Built for (green) speed: Managing ball roll
Golfers often request changes in golf-green quality, and, frequently, they want to see an increase in green speed (though faster greens are not necessarily best for most golfers). Thus, changinggreen speeds is something superintendents often need to do. They can achieve this with a variety of management changes, ranging from subtle to drastic. Following is a summary of research-based information on management and environmental influences on green speed.
Green speed is a term that describes the condition of a putting surface as it relates to ball-roll distance. The term "speed" is technically inaccurate because the device that measures "speed"-the USGA Stimpmeter-does not, in fact, measure velocity. Rather, it measures the distance a golf ball travels when released at a controlled speed on the putting surface. Nevertheless, "green speed" remains the commonly used term. A green that has relatively long ball rolls when measured with the Stimpmeter is "fast," while a green with short ball-roll distance is "slow." The USGA provides guidelines, based on extensive surveys, for Stimpmeter results for various playing conditions. These guidelines are a good start for determining the "optimal" speed your greens should have. How you achieve that "optimal" condition can be as simple as a subtle change in mowing height or as extensive as a comprehensive modification in your overall greens-management program.
Generally, golfers demand an increase in green speed. Rarely do they request slower greens. Thus, most examples I cite in this article-which come from research conducted on more than 100 golf courses in the Northern Great Plains-address increasing green speed. However, if a superintendent is interested in decreasing green speed, the reverse of the recommendations for increasing green speed will usually accomplish this goal.
Ball-roll physics To better understand the effects that a change in management will have on green speed, a simple overview of the physics of how a ball rolls and what might alter its travel is appropriate.
According to classical mechanics, ball-roll distance relates to the ball's initial energy when a putter strikes it (or when you release it from a Stimpmeter) and friction-the resistance between the ball and the turf surface. As the ball rolls across the turf surface, the resistance of the putting surface slows it down. A green with high resistance decreases ball speed more quickly than a green with low resistance and results in a shorter ball roll (a slower green). Thus, any management practice that modifies resistance will subsequently change green speed. For example, all superintendents know that lowering the mowing height will result in faster greens. This is because less leaf tissue is in contact with the ball as it rolls across the green, lowering resistance and resulting in a longer ball roll. Decreasing nitrogen fertilization also can increase green speed. This results from less leaf tissue providing resistance to a rolling ball, as well as, perhaps, lower density in low-fertility turf.
The table at left shows the ball-roll distances of various turf and non-turf surfaces to further illustrate how surface resistance affects ball-roll distance. As you can see from the table, most non-living surfaces are "faster" than an actively growing turfgrass stand.
Environmental effects Environmental factors that the superintendent can't control can affect ball-roll distance. For example, as relative humidity increases, a small decrease in ball roll results. The opposite effect occurs with temperature: as temperature increases, ball roll also increases. These effects are minimal and usually imperceptible to the golfer. Soil type also can influence ball roll. Native-soil "push-up" greens that consist predominantly of clay are slower in spring and faster in summer than their modified, sandier counterparts. This happens because heavier soils dry to a firmer surface during the summer, resulting in faster greens. Although, as I mentioned, superintendents can do little about these factors, you should keep them in mind when you evaluate or compare ball-roll distances.
Management effects Many practices that favor higher green speeds stress the turf in the process of achieving the faster surface. Can we useother management factors that decrease greens' surface resistance and consequently increase green speed without potentially damaging effects on the turf? In many cases, yes. However, stressful practices such as reducing mowing height and lowering fertility remain among the primary tools for managing speed. Just remember that practices such as these exact a price on turf vigor and health, which you must factor into your overall management strategies.
Superintendents have two options when changing green speed. Depending on the needs of golfers, superintendents can change green speed for the short term or for the long term. A short-term change in green speed may last 1 to 3 days, whereas a long-term change can last up to the entire growing season. Superintendents often make short-term changes for special events such as tournaments. Let's look at some specific practices and their effects on ball roll.
* Mowing. Mowing is an effective way to increase ball roll for the short term. Decreasing mowing height 1/16 inch can increase ball roll from 6 to 10 inches. A similar response occurs when you "double-cut" a green (mowing it a second time, perpendicular to the first mowing pass), which can increase ball roll 6 to 12 inches. Some mowers have grooming reels to help achieve a more uniform cut, but grooming also has the effect of increasing ball roll (however, this is not effective with mowing heights above 3/16 inch). Mower type also can influence ball roll. Greens you mow with walk-behind mowers will be 6 to 8 inches "faster" than greens you mow with triplex mowers.
* Irrigation. Dry greens are faster than moist or wet greens. Withholding or decreasing irrigation before an event that requires faster greens will increase ball roll 8 to 14 inches, depending on soil type. However, you must take care to ensure that the greens do not get too dry and that you irrigate as soon as possible after the event is over. Otherwise, significant stand thinning may result. In practice, this approach requires extreme care.
* Rolling. Rolling golf greens is not a new idea, but it is gaining more attention lately due to new equipment and a better understanding of its effects on soil compaction. Depending on the type of roller you use, increases of 4 to 10 inches are possible with minimal compaction problems on sand-based greens. Although some supers report increased compaction with the use of rollers on heavier soils, this effect does not appear to be long-lived if you use routine cultivation practices.
* Topdressing, verticutting and aerating. Light, frequent topdressing-with or without vertical mowing or core aerating-is a common practice on golf greens. The effect of topdressing on ball roll is an initial decrease in speed for up to 1 week after application, followed by an increase of 4 to 8 inches (above the speed before topdressing). The decrease is due to the non-uniform surface created by the sand and an increase in surface resistance. As the sand filters into the grass canopy, the playing surface becomes more uniform and less resistant to roll, and the golf ball rolls farther. Because of the initial decrease in speed, you should avoid topdressing closer than 1 week before an event where green speed and uniformity are critical.
Vertical mowing has an effect similar to topdressing. Core aeration also reduces ball roll initially and, if you don't topdress to fill in the holes, the decrease in speed can be relatively long-term. Other aeration practices that are less surface-disruptive, such as water injection and slicing, do not have a long-term effect on green speed.
* Fertility. Decreasing nitrogen fertility will gradually increase ball-roll distance. A decrease in nitrogen fertility of 10 percent can increase ball roll 8 to 12 percent. However, it may take up to a year to see results, depending on previous fertility practices and residual nitrogen in the soil. Other nutrients, such as potassium and phosphorus, do not appear to affect green speed.
* Plant growth regulators. The use of plant growth regulators (PGRs) can increase ball roll from 4 to 8 inches depending on product, rate and frequency of application. This increase may be due to the slower growth rate of the treated turf or, possibly, from the turf being "tighter," as reported by superintendents using PGRs.
In this article, I've singled out several factors that impact green speed. Remember that these factors do not operate independently of each other. A modification in one may require compensation with a modification in another.
Finally, you should evaluate your situation and educate golfers about realistic expectations before implementing practices that may be economically unfeasible or potentially damaging to the long-term health of the green.
Dr. Roch E. Gaussoin is an extension turfgrass specialist at the University of Nebraska (Lincoln, Neb.).
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