235

directly on the spodic horizon, do not have tongues of such
a subhorizon;

f, If plowed and the upper part of the spodic horizon thus is
mixed in the Ap horizon and the soil does not have a con-
tinuous albic horizon, have more than 1.2 percent organic
carbon in the Ap horizon; and

g. Do not have a surface horizon >30 cm thick that meets all
the requirements for a plaggen epipedon except thickness.
Alfic Fragiorthods are like Typic Fragiorthods except for a,
with or without ¢ or f, or both, and have base saturation of
35 percent or more in some part of the argillic or kandic
horizon or have a mean annual soil temperature less than
8°C.

Aquentic Fragiorthods are like Typic Fragiorthods except for
band c or for b, ¢, and f.

Aquic Fragiorthods are like Typic Fragiorthods except for b.
Cryic Fragiorthods are like Typic Fragiorthods except for d.
Entic Fragiorthods are like Typic Fragiorthods except for c.
Humic Fragiorthods are like Typic Fragiorthods except for
e.

Plaggeptic Fragiorthods are like Typic Fragiorthods except
for g.

Haplorthods
Distinctions between Typic Haplorthods and other subgroups

Typic Haplorthods are the Haplorthods that
a, Do not have an argillic or kandic horizon below the
spodic horizon;
b. Have a spodic horizon that has one or more of the fol-
lowing:
(1) A continuous horizon at least 2.5 cm thick that is
very firm or extremely firm when moist (ortstein);
(2) A texture of very fine sand or finer and is more than
10 cm thick and has a weighted average of at least 1.2
Percent organic carbon in the upper 10 cm; or
(3) A coarse-loamy, loamy-skeletal, sandy-skeletal, or
sandy particle-size class and color value and chroma,
moist, of 3 or less in at least the upper 7.5 cm of the
spodic horizon;
¢. Do not have distinct or prominent mottles of approximate
spherical shape in the spodic horizon unless the variability
in color is associated with differences in consistence in such
a manner that the redder or darker parts are extremely firm
or very firm, or, if the color is due to uncoated sand grains,
do not have the water table within 1 m of the soil surface
for as many as 60 days, cumulative, in most years;
d. Do not have chroma of 2 or less if mottled or chroma less
than 2 if not mottled, that is dominant in the matrix within
15 cm below the base of the spodic horizon and within 1 m
of the surface of the soil;
e. Do not have a horizon 15 cm or more thick below the
spodic horizon and within 1 m of the surface that has a
brittle matrix when wet or contains some durinodes;
f. Do not have a lithic contact within 50 cm of the surface;
g. Do not have a black intermittent upper subhorizon that
has a ratio of free iron (elemental) to carbon that is <0.2;
hh, Have <6 percent organic carbon in the upper 10 cm of
the spodic horizon;


58

B. Other soils that do not have a plaggen epipedon but that

have

either
1. A spodic horizon whose upper boundary is within 2 m
of the surface;

or
2. A placic horizon that meets all the requirements of a
spodie horizon except thickness and index of accumula-
tion and rests on a fragipan, on a spodic horizon, or on
an albic horizon that rests on a fragipan,

podosols, p. 227

C, Other soils that have:

either
1. An oxic horizon with its upper boundary within 150
cm of the soil surface and do not have a clay content
increase necessary to define the upper boundary of a
kandic horizon within a depth of 150 cm of the soil sur-
face,

or
2. 40 percent or more clay in the surface 18 cm, after
mixing, and, with its upper boundary within 150 cm of
the soil surface, either an oxic horizon, or a kandic hori-
zon that meets the weatherable mineral requirements of
an oxic horizon. .

Oxisols, p. 203

D. Other soils that
1, Do not have a lithic or paralithic contact, petrocalcic
horizon, or duripan within 50 cm of the surface;
and
2. After the soil to a depth of 18 cm has been mixed, as
by plowing, have 30 percent or more clay in all subhori-
zons to a depth of 50 cm or more;
and
3, Have, at some time in most years unless irrigated or
cultivated, open cracks’ at a depth of 50 cm that are at
least 1 cm wide and extend upward to the surface or to
the base of the plow layer or surface crust
and
4, Have one or more of the following;
a. Gilgai;
b, At some depth between 25 cm and 1 m, slickensides
close enough to intersect; or
c. At some depth between 25 cm and I m, wedge-
shaped natural structural aggregates that have their
long axes tilted 10° to 60° from the horizontal.
Vertisols, p. 259

Tn open crack is interproted to be a separation between gross polyhedrons.
If the surface horizons are strongly seff-mulching, that is, ifthe soil is a mass
of loose granules, or if the soil is cultivated while the cracks are open, the
cracks may be largely filled with granular materials from the surface. But
‘they are considered to be open in the sense that the polyhedrons are sep:
rated.



264

Coefficient of linear
extensibility, COLE.
Consistence
Contrasting mineralogy modifiers.
Control section for
particle-size classes.,
Control section for soil moisture
Coprogenous eart

Cryandepts 146
Cryaquents 113
Cryaquepts 151
‘Cryaquods .. 228
Cryaquolls.. 174

Cryoboralfs

Cryofluvents
Cryofolists..
Cryohemists
Cryohumods..
Cryopsamments.
Cryorthents
Cryorthods
Cryosaprists.
Cryumbrepts

Depth of soil. oo
Diagnostic subsurface horizons
Diagnostic surface horizons...
Diatomaceous earth
Durandepts.
Duraqualfs
Duraquods..
Duraquolls..
Durargids

Durochrepts ..
Durorthids..
Durustalfs
Durustoll:
Dystrandepts
Dystrochrepts.
Dystropepts

Eutraquox .

Eutroboralfs...
Eutrochrepts
Eutropepts..
Eutroperox
Eutrotorrox
Eutrudox....
Eutrustox,

Family differentiae
Family differentiae for histosols.



125

d. Have base saturation (by NH,OAc) of 60 percent or more
in some part of the soil between depths of 25 cm and 75 cm
below the soil surface.

Aquic Xerorthents are like Typic Xerorthents except for a.
Aquic Durorthidic Xerorthents are like Typic Xerorthents
except for a and b,

Durorthidic Xerorthents are like Typic Xerorthents except
for 6.

Dystric Xerorthents are like Typic Xerorthents except for d.
Lithic Xerorthents are like Typic Xerorthents except for c or
for ¢ and d.

Psamments
Key to great groups

JCA. Psamments that have a cryic or pergelic soil tempera-
ture regime.
Cryopsamments, p. 125

JCB, Other Psamments that have a torric moisture regime.
Torripsamments, p. 127

JCC. Other Psamments that have, in the particle size
control section, more than 90 percent silica minerals
(quartz, chalcedony or opal) or other extremely durable
minerals in the 0.02 to 2mm fraction that are resistant to
weathering.

Quartzipsamments, p. 126

JCD. Other Psamments that have a udic moisture regime and
mean summer and mean winter soil temperatures at a depth
of 50 cm that differ by S°C or more.

Udipsamments, p, 127

ICE, Other Psamments that have a udic moisture regime.
‘Tropopsamments, p. 127

JCF. Other Psamments that have a xeric moisture regime.
Xeropsamments, p. 129

JCG. Other Psamments.
Ustipsamments, p, 128

Cryopsamments

Distinctions between Typic Cryopsamments and other sub-
groups

Typic Cryopsamments are the Cryopsamments that

a. Do not have lamellae within 1.5 m of the soil surface that
meet all requirements for an argillic horizon except thick-
ness;

b. Do not have mottles that have chroma of 2 or less within
50 cm of the soil surface;

by Have @ mean annual soil temperature that is higher than
0°c;

d, Do not have a lithic contact within 50 cm of the soil
surface; and

e. Do not have an albic horizon that is 5 cm or more thick
and underlain by a horizon that has a color value one unit


25

faces, commonly branching, but they may come and go with
the seasons and may be only lime that was precipitated in a
single season by the withdrawal of stored soil moisture
rather than a k horizon.

Soft coatings on hard lime concretions are also excluded
from the meaning of soft powdery lime, These may be thin
or thick, and they may be the result of either current accu-
mulation or removal of lime. That is, the concretion may be
growing or may be undergoing dissolution, and either pro-
cess can produce a soft coating,

Soil moisture regimes

The soil moisture regime, as the term is used here, refers to
the presence or absence either of ground water or of water
held at a tension <1500 kPa in the soil or in specific hori-
zons by periods of the year. Water held at a tension of 1500
kPa or more is not available to keep most mesophytic plants
alive. The availability of water also is affected by dissolved
salts. A soil may be saturated with water that is too salty to
be available to most plants, but it would seem better to call
such a soil salty rather than dry. Consequently, we consider
a horizon to be dry when the moisture tension is 1500 kPa
or more. If water is held at a tension of <1500 kPa but
more than zero, we consider the horizon to be moist. A soil
may be continuously moist in some or all horizons through-
out the year or for some part of the year. It may be moist
in winter and dry in summer or the reverse. In the northern
hemisphere, summer refers to the months of June, July, and
August, and winter means December, January, and Febru-
ary. A soil or a horizon is considered to be saturated with
water when water stands in an unlined borehole close
enough to the soil surface or to the harizon in question that
the capillary fringe® reaches the surface or the top of the
horizon.

Soil moisture control section

‘The intent in defining the soil moisture control section is to
facilitate estimation of soil moisture regimes from climatic
data, The upper boundary of this control section is the
depth to which a dry (tension >1500 kPa but not air dry)
soil will be moistened by 2.5 cm (I in.) of water within 24
hours. The lower boundary is the depth to which a dry soil
will be moistened by 7.5 cm (3 in.) of water within 48
hours, These depths are exclusive of the depth of moisten-
ing along any cracks or animal burrows that are open to the
surface.

If 7.5 cm of water moistens the soil to a lithic, petroferric,
or paralithic contact or to a petrocalcic horizon or a duripan,
the upper boundary of the rock or of the cemented horizon
is the lower boundary of the soil moisture control section,

If 2.5 cm of water moistens the soil to one of these contacts
or horizons, the soil moisture control section is the lithic
contact itself, the paralithic contact, or the upper boundary

"The capillary fringe
sure) that remains almost
382),

bove the water table (zero gauge pres-
sturated (Soil Sci. Soc. Amer. Glostnry, 1986,


158

e. Do not have an argillic horizon in any part of the pedon;
and

f. Have an Ap horizon that has a color value, moist, of 4 or
more or a color value, dry, of 6 or more, crushed and
smoothed, or the upper soil to a depth of 18 cm, after
mixing, has these colors.

Andie Dystrochrepts are like Typic Dystrochrepts except for

awe Dystrochrepts are like Typic Dystrochrepts except for

Fluvaquentic Dystrochrepts are like Typic Dystrochrepts
except for b and c.

Fluventic Dystrochrepts are like Typic Dystrochrepts except
for c.

Fluventic Umbric Dystrochrepts are like Typic Dystrochrepts
except for c and f.

Lithic Dystrochrepts are like Typic Dystrochrepts except for

Lathe Ruptic-Alfic Dystrochrepts are like Typic
Dystrochrepts except for d and e, they have an argillic
horizon in less than half of each pedon, and their base
saturation (by sum of cations) in the subhorizon just above
the lithic contact that is 35 percent or more,

Lithic Ruptic-Ultic Dystrochrepts are like Typic
Dystrochrepts except for d and e, and they have an argillic
horizon in less than half of each pedon and have base
saturation (by sum of cations) in the subhorizon just above
the lithic contact that is <35 percent.

Ruptic-Alfic Dystrochrepts are like Typic Dystrochrepts
except for e and they have an argillic horizon in less than
half of each pedon and base saturation (by sum of cations)
that is 35 percent or more at a depth 1.25 m below the
upper boundary of the argillic horizon or just above a lithic
or paralithic contact if one is present at a shallower depth.
Ruptic-Ultic Dystrochrepls are like Typic Dystrochrepts
except for e, and they have an argillic horizon in less than
half of each pedon and have base saturation (by sum of
cations) that is <35 percent at a depth 1.25 m below the top
of the argillic horizon.

Umbric Dystrochrepts are like Typic Dystrochrepts except
for f.

Eutrochrepts

Distinctions between Typic Eutrochrepts and other
subgroups

Typic Eutrochrepts are the Eutrochrepts that
a. Do not have @ layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction and that
has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
b. Do not have mottles that have chroma of 2 or less within
60 cm of the soil surface if the mottled horizon is saturated


153

(b) If the hue is 2.5Y or redder and the value, moist,
is 5 or less, the chroma, moist, is 1 or less;
(c) If the hue is yellower than 2.5Y, the chroma,
moist, is 2 or less;
(3) The chroma, moist, is 1 or less and mottles may or
may not be present;
b, Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;

¢, Have an Ap horizon that has a color value, moist, of 4 or

more or has a value, dry, of 6 or more when crushed and

smoothed, or have an A horizon that is <15 cm thick if its

color value, moist, is lower than 3.5;

d, Have an 7 value of <0.9 between depths of 50 and 80 cm

and <0.7 in all layers between 20 and 50 cm;

e. Do not have a lithic contact within 50 cm of the soil

surface;

f. Do not have the following combination of characteristics;
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or to the base of an Ap horizon; and
(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
‘upper 1 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
im, and
(3) More than 35 percent clay in horizons that total >50
om in thickness; and

g. Do not have either of the following:

(1) Jarosite mottles and a pH between 3.5 and 4.0 (1:1
water, air dried slowly in shade) in some subhorizon
within 50 cm of the soil surface, or

(2) Jarosite mottles and a pH <4.0 (1:1 water, air dried
slowly in shade) in some subhorizon between depths of
50 and 150 cm.

Aeric Haplaquepts are like Typic Haplaquepts except for a

or for a and c.

Humic Haplaquepts are like Typic Haplaquepts except for c,

and the base saturation (by NH,OAc) is <50 percent in some

horizon and does not increase with depth to a value of 50

percent or more.

Lithic Haplaquepts are like Typic Haplaquepts except for ¢

or for a and e.

Mollic Haplaquepts are like Typic Haplaquepts except for c,

and the base saturation (by NH,OAc) is 50 percent or more

throughout or increases with depth to a value of 50 percent
or more.

Sulfic Haplaquepts are like Typic Haplaquepts except for g,

with or without all or any of a, c, d, or f.

peda, the chroma, moist, should be 1 or less immediately below any surface
horizon that has & value, moist, leo than 5.


ii
KEYS TO SOIL TAXONOMY

Prepared by Agronomy Department
Cornell University
Ithaca, NY

For
THE SOIL MANAGEMENT SUPPORT SERVICES

Soil Management Support Services is a program of interna-
tional technical assistance in soil survey, classification, in-
terpretation, and use and management of soils in the in-
tertropical countries of the Agency for International Devel-
opment implemented by the Soil Conservation Service of the
United States Department of Agriculture under PASA No.
AG/DSB-1129-5-79.

This publication was produced under a cooperative agree-
ment between the Soil Management Support Services (SMSS)
and the College of Agriculture and Life Sciences at Cornell
from funding by the Agency for International Development
(ALD.).

The contents of this publication were provided by the Soil
Conservation Service (SCS). The Agronomy Department pre-
pared the camera-ready manuscript from text-files provided
by SCS, rearranged some sections, produced the index, and
converted measurement units into International System of
Units (SI) terms.

To obtain additional copies in developing countries:

Ask your AID country mission or write to:
SMSS Program Leader

Soil Conservation Service

US. Department of Agriculture

P.O. Box 2890

Washington, DC 20013

To obtain additional copies in the USA and developed coun-
tries write to:

International Soils

Department of Agronomy

Bradfield Hall

Cornell University

Ithaca, NY 14853

US and developed countries’ requests should include a check
for $12.00 in US dollars per copy made out to the Agron-
omy Dept., Cornell University.

Citation:

Soil Survey Staff, 1987. Keys to Soil Taxonomy (third
printing), SMSS technical monograph no. 6, Ithaca, New
York.

Third Printing
1987

ISBN 0-932865-10-0


124

JEB. Other Orthents that have a torric moisture regime or
that have a conductivity of the saturation extract that is 2 dS
m’! or greater at 25°C in some part above whichever of the
following depths is the least; a lithic or paralithic contact or
1.25 m if particle-size class” is sandy, 90 cm if loamy, and
75 cm if clayey.

Torriorthents, p. 112

JEC, Other Orthents that have a xeric moisture regime.
Xerorthents, p, 124

JED, Other Orthents that have a udic moisture regime and
mean summer and mean winter soil temperatures at a depth
of 50 cm that differ by <5°C.

Troporthents, p. 123

JEE. Other Orthents that have a udic moisture regime.
Udorthents, p. 123

JEF, Other Orthents.
Ustorthents, p. 124

Cryorthents
Distinctions between Typic Cryorthents and other subgroups

Typic Cryorthents are the Cryorthents that
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density in the fine~earth fraction (at 33 kPa
water tension) of 0.95 g per cubic centimeter or less and
that has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water >1.5
and more exchange acidity than the sum of bases plus
KCl-extractable aluminum;
b. Do not have mottles that have chroma of 2 or less within
50 cm of the soil surface;
¢. Do not have a lithic contact within 50 cm of the soil
surface;
d. Have a mean annual soil temperature that is higher than
0°C; and
e. Do not have lamellae within 1.5 m of the soil surface that
meet all requirements for an argillic horizon except thick-
ness®,
Alfic Cryorthents are like Typic Cryorthents except for ¢.
Alfic Andeptic Cryorthents are like Typic Cryorthents except
for a, and e,
Andeptic Cryorthents are like Typic Cryorthents except for
a.
Aquic Cryorthents are like Typic Cryorthents except for b.
Lithic Cryorthents are like Typic Cryorthents except for c,
with or without d.

The weighted average ps class between a depth of 1 m or a lithic or
Batalithic contact, whichever is shallower,

"The clay content cannot be estimated with precision in lamellaa that are
vary thin. ‘The lamelige in soils of alfic subgroups generally are about 0.$ to 1
‘em thick, but their total thickness is lees than the 15 cm requited for an
argillic horizon.



68

(a) If the hue is 2.5Y or redder and the value, moist,
is more than 5, the chroma is 2 or less;
(b) If the hue is 2.5Y or redder and the value, moist,
is 5 or less, the chroma, moist, is ! or less;
(c) If the hue is yellower than 2.5Y, the chroma, moist
is 2 or less;
(3) The chroma, moist, is 1 or less whether mottled or
not;
b. Do not have a layer above a depth of 75 cm that has a
texture finer than loamy fine sand, that is as much as 18 cm
thick, that has bulk density (at 33 kPa water tension) of 0.95
& per cubic centimeter or less in the fine-earth fraction, and
that has either
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>LS and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
c. Have an Ap horizon that has either a color value, moist,
of 4 or more or a color value, dry, of 6 or more after the
soil has been crushed and smoothed; or the upper soil to a
depth of 18 cm, after mixing, has these color values;
d. Have texture finer than loamy fine sand in some sub-
horizon within 50 cm of the surface; and
e. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm and at least 30 cm long in
some part and that extend upward to the surface or to
the base of an Ap or an albic horizon,
(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper soil to a depth of 1 m or in the whole soil if a
lithic, paralithic, or petroferric contact is deeper than 50
cm but not deeper than | m, and
(3) More than 35 percent clay in horizons that have total
thickness of >50 cm.
Aeric Ochraqualfs are like Typic Ochraqualfs except for a.
Aeric Umbrice Ochraqualfs are like Typic Ochraqualfs except
for a and c and have an epipedon that meets all the re~
quirements of an umbric epipedon except thickness,
Andaqueptic Ochraqualfs are like Typic Ochraqualfs except
for 5 or for a and b.
Arenic Ochraqualfs are like Typic Ochraqualfs except for d,
with or without a, or c, or both, and have a sandy epipedon
between 50 cm and 1 m thick.
Grossarenic Ochraqualfs are like Typic Ochraqualfs except
for d, or for a and d, and have a sandy epipedon >1 m
thick.
Mollic Ochraqualfs are like Typic Ochraqualfs except for ¢
and have an epipedon that meets all the requirements of a
mollic epipedon except thickness.
Udollic Ochraqualfs are like Typic Ochraqualfs except for a
and ¢ and have an epipedon that meets all the requirements
of a mollic epipedon except thickness.
Umbric Ochraqualfs are like Typic Ochraqualfs except for c
and have an epipedon that meets all the requirements of a
umbric epipedon except thickness.
Vertic Ochraqualfs are like Typic Ochraqualfs except for ¢
with or without a or c, or both,


Kanhaplaqualts

Distinctions between Typic Kanhaplaquults and other sub-
groups

Typic Kanhaplaquults are the Kanhaplaquults that
a. Have an ochric epipedon;
b. Do not have a subhorizon that has dominant chroma of 3
or more within 75 cm of the soil surface;
¢. Do not have a horizon within 150 cm of the soil surface
that has >5 percent plinthite by volume; and
d. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either of the following:
1. A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
2. A ratio of CEC (pH 8.2) to 1500 kPa water of <1.5
and more exchange acidity than the sum of bases plus 1
M KCl-extractable aluminum.
Aeric Kanhaplaquults are like Typic Kanhaplaquults except
for b.
Aerie Umbric Kanhaplaquults are like Typic Kanhaplaquults
except for a and b.
Andie Kanhaplaquults are like Typic Kanhaplaquults except
for d, with or without a or 6, or both.
Plinthic Kanhaplaquults are like Typic Kanhaplaquults ex-
cept for c, with or without b,
Umbric Kanhaplaquults are like Typic Kanhaplaquults except
‘or a.

Ochraquults
Distinctions between Typic Ochraquults and other Subgroups

‘Typic Ochraquults are the Ochraquults that:

a. Have dominant chroma of 2 or less in all subhorizons
between the A or Ap horizon and a depth of 75 cm.

b. Have texture finer than loamy fine sand in some sub-
horizon within 50 cm. of the surface.

Aeric Ochraquults are like Typic Ochraquults except for a.
Arenic Ochraquults are like Typic Ochraquults except for b,
with or without a, and they have a sandy particle-size class
to a depth of between 50 cm and Jm.

Paleaquults
Distinctions between Typic Paleaquults and other subgroups

Typic Paleaquults are the Paleaquults that

a, Do not have a horizon that has dominant chroma of 3 or
more within 75 cm of the soil surface;

b. Do not have an epipedon as thick as 50 cm if the parti-
cle-size class is sandy throughout;

¢. Have <5 percent plinthite (by volume) in all horizons
within 1.5 m of the soil surface; and

d. Have an ochric epipedon.

Aeric Paleaquults are like Typic Paleaquults except for a.


156

Lithic Tropaquepts are like Typic Tropaquepts except for c.

Plinthic Tropaquepts are like Typic Tropaquepts except for ¢
or for a and e,

Sulfic Tropaquepts are like Typic Tropaquepts except for f,

with or without all or any of a, b, or d.

Vertic Tropaquepts are like Typic Tropaquepts except for d,

with or without a.

Ochrepts
Key to great groups

IEA. Ochrepts that have a fragipan.

Fragiochrepts, p. 160
TEB. Other Ochrepts that have a duripan whose upper
boundary is within 1 m of the soil surface.

Durochrepts, p. 157

TEC. Other Ochrepts that have a cryic or pergelic
temperature regime.
Cryochrepts, p. 156

TED. Other Ochrepts that have an ustic moisture regime,
Ustochrepts, p. 160

IEE. Other Ochrepts that have a xeric moisture regime.
Xerochrepts, p, 161

YEF. Other Ochrepts that have one or both of the following:
1. Carbonates in the cambic horizon or in the C horizon
but within the soil; or
2. Base saturation (by NH,OAc) that is 60 percent or
more in some subhorizon between depths of 25 and 75
cm below the soil surface.

Eutrochrepts, p. 158

TEG, Other Ochrepts.
Dystrochrepts, p. 157

Cryochrepts
Distinctions between Typic Cryochrepts and other subgroups

Typic Cryochrepts are the Cryochrepts that

a. Have a mean annual soil temperature higher than 0°C;
b, Do not have a lithic contact within 50 cm of the soi
surface;

c. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizon is saturated
with water at some period when its temperature is 25°C or
the soil has artificial drainage.

d. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either (1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less, or (2) a ratio of CEC (at pH
near 8) to 1500 kPa water of >1.5 and more exchange
acidity than the sum of bases plus KCi-extractable
aluminum;



79

¢. Have an argillic or a kandic horizon that has a color
value, dry, of 5 or more in some subhorizon or a color
value, moist, that is less than the value, dry, by more than |
unit, unless the hue in some part of the argillic or kandic
horizon is SYR or yellower.

Aquic Kanhapludalfs are like Typic Kanhapludalfs except
for a.

Lithic Kanhapludalfs are like Typic Kanhapludalfs except
for b.

Rhodic Kanhapludalfs are like Typic Kanhapludalfs except
for c.

Natrudalfs
Distinctions between Typic Natrudalfs and other subgroups

Typic Natrudalfs are the Natrudalfs that

a, Have mottles that have chroma of 2 or less within 25 cm

of the upper boundary of the natric horizon;

b. Have an Ap horizon that has a color value, moist, of 3 or

more, or the soil to a depth of 18 cm, after mixing, has that

color value;

c. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part and that extend to the surface or to the
base of an Ap horizon;

(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper I m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1 m; and

(3) More than 35 percent clay in horizons that total >50
em in thickness; and

d. Do not have tonguing or interfingering of albic materials

more than 2.5 cm into the natric horizon,

Glossic Natrudalfs are like Typic Natrudalfs except for d.

Vertic Natrudalfs are like Typic Natrudalfs except for c.

Distinctions between Typic Paleudalfs and other subgroups

Typic Paleudalfs are the Paleudalf’s that

a. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizons are satu-
rated with water at some time when the soil temperature at
that depth is 5°C or higher or the soil has artificial drainage;
b. Have texture finer than loamy fine sand in some sub-
horizon within 50 cm of the surface;

. Have an Ap horizon that has a color value, moist, of 3.5
or more or a color value, dry, more than 1 unit higher than
the value, moist, or the upper soil to a depth of 18 cm, after
mixing, has these colors;

d. Have an argillic horizon that has a color value, dry, of
4.5 or more in some subhorizon, or a color value, moist, that
is less than the value, dry, by more than one unit unless the
hue in some part of the argillic horizon is SYR or yellower;
e. Do not have the following combination of characteristics:



274

Horizons dominated by properties of one master horizon
but having subordinate properties of another. Two capital
letter symbols are used, as AB, EB, BE, BC. The master
horizon symbol that is given first designates the kind of
horizon whose properties dominate the transitional horizon.
An AB horizon, for example, has characteristics of both an
overlying A horizon and an underlying B horizon, but is
more like the A than like the B.

In some cases, a horizon can be designated as transitional
even if one of the master horizons to which it is appar-
ently transitional is not present. A BE horizon may be rec-
ognized in a truncated soil if its properties are similar to
those of a BE horizon in a soil in which the overlying E
horizon has not been removed by erosion. An AB or a BA
horizon may be recognized where bedrock underlies the
transitional horizon. A BC horizon may be recognized even
if no underlying C horizon is present; it is transitional to
assumed parent material,

Horizons in which distinct parts have recognizable proper-
ties of the two kinds of master horizons indicated by the
capital letters, The two capital letters are separated by a
virgule (/), as E/B, B/E, B/C, Most of the individual parts
of at least one of the components are surrounded by the
other.

The designation may be used even though horizons similar
to one or both of the components are not present, if the
separate components can be recognized in the transitional
horizon. The first symbol is that of the horizon that makes
up the greater volume.

SUBORDINATE DISTINCTIONS WITHIN MASTER
HORIZONS AND LAYERS

Lower case letters are used as suffixes to designate spe-
cific kinds of master horizons and layers. The symbols and
their meanings are as follows:

The word “accumulation” is used in many of the definitions.
As used here accumulation means that the horizon must have
more of the material in question than the parent material is
presumed to have had.

a Highly decomposed organic material

This symbol is used with “O" to indicate the most
highly decomposed of the organic materials.
Rubbed fiber content averages less than about 1/6
of the volume.

b Buried genetic horizon

This symbol is used in mineral soils to indicate
identifiable buried genetic horizons if the major
features of the buried horizon had been established
before it was buried. It is not used in organic soils
or to separate an organic layer from a mineral
layer. Genetic horizons may or may not have
formed in the overlying material, which may be


Natric horizon

The natric horizon (NL. natrium, sodium; implying presence
of sodium) is a special kind of argillic horizon. It has, in
addition to the properties of the argillic horizon:

1. Either
a. Prisms or, more commonly, columns in some part,
usually the upper part, that may or may not break to
blocks; or
b. Rarely, blocky structure and tongues of an eluvial
horizon, in which there are uncoated silt or sand grains,
extending more than 2.5 cm into the horizon; and

2, Either
a, The SAR® is 213 ( or 15 percent or more saturation
with exchangeable sodium) in some subhorizon within 40
cm of the upper boundary; or
b. More exchangeable magnesium plus sodium than cal-
cium plus exchange acidity (at pH 8.2) in some subhori-
zon within 40 cm of the upper boundary if the SAR is
213 (or ESP 215) in some horizon within 2 m of the sur-
face.

Oxic horizon

The oxic horizon is a horizon beginning at 18 em or more
below the soil surface that;

1. Is at least 30 cm thick;

2. Has a particle-size of sandy loam or finer in the fine
earth fraction;

3. Has a fine-earth fraction (<2 mm) that has an apparent
ECEC (NH,OAc bases plus 1 M KCI extractable Al) equal
or less than'12 cmol(+) kg” clay and has an apparent CEC
PH? (NH OAc CEC) equal to or less than 16 cmol(+) kg”
clay (measured clay or 3 x 1500 kPa water, whichever is
greater but less than 100);

4. Does not have as much as 10 percent weatherable miner-
als in the 50-200 micrometer fraction;

5. Has a diffuse upper particle-size boundary (i.e., <1.2
times clay content increase within a vertical distance of 15
em if the surface horizon contains 20-40 percent clay; less
than 4 percent absolute clay content increase if the surface
She percentage of exchi 1m (ESP) is used in the definition of the
atric horizon and in a number of the taxa. Since thie text was written, the
U.S. Salinity Laboratory (personal commitnication from C. A. Bower) has re-
vised its definition of sodic (alkali) soils and the method for measuting the
sodium adsorption ratio (SAR) as follows: SAR is measured by the normal
‘method if the conductivity (EC) of the saturation extract is <20 d8 m”! at
26°C. If the conductivity is >20 dS m”? and SAR is >10, SAR is determined
on a sample that has been leached with distilled water until EC of the
leachate decreases to about 4 48m" but not to <4. ESP of 216 ia replaced
by SAR of 219 if EC ia lange enough to require a correction for soluble salts
in calculating ESP, If EC is low enough (<4) that no correction is needed for
soluble ealte, ESP is determined directly from the replaced cations.



236

i, Have 1.2 percent or more organic carbon in the Ap hori-
zon if the Ap horizon extends into the upper part of the
spodic horizon,

Alfic Haplorthods are like Typic Haplorthods except for a
or for a and b, with or without i, and the argillic or kandic
horizon either has base saturation of 35 percent or more in
some part or has a mean annual soil temperature lower than
Br,

Aqualfic Haplorthods are like Typic Haplorthods except for
aand c, a and d, or a, ¢ and d, and the argillic or kandic
horizon either has base saturation of 35 percent or more in
some part or has a mean annual soil temperature lower than
Bc,

Aquentic Haplorthods are like Typic Haplorthods except for
b and c with or without d.

Aquic Haplorthods are like Typic Haplorthods except for ¢
or d or for both ¢ and d.

Duric Haplorthods are like Typic Haplorthods except for
or for c and e.

Entic Haplorthods are like Typic Haplorthods except for 6,
with or without i,

Entic Lithic Haplorthods are like Typic Haplorthods except
for f and 6, with or without i.

Humic Haplorthods are like Typic Haplorthods except for g
or h.

Lithic Haplorthods are like Typic Haplorthods except for f.
Ultic Haplorthods are like Typic Haplorthods except for a or
for a and b, with or without i, and the argillic or kandic
horizon has base saturation throughout of <35 percent and
has a mean annual soil temperature of 8°C or more.

Placorthods

These are the orthods that have a placic horizon in the
spodic horizon. They are not known to occur in the United
States, and they are thought to be rare elsewhere in the
world, Subgroups have not been defined.

Troporthods

These are the Orthods that have an isomesic or warmer iso
temperature regime, They are not known to occur in the
United States, but the group is provided for use elsewhere.
Subgroups have not been defined.


279

letter combination is used in both materials: Bs1-Bs2-2Bs3~-
2Bs4 is used, not Bs1~Bs2-2Bs1-2Bs2.

Sometimes, thick layers are subdivided during sampling

for laboratory analyses even though differences in morphol-
ogy are not evident in the field, These layers need to be
identified, and this is done simply by numbering each sub-
division consecutively within a layer having a unique sym-
bol, starting at the top. For example, four layers of a Bt
horizon sampled by 10-cm increments would be designated
Bel, Br2, Br3, Bed,

Discontinuities,--In mineral soils Arabic numerals are

used as prefixes to indicate discontinuities. Wherever
needed, they are used preceding A, E, B, C, and R. These
prefixes are distinct from Arabic numerals used as suffixes
to denote vertical subdivisions.

A discontinuity is a significant change in particle-

size distribution or mineralogy that indicates a difference in
the material from which the horizons formed or, except

for some buried soils, a significant difference in age.
Symbols to identify discontinuities are used only when they
will contribute substantially to the reader’s understanding of
relationships among horizons. The significance of a given
kind of discontinuity may be large in one soil and small in
another, or even large in one horizon and small in another
of the same profile. Stratification common to soils formed
in alluvium is not designated as discontinuities even if par-
ticle size dis mn differs markedly from layer to layer
unless genetic horizons have formed in the contrasting lay-
ers,

Where a soil has formed entirely in one kind of material,

a prefix is omitted from the symbol; the whole profile is
material 1. Similarly, the uppermost material in a profile
having two or more contrasting materials is understood to be
material 1, but the number is omitted. Numbering starts
with the second layer of contrasting material, which is des-
ignated "2". Underlying contrasting layers are numbered
consecutively. Even though a layer below material 2 is sim~
ilar to material 1, it is designated "3" in the sequence. The
numbers indicate a change in the material, not the type of
material. Where two or more consecutive horizons formed
in one kind of material, the same prefix number is applied
to ail of the horizon designations in that material: Ap-E-
Btl-2Bt2~2Bt3-2BC. The number suffixes designating sub-
divisions of the Bt horizon continue in consecutive order
across the discontinuity,

If an R layer is below a soil that formed in residuum and
the material of the R layer is presumed to be like that from
which the material of the soil weathered, the Arabic number
prefix is not used. If the R layer would not produce mate-
rial like that in the solum, the number prefix is used, as in
A-Bt-C-2R or A-Bt-2R. If part of the solum formed in
residuum, “R" is given the appropriate prefix: Ap~Btl-
2Bt2-2Bt3-2C1-2C2-2R,

Buried horizons (designated “b") are special problems. A
buried horizon is obviously not in the same deposit as hori~


201

(1) Cracks at some period in most years that are 1
cm or more wide at a depth of 50 cm, that are at
least 30 cm long in some part, and that extend up-
ward to the surface or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of
0.05 or mose in a horizon or horizons at least 50 cm
thick and a potential linear extensibility of 6 cm or
more in the upper 1.5 m of the soil or in the whole
soil if a lithic or a paralithic contact is deeper than
50 cm but shallower than 1,5 m; and
(3) More than 35 percent clay in horizons that have
a total thickness of >50 cm; and

h. Have a xeric moisture regime.

Aridic Palexerolls are like Typic Palexerolls except for h

and have an aridic moisture regime that borders on xeric.

Aridic Petrocalcic Palexerolls are like Typic Palexerolls ex-

cept for c and A, with or without a, and have an aridic

moisture regime that borders on xeric.

Pachic Palexerolls are like Typic Palexerolls except for d,

with or without all or any of a, 6, or h.

Petrocalcic Palexerolls are like Typic Palexerolls except for

¢, with or without a.

Ultic Palexerolls are \ike Typic Palexerolls except for /,

with or without a.



131

Chapter 8
Histosols
Key To Suborders

AA. Histosols that

1. Are never saturated with water for more than a few

days following heavy rains and
a. Have a lithic or paralithic contact <1 _m from the
surface or have fragmenta! materials in which the in-
terstices are filled or partly filled with organic mate-
rials in half or more of each pedon, or both; and
b, Less than three-fourths of the thickness of organic
materials consists of Sphagnum fibers.

Folists, p. 136

AB. Other Histosols that

1. Are dominantly’ fibric in the subsurface tier if that
tier is wholly organic except for a thin mineral layer or
layers, or the organic parts of the surface and subsurface
tiers are dominantly fibric if a continuous mineral layer
40 cm or more thick begins within the depth limit of the
subsurface tier; or
2. Have a surface mantle that has three-fourths or more
of its volume consisting of fibers derived from Sphagnum
and that rests on a jithic or paralithic contact, fragmental
materials, or mineral soil, or on frozen? materials within
the limits in depth of the surface or subsurface tier; and
3. Do not have a sulfuric horizon whose upper boundary
is within 50 cm of the surface and do not have sulfidic
materials within 1 m of the surface.

Fibrists, p. 132

AC. Other Histosols that

1. Are dominantly hemic in the subsurface tier if that
tier is wholly organic except for a thin mineral layer or
layers; or are dominantly hemic in the organic part of the
surface and subsurface tiers if a continuous mineral layer
40 cm or more thick begins within the depth limits of the
subsurface tier; or
2. Have a sulfuric horizon whose upper boundary is
within 50 cm of the surface or have sulfidic materials
within 1 m of the surface,

Hemists, p. 137

AD, Other Histosols.
Saprists, p. 140

"Dominant, in this context, means the most abundant. If only two kinds of
organic materials are present, the fibrie materials occupy half or more of the
volume. If there are both hemic and sapric materials as well as fibric, the fib-
tie materials may occupy less than half of the volume but have mote volume
than either the hemie or sapric materials

'Froxen 2 months after the summer solatice.



137
Tropofolists

Distinctions between Typic Tropofolists and other subgroups

Typic Tropofolists are the Tropofolists that

Have fragmental materials in which the interstices are
filled or partly filled with organic materials in half or more
of each pedon; and

b. Do not have a lithic contact within 1 m of the surface,
Lithie Tropofolists are like Typic Tropofolists except for b
or for a and b.

Hemists
Key to great groups

ACA. Hemists that have a sulfuric horizon that has its upper
boundary within 50 cm of the surface.
Sulfohemists, p. 140

ACB. Other Hemists that have sulfidic materials within | m
of the surface.
Sulfihemlsts, p, 139

ACC. Other Hemists that have a horizon 2 cm or more thick
in which half or more of the volume is humilluvic materials.
Luvihemists, p. 138

ACD. Hemists that are frozen in some layers within the
control section about 2 months after the summer solstice in
most years or that are never frozen below a depth of 5 cm
in most years but have a mean annual soil temperature lower
than 8°C,

Cryohemists, p. 138

ACE. Other Hemists that have a mean annual soil tempera-
ture lower than 8°C.
Borohemists, p, 137

ACF, Other Hemists that have a difference of <5°C between
mean summer and mean winter soil temperatures at a depth
of 30 cm,

Tropohemists, p. 140

ACG, Other Hemists.
Mi

emists, p. 139
Borohemists

Distinctions between Typic Borohemists and other sub-
groups

Typic Borohemists are the Borohemists that
a, Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier;
b, Have
(1) Less than 25 cm of the subsurface and bottom tiers
consisting of fibric materials; and


258

b. A clay distribution such that the percentage of clay
does not decrease from its maximum amount by >20
percent of that maximum within 1.5 m of the soil sur-
face, or the layer in which the percentage of clay is less
than the maximum has skeletans on ped faces or has 5
percent or more plinthite by volume;

2. Have a color value, moist, of 4 or more in some part of

the epipedon or have an argillic horizon that has a color

value, dry, of 5 or more in some subhorizon or a color

value, moist, of 4 or more;

3. Do not have plinthite that forms a continuous phase or

constitutes more than half the matrix in any subhorizon

within 1.25 m of the soil surface; and

4, Do not have a fragipan.

LITERATURE CITED

Sys, C. 1969. The soils of central Africa in the American
classification - 7th approximation. African Soils. XIV:25-44.


193

Natrustolls
Distinctions between Typic Natrustolls and other subgroups

‘Typic Natrustolls are the Natrustolls that

‘a. Do not have any of the following characteristics within 1

m of the surface:

(1) Dominant chroma of | or less throughout and hue as
yellow or yellower than 2.5 Y in some part;

(2) Dominant chroma of 2 or less and mottles that are
not due to segregated lime; or

(3) Dominant chroma of 2 or less and a decrease in the
percentage of exchangeable sodium from the upper 25-
centimeter layer to the underlying layer;

b. Do not have a brittle horizon 15 cm or more thick that is

within 1 m of the surface and that contains some opal coat-

ings or some durinodes (<20 percent by volume);

¢. Do not have tonguing or interfingering of an albic hori-

zon more than 2.5 cm into a natric horizon;

d. When neither irrigated nor fallowed to store moisture
(1) If the soil temperature regime is mesic or thermic,
are dry less than six-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) during a period when the soil
temperature at a depth of 50 cm exceeds 5°C, or
(2) If the soil temperature regime is hyperthermic, or
isomesic or warmer, are moist in some or all parts of the
moisture control section for 90 consecutive days or more
during a period when the soil temperature at a depth of
50 em exceeds 8°C; and

¢. Do not have visible crystals or nests of gypsum or more

soluble salts within 40 cm of the surface.

Aridic Natrustolls are like Typic Natrustolls except for d.

Glossic Natrustolls are like Typic Natrustolls except for c.

Leptic Natrustolls are like Typic Natrustolls except for e or

for d and e,

Paleustolls
Distinctions between Typic Paleustolls and other subgroups

Typic Paleustolls are the Paleustolls that
a, Are noncalcareous in some horizons after the upper soil
to a depth of 18 cm has been mixed;
b. Do not have mottles that have chroma of 2 or less within
1 m of the surface if artificially drained or, if undrained in
most years, are not continuously saturated with water in the
mottled horizon for as long as 90 days;
c. Have a mollic epipedon that is <50 cm thick or have tex-
ture that is loamy fine sand or coarser if the mollic
epipedon is >50 em thick;
d. Do not have a petrocalcic horizon within 1.5 m of the
surface;
e, When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry for more than four-tenths of the cumulative days
in some part of the moisture control section when the soil
temperature at a depth of 50 cm exceeds 5°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days


182

Torrifluventic Haploborolls are like Typic Haploborolls
except for e and (1), with or without d.

Torriorthentic Haploborolls are like Typic Haploborolls
except for all or part of c/1) and d.

Udertic Haploborolls are like Typic Haploborolls except for
e(2) and g, with or without any or all or ¢(1)(b), e, or i.
Udic Haploborolls are like Typic Haploborolls except for
(2),

Udorthentic Haploborolls are like Typic Haploborolls except
for ¢(2) and d.

Vertic Haploborolls are like Typic Haploborolls except for g,
with or without any or all of c(1)(b), e, or i.

Natriborolls
Distinctions between Typic Natriborolls and other subgroups

Typic Natriborolls are the Natriborolls that
a. Do not have tonguing or interfingering of an albic
horizon more than 2.5 cm into the natric horizon;
b. Have
(1) Either or both
(a) A color value, dry, of less than 4.5 in the upper 18
cm of the mollic epipedon, after mixing, or in any Ap
horizon that is >18 cm; or
(b) A moisture control section that is dry in some part
less than six-tenths of the time that the soil
temperature at a depth of 50 cm is above 5°C in most
years, or
(2) A chroma, moist, after rubbing, of 1.5 or more in the
upper part of the mollic epipedon to a depth of 18 cm,
after mixing, or in any Ap horizon that is more than 18
em thick; and
c. Do not have visible crystals or nests of gypsum or more
soluble salts within 40 cm of the surface of the soil.
Aridic Natriborolls are like Typic Natriborolls except for
1).
Glossic Natriborolls are like Typic Natriborolls except for a.
Glossic Udic Natriborolls are like Typic Natriborolls except
for a and 2/2),
Leptic Natriborolls are like Typic Natriborolls except for c
or for b and c,
Udic Natriborolls are like Typic Natriborolls except for (2).

Paleborolls
Distinctions between Typic Paleborolls and other subgroups

Typic Paleborolls are the Paleborolls that

a. Do not have an argillic horizon that has an increase in
clay content of 20 percent (absolute) or more within a
vertical distance of 7.5 cm below its upper boundary,

b. Do not have mottles that have chroma of 2 or less within
3 m of the surface if artificially drained or, if undrained,
are not continuously saturated with water in the mottled
horizon for as long as 90 days in most years;

c. Have a niean summer soil temperature at a depth of 50
cm or at a lithic or paralithic contact, whichever is
shallower, of 15°C or higher if there is no O horizon and
8°C or higher if there is an O horizon; and

d. Have a mollic epipedon that is <50 cm thick.


74

3. Have one or more of the following in the argillic
horizon:
a. Hue redder than 10YR and chroma more than 4
dominant in the matrix in at least the lower part,
b. Hue of 2.5YR or redder and value, moist, of less
than 4 and value, dry, of less than 5 throughout the
major part;
c. Many coarse mottles that have hue redder than
7,5YR or chroma more than 5, or both in some sub-
horizon.
Paleudalfs, p. 79

HEJ. Other Udalfs that have an argillic horizon that has
throughout its thickness a hue redder than SYR, a color
value, moist of less than 3.5, and a color value, dry, no
more than I unit higher than the value, moist.

Rhodudalfs, p. 80

HEK. Other Udalfs.
Hapludalfs, p, 76

Agrudalfs

Agrudalfs are the Udalfs that have an agric horizon. Some
but not all have an anthropic epipedon. They have been in
farms for many hundreds of years and have received heavy
applications of animal manure and other amendments. They
are not known to occur in the United States, It seems
probable that only the typic and anthropic subgroups are
needed, The Agrudaifs of western Europe have been
farmed for more than 1,000 years®, and the early farmers
selected only the best soils for cultivation. All of them are
well drained, and they seem quite similar in most properties.
The Typic Agrudalfs do not have an anthropic epipedon.

Ferrudalfs
Distinctions between Typic Ferrudalfs and other subgroups

Typic Ferrudalfs are the Ferrudalfs that

a, Do not have mottles that have chroma of 2 or less within
the upper 60 cm if the horizons that have mottles of low
chroma are saturated with water at some time of year or if
the soil has artificial drainage. The mottles should be dis-
tinguished from skeletans that may also have low chroma.
Aquic Ferrudalfs are like Typic Ferrudalfs except for a.

Fragiudalfs
Distinctions between Typic Fragiudalfs and other subgroups

‘Typic Fragiudalfs are the Fragiudalfs that

a. Have an argillic horizon above the fragipan that has clay
skins on at least some vertical and horizontal faces of pri-
mary or secondary peds, or both;

b. Do not have, immediately above the fragipan, thick
skeletans of clean sand and silt on primary ped faces and do
not have an eluvial horizon (E’) that has thick skeletans and



262

Chromoxererts

Distinctions between Typic Chromoxererts and other sub-
groups

Typic Chromoxererts are the Chromoxererts that

a, Do not have distinct or prominent mottles (these terms
refer to contrast, not size) within 50 cm of the soil surface
in more than half of each pedon;

b, Have a color value, moist, less than 3.5 and a value, dry,
less than 5.5 throughout the upper soil to a depth of 30 cm
in more than half of each pedon; and

¢. Do not have, within 1 m of the soil surface, prismatic or
blocky structure accompanied by clay skins on ped faces
that have a color value lower than that in the matrix.

Aquic Chromoxererts are like Typic Chromoxererts except
for a,

Entic Chromoxererts are like Typic Chromoxererts except
for b.

Palexerotlic Chromoxererts are like Typic Chromoxererts
except for c.

Pelloxererts
Distinctions between Typic Pelloxererts and other subgroups

Typic Pelloxererts are the Pelloxererts that

a, Have in all subhorizons to a depth of 1 m a chroma, both
dry and moist, less than 1.5 or, if the chroma is 1,5 or
higher, there are in some subhorizon between 30 cm and 1
m distinct or prominent mottles, or concretions that are due
to segregated iron or manganese; and

b. Have a color value, moist, less than 3.5 and a value, dry,
less than 5.5 throughout the upper 30 cm in more than half
of each pedon.

Chromic Pelloxererts are like Typic Pelloxererts except for

a,
Entic Pelloxererts are like Typic Pelloxererts except for b.


32

natric horizon (clay, silty clay, or sandy clay), 10 mm or
more in a moderately fine textured argillic or natric horizon
(clay loam, sandy clay loam, or silty clay loam), and 15 mm
or more in a medium or coarser textured argillic or natric
horizon (silt loam, loam, very fine sandy loam, or coarser).
The penetrations must occupy more than 15 percent of the
matrix of some part of the argillic or natric horizon before
they are considered tongues.

ing of albic ‘ial

Interfingering of albic materials consists of penetrations of
albic materials into an underlying argillic or natric horizon
along faces of peds, primarily along vertical faces but to a
lesser degree along horizontal faces. No continuous albic
horizon need be present. The penetrations are not wide
enough to constitute tonguing, but they form continuous
skeletans (ped coatings of clean silt or sand defined by
Brewer, 1964) >1 mm thick on the vertical ped faces, which
means a total width >2 mm between abutting peds. Because
quartz is such a common constituent of soils, the skeletans
usually appear to be nearly white when dry and light gray
when moist, but their color is determined in large part by
the color of the sand or silt fraction.

To be recognized as interfingering, all the following re-
quirements must be met in a horizon that is 5 cm or more
thick:

1, Half or more of the matrix consists of peds of the argillic
or natric horizon;

2. Albic materials are thicker than 2 mm on vertical faces
between abutting peds but are too thin to be tongues;

3. Clay skins are present in the peds, at least in pores,

Albic materials meet the following requirements for color.
If the value, dry, is 7 or more, or the value, moist, is 6 or
more, the chroma is 3 or less either dry or moist. If the
value, dry, is 5 or 6 and the value, moist, is 4 or 5, the
chroma is closer to 2 than to 3 either dry or moist.

Weatherable minerals

Several references are made to weatherable minerals in the
text of this chapter and later chapters. Obviously, the sta-
bility of a mineral in a soil is a partial function of the soil
moisture regime, In the context of the references in the
definitions of diagnostic horizons and of various taxa, a hu~
mid climate is always assumed, either present or past.
Minerals that are included in the meaning of weatherable
minerals are:

1, Clay minerals: All 2:1 lattice clays except one that is cur-
rently considered to be an aluminum-interlayered chlorite.
Sepiolite, talc, and glauconite are also included in the
meaning of this group of weatherable clay minerals, al-
though they are not everywhere of clay size.


230

spodic horizon is between 75 cm and 1.25 m_ below the soil
surface,

Entic Haplaquods are like Typic Haplaquods except for a
and d.

Ferrudalfic Haplaquods are like Typic Haplaquods except
for } and e, with or without a or ¢, or both,

Grossarenic Haplaquods are like Typic Haplaquods except
for a and c, and the upper boundary of the spodic horizon
is between 1.25 m and 2 m below the soil surface.

Lithic Haplaquods are like Typic Haplaquods except for /,
with or without @ or d, or both,

Placice Haplaquods are like Typic Haplaquods except for i,
with or without a or h, or both.

Ultic Haplaquods are like Typic Haplaquods except for b,
with or without a or d, or both, and have base saturation
(by sum of cations) <35 percent throughout the argillic or
kandic horizon, and have a mean annual soil temperature of
8°C or higher.

Placaquods

Placaquods are the Aquods that have a placic horizon that
rests on a Spodic horizon, on a fragipan, or on an albic
horizon that is underlain by a fragipan. There may be a
histic epipedon at the surface, The horizons above the
placic horizon are saturated with water at some period and
have faint to distinct mottles of low chroma.

Sideraquods
Distinctions between Typic Sideraquods and other subgroups

Typic Sideraquods are the Sideraquods that
a. Have a spodic horizon that either
(1) Is at least very firm in some subhorizon when moist;
or
(2) Is >10 cm thick and contains 1.2 percent or more or-
ganic carbon in the upper 10 cm;
b. Do not have a histic epipedon;
c. Do not have an argillic or kandic horizon.
Alfic Sideraquods are like Typic Sideraquods except for c,
with or without a, and they have base saturation of 35 per-
cent or more (by sum of cations) in some part of the argillic
or kandic horizon or they have a mean annual soil tempera-
ture lower than 8°C,
Entic Sideraquods are like Typic Sideraquods except for a.

‘Tropaquods
Distinctions between Typic Tropaquods and other subgroups

Typic Tropaquods are the Tropaquods that

a. Do not have a histic epipedon;

b. Have <5 percent by volume of iron~cemented nodules, 2.5
to 30 cm in diameter, in any subhorizon of the spodic hori-
zon;

c. Do not have an argillic or kandic horizon underlying the
spodic horizon;

d. Do not have a lithic contact within 50 cm of the surface;


104

Borollic Calciorthids are like Typic Calciorthids except for d
or for d and e, The soil temperature regime is frigid, and
the moisture regime is aridic but borders on ustic.

Borollic Lithic Calciorthids are like Typic Calciorthids
except for ¢ and d, with or without e. The soil temperature
regime is frigid, and the moisture regime is aridic but
borders on ustic.

Durixeroltic Calciorthids ave like Typic Calciorthids except
for 6 and d, with or without e, and have a mean annual soil
temperature lower than 22°C, The mean summer and mean
winter soil temperatures at a depth of 50 cm differ by 5°C
or more, and the moisture regime is aridic but borders on
xeric.

Lithic Calciorthids are like Typic Calciorthids except for c.
Lithic Ustollic Calciorthids are like Typic Calciorthids
except for c and d, with or without ¢. They have a mean
annual soil temperature that is 8°C or higher and an aridic
moisture regime that borders on an ustic regime.

Lithic Xerollic Calciorthids are like Typic Calciorthids
except for ¢ and d, with or without e. They have a mean
annual soil temperature lower than 22°C, the mean summer
and mean winter soil temperatures at a depth of 50 cm
differ by 5°C or more, and they have an aridic moisture
regime that borders on a xeric regime.

Ustochreptic Calciorthids are like Typic Calciorthids except
for e. They have a mean annual soil temperature that is 8°C
or higher and an aridic moisture regime that borders on an
ustic moisture regime.

