Soils form via unique combinations of parent materials, climate, biological factors, and topography over time. Mississippi has a wide variety of soils, reflecting the diversity of these factors present in the state. Three general land resource regions are identified as (1) river floodplain (the Delta); (2) a loess region (a band of soils formed in windblown material that adjoins the Delta); and (3) Coastal Plain (the rest of the state).
As land management, including forest clearing and more recently forest replanting, transitioned from the pre-Columbian to the modern, the soils within a region led to the current predominant activities on the surface. For example, most Mississippi row crop production (cotton, corn, and soybeans) occurs in the relatively flat, deep alluvial soils of the Delta, which are conducive to mechanized farming. Conversely, animal production and forestry dominate on the shallower soils in the hilly sections of East and South Mississippi.
The general land resource areas of the loess and Coastal Plain regions have smaller subunits based on common soils, geology, climate, water resources, and land use. These Major Land Resource Areas are discussed below.
Southern Mississippi Valley Alluvium: The Delta
Soils are naturally diverse in the Delta as a result of their alluvial origin in sediment from areas north of Mississippi. Particle sizes within the sediment decrease as distance from the originating stream increases—that is, soils closer to running water have proportionally more large silt and sand particles than soils further from the stream. Another factor in Delta soil formation is surface water movement over time. Soils formed under standing water have different properties than soils formed under running water.
Soils with a large proportion of clay particles (the smallest basic soil solid) have some unique features. When these soils dry, small round aggregates that look like shotgun buckshot form at the surface; hence, the popular name for Delta clay soils is buckshot. Soils with high clay content have very slow water infiltration rates, a property that has led to significant aquaculture and rice production in the region. Mississippi Delta soils originate in sediments left by flooding of the various rivers in the region, which is not a traditional delta fan formed at the mouth of a river. Most Delta soils are farmed, with three-quarters of the cropland to the north and less cropland in the south. Controlling surface water and drainage are major soil-management issues.
Southern Mississippi Valley Uplands: Brown Loam Hills and Thin Loess Areas
When floodwaters receded in what is now the Delta, strong west-to-east winds blew some of the dry sediment left by flooded rivers to the adjacent uplands. The deposited material, called loess, is the parent material of soils formed in the hilly region along the eastern edge of the Delta. The depth of loess decreases from west to east across the state as the distance from the originating flatlands increases. This area, the Brown Loam region or Bluff Hills, has some very deep deposits, as evidenced by the bluffs outside Yazoo City. Natchez silt loam, a soil present on about 170,000 acres in this area, has been designated the Mississippi state soil.
Coastal Plain soils in Mississippi are part of an arc along the United States coast from New Jersey to Texas. They are based on unconsolidated fluvial or marine sediments deposited on the edges of ancient seas. These diverse soils are usually best suited to pastures and forests. The northern portion of the Coastal Plain is commonly called the Mississippi Sand Clay Hills. The southern Coastal Plain is the Piney Woods region of the state.
There are two Blackland Prairies, one in northeastern Mississippi in the Tupelo, Aberdeen, and Columbus area, and a smaller area in and near Scott County in south-central Mississippi. Many of the soils are very dark, like midwestern prairies; however, the Mississippi soils form in soft limestone or chalk parent material in humid conditions. Midwestern prairie soils form in glaciated areas predominated by grasslands under drier, less humid conditions.
Gulf Coast Marsh
Zones of marsh along the Gulf of Mexico differ from the rest of the state. The area is almost treeless, has marsh vegetation, and is uninhabited. It is part of the estuarine complex that supports Gulf marine life. Most of the soils of the Gulf Coast Marsh are very poorly drained, and the water table is at or above the surface most of the time. These soils are susceptible to frequent flooding. They formed in alluvial and marine sediments and organic accumulations.
- Stanley W. Buol, ed., Soils of the Southern States and Puerto Rico (1972)
- Douglas Helms, Agricultural History (Fall 2000)
- US Department of Agriculture, Yearbook of Agriculture: Soil (1957)