Abstract
Roadside vegetation is subject to significant salt stress as a result of runoff water and road de-icing practices in cold weather climates. Salt-tolerant turfgrass can play a role in maintaining roadsides that are both functional and sustainable. As such, the objective of this research was to evaluate the differential salt tolerance of turfgrass cultivars that may be suitable for roadside establishment. Three replications of 75 cool-season turfgrass cultivars were established in a randomized complete block design at two locations: Roselawn Cemetery (Roseville, MN, USA) and MnROAD research facility (Albertville, MN, USA). Plots were seeded during August and September of 2010. Visual ratings of establishment were collected throughout the fall, and survival was evaluated visually in spring 2011. Numerous cultivars of perennial ryegrass (Lolium perenne L.) established best at all locations in the fall; however, winter survival varied by location. Cultivars of alkaligrass (Puccinellia spp.), including ‘Fults,’ ‘Salty,’ ‘Oceania,’ and ‘Salton Sea,’ performed best at Albertville. ‘Shoreline’ slender creeping red fescue (Festuca rubra L. ssp. litoralis), ‘Navigator’ strong creeping red fescue (Festuca rubra L. ssp. rubra), and an advanced population of sheep fescue (Festuca ovina L.) from the University of Minnesota turfgrass breeding program were among the most salt tolerant at Roseville. Site-dependent performance and effective salt tolerance of cultivars from numerous species indicate that a carefully chosen mix will be best for establishment and maintenance of high-quality roadsides.
Introduction
Cool-season turfgrasses have been used in adverse environments such as roadsides with limited success. In cold-weather climates, high salt loads from road de-icing practices present a significant challenge to the establishment and maintenance of high-quality turfgrass. Despite being a vital characteristic of successful roadside vegetation, limited information is available on salinity tolerance of cool-season turfgrasses. Several studies have evaluated the performance of numerous species and cultivars in a wide variety of low-input conditions (Diesburg et al. Citation1997, Dernoeden et al. Citation1998, McKernan et al. Citation2001, Watkins et al. Citation2011); however, these studies have not been conducted in high-salt environments.
Evaluation of turfgrass salinity tolerance is typically conducted in a greenhouse environment using drenches or hydroponic culture (Greub et al. Citation1985, Marcum Citation2001, Rose-Fricker and Wipff Citation2001, Qian et al. Citation2007, Wang et al. Citation2011). Using controlled field-screening techniques, Koch and Bonos (Citation2011b) identified differences between cultivars of Kentucky bluegrass (Poa pratensis L.), perennial ryegrass, and creeping bentgrass (Agrostis stolonifera L.) irrigated with saline water. Moreover, these same field-screening techniques have been shown to correlate well with greenhouse methods (Koch and Bonos Citation2011a).
Unfortunately, even controlled field trials often do not replicate the wide range of concurrent stresses and conditions experienced by turfgrass in a roadside environment such as poor soil quality, infrequent mowing, disease, and low fertility. For example, it has been shown that the effect of sodium chloride (NaCl) and calcium chloride (CaCl2) on tall fescue (Festuca arundinacea Schreb.) leaf growth is less severe with reduced nitrogen availability (Bowman et al. Citation2006). These results suggest that evaluation of salinity tolerance in nitrogen-replete nutrient culture, though well-correlated to maintained field conditions, can not necessarily be used to infer roadside performance.
A number of turfgrass evaluations have been conducted on roadsides, creating a solid base of information to draw from. Biesboer et al. (Citation1998) established and evaluated monocultures and mixtures of several warm- and cool-season species of native and introduced origins. They determined that mechanical damage and application of sodium chloride (NaCl) during the winter months were responsible for the decline of desired vegetation within one to three meters of the roadway. Their results showed that alkaligrass performed better than all other species within one meter of the pavement edge, which they attributed to its capability for fast growth and prolific seed production. More recently, the effects of soil amendments on roadside survival of 20 cultivars representing seven species, one mix of a subset of those species, and common creeping red fescue (Festuca rubra L.) control plots were evaluated on highways in Rhode Island (Brown and Gorres Citation2011). It was found that in non-amended loamy sand on roadsides, where differences between cultivars were observed, common creeping red fescue had the best persistence. Moreover, it was suggested that the use of neither ‘Sealink’ slender creeping red fescue nor ‘Epic’ or ‘Cindy Lou’ strong creeping red fescues provided any additional benefits over the common type.
We hypothesize that use of newer, better-adapted cultivars can improve roadside performance of turfgrass exposed to highly saline environments. Therefore, the objective of this study was to further evaluate improved cultivars of several species of turfgrass for use on roadsides where damage from sodium chloride has previously been shown to be a major factor in limiting the establishment and persistence of turfgrasses.