Ustollic Calciorthids are like Typic Calciorthids except for d
or for d and e, They have a mean annual soil temperature
that is 8°C or higher and an aridic moisture regime that
borders on an ustic regime.

Xerollic Calciorthids are like Typic Calciorthids except for d
or for d and e, They have a mean annual soil temperature
lower than 22°C, the mean summer and mean winter soil
temperatures at a depth of 50 cm differ by 5°C or more,
and they have an aridic moisture regime that borders on a
xeric regime.

Camborthids

Distinctions between Typic Camborthids and other
subgroups

Typic Camborthids are the Camborthids that
a. Are not saturated with water for 90 consecutive days or
more within 1 m of the surface in most years and do not
have any of the following characteristics within 1 m of the
soil surface if the soil of that zone is saturated with water at
some period in most years or the soil is artificially drained:
(1) Dominant chroma of 1 or less throughout and hue as
yellow or yellower than 2.SY in some part,
(2) Dominant chroma of 2 or less and mottles that are
due to segregation of iron or manganese, or
(3) Both a dominant chroma of 2 or less and a greater
SAR (or percentage of exchangeable Na) in more than
half the thickness of the horizons between the surface
and a depth of 50 cm than in the saturated zone;
b, Do not have a horizon within 1 m of the surface that is
>15 cm thick that either contains 20 percent or more


4l
Chapter 3
Family Differentiae

Mineral Soils
The differentiae used to distinguish families of mineral soils
within a subgroup are listed next in the order in which the
descriptive terms appear in the family name and in which
the terms are defined in this chapter. .
Particle-size classes a
Mineralogy classes
Calcareous and reaction classes
Soil temperature classes
Soil depth classes
Soil slopes classes
Soil consistence classes
Classes of coatings (on sand)
Classes of cracks

Particle-size classes

Particle size refers to grain-size distribution of the whole
soil and is not the same as texture, which refers to the fine-
earth fraction. The fine-earth fraction consists of the par-
ticles that have a diameter <2 mm. Particle-size classes are
a kind of compromise between engineering and pedologic
classifications. The limit between sand and silt is a diameter
of 74 micrometers in the engineering classification and of
either 50 or 20 micrometers in pedologic classifications. The
engineering classifications are based on percentages by
weight in the fraction <74 mm in diameter, and textural
classes are based on percentages by weight in the fraction <2
mm in diameter.

The very fine sand separate (diameter between 0.05 mm and
0.1 mm) is split in engineering classifications. In defining
particle-size classes, much the same split is made but in a
different manner, A fine sand or loamy fine sand normally
has an appreciable content of very fine sand, but the very
fine sand fraction is mostly coarser than 74 micrometers. A
silty sediment, such as loess, may also have an appreciable
component of very fine sand, but most of the very fine sand
is finer than 74 micrometers. So, in particle-size classes, the
very fine sand is allowed to "float." It is treated as sand if
the texture is fine sand, loamy fine sand, or a coarser class.
It is treated as silt if the texture is very fine sand, loamy
very fine sand, sandy loam, silt loam, or a finer class.

No single set of particle-size classes seems appropriate as
family differentiae for all kinds of soils. The classes that
follow provide for a choice of either 7 or 11 particle-size
classes. This choice permits relatively fine distinctions in
soils if the particle size is important and broader groupings
if the particle size is not susceptible to precise measurement
or if the use of narrowly defined classes produces undesii
able groupings. Thus in some families the term "clayey" in-
dicates that there is 35 percent or more clay in defined
horizons, but in other families the term "fine" indicates that
the clay fraction constitutes 35 through 59 percent of the
fine earth of the horizons, and the term "very-fine" indicates
60 percent or more clay, The term "rock fragments" refers



256

Arenic Kanhaplustults are like Typic Kanhaplustults except
ariie Kanhaplustults are like Typic Kanhaplustults except
Epiajuie Kanhaplustults are like Typic Kanhaplustults except
tants Kanhaplustults are like Typic Kanhaplustults except
Pindhie Kanhaplustults are like Typic Kanhaplustults except
Shodie Kanhaplustults are like Typic Kanhaplustults except
aie Kanhaplustlts are like Typic Kanhaplustults except for

J
Paleustults

Paleustults are the Ustults that
1, Have a clay distribution such that the percentage of clay
does not decrease from its maximum amount by >20 percent
of that maximum within 150 em of the soil surface, or the
layer in which the clay percentage decreases by more than
20 percent has at least 5 percent of the volume consisting of
skeletans on faces of peds and there is at least 3 percent
(absolute) increase in clay below the layer.

2, Do not have plinthite that forms a continuous phase or
constitutes more than half the matrix in any subhorizon
within 150 cm of the soil surface; and

3. Do not have a fragipan or kandic horizon.

Plinthustults

Plinthustults are the Ustults that have plinthite that forms a
continuous phase or constitutes more than half the matrix
within some subhorizon in the upper 150 cm of the soil.

Rhodustults

Rhodustults are the Ustults that do not have a fragipan and
also

1. Have an epipedon that has a color value, moist, less than
4 in all parts;

2, Have an argillic horizon that has a color value, dry, less
than 5 in all subhorizons and not more than | unit higher
than the value, moist;

3. Do not have plinthite that forms a continuous phase or
constitutes more than half the matrix in any subhorizon in
the upper 150 cm of the soil; and

4. Have a clay distribution with depth such that the per-
centage of clay decreases from its maximum amount by >20
percent of that maximum within 150 cm of the soil surface,
and the layer in which the percentage of clay is less than the
maximum has less than 5 percent of the volume consisting
of skeletans on faces of peds or there is less than 3 percent
(absolute) increase ion clay below the layer.

5. Do not have a fragipan or a kandic horizon.


252

Al) in the major part of the argillic or kandic horizon or the
major part of the upper 100 cm of the argillic or kandic
horizon if these horizons are thicker than 100 cm;
2, Do not have a lithic, paralithic, or petroferric contact
within 150 cm of the soil surface; and
3. Have a clay distribution such that the percentage of clay
does not decrease from its maximum amount by as much as
20 percent within a depth of 150 cm from the soil surface
or the layer in which the clay percentage decreases by more
than 20 percent has at least 5 percent of the volume con-
sisting of skeletans on faces of peds and there is at least 3
percent (absolute) increase in clay below the layer,
Kandiustults, p. 253

FDC. Other Ustults that have a CEC <16 cmol(+) ke"! clay
(by 1 M NH,OAc pH 7) and an ECEC <12 cmol(+) kg” clay
(sum of bases extracted with | M NH,OAc pH 7 plus | M
KCl-extractable Al) in the major part (of the argillic or
kandic horizon or the major part of the upper 100 cm of the
argillic or kandic horizon if these horizons are thicker than
100 cm.

Kanhaplustults, p. 254

EDD. Other Ustults that have a clay distribution such that
the percentage of clay does not decrease from its maximum
amount by as much as 20 percent of that maximum within
150 cm of the soil surface or the layer in which the clay
percentage decreases by more than 20 percent has at least 5
percent of the volume consisting of skeletans on faces of
peds and there is at least 3 percent (absolute) increase in
clay below the layer.

Paleustults, p. 256

FDE. Other Ustults that have:

1, An epipedon that has a color value, moist, less than 3.5 in

all parts; and

2. An argillic horizon that has a color value, dry, less than 5

and not more than | unit higher than the value, moist.
Rhodustults, p. 256

FDF. Other Ustults.
Haplustults, p. 252

Haplustults
Distinctions between Typic Haplustults and other subgroups

Typic Haplustults are the Haplustults that
a. Have a continuous argillic horizon throughout each pe-
don, uninterrupted by ledges of bedrock;
b. Do not have a lithic contact within 50 cm of the mineral
soil surface;
c. Have texture finer than loamy fine sand in some part of
the argillic horizon and have an argillic horizon that does
not have lamellae in at least its upper 25 cm;
d. Do not have the following combination of characteristics
in the upper 75 cm of the soil and in the upper 12.5 cm of
the argillic horizon:
(1) Mottles that have a color value, moist, of 4 or more
and chroma, moist, of 2 or less and mottles of higher
chroma that are due to segregation of iron; and


168

cubic centimeter or less in the fine-earth fraction, and that
has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1,25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
b, Have a cambic horizon;
c. Do not have a lithic contact within 50 cm of the surface;
d. Have a mean annual soil temperature higher than 0°C;
e. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizon is saturated
with water at some time of the year when its temperature is
25°C or if there is artificial drainage; and
f. Have an umbric epipedon that is continuous in each
pedon.
Andic Cryumbrepts are like Typic Cryumbrepts except for a.
Aquic Cryumbrepts are like Typic Cryumbrepts except for e
or for b and e.
Entic Cryumbrepts are like Typic Cryumbrepts except for 5,
Lithic Cryumbrepts are like Typic Cryumbrepts except for c,
with or without b or d, or both.
Lithic Ruptic-Entic Cryumbrepts are like Typic Cryumbrepts
except for ¢ and f, with or without 5 or d, or both.
Pergelic Cryumbrepts are like Typic Cryumbrepts except for
d, with or without a or 6 or both.
Ruptic-Lithie Cryumbrepts are like Typic Cryumbrepts
except for ¢, with or without 5 or d, or both, and they have
a lithic contact within 50 cm of the surface in only part of
each pedon.

Fragiumbrepts

Distinctions between Typic Fragiumbrepts and other
subgroups

The definitions that follow are incomplete because there are
few of these soils in the United States.

Typic Fragiumbrepts are the Fragiumbrepts that
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
> 1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum; and
b. Do not have mottles that have chroma of 2 or less within
50 cm of the soil surface.
Andic Fragiumbrepts are like Typic Fragiumbrepts except
for a.
Aquic Fragiumbrepts are like Typic Fragiumbrepts except
for b.


64

subhorizon between 30 cm and 150 cm below the surface of
the soil.
Plinthaqualfs, p. 69

HAB. Other Aqualfs that have a natric horizon and do not
have a duripan.
Natraqualfs, p. 67

HAC, Other Aqualfs that have a duripan.
Duraqualfs, p. 65

HAD, Other Aqualfs that have a fragipan.
Fraglaqualfs, p. 65

HAE, Other Aqualfs that have a CEC <16 cmol(+) kg? clay
(by | M NH,OAc pH7) and an ECEC <12 cmol(+) ke"! clay
(sum of bases extracted with | M NH,OAc pH7 plus 1 M
KCl-extractable Al) in the major part’ of the argillic or
kandic horizon or the major part of the upper 100 cm of the
argillic or kandic horizon if these horizons are thicker than
100 cm,

Kandiaqualfs, p. 66

HAF, Other Aqualfs that have an albic horizon tonguing

Glossaqualfs, p. 66

HAG. Other Aqualfs that have an abrupt textural change
between an ochric epipedon or an albic horizon and an
argillic horizon and have slow or very slow hydraulic con-
ductivity in the argillic horizon’,

Albaqualfs, p. 64

HAH, Other Aqualfs that have an umbric epipedon.
Umbraqualfs, p. 69

HAI, Other Aqualfs.
Ochraqualfs, p. 67

Albaqualfs
Distinctions between Typic Albaqualfs and other subgroups

Typic Albaqualfs are the Albaqualfs that
a. Have chroma of 2 or less in 60 percent or more of the
mass between the bottom of the A or the Ap horizon and a
depth of 75 cm;
b. Do not have a layer above a depth of 75 cm that has
texture finer than loamy fine sand, that is as much as 18 cm
thick, that has a bulk density (at 33 kPa water tension) of
0.95 g per cubic centimeter or less in the fine-earth frac
tion, and that has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less, or

defined as the rate of internal water movement un-
der a unit potential gradient. In this text the term refers to vertical saturated
hydraulic conductivity. Slow and very slow rates refer to 4 to 10 and less
‘than 4 cm water per day respectively.



272

horizon. In some places, as in warm arid climates, the
undisturbed surface horizon is less dark than the ad-
jacent underlying horizon and contains only

small amounts of organic matter. It has a morphology
distinct from the C layer, though the mineral fraction
ig unaltered or only slightly altered by weathering.
Such a horizon is designated A because it is at the
surface. However, recent alluvial or eolian deposits
that retain fine stratification are not considered to

be an A horizon unless cultivated.

E horizons: Mineral horizons in which the main feature is
loss of silicate clay, iron, aluminum, or some combination of
these, leaving a concentration of sand and silt particles of
quartz or other resistant minerals.

An E horizon is usually, but not necessarily, lighter in
color than an underlying B horizon. In some soils the
color is that of the sand and silt particles, but in many
soils coats of iron or other compounds mask the color
of the primary particles, An E horizon is most com-
monly differentiated from an overlying A horizon by
lighter color and generally has measurably less organic
matter than the A horizon. An E horizon is most
commonly differentiated from an underlying B hori-
zon in the same sequum by color of higher value or
lower chroma, by coarser texture, or by a combination
of these properties. An E horizon is commonly

near the surface below an O or A horizon and above a
B horizon, but the symbol E may be used without re-
gard to position in the profile for any horizon that
meets the requirements and that has resulted from soil
genesis,

B horizons: Horizons that formed below an A, E, or O hori-
zon and are dominated by obliteration of all or much of the
original rock structure® and by
(1) illuvial concentration of silicate clay,
iron, aluminum, humus, carbonates, gypsum, or silica,
alone or in combination;
(2) evidence of removal of carbonates:
(3) residual concentration of sesquioxides;
(4) coatings of sesquioxides that make the horizon
conspicuously lower in value, higher in chroma, or red-
der in hue than overlying and underlying horizons
without apparent illuviation of iron;
(5) alteration that forms silicate clay or liberates ox-
ides or both and that forms granular, blocky, or pris-
matic structure if volume changes accompany changes
in moisture content; or
(6) any combination of these.

Obviously there are several kinds of B horizon. No

common location within the soil characterizes them,

but all are subsurface horizons or were originally.

Included as B horizons where contiguous to another

‘Rock structure includes fine stratification in unconsolidated or weakly

consolidated sediment or pseudomorphs of weathered minerals retaining their
positions relative to each other and to unweathered minerals in saprolite from
consolidated rocks.


208

moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface.
Humic Rhodic Eutroperox

CDCL., Other Eutroperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Eutroperox

CDCM. Other Eutroperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Eutroperox

CDCN. Other Eutroperox that have a color hue of 2.5 YR or
redder with moist values of less than 4 in most of the 25 to
125 cm depth from the soil surface.

Rhodic Eutroperox

CDCO. Other Eutroperox that have a color hue of 7.5 YR or
yellower with moist values of 6 or more in most of
the 25 to 125 cm depth from the soil surface,

Xanthic Eutroperox

CDCP. Other Eutroperox.
Typic Eutroperox

Haploperox
Key to subgroups

CDEA. Haploperox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and a petroferric contact within 125 cm of the
soil surface.

Aqulc Petroferric Haploperox

CDEB, Other Haploperox that have a petroferric contact
within 125 cm of the soil surface,
Petroferric Haploperox

CDEC. Other Haploperox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface and a lithic contact within 125 cm of the
soil surface.

Aquic Lithic Haploperox

CDED. Other Haploperox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Haploperox

CDEE. Other Haploperox that have more than 5 percent
plintl in some horizon within a depth of 125 cm of the
soil surface and mottles of 4 or more value moist and 2 or
less chroma within a depth of 125 cm of the soil surface.
Plinthaquic Haploperox



1$2
Fragiaquepts

Distinctions between Typic Fragiaquepts and other
subgroups

Typic Fragiaquepts are the Fragiaquepts that
a, Do not have a histic, moflic, or umbric epipedon; and
. Have, in 60 percent or more of the matrix of all
subhorizons between the plow layer or, if there is no plow
layer, a depth of 15 cm and a depth of 75 cm or more,
moist colors as follows:

(1) If there is mottling, chroma of 2 or less;

(2) If there is no mottling, chroma of | or less.
Aerie Fragiaquepts are like Typic Fragiaquepts except for b.
Humic Fragiaquepts are like Typic Fragiaquepts except for
a.

Halaquepts
Distinctions between Typic Halaquepts and other subgroups

Typic Halaquepts are the Halaquepts that

a. Have chroma of 2 or less and a hue of SY or redder in 60

percent or more of the matrix in all subhorizons between

depths of 15 and 75 cm;

b, Have an ochric epipedon;

cc. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper I m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1 m; and
(3) More than 35 percent clay in horizons that total >50
em in thickness.

Aeric Halaquepts are like Typic Halaquepts except for a.

Mollic Halaquepts are like Typic Halaquepts except for b.

Vertic Halaquepts are like Typic Halaquepts except for c.

Haplaquepts
Distinctions between Typic Haplaquepts and other subgroups

Typic Haplaquepts are the Haplaquepts that
a. Have, in 60 percent or more of the matrix in all
subhorizons between the Ap horizon and a depth of 75 cm,
‘one or more of the following:
(1) If mottled and the mean annual soil temperature is
lower than 15°C, moist chroma of 2 or less;
(2) If mottled and the mean annual soil temperature is
15°C or higher:
(a) If the hue is 2.5Y or redder® and the value, moist,
is more than 5, the chroma, moist, is 2 or less;

"ir the hue is 7.5YR or redder in the matrix and if peds ore present, the ped
exteriors should have dominant chroma, moist, of 1 or less and the ped interi-
core should have mottles that have chroma, moist, of 2 or less; if there are ne


36

thickness rests on rock or on fragmental material having in-
terstices filled with organic materials.

Kinds Of Organic Soil Materials

Three basic kinds of organic soil materials are distinguished,
fibric, hemic, and sapric, according to the degree of decom-
position of the original plant materials.

Fibers

A fiber is a fragment or piece of plant tissue, excluding live
roots, that is large enough to be retained on a 100-mesh
sieve (openings 0.15 mm in diameter) and that retains recog-
nizable cellular structure of the plant from which it came.
The material is screened after dispersion in sodium hexam-
etaphosphate, Fragments larger than 2 cm in cross section
or in their smallest dimension, to be called fibers, must be
decomposed enough that they can be crushed and shredded
with the fingers. Fragments of wood that are larger than 2
cm in cross section and that are so undecomposed that they
cannot be crushed and shredded with the fingers are not
considered fibers,

Fibric soil materials (L. fibra, fiber)
Fibric soil materials have the following characteristics:

1, The fiber content after rubbing is three-fourths’ or more
of the soil volume, excluding coarse fragments and mineral
layers; or

2. The fiber content after rubbing is two-fifths or more of
the soil volume, excluding coarse fragments and mineral
layers, and the material yields a sodium pyrophosphate ex-
tract color on white chromatographic paper that has value
and chroma of 7/1, 7/2, 8/1, 8/2, or 8/3.

Hemic soil materials

Hemic soil materials (Gr. hemi, half; implying intermediate
decomposition) are intermediate in degree of decomposition
between the less decomposed fibric and the more decom-
posed sapric materials. They have morphological features
that give intermediate values for fiber content, bulk density,
and water content. They are partly altered both physically
and biochemically.

Sapric soil materials (Gr. sapros, rotten)

‘These are the most highly decomposed of the organic mate-
rials, They normally have the smallest amount of plant
fiber, the highest bulk density, and the lowest water content
on a dry-weight basis at saturation. They are commonly
very dark gray to black. They are relatively stable, i.e.,
they change very little physically and chemically with time
in comparison to the others.

Tpractions are used rather than percentages to avoid implying » higher degree
of accuracy than is warranted.


67

d. Do not have an epipedon that is >100 cm thick if the
particle-size class is sandy throughout: and

e. Do not have a horizon within 150 cm of the soil surface
that has >5 percent plinthite by volume.

Aerie Kandiaqualfs are like Typic Kandiaqualfs except for

a.
Aeric Umbric Kandiaqualfs are like Typic Kandiaqualfs ex-
cept for a and 6.

Arenic Kandiaqualfs are like Typic Kandiaqualfs except for
c, with or without a.

Grossarenic Kandiaqual/s are like Typic Kandiaqualfs except
for d, with or without a.

Plinthic Kandiaqualfs are like Typic Kandiaqualfs except for

e.
Umbric Kandiaqual fs are like Typic Kandiaqualfs except for
b

Natraqualfs
Distinctions between Typic Natraqualfs and other subgroups

Typic Natraqualfs are Natraqualfs that

a. Have >15 percent saturation with sodium or have more
magnesium and sodium than calcium and extractable acidity
within 15 cm of the upper boundary of the natric horizon;
b. Do not have tonguing or interfingering of albic materials
more than 2.5 cm into the natri¢ horizon;

¢. Have an Ap horizon that has either a color value, moist,
of 4 or more or a color value, dry, of 6 or more after the
soil has been crushed and smoothed; or the soil to a depth of
18 cm, after mixing, has these colors; and

d. Have, within 40 cm of the soil surface, a horizon that has
15 percent or more saturation with sodium or has more
magnesium and sodium than calcium and extractable acidity.
Albic Natraqualfs are like Typic Natraqualfs except for a or
for a and d.

Albic Glossic Natraqualfs are like Typic Natraqualfs except
for 6 and d, with or without a.

Glossic Natraqualfs are \ike Typic Natraqualfs except for b.
Mollic Natraqualfs are like Typic Natraqualfs except for c,
with or without d.

Ochraqualfs
Distinctions between Typic Ochraqualfs and other subgroups

Typic Ochraqualfs are the Ochraqualfs that
a, Have in 60 percent or more of the matrix in all sub-
horizons between the A or Ap horizon and a depth of 75 om
one or more of the following:
(1) If mottled and the mean annual soil temperature is
lower than 15°C, chroma, moist, of 2 or less;
(2) If mottled and the mean annual soil temperature is
15°C or more:

—
if the hue is 7.6YR or redder and, if pedo are present, ped exteriors in the

‘argillic horizon should have dominant chroma, moist, of 1 ot leas and ped in-
teriorn should have mottles that have chroma, moist, of 2 or lesy; if peds wre
absent, the chroma, moist, should be 1 or less immediately below any surface
horizon that has color value, moist, less than 8.5.



194

during a period when the soil temperature at a depth of
50 cm exceeds 8°C;

f. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
or to the base of an Ap horizon,

(2) A coefficient of linear extensibility (COLE) of 0.07
or more in a horizon or horizons at least 50 om thick and
a potential linear extensibility of 6 cm or more in the
upper 1.25 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.25 m, and

(3) More than 35 percent clay in horizons that have total
thickness of >50 cm; and

g. When neither irrigated nor fallowed to store moisture,
(1) If the soil temperature regime is mesic or thermic,
are dry less than six-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) during a period when the soil
temperature at a depth of 50 cm exceeds 5°C, or
(2) If the soil temperature regime is hyperthermic or
isomesic, or warmer, are moist in some or all parts of the
moisture control section for 90 consecutive days or more
during a period when the soil temperature at a depth of
50 cm exceeds 8°C,

Aquic Paleustolls are like Typic Paleustolls except for b.

Aridic Paleustolls are like Typic Paleustolls except for g.

Calcic Paleustolis are like Typic Paleustolls except for a and

have a calcic horizon within a depth a | m if the particle-

size class of the upper 50 cm of the argillic horizon is
sandy, 60 cm if it is loamy, and 50 cm if it is clayey.

Calciorthidic Paleustolls are like Typic Paleustolls except for

aand g and have a calcic horizon within a depth of 1 m if

the particle-size class of the upper 50 cm of the argillic
horizon is sandy, 60 cm if loamy, and 50 cm if clayey.

Pachic Paleustolls are like Typic Paleustolls except for c,

with or without 6 or e, or both.

Petrocalcic Paleustolls are like Typic Paleustolls except for

d, with or without a or g, or both, and have an argillic

horizon.

Torrertic Paleustolls are like Typic Paleustolls except for f,

with or without ¢ or g, or both and the cracks are open

more than 180 days, cumulative, in most years.

Udertic Paleustolls are like Typic Paleustolls except for e

and f, with or without any or all of 5, c, and g, and the

cracks are open less than 135 days, cumulative, in most

years,

Udic Paleustolls are like Typic Paleustolis except for e.
Vertic Paleustolls are like Typic Paleustolls except for f,
with or without any or all of b, c, and g, and the cracks are
open between 135 and 180 days, cumulative, in most years.

Vermustolls

Distinctions between Typic Vermustolls and other subgroups
Typic Vermustolls are the Vermustolls that

a, Have a mollic epipedon that is 50 cm or more thick but is

<75 cm thick;
b, Do not have a cambic horizon;


200

Pachic Ultic Haploxerolts are like Typic Haploxerolis except
for c and h, with or without a or e, or both,

Torrertic Haploxerolls are like Typic Haploxerolls except for
JQ) and k, with or without all or any of a, b, c, or f.
Torrifluventic Haploxerolls are like Typic Haploxerolls ex-
cept for f and k, with or without all or any of 5, e, or h.
Torriorthentic Haploxerolls are like Typic Haploxerolls ex-
cept for e and k, with or without h, and they do not have a
sandy particle-size class in all subhorizons to a depth of 1
m,

Torripsammentic Haploxerolls are like Typic Haploxerolls
except for e and k, with or without h, and they have sandy
particle-size class in all subhorizons to a depth of 1 m or
more.

Ultic Haploxerolls are like Typic Haploxerolls except for h.
Vermic Haploxerolls are like Typic Haploxerolls except for
i, with or without 6,

Vertic Haploxerolls are like Typic Haploxerolls except for j,
with or without all or any or a, 4, ¢, or f.

Natrixerolls
Distinctions between Typic Natrixerolls and other subgroups

Typic Natrixerolls are the Natrixerolls that

‘a. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface;

b. Do not have a horizon within 1 m of the surface that is
>15 cm thick that either contains at least 20 percent durin-
odes in a nonbrittle matrix or is brittle and has firm consis-
tence when moist; and

c. Have a xeric moisture regime.

Aquic Natrixerolls are like Typic Natrixerolls except for a.
Aquic Duric Natrixerolls are like Typic Natrixerolls except
for a and b.

Aridic Natrixerolls are like Typic Natrixerolls except for c,
and have an aridic moisture regime that borders on xeric,
Duric Natrixerolls are like Typic Natrixerolls except for b.

Palexerolls
Distinctions between Typic Palexerolls_and other subgroups

Typic Palexerolls are Palexerolls that

a. Have an argillic horizon that has a clayey particle-size
class in the upper part and an increase in clay content of 20
percent clay (absolute) or more within a vertical distance of
7.5 cm or of 15 percent clay (absolute) within a distance of
2.5 cm at the upper boundary;

b. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface;

c. Do not have a petrocalcic horizon that has its upper
boundary within 1.5 m of the soil surface;

d. Have a mollic epipedon that is <S0 cm thick, or the tex-
ture is loamy fine sand or coarser if the mollic epipedon is
250 em thick;

e. Do not have a natric horizon;

f. Have base saturation of >75 percent throughout the
argillic horizon or in the upper 50 cm of the argillic hori-
zon, whichever is thinner;

g. Do not have the following combination of characteristics:


105

durinodes in a nonbrittle matrix or is brittle and has firm

consistence when moist;

c. Do not have a lithic contact within 50 cm of the surface;

d. Have a weighted average organic-carbon content in the

upper soil to a depth of 40 cm that is <0.6 percent if the

weighted average ratio of sand to noncarbonate clay to this
depth is 1.0 or less, or is <0.15 percent if the ratio is 13 or
more, or an intermediate weighted average percentage of

organic carbon if the ratio is between 1.0 and 13; or a

weighted average percentage of organic carbon in the upper

soil to a depth of 18 cm that is not as much as one-fifth
more than the values just stated if there is a lithic or

paralithic contact shallower than 40 cm but deeper than 18

cm;

¢. Are dry in all parts of the moisture control section for

more than three-fourths of the time (cumulative) that the

soil temperature is 5°C or more at a depth of 50 cm unless
the soil is irrigated;

f. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or to the base of an Ap horizon, a
(2) A coefficient of linear extensibility (COLE) of 0.05 dq
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m, and
(3) More than 35 percent clay in horizons that total >50
cm in thickness;

g. Have a content of organic carbon that decreases regularly

with depth below a depth of 25 cm and, unless a lithic or

paralithic contact occurs at a shallower depth, reaches a level
of <0.2 percent at a depth 1.25 m below the surface;

h, Have an SAR of 45 or less or <40 percent saturation with

sodium throughout the cambic horizon if the saturated hy-

draulic conductivity is slow or very slow; and

i, Do not have an anthropic epipedon,

Anthropic Camborthids are like Typic Camborthids except

for d and i.

Aquic Camborthids are like Typic Camborthids except for a,

with or without d or e, or both.

Aquic Durie Camborthids are like Typic Camborthids except

for a and b, with or without d or e, or both,

Borollic Camborthids are like Typic Camborthids except for

d or for d and e. The mean annual soil temperature is

lower than 8°C, the mean summer and mean winter soil

temperatures at a depth of 50 cm differ by >5°C, and the
moisture regime is aridic bordering on an ustic regime.

Borollic Lithic Camborthids are like Typic Camborthids ex-

cept for ¢ and d, with or without e, The mean annual soil

temperature is lower than 8°C, the mean summer and mean
winter soil temperatures at a depth of 50 cm differ by >5°C,
and the moisture regime is aridic bordering on ustic.

Borollic Vertic Camborthids are like Typic Camborthids ex-

cept for d and f, with or without e. The mean annual soil

temperature is lower than 8°C, and the mean summer and
mean winter soil temperatures at a depth of 50 cm differ by
>S°C. The cracks are not closed for as many as 60 consecu-


71

Chapter 10
Mollisols
Key To Suborders

GA. Mollisols that have all the following:
1. An albic horizon that lies immediately under the
mollic epipedon or that separates horizons that together
meet all the requirements of a mollic epipedon;
2. An argillic or a natric horizon; and
3. Chroma of 2 or less in the albic horizon or
characteristics associated with wetness in the albic,
argillic, or natric horizon, namely mottles or iron-
manganese concretions larger than 2 mm or both.

Albolls, p. 172

GB. Other Mollisols that either have an aquic moisture
regime or are artificially drained, and that have one or more
of the following characteristics associated with wetness;
1. A histic epipedon overlying the mollic epipedon;
2, An SAR 213 (or sodium saturation of >15 percent) in
the upper part of the mollic epipedon and decreasing
SAR (or sodium saturation) with increasing depth below
50 cm;
3. One of the following combinations of colors, moist;
a. If the lower part of the mollic epipedon* has
chroma of ! or less, there are either
(1) Distinct or prominent mottles in the lower part
of the mollic epipedon; or
(2) A color value, moist, of 4 or more immediately
below the mollic epipedon, or within 75 cm of the
surface if a calcic horizon intervenes, and one of
the following:
(a) If the hue is 10YR or redder and there are
mottles, chroma is less than 1.5 on ped surfaces
or in the matrix; if there are no mottles, chroma
is less than 1;
(b) If the hue is nearest 2.5Y and there are
distinct or prominent mottles, chroma is 2 or less
on ped surfaces or in the matrix; if there are no
mottles, chroma is 1 or less;
(c) If the nearest hue is SY or yellower and
there are distinct or prominent mottles, chroma
is 3 or less on ped surfaces or in the matrix; if
there are no mottles, chroma is 1 or less;
(d) The hue is bluer than 10Y or the color is
neutral; or
(e) The color results from uncoated mineral
grains; or
b. If the lower part of the mollic epipedon has chroma
of more than | but not more than 2, there are either
(1) Distinct or prominent mottles in the lower
mollic epipedon; or
(2) Base colors immediately below the mollic
epipedon that have one or more of the following
properties:
Tir the mollc epipedon extends to « lithic contact within 80 cm of the surface,
the requirement for mottles is waived.



128

b, Do not have mottles that have chroma of 2 or less above
a depth of 1 m;

¢. Do not have a lithic contact within a depth of 50 cm;

d, Do not have an albic horizon that is thick enough to be
preserved after the soil has been mixed to a depth of 18 cm
and is underlain by a horizon that has a color value one unit
or more darker and that meets all requirements for a spodic
horizon except the index of accumulation; and

e. Do not have a surface horizon between 25 and 50 cm
thick that meets all requirements for a plaggen epipedon
except thickness,

Alfic Udipsamments are like Typic Udipsamments except
for a and have base saturation of 35 percent or more in
some horizon <1.25 m below the uppermost lamella or have
a frigid temperature regime.

Aquic Udipsamments are like Typic Udipsamments except
for b with or without a or d or both.

Lithic Udipsamments are like Typic Udipsamments except
for c.

Plaggeptic Udipsamments are like Typic Udipsamments ex-
cept for e.

Spodic Udipsamments are like Typic Udipsamments except
for d.

Ultic Udipsamments are like Typic Udipsamments except for
a, have base saturation of <35 percent in some horizon <1.25
m below the uppermost lamella, and have a mesic or warmer
temperature regime.

Ustipsamments

Distinctions between Typic Ustipsamments and other sub-
groups

Typic Ustipsamments are the Ustipsamments that

a, Do not have lamellae within 1.5 m of the soil surface that
meet all requirements for an argillic horizon except thick-
ness!

b, Do not have distinct or prominent mottles above a depth
of 1 m and are not saturated with water within 1 m of the
surface during any time of year in most years; and

c. Do not have a lithic contact within 50 cm of the surface.
Alfic Ustipsamments are like Typic Ustipsamments except
for a, have base saturation of 35 percent of more in some
horizon <1.25 m below the uppermost lamella, and have a
color value, moist, of 4 or more within 25 cm of the sur-
face.

Aquic Ustipsamments are like Typic Ustipsamments except
for b.

Lithic Ustipsamments are like Typic Ustipsamments except
for ¢.

‘em thick, but their total thickness is leas than the 18 em required for an
argillic horizon.

Uthe clay content cannot be estimated with precision in lametine that are
very thin, The lamellae in solls of alfic subgroups generally are about 0.5 to 1
cm thick, but their total thickness is lens than the 15 em required for an
argillic horizon.


257
Xerults

Key to great groups

FEA. Xerults that have an argillic horizon that has <10
percent weatherable minerals in the 20- to 200-micrometer
fraction in its upper 50 cm and have a clay distribution such
that the percentage of clay does not decrease from its maxi-
mum amount by >20 percent of that maximum within 1.5 m
of the soil surface, or the layer in which the percentage of
clay is less than the maximum has skeletans on ped faces or
has 5 percent or more plinthite by volume.

Palexerults, p. 257

FEB. Other Xerults.
Haploxerults, p. 257

Haploxerults

Distinctions between Typic Haploxerults and other sub-
groups

‘Typic Haploxerults are the Haploxerults that
a. Do not have the following combination of characteristics
in the upper 25 cm or more of the argillic horizon:
(1) Mottles that have a color value, moist, or 4 or more
and chroma, moist, of 2 or less and also mottles of higher
chroma that are due to segregation of iron; and
(2) Saturation with water in the mottled zone at some
time of year when the soil temperature in that zone is
5°C or higher, or the soil is artificially drained;
b. Do not have a lithic contact within 50 cm of the mineral
soil surface;
c. Have texture finer than loamy fine sand in some part of
the argillic horizon and have an argillic horizon that does
not have lamellae in at least its upper 25 cm;
d. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
e. Have a continuous argillic horizon throughout each pedon,
not interrupted by ledges of bedrock; and
f. Do not have an epipedon as thick as 50 cm if its particle-
size class is sandy throughout.
Ruptic-Lithic-Xerochreptic Haploxerults are like Typic
Haploxerults except for b and e.

Palexerults

Palexerults are the Xerults that

1, Have both the following characteristics:
a. An argillic horizon that in its upper 50 cm has <10
percent weatherable minerals in the 20- to 200-microm-
eter fraction; and


47

30. Fine-silty over fragmental.

31. Fine-silty over sandy or sandy-skeletal.

32. Fine-silty over clayey if there is an absolute
difference of >25 percent in the percentages of clay.
33. Clayey over fragmental.

34, Clayey over sandy or sandy-skeletal.

35. Clayey over loamy-skeletal if there is an absolute
difference of >25 percent in the percentages of clay in
the fine-earth fraction.

36. Clayey over loamy if there is an absolute difference
of >25 percent in the percentages of clay.

37. Clayey over fine-silty if there is an absolute
difference of >25 percent in the percentages of clay.
38. Thixotropic over fragmental.

39, Thixotropic over sandy or sandy-skeletal.

40. Thixotropic over loamy-skeletal.

41. Thixotropic over loamy.

42. Cindery over medial,

43, Cindery over medial-skeletal.

44, Ashy over medial.

The intent in setting up classes of strongly contrasting par-
ticle sizes is to identify changes in pore-size distribution
that seriously affect movement and retention of water and
that have not been identified in higher categories, The list
given is intended for use in grouping the soil series of the
United States into families. It is not intended as a complete
list. For example, fine sand over coarse sand is common in
the Udipsamments of western Europe but is not known to
be important in the United States.

Choice of 7 or 11 particle-size classes

Only the seven particle-size classes are used in lithic, arenic,
and grossarenic subgroups and in shallow families.

In families of Ultisols not included in the preceding item,
subclasses of loamy particle-size classes are used but not
subclasses of the clayey classes.

If only a part of the control section of a soil in an andic or
andeptic subgroup or other group where substitute terms are
used is cindery, ashy, medial, or thixotropic, contrasting
families are recognized, but only the seven particle-size
classes are used. For example, we might use cindery over
loamy but not cindery over fine-loamy.

Only two particle-size classes are used to separate families in
Vertisols, fine if there is <60 percent clay and very-fine if
there is 60 percent or more clay in the weighted average of
the control section,

Mineralogy classes

‘The control section

Mineralogy classes are based on the approximate mineralog-
ical composition of selected size fractions of the same seg-

ment of the soil (control section) that is used for application
of particle-size classes,


87

J. Have an argillic horizon that has a color hue of SYR or
yellower in some part, or has a value, moist, of 3.5 or more
in some part, or has a value, dry, that is more than one unit
higher than the value, moist; and

k. Have an argillic horizon that is continuous horizontally,
that is continuous vertically for at least the upper 20 cm,
and that has a texture finer than loamy fine sand.

Aquic Paleustalfs are like Typic Paleustalfs except for a,
with or without d or e, or both.

Aquic Arenic Paleustalfs are like Typic Paleustalfs except for
a and b, with or without d or e, or both, and they have a
sandy epipedon (loamy fine sand or coarser) between 50 cm
and 1 m thick,

Arenic Paleustalfs are like Typic Paleustalfs except for b ot
for & and d, and they have a sandy epipedon (loamy fine
sand or coarser) between 50 cm and | m thick.

Arenic Aridic Paleustalfs are like Typic Paleustalfs except
for b and h and they have a sandy epipedon (loamy fine
sand or coarser) between 50 cm and 1 m thick.

Aridic Paleustalfs are like Typic Paleustalfs except for h,
and either they are noncalcareous in some subhorizon above
the calcic horizon or they do not have a calcic horizon
whose upper boundary is within a depth of | m below the
soil surface if the weighted average particle-size class of the
upper 50 cm of the argillic horizon is sandy, or 60 cm if it
is loamy, or 50 cm if it is clayey.

Calciorthidic Paleustal fs are like Typic Paleustalfs except
for A, and they have a calcic horizon within a depth of 1 m
if the weighted average particle-size class of the upper 50
cm of the argillic horizon is sandy, 60 cm if it is loamy, or
50 cm if it is clayey, and they have carbonates in all sub-
horizons above the calcic horizon.

Grossarenic Paleustalfs are like Typic Paleustalfs except for
>, with or without a or d, or both, and they have a sandy
epipedon (loamy fine sand or coarser) >] m thick.

Kandic Pateustalfs are like Typic Paleustalfs except for i,
with or without d or e, or both.

Petrocalcic Paleustalfs are like Typic Paleustalfs except for
8, with or without A or j, or both.

Psammentic Paleustalfs are tike Typic Paleustalfs except for
k, with or without some or all of 5, d, or e.

Rhodic Paleustalfs are like Typic Paleustalfs except for j,
with or without d or e or both, and the hue in the argillic
horizon is redder than SYR in all parts.

Udertic Paleustalfs are like Typic Paleustalfs except for d
and f, with or without a.

Udic Paleustalfs are like Typic Paleustalfs except for d.
Ultic Paleustalfs are like Typic Paleustalfs except for e and
d,

Plinthustalfs

Plinthustalfs are the Ustalfs that have plinthite that forms a
continuous phase or that constitutes more than half the ma-
trix of some subhorizon of the argillic horizon within 1,25 m
of the soil surface. There are no soil series in the United
States that are presently classified in this great group, but
the group is provided for other parts of the world, Sub-
groups have not been developed. Plinthustalfs were in-
cluded with Ground-Water Laterite soils in the 1938 classi-
fication.


Agric horizon

The agric horizon (L. ager, field) is an illuvial horizon
formed under cultivation that contains significant amounts
of illuvial silt, clay, and humus. After long~continued culti-
vation, changes in the horizon immediately below the plow
layer become apparent and cannot be ignored in classifying
the soil. The worm channels, root channels, or ped surfaces
become coated with a dark-colored mixture of organic mat-
ter, silt, and clay. The accumulation on the sides of worm-
holes becomes thick and eventually can fill them. If worms
are scarce, the accumulation may take the form of thick
lamellae that may range in thickness from a few millimeters
to about I cm, The coatings on the sides of wormholes and
lamellae always have lower color value and chroma than the
soil matrix.

The agric horizon has somewhat different forms in different
climates if there are differences in soil fauna. In a humid
temperate climate, where soils have what is later defined as
an udic moisture regime and a mesic temperature regime,
earthworms can become abundant. If there are earthworm
holes that, with their coatings, constitute 5 percent or more
of the volume and if the coatings are 2 mm or more thick
and have color value of 4 or less and chroma of 2 or less,
moist, the horizon is considered an agric horizon. After
long-continued cultivation, the content of organic matter is
not likely to be high, but the carbon-nitrogen ratio in the
agric horizon is low, usually <8, The pH of the agric hori-~
zon is close to neutrality, 6 to 6.5.

In a Mediterranean climate, where soils have what is later
defined as a xeric soil moisture regime, earthworms are less
common and the illuvial materials accumulate as lamellae
directly below the Ap horizon. If the lameliae are 5 mm or
more thick, have color value of 4 or less, moist, and chroma
of 2 or Jess, and constitute § percent or more by volume of
a horizon that is 10 cm or more thick, the horizon is con-
sidered an agric horizon.

Albic horizon

The albic (L, albus, white) horizon is one from which clay
and free iron oxides have been removed or in which the
oxides have been segregated to the extent that the color of
the horizon is determined by the color of the primary sand
and silt particles rather than by the coatings on these parti~
cles. An albic horizon may be at the surface of the mineral
soil; it may lie just above an argillic or a spodic horizon;
may lie between a spodic horizon and either a fragipan or
an argillic horizon; or it may lie between an argillic horizon
and a fragipan or between a cambic horizon and an argillic
horizon, natric horizon, or fragipan. It is usually underlain
by a spodic, natric, or argillic horizon, a fragipan, or a rela—
tively impervious layer that can produce a perched water
table and either stagnant or moving water.

Deep deposits of pure white sand can be formed by wind or
wave action, Although these deposits have the apparent
morphology of an albic horizon, they are in fact a parent
materia), The white sand in such a deposit does not overlie


Chapter 1

The Soil That We Classify and Horizons
and Properties Diagnostic for the Higher
ategories: Mineral Soils

The Soil That We Classify

Soil, as used in this text, is the collection of natural bodies
on the earth’s surface, in places modified or even made by
man of earthy materials, containing living matter and
supporting or capable of supporting plants out-of-doors, Its
upper limit is air or shallow water, At its margins it grades
to deep water or to barren areas of rock or ice. Its lower
limit to the not-soil beneath is perhaps the most difficult to
define. Soil includes the horizons near the surface that
differ from the underlying rock material as a result of
interactions, through time, of climate, living organisms, par-
ent materials, and relief. In the few places where it con-
tains thin cemented horizons that are impermeable to roots,
soil is as deep as the deepest horizon. More commonly soil
grades at its lower margin to hard rock or to earthy materi-
als vitually devoid of roots, animals, or marks of other
biologic activity. The lower limit of soil therefore is
normally the lower limit of biologic activity, which
generally coincides the common rooting depth of native
perennial plants. If either biological activity or current
pedogenic processes extend to depths greater than 2 m, the
lower limit of the soil we classify is arbitrarily set at 2m,
Yet in defining mapping units for detailed soil surveys,
lower layers that influence the movement and content of
water and air in the soil of the root zone must also be
considered.

Buried Soils

A soil is considered to be a buried soil if there is a surface
mantle of new material that is 50 cm or more thick or if
there is a surface mantle between 30 and 50 cm thick and
the thickness of the mantle is at least half that of the named
diagnostic horizons that are preserved in the buried soil. A
mantle that is <30 cm thick is not considered in the taxon-
omy but, if important to the use of the soil, is considered in
establishing a phase. The soil that we classify in places
where a mantle is present, therefore, has its upper boundary
at the surface or <50 cm below the surface, depending on
the thickness of its horizons.

A surface mantle of new material as defined here is largely
unaltered. It is usually finely stratified and overlies a hori-
zon sequence that can be clearly identified as the solum of a
buried soil in at least part of the pedon, as defined in the
following chapter. The recognition of a surface mantle
should not be based solely on studies of associated soils.


210
SI Units Conversion Table

The following conversions have been made in the text of the
Keys.

CEC:

1 meq/100 g soil = 1 cmol(+) kgTM soil !
Conductivity:

1 mmho/em = 1 dS m‘?

Pressure:

15-bar water = 1500 kPa water

1/3-bar water = 33 kPa water

Concentration:

IN = 1M

Length:

1 micron = 1 micrometer


154

Vertic Haplaquepts are like Typic Haplaquepts except for /,
with or without a or c, or both.

Humaquepts
Distinctions between Typic Humaquepts and other subgroups

Typic Humaquepts are the Humaquepts that
a. Have chroma of 2 or less, moist, and hue of SY or redder
in 60 percent or more of the matrix in all subhorizons
between depths of 15 and 75 cm;
b. Have mottles or have iron-manganese concretions within
a depth 30 cm below the base of the epipedon if the chroma
within that depth is | or more, the hue is redder than 5Y,
and the value, moist, is 5 or more;
¢. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less, or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
d. Have an epipedon that is <60 cm thick;
¢. Have a content of organic carbon that decreases regularly
with depth and, unless a lithic or a paralithic contact occurs
at a shallower depth, reaches a level of 0.2 percent or less
within 1.25 m of the soil surface;
f. Do not have a histic epipedon whose upper boundary is at
or near the soil surface; and
g. Have an m value of <0.9 between depths of 50 and 80 cm
and of 0.7 or less in all layers between depths of 20 and 50

cm.
Cumulic Humaquepts are like Typic Humaquepts except for
dande.

Fluvaquentic Humaquepts are like Typic Humaquepts except
for e.

Histic Humaquepts are like Typic Humaquepts except for f,
with or without all or any of a, 6, or e.

Placaquepts
Distinctions between Typic Placaquepts and other subgroups

Typic Placaquepts are the Placaquepts that

‘a. Do not have a histic epipedon; and

b. Have a continuous placic horizon within 1 m of the soil
surface throughout each pedon.

Histic Placaquepts are like Typic Placaquepts except for a,

Plinthaquepts

These are mainly Aquepts of intertropical regions. They
have plinthite that forms a continuous phase or occupies
more than half the matrix of some subhorizon deeper than
30 cm but within 1.25 m of the soil surface. These are soils
in which the ground-water level fluctuates appreciably
during the year. Water is at or near the surface during the
tainy season but drops during a dry season. Most of these



44

hy-skel .--These are mainly soils that have a
fine-earth fraction that feels like a sand or a loamy sand
after prolonged rubbing.

Ashy. Sixty percent or more of the whole soil (by weight)
volcanic ash, cinders, and pumice; <35 percent (by volume)
is 2 mm in diameter or larger.

Ashy-skeletal. Rock fragments other than cinders are 35
percent or more (by volume); the fine-earth fraction is oth-
erwise ashy.

Medial and medial-skeletal,--These are soils that have a
fine-earth fraction that feels loamy, as the term is defined
earlier in this chapter, after prolonged rubbing.

Medial. Less than 60 percent of the whole soil (by weight)
volcanic ash, cinders, and pumice; <35 percent (by volume)
is 2 mm if diameter or larger, the fine-earth fraction is not
thixotropic; the exchange complex is dominated by amor-
phous materials.

Medial-skeletal. Thirty-five percent (by volume) or more
rock fragments other than cinders 2 mm in diameter or
larger; the fine-earth fraction is otherwise medial.

+ ic --These are soils that
have a fine-earth fraction that is thixotropic and an ex~
change complex dominated by amorphous clays.

Thixotropic. Less than 35 percent (by volume) has diameter
of 2 mm or larger; the fine~earth fraction is thixotropic; the
exchange complex is dominated by amorphous materials.
Thixotropic-skeletal. Thirty-five percent or more (by vol-
ume) rock fragments other than cinders 2 mm in diameter or
larger; the fine-carth fraction is thixotropic.

0 jon ft Sele: se eubeti

Names of particle-size classes or their substitutes as defined
are not applied to a fragipan, duripan, or petrocalcic horizon
but are applied to specific horizons or to the materials be-
tween given limits of depth that are defined in terms of ei-
ther the distance below the surface of the mineral soil or the
upper boundary of a specified horizon or root-limiting
Jayer. The vertical section so defined is called the control
section, Definitions of the contro! section for determination
of the particle-size classes are arranged as a key.

A. Particle-size modifiers or substitutes are used to describe
material from the surface to a lithic or paralithic contact, or
to a fragipan, duripan, or petrocalcic horizon if any of these
come within a depth of 36 cm (14 in.) or less; or to a depth
of 36 cm if the soil temperature is 0°C or lower within this
depth about 2 months after the summer solstice.

B, In other soils that do not have an argillic or kandic
horizon or a natric horizon and in great groups of Spodosols,
Alfisols, and Ultisols that have a spodic horizon or a fragi~
pan in or above an argillic horizon:
1. Particle-size modifiers or substitutes are used to
describe material from the base of the Ap horizon or
from a depth of 25 cm, whichever is greater, to a root-
limiting layer if the depth is <1 m; or to a depth 25 cm
below the level at which the soil temperature is 0 degree


165

(2) A satio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;

b. Do not have mottles that have chroma of 2 or less within

1 m of the soil surface if the mottled horizon is saturated

with water at some time during the year or if there is

artificial drainage.

¢. Have a content of organic carbon'® that decreases

regularly with depth and, unless a lithic or a paralithic

contact is present at a shallower depth, reaches a level of 0.2

percent organic carbon or less within 1.25 m of the soil

surface; or have slopes >25 percent;

d. Do not have a lithic contact within 50 cm of the soil

surface;

e, Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part and that extend upward to the soil
surface or to the base of an Ap horizon;

(2) A coefficient of linear extensibility (COLE) of 0.09
of more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper | m of the soil, or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1 m; and

(3) More than 35 percent clay in horizons that total >50
cm in thickness; or

f, Have a cambic horizon.

Andic Eutropepts are like Typic Eutropepts except for a.

Aquic Eutropepts are like Typic Eutropepts except for b.

Fluvaquentic Eutropepts are like Typic Eutropepts except for

band c.

Fluventic Eutropepts are like Typic Eutropepts except for c.

Lithic Eutropepts are like Typic Eutropepts except for d,

Vertic Eutropepts are like Typic Eutropepts except for e,

with or without any or all of 4, ¢, or f.

Humitropepts

Distinctions between Typic Humitropepts and other
subgroups

Typic Humitropepts are the Humitropepts that
a, Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either
GJ) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
b. Do not have mottles that have chroma of 2 or less within
1 m of the soil surface if the mottled horizon is saturated
with water at some time of year or if there is artificial
drainage;

T5ohe carbon should be of Holocene ag 4
arbon should be of Holocene age. It is not the intent to include fossil

carbon from bedrock.



73

HEC. Other Udalfs that
1, Do not have a continuous albic horizon above the
argillic horizon;
2, Have a broken upper boundary of the argillic
horizon; and
3. Have discrete nodules in the argillic horizon that
range from 2.5 to 5 cm to about 30 cm in diameter;
exteriors of nodules are enriched and weakly ce-
mented or indurated with iron and have redder hue
or stronger chroma than interiors of nodules.

Ferrudalfs, p. 74

HED. Other Udalfs that have tongues of albic materials in
the argillic horizon and do not have a fragipan.
Glossudalfs, p. 76

HEE. Other Udalfs that have tongues of albic materials in
the argillic horizon and have a fragipan,
Fraglossudalfs, p. 75

HEF. Other Udalfs that have a fragipan,
Fragiudalfs, p. 74

HEG. Other Udalfs that
1. Have a CEC <16 cmoi(+) kg” play (by 1 Mf NH,OAc pH
7) and an ECEC <12 cmol(+) kg” clay (sum of bases ex-
tracted with 1 M NH,OAc pH 7 plus | M KCl-extractable
Al) in the major part of the argillic or kandic horizon or the
major part of the upper 100 cm of the argillic or kandic
horizon if these horizons are thicker than 100 cm;
2. Do not have a lithic, paralithic, or petroferric contact
within 150 cm of the soil surface; and
3. Have a clay distribution such that the percentage of clay
does not decrease from its maximum amount by as much as
20 percent within a depth of 150 cm from the soil surface
or the layer in which the clay percentage decreases by more
than 20 percent has at least 5 percent of the volume con-
sisting of skeletans on faces of peds and there is at least 3
Percent (absolute) increase in clay below the layer.
Kandiudalfs, p. 78

HEH, Other Udalfs that have a CEC <16 cmol(+) kg? clay
(by 1 M NH,OAc pH 7) and an ECEC <12 cmol(+) kg” clay
(sum of bases extracted with 1 M NH,OAc pH 7 plus 1 M
KCl-extractable Al) in the major part’ of the argillic or
kandic horizon or the major part of the upper 100 cm of the
argillic or kandic horizon if these horizons are thicker than
100 cm;

Kanhapludalfs, p. 78

HEI. Other Udalfs that

1. Do not have a lithic or paralithic contact within 1.5 m
of the soil surface;

2. Have clay distribution such that the percentage of clay
does not decrease by as much as 20 percent of the maxi-
mum within a depth of 150 cm from the soil surface or
the layer in which the clay percentage decreases by more
than 20 percent has at least 5 percent of the volume con-
sisting of skeletans on faces of peds and there is at least
3 percent (absolute) increase in clay below the layer; and


82

(1) Hues redder than 1OYR and chroma of more
than 4 in the matrix of at least the lower part of
the horizon;

(2) Hues of 7.5YR or redder and value, moist, that
is less than 4 and value, dry, that is less than 5
throughout the major part of the horizon; or

(3) Common coarse mottles that have hue of 7.5YR
or redder or chroma of more than 5 in the lower
part of the horizon; or

2. Does not have a lithic or paralithic contact within 50

cm of the surface and has an argillic horizon in which

the upper part has a clayey particle-size class and there is

an increase of at least 20 percent clay (absolute) within a

vertical distance of 7.5 cm, or of at least 15 percent clay

(absolute) within a vertical distance of 2.5 cm at the up-

per boundary.

