Crider Soil Series

The Crider soil series is Kentucky's official state soil. It sits on the gently rolling uplands and ridgetops of the Pennyroyal Plateau — the broad limestone plain that covers much of western and south-central Kentucky, named for the pennyroyal mint that grows along its roadsides.

Crider soil is an Alfisol, a soil order that forms under forests in humid climates. It has a silty, well-structured surface and a clay-enriched argillic subsoil, but its most distinctive feature is what happens deeper down: the subsoil turns reddish yellow and then red, stained by iron oxide released as the limestone bedrock weathered over thousands of years.

The same limestone that colored the Crider subsoil also created the landscape it sits on. Rainwater dissolved the limestone beneath the plateau, forming the sinkholes, springs, and caves — including Mammoth Cave — that make this region unique. The soil and the landscape are products of the same geology.

The Crider series was established and named for Crider, a small community in Webster County in western Kentucky. USDA soil scientists name series after local geographic features — towns, creeks, or counties — near where the soil was first formally studied and described.

The Kentucky Legislature designated the Crider series as the official state soil in 1990. Soil scientists from the University of Kentucky and the USDA Natural Resources Conservation Service identified Crider as the most representative soil of the Pennyroyal Plateau, the dominant upland landscape of western and south-central Kentucky.

The series was chosen for its agricultural significance, its geographic extent, and its direct connection to Kentucky's limestone geology. No other soil captures the state's physical character — karst uplands, weathered limestone, deep fertile profiles — as directly as the Crider series.

The Crider profile shows what happens when limestone dissolves from the bottom up. Near the surface, the soil looks like any well-drained forest and farm soil — brown silt loam. But as you go deeper, the color shifts through yellowish brown into reddish yellow and finally red. That reddening is iron oxide concentrated over millennia as the limestone parent material slowly decomposed and its calcium carbonate dissolved away.

Below the red clay subsoil, fragments of chert — the flint-like mineral that was embedded in the limestone — remain in the parent material. Farmers on Crider soil often turn up chert gravel when tilling or grading, a reminder of the limestone bedrock a few feet below their fields.

Crider soil covers the rolling uplands and ridgetops of the Pennyroyal Plateau across western and south-central Kentucky. The plateau is a broad, nearly continuous band of limestone terrain that runs from the Ohio River south to the Tennessee border.

Webster County, where the series was first named and described, sits near the northern edge of the Pennyroyal. The soil extends south and east through Hopkins, Muhlenberg, Butler, Logan, Todd, and Christian counties — the core of Kentucky's traditional tobacco-growing region.

The Pennyroyal Plateau is bordered to the north and east by the Knobs — a ring of eroded hills that separates the plateau from the Bluegrass region — and to the south by the Highland Rim of Tennessee, where similar limestone soils continue across the state line.

Burley tobacco built the agricultural economy of the Pennyroyal Plateau, and Crider soil was under most of it. Tobacco is a demanding crop — it needs deep, well-drained soil with good fertility and a long growing season. Crider provides all three. Kentucky was the leading burley tobacco state for most of the twentieth century, and the Crider series supported a large part of that production.

As tobacco farming declined after the federal tobacco buyout program ended in 2004, Pennyroyal farmers shifted toward corn, soybeans, hay, and cattle. Crider soil handles all of these crops. Its silty surface and deep argillic subsoil give it better water-holding capacity than many surrounding soils, which is important in Kentucky's occasional summer dry spells.

Before European settlement, Crider soil supported oak-hickory forest — the eastern deciduous forest that covered most of Kentucky before clearing. Post oak, black oak, white oak, shagbark hickory, and sugar maple grew on these well-drained uplands. Some older farm woodlots on Crider soil still support these species.