Be extra attentive to soil type when managing sports fields
December 12, 2014 By Mike Jiggens
Having the right field slope and drainage system in accordance to a sports field’s soil type is essential to maintaining healthy turf and playability, members of Sports Turf Canada were told in September at the association’s annual fall field day at Guelph, Ont.’s Cutten Fields.
Keynote speaker Dr. Jason Henderson of the University of Connecticut’s department of plant science said whether a field is 12 per cent silt plus clay content or is 40 per cent, “it’s still going to be susceptible to compaction and has to be managed.”
Typically, “native” soils are those with a higher silt plus clay content, he said.
“When we work with native soils and higher silt plus clay contents, we need to be very careful when we’re working the soil.”
Managing excess water on a sports field is paramount, Henderson said. Not only will sports turf managers have to deal with irrigation in terms of adding water, but they must also manage excess water to the point where it can be too much of a good thing and is starting to affect the performance of the turf.
“Soil selection is key. Soil texture is the most important soil physical property we’re going to deal with because it drives so many things.”
Among them is aeration, including gas exchange between the atmosphere and the soil, and the soil’s macropores will drive the vertical movement of water. Through gravity, the larger the pores, the quicker the water will move down.
Surface drainage is a field’s first defence in terms of maintaining the right water content at its surface “because gravity has to be our friend or else we’re in bad shape.”
Good surface drainage requires a 11/2 per cent slope. When building a new native soil field, “stick to your guns,” Henderson said, suggesting there are soccer coaches who may not want a higher pitch, claiming they can’t see the ball at the edges.
“If it’s a native soil field relatively high in silt and clay, you have to have that pitch or else you’re not going to be happy with your outcome.”
Dealing with a native soil has its advantages, Henderson said. One isn’t buying material or a specific sand. Establishing on soil is also easier than sand because of the soil’s water-holding capability. On a sand-based system, if there is no cover, there won’t be a playing surface.
“Native soils still have a lot of advantages.”
Native soil fields, he said, tend to get a bad rap, but if they are managed properly with “outside of the box” thinking, they can be some of the best playing surfaces around.
A good example is Penn State Stadium which is a silt-loam texture field, 22 inches all the way to the drain tile. Built in the 1960s, its root zone is heavy, but things have been done outside the box, Henderson said, such as drilling holes and filling them with sand. It’s one of the best cool season fields to be found anywhere, he said.
“If you think outside the box and are doing things differently, there are certainly some opportunities to have excellent playing surfaces.”
Anytime soil is altered, whether it’s through excavating, moving or shaping, particularly with golf courses or athletic fields, “we’re already behind the eight ball as managers because we’re not managing a natural soil anymore. It’s been excavated and recompacted, so the natural structure has been destroyed likely.”
Native soils rely on their structure to be permeable and to have gas exchange. Peds or larger particles have greater interped spacing which allows soils to act like sands. But it’s extremely delicate, Henderson said, and a ped can easily be crushed between two fingers. Peds will be crushed by foot traffic alone.
“That’s the challenge we’re constantly dealing with with native soils.”
Soil selection is therefore important, he said, noting the various textural classes within the soil triangle. Even when dealing with sandy loam, it is still susceptible to compaction.
“If we have a choice, we want to choose something on the coarse side.”
Henderson said if core cultivating is done on a silt-loam field, it will take longer for the cores to dry and, once they do, they will be extremely hard. They will be difficult to break up and difficult to incorporate, causing not only field use issues but management issues.
Special considerations need to be made when building fields, he said. It is preferable to stay at the coarse end when possible and not to work the soil while it is wet. It should be dry, he said.
With native soils, ensure they are screened while building and not just for rock or other debris which weren’t present at the time of construction. Depth must also be kept in mind, Henderson said. Once a site is stripped of its native soil and the subsurface horizons are reshaped and soil put back in, there needs to be six to eight inches of topsoil put in.
“Anyone who knows anything about agronomics will know that two inches is not enough to develop a root zone system.”
A mere two inches of soil will also not release water until it reaches 100 per cent saturation or near saturation.
If a sports turf manager wishes to take a loam or silt-loam site and construct a field with a higher sand content, he will have to amend it with a good, uniform coarse sand.
