We’ve all been watching a golf telecast and heard the broadcasters say something like, “Even though we’ve had some rain, the greens here have SubAir, so firmness should not be a problem.” You might know that they are talking about some kind of air system under the greens, but how do these systems work and what can they actually do? Spoiler alert: if it’s been raining all day, subsurface air isn’t going to make the greens firm tomorrow morning.
The first thing to realize is that the term “SubAir” is to subsurface putting green air systems as “Xerox” is to copiers. It’s a single brand name that has come to describe a whole group of systems that move air through the putting green drainage pipes. There are multiple manufacturers and several types of these systems used on golf courses. Some only move air in or out of the drainage system, while others have the ability to heat or cool the air to change putting green soil temperature. Installing, operating and maintaining these systems is expensive, and a cost-benefit analysis is a must before courses decide to move forward with them. Costs vary based on manufacturer, features selected, and whether portable units or permanent in-ground vaults are chosen. There are certainly benefits to these systems, but they might not be able to deliver everything your favorite golf broadcaster thinks. Let’s take a look at some of the facts:
What Can Subsurface Air Systems Do?
They can remove water from the soil profile by applying suction through the drain lines of a green. In the process, they also pull air into the rootzone from the surface. The combination of these two effects can accelerate drying after it rains.
Units can also push air into the drain lines and ultimately into the soil profile, which may help reduce soil temperatures during hot weather. The roots of cool-season grasses like bentgrass and Poa annua struggle to function properly when soil temperatures get too high, so cooling the soil alleviates some stress on the grass.
If equipped with heating and cooling units, subsurface air systems can improve the soil growing environment by warming or cooling it. Pumping warm air into the drainage system can prevent light coatings of snow or ice from accumulating on the greens, accelerate melting, and help get growth started earlier in the spring. Conversely, during the heat of the summer, cooler air can be pumped into the profile to alleviate turf stress. In-ground sensors confirm that these heating and cooling functions really do affect soil temperature.
What Limitations Do Subsurface Air Systems Have?
At times, subsurface air systems are characterized as a “silver bullet” for putting green firmness under wet conditions. In my experience, this is not the case. Other factors beyond soil moisture influence firmness – like thatch content and makeup of the greens mix – so there is only so much that subsurface air can accomplish.
Moisture and soil conditions in the top inch of the soil profile have the biggest impact on firmness. This top layer has the highest organic matter content so it holds water very tightly. Removing water from the top inch of the green with a subsurface air system is not likely. Removing water from deeper in the profile can speed up overall drying, but this occurs over a period of days, not hours.
There are limits on how much heating and cooling the rootzone can influence grass health and overall playing conditions. Regardless of our ability to modify soil temperature, the grass is not growing in a greenhouse. It is still subject to factors like sunlight, air temperature and humidity that all affect how it performs.
Subsurface air systems offer a variety of features and investing in this infrastructure may have playability and turf health benefits. However, if the main reason for installing one of these systems is a belief that greens will always be firm no matter how much it rains, the user may be disappointed.