12 Soil Types

Arctic and Tropical

• Gelisols have a dark layer of organic matter and minerals on top of permafrost. In many gelisols the surface turns into peat. Alternate freezing and thawing often distorts the landscape by frost heaving. This soil type is common in Alaskan, Canadian and Siberian tundras. Oxisols are yellow to red soils found only in hot tropical and subtropical climates with high levels of rainfall. Heavy leaching from rain leaves the soil abundant in rust-colored clay, quartz, aluminum and iron oxides and organic matter. Oxisols are usually deep and unable to retain nutrients, so large amounts of fertilizer are required for agriculture.

Swamp and Desert

• Decaying grasses, leaves, sedges, dead trees and other plants accumulate in poorly drained histosols, organic soils that form in coastal marshes, swamps and river deltas. Histosol wetlands are found in tropical areas where the soil is saturated and in cold regions where low temperatures retard decomposition. Aridsols are poor, shallow soils found on top of clay, carbonates or salt deposits in deserts. High temperature causes water to rise upward where it evaporates forming salt deposits that are a danger when aridsols are irrigated for agriculture.

Agricultural Soils

• Mollisols are rich, fertile, dark-colored soils found in U.S. grasslands. The dark color of mollisol comes from humus formed by decomposed litter. Most natural grasslands in the country have been converted to agricultural use. Alfisols are light-colored soils that originally were formed from weathered forest vegetation. Their subsoil is enriched by nutrients and clay. Alfisols can be productive for agriculture use but degrade rapidly when they are eroded. They are found from northern Minnesota to southern Florida. Highly porous, lightweight andisols evolve from accumulations of volcanic ash. They form layers on the flanks of volcanos and are prized for agriculture because of their ability to hold water. They are most often found on land surrounding volcanoes in the Pacific Rim.

Clay and Sand

• Ultisols, usually reddish in color and highly weathered, are common to the southeastern U. S. The surface of ultisols are coarsely textured and easy to till, and they sit on top of subsoils enriched by clay that store water for plant roots, however thunderstorms and hot weather leach their nutrients. When ultisols are amended they are highly productive for agriculture.

  Vertisol is a heavy, clay soil rich in the mineral montmorillonite that contracts and expands, depending on rainfall. When a vertisol is dry it shrinks and develop cracks; when it is wet it swells shut. Cotton is grown in vertisols located in Texas.

  Acidic, sandy spodosols develop under coniferous trees and are common in Florida, higher levels of the Rocky Mountains and in the Northeastern U.S. A dark layer of soil sits on top of a light layer formed by blowing sand or sits on top of a reddish layer enriched by aluminum or iron. Spondosols are formed in areas where sand is subject to heavy rainfall.

Recent Soils

• Water, wind and the erosion of ice deposit sediments that form entisols, soils found on deep deposits of sand and on rocks found on sand dunes, flood plains and steep slopes. They lack layers, called horizons, and will eventually develop into another type of soil. Inceptisols are young soils commonly found in glacial deposits, the tundra and stream sediments. They have not weathered enough to form horizons. They are more developed than entisols.