carboxylic acid ethyl ester] while subjected to traffic and variable N rates would facilitate recommendations regarding its safe and effective use. The objectives of this study were (i) to investigate the extent and duration of TE-induced shoot growth suppression on Kentucky bluegrass and determine any interactive traffic or N effects, and (ii) to investigate if TE-induced reductions in shoot growth affect tillering, rooting, and quality of Kentucky bluegrass, and determine any interactive traffic or N effects. Trinexapac-ethyl (0.27 kg ha-1) was applied to main plots three times a year at 6-wk intervals. Traffic was applied to subplots with a cleated roller. Four increasing rates of a slow-release N source were applied annually to sub-subplots. Trinexapac-ethyl consistently reduced clippings by 1 to 2 wk after treatment (WAT), with maximum suppression occurring at 3 to 4 WAT. Greater suppression occurred for July and August application dates relative to May. Traffic consistently reduced clippings and tiller density. Tiller density was increased by TE in 1996. Higher annual N did not, in general, affect tiller density, root mass, or quality. Repeated TE application did not affect Kentucky bluegrass root mass. Trinexapac-ethyl did not affect quality, while traffic consistently reduced it. Quality was poorest at the three highest N-rates under TE and traffic during the last treatment cycle of 1997. These results suggest caution when using TE on highly trafficked Kentucky bluegrass.
Abbreviations: LAI, leaf area index • PGR, plant growth regulator • TE, trinexapac-ethyl • WAT, weeks after treatment
|
INTRODUCTION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
A number of researchers have reported that TE reduces cool-season turfgrass shoot growth (Ervin and Koski, 1998; Burpee et al., 1996; Daniels and Sugden, 1996; Johnson, 1993). However, limited published research is available regarding other morphological and physiological responses of turfgrasses to TE such as photosynthesis, carbohydrate partitioning and storage, rooting, tiller density, traffic tolerance, and N rates.
It has been reported that TE does not negatively affect cool- or warm-season photosynthesis (Stier et al., 1997; Qian et al., 1998). Photosynthate, not utilized for leaf expansion during PGR-induced suppression, may be redirected to other sink tissues such as the stems and roots (Cooper et al., 1988). Since the accumulation of carbohydrates is greatest during periods of minimal shoot growth (Hull, 1992; Beard, 1973), it seems reasonable to assume that shoot growth suppression caused by TE may result in an increase in carbohydrate content in stem or root tissue. These additional carbohydrates may be used for resumption or enhancement of longitudinal shoot growth once the suppressive effects of TE have dissipated (Bingaman and Christians, 1997; Cooper et al., 1988), or they may be used for enhanced root or tiller growth.
Maximum rooting depth, total root length, and root length density of greenhouse-grown Kentucky 31 tall fescue (Festuca arundinacea Schreb.) were unaffected by TE treatment (Marcum and Jiang, 1997). Final root mass of growth chamber and greenhouse grown perennial ryegrass (Lolium perenne L.), following multiple applications of TE, were also unaffected, relative to the control (Ervin and Koski, 1998).
Application of TE to turfgrasses may alter the pattern of carbohydrate partitioning to favor the initiation of axillary bud development, resulting in increased tiller formation. Research pertaining to the effects of another anti-gibberellin PGR, flurprimidol [-(1-methylethyl)--[trifluourmethoxy)phenyl]-5-pyrimidinemethanol], on turfgrass tillering indicate positive benefits. Dernoeden (1984) reported increased tiller density of a field-grown Kentucky bluegrass/red fescue (Festuca rubra ssp. rubra) turf following eight applications of flurprimidol across 4 yr. Similarly, Breuninger (1984) reported that flurprimidol stimulated Kentucky bluegrass tiller production, while not affecting total shoot tissue carbohydrate levels or photosynthetic rate. Ervin and Koski (1998) reported that multiple applications of TE to greenhouse-grown perennial ryegrass increased final tiller density. At present, we are not aware of any published research information concerning the effect of TE on Kentucky bluegrass tiller density.