Paleustalfs, p. 86

HCG. Other Ustalfs that have an argillic horizon that has
throughout its thickness a hue redder than SYR, a color
value, moist, less than 3.5, and a color value, dry, no more
than one unit higher than the value moist.

Rhodustalfs, p. 88

HCH, Other Ustalfs.
Haplustalfs, p. 82

Durustalfs

Durustalfs are the Ustalfs that have a duripan whose upper
boundary is within 1 m of the surface. They are not known
to occur in the United States, and subgroups have not been
developed. They are provided for use in other countries,

Haplustalfs
Distinctions between Typic Haplustalfs and other subgroups

Typic Haplustalfs are the Haplustaifs that
a, Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizon is saturated
with water at some time during the year or the soil has arti-
ficial drainage;
b. Have texture finer than loamy fine sand in some sub-
horizon within 50 cm of the soil surface;
c. Do not have a lithic contact within 50 cm of the soil
surface;
d. Have CEC of 24 or more cmol(+) kgTM clay (by 1 af
NH,OAc pH7),
e. Have an argillic horizon that is continuous horizontally,
that is continuous vertically for at least the upper 20 cm,
that is not composed entirely of lamellae, and that has a
texture finer than loamy fine sand;
f. When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry for more than four-tenths of the cumulative days
in some part of the moisture control section when the soil
temperature at a depth of 50 cm exceeds 5°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days


KEYS TO
SOIL TAXONOMY

by
Soil Survey Staff

Agency for International Development
United States Department of Agriculture
Soil Management Support Services

SMSS Technical Monograph #6

Third Printing, 1987
Comell University


Salorthids

Distinctions between Typic Salorthids and Aquollic Salor-
thids

‘Typic Salorthids are the Salorthids that
a, Have a salic horizon that has its upper boundary within
18 cm of the soil surface; and

b. Have a weighted average content of organic carbon in the
upper soil to a depth of 40 cm that is <0.6 percent if the
weighted average ratio of sand to noncarbonate clay to this
depth is 1.0 or less, or is <0.15 percent if the ratio is 13 or
more, or is intermediate if the ratio of sand to clay is be-
tween 1.0 and 13.

Aquollic Salorthids are like Typic Salorthids except for b.


186

d. Have a regular decrease in organic carbon content with

increasing depth and unless a lithic or a paralithic contact is

at some depth between 50 cm and 1.25 m below the soil

surface, have an organic carbon content of 0.3 percent or

less at a depth within 1,25 m of the surface; or the slope is

>25 percent;

e. Do not have a lithic contact within 50 cm of the surface;

and

f. Do not have the following combination of characteristics;
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1m, and
(3) More than 35 percent clay in horizons that total >50
cm in thickness,

Aquic Hapludolls are like Typic Hapludolls except for a, or

aand c,

Cumulic Hapludolts are like Typic Hapludolls except for b

and d, with or without a or c, or both.

Entic Hapludolls ate like Typic Hapludolls except for c.

Fluvaquentic Hapludolls are like Typic Hapludolls except for

aand d or for a, c, and d.

Fluventic Hapludolls are like Typic Hapludolls except for d

or for ¢ and d.

Lithic Hapludolls are like Typic Hapludolls except for e,

with or without a or c, or both.

Vermic Hapludolls are like Typic Hapludolls except for b

and ¢ and have mollic epipedon that, below any Ap horizon,

has 50 percent or more by volume of wormholes, wormcasts,

or filled animal burrows.

Vertic Hapludolls are like Typic Hapludolls except for f,

with or without all or any of a, 6, and d.

Paleudolls
Distinctions between Typic Paleudolls and other subgroups

Typic Paleudolls are the Paleudolls that

a. Do not have mottles that have chroma of 2 or less in the
upper 50 cm of the argillic horizon if the mottled horizon is
saturated with water at some period when its temperature is
>S°C or if the soil has artificial drainage.

Aquic Paleudolls are like Typic Paleudolls except for a.

Vermudolls
Distinctions between Typic Vermudolls and other subgroups

Typic Vermudolls are the Vermudolls that

a, Have a mollic epipedon that is 75 cm or more thick;
b. Do not have a cambic horizon;

c. Have a mollic epipedon that has a transition to the
underlying horizon in which $0 percent or more of the
material is discrete wormholes, wormcasts, or animal


134
Medifibrists

Distinctions between Typic Medifibrists and other subgroups

Typic Medifibrists are the Medifibrists that
a, Have
(1) Less than 25 cm of the subsurface and bottom tiers
occupied by hemic materials; and
(2) Less than 12.5 cm of the subsurface and bottom tiers
occupied by sapric materials,
b, Have less than three-fourths of the fiber volume in the
surface tier or more of the control section derived from
Sphagnum,
¢, Do not have limnic layer(s) that are 5 cm or more thick
within the control section;
d, Do not have a lithic contact within the control section;
e. Do not have a mineral layer between 5 cm and 30 cm
thick within organic materials or do not have two or more
thin continuous mineral layers in the control section below
the surface tier;
f, Do not have a mineral layer 30 cm or more thick whose
upper boundary in the control section is below the surface
tier; and
g. Do not have a layer of water within the control section
beneath the surface tier,
Fluvaquentic Medifibrists are like Typic Medifibrists except
for e, with or without a,
Hemic Medifibrists are like Typic Medifibrists except for
a(1).
Hemic Terric Medifibrists are like Typic Medifibrists except
for a(/) and f, with or without c or e, or both.
Hydric Medifibrists are like Typic Medifibrists except for g.
Limnic Medifibrists are like Typic Medifibrists except for c,
with or without e or a, or both.
Lithic Medifibrists are like Typic Medifibrists except for d,
with or without all or any of a, B, c, e, or f.
Sapric Medifibrists are like Typic Medifibrists except for
a(2).
Sapric Terric Medifibrists are like Typic Medifibrists except
for a(2), and f, with or without ¢ or e, or both.
Sphagnie Medifibrists are like Typic Medifibrists except for

Sphagnic Terric Medifibrists are like Typic Medifibrists
except for b and f, with or without c or e, or both.

Terric Medifibrists are like Typic Medifibrists except for /,
with or without ¢ or e, or both.

Sphagnofibrists

Distinctions between Typic Sphagnofibrists and other sub-
groups

Typic Sphagnofibrists are the Sphagnofibrists that
a. Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin
continuous mineral layers in the contro} section below the
surface tier;
b. Have
(1) Less than 25 cm of the subsurface and bottom tiers
occupied by hemic materials; and


163
Plaggepts

Plaggepts are the soils that have a plaggen epipedon that is
composed of crystalline rather than pyroclastic materials.
This suborder includes all freely drained soils that have a
plaggen epipedon except a few Andepts.

Tropepts
Key to great groups

IDA. Tropepts that have base saturation of <50 percent (by
NH,OAc) in some subhorizon between depths of 25 cm and
1 m and have 12 kg or more organic carbon, exclusive of
surface litter, per square meter in the soil to a depth of | m,
or to a lithic, paralithic, or petroferric contact if one is
shallower than 1 m, and do not have a sombric horizon.
Humitropepts, p. 165

IDB. Other Tropepts that have a sombric horizon,
Sombritropepts, p. 166

IDC. Other Tropepts that have an ustic moisture regime or
have soft powdery lime within 1.5 m of the soil surface and
have base saturation (by NH,OAc) of 50 percent or more in
all subhorizons between depths of 25 em and 1 m, or
between 25 cm and a lithic, paralithic or petroferric contact
if one is shallower than } m,

Ustropepts, p. 166

IDD, Other Tropepts that have base saturation (by NH,OAc)
of 50 percent or more in all subhorizons between depths of
25 cm and I m, or between 25 cm and a lithic or paralithic
contact if one is shallower than 1 m.

Eutropepts, p. 164

IDE. Other Tropepts.
Dystropepts, p. 163

Dystropepts
Distinctions between Typic Dystropepts and other subgroups

Typic Dystropepts are the Dystropepts that
a. Do not have mottles that have chroma of 2 or less within
1 m of the soil surface if the mottled horizon is saturated
with water at some time of year or the soil has artificial
drainage.
'b. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
¢. Have a cambic horizon;

INC


iv

Foreword

This publication, Keys to Soil Taxonomy, serves two
purposes. It provides the taxonomic keys required for the
classification of a soil in a form that can be used easily in
the field, and it serves as a means of providing an up-to-
date version of Soil Taxonomy that includes all revisions to
the keys that have been approved. It replaces the keys in
Soil Taxonomy, but it does not replace Agriculture
Handbook 436, which contains descriptive material,
laboratory data, and chapters on other subjects related to
Soil Taxonomy. This is the second update of the Keys to
Soil Taxonomy, which was originally printed in 1983, and
we plan to continue reprinting the keys about every two
years. Agriculture Handbook 436 will be revised and
reissued in the future, after most of the current ongoing
International Soil Classification Committees (ICOMs) have
completed their mandates, but probably not before about
1995.

This publication incorporates all amendments approved to
date and published in National Soil Taxonomy Handbook
(NSTH) Issues 1 through 11. It includes the
recommendations of the International Committee on Low
Activity Clays (NSTH Issue #8) and the International
Committee on Oxisols (NSTH Issue #11). The keys
reproduced here were extracted from a computerized copy
of Soil Taxonomy which is maintained in complete, up-to-
date form.

RICHARD W. ARNOLD
1987

Director, Soil Survey Division
Soil Conservation Service


195

¢. Have a mollic epipedon that, below any Ap horizon, has a
transition to the underlying horizon in which 50 percent or
more of the volume is wormholes and wormcasts or filled
animal burrows;

d. Do not have a lithic contact within 50 cm of the surface;
e. Have a mollic epipedon that has granular structure and is
composed almost entirely, below any Ap horizon, of worm-
holes, wormeasts, or filled animal burrows; and

f, Do not have mottles that have chroma of 2 or less within
1 m of the surface.

Entic Vermustolls are like Typic Vermustolls except for a,
and the epipedon is <50 cm thick.

Haplic Vermustolls ate like Typic Vermustolls except for b
and c, with or without a, and the epipedon is <75 cm thick.
Lithic Vermustolls are like Typic Vermustolls except for d
and a, with or without 6 or c, or both, and the epipedon is
<75 cm thick,

Pachic Vermustolls are like Typic Vermustolls except for a,
and the epipedon is 75 cm or more thick.

Xerolls
Key to great groups

GDA. Xerolls that have a duripan within 1 m of the soil
surface.
Dutixerolls, p. 198

GDB. Other Xerolls that have a natric horizon but do not
have a petrocalcic horizon that has its upper boundary
within 1.5 m of the soil surface,

Nal

‘ixerofls, p, 200

GDC, Other Xerolls that have a petrocalcic horizon that has
its upper boundary within 1.5 m of the soil surface or an
argillic horizon that has either or both
1. A vertical clay distribution such that the clay content
does not decrease by as much as 20 percent of the maxi-
mum clay content within 1.5 m of the soil surface, and
also one or more of
a. A hue redder than 10YR and chroma higher than 4
in the matrix; or
b. Common coarse mottles that have a hue of 7.5YR
or redder or chroma higher than 5, or both; or
2, A particle-size class in the upper part that is clayey
and an increase in clay content of at least 20 percent clay
(absolute) within a vertical distance of 7.5 cm or an in-
crease of 15 percent clay (absolute) within a distance of
2.5 cm at the upper boundary and no lithic or paralithic
contact within 50 cm of the soil surface.
Palexerolls, p. 200

GDD. Other Xerolls that have a calcic or gypsic horizon that
has its upper boundary within 1.5 m of the soil surface and
that are calcareous in all parts of all horizons above the cal-
cic or gypsic horizon after the upper soil to a depth of 18
cm has been mixed unless the texture is coarser than loamy
very fine sand or very fine sand.

Calcixerolls, p. 197


216

surface and a petroferric contact within 125 cm of the soil
surface,
Aqui Petroferric Hapludox

CEEB, Other Hapludox that have a petroferric contact
within 125 om of the soil surface,
Petroferric Hapludox

CEEC, Other Hapludox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and a lithic contact within 125 cm of the soil
surface,

Aquic Lithic Hapludox

CEED, Other Hapludox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Hapludox

CEEE. Other Hapludox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface and mottles of 4 or more value moist and 2 or
less chroma within a depth of 125 cm of the soil surface.
Plinthaquic Hapludox

CEEF. Other Hapludox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Hapludox

CEEG. Other Hapludox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface.

Aquic Hapludox

CEEH, Other Hapludox that have the lower boundary of the
oxic horizon within a depth or 125 cm of the soil surface.
Inceptic Hapludox

CEEI. Other Hapludox that have an 18 cm or thicker layer
in the upper 75 cm with a bulk density less than 1 g/cc and
in which all the Al plus one-half the Fe that is extractable
with acid oxalate totals more than 1.0 percent.

Andic Hapludox

CEE), Other Hapludox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 125 to 125 cm
depth from the soil surface.

Humic Rhodic Hapludox

CEEK. Other Hapludox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Hapludox


ut

Chapter 7
Entisols
Key To Suborders

JA, Entisols that
1. Have sulfidic materials within 50 cm of the mineral
soil surface; or
2. Are permanently saturated with water and have in all
horizons below 25 cm
a. Dominant hue that is neutral or bluer than 10Y and
b. Colors that change on exposure to the air; or
3. Are saturated with water at some time of year or are
artificially drained and have, within 50 cm of the
surface, dominant color (moist) in the matrix as follows:
a. In horizons that have texture finer than loamy fine
sand in some or all subhorizons, or that have >35
percent (by volume) of rock fragments in some
subhorizon
(1) If there is mottling, chroma is 2 or less;
(2) If there is no mottling and the value is less than.
4, chroma is less than 1; if the value is 4 or more,
chroma is | or less;
b. In horizons that have texture of loamy fine sand or
coarser in all subhorizons
(1) If the hue is as red or redder than 10YR and
there is mottling, chroma is 2 or less; if there is no
mottling and the value is less than 4, chroma is less
than 1; or if the value is 4 or more, chroma is | or
less;
(2) If the hue is between 10YR and 10Y and there
is distinct or prominent mottling, chroma is 3 or
less; if there is no mottling, chroma is 1 of less;
(3) Hue is bluer than 10Y; or
(4) Any color if the color is due to uncoated grains
of sand.
Aquents, p. 112

JB, Other Entisois that have fragments of diagnostic
horizons between 25 cm and 1 m below the surface, but the
fragments are not arranged in discernible order.

Arents, p. 116

JC. Other Entisols that have below the Ap horizon or below
a depth of 25 cm, whichever is deeper, <35 percent (by
volume) of rock fragments and that have texture of loamy
fine sand or coarser in all subhorizons! either to a depth of
1 m or to a lithic, paralithic, or petroferric contact,
whichever is shallower.

Psamments, p, 125

JD, Other Entisols that do not have a lithic or paralithic
contact within 25 cm of the soil surface and that have slopes
of <25 percent and organic carbon content that decreases
irregularly with depth or remains above a level of 0.2
TLamaling that are <1 cm thick or that are too few to meet the requirements
for an argillic horizon are permitted to have texture of sandy loam. See the
definition of an argillic horison (ch. 1),



30

out this text all isofrigid soils without permafrost are con-
sidered to have a cryic temperature regime.

Frigid.--The frigid regime and some of the others that fol~
low are used chiefly in defining classes of soils in the low
categories. In the frigid regime the soil is warmer in sum-
mer than one in the cryic regime, but its mean annual tem-
perature is lower than 8°C (47°F), and the difference be-
tween mean winter and mean summer soil temperature is
more than 5°C (9°F) at a depth of 50 cm or at a lithic or
paralithic contact, whichever is shallower.

Meslc.--The mean annual soil temperature is 8°C or higher
but lower than 15°C (59°F) and the difference between
mean summer and mean winter soil temperature is more
than 5°C at a depth of 50 cm or at a lithic or paralithic
contact, whichever is shallower.

Thermic.--The mean annual soil temperature is 15°C (59°F)
or higher but lower than 22°C (72°F), and the difference
between mean summer and mean winter soil temperature is
more than 5°C at a depth of 50 cm or at a lithic or par-
alithic contact, whichever is shallower.

Hyperthermic.--The mean annual soil temperature is 22°C
(72°F) or higher, and the difference between mean summer
and mean winter soil temperature is more than 5°C at a
depth of 50 cm or at a lithic or paralithic contact, whichever
is shallower.

If the name of a soil temperature regime has the prefix iso,
the mean summer and winter soil temperature for June,
July, and August and for December, January, and February
differ by less than 5°C at a depth of 50 cm or at a lithic or
paralithic contact, whichever is shallower.

Isofrigid,--The mean annual soil temperature is lower than
8°C (47°F).

Isomesic,--The mean annual soil temperature is 8°C or
higher but Jower than 15°C (59°F).

Isothermic.--The mean annual soil temperature is 15°C or
higher but lower than 22°C (72°F).

Isohyperthermic.--The mean annual soil temperature is 22°C
or higher,

The limit between isofrigid and isomesic cannot be tested in
the United States and is tentative.

Sulfidic materials

Sulfidic materials are waterlogged mineral or organic soil
materials that contain 0.75 percent or more sulfur (dry
weight), mostly in the form of sulfides and that have less
than three times as much carbonate (CaCO, equivalent) as
sulfur. Sulfidic materials accumulate in a soil that is perma-
nently saturated, generally with brackish water. The sulfates
in the water are biologically reduced to sulfides as the soil
materials accumulate, Sulfidic materials are most common


218

g/cc and in which all the Al plus one-half the Fe that is
extractable with acid oxalate totals more than 1.0 percent.
Andic Kandiudox

CEDI. Other Kandiudox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface. °

Humic Rhodic Kandiudox

CEDS. Other Kandiudox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Kandiudox

CEDK. Other Kandiudox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Kandiudox

CEDL, Other Kandiudox that have a color hue of 2,5 YR or
redder with moist values of less than 4 in most of the 25 to
125 cm depth from the soil surface.

Rhodic Kandiudox

CEDM. Other Kandiudox that have a color hue of 7.5 YR
or yellower with moist values of 6 or more in most of the 25
to 125 cm depth from the soil surface.

Xanthic Kandiudox

CEDN. Other Kandiudox.
Typic Kandiudox

Sombriudox

Kev to subgroups

CEAA. Sombriudox that have a petroferric contact within a
depth of 125 cm of the soil surface.
Petroferric Sombriudox

CEAB. Other Sombriudox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Sombriudox

CEAC. Other Sombriudox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Sombriudox

CEAD. Other Sombriudox.
Typic Sombriudox


89

1, A vertical clay distribution such that the percentage of
clay does not decrease from the maximum by as much as
20 percent of that maximum throughout a depth of 1,5 m
from the soil surface, or the horizon in which the clay
decreases has either
a. More than 5 percent by volume of plinthit
b. Skeletans or other evidences of clay eluviation, and
there is no lithic or paralithic contact within 1.5 m of
the soil surface, and either
(1) A hue redder than 10YR and chroma more than 4
in the matrix of at least the lower part of the argillic
horizon; or
(2) Common coarse mottles that have a hue of 7.5YR
or redder or chroma greater than 5S or both in the
lower part of the argillic horizon;
2. An argillic horizon that has a clayey particle-size class
in the upper part and an increase of at least 20 percent
clay (absolute) within a vertical distance of 7.5 cm or at
least 15 percent clay (absolute) within a vertical distance
of 2.5 cm at the upper boundary; and there is no lithic or
paralithic contact within 50 cm of the surface of the soil.
Palexeralfs, p, 91

HDG, Other Xeralfs.
Haploxeralfs, p. 90

Durixeralfs
Distinctions between Typic Durixeralfs and other subgroups

Typic Durixeralfs are the Durixeralfs that

a. Have an argillic horizon that has <35 percent clay in all
parts, or the increase in clay content is <15 percent clay
(absolute) within a vertical distance of 2.5 cm at the upper
boundary of the argillic horizon, or the increase is <10 per-
cent clay (absolute) if the soil is cultivated and the lower
boundary of the Ap horizon is the upper boundary of the
argillic horizon;

b, Do not have mottles in the argillic horizon that have
chroma of 2 or less;

c. Have a duripan that is massive, platy, or prismatic and
that has half or more of its upper boundary indurated and
coated with opal or with opal and sesquioxides or that is in-
durated in some subhorizon below the upper boundary; and
d, Do not have a natric horizon.

Abruptic Durixeralfs are like Typic Durixeralfs except for a.
Abruptic Haplic Durixeralfs are like Typic Durixeralfs ex-
cept for a and c.

Haplic Durixeralfs are like Typic Durixeralfs except for c.
Natric Durixeralfs are like Typic Durixeralfs except for d,
with or without 4 or c, or both.

Fragixeralfs

Distinctions between Typic Fragixeralfs and other subgroups
Typic Fragixeralfs are the Fragixeralfs that

a, Above the fragipan have an argillic horizon that has clay

skins on at least some vertical and horizontal faces of pri-
mary or secondary peds, or both;


204

Acraquox

Key to subgroups

CAAA. Acraquox that have More than 5 percent plinthite in
some horizon within a depth of 125 cm of the soil surface.
Plinthic Acraquox

CAAB. Other Acraquox that have mottles with chroma of
more than 2 in 50 percent or more of the horizon immedi-
ately below the epipedon.

Aerie Acraquox

CAAC. Other Acraquox.
Typic Acraquox

Eutraquox
‘Kev to subgroups

CACA. Eutraquox that have a histic epipedon.
Histic Eutraquox

CACB. Other Eutraquox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Eutraquox

CACC. Other Eutraquox that have mottles with chroma of
more than 2 in 50 percent or more of the horizon immedi-
ately below the epipedon.

Aeric Eutraquox

CACD. Other Eutraquox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Eutraquox

CACE. Other Eutraquox.
‘Typic Eutraquox

Haplaquox
to rou!

CADA. Haplaquox that have a histic epipedon.
Histic Haplaquox

CADB. Other Haplaquox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Haplaquox

CADC. Other Haplaquox that have mottles with chroma of
more than 2 in 50 percent or more of the horizon immedi-
ately below the epipedon.

Aeric Haplaquox


84

a. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizon is saturated
with water at some time of the year when the soil tempera-
ture at that depth is 5°C or higher or the soil has artificial
drainage;
b. Do not have an epipedon that is 50 cm to 100 cm thick if
the particle-size class is sandy throughout;
c. Do not have an epipedon that is >100 cm thick if the
particle-size class is sandy throughout;
d, Do not have a horizon within 150 cm of the soil surface
that has >5 percent plinthite by volume;
e. When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are moist more than six-tenths of the time in half or
More years in some part of the moisture control section
(not necessarily the same part) when the soil temperature
at a depth of 50 cm exceeds 5°C; or
(2) If the soit temperature regime is hyperthermic,
isomesic, or warmer, are moist in most years in some or
all parts of the moisture control section for 180 or more
days during a period when the soil temperature at a
depth of 50 cm exceeds 8°C; and
f. When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry for more than 135 cumulative days in some part
of the moisture control section when the soil temperature
at a depth of 50 cm exceeds 5°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days
during a period when the soil temperature at a depth of
50 cm exceeds 8°C; and
g. Have an argillic or kandic horizon that has a color hue of
SYR or yellower in some part, or has a value, moist, of 3.5
or more in some part, or has a value, dry, that is more than
one unit higher than the value, moist.
Aquic Kandiustalfs are like Typic Kandiustalfs except for a,
with or without e.
Aquic Arenic Kandiustalfs are like Typic Kandiustalfs except
for a and b.
Arenic Kandiustalfs are like Typic Kandiustalfs except for

b.

Arenic Aridic Kandiustalfs are like Typic Kandiustalfs ex-
cept for b and e.

Aridie Kandiustalfs are like Typic Kandiustalfs except for

e.
Grossarenic Kandiustalfs are like Typic Kandiustalfs except
for c, with or without a.

Rhodic Kandiustalfs are like Typic Kandiustalfs except for
g.

Udic Kandiustalfs are like Typic Kandiustalfs except for .
Kanhaplustalfs

Distinctions between Typic Kanhaplustalfs and other sub-
groups

Typic Kanhaplustalfs are the Kanhaplustalfs that
a. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizon is saturated


12

d. If carbonates are absent in the parent material and
in the dust that falls on the soil, the required evidence
of alteration is satisfied by the presence of soil struc-
ture and the absence of rock structure if the moisture
regime is not aquic or the chroma is higher than those
listed:
(1). if there is mottling, the chroma is 2 or less;
(2). if there is no mottling and the value is less
than 4, the chroma is less than 1; if the value is 4
or more, the chroma is 1 or less;
(3). the hue is no bluer than 10Y if the hue
changes on exposure to air (a hue bluer than 10Y
that does not change on exposure is not diagnostic);

5. Properties that do not meet the requirements of an
argillic, kandic, or spodic horizon;

6. No cementation or induration and no brittle consistence
when moist; and

7. Enough thickness that its base is at least 25 cm (10 in.)
below the soil surface unless the soil temperature regime is
cryic or pergelic.

Duripan

The duripan (L. durus, hard, plus pan; meaning hardpan) is
a subsurface horizon that is cemented by silica to the degree
that fragments from the air-dry horizon do not slake during
prolonged soaking in water or in HCl.

In summary, the duripan is a silica-~cemented subsurface
horizon in which

1. Cementation is strong enough that dry fragments from
some subhorizon do not slake in water, even during pro-
longed wetting;

2. Coatings of silica, insoluble in 1 M HCI even during pro-
longed soaking but soluble in hot concentrated KOH or in
alternating acid and alkali, are present in some pores and on
some structural faces; or some durinodes are present; and

3. Cementation is not destroyed by soaking in acid in more
than half of any laminar capping that may be present or in
some other continuous or imbricated subhorizon. Cementa-
tion in such layers is completely destroyed by hot concen-
trated KOH, either by a single treatment or by alternating
with acid.

4, If fractured, the average lateral distance between fracture
points is 10 cm or more.

Fragipan

A fragipan (modified from L. fragilis, brittle, and pan;
meaning brittle pan) is a loamy or uncommonly a sandy
subsurface horizon that may but does not necessarily under-
lie a cambic, spodic, argillic, or albic horizon. It has a very
low content of organic matter, has high bulk density relative
to the horizons above it, and is seemingly cemented when


210

CDDC, Other Kandiperox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface and a lithic contact within 125 cm of the
soil surface.

Aquic Lithic KandIperox

CDDD. Other Kandiperox that have a lithic contact within a
depth of 125 em of the soil surface.
Lithic Kandiperox

CDDE. Other Kandiperox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface and mottles of 4 or more value moist and 2 or
less chroma within a depth of 125 cm of the soil surface.
Plinthaquic Kandiperox

CDDF, Other Kandiperox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Kandiperox

CDDG, Other Kandiperox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface.

Aquic Kandiperox

CDDH. Other Kandiperox that have an 18 cm or thicker
layer in the upper 75 cm with a bulk density less than 1
g/cc and in which all the Al plus one-half the Fe that is
extractable with acid oxalate totals more than 1.0 percent.
Andic Kandiperox

CDDI. Other Kandiperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, oxclusive
of surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface.

Humic Rhodic Kandiperox

CDDJ. Other Kandiperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Kandiperox

CDDK. Other Kandiperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Kandiperox

CDDL. Other Kandiperox that have a color hue of 2.5 YR
or redder with moist values of less than 4 in most of the 25
to 125 cm depth from the soil surface.

Rhodic Kandiperox

CDDM. Other Kandiperox that have a color hue of 7.5 YR
or yellower with moist values of 6 or more in most of the 25
to 125 cm depth from the soil surface.

Xanthic Kandiperox


Table 1 - Key to mineralogy classes (except for Oxtsols ~ see table 3 )

Crass DEFINITION DETERMINANT SIZE FRACTION
CLASSES APPLIED TO SOILS OF ANY PARTICLE-SIZE CLASS
Carbonatic More than 40% by weight carbonates (expressed as Whole soil, particles < 2 mm in diameter or whole soil

Ferritic..

Serpentinitic.

Gypsic..

CLASSES APPLIED TO SOILS THAT HAVE A FRAGMENTAL, SANDY, SANDY-SKELETAL,

Kaolinitic..

Mont-
morillonitic..

Illitic..

Vermiculitic

CaCO,) plus gypsum, and the carbonates are > 65% of
the sum of carbonates and gypsum.

More than 40% by weight iron oxide extractable by

citrate-dithionite, reported as Fe,0, (or 28% reported as Fe).

More than 40% by weight hydrated aluminum oxides,
reported as gibbsite and bohemite.

Less than 90% quartz: < 40% any other single mineral
listed subsequently; and the ratio, percent extractable iron
oxide plus percent gibbsite to percent clay!,

is 0.20 or more. That is

% Clay 202

More than 40% by weight serpentine minerais (antigorite,
chrystolite, fibrolite, and talc).

More than 40% by weight of carbonates (expressed as
CaCO,) plus gypsum, and the gypsum is > 35% of the
sum of carbonates and gypsum.

More than 40% glauconite by weight.

More than 40% mica by weight”,

More than 90% by weight® of silica minerals (quartz,
chalcedony, or opal) and other extremely durable
minerals that are resistant to weathering.

All others that have less than 40% of any one mineral
other than quartz or feldspars.

< 20 mm, whichever has highest percentage of carbonates
plus gypsum.

Whole soil, particles < 2 mm in diameter.

Whole soil, particles < 2 mm in diameter,

For quartz and other minerals, fraction 0.02 to 2 mm in
diameter, for ratio of iron oxide and gibbsite to clay,
whole soil < 2 mm.

Whole soil, particles < 2 mm in diameter.

Whole soil, particles < 2 mm in diameter, or whole soil
< 20 mm, whichever has higher percentage of carbonates
plus gypsum.

Whole soil, particles < 2 mm in diameter.
LOAMY, OR LOAMY-SKELETAL PARTICLE SIZE CLASS

0.02 to 20 mm,
0.02 to 2 mm,

0,02 to 2 mm,

CLASSES APPLIED TO SOILS THAT HAVE A CLAYEY OR CLAYEY-SKELETAL PARTICLE-SIZE CLASS

More than half halloysite* by weight and smaller amounts
of allophane or kaolinite or both.

More than half kaolinite, tabular halloysite, dickite, and
nacrite by weight, smatler amounts of other 1:1 or non-
expanding 2:1 layer minerals or gibbsite, and < 10%
montmorrillonite,

More than half montmorillonite and nontronite by weight
or a mixture that has more montmoriltonite than any
other one clay mineral,

More than half illite (hydrous mica) by weight and
commonly > 4% K,O.

More than half vermiculite by weight or more
vermiculite than any other one clay mineral.

More than half chlorite by weight or more chlorite than
any other clay mineral.

Other soils®.

< 0.002 mm,

< 0.002 mm,

< 0.002 mm.

< 0.002 mm.

< 0.002 mm,

< 0.002 mm.

< 0.002 mm.

Percentage of clay or percentage of 1500 kPa water times 2.6, whichever is greater, provided the ratio of 1600 kPa water to clay is 06 or more in half or more of the control section.

2.8 Percentages by weight sre ertimated from grain counts. Usually, » count of one or two of the dominant sie fractions of « conventional mechanical analysis aufficient for placement of the
‘Gialcysite as used here includes only the tubular forms. What has been called tabular balloysite is grouped here with Kaolinite,

"sepioliti, defined as containing more than half by weight of sepiolite, attapulgite, and palygorskite, should be named if found


175

&. Do not have a buried Histosol that has its upper boundary
within a depth of 1 m,

Argic Cryaquolls are like Typic Cryaquolls except for b, for
band c, or for 5, c, and d.

Calcic Cryaquolls are like Typic Cryaquolls except for c.
Cumulic Cryaquolls are like Typic Cryaquolls except for d.
Histic Cryaquoils are like Typic Cryaquolls except for e.
Pergelic Cryaquolls are like Typic Cryaquolls except for f or
for e and f.

Thapto-Histic Cryaquolls are like Typic Cryaquolls except
for g or for g and d.

Duraquolls
Distinctions between Typic Duraquolls and other subgroups

Typic Duraquolls are the Duraquolls that
a. Do not have an argillic horizon; and

b. Do not have a natric horizon,

Argic Duraquolls are like Typic Duraquolls except for a.
Natric Duraquolls are like Typic Duraquolls except for b.

Haplaquolls
Distinctions between Typic Haplaquolls and other subgroups

Typic Haplaquolls are the Haplaquolls that
a. Do not have a layer in the upper 75 cm that has a texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0,95 g
per cubic centimeter or less in the fine-earth fraction, and
that has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1,5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
b. Do not have a buried Histosol that has its upper boundary
within 1 m of the soil surface;
c. Have a mollic epipedon that is <60 cm thick;
4, Do not have a horizon 15 cm or more thick that is within
1 m of the surface and that contains at least 20 percent (by
volume) of durinodes or is brittle and has firm consistence
when moist;
e. Have a content of organic carbon that decreases regularly
with increasing depth and reaches a level of 0.3 percent
carbon or fess in some subhorizon within 1.25 m of the soil
surface, or the slope is >25 percent;
f. Do not have a histic epipedon;
8. Do not have a lithic contact within 50 cm of the surface;
and
h, Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
or to the base of an Ap horizon; and
(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper | m of the soil or in the whole soil if a lithic or



97

(2) Dominant chroma of 2 or less and mottles that are
not due to segregated lime: or

(3) Both a dominant chroma of 2 or less and a greater
SAR (or percentage of exchangeable Na) in more than
half the thickness of the horizons between the surface
and 50 cm depth than in the saturated zone;

b, Have texture finer than loamy fine sand in some

subhorizon above a depth of 50 cm;

¢, Do not have a horizon within 1 m of the surface that is

>1S cm thick and that either contains 20 percent or more

(by volume) durinodes in a nonbrittle matrix or is brittle

and has firm consistence when moist;

d, Do not have a lithic contact within 50 cm of the surface;

e. Have a weighted average percentage of organic carbon in

the upper 40 cm that is <0.6 percent if the weighted average

ratio of sand to clay in the soil above that depth is 1.0 or
less, or is less than one~seventh percent if the ratio is 13 or
more, or have an intermediate percentage of organic carbon

if the ratio of sand to clay is between 1.0 and 13; or have a

weighted average percentage of organic carbon in the soil to

a depth of 18 cm that is not as much as one-fifth more than

the values just stated if there is a lithic or paralithic contact

at a depth <40 cm but >18 cm;

f. Have an argillic horizon that is continuous throughout the

area of each pedon;

8. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface,
to the base of an Ap horizon, or to the top of the argillic
horizon;

(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m; and

(3) More than 35 percent clay in horizons that total >50
cm in thickness; and

h, Are dry in all parts of the moisture contro! section more

than three-fourths of the time (cumulative) that the soil

temperature is 5°C or higher at a depth of 50 cm.

Aquic Haplargids are like Typic Haplargids except for a,

with or without e or h, or both.

Arenic Haplargids are like Typic Haplargids except for 5.

Arenic Ustalfic Haplargids are like Typic Haplargids except

for b and h. They have a mean annual soil temperature of

8°C or higher and an aridic moisture regime that borders on
an ustic regime,

Arenic Ustollic Haplargids are like Typic Haplargids except

for 6 and e, with or without 4. They have a mean annual

soil temperature of 8°C or higher and an aridic moisture
regime that borders on an ustic regime.

Borollic Haplargids are like Typic Haplargids except for e,

with or without h. The mean annual soil temperature is

lower than 8°C, and the mean summer and mean winter soil
temperatures at a depth of 50 cm differ by 5°C or more,

Their aridic moisture regime borders on an ustic regime,

Borollic Lithie Haplargids are like Typic Haplargids except

for d and e, with or without 4, They have a frigid


189

(2) If the soil temperature regime is hyperthermic, or
isomesic, or warmer, are moist in some or all parts of the
moisture control section for 90 consecutive days or more
during a period when the soil temperature at a depth of
50 cm is higher than 8°C.
Alfic Lithic Argiustolls are like Typic Argiustolls except for
cand d, with or without f or A, or both,
Aquic Argiustolls are like Typic Argiustolls except for a or
for a and /.
Aridic Argiustolls are like Typic Argiustolls except for h.
Boralfic Argiustolls are like Typic Argiustolls except for d,
with or without all or any of a, f, or h, and the mean
annual soil temperature is lower than 10°C.
Lithie Argiustolls are like Typic Argiustolls except for c,
with or without f or A, or both,
Pachic Argiustolls are like Typic Argiustolls except for e,
with or without @ or f, or both.
Torrertic Argiustolls are like Typic Argiustolls except for g,
with or without e or A, and the cracks are open 6 months or
more in most years.
Udertic Argiustolls are like the Typic Argiustolls except for
f and g, with or without a or e, or both, and cracks are
open less than 135 days in most years.
Udic Argiustolls are like Typic Argiustolls except for f.
Ustalfie Argiustolls are like Typic Argiustolls except for d
with or without a, /, and A, and the mean soil temperature
is 10°C or more.
Vertic Argiustolls are like Typic Argiustolls except for g
with or without a or e or both, and cracks are open between
135 and 180 days in most years,

Calciustolls
Distinctions between Typic Calciustolls and other subgroups

Typic Calciustolls are the Calciustolls that

a, Do not have mottles within 75 cm of the surface that are

due to segregation of iron or manganese accompanied by

seasonal ground water and, if undrained, are not
continuously saturated with water for as long as 90 days
within 1 m of the surface;

b, When neither irrigated nor fallowed to store moisture
(1) If the soil temperature regime is mesic or thermic,
are dry less than six-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) during a period when the soil
temperature at a depth of 50 cm exceeds 5°C, or
(2) If the soil temperature regime is hyperthermic or
isomesic, or warmer, are moist in some or all parts of the
moisture control section for 90 consecutive days or more
during a period when the soil temperature at a depth of
50 cm exceeds 8°C;

¢. Do not have a lithic contact within 50 cm of the soil

surface;

4, Have a mollic epipedon that is <50 cm thick, or the

texture is loamy fine sand or coarser if the mollic epipedon

is >50 cm thick;

e. Do not have a petrocalcic horizon that has its upper

boundary within 1 m of the surface;

f. Do not have a salic horizon that has its upper boundary

within 75 cm of the surface; and

MOL


261

Chromusterts

Distinctions between Typic Chromusterts and other sub-
groups

Typic Chromusterts are the Chromusterts that

a, Have a color value, moist, less than 3.5 and a value, dry,
less than 5.5 throughout the upper 30 cm or more in more
than half of each pedon;

b. Do not have, within I m of the soil surface, prismatic or
blocky structure accompanied by clay skins on ped faces
that have a color value lower than that in the matrix; and

¢. Have cracks that remain open more than 150 cumulative
days in most years and have a mean annual soil temperature
that is 15°C or higher.

Entic Chromusterts are like Typic Chromusterts except for a.
Paleustollic Chromusterts are like Typic Chromusterts except
for bor for a and b.

Udic Chromusterts are like Typic Chromusterts except for c
and have cracks that remain open from 90 to 150 cumulative
days in most years.

Udorthentic Chromusterts are like Typic Chromusterts except
for a and c and have cracks that remain open from 90 to
150 cumulative days in most years.

Pellusterts
Distinctions between Typic Pellusterts and other subgroups

Typic Pellusterts are the Pellusterts that
a. Have a color value, moist, less than 3.5 and a value, dry,
Jess than 5.5 throughout the upper 30 cm in more than half
of each pedon;
b, Have cracks that remain open for more than 150 cumula-
tive days during each year and have a mean annual soil
temperature that is 15°C or higher; and

¢. Do not have within | m of the soil surface prismatic or
blocky structure accompanied by clay skins on ped faces
that have a color value lower than that in the matrix.

Entic Pellusterts are like Typic Pellusterts except for a.

Udic Pellusterts are like Typic Pellusterts except for b.
Udorthentic Pellusterts are like Typic Pellusterts except for a
and 6.

Xererts
Key to great groups

DAA. Xererts that have a dominant chroma, moist, of 1.5 or
more in the matrix of some subhorizon in the upper 30 cm
in more than half of each pedon.

Chromoxererts, p. 262

DAB, Other Xererts.
Pelloxererts, p. 262

VER


268

Salic horizon...
Salorthids

Slope or shape of soil
Soft powdery lime
Soil depth classes.
Soil moisture control section
Soil moisture regimes...
Soil temperature classes ..
Soil temperature regimes
Sombric horizon

Sulfidic materials.

Sulfihemists.. 139
Sulfohemists 140
Sulfuric horizon..

Surface tier...

Temperature regimes. 29

Tropofluvents 19
Tropofolists.. 137
Tropohemists .. 140
Tropohumods..

Udifluvents
Udipsamments
Udolls....


174

(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the soil
to a depth of 1 m or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1m, and
(3) More than 35 percent clay in horizons that total >S0
cm in thickness.
Abruptic Argiaquolls are like Typic Argiaquolls except for a.
Arenic Argiaguolls are like Typic Argiaquolis except for 6
and have a sandy epipedon between 50 cm and I m thick.
Grossarenic Argiaquolls are like Typic Argiaquolls except for
6 and have a sandy epipedon >) m thick.
Vertic Argiaquolls are like Typic Argiaquolls except c.

Calciaquolls
Distinctions between Typic Calciaquolls and other subgroups

Typic Calciaquolls are the Calciaquolls that
a. Do not have color that has dominant chroma of 3 or more
in the matrix or on the ped surfaces in any subhorizon
within 75 cm of the surface and do have one or more of the
following colors immediately below the mollic epipedon:
(1) If the nearest hue is 2.5Y or yellower and there are
distinct or prominent mottles, the chroma, moist, is 2 or
less; if there are no mottles, the chroma, moist, is 1 or
less; or
(2) If the nearest hue is 10YR or redder and there are
distinct or prominent mottles, the chroma is nearer to 1
than to 2; if there are no mottles, the chroma is | or less;
and
b. Do not have a petrocalcic horizon that has its upper
boundary within | m of the surface.
Aerie Calciaquolls are like Typic Calciaquolls except for a.
Petrocaleic Calciaquolls are like Typic Calciaquolls except
for b,

Cryaquolls
Distinctions between Typic Cryaquolls and other subgroups

Typic Cryaquolls are the Cryaquolls that
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy sand, that is as much as 18 cm thick, that
has a bulk density (at 33 kPa water tension) in the fine-
earth fraction of 0.95 g per cubic centimeter or less, and
that has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
b. Do not have an argillic horizon;
¢. Do not have a calcic horizon within or immediately
underlying the mollic epipedon;
d. Have a mollic epipedon that is <50 cm thick;
e. Do not have a histic epipedon;
f. Have a mean annual soil temperature higher than 0°C;
and



247

b. Do not have an epipedon as thick as 50 cm if the parti-

cle-size class is sandy throughout;

c, Have an argillic horizon >25 cm thick;

d. Have an Ap horizon that has a color value, moist, of 4 or

more or has a value, dry, of 6 or more when crushed and

smoothed; or the A horizon is <15 cm thick if its color

value, moist, is less than 3,5;

e. Do not have a lithic contact within 50 cm of the surface

of the mineral soil;

f. Have texture finer than loamy fine sand in some part of

the argillic horizon and have an argillic horizon that, in at

least its upper 25 cm, does not have lamellae;

g- Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part, and that extend upward to the soil
surface, to the base of an Ap horizon, or to a depth
within 25 cm of the soil surface; an
(2) A coefficient of linear extensibi (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper | m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1 m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness; and

h, Have a continuous argillic horizon throughout each pe-

don, not interrupted by ledges of bedrock.

Aguic Hapludults are like Typic Hapludults except for a or

for a and d,

Arenic Hapludults are like Typic Hapludults except for b,

with or without a or c or both, and the epipedon is between

50 cm and } m thick.

Humic Hapludults are tike Typic Hapludults except for d.

Lithic Hapludults are like Typic Hapiudults except for e or

for c and e.

Ochreptic Hapludults are like Typic Hapludults except for c.

Psammentic Hapludults are like Typic Hapludults except for

f or for f and 6.

Ruptic-Lithic-Entic Hapludults are like Typic Hapludults

except for A and ¢ or for h, c, and e.

Vertic Hapludults are like Typic Hapludults except for g,

with or without a.

Kandiudults
Distinctions between Typic Kandiudults and other subgroups

Typic Kandiudults are the Kandiudults that
a. Do not have the following combination of characteristics
in the upper 75 cm of the soil if the chroma throughout the
upper 75 cm is not controlled by uncoated sand grains; or if
the chroma throughout the upper 75 cm is controlled by
uncoated sand grains, do not have the following combination
of characteristics throughout the upper 12.5 cm of the
argillic or kandic horizon:
1, Mottles that have a color value, moist, of 4 or more
and chroma, moist, of 2 or less accompanied by mottles
of higher chroma that are due to segregation of iron; and

ULT


75

as much as 3 percent (absolute) less clay than both the
overlying and underlying horizons;
¢. Do not have a layer in the upper 75 cm that has a texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
per cubic centimeter or less in the fine-earth fraction, and
that has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
d. Either have an Ap horizon that has a color value, moist,
of 4 or more or a color value, dry, of 6 or more, when.
crushed and smoothed, or the soil to a depth of 18 cm, after
mixing, has those colors; and
e. Do not have mottles that have chroma of 2 or less in the
upper 25 cm of the argillic horizon and do not have mottles
that have chroma of 2 or less within 40 cm of the surface if
the horizons that have mottles of low chroma are saturated
with water at some time of year when the soil temperature
is 5°C or higher in those horizons. Mottles are not the same
as skeletans that may also have low chroma.
Albaquic Fragiudal fs are like Typic Fragiudalfs except for
e, and they have, within a vertical distance of 7.5 cm at the
top of the argillic horizon, a clay increase of >15 percent
(absolute) in the fine-earth fraction.
Aqueptic Fragiudalfs are like Typic Fragiudalfs except for a
and e.
Aquic Fragiudalfs are like Typic Fragiudalf's except for e.
Glossaquic Fragiudalfs are like Typic Fragiudalfs except for
6 and e, with or without a.
Glossic Fragiudalfs are like Typic Fragiudalfs except for b,
with or without a.
Mollic Fragiudalfs are like Typic Fragiudalfs except for d,
with or without e, and have base saturation of 50 percent or
more (by NH,OAc) in the major part of the epipedon.
Ochreptic Fragiudalfs are like Typic Fragiudalfs except for
a,
Umbreptic Fragiudalfs are like Typic Fragiudalfs except for
a, b, and d, and have base saturation <50 percent (by
NH,OAc) in the epipedon.

Fraglossudalfs

Fraglossudalfs have a fragipan and an overlying argillic
horizon that has evidences of destruction in the form of
deep wide tongues of albic materials that normally extend
through the argillic horizon, The upper boundary of the
argillic horizon is usually broken, but there is little or no
cementation by iron, These soils are more extensive in Eu-
rope than in the United States. The epipedon may approach
an umbric epipedon,

Distinctions between Typic Fraglossudalfs and other sub-
groups

Typic Fraglossudalfs are the Fraglossudalfs that
a, Do not have mottles that have a chroma of 2 or less in
the upper 25 cm of the argillic horizon if the mottled hori-


243
Kandihumults

Distinctions between Typic Kandihumults and other sub-
groups

Typic Kandihumults are the Kandihumults that
a. Do not have the following combination of characteristics
in the upper 25 cm or more of the argillic or kandic hori-
zon:
1. Mottles that have a color value, moist, of 4 or more,
and chroma, moist, of 2 or less accompanied by mottles
of higher chroma that are due to segregation of iron; and
2. Saturation with water in the mottled zone at some tim
of year when the soil temperature in that zone is 5°C or
more or there is artificial drainage;
b. Have an udic moisture regime;
¢. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 ¢
per cubic centimeter or less in the fine-earth fraction, and
that has either of the following:
1. A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
2. A ratio of CEC (pH 8.2) to 1500 kPa water of >1.5
and more exchange acidity than the sum of bases plus
KCl-extractable aluminum;
d. Do not have a horizon within 150 cm of the soil surface
that has >S percent plinthite by volume;
e. Have a hue redder than 10YR in all parts of the soil
above a depth of 75 cm that have a color value, moist, of 4
or more if there are mottles of high chroma within that
depth and if the hue becomes redder with depth within 100
cm of the soil surface; and
f. Do not have an anthropic epipedon.
Andic Kandihumults are like Typic Kandihumults except for
a
Andic Epiaquic Kandihumults are like Typic Kandihumults
except for ¢ and e.
Andic Ustic Kandihumults are like Typic Kandihumults
except for 6 and c and they have an ustic moisture regime.
Anthropic Kandihumults are \ike Typic Kandihumults except
for f.
Epiaquic Kandihumults are like Typic Kandihumults except
for e.
Plinthic Kandihumults are like Typic Kandihumults except
ford. *
Ustic Kandihumults are like Typic Kandihumults except for
b and they have an ustic moisture regime.

Kanhaplohumults

Distinctions between Typic Kanhaplohumults and other sub-
groups

Typic Kanhaplohumults are the Kanhaplohumults that
a, Do not have the following combination of characteristics
in the upper 25 cm or more of the argillic or kandic hori-
zon;
1. Mottles that have a color value, moist, of 4 or more
and chroma, moist, of 2 or less accompanied by mottles
of higher chroma that are due to segregation of iron; and

ULT


223

CCEH, Other Haplustox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface.

Aquic Haplustox

CCEI. Other Haplustox that have the lower boundary of the
oxic horizon within a depth or 125 cm of the soil surface.
Inceptic Haplustox

CCEJ. Other Haplustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface.

Humle Rhodic Haplustox

CCEK. Other Haplustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface,

Humic Xanthic Haplustox

CCEL. Other Haplustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Haplustox

CCEM, Other Haplustox that have a color hue of 2.5 YR or
redder with moist values of less than 4 in most of the 25 to
125 cm depth from the soil surface.

Rhodic Haplustox

CCEN. Other Haplustox that have a color hue of 7.5 YR or
yellower with moist values of 6 or more in most of the 25 to
125 cm depth from the soil surface,

Xanthic Haplustox

CCEO. Other Haplustox.
Typic Haplustox

Kandiustox

Key to subgroups

CCDA. Kandiustox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and a petroferric contact within 125 cm of the
soil surface.

Aquic Petroferric Kandiustox

CCDB. Other Kandiustox that have a petroferric contact
within 125 cm of the soil surface.
Petroferric Kandiustox

CCDC. Other Kandiustox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface and a lithic contact within 125 cm of the
soil surface.

Aquic Lithic Kandiustox


37

Sapric materials have the following characteristics:

1. The fiber content after rubbing is less than one-sixth of
the soil volume, excluding coarse fragments and mineral
layers; and

2, The sodium pyrophosphate extract color on chromato-
graphic paper is below or to the right of a line drawn to
exclude blocks 5/1, 6/2, and 7/3 on the chart,

Humilluyic materials

Mluvial humus accumulates in the lower parts of some or~
ganic soils if they are acid and have been drained and culti-
vated. The illuvial humus has a younger C’ age than the
overlying organic materials, It has very high solubility in
sodium pyrophosphate and rewets very slowly after drying.
Most commonly it accumulates near a contact with a sandy
mineral horizon. To be recognized as a differentia in clas-
sification, the illuvial humus should constitute at least half
the’ volume of a layer at least 2 cm thick.

Limnic materials

Limnic materials include both organic and inorganic materi-
als that were either (1) deposited in water by precipitation
or through the action of aquatic organisms such as algae or
diatoms, or (2) derived from underwater and floating aquatic
plants and subsequently modified by aquatic animals. They
include coprogenous earth (sedimentary peat), diatomaceous
earth, and marl.

Coprogenous earth

‘A coprogenous earth (sedimentary peat) layer is a limnic
layer that

1, Contains many fecal pellets a few hundredths to a few
tenths of a millimeter in diameter;

2, Has a color value, moist, <5;

3. Either forms a slightly viscous water suspension and is
slightly plastic but not sticky or shrinks upon drying to form
clods that are difficult to rewet and that often tend to crack
along horizontal planes;

4, Is normally but not necessarily nearly devoid of fragments
of plants that can be recognized with the eye; and

5. Yields a saturated sodium pyrophosphate extract on white
filter paper that has higher color value and lower chroma
than 10 YR 7/3 or the cation-exchange capacity is <240
cmol(+) kg”? of organic matter (measured by loss on igni-
tion) or both.


185

soil temperature in the mottled horizon is above 5°C or if
the soil is artificially drained; or

(2) Has a hue of 2.5Y or redder and chroma of 4 or
more;

b. Do not have a lithic contact within 50 cm of the surface;

c. Have texture finer than loamy fine sand in the argillic

horizon, or the argillic horizon does not consist entirely of

lamellae with a combined thickness of <15 cm;

d. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
or to the base of an Ap horizon,

(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper I m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1 m, and

(3) More than 35 percent clay in horizons that total >50
cm in thickness; and

e. Have CEC (by 1 M NH,OAc pH7) of 24 or more in the

‘major part of the argillic horizon or the major part of the

upper 100 cm of the argillic horizon if the argillic horizon is

thicker than 100 cm.

Aquic Argiudolls are like Typic Argiudolls except for a,

Lithic Argiudolls are like Typic Argiudolls except for b.

Oxic Argiudolls are like Typic Argiudolls except for e.

Psammenti¢c Argiudolls are like Typic Argiudolls except for

c

Vertic Argiudolls are like Typic Argiudolls except for d with

or without a.

Hapludolls
Distinctions between Typic Hapludolls and other subgroups

Typic Hapludolls are the Hapludolls that
a. Do not have mottles within 40 cm of the surface if the
mottled horizon is saturated with water at some period of
the year when the soil temperature in the mottled horizon is
above 5°C or if the soil is artificially drained; and have a
horizon 15 cm or more thick immediately below the mollic
epipedon that either
(1) Has a hue of 10YR or redder and chroma of 3 or
more, and does not have mottles that have chroma of 2 or
less and value of 4 or more if the mottled horizon is
saturated with water at some period of the year when the
soil temperature in the mottled horizon is above 5°C or if
the soil is artificially drained, or
(2) Has a hue of 2.5 Y or redder and chroma of 4 or
more;
b. Have a mollic epipedon <60 cm thick or texture that is
loamy fine sand or coarser if the mollic epipedon is >60 cm
thick;
ce. Have a cambic horizon, or the lower part of the mollic
epipedon meets the requirements of a cambic horizon except
for color value and organic-carbon content, and either the
cambic horizon or the lower part of the epipedon is free of
carbonates in some part;



225

CCAB. Other Sombriustox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Sombriustox

CCAC. Other Sombriustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Sombriustox

CCAD. Other Sombriustox.
Typic Sombriustox


50

carries the same limitation. Thus, frigid is implied in all
boric suborders and cryic great groups, and is redundant if
used in the name of a family.

