Tips From The Pros

SPORTS FIELD SOD – PART 1: PRE-HARVEST

10 or 15 years ago, re-sodding projects on sports fields were often seen as an emergency procedure when our other field plans failed, for whatever reasons. Today, with an increasing schedule of non-sporting and sporting events on our fields at all levels, we need to start seeing sod repair as more of a routine maintenance type of operation, one that makes it possible for the venue to host all these revenue-producing events and still maintain acceptable levels of play on the surface.

Whether a new field construction, repair from a concert at a big stadium or changing-out soccer goal mouths at a park athletic field to increase the amount of play on the field, sod works wonders. Those who would think that a field manager that uses sod for repair lacks the skills needed to keep the grass field in shape through the event stress just doesn’t know what is happening at today’s sports fields.

Sports field designers and specifiers typically rely on fairly well documented and well-researched resources and guidelines in planning sand based sports field rootzones and underdrain systems. Native soil fields are usually tested and amended as needed. But too often, the owner’s rep and/or designer will not put as much focus on the sod that will be placed on top of the rootzone during initial construction and/or subsequent field repair and renovation projects. Specifications for these sods often rely on subjective turfgrass variety assessments and subjective evaluations of the condition of the sod. The local availability is too often the main criteria for selecting sod and a turfgrass producer to grow it.

When sand-based fields fail, it is often at the top inch or two. We engineer the bottom 12-20 inches of the field’s profile quite well, then we employ vague or loose specifications for the sod and doom the endeavor. And the bottom 20 inches, where we pay attention to detail, is basically a set of support systems for the playing surface. Yet we neglect the actual playing surface (sod) specifications.

Every field sod project has unique requirements and these recommendations are not intended to replace the need for project-specific expert consultation. Rather, this blog is intended for the facility owners/operators, as well as field designers to use in planning a successful sod operation for new field construction and as part of today’s routine maintenance and event-repair programs for high-performance, high-use sports fields.

Planning.

A successful sports field sod project, whether for new construction or repair, should be planned out at least one year, if not more, in advance of the harvest. The production, harvest, transport, installation and grow-in of a sports field sod is very different from sods used for lawns. Extra attention and planning ahead are critical to developing a good sports field sod, especially on sand based rootzones. Waiting for a natural grass field to wear out from play and events, and then going out hunting for good sod is risky at best. A well-managed sports field management program will include a relationship with an appropriate turfgrass producer that was started at least one year before harvest. But before you go out shopping for a sod producer, you’ve got to have a good set of specifications for the sod.

The soil in the sod.

Perhaps most critical to success is the soil that the sod will be growing in at the farm as it will eventually come to rest over the top of the fields existing soil. The grass can be manipulated and changed over time. Changing a soil over time is more difficult. So get your sod soil right. The key to remember here is that layers of different soils and/or thatch, even if slight, may impede water drainage and air movement into the soil. Layers may be good on a birthday cake, but not sports fields. If an exact sod-field soil match is not practical or possible, it’s my opinion that it’s better to lay a more-coarse textured sod-soil over a finer textured existing soil, within reason, than the other way around. If your sod soil is finer than the base soil it is laid on, you might tend to “hang onto” water in the top of the profile as you create a perched water table. Where water doesn’t go freely, air will not be exchanged in the soil pores. No water and no air equals no roots.

On sand based fields, I don’t believe it is good enough to just specify a “sandy” soil or a simple percentage of sand in the sod farm soil. Native sand soils that will ‘marry’ with the underlying rootzone mixes typically specified in today’s sand-based fields are quite rare, but may be found. The only way to know is qualified sampling and independent testing from the farm field. Unless you bring in engineered, tested sand to the farm and grow on that, you will want to do a good, independent soil test at the sod farm. In my experiences, any native (natural, in the field) soil tends to be pockety. It doesn’t mean you can’t find an appropriate soil at a sod farm, it just means you should test extensively in advance and know exactly what is out there.