Materials and methods
Locations
Plots were established during August and September of 2010 at two locations in the metropolitan area surrounding Minneapolis, MN, USA. The selected research sites were: (1) Larpenteur Ave. along Roselawn Cemetery (Roseville, MN, USA) and (2) MnROAD research facility (Albertville, MN, USA). Sites were chosen to represent a wide range of salt application levels, traffic volumes, and soil types. The portion of Larpenteur Ave. along Roselawn Cemetery is a four-lane residential street which carries a total estimated daily traffic volume of 13,700 vehicles, and Interstate 94, which runs along the MnROAD research facility, is a four-lane divided highway that carries an estimated daily traffic volume of 63,000 vehicles (Minnesota Department of Transportation Citation2010). Mean temperatures for Roseville and Albertville, MN were 17 °C and 16 °C, respectively, during the establishment period of August through October, 2010. These temperatures are similar to the 1961 to 1990 regional average of 15.5 °C for those 3 months. Precipitation during that same period totaled 34.7 cm and 33.27 cm for the Roseville and Albertville sites, respectively, as compared with the 30-year regional average of 21.7 cm. The majority of the precipitation fell during August and early September with an extended period of limited precipitation during late September and October. Sunlight levels varied throughout the year and across locations, although most plots received direct sunlight for the majority of the day. Although salt application records were not available from the Minnesota Department of Transportation, both roads were regularly salted before, during, and after winter storm events with the Albertville site receiving a greater volume annually.
Plant material
Entries were selected based on input from turfgrass breeders and published data from trials throughout the northern United States (Rose-Fricker and Wipff Citation2001, Koch and Bonos Citation2011a, Citation2011b). In total, 75 cultivars, representing 14 species of turfgrass, were included in the trial (). Species included Kentucky bluegrass, perennial ryegrass, tall fescue, tufted hairgrass (Deschampsia cespitosa (L.) P. Beauv.), prairie junegrass (Koeleria macrantha (Ledeb.) Schult.), creeping bentgrass, alkaligrass, Idaho bentgrass (Agrostis idahoensis Nash), hard fescue (Festuca trachyphylla (Hack.) Krajina), sheep fescue, chewings fescue (Festuca rubra var. commutata), slender creeping red fescue, and strong creeping red fescue.
Table I. Cultivars and entries included in the roadside salt tolerance trial.
Site design and establishment
Each site was arranged as a randomized complete block design with three replications. Plots at the Albertville site were 1.52 m by 5.48 m. At the Roseville site, each plot was split into two sections: (1) main plot – the area opposite the sidewalk from the road measuring 1.52 m wide by 4.57 m deep, and (2) boulevard – the 1.52 m by 0.91 m area between the sidewalk and the road. These sections were treated as separate locations for data collection and analysis due to suspected differences in salt loading, amount of shade, and runoff water patterns. Seeding rates () were chosen for each species based on suggested rates (Christians Citation2011). Because purity for the Minnesota ecotype of prairie junegrass was known to be low, the bulk seeding rate was increased to approximate the same effective seeding rate as the European cultivar ‘Barkoel’. This resulted in a range of seeding rates for that species only, as reflected in .
Table II. Seeding rates for the turfgrass species included in the salt tolerance trial.
Site preparation began with a single application of glyphosate (Roundup Weather Max, Monsanto Co., St. Louis, MO, USA) at a rate of 7.68 L ha−1 followed by tilling and smoothing either by hand or using an Infield Rascal (ABI Inc., Osceola, IN, USA). Starter fertilizer (10-18-22) was applied to all sites at a rate of 271.1 kg ha−1 prior to seeding. Seeding was done by hand and plots were hand raked to ensure good seed to soil contact. SeedAide Aero Mulch (Profile Products LLC, Buffalo Grove, IL, USA) was applied at 3360 kg ha−1 and watered in after seeding at each site.Subsequent maintenance included occasional mowing of the Roseville site but no regular irrigation at either location.
Soil sample collection
Following seeding, soil samples were collected to a depth of 0.15 m. Samples were collected from every fourth plot in a zigzag pattern at 1.52 m increments from the road. Samples from each replication were bulked together for analysis. Bulk samples were analyzed for pH, organic matter, and saturated paste extract electrical conductivity (EC) as well as extractable phosphorus, potassium, calcium, magnesium, and sodium (). Analysis was done at the University of Minnesota Soil Analytical Laboratory using standard procedures.
Table III. Soil physical properties for sites in the salt-tolerant turf trial.
Data collection and analysis
During fall 2010, establishment of turf plots was monitored on a biweekly basis. Establishment ratings were based on visual assessment of ground cover and canopy density. Each plot was assigned a rating on a 1–9 scale with 9 representing complete establishment of a dense turf canopy, and 1 representing no germination. Ratings were taken throughout the fall and ended after the second week of November, 2010.