The Celsius (centigrade) scale is the standard. Approximate
Fahrenheit equivalents are indicated parenthetically. It is
assumed that the temperature is that of a soil that is not
being irrigated.

For soils in which the difference is 5°C (9°F) or more be-
tween mean summer (June, July, and August in the northern
hemisphere) and mean winter (December, January, and
February in the northern hemisphere) soil temperature at a
depth of 50 cm or at a lithic or paralithic contact, whichever
is shallower, the classes, defined in terms of the mean an-
nual soil temperature, are as follows:

Frigid,--Below 8°C (47°F).

Mesic,--From 8° to 15°C (47° to 59°F).
Thermic,--From 15° to 22°C (59° to 72°F).
Hynerthermic,--22°C (72°F) or higher.

For soils in which the difference is less than 5°C (9°F) be-~
tween mean summer and mean winter soil temperature at a
depth of 50 cm or at a lithic or paralithic contact, whichever
is shallower, the classes, defined in terms of the mean an-
nual soil temperature, are as follows:

Isofrigid,--Below 8°C (47°F).
Tsomesic,--From 8° to 15°C (47° to 50°F).
Isothermic.--From 15° to 22°C (59° to 72°F).
Isohyverthermic,--22°C (72°F) or higher.

The appropriate limit between isofrigid and isomesic cannot
be tested in the United States and probably will need to be
revised.

Other characteristics

Several soil characteristics other than those already men-
tioned are needed in particular taxa to provide reasonable
groupings of series into families. Some of these seem to be
logical family criteria, Others probably should have been
used in higher categories, but the lack of information about
them makes it much safer to use them as family differentiae
at this time. These characteristics include depth of soil,
consistence, moisture equivalent, slope of soil, and perma-
nent cracks.

Denth of soil
Classes of shallow and deep soils may be needed at the fam-

ily level in all the orders of mineral soils. Some distinctions
in depth are made in great groups and in arenic, paralithic,



119

regime and a torric moisture regime that borders on a xeric
regime.

Tropofluvents

Tropofluvents are the Fluvents that
1. Have an isomesic or warmer iso temperature regime; and
2, Have a udic moisture regime,

Only one series of Tropofluvents has been recognized in the
United States, and subgroups have not been defined. It is
suggested that the definition of the typic subgroup should
parallel that of Typic Udifluvents in the great group that is
defined next,

Udifluvents
Distinctions between Typic Udifluvents and other subgroups
Typic Udifluvents are the Udifluvents that

a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density in the fine-earth fraction (at 33 kPa
moisture tension) of 0.95 g per cubic centimeter or less, and
that has either (1) a ratio of measured clay to 1500 kPa wa-
ter (percentages) of 1.25 or less or (2) a ratio of CEC (at pH
near 8) to 1500 kPa water of >1.5 and more exchange acid-
ity than the sum of bases plus KCl-extractable aluminum;
b. Do not have mottles within 50 cm of the surface that
have chroma of 2 or less or, at a depth between 50 cm and
1 m, do not have any horizons that are saturated with water
at some period or that are artificially drained and have
chroma less than 1 or hue biuer than 10Y and value, moist,
of 4 or more; and

¢. Have an Ap horizon that has a color value, moist, of 4 or
more or has a color value, dry, of 6 or more when crushed
and smoothed, or the A horizon is <15 cm thick if its color
value, moist, is less than 3.5.

Aquic Udifluvents are like Typic Udifluvents except for 5 or
for b and c.

Mollic Udifluvents are like Typic Udifluvents except for c,

‘Ustifluvents
Distinctions between Typic Ustifluvents and other subgroups

Typic Ustifluvents are the Ustifluvents that

a. Do not have mottles within 50 cm of the surface that

have chroma of 2 or less and do not have, at a depth within

1.5 m of the surface, a horizon that is saturated with water

at some period or is artificially drained and that has chroma

Jess than J or a hue bluer than LOY; and

b. Do not have the following combination of characteristics:
(1) Cracks at some period in most years, when the soil is
not irrigated, that are 1 cm or more wide at a depth of
50 cm, that are at least 30 cm long in some part, and that
extend upward to the soil surface or to the base of an Ap
horizon;
(2) A coefficient of linear extensibility (COLE) of 0.07
or more in a horizon or horizons at least 50 cm thick and


55

Micro families.--Used to indicate a lithic contact shallower
than 18 cm without regard to soil temperature, (In mineral
soils, micro families are restricted to cryic great groups.)

LITERATURE CITED

Soil Survey Staff, 1951, Soil survey manual, U.S. Dept. Agr.

Handb. 18. U.S. Govt. Printing Office, Washington, D.C.


209

CDEF, Other Haploperox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Haploperox

CDEG. Other Haploperox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface.

Aquic Haploperox

CDEH, Other Haploperox that have an 18 cm or thicker
layer in the upper 75 cm with a bulk density less than 1
g/cc and in which all the Al plus one-half the Fe that is
extractable with acid oxalate totals more than 1.0 percent.
Andic Haploperox

CDEI, Other Haploperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and a color hue of 2.5 YR ot redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface.

Humic Rhodic Haploperox

CDE. Other Haploperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface,

Humic Xanthic Haploperox

CDEK. Other Haploperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Haploperox

CDEL. Other Haploperox that have a color hue of 2.5 YR or
redder with moist values of less than 4 in most of the 25 to
125 cm depth from the soil surface.

Rhodic Haploperox

CDEM. Other Haploperox that have a color hue of 7.5 YR
or yellower with moist values of 6 or more in most of the 25
to 125 cm depth from the soil surface.

Xanthic Haploperox

CDEN, Other Haploperox.
Typle Haploperox

Kandiperox

Key to subgroups

CDDA, Kandiperox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the

soil surface and a petroferric contact within 125 cm of the
soil surface.

Aquic Petroferric Kandiperox

CDDB, Other Kandiperox that have a petroferric contact
within 125 cm of the soil surface.
Petroferric Kandiperox


141

ADB. Other Saprists that have a mean annual soil tempera-
ture lower than 8°C.
Borosaprists, p. 141

ADC. Other Saprists that have <5°C difference between
summer and mean winter soil temperatures at a depth of 30
cm.

‘Troposaprists, p. 143

ADD. Other Saprists that do not have a horizon of humillu-
vic materials 2 cm or more thick,
Medisaprists, p. 142

In addition to the great groups listed in the key, a great
group of Vermisaprists may be needed, particularly for soils
that have been drained for a long time, but a definition
cannot be suggested at present.

Borosaprists
Distinctions between Typic Borosaprists and other subgroups

Typic Borosaprists are the Borosaprists that
a, Do not have a mineral layer between 5 and 30 cm thick
with organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier;
b. Have
(1) Less than 12.5 cm of the subsurface and bottom tiers
consisting of fibric materials; and
(2) Less than 25 cm of the subsurface and bottom tiers
consisting of hemic materials;
¢. Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier;
d, Do not have a layer of water within the control section
beneath the surface tier;
e, Do not have limnic layer(s) that are 5 cm or more thick
within the control section, and
f, Do not have a lithic contact within the contro} section.
Fibrie Borosaprists are like Typic Borosaprists except for

Fibric Terrie Borosaprists are like Typic Borosaprists except
for b(1) and c, with or without @ or e, or both,
Fluvaquentic Borosaprists are like Typic Borosaprists except
for a, with or without 5.

Hemic Borosaprists are like Typic Borosaprists except for
(2).

Hemic Terric Borosaprists are like Typic Borosaprists except
for (2) and c, with or without a or e, or both.

Limnic Borosaprists are like Typic Borosaprists except for e,
with or without a or b, or both.

Lithic Borosaprists are like Typic Borosaprists except for /,
with or without all or any of a, b, ¢, or e.

Terric Borosaprists are like Typic Borosaprists except for c,
with or without a or e, or both,


51

and lithic subgroups, but some other soils should also be
grouped in families according to depth. Some soils have a
paralithic contact over soft rock such as clay shale that is
too compact for penetration by roots. The soil depth classes
follow:

Micro. Less than 18 cm through diagnostic horizons. Used
in cryic great groups but not in pergelic subgroups or in
Entisols.

Shailow. Less than 50 cm to the upper boundary of a
duripan or a petrocalcic horizon or to a lithic, paralithic or a
petroferric contact. Used in lithic and petroferric subgroups
of Oxisols and all great groups of Alfisols, Aridisols,
Entisols, Inceptisols, Mollisols, Spodosols, and Ultisols,
except pergelic subgroups of the cryic great groups and
lithic subgroups. It is emphasized that the adjective
"shallow" is not used in the family name of lithic subgroups
of orders, other than Oxisols, because it would be
redundant.

Consistence

Some cemented horizons, for example, a duripan, are dif-
ferentiae in the classification in categories above the family.
Others such as a cemented spodic horizon (ortstein) are not,
but no single family should include soils that have a contin-
uous, shallow, cemented horizon and soils that do not. In
Spodosols, in particular, a cemented spodic horizon needs to
be used as a family differentia. The following classes of
consistence are defined for Spodosols,

Ortstein. All or part of the spodic horizon is at least weakly
cemented, when moist, into a massive horizon that is present
in more than half of each pedon.

Noncemented. The spodic horizon, when moist, is not
cemented into a massive horizon in as much as half of each
pedon,

Cementation of a small volume into shot or concretions does
not constitute cementation to form a massive horizon, The
name of a family of noncemented Spodosols normally does
not have a modifier to imply lack of cementation. The
name of a family of cemented Spodosols contains the
modifier “ortstein.”

A cemented calcic or gypsic horizon is not identified in the
family name. Many calcic and some gypsic horizons are
weakly cemented and some are indurated. The recognition
of a petrocalcic or petrogypsic horizon is expected to meet
most, if not all, the needs for recognition of cementation in
those horizons, Taxa of these cemented soils are not named
in the family category.

Classes of coatings (on sands)

Despite the emphasis given to particle-size classes in the
taxonomy, variability remains in the sandy particle-size
class, which takes in sands and loamy sands. Some sands are
very clean, almost completely free of silt and clay, Others
are mixed with appreciable amounts of finer grains. A
moisture equivalent of 2 percent makes a reasonable division
of the sands at the family level. Two classes of Quartzip-
samments are defined in terms of their moisture equivalent,
Coated. The moisture equivalent is 2 percent or more.

M


220

cm or more thick within a depth of 125 cm of the soil sur-
face.
Anionic Acrustox

CCBG. Other Acrustox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Acrustox

CCBH. Other Acrustox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface.

Aquic Acrustox

CCBI. Other Acrustox that have more than 35 percent base
saturation (NH,OAc) in all parts within a depth of 125 cm
of the soil surface.

Eutric Acrustox

CCBJ. Other Acrustox that have 16 Kg or more organic car-
bon per square meter to a depth of one meter, exclusive of
surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface,

Humic Rhodic Acrustox

CCBK. Other Acrustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Acrustox

CCBL. Other Acrustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Acrustox

CCBM, Other Acrustox that have a color hue of 2.5 YR or
redder with moist values of less than 4 in most of the 25 to
125 cm depth from the soil surface.

Rhodic Acrustox

CCBN, Other Acrustox that have a color hue of 7.5 YR or
yellower with moist values of 6 or more in most of the 25 to
125 cm depth from the soil surface.

Xanthic Acrustox

CCBO, Other Acrustox.
Typic Acrustox

Eutrustox

Key to subgroups

CCCA. Eutrustox that have mottles of 4 or more value moist
and 2 or less chroma within a depth of 125 cm of the soil
surface and a petroferric contact within 125 cm of the soil
surface.

Aquic Petroferric Eutrustox


214

of surface litter and color hue of 7,5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Acrudox

CEBL. Other Acrudox that have 16 Kg or more organic car-
bon per square meter to a depth of one meter, exclusive of
surface litter.

Humic Acrudox

CEBM, Other Acrudox that have a color hue of 2,5 YR or
redder with moist values of less than 4 in most of the 25 to
125 cm depth from the soil surface.

Rhodic Acrudox

CEBN. Other Acrudox that have a color hue of 7.5 YR or
yellower with moist values of 6 or more in most of the 25 to
125 cm depth from the soil surface.

Xanthic Acrudox

CEBO. Other Acrudox.
Typic Acrudox

Eutrudox
Kev to subgroups

CECA. Eutrudox that have mottles of 4 or more value moist
and 2 or less chroma within a depth of 125 cm of the soil
surface and a petroferric contact within 125 cm of the soil
surface.

Aquic Petroferric Eutrudox

CECB. Other Eutrudox that have a petroferric contact
within 125 cm of the soil surface.
Petroferric Eutrudox

CECC, Other Eutrudox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and a lithic contact within 125 cm of the soil
surface.

Aquic Lithic Eutrudox

CECD, Other Eutrudox that have a lithic contact within a
depth of 125 cm of the soil surface,
Lithic Eutrudox

CECE. Other Eutrudox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface and mottles of 4 or more value moist and 2 or
less chroma within a depth of 125 cm of the soil surface.
Plinthaquic Eutrudox

CECF. Other Eutrudox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Eutrudox


221

CCCB, Other Eutrustox that have a petroferric contact
within 125 cm of the soil surface.
Petroferric Eutrustox

CCCC. Other Eutrustox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and a lithic contact within 125 cm of the soil
surface,

Aquic Lithic Eutrustox

CCCD. Other Eutrustox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Eutrustox

CCCE, Other Eutrustox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface and mottles of 4 or more value moist and 2 or
less chroma within a depth of 125 cm of the soil surface.
Plinthaquic Eutrustox

CCCF. Other Eutrustox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
surface,

Plinthic Eutrustox

CCCG, Other Eutrustox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface.

Aquic Eutrustox

CCCH. Other Eutrustox that have more than 40 percent clay
in the surface 18 cm after mixing and the upper boundary
of a kandic horizon within a depth or 150 cm of the soil
surface.

Kandiustalfic Eutrustox

CCCI. Other Eutrustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and have the lower boundary of the oxic
horizon within a depth of 125 cm of the soil surface.
Umbreptic Eutrustox

CCCI. Other Eutrustox that have the lower boundary of the
oxic horizon within a depth of 125 cm of the soil surface.
Inceptle Eutrustox

CCCK. Other Eutrustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface.

Humic Rhodic Eutrustox

CCCL. Other Eutrustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Eutrustox

OxI


78

Psammentic Hapludalfs are like Typic Hapludalfs except for
A, with or without all or any of d, g, or i.

Ultic Hapludaifs are like Typic Hapludalfs except for i,
with or without g.

Vertic Hapludalfs are like Typic Hapludalfs except for j,
with or without any or all of a, c, g, and i.

Kandiudalfs
Distinctions between Typic Kandiudalfs and other subgroups

Typic Kandiudalfs are the Kandiudalfs that

a. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizon is saturated
with water at some time when the soil temperature at that
depth is 5°C or higher or the soil has artificial drainage;

b. Do not have an epipedon that is 50 cm to 100 cm thick if
the particle-size class is sandy throughout;

¢. Do not have an epipedon that is >100 cm thick if the
particle-size class is sandy throughout;

d. Have an Ap horizon that has either a color value, moist,
of 4 or more or a color value, dry, or 6 or more after the
soil has been crushed, or the upper soil to a depth of 18 cm,
after mixing, has these color values;

e. Have an argillic or kandic horizon that has a color value,
dry, of 5 or more in some subhorizon, or a color value,
moist, that is less than the value, dry, by more than one unit
unless the hue in some part of the argillic or kandic horizon
is SYR or yellower; and

f. Do not have a horizon within 150 cm of the surface that
has >5 percent plinthite by volume.

Aquic Kandiudalfs are like Typic Kandiudalfs except for a,
with or without d.

Arenic Kandiudalfs are like Typic Kandiudalfs except for 3.
Arenic Plinthic Kandiudalfs are like Typic Kandiudalfs ex-
cept for b and f.

Grossarenic Kandiudalfs are like Typic Kandiudalfs except
for c.

Grossarenic Plinthic Kandiudalfs are like Typic Kandiudalfs
except for c and f.

Mollic Kandiudalfs are like Typic Kandiudalfs except for d.
Plinthaquic Kandiudalfs are like Typic Kandiudalfs except
for a and f.

Plinthic Kandiudalfs are like Typic Kandiudaifs except for

f
Rhodic Kandiudalfs are like Typic Kandiudalfs except for @
and e.

Kanhapludalfs

Distinctions between Typic Kanhapludalfs and other sub-
groups

Typic Kanhapludalfs are the Kanhapludalfs that

a, Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizons are satu-
rated with water at some time when the soil temperature at
that depth is 5°C or higher or the soil has artificial drainage;
b. Do not have a lithic contact within 50 cm of the soil
surface; and


88
Rhodustalfs

Distinctions between Typic Rhodustalfs and other subgroups

Because these soils are rare in the United States, the classi-
fication that follows probably is incomplete, and it is provi-
sional.

Typic Rhodustalfs are the Rhodustalfs that

a. Do not have a lithic contact within 50 cm of the soil

surface;

b. Have CEC of 24 or more cmol(+) kg" (by 1 M NH,OAc

pH7) in the major part of the argillic horizon or the major

part of the upper 100 cm of the argillic horizon if the

argillic horizon is thicker than 100 cm; and

c. When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry for more than four-tenths of the cumulative days
in some part of the moisture control section when the soil
temperature at a depth of 50 cm exceeds 5°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days
during a period when the soil temperature at a depth of
50 cm exceeds 8°C;

Kandic Rhodustalfs are like Typic Rhodustalfs except for b,

with or without c.

Lithic Rhodustalfs are like Typic Rhodustalfs except for a,

with or without c,

Udie Rhodustalfs are like Typic Rhodustalfs except for c.

Xeralfs

Key to great groups

HDA. Xeralfs that have a duripan whose upper boundary is
within 1 m of the soil surface but below an argillic or a na-
tric horizon,

Durixeralfs, p. 89

HDB. Other Xeralfs that have a natric horizon.
Natrixeralfs, p. 91

HDC. Other Xeralfs that have a fragipan.
Fragixeralfs, p. 89

HDD. Other Xeralfs that have plinthite that forms a contin-
uous phase in or constitutes more than half the matrix of
some subhorizon of the argillic horizon within 150 cm of the
soil surface,

Plinthoxeralfs, p. 92

HDE. Other Xeralfs that have an argillic horizon that, in all
parts, has a color hue redder than SYR and a value, moist,
less than 3.5 and a value, dry, no more than one unit higher
than the value, moist.

Rhodoxeralfs, p. 92

HDF. Other Xeralfs that have either a petrocalcic horizon
whose upper boundary is within 1,5 m of the soil surface or
have one or both of


45

C about 2 months after the summer solstice; whichever is
shallower,

2. Otherwise, particle-size modifiers or substitutes are
used to describe material from a depth of 25 cm to a
depth of ! m.

C, In other soils of the orders Alfisols and Ultisols and in
great groups of Aridisols and Mollisols that have an argillic
or kandic horizon that has (a) a lower boundary deeper than
25 cm (see E) and (b) an upper boundary shallower than
m, or the soil is in a grossarenic subgroup:
1. If there are no strongly contrasting particle-size
classes, as defined later, and there is no root-limiting
layer between the top of the argillic, kandic, or natric
horizon and a depth of 1 m, particle-size modifiers or
substitutes are used to describe the whole argillic or
natric horizon if it is <50 cm thick® or the upper 50 cm
of the argillic, kandic, or natric horizon if it is >50 cm
thick.
2. If there are horizons or layers of strongly contrasting
Particle-size classes, as defined later, within or below the
argillic, kandic, or natric horizon and within a depth of
1 m, particle-size modifiers or substitutes are used to
describe material from the top of the argillic, kandic, or
natric horizon to a depth of 1 m or to a lithic or
Paralithic contact, duripan, fragipan, or petrocalcic
horizon, whichever is shallower,
3. If there is a root-limiting layer below an argillic,
kandic, or natric horizon, particle-size modifiers or
substitutes are used to describe material from the top of
the argillic horizon, excluding any part incorporated in an
Ap horizon, to the top of the fragipan, duripan, or
petrocalcic horizon, or are used to describe the upper 50
cm of the argillic, kandic, or natric horizon whichever
of these is less.

D, In other soils in the orders Alfisols and Ultisols and in
great groups of Aridisols and Mollisols that have an argillic,
kandic, or natric horizon that has its upper boundary at a
depth >1 m and that are not in a grossarenic subgroup, par-
ticle-size modifiers or substitutes are applied to describe
material from a depth of 25 cm to a depth of 1 m below the
mineral surface.

E, In other soils in which the lower boundary of the argillic
or natric horizon is shallower than 25 cm, that is, they have
a k horizon in which there is soft powdery lime, or have a
calcic or other named diagnostic horizon that has its upper
boundary within 25 cm of the surface, or have rock struc-
ture dominant within that depth, particle-size classes are
used to describe material from the top of the argillic horizon
or the base of an Ap horizon, whichever is shallower, to a

"rhe upper boundary of the argillic or kandic horizon is not always obvious.
If propertias of an argillic horizon are present but the upper boundary is
Gradual, use the depth at which the percentage of clay exceeds that of a
higher lying horison by the appropriate amount after fitting to a smooth
curve. If the boundary is irregular or broken, as in A&B or B&A horizons, use
tha depth at which half or more of the volume has the fabric of an argillic
horizon,


132
Fibrists

Key to great groups

ABA. Fibrists that have a surface mantle that is three-
fourths or more fibric Sphagnum spp. and that either is 90
cm or more thick, or extends 10 cm or more below per-
mafrost, or rests on a lithic or paralithic contact, fragmental
materials, or mineral soil materials.

Sphagnofibrists, p, 134

ABB. Other Fibrists that are frozen in most years in some
layer within the control section about 2 months after the
summer solstice or that are never frozen in most years below
a depth of 5 cm but have a mean annual soil temperature
that is lower than 8°C,

Cryofibrists, p. 133

ABC. Other Fibrists that have a mean annual soil tempera-
ture lower than 8°C,
Borofibrists, p. 132

ABD. Other Fibrists that have a difference of <5°C between
mean summer and mean winter soil temperatures at a depth
of 30 cm.

Tropofibrists, p. 135

ABE, Other Fibrists that do not have a horizon 2 cm or
more thick that is half or more humilluvic materials.
Medifibrists, p. 134

ABF. Other Fibrists,
Luyifibrists, p. 133

Borofibrists
Distinctions between Typic Borofibrists and other subgroups

‘Typic Borofibrists are the Borofibrists that
a. Have
(1) Less than 25 cm of the subsurface and bottom tiers
occupied by hemic materials; and
(2) Less than 12.5 cm of the subsurface and bottom tiers
occupied by sapric materials;
b. Have less than three-fourths of the fibers (by volume)
derived from Sphagnum in the surface tier or more of the
control section;
¢. Do not have limnic layer(s) within the control section 5
cm or more thick;
d. Do not have a lithic contact within the control section;
e. Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin
continuous mineral layers in the control section below the
surface tier;
f, Do not have a mineral layer 30 cm or more thick whose
upper boundary is below the surface tier in the control sec-
tion; and
g. Do not have a layer of water within the control section
beneath the surface tier.
Fluvaquentic Borofibrists are like Typic Borofibrists except
for e with or without a.


15

(c) If the hue is yellower than 2.5, the chroma,
moist, is 2 or less; or
(2) The chroma, moist, is 1 or less and mottles may or
may not be present,
b. Have an Ap horizon that has a color value, moist, of 4 or
more or that has a color value, dry, of 6 or more when
crushed and smoothed, or the Al horizon is <15 cm thick if
its color value, moist, is less than 3.5;
¢. Do not have a lithic contact within 50 cm of the soil
surface; and
d. Do not have sulfidic materials within 1 m of the mineral
soil surface.
Aeric Haplaquents are like Typic Haplaquents except for a
or aand b.
Mollic Haplaquents are like Typic Haplaquents except for b,
Sulfic Haplaquents are like Typic Haplaquents except for d.

Hydraquents

Hydraquents are the Aquents that do not have sulfidic
materials within 50 cm of the mineral soil surface and

1. Have a mean annual soil temperature higher than 0°C;

2. In all subhorizons between 20 and 50 cm below the
mineral surface have both an n value of more than 0.7 and
at least 8 percent clay; and

3. Have texture that is loamy very fine sand or finer in
some horizon below the Ap horizon or a depth of 25 cm,
whichever is deeper, but above a depth of | m or a lithic or
a paralithic contact, whichever is shallower.

The Hydraquents have been little used or studied in the
United States, and subgroups have not been developed. The
typic subgroup could be defined as having a high n value, 1
or more, in all subhorizons between a depth of 20 cm and I
m. Hydraquents that have n values <I in the upper 25 cm
or more could be Haplic Hydraquents, which are intergrades
to Haplaquents. Thapto-Histic Hydraquents, which have a
buried Histosol or histic epipedon whose upper boundary is
within a depth of 1 m, doubtless exist. Hydraquents that
have a small amount of sulfides or none in the upper
horizons can be drained and cultivated. A sulfic subgroup
might be useful for those soils that, after drainage, have a
pH <4,5 (1:1 water) in the upper 25 cm or more, those that
have enough sulfides in the undrained soil to produce this
pH on drainage, and those that have a larger amount of
sulfides at a depth between 50 cm and 1 m. A large amount
of sulfides at a depth below 1 m should be noted but could
be shown as a phase.

Psammaquents

Distinctions between Typic Psammaquents and other
subgroups

Typic Psammaquents are the Psammaquents that

a. Do not have a lithic contact within 50 cm of the soil
surface;

b. Have an Ap horizon that has a color value, moist, of 4 or
more or has a value, dry, of 6 or more when crushed and
smoothed (smoothed with a knife to eliminate shadows), or


277

rock; partly consolidated soft sandstone, siltstone,
or shale; roots cannot enter except along fracture
planes. The material can be dug with a spade,

Mlavial accumulation of sesquioxides and
organic matter

This symbol is used with "B" to indicate the accu-
mulation of illuvial, amorphous, dispersable organic
matter-sesquioxide complexes if both the organic
matter and sesquioxide components are significant
and the value and chroma of the horizon is

more than 3. The symbol is also used in combina-
tion with "h” as "Bhs" if both the organic matter
and sesquioxide components are significant and the
value and chroma are 3 or less.

Accumulation of silicate clay

This symbol is used to indicate an accumulation of
silicate clay that either has formed in the horizon
or has been moved into it by illuviation. The clay
can be in the form of coatings on ped surfaces or
in pores, lamellae, or bridges between min-

eral grains,

Plinthite

This symbol is used to indicate the presence of
iron-rich, humus-poor, reddish material that is
firm or very firm when moist and that hardens ir-
reversibly when exposed to the atmosphere and to
repeated wetting and drying. These properties
are characteristic of plinthite.

Development of color or structure

This symbol is used with "B" to indicate develop-
ment of color or structure, or both, with little or no
apparent illuvial accumulation of material. It
should not be used as a substitute for a transitional
horizon.

Fragipan character

This symbol is used to indicate genetically devel-
oped firmness, brittleness, or high bulk density.
These features are characteristic of fragipans, but
some horizons designated "x" do not have all prop-
erties of a fragipan.

Accumulation of gypsum

This symbol is used to indicate accumulation of
gypsum.

Accumulation of salts more soluble than gypsum

This symbol is used to indicate accumulation of
salts more soluble than gypsum,


124

¢, Do not have a lithic contact within 50 cm of the surface;
and

d. Have <50 percent by volume of wormholes, wormcasts,
and filled animal burrows between the bottom of the Ap
horizon or a depth of 25 cm, whichever is deeper, and ei-
ther a depth of I m or a lithic or paralithic contact if one is
Present above a depth of 1 m.

Andeptic Udorthents are like Typic Udorthents except for a.
Aquic Udorthents are like Typic Udorthents except for 6,
Lithic Udorthents are like Typic Udorthents except for c or
for ¢ and d.

Vermic Udorthents are like Typic Udorthents except for d.

Ustorthents
Distinctions between Typic Ustorthents and other subgroups

Typic Ustorthents are the Ustorthents that

a. Are not saturated with water within 1.5 m of the surface

for as long as 1 month in most years;

b. Do not have a horizon within 1 m of the surface that is

>15 cm thick that either contains 20 percent or more durin-

odes in a nonbrittle matrix or is brittle and has firm consis-

tence when moist;

¢. Do not have a lithic contact within 50 cm of the surface;

d. Have <50 percent (by volume) wormholes, wormcasts, and

filled animal burrows between the bottom of the Ap horizon

or a depth of 25 cm, whichever is deeper, and a depth of 1

m or a lithic or paralithic or petroferric contact, whichever

is shallower; and

e. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part, and that extend upward to the soil
surface or to the base of an Ap horizon; and
(2) A coefficient of linear extensibility (COLE) of 0.07
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.25 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
41,25 m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness.

Aquic Ustorthents are like Typic Ustorthents except for a.

Lithic Ustorthents are like Typic Ustorthents except for c.

Vermic Ustorthents are like Typic Ustorthents except for d.

Vertic Ustorthents are like Typic Ustorthents except for e.

Xerorthents
Distinctions between Typic Xerorthents and other subgroups

Typic Xerorthents are the Xerorthents that

a. Are not saturated with water within 1.5 m of the surface
at any time of year in most years;

b. Do not have a horizon within 1 m of the surface that is
>15 cm thick, that either contains 20 percent or more durin-
odes in a nonbrittle matrix or is brittle and has firm consis-
tence when moist;

¢. Do not have a lithic contact within 50 cm of the soil
surface; and


215

CECG. Other Eutrudox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface.

Aquic Eutrudox

CECH. Other Eutrudox that have more than 40 percent clay
in the surface 18 cm after mixing and the upper boundary
of a kandic horizon within a depth or 150 cm of the soil
surface.

Kandiudalfic Eutrudox

CECI. Other Eutrudox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and have the lower boundary of the oxic
horizon within a depth of 125 cm of the soil surface,
‘Umbreptic Eutrudox

CECI. Other Eutrudox that have the lower boundary of the
oxic horizon within a depth of 125 cm of the soil surface.
Inceptic Eutrudox

CECK, Other Eutrudox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface.

Humic Rhodic Eutrudox

CECL, Other Eutrudox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Eutrudox

CECM, Other Eutrudox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Eutrudox

CECN. Other Eutrudox that have a color hue of 2.5 YR or
redder with moist values of less than 4 in most of the 25 to
125 cm depth from the soil surface.

Rhodic Eutrudox

CECO, Other Eutrudox that have a color hue of 7.5 YR or
yellower with moist values of 6 or more in most of the 25 to
125 cm depth from the soil surface.

Xanthic Eutrudox

CECP. Other Eutrudox.
Typic Eutrudox

Hapludox
Key to subgroups

CEEA. Hapludox that have mottles of 4 or more value moist
and 2 or less chroma within a depth of 125 cm of the soil

Ox!


129
Xeropsamments

Distinctions between Typic Xeropsamments and other sub-
groups

Typic Xeropsamments are the Xeropsamments that

a. Do not have lamellae within 1.5 m of the soil surface that
meet all requirements for an argillic horizon except thick-
ness!?;

b. Do not have distinct or prominent mottles above a depth
of 1 m and are not saturated with water within | m of the
surface during any time of year in most years;

¢. Do not have a horizon within 1 m of the surface that is
>15 cm thick and that either contains 20 percent or more
durinodes in a nonbrittle matrix or is brittle and has firm
consistence when moist;

d. Do not have a lithic contact within 50 cm of the soil
surface; and

e. Have base saturation (by NH,OAc) of 60 percent or more
in some part of the soil between depths of 25 cm and 75 cm
below the soil surface,

Alfic Xeropsamments are like Typic Xeropsamments except
for a and have base saturation of 35 percent or more in
some horizon <1.25 m below the uppermost lamella.

Aquic Xeropsamments are like Typic Xeropsamments except
for b,

Aguic Durorthidic Xeropsamments are like Typic Xeropsam~
ments except for b and c.

Dystric Xeropsamments are like Typic Xeropsamments ex-
cept for e,

Lithic Xeropsamments are like Typic Xeropsamments except
for d or for d and e.

Thye clay content cannot be estimated with precision in lamellae that are
very thin. The lamellae in soile of alfic subgroups generally are about 0.6 to 1
‘em thick, but their total thickness ie less than the 15 em required for on
orgillic horizon,


239

‘They are moderately extensive in the United States on parts
of the coastal plains in the southeastern states.

Aeric Albaquults.--These soils are not known to occur in
significant areas in the United States, but the subgroup is
provided for use if needed. Either they have the colors that
are definitive for the suborder on ped faces but not in the
ped interiors or they have an ochric epipedon that has
higher chroma or a redder hue, or both.

Fragiaquults
Distinctions between Typic Fragiaquults and other subgroups

Typic Fragiaquults are the Fragiaquults that

a, Have an ochric epipedon;

b. Have mottles and have dominant chroma of 2 or less in
all horizons between the A or Ap horizon and the fragipan;
and

c. Have <5 percent plinthite (by volume) in all subhorizons
within 1.5 m of the soil surface.

Aeric Fragiaquuits are like Typic Fragiaquults except for b.
Plinthic Fragiaguults are like Typic Fragiaquults except for
¢ and have lenticular platy structure in the fragipan.
Plinthudic Fragiaquults are like Typic Fragiaquults except
for b and ¢ and have lenticular platy structure in the fragi-
pan.

Kandiaquults

Distinctions between Typic Kandiaquults and other sub-
groups

Typic Kandiaquults are the Kandiaquults that

a. Do not have a subhorizon that has dominant chroma of 3
or more within 75 cm of tho soil surface;

b, Do not have an epipedon that is 50 cm to 100 cm thick if
the particle-size class is sandy throughout;

c. Do not have an epipedon that is >100 cm thick if the
particle-size class is sandy throughout;

d. Do not have a horizon within 150 cm of the soil surface
that has >5 percent plinthite by volume;

e, Have an ochric epipedon; and

f. Have an ECEC (sum of bases plus 1 M KCl-extractable
Al) of more than 1.5 cmol(+) kg” clay in all subhorizons to
a depth of 150 cm below the soil surface.

Acric Kandiaquults are like Typic Kandiaquults except for /,
with or without a or d, or both.

Aeric Kandiaquults are like Typic Kandiaquults except for a.
Arenic Kandiaquults are like Typic Kandiaquults except for

b

Arenic Plinthic Kandiaquults are like Typic Kandiaquults
except for b and d.

Arenic Umbric Kandiaquults are like Typic Kandiaquults
except for 6 and e,

Grossarenic Kandiaquults are like Typic Kandiaquults except
for c.

Plinthic Kandiaquults are like Typic Kandiaquults except for

d.
Umbric Kandiaquults are like Typic Kandiaquults except for
e


228

BAD. Other Aquods that have a placic horizon that rests on
@ spodic horizon or on a fragipan or on an albic horizon that
rests on a spodic horizon.

Placaquods, p. 230

BAE. Other Aquods that have a mean annual soil tempera-

ture of 8°C or higher and mean summer and mean winter

soil temperatures at a depth of 50 cm that differ by <5°C.
Tropaquods, p. 230

BAF. Other Aquods that have in >50 percent of each pedon
a spodic horizon in which some subhorizon has a ratio of
free iron (by dithionite-citrate) to carbon (both elemental)
that is <0.2.

Haplaquods, p. 229

BAG. Other Aquods.
Sideraquods, p. 230

‘Cryaquods
Distinctions between Typic Cryaquods and other subgroups

Typic Cryaquods are the Cryaquods that

a. Do not have a lithic contact within 50 cm of the surface
of the mineral soil;

b. Have a mean annual soil temperature higher than 0°C;

¢. Have a ratio of free iron to carbon (elemental) of <0.2 in
some subhorizon;

4, Do not have mottles above the spodic horizon that are
due to segregation of i
e. Do not have an argi
horizon; and

f. Have a continuous spodic horizon that is 10 cm or more
thick or that is very firm when moist.

Lithic Cryaquods are like Typic Cryaquods except for a or
for a and b.

Pergelic Cryaquods are like Typic Cryaquods except for b.
Pergelic Sideric Cryaquods are like Typic Cryaquods except
for 6 and c or for b, ¢, and d.

Sideric Cryaquods are like Typic Cryaquods except for ¢ or
for c and d.

lic horizon underlying the spodic

Duraquods

Duraquods are the Aquods that have a duripan in the albic
horizon and have a temperature regime warmer than that of
Cryaquods.

Fragiaquods
Distinctions between Typic Fragiaquods and other subgroups

Typic Fragiaquods are the Fragiaquods that

a. Have a frigid or warmer temperature regime;

b. Do not have a histic epipedon;

¢. Have <5 percent by volume of iron-cemented nodules 2.5
to 30 cm in diameter in any subhorizon of the spodic hori-
zon;

d. Do not have a surface horizon >30 cm thick that meets all
requirements of a plaggen epipedon except thickness;


155

soils are in relatively recent alluvium, probably of late-
Pleistocene or Holocene age. Weatherable minerals are
Present in appreciable amounts, These soils are not known
to occur in the United States, but the great group is
provided because the soils are thought to be extensive in
parts of the Amazon basin.

Sulfaquepts

Sulfaquepts are the Aquepts that have a sulfuric horizon that
has its upper boundary within 50 cm of the soil surface,

Subgroups of Sulfaquepts have not been fully developed. It
is thought that few subgroups are needed because the
sulfuric horizon is so highly toxic. The Typic Sulfaquepts
have a sulfuric horizon within 50 cm of the soil surface. A
histic epipedon is permitted but is not required.

Tropaquepts
Distinctions between Typic Tropaquepts and other subgroups

Typic Tropaquepts are the Tropaquepts that
a, Have in 60 percent or more of the matrix in all
subhorizons between the A or Ap horizon and a depth of 75
cm one or more of the following:
(1) If mottled and if the hue is 2.5Y or redder and the
value, moist, is >5, the chroma, moist, is 2 or less; if the
value, moist, is 5 or less, the chroma, moist, is 1 or less;
(2) If mottled and if the hue is yellower than 2.5Y, the
chroma, moist, is 2 or less;
(3) The chroma, moist, is 1 or less whether mottled or
not;

b. Do not have a histic epipedon that has its upper boundary

fat or near the surface:

¢, Do not have a lithic contact within 50 cm of the soil

surface;

d. Do not have the following combination of characteristics:
(1) Cracks at some time in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part, and that extend upward to the soil
surface or to the base of an Ap horizon;

(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
@ potential linear extensibility of 6 cm or more in the
upper | m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
Im; and

(3) More than 35 percent clay in horizons that total >50
cm in thickness;

e, Have <5 percent (by volume) of plinthite in all

subhorizons within 1.5 m of the soil surface;

f. Do not have either of the following:

(1) Jarosite mottles and a pH between 3.5 and 4.0
(1:1 water, air dried slowly in shade) in some
subhorizon within 50 cm of the soil surface; or
(2) Jarosite mottles and a pH <4.0 (1:1 water, air
dried slowly in shade) in some subhorizon between
depths of 50 and 150 cm,

Aeric Tropaquepts are like Typic Tropaquepts except for a.

Histic Tropaquepts are like Typic Tropaquepts except for b.


159

with water at some period when its temperature is 25°C or

if the soil has artificial drainage;

c. Have texture of very fine sand or finer within 50 cm of

the soil surface;

d, Have carbonates within a depth of 1 m in some part of

each pedon;

e. Have a content of organic carbon that decreases regularly

with depth and, unless a lithic or a paralithic contact occurs

at a shallower depth, reaches a level of 0.2 percent or less
within 1.25 m of the soil surface; or have slopes >25
percent;

f. Do not have a lithic contact within 50 cm of the soil

surface in any part of the pedon;

g- Do not have an argillic horizon in any part of the pedon;

h. Have an ochric epipedon;

i, Do not have the following combination of characteristics;
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend to the soil surface or
to the base of an Ap horizon,

(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper ! m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1 m, and

(3) More than 35 percent clay in horizons that total >50
cm in thickness; or

j. Have <40 percent carbonates, including the coarse

fragments up to 75 mm in diameter, in and below the

cambic horizon but above a lithic or paralithic contact and

above a depth of I m.

Andic Dystric Eutrochrepts are like Typic Eutrochrepts

except for a and d,

Aquic Eutrochrepts are like Typic Eutrochrepts except for b.

Aquic Dystric Eutrochrepts ate like Typic Eutrochrepts

except for 6 and d.

Arenic Eutrochrepts are like Typic Eutrochrepts except for c.

Dysiric Eutrochrepts are like Typic Eutrochrepts except for

Spstrie Fluventic Eutrochrepts are like Typic Eutrochrepts
except for d and e,

Fluvaquentic Eutrochrepts are like Typic Eutrochrepts except
for 6 and e, with or without d.

Fluyentic Eutrochrepts are like Typic Eutrochrepts except for
e

Lithic Eutrochrepts are like Typic Eutrochrepts except for f
or for d and f,

Lithic Ruptic-Alfic Eutrochrepts are like Typic Eutrochrepts
except for f and g, and they have an argillic horizon in
some part but in less than half of each pedon.

Rendollic Eutrochrepts are like Typic Eutrochrepts except
for j.

Ruptic-Alfic Eutrochrepts are like Typic Eutrochrepts except
for g and have an argillic horizon in some part but in less
than half of each pedon.

Vertic Eutrochrepts are like Typic Eutrochrepts except for i,
with or without ¢ or b, or both,

INC


iii
- Table of Contents
Chapter 1: The Soil That We Classify and Horizons and

Properties Diagnostic for the Higher Categories:
Mineral Soils

Chapter 2: Horizons and Properties Diagnostic
for the Higher Categories; Organic Soils.

Chapter 3: Family Differentiae..........ss0ss0

Chapter 4: Identification of the
Taxonomic Class of a Soil...

Chapter 5: Alfisols ....

Chapter 6; Aridisols......

Chapter 7: Entisols....

Chapter 8: Histosols ..

Chapter 9: Inceptisols.........

Chapter 10: Mollisols ....
Chapter !1: Oxisols...

Chapter 12: Spodosols ...

Chapter 13: Ultisols...

SI conversion tabie....

Designations for Master Horizons
and Layers in Soils...



255

1. Mottles that have a color value, moist, of 4 or more
and chroma, moist, of 2 or less accompanied by mottles
of higher chroma that are due to segregation of iron; and
2, Saturation with water in the mottled zone at some time
of year when the soil temperature in that zone is 5°C or
higher or there is artificial drainage;
¢. Have a hue redder than 10YR in all parts of the soil
above a depth of 75 cm that have a color value, moist, of 4
or more if there are mottles of high chroma above that
depth and if the hue becomes redder with depth within 100
cm of the soil surface;
d. Do not have a horizon within 150 cm of the soil surface
that has >5 percent plinthite by volume;
e. Do not have an epipedon that is 250 cm thick if the par-
ticle-size class is sandy throughout;
f. Have an argillic or kandic horizon that has a color hue of
SYR or yellower in some part, or has a value, moist, of 3.5
or more in some part, or has a value, dry, that is more than
one unit higher than the value, moist;
g- Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either of the following:
1, A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
2. A ratio of CEC (pH 8.2) to 1500 kPa water of >1.5
and more exchange acidity than the sum of bases plus
KCl-extractable aluminum;
h. Have an ECEC (sum of bases KCl-extractable Al) of
more than 1.5 cmol(+) kg” clay in all subhorizons to a depth
of 150 cm below the soit surface; and
i, When neither irrigated nor fallowed to store moisture:
1. If the soil temperature regime is mesic or thermic, are
moist more than six-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) when the soil temperature at a
depth of 50 cm exceeds 5°C; or
2. If the soil temperature regime is hyperthermic,
isomesic, or warmer, are moist in most years in some or
all parts of the moisture control section for 180 or more
days during a period when the soil temperature at a
depth of 50 cm exceeds 8°C; and
J, When neither irrigated nor fallowed to store moisture:
1, If the soil temperature regime is mesic or thermic, are
dry for more than 135 cumulative days in some part of
the moisture control section when the soil temperature at
a depth of 50 cm exceeds 5°C; or
2. If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days
during a period when the soil temperature at a depth of
50 cm exceeds 8°C;,
Acric Kanhaplustults are like Typic Kanhaplustults except
for A, with or without any of c, d, or g.
Andi¢c Kanhaplustults are like Typic Kanhaplustults except
for g, with or without ¢ or @ or both.
Andic Udic Kanhaplustults ave like Typic Kanhaplustults
except for g and j.
Aquic Kanhaplustults are like Typic Kanhaplustults except
for b.

ULT


259

Chapter 14
Vertisols
Key To Suborders

DA. Vertisols that have a thermic, mesic, or frigid soil tem-
perature regime and, unless irrigated, have cracks that open
and close once each year and remain open for 60 consecu-
tive days or more in the 90 days following the summer sol-
stice in more than 7 out of 10 years but that are closed for
60 consecutive days or more during the 90 days following
the winter solstice.

Xererts, p. 261

DB. Other Vertisols that, unless irrigated, have in most years
cracks that either remain open throughout the year or are
closed for less than 60 consecutive days at a period when the
soil temperature at a depth of 50 cm is continuously higher
than 8°C.

Torrerts, p. 259

DC. Other Vertisols that have cracks that open and close one

or more times during the year in most years but do not re-

main open for as many as 90 cumulative days in most years,
Uderts, p. 259

DD. Other Vertisols.
Usterts, p. 260

Torrerts
Distinctions between Typic Torrerts and other subgroups

Typic Torrerts are the Torrerts that

a. Have a color value, moist, of 4 or more in the surface
horizon in more than half of each pedon, or the upper
horizon that has a color value (moist) less than 4 is <30 cm
thick; and

b. Do not have prismatic or blocky structure accompanied
by clay skins on ped faces that have a color value lower
than that in the matrix within 1 m of the soil surface.
Mollic Torrerts are like Typic Torrerts except for a,
Paleustollic Torrerts are like Typic Torrerts except for a and
b

Uderts
Key to great groups
DCA. Uderts that have a chroma, moist, of 1.5 or more

dominant in the matrix of some subhorizon in the upper 30
cm in more than half of each pedon.

DCB. Other Uderts,

Pelluderts, p. 260

VER


149
Hydrandepts
Distinction between Typic and Lithic Hydrandepts

Typic Hydrandepts are the Hydrandepts that

a, Do not have a lithic contact within 50 cm of the soil
surface.

Lithic Hydrandepts are like Typic Hydrandepts except for a.

Placandepts

‘These are the Andepts that have a placic horizon. Like the
Hydrandepts, they are mostly in very humid climates that do
not have a dry season. The placic horizon is a barrier to
water movement and root development. Water commonly
saturates much of the soil above the pan for variable
periods, This great group is represented by a very few soil
series in the United States. The soils have been reported in
other countries, These soils were called Hydrol Humic
Latosols in the 1938 classification as modified in 1955.

Subgroups have not been developed because the soils are too
poorly represented in the United States. It is thought that
soils of the typic subgroup should have, within 1 m of the
surface, a placic horizon that is continuous through each
pedon.

Vitrandepts
Distinctions between Typic Vitrandepts and other subgroups

Typic Vitrandepts are the Vitrandepts that

a, Do not have mottles that have chroma of 2 or less within
1 m of the soil surface if the mottled horizon is saturated
with water in most years at some period when its
temperature is >5°C or if the soil is artificially drained;

b. Do not have a lithic contact within 50 cm of the soil
surface; and

c. Have an ochric epipedon,

Aquic Vitrandepts are like Typic Vitrandepts except for a.
Lithic Vitrandepts are like Typic Vitrandepts except for 5.
Lithic Mollic Vitrandepts are like Typic Vitrandepts except
for 6 and c, and they have a mollic epipedon.

Lithic Umbric Vitrandepts are like Typic Vitrandepts except
for b and c, and they have an umbric epipedon.

Mollic Vitrandepts are like Typic Vitrandepts except for c,
and they have a mollic epipedon.

Plaggic Vitrandepts are like Typic Vitrandepts except for c,
and they have either a plaggen epipedon or an epipedon that
meets all requirements for a plaggen epipedon except
thickness and is 30 cm or more thick.

Umbric Vitrandepts are \ike Typic Vitrandepts except for c,
and they have an umbric epipedon.

Aquepts
Key to great groups
IAA. Aquepts that have a sulfuric horizon whose upper

boundary is within 50 cm of the mineral soit surface.
Sulfaquepts, p. 155



107
Durorthids
Distinctions between Typic Durorthids and other subgroups

Typic Durorthids are the Durorthids that
a, Are not saturated with water for 90 consecutive days or
more in most years within 1 m of the surface and do not
have a subhorizon within | m of the soil surface that has the
following characteristics if the horizon is saturated with
water at some period in most years or the soil is artificially
drained:
(1) Dominant chroma of | or Jess throughout and hue as
yellow or yellower than 2.5Y in some part;
(2) Dominant chroma of 2 or less accompanied by mot-
tles that are not due to segregated lime, or
(3) Both a dominant chroma of 2 or less and a greater
SAR (or percentage of exchangeable sodium) in more
than half the thickness of the horizons between the sur-
face and 50 cm depth than in the saturated zone;
b, Have a platy or massive duripan that is indurated in some
subhorizon,
c. Have a duripan whose upper boundary is shallower than
18 cm; or have a weighted average content of organic car-
bon in the upper soil to a depth of 40 cm that is <0.6 if the
weighted average ratio of sand to noncarbonate clay above
that depth is 1.0 or less or is <0.15 percent if the ratio is 13
or more, or is intermediate if the ratio of sand to clay is
between 1.0 and 13;
of a weighted average percentage of organic carbon in the
surface soil to a depth of 18 cm that is not one-fifth more
than the values just stated if there is a duripan shallower
than 40 cm but deeper than 18 cm; and
d. Are dry in all parts of the moisture control section for
more than three-fourths of the time that the soil tempera-
ture at a depth of 50 cm is 5°C or higher.
Aquentic Durorthids are like Typic Durorthids except for a
and 5, with or without c or d, or both.
Aquic Durorthids are like Typic Durorthids except for a,
with or without ¢ or d, or both.
Entic Durorthids are like Typic Durorthids except for b.
Haploxerollic Durorthids are like Typic Durorthids except
for b and c, with or without d. They have a mean annual
soil temperature lower than 22°C, and the mean summer and
mean winter soil temperatures at a depth of 50 cm differ by
5°C or more, They have an aridic moisture regime that
borders on a xeric regime.
Xerollic Durorthids are like Typic Durorthids except for ¢ or
for c and d. They have a mean annual soil temperature
lower than 22°C, and the mean summer and mean winter
soil temperatures at a depth of 50 cm differ by 5°C or more.
They have an aridic moisture regime that borders on a xeric
regime.

Gypsiorthids

Distinctions between Typic Gypsiorthids and other sub-
groups

Typic Gypsiorthids are the Gypsiorthids that
a. Do not have a petrogypsic horizon whose upper boundary
is within | m of the soil surface; and


66

Aerie Fragiaqualfs are like Typic Fragiaqualfs except for a.
Umbric Fragiaqualfs are like Typic Fragiaqualfs except for
c.

Glossaqualfs
Distinctions between Typic Glossaqualfs and other subgroups

Typic Glossaqualf’s are the Glossaqualfs that
a. Have in 60 percent or more of the matrix® in all sub-
horizons between the A or Ap horizon and a depth of 75 cm
‘one of the following:
(1) If mottled and the value, moist, is 4 or more, the
chroma, moist, is 2 or less;
(2) If not mottled, the chroma, moist, is 1 or less;
b, Have texture finer than loamy fine sand in some sub-
horizon within a depth of 50 cm below the surface; and
c. Have an Ap horizon that has either a color value, moist,
of 4 or more, or a color value, dry, of 6 or more after the
soil has been crushed and smoothed; or the soil to a depth of
18 cm, after mixing, has these colors.
Aerie Glossaqualfs are like Typic Glossaqualfs except for a
or for a and c.
Arenic Glossaqualfs are like Typic Glossaqualfs except for b
or for a and b ; they have a sandy epipedon between 50 cm
and 1 m thick.
Mollic Glossaqualfs are like Typic Glossaqualfs except for c.

Kandiaqualfs

Distinctions between Typic Kandiaqualfs and other sub-
groups

Typic Kandiaqualfs are the Kandiaqualfs that
a. Have in 60 percent or more of the matrix in all subhori-
zons between the A or Ap horizon and a depth of 75 cm
one or more of the following:
(1) If mottled and the mean annual soil temperature is
lower than 15°C, has chroma, moist, of 2 or less;
(2) If mottled and the mean annual soil temperature is
15°C or more:
(a) If the hue is 2.5Y or redder and the value, moist,
is more than 5, the chroma, moist, is 2 or less;
(b) If the hue is 2.5Y or redder and the value, moist,
is 5 or less, the chroma, moist, is 1 or less;
(c) If the hue is yellower than 2.5Y, the chroma,
moist, is 2 or less,
(3) The chroma, moist, is 1 or less whether mottled or
not;
b. Have an Ap horizon that has either a color value, moist,
of 4 or more or a color value, dry, or 6 or more after the
soil has been crushed; or the upper soil to a depth of 18 cm,
after mixing, has these color values;
c. Do not have an epipedon that is 50 cm to 100 cm thick if
the particle-size class is sandy throughout;

Sif the hue is 7.6YR or redder and, if pads are present, ped exteriors in the
argillic horizon should have dominant chroma, moist, of 1 or less and ped in-
teriors should have mottles that have chroma, moist, of 2 or leas; if pede are
absent, the chroma, moist, should be 1 or less immediately below any surface
horizon that has color value, moist, leas than 3.5.


54

content of free iron oxide should exceed 10 percent (7 per-
cent Fe), but the horizon may be either organic or mineral
provided there is at least 1 percent organic matter. The
materials should have >2 percent (by weight) concretions of
iron, which may range in size from fine (<5 mm) to | m or
more in the largest lateral dimension, Colors should be dark
reddish brown or reddish brown, or should be close to those
colors. The presence of ferrihumic material within the con-
trol section is one of the family differentiae.