On high performance sand based fields, it’s best to bring in your own engineered sand to the farm. The best way to do that is on plastic, in my opinion. I will discuss some of the advantages to plastic grown sod for sports fields in next month’s (January 2018) Tips from the Pros. It may be possible to bring in a layer of clean sand over the existing farm soil, like a sand-cap. Growing and cut harvest may be difficult, in my experiences. Another method involves an aggressive sand topdressing at the sod farm into existing grass. The idea is to build up a layer of clean sand that is then harvested with the sod. This can work but may take time, a year or more in my experiences, depending on how thick the sod will be harvested, but if you get some of the native soil at the bottom of the sod, you have a layer.

Generally clean, engineered sand is used in sand-based sports sods, without adding amendments like organics (peats). The thought is that the surface few inches will tend to accumulate organic content naturally at a fairly fast clip in a highly managed, sand-based field. Why start with more organics in the sod? Inorganic amendments, like porous ceramics, would not add to this accumulation of organic matter at the surface, in my opinion.

*Assuming 1.25 tons per cubic yard of sand. Different sands at different moisture contents will vary. Get this conversion from your sand supplier.

Species and variety selection in sports field sods.

There are exceptions, but the vast majority of sods grown for high-performance athletic fields in cool-season grass type environments is Kentucky bluegrass. In the warmer climates, Bermudagrass hybrid sods are generally used, especially on high-traffic, high-performance fields.

There are always a few generally accepted varieties and hybrids in vogue in any given decade, in my experience, bluegrasses in the north, bermudagrasses in the south. And while I think it’s a good idea to talk with fellow field managers as to their preferences and experiences with particular varieties and hybrids; I would advise not to fall in love unscientifically with any variety, blend or new hybrid. Do your own homework when it comes to the genetics of your playing surface grass in the sports field sod.

In a blend of different bluegrasses, make sure you have evaluated each variety separately. Make sure they all perform and you are not getting one star performer with several duds, or years 2, 3 and beyond may not be what you want.

The best method we have, in my opinion, for independently predicting the performance of bluegrass varieties is the National Turfgrass Evaluation Program (NTEP), which is a partnership program with the United States Department of Agriculture (USDA). Turfgrass quality evaluations are best done by trained personnel in controlled plots. Word of mouth alone is no way to select a variety or a blend of varieties. Using objective data, not flashy marketing in the varietal design of the sports field sod is always the best way to go.

Depending on how far in advance you can plan your project, you may have the opportunity to grow the varieties you want at the farm you have selected. Sometimes, you may have to work with the varieties and blends that your chosen sod farmer uses, and that could be a good thing. Turfgrass producers get their genetics right or go out of business.

Hybrids bermudagrass sods differ from bluegrass sods in that they are more proprietary. They are not farmed in blends of different varieties like bluegrass sods usually are. Bermudagrasses don’t play nice with each other in blends like bluegrasses do. If you want a particular bermudagrass hybrid, you will need to find a sod farm licensed to grow that hybrid in many cases.

So much more can be said for the genetics of your sports field sods. The takeaway brief here is that your sports field sod genetics should not be neglected and the better sod farms will be able to document their sod genetics in some way.

Seed vs re-grown sod.

Traditionally cut sod fields are re-grassed after harvest in one of two ways (or both). In thinner cuts, the underground rhizomes will regenerate growth and an entire field can be re-established without re-seeding. Sometimes, with bluegrass and seeded bermudagrass sods, a little seed is planted to grow-in with the regenerated grass from below. This can work fine, but it is important to understand that different varieties will re-grow after harvest at different rates of success. So, unless you establish your sod grasses with new seed alone, it may not be the varieties you originally started with (or even wanted).

Turf Tips 101:

Pre-harvest maintenance at the farm.

