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II. Horizons of Fragipan Soils
FRAGIPAN SOILS OF THE EASTERN UNITED STATES
containing discontinuous eluvial parts. The Be notation may find use as a
designation for lower eluvial horizons that cannot be designated A'2 or
B & A.
The uppermost panel of Fig. 2 illustrates the most general statements
that may be made about the position of the fragipan. All fragipans occur
beneath an eluvial horizon unless the soil has been eroded severely. In
FIG.2. Horizon sequences of soils with fragipans in the eastern United States. Elements
within brackets indicate characteristics that are not essential to the definition of the sequence. The fragipan horizons are indicated by the suffix x: the suffix t denotes silicate
clay sufficient for recognition of an argillic horizon.
some soils, more often the wetter ones, the fragipan occurs immediately
beneath the eluvial horizon. In many soils, however, there is an intervening B horizon, which may be a spodic horizon, a cambic horizon, or
an argillic horizon. Some soils with fragipans are bisequal. The fragipan
may occur in the lower eluvial horizon and not in the underlying B
horizon, in the lower B horizon but not in the second eluvial horizon,
or in both. These variations form the basis for the four classes of horizon
sequences shown in the set of panels designated Ia through Id; these are
illustrated by soil descriptions in the Appendix. These four classes are
B. GROSSMAN A N D F. J. CARLISLE
subdivided to give the eight classes, IIa through IIh. Accumulation of
clay and occurrence of the fragipan in the lower eluvial horizon are the
criteria for these subdivisions. Further subdivisions could be made. Panel
IIf, for example, could be subdivided into soils with argillic, spodic, or
cambic horizons above the fragipan. Brackets are placed around the
horizon designations or elements of the horizon designations that are not
necessary to the definition.
In Fig. 2 the suffix t denotes an accumulation of silicate clay sufficient
for recognition of an argillic horizon. This is a more limiting use of the t
suffix than is specified by the Soil Survey Staff ( 1 962). The horizon symbols in Fig. 2 are only for convenience in discussing this subject; it is
not suggested that any of these symbols should replace horizon designations in current use.
Soils with horizon sequences Ha, Ilc, and IIe have fragipans in
horizons where the parent material has been weakly altered. Many of
the soils with fragipans in the northeastern United States developed in
Wisconsin glacial till belong in one of these three classes. In contrast
are fragipans in soils that have horizon sequences IIb, IId, IIf, IIg, and
IIh. In these soils, alteration of the parent material of the fragipan by
eluviation, illuviation, or both, has been strong. Hence, influence of the
parent material in determining the properties of the fragipan is less important. Fragipans in soils south of the Wisconsin glacial advance tend
to exhibit stronger alteration of the parent material.
Fragipan expression involves thickness and depth to its upper boundary. These are considered in subsequent paragraphs of this section. It
also involves properties, such as consistence, structure, and pore
arrangement, that determine mechanical impedance to root penetration
and rate of movement of low-tension water. Objective measurement and
integration of these properties has not been achieved. Within a local
association of soils, however, evaluation of relative degree of fragipan
expression has validity. Maximum degree of expression of the fragipan is
commonly reported for the soils of intermediate wetness (Neeley, 1965;
A. E. Thomas, 1967; Redmond and Engberg, 1967; Grossman et al.,
1959a; Nettleton et al., 1968a). This intermediate wetness is described
approximately by the terms somewhat poorly and poorly drained (Soil
Survey Staff, 195 1) and by the Aquic subgroups of the soil classification
system (Soil Survey Staff, 1967). The relationship is widespread enough
to suggest implication in the genesis of the fragipan.
FRAGIPAN SOILS OF THE EASTERN UNITED STATES
Excluding severely eroded soils, the depth to the fragipan ranges from
about 10 to 150 cm., with the upper boundary for most between 25 and
100 cm. In landscapes that have been affected by severe erosion, depth
to the fragipan often is closely related to past land use and to the slope.
The area of occurrence of Grenada soils in Grenada County, Mississippi
(A. E. Thomas, 1967) is an example (see Appendix for description).
Concepts have centered on the less eroded soils. Consequently, in many
areas fragipans are shallower than much of the literature would suggest.
On a given landscape the depth is frequently relatable to wetness of the
soil. Two of many examples have been selected. Neeley ( 1965), studying
fragipans in soils of New York developed in medium-textured glacial till,
reported a range of 75 to 30 cm. to the top of the fragipan from the drier
to the wetter soils. The soils range from sequence IIe through IIc to I Ia of
Fig. 2. A. E. Thomas ( 1 967), working with soils developed in loess in
Mississippi, reports a range from 50 to 10 cm. Sequences involved are
IIf and IIb.
In some associations, the fragipan is not shallower in the wetter soils.
Soils of the Lebanon series and related soils in the Missouri Ozarks
(Krusekopf, 1942; Scrivner, 1960) have a fragipan immediately beneath
and perhaps partly within the loess that covers a buried soil (sequence
1Ig or JIh). Fragipans in this soil association are no shallower in the somewhat wetter soils that occur in slight depressions than in the associated
better drained soils.
