Cultural and environmental factors influence green speed

The effects of nitrogen and mowing height on putting-green speed are well-known. Less obvious are the long-term effects of secondary practices, such as topdressing, aerating and grooming-among other practices-and the interaction of these practices. As a result, getting the "right" speed for your putting greens may not be as simple as adjusting mowing height or fertility. despite conventional wisdom.

Researchers at the University of Nebraska-Lincoln surveyed 107 golf courses in Nebraska, South Dakota and Iowa from 1994 to 1996. The superintendents provided information on nitrogen rate and frequency, mowing height and frequency, irrigation frequency, verticutting and topdressing frequency, aerating, grooming and using plant growth regulators (PGRs) in their programs. The researchers also collected environmental data such as temperature, humidity, surface hardness and soil-moisture content from several greens on each golf course. They obtained information on each course's type of membership (private, semi-private or public) and the type of mowers the grounds crews used (riding or walk-behind). The researchers' primary interest, however, was the "speed" of the putting greens relative to the overall greens-management program of each golf-course superintendent.

Using a USGA Stimpmeter, the research staff determined each putting green's speeds. The stimpmeter is a device that enables users to make an accurate, standard measurement of ball-roll distance (BRD) (often incorrectly referred to as green speed). (See related article, "How To: Measure putting-green speeds," January 1997.) Longer BRDs indicate "faster" putting greens.

What did researchers discover? That interactions among management practices occur and that the use and intensity of one management practice may influence the effects of others. The next step, then, was for the researchers to subject the data to further analysis to determine whether two practices "interacted" and whether these two depended on each other.

The number of golf courses and their relatively broad geographic distribution resulted in differences among creeping-bentgrass cultivars on the surveyed putting greens. To evaluate cultivar as well as seasonal differences, the researchers collected data from cultivar trials located near Lincoln, Neb., and Manhattan, Kan. They measured BRDs in the spring, summer and fall on 18 different cultivars.

Cultivar, location and seasonal effects on BRD BRD measurements did not differ among cultivars at either the Nebraska or Kansas location (see table, page G 52). Although the newer creeping bentgrass cultivars have markedly different growth characteristics, these differences did not influence BRD.

Location and time of year, however, strongly affected BRD. It was consistently longer at the Nebraska site compared to the Kansas site, primarily due to a slightly higher mowing height at the Kansas location. Seasonal effects also were evident, with the longest BRDs occurring in the spring and fall.

Because of the seasonal effects observed in the cultivar study, the research staff also analyzed BRD data for the management practices according to season (spring vs. summer). We'll confine this article to discussing those management practices or their interactions that resulted in statistical differences. (In other words, if we don't discuss a management practice here, then its influence on BRD was not noteworthy.)

Spring BRD differences * Nitrogen (N) and topdressing. Researchers found the longest BRD when superintendents aggressively top-dressed (16 times a year) and fertilized (at 0.33 pound N per 1,000 square feet per month) their greens. When N rates exceeded 0.5 pound per 1,000 square feet per month, BRD decreased with increased topdressing frequency.

* Nitrogen and grooming. As N rates and grooming frequency increased, BRD decreased, except when N rates exceeded 0.75 pound per 1,000 square feet per month. At N rates greater than 0.75 pound per 1,000 square feet per month, BRD increased as grooming frequency increased. It is not surprising that high N application rates resulted in greater grooming requirements. The increased BRD at higher N rates, however, was less than 6 inches and few golfers would notice it.

* Verticutting and topdressing. BRD decreased with increases in verticutting and topdressing-practices that superintendents often conducted concurrently. When topdressing and verticutting are frequent and aggressive (more than 16 times per year), you may not have adequate time between treatments for recovery from the resulting surface disruption. Such disrupted putting surfaces result in shorter BRDs.

Summer BRD differences * Nitrogen and mowing. Mowing heights of less than 0.156 inch did not affect BRD when N rates were between 0.125 and 1.25 pound per 1,000 square feet per month. At mowing heights of 0.156 inch or greater, an increase in N decreased BRD.

* Nitrogen and verticutting. N rates between 0.125 and 0.75 pound per 1,000 square feet per month increased BRD when combined with more frequent verticutting. At higher N rates (in excess of 0.75 pound per 1,000 square feet per month), BRD decreased with more frequent verticutting.

* Mowing and grooming. BRD increased as grooming frequency increased at mowing heights less than 0.188 inch. Researchers measured the longest BRD at a mowing height of 0.156 inch where the superintendent groomed the green every day. (Only one golf course surveyed followed this practice.) To realize an increase in BRD at the most commonly used mowing heights of 0.125 and 0.156 inch, you must groom the green at least four times each week. At a mowing height of 0.188 inch, BRD-in fact-decreases with increased grooming frequency.

BRDs for all seasons * Irrigation. Irrigation frequency also influenced BRD. Superintendents who irrigated five times per week or less had longer BRDs than those who irrigated six to seven times per week.

* PGRs. The use of PGRs increased BRD regardless of season. Although only 8 of the 107 golf courses surveyed used PGRs, all had longer BRDs than courses with similar management practices that did not apply PGRs. The PGR predominately used by surveyed superintendents was trinexapac-ethyl (Primo by Novartis) and paclobutrazol (Scotts' TGR).

Other influences * Environmental influences on BRD. Temperature and humidity did not significantly influence BRD. Soil moisture, however, did affect BRD; greens with lower summer soil moisture had longer BRDs.

* Membership and mower type. Golfers on private courses experience longer BRDs than those who play on semi-private or public courses. Private-course BRDs were 4 percent faster than semi-private-course greens and almost 9 percent faster than greens on public courses.

As for mower type, superintendents who used walk-behind greens mowers had 20-percent-longer BRDs than those who used riding mowers. This is about a 12-inch increase in BRD.

The bottom line The number and variety of surveyed golf courses provided a large range of management practices. Researchers found that practices normally associated with increased BRDs worked toward that end only when other cultural practices were at specific levels. Although superintendents have, for years, decreased mowing heights and N fertility to increase BRD, the negative agronomic effects of such practices were also well-known. The modification of other, less stressful cultural practices, such as topdressing and grooming, may help you achieve your desired end result without sacrificing turf quality and health. Carefully weigh the positive and negative effects a management change might impose and keep in mind that alternatives may exist that are less stressful.

Dr. Roch Gaussoin is an extension turfgrass specialist at the University of Nebraska--Lincoln.

The author would like to acknowledge the assistance of Anne Rist, graduate student, and the superintendents who participated in the survey.

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