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MISSISSIPPI TURFGRASS: Barry Stewart, William Stark and Jay McCurdy

It all started with a contest/challenge from Cubico Sustainable Investments. Cubico is a global renewable energy infrastructure company, owning and operating large-scale solar farms. As part of its corporate responsibility program, Cubico created a competition for MSU College of Agriculture and Life Sciences (CALS) students to design potential agrivoltaic solutions to control vegetation on solar farms with diverse landscapes. William Stark, then a senior Golf and Sports Turf Management major at MSU, led a team of students from Dr. Jay McCurdy’s Turf Weed Management Class in authoring a research proposal that was funded by Cubico. William is now working on this project as part of his master’s degree under the direction of Dr. Barry Stewart. The research will be conducted at the Delta’s Edge Solar Project located in Carroll County near Greenwood, MS.

When completed, the Delta’s Edge site will have a capacity of 100 MW and be the largest solar installation in Mississippi. According to the publication NS Energy, the site will generate enough clean electricity to power 16,400 homes annually. The 652-acre site will be home to approximately 280,000 solar panels.

The focus of the research project will be to select the best grass or mixture of grasses to revegetate the area under the solar panels. This presents a challenge, as the solar panels will produce shade and may also alter how rainfall reaches the ground. However, the site is not totally covered with solar panels, and there is about an eight foot gap between the rows of solar panels. The panels pivot on their stanchions to allow them to follow the sun during the day (Photo 1). So, the grasses used must be able to thrive in full sun and in shade. This is why a mixture of grass species may be superior to a monoculture. The site is next to the Yalobusha River Levee so the grasses must also be tolerant of wet conditions parts of the year and dry conditions in other parts.

For Cubico’s interest the grasses should be low maintenance, as it will be difficult to mow under the panels, and maintenance operations have a potential to damage the panels. The likely mowing height for the site may be about six inches. Grasses that have high fertility requirements also usually have high mowing requirements and may not be well suited for this site.

Some of the grasses being evaluated at Delta’s Edge and our rationale for using them:

Common Carpetgrass (Axonopus fissifolius):

Carpetgrass is a slow-growing, medium green (and sometimes greenish yellow), coarsely textured turfgrass that is adapted to low-maintenance, general-purpose turf. It prefers full sun to moderate shade and performs well in wet, shady, acidic soils where other grasses may not. Carpetgrass looks similar to centipedegrass except that it produces a crabgrass-like seedhead, and centipedegrass has hairs along the edges of the leaves.

When I first came to MSU, and Dr. Goatley took me out to show me some carpetgrass, I thought, “man with a name like carpetgrass this must be one of the best grasses out there.” Then I was told it was a weedy grass at best and often something you wanted to get rid of. Through the years carpetgrass came up here and there. One year at the Golf Course Show Turf Bowl, the centipedegrass samples were actually carpetgrass (this was caught before it was used in the contest). Dr. Gregg Munshaw and Wayne Philley once presented a project to do carpetgrass breeding work to have a low growing native grass for highway right of way. A few years later many homeowners found out that much of their centipedegrass lawns were actually carpetgrass when the Scotts Company changed the active ingredient in Bonus S fertilizer from simazine to metsulfuron. I have encountered some stands of carpetgrass that were well kept and quite attractive. It is a niche grass that often thrives in moderately well drained to wet acid environments. These are the conditions we have at the Delta’s Edge site.

Why Carpetgrass at Delta’s Edge?

Seed is inexpensive [$8 per lb. Pure Live Seed, PLS (Pure Live Seed)] and is readily available. It is a native grass and is adapted to the conditions at this site. It has low fertility and maintenance requirements. Other than seedhead control, carpet grass has a low mowing requirement and, at the desired height of cut for this site, even the seedheads may not be an issue. Carpetgrass establishes rapidly with a germination time of four to seven days. We are testing carpetgrass alone, in a mixture with tall fescue, and in a mixture with centipedegrass.

