By: Carl Schimenti, Urban Environmental Scientist
Scholastic sports have been underway – since March 9th – for quite some time in New York state. Notably for turfgrass managers, this contrasts with the ability for natural grass fields to handle field use this early in the year.
A single metric – Percent Turf Cover – is an excellent proxy for the entirety of field safety and quality metrics on natural grass fields. When percent cover is 100%, there is high confidence that athletes have sufficient traction during athlete-surface interactions and that the surface is not overly compact, i.e. hard. Percent Turf Cover is therefore a key performance indicator.
The growth rate of the grass dictates percent turf cover. As the grass grows more vigorously percent cover increases, and conversely as the growth rate declines, so too does percent cover. The main governors of growth rate are the following:
– Traffic = field use. As athletes use the fields, they wear the turfgrass plants down through their movement and compact the ground which slowly creates restrictive soil conditions for turfgrass to grow. As traffic increases, growth rate declines.
– Weather. Turfgrass physiology requires reasonable weather conditions for growth, most notably temperature. Photosynthesis – the biological process to produce energy in plants– is optimally conducted in most cool-season turfgrasses at 67F. The rate at which turf grows in relation to daily weather can be modeled using the PaceTurf Growth Potential model.
– Management. Growth can be encouraged through a variety of management factors, but most importantly through the constant application of new turfgrass seed (overseeding), and application of nitrogen fertilizer.
There exists a PaceTurf growth potential model which allows a general estimation of the potential for growth based on daily average temperature through output on a scale from 0 to 100%. A value of 50% or above indicates reasonable growth rates that can counteract the effects of moderate traffic. This model is an excellent tool to explain the reason that school fields across New York state are often plagued by imperfect, bare and low-quality natural grass fields in the Spring.
This is a slide I typically show to explain why spring in New York is a poor time to grow grass. This is the 18-year average growth potential curve for Ithaca, NY, showing that May 7 is the date where growth potential first crosses above 50%. Of course, 2/3 of the scholastic sports season has already occurred by then! This means the balance between growth and traffic is significantly tilted towards traffic, leading to significant decline in percent cover during the spring.
In contrast, the fall sports season is much more conducive to recovery under traffic. Fall sports begin August 18, meaning the majority of the fall sports season is spent well above the 50% growth potential threshold, which typically lasts until October 7th. I assure you the football teams in the fall are not getting special treatment, they’re just getting better grass growing weather!
If fields can begin the spring season with 100% turf cover, they may be able to sustain the early season traffic (assuming traffic is not in excess). But this is dependent on all the previous season’s maintenance practices. Often, school districts will annually lament spring field conditions, often leading to the decision to install synthetic fields.
Synthetic fields are a useful tool in many situations; however, I would caution school districts making the synthetic vs. natural decision to ensure they have whole-heartedly attempted to implement minimum field care standards before concluding they cannot manage natural grass fields for spring sports. So, before a district makes this decision, I would recommend they first implement the following minimum field care practices to determine if, in fact, they are unable to maintain satisfactory fields in the spring:
1. MOW at least two times, per week, in season
2. OVERSEED bare and high-traffic areas at least once per month, in season
3. FEED the grass with nitrogen fertilizer at least twice per year at a minimum of 0.5 lbs nitrogen per 1000 ft2.
4. RELIEVE compaction by aerating heavily trafficked and/or compacted areas at least once per year.
5. REST the fields with at least one rest period of 4-6 weeks to allow for recovery.
These minimum standards of care are just that: MINIMUM. If you would like to evaluate additional levels of care, you can find descriptive management schedules on our safe sports fields website.
Increasingly, school districts are facing opposition from their communities when installing synthetic turf for a myriad of reasons from concerns of PFAS contamination to athlete injury risk. This is an incredibly complex issue, and often there is no clear answer, but a reasonable attempt should be made to manage natural fields using the above minimum standards of care before deciding on alternative options.