Low-input conditions for high maintenance turf

Editor's note: This post is the  “Verdure” column by Beth Guertal, Ph.D., as seen in the September 2014 issue of GCM.

Several years ago, in hot and humid Auburn, Alabama, we had the pleasure of having the National Turfgrass Evaluation Program’s (NTEP) bentgrass putting green trial. Let’s just say that I think we were selected as the “really bad place to be” trial location. In that trial, there were a few velvet bentgrass cultivars, luxurious and sensual cool-season turfs that never failed to become dyspeptic and chlorotic each summer. While they may not have proven to be “the thing” for the Deep South, velvet bentgrasses are a turf of interest in Europe and other regions with a more moderate climate.

In 2009, members of Dr. John Stiers’ highly productive research program at the University of Wisconsin-Madison published a paper that evaluated velvet and creeping bentgrasses, examining the effect of nitrogen rates and mowing heights on these grasses. The objective was to examine the grasses’ utility in low-input putting greens, since velvet bentgrass is widely considered able to handle more austere conditions than creeping bentgrass.

This elegant study was simple in its approach: four bentgrass cultivars on a sand-based root zone (SR 7200 and Vesper velvet bentgrass, and Penncross and L-93 creeping bentgrass), all of which were mowed at various heights (0.25, 0.156 and 0.10 inch) [6.4, 4.0 and 2.5 millimeters]) and received two different nitrogen rates (⅓ or ½ pound nitrogen/1,000 square feet/application [48 or 146 kilograms/hectare/
year]). The nitrogen was applied as split applications from May through October (three apps for the low nitrogen rate; six apps for the high  nitrogen rate; nitrogen supplied via a 21-1-10 N-P-K granular). Artificial traffic was used to simulate 21,000 rounds of golf, and the green was mowed with a reel mower six days a week. Data collection included green-up, quality, shoot density and ball roll.

Over two years, the velvet and creeping bentgrasses reacted differently to mowing height and nitrogen rate. In fact, it wasn’t just the species that reacted differently — it was the specific cultivars. For example, the Vesper velvet bentgrass and the Penncross creeping bentgrass responded to the higher nitrogen rate with better quality, while SR 7200 and L-93 were unaffected by nitrogen rate. “Unaffected” does not mean “You can grow these with that low rate of nitrogen.” In fact, none of the cultivars had long-term satisfactory quality at the low nitrogen rate, and only Vesper had any degree of acceptable quality at the low rate. As the researchers said: “Ultimately, it may be impossible to achieve high-quality bentgrass turf with nitrogen rates as low [as those used in this study] on sand-based root zones.”

Vesper had the highest shoot density of all the cultivars, and it was best at the higher nitrogen rate. Nitrogen rate did not affect ball roll to any significant degree, and as mowing height decreased, ball roll increased. Mowing lower also slowed creeping bentgrass invasion into the velvet. Ball roll was variable among cultivars, and the velvet bentgrasses did not have consistently longer roll than the creeping bentgrasses.

This study demonstrated that it can be hard to make generalizations about the performance of a turfgrass species (that is, velvet versus creeping bentgrass) and that differences in turf performance between cultivars were greater than those between species. Overall, the Vesper velvet bentgrass (at the higher nitrogen rate) had the best turf quality and shoot density, and it was the only cultivar that even looked marginally decent at the lower nitrogen rate. This study indicated that one cannot make assumptions about the “low-input nature” of velvet bentgrasses. This work showed no evidence that velvet bentgrass could produce quality turf with any less nitrogen than that required by creeping bentgrass.

 Source: Koeritz, E.J., and J.C. Stier. 2009. Nitrogen rate and mowing height effects on velvet and creeping bentgrasses for low-input putting greens. Crop Science 49:1463-1472.

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Beth Guertal is a professor in the department of agronomy and soils at Auburn University in Auburn, Ala.,and the incoming editor-in-chief for the American Society of Agronomy. She is a 17-year member of GCSAA.