How Did Iowa Get Such Great Soil?
An overview of how Iowa's amazing soils developed--and a cautionary tale about protecting this heritage
Iowa is blessed with some of the world’s most fertile soil. Ever wondered why? It goes much deeper than the prairies that once covered the state.
“Iowa’s soils start with glaciers that moved across this region thousands of years ago,” noted Dr. C. Lee Burras, a professor of agronomy at Iowa State University. “Glaciers are huge masses of flowing ice that have shaped our world.”
Thousands of years ago, Iowa was covered by a series of glaciers. Glaciers are akin to a river with a turbulent current, Burras added. “The bottom of all that moving ice breaks rocks free. Rocks break apart. When the glaciers got far enough south of the North Pole, they started to melt, and all that sediment dropped out.”
The most recent glacier that pushed into Iowa (roughly 15,000 years ago) created the Des Moines Lobe, which covers all or parts of 22 counties in north-central, northwest, west-central Iowa and central Iowa. The level to gently-rolling land in the Des Moines Lobe is intensively cropped.
In the world of glaciers, the one that formed the Des Moines Lobe was a tiny bit of ice. “From a human perspective, however, it was huge,” said Burras, who discussed the history of Iowa’s soils during an Iowa Learning Farms webinar earlier this year. “The Des Moines Lobe covers about 12,000 to 14,000 square miles. In certain places, it’s well over 100 feet thick. That tiny bit of ice left us more than 800 billion tons of ground-up sediment that help make our soils so productive in parts of Iowa.”
Nurturing life, building soil
As glaciers moved into the region that would become Iowa, they kept bringing new material that could nurture life and build soil. The glaciers stopped in Iowa thousands of years ago, because this is the “midway” point between the North Pole and the equator, Burras said. “Iowa is where glaciers fall apart.”
What occurred “off glacier” is also key to understanding Iowa’s soils, Burras added. Every time a glacier pushed into Iowa, it would ablate (meaning a lot of melting occurred), so there was a huge discharge every summer. “Think of a nearby stream you can hop across,” Burras said. “Back when a glacier was feeding it, that stream was the size of the Mississippi River.”
That water carried boulders, rocks and other minerals. This flow froze in the winter. Sand and gravel would fill the valleys on the landscape. As intense winds blew across Iowa, this whipped that material in the valleys upward and deposited loess on the upland. In western Iowa, soils like Galva, Primghar and Sac were formed from loess blowing northeast.
“The most recent glacier, which created the Des Moines Lobe, left about 600 billion tons of loess in Iowa,” Burras said. “If you go over to Sioux City, there’s well over 100 feet of loess in that area.”
Why isn’t New England part of the Corn Belt?
The glacial boundary (the region representing the farthest advance of a glacier that has retreated) corresponds with America’s Corn Belt. Glaciers also covered New England, Burras noted, so why isn’t that area part of the Corn Belt?
Those glaciers pushed over a different type of bedrock in New England. “They didn’t pick up the minerals that are essential for crop production,” Burras explained. “Our glaciers overrode a lot of limestone and feldspars (groups of minerals that contain calcium, magnesium or potassium). Those rocks the glaciers ‘stole’ from Canada had exactly the right materials to turn into great soils in Iowa.”
From a soil classification perspective, Iowa has six soil orders, 10 major soil regions and 507 soil series (including locally-named soils like Fayette or Tama). Yet it all comes down to two major groupings of soils—mollisols, which correspond to areas that were prairie ecosystems for thousands of years, and alfisols, which occur where there were major forest areas for thousands of years, usually near river valleys.
“Both mollisols and alfisols are incredibly productive soils naturally,” Burras said. “They are inherently fertile throughout the soil profile. It all goes back to the geology of the parent materials of those soils.”
Parent material can include glacial till in the Des Moines Lobe (where Clarion, Nicollet and Webster soils are common), deep loess (in the Loess Hills) and alluvium (in the Missouri River Valley).
“The glaciers gave us our fundamental landscapes and the fundamental rooting material that plants grow in,” Burras said. “As that rooting material weathers, it releases nutrients naturally. Anytime you expose fresh sediment, living organisms capitalize on the landscape.”
Those living organisms range from soil microbes to plants. As these organisms grow and die, this adds organic matter and influences the plants that can grow in the soil. Those plants have changed through the centuries. Once the glaciers receded and loess stopped being deposited, four major climate-ecosystem “waves” progressively moved across the region that would become Iowa, including tundra/conifer forest to deciduous forest to prairie to deciduous forests, Burras said. “The world never stays the same. The landscape and soils evolve, due to the weather, the vegetation, and the way the weather and vegetation interact with the geology.”
