KINGSTON, RI--Highway rights-of-way are routinely planted with turfgrasses to prevent erosion, filter runoff, and improve aesthetics. But roadsides are harsh environments, and perennial grasses often die within the first year, resulting in bare ground and a proliferation of weeds. Researchers set out to find solutions to these issues by evaluating the effects of improved cultivars, salt tolerance, and organic matter amendments on perennial grass survival along two highways in Rhode Island. "Our study was initiated in response to widespread erosion and slope failure along highways after two unusually snowy winters and extensive loss of perennial turf cover," explained Rebecca Nelson Brown from the University of Rhode Island. Brown and colleague Josef Gorres from the University of Vermont published their findings in HortScience.
Mowed turfgrasses are the most common types of vegetation used on shoulders and medians of limited access roadways across the United States. In addition to their aesthetic qualities, the grasses prevent soil erosion, trap dust, and filter storm water. Roadside turfgrasses struggle to survive, particularly those growing closest to the pavement. "The soil remaining in the highway right-of-way after construction is generally of poor quality, and heat reflected from the pavement and the constant wind from passing vehicles creates a droughty microclimate," Brown and Gorres noted. In colder regions where salt (sodium chloride) is used to keep the roads free of snow and ice, roadside turfgrasses have to stand up to salt and other chemicals. Consider all of these challenges and it's easy to see why road shoulders and medians are often bare or overtaken by annual weeds such as crabgrass.
Brown and Gorres' research study evaluated the effects of improved cultivars, salt tolerance, and organic matter amendments on perennial grass survival along two highways in Rhode Island. The study was conducted in two locations that represent extremes in snowfall for mainland Rhode Island. The first test site was located in southwestern Rhode Island and is under coastal influence, receiving more rain and less snow than the second site, which was inland in north–central Rhode Island.
The team studied 22 turfgrasses representing seven species and used three soil treatments: unamended soil, soil amended with 50% biosolids by volume, and soil amended with 50% composted yard waste by volume.
"We found significant differences between locations, between soil amendment treatments within location, between species within soil amendment treatment, and between turfgrass cultivars," Brown and Gorres said. "A one-time amendment of soil with organic matter significantly improved turfgrass cover for the entire 2-year study. Biosolids had a significantly greater effect than yard waste compost; the effect of the single incorporation of biosolids continued to persist after 3 years."
As for turfgrass species performance, Kentucky bluegrass, tall fescue, red fescue, and idaho bentgrass showed the best persistence at the species level, with no consistent differences noted among cultivars.
The researchers concluded that that soil amendment was more effective than either improved genetics or salt tolerance. Establishment, vertical growth, and persistence of vegetation cover were significantly improved by amendment with organic matter, particularly biosolids.
The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/content/46/10/1404.abstract
Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at ashs.org