ROOTED INRESEARCH HOW STRONG IS BERMUDAGRASS?


By Mike Fidanza, PhD


Te top seven sod producing states, in alphabetical order, are: Alabama, California, Florida, Georgia, Oklahoma, South Carolina, and Texas. Among those states, bermudagrass [Cynodon dactylon (L.) × C. transvaalensis Burtt-Davy] is the most commonly grown turfgrass sod species. Te term “sod strength” is commonly used to describe the harvested sod’s ability to essentially hold itself together and not break apart prior to installation and use.


Sod strength can be determined by measuring the sod tensile strength. What is sod tensile strength? Sod tensile strength is a measurement of the sod’s resistance to being torn and pulled apart. Basically, sod tensile strength is the minimum amount of longitudinal stress and maximum shear force that is required to separate the sod. In other words, how much force does it take to tear apart a piece of sod? A small amount of force reflects low tensile strength, whereas a large amount of force indicates high tensile strength.


Research was conducted at Oklahoma State University (Stillwater, OK) to evaluate sod tensile strength, sod handling quality, and rhizome traits of commercial and experimental bermudagrass cultivars. Another objective of this research was to examine the relationship between the underground or rootzone characteristics (i.e., rhizomes) and their impact on sod tensile strength. Te field study was conducted at the Oklahoma State University Botanical Garden and Turfgrass Research Center, in Stillwater, OK. Te bermudagrasses consisted of five commercial cultivars (Latitude 36, Midlawn, Northbridge, Tifway, and Tahoma 31) and five experimental cultivars. Te experimentals were obtained from the Oklahoma State University’s turfgrass breeding program. Tis summary, however, will focus only on the five commercially available bermudagrass cultivars.


Te study site consisted of a loam soil with a pH of 7.0. All bermudagrass cultivars were established in July 2014 by sprigging into 40 ft2


(3.7 m2 ) plots. All bermudagrasses


were arranged as a randomized complete block design with three replications. Te study site was irrigated to prevent


40


drought stress, mowed three days per week at a 1.5 inch (3.8 cm) height-of-cut, and fertilized in accordance with normal or routine maintenance practices for bermudagrass sod production. Pesticide applications were implemented when needed to manage diseases, insects, and weeds. Te study was conducted from 2015 through 2018.


Sod tensile strength was measured using a specially constructed device. A harvested sod piece was vertically loaded and clamped into the device. Next, the sod piece was slowly pulled apart until tearing occurred, and this “pulling force” was measured as kgf/dm2


(kilogram force


per square decimeter). Of note, 1 pound per square inch = 7.03 kgf/dm2


. Sod handling quality was evaluated on a


visual scale of 1 to 5, where 1 = complete sod breakage and 5 = no breakage. For example, a sod piece was harvested and then sod handling quality was rated while the sod was being transported by hand to the device used for the tensile strength measurement. Te sod rhizome properties were characterized by detailed measurements of rhizome strength, length and volume, surface area, and weight.


Figure 1.


Figure 1. Sod tensile strength for each bermudagrass cultivar. Data statistically analyzed separately for each year. Terefore, within each year, data means with the same letter are not significantly different at p £ 0.05; as adapted from Segars et al. (2022). Conversion factor: 1 pound per square inch = 7.03 kgf/dm2


.


Let’s take a look at what the researchers learned in this study. In 2015, Tifway had the highest sod tensile strength, followed by Northbridge, Tahoma 31, and Latitude 36, and the lowest sod tensile strength was Midlawn (Figure 1). In 2016, Latitude 36, Northbridge, Tahoma 31, and Tifway all had the highest sod tensile strength, and again the lowest sod tensile strength was Midlawn (Figure 1).


TPI Turf News March/April 2025


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