If ferrihumic is used as a modifier in the technical family
name, no other mineralogy modifier is used because the
presence of the iron is considered to be, by far, the most
important characteristic.

Modifiers applied onlv to terric subgroups.--The mineralogy
modifiers used for mineral soils are applied to the mineral
parts of the soil for which a particle-size modifier has been
used if the mineralogy is not ferrihumic.

Modifiers applied to limnic suberoups,--If limnic materials
are present in the control section, if they are 5 cm or more
thick, and if the materials do not have ferrihumic mineral-
ogy, the following modifiers are used. These terms are de-
fined in chapter 2.

Coprogenous. Limnic materials that consist of coprogenous
earth are present.

Diatomaceous. Limnic materials that consist of diatomaceous
earth are present.

Marly. Limnic materials that consist of marl are present.

Reaction classes

Modifiers to indicate reaction are used in all subgroups.
The meanings follow.

Euic,--The pH of undried samples is 4.5 or more (0.01 M
CaCl,) in at least some part of the organic materials in the
control section.

Dysic,--The pH is <4.5 (in 0.01 M CaCl,) in all parts of the
organic materials in the control section.

Soil temperature classes

Names and definitions of classes follow the rules given for
soil temperature classes of mineral soils. Frigid, however, is
redundant in boric and cryic great groups and is not used.
No temperature modifier is used in pergelic subgroups.

Soil depth classes

Soil depth modifiers are used in all lithic subgroups of His-
tosols except in the suborder of Folists. It is assumed that
lithic Folists have a shallow lithic contact. Other lithic His-
tosols have a lithic contact within the control section but it
may be as much as 160 cm deep.

Shallow families,--Used in lithic subgroups to indicate a
lithic contact between a depth of 18 cm and 50 cm.


177

GEF. Other Borolls that have a calcic or petrocalcic horizon
whose upper boundary is within 1 m of the soil surface and
that are calcareous in all parts of all horizons above the
calcic or petrocalcic horizon, after the upper soil to a depth
of 18 cm has been mixed, unless the texture is coarser than
joamy very fine sand.

Calciborolls, p. 178

GEG. Other Borolls.
Haploborolls, p. 180

Argiborolls
Distinctions between Typic Argiborolls and other subgroups

Typic Argiborolls are the Argiborolls that
a. Do not have an argillic horizon that has an increase in
clay content of 20 percent (absolute) or more within a
vertical distance of 7.5 cm from the upper boundary;
b. Do not have either
(J) An albic horizon that lies immediately under the
mollic epipedon; or
(2) Tonguing or interfingering of albic materials in the
upper part of the argillic horizon, or skeletans of clean
silt and sand covering more than half the ped faces in the
upper 5 cm or more of the argillic horizon;
c. Do not have a layer in the upper 75 cm that has a texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 ¢
per cubic centimeter or less in the fine-earth fraction, and
that has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
d, Do not have mottles that have chroma of 2 or less within
1 m of the surface or, if undrained, are not continuously
saturated with water for as long as 90 days within 1 m of
the surface;
e. Do not have a lithic contact within 50 cm of the surface;
f. Have
(1) Either or both
(a) A color value, dry, of less than 4.5 in the upper 18
cm of the mollic epipedon, after mixing, or in any Ap
horizon that is >18 cm thick; or
(b) A moisture control section that is dry in some part
less than six-tenths of the time that the soil
temperature at a depth of 50 cm is above 5°C in most
years; and
(2) A chroma (rubbed), moist, of 1.5 or more in the
upper 18 cm of the mollic epipedon after mixing, or in
any Ap horizon that is >18 cm thick and the soil is dry in
all parts of the moisture control section at some time in
most years;
g. Have a mollic epipedon that is <40 cm thick, or its
texture is loamy fine sand or coarser; and
h. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm


102

Borollic Vertic Paleargids are like Typic Paleargids except
for 6 and e, with or without f. The mean annual soil
temperature is lower than 8°C, the mean summer and mean
winter soil temperatures at a depth of 50 cm differ by >5°C,
and the cracks are not closed for as many as 60 consecutive
days of the 120 days following the winter solstice in 3 or
more years out of 10.

Petrocalcic Paleargids are like Typic Paleargids except for c
or for ¢ and d.

Petrocalcie Ustalfic Paleargids are like Typic Paleargids
except for c and f, with or without d. They have a mean
annual soil temperature that is 8°C or higher and an aridic
moisture regime that borders on an ustic regime.

Petrocalcic Ustollic Paleargids are like Typic Paleargids
except for b and c, with or without d or f, or both. They
have a mean annual soi! temperature that is 8°C or higher
and an aridic moisture regime that borders on an ustic
regime.

Petrocalcie Xerollic Paleargids are like Typic Paleargids
except for 6 and c, with or without d or f, or both. They
have a mean annual soil temperature fower than 22°C, and
the mean summer and mean winter soil temperatures at a
depth of 50 cm differ by 5°C or more. They have an aridic
moisture regime that borders on a xeric regime.

Ustollic Paleargids are like Typic Paleargids except for b or
for 6 and f. They have a mean annual soil temperature that
is 8°C or higher and an aridic moisture regime that borders
on an ustic regime.

Xeralfic Paleargids are like Typic Paleargids except for f.
They have a mean annual soil temperature lower than 22°C,
and the mean summer and mean winter soil temperatures at
a depth of 50 cm differ by 5°C or more, They have an
aridic moisture regime that borders on a xeric regime.
Xerollic Paleargids are like Typic Paleargids except for 5,
with or without /. They have a mean annual soil
temperature lower than 22°C, and the mean summer and
mean winter soil temperatures at a depth of 50 cm differ by
5°C or more, They have an aridic moisture regime that
borders on a xeric regime.

Orthids
Key to great groups

EBA. Orthids that have a salic horizon whose upper
boundary is within 75 cm of the soil surface and are
saturated with water within a depth of 1 m for 1 month or
more in most years or have artificial drainage and lack a
duripan that has an upper boundary within 1 m of the soil
surface,

Salorthids, p. 109

EBB. Other Orthids that have a petrocalcic horizon whose
upper boundary is within 1 m of the soil surface and is not
overlain by a duripan,

Paleorthids, p. 108

EBC, Other Orthids that have a duripan whose upper
boundary is within 1 m of the soil surface.
Durorthids, p. 107


265

Fragiaqualfs
Fragiaquepts.
Fragiaquods.
Fragiaquults
Fragiboralfs..
Fragihumods
Fragiochrepts

Fragiumbrepts..
Fragixeralfs..
Fraglossudalfs..

Gilgai
Glossaqualfs
Glossoboralfs
Glossudalfs
Gypsic horizo
Gypsiorthids

Halaquepts
Haplaquents
Haplaquepts
Haplaquods ..
Haplaquolls ..

Haplumbrepts .
Haplustalfs
Haplustolls
Haplustox.
Haplustults.
Hemic soil materials.
Hemists.

Histic epipedos 3
Humaquepts.. 154
Humilluvic materials 37

Humitropepts...


26

© cemented horizon. The control section of the latter
soil is moist if the upper boundary of the rock or the ce-
mented horizon has a thin film of water. If the upper
boundary is dry, the control section is dry.

As a rough guide to the limits, the soil moisture control sec-
tion lies approximately between 10 and 30 cm (4 and 12 in.)
if the particle-size class is fine-loamy, coarse-silty, fine-
silty, or clayey. The control section extends approximately
from a depth of 20 cm to a depth of 60 cm (8 to 24 in.) if
the particle-size class is coarse-loamy, and from 30 to 90 cm
(12 to 35 in.) if the particle-size class is sandy.

Classes of soil moisture yezimes

The moisture regimes are defined in terms of the ground-
water level and in terms of the presence or absence of water
held at a tension <1500 kPa in the moisture control section
by periods of the year. It is assumed in the definitions that
the soil supports whatever vegetation it is capable of sup-
porting. In other words, it is in crops, grass, or native veg-
etation; it is not being fallowed to increase the amount of
stored moisture, nor is it being irrigated by man. These
cultural practices affect the soil moisture condition as long
as they are continued.

Aquic moisture regime.--The aquic (L. aqua, water) mois-
ture regime implies a reducing regime that is virtually free
of dissolved oxygen because the soil is saturated by ground
water or by water of the capillary fringe. An aquic regime
must be a reducing one. Some soil horizons, at times, are
saturated with water while dissolved oxygen is present, ei-
ther because the water is moving or because the environ-
ment is unfavorable for micro-organisms, for example, if
the temperature is <1°C such a regime is not considered
aquic.

For differentiation in the highest categories of soils that
have an aquic regime, the whole soil must be saturated, In
the subgroups, only the lower horizons are saturated. The
soil is considered to be saturated if water stands in an un-
lined borehole at such a shallow depth that the capillary
fringe (see footnote 5) reaches the soil surface except in
noncapillary pores, The water in the borehole is stagnant
and remains colored if a dye is placed in the water. Ina
sandy soil, the thickness of the capillary fringe may be only
10 to 15 cm. In a loamy or clayey soil that does not shrink
or swell appreciably, the thickness may be 30 cm or more,
depending on the size distribution of the pores.

The duration of the period that the soil must be saturated to
have an aquic regime is not known. The duration must be
at least a few days, because it is implicit in the concept that
dissolved oxygen is virtually absent, Because dissolved oxy-
gen is removed from ground water by respiration of micro-
organisms, roots and soil fauna, it is also implicit in the
concept that the soil temperature is above biologic zero
(5°C) at some time while the soil or the horizon is saturated.

Very commonly, the level of ground water fluctuates with
the seasons, The level is highest in the rainy season, or in


234

BDD, Other OrthodS that have an isomesic or warmer iso
temperature regime.
Troporthods, p. 236

BDE. Other Orthods.
Haplorthods, p. 235

Cryorthods
Distinctions between Typic Cryorthods and other subgroups
Typic Cryorthods are the Cryorthods that

a. Do not have an argillic or kandic horizon below the
spodic horizon;

b. Have a cemented or indurated spodic horizon or have 1.2
to 6 percent organic carbon in the upper 10 cm of the
spodic horizon;

¢. Do not have a lithic contact within 50 cm of the soil
surface;

d. Have a mean annual soil temperature higher than 0°C,
Boral fic Cryorthods are like Typic Cryorthods except for a
or for a and 6,

Enti¢ Cryorthods are like Typic Cryorthods except for 6 in
that they contain less than 1.2 percent organic carbon in the
upper 10 cm of the spodic horizon.

Humic Cryorthods are like Typic Cryorthods except for 5 in
that they contain >6 percent organic carbon in the upper 10
cm of the spodic horizon.

Humic Lithic Cryorthods are like Typic Cryorthods except
for ¢ and b and they contain >6 percent organic carbon in
the upper 10 cm of the spodic horizon.

Lithic Cryorthods are like Typic Cryorthods except for ¢ or
for c and d.

Pergelic Cryorthods are like Typic Cryorthods except for d.

Fragiorthods

Distinctions between Typic Fragiorthods and other sub-
groups

Typic Fragiorthods are the Fragiorthods that
a. Do not have an argillic or kandic horizon below the
spodic horizon;
b. Do not have distinct or prominent mottles in the spodic
horizon;
c. Have a spodic horizon that has one or more of the fol-
lowing:
(1) A continuous horizon that is at least 2.5 cm thick and
is very firm or extremely firm when moist (ortstein);
(2) A texture of very fine sand or finer and is more than
10 cm thick and has at least 1.2 percent organic carbon
(weighted average) in the upper 10 cm;
(3) A coarse-loamy, loamy-skeletal, sandy-skeletal, or
sandy particle-size class and has color value and chroma
of 3 or less in at least the upper 7.5 cm;
d, Have a temperature regime warmer than that of Cryorth-
ods;.
e. Do not have an intermittent upper black subhorizon of
the spodic horizon that has a ratio of free iron (elemental) to
carbon that is <0.2; or, if plowed and the Ap horizon rests


242

tracted with 1 M NH,OAc pH 7 plus | M KCl-extractable
Al) in the major part of the argillic or kandic horizon or the
major part of the upper 100 cm of the argillic or kandic
horizon if these horizons are thicker than 100 cm;
2. Do not have a lithic, paralithic, or petroferric contact
within 150 cm of the soil surface; and
3. Have a clay distribution such that the percentage of clay
does not decrease from its maximum amount by as much as
20 percent within a depth of 150 cm from the soil surface
or the layer in which the clay percentage decreases by more
than 20 percent has at least 5 percent of the volume con-
sisting of skeletans on faces of peds and there is at least 3
percent (absolute) increase in clay below the layer.
Kandihumults, p. 243

FBD. Other Humults that have a CEC <16 cmol(+) kg” clay
(by 1 M NH,OAc pH 7) and an ECEC 12 cmol(+) kg” clay
(sum of bases extracted with 1 M NHOAc pH 7 plus 1 M
KCl-extractable Al) in the major part of the argillic or
kandic horizon or the major part of the upper 100 cm of the
argillic or kandic horizon if these horizons are thicker than
100 cm.

Kanhaplohumults, p, 243

FBE. Other Humults.
Haplohumults, p. 242

Haplohumults

Distinctions between Typic Haplohumults and other sub-
groups

Typic Haplohumults are the Haplohumults that
a, Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
or less per cubic centimeter in the fine-earth fraction, and
that has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
b, Have a udic moisture regime;
¢, Do not have the following combination of characteristics
in the upper 25 cm or more of the argillic horizon:
(1) Mottles that have a color value, moist, of 4 or more
and chroma, moist, of 2 or less accompanied by mottles
of higher chroma that are due to segregation of iron; and
(2) Saturation with water in the mottled zone at some
time of year when the soil temperature in that zone is
S°C or more or artificial drainage; and
d, Do not have a lithic contact within 50 cm of the mineral
soil surface.
Andeptic Haplohumults are like Typic Haplohumults except
for a.
Aquic Haplohumults are like Typic Haplohumults except for

¢.
Xeric Haplohumults are like Typic Haplohumults except for
band have a xeric soil moisture regime.


22

the temperature of the horizon is above the biologic zero,
which is about 5°C (41°F), during at least a part of the time
that the horizon is saturated.

n value

The » value (Pons and Zonneveld 1965) refers to the relation
between the percentage of water under field conditions and
the percentages of inorganic clay and of humus. The n
value is helpful in predicting whether the soil may be grazed
by livestock or will support other loads and the degree of
subsidence that would occur after drainage. The ” value can
be calculated for mineral soil materials that are not
thixotropic by the formula:

n=(A - O.2R)(L + 3H)

A is the percentage of water in the soil in field condition,
calculated on a dry-soil basis; R is the percentage of silt
plus sand; L is the percentage of clay; and H is the per-
centage of organic matter (organic carbon x 1.724).

Few data are available in the United States for calculations
of the n value, but the critical n value of 0.7 can be ap-
proximated closely in the field by a simple test of squeezing
the soil in the hand. If the soil flows with difficulty be
tween the fingers, the n value is between 0.7 and 1.0. If the
soil flows easily between the fingers, the x value is 1 or
more,

Organic soil materials
Organic soil materials either

1. Are saturated with water for long periods or are artifi-
cially drained, and have 18 percent or more organic carbon
if the mineral fraction is 60 percent or more clay, 12 per-
cent or more organic carbon if the mineral fraction has no
clay, or a proportional amount of organic carbon between 12
and 18 percent if the clay content is between zero and 60
percent; or

2. Are never saturated with water for more than a few days
and have 20 percent or more organic carbon.

Item | in this definition covers materials that have been
called peat and muck. Item 2 is intended to include materi-
als that have been called "litter" or O horizons. Not all or-
ganic soil materials accumulate under water. Leaf litter may
rest on a lithic contact and yet may support a forest. The
only "soil" in this situation is organic in the sense that the
mineral fraction may be appreciably less than half the
weight and only a small proportion of the volume of the
soil.

Paralithic contact

A paralithic (lithic-like) contact is a boundary between soil
and continuous coherent underlying material. It differs
from a lithic contact in that the underlying material, if a
single mineral, has a hardness by Mohs scale of <3. If the


106

tive days of the 120 days following the winter solstice in 3
or more years out of 10,

Duric Camborthids are like Typic Camborthids except for 5.
Durixerollic Camborthids are like Typic Camborthids except
for b and d, with or without e. They have a mean annual
soil temperature lower than 22°C, and the mean summer and
mean winter soil temperatures at a depth of 50 cm differ by
5°C or more. They have an aridic moisture regime that
borders on a xeric regime.

Durixerollic Lithic Camborthids are like Typic Camborthids
except for 6, c, and d, with or without e, They have a
mean annual soil temperature lower than 22°C, and the
mean summer and mean winter soil temperatures at a depth
of 50 cm differ by 5°C or more, They have an aridic
moisture regime that borders on a xeric regime.

Fluventic Camborthids are like Typic Camborthids except for

&
Lithic Camborthids are like Typic Camborthids except for c.
Lithic Xerollic Camborthids are like Typic Camborthids ex-
cept for c and d, with or without ¢. They have a mean an-
nual soil temperature lower than 22°C, and the mean sum-
mer and mean winter soil temperatures at a depth of 50 cm
differ by 5°C or more, They have an aridic moisture regime
that borders on a xeric regime,

Natric Camborthids are like Typic Camborthids except for h,
with or without any or all of a, d, e, f, and g, and they
have slow or very slow saturated hydraulic conductivity.
Ustertic Camborthids are like Typic Camborthids except for
J, with or without any or all of d, e, and g. In most years,
unless irrigated, they have cracks that remain open for 175
to 240 days, cumulative. The cracks are not closed for as
many as 60 consecutive days during the 120 days following
the winter solstice in 3 or more years out of 10 if the soil
temperature regime is thermic, mesic, or frigid.

Ustochreptic Camborthids are like Typic Camborthids except
for e. They have an aridic moisture regime that borders on
an ustic moisture regime and a hyperthermic, thermic, or
mesic soil temperature regime.

Ustoltic Camborthids are like Typic Camborthids except for
d or for d and e, have a mean annual soil temperature that
is 8°C or higher, and have an aridic moisture regime that
borders on an ustic regime.

Vertic Camborthids are like Typic Camborthids except for f
or for e and f. Unless the soils are irrigated, the cracks re-
main open in most years for more than 240 days, cumula-
tive, and are not closed in most years for as many as 60
consecutive days at any season.

Xerertic Camborthids are like Typic Camborthids except for
7, with or without any or all of d, e, and g. They have a
thermic, mesic, or frigid soil temperature regime and have
cracks that are closed for 60 consecutive days or more dur-
ing the 120 days following the winter solstice in more than 7
years out of 10.

Xerollic Camborthids are like Typic Camborthids except for
dor for d and e, They have a mean annual soil temperature
lower than 22°C, and the mean summer and mean winter
soil temperatures at a depth of 50 cm differ by 5°C or more.
They have an aridic moisture regime that borders on a xeric
regime.



166

¢. Do not have a lithic contact within 50 cm of the soil
surface;

d. Have a CEC (by NH,OAc pH 7) of 24 or more cmol(+)
kg"! clay*® in the major part of the soil below a depth of 25
cm but above 100 cm or a lithic or paralithic contact if one
is shallower than 100 cm.

e. Have a content of organic carbon that decreases regularly
with depth to the base of the cambic horizon, or have slopes
>25 percent; and

f. Have a udic moisture regime.

Andic Humitropepts are like Typic Humitropepts except for
@ or for a and e.

Andic Ustic Humitropepts are like Typic Humitropepts
except for a and /, with or without e, and they have an
ustic moisture regime,

Fluventic Humitropepts are like Typic Humitropepts except
for e.

Lithic Humitropepts are like Typic Humitropepts except for

c.
Oxic Humitropepts are like Typic Humitropepts except for
d.

Ustic Humitropepts are like Typic Humitropepts except for
f, and they have an ustic moisture regime,

Ustoxie Humitropepts ate like Typic Humitropepts except
for d and f, and they have an ustic moisture regime,

Sombritropepts

These soils are the dark, humus-rich Tropepts of perhumid,
cool, hilly or mountainous regions. They have a sombric
horizon in or below a cambic horizon. Most of them have
an umbric epipedon, a perudic soil moisture regime, and an
isomesic temperature regime. They are not known to occur
in the United States and their classification has not been
developed.

Ustropepts
Distinctions between Typic Ustropepts and other subgroups

Typic Ustropepts are the Ustropepts that

a. Do not have mottles that have chroma of 2 or less within
1 m of the soil surface if the mottled horizon is saturated
with water at some time of the year or if there is artificial
drainage;

b. Have a content of organic carbon that decreases regularly
with depth and, unless a lithic or a paralithic contact occurs
at a shallower depth, reaches a level of 0.2 percent organic
carbon or less within 1.25 m of the soil surface; or have
slopes >25 percent;

c. Have a cambie horizon;

d. Do not have a lithic contact within 50 cm of the soil
surface;

‘Tesome cambio horiaone that have pra
‘some cambic horizons that have properties that approach thore of an oxic

horizon do not disperse well. If the ratio of the percentage of water retained

at tension of 1500 kPa to the percentage of measured clay is 0.6 or more, the
percentage of clay is determined by the higher value of (1) the measured per-
cantage of clay or (2) 2.6 times the percentage of water retained at tension of
1500 kPa.



169
Haplumbrepts

Distinctions between Typic Haplumbrepts and other
subgroups

Typic Haplumbrepts are the Haplumbrepts that
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
b. Do not have mottles that have chroma of 2 or less within
50 cm of the soil surface if the mottled horizon is saturated
with water at some time of the year when its temperature is
>5°C or if there is artificial drainage;
c. Have a cambic horizon;
d. Have a content of organic carbon’® that decreases
regularly with depth or have slopes >25 percent;
e. Do not have a lithic contact within 50 cm of the soil
surface;
f. Have an umbric or a mollic epipedon that is <50 cm
thick; and
g. Have texture finer than loamy fine sand within a depth
of 50 cm,
Andic Haplumbrepts are like Typic Haplumbrepts except for
a or for a and f,
Andaquic Haplumbrepts are like Typic Haplumbrepts except
for a and b or a, b, and f.
Cumulic Haplumbrepts are like Typic Haplumbrepts except
for f and d, with or without 6 or c, or both.
Entic Haplumbrepts are like Typic Haplumbrepts except for

c.
Fluventic Haplumbrepts are like Typic Haplumbrepts except
for d.

Lithic Haplumbrepts are like Typic Haplumbrepts except for
e or for c and e.

Pachic Haplumbrepts are like Typic Haplumbrepts except for
J, with or without 6 or c, or both,

Quartzipsammentic Haplumbrepts are like Typic
Haplumbrepts except for c and g, with or without f. They
have sandy texture to a depth of 1 m or more, and have in
the 0.02 to 2mm fraction more than 90 percent silica
minerals (quartz, chalcedony or opal) or other extremely
durable minerals that are resistant to weathering.

Xerumbrepts

Distinctions between Typic Xerumbrepts and other
subgroups

Typic Xerumbrepts are the Xerumbrepts that
a, Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizon is saturated
Tre cubon Should bo ol Holecaunn, ‘

"The carbon should be of Holocene age It is not the intent to include foesil
carbon from bedrock.


173

(1) a ratio of measured clay to 1500 kPa water
(percentages)of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
b. Have an abrupt textural change from the albic to the
argillic horizon;
¢. When not irrigated, are not dry in all parts of the
moisture control section for as long as 45 consecutive days
during the 120 days following the summer solstice in more
than 6 out of 10 years.
Argiaquic Argialbolls are like Typic Argialbolis except for b.
Argiaquic Xeric Argialbolls are like Typic Argialbolls except
for b and c.
Xeric Argialbolls are like Typic Argialbolls except for c.

Natralbolls
Natralbolls are the Albolls that have a natric horizon,
Aquolls

Key to great groups

GBA, Aquolls that have a cryic or pergelic temperature
regime,
Cryaquolls, p. 174

GBB. Other Aquolls that have a duripan that has its upper
boundary within 1 m of the surface.
Duraquolls, p, 175

GBC. Other Aquolls that have a natric horizon,
Natraquolls, p. 176

GBD. Other Aquolls that have a calcic or gypsic horizon

that has its upper boundary within 40 cm of the surface and

do not have an argillic horizon unless it is a buried horizon.
Calciaquolls, p. 174

GBE. Other Aquolls that have an argillic horizon.
Argiaquolls, p. 173

GBF, Other Aquolls.
Haplaquolls, p. 175

Argiaquolls
Distinctions between Typic Argiaquolls and other subgroups

Typic Argiaquolls are the Argiaquolls that

a, Do not have an argillic horizon that has an increase in

clay content of 20 percent (absolute) or more within a

vertical distance of 7.5 cm from the upper boundary;

b. Have a texture finer than loamy fine sand in some

subhorizon within 50 cm of the surface; and

¢. Do not have the following combination of characteristics:
(4) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
of the soil or to the base of the Ap horizon,



35
Chapter 2

Horizon: d_ Pi rties Diagnostic for th
onbligher Categories: Organic Soils

Organic Soil Materials
Organic soil materials and organic soils:

1. Are saturated with water for long periods or are artifi-
cially drained and, excluding live roots, (a) have 18 percent
or more organic carbon if the mineral fraction is 60 percent
or more clay, (b) have 12 percent or more organic carbon if
the mineral fraction has no clay, or (c) have a proportional
content of organic carbon between 12 and 18 percent if the
clay content of the mineral fraction is between zero and 60
percent; or

2. Are never saturated with water for more than a few days
and have 20 percent or more organic carbon.

Definition Of Organic Soils
Organic soils (Histosols) are soils that

1, Have organic soil materials that extend from the surface
to one of the following:
a. A depth within 10 cm or less of a lithic or paralithic
contact, provided the thickness of the organic soil mate-
rials is more than twice that of the mineral soil above the
contact; or
b. Any depth if the organic soil material rests on frag-
mental material (gravel, stones, cobbles) and the inter-
stices are filled with organic materials, or rests on a lithic
or paralithic contact; or

2. Have organic materials that have an upper boundary
within 40 cm of the surface and
a. Have one of the following thicknesses:

(1) 60 cm or more if three-fourths or more of the

volume is moss fibers or the moist bulk density is <0.1

g per cubic centimeter (6.25 Ibs per cubic foot);

(2) 40 cm or more if
(a) The organic soil material is saturated with water
for long periods (>6 months) or is artificially
drained; and
(b) The organic material consists of sapric or hemic
materials or consists of fibric materials that are less
than three-fourths moss fibers by volume and a
moist bulk density of 0.1 or more; and

b. Have organic soil materials that

(1) Do not have a mineral layer as much as 40 cm

thick either at the surface or whose upper boundary is

within a depth of 40 cm from the surface; and

(2) Do not have mineral layers, taken cumulatively, as

thick as 40 cm within the upper 80 cm.

It is a general rule that a soil is classed as an organic soil
(Histosol) either if more than half of the upper 80 cm (32
in.) of soil is organic or if organic soil material of any


179
Cryoborolls
Distinctions between Typic Cryoborolls and other subgroups

Typic Cryoborolls are the Cryoborolls that
a, Do not have an argillic horizon;
b. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
per cubic centimeter or less in the fine-earth fraction, and
that has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
c. Do not have distinct or prominent mottles that are due to
segregation of iron or manganese within | m of the surface
if artificially drained, or if undrained, are not continuously
saturated with water within a depth of | m for as long as 90
days;
d, Do not have a calci¢ horizon within or immediately under
the mollic epipedon unless the lower part of the mollic
epipedon is also an argillic horizon;
e. Have a mollic epipedon that is <40 cm thick or that has
texture of loamy fine sand or coarser;
f. Have a mollic epipedon that is continuous throughout
each pedon;
g. Do not have a lithic contact within 50 cm of the surface;
h. Have a mean annual soil temperature higher than 0°C;
i, Do not have an albic horizon immediately below the
molli¢ epipedon;
j. Do not have a duripan that has its upper boundary within
1 m of the soil surface;
k, Have a regular decrease in organic carbon content with
increasing depth and unless a lithic or a paralithic contact is
at some depth between 50 cm and 1.25 m below the soil
surface, have an organic carbon content of 0.3 percent or
Jess at a depth within 1.25 m of the surface; or the slope is
>25 percent; and
1, Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are I cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part, and that extend upward to the surface
or to the base of an Ap horizon; and
(2) A potential linear extensibility of 6 cm or more in
the upper I m of the soil or the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1m; and
(3) More than 35 percent clay in horizons that total more
than 50 cm in thickness,
Abruptic Cryoborolls are like Typic Cryoborolls except for a
and j and have an increase in clay content of 20 percent
(absolute) or more within a vertical distance of 7.5 cm below
the upper boundary of the argillic horizon,
Andeptic Cryoborolls are like Typic Cryoborolls except for b
or for 6 and e.
Aquic Cryoborolts are like Typic Cryoborolls except for c.
Argiaquic Cryoborolls are like Typic Cryoborolls except for
g and c.

Mi


237

Chapter 13
Ultisols
Key To Suborders

FA, Ultisols, either saturated with water at some time of
year or artificially drained, that have characteristics associ-
ated with wetness, namely, mottles, iron-manganese concre-
tions >2 mm in diameter, or chroma, moist, of 2 or less im-
mediately below any Ap or A horizon that has a value,
moist, of fess than 3.5 when rubbed; and also one or more of
the following:
1, Dominant chroma, moist, of 2 or less in coatings on the
surface of peds and mottles within the peds, or dominant
chroma of 2 or less in the matrix of the argillic or kandic
horizon and mottles of higher chroma (if the hue is redder
than 10YR because of parent materials that remain red after
citrate-dithionite extraction, the requirement for low chroma
is waived);
2. Chroma, moist, of | or less on surfaces of peds or in the
matrix of the argillic or kandic horizon; or
3, Dominant hue of 2.5Y or 5Y in the matrix of the argillic
or kandic horizon and distinct or prominent mottles and also
a thermic or isothermic or warmer soil temperature regime.
Aquults, p. 237

FB, Other Ultisols that have either or both of the following

characteristics:

1, Have 0.9 percent or more organic carbon in the upper 15

cm of the argillic horizon; or

2. Have !2 kg or more organic carbon in the soil per square

meter to a depth of 1 m below the top of the mineral soil

surface, exclusive of any O horizon that may be present,
Humults, p. 241

FC, Other Ultisols that have a udic moisture regime.
Udults, p. 245

FD, Other Ultisols that have an ustic moisture regime.
Ustults, p. 252

FE. Other Ultisols that have a xeric moisture regime.
Xerults, p. 257

Aquults
Key to great groups

FAA. Aquults that have plinthite that forms a continuous
phase or constitutes more than half the matrix of some sub-
horizon within 1.5 m of the soil surface.

Plinthaquults, p. 241

FAB. Other Aquults that have a fragipan and, if there is 5
percent or more by volume of plinthite in some subhorizon,
the upper boundary of the fragipan is within 1 m of the
surface of the soil.

Fragiaquults, p. 239


117

present, few series have been established for Arents in the
United States.

Arents are the Entisols that

1, Have fragments of diagnostic horizons that occur more or
less without discernible order in the soil below any Ap
horizon but within a depth of | m; and

2, Are not permanently saturated with water and do not
have the characteristics associated with wetness that are de-
fined for Aquents.

Hapludollic Arents have a udic moisture regime and frag-
ments of a mollic epipedon within the upper 1 m of the soil.
Udalfic Arents have a udic moisture regime and fragments
of an argillic horizon that has base saturation (by sum of
cations) that is 35 percent or more within the upper 1 m of
the soil.

Fluvents
Key to great groups

IDA. Fluvents that have a cryic soil temperature regime.
Cryofluvents, p. 117

IDB. Other Fluvents that have a xeric moisture regime.
‘Xerofluvents, p. 120

JDC. Other Fluvents that have an ustic moisture regime.
Ustifluvents, p 119

JDD. Other Fluvents that have a torric moisture regime.
Torrifluvents, p. 118

IDE. Other Fluvents that have an isomesic, isothermic, or
isohyperthermic temperature regime,
Tropofluvents, p. 119

IDF. Other Fluvents.
Udifluvents, p. 119

Cryofluvents

Distinctions between Typic Cryofluvents and other sub-
groups

Typic Cryoftuvents are the Cryofluvents that

a, Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density in the fine-earth fraction (at 33 kPa
moisture tension) of 0.95 g per cubic centimeter or Jess, and
that has either (1) a ratio of measured clay to 1500 kPa wa-
ter (percentages) of 1.25 or less or (2) a ratio of CEC (at pH
near 8) to 1500 kPa water of more than 1,5 and more ex-
change acidity than the sum of bases plus KCl-extractable
aluminum;

b. Do not have mottles that have chroma of 2 or less within
50 cm of the soil surface; and

¢. Have an Ap horizon that has a color value, moist, of 4 or
more or has a color value, dry, of 6 or more when crushed


271
DESIGNATIONS FOR HORIZONS AND LAYERS

Genetic horizons are not the equivalent of the diagnos-
tic horizons of Soil Taxonomy. Designations of genetic
horizons express a qualitative judgment about the kind of
changes that are believed to have taken place. Diagnostic
horizons are quantitatively defined features used to differ
entiate between taxa. The diagnostic horizons may encom-
pass several genetic horizons, and changes implied by ge-
netic horizon designations may not be large enough to jus-
tify recognizing different diagnostic criteria

MASTER HORIZONS AND LAYERS

The capital letters O, A, E, B, C, and R represent

the master horizons and layers of soils. The capital letters
are the base symbols to which other characters are added to
complete the designations, Most horizons and layers are
given a single capital letter symbol; some require two.

O horizons or layers: Layers dominated by organic material,
except limnic layers! that are organic. Some are saturated
with water for long periods or were once saturated but are
now artificially drained; others have never been saturated.

Some O layers consist of undecomposed or partially de-
composed litter, such as leaves, needles, twigs, moss, and
lichens, that has been deposited on the surface; they may
be on top of either mineral or organic soils, Other O
layers, called peat, muck, or mucky peat, are organic
material that was deposited underwater and that has de-
composed to varying stages. The mineral fraction of such
material is only a small percentage of the volume of

the material and generally is much less than half of the
weight. Some soils consist entirely of material designated
as O horizons or layers.

An O layer may be on the surface of a mineral soil or at
any depth beneath the surface if it is buried. A horizon
formed by illuviation of organic material into a mineral
subsoil is not an O horizon, though some horizons formed
in this manner contain much organic matter.

A limnic layer that is organic is designated a C layer.

A horizons: Mineral horizons that formed at the surface or
below an O horizon and
(1) are characterized by an accumulation of humified
organic matter intimately mixed with the mineral frac-
tion and not dominated by properties characteristic of
E or B horizons (defined below) or
(2) have properties resulting from cultivation, pastur-
ing, or similar kinds of disturbance.

If a surface horizon has properties of both A and E
horizons but the feature emphasized is an accumula-
tion of humified organic matter, it is designated an A

ee
Coprogenous earth, diatomaceous earth, mari.



198

Durixerolls
Distinctions between Typic Durixerolls and other subgroups

Typic Durixerolls are the Durixerolls that

a. Do not have an argillic horizon that has an increase in
clay content of 20 percent (absolute) or more within a ver-
tical distance of 7.5 cm or an increase of 15 percent or more
(absolute) within a distance of 2.5 cm at the upper bound-
ary;

'b. Have a duripan that is massive, platy, or prismatic and
that has half or more of its upper boundary indurated or
coated with opal or opal and sesquioxides or that is in-
durated in some subhorizon below its upper boundary;

c. Have an argillic horizon above the duripan;

d, Have a xeric moisture regime; and

e, Do not have mottles that have chroma of 2 or less above
the duripan.

Abruptic Aridic Durixerolls are like Typic Durixerolls except
for a and d and have an aridic moisture regime that borders
on xeric,

Argic Durixerolls are like Typic Durixerolls except for b.
Aridic Durixerolls are like Typic Durixerolls except for d
and have an aridic moisture regime that borders on xeric.
Entic Durixerolls are like Typic Durixerolls except for b and

co
Haplic Durixerolls are like Typic Durixerolls except for c.
Orthidic Durixerolls are like Typic Durixerolls except for ¢
and d and have an aridic moisture regime that borders on
xeric.

Haploxerolls
Distinctions between Typic Haploxerolls and other subgroups

Typic Haploxerolls are the Haploxerolls that

a. Do not have mottles that have chroma of 2 or less within
75 cm of the surface if artificially drained and if undrained,
are not continuously saturated with water within 1 m of the
soil surface for 90 days or more in most years;

b. Do not have a calcic horizon or soft, powdery secondary
lime within a depth of 1.5 m if the weighted average parti-
cle-size class of all horizons between a depth of 25 cm and
1 m, or between a depth of 25 cm and a lithic or paralithic
contact that is shallower than | m, is sandy; within 1.1 m if
the average particle-size class is loamy; or within 90 cm if it
is clayey;

c, Have a mollic epipedon that is <50 cm thick or texture
that is loamy fine sand or coarser if the mollic epipedon is
250 cm thick;

d. Do not have a horizon within 1 m of the surface that is >
15 cm thick that either contains at least 20 percent durin-
odes in a nonbrittle matrix or is brittle and has firm consis-
tence when moi:

e, Have a cambic horizon, or the lower part of the epipedon
meets the requirements of a cambic horizon except for color
value, and either the cambic horizon or the lower part of
the epipedon is free of carbonates in some part;

f. Have a regular decrease in organic carbon content with
increasing depth and unless a lithic or a paralithic contact is
at some depth between 50 cm and 1.25 m below the soil



269
Udorthents

Ustropepts..
UStults ...sssessee

Vermiborolls ...sesesee
Vermudolls.
Vermustolls.......
Vitrandepts

Weatherable minerals ..

Xerofluvents.
Xerolls.....
Xeropsamments
Xerorthents
Xerults oo
Xerumbrepts..



263
Index

Abrupt textural change.

Be BBB oo

3

19
50
146

0

3

Argillic horizon ..
Argiudolls
Argiustolls.
Argixerolls

Calcic horizon and k horizon
Calciorthids.
Calciustolls.
Calcixerolls
Cambic horizon ..
Camborthids..

Classes of permanent cracks.


278

Conventions for using letter suf fixes.--Many master hori-
zons and layers that are symbolized by a single capital letter
will have one or more lower case letter suffixes. Common
exceptions are an undisturbed A horizon and many, if not
most, E and C horizons and layers. Seldom are more than
three suffixes needed.

When letter suffixes are used, they immediately follow
the capital letter. If a surface horizon is disturbed, only "
is used except where there are surface accumulations of
CaCO,, CaSO, or more soluble salts.

When more than one suffix is needed, the following letters,
if used, are written first: a, e, i, h, r, s, t, and w. Except
for Bhs or Crt‘ horizons, none of these letters are used in
combination in a single horizon.

A horizon is never designated Bth, Bts, or Btw, though a
Bw, Bs, or Bh horizon may be above or below a Bt horizon.
AB horizon that has a significant accumulation of clay and
also shows evidence of development of color or structure, or
both, is designated Bt, ("t" has precedence over "w", "s", and
“h"). A B horizon that is gleyed or that has accumulations of
carbonates, silica, gypsum, salts more soluble than gypsum,
or residual accumulation of sesquioxides carries the appro-
priate symbol--g, k, q, y, 2, or 0. If illuvial clay is also
present, "t" precedes the other symbol: Bto. Suffixes "h*,
"s", and "w" are not used with g, k, q, y, z, or 0.

If a horizon is buried, the suffix “b" is written last.
Suffix "b" is used only for buried mineral soils. If more
than one suffix is needed and the horizon is not buried,
these symbols, if used, are written last: c, f, g, m, and x,
Some examples: Btc, Ckm, and Bsv.

Lower case letter suffixes are not used with transi-

tional horizons unless needed for explanatory purposes; for
example, use of "k" is appropriate in the sequence A~ACkI-
ACKk2-AC-C to indicate an accumulation of carbonates in
the upper parts of the AC horizon,

Vertical subdivision.--Commonly a horizon or layer desi
nated by a single combination of letters needs to be subdi-
vided. The Arabic numerals used for this purpose always
follow all letters, Within a C, for example, successive layers
could be Cl, C2, C3, etc.; or if the lower part is gleyed and
the upper part is not, the designations could be C1-C2-Cgl-
Cg? or C-Cgl-Cg2-R.

‘These conventions apply whatever the purpose of subdivi-
sion. In many soils, horizons that would be identified by
one unique set of letters are subdivided on the basis of evi-
dent morphological features, such as structure, color, or
texture, These divisions are numbered consecutively. The
numbering starts with 1 at whatever level in the profile any
element of the letter symbol changes. Thus Btl-Bt2-Btkl-
Btk2 is used, not Btl-Bt2-Btk3-Btk4, The numbering of
vertical subdivisions within a horizon is not interrupted at a
discontinuity (indicated by a numerical prefix) if the same

Tindicating weathered bedrock or eapr is
Indicating waathared bedrock or esprolite in which clay akins are present.


231

e, Have an umbric epipedon or one that would meet the re-
quirements for an umbric epipedon if plowed to a depth of
25 to 30 cm;
f. Do not have a sandy epipedon (loamy fine sand or coarser
throughout) that is 75 cm or more thick on the average for
the thinnest half of the pedon;
g. Have a spodic horizon that has a weighted average of 0.6
percent or more organic carbon in the matrix of the upper
30 cm of the spodic horizon or have an upper subhorizon of
the spodic horizon that
(1) Has 2,3 percent or more organic carbon in the upper
2 cm; and
(2) Is continuous or is present in >90 percent of each pe-
don; and
h, Have in 50 percent or more of each pedon a spodic
horizon in which some subhorizon has a ratio of free iron
(by dithionite-citrate) to carbon (both elemental) of <0.2.
Aeric Tropaquods are like Typic Tropaquods except for e.
Aeric Arenic Tropaquods are like Typic Tropaquods except
for e and f, and the upper boundary of the spodic horizon is
between 75 cm and 1.25 m below the soil surface.
Aeric Grossarenic Tropaquods are like Typic Tropaquods
except for e and f, and the upper boundary of the spodic
horizon is between 1.25 m and 2 m below the soil surface.
Entic Tropaquods are like Typic Tropaquods except for g.
Histic Tropaquods are like Typic Tropaquods except for a.
Histic Lithic Tropaquods are like Typic Tropaquods except
for a and d.
Ultic Tropaquods are like Typic Tropaquods except for c,
with or without e.

Ferrods

This suborder is provisional. Ferrods are not known to oc-
cur in the United States, but the suborder is provided for
use elsewhere. The classification has not been developed.

Ferrods are the Spodosols that

1, Have a spodic horizon that has in all subhorizons a ratio
of percentage of free iron (by dithionite-citrate) to per-
centage of carbon (both elemental) of 6 or more; and

2, Do not have an aquic moisture regime or artificial
drainage or do not have the characteristics associated with
wetness as defined for Aquods.

Humods
Key to great groups

BCA. Humods that have a placic horizon in the spodic
horizon.

Placohumods, p. 233

BCB. Other Humods that have an isomesic or warmer iso
temperature regime.
Tropohumods, p. 233

BCC, Other Humods that have a fragipan below the spodic
horizon,
Fragihumods, p. 232


139

the United States, a precise definition is not attempted here.
It should be noted, however, that they are normally acid and
that they have been cultivated for a long time.

Medihemists

Distinctions between Typic Medihemists and other sub-
groups

Typic Medihemists are the Medihemists that
a. Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier;
b, Have
(1) Less than 25 cm of the subsurface and bottom tiers
consisting of fibric materials; and
(2) Less than 25 cm of the subsurface and bottom tiers
consisting of sapric materials,
¢, Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier;
d, Do not have a layer of water within the control section
beneath the surface tier;
¢. Do not have limnic layer(s) that are 5 cm or more thick
within the control section; and
f. Do not have a lithic contact within the control section,
Fibric Medihemists are like Typic Medihemists except for
1).
Fibric Terric Medihemists are like Typic Medihemists except
for b(1) and ¢, with or without a or e, or both.
Fluvaquentic Medihemists are like Typic Medihemists except
for a, with or without b.
Hydric Medihemists are like Typic Medihemists except for
d.

Limnic Medihemists are like Typic Medihemists except for
e, with or without a or 4, or both.

Lithic Medihemists are like Typic Medihemists except for /,
with or without all or any of a, 6, c, or e.

Sapric Medihemists are like Typic Medihemists except for
(2).

Sapric Terric Medihemists ate like Typic Medihemists ex-
cept for b(2) and c, with or without a or e, or both.

Terric Medihemists are like Typic Medihemists except for c,
with or without a or e, or both.

Sulfihemists
Distinctions between Typic Sulfihemists and other subgroups

Typic Sulfihemists are the Sulfihemists that

a, Do not have a mineral layer 30 cm or more thick that has
its lower boundary in the control section below the surface
tier,

Terric Sulfihemists are like Typic Sulfihemists except for a.


181

(b) A moisture control section that is dry in some part
Jess than six-tenths of the time that the soil
temperature at a depth of 50 cm is above 5°C in most
years; and
(2) A chroma, moist, after rubbing of 1.5 or more in the
upper part of the mollic epipedon after it has been mixed
to a depth of 18 cm or in any Ap horizon that is >18 cm
thick, and the soil is dry in all parts of the moisture
control section at some time in most years;
d. Have a cambic horizon, or the lower part of the mollic
epipedon meets the requirements of a cambic horizon except
for color and organic-carbon content;
e. Have a regular decrease in organic carbon content with
increasing depth and unless a lithic or a paralithic contact is
at some depth between 50 cm and 1.25 m below the soil
surface, have an organic carbon content of 0.3 percent or
less at a depth within 1.25 m of the surface; or the slope is
>25 percent; and
f. Do not have a lithic contact within 50 cm of the surface;
g. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm and that are at least 30
cm long in some part and that extend upward to the
surface or to the base of an Ap horizon;
(2) Potential linear extensibility of 6 cm or more in the
upper | m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness;
‘h, Do not have a salic horizon that has its upper boundary
within 75 cm of the surface; and
i. Have a mollic epipedon <40 cm thick, or the epipedon has
a sandy particle-size class in the major part, or there is a
paralithic contact or a sandy contrasting layer between
depths of 40 and 50 cm.
Aquic Haploborolls are like Typic Haploborolls except for b,
with or without c or d, or both.
Aridi¢ Haploborolls are like Typic Haploborolls except for
all or part of ¢(1).
Cumulic Haploborolls are like Typic Haploborolls except for
i and e, with or without all or any of b, d, and c(/), and
have a concave shape.
Cumulic Udic Haploborolls are \ike Typic Haploborolls
except for i, e, and c(2), with or without 5 or d, or both,
and have a concave shape.
Entic Haploborolls are like Typic Haploborolls except for d.
Fluvaquentic Haploborolls are like Typic Haploborolls except
for b and ¢, with or without either d or ¢, or both.
Fluventic Haploborolls are like Typic Haploborolls except for
e, with or without d.
Lithic Haploborolls are like Typic Haploborolls except for f,
with or without any or all of c, d, or i,
Pachic Haploborolls are like Typic Haploborolls except for i,
with or without any or all of 5, d, or (1).
Pachi¢ Udic Haploborolls are \ike Typic Haploborolls except
for i and ¢(2), with or without 4 or d, or both.
Ruptic-Lithic Haploborolls are like Typic Haploborolls
except for /, with or without @, and bedrock is within a
depth of 50 cm in part of each pedon.


57

Chapter 4

Identification of the Taxonomic
lass of a Soil

Key To Soil Orders

In this key and the other keys that follow, the diagnostic
horizons and the properties mentioned do not include the
Properties of buried soils except their organic carbon if of
Holocene age and base saturation. Properties of buried soils
are considered in the categories of subgroups, families, and
series but not in those of order, suborder, and great group.
The meaning of the term “buried soil" has been given previ-
ously.

A. Soils that

either
1, Have organic soil materials that extend from the sur-
face to one of the following:

a, A depth within 10 cm or Jess of a lithic or par-
lithic contact, provided the thickness of the organic
soil materials is more than twice that of the mineral
soil above the contact; or
b. Any depth if the organic soil material rests on
fragmental material (gravel, stones, cobbles) and the
interstices are filled with organic materials, or rests on
a lithic or paralithic contact;

or
2. Have organic materials that have an upper boundary
within 40 cm of the surface,
and
a. Have one of the following thicknesses:
(1) 60 om or more if three-fourths or more of the
volume is moss fibers or the moist bulk density is
<0.1 g per cubic centimeter (6.25 Ibs per cubic
foot); or
(2) 40 cm or more if
(a) The organic soil material is saturated with
water for long periods (>6 months) or is artifi-
cially drained: and
(b) The organic material consists of sapric or
hemic materials or consists of fibric materials
that are less than three-fourths moss fibers by
volume and have a moist bulk density of 0.1 or
more;
and
b. Have organic soil materials that
(1) Do not have a mineral layer as much as 40 cm
thick either at the surface or whose upper boundary
is within a depth of 40 cm from the surface; and
(2) Do not have mineral layers, taken cumulatively,
as thick as 40 cm within the upper 80 cm.
Histosols, p. 131


114

paralithic contact is deeper than 50 cm but shallower than
1m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness;
d. Have an Ap horizon that has a color value, moist, of 4 or
more or has a color value, dry, of 6 or more when crushed
and smoothed, or the A horizon is <15 cm thick if its color
value, moist, is <3.5;
e. Do not have a buried Histosol or a buried histic epipedon
that has its upper boundary within 1 m of the soil surface;
f. Do not have sulfidic materials within 1 m of the mineral
soil surface; and
g. Have a difference of 5°C or more between the mean
summer and mean winter soil temperatures at a depth of 50
cm or at a lithic or paralithic contact, whichever is
shallower.
Aeric Fluvaquents are like Typic Fluvaquents except for a or
aand d.
Aeric Tropic Fluvaquents are like Typic Fluvaquents except
for a and g, with or without d.
Andaqueptic Fluvaquents are like Typic Fluvaquents except
for 6.
Humaqueptic Fluvaquents are like Typic Fluvaquents except
for d, and the base saturation (by NH,OAc) is <50 percent
in some horizon and does not increase’ to 50 percent or more
within a depth of 1 m below the soil surface.
Mollic Fluvaguents are like Typic Fluvaquents except for d,
and the base saturation (by NH,OAc) is 50 percent or more
throughout the soil or increases “to 50 Percent or more within
a depth of 1 m below the soil surface.
Sul fic Fluvaquents are like Typic Fluvaquents except for f.
Thapto-Histic Fluvaquents are like Typic Fluvaquents except
for e with or without a or d or both.
Thapto-Histic Tropic Fluvaquents are like Typic Fluvaquents
except for e and g, with or without d.
Tropic Fluvaquents are like Typic Fluvaquents except for g
or for g and d.
Vertic Fluvaquents are like Typic Fluvaquents except for c,
with or without a or @, or both, and the cracks are not open
permanently,

Haplaquents
Distinctions between Typic Haplaquents and other subgroups

Typic Haplaquents are the Haplaquents that
a, Have in 60 percent or more of the matrix in all
subhorizons between the Ap horizon or a depth of 25 cm,
whichever is deeper, and 75 cm one or more of the
following:
(1) If mottled and
(a) If the hue is 2.5Y or redder® and the value, moist,
is more than 5, the chroma, moist, is 2 or less;
(b) If the hue is 2.SY or redder and the value, moist,
is 5 or less, the chroma, moist, is 1 or less;

Sir the hue of the matrix is 7.6YR or redder and if pede are present, pad exte-
iors have dominant chroma, moist, of 1 or leso, and ped interiors have mottles
that have chrome, moist, of 2 or less; if peds are absent, the chroma, moist, is
1 oF less immediately below any surface horizon that has value, moist, lesa
than 3.5,



76

zons are saturated with water at some season when the soil
temperature is 5°C.

Aquic Fraglossudalfs are like Typic Fraglossudalfs except
for a.

Glossudalfs
Distinctions between Typic Glossudalfs and other subgroups

Typic Glossudalfs are the Glossudalfs that

a. Do not have mottles that have chroma of 2 or less in the
upper 25 cm of the argillic horizon if the mottled horizons
are saturated with water at some season when their temper-
ature is 5°C or higher;

b. Have tongues of afbic materials that extend through at
least the upper 50 cm of the argillic horizon;

c. Do not have a brittle matrix in one-fourth or more of
some subhorizon that is at least 10 cm thick and that has an
upper boundary within 1,25 m of the surface; and

d, Have within 50 cm of the surface a texture finer than
loamy fine sand in some subhorizon.

Aquic Glossudalfs are like Typic Glossudalfs except for a,
with or without b.

Arenic Glossudalfs are like Typic Glossudalfs except for d.
Fragic Glossudalfs are like Typic Glossudalfs except for c,
or for a and c.

Haplic Glossudalfs are like Typic Glossudalfs except for b.

Hapludalfs
Distinctions between Typic Hapludalfs and other subgroups

Typic Hapludalfs are the Hapludalfs that
a, Do not have an abrupt textural change if there are mot-
tles in the upper 25 cm of the argillic horizon;
b. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
per cubic centimeter or less in the fine-earth fraction, and
that has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
. Have an argillic horizon that
(J) If its upper boundary is <50 cm below the soil sur-
face, does not have motties that have chroma of 2 or less
in the upper 25 cm if it is saturated with water within
that depth at some time when the soil temperature is 5°C
or higher; or
(2) If the upper boundary of the argillic horizon is
deeper than 50 cm, does not have mottles that have
chroma of 2 or less within a depth of 75 cm below the
soil surface;
d, Have, within 50 cm of the surface, texture finer than
loamy fine sand in some subhorizon;
e. Do not have interfingering of albic materials and albic
materials surrounding some peds in the upper part of the
argillic horizon;



28

If precipitation exceeds evapotranspiration in all months of
most years, there are occasional brief periods when some
stored moisture is used, but the moisture tension rarely be-
comes as great as 100 kPa in the soil moisture control sec~
tion. The water moves through the soil in all months that it
is not frozen, This extremely wet moisture regime is called
“perudic" (L. per, throughout in time, L. udus, moist). The
formative element ud is used in the names of most taxa to
indicate either a udic or a perudic regime. The formative
element per is used in selected taxa,

Ustic moisture regime.--The ustic (L. ustus, burnt, implying
dryness) moisture regime is intermediate between the aridic
and the udic regime. The concept is one of limited mois-
ture, but the moisture is present at a time when conditions
are suitable for plant growth. The ustic moisture regime is
not applied to soils that have cryic or pergelic temperature
regimes, which are defined later.

