The Past, Present and Future of Iowa Soils

Photo by Jim Richardson

Iowa’s soils are one of our most precious resources. Without it, we wouldn’t be known as the agriculture powerhouse we are today, nor would we have the flora and fauna unique to our midwestern state. Yet in the last 200 years, we’ve lost half of the organic-matter-rich soil we have, and by some estimations, we may be a handful of generations away from losing the other half. How did we get here, and can we get back the soil we’ve lost? Is our soil today as healthy as it once was? 

Iowa’s Soil Before the 1800s

The prairie grasslands you know and love in Iowa today began forming around 9,000 years ago. The extensive, deep root systems of the prairie reached more than 12 feet into the ground. These roots cycled organic matter, depositing carbon and nutrients into the soil as they grew, died and decomposed. Dense root networks held soil in place, preventing erosion and promoting water trickling slowly through the soil. Advancing and retreating glaciers dragged magnesium, calcium and potassium from parent material in Canada, grinding the minerals into our soil and creating optimal conditions for future crop production. Roaming herds of bison and elk traded nutrients with the soil. Natural and human-caused fires supported the prairie’s diversity and function. 

Over thousands of years, this constant cycle of growth and decay built thick layers of nutrient-rich topsoil, known as Mollisols. Iowa’s Mollisols are so rich and fertile that they rival the most productive soils in the world. 

The natural forces that created Iowa’s soils are almost foreign to us today. It might be hard to imagine an Iowa not so long ago that had clear, drinkable streams and rolling prairies as far as the eye could see. 

The Agricultural Boom

Around 200 years ago, Europeans moved across the country in search of a chance at a new life in the west. Human innovation quickly moved from wooden plows to steel plows pulled by yoked oxen and guided by three humans. With this team of five, one acre of land could be cleared a day. 

Farmers planted many different crops in the 1800s. Wheat dominated, but immigrants from all over the world brought different methods, crops and livestock. Corn, barley, rye and oats all rotated through these freshly plowed fields. Some Europeans brought seeds to start orchards, and some focused on their knowledge of livestock breeding, taking advantage of the grasslands of southern Iowa. 

Iowa was a varied place and continued to be for decades. Still, the soil began to erode from the moment the plow hit the prairie. Wheat yields dropped by the end of the Civil War, causing many farmers to switch to the more profitable corn. Livestock also became more profitable and paired well with corn production. 

Farming hit its golden age in Iowa by the early 1900s. Continual inventions, livestock breeding and crop rotations brought wealth to the state. But nature, economic pressure and a slow response from the government would come calling by the 1930s, when the Dust Bowl hit. Though Iowa didn’t face as many hardships as Kansas or Oklahoma, it was bad enough that the Iowa General Assembly created the Soil Conservation Committee in 1939 after 22 other states did the same. Nationwide, the Soil Conservation Service, known today as the Natural Resources Conservation Service (NRCS), was formed to prevent the Dust Bowl from happening again. 

Throughout the mid to late 1900s, Iowa continually intensified its agricultural production, slowly moving from varied crop rotations to a simpler corn-soybean rotation. The use of chemicals and manufactured fertilizers became more widespread. Livestock rearing changed to mass production. Eventually, agricultural production transformed into what we know it as today, and along the way, Iowa lost 50 percent of its rich soil, the same soil this state was founded on. 

After the boom of chemical use in the 1970s, concerns grew over soil erosion, declining organic matter, and water pollution from nutrient runoff. Intensive tillage and monoculture cropping left soils vulnerable, and heavy rains often washed topsoil into rivers and streams. By the mid-1980s, programs like the Conservation Reserve Program (CRP), established by NRCS, offered farmers incentives to restore and rest erodible land with grasses and trees. At the same time, local organizations supported farmers in adopting soil conservation practices like no-till farming, cover crops and crop rotations. These efforts marked a shift toward regenerative practices that rebuild soil and reduce inputs. But where does that leave our soils today, and is enough being done?

 

What in the World is Soil Health?

The next chance you get, walk into your yard or the nearest park and smell the soil. No, really! Grab a clump with your hand or use a spade to cut a slice of soil out of the ground. Smelling and feeling soil is a great way to tell how healthy it is. Then, head into your nearest prairie and compare the scent. Healthy soil smells sweet or pleasing, like minerals and organic matter. It feels solid in the hand. Try playing with each soil. Which holds its shape? Which one blows away in the wind easily? Not all soils are the same, but you likely already instinctually can tell when a soil is not healthy. 

According to the NRCS, soil health is “the continued capacity of the soil to function as a vital living ecosystem that sustains plants, animals, and humans.”  Healthy soil is rich in nutrients, has good structure for water and air movement and supports a diverse community of microorganisms that break down organic matter and cycle nutrients. Dr. Bonnie McGill, Senior Climate and Ecosystem Scientist at American Farmland Trust, explains it this way: “The soil health mindset is a transition away from the industrial, soil-as-a-machine thinking toward thinking of soil as an ecosystem that farmers, and all people, live in reciprocity with. In other words, we take care of the soil, the soil takes care of us.”

