In sod production, mechanical strength is important to withstand harvest, transport, handling, and installation. Previous research has tested the effects of mixture proportions and seeding rate in mixtures of Kentucky bluegrass, fine fescue species, and bentgrass species on sod tearing strength and concluded that the rhizomatous components, including Kentucky bluegrass, strong creeping red fescue, and browntop bentgrass were responsible for improved sod tearing strength when seeded in mixtures. Additional research has ranked rooting characteristics and sod tearing strength from strongest to weakest, as Kentucky bluegrass, Festuca spp., perennial ryegrass, and Agrostis spp., which corroborated previous findings that mixtures of Festuca spp. and Kentucky bluegrass had lower tearing strength than Kentucky bluegrass alone. Furthermore, hard fescue is a heavy root producer with a high root/shoot ratio indicating the ability to produce sod strong enough for production. Taken together, these previous studies indicate the potential to create sufficiently strong sod from alternative turf species, like fine fescues, and the need to identify proper species and mixture proportions when producing sod. Terefore, the objective of this study was to evaluate tensile strength and work required to tear sod of mixtures of nine species of cool-season turfgrass previously determined to perform well on Minnesota roadsides.
A single cultivar was selected to represent each of nine cool-season turfgrass species, including Kentucky bluegrass, tall fescue, creeping bentgrass, weeping alkaligrass, slender creeping red fescue, strong creeping red fescue, Chewings fescue, hard fescue, and sheep fescue. Selections were based on previous suitability studies for Minnesota roadsides and direct evaluations of salt tolerance. Using the nine selected cultivars (Table 1),
50 seed mixtures were designed and assigned a number where each mixture contained between three and six species. A standard species mixture representing the salt-tolerant turfgrass mixture specified by the Minnesota Department of Transportation (MnDOT) was also included. Tat mixture, MNDOT, is commonly used and is considered to possess sufficient strength for harvest, shipping, and handling.
Tree replications of the 51 mixtures were established at the Rosemount Research and Outreach Center (Rosemount, MN) and at the University of Minnesota (St. Paul, MN). Te 51 total mixtures were allowed to establish for approximately 22 months before a small sample area of each plot was harvested using a Turfco KisCutter sod cutter and subjected to mechanical testing. Sod tensile strength was tested using a custom-built tensile testing device, and quantitative measures of strength were measured to determine differences among mixtures. Tensile load was measured via an Omega LC703-300 load cell, and the total distance that the sod was stretched was recorded using a Unimeasure LX-PA-15 string potentiometer. Plant community composition and thatch depth were also recorded after harvest.
Analyzed results revealed that Mixture 48 (40 percent STCRF; 20 percent ALK; 40 percent CHF) was the strongest mixture, with a mean maximum tensile load of 507.74 newtons (N). Te final plant community of Mixture 48 averaged across both sites contained 98 percent fine fescues and no alkaligrass. Of the mixtures in the top statistical grouping, only Mixture 48 was seeded with any alkaligrass. Mixture 30 (40 percent ALK; 20 percent KBG; 40 percent SHF) had the lowest mean maximum tensile load of 142.84 N and was not
Table 1. Species and Cultivars used in Sod Strength experiments Species
Agrostis stolonifera Poa pratensis
Puccinellia distans
Common Name Creeping bentgrass Kentucky bluegrass Alkaligrasss
Festuca rubra ssp. Rubra Strong creeping red fescue Festuca rubra ssp. Litoralis Slender creeping red fescue Festuca trachyphylla Festuca ovina
Fesctua arundinacea Festuca rubra ssp. fallax
Hard fescue Sheep fescue Tall fescue
Chewings fescue TPI Turf News September/October 2018
Abbreviation CBG KBG ALK
STCRF SLCRF HDF SHF TF
CHF
Cultivar Mariner
Moonlight SLT Salty
Navigator Shoreline Beacon
Marco Polo Grande II Radar
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