February 2021 Ι Landscape Architecture Magazine
Republic Square in Austin, Texas, is one of the city’s most historic, sensitive, and heavily trafficked public green spaces. In the heart of downtown, it’s one of the original four public squares dating back to the city’s founding. In 1839, the city’s initial run of surveyed and platted blocks was auctioned off beneath what became known as the Auction Oaks. Recently revitalized by Design Workshop, the square is a broad public green and plaza outlined by native plantings and groves of trees, some of which are nearly 600 years old.
Matt Macioge, the director of operations for the Downtown Austin Alliance, which operates the park, wanted to protect this valuable place. He has a background in design and construction, so he could anticipate the typical array of maintenance issues, but with an added layer of complexity. “The plants within [these landscapes] are dynamic. They’re growing, they’re dying, they’re pollinating, they have seasonal changes and cycles,” he says. “You really need to be able to live and breathe with the plants with your operations manual.” Macioge says he wanted “world-class standards,” a maintenance regimen that would react and adapt to changes in both programming and ecology.
The task of moving Republic Square far beyond the standard “mow, blow, and go” fell to the Austin landscape architecture studio dwg. “From a landscape performance standpoint,” says Jason Radcliff, ASLA, one of the firm’s principals, it would be “the best park in town.” One thing Radcliff was certain of is that landscape performance starts with the soil. So, he would need new tools to monitor soil health, preserve nutrients, rehabilitate what’s been degraded, and hopefully come up with new processes and standards that could be adopted for all city parks.
But there wasn’t much there. “Our industry does not seem to be well served in terms of soil [and] plant tissue testing agencies or soil amendment products,” Radcliff says. “When discussing fertilizer application rates with vendors, they have plenty of recommendations for either farm crops or putting greens, and not so much for upper plateau sedges or successional woody plants. I’ve been struggling in trying to find out how landscape architecture fits in between growing soybeans or growing golf greens. I’m trying to [figure] out how we can fill our own void.”
Radcliff says that so far, the best soil health monitoring tool he’s found is a portable test kit called microBIOMETER, made by Prolific Earth Sciences, that measures soil biology and quantifies microbial populations and the bacteria-to-fungi ratio in soil samples. “The thing about microbes is that they’re very volatile,” Radcliff says, and the accuracy of the sample can be affected by temperature changes and long shipping delays. The test takes 20 minutes and uses a smartphone app, which makes it easily deployable on site. Currently, a microBIOMETER starter kit costs $135—each test is about $10. It’s not an exhaustive catalog of soil biology (it doesn’t measure protozoa or nematodes, for example), but compared to gold-standard carbon fumigation extraction tests that require toxic chemicals, cost $500, and can take a week to process, Radcliff says the test provides a reliable result at a fraction of the cost and time.
“With a test that costs $500, nobody has ever used it as a tool for guiding agricultural or landscape practice,” says Judith Fitzpatrick, a cofounder of Prolific Earth Sciences. Trained as a microbiologist and the holder of about a dozen medical diagnostics patents, Fitzpatrick (with the support of the National Science Foundation) invented the portable soil test with the soil scientist James Sotillo, who died in 2019, soon after the product was introduced to the market in 2018. Coinventor Brady Trexler developed the smartphone reader for the test.
The test works by taking a soil sample and mixing it with water and a packet of salt and detergent. When the soil separates from the microbes after 20 minutes, a few drops of water are deposited onto a test card. Testers take a photo of the card and analyze it with a smartphone app. The data that comes back includes the total amount of microbes in a sample and the ratio of bacteria to fungi, which the test determines by differentiating the pigment of different types of microbes.