Assessment of survival began during the second week of April, 2011. Survival was determined by visually estimating the proportion of existing turf tissue that was present in the fall, and remained alive and healthy in the spring. Ratings were assigned on a 1–9 scale with 9 representing no salt damage and 1 representing complete death of all existing turf. Evaluation of plots in this manner provided for separation of the effects of establishment and salt tolerance.
Data were analysed using the R Project for Statistical Computing (R Development Core Team Citation2010). Because of large differences in traffic volumes, site conditions, and soil types, it was decided that combining data from sites was not desirable, and each location should be analyzed independently. Analysis of variance was performed using the aov() and anova() functions in R, with subsequent means separation by Fischer's protected LSD at the α = 0.05 level.
Results
Analysis of variance for the data () showed a significant cultivar effect for fall establishment ratings at each site. Significant cultivar effects were observed for spring survival in both sections at the Roseville site as well as at the Albertville site. Blocking was not found to be significant for spring survival at any location, nor for establishment in the boulevard at Roselawn. After means separation based on cultivar effect, a list of the top 25 plus statistically similar entries was created for establishment (not shown) and survival at each site. A complete summary of survival data, including the top performers as well as all remaining entries, is shown in , , and .
Table IV. Analysis of variance of establishment and survival data for cultivars and entries included in the roadside salt tolerance trial.
Table V. Mean survival ratings in the boulevard at Roseville for each cultivar or entry in the salt tolerance trial.
Table VI. Mean survival ratings in the main plot at Roseville for each cultivar or entry in the salt tolerance trial.
Table VII. Mean survival ratings at Albertville for each cultivar or entry in the salt tolerance trial.
Roseville
Data from the final establishment rating for the Roseville site, taken November 10, 2010, showed that the list of top performing cultivars for establishment in the boulevard section at Roseville was composed primarily of perennial ryegrass and tall fescue cultivars. ‘Apple GL’ and ‘Caddyshack II’ had the highest mean establishment ratings, but were not statistically different than each of the other top 25 performers. Seven cultivars of fine fescue made the list of top performers for establishment in the boulevard, led by ‘Shoreline’ slender creeping red fescue and ‘Navigator’ strong creeping red fescue. In the main plot section, ‘Caddyshack II’ perennial ryegrass had the highest mean establishment rating, but was not statistically different from ten other cultivars in the list of top performers for establishment. The list of top performers included a greater number of fine fescue than tall fescue cultivars, and ‘Shoreline’ slender creeping red fescue had the highest mean rating of all fine fescue cultivars.
Survival in both sections at Roseville was based on data collected April 27, 2011. In the boulevard section, the list of top performers was composed primarily of fine fescue cultivars of which strong creeping red fescue represented the greatest proportion. The mean rating for survival in the boulevard section was highest for ‘Shoreline’ slender creeping red fescue which was not statistically different than 17 other entries in the list of top performers, and all four cultivars of alkaligrass appeared in the list of top performers. In the main plot section, ‘Shoreline’ slender creeping red fescue had the highest mean rating for survival followed by ‘Fults’ alkaligrass, both of which were not statistically different than 14 other cultivars. The rest of the entries in the list of top performers were primarily fine fescue cultivars. Interestingly, a number of perennial ryegrass cultivars appeared in the list of top performers for survival which was not observed at any other location.
Albertville
Data from the final establishment rating for the Albertville site, taken October 28, 2010, showed that the list of top performing cultivars for establishment was composed primarily of perennial ryegrass and tall fescue cultivars. ‘Sealink’ slender creeping red fescue did make the list of top performers but was not statistically different than 18 other entries in the list. The mean establishment rating of ‘Gray Fox’ perennial ryegrass was the highest of all cultivars, but was not statistically different than three other entries, all of which were perennial ryegrass cultivars.
Data collected May 13, 2011 showed three notable results for survival at the Albertville location. Firstly, all alkaligrass cultivars had higher survival ratings than all other entries, but were not statistically different from one another. Secondly, ‘Mariner’ creeping bentgrass showed good survival, which had not been observed at any of the other sites. Finally, the list of top performers was again composed primarily of fine fescue cultivars of which strong creeping red fescue represented the greatest proportion.
Discussion
This trial was conducted to evaluate differences between improved cultivars of several species of turfgrass for establishment and survival of winter conditions in a roadside environment. Rapid establishment is a desirable trait for any mix of vegetation used in this type of environment as it minimizes the time of exposure of bare soil. Results for establishment were generally consistent with perennial ryegrass cultivars representing the greatest proportion of the top 25 at each site. Limited precipitation during the months of September and October in the fall of 2010 may have affected the establishment performance of a number of species, particularly those that have longer germination times, such as Kentucky bluegrass. Although perennial ryegrass was consistently the top performer for establishment, relative performance of the cultivars was observed to be site-dependent. Perennial ryegrass did not perform well under stressful winter conditions as indicated by its absence from the list of top performers for survival. These results agree well with previously published data for roadside performance in non-amended soil (Brown and Gorres Citation2011) and may be taken to mean that although perennial ryegrass works well as a cover crop during establishment of a seeded mix, its usefulness on roadsides is limited.
