Creative cultural practices

With the advent of newer bentgrasses about 20 years ago, thatch management has come to the forefront of today’s greens management. Once the barrier of using Penncross was broken (primarily by Providence and SR1020 in the mid-1980s) and the use of the new superbents became more popular, the concern about different management programs seemed to revolve around the thatching potential and management of the thatch make-up.

The development of "superbents" for greens moved thatch management to the forefront of superintendents' agronomic programs.

Then in 1995, the concerns grew deeper with the release of the denser A and G series bentgrasses. So superintendents started to think more creatively about managing these turfgrasses because of the initial concerns that the A and G series would become thatchy and impossible to manage.
These thatch problem concerns prompted equipment manufactures to respond by developing specific machinery to address the potential problem. Presently, most manufacturers offer aerification equipment that reduces tine spacing as close as one inch. This close aerification spacing was termed quad-tine setup and originally was designed for use with quadratines (one-quarter inch). Initially, the quad-tine setup using quadratines became a popular management technique for superbents. Superintendents liked the benefits of aerification without the drawbacks of disrupting the playability of the greens with these small tines. The popularity of this method became so great that some courses were doing this monthly.

Dethatching developments
Shortly after quadratine use became popular, possibly the two most significant developments in thatch management occurred: the development of larger diameter tines to fit a quad-tine setup and the introduction of the Graden dethatching unit to the United States. These developments have changed the way superintendents manage their cultural practices on greens.
The Graden dethatching unit is probably responsible for the latest agronomic buzz term – “surface area removal/impacted.”

This term came to light as the use of the Graden dethatching unit increased. Superintendents began calculating the difference between quadratine aerification and the dethatching unit to determine which method would have the greatest impact on greens.
Next came an article by Chris Hartwiger and Patrick O’Brien that was published in the July/August 2001 issue of the USGA Green Section Record. The article, “Core Aeration by the Numbers,” stated that 15 percent to 20 percent of the surface area should be impacted per year on the green. The 15-percent-to-20-percent guideline wasn’t based on scientific research. It was based on field experience through numerous visitations by U.S. Golf Association agronomists. The article included a table that compared various tine sizes and spacings of the aerification procedure, along with the dethatching blade thickness and spacings to calculate SARI.
As a result, superintendents now are focusing on SARI instead of just guessing at their aerification procedures. Superintendents think about thatch management much differently than they did before the USGA article was printed. However, information in the USGA table was misleading slightly. The table presenting tine sizes tended to overstate the amount of true SARI because of how the diameter of the hole was determined.

Size it up
When selecting aerification tines and calculating SARI, the most important consideration is the inside diameter of the tine. For example, a 5/8-inch tine doesn’t make a 5/8-inch hole, and it doesn’t remove a 5/8-inch plug. Aerification tines have a cookie-cutter effect when operating. This is why the inside diameter is the critical measuring area when calculating SARI. The tine also tends to push or compact the turf outward in a circular direction as it enters the ground.

The Graden dethatching unit might be responsible for starting the agronomic buzz term "surface area removal/impacted."

If a 5/8-inch tine made a hole of equal size, it should be possible to drop (or slightly push) the same size tine into that hole. This can’t be done. In fact, there might be a release of some lateral compaction, which might result in the hole diameter being smaller than that of the tine’s inside diameter. For example, the inside diameter of a tine sold as a 5/8 inch – to fit a quadratine setup – actually measures 0.390 of an inch. If the outside diameter of 0.625 of an inch (5/8 inch) is used to calculate SARI, the percentage will be considerably overstated.
Additionally, when 1-inch-by-1-inch spacings are used, the inside diameter (.0390 of an inch) equals 11.9 percent SARI. Using the outside diameter (0.625 of an inch) equals 30.68 percent SARI. This calculates to 61 percent less SARI when using the correct inside diameter measurement instead of the incorrect outside diameter measurement.
One of the main points to remember about aerification tines is that they vary greatly from one company to another. So it’s critical to select tines based on the inside diameter, which generally isn’t advertised. Presently, there’s one company selling tines using three criteria: inside diameter, outside diameter and wall thickness. This could be the standard in the future and how superintendents purchase tines.

Wear it down
Another factor that greatly affects SARI is tine wear. If a superintendent aerified nine greens and did them in order (one through nine), the first green would be much different from the ninth. For example, using a 0.390-inch inside-diameter tine starting on the first green, the SARI would be calculated at 11.9 percent. That same tine, after aerifying eight greens, would measure 0.50-of an inch inside diameter on the ninth green or 19.6 percent SARI. This is a drastic 40 percent increase throughout the course of nine greens.
So, if greens are aerified in the same order every year, year after year, the thatch composition would vary greatly from the first green to the ninth green. To equalize SARI during the process, the reverse order needs to be performed with each aerification. This will allow a more even SARI from green to green.

Maintaining an edge
The Graden dethatching unit creates another factor that complicates the amount of SARI on greens: The blades wear throughout time, and the amount of material removed reduces. Remember, just like tines, all blades are different. Most 2-mm dethatching blades actually measure 0.10 of an inch thick, which is 10 percent SARI using the blades on one-inch centers.

With the development of larger-diameter tines using close 1-inch scacing, surface area removal/impacted can increase dramatically.

After 15,000 to 20,000 square feet of use on sand-based greens, various superintendents reported the SARI is reduced about 50 percent. This makes calculating true SARI even more difficult. Keeping sharp blades will benefit only the dethatching result. This can be costly because blades aren’t cheap. One way to maintain a sharp edge is to invest in a carbide sharpening stone and face the carbide tips every 15,000 square feet.

It’s the matter
Some of the latest research that deals with organic matter build-up and relates directly to SARI on greens is by Dr. Robert Carrow of the University of Georgia. Funded by a research grant from the USGA, Carrow’s work – titled “Surface Organic Matter in Bentgrass Greens” – determined a level of organic matter in the upper 2-inch zone of 4 percent as a breaking point for green performance. Carrow cites greater than 4-percent organic matter should send a red flag to superintendents indicating potential problems could be on the horizon.
The research shows, however, that the 4-percent guideline isn’t a steadfast rule. Carrow indicates that in cooler climates greens might do fine above 4-percent organic matter; but in the southern zone, it can be critical. This is a critical finding because it gives a number to use when designing cultural practices. It lets superintendents know if they need to be aggressive or not in an aerification program.
A numbers game
So, where do these underlying factors leave golf course superintendents concerned about SARI? First, Hartwiger and O’Brien should be commended for such a great food-for-thought article.

Their guidelines of 15-percent-to-20 percent SARI gives superintendents some numbers to communicate to green committees or owners about why the dastardly deed of aerification must be performed regularly. Then, superintendents should realize that true calculations aren’t as easy as putting tines on and away they go.
Thirdly, kudos need to be given for Carrow’s research identifying the 4-percent organic matter guideline in the upper 2-inch zone.
Maybe this is how superintendents should base their aerification programs in the future when considering how much SARI is needed. However superintendents choose to manage their thatch, it’s nice to know that managing these superbents (and other new bents years from now) will be much easier thanks to aerification and dethatching equipment and solid research. GCN

Kevin J. Ross, CGCS, is director of golf course management at Country Club of the Rockies in Vail, Colo., and is a contributing writer for Golf Course News. He can be reached at kjross@vail.net.