Rooted in St. Louis: ‘Dirt’ is a dirty word
The quality of being rooted, or “rootedness,” is a particular strength of the kingdom Plantae. While we animals are always moving, uprooted and transplanted daily, trees remain in their birthplace for a lifetime. A plant does not exist without its soil.
I have covered many plants in this series, but rarely have I mentioned their planting medium. Soil, known to some farmers as black gold, is as much a necessity as water, but is nowhere near as simple. Beneath your feet lives a complex chemical stew of geologic and organic components, of swimming microbes and rhizomatic networks.
This diverse microparticulate gumbo is the crossroads of many sciences, as Washington University Professor of Earth and Planetary Sciences Jeff Catalano explained.
“There’s a lot more plant inputs in soils than geologists normally think about, and a lot of fungi that geologists don’t think about,” Catalano said. “There are burrowing animals, like worms. As a geologist, though, working on problems associated with our surface, I had to be trained in an interdisciplinary way.”
Catalano is not a soil scientist by training, but knew the topic well enough to offer a course after coming to WashU in 2007. While studying in graduate school, he saw soil science had the potential to connect students of diverse academic backgrounds. Soil is not a common curriculum outside of agricultural schools, so initiates of the loamy mysteries enter with misperceptions and anti-soil biases.
“We have a rule in my class that soil is not dirt, and you can’t call it dirt,” Catalano said. “Dirt is the stuff you sweep up and put in a dustpan, while soil is…the skin of the earth. When you go outside, it’s the stuff we think of as dirt, below the long grass or in the forest, but soil is really a complex, active, dynamic system.”
The development of that dynamic system extends across millennia; take, for example, our own St. Louis soil, the formation of which began roughly 15,000 years ago. Glaciers then still extended to northern Illinois and as they receded, they crushed up rocks into a “loess” (pronounced low-us) the consistency of flour, which blew down into Missouri.
This non-organic loess base was then colonized by small plants laying down the soil’s first roots, anchoring it and exuding organic compounds. As those plants died, their leaves and twigs became food for a burgeoning population of soil microorganisms. These organics and microbes alter the nonorganic base, and the soil becomes layered and structured, varying across depth ever-deepening through root penetration.
Yet 15,000 is nothing in soil years; soils in the Southeast U.S. are hundreds of thousands of years old and those in the Amazon are over a million.
Soil is a non-renewable resource, at least on a human timescale, which makes it all the more important to protect.
“Soil sustainability,” Catalano said, “doesn’t get talked about much.” Extensive industrial agriculture, he explained, depletes soil resources at an unhealthy rate. “When we do that sort of agriculture, no matter how we do it, we cause soil to erode off. We lose some of it, and we lose it faster than it naturally regenerates. When we look at those rates they suggest that in the future we’re going to have a problem.”
Soil-degrading farm practices have caused major crises in the past.
“The Dust Bowl was a human-made disaster,” Catalano said. “We were plowing lands we shouldn’t have touched.” Native plants of the arid Midwest, especially deep-rooted prairie grass, had previously prevented such catastrophes, “but when you plow it, there’s nothing to hold the soil in place, and when you have a drought, nothing grows and so you have bare soil that just blows away.” While irrigation has prevented another Dust Bowl so far, intensive farming continues to erode and degrade soils.
Protecting the soil is not only important for agricultural systems, but also for preventing climate change. Healthy soils are carbon sequesters which reduce atmospheric carbon dioxide.
“Soil itself holds more carbon than all of the atmosphere and all land vegetation,” Catalano said. Much of the carbon is in the form of dead plants, fungi and microorganisms, while some is held in air pockets. Yet soil’s climatological implications go far beyond carbon dioxide.
Wetland soils, as a major source of the greenhouse gas methane, are of particular concern. Catalano himself researches this topic, as it relates to his expertise in heavy metals. Low-oxygen wetland soils are inhabited by ancient microorganisms called Archaea, which intake heavy metals like nickel and cobalt to construct enzymes.
In laboratory settings, they have been found to “grow best in concentrations of nickel that are so high, we would consider them contaminated drinking water,” Catalano said. This led him to hypothesize that wetlands subject to industrial runoff might produce more methane. His ongoing field research has revealed this to be a rich and complex topic.
Catalano also advises the St. Louis City Parks Department on soil contamination by lead, another heavy metal. Decades of lead accumulation from paint and gasoline have accumulated in the loose topsoil of city parks, now a primary vector of lead exposure for urban children. The solution, it turns out, is as simple as burying the old soil with some new, preventing lead particles in soil from entering food and airways.
In soil science, the deeper you dig, the more you find. “Not all soils are the same,” Catalano said. “Just because it’s brown stuff scooped from the ground doesn’t mean it works well.”