Because roadside establishment of turfgrass is highly dependent on external factors such as precipitation, time of seeding, and soil type, it is most useful to consider cultivar performance differences in the context of survival based on spring rating data. Snowfall during the winter of 2010, as recorded near the Roseville site, totaled 213.4 cm. This was significantly higher than the 30-year mean annual snowfall of 137.2 cm. The extreme amount of snow resulted in more salt applied on the roads, but also provided more spring runoff to help leach salts through the soil. In addition, the large bank of snow along the road was observed to act as a wall in some areas and kept much of the salt on the roadway.
All cultivars of alkaligrass were observed to have good overall survival at all locations, especially at Albertville where greater traffic volumes often necessitate higher salt application rates. At that location, most other entries were either severely damaged or completely dead at the time of rating in the spring. The success of alkaligrass in high-salt environments generally agrees with the findings of Biesboer et al. (Citation1998), but contrasts with the findings of Brown and Gorres (Citation2011) where alkaligrass was observed to have unacceptable establishment and persistence in non-amended soil. It was hypothesized in that study that soil fertility played a role in the salt tolerance and ability of turfgrasses to recover from damage in roadside environments. Furthermore, other studies have shown alkaligrass to perform poorly under conditions of limited water and fertility (Watkins et al. Citation2011). Soil samples from the Albertville site showed considerably higher concentrations of sodium and magnesium in the soil, but did not indicate any differences in fertility from the other trial locations. Taken together, these results indicate that alkaligrass could be used in any area where sodium chloride is applied to the road at high rates or where aesthetic quality is of little concern, but would be best used as part of a mix with cultivars of other species better adapted to low-input conditions.
‘Shoreline’ slender creeping red fescue was the best cultivar overall in both the main plot and boulevard section at Roseville, but strong creeping red fescue had the greatest number of entries in the list of top performers. These results agree with other previous studies where slender and strong creeping red fescues have been found to be tolerant of salts during both germination and vegetative growth (Greub et al. Citation1985, Rose-Fricker and Wipff Citation2001). This is especially important in light of previous research indicating that relative salinity tolerance of species and cultivars can vary with plant developmental stage (Aamlid and Landschoot Citation2007, Marcar Citation1987, Wang et al. Citation2011). Furthermore, several fine fescue species have been shown to be well-adapted to low-input conditions (Diesburg et al. Citation1997, Watkins et al. Citation2011). Because the ability to survive winter salt loading even under conditions of reduced fertility is a prerequisite for success on roadsides, these results indicate that mixtures used in those locations would benefit from containing a large proportion of either slender or strong creeping red fescues. Cultivars of other fine fescues also performed well. For example, ‘67135’ sheep fescue, an advanced population from the University of Minnesota turfgrass breeding program, survived well at Roseville and made the list of top performers at Albertville indicating it may have promise for a wide variety of roadside conditions.
No Kentucky bluegrass cultivars performed well in the trial. Because of poor establishment it was often difficult to judge their survival capability; however, even at locations where establishment was acceptable, survival was not. This is evidenced by the absence of any Kentucky bluegrass cultivar in the list of top performers for survival at any location. Improved cultivars of Kentucky bluegrass provide good quality turf typically only under high-moisture high-fertility conditions, and only the older common varieties are adapted to low-input conditions (Christians Citation2011). Unfortunately, Kentucky bluegrass is often included in large proportions in roadside mixes due to its sod-forming capability. ‘Mariner’ creeping bentgrass did perform well at the Albertville location and, because of its stoloniferous growth habit, has some potential to be used in small quantities as a replacement for Kentucky bluegrass in areas where it is not considered to be a noxious weed.
Because cultivars exhibited site-dependent performance and a number of species performed well for different attributes, it is clear that a well-chosen turfgrass mix will be best suited for use on roadsides. The cultivars included in this trial must be further evaluated for tolerance to other stresses, such as drought, that will be experienced in that type of extreme environment. Results presented here can guide this future research through the evaluation of mixes containing the best-performing cultivars from this trial.
Acknowledgements
We would like to thank the Minnesota Local Road Research Board and the Minnesota Department of Transportation for funding and support of this project. Also, thank you to Roselawn Cemetery and the MnROAD research facility for the use of the study area. Finally, we gratefully acknowledge the invaluable advice of our reviewers.
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