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Simplot, West 5300 Riverbend Ave., Post Falls, ID 83854
* Corresponding author (doug.brede{at}simplot.com).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Abbreviations: NTEP, National Turfgrass Evaluation Program • TQ, turfgrass quality
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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A decade later, Funk et al. (1968) tested bluegrass blends using the few cultivars available in that era. Again, stripe smut was a factor. However, Merion, even though it was susceptible, remained in high populations years after sustaining stripe smut damage. As in the earlier study, Funk concluded that no blend exceeded the quality performance of the best component.
Since that time, as the number of bluegrass cultivars has grown, so has the number of theories on how to combine them. The reason for the proliferation of theories probably relates to the difficulty of the trialing required: Constructing a replicated field trial of all possible four-way blends of the cultivars in the current national trial (Morris, 2002) would require more than 2 billion test plots and 25 million kg of seed.
Madison (1971) advocated blending cultivars with similar growth habits and discouraged blending together standard and dwarf cultivars because they thrive under different cultural regimes. Beard (1973) recommended that cultivars in blends be matched for similar leaf texture, growth habit, color, shoot density, and vertical growth rate. Moreover, each component should be resistant to a major disease, otherwise there is no advantage to using a blend. Vargas and Turgeon (1980) encouraged blends based on the desired adaptation spectrum, anticipated pest problems, and sod scheduling issues.
During the 1990s, the paradigm shifted. Instead of recommending blends of similar cultivars, some researchers began recommending blends of diverse, unrelated cultivars instead. Group and category systems were developed to classify cultivars for blending. Categories were based on growth appearance (Bonos et al., 2000) or DNA banding pattern (Jung and Stier, 2000). Although these group blending systems have been promoted in the popular press (Bonos et al., 2002), to this writer's knowledge, no one to date has constructed and field tested the recommended combinations of diverse cultivars to determine if they indeed produce a better turf.
Slowly, some existing blending theories are being questioned, both in turfgrass science and in the agronomic crops. Sij et al. (1999) challenged the prevailing theory that blending provides insect protection. In soybean [Glycine max (L.) Merr.], blending a resistant cultivar with a susceptible cultivar did not present a valid insect management strategy. In fact, susceptible plants acted as a safe harbor for insect growth and development. Vargas and Turgeon (1980) found that stripe smut and leaf spot [Drechslera poae (Baudys) Shoemaker] resistance of bluegrass blends were almost always less than that of the best component. They hypothesized that the susceptible cultivar was generating inoculum that later infected the more-resistant cultivar. Shearman et al. (1983) found similar results with bluegrass billbug (Stenophorus parvulus Gyllenhal). Larval numbers and insect damage were always more favorable in the monoculture than in the blend.
A shortcoming of prior Kentucky bluegrass blending studies has been their use of limited blend ratios. Funk et al. (1968), Oral and Acykgoz (2001), Shearman et al. (1983), and Vargas and Turgeon (1980) tested just one mixture ratio, in addition to monocultures, while Juska and Hanson (1959) tested only two. Although one or two mixture treatments allow a statistical comparison against the monocultures, no information is offered as to the possible shape of the ratio-vs.-TQ curve. A strictly linear curve would indicate a simple dilution effect. A nonlinear curve would provide added information as to the underlying nature of the competitive relationship (deWit, 1960).
Cost mitigation has long been a major impetus for blending (Vargas and Turgeon, 1980; Oral and Acykgoz, 2001). Blending an inexpensive low-performance cultivar with an expensive high-performance component lets a vendor highlight the good cultivar while selling the blend at a lesser price. The consumer is led to believe that the blend will behave like the high-performance cultivar and that the diluent will disappear or will provide sporadic advantages such as earlier spring greenup (T. Breier, 2002, personal communication).
The purpose of this study was to answer a few of the many questions underpinning the current theories of blending: Does adding a lower-performing cultivar in with a high-performance cultivar always decrease TQ? Is the relationship between mixture ratio and TQ linear, or can it be better defined by a curvilinear or segmented curve? Can a certain quantity of diluent (i.e., a lower-performing cultivar) be added without diminishing TQ? Does the lower-performing component's effects diminish over time? And can the lower-performing component benefit the blend during certain months of the year?
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The experiment was a randomized complete block design with three replicates in the 1998 trial and four in 1999 and 2000 trials. In the 2000 trial, one additional set of treatments was included: three-way blends. NuBlue and Huntsville were mixed in a 50:50 ratio. Then, this combination was blended with Award at the same fractions listed above.
Each plot was established at a seeding rate of 10 g m–2. Seed was sown by hand within wind boxes in 0.9-by-1.5-m plots onto a prepared seedbed. A cultipacker was used to incorporate the seed. No mulch was used. Soluble starter fertilizer was applied at 10 g nitrogen m–2. Slow-release sulfur-coated-urea maintenance fertilizer was applied annually at 20 g nitrogen m–2 yr–1, beginning at 4 wk after sowing. Potassium and phosphorus were adjusted as per soil test. Soil pH was 6.5. In the 1998 trial, fertilizer was withheld during 2001 to allow assessment at a lower maintenance level.
Dicamba (3,6-dichloro-2-methoxybenzoic acid) and 2,4-D (2,4-dichlorophenoxy acetic acid) were applied to eliminate broadleaf weeds in May of each year on all trials. The 2000 trial sustained annual bluegrass (Poa annua L.) encroachment and was treated each year (late fall or early spring) with ethofumesate (2-ethoxy-2,3-dihydro-3,3-dimethyl-5-benzofuranyl methanesulfonate). As a result, no ratings were taken for the 2000 trial during spring. No other pesticides were used.
