Soil Amendments and the Survival of Roadside Turfgrasses.

Mowed turfgrasses are a preferred groundcover along highways for reasons of safety and aesthetics. However, the turf receives no maintenance other than periodic mowing after planting. Poor soil, a harsh microclimate, and winter salt exposure limit turf survival, especially within 4 m of the pavement. The objectives of this study were to determine the impact of organic soil amendments on turf survival, and to determine whether the performance of improved turfgrass varieties under roadside conditions justified the increased cost of seed. The study was conducted from September 2007 to August 2009 at two locations on the shoulder of interstate highways in Rhode Island. Two soil amendments, processed biosolids and municipal yard waste compost, were compared to the unammended sandy loam soil. Twenty-one improved turfgrass varieties were compared to common red fescue. The turfgrasses were chosen by breeders with the expectation that they would be adapted to roadside conditions; species included perennial ryegrass, tall fescue, red fescue, Kentucky bluegrass, alkali grass, Idaho bentgrass, and tufted hairgrass.

Processed biosolids resulted in the best turfgrass survival at both locations, followed by the yard waste compost. Both soil amendments were superior to the unammended soil, which had no surviving cover at one site and an average of only 13% cover at the other site. Kentucky bluegrass and tall fescue maintained the most complete cover with means of 75% and 71% respectively on the biosolids-amended soil.  Red fescue was similar, with a mean of 65%. On the compost-amended soil tall fescue, red fescue, and Idaho bentgrass maintained the best cover with means of 40%, 38%, and 27%, respectively, at the end of the study. Multiple cultivars were tested for red fescue, tall fescue, perennial ryegrass, and alkali grass. There were no significant differences in performance between cultivars of the same species on any of the soils. The results of this study indicate that soil amendments are more important than the use of improved varieties in ensuring survival of roadside grasses.