Mowing, Fertilization and Irrigation are often taught to be the “primary” cultural practices utilized in turfgrass maintenance. There are other practices, often referred to as “secondary,” which include operations like coring and topdressing.
Topdressing refers to the application of a fine layer of soil over an existing turf surface. It’s used, among other reasons, to smooth and level playing surfaces such as putting greens and athletic fields. But of all the cultural practices mentioned above, topdressing is often the one that gets skipped. Why? It may be because a field manager doesn’t recognize and understand the benefits or importance of it. Or, it may be that the field manager wants the benefit but can’t afford it. In other words, topdressing materials and the equipment aren’t cheap.
While outside contractors can be brought in, topdressing isn’t a one-time event and thus this route would result in an annual recurring expense. In this article we’ll go over the benefits of topdressing and review some points to maximize success in the practice. We’ll also discuss materials that are most often used to topdress athletic fields.
Benefits of topdressing
Topdressing results in filling in of ruts, depressions or other surface imperfections. This means a truer and smoother surface, which can decrease the likelihood of player injury. Another important benefit, especially on fields where games like soccer are played, is that the ball rolls truer. Beyond these there are many other – perhaps subtler – benefits.
Some thatch on an athletic field is a good thing because it provides cushioning for the athlete. But excessive thatch can cause problems because of the development of hydrophobic dry spots, or rooting of the grass into the thatch instead of the underlying soil. Topdressing helps to control thatch problems by incorporating material into the thatch layer, improving the environment for soil microorganisms that decompose the thatch. Topdressing can also be conducted during establishment by sod or stolonizing, in order to level uneven areas and make the surface more uniform.
Of course, topdressing can also be used to alter the turfgrass growing medium (e.g. change a fine-textured, compacted soil to sand-based). But done incorrectly, this can actually make drainage worse rather than better.
Topdressing may help protect from winter desiccation in regions with mild winters – topdressing material provides an insulating effect to the crowns of the grass plant.
Points to consider when topdressing athletic fields
On athletic fields, topdressing schedules and approaches differ compared to golf course putting greens. One thing that may influence your decision as to what topdressing schedule to follow more than anything is your budget. For example, on high-budget fields, light applications of topdressing might be applied every few weeks. Other fields may be topdressed a few times per year or, on a tight budget, once or twice per year when the field isn’t being used.
Regardless of the topdressing program you choose, once initiated it must be continued at a frequency that matches the growth rate of the turf. If applied too slowly, alternating layers of thatch and soil will result. If applied too quickly, thatch can be buried and cause a barrier to root growth.
In addition to the agronomic effects on the turf, the timing of the topdressing application is important for a couple of reasons. The first is that the actual topdressing operation will result in a disruption of play for a period of time. The reason for this is that after application, time is needed in order for the topdressing material to shift vertically down to the interface between the thatch and soil. Play or heavy use before the topdressing material has settled can be a problem. Initially, the lateral stability of the field decreases a bit until the topdressing material has settled. While settled topdressing can be beneficial to top turf growth and injury recovery, another problem is that, regardless of the material applied, topdressing materials by their nature will have some abrading characteristics that are injurious to the grass tissues. This is exacerbated if play occurs prior to settling. Because of these factors, it’s generally best to topdress out of season on fields with intensive use, but when growing conditions are ideal.
Materials used to topdress athletic fields
Selection of the proper topdressing material is critical to success. Unless using topdressing applications to convert a field to sand-based using a prescribed method, the topdressing material should be as close to the underlying soil as possible. Otherwise, topdressing may contribute to problems caused when soil layers possess different physical characteristics. Core aerification or shatter-hole aeration is usually performed in conjunction with topdressing to help alleviate this problem. Even if layering isn’t a concern, in most cases topdressing will provide more benefits to the field if applied in conjunction with cultivation.
Regardless of the source used, there’s one universal truth about topdressing: the source of material needs to be local, because it’s very heavy. Otherwise the cost of shipping will often exceed the cost of the material. This can add to the challenge of finding the right topdressing material because, for example, your locally sourced materials may not be desirable to topdress your fields with.
