Tips From The Pros

BASICS OF SAND PART 2 – IN THE SPORTS FIELD

In part 1 of The Basics of Sand, I discussed some of the basic properties of sand as used in athletic fields. This month we take it out to the sports field. Not every sports field manager will have the great opportunity and challenge of building a sand based sports field, but most will engage in using sand out in the field for topdressing and other uses.

First, an important caution. Be very careful topdressing sand onto a native soil field, especially those with a decent amount of clay and/or silt in the base soil. Unless you can make the final percentage of sand in the soil at least about 75-80% or greater, you may make things worse. Mixing a sand into a clay soil can create a hard, poorly draining soil. Like my old college professor Dr. Butler used to say “Sand plus clay plus grass equals adobe”. Get expert help and know the soil you’ll be engineering will work.

Sand Cap. There may be a place to create a layer of appropriate sand on top of a native soil that is a few inches thick. This idea is commonly called a sand cap. The idea is to build up a layer of appropriate sand on top of the native soil base, kind of a less expensive sand based field. This can work very well when carefully engineered and maintained, and it is typically a lower cost way to gain some of the benefits of converting to a sand-based field. A sand-cap field can be built from scratch or an existing native soil field can be converted to a sand-cap field. I believe it is important to add in an internal drainage system with a sand cap, especially in wetter climates. Michigan State University Turfgrass has a good paper on sand-caps here.

Sand storage. Soil bins, located close to your fields, are the best way to store sand. I like to have 3-4 bins, one for clean sand, one for organic materials like peats etc., one for your native soil (if you have it), and one for waste. Concrete is best, especially on the floor of the bins. Build a concrete or asphalt platform in front for loading. Locate your soil bins in such a way as to allow for sand delivery trucks to get in and out easily. Use an appropriate sweeping compound when cleaning up the areas after topdressing treatments to keep dust down.

Before the delivery truck dumps sand at your facility, grab a handful of your known field sand and compare that visually to the sand in the truck. It’s probably not practical to do on-spot particle size analysis here, you just want to rule out somebody loading from the wrong pile at the sand pit.

Calibration and rates:

Sand topdressing is a little tricky to calibrate, but with some basic math and experience you will be able to project quantities accurately. The first thing to keep in mind is that sand is generally sold by the ton and not cubic yards. To complicate things more, we sports field managers often speak of topdressing rates in terms of the thickness of sand “blanket” we are laying down. For example, we may feel like a 1/8-inch (thick) of topdressing would be perfect. But how do we achieve that 1/8-inch? The key conversion you want to get from your sand supplier is how many tons per cubic yard does their sand weigh? Usually, you are looking at about 1.0-1.3 tons of clean, dry sand per cubic yard.

First a little mental exercise. Visualize a 36-inch cubic yard of sand, a perfect 3-ft by 3-ft cube of sand. Now imagine cutting it into 1-inch thick slabs. Each slab would be 3-ft x 3-ft x 1-inch. Each slab, regardless of the thickness covers 9 sq. ft. So it’s just a matter of how many slabs can you cut at the thickness you want to topdress at. If we visualize 1-inch thick slabs, we see that we could cut 36 of them off our cube of sand. So we could cover 9 x 36 or 324 sq. ft. for each 1-inch of slab thickness.

Mathematically, we can plug the tons/cubic-yard conversion we get from our sand supplier into a simple conversion equation to get a basic calibration plan.

Tons of sand = (Sq. ft. of area treated ÷ 324) x (tons per cu. yd.*) x (depth in inches)

*Value from sand supplier

Example 1: Our field is 2.0 acres (1 acre = 43,560 sq. ft.). We want to apply a 1/8th (.125) inch thick sand topdressing to the entire area. Our sand supplier tells us that our sand is 1.4 tons/cubic-yard. How much sand will we need for the project?

(87120 ÷ 324) x (1.4) x (.125) = 47 Tons of this sand is needed to cover 2.0 acres with a 1/8th inch blanket of sand.

Example 2: Our field is 1.5 acres. We have 50 tons of sand to apply. Sand supplier says our sand weighs 1.2 tons/cu. yd. If we spread all 50 tons evenly over our field, how thick of an application would that be?

Using simple algebra we can flip our equation to suit our question.

Depth (inches) = (Tons of sand) ÷ [(Sq. ft. of treated area ÷ 324) x (tons per cu. yd.*)] *Value from sand supplier Plug in our numbers: Depth of application (inches) = 50 ÷ [(65,340 ÷ 324) x 1.2] = .206 inches thick. Or about 2/10 of an inch thick if we evenly apply all 50 tons.

