Iowa has some of the most productive soil resources in the world, shaped largely by glaciation, prairie vegetation, and loess deposition. Much of the state is covered by deep, fertile Mollisols that formed under wetlands and tallgrass prairie, characterized by thick, dark, organic-rich surface horizons and high natural fertility. These soils are well-suited for row-crop agriculture and support Iowa’s dominance in corn and soybean production.
Parent materials vary across the state and strongly influence soil properties. In north-central Iowa, relatively recent glaciation produced young glacial till and a closed basin topography characterized by relatively poorly drained soils. In contrast, older, more weathered tills in southern Iowa yield more acidic and clay-rich profiles. Western Iowa is mantled by thick deposits of loess, creating highly productive but erosion-prone soils, especially on steep slopes of the Loess Hills. Eastern Iowa encompasses areas of loess over till and alluvial soils along major river valleys, which are highly fertile but prone to flooding.
Soil drainage ranges from excessively drained on uplands to very poorly drained in depressions and floodplains, leading to widespread use of subsurface tile drainage to improve agricultural productivity. While Iowa’s soils are a major natural asset, they are also vulnerable to degradation through erosion and organic matter loss. Conservation practices are therefore critical to sustaining Iowa’s soil resources over the long term.
