Q: Our high school football field has turfgrass discoloration localized to the places where the numbers and hash marks were painted during the season. Soil analysis from the painted and non-painted areas were similar except for pH and calcium levels. The non-painted areas had a pH of 5.8 and the painted area pH values ranged from 7.1 to 7.5. Do you have any recommendations on how to deal with this issue?
A: The sample analysis provided great diagnostic data, so I’ll start by giving accolades for their sampling approach. In this case, they independently sampled multiple problem areas and collected a composite sample from non-problem areas. These were then analyzed so that results could be compared among sample locations. In this case, the sampling strategy employed provided an indicator of what was causing the symptoms.
Sampling strategy can be very important for proper diagnosis of problems. For example, consider a large dead patch of turfgrass that may have succumbed to a disease. A first reaction may be to sample from the middle of the dead patch and sample in a healthy area of turfgrass. But the fungi that caused the patch has already moved out of the dead grass, so sampling the middle would not be useful for diagnosis. The margin where the healthy and unhealthy turfgrass meet is the zone where pathogen activity is greatest, so it would be better to take a sample from the leading edge of the damage. In other scenarios, such as searching for immobile nutrients or pesticides, sampling depth in soil may be important.
Paints commonly contain calcium carbonate, the same base ingredient used to increase soil pH in agriculture lime. Even calcium carbonate applied within paint can have a liming effect on soil pH. But there are white athletic field paints formulated with alternative pigments (e.g., titanium dioxide) that do not alter soil pH. As with most compound products, ingredients can influence short- and long-term performance of the product, but may also influence the cost of the end product.
In addition, there are paints designed for application to natural grass. “House paints” and paints for synthetic turf are more likely to contain ingredients at concentrations that may not be safe for turfgrasses. So be sure to select paints that are designed to be applied to natural grass.
Following application, ingredients in the paint may move into the soil profile. Some components of paint are more soluble than others; whereas others may accumulate in the soil profile. I have seen the grass surface removed from a football field, with all the lines and logos still visible on the bare soil. This build-up can have antagonistic effects in the soil, which can result in off-color turfgrass. The directed process used for painting numbers and hash marks often concentrates greater amounts of paint per unit area compared to yard lines. This is probably why the symptoms are showing up in these areas and not across all the painted areas.
If not managed appropriately, paint can build up and impede water infiltration or reduce the uptake of plant nutrients from physical and chemical reactions. A high soil pH can limit the availability of nutrients like iron, manganese and phosphorus.
To help prevent issues, it is best to core aerify these painted areas to open up channels through the soil profile. It is also advantageous to backfill aerification holes with an appropriate sand or soil to keep these channels open and dilute paint residue. These practices address the chemical and physical problems associated with paint buildup in the soil. Managers at some facilities prefer to cut out and re-sod the numbers or logos every few years to remove paint build-up. I do not suggest field managers try to chemically reduce soil pH in these localized areas with products such as elemental sulfur.
Grady Miller, Ph.D.
Professor and Extension Turf Specialist
North Carolina State University
Questions?
Send them to Grady Miller at North Carolina State University, Box 7620, Raleigh, NC 27695-7620, or e-mail grady_miller@ncsu.edu
Or send your question to Pamela Sherratt at 202 Kottman Hall, 2001 Coffey Road, Columbus, OH 43210 or sherratt.1@osu.edu