Turf Tip 101: More Tips on Using Sand in the Sports Field

Topdresser settings. Topdressers typically have a variable application rate and use a somewhat arbitrary number. So a topdresser setting of “3” for example, is typically just a reference number for us, and is not connected to actual topdressing rates. Ultimately and with experience, with one topdresser and one sand supplier, we can pass over doing all the math every topdressing and begin to correlate our topdresser settings along with the ground speed we use, to be able to develop a set general “boiler-plate” application rates of tons/acre for our rates. Keep good topdressing application logs. Before you know it, you’ll be projecting a topdresser setting number to how many ton/acre that means.

Patterning the topdressing application:

As best you can, try to avoid driving carts, tractors or other heavier equipment over already topdressed areas on the grass. Rolling and especially turning heavy wheels on sanded grass may bruise the grass canopy. Allow plenty of room at the end of each swath for turnarounds after then do clean-ups to finish. By designing the longest swaths possible, you can minimize turn damage. Unless you can really measure-out and hit the targets of a “Zamboni” or “Farmer rows” type of patterning, it is best to do simple back and forth patterning when you first start topdressing. You want to avoid overlaps, especially at higher topdressing rates as this may create unevenness in your surface. Again, allow plenty of room at the ends of swaths to turn off sand and make an easy turn around to line-up for the next swath. Depending on the equipment you use, tight turns can bruise or tear turf.

With experience, you can figure out exactly how much to load the topdresser at the bins so that it empties right at the ends of swaths, not half-way down a swath. This way you minimize start-stop overlapping and also minimize cart/tractor traffic damage for your treatment.

Use caution in winter time topdressing. Sand stored outside in cold temperatures may freeze into icy sand-chunks that can damage topdressing equipment if you try to run it through the unit. If you have an appropriate heated shop area, you can move enough sand inside to complete your topdressing project a few days ahead of time to thaw it out and avoid icy sand chunks.

Working topdressed sand into the grass canopy.

After you evenly spread the sand, you want to get the sand worked down into the canopy and eventually to settle in the soil/thatch surface, or into core aeration holes. First, dry the topdressed sand as best you can. Dry sand works down into the turf much better than moist or especially wet sand. In the warmer months, be careful not to let the topdressed sand lay for too long on the grass canopy waiting for it to dry. Sand can heat up and may burn the turf canopy.

Also try to topdress dry sand onto a dry grass canopy for the same reasons.

For lighter rates of topdressing (maybe <5 tons/acre), and depending on the condition of the grass stand, you may be able to “wash” the sand down into the surface with simple irrigation or natural rainfall

With heavier rates, I thinks it’s best to broom it in using a pull-behind topdressing broom. There are many turf brooms and brushes and I look for a couple things. How easy is it to set up and use. Can you vary the stiffness and replace bristles? Can you add or subtract small amounts of weights to get the results you are looking for in all conditions? Is the pull-behind turf brush wider than the width of tires on the cart or tractor I use? Again, you don’t want to drive over topdressed sand before you have worked it into the canopy.

Maintaining sand rootzones.

Over time, the grass will fix carbon from CO₂ into organic plat material. Eventually that dies and decays, along with soil microbes, into an increasing amount of soil organic matter (OM) in a sand rootzone. This natural organic accumulation is generally not an issue on sports fields, in my opinion, until the top of the rootzone accumulates to above 3-5% by weight. A simple “loss on ignition” test conducted at your favorite soils laboratory can give you this value and it is wise to chart your percent OM over time in the upper part of your sand rootzone.

To combat excessive OM build-up, we “dilute” the OM by applying clean, engineered topdressing sand. Core aeration and core-removal before topdressing can give better results and added benefits in my experiences. Some sports field managers have had great success by topdressing sand first, then core aerating afterwards. The idea is that the tines penetrating the soil surface aid in getting the topdressed sand down into the soil profile. Like any treatment, I advise trying on a non-critical part of your field first before proceeding to the rest of the field.

Get some grit.

On sand based fields, a light topdressing (2-4 tons/acre) of appropriate sand a few days ahead of the game may aid in getting a little grit into the surface. I’ve found this to work well, especially at times of year when the grass is thick and the surface can get a little slimy. A light topdressing of sand may also help right before an expected rain game for the same reasons. Again, you don’t want to introduce a large amount of sand into the grass right before a game without time to properly settle it. The traffic may beat the grass up pretty good depending on conditions. But a light shot of sand (on a sand-based field) can really help.

Check irrigation heads after sanding, sand can clog up and make heads stick in the up position.

Sand is brutal on working equipment. Clean your equipment well.

May your feet be in the sand with a cold drink in your hand.

Resources of the Month

If you don’t like math, maybe try this online sand calculator from Purdue University. University of Missouri Turf has a downloadable Excel spreadsheet for topdressing and or aeration calculations.

Raising Arizona – We ate sand because I don’t know why.

Ever been on a bioluminescent beach sand?

End Quote

“Write your hurts in the sand. Write your blessings in stone.” -Unknown