Soil suborders are divided into great groups on the basis of uniformity in the kinds and sequence of major soil horizons and features. The horizons used to make separations are those in which clay, iron, or humus have accumulated; those that have a pan that interferes with growth of roots, movement of water, or both; and those that have a thick, dark colored surface horizon. The features used are the self mulching properties of clay, soil temperature, major differences in chemical composition (mainly calcium, magnesium, sodium, and potassium), dark red and dark brown colors associated with basic rocks, and the like. The names of great groups have three or four syllables and are made by adding a prefix to the name of the suborder. An example is Fragiaqualfs (Fragi, meaning having a fragipan horizon, aqu for wetness or water, and alf, from Alfisols). The great group is not shown separately in table 10, because it is the last word in the name of the subgroup.

10/15/98