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Football field irrigation options

By Heath Traver, CIC, CLIA

One of the great American
pastimes is gathering together around the TV on game day to watch our favorite
teams gear up and play football. There are a lot of factors that go into
enabling these athletes to perform at such a high level and still remain as
safe as possible. Yes, the equipment that they are wearing helps to protect
them, but what is under their cleats is just as important. A field that is too
dry (or too wet) can easily be the cause of serious injuries. Lower leg
injuries have always been very common in the game, and now concussions are in
the spotlight. 

You rarely hear an announcer
talking about the field’s playing surface unless there’s an issue. Many
onlookers (if they are even thinking about the grass) rarely consider the
effort that goes into keeping a field of that caliber in pristine shape. Most
fail to realize the challenges that are faced by people in the sports turf
world. They do not think about weather or other factors that would inhibit the
field from being ready for game day, or the events that may have been held in
between games. 

Many things have to happen
before a field is ready for the TV cameras. Of course, at the higher levels of
play, teams have the resources to ensure that the field will be close to
perfect. One of the biggest complaints that I hear while talking to people in
the sports turf industry, is that their fields are being overplayed without the
resources to be able to keep the fields up to the standard that is expected of
them. Most of the professionals in our industry are asked to do more with fewer
resources, and I expect that trend to continue.

A tool that can help a sports
turf manager control the moisture content of a playing surface is irrigation. Sometimes
Mother Nature does not provide us with the amount of water required to keep
plant material healthy, and supplemental water must be applied. An irrigation
system can come in many forms. There are portable types of irrigation, such as
quick couplers, which are typically underground in a valve box and can be
hooked into with a key. The key, which is attached to a garden hose, opens a
valve, and water is allowed to pass through the hose, enabling the end user to
put down water wherever needed.

Another type of portable irrigation
system is a water reel. These reels can be moved from field to field, and
automatically travel in a straight line while they apply water.  Portable irrigation systems have less upfront
costs, but are more labor intensive. 

In-ground irrigation systems
are more expensive up front, but are typically automatic.  The ideal time for running a system will vary
from field to field based on a variety of conditions. They are usually set to
run overnight. Ideally, the field should have enough time for the surface to
dry before anyone is using it, but not too early in the evening. If the field
is allowed to be wet for a long time overnight, fungi and other types of
diseases have a better chance of taking root. 

How often and how much water
is applied is also field-specific, and has always been a debated topic. Most
professionals believe that a greater amount of water applied less frequently,
promotes deeper root growth and encourages overall healthier turf. If the
moisture in the soil profile is below the majority of the root system, the
roots are forced to grow deeper into the soil in order to find the water.

It is very typical that a
grass field will require an inch of water per week to remain healthy. This
number may climb if the field is under heavy usage or if harsh climactic
conditions exist. If we were to apply 1 inch of water per week to a typical
football field, we would need approximately 60,000 gallons of water. If we
multiply that number out using the typical 6-month growing season that we have
in the Northeast for example, the turf will need approximately 1.5 million
gallons of water in a season. These are very conservative numbers.  Since we are dealing with a very large amount
of water, it is critical that we are intelligent in the way we approach
irrigation.  This means only applying
water when needed, and only applying the amount of water that is required by
the soil to keep the turf healthy. 

There are many ways to
determine how much water needs to be applied. The first and simplest method is
with the naked eye. Most sports turf professionals can look at the turf, and
immediately tell if it is stressed. Some signs are that it may have a
blue-green hue, or if a footprint fails to go away in a timely manner. These
are indications that there is a lack of turgidity due to dry soil conditions.
This is not the worst thing in the world, as many believe these conditions
encourage the roots to grow deeper looking for water.  However, if the soil is left dry for too long
a period, the grass will eventually die. 
Secondly, soil probes can be used to determine how much moisture is in
the soil, and how deep the water exists in the profile. These two methods for
determining soil moisture content have less upfront costs, but are more
labor-intensive. 

There are also automatic
methods for determining soil moisture. Rain sensors and soil sensors can also
be used to monitor the moisture levels, and can shut off a system when the soil
gets to a preset threshold due to a rain event. New irrigation systems also
have the ability to utilize weather data to adjust how much irrigation water is
applied.  The system can use an onsite
weather station, or use online sources to get evapotranspiration (ET) data,
which is a combination of the water evaporating from the soil and the plant
transpiring, or “sweating.” ET is affected by weather conditions (wind, solar
radiation, temperature, humidity), and represents the amount of water that must
be put back into the soil to keep the plant material healthy. The EPA estimates
that these types of smart controllers provide water savings of about 30%.

Since we are dealing with
millions of gallons of water, it is important that we irrigate as efficiently
as possible. This all starts with the design and installation of the
system.  Proper design by a certified
professional is the best way to ensure that the system has been designed with
optimum uniformity based on available pressure and flow. The installation
contractor also has an important role, and should install the system following
the designer’s specifications. If the contractor decides to value engineer the
project by eliminating heads, the system will probably end up with poor
uniformity. When a system has poor uniformity, the end user will typically
increase the zone runtimes to compensate for the weaknesses in the system, and
the rest of the field will end up being overwatered. This is a very wasteful
practice, and can be avoided with proper design and installation.

Another trend that is slowly
being adopted by the sports turf industry is the use of sub-surface drip to
irrigate turf. Since this is considered unproven technology, there has been
resistance, but in parts of the country where water is less plentiful, this
method of irrigating sports turf is slowly being adopted. The main things to
consider when utilizing subsurface drip are that the drip will need to be deep
enough to be clear of the aerator that will be used for regular maintenance,
and that traditional overhead irrigation will need to be used in order to
establish the seed or sod for a period of time until the roots find the water
below.

Regardless of how we elect to
manage moisture on a playing surface, the fact remains that moisture management
is critical in ensuring that players are as safe as possible.  This remains true at all levels of sports
turf management, and is not going to change any time soon.  Whether we are talking about million dollar
athletes in high stakes games, or our children running around, keeping the
playing surface as safe as possible will always be crucial.  As always, it will be up to the sports turf
professionals who are on the front lines of the ongoing battle, protecting those
who have the privilege of playing on their turf.

Heath Traver, CID, CIC, CLIA
is a specification manager for Rain Bird in the Northeast US, and is licensed
to practice irrigation in New Jersey. Heath can be reached at htraver@rainbird.com

High-end moisture control

One of the most important
factors involved in keeping a grass field healthy is moisture control. Many
stadiums employ a SubAir (or similar) system to control soil moisture content. These
systems are essentially giant blowers that are hooked into the existing
draining system below the playing surface. With the flip of a switch, the
SubAir system’s vacuum mode can be activated. Negative pressure is created
under the playing surface, and water and air are sucked through the soil,
pulling through any unwanted moisture. Conversely, the SubAir can blow air into
the drainage forcing air up through the soil profile. This can help aerate the
soil with fresh oxygen, as well as help to control the temperature of the soil.
It can be cooled when the temperature gets too hot, and it can also warm up the
soil in order to “wake up” the grass earlier in the spring. This can be an
excellent tool but comes with a hefty price tag.