SL43

Key to Soil Orders in Florida 1

M.E. Collins2

1. This document is SL43, one of a series of the Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural 

Sciences, University of Florida. Original publication date August 1985. Reviewed March 2009. Visit the EDIS Web site at http://edis.ifas.ufl.edu.

2. M.E. Collins, professor, Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University 

of Florida, Gainesville, FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and 

other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, 

sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, 

University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Millie

 Ferrer, Interim Dean 

This fact sheet is intended for anyone who has 

some understanding of Soil Taxonomy but who needs 

a simplified key to help distinguish one soil order 

from another. There are 12 soil orders: Andisols, 

Gelosols, Entisols, Inceptisols, Alfisols, Ultisols, 

Spodosols, Histosols, Mollisols, Aridisols, Vertisols, 

and Oxisols. Only seven of these soil orders are 

present in Florida. The soil orders not recognized in 

Florida are the Aridisols, Vertisols, Andisols, 

Gelosols, and Oxisols. The distribution of dominant 

soil orders in Florida is shown in Figure 1. Alfisols, 

Inceptisols, and Mollisols are not shown because: 

Alfisols are widely interspersed throughout the state; 

and the aerial extent of Inceptisols and Mollisols is 

too small to be shown at this scale of map (source: 

Carlisle and Brown, 1982). 

Figure 1. Distribution of soil orders in Florida.

To determine the order to which a soil belongs, 

you must follow the "Keys to Soil Taxonomy" (Soil 

Survey Staff, 1996). But before you can use the key, 

you must know which diagnostic horizon(s) is 

present in the soil that you are classifying. These 

diagnostic horizons are particular kinds of horizons in 

the soil that indicate the degree and kind of dominant 

sets of soil-forming processes that have occurred. 

Therefore, you must know the epipedon (diagnostic 

surface horizon) and what, if any, diagnostic 

subsurface horizons exist. 

The soil order is the highest category in Soil 

Taxonomy. At this hierarchical level, soils are 

distinguished in relation to the five soil-forming 

factors: (1) climate and (2) living organisms acting 

on (3) parent materials over (4) time as conditioned 

by (5) relief. 

The seven soil orders recognized in Florida and 

the major properties that differentiate them are 

discussed next. Complete definitions for the soil 

orders and diagnostic horizons are available in "Keys 

to Soil Taxonomy" (Soil Survey Staff, 1996). 
Key to Soil Orders in Florida 2

 ALFISOLS 

Soils in the Alfisol order are characterized by 

having undergone processes that translocate silicate 

clays to form an argillic horizon. Clay translocation 

in Alfisols takes place without the depletion of bases. 

The unique properties of Alfisols in Florida are a 

combination of an argillic horizon, a medium to high 

amount of bases in the soil, water generally available 

to plants during the growing season, and an ochric 

epipedon. In general, these soils are intensively 

cropped. An example of a generalized profile 

description of an Alfisol is shown in Figure 2. 

Presently, Alfisols have been mapped on 

approximately 4.6 million acres in Florida. 

Figure 2. Profile descriptions of soil orders in Florida.

 ENTISOLS 

A soil that does not reflect any major set of soilforming processes belongs to the Entisol order. 

Entisols are able to support any vegetation and occur 

in any climate. Commonly, they form in inert parent 

materials such as quartz sand (Central Ridge of 

Florida) or slowly soluble rock such as limestone 

(South Florida). There also may have been 

insufficient time, as in recent alluvial deposits, for 

diagnostic horizons to have formed. Entisols could 

occur on steep slopes, where the rate of erosion 

exceeds the rate of formation of pedogenic horizons. 

The properties unique to Florida Entisols are a 

dominance of mineral soil and an absence of distinct 

pedogenic horizons except for an ochric epipedon, an 

albic horizon, and a spodic or argillic diagnostic 

subsurface horizon that is below 80 inches. 

An example of a generalized profile description 

of an Entisol is shown in Figure 2. Presently, Entisols 

have been mapped on approximately 7.5 million acres 

in Florida. 

 HISTOSOLS 

Soils that belong to the Histosol order have a 

very high content of organic carbon (more than half 

of the soil's thickness is organic) in the upper 32 

inches of the soil. These soils are considered to be 

organic rather than mineral soils. The amount of 

organic carbon required for Histosols depends on the 

amount of clay. Most Florida Histosols formed from 

partially decomposed plant remains that accumulated 

in water. More common names for Histosols are 

peats or mucks. 

An example of a generalized profile description 

of a Histosol is shown in Figure 2. Presently, 

Histosols have been mapped on approximately 4.0 

million acres in Florida. 

