One of the many things that complicate the job of an athletic turf manager is that in most cases, not all of the turf on a given property is grown under exactly the same conditions. Whether it’s variations in the soil, such as compaction, or areas of localized dry spot, or things such as shade or proximity to heat sinks, the turfgrass microenvironment tends to vary. Our goal is for turf to be both functional (provide a safe surface) and uniform in appearance.
Microclimates or microenvironments, as the “micro” part of the name implies, are localized variations that occur on a small scale, which can result in either a change in the appearance of the turf or the need to alter management practices. There is some variation in how the term is utilized. In some instances, the term micro is used to refer to the area immediately surrounding an individual grass plant or seed. In other instances, and for this month’s column, I’m using the term to describe changes in climate on a small scale (ranging from many feet to within the confines of your property).
Some things that can cause microclimate variations include buildings, landscaping or bodies of water. These attenuate either the temperature or the amount of light the turfgrass receives. Further complicating this is that seasonal variations will interact with things like buildings so that, for example, the shade cast by a tree or a building is different in June than in October.
Management practices can also affect the microclimate. For example, grass mowed at a lower height will have different evaporation rates compared to higher-cut turfgrass on the same property.
Regardless of the cause of microclimate variation on your property, it’s a good idea to have these areas mapped out. You can then develop strategies and make any adjustments to your management calendar in order to effectively deal with them, resulting in more uniform and functional turfgrass throughout the complex.
When I think of shade, I usually think of trees. Since we don’t plant trees in the middle of athletic fields, it would seem that this shouldn’t be much of a concern for a field manager. But many athletic complexes have trees surrounding fields (Figure 1). Shade may also be cast by structures around the field, such as stadium seating.
Grass needs sunlight in order to survive. While grasses have some capacity to deal with shaded conditions, and this varies considerably among species, they mostly prefer full sun. Plants have a sophisticated way of sensing shade, and when they do, they’ll alter their physiology, basically in an attempt to outgrow whatever it is that is blocking the light (Figure 1, middle image at top). This is usually at the expense of things like roots and leaf structure that make the grass tolerant of traffic. What is interesting about turfgrass response to shade is that the type of shade can have a big impact on the severity of the problem.
Plants can sense the quality of light the leaves receive, which is referred to as the red/far-red ratio. Tree shade has more far-red light (because the tree absorbs the red light). The red/far-red ratio alteration is more harmful to the grass than the reduction in light quantity. Grass tends to grow better under shade cast by a structure compared to shade at that same intensity that is cast by a tree.
Unless you’re managing shaded turf caused by a large stadium built for a professional team, artificial lighting is probably not an economically viable option. But there are some management strategies that can help. If possible, you can switch to a more shade-tolerant turf. If it’s a lower-maintenance field or the areas surrounding the field, tall fescue may be a better choice. If it’s a lightly trafficked area, then you could consider fine fescue.
Another important point when choosing a turfgrass for shade tolerance is that there can be a great deal of variation among cultivars of the same species. Having said this, Kentucky bluegrass and perennial ryegrass, for the most part, don’t perform as well in shade.
Figure 1 shows the effect that tree row orientation can have on shade patterns and the turfgrass growing beneath them. If possible, try to have rows of trees oriented north to south instead of east to west. That way, the turf under the trees will be exposed to some full sunlight during the day and no alterations to management may be needed. Grass on the north side of an east-west line of trees will be in the shade all day, which may result in thin patches of turf or encroachment by weedy species, such as annual bluegrass. If you have the ability to influence species choice during installation, the species of tree can have a big impact on your ability to maintain consistent turf under it. Honey locust, as an example, tends to provide a lighter, more filtered shade. In contrast, species like Norway maple produce dense, heavy shade that turfgrass doesn’t grow well under.
For turfgrass under shade, one of the most important cultural practices you can do is to raise the height of cut, even by a little bit, in order to improve the plant’s capacity to absorb light. Some turfgrass managers respond to the thinning observed in shade by increasing water and fertility. But, based on research, you should reduce water and fertility by about 50 percent on shaded turfgrass.
Other factors that contribute to turfgrass decline in shade are the decrease in wind and increase in relative humidity, compared to sunny areas. (Under these conditions disease pressure can be more severe.) You may need to increase your use of fungicides in areas that are densely shaded.
Culturally, you can reduce disease pressure by thinning some of the branches of the tree in a way that will increase air movement or increase the amount of time that the grass is in full sunlight.
Like shade, sloped land is not something you’d typically expect to find in the middle of an athletic field. But this may be present within the confines of an athletic field complex or in high-visibility areas immediately adjacent to the field (Figure 2). Slopes can alter the microenvironment in a couple of different ways.
One potential difference on slopes is temperature and the other is soil moisture status. South-facing slopes tend to heat up and dry out more quickly in the spring, compared to flat ground or a slope that is facing north. This can often result in a difference in timing of crabgrass germination or dandelion bloom by up to a couple of weeks. Slopes may also have different irrigation requirements.
The best strategy to deal with changes in weed timing is to document the differences so that adjustments to application schedules can be made in subsequent years. As far as the differences in soil moisture status caused by slopes, one solution is to have a set of irrigation heads that is specifically zoned for the sloped area. Depending on the severity of the slope, runoff is more of a concern, which means that the delivery rate of irrigation needs to be adjusted down.
If you have access to a point-and-shoot thermometer, then take a few minutes to document the differences in the temperature of the turfgrass next to asphalt, concrete or a baseball infield compared to the middle of the field. The difference can be quite dramatic (10 to 20 degrees or more).
This is going to result in the same susceptibility to excessive drying and changes to weed prevalence (Figure 3) as was discussed on south-facing slopes. The image of dormant turf next to an infield skin isn’t something that you typically see during summer months. But some complexes, such as those on college campuses, may have intramural fields that aren’t used on a daily basis during the summer. This is more commonly a problem when turfgrass is located adjacent to either a walking path or even synthetic turf. Regardless of the source, the issue is the same. Sustained heat stress results in increased soil temperatures, which, over time, results in either dormancy or decreased production of roots.
When turfgrass is grown adjacent to heat sinks, adjustments need to be made to the irrigation schedule to compensate for the higher temperatures and, potentially, more rapid drying of the soil. If possible, you can also consider syringing these areas during periods of excessive heat. Where cool- season turfgrass is grown, syringing can reduce the canopy temperature by several degrees for a period of a couple of hours, which in many instances can be enough to get the turf through the day without excessive wilting.
One mistake that is sometimes made on these areas is to overwater them. This can result in decreased rooting, making the grass more susceptible to other issues. Since the soil in these areas is warmer, this microenvironment is going to favor warm-season weeds, such as crabgrass, over cool-season turfgrass.
ALTERED SOIL CONDITIONS
Areas where turf is grown in compacted soil require adjustments in management in order to favor the turfgrass. While you want to take steps to alleviate the compacted conditions, this is a long-term process.
Water doesn’t infiltrate as rapidly into the soil, and drainage is impeded. In addition, certain weed species, such as goosegrass (a summer annual grassy weed) and knotweed (a cool-season annual broadleaf weed) are favored over turfgrass under these conditions.
The rate of irrigation delivery needs to be adjusted down so that the delivery rate doesn’t exceed the reduced infiltration capacity typical of these areas. In addition, areas that are slow to drain should be mapped out so they can be avoided by heavy equipment in the days following large rain events. Mowing a saturated area, such that muddy wheel tracks are visible, causes a significant amount of damage to a soil’s ability to drain properly.