A further benefit of enhanced tiller density due to TE may be increased traffic tolerance. Traffic causes wear injury to turfgrass foliage and compaction of the soil (Carrow and Petrovic, 1992). Wear injury is often due to physical abrasion and tearing of aboveground plant parts (Beard, 1973). Any practice that increases the verdure and root density of a turf increases the probability of tolerance to traffic stress (Carrow and Wiecko, 1989). Carrow (1980), reported that Kentucky bluegrass shoot density, verdure, and root weight in the 0- to 10-cm soil profile were significantly decreased by compaction treatments with a smooth roller that resulted in an increase in soil bulk density. Agnew and Carrow (1985), reported that long-term compaction increased Kentucky bluegrass root weights in the upper 5-cm and decreased them in the lower 10- to 20- cm soil profile. Shearman and Beard (1975) concluded that turf which maintained the greatest amount of verdure following wear treatments possessed the greatest wear tolerance.
Greater applied N will increase aboveground biomass and should increase recovery from traffic, but could have mixed effects on turfgrass traffic tolerance. Higher N rates during establishment will increase tiller density (Simon and Lemaire, 1987; Canaway, 1984a; Beard, 1973). However, once a leaf area index (LAI) of three is reached, photomorphogenic promotion of tillering has been reported to be restricted due to the almost complete extinction of light at the level of tiller buds, one of the results being that N additions may no longer promote tillering (Simon and Lemaire, 1987; Davies et al., 1983). Under regular mowing, cool-season grasses can reach and maintain an LAI of three or greater after 2 to 3 mo of development (Brede and Duich, 1984).
Obviously, traffic will damage turf plants and reduce LAI to the point where N fertilization will aid substantially in recovery of density. However, it is not clear what affect higher relative N rates may have on the traffic tolerance of mature turfs with a LAI of three or greater. Canaway (1984b), reported that established perennial ryegrass plots receiving high annual N rates (>290 kg ha-1) deteriorated faster under artificial wear than those receiving moderate levels (100–225 kg ha-1). There were no reported differences in wear tolerance or recovery of Kentucky bluegrass that received annual N rates of 96 or 192 kg ha-1 (Carroll and Petrovic, 1991). We are not aware of any published research concerning the response of TE-treated turf to traffic and N.
Given the available evidence, we hypothesize that TE-induced reductions in shoot growth may result in increased tillering, increased rooting, and quality equivalent to untreated turf while receiving reduced annually applied N. We further hypothesize that tillering and rooting increases may result in improved traffic tolerance. The objectives of this study were: (i) to investigate the extent and duration of TE-induced shoot growth suppression on Kentucky bluegrass when applied at different times of the year, and determine any interactive effects that traffic or N treatments may have on such suppression; and (ii) to investigate if TE-induced reductions in shoot growth affect tillering, rooting, and quality of Kentucky bluegrass and determine any interactive effects that traffic or N treatments may have on these performance variables.
|
MATERIALS AND METHODS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
1500 m above sea level. The climate is semiarid with average annual maximum temperature of 16.8 °C, average minimum of 1.2 °C, and average annual precipitation of 365 mm. The soil is a Nunn clay loam (fine, montmorillonitic, mesic, Aridic Argiustoll), with a pH of 7.8 and an organic matter content of 3.0%. The experimental design was a three factor split plot arranged in four randomized complete blocks. Each block contained 16 experimental units 2.7 by 1.8 m. The factors were TE, traffic, and N levels. Main plots (10.8 by 3.6 m) were either treated or not with TE at 0.27 kg ha-1 three times each year at 6-wk intervals. Each main plot was split vertically, and half of these subplots received periodic traffic events. Each subplot was also divided into four sub-subplots and four annual N levels were randomly applied to these sub-subplots.
Trinexapac-ethyl application dates were: 27 June, 14 August, and 26 September in 1995; 22 May, 05 July, and 16 August in 1996; and 20 May, 02 July, and 07 August in 1997. Trinexapac-ethyl was applied with a CO2 sprayer at a pressure of 242 kPa and a spray volume of 0.10 L m-2.
