Features Agronomy
Manage sports turf based on root zone

Municipal sports turf managers who know how their playing fields are categorized have a better chance to manage them more efficiently based on agronomics. By paying close attention to the root zone, sports turf can be better managed than by simply basing maintenance practices on usage time.

The University of Guelph’s Dr. Eric Lyons addressed the issue in December at the second annual Nutrite sports turf seminar in Guelph.

Sports fields may be equipped with washrooms, lights, a parking lot and a perimeter track and, although such features may influence how much use they get, they don’t determine how the field functions or how the grass is growing.

“It might influence your management quite a bit, based on use,” Lyons said, “but in the end, there’s a better way to talk about agronomics, and that’s based on the root zone.”

Sports Turf Canada has developed a rationale for its field classification system, clearly spelling out the specifications in an instructional manual it has produced for the industry. The manual’s purpose is to provide guidance for the selection, construction and classification of newly constructed sports fields. The resource can be referenced during the tendering process, and it provides landscape architects and sports field designers with valuable information. Lyons said Sports Turf Canada has been struggling with specifications being put out by municipalities that reference the manual yet don’t actually meet the specifications as printed in the publication.

Municipalities tend to classify fields based on the number of users who wish to rent them. But true field classifications, from a sports turf manager’s perspective, should be based on root zones, based on their soil, silt and clay makeup. Root zones that are less than eight per cent silt and soil are classified as sand-based root zones or USGA-specification root zones, and are considered Category 1 fields. If the root zone is less than 25 per cent silt and soil, or 75 per cent or more sand, it is a Category 2 field. A Category 3 field has a 25 to 40 per cent silt and soil root zone while a Category 4 field is silt and soil greater than 40 per cent.

Most of the fields in the region of Guelph and surrounding area are Category 4 fields, he said.

“It doesn’t mean they don’t function well. It just means that’s what we have.”

Knowing how fields are categorized allows the sports turf manager to change the way he manages them. For example, high-usage fields require more nitrogen.  Greater use produces more wear and tear and requires more growth.

“More nitrogen on a Category 1 field is more than more nitrogen on a Category 3 field.”

Knowing the soil type enables the sports turf manager to manage his fields differently and to make his program more efficient. A sand-based field is less likely to be closed following a rain event than other category fields. A field with a well-structured soil that drains efficiently is one that can take the most use. Category 3 fields can typically take the most use, Lyons said.

When turf is eroded from a sand-based field, the sand will move around because it has no stability without turf cover. Once a Category 1 field experiences bare root zone, it needs to be closed because a “trough” will quickly be created.

“So Category 1 fields should be our least used fields, but you can charge a premium for use because you’re less likely to have to close it on Saturday afternoon when there’s a big event because you had rain all day Friday. It’s going to drain. That’s really hard for city planners to get through their head – that we spend the most on the field that we can use the least. But you don’t have to close it.”

Sand-based fields cost the most to maintain. A Category 1 field can take 250 hours of use with significantly high maintenance and probably survive, Lyons said. The only time that field is used is when it has been permitted. If the number of hours reaches as high as 700, it is almost guaranteed that bare soil will abound, he added.

Test for soil type
To determine a field’s soil type, a sample will need to be taken and analyzed for its physical properties. The size of the soil particles is measured when testing.

Sand-based fields are preferred because they resist compaction and the soil doesn’t hold together when no turf is present. Layers impact water movement, and water likes to stay in the smaller pores.

“When we get to repairs and how a Category 1 or 2 field impacts how you repair a goalmouth, this becomes important.”

Not all sands are the same, Lyons said, even if two fields are both 95 per cent sand. One might be 53 per cent medium sand and 21 per cent fine sand while the other might be 30 per cent fine sand and 19 per cent very fine sand. One field will percolate at a rate of about 15 inches an hour while the other’s percolation rate will be about 2½ inches an hour.

Knowing the percentage of sand, silt and clay is a good starting point for the sports turf manager. Understanding that all sands aren’t the same is important to know when choosing a topdressing mix, Lyons said.

Root zone types affect management practices, especially mowing, he said. If it rains all day Thursday, and mowing is to take place on Friday, the fields that should be cut first are the sand-based fields in order to prevent rutting. If rutting is a possibility on a Category 1 field, efforts should be made to stay off the field because it’s a premier playing surface. It’s still the one that will dry the fastest.

Irrigation varies with the different root zones. There are more pore spaces in clay than in sand, enabling more water-holding capacity. Pore spaces in sand, however, are larger and allow for drainage. It means less irrigation each time but it must be done more frequently. Water amounts are based on infiltration rates.

