Topdressing is important if you want to reduce thatch. Topdressing aggressively growing grasses helps in breaking down that slimy layer that can exist between the plant and soil surface. Topdress is needed to protect turf injury after an aerification, depending on the time of year and timing of sports seasons. During football season, for example, after an aerification, topdressing is important to re-fill aerification holes to help provide vertical and lateral stability.
Advice on topdressing
Topdressing at lighter rates is important to “level” divots during the season and protect from further turf injury. Topdressing at heavier rates is important to protect turf heading into winter to help prevent dessication.
Topdressing is not always necessary after an aerification process. With little spring activity, leaving the aerification holes open and not topdressing will provide increased rooting and cavities in the soil for which roots and water to travel. However, a light application of sand topdressing during slow spring growth may help increase the soil temperature.
Compatibility in topdressing is comparing the particle sizes of a topdressing product with the underlying soil medium and seeing if the two materials can work together. Using a topdressing material different or not closely associated with the underlying material will start to cause layering in the soil profile, which can adversely affect internal drainage in an athletic field.
If a topdressing material is to be changed, the topdressing program should stay consist with that same material. The biggest problems in a soil profile occur when there is finer grade topdressing material overlying a courser soil. The finer material will seal off the draining capabilities of the underlying soil.
Composition choices could include mixes of different ratios of soils, sands, peats, and calcined clays. For example, a sand-based field rootzone that was originally a 94% sand 6% peat, you might use a 100% sand topdressing that is the same particle size as the sand in the rootzone. On a native soil based field, you might use a well-balanced soil with a little higher sand content mixed with 50% by volume of calcined clay. When you use sand topdressing on some fields, try and stay away from sands with 40% fine/very fine sands.
Example of application process
After the football season is over and your field has been aerified and cores removed, apply a little more than 3/4 of an inch of topdressing over 80,000 square feet, or about 25 ton of sand material. After the sand is spread, allow it to dry and then brush it into the aerification holes and divots. This is the best time to apply a heavy application of sand topdressing while the grass growth has slowed down, allowing the sand to effectively be moved in the aerification holes. The heavy amount also gives you that added protection going into the winter months.
During the season, periodically apply light (1/8 to 1/4 inch) amounts to topdressing between the hashes to help fill divots and protect exposed crowns and rhizomes.
At Iowa State, we have four specific topdressing processes we use. In-season/post-season/off-season all have different philosophies applied to them. The only common denominator is that in each we use 100% sand.
We topdress after every other aerification process (smooth surface of field) and also after every seeding operation (cover seed to help seed-soil contact). We also topdress lightly after each game to help control snot/hydrated clipping layer.
Compatibility means making sure the topdressing material you apply matches up with the material you are applying it to. The materials must adhere positively to prevent a shear plane, allowing a field to point at which to break apart.
Mike Andresen is facilities and grounds manager for Iowa State University; Jeff Salmond is athletic turf manager for the University of Oklahoma.