Features Agronomy
Soil structure an important consideration managing sports turf

Sports turf managers are in the business of developing playing surfaces and not in the business of growing grass, and everything they do to grow grass on athletic field surfaces is likely contrary to what the turf wants done, those attending the eighth annual Nutrite lawn care seminar in Guelph were told in March.

Dave Smith, principal of DCS Agronomics, addressed a gathering of lawn care operators and other turfgrass professionals to speak about proper sports turf construction and evaluation.

Much of what a sports turf manager does to develop his playing surfaces, such as topdressing in hot weather, is not good for the grass, but is good for the games that will be played on the surface, Smith said.

“We build a lot of things and then use them for things they weren’t designed for.”

Those in the business of managing sports fields have much to consider and evaluate, Smith said, including water quality and quantity, shade issues, budgets, drainage, thatch, layering, pests and aeration scheduling.

He said he was recently consulted for a municipal parks project, but first looked at the park on Google Earth, asking what the city planned to do about the abundance of trees that were casting extensive shade on the area. He was told he was hired with regard to growing grass, and that the trees were a separate issue. He said when faced with such adversity, he has occasionally recommended the installation of synthetic turf because some sites are not conducive to growing grass.

“Ninety-five per cent of what we need to grow plants we get for nothing,” Smith said, citing light, water and air. He added, however, the plant will suffer if any of those items is missing.

Soil nutrition must be provided by the turfgrass professional, accounting for the remaining five per cent. Smith said it’s been calculated that the soil can handle about .7 pounds of nitrogen per growing month or about three pounds per year. He said he likes to split soil fertility into two parts: nitrogen and everything else.

“Nitrogen drives the bus.”

Balanced soil
Although people have different interpretations of what a balanced soil is, Smith said he defines it as one with a balance among its chemical, physical and biological properties. He said that when dealing with plants, managers can’t think about the biological properties first followed by its chemical properties and finally its physical properties.

“We have to think about all of them at the same time.”

Chemical properties include fertility while physical properties include soil texture and layering. Microorganisms represent the biological properties in soil. Smith said turfgrass managers must appreciate their presence because they break things down and help with fighting disease and other issues.

“It’s important we manage them and appreciate that they’re down there.”

Layering is something that is going to occur, even if it’s a brand new sand-based category one athletic field.

“I don’t think there’s a green or an athletic field or a home lawn or anything that isn’t layered. That’s the reality of it.”

Smith presented a picture of a soil profile on a field that had yet to make it to its opening day. At the top was a layer of organic matter. He said when the field was irrigated while plants had yet to develop from seedlings, the water washed organic matter out of the surface, allowing it to accumulate directly beneath. He said that is why it is so important to core aerate, noting soccer fields are especially in need of the practice.

He demonstrated water’s ability to get through both clay and sand layers, noting the specific soil texture dictates the rate at which water is allowed to pass. Water just “hanging” at a layer isn’t just sitting there, he said.

“The water is fighting the resistance of going and wetting that layer and moving through it. The water is trying to stay above it.”

The hanging water is attracted to itself, he said, adding water holding onto itself needs gravity or weight to push it to the bottom.

Smith asked his audience if they believed soil drains better if it is deeper or shallower, comparing a three-inch depth to one of 12 inches. Demonstrating his example with a sponge saturated in water, he turned it lengthwise to mimic a deeper soil, concluding it allows water to drain better and it provides more air space at the surface.

Those who care for home lawns are lucky to have an inch and a half of soil at the top, he said. Sometimes lawn care professionals work with shallow soils that are heavy and consequently hold too much water. Fine-textured soils are easier to compact, hold too much water and drain poorly, making them unsatisfactory for sports field construction.

The finer the texture of the soil, yet the more silt and clay that is in it – primarily the more clay content – then the more water the soil holds, Smith said.

Overprotection of drain lines
He said it has been his experience that when athletic fields are designed, there is a tendency to overprotect the drain lines to the point where water has difficulty getting in.

Sports fields must be designed for surface runoff, especially in climates where there is snow. Fields may be equipped with good drainage, but soils tend to be frozen for about one-third of the year, emphasizing the need for good surface drainage.

Smith asked his audience if – when monitoring their soils – they take only one sample from the middle of a field or if several samples are collected at various field locations to check it for uniformity.

If a sports field manager becomes a part of the building process for a new field, it is advised he be present during construction to be sure of the depth of the mix and to ensure all is satisfactory, he recommended.

There is no substitute for proper field construction even with the sophisticated tools available today, Smith said.

A sports turf manager needs to know the type of field slated for construction (its category type, whether it will be lit, etc.) and may have to spend more time with the soil triangle to figure out its porosities or if it’s to be a sand-based field not quite to USGA specifications.

A perfect soil, Smith said, will be 50 per cent pore space and 50 per cent mineral matter or sand particles. Of the 50 per cent pore space, about half will be draining pores and half will be water-holding pores. It’s then all figured to a depth.

Careful thought must be given if the intention is to blend onsite soils high in silt and clay with sand. It’s a real science, Smith said, and something that will require good equipment to do properly. He recommended no more than 20 to 25 per cent silt and clay when soil is to be imported to put them together or blending in onsite soils.

“It’s very important we consider depth when we’re building fields, whether it’s the depth of the drain or the depth of the mix.”

Blending Southern Ontario soils high in silt and clay (54 per cent silt and clay, for example) with heavy sand can be a recipe in futility, Smith said. It’s not homogenous and is difficult to blend properly.

“You’re best sometimes to just go with something that contains more material and just takes a bit more water to be more successful.”

The United States Golf Association recommends staying below 25 per cent silt plus clay when developing a mix if blending sands. Smith said the percentage of silt plus clay is his first consideration when evaluating blends because anything higher than 25 per cent, “You’re starting to mix cement.”

High-grade golf course sand is an excellent product, he said, but it doesn’t work so well when mixed with soils. It is too uniform and too expensive to be used in a blend with topsoil. He said there exists a mindset that because the high-grade sand works as well as it does on golf courses that if it’s mixed with soil it should do wonders for athletic fields, but he reiterated that it will have the properties of cement.

For drains to work properly, they should be 18 inches or 45 centimetres in depth, Smith said.

“You can’t have drains up near the surface.”

There is much to think about before starting construction on athletic fields, he said.

“We need to think about drainage and drainage and drainage.”

When sodding a field, the various layers must be considered. Smith suggested buying sod that has some sand in it, is uniform and meets the soil specifications.