Artificial traffic was applied periodically to one half of each main plot with a 200 kg, 76-cm wide turf roller (Brouwer TR130, Brouwer Turf Equipment, Dalton, OH) modified by bolting rubber soccer cleat soles to the roller. Traffic treatments began on 22 Aug. 1995 with each plot receiving 25 to 75 passes per week during the TE application cycles with the cleated roller. The number of passes per week could not be held constant because of a periodic need to reduce traffic pressure and allow some turf recovery so that clipping samples of a measurable amount could be collected. The number of traffic passes during each 6-wk TE application cycle were: Cycle 1, 1995 (none, roller not yet available); Cycle 2, 1995 (140); Cycle 3, 1995 (none, snow did not permit); Cycle 1, 1996 (450); Cycle 2, 1996 (none, dry-down cycle); Cycle 3, 1996 (325); Cycle 1, 1997 (300); Cycle 2, 1997 (125); Cycle 3, 1997 (225).
Yearly N rate was the third factor in this experiment. The N source used was Nutralene Granular (40-0-0) (AgrEvo, Wilmington, DE). Nutralene is a controlled release N source containing 5% urea, 20.5% slowly available methylene urea polymers, and 14.5% water insoluble N. Nitrogen was applied at 49, 98, 147, and 196 kg ha-1 yr-1, splitting the subplots horizontally. Each year, 49 kg N ha-1 was applied on 20 April, another 49 kg N ha-1 was applied to the second, third, and fourth levels on 20 June, another 49 kg N ha-1 was applied to the third and fourth levels on 20 August, and a final 49 kg N ha-1 was applied to the fourth level on 20 October.
The experimental area was irrigated every 3 d to replace 100% of Penman-Monteith estimated reference grass evapotranspiration (Jensen et al., 1990). Mecham (1996) has shown that the Penman-Monteith equation, which accounts for elevation, geographical location, and crop height provides better evapotranspiration estimates in northern Colorado than other commonly used equations. These estimates were made daily based on data from a weather station located 4.0 m from the southern border of the experimental site. The weather station was located over a sward of well-watered Kentucky bluegrass mowed twice weekly at a height of 6.4 cm.
Variables Sampled
Clipping dry weights were obtained each week of the TE application cycles, weather and other factors permitting, by mowing down the center of each experimental unit with a rotary mower set at 5.7 cm and catching the clippings in a 20 L paint straining bag. The mower deck is 0.46 m wide and the length of each experimental unit cut was 2.74 m. Thus, weekly clipping dry weights were collected from a 1.25 m2 area. All clippings were dried in a forced air oven at 70 °C for 48 h, weighed, and reported as g m-2.
No clipping dry weight data were taken during the third TE-application cycle in 1995, from 27 September to 9 November, because of snow and cold weather. During the second TE-application cycle of 1996 (5 July–15 August), no clipping data were taken because irrigation was being withheld to observe the effects of TE on Kentucky bluegrass drought avoidance (data not presented).
Weekly visual quality was rated on a scale of one to nine, where nine is an ideal turf area, six corresponds to a turf of minimum acceptable quality, and one indicates a turf that is completely dormant or dead.
Root samples were obtained using a truck-mounted Gidding's hydraulic soil probe (Gidding's Manufacturing, Fort Collins, CO) in May and October, before and after each year's three TE application cycles. Three depths were sampled: (i) 0 to 20 cm, (ii) 21 to 40 cm, and (iii) 41 to 60 cm. The diameter of the soil probe was 3.2 cm. Two subsamples per depth were taken on each experimental unit and combined as one sample. The roots were separated from the soil with a hydropneumatic elutriation system (Smucker et al., 1982), dried at 70 °C in a forced air oven for 24 h, and weighed to obtain root mass.
A bulk density sampling tool (Gidding's Manufacturing, Fort Collins, Colorado) was used to obtain two 23.0-cm2 subsamples per experimental unit for tiller density counts in October of each year. Bulk density subsamples with a volume of 730 cm3 were obtained simultaneously. The verdure of each subsample was separated from the soil and used for tiller density counts; the number of tillers per 23.0-cm2 subsample were counted by hand. The 730-cm3 volume of soil was oven dried at 105 °C for 48 h and weighed to obtain bulk density.
