Te sod tensile strength testing apparatus shown here contains a sod sample prior to testing at the St. Paul site. Photo courtesy of Joshua Friell, PhD
to roadside construction sites. Te standard MnDOT mixture, which included the same cultivars as all other mixtures, produced sod that provided low maximum tensile load and required minimal work to tear the sod in half. In this trial, sod was allowed to grow for 22 months before testing; however, the typical production period for Kentucky bluegrass sod in Minnesota is 15 months. Further research is necessary to positively determine the mechanisms by which species selection and management practices interact to convey sod strength.
Te core take-away messages from this research include:
1. Turfgrass seed mixtures containing fine fescue species can produce sod that achieves equal or greater strength than those containing large amounts of Kentucky bluegrass when harvested 22 months after establishment.
Tis view of the sod tensile strength testing apparatus shows the linear actu- ator, string potentiometer, load cell, and clamping system. Photo courtesy of Joshua Friell, PhD
fescue from the initial seed mixture to the final grid count data was negatively correlated with maximum tensile load and work to tear each sample. Tese data indicate that plots seeded with lower rates of fine fescues but resulting in high proportions of fine fescue in the final turf stand tend to result in weak sod. It is likely that thinning due to species competition and management practices that are unfavorable to some species in the stand are responsible and should be considered during sod production.
Results indicate that seed mixtures containing Kentucky bluegrass do not necessarily create stronger sod and that mixtures containing fine fescue species can achieve similar or superior sod strength. Tose fine fescue species also tended to produce sod that required the most work to separate the two halves of the sample. Many of the mixtures presented here were able to improve on the mechanical properties of the MnDOT sod, which is considered to be acceptable for harvest and transport
TPI Turf News September/October 2018
2. Change in proportion of fine fescues from each initial seed mixture to the resulting final plant community was negatively correlated with sod strength characteristics.
3. Tatch development was only weakly correlated with either maximum tensile load or work required to tear sod.
4. Mixtures with different seed compositions, but resulting in similar or identical final species compositions, often possessed very different mechanical properties.
Tis work was first presented at the International Turfgrass Research Conference in New Jersey in 2017 and was published in Agronomy Journal (Agron.J. 108:1749-1757 (2016).
Joshua Friell was a graduate research assistant at the University of Minnesota when this project started. Dr. Friell contributed to the testing and paper development while in his current position as senior research scientist for The Toro Company. Eric Watkins, PhD, is Professor of Turfgrass Science and Brian Horgan, PhD, is Professor and Extension Turfgrass Horticulturist in the Department of Horticulture at the University of Minnesota. Matthew Cavanaugh was a Turfgrass Research Scientist at that facility during this research project and is now assistant superintendent at Rush Creek Golf Club. Casey Reynolds, PhD, is executive director of Turfgrass Producers international.
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