Soil is far more than the dirt under our feet that occasionally gets on our clothes. Soil is a living, breathing medium that holds the key to all life. Clay, sand, silt, minerals, organic matter, air, water and microorganisms make up the building blocks of soil, all existing in different compositions to one another depending on a multitude of factors. 

It begins with parent material, which is the rock or sediment from which soil forms, influencing its mineral content. In Iowa, a common parent material is glacial till, the rocky mixture pushed by glaciers thousands of years ago into Iowa. Loess (wind-blown material) and Alluvium (river-deposited material) are also commonly found in Iowa. If you made the connection with the Loess Hills, you’re on the right track! The Loess Hills have soils dominated by wind-blown parent material.

Climate plays a key role, as temperature and precipitation drive weathering and organic matter breakdown. Have you noticed potholes forming in streets on the first nice day in spring after a long winter? The constant freezing and thawing of water turn little cracks into big headaches. That same action impacts soil health. Dr. McGill pointed out that increasingly warmer winters mean more frequent freezing and thawing of soils, which can breakup important soil structure. Warmer winters also mean soil microbes are more active, converting more soil organic matter into carbon dioxide. So, farmers face a kind of “arms race” between building soil organic matter with soil health practices and losing it more rapidly due to climate change.

Topography affects how water flows across the landscape, with steep slopes prone to erosion and low spots, like wetlands, collecting nutrient-rich sediment. Next time you’re on a hilly hike, check the soil at the top of the hill, and then compare it to the soil at the bottom of the hill. Have you ever noticed that valleys or the bottoms of hills tend to have darker soil full of organic matter? Have you ever noticed that the tops of hills tend to have sandier soil? 

Biological activity enriches the soil, as plant roots, microorganisms and insects cycle nutrients and improve structure. Soil microbes are like nature's cleanup crew, breaking down plant material and recycling nutrients so plants can grow strong. Just one teaspoon of healthy soil can contain billions of microbes, all working together to improve soil health. Supporting this biological activity is at the heart of the four soil health principles: promote living roots year-round, keep the soil covered, reduce disturbance and maximize biodiversity.

Time is another factor, with soil developing over thousands of years as minerals break down and organic matter accumulates. 

Human activity also leaves its mark, with intensive farming, deforestation, and urbanization degrading soil, while conservation efforts like cover cropping and no-till farming can restore its health. 

Together, these forces shape Iowa’s diverse soils, forming the foundation of the state’s agricultural productivity.

 

Rebuilding and Protecting Iowa’s Soil

Humans have replicated the nutrients needed for crop production, but we cannot replicate the thousands of years process that created Iowa’s rich soils without simply planting prairies and forests again. From no-till to prairie strips to cover crops, there are many practices that are the next best thing, however.

“Cover crops do a lot of great things,” Dr. McGill explains. “For example, they provide living roots — which release liquid carbon resources that fuel the soil food web — for seven months of the year that corn and soybeans aren’t growing. Beneficial bacteria and fungi (below ground livestock, if you will) need to be fed year-round in order to provide services to the cash crop. Cover crops and the soil food web help farmers build resilience: during the drought of 2012, midwestern fields that had a cover crop the previous fall had 11% greater corn yields and 14% greater soybean yields than fields with no cover crop." 

Greene County farmer, INHF supporter and Practical Farmers of Iowa (PFI) member Chris Henning first embarked on her soil health journey after the ’93 floods underscored for her the connection between her farm ground and everyone downstream. Jefferson received eight inches of rain in one afternoon, cutting gullies into her land deep enough to lose a tractor in.

“That’s when I got involved in conservation… because I had to,” Chris reflects. “I decided to do everything I could to keep my soil, my chemicals, my farm out of your drinking water.” 

Chris was an early adopter of practices like prairie buffer strips, wetland incorporation, minimum tillage and cover crops. But while it was easy for her to see how her choices on her marginal, flood-prone, rolling farm ground above the Raccoon River had implications for others, she understood why it wasn’t so apparent for her neighbors with flat ground.

“The erosion happening on their land doesn’t show up in the form of gullies. But it’s happening. Protecting soil health takes extra work, extra time, extra thought,” Chris says. “We incentivize yield with crop prices. We don’t incentivize soil health in the same way. But there are resources for those looking to invest in their land’s legacy. The research and farmer-to-farmer work that PFI does very well has been a big part of my journey.”

 There are a multitude of factors that play into how Iowa’s soil has ended up where it is now. What matters most is what we do next. Iowa’s soils are who we are as a people. We must tend to the land to have a future. Luckily, it’s not too late. A combination of regenerative agriculture, permanent land protection and careful stewardship of our natural resources will ensure Iowa and its people have a future as rich as our deep, black soils.