Statistical Analysis
Six-week averages of clipping dry weight and quality ratings, plus root mass, tiller density, and bulk density data were subjected to analysis of variance using the general linear models procedure in the Statistical Analysis System (SAS Institute, 1990). Mean differences were ascertained using Fisher's protected LSD for a split-split plot design, as outlined by Steel and Torrie (1980). Clipping dry weight and quality data were subjected on a weekly basis to analysis of variance as split-split-split plot repeated measures using the general linear models procedure in the Statistical Analysis System. Significant year-by-year interactions occurred for all parameters measured, and therefore data are presented separately by treatment cycle and year.
|
RESULTS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
|
During the May–June 1997 cycle, 196 kg N ha-1 resulted in the greatest clipping amounts across all treatments (Table 2). During the Aug–Sept 1997 cycle, 147 kg N ha-1 resulted in the greatest average clipping amounts for the no TE, no traffic treatment, while 196 kg N ha-1 resulted in the highest amounts for the other three treatments.
|
Analysis of variance including week as a fourth factor indicates an interactive effect of TE, traffic, and week on clipping dry weight during all treatment cycles, except during the May–June cycle of 1997 (Table 1). The pattern of clipping production due to TE and traffic treatments across weeks for the May–June and August–September 1997 cycles are presented in Fig. 1 and 2 , respectively. The No TE-NT lines in both figures provide an indication of untreated Kentucky bluegrass response to changes in temperature and N application. As would be expected, clippings increased following scheduled N treatment applications on the No TE-NT plots, with clipping reductions often following increases in weekly average high air temperatures (Fig. 1 and 2).
|
|
A comparison of the two traffic treatments also indicates response differences. Trinexapac-ethyl and traffic reduced clippings, relative to traffic alone, at 2 WAT (-55%) and 3 WAT (-34%) during the May–June 1997 cycle (Fig. 1). No reductions occurred during the May–June 1996 cycle. Trinexapac-ethyl and traffic reduced clippings at 2 (-74%), 4 (-87%), 5 (-67%) and 6 WAT (-46%), relative to traffic alone, during the August–September 1997 cycle (Fig. 2). No reductions due to TE and traffic were noted during the August–September 1996 cycle.
Root Mass
There were no treatment effects on Kentucky bluegrass root mass measured in 1995 at the 0- to 20-cm depth. Increased root mass was measured due to traffic in October 1996 (0.97 mg cm-3 no traffic vs. 1.14 mg cm-3 traffic). Alternatively, traffic was associated with decreased 0- to 20-cm depth root mass on no TE plots (0.65 vs. 0.81 mg cm-3) in October 1997. There were no main or interactive effects of N on root mass during the course of this study. There were also no treatment effects on 21- to 40-cm or 41- to 60-cm depth root mass.
Tiller Density
Analysis of variance indicated that N increased tiller density in 1995 (232.6 tillers dm-2 for 49 kg N ha-1 vs. 243.6 tillers dm-2 for 196 kg N ha-1), but had no effect in 1996 or 1997. At the end of the 1996 and 1997 treatment periods, traffic had significantly thinned Kentucky bluegrass tiller density (Table 3). Further, TE treatment resulted in higher tiller density in 1996. In 1997, there was no difference between TE and traffic and traffic-alone treatments.
|
|
|
|
DISCUSSION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
4 WAT. Greater growth suppression occurred for July and August application dates relative to May, most likely due to increased air temperatures (3–8 °C, Fig. 1 and 2) during the 4 wk following treatment in the summer periods. These results are consistent with previous research (Fagerness and Penner, 1998; Johnson, 1993). Turf managers would be advised to apply TE monthly to achieve continuous growth inhibition and avoid the post-inhibition flush of growth which has been noted to occur at 5 to 6 WAT (Bingaman and Christians, 1997; Spak et al., 1993). Repeated application of TE did not affect Kentucky bluegrass root mass at any of the depths sampled. These field results agree with the results of greenhouse experiments conducted with TE-treated tall fescue and perennial ryegrass (Ervin and Koski, 1998; Marcum and Jiang, 1997).
At the 0- to 20-cm sample depth, traffic increased root mass in 1996 and decreased it in 1997. By sampling smaller increments, Agnew and Carrow (1985) reported root mass increases from 0 to 5 cm associated with compaction. Alternatively, Sills and Carrow (1983) have reported compaction-related decreases from 0 to 5 cm, 5 to 15 cm, and 15 to 25 cm. In our study, division of sample depths into more discrete increments may have provided greater ability to measure possible treatment effects. As it is, our data is inconclusive.