If the mean annual soil temperature is 22°C or higher or if
the mean summer and winter soil temperatures differ by
<5°C at a depth of 50 cm, the soil moisture control section
in the ustic moisture regime is dry in some or all parts for
90 or more cumulative days in most years. But the moisture
control section is moist in some part for more than 180 cu~
mulative days, or it is continuously moist in some part for at
least 90 consecutive days.

If the mean annual soil temperature is lower than 22°C and
if the mean summer and winter soil temperatures differ by
53°C or more at a depth of 50 cm, the soil moisture controf
section in the ustic regime is dry in some or all parts for 90
or more cumulative days in most years. But it is not dry in
all parts for more than half the time that the soil tempera-
ture is higher than 5°C at a depth of 50 cm (the aridic and
torric regimes). Also, it is not dry in all parts for as long as
45 consecutive days in the 4 months that follow the summer
solstice in 6 or more years out of 10 if the moisture control
section is moist in all parts for 45 or more consecutive days
in the 4 months that follow the winter solstice in 6 or more
years out of 10 (xeric regime).

In tropical and subtropical regions that have either one or
two dry seasons, summer and winter have little meaning, In
those regions, the ustic regime is that typified in a monsoon
climate that has at least one rainy season of 3 months or
more. In temperate regions of subhumid or semiarid cli-
mates, the rainy seasons are usually spring and summer or
spring and fall, but never winter. Native plants are mostly
annuals or they have a dormant period while the soil is dry.

Xeric moisture regime,-~-The xeric moisture regime (Gr.
xeros, dry) is that typified in Mediterranean climates, where
winters are moist and cool and summers are warm and dry.
The moisture, coming in winter when potential evapotran-
spiration is at a minimum, is particularly effective for
leaching. In a xeric moisture regime, the soil moisture con~
trol section is dry in all parts for 45 or more consecutive
days within the 4 months that follow the summer solstice in
6 or more years out of 10. It is moist in all parts for 45 or
more consecutive days within the 4 months that follow the


95

Chapter 6
Aridisols
Key To Suborders

EA, Aridisols that have an argillic or a natric horizon.
Argids, p, 95

EB. Other Aridisols.
Orthids, p. 102

Argids
Key to great groups

EAA. Argids that have a duripan? below an argillic horizon
and do not have a natric horizon.
Durargids, p. 95

EAB, Other Argids that have a duripan below a natric
horizon,
Nadurargids, p. 99

EAC. Other Argids that have a natric horizon and do not
have a petrocalcic horizon.
Natrargids, p. 99

EAD, Other Argids that do not have a lithic or paralithic
contact within 50 cm of the soil surface, that have a
petrocalcic horizon or that have an argillic horizon that has
35 percent or more clay in some part, and that have either:
1, An increase of 15 percent or more clay (absolute)
within a vertical distance of 2.5 cm at the upper
boundary of the argillic horizon; or
2. An increase of 10 percent or more clay (absolute) if
cultivated and the lower boundary of the Ap horizon is
the upper boundary of the argillic horizon,
Paleargids, p. 101

EAE. Other Argids.
Haplargids, p. 96

Durargids
Distinctions between Typic Durargids and other subgroups

Typic Durargids are the Durargids that
a. Are not saturated with water for 90 consecutive days or
more within 1 m of the surface in most years and do not
have any of the following characteristics within 1 m of the
soil surface if there is ground water within this depth at
some time in most years:
(1) Dominant chroma of 1 or less throughout the horizons
and hue as yellow or yellower than 2.5Y in some part;
(2) Dominant chroma of 2 or less and mottles that are not
due to segregated lime;

Ty auspan ov u paivacaicle hovison this
‘A duripan or a petrocalcic horizon must have its upper boundary within 1m
of the surface to be diagnostic in Aridisols.


9

a B horizon or any other soil horizon except, in some places,
a buried soil,

An albic horizon, therefore,is defined as a surface or a
lower horizon that has such thin or discontinuous coatings
on the sand or silt particles that the hue and chroma of the
horizon are determined chiefly by the color of the sand and
silt particles.

The color value, moist, of an albic horizon is 4 or more, or
the value, dry, is 5 or more, or both. If the value, dry, is 7
or more, or the value, moist, is 6 or more, the chroma is 3
or less either dry or moist. If the value, dry, is 5 or 6, or
the value, moist, is 4 or 5, the chroma is closer to 2 than to
3 either dry or moist. If parent materials have a hue of
SYR or redder, a chroma, moist, of 3 is permitted in the al~
bic horizon if the chroma is due to the color of uncoated silt
or sand grains. Under an albic horizon there is usually a B
horizon that is an argillic or a spodic horizon, but in some
few sandy soils the underlying horizon is too weakly devel-
oped to meet the levels of accumulation required for those
horizons.

Argillic horizon.

In summary, we can say that an argillic horizon is one that

layer-lattice clays. This horizon forms be-
horizon, but it may be at the surface if a soil
has been partially truncated. It has the following properties
that can be used for identification:

1. If an eluvial horizon remains and if there is no lithologic
discontinuity between it and the argillic horizon, the argillic
horizon contains more total clay and more fine clay than the
eluvial horizon, as follows. The increases in clay are
reached within a vertical distance of 30 cm or less.
a. If any part of the eluvial horizon has <15 percent total
clay in the fine-earth fraction (<2 mm), the argillic
horizon must contain at least 3 percent more clay (13
percent versus 10 percent, for example). The ratio of
fine clay to total clay normally is greater in the argillic
horizon than in the overlying eluvial horizons or the un-
derlying horizon by about one-third or more.
b, If the eluvial horizon has >15 percent and <40 percent
total clay in the fine-earth fraction, the ratio of clay in
the argillic horizon to that in the eluvial horizon must be
1,2 or more, The ratio of fine clay to total clay in the
argillic horizon is normally greater than in the eluvial
horizon by about one-third or more.
¢. If the eluvial horizon has >40 percent total clay in the
fine-earth fraction, the argillic horizon must contain at
least 8 percent more clay or, if the total clay content ex-
ceeds 60 percent, 8 percent more fine clay (50 percent
versus 42 percent, for example).

2. An argillic horizon should be at least one-tenth as thick
as the sum of the thickness of all overlying horizons, or it
should be 15 cm or more thick if the eluvial and illuvial
horizons together are more than 1.5 m thick, If the argillic
horizon is sand or loamy sand, it should be at least 15 cm
thick. If it is composed entirely of lamellae, tamellae >] cm


7

f. Do not have a lithic contact within 50 cm of the soil sur-

face;

g. Have an Ap horizon that has a color value, moist, of 4 or

more or has a color value, dry, of 6 or more (crushed and

smoothed) or the upper soil to a depth of 18 cm, after mix-

ing, has these colors,

h, Have an argillic horizon that is continuous horizontally

and continuous vertically for at least the upper 20 cm of its

thickness and that has texture finer than loamy fine sand;

i, Have base saturation (by sum of cations) of 60 percent or

more at a depth 1.25 m below the top of the argillic hori-

zon, or 1.8 m below the soil surface, or immediately above a

lithic or paralithic contact, whichever is least;

J. Do not have the following combinations of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm and at least 30 cm long in
some part and that extend to the surface or to the base of
an Ap horizon;

(2) A coefficient of linear extensibility (COLE) of 0,09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper | m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1m; and

(3) More than 35 percent clay in horizons that total >50
cm in thickness within the control section; and

k. Do not have albic materials that constitute as mu:

percent of the volume of any subhorizon of the argilli

horizon.

Albaquic Hapludalfs are like Typic Hapludalfs except for a

and c, with or without g.

Albaquultic Hapludalfs are like Typic Hapludalfs except for

a, c, and i,

Andeptic Glossoboric Hapludalfs are like Typic Hapludalfs

except for b and e, and their mean annual soil temperature

is lower than 10°C.

Aquic Hapludalfs are like Typic Hapludalfs except for c.

Aquic Arenic Hapludalfs are like Typic Hapludalfs except

for c and d, with or without g or i, or both,

Aquic Lithic Hapludalfs are like Typic Hapludalfs except for

cand f.

Aquollic Hapludalfs are like Typic Hapludalfs except for ¢

and g.

Aquultic Hapludal fs are like Typic Hapludalfs except for c

and i, with or without g.

Arenic Hapludalfs are like Typic Hapludalfs except for d,

with or without g or i, or both.

Glossaquic Hapludalfs are like Typic Hapludalfs except for

e and c or for e, c, and g.

Glossic Hapludalfs ase like Typic Hapludalfs except for k,

with or without e or g, or both, and the mean annual soil

temperature is 10°C or higher.

Glossoboric Hapludalfs are like Typic Hapludalfs except for

e or for e and g, and their mean annual soil temperature is

Jower than 10°C.

Lithic Hapludalfs are like Typic Hapludalfs except for /,

with or without g.

Mollic Hapludalfs are like Typic Hapludalfs except for g.

Psammaquentic Hapludalfs are like Typic Hapludalfs except

for c and A, with or without all or any of d, g, or i.

ALF



83

during a period when the soil temperature at a depth of
50 cm exceeds 8°C;

g. Have an argillic horizon that has base saturation (by sum

of cations) of 75 percent or more in some part;

h, Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend to the surface or to
the base of an Ap horizon if the soil is not irrigated;

(2) A coefficient of linear extensibility (COLE) of 0.07
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.25 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.25 m; and

(3) More than 35 percent clay in horizons that total >50
cm in thickness; and

i, When neither irrigated nor fallowed to store moisture:

(1) If the soil temperature regime is mesic or thermic,
are dry less than six-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) during a period when the soil
temperature at a depth of 50 cm exceeds 5°C; or

(2) If the soil temperature regime is hyperthermic, or
isomesic or a warmer iso-temperature regime, the soils
are moist in most years in some or all parts of the mois-
ture control section for 90 consecutive days or more
during a period when the soil temperature at a depth of
50 cm exceeds 8°C.

Aquic Haplustalfs are like Typic Haplustalfs except for a or

for a and f.

Aquic Arenic Haplustalfs are like Typic Haplustalfs except

for a and 6, with or without f or g, or both.

Aquultic Haplustalfs are like Typic Haplustalf's except for a

and g, with or without /.

Arenic Haplustalfs are like Typic Haplustalfs except for 5,

with or without f or g, or both,

Arenic Aridic Haplustalfs are like Typic Haplustalfs except

for b and i.

Aridic Haplustalfs are like Typic Haplustalfs except for i.

Kanhaplic Haplustalfs are like Typic Haplustalfs except for

d, with or without g or f, or both.

Lithic Haplustalfs are like Typic Haplustalfs except for ¢,

with or without f or i, or both.

Psammentic Haplustalfs are like Typic Haplustalfs except

for e, with or without any or all of b, f, and g.

Udertic Haplustalfs are like Typic Haplustalfs except for f

and A, with or without a.

Udic Haplustalfs are like Typic Haplustalfs except for f.

Ultic Haplustalfs are like Typic Haplustalfs except for g or

for f and g.

Vertic Haplustalfs are like Typic Haplustalfs except for h,

with or without a or i or both.

Kandiustalfs

Distinctions between Typic Kandiustalfs and other sub-
groups

Typic Kandiustalfs are the Kandiustalfs that


233

g. Do not have a sandy epipedon (loamy fine sand or coarser
throughout) that is 75 cm or more thick.

Arenic Haplohumods are like Typic Haplohumods except for
g, and the upper boundary of the spodic horizon is between
75 cm and 1.25 m below the soil surface.

Arenic Ultic Haplohumods are like Typic Haplohumods ex-
cept for ¢ and d, with or without a, and the upper bound-
ary of the spodic horizon is between 75 cm and 1.25 m be-
tow the soil surface.

Entic Haplohumods are like Typic Haplohumods except for a
or for a and g, and the upper boundary of the spodic hori-
zon is within 1.25 m of the soil surface.

Ferrudalfic Haplohumods are like Typic Haplohumods ex-
cept for b.

Grossarenic Entic Haplohumods are like Typic Haplohumods
except for a and g, and the upper boundary of the spodic
horizon is between 1.25 m and 2 m below the soil surface,
Lithic Haplohumods are like Typic Haplohumods except for
c.
Orthic Haplohumods are like Typic Haplohumods except for
a(2), and the subhorizon is present in <90 percent of the
pedon,

Plaggeptic Haplohumods are like Typic Haplohumods except
for e.

Ultic Haplohumods are like Typic Haplohumods except for d
or for a and d.

Xeric Haplohumods are like Typic Haplohumods except for
f, and they have a xeric moisture regime.

Placohumods

Distinctions between Typic Placohumods and other sub-
groups

Typic Placohumods are the Placohumods that

a. Have a frigid or warmer temperature regime.

Cryic Placohumods are like the Typic Placohumods in de-
fined properties except for a. They have, however, more
organic carbon than Typic Placohumods, and in that way
they resemble Cryohumods.

Tropohumods

Tropohumods are the Humods that have an isomesic or a
warmer iso temperature regime.

Orthods
Key to great groups

BDA. Orthods that have a placic horizon in the spodic
horizon.
Placorthods, p. 236

BDB. Other Orthods that have a fragipan below the spodic
horizon.

Fraglorthods, p. 234

BDC. Other Orthods that have a cryic or pergelic tempera-
ture regime.
Cryorthods, p. 234


5

and low chroma. Soils formed in such materials may accu-
mulate appreciable amounts of organic matter but have no
visible darkening in the epipedon. In this situation, the re~
quirement that the mollic epipedon have lower value or
chroma than the 1C horizon, or than the next underlying
horizon if there is no IC, is waived if (a) the surface hori-
zon (horizons) meets all other requirements for a mollic
epipedon and, in addition, has at least 0.6 percent more or-
ganic carbon than the 1C or the 2C horizon or if (b) the
epipedon extends to rock (either a lithic or paralithic contact
as defined later).

The mollic epipedon is expected to have dark color and low
chroma throughout the major part of its matrix, If the
structure is fine granular or fine blocky, the color when
broken may be only the color of the coatings. The color of
the matrix in such situations can be determined only by
crushing or briefly rubbing the sample, Prolonged rubbing
should be avoided because it may cause darkening of a sam-
ple if soft iron-manganese concretions are present; crushing
should be only enough to break and mix the coatings. The
color value when dry should determined after the crushed
sample has been smoothed to eliminate shadows.

If there is >40 percent finely divided lime, the limits of
color value, dry, are waived; the color value, moist, then
should be 5 or less. This waiver is necessary because finely
divided lime acts as a white pigment.

3, Base saturation is 50 percent or more by the NH,OAc
method.

4. The organic-carbon content is 2.5 percent or more in the
upper 18 cm if the color requirement is waived because of
finely divided lime. Otherwise, the organic-carbon content
is at least 0.6 percent (1 percent organic matter) throughout
the thickness of soil specified in item 5.

The mollic epipedon consists of mineral rather than organic
soil material. Its organic-carbon content, therefore, has an
upper as well as a lower limit. The upper limit of organic
carbon in a mollic epipedon is the same as that of mineral
soil material; in part it is the lower limit for the histic
epipedon, defined later in this chapter, Because an organic
horizon can form above a mollic epipedon in a wet soil, the
mollic epipedon is not necessarily the surface horizon but is
the uppermost horizon composed of mineral soil material.

$.The thickness is one of the following after mixing the up-
per 18 cm of soil or the whole soil if the depth to rock,
petrocalcic horizon, or duripan is <18 cm:
a. Ten cm or more if the epipedon is underlain directly
by a lithic contact; 10 cm or more in soils of shallow
families in which the epipedon is underlain directly by a
paralithic contact, a petrocalcic horizon, or a duripan, all
defined tater in this chapter;
b. In other soils the epipedon must be >25 cm thick if its
texture if finer than loamy fine sand and
(1) The upper boundary of pedogenic lime that is
present as filaments, soft coatings, or soft nodules is
deeper than 75 cm;


3
Cryaquents
Distinctions between Typic Cryaquents and other subgroups

Typic Cryaquents are the Cryaquents that
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density of the fine-earth fraction (at 33 kPa
moisture tension) of 0.95 g per cubic centimeter or less, and
that has either
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less, or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
more than 1.5 and more exchange acidity than the sum of
bases plus KCl-extractable aluminum.
Andaqueptic Cryaquents are like Typic Cryaquents except for
a,

Fluvaquents
Distinctions between Typic Fluvaquents and other subgroups

Typic Fluvaquents are the Fluvaquents that
a. Have, in 60 percent or more of the matrix in all
subhorizons between the Ap horizon or a depth of 25 cm,
whichever is deeper, and a depth of 75 cm, one or more of
the following:
(1) If mottled and
(a) If the hue is 2.5Y or redder‘ and the value, moist,
is more than 5, the chroma, moist, is 2 or less;
(b) If the hue is 2.5Y or redder and the value, moist,
is 5 or less, the chroma, moist, is 1 or less; or
(c) If the hue is yellower than 2.5Y, the chroma,
moist, is 2 or less; or
(2) The chroma, moist, is 1 or less and mottles may or
may not be present;
b. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density in the fine-earth fraction (at 33 kPa
moisture tension) of 0,95 grams per cubic centimeter or less,
and that has either (1) a ratio of measured clay to 1500 kPa
water (percentages) of 1.25 or less or (2) a ratio of CEC (at
pH near 8) to 1500 kPa water of >1.5 and more exchange
acidity than the sum of bases plus KCl-extractable
aluminum,
¢. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
‘or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper I m of the soil or in the whole soil if a lithic or

If the hue of the matrix is 7.5YR ot redder and if peds are present, ped exte-

riors have dominant chroma, moist, of 1 or lass, and ped interiors have mottles
that have chroma, moist, of 2 oF less; if pede are absent, the chroma, moist, is
1 or less immediately below any surface horizon that haa value, moist, leas
than 8.5.


81

are basic. These soils are rare in the United States. Defini-
tions of subgroups have not been developed.

Ustalfs
Key to great groups

HCA. Ustalfs that have a duripan that has its upper bound-
ary within 1 m of the surface.
Durustalfs, p. 82

HCB. Other Ustalfs that have plinthite that forms a continu-
ous phase or constitutes more than half the matrix within
some subhorizon of the argillic horizon within 150 cm of the
surface.

Plinthustalfs, p. 87

HCC. Other Ustalfs that have a natric horizon,
Natrustalfs, p. 85

HCD. Other Ustalfs that
1. Have a CEC <16 cmol(+) kg"! flay (by 1 M NH,OAc pH
7) and an ECEC <12 cmol(+) kg” clay (sum of bases eX~
tracted with 1 M NH,OAc pH 7 plus | M KCl-extractable
Al) in the major part of the argillic or kandic horizon or the
major part of the upper 100 cm of the argillic or kandic
horizon if these horizons are thicker than 100 cm;
2. Do not have a lithic, paralithic or petrofertic contact
within 150 cm of the soil surface; and
3. Have a clay distribution such that the percentage of clay
does not decrease from its maximum amount by as much as
20 percent within a depth of 150 cm from the soil surface
or the layer in which the clay percentage decreases by more
than 20 percent has at least 5 percent of the volume con-
sisting of skeletans on faces of peds and there is at least 3
percent (absolute) increase in clay below the layer.
Kandiustalfs, p. 83

HCE. Other Ustalfs that have a CEC <16 cmol(+) kg” olay
(by 1 M NH,OAc pH 7) and an ECEC <12 cmol(+) kg” clay
(sum of baseS extracted with 1M NH,OAc pH 7 plus 1 M
KCl-extractable Al) in the major part of the argillic or
kandic horizon or the major part of the upper 100 cm of the
argillic or kandic horizon if these horizons are thicker than
100 cm,

Kanhaplustalfs, p, 84

HCF. Other Ustalfs that either have a petrocalcic horizon
that has its upper boundary within 1.5 m of the surface or;
1. Does not have a lithic or paralithic contact within 1.5
m of the surface; and the argillic horizon
a, Has a clay distribution such that the percentage of
clay does not decrease by as much as 20 percent of the
maximum within a depth of 150 cm from the soil
surface, or the layer in which the clay percentage de-
creases by more than 20 percent has at least 5 percent
of the volume consisting of skeletans on faces of peds
and there is at least 3 percent (absolute) increase in
clay below the layer, and
b, Has one or more of the following:


192

during a period when the soil temperature at a depth of
50 cm exceeds 8°C;
J. When neither irrigated nor fallowed to store moisture,
(1) If the soil temperature regime is mesic or thermic,
are dry less than six-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) during a period when the soil
temperature at a depth of 50 cm exceeds 5°C, or
(2) If the soil temperature regime is hyperthermic or
isomesic, or warmer, are moist in some or all parts of the
moisture control section for 90 consecutive days or more
during a period when the soil temperature at a depth of
50 cm exceeds 8°C; and
k. Have CEC (by 1 M NH,OAc pH7) of 24 or more cmol(+)
kg" clay in the major part of the soil below a depth of 25
cm but above 100 cm or a lithic or paralithic contact if one
is shallower than 100 cm.
Aquic Haplustolls are like Typic Haplustolls except for a,
with or without d or i, or both.
Aridic Haplustolls are like Typic Haplustolls except for j.
Cumulic Haplustolls are like Typic Haplustolls except for b
and e, with or without all or any of a, d, i, and j.
Entic Haplustolls are like Typic Haplustolls except for d and
either do not have a cambic horizon or the epipedon is cal-
careous,
Fluvaquentic Haplustolls are tike Typic Haplustolls except
for a and e, with or without d or i, or both.
Fluventic Haplustolis are like Typic Haplustolls except for e,
with or without d or i, or both.
Lithic Haplustolls are like Typic Haplustolls except for /,
with or without any or all of d, i, and j.
Lithic Ruptic-Entic Haplustolls are like Typic Haplustolls
except for f and d and have a cambic horizon in some part
but in less than half of each pedon.
Oxic Haplustolls are like Typic Haplustolls except for k,
with or without b or e, or both.
Pachic Haplustolls are like Typic Haplustolls except for b,
with or without all or any of a, d, or i.
Ruptic-Lithic Haplustolls are like Typic Haplustolls except
for f in part of each pedon.
Salorthidic Haplustolls are like Typic Haplustolls except for
g, with or without all or any of a, 6, e, i, or j.
Torrertie Haplustolls are like Typic Haplustolls except for
JC), with or without all or any of 6, d, e, i, or j, and the
cracks are open more than 6 months in most years.
Torrifluventic Haplustolls are like Typic Haplustolls except
for e and j, with or without d.
Torriorthentic Haplustolls are like Typic Haplustolls except
for d and j.
Torroxic Haplustolls are like Typic Haplustolls except for j
and k, with or without 4 or e.
Udertic Haplustolls are like Typic Haplustolls except for
h(1) and i, with or without all or any of a, b, d, e, or j,
and the cracks are open less than 135 days in most years,
Udie Haplustolls are like Typic Haplustolls except for i.
Udorthentic Haplustolls are like Typic Haplustolls except for
d and i.
Vertic Haplustolls are like Typic Haplustolls except for h(1),
with or without all or any of a, 5, d, e, or j, and the cracks
are open between 135 and 180 days in most years.



108

b, Have a gypsic horizon in which the product of the per-
centage of gypsum and the thickness in centimeters above a
depth of 1.5 m is 3,000 or more.

Calci¢e Gypsiorthids are like Typic Gypsiorthids except for 5
and have a calcic horizon above the gypsic horizon.

Cambic Gypsiorthids are like Typic Gypsiorthids except for
b and do not have a calcic horizon above the gypsic horizon,
Petrogypsic Gypsiorthids are like Typic Gypsiorthids except
for a with or without b.

Paleorthids
Distinctions between Typic Paleorthids and other subgroups

Typic Paleorthids are the Paleorthids that
a, Are not saturated with water for 90 consecutive days or
more in most years within 1 m below the soil surface and do
not have a subhorizon that has the following characteristics
within 1 m of the surface if the horizon is saturated with
water at some period in most years or the soil is artificially
drained. The soils do not have:

(1) Dominant chroma of 1 or less throughout and hue as

yellow or yellower than 2.5Y in some part;

(2) Dominant chroma of 2 or less and mottles that are

not due to segregated lime; or

(3) Both a dominant chroma of 2 or less and a greater

SAR (or percentage of exchangeable Na) in more than

half the thickness of the horizons between the surface

and 50 cm depth than in the saturated zone;
b. Have a petrocalcic horizon whose upper boundary is
shallower than 18 cm, or have a weighted average content of
organic carbon in the upper soil to a depth of 40 cm that is
<0.6 percent if the weighted average ratio of sand to non-
carbonate clay to this depth is 1.0 or less, or is <0,15 percent
if the ratio is 13 or more, or is intermediate if the ratio of
sand to clay is between 1.0 and 13; or have a weighted av-
erage percentage of organic carbon in the surface soil to a
depth of 18 cm that is not one-fifth more than the values
just stated if there is a petrocalcic horizon that is shallower
than 40 cm but deeper than 18 cm; and
¢. Are dry in all parts of the moisture control section for
more than three-fourths of the time (cumulative) that the
soil temperature is 5°C or higher at a depth of 50 cm.
Aquic Paleorthids are like Typic Paleorthids except for a,
with or without 6 or c, or both,
Ustochreptic Paleorthids are like Typic Paleorthids except
for c, They have a mesic, thermic, or hyperthermic soil
temperature regime and an aridic moisture regime that bor-
ders on an ustic regime.
Ustollic Paleorthids are like Typic Paleorthids except for b
or for 6 and c. They have a mean annual soil temperature
that is 8°C or higher and an aridic moisture regime that
borders on an ustic regime.
Xerollic Paleorthids are like Typic Paleorthids except for b
or for band c. They have a mean annual soil temperature
lower than 22°C, and the mean summer and mean winter
soil temperatures at a depth of 50 cm differ by 5°C or more.
They have an aridic moisture regime that borders on a xeric
regime.



92

organic carbon, or they have an Ap horizon that has a color

value, moist, of 3.5 or more or contains <0.7 percent organic

carbon;

d. Do not have a petrocalcic horizon whose upper boundary

is within 1.5 m of the soil surface;

e. Have an argillic horizon that has at least 75 percent base

saturation (by sum of cations) in some part;

f. Have an argillic horizon in which the upper part has a

clayey particle-size class and there is an increase of at least

20 percent clay (absolute) within a vertical distance of 7.5

cm or of at least 15 percent clay (absolute) within 2.5 cm at

the upper boundary;

g- Have <5 percent plinthite (by volume) in all subhorizons

within 1.5 m of the soil surface;

h. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part and that extend upward to the surface
or to the base of an Ap horizon if the soil is not irri-
gated; and
(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m, and
(3) More than 35 percent clay in horizons that total >50
om in thickness;

i. Have texture finer than loamy fine sand in some sub-

horizon within 50 cm of the soil surface; and

J. Have <I5 percent saturation with sodium in all subhori-

zons within } m of the soil surface.

Aquic Palexeralfs are like Typic Palexeralfs except for a or

for a and c.

Calcic Palexeralfs are like Typic Palexeralfs except for b.

Mollic Palexeralfs are like Typic Palexeralfs except for c.

Natric Paiexeralfs are like Typic Palexeralfs except for j.

Petrocalcic Palexeralfs are like Typic Palexeralfs except for

d, or for d and f.

Ultic Palexeralfs are like Typic Palexeralfs except for e,

with or without / or c, or both.

Vertic Palexeralfs are like Typic Palexeralfs except for h,

with or without @ or ¢, or both.

Plinthoxeralfs

Plinthoxeralfs are the Xeralfs that have plinthite that forms
a continuous phase or that constitutes more than half the
matrix of some subhorizon within 150 cm of the soil sur-
face. Few of these soils are in the United States, but the
soils are moderately extensive in some parts of the world.
Subgroups have not been developed. The Plinthoxeralfs
were included with Ground-Water Laterite soils in the 1938
classification.


184

Cryie Lithic Rendolls are like Typic Rendolls except for a
and ¢ or for a, 6, and c.

Entic Rendolls are like Typic Rendolls except for e.
Eutrochreptic Rendolls are like Typic Rendolls except for b,
and the mean summer and mean winter soil temperatures at
a depth of 50 cm differ by 5°C or more.

Eutropeptic Rendolls are like Typic Rendolls except for b
and the mean summer and mean winter soil temperatures at
a depth of 50 cm differ by <5°C.

Lithic Rendolls ate like Typic Rendolls except for c.

Vertic Rendolls are like Typic Rendolls except for d.

Udolls
Key to great groups

GGA. Udolls that have an argillic horizon and a clay
distribution such that the clay content does not decrease by
as much as 20 percent of the maximum clay content within
1.5 m of the soil surface and there is no lithic or paralithic
contact within that depth, and there is one or both of the
following features:

1. Hue redder than JOYR and chroma greater than 4
dominant in the matrix in at least the lower part of an
argillic horizon; or

2, Many coarse mottles that have hue redder than 7.5YR or
chroma greater than 5,
Paleudolls, p. 186

GGB. Other Udolls that have an argillic horizon.
Argludolls, p. 184

GGC. Other Udolls that have a mollic epipedon that, below
any Ap horizon, is $0 percent or more by volume
wormholes, wormeasts, or filled animal burrows and that
either rests on a lithic contact or has a transition to an
underlying horizon in which 25 percent or more of the
material is discrete wormholes, wormcasts, or filled animal
burrows that contain material from the mollic epipedon and
from the underlying horizon,

Vermudolls, p. 186

GGD. Other Udolls,
Hapludolls, p. 185

Argiudolls
Distinctions between Typic Argiudolls and other subgroups

Typic Argiudolls are the Argiudolls that
a. Do not have mottles within 50 cm of the surface if the
mottled horizon is saturated with water at some period of
the year when the soil temperature in the mottled horizon is
above 5°C or if the soil is artificially drained; and have a
horizon 15 cm or more thick immediately below the mollic
epipedon that either
(1) Has a hue of LOYR or redder and chroma of 3 or
more, and does not have mottles that have chroma of 2 or
less and value of 4 or more if the mottled horizon is
saturated with water at some period of the year when the


187

burrows filled with material from the mollic epipedon and
the underlying horizon;

d. Do not have a lithic contact within 50 cm of the surface;
and

e. Have a mollic epipedon that below any Ap horizon has
granular structure formed mainly from wormholes,
wormeasts, or filled animal burrows.

Entic Vermudolls are \ike Typic Vermudolls except for a.
Haplic Vermudolls are like Typic Vermudolls except for 6
and c, with or without a.

Lithic Vermudolls are like Typic Vermudolls except for d
and a, with or without c.

Ustolls
Key to great groups
GFA. Ustolls that have a duripan with its upper boundary
within 1 m of the soil surface,
Durustolls, p. 190

GFB. Other Ustolls that have a natric horizon.

Natrustolls, p, 193

GFC. Other Ustolls that have a petrocalcic horizon that has
its upper boundary within 1.5 m of the soil surface, and that
have an argillic horizon or are noncalcareous in some
subhorizon above the petrocalcic horizon after the surface
soil to a depth of 18 cm has been mixed, or that have an
argillic horizon that has one or both of the following:
1. A vertical clay distribution such that the clay content
does not decrease by as much as 20 percent of the
maximum clay content within 1.5 m of the soil surface
and the soil does not have a lithic or paralithic contact
within that depth, and the argillic horizon has one or
both of these:
a. A hue redder than 10YR and chroma higher than 4
in the matrix; or
b. Common coarse mottles that have a hue of 7.5YR
or redder or chroma higher than 5; or
2. A particle-size class in the upper part that is clayey
and an increase of at least 20 percent clay (absolute)
within a vertical distance of 7.5 cm or of 15 percent clay
(absolute) within 2.5 cm at the upper boundary, and there
is no lithic or paralithic contact within 50 cm of the
surface of the soil.

Paleustolis, p. 193

GFD. Other Ustolls that do not have an argillic horizon
above a calcic, gypsic, or petrocalcic horizon, and that have
a calcic or gypsic horizon that has its upper boundary within
1.5 m of the surface, and that are calcareous in all overlying
subhorizons after the upper soil to a depth of 18 cm has
been mixed, unless the texture is coarser than loamy very
fine sand or very fine sand,

Calclustolls, p. 189

GFE. Other Ustolls that have an argillic horizon.
Argiustolls, p. 188


59

E, Other soils that have an ochric or anthropic epipedon and
either
1, Do not have an argillic or a natric horizon but
a. Are saturated with water within 1 m of the surface
for 1 month or more in some years and have a salic
horizon whose upper boundary is within 75 cm of the
‘surface; or
b. Have one or more of the following horizons whose
upper boundary is wit 1 m of the soil surface: a
petrocalcic, calcic, gypsic, petrogypsic, or cambic
horizon or a duripan; and have an aridic moisture
regime,

or
2. Have an argillic or a natric horizon and have
a. An aridic moisture regime; and
b. An epipedon that is not both massive and hard or

very hard when dry. Aridisots, p. 95
NSOIS, p.

F. Other soils
~ that have a mesic, isomesic, or warmer temperature
regime, and
- do not have tongues of albic materials in the ar;
horizon that have vertical dimensions of as much as 50 cm if
there is >10 percent weatherable minerals in the 20- to 200-
micrometer fraction, but
- have one of the following combinations of characteristics:
either
1, Have an argillic or kandic horizon but not a fragipan
and have base saturation (by sum of cations) of <35 per-
cent at the following depths:
a. If the argillic or kandic horizon has in some part a
hue of SYR or yellower, or a color value, moist, of 4
or more, or a color value, dry, that is more than |
unit higher than the value, moist, the shallowest of the
following:
(1) 1.25 m below the upper boundary of the argillic
or kandic horizon;
(2) 1.8 m below the surface of the soil; or
(3) Immediately above a lithic or paralithic contact;
b. If the argillic or kandic horizon has some other
color or if the epipedon has a sandy or sandy-skeletal
particle-size class throughout, the deepest of 1.25 m
below the upper boundary of the argillic horizon, 1.8
m below the surface of the soil, or immediately above
a lithic or a paralithic contact if it is shallower;

or
2. Have a fragipan that
a. Meets all the requirements of an argillic or kandic
horizon or has clay skins >1 mm thick in some part, or
underlies an argillic or kandic horizon;
and
b. Has base saturation (by sum of cations) of <35
percent at a depth of 75 cm below the upper boundary
of the fragipan or immediately above a lithic or par-
alithic contact, whichever is shallower,
Ultisols, p. 237


Table 2-(continued )

Feature MoLusoLs ‘OxisoLs SPODOSOLS Uxrisors VERTISOLS
Panqicie- Upper 50 cm of Bt or whole 25 cm to I m. 25 cm to 1 m; not used for Upper 50cm of Btor whole 25 cm to I m. Fine 30-60%
sae! Bt if < $0 cm thick? ——— spodic horizons of cryic Bt if < 50 cm thick”. If upper clay. Very fine 60% clay.

—————_— Subclasses of loamy families great groups or cryic boundary of Bt is > 1 m deep

If without Bt, 25 cm but not of clayey families; subgroups®. and not in grossarenic sub-

to 1m. all other classes are used. § ———_______ group, 25 cm to 1 m.

7 classes in lithic, arenic, _§ ————————

11 classes except in lithic, and grossarenic subgroups Subclasses of loamy classes

andic, or arenic subgroups or and shallow families, but not of clayey classes,

shallow families where 11 classes in all others. and all other classes. Only

7 classes are used. 7 classes in lithic, andic, or

arenic subgroups or
shallow famites.

MINERALOGY —Same as particle-size classes; Same as particle-size Same as particle-size classes. Same as particle-size Same as particle-size classes.

if contrasting classes, only " classes, If contrasting classes, only classes. If contrasting classes,

upper materials; in andeptic used for upper materials. use upper materials.

subgroups, used for lower

materials.
COMBINATION oF Used for spodic horizons
PARTICLE-SIZE of cryic great groups and
AND MINERALOGY In andeptic subgroups. Not used. cryic subgroups®. Not used. Not used.

AND Calcareous classes used in _ Not used. Not used. Not used. Not used.

CALCAREOUS

REACTION CLASSES all Aquolls except Calci
quolls and Argiaquolls
between 25 and $0 cm depth;
not used with carbonatic or
gypsic mineralogy.

Som Not used in cryic great
TEMPERATURE — groups or Borolls.

‘Used in alt families,

Not used in cryic great
groups or cryic subgroups.

Deprs* Not used in pergelic sub- Shallow, <1 m to lithic Not used in pergelic
groups or lithic subgroups. or petroferric contact. or lithic subgroups.

SLOPE ‘Used in Aquolls. Not used. Not used.

CoNsISTENCE —_Not used. Not used. ‘Used for cemented spodic

rizons.

MotstuRE

EQUIVALENT Not used. Not used, Not used.

CRACKS Not used. Not used. Not used.

‘Used in all familes. ‘Used in all famities.

‘Used in all familes, Not used.
Not used. Not used.
Not used. Not used.
Not used. Not used.
Not used. Not used.

‘Control section for particle-sive classes never includes rock, petrocalcic horizons, duripans, fragipans or permofrost tones (25 cm below frost 2 months after surmmer slatice). If any of these are within 96 cmn of the

soil surface, the control section is from the surface to the listed feature,
2r¢ base of Bt is lees than 25 em, from top of Bt or base of Ap to 1m.

'epth to parslithic contact, duripan, petrocalcic horizon or petroferric contact. Shallow is never used in lithic subgroups or mineral soils; otherwise refers to dept to listed features at < 50 em unless noted.
‘diagnostic

Micro reters to base of ‘at depths < 18 cm.

See text of Soil T:

‘classes are used only for

£Some0
5In the absence of rock or ice within $6 cm, the spodic horizon must extend below a depth.

389,
‘of > 25 em before this applies


18

the morphological or the chemical and physical characteris-
tics that are listed next, and its hue and chroma remain
constant with increasing depth or the subhorizon that has the
reddest hue or the highest chroma is near the top of the
horizon. The color changes within 50 cm from the top of
the horizon’. If the soil temperature regime is frigid or
warmer, some part of the spodic horizon must meet one or
more of the following requirements below a depth of 12.5
cm or below any Ap horizon that is present. If the soil
temperature regime is cryic or pergelic, there is no require-
ment for depth. In addition, the spodic horizon must meet
one or more of the following requirements:

1, Have a subhorizon > 2,5 cm thick that is continuously
cemented by some combination of organic matter with iron
or aluminum or with both;

2. Have a particle-size class that is sandy or coarse-loamy,
and sand grains are covered with cracked coatings or there
are distinct dark pellets of coarse-silt size or larger, or both;
or

3. Have one or more subhorizons in which
a. If there is 0.1 percent or more extractable iron, the
ratio of iron plus aluminum (elemental) extractable by
pyrophosphate at pH 10 to percentage of clay is >0.2
(percentage of pyrophosphate-extractable Fe + Al at pH
10/clay percentage 20.2) or if there is <0.1 percent ex~
tractable iron, the ratio of aluminum plus carbon ex-
tractable by pyrophosphate at pH 10 to percentage clay is
20.2.
b.The sum of pyrophosphate-extractable iron plus alu~
minum is half or more of the extractable sum of dithion-
ite-citrate extractable iron plus aluminum (percentage of
pyrophosphate-extractable Fe + Al/percentage of
dithionite-citrate extractable Fe + Al 20.5); and
¢, The combined index of accumulation of amorphous
material must be 65 or more. The index for each sub~
horizon is calculated by subtracting half of the clay per-
centage from CEC at pH 8.2 and multiplying the remain-
der by the thickness of the subhorizon in centimeters.
The results for all subhorizons are then added and the
total must be 65 or more.

Sulfuric horizon

The sulfuric (L. sulfur) horizon is composed either of min-
eral or organic soil material that has both a pH <3.5 (I:1 in
water) and jarosite mottles (the color of fresh straw that has
a hue of 2.5Y or yellower and chroma of 6 or more).

A sulfuric horizon forms as a result of artificial drainage
and oxidation of sulfide-rich mineral or organic materials.
Such a horizon is highly toxic to plants and virtually free of
living roots.

74 thin black horiaon that hag color value of 2 or less may overlie this hori-
ton.


241

Arenic Paleaquults are like Typic Paleaquults except for b,
and they have a sandy particle-size class to a depth between
50 cm and 1 m,

Arenic Plinthic Paleaquults are like Typic Paleaquults except
for 5 and c, and they have a sandy particle-size class to a
depth between 50 cm and | m.

Arenic Umbric Paleaquults are like Typic Paleaquults except
for 6 and d, and they have a sandy particle-size class to a
depth between 50 cm and 1 m,

Grossarenic Paleaquults are like Typic Paleaquults except for
b, and they have a sandy particle-size class to a depth of 21
m in half or more of the pedon.

Plinthic Paleaquults are like Typic Paleaquults except for ¢.
Umbric Paleaquults are like Typic Paleaquults except for d.

Plinthaqualts

Distinction between Typic Plinthaquults and other sub-
groups,

Typic Plinthaquults are the Plinthaquults that

a. Have a CEC of 24 or more cmol(+) kgTM of clay (by 1 M
NH,OAc pH7) in the major part of the argillic or kandic
horizon or the major part of the upper 100 cm of the
argillic or kandic horizon if these horizons are thicker than
100 cm,

Kandic Plinthaquults are like Typic Plinthaquults except for
a.

Umbraquults

Umbraquults are the Aquults that

1, Have an umbric or mollic epipedon;

2. Do not have a fragipan;

3. Do not have plinthite that forms a continuous phase or
constitutes more than half of the matrix of any subhorizon
within 150 cm of the soil surface;

4, Have a clay distribution such that the percentage of clay
decreases from its maximum by 20 percent or more of the
maximum within a depth of 150 cm below the soil surface,
and the layer in which the percentage of clay is less than the
maximum has less than 5 percent of the volume consisting
of skeletans on faces of peds or there is less than 3 percent
(absolute) increase in clay below the layer.

Humults
Key to great groups

FBA. Humults that have a sombric horizon within 1 m of
the soil surface,
Sombrihumults, p. 244

FBB. Other Humults that have plinthite that forms a contin-

uous phase or constitutes >50 percent of the volume of some

subhorizon within 150 cm of the soil surface.
Plinthohumults, p. 244

ULT

FBC. Other Humults that
1, Have a CEC <16 cmol(+) kg! flay (by 1 M NH,OAc pH
7) and an ECEC <12 cmol(+) kg”! clay (sum of bases ex-


49

classes are applied to the section between a depth of 25 and
50 cm or between a depth of 25 cm and a lithic or paralithic
contact that is below a depth of 25 but not 50 cm, or to
some part of the soil above a lithic or paralithic contact that
is shallower than 25 cm. Two classes, calcareous and non-
calcareous, are used in selected taxa. The definitions follow.

Calcareous.--The fine-earth fraction effervesces in all parts
with cold dilute HCI.

Noncalcareous.--The fine-earth fraction does not effervesce
in all parts with cold dilute HCl, The term noncalcareous is
not used as a part of a family name.

It should be noted that a soil that contains dolomite is cal-
careous and that effervescence of dolomite, when treated
with cold dilute HCl, is slow.

Reaction classes are applied to the control section that is
defined for particle-size classes. Three classes (acid,
nonacid, and allic) are used in selected taxa, The definitions
follow.

Acid.--The pH is <5.0 in 0.01 1 M CaCl, (2:1) throughout
the control section (about 5.5 in H,O, 1:1).

Nonacid.--The pH is 5.0 or more in 0.01 M CaCl, (2:1) in at
least some part of the control section. The term nonacid is
not used in the family name of calcareous soils.

Allic.--There is more than 2 cmol(+) of KCI extractable Al
per kg soil (<2 mm fraction) in some 30 cm layer in the
control section.

Acid and nonacid classes are used only in the names of
families of Entisols and Aquepts; they are not used in sandy,
sandy-skeletal, and fragmental families of these taxa, nor
are they used in Sulfaquepts and Fragiaquepts, or in families
that have carbonatic or gy: mineralogy. The allic class is
used only in names of fami of Oxisols.

Calcareous classes are used if appropriate in the same taxa as
reaction classes and, in addition, are used in families of
Aquolis except for Calciaquolls and and for Aquolls that
have an argillic horizon. Calcareous and reaction classes are
not used in soils that have carbonatic or gypsic mineralogy.
A soil that is calcareous is never acid. Calcareous therefore
implies nonacid, and both names are not used because
nonacid would be redundant. Similarly, noncalcareous
would be redundant in acid families, and it is not used as
part of the family name. If calcareous is used in a family
name, calcareous is considered to be a subclass of mineral-
ogy. It follows the mineralogy class name and is shown in
parenthesis, for example: fine-loamy, mixed (calcareous),
mesic Typic Haplaquolls,

Soil temperature classes
Soil temperature classes, as named and defined here, are

used as family differentiae in all orders. The names are
used as family modifiers unless the name of a higher taxon


275

either like or unlike the assumed parent material of
the buried soil.

Concretions or hard nonconcretionary nodules

This symbol is used to indicate a significant accu-
mulation of concretions or nonconcretionary nod-
ules cemented by material other than silica. This
symbol is not used if concretions or nodules are
dolomite or calcite or more soluble salts, but it

is used if the nodules or concretions are iron, alu-
minum, manganese, or titanium. Their consistence
is specified in the horizon description.

Dense unconsolidated sediments or materials

This symbol is used to indicate naturally occurring
or man-made, unconsolidated sediments or materi-
als with high bulk density such as dense basal till,
plow pans and other mechanically compacted zones.
The layer is root restrictive and roots do not enter
except along fracture planes,

Organic material of intermediate decomposition

This symbol is used with "O" to indicate organic
materials of intermediate decomposition. Rubbed
fiber content is 1/6 to 2/5 of the volume,

Frozen soil

This symbol is used to indicate that the horizon or
layer contains permanent ice. Symbol is not used
for seasonally frozen layers or for "dry permafrost"
(material that is colder than 0 °C but does not con-
tain ice).

Strong gleying

This symbol is used to indicate either that iron has
been reduced and removed during soil formation or
that saturation with stagnant water has preserved a
reduced state. Most of the affected layers have low
chroma and many are mottled. The low chroma
can be the color of reduced iron or the color of
uncoated sand and silt particles from which iron
has been removed. Symbol "g" is not used for soil
materials of low chroma, such as some shales or E
horizons, unless they have a history of wetness.

If “g* is used with "B", pedogenic change in addi-
tion to gleying is implied, If no other change has
taken place, the horizon is designated Cg.

Mluvial accumulation of organic matter

This symbol is used with "B" to indicate the accu-
mulation of illuvial, amorphous, dispersible organic
matter-sesquioxide complexes if the sesquioxide
component is dominated by aluminum but is pre-
sent only in very small quantities,
The organosesquioxide material coats sand and silt



53
Family Differentiae For Histosols

Most of the differentiae used to distinguish families of His-
tosols have been defined earlier, either because they are
differentiae in mineral soils as well as in Histosols; or be-
cause their definitions are essential for the classification of
some Histosols in categories higher than the family. The
differentiae that are not defined elsewhere are defined in
this section and the taxa in which they are used are enu-
merated.

The order in which family modifiers are placed in the tech-
nical family names of Histosols follows. The modifiers
chosen are those appropriate to the particular family.
Particle size
Mineralogy, including nature of limnic deposits
Reaction
Soil temperature regime
Soil depth

The differentiae are discussed in the remainder of this sec-
tion,

Particle-size classes

Particle-size modifiers are used in family names of Histosols
only in terric subgroups. The terms used follow.
Fragmental
Loamy-skeletal or clayey~skeletal
Sandy or sandy-skeletal
Loamy
Clayey

‘The meaning of each of these terms is the same as that de-
fined for particle-size classes of mineral soils, The proper
term js selected to describe the weighted average particle
size of the upper 30 cm of the mineral layer or that part of
the mineral layer that is within the control section,
whichever is thicker.

Mineralogy classes

Mineralogy classes of Histosols ate of three kinds, according
to the nature of the subgroup or great group.

Ferrihumic.--Containing ferrihumic materials within the
control section (applied to Fibrists, Hemists, and Saprists,
except Sphagnofibrists and sphagnic subgroups of other
great groups), Bog iron is present in some Histosols or in
organic soi! materials. It is called ferrihumic material. It
consists of authigenic deposits (formed in place) of hydrated
iron oxides mixed with varying kinds or amounts of organic
materials. The iron in some places is present in large ce-
mented aggregates. In others it may be mostly dispersed and
soft. The colors normally are; shades of dark reddish
brown, commonly mixed with black, and the colors change
little on drying. The content of iron oxide ranges from 10
percent to >20 percent.

Ferrihumic material either is saturated with water for long
periods (>6 months) or is in an artificially drained soil. The



Oxic horizon...

Paleaquults

Plinthaquepts
Plinthaquox
Plinthaquults..
Plinthite.
Plinthohumults..



80

(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part and that extend upward to the surface
or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper | m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness;
f. Have > 5 percent plinthite (by volume) in all subhorizons
within 1.5 m of the surface;
g. Have an argillic horizon that is continuous horizontally,
that is continuous vertically for at least the upper 20 cm,
and that has a texture finer than loamy fine sand;
h. Do not have subhorizons in the upper part of the argillic
horizon that have skeletans that
(1) Have moist chroma of 2 or fess; and
(2) Occupy 5 percent or more of the volume of the sub-
horizon;
1, Do not have albic materials that constitute as much as 5
percent of any subhorizon of the argillic horizon.
Albaquic Paleudalfs are like Typic Paleudalfs except for a
and have an increase of 15 percent clay or more (absolute)
within a vertical distance of 2.5 cm at the upper boundary
of the argillic horizon.
Aguic Paleudalfs are like Typic Paleudalfs except for a,
with or without c.
Arenic Paleudalfs are like Typic Paleudalfs except for b and
have a sandy epipedon that is between 50 cm and I m thick.
Arenic Plinthic Paleudalfs are like Typic Paleudalfs except
for b and f and have a sandy epipedon that is between 50
cm and | m thick,
Glossaquic Paleudalfs are like the Typic Paleudaifs except
for a and h, with or without c or i, or both,
Glossic Paleudalfs are like Typic Paleudalfs except for h or
i, or both.
Grossarenic Paleudalfs are like Typic Paleudalfs except for
6 and have a sandy epipedon that is >1 m thick.
Grossarenic Plinthic Paleudalfs are like Typic Paleudalfs
except for 6 and f and have a sandy epipedon that is >1 m
thick,
Mollic Paleudalfs are like Typic Paleudalfs except for c.
Plinthaquic Paleudalfs are like Typic Paleudalfs except for a
and f with or without c.
Plinthic Paleudalfs are like Typic Paleudalfs except for f
with or without c.
Psammentic Paleudalfs are like Typic Paleudalfs except for
g, with or without 5 or c, or both,
Rhodic Paleudalfs are like Typic Paleudalfs except for c and

d.
Vertic Paleudalfs are like Typic Paleudalfs except for e,
with or without a or c, or both.

Rhodudalfs
Rhodudalfs are dark red Udalfs of midlatitudes that have a

thinner solum than the Paleudalfs. The definition is parallel
to that of other rhodic great groups. Their parent materials


146

TE. Other Inceptisols that have an ochric epipedon; or that

have an umbric or mollic epipedon that is <25 cm thick and

have also a mesic or warmer soil temperature regime,
Ochrepts, p. 156

IF. Other Inceptisols.
Umbrepts, p. 167

Andepts
Key to great groups

TBA, Aadepts that have a cryic or pergelic temperature
regime.
Cryandepts, p. 146

IBB. Other Andepts that have a duripan that has its upper
boundary within 1 m of the soil surface.
Durandepts, p. 147

IBC. Other Andepts that have clays that dehydrate
irreversibly into aggregates of sand and gravel size.
Hydrandepts, p. 149

IBD. Other Andepts that have a placic horizon within tm
of the soil surface in half or more of each pedon.
Placandepts, p. 149

IBE. Other Andepts that are not thixotropic and in which
the weighted average 1500 kPa water retention‘ of the fine-
earth fraction
is <20 percent for all horizons between a depth of 25 cm
and 1 m or between 25 cm and a lithic or paralithic contact
if one is shallower than 1 m.

Vitrandepts, p. 149

IBF. Other Andepts that have a base saturation (by
NH,OAc) of 50 percent or more in some subhorizon
between a depth of 25 and 75 cm.

Eutrandepts, p. 148

IBG. Other Andepts.
Dystrandepts, p. 147

Cryandepts
Distinctions between Typic Cryandepts and other subgroups

The subgroups of Cryandepts have not been fully developed
because the soils are too few and those in the United States

are too inaccessible, To date they have had only preliminary
study.

T rhe amount of water retained at a tention of 1600 kPa may be reduced by
drying these soile, Since 1600 kPa water retention is used as a measure of ef-
fective clay content, it would be unrealistic to use the extremely high value
‘obtained on a field-moist Andept, That value reflects mostly the climatic
history rother than w basic soil property. The value for 1500 kPa water re-
tention that is referred to here, therefore, is that of a sample that has bean
dried at 40°C.


138

(2) Less than 25 cm of the subsurface and bottom tiers

consisting of sapric materials;
¢. Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier;
d, Do not have a layer of water within the control section
beneath the surface tier;
e. Do not have limnic layer(s) 5 cm or more thick within the
control section; and
f. Do not have a lithic contact within the control section,
Fibric Borohemists ate like Typic Borohemists except for
(1).
Fibric Terric Borohemists are like Typic Borohemists except
for b(1) and c, with or without a or e, or both.
Fluvaquentic Borohemists are like Typic Borohemists except
for a, with or without b.
Hydric Borohemists are like Typic Borohemists except for d.
Limnic Borohemists are like Typic Borohemists except for e,
with or without a or 6, or both.
Lithic Borohemists are like Typic Borohemists except for f,
with or without all or any of a, b, c, or e,
Sapric Borohemists are like Typic Borohemists except for
(2).
Sapric Terric Borohemists are like Typic Borohemists except
for b(2) and c, with or without a or e, or both.
Terric Borohemists are like Typic Borohemists except for c,
with or without all or any of a, d, or e.

Cryohemists
Distinctions between Typic Cryohemists and other subgroups

Typic Cryohemists are the Cryohemists that

a. Do not have a lithic contact within the control section;
b. Have a mean annual soil temperature higher than 0°C;

c, Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier;

d. Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier;

e. Have organic materials that are continuous laterally
throughout each pedon in at least the surface tier.
Fluvaquentic Cryohemists are like Typic Cryohemists except
for d.

Lithic Cryohemists are like Typic Cryohemists except for a
or for a and 5,

Pergelic Cryohemists are like Typic Cryohemists except for
6, with or without d.

Terrie Cryohemists are like Typic Cryohemists except for c,
with or without d.

