Natchez Silt Loam

The Natchez Silt Loam is Mississippi's official state soil. It sits on the bluff hills — a narrow belt of steep, loess-covered hillsides that runs along the entire western edge of the state, from the Tennessee border to the Louisiana line, rising above the Mississippi River floodplain.

Natchez is an Inceptisol: a relatively young soil that has not yet developed the thick clay-enriched layers of older soils. What it has instead is depth — loess deposits up to 50 feet thick in the most dramatic bluffs — and natural fertility from the minerals packed into every grain of wind-blown silt.

In 1988, the Professional Soil Classifiers Association of Mississippi, working with soil scientists at Mississippi State University, selected Natchez silt loam to represent the state's soil resources. The criteria were coverage, productivity, and significance to Mississippi's agricultural and natural history.

It took 15 more years for the Legislature to act. Representative Reecy Dickson of Macon sponsored House Bill 1273, noting that 15 other states had already officially designated state soils. The Mississippi Legislature passed the bill, and it was signed into law on March 13, 2003.

The Natchez series was named after the city of Natchez — itself named after the Natchez people, a Native American nation who built their civilization on these same loess bluffs long before European contact. The soil series, the city, and the people share one name.

Natchez silt loam has a straightforward profile: a thin, darker surface layer above a yellowish-brown subsoil, all sitting on the pale, deep loess that continues far below. What makes it unusual is how uniform it is — silt loam from top to bottom, all the way down through the bluff.

The slope is the story here, not the layers. These hillsides run from 12 to 60 percent grade — steep enough that a person standing on them leans into the hill. The soil is fertile and deep, but water moves across it fast, and any ground cover removed from these slopes erodes quickly.

Natchez silt loam covers 171,559 acres — less than one percent of Mississippi — but its footprint stretches the full length of the state. It sits in the narrow band of bluff hills that rises above the Mississippi River alluvial plain on the west and the Yazoo Basin on the east, running from the Tennessee border to the Louisiana border.

This zone is called the Brown Loam region, or the Bluff Hills. The soil sits on hillsides so steep — often 30 to 60 percent grade — that most of it has never been farmed. The bluffs outside Yazoo City are among the most dramatic examples, rising sharply above the flatlands below.

Beyond Mississippi, the Natchez series also appears in Arkansas, Louisiana, and Tennessee, wherever the same loess deposits from the glacial-era Mississippi River reach the bluffs. Mississippi has the largest and deepest concentrations.

Most Natchez silt loam is too steep to farm. Slopes of 12 to 60 percent mean water runs off fast, and any disturbed ground erodes quickly. The soil's main use is timber, and it is very good at it.

Loblolly pine reaches a site index of 90 to 100 on Natchez silt loam — good growing conditions for commercial timber. Cherrybark oak, white ash, and sweetgum reach a site index of 105 — excellent hardwood timber. These species define the natural forest of the Mississippi loess bluffs.

Where slopes are gentler — under 12 percent — farmers grow pasture, hay, and row crops. The soil is naturally fertile and productive when well managed, but maintaining ground cover is essential on any slope to prevent erosion. The loess is fine and uniform enough that once it starts moving, it moves fast.

The loess bluffs historically supported a mix of beech, magnolia, white oak, and other southern hardwoods. Many of those forests were cleared during the antebellum plantation era, and the bluffs that were farmed or grazed without care eroded severely. The steep, straight-sided bluff faces visible today are partly natural and partly the result of 200 years of land use.