Growing pains? U of MN’s St. Paul soil testing lab to the rescue

Frederick Melo, Pioneer Press
Updated ·5 min read

Anxious about the rueful state of his peas, radishes and onions, Rod Marquardt arrived at the University of Minnesota’s soil testing laboratory with two lunch bag-sized containers of dirt.

“We’re just trying to figure out if it’s too much compost or what’s going on with our soil,” said Marquardt, who tends both his Stillwater lawn and a community garden plot.

As far as Marquardt is concerned, he went straight to the top to get his soil analyzed. The St. Paul facility anonymizes its testing, treating walk-in samples with as much care and prestige as those involved in an academic study or commercial agriculture. In fact, the Dudley Avenue laboratory on the U’s St. Paul campus is the only soil testing lab in the metro area certified by the Minnesota Department of Agriculture.

Residents can opt for a basic $19 analysis, letting them know within a matter of days how much organic matter, phosphorous, potassium and lime resides in their soil, as well as recommendations for the right type and amount of fertilizer.

With an eye toward environmental impacts, the lab’s scientists have discouraged the “if a little is good, a lot must be better” approach toward fertilizing lawns and gardens in favor of more surgical applications.

“The soil test is the place to start when you’re growing anything, so you don’t end up over-fertilizing, which ends up in the Mississippi River,” said Andrew Scobbie, campus operations manager with the Minnesota Agricultural Experiment Station.

Additional soil tests, available a la carte, can identify lead and micronutrients that are usually the realm of crop professionals. Those tests include soluble salts ($8), lead ($20), sulfur ($8), nitrates ($8), boron ($8), calcium and magnesium ($8), and iron, zinc, copper and manganese ($14).

An uptick in interest in urban gardening during the dog days of the pandemic has kept the soil lab especially busy, with more than 6,100 samples from lawn, garden, farm and field dropped off last year, compared to some 4,500 annually in years prior. That’s on top of testing some 25,000 research samples, much of it generated by U academics and other Minnesota state colleges and universities, with some samples sent in by out-of-state research institutions.

“It makes us of value to the academic community, just like to the general community,” said lab manager Keith Piotrowski, noting the lab’s only advertising has been through word-of-mouth or on the U website.

An especially busy time amidst year-round demand

Now is an especially busy time for the soil lab, given climbing temperatures, though large research jobs keep their scientists occupied year-round.

“You never know what’s coming in the door,” Piotrowski said. “The spring soil test rush is overall probably a quarter of our annual business, and half of that comes within six weeks of snow melt.”

Over the years, the lab has serviced florists and greenhouses from Texas to Hawaii, and even criminal investigators attempting to match soil found in the trunk of a car — next to a dead body — with the soil by a spouse’s driveway. And it’s not just soil that cycles through the soil lab.

The lab, which employs seven full-time staff, two part-time professionals and as many as six undergraduates at a time, handles plant samples, water samples and even fungus, dental amalgams and urine for a cancer study.

For farmers, the lab asks what the last crop grown on the site was, as well as the crop before that, using some 61 different crop options to help render recommendations for an optimal grow. A blueberry is not a soybean, and each draws different amounts and types of nutrients from the soil, leading to different recommendations as to how to replenish the dirt for each crop.

“There’s uncountable amounts of potential recommendations,” Piotrowski said. “Do you need 2 pounds of phosphorous per 100 square feet, or 100 pounds per acre? It’s a question of scale.”

It’s also a question of maintaining a soil testing database that can handle some 7,000 potential inputs and an exponentially larger array of potential outcomes. The current database, erected around 1997 or so, is “held together by by bubble gum and bailing wire,” quipped Piotrowski, who said plans call for a full overhaul. “If you change your mailing address, it might crash.”

From microwaves to ancient alchemy

So how does one test soil for potassium levels, anyway? The two-part answer is A) very carefully and B) with a flame atomic absorption spectrometer, of course.

That’s not to be confused with a manual colorimeter, the device that displays soil pH, or acid levels, on a color spectrum, or the flow injection analyzer, which might yield a rusty red liquid as it tests for chloride. The lab’s four rooms hum with equipment that parse soil any number of different ways to get at its underlying composition.

The atomic spectrometer harkens to ancient alchemy, searing away a soil sample with open flame in an enclosed space at temperatures approaching the surface of the sun. Light emitted at a specific wavelength passes through the fire, creating patterns that can be plotted on calibration graphs, revealing concentrations of specific nutrients such as potassium.

Other tests rely on microwave technology, while still others growl and gurgle as they spin plant samples through a high-speed carousel heated to at least 900 degrees Celsius. The latter is a test for elemental sulphur, a once-dreaded emblem of acid rain (or hellfire) that’s now coming up in short supply in agriculture. Like anything else in life, too much or not enough can be detrimental for growers.

The soil lab has occupied its present site since 1985, and underwent a $3.2 million renovation in 2016 that temporarily scattered operations to various corners of campus.

“Ever since then, things have been trending up,” Piotrowski said, noting the lab has no advertising budget yet still commands healthy interest from professional growers, researchers and everyday gardeners like Marquardt.

“It’s a great service, if we can educate more people,” Marquardt said.

Testing info at soiltest.cfans.umn.edu.

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