Centipedegrass (Eremochloa ophiuroides)

Centipedegrass is often called a “poor man’s grass” due to its low mowing and fertility requirements, but if one considers the price of centipedegrass seed ($30 per lb. PLS) it is probably more of a “lazy man’s grass”. Centipedegrass is a slow-growing, coarse-textured, warm-season turf that is adapted for use in low maintenance situations. It also has a light-green color and spreads by stolons. One drawback to centipedegrass is slow establishment. An old saying about centipedegrass is “first it sleeps” (germination time of 21 days or more), “then it creeps” (slow growth in the first year), “then it leaps” (more rapid fill in the second year).

Why Centipedegrass at Delta’s Edge?

Seed is available, albeit expensive. Once established, centipedegrass has good turf quality for a low maintenance turfgrass. We are using centipedegrass in a mixture with carpetgrass. Mixtures like these were once sold as “Centiseed” in which carpetgrass was used as a nurse-grass for centipedegrass, and then the carpetgrass was outcompeted by the centipedegrass or removed with herbicides.

Turf-type tall fescue (Schedonorus arundinaceus)

Each semester in PSS 1313 lab, we take the students to the R.R. Foil Plant Science Research Center (North Farm) to look at turfgrasses. One stop is always the NTEP Tall Fescue test. Turf-type tall fescue is one of the best examples of the impacts of plant breeding we have. Kentucky 31 is included as a standard in this test and represents a starting point. Although not a turf-type tall fescue, K31 was a pasture cultivar that was mowed closely and was used as turf. Through the work of plant breeders, we now have dark green cultivars that are much finer in texture and have high turf quality. In a project we did with Mississippi Department of Transportation about ten years ago, we found that turf-type tall fescue did very well on roadsides, and if the mowing height was six inches or above, it would not be touched by a mower until flowering stage in the spring. Our NTEP tall fescue test on the north farm is in full sunlight, and it does very well each year. In most of Mississippi, tall fescue is used as a shade grass but our experience with the NTEP test suggests that modern turf-type tall fescue cultivars can thrive in the north Mississippi climate with minimal inputs.

Why tall fescue at Delta’s Edge?

Seed is readily available and inexpensive ($4 per lb. PLS). It establishes well from seed. It is somewhat shade tolerant. It has moderate fertility requirements and is otherwise low maintenance. It has proven to do well in Mississippi’s Highway 82 corridor. We are using turf-type tall fescue alone, in mixture with carpetgrass, and in mixture with fine fescues to enhance shade tolerance.

Seeded turf-type bermudagrass (Cynodon dactylon)

Bermudagrass is the standard for low maintenance areas in Mississippi. It has some drawbacks that may limit its effectiveness at Delta’s Edge. It is a full sun grass, so it may struggle with the shade of the solar panels. It has a relatively high fertility requirement to remain competitive. Without these inputs, its turf quality will suffer—it will be light green, prone to weed invasion, and may have decreased winter hardiness. Seed is moderately expensive (for high quality cultivars) but is readily available.

Buffalograss (Bouteloua dactyloides)

Establishment of buffalograss on MSU’s North Farm was once a struggle, but the seeded cultivar ‘Cody’ (and more knowledge) has changed that. Cody was included in two NTEP tests, and it has thrived to the point of expanding well beyond its plot boundaries. What have we learned? Buffalograss thrives in moderate to heavy textured soils and on low fertility (no more than 2 lbs. N per 1000 square feet per year). One drawback to buffalograss is poor shade tolerance, but research at a similar site in Texas suggests that buffalograss works well for solar farms.

In summary

Our two-year experiment at Delta’s edge will give us insights into how these grasses and mixtures perform in this environment. Our goal is to be able to make evidence-based recommendations for this and other solar installations in Mississippi and the larger Southeast. The next step will be to incorporate flowering forbs to provide pollinator habitat. •