As expected, traffic consistently reduced clipping dry weights across all 3 yr of this study. Traffic, coupled with TE application, often resulted in the greatest clipping dry weight reductions, especially during the periods of highest TE-induced suppression (2–4 WAT) (Fig. 1 and 2). One practical implication of such a severe reduction in clippings under traffic and TE may be a reduction in quality (or traffic tolerance), as was observed during the last cycle of the experiment (Table 5).
Although reduced traffic tolerance is a concern, the maintenance of greater tiller density due to TE under traffic may serve to partially offset this problem (Table 3). Our results concerning this point were not clear. Greater density was maintained with TE under traffic in 1996, but not quite in 1997. Our data indicate that heavy 2-yr traffic pressure on TE-suppressed Kentucky bluegrass resulted in the poorest quality. Our information would have been more useful to turfgrass managers if we would have monitored turfgrass recovery following the end of traffic treatments each autumn.
Higher annual rates of slowly available N did not play a significant role in tiller density, root mass, or increased quality under traffic. Typical responses to increased N rates are greater tiller density (Canaway, 1984a; Beard, 1973) and decreased root mass (Turner and Hummel, 1992; Beard, 1973). Increased N rates have been shown to improve wear tolerance up to a threshold (200–300 kg N ha-1 yr-1), whereby additional N may deteriorate it (Canaway, 1984b). We can only speculate that the lack of tiller density response to increased N in our study may have been associated with this previously well-fertilized 5-yr-old turf already being at its carrying capacity or optimum density (LAI) (Lush, 1990; Simon and Lemaire, 1987). Tiller density of the untrafficked plots did remain quite stable across all 3 yr (Table 3). Deficiency symptoms were never observed on plots receiving only 49 kg N ha-1. We speculate that moderately high levels of soil organic matter (3%), optimum N fertilization in the 3 yr prior to treatment initiation, and the fact that, prior to sodding, this field had been in continuous alfalfa (Medicago sativa L.) production for many years may have resulted in enough yearly N mineralization to reduce any potential N treatment effects.
Root mass may not have been negatively affected by higher annual N rates because the slow-release properties of the N source probably did not overstimulate shoot growth at the expense of root growth. Alternatively, some N effect on root mass may have gone undetected due to our relatively infrequent sampling periods and broad sampling increments (20 cm). The highest yearly N rate of 196 kg ha-1 was not excessive and did not result in changes in Kentucky bluegrass quality under traffic, relative to the lower N rates.
In summary, our data does not fully support our working hypothesis that reductions in shoot growth due to TE would result in greater tiller density and root mass under nontraffic conditions. A further hypothesis, however, was that increased tiller density under traffic would result in improved quality. Greater tiller density due to TE under traffic was not measured. This result, in combination with reduced quality of trafficked-TE plots in 1997, implies a rejection of this second hypothesis. Continual traffic on TE-suppressed leaf blades, with little tissue removal and regrowth following mowing, resulted in more cumulative wear on blades within the canopy; hence, the visual reduction in quality relative to the control. Additionally, because of a lack of N response on quality, our results do not provide any evidence for our hypothesis that growth suppression due to TE will allow for the maintenance of high quality turf with reduced annual N inputs. Further research investigating the effects of differential rates, timings, and intervals of TE application on turf recovery following traffic, specifically the possibility of decreasing the time required for a thinned stand to regain carrying capacity, would be another step forward in refining recommendations regarding the utility of this PGR in sports turf situations.
|
NOTES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Received for publication March 1, 2000.
|
REFERENCES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  J. C. Inguagiato, J. A. Murphy, and B. B. Clarke Anthracnose Severity on Annual Bluegrass Influenced by Nitrogen Fertilization, Growth Regulators, and Verticutting Crop Sci., July 1, 2008; 48(4): 1595 - 1607. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S. E. McCann and B. Huang Effects of Trinexapac-Ethyl Foliar Application on Creeping Bentgrass Responses to Combined Drought and Heat Stress Crop Sci., September 1, 2007; 47(5): 2121 - 2128. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
L. B. McCarty, J. S. Weinbrecht, J. E. Toler, and G. L. Miller St. Augustinegrass Response to Plant Growth Retardants Crop Sci., July 1, 2004; 44(4): 1323 - 1329. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Natural Resources and Life Sciences Education |
Soil Science Society of America Journal | ||||
| Journal of Plant Registrations | Journal of Environmental Quality |
The Plant Genome | |||
