Miami Soil Series

The Miami soil series is Indiana's official state soil. It sits on the gently rolling ridges and sideslopes of the central till plain — the broad, glacially leveled landscape that covers most of the state's midsection.

Miami soil has two layers stacked on top of each other. The upper portion is silty loess — fine, fertile sediment blown in by wind after the glaciers retreated. Below it is calcareous glacial till, the stony, lime-rich material the ice sheet scraped and deposited as it moved across Indiana.

The soil is well drained to moderately well drained. It sits on high ground — ridges and gentle slopes where water runs off rather than pooling — which made it easier to plow and farm than the wetter, flatter soils in adjacent low-lying areas.

The Miami series was first described and established in Miami County, Indiana — the county at the heart of the central till plain and the county that gives the soil its name. Miami County itself was named for the Miami Nation, the Indigenous people who inhabited this region for centuries before European settlement.

Indiana soil scientists and the USDA Natural Resources Conservation Service identified the Miami series as the soil that best represents the state's dominant landscape. The central till plain covers the majority of Indiana's land area, and the Miami series is the most characteristic well-drained soil of that landscape — the ridgetop counterpart to the wetter Brookston and Crosby soils that fill in the low areas around it.

The soil was chosen for its agricultural importance, its geographic extent, and how clearly it captures Indiana's glacial heritage. No other soil series captures Indiana's landscape — loess over till, ridge over flat, glaciated heartland — more directly than the Miami series.

If you dug into a Miami soil field, you would pass through a brown silt loam surface, then enter a zone where the soil gets noticeably stickier and heavier — the argillic horizon where clays have accumulated over thousands of years. Below that, the soil turns pale and crumbly: calcareous glacial till, fizzing slightly with lime when you drip acid on it.

That fizzing reaction is one of the Miami series's most distinctive features. The till layer contains calcium carbonate from limestone and dolomite that the glacier ground up as it pushed across Indiana. The lime neutralizes soil acidity in the lower layers and makes the soil easier to farm than more acidic soils elsewhere.

Miami soil is concentrated across the central till plain of Indiana — the broad, slightly rolling landscape that the Laurentide ice sheet left behind when it retreated roughly 14,000 years ago. The series covers millions of acres and is one of the most widespread soils in the state.

It sits on ridges, interfluves, and gentle slopes where natural drainage keeps water from pooling. Adjacent to Miami soil on the lower landscape positions are wetter soils like Brookston and Crosby — the undrained depressions and flats that needed tile drainage before they could be farmed.

Miami County in north-central Indiana, where the series was first named, remains one of the core areas. The soil extends north, east, and south through the counties of the till plain, covering most of Indiana's agricultural heartland.

Corn and soybeans are the defining crops of Miami soil. Indiana is consistently among the top five states in corn production, and the Miami series — along with the wetter soils it neighbors on the till plain — underlies most of that production. The loess surface provides good tilth and fertility; the calcareous till below maintains a near-neutral pH that corn and soybeans prefer.

Before European settlement, much of the Miami soil landscape was covered by a mix of tallgrass prairie and oak savanna — the transition zone between the eastern deciduous forests and the open grasslands to the west. Sugar maple, beech, oak, and hickory grew on the better-drained ridges. Prairie grass covered the flatter areas. Both were cleared for farming in the 1800s.

Some Miami soil ground is used for hay, pasture, and winter wheat. Small grain production was historically more common in Indiana before corn-soybean rotation became standard, and Miami soil supported all of it. Orchards and vegetable operations occupy smaller acreages on the same ridgetop positions.