Which Kentucky bluegrass cultivars perform better with less water?
Twenty-eight Kentucky bluegrass cultivars and two hybrid bluegrasses were tested for their ability to retain visual quality under reduced irrigation.
Dale Bremer, Ph.D.; Steve Keeley, Ph.D.; Jack Fry, Ph.D.; and Jason Lewis, Ph.D.
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Well-watered plots are shown at the beginning of the
dry-down study on June 4, 2007 .
Photos by Jason Lewis
research at Kansas State University indicates that water requirements may
differ significantly among cultivars of Kentucky bluegrass (Poa pratensis L.), depending
upon desired turfgrass quality. Given the certainty of periodic drought, limited
water availability and increasing irrigation costs, having choices of Kentucky
bluegrass cultivars that may maintain better quality with less water is an
attractive option. Ideally it would be helpful to select a turfgrass that can
perform well with less water.
Kentucky bluegrass plots with obvious drought stress are shown at two months into the study, Aug. 4, 2007. Plots were sheltered from precipitation by the rainout shelter (upper left in each photo), which automatically moved on tracks to cover the plots during rainfall.
helpful concept when discussing Kentucky bluegrasses is their classification into
phenotypic groups. Individual cultivars of Kentucky bluegrass are classified
into phenotypic groups based on common growth and stress performance
characteristics gathered from field trials (1). Previous research has indicated
that such groupings may be useful in predicting drought tolerance. Because
cultivar turnover is rapid in the turfgrass industry, determining the relative
irrigation requirements of phenotypic groups may enable researchers to predict
irrigation requirements of cultivars not included in any particular study.
a rainout shelter, we compared seasonal irrigation amounts among 28 Kentucky
bluegrass cultivars for two growing seasons. By shielding plots from rainfall,
water could be withheld until wilt symptoms were evident. Our objectives were
to identify Kentucky bluegrass cultivars and phenotypic groups that maintain
better visual quality with less irrigation, using wiltbased irrigation. We
hypothesized that if visual quality were good at the beginning of the season,
we would maintain minimally acceptable quality in Kentucky bluegrass (for
example, for a moderately maintained lawn or golf course rough with in-ground
sprinklers) by irrigating when at least 50% of a given cultivar showed signs of
wilt. Two hybrid bluegrasses (Poa arachnifera Torr. × P. pratensis) were also
included in the study.
study was conducted at the Rocky Ford Turfgrass Research Center near Manhattan,
Kan. Data were collected for 105 days in 2007 (June 19- Oct. 1) and 108 days in
2009 (June 22-Oct. 7). Turfgrasses included 28 Kentucky bluegrass cultivars and
two hybrid bluegrasses (Table 1). Commercially available cultivars of Kentucky
bluegrass were selected to include representatives from major Kentucky
bluegrass phenotypic groups (in the results section, only groups with three or
more cultivars were used when comparing groups). Also, because visual quality
was of interest, cultivars were selected based on performance in National
Turfgrass Evaluation Program (NTEP) trials.
plots were maintained and well watered until the study began each year.
Thereafter, water was withheld until 50% or more of a plot displayed drought
stress. One inch (2.54 centimeters) of water was then applied by hand to the
individual plots. Turfgrass quality and drought stress symptoms were evaluated
daily. This process continued until the end of the study, after which all plots
were re-watered and allowed to recover. Plots were mowed weekly at 3 inches
quality evaluations, based on color, density and uniformity of the canopies, were
made using a visual rating scale of 1 to 9, where 1 = brown turf, 6 = minimally
acceptable turf or a home lawn or golf course rough and 9 = optimal turf.
Drought stress was defined as the turf displaying wilting, failure of the
canopy to remain upright after foot traffic and a general darkening color of the
turf. Because drought stress sometimes changed rapidly from day to day,
particularly under high temperatures, it was not unusual for irrigation to be
applied when more than 50% of a plot (for example, up to 70% or 80%) displayed
water applied and days to wilt between irrigation cycles
applications, averaged over the approximately 3.5-month period in each year of
the study, ranged widely from 9.17 inches (23.3 centimeters) [mean = 0.086 inch
(2.2 millimeters)/day)] in Bedazzled to 17.67 inches (44.9 centimeters) [0.165
inch (4.2 millimeters)/day)] in Kenblue (Figure 1). In Bedazzled, Apollo,
Cabernet and Unique, 9.84 inches (25.0 centimeters) [0.090 inch (2.3
millimeters)/day] or less of water was applied, which was significantly less
than that applied to Kenblue, Blue Knight, Wellington, Moonlight, Baron, Diva,
Midnight II, Touchdown, Shamrock and Blue Velvet. In the latter 10 cultivars,
13.81 inches (35.1 centimeters) [0.129 inch (3.3 millimeters)/day) or more of
water was applied. However, there were no statistical differences among the 15 cultivars
that received the least amount of water (Figure 1, Bedazzled through Skye).
to wilt between irrigations, which was roughly inverse to the amount of water applied
−0.91), ranged from 6.4 days in Kenblue to 13.1 days in Cabernet, a difference of
nearly one week (Figure 2). Days to wilt was greater in Cabernet, Bedazzled, Unique
and Apollo (11.9 to 13.1 days) than in the 18 bluegrasses with the least days
to wilt (6.4 to 9.0 days; Kenblue through Park in Figure 2). These intervals
provide the practitioner with an estimate of irrigation frequency required to
maintain the various Kentucky bluegrasses at a performance level similar to
this study, at least in the transition zone of the United States. In addition
to requiring less frequent irrigation, cultivars with more days to wilt have a
greater likelihood of receiving rainfall between irrigations; this could result
in further water conservation and reduced irrigation costs.