“We See What We Know”
It’s easy to forget this history, however, and overlook these changes, since “we see what we know,” Burras said. He cites the example of an aerial photo taken northwest of Jewell in Hamilton County.
He points out that there’s a big blob in the middle of picture that looks quite different from the surrounding landscape. That large blob was Lake Cairo, which was drained years ago. The former 1,300-acre former lake is now farmland that grows corn and soybeans, according to Prairie Rivers of Iowa. Lake Cairo is one example of countless drainage projects that shifted the ecology of Iowa, setting into motion changes that would affect the state’s communities, economy and the environment for decades to come.
“We often think something doesn’t matter if we can’t see it,” Burras said. “When I take people out to where Lake Cairo used to be, for example, they only see crop fields.”
Burras acknowledges that land in Iowa is farmed intensely, and the goal is to farm it even more intensively in the future. “I always have to ask myself, ‘How important is natural pedology [soil science focused on the formation, nature, ecology, and classification of soil], when most people in Iowa see soils as economic features that are to be intensely managed?’”
Most people who have questions about soil in Iowa ask Burras about the Corn Suitability Rating index (CSR2), which provides valuable insights into soil’s potential productivity. “People want to know how good or bad a soil is for growing corn or other crops,” Burras said. “They also want to know how can they manage that soil to keep yields going up.”
To increase yields, farmers change the soil, said Burras, citing tons of manure, nutrients and other amendments that farmers have added to the soil through the decades. “We’ve been intensely modifying our soils in Iowa for 190 years, and we’re going to keep modifying the soil. Iowa has incredible soils that continue to change.”
Growing a Revolution: Bringing Iowa’s Soil Back to Life
Now let’s switch gears a bit. As someone who grew up on a farm and still helps manage that farm (in Calhoun County), I’ve become more interested in learning how to protect the soil. My 28 years as an ag journalist have also exposed me to some of the best minds, from ecologists to historians to agronomists, who understand the soil at a deep level. Healthy soil, healthy planet.
Soil is truly the essence of life. Soil has been called a reservoir of wisdom, patiently teaching us the ways of growth and resilience. I love the quote (which I’ve seen attributed to photographer Robert Adams) that “The dirt beneath our feet holds the stories of our ancestors and the promise of our future.” I would only add that “dirt” should be changed to “soil.” Dirt is what you get on your clothes and hands while working with the soil, which is a living microbiome filled with beneficial fungi, bacteria and other helpful microbes.
I’m so grateful that I had the chance to hear Dr. David Montgomery speak in Ames a few years ago. The wisdom he shared has stuck with me all these years. Here’s what I wrote back then about Montgomery’s presentation. I hope you find it valuable, sobering, thought-provoking and hopeful, as I did.
From a distance, the global soil map with its red, yellow and white splotches projected on the big screen in Benton Auditorium in Ames is somewhat pretty, almost like an abstract piece of art. But a closer look reveals a shocking story that hits close to home.
“The soil in one fourth to one third of the world's agricultural lands has been degraded in ways that could impact agricultural productivity,” said Dr. David Montgomery, a professor of earth and space sciences at the University of Washington in Seattle and author of “Dirt: The Erosion of Civilizations,” “The Hidden Half of Nature: The Microbial Roots of Life and Health” and “Growing a Revolution: Bringing Our Soil Back to Life.”
Iowa is among the regions of the world with “very degraded soil,” according to the map from the United Nations (UN) that Montgomery shared during his March 13 presentation at the 2019 Iowa Water Conference in Ames.
If this statement seems implausible, maybe it’s because soil degradation usually happens at a slow pace. Humanity loses another 0.3 percent of our global food production capacity each year to soil erosion and degradation, according to the UN Global State of the Soil Assessment in 2015. “It’s hard to get excited about 0.3 percent, right?” Montgomery asked. “That’s what most of us are earning with our savings accounts.”
Little things can add up, however, given enough time. In 100 years, that 0.3 percent every year equates to 30 percent, he added.
“Soil is the fundamental resource on which human civilization depends. If you study history, there’s a clear connection between degraded soils and impoverished human societies.”
Erosion of Civilizations
Soil erosion and degradation played a role in the demise of numerous ancient civilizations, including Neolithic Europe, Greece, Rome and Central America.
Cycles of erosion in ancient Greece began in the Bronze Age after the introduction of plow-based agriculture, Montgomery noted. The Greek philosopher Plato (428-347 B.C.) saw this play out, noting “the rich, soft soil has all run away, leaving the land nothing but skin and bones.”
