Air it out

Aerification evolves as it alleviates compaction and helps control organic matter in the soil.

Aeration has changed drastically in recent years to encompass many types. Superintendents have many options, including coring, linear, deep tine, solid tine, drill, hollow tine, star tine, needle tine and water aeration. Even with all the options, the scientific basis for aerification remains the same: to supply with air or expose to the circulation of air.

Close spacings allow for extensive organic matter removal.

Aeration has many benefits such as enhancing root growth, oxygenation, and gas exchange for the soil, thatch control and eliminating compaction. And the aeration process and equipment continue to evolve.

Greens aerification
Greens aerification can be separated into two groups: aerification of native soil (push-up) greens and aerification of sand-based root zones (USGA, California). Push-up greens are prone to more soil-related agronomic problems – primarily compaction – than high sand-based greens. Aerification principles for these greens are related directly to those soil issues. The two vary because of the growing medium but have similarities.

When the first practical core aeration machine was introduced in the late 1940s, soil-based greens were aerated primarily to eliminate soil compaction. Core aeration, or coring, is the oldest form of aeration and can be defined as the mechanical removal of a soil core from a specific area. For many years, eliminating compaction was the primary benefit. This still might hold true, but the major benefits of core aeration nowadays seem to be more about organic matter control.

As sand mixes and straight sand were introduced as topdressing materials, the thought process of the main benefit of aeration shifted slightly, from compaction reduction to modifying the soil conditions within the green profile. Core aeration was performed, cores were removed, then holes were filled with a high-sand-content mix or straight sand to modify the soil-based growing medium and gradually switch to a sand-based environment. Through soil modifying and the use of a lot of sand for topdressing, many older push-ups have been modified to the extent that they perform similarly to a high-sand root-zone green. Many superintendents report modifying their older soil-based greens and developing a surface layer of a sandy-type soil with accumulated depths of six to 12 inches. So, should these greens be called modified push-ups? The definition of a modified push-up could be: a green that has been modified to a high-sand growing mix through years of core removal with sand backfill, along with many years of sand-based topdressing. When a green reaches this point, some principles of aerification become similar to that of high-sand-based greens.

One of the main benefits of high-sand-based greens is the general resistance to compaction. The bridging of the sand particles allows for the stability of the green surface and compaction resistance. However, poor sand-particle-size selection and mixes can compromise the compaction integrity of a green.
Bob Carrow, Ph.D., from the University of Georgia researched the role that organic matter dynamics plays in sand-based greens performance. His research spurred a new outlook on the amount of organic matter removal through aerification practices on greens. Carrow’s work was highlighted by a maximum 4-percent organic-matter guideline in the upper 2-inch surface. An amount higher than this would send a red flag about greens performance. Aerification programs for sand-based greens are a function of this organic-matter research, as well as removing sufficient amounts to stay below the 4-percent guideline.

Dethatching machines such as the Graden offer a linear aeration technique.

Equipment
Maybe two of the most important advances in aerification are the development of new aeration machinery and increased tine diameters that work with quad-tine setups. The major advantage is the ability to vary the tine spacings and to have them as close as one inch on center. When compared to old machines (which have two-inch spacings or greater), tine sizes can be reduced by 50 percent using one-inch spacings and still achieve the same surface area removal impacted. For example, with 1-inch spacing, a 0.25-inch inside-diameter tine could be used, while a 2-inch spacing would need a 0.5-inch inside-diameter tine to achieve the same SARI. These tight spacings offer more distribution of holes over the entire surface area, plus a faster healing time because of the smaller hole size.

The future of greens aerification might tie together these close spacings and Carrow’s maximum 4-percent organic matter guideline. Most soil labs are reporting a drastic increase of requests from superintendents throughout the country to measure greens surface organic matter. These organic-matter-percentage results are converted to the amount of SARI needed for greens aerification. For example, in the chart above, a 4.49-percent organic-matter test result is used to determine the amount SARI needed to reduce the organic matter down to a 3.5-percent level.

The example illustrates 22-percent SARI is needed to lower the organic matter percentage to a more desired 3.5 percent.

Venting, quad-tining
Summer aeration practices, which were once considered taboo, continue to become more popular. Although these practices have taken on different names such as venting, quad-tining and spiking, the agronomic purposes are the same as true aeration. These practices have eliminated the sealing off of the upper surface that occurs in mid- to late summer. This type of procedure breaks up the upper compacted surface area (thatch matrix) to allow for better aeration of the root zone. These practices are performed as frequently as every two weeks, with minimal to no disturbance of playability.

Deep-tine
Another form of greens aeration that has become more standard is the use of deep-tine aeration or drilling machines. This type of machinery can penetrate as deep as 12 to 16 inches. This offers a major benefit over conventional aerification, which is limited to about a 4-inch depth. Research has shown years of conventional aerification tends to develop a hardpan layer just below the 4-inch depth of conventional machines. This deep-tining or drilling has been successful in managing this hardpan layer.

Aerification equipment has evolved to include large units such as the Verti-Drain.

An additional major benefit of this type of aeration is the ability to aerate the 4-inch to 12-inch zone in USGA type greens. This zone has been shown to build up harmful gases, which can affect turfgrass health. By aerating to that 12-inch depth, gas exchange can be accomplished for healthier root-zone management. One deep-tine machine, the Verti-Drain, has a kicking-type or pitchfork action in the soil that tends to fracture the underlying soil structure to allow for better drainage. Although this isn’t a benefit for USGA-type greens, it has become a great tool for modified push-up greens.

Sub-air
A nonmechanical form of greens aeration that’s gaining acceptance is the use of a sub-air-type system. This system aerates from below ground through the drainage system and was designed for use with USGA greens. The benefits of these systems are becoming apparent. As a water management tool, it has shown a tremendous ability to pull water from the root zone into the drainage system to dry down greens during wet periods. Another main benefit of sub-air systems is the ability to manipulate the gas levels in the root zone, especially the difficult 4- to 12-inch area. Never designed with the purpose of eliminating true aeration practices, sub-air systems are becoming a great greens management tool without surface disruption.

Fairways
Fairway aerification has made great strides, too. Long gone are the days of the old drum-type open-spoon, tractor-pull units. At many higher-end clubs, greens type aerification equipment has been adopted for fairway aerification. Fairway aerification agronomics have focused on thatch reduction, compaction and soil modification. Many operations have been incorporating sand fairway topdressing along with aerification programs to help modify existing soil conditions.

Fairway management can almost be equated to what has been done for years with push-up greens. This has been spurred by the demands of club memberships. Players are more demanding about the playability of fairway turf, and firmer, faster and smoother fairways are requested. Many golfers complain about fairway being too wet. As superintendents know, proper watering of fairways might be one of the most difficult daily tasks. The combination of this greens-type coring, followed by heavy topdressing to backfill the aerification holes and build a surface sand layer, is starting to produce drier, firmer conditions. This also is making it much easier to manage irrigation-watering amounts.

One other area that’s gaining popularity with fairways is the use of deep tine equipment such as the Verti-Drain machine. The major benefit of this machine is improved drainage. The better fairways drain, the easier it is to produce firmer conditions. Again, it seems similar to the aerification management of push-up greens. It seems safe to say, yesterday’s soil push-up aerification programs are quickly becoming today’s fairway aerification programs.

Although aerification equipment continues to evolve, the science still remains the same. There might be shifts of the main benefit, such as from compaction to organic matter management on greens, but one thing is certain, it’s all related to air. GCN

Kevin J. Ross, CGCS, is director of golf course management at Country Club of the Rockies in Vail, Colo., and president of Ross Golf Agronomy. He can be reached at kjross@vail.net.