• Clay soil can prevent plants from growing properly.Crackled soil image by Trombax from Fotolia.com
  
  Soils are divided into four basic texture types, depending on the the relative amounts of clay, silt and sand particles they contain. Of these three fundamental soil components, clay particles come in the widest range of sizes but on average are the finest. Clay soils are mainly made of clay, too much silt defines a silty soil, and sandy soils are composed of more than the ideal amount of sand, which is the largest of the three particles. Loam is the fourth and best type of soil texture for agriculture and many other purposes, too. It contains the three mainly inorganic constituents of soil in the ideal proportion: 40 percent of both silt and sand and 20 percent of clay. The relative sizes of these particles can be envisioned with the help of this rough comparison: a basketball (sand), a baseball (silt) and a golf ball (clay).
  
  

Clay

• Clay soils are able to retain a lot more water and nutrients than the other soil textures, but that can be a problem when there's too much of either. Soils consisting heavily of clay can become highly compacted, with very little space between the tiny individual particles. This makes for a dense, heavy soil that becomes very hard and clotted when dry and quite sticky when wet. Of the twelve soil orders comprising the major categories in the USDA taxonomy scheme, aridisols, ultisols, alfisols and vertisols contain the most clay. Aridisols are highly concentrated in mountainous areas and desert regions in the American West and make up a little over 8 percent of its land area. Ultisols are found predominantly in the southeastern United States, and altogether they occupy a bit under 10 percent of America's land surface. About 14 percent consists of the moderately fertile alfisol order of soils. Especially clay-rich vertisols account for another 2 percent of land area, and these are found mainly in Texas and along the Mississippi River south of Illinois. Vertisols swell and shrink dramtically, depending on the amount of water they contain. During droughts they shrink, harden and crack deeply.
  
  

Silt

• Silty soils are composed mostly of the particle intermediate in grain between clay and sand, and is a soil that permits nutrients and water to drain through it rather quickly---again, intermediate in drainage between clay soils and sandy ones. It tends to produce a relatively fine, light soil that strong winds can easily blow away. Silt is composed mostly of particles of weathered quartz and feldspar, which, unlike clay particles, are very uniform in size. The soils of the Mississippi delta of southern Louisiana are high in silt deposited there by the Mississippi River. The long-enduring civilization of ancient Egypt owed its existence mainly to the rich and fertile silty soil deposits left by the annual flooding of the Nile.
  
  

Sand

• Sandy soils are composed of large, coarse particles, through which water and nutrients tend to drain very quickly. Plants growing in this type of soil need more frequent watering during hot periods of the year and especially during drought. They may also require fertilizing or other types of soil amendments to restore lost nutrients. Acidic, sandy spodosol soils are relatively infertile and do not support agriculture without a lot of human help---mainly in the form of lime supplements to raise their pH---but they do naturally support many trees and are often found beneath coniferous forests. Mainly occurring in Florida, the northernmost sections of New England, New York, Wisconsin and Michigan, and in thin strips of central Washington and Oregon, spodosols make up about 3.5 percent of United States land area.
  
  

Loam

• Loam is the ideal soil texture for agriculture. It drains just right and so retains the amount of moisture and plant nutrients best suited to healthy plant and crop growth. Loam has equal parts of sand and silt and a low clay content. The histosol and mollisol orders in soil taxonomy are composed of rich and fertile loam-textured soils. Histosols are comparatively rare in the United States, making up less than 2 percent of its land surface, and mainly scattered in northernmost Indiana, New York and Wisconsin, and along the Gulf coast of Louisiana and parts of Florida. Michigan---especially its panhandle--- Northeast Minnesota, and the North Carolina coast have the highest concentration of histosols in America. The family of mollisols are vastly more common in the United States. Mollisols constitute the main soil types found in the great agricultural regions west of the Mississippi River, stretching from central Texas all the way up to North Dakota. East of the river, they cover almost all of Iowa and southern and western Minnesota, as well as much of northern Illinois and Missouri, among other states. The most widespread soil order in the United States, it accounts for more than one-fifth of its land surface.