Thickness ranges from about I5 to 125 cm. In some local associations
in the northeastern states, thickness remains fairly constant over a considerable range in wetness (Carlisle, 1954; Neeley, 1965). These fragipans are weakly altered and bear a strong imprint of the compact glacial
till parent material. The drier soils have sequences IIc and IIe of Fig. 2;
the wetter, sequence IIa. Constant thickness over a wide range in wetness is not restricted to fragipans with strong parent material influence.
Bailey (1964) reports rather constant thickness for the fragipans in
strongly illuvial horizons (sequence Ild, Fig. 2 ) of some soils developed
from limestone residuum and mixed sedimentary rocks in Kentucky. In
certain loess-derived soils of the middle and lower Mississippi Valley,
the fragipans become thicker in the wetter soils of the association (A. E.
Thomas, 1967; Bailey, 1964). The fragipans in these soils are strongly
affected by illuviation, eluviation, or both. The drier of these soils have
sequences IId, IIf, and IIg; the wetter soils, sequence IIb. In other
associations of loess-derived soils in the same general area, the fragipan
thins with increasing wetness (Grossman el al., 1959a). Nettleton et al.
( 1968a), in their study of fragipans in certain soils of North Carolina de-
R. B. GROSSMAN A N D F. J . CARLISLE
veloped from Coastal Plain sediments (sequence IIh, Fig. 2), also report
thinning of the fragipan with increasing wetness.
111. Occurrence of Fragipan Soils
The occurrence of soils with fragipans may be considered at several
scales. Looking at the country as a whole, fragipans have been recognized in some soils in all states east of the Mississippi River and in adjacent Minnesota, Missouri, Arkansas, Oklahoma, Louisiana, and eastern
Texas. Soils with fragipans are the principal soils in some parts of that
area, and they are of minor extent in other parts. They have been reported
in the western states (Cline, 1952; Whittig et al., 1957) but seem to be
of very minor extent and importance there. Figure 3 shows areas in the
United States where one or more of the principal kinds of soils have
FIG. 3. Areas in the United States where one or more of the principal kinds of soils have
fragipans. The most extensive soils in the areas delineated are: A, Altisols: I , Inceptisols;
S , Spodosols: U and U 2 , Ultisols (generalized from Soil Conservation Service, 1969, except U 2 delineations, which are from Bartelli, 1968). Dashed line shows the approximate
eastern boundary of the prairie (generalized from Shantz and Zon, 1914).
FRAGIPAN SOILS OF THE EASTERN UNITED STATES
fragipans. They are extensive and may be among the principal soils in
areas where the dominant soils are Spodosols, Inceptisols, Alfisols, or
Ultisols in the warm humid and the cold humid, central and eastern parts
of the country. Fragipans apparently do not occur in soils of the humid
prairies, the Great Plains, or the semiarid and arid areas of the west.
The following relationships are evident in the broad-scale occurrence
of fragipan soils: ( 1 ) Fragipans are restricted to areas where the excess
of precipitation over evapotranspiration is sufficient at some time of the
year for movement of water down through the soil. (2) They occur in
both warm and cold climates. (3) Fragipans seemingly are absent in soils
of the extensive natural grasslands of the humid prairies and the Great
Plains. (4) Fragipans occur in Spodosols, lnceptisols, Alfisols, and
Ultisols. Spodosols with fragipans are so common as to suggest a genetic
Other relationships may be evident at the larger scale of soil association maps for counties where fragipans are important. The occurrence
of fragipan soils in relation to composition of soil parent materials
apparently is complex when viewed generally. But local relationships
may be evident, especially if the soils are not old. The surveys of Tompkins County, New York (Neeley, 1965) and of Franklin County, New
York (Carlisle, 1958) illustrate the influence of lime content of parent
material on occurrence of soils with fragipans. In these areas soils with
well expressed fragipans are prevalent in areas of low-lime glacial till
and absent in areas of high-lime till. The Franklin County, New York,
survey illustrates the influence of texture of soil materials on the occurrence of soils with fragipans. I n that area fragipans are present in Spodosols developed in relatively well-graded glacial till and are absent in
Spodosols developed in poorly graded glaciofluvial materials of roughly
comparable mineralogical composition. In Tate County, Mississippi (J. S.
Huddleston, 1967) the distribution of soils with fragipans on the countywide scale is related in part to the loess distribution pattern and to the
pattern of geological erosion. Other illustrations of these kinds of local
relationships may be found in published soil surveys of areas shown in
For a multicounty area in southern New York and northern Pennsylvania, Denny and Lyford ( 1963) showed the distribution of soil associations in which soils with fragipans are extensive. They concluded that
within the region studied many of the soil differences are primarily related to kind of parent material and its hydrologic characteristics.
A third and still larger scale is the detailed soil map showing delineations dominated by a particular kind of soil. This is the scale commonly
used in planning farming practices for individual fields and farms. To