“The soil biology is probably the critical component of overall soil health,” says Ted Hartsig, a senior soil scientist with the engineering and design firm Olsson Associates. He recently appeared on a reVISION ASLA 2020 panel on soil health with Radcliff and Paul Josey, ASLA, of Wolf Josey Landscape Architects. Healthy microbial populations in soil ensure nutrient exchange between plants and fungi, which provide minerals like phosphorus and nitrogen in exchange for carbon-rich sugars. These microbes also function as a communication network. When plants are stressed, they exude polysaccharides into the soil from their root tips, triggering microbes to start feeding plants organic compounds that ameliorate stress. And the presence of bacteria and fungi also indicates healthy levels of water filtration and carbon sequestration. Healthy microbes also aid soil structure, as they secrete a substance called glomalin that acts as an organic glue, binding clays and silts together to form high-quality soil structure. “The structure is actually built by the organic matter and the microbial community,” Hartsig says. “It’s a very intricately connected system where the microbes and plants work together to build its living environment.”
For its work at Republic Square, dwg. took five samples in September of 2019, two on the wide lawn and three in planting beds near trees. The soil with the most robust microbe populations was found closer to trees. In addition to being more heavily impacted and trod on, Radcliff says, the lawn’s lack of healthy microbe levels is likely because the turfgrass soil there is screened (which harms soil structure) and imported, and it receives more synthetic fertilizer that diminishes microbe populations than the planted areas near trees. In November of 2020, dwg. took another set of samples at the same five sites, this time testing for the ratio of bacteria to fungi in addition to overall microbe levels. This time, overall microbe levels had dropped dramatically, which Radcliff says is likely owing to seasonal variation, and the soil was dominated by bacteria. But the bacteria-to-fungi ratios reflected distance from the turfgrass green. The three sites closest to trees had the highest ratios of fungi. “Fungi levels,” Radcliff says, “are our real scorecard.”
“This is the best tool to tell us if we’ve got a problem or not in certain areas,” he says. “Now that they have the ability to show us what that ratio is, we’ll be able to monitor over time and see if we’re headed in the right direction. It’s going to be a lot of trial and error.”
To improve bacteria-to-fungi ratios and the overall microbe community, dwg. is planning to aerate the soil in turfgrass and planter areas in the spring. The firm may also use commercially available bioinoculants in some areas to propagate more strains of bacteria and fungi.
But as effective as it’s been so far for Radcliff, the test wouldn’t be able to pinpoint what those strains are. The test doesn’t determine exactly which species of fungi or bacteria are present, and this kind of information (obtained with more expensive DNA sequencing tests in a lab) could be important to landscape architects in some cases, says Meghan Midgley, a soil ecologist at the Morton Arboretum outside Chicago. “Some plants are more reliant on mycorrhizal fungi to get nutrients than other plants,” she says, while particular bacteria help certain plant species break down and process nitrogen. Most landscapes won’t need this granular level of detail, and microbial biomass in general is one critical factor among others. “It’s not that microbial biomass isn’t important,” Midgley says. “It’s that microbial biomass isn’t the only thing that’s important.” While there’s a correlation between microbe populations and the nutrients available for plants, she says, it’s still important to test for the actual nutrients and minerals, as well as pH values, moisture, soil structure, and more.
Prolific Earth Sciences plans to launch a project management platform that will allow users to upload data to the cloud so that users can pull reports on soil across multiple projects and devices. Next, the company plans to add an integrated GIS mapping function so that clients are able to create maps with layers of their soil biology data (which dwg. does manually today) in the app.
Investing in soil early and organically means fewer maintenance expenses later on. “The soil biology mediates that nutritional aspect,” Hartsig says. “We can manage the soils with fewer fertilizers, with fewer pesticides, and with healthier soils that will better serve the planet, rather than having to feed it inorganically or chemically or hydroponically.”
These blunt soil remediation tools can create complications down the line, such as phosphorus algae blooms, and they don’t offer the nuanced and responsive symbiotic benefits of fungi networks. Diagnostic tools can give landscape designers more granular knowledge of the specific conditions within soil that need to be addressed. For Radcliff, there’s an easy health care analogy at hand: “A doctor would never prescribe a medication without having some indication of our current health status.” More often, landscapes get the generalist “multivitamin approach,” he says: a broad range of fertilizers, and then you “hope for the best.”