Luyihemlsts

Luvihemists are not known to occur in the United States but
the great group is provided tentatively for use in other
countries if needed. They are the Hemists that have a
horizon that is 2 cm or more thick within the control sec-
tion, and half or more of the volume of that horizon is h
milluvi¢ materials. Because these soils cannot be studied in



13

dry, having then hard or very hard consistence. When
moist, a fragipan has moderate or weak brittleness, which is
the tendency for a ped or clod to rupture suddenly when
pressure is applied rather than to undergo slow deformation,
A dry fragment slakes or fractures when placed in water, A
fragipan is usually mottled, is slowly or very slowly perme-
able to water, and has few or many bleached, roughly ver~
tical planes that are faces of coarse or very coarse polyhe-
drons or prisms.

Identification

There is no known laboratory procedure for identifying a
sample of a fragipan. Identification is primarily a field
problem. A combination of clues must be used because
there is no single unique property of fragipans, First, posi-
tion is important. A fragipan lies below an eluvial horizon
unless the soil has been truncated, but it is not necessarily
immediately below. If the soil has been truncated, the pan
can be traced up slope until it lies under an eluvial horizon,

Second, if there is an argillic or a cambic horizon above a
fragipan, there is commonly an E’ horizon between the
fragipan and the overlying horizon, The E’ horizon is
marked by uncoated grains of sand and silt. This horizon
seems related to water that either stands above the pan or
moves laterally along its surface.

Third, if the pan is not saturated for long periods, some or
all pedons normally have bleached vertical streaks that form
a roughly polygonal pattern on a horizontal plane. The
bleached streaks are bounded by strong brown or reddish
brown streaks where iron and manganese have accumulated.
If the pan is saturated for long periods or if the texture is
sandy, the polygonal color pattern may be absent.

Fourth, if the moisture content is near the wilting point, the
matrix between the streaks is very firm. If it is near field
capacity, the matrix is brittle, The brittle matrix should
constitute 60 percent or more of the volume of some sub-
horizon.

Fifth, fine feeder roots are virtually absent in the brittle
parts of a fragipan. If brittleness is so weakly expressed
that fine feeder roots are present throughout the horizon,
the horizon should not be considered a fragipan. It should
be noted, however, that some trees have tap roots that ex-
tend through a well-expressed fragipan, but this is the ex-
ception rather than the rule. It is characteristic of fragipans
that few or many roots may be present in the bleached ver-
tical streaks and that few or no fine roots are present in the
brittle matrix between the bleached streaks. The fine roots
should not be present at intervals of <10 cm except within
bleached vertical streaks, and the mean horizontal dimen-
sions of the brittle matrix should be at least 10 cm.

Sixth, texture of the fine~earth fraction of a fragipan is
finer than fine sand, and the percentage of clay is generally
<35; in most soils appreciably less. The texture normally is
loamy, that is, silt loam, loam, or sandy loam,


140
Sulfohemists

Sulfohemists are the Hemists that have a sulfuric horizon
whose upper boundary is within 50 cm of the surface.

The Sulfohemists are rare in the world and, provisionally, all
Sulfohemists are considered to be Typic Sulfohemists.

Tropohemists

Distinctions between Typic Tropohemists and other sub-
groups

Typic Tropohemists are the Tropohemists that
a. Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier;
b. Have
(1) Less than 25 cm of the subsurface and bottom tiers
consisting of fibric materials; and
(2) Less than 25 cm of the subsurface and bottom tiers
consisting of sapric materials;
c. Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier;
d. Do not have a layer of water within the control section
beneath the surface tier;
e. Do not have a limnic layer(s) that are 5 cm or more thick
within the control section; and
f. Do not have a lithic contact within the control section.
Fibric Tropohemists are like Typic Tropohemists except for
o(1).
Fibric Terric Tropohemists are like Typic Tropohemists ex-
cept for b(J) and c, with or without a.
Fluvaquentic Tropohemists are like Typic Tropohemists ex-
cept for a, with or without 5.
Hydric Tropohemists are like Typic Tropohemists except for
a.

Limnic Tropohemists are like Typic Tropohemists except for
e, with or without a or 6, or both,

Lithic Tropohemists are like Typic Tropohemists except for

'f, with or without all or any of a, 6, c, ore,

Sapric Tropohemists are like Typic Tropohemists except for
b(2).

Sapric Terric Tropohemists are like Typic Tropohemists ex-
cept for b(2) and c, with or without a or e, or both,

Terric Tropohemists are like Typic Tropohemists except for

¢, with or without a or e, or both,

Saprists
Key to great groups

ADA. Saprists that are frozen in some layer within the con-
trol section about 2 months after the summer solstice or that
are never frozen below a depth of 5 cm but have a mean
annual soil temperature lower than 8°C.

Cryosaprists, p. 142


Table 2-Summary of Soil Family and Control Section Criteria - For Complete Definition Refer to Appropriate Section

FEATURE ALFISOLS ARIDISOLS ENTISOLS HisTosois INCEPTISOLS
PARTICLE- Upper 50 cm of Bt or whole Upper 50 cm of Bt or 25 cm to | m, but not Only in terric subgroups; 25 cm to | m except in
size’ Bt if Jess than 50 cm whole Bt if < 50 cm thick”. used in Psamments or the thicker of upper Andepts and Andaquepts.
thick®. If Bt > 4 m deep Psammaquents. 30 cm of mineral layer ot i
and not in upper boundary without Bt, 25 em to 1m, i] Claes except i or within control section, _1 classes used except in
of of grossarenic subgroup, 25 11 classes, except in lithic _ 1.1 Classes except in —— lithic and andic subgroups
‘to 1 m. subgroups and shallow lithic subgroups and 5 classes. and shallow fe
“= __ families, where 7 classes are shallow families where 7 classes are used.
Tr classes, except in lithic, used. 7 classes are used.
andeptic, and arenic
subgroups, and shallow
families, where 7 classes are
used.

Mrveratocy Same as particle-size classes. Same as particle-size Not used in Quartzi- _ Same as particle-size Same as particle-size classes;
If contrasting classes are classes. If contrasting psamments, but used in classes‘ and in if contrasting, onl only upper
present, only the upper classes are present, only other Psamments and all —_—limnic subgroups. materials;in andic subgroups,
materials. the upper materials. other great groups used in lower part of control

with same depth section.

COMBINATION OF
PARTICLE-SIZE
AND MINERALOGY

‘CALCAREOUS AND
REACTION
CLASSES

Som

Depra®

SLOPE

CONSISTENCE

MolsTuRE
‘EQUIVALENT

CRacKs

Not used.

Not used.

Not used in cryic great
groups or Boralfs.

Micro, used in cryic great
groups but not in pergelic
subgroups. Shallow not used
in pergelic subgroups or
lithic subgroups. Used in all
others.

Used in typic, aeric
and udollic subgroups
of Orchraqualfs.

Not used.

Not used.

Not used.

Ashy or cindery used if
relevant.

Not used.

‘Used in all families, except
for borollic subgroups.

Micro and shallow used in
all subgroups but lithic,

Not used.

Not used.

Not used.
Not used.

limits as particle-size
classes. If contrasting
classes are present, only
the upper materials.

Ashy or cindery
used if relevant.

Caicareous classes

25 to 50 om, or

Some soil above lithic

or paralithic contact

shallower than 25 cm.

Not used in sandy,

sandy-skeletal or

fragmental families

or with carbonic or gypsic
mineralogy or Sulfaquents.

Reaction Classes same

control section as for

particle-size.

Not used in cryic
great groups.

Micro not used.
Shallow used in all
subgroups except

lithic and pergelic.

‘Used in Aeric Haplaquents.

Not used.

Used only in Quartzipsam-

Used only in Fluvaquents.

Not used except in
terric subgroups.

Euic and Dysic classes
for whole control
section.

Not used in cryic

or boric great groups.
Micro, in all lithic sub-
groups except Folists for
lithic contact < 18 cm.
Shallow in lithic subgroups
except in Folists for lithic
contact 18-50 cm deep.

Not used.
Not used.

Not used.
Not used.

In Andepts, Andaquepts and
andic subgroups.

Used only in Aquepts other
than Fragiaquepts.
Calcareous classes, 25 to

50 cm, Reaction classes,

25 cm to | m.

Not used in eryic
great groups.

Not used in pergelic
subgroups.

Not used.

Not used.

Not used.
Not used.


Mineral Soil Material
Mineral soil material either

1. Is never saturated with water for more than a few days
and has <20 percent organic carbon by weight; or

2. Is saturated with water for long periods or has been arti-
ficially drained, and has
a. Less than 18 percent organic carbon by weight if 60
percent or more of the mineral fraction is clay;
b, Less than 12 percent organic carbon by weight if the
mineral fraction has no clay; or
c. A proportional content of organic carbon between 12
and 18 percent if the clay content of the mineral fraction
is between zero and 60 percent.
Soil material that has more organic carbon than the amounts
just given is considered to be organic material.

Definition Of Mineral Soils

Mineral soils, in this taxonomy, are soils that meet one of
the following requirements:

1, Mineral soil material <2 mm in diameter (the fine-earth
fraction) makes up more than half the thickness of the up-
per 80 cm (31 in.);

2. The depth to bedrock is <40 cm and the layer or layers of
mineral soil directly above the rock either are 10 cm or
more thick or have half or more of the thickness of the
overlying organic soil material; or

3. The depth to bedrock is 240 cm, the mineral soil material
immediately above the bedrock is 10 cm or more thick, and
either
a. Organic soil material is <40 cm thick and is decom-
posed (consisting of hemic or sapric materials as defined
later) or has a bulk density of 0.1 g cm*® or more; or
b. Organic soil material is <60 cm thick and either is un-
decomposed sphagnum or moss fibers or has a bulk den-
sity that is <0.1.

Diagnostic Surface Horizons; The Epipedon

Six diagnostic horizons that form at the surface are defined.
Any horizon, however, may be at the surface of a truncated
soil. A horizon that forms at the surface is called an
epipedon (Gr. epi, over or upon, and pedon, soil). The
epipedon not only has formed at the surface but it also has
been either appreciably darkened by organic matter or elu-
viated or, as a minimum, rock structure has been destroyed.
Such a horizon may become covered by thin deposits of
fresh alluvium or by thin eolian deposits without losing its
identity as an epipedon. The depth to which an epipedon
must be buried to be considered part of a buried soil is de-
fined below. Generally a buried horizon lies below a depth
of 50 cm or more, usually more.

There can be only one epipedon formed in the mineral sur-
face horizon(s) of a soil. This epipedon may be overlain by


178

long in some part, and that extend upward to the surface
or to the base of an Ap horizon;
(2) A potential linear extensibility of 6 cm or more in
the upper I m of the soil or in the whole soil if a lithic
or paralithic contact is deeper than 50 cm but shallower
than | m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness,
Abruptic Argiborolls are like Typic Argiborolls except for a,
with or without 6/1) or h, or both.
Abruptic Aridic Argiborolls are like Typic Argiborolls except
for a and part of or all of f(1), with or without 6(1) or h,
or both.
Abruptic Udic Argiborolls are like Typic Argiborolls except
for a and f(2), with or without (1) or A, or both.
Albie Argiborolls are like Typic Argiborolls except for a,
(1), and d; or for a and d, with or without (2).
Aguic Argiborolts are like Typic Argiborolls except for d,
with or without f(2).
Aridic Argiborolls are like Typic Argiborolls except for f(1).
Boralfic Argiborolls are like Typic Argiborolls except for
(2).
Borat fic Udie Argiborolls are like Typic Argiborolls except
for b(2) and f(2),
Lithic Argiborolls are like Typic Argiborolls except for ¢ or
for e and f(1).
Pachic Argiborolls are like Typic Argiborolls except for g
with or without d or f(1) or both,
Pachic Udic Argiborolls are like Typic Argiborolls except
for f(2) and g, with or without d.
Udic Argiborolls are like Typic Argiborolls except for /(2).
Ustertic Argiborolls are like Typic Argiborolls except for h
and (1), with or without d or g, or both.
Pertic Argiborolls are like Typic Argiborolls except for h,
with or without d or g, or both.

Calciborolls
Distinctions between Typic Calciborolls and other subgroups

Typic Calciborolls are the Calciborolls that
a. Do not have mottles that have chroma of 2 or less within
1 m of the surface if artificially drained or if the mottled
horizon is continuously saturated with water for as long as
90 days;
b. Have either or both
(1) A color value, dry, of less than 4,5 in the upper 18
cm of the mollic epipedon after mixing, or in any Ap
horizon that is >18 om thick; or
(2) A moisture control section that is dry in some part
less than six-tenths of the time in most years that the soil
temperature at a depth of 50 cm is above 5°C;
c. Do not have a lithic contact within 50 cm of the surface;
and
d. Do not have a petrocalci¢ horizon that has its upper
boundary within 1 m of the surface.
Aridic Calciborolls are like Typic Calciborolls except for .
Lithie Calciborolls are like Typic Calciborolls except for ¢
or for B(1) and ¢.
Petrocatcic Calciborolls are Sike Typic Calciborolls except
for d.


203
Chapter 11

Oxisols

Key To Suborders

CA. Oxisols that are either saturated with water within 30
om of the mineral soil surface 30 days per year in most
years or artificially drained, and have one or more of the
following:
1) a histic epipedon;
2) if faintly mottled or not mottled within 50 cm of the soil
surface, an epipedon that has a moist color value less than
3.5 and chroma of 2 or less immediately below the epipedon;
or
3) if there are distinct or prominent mottles within 50 cm of
the soil surface, a chroma of 3 or less or a hue of 2.5Y or
yellower in 50 percent or more of the horizon immediately
below the epipedon.

Aquox, p. 203

CB, Other Oxisols that have an aridic soil moisture regime,
Torrox, p. 211

CC. Other Oxisols that have an ustic soil moisture regime.
Ustox, p. 219

CD. Other Oxisols that have a perudic soil moisture regime.
Perox, p, 205
CE. Other Oxisols.
Udox, p. 212

Aquox
Key to great groups

CAA, Aquox that have an apparent ECEC of less than 1.50
emol(+) kg"! clay and a pH value (1 M KCl) of 5 or more in
some part of the oxic horizon within a depth of 150 cm of
the soil surface.

Acraquox, p. 204

CAB. Other Aquox that have plinthite forming a continuous
phase within a depth of 125 cm of the soil surface.
Plinthaquox, p. 205

CAC. Other Aquox that have more than 35 percent base sat-
uration (NH,OAc) in all parts within a depth of 125 cm of
the soil surface,

Eutraquox, p, 204

CAD. Other Aquox.
Haplaquox, p. 204

OXI


227

Chapter 12
Spodosols
Key To Suborders

BA, Spodosols that either have an aquic moisture regime? or
are artificially drained and have characteristics associated
with wetness, namely one or more of the following:
1, A histic epipedon;
2. Mottling in an albic horizon or in the upper part of the
spodic horizon;
3. A duripan in the albic horizon;
4, If free iron and manganese are absent or if the color
value, moist, is less than 4 in the upper part of the spodic
horizon, either
a, Have any color if there are no coatings of iron oxides
on the individual grains of silt and sand in or immedi-
ately below the spodic horizon wherever the value, moist,
is 4 or more; or
b. Have fine or medium mottles of iron or manganese in
the materials immediately below the spodic horizon;
5. A placic horizon that rests on a fragipan or on a spodic
horizon or on an albic horizon that is underlain by a spodic
horizon but is not in a spodic horizon.
Aquods, p. 227

BB. Other Spodosols that have a spodic horizon in which the
ratio of free iron (by dithionite-citrate) to carbon (both ele-
mental) is 6 or more in all subhorizons.

Ferrods, p. 231

BC. Other Spodosols that have a spodic horizon in which
some subhorizon that is present in more than half of each
pedon has a ratio of free iron to carbon of <0.2.

Humods, p, 231

BD. Other Spodosols.
Orthods, p. 233

Aquods
Key to great groups
BAA. Aquods that have a fragipan below the spodic horizon

but do not have a placic horizon above the fragipan.
Fragiaquods, p. 228

BAB. Other Aquods that do not have a placic horizon but
have a cryic temperature regime.
Cryaquods, p. 228

BAC. Other Aquods that have a strongly cemented or in-
durated albic horizon that does not slake in water when a
dry fragment is immersed.

Duraquods, p. 228

horizon, duripan, or fragipan is present, the soil need not be sat-
urated below that horizon.

SPO


167

e. Have a CEC (by NH,OAc pH7) of 24 or more cmol(+)
kg"! clay!” in the major part of the soil below a depth of 25
em but above 100 cm or a lithic or paralithic contact if one
is shallower than 100 cm; and
f, Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0,07
or more ina horizon or horizons at least 50 cm thick
and a potential linear extensibility of 6 em or more in
the upper 1,25 m of the soil or in the whole soil if a
lithic or paralithic contact is deeper than 50 cm but
shallower than 1.25 m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness;
Fluventic Ustropepts are like Typic Ustropepts except for 5,
with or without c or e, or both, and the organic-carbon
content is >0.5 percent at a depth of 1.25 m of the cambic
horizon or of the whole soil if there is no cambic horizon.
Lithic Ustropepts are \ike Typic Ustropepts except for d.
Oxic Ustropepts are like Typic Ustropepts except for e or
for e and 6, and the organic-carbon content is <0.5 percent
at a depth 1,25 m below the soil surface.
Vertic Ustropepts are like Typic Ustropepts except for f(1),
with or without any or all of a, 6, or c.

Umbrepts
Key to great groups

IFA. Umbrepts that have a fragipan.
Fragiumbrepts, p. 168

IFB, Other Umbrepts that have a cryic or pergelic
temperature regime.
Cryumbrepts, p. 167

IFC, Other Umbrepts that have a xeric moisture regime,
Xerumbrepts, p. 169

IFD, Other Umbrepts.
Haplumbrepts, p. 169

Cryumbrepts

Distinctions between Typic Cryumbrepts and other
subgroups

Typic Cryumbrepts are the Cryumbrepts that
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
‘Some cambic horizons t! ave properties that approach those of an oxic
horizon do not disperse well. If the ratio of the percentage of water retained
at tension of 1500 kPa to the percentage of measured clay is 0.6 or more, the
parcentage of clay is determined by the higher value of (1) the mesaured per-
centage of clay or (2) 2.5 times the percentage of water retained at tension of
1500 kPa.



72

b, Have tongues of albic materials in the argillic horizon;
cc. Do not have a lithic contact within 50 cm of the soil
surface; and

d. Have an argillic horizon that has a texture finer than
loamy fine sand and is continuous vertically for at least the
upper 15 cm (not in lamellae),

Aquic Glossoboralfs are like Typic Glossoboralfs except for
a, with or without 5 or d, or both,

Eutrie Glossoboralfs are like Typic Glossoboralfs except for
6.

Lithic Glossoboralfs are like Typic Glossoboralfs except for
¢, with or without @ or b, or both.

Psammentic Glossoboralfs are like Typic Glossoboralfs ex-
cept for d, with or without 5.

Natriboralfs

Natriboralfs are the Boralfs that have a natric horizon.
‘They are rare in the United States, and subgroups have not
been developed.

Paleboralfs
Distinctions between Typic Paleboralfs and other subgroups

Typic Paleboralfs are the Paleboralfs that
a. Have an argillic horizon that has an increase in clay con-
tent of <20 percent (absolute) within a vertical distance of
7.5 em from its upper boundary;
b, Do not have a fayer in the upper 75 cm that has a texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
per cubic centimeter or less in the fine-earth fraction, and
that has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1,25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
¢. Do not have mottles that have chroma of 2 or less within
1 m of the surface; and
d, Have an Ap horizon that has a color value, moist, of 4 or
more or a color value, dry, of 6 or more when crushed and
smoothed, or the soil to a depth of 18 cm has these colors
after mixing,
Aquic Paleboralfs are like Typic Paleboralfs except for c.
Mollie Paleboralfs are like Typic Paleboralfs except for d.
The Paleboralfs have had relatively little study in the field
or laboratory. It seems best at this time to consider the
definitions of the great group and of its subgroups as tenta-
tive.

Udalfs
Key to great groups

HEA, Udalfs that have an agric horizon,
Agrudalfs, p. 74

HEB. Other Udalfs that have a natric horizon.
Natrudalfs, p. 79


27

fall, winter, or spring if cold weather virtually stops evapo-
transpiration, There are soils, however, in which the ground
water is always at or very close to the surface. A tidal
marsh and a closed, landlocked depression fed by perennial
streams are examples, The moisture regime in these soils is
called “peraquic." Although the term is not used as a for-
mative element for names of taxa, it is used in their de-
scriptions as an aid in understanding genesis.

Aridic and torric (L. aridus, dry, and L. torridus®, hot and
dry) moisture regimes.--These terms are used for the same
moisture regime but in different categories of the taxonomy.

In the aridic (torric) moisture regime, the moisture control
section in most years is

1, Dry in all parts more than half the time (cumulative) that
the soil temperature at a depth of 50 cm is above 5°C; and

2, Never moist in some or all parts for as long as 90 consec-
utive days when the soil temperature at a depth of 50 cm is
above 8°C.

Soils that have an aridic or a torric moisture regime are
normally in arid climates, A few are in semiarid climates
and either have physical properties that keep them dry, such
as a crusty surface that virtually precludes infiltration of
water, or they are very shallow over bedrock. There is little
or no leaching in these moisture regimes, and soluble salts
accumulate in the soil if there is a source of them.

The limits of soil temperature exclude from these moisture
regimes the very cold and dry regions of Greenland and
adjacent islands. Such fragmentary data are available on the
soils of those regions that no provision is made for their
moisture regimes in this taxonomy.

Udic moisture regime.--The udic (L. udus, humid) moisture
regime implies that in most years the soil moisture control
section is not dry in any part for as long as 90 days
(cumulative). If the mean annual soil temperature is lower
than 22°C and if the mean winter and mean summer soil
temperatures at a depth of 50 cm differ by 5°C or more, the
soil moisture control section is not dry in all parts for as
fong as 45 consecutive days in the 4 months that follow the
summer solstice in 6 or more years out of 10. In addition,
the udic moisture regime requires, except for short periods,
a three-phase system, solid-liquid-gas, in part, but not nec-
essarily in all, of the soil when the soil temperature is above
5°C.

The udic moisture regime is common to the soils of humid
climates that have well-distributed rainfall or that have
enough rain in summer that the amount of stored moisture
plus rainfall is approximately equal to or exceeds the amount
of evapotranspiration. Water moves down through the soil
at some time in most years.

z ideal root, but a better one could not be found. Although
soils may not be hot throughout the year, solls that have a torric moisture
regime are hot and dry in summer,



70

HBD. Other Boralfs that have a cryic temperature regime.
Cryoboralfs, p, 70

HBE. Other Boralfs that have base saturation (by sum of
cations) of 60 percent or more in all subhorizons of the
argillic horizon and are dry in some horizon at some time in
most years.

Eutroboralfs, p. 70

HBF. Other Boralfs that either are never dry in any horizon

in most years or have base saturation (by sum of cations) of

<60 percent in some subhorizon of the argillic horizon.
Glossoboralfs, p. 71

Cryoboralfs
Distinctions between Typic Cryoboralfs and other subgroups

Typic Cryoboralfs are the Cryoboralfs that

a. Do not have a layer above a depth of 75 cm that has
texture finer than loamy fine sand, that is as much as 18 cm
thick, that has a bulk density (at 33 kPa water tension) of
0.95 g per cubic centimeter or less in the fine-earth frac-
tion, and that has either (1) a ratio of measured clay to 1500
kPa water (percentages) of 1.25 or less or (2) a ratio of CEC
(at pH near 8) to 1500 kPa water >1.5 and has more ex-
change acidity than the sum of bases plus KCl-extractable
aluminum;

b. Do not have albic materials tonguing in an argillic hori-
zon;

c. Do not have a lithic contact within 50 cm of the surface;
d. Have an Ap horizon that has a color value, moist, of
more than 3, or the upper soil, to a depth of 15 cm after
mixing, has a moist color value of 4 or more;

e. Have an argillic horizon that has a texture finer than
loamy fine sand and is continuous vertically for at least the
upper 15 cm (not in lamellae); and

f. Do not have mottles that have chroma of 2 or less within
75 cm of the surface, or the soils are not continuously satu-
rated with water for as long as 3 months within 1 m of the
surface where undrained.

Andeptic Cryoboralfs are like Typic Cryoboralfs except for a
or for a and b.

‘Aquic Cryoboralfs are like Typic Cryoboralfs except for /,
with or without 6 or d, or both.

Glossic Cryoboralfs are like Typic Cryoboralfs except for .
Lithic Cryoboralfs are like Typic Cryoboralfs except for c.
Lithic Mollic Cryoboralfs are like Typic Cryoboralfs except
for ¢ and d, with or without 6.

Mollic Cryoboralfs are like Typic Cryoboralfs except for d
or band d.

Psammentic Cryoboralfs are like Typic Cryoboralfs except
for e, with or without 6 or d, or both,

Eutroboralfs
Distinctions between Typic Eutroboralfs and other subgroups

Typic Eutroboralfs are the Eutroboralfs that
a. Have an argillic horizon that


150

IAB, Other Aquepts that have a placic horizon within 1 m
of the mineral soil surface in half or more of each pedon.
Placaquepts, p. 154

IAC, Other Aquepts that have an SAR 213 (or have sodium

saturation that is 215 percent) in half or more of the upper

50 cm of soil that decreases with depth below 50 cm,
Halaquepts, p. 152

IAD, Other Aquepts that have a fragipan.
Fragiaquepts, p, 152

IAE, Other Aquepts that have a cryic or pergelic soil
temperature regime.
Cryaquepts, p. 151

IAF, Other Aquepts that have plinthite that forms a

continuous phase or constitutes more than half the matrix

within some subhorizon in the upper 1.25 m of the soil.
Plinthaquepts, p, 154

IAG. Other Aquepts that have, to a depth of 35 cm or more

or to a lithic or paralithic contact if one is shallower than 35

cm, one or both of the following:

1. Bulk density (at 33 kPa water retention) of the fine-earth

fraction that is <0.85 g per cubic centimeter and an

exchange complex that is dominated by amorphous materials;

or

2, Sixty percent or more of the soil (by weight) is vitric”

volcanic ash, cinders, or other pyroclastic materials.
Andaquepts, p. 150

IAH. Other Aquepts that have a difference of <5°C between
the mean summer and mean winter soil temperatures at a
depth of 50 cm or at a lithic or paralithic contact, whichever
is shallower.

Tropaquepts, p. 155

IAI, Other Aquepts that have an umbric, a mollic, or a
histic epipedon.
Humaquepts, p. 154

TAI. Other Aquepts.
Haplaquepts, p. 152

Andaquepts
Distinctions between Typic Andaquepts and other subgroups

Typic Andaquepts are the Andaquepts that
a. Have in 60 percent or more of the matrix in all
subhorizons between the A or Ap horizon and a depth of 75
cm one or more of the following:
(1) If mottled and if the hue is 2.5Y or redder and the
value, moist, is 5 or more, the chroma, moist, is 2 or less;
(2) If mottled and if the hue is yellower than 2.5Y, the
chroma, moist, is 2 or less;
Included in the meaning of vitric materials in this definition are crystalline
patticles that are coated with glasw and partially devitrified glase as well as
alass,


63

Chapter 5
Alfisols
Key To Suborders

HA. Alfisols that have an aquic moisture regime or are arti-
ficially drained and that have characteristics associated with
wetness, namely, mottles, or iron~manganese concretions >2
mm in diameter, or chroma of 2 or less immediately below
any Ap horizon or below any dark A horizon in which the
moist color value is less than 3,5 after the material is
rubbed, and one of the following:

1, Dominant chroma of 2 or less’ in coatings on the sur-

face of peds and mottles within peds of the argillic or

kandic horizon, or a dominant chroma of 2 or less in the

matrix of the argillic or kandic horizon and mottles of

higher chroma;

2. If there are no motties in the argillic or kandic hori-

zon, a dominant chroma of | or less,

Aqualfs, p. 63

HB. Other Alfisols that have
1. A frigid temperature regime but do not have a xeric
moisture regime; or
2. A cryic temperature regime.
Boralfs, p, 69

HC, Other Alfisols that have one of the following:
1, An ustic moisture regime;
2, An epipedon that is both massive and hard or very
hard when dry and a moisture regime that is aridic but
marginal to ustic;
Ustalfs, p. 81

HD, Other Alfisols that have one of the following:
1. A xeric moisture regime; or
2, An epipedon that is both massive and hard or very
hard when dry and a moisture regime that is aridic but
marginal to xeric.
Xeralfs, p. 88

HE, Other Alfisols that have a udic moisture regime.
Udalfs, p. 72

Aqualfs
Key to great groups

HAA. Aqualfs that have plinthite that forms a continuous
phase or constitutes half or more of the matrix within some

the hue is redder than 10YR because of red patent materials that remain
red after citrate-dithionite extraction, the requirement for low chroma is
waived. Where the soil temperature regime is hyperthermic, inothermie, or
isohyparthermic, chroma up to 4 is tentatively permitted if the hue is 2.6Y or
SY and if mottles are distinct or prominent, Such soils are too few in the
United States to permit testing these limits,



20

3. The ratio of 1500 kPa water content to measured clay is
more than 1.0.

4, The amount of organic carbon exceeds 0.6 percent.

5. Differential thermal analysis shows a low-temperature
endotherm.

6, The bulk density of the fine-earth fraction is <0.85 g per
cubic centimeter at 33 kPa tension.

Andic soil properties

Andic soil properties are tentatively defined as soil materials

meeting one or more of the following three requirements:
J.a. Acid oxalate extractable aluminum plus 1/2 acid ox-
alate extractable iron is 2,0 percent or more in the <2 mm
fraction;

b, Bulk density of the <2 mm fraction, measured at 33
kPa water retention, is <0.90 g cm”; and

c. Phosphate retention is more than 85 percent; or
2.a. More than 60 percent by volume of the whole soil is
volcaniclastic material coarser than 2 mm; and

b. Acid oxalate extractable aluminum plus 1/2 acid ox~
alate extractable iron is 0.40 percent or more in the <2
mm fraction; or
3. The 0.02 to 2.0 mm fraction is at least 30 percent of
the <2 mm fraction and meets one of the following:

a. If the <2 mm fraction has acid oxalate extractable
aluminum plus 1/2 acid oxalate extractable iron of 0.40
percent, there is at least 30 percent volcanic glass in the
0.02 to 2.0 mm fraction;

b. If the <2 mm fraction has acid oxalate extractable
aluminum plus 1/2 acid oxalate extractable iron of 2.0
percent or more, there is at least 5 percent volcanic glass
in the 0.02 to 2.0 mm fraction; or

c. If the <2 mm fraction has acid oxalate extractable
aluminum plus 1/2 acid oxalate extractable iron of be-
tween 0.40 percent and 2.0 percent, there is a propor-
tional content of volcanic glass in the 0.02 to 2.0 mm
fraction between 5 and 30 percent,

Coefficient of linear extensibility, COLE

This coefficient is the ratio of the difference between the
moist length and the dry length of a clod to its dry length.
It is (Lm - Ld)/Ld, where Lm is the length at 33 kPa ten-
sion and Ld is the length when dry, It can be calculated
from the difference in bulk density of the clod when moist
and when dry. COLE can be estimated from shrinkage of a
sample that has been packed at field capacity into a mold
and then dried.

Durinodes

Durinodes (L. durus, hard; nodus, knot) are weakly ce-
mented to indurated nodules. The cement is SiO,, presum-
ably opal and microcrystalline forms of silica, Te’breaks
down in hot concentrated KOH after treatment with HCI to
remove carbonates but does not break down with concen-
trated HCI alone. Dry durinodes do not slake appreciably in


38

Diatomaceous earth
A diatomaceous earth layer is a limnic layer that

1, Has a matrix color value of 3 through $ if not previously
dried, and the value changes irreversibly on drying. The
color change results from irreversible shrinkage of organic
matter coatings on diatoms, which can be identified by mi-
croscopic (440X) examination of dry samples; and

2. Yields a color higher in value and lower in chroma than
10 YR 7/3 on white filter paper that is inserted into a paste
made of the material in a saturated sodium pyrophosphate
solution or the cation-exchange capacity is <240 cmol(+)
kg”! of organic matter (by loss on ignition) or both.

Marl
A marl layer is a limnic layer that
1. Has a color value, moist, of 5 or more; and

2, Reacts with dilute HCl to evolve CO,. Marl usually does
not change color irreversibly on drying. A layer of marl
contains too little organic matter to coat the carbonate, even
before it has been shrunk by drying.

Thickness Of Organic Materials (control
section;

For practical reasons an arbitrary control section has been
established for taxonomy of Histosols. It is either 130 cm
(51 in.) or 160 cm (63 in.) thick, depending on the kind of
material, provided that no lithic or paralithic contact, thick
layer of water, or frozen soil occurs within those limits.
The thicker control section is used if the surface layer to a
depth of 60 cm (24 in.) has three-fourths or more fibers
derived from Sphagnum or from Hypnum or other mosses or
has a bulk density <0.1. Layers of water may be thin or
thick, from a few centimeters to many meters. Water is
taken as the base of the control section only if the water
extends below a depth of 130 cm or 160 cm, depending on
the kind of material above it. A lithic or a paralithic con-
tact shallower than 130 cm (51 in.) or 160 cm (63 in.), de-
pending on the kind of material above it, is taken as the
base of the control section, or the base is placed 25 cm (10
in.) below the depth at which the soil is frozen about 2
months after the summer solstice, An unconsolidated min-
eral substratum shallower than those limits does not change
the base of the control section.

The control section has been divided somewhat arbitrarily
into three tiers, the surface, subsurface, and bottom tiers.

Surface tier

The surface tier is the upper 60 cm (24 in.) if (1) the mate-
rials is fibric and three-fourths or more of the fiber volume
is derived from Sphagnum or mosses or (2) the material has
a bulk density <0.1 g cm, otherwise, the surface tier is the


161

of the moisture control section for more than 90 days
during a period when the soil temperature at a depth of
50 cm exceeds 8°C;
f. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
g. When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry less than sixth-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) during the period when the soil
temperature, at a depth 50 cm below the surface, exceeds
5°CS
(2) If the soil temperature regime is hyperthermic or
isomesic or warmer, are moist in some or all parts of the
soil moisture control section for 90 consecutive days or
more during a period when the soil temperature at a
depth 50 cm below the soil surface is higher than 8°C.
Andic Ustochrepts are like Typic Ustochrepts except for f or
for f and e.
Aridic Ustochrepts are like Typic Ustochrepts except for g.
Fluventic Ustochrepts are like Typic Ustochrepts except for

a.
Lithic Ustochrepts are like Typic Ustochrepts except for 6,
with or without e or g, or both,

Udertic Ustochrepts ate like Typic Ustochrepts except for c
and e, with or without @ or d, or both.

Udic Ustochrepts are like Typic Ustochrepts except for e.
Vertic Ustochrepts are like Typic Ustochrepts except for c,
with or without a or d, or both.

Xerochrepts
Distinctions between Typic Xerochrepts and other subgroups

Typic Xerochrepts are the Xerochrepts that

a. Do not have mottles that have chroma of 2 or less within

75 cm of the soil surface;

b, Have base saturation (by NH,OAc) of 60 percent or more

in some part of the soil between depths of 25 and 75 cm

below the soil surface;

¢. Have a content of organic carbon that decreases regularly

with depth, and unless a lithic or a paralithic contact occurs

at a shallower depth, reaches a level of 0,2 percent or less
within 1.25 m of the soil surface; or have slopes >25
percent,

d, Do not have a lithic contact within 50 cm of the soil

surface;

e, Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or to the base of an Ap horizon;


250

Epiaquic Kanhapludults are like Typic Kanhapludults except
for e.

Lithic Kanhapludults are like Typic Kanhapludults except
for d, with or without a, e, f, or g.

Plinthaquic Kanhapludults are like Typic Kanhapludults ex-
cept for a and c, with or without g.

Plinthie Kanhaptudults are like Typic Kanhapludults except
for c, with or without g.

Rhodic Kanhapludults are like Typic Kanhapludults except
for f.

Paleudults
Distinctions between Typic Paleudults and other subgroups

Typic Paleudults are the Paleudults that
a. Do not have the following combination of characteristics
in the upper 75 cm of the soil if the chroma throughout the
upper 75 cm is not controlled by the uncoated sand grains;
or if the chroma throughout the upper 75 cm is controlled
by uncoated sand grains, do not have the following combi-
nation of characteristics throughout the upper 12.5 cm of
the argillic horizon:
(1) Mottles that have a color value, moist, of 4 or more
and chroma, moist, of 2 or less and mottles of higher
chroma that are due to segregation of iron; and
(2) Saturation with water in the mottled zone at some
time of year when the soil temperature in that zone is
5°C higher, or artificial drainage;
b. Do not have an epipedon as thick as 50 cm if the parti-
cle-size class is sandy throughout;
c. Do not have a subhorizon within 1.5 m of the soil surface
that has >5 percent plinthite;
d. Have an argillic horizon that has a color value, moist, of
4 or more or that has mottles of high chroma in some sub-
horizon within 1 m of the top of the argillic horizon, or
have a color value, dry, more than 1 unit higher than the
value, moist, in some part of the soil within that depth;
e. Have texture finer than loamy fine sand in some part of
the argillic horizon and do not have lamellae in at least the
upper 1 m of the argillic horizon;
f. Do not have a horizon that is above the argillic horizon
whose lower boundary is deeper than 18 cm and that meets
all requirements for a spodic horizon except the horizon is
intermittent; and
g. Do not have a subhorizon in the argillic horizon and
within 1.25 m of the soil surface that has all the properties
of a fragipan except that it is brittle in 40 to 60 percent of
the volume.
Aquic Paleudults are like Typic Paleudults except for a.
Aquic Arenic Paleudults are like Typic Paleudults except for
aand
b, and they have a sandy epipedon that is 50 cm to 1 m
thick.
Arenic Paleudults are like Typic Paleudults except for b, and
they have a sandy epipedon that is 50 cm to 1 m thick.
Arenic Plinthaquic Paleudults are like Typic Paleudults ex-
cept for a, 6, and c, with or without g. They have a sandy
epipedon that is 50 cm to 1 m thick, and have mottles that
have chroma of 2 or less and also have high-chroma mottles


Table 3.--Key to mineralogy classes of Oxisols

Does the mineralogy control section have:

1. More than 40 percent iron oxide (>28 percent Fe) by citrate-dithionite in the
<2 mm fractions?

2. More than 40 percent gibbsite in the <2 mm fractions?

3. 18-40 percent iron oxide (12.6- 28 percent Fe) by citrate-dithionite in the
<2 mm fractions?

4. 18-40 percent gibbsite in the <2 mm fractions?

5. More than 50 percent by weight kaolinite in the <0.002 mm fraction?

6. More than 50 percent by weight halloysite in the <0.002 mm fraction?

none of the above---Mixed

J with or without 2, 4, 5, 6---Ferritic
2 with or without 3, 5, 6---Gibbsitic

3 with or without 5, 6---Ferruginous
4 with or without 5, 6---Allitic

3 and 4 with or without 5, 6---Sesquic
5-~-Kaolinitic

6-~--Halloysitic


249
Sombric Kandiudults are like Typic Kandiudults except for

ir
Kanhapludults

Distinctions between Typic Kanhapludults and other sub-
groups

Typic Kanhapludults are the Kanhapludults that
a, Do not have the following combination of characteristics
in the upper 75 cm of the soil if the chroma throughout the
upper 75 cm is not controlled by the uncoated sand grains;
or if the chroma throughout the upper 75 cm is controlled
by uncoated sand grains, do not have the following combi-
nation of characteristics throughout the upper 12.5 cm of
the argillic or kandic horizon;
1. Mottles that have a color value, moist, of 4 or more
and chroma, moist, of 2 or less accompanied by mottles
of higher chroma that are due to segregation or iron; and
2. Saturation with water in the mottled zone at some time
of year when the soil temperature in that zone is 5°C or
higher or there is artificial drainage;
b. Do not have an epipedon that is 250 cm thick if the par-
ticle-size class is sandy throughout;
c. Do not have a horizon within 150 cm of the soil surface
that has >5 percent plinthite by volume;
d, Do not have a lithic contact within 50 cm of the soil
surface;
e. Have a hue redder than 10YR in all parts of the soil
above a depth of 75 cm that have color value, moist, of 4 or
more if there are mottles of high chroma within that depth
and if the hue becomes redder with depth within 100 cm of
the soil surface;
f. Have an argillic or kandic horizon that has a color hue of
SYR or yellower in some part, or has a value, moist, of 3.5
Or more in some part, or has a value, dry, that is more than
one unit higher than the value, moist;
g. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction and that
has either of the following:
1. A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
2. A ratio of CEC (pH 8.2) to 1500 kPa water of >1.5
and more exchange acidity than the sum of bases plus
KCl-extractable aluminum; and
h, Have an ECEC (sum of bases plus 1 M KCl-extractable
Al) of more than 1.5 cmol(+) kg” clay in all subhorizons to
a depth of 150 cm below the soil surface.
Acric Kanhapludults are like Typic Kanhapludults except for
h, with or without any of ¢, e, or g.
Andie Kanhapludults are like Typic Kanhapludults except
for g, with or without e.
Aquic Kanhapludults are like Typic Kanhapludults except for

a,
Arenic Kanhapludults are like Typic Kanhapludults except
for b.

Arenic Plinthic Kanhapludults are like Typic Kanhapludults
except For b and ¢,

ULT


23

underlying material is not a single material, chunks of gravel
size that can be broken out disperse more or less completely
during 15 hours of end-over-end shaking in water or in
sodium hexametaphosphate solution and, when moist, the
material can be dug with difficulty with a spade.

Permafrost

Permafrost is a layer in which the temperature is perennially
at or below 0°C, whether the consistence is very hard or
loose. Dry permafrost has loose consistence.

Petroferric contact

A petroferric (Gr. petra, rock, and L, ferrum, iron; implying
ironstone) contact is a boundary between soil and a continu-
ous layer of indurated material in which iron is an impor-
tant cement and organic matter is absent or is present only
in traces, The indurated layer must be continuous within
the limits of a pedon but may be fractured if the average
lateral distance between fractures is >10 cm, The indurated
layer is distinguished from a placic horizon and from an in-
durated spodic horizon (ortstein) because it contains little or
no organic matter. Organic matter is present in both the
other horizons.

Several features can aid in making the distinction between a
lithic and a petroferric contact. First, a petroferric contact
is roughly horizontal, Second, the amount of iron in the
material immediately below a petroferric contact is high,
The content of Fe,0, normally ranges upward from 30 per-
cent. Third, the ironstone sheets below a petroferric contact
are thin, Their thickness ranges from a few centimeters to a
very few meters. Sandstone, on the other hand, may be thin
or very thick, may be level bedded or tilted, and may have
only a small percentage of Fe,O,. In the Tropics the iron-
stone commonly is more or less vesicular.

Plinthite

Plinthite (Gr. plinthos, brick) is an iron-rich, humus-poor
mixture of clay with quartz and other dilutents, It com-
monly occurs as dark red mottles, which usually are in
platy, polygonal, or reticulate patterns, Plinthite changes
irreversibly to an ironstone hardpan or to irregular aggre-
gates on exposure to repeated wetting and drying, especially
if it is exposed also to heat from the sun. The lower
boundary of a zone in which plinthite occurs usually is dif-
fuse or gradual, but it may be abrupt at a lithologic discon-
tinuity,

Generally, plinthite forms in a horizon that is saturated with
water at some season. The original segregation of the iron
normally is in the form of soft, more or less clayey, red or
dark red mottles. The mottles are not considered plinthite
unless there has been enough segregation of iron to permit
irreversible hardening on exposure to wetting and drying.
Plinthite in the soil usually is firm or very firm when the
soil moisture content is near field capacity and hard when
the moisture content is below the wilting point. Plinthite
does not harden irreversibly as a result of a single cycle of


148

b. Have an epipedon that is 25 cm or more thick and meets
the color requirements of a mollic epipedon;

¢. Are not thixotropic in any horizon between depths of 25
cm and 1 m;

d. Do not have a lithic contact within 50 cm of the soil
surface;

e. Have cation-exchange capacity® of >30 cmol(+) kg” soil
(by NH,OAc) in all subhorizons above a lithic contact or a
depth of 1 m, whichever is shallower, or have >10 percent
weatherable minerals in the 20- to 200-micrometer fraction.
Aquic Dystrandepts are like Typic Dystrandepts except for a.
Entic Dystrandepts are like Typic Dystrandepts except for b.
Hydric Dystrandepts are like Typic Dystrandepts except for
¢, with or without b.

Hydric Lithic Dystrandepts are like Typic Dystrandepts
except for c and d, with or without b.

Lithic Dystrandepts are like Typic Dystrandepts except for
d, with or without b.

Oxic Dystrandepts are like Typic Dystrandepts except for e,
with or without 4, and they have <10 percent weatherable
minerals in the 20- to 200-micrometer fraction.

Eutrandepts
Distinctions between Typic Eutrandepts and other subgroups

Typic Eutrandepts are the Eutrandepts that

a. Do not have mottles that have chroma of 2 or less within
1 m of the soil surface;

b. Have an epipedon, 25 cm or more thick, that meets the
color requirements of a mollic epipedon;

c, Do not have a lithic contact within 50 cm of the soil
surface;

d. Do not have a subhorizon within 1.5 m of the surface
that contains soft, powdery secondary lime;

e. Have an ustic moisture regime;

f. Do not have a horizon within | m of the surface that is
>15 cm thick and that either contains 20 percent or more
(by volume) durinodes or has >50 percent (by volume)
fragments of a duripan in which the average horizontal
repeat distance between vertical cracks is <J0 cm.

Duric Eutrandepts are like Typic Eutrandepts except for f.
Entic Eutrandepts are like Typic Eutrandepts except for b or
for b and d.

Lithie Eutrandepts are like Typic Eutrandepts except for c.
Udic Eutrandepts are like Typic Eutrandepts except for e,
and they have a udic moisture regime.

Ustollic Eutrandepts are like Typic Eutrandepts except for d.
Xeric Eutrandepts are like Typic Eutrandepts except for e,
and they have a xeric moisture regime.

"andepts in » perhumid climate are nevar dry while they remain in place,
‘They lose CEC if allowed to become air dry before the determination is made.
‘The values used in these definitions are those determined on soil samples that
have never been allowed to dry, but the values have been recalculated to an
ovendry basis. The CEC of samples that have been air dried may be used if it
has been determined that drying does not affect the CEC of that soil.


90

b, Do not have a layer in the upper 75 cm that has a texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
per cubic centimeter or less in the fine-earth fraction, and
that has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
1.5 and more exchange acidity than the sum of bases plus
KCl-extractable aluminum;
c, Either have an Ap horizon that has a color value, moist,
of 4 or more or a color value, dry, of 6 or more, when
crushed and smoothed, or the soil to a depth of 18 cm, after
mixing, has those colors; and
d. Do not have mottles that have chroma of 2 or less in the
upper 25 cm of the argillic horizon and do not have mottles
that have chroma of 2 or less within 40 cm of the surface if
the horizons that have mottles of low chroma are saturated
with water at some time of the year when the soil tempera-
ture is 5°C or higher in those horizons. Mottles are not the
same as skeletans that may also have low chroma.
Mollic Fragixeralfs are like Typic Fragixeralfs except for c,
with or without d.
Ochreptic Fragixeralfs are like Typic Fragixeralfs except for
a.

Haploxeralfs

Distinctions between Typic Haploxeralfs and other sub-
groups

Typic Haploxeralfs are the Haploxeralf's that

a, Do not have mottles that have chroma of 2 or less within

75 cm of the soil surface if the mottled horizon is saturated

with water at some time when the temperature of that

horizon is 5°C or higher or there is artificial drainage;

b, Have an A horizon that throughout its upper 10 cm has a

color value, moist, of 3.5 or more or has <0.7 percent or-

ganic carbon in some part, or have an Ap horizon that has a

color value, moist, of 3.5 or more or contains <0.7 percent

organic carbon;

c. Do not have a lithic contact within 50 cm of the soil

surface;

d, Have exchangeable sodium that is <15 percent of the CEC

(at pH 8.2) throughout the argillic horizon;

e. Have <5 percent plinthite (by volume) in all subhorizons

within 1,5 m of the soil surface;

f, Have an argillic horizon that has base saturation (by sum

of cations) of 75 percent or more throughout the upper 75

cm or to a lithic or paralithic contact, whichever is shal-

lower;

g. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
or to the base of an Ap horizon if the soil is not irri-
gated;

(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or


176

paralithic contact is deeper than 50 cm but shallower than
1 m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness.
Andaqueptic Haplaquolls are like Typic Haplaquolls except
for a or for a and c,
Cumulic Haplaquolls are like Typic Haplaquolls except for c
or for c and e.
Durie Haplaquolls are like Typic Haplaquolls except for d.
Fluvaquentic Haplaquolls are like Typic Haplaquolls except
for e.
Histic Haplaquolls are like Typic Haplaquolls except for f.
Lithie Haplaquolls are like Typic Haplaquolls except for g.
Vertic Haplaquolls are like Typic Haplaquolls except for h,
with or without c or e, or both,

Natraquolls

Natraquolls are the Aquolis that

1, Have a natric horizon; and

2. Do not have a duripan that has its upper boundary within
J m of the soil surface.

Borolls
Key to great groups

GEA. Borolls that have an argillic horizon that has its upper
boundary deeper than 60 cm below the mineral soil surface”
and that have texture finer than loamy fine sand in all
subhorizons above the argillic horizon.

Paleborolls, p. 182

GEB. Other Borolls that have a cryic or pergelic temperature
regime.
Cryoborolls, p. 179

GEC. Other Borolls that have a natric horizon but do not
have a cambic horizon that is above the natric horizon and
separated from it by an albic horizon.

Natriborolls, p. 182

GED. Other Borolls that have an argillic horizon but do not
have a cambic horizon that is above the argillic horizon and
separated from it by an albic horizon.

Argiborolls, p. 177

GEE. Other Borolls that have a mollic epipedon that, below
any Ap horizon, is 50 percent or more by volume
wormholes, wormcasts, or filled animal burrows and that
either rests on a lithic contact or has a transition to the
underlying horizon in which 25 percent or more of the
material is discrete wormholes, wormeasts, or animal
burrows filled with material from the mollic epipedon and
the underlying horizon.

Vermiborolls, p. 183

21 there in a nurface mantle that has >60 percent vitric volcanic sh, cinders,
‘or other vitrie pyroclastic materials, the depth to the argillic horizon is mea-
sured from the base of this mantle rather than from the mineral eoil surface.



46

lithic or paralithic contact, a petrocalcic or petrogypsic
horizon, duripan, or to a depth of 1 m, whichever is shal-
lowest.

Strongly contrasting particle-size classes

In applying names of particle-size classes, the weighted av-
erage particle-size class of the control section or of the
horizon listed is named unless there are strongly contrasting
particle-size classes within the control section or the hori-
zons. If there are strongly contrasting particle-size classes,
both particle-size classes are named. Thus, if the weighted
average of the upper part of the control section is loamy
fine sand and the lower part is clay, the family differentia is
sandy over clayey. If there are more than two contrasting
particle-size classes within the control section, the classes
differing most in median particle size are named. Sandy
includes fine sand as well as coarser sands. Medial, ashy, or
thixotropic substitutes are applied only if the materials ex-
tend at least 10 cm into the upper part of the control sec-
tion.

The following particle-size classes are strongly contrasting if
the transition between them is less than 12.5 cm thick:
1. Cindery over sandy or sandy-skeletal.
2. Cindery over loamy.
3. Sandy-skeletal over loamy if the loamy material has
<50 percent fine or coarser sand.
4. Sandy over loamy if the loamy material has <50
percent fine or coarser sand.
5. Sandy over clayey.
6. Ashy over cindery.
7. Ashy over loamy-skeletal.
8. Ashy over loamy.
9. Loamy-skeletal over fragmental.
10. Loamy-skeletal over sandy.
11, Loamy-skeletal over clayey if there is an absolute
difference of >25 percent in the percentages of clay in
the fine-earth fractions.
12, Clayey-skeletal over sandy.
13, Medial over fragmental.
14. Medial over cindery.
15, Medial over sandy or sandy-skeletal,
16, Medial over loamy-skeletal.
17. Medial over loamy.
18. Medial over clayey.
19. Medial over thixotropic.
20, Coarse-loamy over fragmental.
21, Coarse-loamy over sandy or sandy-skeletal if the
coarse-loamy material has <50 percent fine or coarser
sand,
22, Loamy over sandy or sandy-skeletal if the loamy
material has <50 percent fine or coarser sand.
23. Coarse-loamy over clayey.
24. Coarse-silty over sandy or sandy-skeletal.
25, Coarse-silty over clayey.
26, Fine-loamy over fragmental.
27. Fine-loamy over sandy or sandy-skeletal.
28, Fine-loamy over clayey if there is an absolute
difference of >25 percent in the percentage of clay.
29, Fine-loamy over cindery.


85

with water at sometime when the soil temperature at that

depth is 5°C or higher or the soil has artificial drainage;

b. Do not have a lithic contact within $0 cm of the soil

surface;

c. When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are moist more than six-tenths of the time in half or
more years in some part of the moisture control section
(not necessarily the same part) when the soil temperature
at a depth of 50 cm exceeds 5°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, are moist in most years in some or
all parts of the moisture control section for 180 or more
days during a period when the soil temperature at a
depth of 50 cm exceeds 8°C; and

4, When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry for more than 135 cumulative days in some part
of the Moisture control section when the soil temperature
at a depth of 50 cm exceeds $°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some of all parts
of the moisture control section for more than 90 days
during a period when the soil temperature at a depth of
50 cm exceeds 8°C; and

e. Have an argillic or kandic horizon that has a color hue of

SYR or yellower in some part, or has a value, moist, of 3.5

or more in some part, or has a value, dry, that is more than

one unit higher than the value, moist.

Aquic Kanhaplustalfs are like Typic Kanhaplustalfs except

for a,

Aridic Kanhaplustalfs are like Typic Kanhaplustalfs except

for ¢.

Lithic Kanhaplustalfs are like Typic Kanhaplustalfs except

for b with or without c.

Rhodic Kanhaplustal/s are like Typic Kanhaplustalfs except

for e.

Udic Kanhaplustalfs are like Typic Kanhaplustalfs except

for d.