all cultivars in the phenotypic group Mid-Atlantic (Cabernet, Eagleton and Preakness)
and four of five in the Compact America group (Apollo, Bedazzled, Kingfisher and
Unique) were among the 15 cultivars that received the least amount of water (Table
1, Figure 1). When averaged over all cultivars within each phenotypic group, 10.75
inches (27.3 centimeters) of water was applied to Compact America types and 11 inches
(27.7 centimeters) to Mid-Atlantic types [both about 0.102 inch (2.6
millimeters)/ day), which was less than the Common, Compact and Compact
Midnight groups (Figure 3). The Common types received more water (15.79 inches
[40.1 centimeters]; 0.149 inch [3.8 millimeters]/day]) than all other groups
except Compact. Days to wilt was also greater in Mid-Atlantic and Compact America
than in all other groups (Figure 4), indicating cultivars in Mid-Atlantic and Compact
America could generally go longer without irrigation.
the exception of the Common types in 2007, the visual quality of all
bluegrasses was acceptable (>6) at the beginning of the study in each year
(see the top photo, Page 76). In all bluegrasses and in both years, however, visual
quality declined to below what was considered minimally acceptable (bottom photo,
Page 76). This indicates waiting until 50% wilt to apply irrigation was
insufficient to maintain acceptable visual quality in Kentucky bluegrass, at
least for homeowners or superintendents who desire a moderate standard of
quality in the stressful climate of the transition zone. Perhaps visual quality
could have been maintained at acceptable levels by applying water when only 25%
of the plot exhibited symptoms of drought stress; further research is required.
Our method may be appropriate, however, for the typical homeowner with no
in-ground sprinklers or superintendents with low-maintenance roughs on their
golf courses, or where the primary concern is water conservation and some
dormancy is acceptable. Visual quality in all bluegrasses generally remained
>4, and recovery was rapid in the fall after resuming irrigation (data not
visual quality declined to <6 in all cultivars, the time required to do so ranged
widely from 8.1 days in Kenblue to 44.8 days in Blue Velvet (data not shown for
all cultivars; for greater detail, see [2,3]). The decline was slower in Blue
Velvet, Award, Midnight, Cabernet, Unique and NuDestiny (36 to 44.8 days) than
in Park, Baron, Wellington and Kenblue (8.1 to 14.2 days). Thus, four of five
cultivars in the Compact Midnight group maintained quality longer than all
cultivars in the Common group (Table 1). As a group, the Compact Midnight types
maintained quality >6 for longer than the Common as well as the BVMG types,
but also received more water than the Compact America and Mid-Atlantic groups
between water applied and visual quality
cultivars or groups that require the least water would also have the highest
visual quality. Those relationships are illustrated in the scatter biplot in
Figure 5, in which cultivars with the most favorable characteristics appear in
the lower right section. In general, irrigation applications were greater in
bluegrasses with poorer quality (Figure 5, upper left section). This pattern
probably resulted from improved cultivars with morphological properties that
both enhanced turf quality and reduced evapotranspiration (water use). Such
improved properties include compact or dwarfed growth habits, horizontal leaf
orientation and greater shoot density.
15 bluegrasses with the lowest water applications were also ranked among those with
the highest visual quality (Figure 5; there were no statistical differences
among cultivars with average visual quality >5.5). The amount of water
applied to these 15 cultivars with superior turf quality was also below the
mean water applied to all 30 bluegrasses (13 inches [32.8 centimeters]).
Similarly, visual quality in 12 of the 15 bluegrasses that received the least
water was greater than the mean of all 30 bluegrasses (5.78), although all 15
were statistically similar.
contrast to the 15 top performers, six cultivars were ranked within the group
that received the most water and had the lowest visual quality (Figure 5). Those
six cultivars — Kenblue, Wellington, Midnight II, Baron, Diva and Shamrock —
had neither the high visual quality nor low water requirement traits we were
screening for in this study.
selection in Kentucky bluegrass had significant impacts on water requirements and
visual quality ratings. Among cultivars, differences in seasonal water
applications were as great as 8.5 inches (21.6 centimeters), and differences in
days to 50% wilt between irrigations were as great as 6.7 days (that is, nearly
one week). Based on statistical range tests, only 15 of the 30 cultivars were
in the group that both received the least water and had the greatest visual
quality. Results indicated that, under conditions similar to those in our
study, Kentucky bluegrass in the Compact America and Mid-Atlantic phenotypic groups
can be selected for their lower irrigation requirements without sacrificing visual
quality, and types from those two groups may represent the best selections for breeding
efforts to achieve such goals. More detailed results from this study can be
found elsewhere (2,3).
research was funded by United States Golf Association (USGA), Turfgrass Producers
International (TPI) and the Kansas Turfgrass Foundation.
technical assistance of Tony Goldsby was greatly appreciated.This
article was published in the Spring 2013 (Vol. 26, No. 1) issue of Sports Turf Manager.
- Bonos, S.A., W.A. Meyer and J.A. Murphy. 2000. Classification of Kentucky
bluegrass genotypes grown as spaced-plants. HortScience 35:910-913.
- Bremer, D., J. Lewis, S. Keeley and J. Fry. 2012. Effects of wilt-based
irrigation on visual quality and seasonal water applications on 30 bluegrasses
in the transition zone. USGA Turfgrass and Environmental Research Online
- Lewis, J.D., D.J. Bremer, S.J. Keeley and J.D. Fry. 2012. Wilt-based irrigation
in Kentucky bluegrass: Effects on visual quality and irrigation amounts among
DaleBremer, Steve Keeley and Jack Fry are professors in the
department of horticulture, forestry and recreation resources, Kansas State
University, Manhattan, Kan.; and Jason D. Lewis was an assistant professor in
the department of horticulture and crop science, California Polytechnic State
University, San Luis Obispo, Calif.