 INCEPTISOLS 

Soils of the Inceptisol order have a unique 

combination of properties that include water 

available to plants during the growing season, one or 

more pedogenic horizons of alteration or 

concentration with little accumulation of translocated 

materials, some unweathered minerals, a moderate to 

high cation exchange capacity in the clay fraction, 

and usually textures finer than loamy sand. Even 

though most Inceptisols in Florida have loamy sand 

or coarser (more sandy) textures, these soils are 

classified as Inceptisols because of a dark, thick, and 

low base saturation (<35%) surface horizon (umbric 

epipedon). Inceptisols in Florida are of minor extent. 

An example of a generalized profile description 

of an Inceptisol is shown in Figure 2. Presently, 

Inceptisols have been mapped on approximately 1.0 

million acres in Florida. 

 MOLLISOLS 

Soils that belong to the Mollisol order have a 

very dark brown to black surface horizon (mollic 

epipedon), a high amount of calcium versus other 

extractable cations present in the soil, and clay 

minerals of moderate or high cation-exchange 

capacity. The mollic epipedon forms mainly from the 

decomposition of organic matter in a soil that has a 

considerable amount of divalent cations, especially 

calcium. Soil properties associated with a mollic 
Key to Soil Orders in Florida 3

epipedon are a reasonable reserve of plant nutrients 

(Ca, Mg, K, and sometimes N), soil structure that 

allows movement of air and water when the soil is not 

saturated, and good permeability. The vast majority 

of Mollisols presently recognized in Florida are 

poorly to very poorly drained. 

An example of a generalized profile description 

of a Mollisol is shown in Figure 2. Presently, 

Mollisols have been mapped on approximately 1.0 

million acres in Florida. 

 SPODOSOLS 

Spodosols are characterized by having undergone 

soil processes that translocate organic matter and 

aluminum, or organic matter, aluminum, and iron, as 

amorphous materials. The most striking property 

Spodosols have is a horizon that has resulted from 

accumulation of black or reddish amorphous 

materials having a high cation-exchange capacity. 

This horizon is called a spodic horizon. In some 

Spodosols a leached horizon, which can range from 

white to gray, overlies the spodic horizon. Many 

Spodosols in Florida are poorly to very poorly 

drained, and all Spodosols in Florida have developed 

in sandy, acid parent materials. 

An example of a generalized profile description 

of a Spodosol is shown in Figure 2. Approximately 

8.4 million acres in Florida have been mapped as 

Spodosols. 

 ULTISOLS 

Ultisols are like Alfisols in that they have a 

horizon in which clay has accumulated to a 

significant extent (argillic horizon). Ultisols, 

however, are more developed and more leached than 

Alfisols. The soil properties associated with Ultisols 

are an argillic horizon, enough moisture for crops in 

most years, and a low supply of bases. They exist in 

relatively warm and moist climates, like northwest 

Florida, and therefore can be highly productive if 

managed properly. 

An example of a gene profile description of an 

Ultisol is shown in Figure 2. There are approximately 

6.9 million known acres of Ultisols in Florida. 

 KEY TO SOIL ORDERS IN FLORIDA 

In this gene key the soil orders are listed in the 

same sequence as in Soil Taxonomy. This key is an 

abbreviated guide. 

A. Soils that are organic in more than half the 

thickness of the upper 32 inches. 

Histosols 

B. Other soils that are mineral with an illuvial 

horizon of amorphous aluminum and organic matter 

with or without iron (a spodic horizon) within 80 

inches of the surface. 

Spodosols 

C. Other mineral soils with an illuvial horizon 

of clay (an argillic horizon), relatively low base 

saturation (< 35 %), and enough moisture for crops in 

most years. 

Ultisols 

D. Other mineral soils that have a thick, dark 

surface horizon which is relatively rich in organic 

matter (a mollic epipedon), have a high base 

saturation (> 50 %) throughout the soil, and do not 

have deep, wide cracks. 

Mollisols 

E. Other mineral soils with an illuvial horizon 

of clay (an argillic horizon), relatively high base 

saturation (> 35 %), and enough moisture for crops in 

most years. 

Alfisols 

F. Other mineral soils that have no horizon of 

illuvial clays, relatively little organic matter or base 

saturation or both, some diagnostic horizons and 

weatherable minerals, and enough moisture for a crop 

in most years. 

Inceptisols 

G. Mineral soils with weak or no diagnostic 

horizons. 
Key to Soil Orders in Florida 

4

Entisols 

 LITERATURE CITED 

Carlisle, V. W. and Brown, R. B. (eds.). 1982. 

Florida Soil Identification Handbook . IFAS 

Publication. 

Soil Survey Staff. 1996. Keys to Soil Taxonomy. 

U.S. Government Printing Office, Washington, D.C.