We have received several questions recently about rolling athletic fields. What benefits, if any, does it provide? How often should a field be rolled? Does it cause compaction? Here are some thoughts on the practice of rolling and some tips on how to make the most of this operation.
Roller Types & Weight:
There are many types of roller - walk-behind, ride-on, or pull-behind (picture, left). Turf rollers should always have rounded edges, to prevent damage to the turf. Rollers come in all sizes and weights, but are typically 300-2,000 lbs in weight or greater - this equates to approx 3-15 lbs per sq.in. (psi) load applied to the soil surface and is similar in weight to vehicular traffic like ride-on mowers. While there is no set weight for athletic field rollers, on native soil fields the maximum recommended weight is 1 ton (2,000 lbs) (Minner 2005). The weight of a roller can be increased by filling the roller with a material like water, sand or cement.
How Much Stress is Applied to Soil?
As mentioned above, the action of a roller is similar to that of vehicular traffic (e.g. ride-on mowers). The stress at the soil surface is proportional to tire pressure, or psi. Therefore, a roller or mower with tires inflated to 15 psi will apply 12-15 psi pressure to the soil surface. What's also interesting to note is that the force applied dissipates as a function of depth. For higher loads, the stress penetrates more deeply into the soil. How much stress a certain soil can withstand depends upon many factors. In particular, a soils' ability to resist compaction depends upon soil texture (sand or native soil) and moisture content
Benefits of Rolling:
* To smooth out uneven surfaces after winter heave or heavy traffic. Rolling cannot rectify poor grades, but is used to address minor surface undulations
* To produce a firm surface that would be considered "faster". Rolling is a common practice in golf green & soccer field management to increase speed short-term (hours)
* To produce a firm surface critical for those sports that require ball bounce, such as tennis, cricket, & baseball
* Rolling is often used on newly seeded or sodded turf areas to aid turf:soil contact and speed-up establishment
* Mowing patterns, typically created by the rear roller on a cylinder mower, can also be achieved by using a roller
* There have been some research reports of rolling reducing disease incidence, such as dollar spot, on golf greens. This is directly related to the use of lightweight rollers used first thing in the morning, whereby the roller is helping to remove dew/guttation water from the leaf tissue.
Issues Associated with Rolling:
* Rolling does not improve turf quality. In fact, over use results in turf thinning and quality is significantly reduced
* Soils that are wet &/or frozen are susceptible to surface compaction. Over use of rollers will also result in surface compaction. It is critical that rolled fields are regularly aerated
* Soils that are too dry will not benefit from the impact of rolling. Furthermore, if the turf is wilted or dormant it will be severely stressed and may die. Rolling should only be carried out if grass is actively growing
* Fields with 100% grass cover and a moderate thatch layer are less likely to be affected by rolling as a method to increase field "speed"
* Never roll fields that have disease problems, particularly infectious diseases like gray leaf spot, pythium, or brown patch
This is a decision that should be made by the field manager & coach on a field-by-field basis. Factors such as athlete safety & playability, soil moisture, recovery time and turf quality all come into play. As a general rule of thumb, rolling should only be carried out "as-needed", not routinely. This may be once per year in the spring (after winter soil heave) or several times during the playing season to keep the field safe & playable if grass cover is lost.
Lastly, keep in mind that athletic fields are already prone to compaction, so any rolling that is carried out should always be counter-balanced by a strong aeration program.
Ref: Minner D., Just Rolling Along, Sports Turf magazine, September 2005, p.50