By: Brooke Bouma Kohlsdorf
Edited by: Dave Price
When a 76-acre farm outside the northwest Iowa town of Hull was auctioned off this past December, the sale price of $26,750 per acre came as no surprise. The land’s reputation for premium soil quality, along with its long, flat rows, and a good drainage system made it an attractive purchase for a local farmer, who paid a total of $2,047,980 for the small property.
The price is just one of the many indicators of why northwest Iowa’s soil is considered among the best in the country. Here is the story of how this treasure formed and why it’s still so rich today.
RELATED: This northwest Iowa farm pushed toward a record sale price. Find out what made the land so appealing in this story from Successful Farming in 2024.
The Unique Geology Behind the Region’s Soil Quality
To understand why the soil is considered some of the best in the country for growing corn and soybeans, you must look back in time.
Dr. C. Lee Burras is Morrill Professor of agronomy at Iowa State University and said the soil found in northwest Iowa is largely the result of the region’s geological history. The area’s soil is primarily composed of Loess, a wind-deposited silt and clay mixture that covers the top of the land. This silt is good at allowing water to infiltrate and be stored in a plant-friendly form throughout the growing season.
The Loess was deposited by winds from the Missouri River about 20,000 years ago. Burras said, “That may sound like a long time. But in the world of soil, 20,000 years is like a 25-year-old in human terms.”
RELATED: Learn more about the Loess Hills, an area formed by and named after the Loess soil in this documentary from Iowa PBS.
The Soil Trifecta
The Loess, along with Iowa’s climate, created three things that make the soil so rich and perfect for farming.
Texture: The Loess deposits in northwest Iowa have created the ideal texture for soil—silty enough to retain moisture while still allowing it to drain properly.
Minerals: It has the right mineral. And according to Burras, those minerals came from the native tallgrass in that area and are still readily available in the soil today. The deep-root systems of native prairie grasses helped to build up organic matter over time, which is key for holding moisture and cycling nutrients.
Flat landscape: The way the Loess landed resulted in gentle rolling hills or flat ground. This is ideal for equipment to easily plant and harvest crops.
The Right Climate
In addition to the texture, mineral density, and favorable landscape, the weather is another important factor. And Burras said if you study weather records, you will notice that part of the state has seen an average rainfall increase of about 5 inches in the past 60 years, further enhancing the region’s already favorable conditions.
Soil Quality and the Role of the CSR Rating
One of the most widely recognized measures of soil productivity in Iowa is the Corn Suitability Rating (CSR), which helps farmers, realtors, and landowners assess the quality and potential of agricultural land. It was created in 1971 by Tom Fenton of Iowa State University and later tweaked by Burras.
RELATED: Get a deeper knowledge on how to CSR in this breakdown from the Iowa State University Extension and Outreach Ag Decision Maker.
The CSR rating system considers factors like soil texture, depth, drainage, and how conducive the land is to crop growth. While not a direct measure of yield, the CSR offers a snapshot of the land’s inherent productivity and potential.
In northwest Iowa, the soil often has a high CSR rating. For instance, the land that sold in December for $26,750 an acre had a CSR of between 94.3 and 95.5 (100 is the highest).
Even in difficult years, the land's resilience due to these inherent qualities allows farmers to see relatively stable yields. However, good soil alone doesn’t guarantee success—farming is a combination of soil health, weather, and management.
As Burras noted, “A really good farmer can get good yields even on bad soil. A terrible farmer can get terrible yields on the best soil.”
Preserving Soil for Future Generations
While northwest Iowa’s soil is currently a highly productive resource, maintaining its health for future generations requires ongoing care. Burras said root growth is important to care for the ground.
That is why he gets excited when he sees farmers plant cover crops in the off-season to offset the wear of the land. He said caring for the surface layer of the ground, also called the (A) Horizon, is important. “For every inch your (A) Horizon gets thinner, there’s generally a 5 percent yield decrease.”
RELATED: The use of cover crops has been gaining in importance as farmland owners and operators look to preserve their soil health. This Iowa Capital Dispatch story looks at the benefits and how it can reduce nitrogen runoff by 50%.
