Alfisols

What Are Alfisols

Alfisols are mineral soils characterized by a subsurface horizon enriched with clay that has been translocated — washed downward — from the upper soil layers. This clay-rich layer, called an argillic horizon, is the hallmark of the order. The name comes from "Al" (aluminum) and "Fe" (iron), the elements that dominate their mineral composition.

Unlike the heavily leached ultisols of the Deep South, alfisols retain moderate to high base saturation — meaning they still hold plenty of calcium, magnesium, and potassium for plant growth. This makes them naturally fertile, requiring less lime and fertilizer than their more weathered cousins.

Where Alfisols Are Found

Alfisols form a broad arc across the eastern United States, from the upper Midwest through the Ohio Valley, into the Mid-Atlantic, and south through Georgia, Mississippi, and Louisiana. They dominate where deciduous or mixed forests once stood — particularly the oak-hickory forests of the central hardwood region.

In our dataset, 170 counties show alfisols as the dominant soil order, concentrated in Arkansas, Georgia, Indiana, Ohio, Michigan, and Wisconsin. States like Iowa and Illinois show alfisols along their eastern edges where forests historically transitioned to prairie.

Farming and Gardening in Alfisols

Alfisols are the workhorses of eastern agriculture. Their natural fertility supports corn, soybeans, and hay production across the Ohio Valley and upper South. The clay-enriched subsoil provides excellent nutrient and water retention, while the silt loam surface layer is easy to work when conditions are right.

The clay subsoil is both a blessing and a challenge. It holds water and nutrients well, but can create perched water tables and slow drainage in spring. Gardeners in alfisol country often deal with wet, sticky conditions in March and April, followed by productive growing seasons.

For home gardens, alfisols support a wide range of vegetables and fruits. The slightly acidic pH is ideal for blueberries, potatoes, and most root crops. Adding organic matter to the surface improves structure and drainage — but unlike sandy or heavily leached soils, alfisols do not need heavy amendment to be productive.

How Alfisols Form

Alfisol formation requires enough rainfall to wash clay particles downward through the soil profile, but not so much that all nutrients are leached away. This Goldilocks zone — roughly 500-1,200 mm of annual rainfall — is why alfisols concentrate in the humid eastern US rather than the arid West or the tropical Southeast.

The parent material is typically glacial till or loess (wind-deposited silt). Thousands of years of forest litter decomposition add a thin but important organic-rich surface layer. The seasonal wetting and drying cycles drive the clay translocation that defines the order.

Alfisols are a "middle-aged" soil order — younger and less weathered than ultisols, but more developed than inceptisols. They represent a stable, productive stage in soil evolution that can persist for tens of thousands of years under forest vegetation.

All Counties with Alfisols as Dominant Order(170)

Showing 50 of 170 counties. Search all counties

Other Soil Orders