“Anytime you take a native soil and you want to increase the sand content, you will have to be very careful with how much sand you put in there. If you put too much—you get into that 80-85 per cent by weight range—you’ve basically created optimum conditions for compaction. Basically it will turn into concrete.”
Henderson recommended working with a lab to determine the ideal sand-soil mixture, adding if one gets into that “tough” zone, he’s going to spend a lot of time and money and make his conditions worse if he’s not careful.
With such mixes, an organic matter goal of four to six per cent by weight should be targeted.
“Organic matter helps reduce the bulk density…how much it’s going to compact and also helps moderate soil moisture.”
When there is a lot of silt and clay in the soil, it is a mess to work with when wet and it is extremely hard when dry. Organic matter helps moderate the soil moisture to the point where when it is dry, there is a little bit of organic material to help break it up, and when it is wet it is not as “greasy.”
“Test all these materials, both the organic source and sand source and the native soil, and come up with an optimum mix ratio before doing this.”
Henderson said not only must the construction specifications be considered, but also the growing specifications. It must be made clear who will be responsible for the grow-in and at what point during the building process will the project be turned over to the manager.
“A lot of these fields which you may be managing are really compacted, not just because kids are out there running around, but because they (building contractor) were using the wrong equipment when it was being placed and it’s compacted down three or four feet and not just the top three or four inches which we can reach with our traditional management equipment.”
Henderson said an experienced contractor will build a field using lighter, low ground pressure equipment fitted with flotation tires.
Having laid out specifications will catch mistakes made by a contractor and will ensure he does the work correctly.
Whether seeding or sodding, Henderson said to ensure approved varieties of seed are used and that sod be of sufficient quality. Turf varieties need to take into account disease and wear tolerance attributes.
Provisions must be made for establishment, whether irrigating with an in-ground system or by water reels.
Fertility considerations are often absent in building specifications, but Henderson said it’s a key aspect no matter if the field is being established from sod or seed. Such considerations include who is responsible for fertilizing, what the rates are, when it is to be done, the sources of nitrogen, and who will be paying for it.
Mowing is something sports turf managers might not consider as a big issue, especially after establishment in a pesticide-free environment, but it’s a key practice that must be properly timed, Henderson said.
“The earlier you mow, the quicker that plant has to adjust, produce more tillers, is likely to get more density faster…as long as you’re mowing early and mowing often as opposed to waiting until you get six inches come in and cutting it down to three inches.”
When sod is used, early cultivation punching as many holes into it as possible will ensure roots develop in the soil and sod and not in the thatch. Henderson said an aggressive core cultivation unit should be used once construction has taken place to alleviate compaction. If the field has been constructed properly, it may not be necessary, he said, but the field manager must ensure compaction is alleviated through normal use as subsequent field use ensues.
He recommended the use of a PTO-driven core cultivation unit which will consistently go down three or four inches. Doing that at least once, but preferably twice, a season will make a noticeable difference in the quality of a field.
Cultivation practices shouldn’t be limited to only three or four inches, however, Henderson said.
“Every other year, depending on the soil type you have, go in with a deeper tine unit that’s going to go beyond that three or four inches because, if you’re cultivating at three to four inches every year, you’re going to develop a compacted layer at that three or four-inch depth which will affect not only water movement, but also your rooting depth.”
The finer the texture of the soil, he said, the higher the soil will move into a profile. Sand will not move water vertically as high because there isn’t the tension between the particles to be able to move it upward.
The advantage of having a six to eight-inch soil layer is that if a compaction issue occurs and drainage is impeded, the field manager can come in with units to go through the soil into the more permeable material, fill the holes with sand and have a native soil field that essentially has French drains throughout the root zone.
Sand trench systems are good because they can be done regardless of construction, Henderson said. A poorly-drained field can have sand slits cut into it as long as good surface drainage exists. Narrow slits eight inches deep with tight spacing can be effective.
Infiltration at one to four inches per hour doesn’t sound tremendously high, he said, but added it’s important to be careful when selecting the material because greater permeability than what was pulled out is desired. It can’t be so high that every time there is moisture stress that the lines will show up time and again across the field. Typically a 6-2-2 sand-soil-organic matter mix is ideal.
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