America is not immune from the lessons of history. The Dust Bowl blew away tons of topsoil in the Southern Plains region of the United States during the 1930s. “Tillage is a slow-motion catastrophe playing out on the landscape,” Montgomery said.
The soil organic matter content of many soils in North America is only about 50 percent of the level present at the time they were converted from forests or prairie to farm lands, according to a 2015 report on North American soil degradation published in the journal Sustainability. While Montgomery isn’t convinced that 50 percent is the real number, he’s certain the actual number isn’t small.
He cited America’s Piedmont region from Virginia to Alabama, where 4 to 10 inches of soil loss have occurred since the first colonists settled the area. “I’ve been to parts of the Carolinas where the subsoil is at the surface, meaning farmers have to use lots of supplements to grow a crop. Want to impoverish your descendants? Soil degradation and soil loss will do it.”
Think of Soil as a Bank Account
How fast is soil eroding from farms? Montgomery says 1. 5 millimeters a year, meaning it takes less than 20 years to erode 1 inch of soil. How fast does nature make soil? About 0.02 millimeters a year, meaning it takes more than 1,000 years to make 1 inch of soil.
“Think of soil as a bank account, where soil erosion is like spending money,” Montgomery said. “You can drive the balance to zero much faster than you can replace it.”
Restoring Life to the Soil
With all these realities, is soil restoration possible? “Yes, and it can happen remarkably fast,” said Montgomery, who witnessed this first-hand when his wife, Anne Biklé, transformed an unproductive, barren lot on their property in the Seattle suburbs into a thriving, lush garden, thanks to manure from the local zoo and a focus on building soil health.
“’The soil is hungry—let’s feed it,’ is Anne’s motto, and I believe it,” Montgomery said.
This doesn’t mean the farmer or gardener has to do all the work. “We just set the table,” added Montgomery, who noted the magic lies in the soil food web, which consists of bacteria, fungi, nematodes and millions of other soil microorganisms. “These microorganisms build soil health from the inside out.”
Enhancing the soil food web and increasing organic matter involves (1) minimal disturbance of the soil; (2) growing cover crops and (3) diverse crop rotations. “Ditch the plow, cover up and grow diversity,” said Montgomery, who noted these principles can be applied anywhere, on organic or conventional farms, with or without genetically modified crops.
Regenerative Ag in Action
Montgomery cited several examples of regenerative agriculture transforming the soil across America and around the globe, including the Dakota Lakes Research Farm east of Pierre, South Dakota. Montgomery interviewed the farmer’s director, Dwayne Beck, who has adopted no-till, cover crops and more complex crop rotations. These practices have reduced inputs of diesel, fertilizer and crop protection products by more than half, while crop yields have increased.
“The producer is often faced with the decision whether to conserve the resource or maximize profit,” said Beck, who shares his farming philosophy on the Dakota Lakes Research Farm’s website. “If he doesn’t do the latter, someone else will be farming his land in the future, mining the soil that he conserved. For this reason, conservation cannot be the only goal. Maximizing short-term profitability also cannot be the only goal if a producer hopes to remain (or have his family remain) on the land he farms.”
The Dakota Lakes Research Farm didn’t initially choose reduced tillage for soil and water conservation benefits or improved soil health, Beck said. The potential to improve profitability through moisture conservation and spreading out the workload drove the decision.
It proved to be a smart choice. While the farm reported soybean yields of 63 bushels per acre and 217 bushels per acre of corn in the traditional farming system, soybean yields rose to 79 bushels per acre and corn jumped to 235 bushels per acre with no-till, cover crops and crop rotation.
“Much of this [success] is due to a better understanding of natural cycles,” Beck said. “It’s also quite possible that soil health and soil ecology play a much greater role than has been realized in the past.”
Montgomery also shared the story of Brandt Farm in Ohio, where no-till has been practiced for 44 years and cover crops are part of the operation. These practices help reduce the farm’s need for crop protection products. While neighboring fields with conventional ag, including full tillage, were losing $100 bushels an acre at $4 corn, Brandt Farm was making $400 an acre, Montgomery said.
“Adopting regenerative ag practices can be more profitable for farmers, due to fewer inputs and yields comparable to conventional systems,” he said.
While soil degradation is one of the most challenging issues facing our world, it’s also one of the most readily solvable, concluded Montgomery, who believes soil health will usher in the next agricultural revolution. “It’s time to change the way you think about the soil. How people today treat the land influences how the land will treat future generations.”
Encouraging words. Thank you.
Fascinating, Darcy. Thank you.