The importance of the maintenance regime at the sod farm cannot be overstated. It is recommended that for at least one full growing season, if not more, the sod at the farm will be maintained in a way specified to closely match the regime at the install field and to enhance the playability characteristics of the sod. At the stadium field, there is typically little time from install to play and so the sod farmer becomes the de facto sports field manager. Any additional maintenance procedures and treatments will add cost to the sod production. While each situation is different, the cost does not have to be substantial and the added costs will always be far less than a second sodding due to failure, both in direct costs and lost credibility. A top-tier supplemental maintenance program at the farm will add up to 10% to the cost of a sports field sod, but it is well worth it in my opinion.

Watch the thatch.

Sod farm maintenance practices that encourage an excessive, distinctly organic thatch on top of the mineral soil should be avoided on high-traffic cleated fields in my opinion as this may create a weaker shear-zone right at cleat depth. Sod forming grasses like Kentucky bluegrasses and hybrid bermudagrasses are usually known to be strong thatch producers. In addition to proper fertility and mowing at the sod farm, cultural practices like core aeration, verticutting and frequent, light topdressing with appropriate soil may be needed to minimize and dilute the thatch.

Mowing. The general guideline is to mow the sod at the farm at the same height as the turf will maintained at when it gets to the field. In today’s high-profile stadiums, this usually means between 5/8 -1 1/4-inch heights of cut (HOC) on bluegrasses and 3/8-3/4-inch on bermudagrasses. The sod at the farm may be maintained slightly lower in HOC than it will be at the stadium field, within reason and assuming the HOC is within accepted limits for the species. Reducing the mowing height of the sod after it has been installed at the stadium is not recommended. It is an avoidable stress at an already stressful time for the plant.

Fertility. Match as closely as reasonably possible the fertility program at the farm to the fertility program used in the field where the sod will be installed. Allowances should be made for variance encountered at the farm. You may have the same soil at the farm, but the irrigation water may be quite different, requiring adjustments be made to the field fertility program.

Plant Growth regulators (PGRs). The use of certain plant growth regulators (PGRs) in sod production has gained popularity recently, and the benefits in producing high-performance sports field sod can be significant. Trinexapac-ethyl (TE), commonly referred to by the brand name “Primo” is one typically used at sod farms because of its specific effects on turf. TE has several advantageous effects on the growth and development of a turf, some of which are advantageous to sod production and ultimately playing surface stability and durability. The enhanced rooting mass seen with TE use may tend to increase the shear strength or ‘harvestability’ of the sod. This may be especially beneficial for expedited grow-ins.

Sports field sod maturity.

Developing quality thick-cut sod for a high-performance field takes time. Getting the grass to hold together during harvest, transport and install requires a certain level of maturity in the sod. Time can be saved with the use of netting at harvest, but the key here is that harvestability and playability are two different worlds. Just because it is mature enough to harvest, does not mean it is necessarily ready for play at or shortly after installation. Using immature sod risks poor root and rhizome development and a weak sod. The heavy mechanical forces and stresses from cut, transport and install compel sod that is more than mature enough to handle the load. Erring on the side of maturity is the recommended path. Finding out that the sod was not mature or strong enough once laid at the stadium is an expensive mistake.

Obviously, if you have enough time on the field after sod installation to fully establish and tighten-up your playing surface sufficiently, you can use sod of less maturity, in my opinion.

Knowing that each situation requires its own assessment in terms of sod thickness and maturity, I use this basic guideline:

6 calendar months of age for every ½ inch of sod thickness. This is just a basic starting point. Depending on where the grass is grown, this model can vary. I add a few months as I go further north into the zone of adaptation of the particular sod grass. I’ll subtract a few months for bermudagrass hybrids further south. I believe you are best to overshoot on maturity if there is any question as to whether you have enough establishment time for play after install.

Next Month in January TFTP: Part 2 – Sports Field Sod Harvest and Installation.

Resources of the Month

Turfgrass Producers International (TPI) is a great place for sod information.

At Kenan Stadium at the University of North Carolina, they re-sodded and painted a full football field, start to finish, ready for play in 18 hours.

It is unfortunate that the word “Sod” is not a positive one in British slang.

End Quote

“That divot is so deep, I will need a sod cutter to fix it” – Brian Weiss