“How longer will it take to get the same amount of water into a Category 4 field versus a Category 1? It will take a lot longer so you need to soak it in.”

For Category 1 fields, deep and infrequent watering sometimes means twice a week and likely more often during the heat of summer.

Dr. Eric Lyons of the University of Guelph says root zone type, not usage amounts, should determine how a sports field is managed.

“Hot and dry periods may require more frequent irrigation than that. You might start to see wilt after a day or two.”

Moisture meters tend to provide accurate readings when used on sand-based fields, Lyons said, adding the numbers are consistent “from one sand to another sand to another sand.” The meters tend to be less accurate when reading Category 2 and 3 fields.

“You have to create your own little curve on what’s OK for that field for each field independently because they’re not all going to act the same.”

Watering during drought
A lack of water availability can lead to turfgrass death on a sand-based field while soil-based fields can typically survive six to eight weeks of drought, assuming they are Kentucky bluegrass fields able to come back from drought. Watering bans can have a negative effect on sand-based fields.

For Category 2 fields, irrigation is highly recommended. Deep and infrequent means one watering event a week. A little silt and clay is present to hold onto some water and slow its movement. Soil moisture meters can be used, but Lyons warned comparisons between different category fields should not be made. He said when one field gets to 12 per cent volumetric water content, it is pretty dry while another field might get down to nine per cent and still be fine.

For Category 3 fields, irrigation aids in growth and recovery.

“Irrigate to promote growth only when needed. One time a week during extended drought should be enough.”

Extended drought conditions can be scary, Lyons cautioned, noting brown turf provides a harder playing surface than green turf. Brown, dormant turf poses a more serious threat to athlete concussions than a green, actively growing field.

“It’s a good reason to turn on your irrigation, even in a watering ban situation.”

Watering sports fields is important for not only maintaining the playing surfaces, but to provide greater safety among those using the facilities. Sand-based fields will become harder quicker and will harden up after a couple weeks of drought. The indicator is the change in the colour of the turf, from green to brown. Lyons suggested that because a lot is invested into sand-based fields, that they should be sufficiently watered and kept open.

“If you know what sand is out there and if you know what root zone is out there, you can manage it differently.”

Category 4 fields shouldn’t be irrigated, Lyons said, suggesting if they are more than 40 per cent silt and clay, there is no point watering them because they won’t stand up.

Sports fields in Canada are typically in use from April to October in most regions. When considering seeding practices, Lyons noted perennial ryegrass either germinates or dies.

“If you’re not constantly replenishing that perennial ryegrass seed, it’s dying on you. You have to overseed constantly.”

Falling behind on Category 1 and 2 fields to the point where bare areas are exposed, getting them back is “super” difficult, Lyons said.

“You never want to fall behind on Category 1 or 2 fields with overseeding.”

Falling behind on Category 3 and 4 fields isn’t as consequential, but compaction issues will need to be addressed, he added.

On Category 1 fields, sand is harder to successfully overseed once turf loss has occurred. Overseeding should be done with heavier rates and more frequently on Category 1 fields. Turf loss leads to erosion of the soil mix. Irrigation for surface moisture may be necessary, especially for rehabilitation, and field closure may be required.

Because Category 2 fields have better water-holding and nutrient-holding capacities than Category 1 fields, overseeding tends to be more successful, but erosion can still occur. A slightly lighter overseeding rate is typically used. Lyons said no matter if the field is Category 1 or 2, overseeding should be done before a problem is observed.

On Category 3 and 4 fields, compaction may need relieving to ensure germination occurs. Slit seeding is helpful because it not only relieves compaction, but it increases soil to seed contact.

When sod is used for repairs on Category 1 and 2 fields, holes should be created through the sod layer because it’s unlikely Category 1 and 2 sod will be available.

“Attempt to get a matching sod, but it’s rarely available.”

Plant nutrition is dependent upon soil properties, Lyons said. Sand is more susceptible to wear and usually needs higher fertilizer rates. There must be a balance between recovery and excessive growth.

Mowing three times a week allows sufficient fertilizer can be applied for the turf to compete with weeds because grass is better under highly mowed, high nutrient conditions. If mowing three times a week, Lyons said it’s possible for goalmouths to be seeded without the need for sodding or worrying about getting 100 per cent weed cover when both mowing and fertilizing. But, he said, taxpayers likely won’t stand for mowing to take place as often as three times a week.

Category 3 fields have high nitrogen needs because of their high usage. They can take the most hours of play and have almost no need for micronutrients.

“Never forget that soils impact management.”