Common topdressing materials are as follows:
- There’s a debate about the merits of pure sand topdressing. On one hand, it’s less expensive and much easier to use than a mix with exacting standards. But hydrophobic dry spots, nutrition problems, reduced water-holding capacity and winter desiccation may lead to undesirable results.
- If the field is over native soil, then the sand can be applied by itself or mixed with compost or calcined clay. A quality, sandy topsoil with similar texture to the underlying soil can also be used. If the field is grown on sand, then the most typical topdressing materials are either sand or sand mixed with calcined clay. The purpose behind the calcined clay is to improve the moisture retention characteristics.
- Not all sands are created equally and, unfortunately, a good predictor of whether it’s a good idea to topdress with a particular source of sand is its cost. A low cost sand is more likely to have excessively small particles (silt), which will impede drainage, or excessively large particles (gravel), which will not improve uniformity and in the extreme can even result in increased hazard for athletes.
- When first sourcing a sand for use as a topdressing, send a sample to a soil testing lab, which can provide you with a textural analysis. This will allow you to determine if the amount of fine, medium or coarse sand in the sample is suitable for use on your field.
- Decomposing organic matter from many different sources, such as sewage sludge, animal manures and food waste, are used to produce commercial compost products. Composts are often thought of as garden amendments, but their application to turf as topdressing can produce desirable results.
- First, realize that not all composts are the same. Thus, two finished composts might differ significantly in organic matter content, nutrient analysis and/or presence of undesirables such as excess salts or heavy metals.
- It’s important to source your compost from an entity that adheres to quality control standards. You can also get it tested to be sure that no issues exist with its use.
- Whether it may be a good idea to topdress with compost depends entirely on what type of field you have. On a sand-based field, the addition of compost would provide nothing more than a layer of organic matter that the sand-based field manager normally strives to avoid. But on a native soil field, particularly one on heavy clay, composts can be quite beneficial as they can improve the nutrient status and reduce the bulk density of the soil.
- One thing to consider with use of compost is whether a bulking agent may need to be mixed with the compost so that its application doesn’t cause drainage issues. (Wood chips can be used for this purpose). But sand may also be mixed with compost – ratios of sand to compost of 70/30 are quite common.
Internally porous inorganic materials
- Calcined clay, diatomeaceous earth and porous ceramics are components in several commercially-available topdressing products.
- Calcined clay has some interesting properties in that it can absorb and retain large amounts of moisture but also have a lot of airspace. These are manufactured products, so the cost is going to be much higher compared to sand.
- There different opinions about the merits of using calcined clay. On a native soil field, one school of thought is that use would be akin to adding clay to clay. But calcined clay has more desirable moisture retention characteristics compared to native clay.
- A logical place to consider their use is on a sand-based field because of their moisture retaining properties. But others argue that the sand-based field is under irrigation anyway. Regardless, there are many fields on which these products are used quite successfully as topdressings.
- Topdressing with nonsoil materials such as crumb rubber can be effective in softening the soil surface, reducing traffic stress and improving wear tolerance.
- Some recent research has been done to investigate ideal depths of application and particle sizes distributions of crumb rubber. Research has also focused on extending growing conditions during the fall on bermudagrass. Some of this research is in its preliminary stages, but look for management recommendations for use of crumb rubber to continue to evolve.
- Note that crumb rubber is much more expensive than sand and because of this, is often restricted to high-traffic areas of the field.
Recycling the soil you already have
- Recycling dressers are units that core cultivate and, in doing so, break up the soil in the core and redistribute it over the turf surface. Since the field’s own soil is used in this process, layering is avoided. Also, the process helps to break up layering that may already be present.
- Some of these units also contain sieves that will filter out courser material such as gravel. The field is intensely aerated during the process, which provides some short-term improvement for drainage issues.
- Another potential advantage if your field is weed-free is that the seed bank in your soil may be less than that of a topdressing material that is brought from off-site.