The plots were irrigated to minimize stress. During hot weather (>35°C), some drought stress did occur (noted in Table 1). Plots were mowed thrice weekly during the growing season with a reel mower at a 32-mm bench cutting height. Clippings were not removed. In the 1999 trial, the mowing height was dropped to 13 mm in March 2002 to allow assessment under a higher maintenance level. From the appearance of the stand in terms of density and color, the plots had substantially equilibrated to the new height by the May 2002 rating date.
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pivot point" segment in the equation that functions as an if-then statement, setting the slope to zero below a computed pivot point. Results with a nonsignificant pivot point and a significant slope would indicate a simple linear relationship between blend ratio and TQ.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Above the pivot point, the low-performance cultivar exerts a downward pressure on TQ, decreasing logically and linearly to the mean value of the monoculture. This relationship is illustrated in Fig. 1 with data from the 1999 trial. It shows the area of no influence, the pivot point, and the area of decreasing slope.
Not all of the data had a clear pivot point. In the 1998 trial, fewer replicates and treatment levels were used, and the levels chosen had an unfortunate emphasis on the left-hand side of the graph. That perhaps explains why only one significant pivot point was detected in the 1998 trial, vs. 10 in the 1999 trial and 5 in the 2000 trial (from monthly means) (Table 2).
In the entire study, there were 52 monthly data means recorded, 10 yearly means, and three trial means (Table 2). Throughout the study, there were 37 monthly ratings in which Huntsville (the low-performance cultivar) decreased the TQ of the Award blend, as evidenced by a significant negative slope. Thus, 71% of the time, adding Huntsville was detrimental. In 13 monthly cases (25% of the time), there was no effect on TQ. In two monthly cases (4% of the time), adding Huntsville to Award improved the TQ of the stand, as evidenced by a significant positive slope. Both of these cases were during establishment. Award is known to possess after-ripening seed dormancy, whereby freshly harvested seed can exhibit delayed establishment (Brede, 2001b).
Huntsville had a negative effect on Award blends in 8 of 10 yearly means and a positive effect in none. In the overall trial means, Huntsville had a negative effect in three of the three trials. Pivot points were significant in 14 of the 52 monthly means for Huntsville, or 26% of the time. They were significant in three of the 10 yearly means and in one of the three trial means.
NuBlue decreased the TQ of the Award blend in 31 of 52 monthly means or 60% of the time. There was no effect on TQ in 19 monthly cases (36% of the time). In two monthly cases (4% of the time), adding NuBlue to Award improved the TQ of the stand. Again, both were related to establishment. NuBlue had a negative effect on Award blends in seven of 10 yearly means. It had a positive effect in one (the 1999 mean of the 1999 trial). In the overall trial means, NuBlue had a negative effect in three of the three trials. Pivot points were significant in two of 52 monthly means for NuBlue, or 4% of the time. Pivot points were not significant in yearly or trial means.
In the 2000 trial, a series of three-way Award + NuBlue + Huntsville blends were tested (Table 3). NuBlue + Huntsville decreased the TQ of the Award blend in nine of nine monthly means. Pivot points were not significant.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Results from the present study overwhelmingly indicate that the addition of a diluent cultivar into a blend serves to decrease the TQ performance of the elite cultivar. This was seen both with the midranged and the low-end cultivars. The only advantage from the addition of these diluents was more rapid stand fill after planting, which represented 4% of rating dates (Table 2). In other words, the diluent may act as a nurse grass until the slower-establishing elite grass establishes. The superior NTEP greenup ranking of Huntsville benefited the blended stand on only 1 of 57 monthly means, and that particular advantage may have been confounded with remaining seedling establishment effects.
The segmented curve (with a significant pivot point) was prevalent with the low-performance cultivar but it was rare with the midranged cultivar. With NuBlue, quality was a simple linear function of NuBlue content. Three-way blends of Award + NuBlue + Huntsville tended to perform more as Award + NuBlue blends than as Award + Huntsville blends (Table 3, Fig. 2) . One can speculate that the reason for this lies in the fact that NuBlue, being more fit, disguises or forces out Huntsville.
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The effect of the diluent cultivar appears to diminish with time, but it is never eliminated. Similar results can be seen in the longer term 6-yr trial of Funk et al. (1968) and the 4-yr trial of Vargas and Turgeon (1980).
Maintenance level during the third year of the 1998 and 1999 trials was adjusted to observe effects. Lowering the nitrogen fertility in the 1998 trial seemed to have little effect on calculated parameters. In the 1999 trial the cutting height was reduced to 13 mm in 2002. The resulting pivot points remained virtually the same but the slope changed 63% for NuBlue and 55% for Huntsville from 2001 to 2002. Part of this change may be attributable to aging of the stand, since an 11% increase in slope was observed in both cultivars in the 2000 trial between 2001 and 2002 with no alteration in cutting height.
Results of the present study pose an intriguing question: With the broad pest and adaptation spectrum of today's top Kentucky bluegrass cultivars, is the requirement for blending becoming obsolete? Can top cultivars be managed as a monoculture? Time and further research may provide the answer.
Consumers desiring the highest TQ should avoid adding mid- or low-performance cultivars to their blend as, according to the results herein, the short- and long-term TQ may suffer. The best compromise may be to recommend blending together only top-performing cultivars, rather than cultivars of disparate performance levels.
Future research is needed on turfgrass blending to reconcile the abundant theories with actual field results of constructed blends. Hopefully, this will allow our understanding of blending to progress beyond theory and intuition and into science and hard facts.
Received for publication February 16, 2003.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