Natrustalfs
Distinctions between Typic Natrustalfs and other subgroups

Typic Natrustalfs are the Natrustalfs that

a. Do not have mottles that have chroma of 2 or less within
50 cm of the soil surface if there is ground water in the
mottled horizon at some time of year when the soil temper-
ature is 5°C or higher;

b, Have an Ap horizon that has a color value, moist, more
than 3, of the surface soil to a depth of 18 cm, after mixing,
has a color value, moist, more than 3;

c. Do not have a salic horizon that has its upper boundary
within 75 cm of the soil surface; and

4. Do not have a petrocalcic horizon that has its upper
boundary within 1.5 m of the surface.

Aquic Natrustalfs ave \ike Typic Natrustalfs except for a,
with or without 5.

Mollic Natrustalfs are \ike Typic Natrustalfs except for b,
Petrocalcic Natrustalfs are like Typic Natrustalfs except for


260
Chromuderts

Distinctions between Typic Chromuderts and other sub-
groups

Typic Chromuderts are the Chromuderts that

a. Do not have distinct or prominent mottles within 50 cm
of the soil surface in more than half of each pedon (the
terms refer to contrast, not to size of the mottles); and

b. Have a color value, moist, less than 3.5 and a value, dry,
less than 5.5 throughout the upper 30 cm in more than half
of each pedon.

Aquentic Chromuderts are like Typic Chromuderts except for
aand b.

‘Aquic Chromuderts are like Typic Chromuderts except for a.
Entic Chromuderts are like Typic Chromuderts except for 6.

Pelluderts

Typic Pelluderts are the Pelluderts that have a color value,
moist, less than 3.5 and a value, dry, less than 5.5 through-
out the upper 30 cm in more than half of each pedon.

Description of subgroups

‘Typic Pelluderts.--The central concept or typic subgroup of
Pelluderts is fixed on soils that have a thick, dark epipedon.
The color of the surface layer and the content of organic
matter are about the only visible properties that vary in the
great group. Base saturation also varies. These soils are
extensive locally on the Gulf Coast in Texas, They were
formerly cultivated, but most of them are now used for
pasture.

Entic Pelluderts.~-These soils are like Typic Pelluderts ex-
cept for their color value. This is the only subgroup besides
Typic Pelluderts that has been recognized in the United
States. A surface horizon that has a color value, moist, less
than 3.5 and a color value, dry, less than 5.5 either is absent
or is <30 cm thick in more than half of each pedon. These
soils are not extensive in the United States. They are used
mostly for pasture.

Usterts

Key to great groups

DDA. Usterts that have a chroma, moist, of 1.5 or more in
some part of the matrix of the upper 30 cm in more than

half of each pedon.
Chromusterts, p, 261

DDB. Other Usterts.
Pellusterts, p. 261


180

Argic Cryoborolls are like Typic Cryoborolls except for a,
and the argillic horizon is continuous throughout each
pedon.

Argic Lithic Cryoborolls are like Typic Cryoborolls except
for a and g, with or without e, and the argillic horizon is
continuous throughout each pedon.

Argic Pachic Cryoborolls are like Typic Cryoborolls except
for a and e, with or without c.

Argic Vertic Cryoborolls are like Typic Cryoborolls except
for a and /, with or without any or all of c, e, and k.
Boralfic Cryoborolts are like Typic Cryoborolls except for a
and i, with or without e.

Boralfic Lithic Cryoborolls are like Typic Cryoborolls except
for a, g, and i, with or without d or e, or both.

Caleic Cryoborolls are like Typic Cryoborolls except for d.
Calcic Pachic Cryoborolls are like Typic Cryoborolls except
for d and e, with or without a or c, or both.

Cumulic Cryoborolls are like Typic Cryoborolls except for e
and k or for c, e, and k.

Duric Cryoborotls are like Typic Cryoborolls except for j or
for j and a.

Lithic Cryoborolls are like Typic Cryoborolls except for g,
with or without any or all of d, e, and A.

Lithie Ruptic-Argie Cryoborolls are like Typic Cryoborolls
except for a and g, and the argillic horizon is intermittent in
each pedon.

Lithic Ruptic-Entic Cryoborolls are like Typic Cryoborolls
except for g and f, with or without h,

Natric Cryoborolls are like Typic Cryoborolls except for a,
with or without /, and have an SAR 213 (or 215 percent
saturation with exchangeable sodium) in the major part of
the argillic horizon.

Pachic Cryoborolls are like Typic Cryoborolls except for e,
with or without ¢.

Pergelic Cryoborolls are like Typic Cryoborolls except for A.
Vertic Cryoborolls are like Typic Cryoborolls except for /,
with or without all or any of c, e, or k,

Haploborolls

Distinctions between Typic Haploborolls and other
subgroups
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
per cubic centimeter or less in the fine-earth fraction, and
that has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of the bases
plus KCl-extractable aluminum;
b. Do not have mottles that have chroma of 2 or less within
1 m of the surface if artificially drained, or if undrained,
are not continuously saturated with water in the mottled
horizon for as long as 90 days in most yea
¢. Have both the following:
(1) Either or both:
(a) A color value, dry, of less than 4.5 in the upper 18
cm of the mollic epipedon, after mixing, or in any Ap
horizon that is >18 cm thick; or



217

CEEL. Other Hapludox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Hapludox

CEEM. Other Hapludox that have a color hue of 2.5 YR or
redder with moist values of less than 4 in most of the 25 to
125 cm depth from the soil surface.

Rhodic Hapludox

CEEN. Other Hapludox that have a color hue of 7.5 YR or
yellower with moist values of 6 or more in most of the 25 to
125 cm depth from the soil surface.

Xanthic Hapludox

CEEO. Other Hapludox.
Typic Hapludox

Kandiudox
Key to subgroups

CEDA. Kandiudox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and a petroferric contact within 125 cm of the
soil surface.

Aquic Petroferric Kandiudox

CEDB, Other Kandiudox that have a petroferric contact
within 125 cm of the soil surface.
Petroferric Kandiudox

CEDC. Other Kandiudox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface and a lithic contact within 125 cm of the
soil surface.

Aquic Lithic Kandiudox

CEDD, Other Kandiudox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Kandiudox

CEDE, Other Kandiudox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface and mottles of 4 or more value moist and 2 or
less chroma within a depth of 125 cm of the soil surface.
Plinthaquic Kandiudox

CEDF. Other Kandiudox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Kandiudox

CEDG. Other Kandiudox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface.

Aqule Kandiudox

CEDH, Other Kandiudox that have an 18 cm or thicker
layer in the upper 75 cm with a bulk density less than 1

OXI


207
Eutroperox
Key to subgroups

CDCA. Eutroperox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and a petroferric contact within 125 cm of the
soil surface.

Aquic Petroferric Eutroperox

CDCB. Other Eutroperox that have a petroferric contact
within 125 cm of the soil surface,
Petroferric Eutroperox

CDCC. Other Eutroperox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface and a lithic contact within 125 cm of the
soil surface.

Aquic Lithic Eutroperox

CDCD. Other Eutroperox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Eutroperox

CDCE. Other Eutroperox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface and mottles of 4 or more value moist and 2 or
less chroma within a depth of 125 cm of the soil surface.
Plinthaquic Eutroperox

CDCF, Other Eutroperox that have more than 5 percent
Plinthite in some horizon within a depth of 125 cm of the
soil surface,

Plinthic Eutroperox

CDCG. Other Eutroperox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface.

Aquic Eutroperox

CDCH, Other Eutroperox that have more than 40 percent
clay in the surface 18 cm after mixing and the upper
boundary of @ kandic horizon within a depth or 150 cm of
the soil surface.

Kandiudalfic Eutroperox

CDCI. Other Eutroperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and have the lower boundary of the oxic
horizon within a depth of 125 cm of the soil surface.
Umbreptic Eutroperox

CDCJ. Other Eutroperox that have the lower boundary of
the oxic horizon within a depth of 125 cm of the soil sur-
face.

Inceptic Eutroperox

CDCK. Other Eutroperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and a color hue of 2.5 YR or redder with

<j
oO


61

1. Other soils that
~ have no sulfidic material within 50 cm of the mineral soil
surface; and
- have between 20 and 50 cm below the mineral soil surface
an 1 value of 0.7 or less in one or more subhorizons or less
than 8 percent clay in one or more subhorizons; and
~ have one or more of the following:
1. An umbric, mollic, histic (either mineral or organic) or
plaggen epipedon; or
2. A cambic horizon or both an aquic moisture regime
and permafrost; or
3. Within 1 m of the surface, a calcic, petrocalcic, gypsic,
petrogypsic, or placic horizon or a duripan; or
4. A fragipan or an oxic horizon with its upper boundary
between a depth of 150 and 200 cm; or
5. A sulfuric horizon whose upper boundary is within 50
cm of the soil surface; or
6. In half or more of the upper 50 cm, an SAR of >13°
(or sodium saturation that is >15 percent) that decreases
with depth below 50 cm and, within a depth of 1 m,
have ground water at some period during the year when
the soil is not frozen in any part. .
Inceptisols, p. 145

J. Other solls .
Entisols, p. 111

She percentage of exchangeable sodium (ESP) is used in the definition of the
natric horizon and in a number of the taxa, Since this text was written, the
jalinity Laboratory (personal communication from C.A. Bower) has
vised its definition of sodic (atkali) soils and the method for measuring the
sodium adsorption ratio (SAR) ae follows: SAR is measured by the normal
mathod if the conductivity (EC) of the saturation extract is 20 a8 m ~! at
28°C. If the conductivity is > 20 dS mTM! and SAR is 10, SAR is determined
‘on a sample thst has been leached with dlatilled water until EC of the
leachate decreases to about 4 dS m”? but not to 4. ESP of 2 15 ia replaced
by SAR of 21S if EC is large enough to require a correction for soluble salts in
caleulating ESP. If EC is low enough (<4) that no correction is needed for
soluble salts, ESP is determined directly from the replaced cations,



86

Salorthidic Natrustalfs are like Typic Natrustalfs except for
c.

Paleustalfs
Distinctions between Typic Paleustalfs and other subgroups

Typic Paleustalfs are the Paleustalfs that

a. Do not have mottles that have chroma of 2 or less within

75 cm of the soil surface if the mottled horizon is saturated

with water at some time of the year when the temperature

of the horizon is 5°C or higher,

b. Have texture finer than loamy fine sand in some sub-

horizon within 50 cm of the soil surface;

c. Have <5 percent plinthite by volume in all subhorizons

within 1.5 m of the soil surface;

d. When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry for more than four-tenths of the cumulative days
in some part of the moisture control section when the soil
temperature at 2 depth of 50 cm exceeds 5°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days
during a period when the soil temperature at a depth of
50 cm exceeds 8°C;

e. Have an argillic horizon that has base saturation (by sum

of cations) of 75 percent or more in some part;

f. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part, and that extend upward to the surface
or to the base of an Ap horizon if the soil is not irri-
gated;

(2) A coefficient of linear extensibility (COLE) of 0.07
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.25 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.25 m; and

(3) More than 35 percent clay in horizons that total >50
cm in thickness;

g. Do not have a petrocalcic horizon that has its upper

boundary within 1,5 m of the soil surface;

h, When not irrigated and when not fallowed to store mois-

ture:

(1) If the soil temperature regime is mesic or thermic,
are dry less than six-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) during a period when the soil
temperature at a depth of 50 cm exceeds 5°C; or

(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, are moist in most years in some or
all parts of the moisture control section for 90 consecu-
tive days or more during a period when the soil temper-
ature at a depth of 50 cm exceeds 8°C;

i. Have CEC of 24 or more cmol(+) kg”! clay (by 1 M

NH,OAc pH7) in the major part of the argillic horizon or

the ‘major part of the upper 100 cm of the argillic horizon is

thicker than 100 cm;



123

Ustie Torriorthents are like Typic Torriorthents except for d,
They either (I) have a hyperthermic or an iso soil tempera-
ture regime or (2) have a thermic, mesic, or a frigid soil
temperature regime and have an aridic moisture regime that
borders on an ustic regime,

Vertic Torriorthents are like Typic Torriorthents except for c
or for c and d. Unless the soil is irrigated, the cracks re-
main open in most years for more than 240 days, cumula-
tive, and are not closed in most years for as many as 60
consecutive days at any season,

Xerertic Torriorthents are like Typic Torriorthents except for
c, with or without d or e, or both. They have a thermic,
mesic, or frigid soil temperature regime and have cracks that
are closed for 60 consecutive days or more during the 120
days following the winter solstice in more than 7 years out
of 10.

Xeric Torriorthents are like Typic Torriorthents except for
d, They have a thermic, mesic, or frigid soil temperature
regime and a torric moisture regime that borders on a xeric
regime.

‘Troporthents

Distinctions between Typic Troporthents and other sub-
groups

Typic Troporthents are the Troporthents that
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density in the fine-earth fraction (at 33 kPa
moisture tension) of 0.95 g per cubic centimeter or less, and
that has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
more than 1.5 and more exchange acidity than the sum of
bases plus KCl-extractable aluminum; and
b. Do not have a lithic contact within 50 cm of the soil
surface,
Andeptic Troporthents are like Typic Troporthents except for

a,
Lithic Troporthents are like Typic Troporthents except for b.
Udorthents

Distinctions between Typic Udorthents and other subgroups

Typic Udorthents are the Udorthents that
a, Do not have a Jayer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density in the fine-earth fraction (at 33 kPa
moisture tension) of 0.95 g per cubic centimeter or less, and
that has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less, or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water >1.5
and more exchange acidity than the sum of bases plus
KCl-extractable aluminum.
b. Are not saturated with water for as long as | month
within 1.5 m of the surface;


199

surface, have an organic carbon content of 0.3 percent or

less at a depth within 1.25 m of the surface; or the slope is

>25 percent;

g. Do not have a lithic contact within 50 cm of the soil

surface;

h. Have base saturation (by sum of cations) of >75 percent

throughout the upper soil to a depth of 75 cm or above a

lithic or paralithic contact, whichever is shallower;

i. Do not have a mollic epipedon that has granular structure

and that, below any Ap horizon, has 50 percent or more by

volume or wormholes, wormcasts, or filled animal burrows;

J. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m; and
(3) More than 35 percent clay in horizons that have a
total thickness of >50 cm;

k. Have a xeric moisture regime.

Aquic Haploxerolls are \ike Typic Haploxerolls except for a,

with or without 6 or e, or both,

Aquic Duric Haploxerolls a and d, with or without all or any

of b, e, or f.

Aquultic Haploxerolls are like Typic Haploxerolls except for

aand h, with or without e.

Aridic Haploxerolls are like Typic Haploxerolls except for k

or for h and k and have an aridic moisture regime that bor-

ders on xeric,

Aridic Duric Haploxerolls are like Typic Haploxerolls except

for d and k, with or without all or any of b, e, or h, and

have an aridic moisture regime that borders on xeric.

Calcic Haploxerolls are like Typic Haploxerolls except for 6

or for and e.

Calcic Pachic Haploxerolls are like Typic Haploxerolls ex-

cept for 6 and c, with or without a or e, or both.

Calciorthidic Haploxerolls are like Typic Haploxerolls except

for 6 and k, with or without e, and have an aridic moisture

regime,

Cumulic Haploxerolls are like Typic Haploxerolls except for

¢ and f, with or without all or any of a, 6, e, and k.

Cumulic Ultic Haploxerolls are like Typic Haploxerolls ex-

cept for c, f, and A, with or without all or any of a, b, or e.

Entic Haploxerolls are like Typic Haploxerolls except for e.

Entic Ultic Haploxerolls are like Typic Haploxerolls except

for e and h.

Fluvaquentic Haploxerolls are like Typic Haploxerolls except

for a and f, with or without 4 or e, or both.

Fluyentic Haploxerolls are like Typic Haploxerolls except for

f, with or without or e, or both.

Lithic Haploxerolls are like Typic Haploxerolls except for g,

with or without all or any of e, b, or k.

Lithic Ultic Haploxerolls are like Typic Haploxerolls except

for g and h, with or without e.

Pachic Haploxerolls are like Typic Haploxerolls except for

¢, with or without ail or any of a, e, or k.



126

or more darker and that meets all requirements of a spodic
horizon except the index of accumulation,

Alfie Cryopsamments are like Typic Cryopsamments except
for a.

Aquic Cryopsamments are like Typic Cryopsamments except
for b.

Lithic Cryopsamments are like Typic Cryopsamments except
for d or for c and d.

Pergelic Cryopsamments are like Typic Cryopsamments ex-
cept for c, with or without b.

Spodic Cryopsamments are like Typic Cryopsamments except
for e.

Quartzipsamments

Distinctions between Typic Quartzipsamments and other
subgroups

Typic Quartzipsamments are the Quartzipsamments that

a, Do not have mottles above a depth of 1 m that have
chroma of 2 or less or, if the color is due to uncoated sand
grains, do not have the water table within 1 m of the soil
surface for as many as 60 days, cumulative, in most years;
b. Do not have an albic horizon? at the surface or immedi-
ately under an A or an Ap horizon that is underlain by an-
other horizon that has a color value more than one unit
darker or chroma of 6 or more;

c. Do not have a lithic contact within 50 cm of the soil
surface;

d. Have a clay fraction that has a higher CEC than that of
the clay of an oxic horizon or >25 percent of the surfaces of
sand grains are uncoated;

e, Have <5 percent plinthite in all horizons above a depth of
1 m; and

f. Have a udic moisture regime,

Aquic Quartzipsamments ate like Typic Quattzipsamments
except for a.

Haplaquodic Quartzipsamments are like Typic Quartzipsam-
ments except for a and 6. They have a ground-water table
that is within 1 m of the soil surface for 6 months or more
in most years or are a ‘ially drained, and they have a
difference of 5°C or more between the mean summer and
mean winter soil temperatures at a depth of 50 cm.

Lithic Quartzipsamments are like Typic Quartzipsamments
except for c.

Orthoxic Quartzipsamments are like Typic Quartzipsamments
except for d, with or without e, and they have enough clay
to coat at least 75 percent of the surfaces of the sand grains.
Spodic Quartzipsamments are like Typic Quartzipsamments
except for b.

Tropaquodie Quartzipsamments are like Typic Quartzipsam-
ments except for a and 4, and they have a difference of
<5°C between the mean winter and mean summer soil tem-
peratures at a depth of 50 cm.

Ustic Quartzipsamments are like Typic Quartzipsamments
except for /.

Ustoxic Quartzipsamments are like Typic Quartzipsamments
except for d and f, with or without e. They have an ustic

Fhe albic horizon must be thick enough to be preserved after the soll to =
depth of 18 cm is mixed.


31

in coastal marshes near the mouths of rivers that carry
noncalcareous sediments, but they may occur in fresh-water
marshes if there is sulfur in the water. If the soil is
drained, the sulfides oxidize and form sulfuric acid. The
pH, which normally is near neutrality before drainage, may
drop below 2. The acid reacts with the soil to form iron
and aluminum sulfates. The iron sulfate, jarosite, segregates
and forms the bright-yellow mottles that characterize a sul-
furic horizon, The transition from sulfidic materials to a
sulfuric horizon normally requires a very few years. A
sample of sulfidic materials, if air dried slowly in shade for
about 2 months with occasional remoistening, becomes ex-
tremely acid, For quick identification in the field, a sample
can be oxidized by boiling i in concentrated H,O, and mea-
suring the drop in pH’,

Thixotropy

Thixotropy is "a reversible gel-sol transformation under
isothermal shearing stress following rest" (Webster’s 1967).
The term means "to change by touch". Many kinds of
thixotropic substances have been identified and studied, in-
cluding some sesquioxide gels, kaolinite gels, montmoril-
lonite gels, greases, inks, paints, protoplasm, blood coagula,
nitrocellulose solutions, and drilling muds. Thixotropy ap-
parently is the result of a kind of structure that, if broken
down, can rebuild itself. The breakdown may be caused by
one of several actions; by agitation, by shearing, or even by
ultrasonic waves. Some natural (untreated) soil materials ex-
hibit this property. A field test of thixotropic soil is this:
Press a bit of wet soil between thumb and forefinger; at
first it resists deformation, having some rigidity, or elastic-
ity, or both; under increasing pressure the soil can be
molded and deformed; under greater pressure, suddenly the
soil changes from a plastic solid to a liquid, and the fingers
skid. After the soil smears in this fashion, usually free wa-
ter can be seen on the fingers. In a matter of a second or
two the liquefied soil sets again to its original solid state, If
a knife blade is pushed into the soil mass in a pit and re-
moved suddenly, it has only a staining of muddy water; if
pressed into the soil and slowly pulled out, a large mass of
soil adheres to the blade. In the literature of soils of west-
ern United States, particularly of Hawaii, the consistence
term "smeary" is used to characterize soil materials that are
thixotropic.

Tonguing and interfingering
Tonguing of albi

Tongues of albic materials consist of penetrations of
bleached material that has the color of an albic horizon in
an argillic or a natric horizon, along ped surfaces if peds are
present. No continuous albic horizon need be present above
the tongues. The penetrations have a vertical dimension of
>5 cm in any argillic or natric horizon, Their horizontal
dimension is 5 mm or more in a fine-textured argillic or

———
‘Concentrated HO, can cause serious burna and is dangerous. Gloves should

be worn, and precautions should be taken against spilling, leakage, or spat-
tering.



160
Fraglochrepts

Distinctions between Typic Fragiochrepts and other
subgroups

Typic Fragiochrepts are the Fragiochrepts that

a, Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either (1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less, or (2) a ratio of CEC (at pH
near 8) to 1500 kPa water of >1,5 and more exchange
acidity than the sum of bases plus KCl-extractable
aluminum;

b, Do not have distinct or prominent mottles in the upper 30
cm of the soil; and

c. Have an ochric epipedon.

Andic Fragiochrepts are like Typic Fragiochrepts except for

a.
Aquic Fragiochrepts are like Typic Fragiochrepts except for
b

Ustochrepts
Distinctions between Typic Ustochrepts and other subgroups

Typic Ustochrepts are the Ustochrepts that
a, Have a content of organic carbon" that decreases
regularly with depth and, unless a lithic or a paralithic
contact occurs at a shallower depth, reaches a level of 0.2
percent or less within 1.25 m of the soil surface; or have
slopes >25 percent,
b, Do not have a lithic contact within 50 cm of the surface;
c. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm and that are at least 30
cm long in some part and that extend upward to the soil
surface or the base of an Ap horizon,
(2) A coefficient of linear extensibility (COLE) of 0.07
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1,25 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.25 m, and
(3) More than 35 percent clay in horizons that total >50
cm in thickness;
d. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizon is saturated
with water at some period when its temperature is 5°C or
more or if the soil has artificial drainage;
e. When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry for more than four-tenths of the cumulative days
in some part of the moisture control section when the soil
temperature at a depth of 50 cm exceeds 5°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts

Tro ca bon should be af Holocsne ay a a
"The carbon should bo of Holocene age. It is not the intent to include fossil

carbon from bedrock.


183

Abruptic Cryic Paleborolis are like Typic Paleborolls except
for a and c, with or without 6.

Cryic Paleborolls are like Typic Paleborolls except for c.
Cryic Pachic Paleborolls are like Typic Paleborolls except
for c and d, with or without 6.

Pachic Paleborolls are like Typic Paleborolls except for d,
with or without 5.

Vermiborolls.

Distinctions between Typic Vermiborolls and other
subgroups

Typic Vermiborolls are the Vermiborolls that
a. Have a mollic epipedon 75 cm or more thick;
b. Have
(4) Either or both
(a) A color value, dry, of less than 4,5 in the upper 18
cm of the mollic epipedon, after mixing, or in any Ap
horizon that is >18 cm thick; or
(b) A moisture control section that is dry in some part
less than six-tenths of the time that the soil
temperature at a depth of 50 cm is above S°C in most
years; and
(2) A chroma, moist, after rubbing, of 1.5 or more in the
upper part of the mollic epipedon to a depth of 18 cm,
after mixing, or in any Ap horizon that is more than 18
em thick; and
c. Do not have a lithic contact within 50 cm of the surface.
Haplic Vermiborolls are like Typic Vermiborolls except for

a.
Hapludic Vermiborolls are like Typic Vermiborolls except
for a and 6(2).

Rendolls
Distinctions between Typic Rendolls and other subgroups

Typic Rendolls are the Rendolls that

a. Have a soil temperature regime warmer than cryic;

b. Do not have a cambic horizon throughout the pedon;

c. Do not have a lithic contact within 50 cm of the surface;

and

d. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part, and that extend upward to the surface
or to the base of an Ap horizon, and
(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper | m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1 m, and
(3) More than 35 percent clay in horizons that total >50
cm in thickness.

e. Have a dry color value of 5.5 or less after the surface soil

to a depth of 18 cm has been mixed or of any Ap horizon

that is deeper than 18 cm.

Cryic Rendolls are like Typic Rendolls except for a.

MOL


7

the surface (the E horizon and an albic horizon, which is
defined later) and extends to the first underlying diagnostic
illuvial horizon (defined later as an argillic, natric, or spodic
horizon). If the underlying horizon is a B horizon of alter-
ation (defined later as a cambic or oxic horizon) and there is
no surface horizon that is appreciably darkened by humus,
the most convenient lower limit of the ochric epipedon is
the base of the plow layer or an equivalent depth in a soil
that has not been plowed. Actually, the same subhorizon in
an unplowed soil may be both a part of the epipedon and a
part of the cambic horizon, The epipedon and the subsur-
face diagnostic horizons are not mutually exclusive. The
ochric epipedon does not have rock structure, It does not
include fresh sediments that are finely stratified,

Plaggen epipedon (Ger. plaggen, sod)

The piaggen epipedon is a manmade surface layer 50 cm (20
in.) or more thick that has been produced by long-continued
manuring.

The color of a plaggen epipedon and its organic-carbon
content depend on sources of the materials used for bedding.

The plaggen epipedon can be identified by several means,
Commonly it contains artifacts, such as bits of brick and
pottery, throughout its depth, Chunks of diverse materials,
such as black sand and light gray sand, as large as the size
held by a spade may be present. The plaggen epipedon
normally shows spade marks throughout its depth and also
remnants of thin stratified beds of sand that probably were
produced on the surface by beating rains and later were
buried by spading.

‘Umbric epipedon (L. umbra, shade, hence dark)

Requirements of the umbric epipedon are comparable to
those of the mollic epipedon in color, organic-carbon and
phosphorus content, consistence, structure, 2 value, and
thickness. The umbric epipedon includes those thick, dark-
colored surface horizons, that have base saturation of <S0
percent (by NH,OAc). It should be noted that the restric-
tion against a hard or very hard and massive epipedon when
dry is applied only to those epipedons that become dry. If
the epipedon is always moist, there is no restriction on its
consistence or structure when dry. It should also be noted
that some plaggen epipedons, defined later, meet all these
requirements but also have evidences of slow addition of
materials under cultivation. The umbric epipedon does not
have the artifacts, spade marks, and raised surfaces that are
evidences of slow additions in the plaggen epipedon.

Diagnostic Subsurface Horizons

The horizons discussed in this section form below the sur-
face of the soil, although in some places they form immedi-
ately below a layer of leaf litter. They may be exposed at
the surface by truncation of the soil. Some of these hori-
zons are generally considered to be B horizons; some are
considered B horizons by many but not all pedologists; oth-
ers are generally considered to be parts of the A horizon.


Qu

CDDN. Other Kandiperox.
Typic Kandiperox

Sombriperox
Key to subgroups

CDAA. Sombriperox that have a petroferric contact within a
depth of 125 cm of the soil surface.
Petroferric Sombriperox

CDAB. Other Sombriperox that have a lithic contact within
a depth of 125 cm of the soil surface.
Lithic Sombriperox

CDAC. Other Sombriperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface Jitter.

Humic Sombriperox

CDAD. Other Sombriperox.
Typic Sombriperox

Torrox
Key To Great Groups

CBA: Torrox that have both an apparent ECEC of less than
1.50 cmol(+) kgTM! clay and a pH value (1 M KCl) of 5 or
more in some part of the oxic horizon within a depth of 150
cm of the soil surface,

Acrotorrox, p. 211

CBB: Other Torrox that have more than 35 percent base sat-
uration (NH,OAc) in all parts within a depth of 125 cm of
the soil surface.

Eutrotorrox, p. 212

CBC: Other Torrox.
Haplotorrox, p. 212

Acrotorrox
Kev to subgroups.
CBAA, Acrotorrox that have a petroferric contact within a
depth of 125 cm of the soil surface.

Petroferric Acrotorrox
CBAB, Other Acrotorrox that have a lithic contact within a
depth of 125 cm of the soil surface.

Lithic Acrotorrox

CBAC. Other Acrotorrox.
Typic Acrotorrox

OxI


142
Cryosaprists
Distinctions between Typic Cryosaprists and other subgroups

Typic Cryosaprists are the Cryosaprists that

a, Do not have a lithic contact within the control section;
b. Have a mean annual soil temperature higher than 0°C;

c. Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier;

d, Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier; and

e. Have organic materials that are continuous laterally in at
least the surface tier throughout each pedon.

Fluvaquentic Cryosaprists are like Typic Cryosaprists except
for d.

Lithic Cryosaprists are like Typic Cryosaprists except for a
or for a and b.

Pergelic Cryosaprists are like Typic Cryosaprists except for
b or for b and d.

Terric Cryosaprists are like Typic Cryosaprists except for c.

Medisaprists
Distinctions between Typic Medisaprists and other subgroups

Typic Medisaprists are the Medisaprists that
a. Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier;
b, Have
(1) Less than 12.5 cm of the subsurface and bottom tiers
consisting of fibric materials; and
(2) Less than 25 cm of the subsurface and bottom tiers
consisting of hemic materials;
¢, Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier;
4. Do not have a layer of water within the control section
beneath the surface tier;
e. Do not have limnic layer(s) that are 5 cm or more thick
within the control section; and
f. Do not have a lithic contact within the control section.
Fibric Medisaprists are like Typic Medisaprists except for
(1),
Fibric Terrie Medisaprists are like Typic Medisaprists except
for b(1) and c, with or without a or e, or both.
Fluvaquentic Medisaprists are like Typic Medisaprists except
for a, with or without 5.
Hemic Medisaprists are like Typic Medisaprists except for
(2).
Hemic Terric Medisaprists are ike Typic Medisaprists ex-
cept for 4(2) and c, with or without a or e, or both.
Limnic Medisaprists are like Typic Medisaprists except for
e, with or without a or 6, or both,
Lithic Medisaprists are like Typic Medisaprists except for f,
with or without all or any of a, 5, ¢, or e.


ISL

(3) Whether mottled or not, the chroma, moist, is 1 or
less; and
b. Have an umbric epipedon,
Aeric Andaquepts are like Typic Andaquepts except for a.
Aeric Mollic Andaquepts are like Typic Andaquepts except
for a and 6, and they have a mollic epipedon.
Haplic Andaquepts are like Typic Andaquepts except for b,
and they have an ochric epipedon.
Mollic Andaquepts are like Typic Andaquepts except for b,
and they have a mollic epipedon.

Cryaquepts

Distinctions between Typic Cryaquepts and other defined
subgroups

It seems probable that a number of subgroups besides those
here defined will be needed when the soils that occur in
striped or polygonal patterns have been studied in more
detail.

Typic Cryaquepts are the Cryaquepts that

a. Have chroma of 2 or less in 60 percent or more of the

mass of all horizons between depths of 15 and 50 cm;

b. Do not have a layer in the upper 75 cm that has texture

finer than loamy fine sand, that is as much as 18 cm thick,

that has a bulk density (at 33 kPa tension) of 0.95 g per

cubic centimeter or less in the fine-earth fraction and that

has either (1) a ratio of measured clay to 1500 kPa water

(percentages) of 1,25 or less, or (2) a ratio of CEC (at pH

near 8) to 1500 kPa water of >1,5 and more exchange

i than the sum of bases plus KCl-extractable

aluminum,

c. Do not have a histic epipedon;

d. Do not have an umbric or a mollic epipedon;

e. Do not have a lithic contact within 50 cm of the soil

surface;

oe’ mean annual soil temperature that is higher than
Cc.

INC

Aeric Cryaquepts are like Typic Cryaquepts except for a.
Aeric Humic Cryaquepts are like Typic Cryaquepts except
for a and d, and they have an umbric epipedon.

Andic Cryaquepts are like Typic Cryaquepts except for b or
for b and d.

Histic Cryaquepts are like Typic Cryaquepts except for c or
for ¢ and d.

Histic Lithic Cryaquepts are like Typic Cryaquepts except
for c and e, with or without /.

Histic Pergelic Cryaquepts are like Typic Cryaquepts except
for ¢ and f, and the histic epipedon is continuous in each
pedon,

Humic Cryaquepts are like Typic Cryaquepts except for d,
and they have an umbric epipedon.

Humic Pergelic Cryaquepts are like Typic Cryaquepts except
for d and f, with or without a, and they have an umbric
epipedon,

Pergelic Cryaquepis are like Typic Cryaquepts except for f
or for f and a.

Pergelic Ruptic-Histic Cryaquepts are like Typic Cryaquepts
except for ¢ and /, and the histic epipedon is not continuous
in each pedon.


251

in the sandy epipedon and in the upper 12.5 cm of the
argillic horizon.

Arenic Plinthic Paleudults are like Typic Paleudults except
for 6 and c or for b,c, and g, and they have a sandy
epipedon that is 50 cm to I m thick.

Arenic Rhodic Paleudults are like Typic Paleudults except
for b and d, and they have a sandy epipedon that is 50 cm
to 1 m thick,

Fragiaquic Paleudults are like Typic Paleudults except for a
and g.

Fragic Paleudults are like Typic Paleudults except for g,
Grossarenic Paleudults are like Typic Paleudults except for b
or for a and 6, and they have a sandy epipedon that is be~
tween 1 and 2 m thick in half or more of each pedon.
Grossarenic Plinthic Paleudults are like Typic Paleudults
except for b and c or for 6, c, and g, and they have a sandy
epipedon that is between | and 2 m thick in half or more of
each pedon.

Plinthaquic Paleudults are like Typic Paleudults except for a
and c, with or without g.

Plinthic Paleudults are like Typic Paleudults except for c,
with or without g.

Psammaquentic Paleudults are like Typic Paleudults except
for a and e, with or without 5,

Psammentic Paleudults are like Typic Paleudults except for
e.

Rhodic Paleudults are like Typic Paleudults except for d.
Spodic Paleudults are like Typic Paleudults except for /,
with or without a or 6, or both,

Plinthudults

Plinthudults are the Udults that have plinthite that forms a
continuous phase or constitutes more than half the matrix of
some subhorizon in the upper 150 cm of the soil.

Rhodudults
Distinctions between Typic Rhodudults and other subgroups

Typic Rhodudults are the Rhodudults that

a. Have an argillic horizon that is continuous vertically and
horizontally and has a hue redder than 5YR:

b. Have texture finer than loamy fine sand in some part of
the argillic horizon; and

¢. Do not have a lithic contact within 50 cm of the soil
surface.

Ustults
Key to great groups

FDA. Ustults that have plinthite that forms a continuous
phase or that constitutes more than half the volume of some
subhorizon within 150 cm of the soil surface.

Plinthustults, p. 256

FDB. Other Ustults that

1, Have a CEC <16 cmol(+) kg"! lay (by 1 M NH, (OAc pH
7) and an ECEC <12 cmol(+) kg clay (sum of bases ex-
tracted with 1M NH,OAc pH 7 plus 1 M KCl-extractable

ULT


157

¢. Have base saturation (by NH,OAc) that is 60 percent or
More in some subhorizon within 75 cm of the surface; and
f, Do not have lametlae within 75 cm of the soil surface that
meet all requirements for an argillic horizon except
thickness.

Alfic Cryochrepts are like Typic Cryochrepts except for /.
‘Andic Cryochrepts are like Typic Cryochrepts except for d
or for d and e.

Aquic Cryochrepts are like Typic Cryochrepts except for c or
cand e.

Dystric Cryochrepts are like Typic Cryochrepts except for e.
Lithic Cryochrepts are like Typic Cryochrepts except for b,
with or without @ or d, or both,

Pergelic Cryochrepts are like Typic Cryochrepts except for a
or for a and c.

Durochrepts
Distinctions between Typic Durochrepts and other subgroups

Typic Durochrepts are the Durochrepts that

a. Have a platy or massive indurated duripan;

b. Do not have distinct or prominent mottles within the
upper 30 cm:

¢. Have a xeric moisture regime, and

d. Have base saturation (by NH,OAc) of 60 percent or more
in some part of the soil between depths of 25 and 75 cm
below the soil surface.

Dystric Entic Durochrepts are like Typic Durochrepts except
for aand d.

Entic Durochrepts are like Typic Durochrepts except for a.

Dystrochrepts

Distinctions between Typic Dystrochrepts and other
subgroups

Typic Dystrochrepts are the Dystrochrepts that
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
per cubic centimeter or less in the fine-earth fraction, and
that has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum;
b. Do not have mottles that have chroma of 2 or less within
60 cm of the soil surface if the mottled horizon is saturated
with water at a time when its temperature is 5°C or higher,
or the soil has artificial drainage.
c. Have a content of organic carbon? that decreases regularly
with depth and, unless a lithic or a paralithic contact occurs
at a shallower depth, reaches a level of 0.2 percent or less
within 1.25 m of the surface; or have slopes >25 percent;
d. Do not have a lithic contact within 50 cm of the soil
surface;
‘The carbon should be of Holocene age. It is not the intent to include fossil
carbon from bedrock,



48
Contrasting mineralogy modifiers

Contrasting mineralogy modifiers are not recognized except
where substitutes for particle-size class modifiers have been
used. In those soils there is an overlay of ash or cinders, or
an upper medial or thixotropic layer, and the ashy, cindery,
medial, or thixotropic layer extends at least 10 cm into the
upper part of the control section. In identifying and naming
the contrasting mineralogy modifiers in families of those
soils, the seven particle-size classes are used to describe the
lower part of the section, For example, a pair of contrasting
layers is named as medial over loamy, mixed, not medial
over coarse-loamy, mixed.

If there are layers of contrasting particle size in the control
section, the mineralogy class of the upper part of the control
section is definitive of the family mineralogy. For example,
if there is fine-loamy material of mixed mineralogy over
sandy material that is siliceous, the proper modifiers to de-
scribe the family are fine-loamy over sandy, mixed, not
fine-loamy, mixed, over sandy, siliceous.

Key to mineralogy classes

All mineral soils, except Oxisols, are placed in the first
mineralogy class of the key (table 1) that accommodates
them although they may appear also to meet the require-
ments of other mineralogy classes. The correct mineralogy
class for Oxisols is determined by using the key in table 3.
These are keys, not complete definitions. Substitute terms
connoting both particle size and mineralogy are based on
combined texture, consistence, and mineralogy classes and
are used to indicate important variations in Andaquepts,
Andepts, andic, andaqueptic, and andeptic subgroups, in
cryic great groups and cryic subgroups of Spodosols, and in
cindery and ashy families of Aridisols and Entisols. Miner-
alogy classes are not named in Calciaquolls because the ef-
fect of the carbonates overshadows other differences in
mineralogy, and they are not named in Quartzipsamments,
which, by definition, are siliceous.

It is recognized that it is normally impossible to be certain
of the percentages of the various kinds of clay minerals,
Quantitative methods of identification are still subject to
change. Although much progress has been made in the past
few decades, an element of judgment enters into the estima~
tion. All the evidence does not need to come from X-ray,
surface, and DTA determinations. Other physical and
chemical properties suggest the mineralogy of many clayey
soils. Changes in volume, cation-exchange capacity, and the
consistence are useful in estimating the nature of clay.

The description of clay mineralogy in naming families of
clayey soils is based on the weighted average of the control
section.

Calcareous and reaction classes
The presence or absence of carbonates and the reaction are

treated together because they are so intimately related. A
calcareous horizon cannot be strongly acid. Calcareous


253

(2) Saturation with water in the mottled zone at some
time of year when the soil temperature in that zone is
5°C or higher or artifjcial drainage;
e. Have a hue redder than 10YR in all parts of the upper 75
cm of soil that have a color value, moist, of 4 or more if
there are mottles of high chroma within that depth and if
the hue becomes redder with depth within 1 m of the soil
surface;
f. Do not have a petroferric contact within 1 m of the soil
surface;
g. Do not have a horizon within 1.5 m of the soil surface
that has > 5 percent plinthite by volumes
hh, Have CEC of 24 or more cmol(+) kg"! clay (by 1 M
NH,OAc pH7) in the major part of the argillic horizon or
the ‘major part of the upper 100 cm of the argillic horizon if
the argillic horizon is thicker than 100 cm; and
i, Do not have an epipedon as thick as 50 cm if its particle-
size class is sandy throughout.
Aquic Haplustults are like Typic Haplustults except for d.
‘Arenic Haplustults are like Typic Haplustults except for i,
and they have a sandy epipedon that is 50 cm to 1 m thick.
Epiaquic Haplustults are like Typic Haplustults except for e.
Kanhaplic Haplustults are like Typic Haplustults except for

Litkie Haplustults are like Typic Haplustults except for 5.
Petroferric Haplustults are like Typic Haplustults except for

f.
Plinthic Haplustults are like Typic Haplustults except for g.
Kandiustults

Distinctions between Typic Kandiustults and other sub-
groups

Typic Kandiustults are the Kandiustults that
a. Do not have the following combination of characteristics
in the upper 75 cm of the soil if the chroma throughout the
upper 75 cm is not controlled by uncoated sand grains; or if
the chroma throughout the upper 75 cm is controlled by
uncoated sand grains, do not have the following combination
of characteristics throughout the upper 12,5 cm of the
argillic or kandic horizon:
1. Mottles that have a color value, moist, of 4 or more
and chroma, moist, of 2 or less accompanied by mottles
of higher chroma that are due to segregation of iron; and
2, Saturation with water in the mottled zone at some time
of year when the soil temperature in that zone is 5°C or
higher or there is artificial drainage;
b. Do not have a horizon within 150 cm of the soil surface
that has >5 percent plinthite by volume;
c. Do not have an epipedon that is >50 cm thick if the par-
ticle-size class is sandy throughout;
d. Have an argillic or kandic horizon that has a color hue of
SYR or yellower in some part, or has a value, moist, of 3.5
or more in some part, or has a value, dry, that is more than
one unit higher than the value, moist;
e. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
per cubic centimeter or less in the fine-earth fraction, and
that has either of the following:

ULT


213

Acrudox

Kev to subgroups

CEBA. Acrudox that have mottles of 4 or more value moist
and 2 or less chroma within a depth of 125 cm of the soil
surface and a petroferric contact within 125 cm of the soil
surface,

Aquic Petroferric Acrudox

CEBB. Other Acrudox that have a petroferric contact within
125 cm of the soil surface.
Petroferric Acrudox

CEBC. Other Acrudox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and a lithic contact within 125 cm of the soil
surface.

Aquic Lithic Acrudox

CEBD, Other Acrudox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Acrudox

CEBE. Other Acrudox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and have a delta pH (KCI pH - 1:1 water pH)
with a 0 or net positive charge in some layer 18 cm or more
thick within a depth of 125 cm of the soil surface.

Aquic Anionic Acrudox

CEBF. Other Acrudox that have a delta pH (KCI pH - 1:1
water pH) with a 0 or net positive charge in some layer 18
cm or more thick within a depth of 125 cm of the soil sur-
face.

Anionic Acrudox

CEBG, Other Acrudox that have more than 5 percent
thite in some horizon within a depth of 125 cm of the
soil surface.

Plinthie Acrudox

CEBH, Other Acrudox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface.

Aquic Acrudox

CEBI, Other Acrudox that have more than 35 percent base
saturation (NH,OAc) in all parts within a depth of 125 cm
of the soil surface.

Eutrle Acrudox

CEBJ. Other Acrudox that have 16 Kg or more organic car-
bon per square meter to 2 depth of one meter, exclusive of
surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface.

Humic Rhodic Acrudox

CEBK, Other Acrudox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive


232

BCD. Other Humods that have a cryic temperature regime.
‘Cryohumods, p. 232

BCE. Other Humods.
Haplohumods, p. 232

Cryohumods

Distinctions between Typic Cryohumods and other sub-
groups

Typic Cryohumods are the Humods that

‘a. Have 6 percent or more organic carbon (weighted aver-
age) in the matrix of the upper 30 cm of the spodic horizon
or, if the spodic horizon is <30 cm thick, in the 30 cm di-
rectly below the top of the spodic horizon;

b, Do not have a lithic contact within 50 cm of the mineral
soil surface;

c. Do not have an intermittent placic horizon in the spodic
horizon;

d, Do not have an argillic or kandic horizon below the
spodic horizon;

e, Have a mean annual soil temperature higher than 0°C.
Haplic Cryohumods are like Typic Cryohumods except for a.
Lithic Cryohumods are like Typic Cryohumods except for b,
with or without a or e, or both,

Pergelic Cryohumods are like Typic Cryohumods except for
e or for a and e,

Fragihumods

These are the Humods that have a fragipan below the spodic
horizon and do not have a placic horizon, They are not
known to occur in the United States, and the classification
of subgroups has not been developed.

Haplohumods

Distinctions between Typic Haplohumods and other sub-
groups

Typic Haplohumods are the Haplohumods that

a. Have either
(1) A spodic horizon that has a weighted average of 0.6
percent or more organic carbon in the matrix of the up-
per 30 cm of the spodic horizon or below any Ap hori-
zon; of
(2) A black upper subhorizon of the spodic horizon that
has 3 percent or more organic carbon in the upper 2. cm
and that is continuous or is present in >90 percent of the
area of each pedon;

b. Have <5 percent by volume of iron-cemented nodules, 2.5

to 30 cm in diameter, in any subhorizon of the spodic hori-

zon;

¢. Do not have a lithic contact within 50 cm of the soil

surface;

d. Do not have an argillic or kandic horizon below the

spodic horizon;

e. Do not have a surface horizon >30 cm thick that meets all

the requirements for a plaggen epipedon except thickness;

f. Have a udic moisture regime; and


6

(2) The base of any argillic, natric, spodic, cambic, or
oxic horizon is deeper than 75 cm; and

(3) The upper boundary of any petrocalcic horizon,
fragipan, or duripan is deeper than 75 cm;

c. In other soils that have a loamy or clayey epipedon,

the thickness of the epipedon must be 18 cm or more and

it must be more than one-third of the depth from the top
of the epipedon to the shallowest of one of the features
listed in (b) if that is <75 cm;

d. In other soils the epipedon must be >25 cm thick if
(1) The texture of the epipedon is as coarse as or
coarser than loamy fine sand throughout its thickness
or
(2) If there are no underlying diagnostic horizons and
the organic-carbon content of the underlying materials
decreases irregularly with increasing depth (as in re~
cent alluvium that is not finely stratified); or

e. In other soils, the epipedon must be 18 cm (7 in.) or

more thick if none of the conditions that are listed in 6,

c, and d exist.

6. The epipedon has <250 mg kg”! of P,O, soluble in 1
percent citric acid or it either has increasing amounts of
P,O, soluble in citric acid below the epipedon or the
amounts of P.O, soluble in citric acid decrease or increase
irregularly with depth below the epipedon, or there are
phosphate nodules within the epipedon. This restriction is
made to eliminate plow layers of very old arable soils and
kitchen middens that have acquired, under use, the proper-
ties of the mollic epipedon but to include the epipedon of a
soil developed in highly phosphatic parent material.

7, If the soil is not irrigated, some part of the epipedon is
moist 3 months or more of the year (cumulative) in more
than 7 out of 10 years at times when the soil temperature at
a depth of 50 cm is 5°C or higher.

8. The n value (defined later in this chapter) is <0.7. Al-
though many soils that have a mollic epipedon are very
poorly drained, a mollic epipedon does not have the very
high water content of sediments that have been continuously
under water since deposition.

Ochric epipedon (Gr. ochros, pale)

An ochric epipedon is one that is too high in value or
chroma, is too dry, has too little organic matter, has an 1
value too high, or is too thin to be mollic, umbric, an~
thropic, plaggen or histic, or it is both hard and massive
when dry. An epipedon is ochric if the Munsell color value
after rubbing is 5.5 or higher when dry of 3.5 or higher
when moist, if the chroma is 3.5 or more’, or if the A or
Ap horizon that has both low value and low chroma is too
thin to be a mollic or an umbric epipedon. Epipedons that
have a color value after rubbing lower than 5.5, dry, and
lower than 3.5, moist, are also ochric provided they are no
darker than the 1C horizon and do not have as much as 0.6
percent more organic carbon than the 1C horizon. The
ochric epipedon includes eluvial horizons that are at or near

Totoslelimth chute
‘See footnote 1 in this ehapter.


246
Fragiudults

Distinctions between Typic Fragiudults and other subgroups

Typic Fragiudults are the Fragiudults that
a. Meet these two requirements:
(1) Have an argillic or kandic horizon above the fragipan
that has some clay skins on both vertical and horizontal
surfaces of some structural aggregates; and
(2) Do not have an intervening horizon (one or more)
between the argillic or kandic horizon and the fragipan
that has dominant chroma of 3 or less and that has as
much as 3 percent less clay (absolute) than both the
overlying argillic or kandic horizon and the underlying
fragipan;
b. Do not have mottles that have chroma of 2 or less;
(1) Within the upper 25 cm of the argillic or kandic
horizon or above the fragipan if the part of the argillic
or kandic horizon above the fragipan is less than 25 cm
thick; or
(2) Within 40 cm of the surface of the soil if the argillic
or kandic horizon is lacking above the fragipan or there
is an intervening horizon between the argillic or kandic
horizon and the fragipan that has as much as 3 percent
less clay (absolute) than both the overlying argillic or
kandic horizon and the underlying fragipan.
c. Do not have an epipedon as thick as 50 cm if the parti-
cle~size class is sandy throughout,
d. Have <5 percent plinthite by volume in all horizons
within 1.5 m of the soil surface; and
e. Have an Ap horizon that has a color value, moist, of 4 or
more or has a value, dry, of 6 or more when crushed and
smoothed (smoothed with a knife to eliminate shadows), or
the A_ horizon is <15 cm thick if its color value, moist, is
lower than 3.5.
Aguic Fragiudults are like Typic Fragiudults except for 6(1).
Arenic Fragiudults are like Typic Fragiudults except for c or
for a and c, and they have a sandy epipedon that is 50 cm
to 1 m thick.
Glossaquic Fragiudults are like Typic Fragiudults except for
aand 52).
Glossic Fragiudults are like Typic Fragiudults except for a.
Plinthaguic Fragiudults are like Typic Fragiudults except for
a, b(2), and d.
Plinthic Fragiudults are like Typic Fragiudults except for a
and d.

Hapludults
Distinctions between Typic Hapludults and other subgroups

Typic Hapludults are the Hapludults that

a. Do not have the following combination of characteristics

in the upper 60 cm of the argillic horizon:
(J) Mottles that have a color value, moist, of 4 or more
and chroma, moist, of 2 or less, and also mottles of
higher chroma that are due to segregation of iron; and
(2) Saturation with water in the mottled zone at some
time of year when the soil temperature in that zone is
5°C or higher, or artificial drainage;


42

to particles 2 mm in diameter or larger and includes all sizes
that have horizontal dimensions tess than the size of a pe-
don. It is not the same as coarse fragments, which excludes
stones and boulders larger than about 25 cm. The term "fine
earth" refers to particles smaller than 2 mm in diameter.

Definition of classes

Fragmental,--Stones, cobbles, gravel, and very coarse sand
particles; too little fine earth to fill some of the interstices
larger than 1 mm in diameter.

Sandy-skeletal,--Rock fragments 2 mm in diameter or larger
make up 35 percent or more by volume; enough earth to fill
interstices larger than 1 mm; the fraction finer than 2 mm is
sandy as defined for the sandy particle-size class.

Loamv-skeletal.--Rock fragments make up 35 percent or
more by volume; enough fine earth to fill interstices larger
than 1 mm; the fraction finer than 2 mm is loamy as de~
fined for the loamy particle-size class.

Clavey-skeletal.--Rock fragments make up 35 percent or
more by volume; enough fine earth to fill interstices larger
than | mm; the fraction finer than 2 mm is clayey as de-
fined for the clayey particle-size class.

Sandv.--The texture of the fine earth is sand or loamy sand
that contains less than 50 percent very fine sand; rock frag-
ments make up less than 35 percent by volume.

Loamy!,--The texture of the fine earth is loamy very fine
sand, very fine sand, or finer, but the amount of clay is <35
percent; rock fragments are <35 percent by volume, *
Coarse-loamy. By weight, 15 percent or more of the parti-
cles are fine sand (diameter 0.25-0.1 mm) or coarser, in-
cluding fragments up to 7.5 cm in diameter; <18 percent
clay in the fine-earth fraction,

Fine-loamy. By weight, 15 percent or more of the particles
are fine sand (diameter 0.25-0.1 mm) or coarser, including
fragments up to 7.5 cm in diameter; 18 through 34 percent
clay in the fine-earth fraction (<30 percent in Vertisols).
Coarse-silty. By weight, <15 percent of the particles are
fine sand (diameter 0.25-0.1 mm) or coarser, including
fragments up to 7.5 cm in diameter; <18 percent clay in the
fine-earth fraction,

Fine-silty, By weight, <15 percent of the particles are fine
sand (diameter 0.25-0.1 mm) or coarser, including fragments
up to 7,5 cm in diameter; 18 through 34 percent clay in the
fine-earth fraction (<30 percent in Vertisols).

.———
Hf the ratio of 1500 kPa water to clay is 0.6 of more in half or more of the

control section, the percentage of clay is considered to be 2.6 times the per-
centage of 1600 kPa water. Catbonater of clay size are not considered to be
clay but are treated as silt in all particle-size clasaes,


122

Pergelic Cryorthents are like Typic Cryorthents except for d,
with or without @ or 4, or both.

Torriorthents

Distinctions between Typic Torriorthents and other sub-
groups

Typic Torriorthents are the Torriorthents that

a, Do not have a horizon within 1 m of the surface that is

>15 cm thick that either contains 20 percent or more durin-

odes in a nonbrittle matrix or is brittle and has firm consis-

tence when moist;

b. Do not have a lithic contact within 50 cm of the surface;

c. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or the base of an Ap horizon,
(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potential finear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness;

d, Are dry in all parts of the moisture control section three-

fourths or more of the time (cumulative) that the soil tem-

perature at a depth of 50 cm is 5°C or higher; and

e, Are not saturated with water within 1.5 m of the surface

at any time of year in most years,

‘Aguic Torriorthents are like Typic Tortiorthents except for €

or for d and e.

Aquic Durorthidic Torriorthents are like Typic Torriorthents

except for a and e, or for a, d, and e.

Durorthidic Torriorthents are like Typic Torriorthents except

for a.

Durorthidic Xeri¢ Torriorthents are like Typic Torriorthents

except for a and d. They have a thermic, mesic, or frigid

soil temperature regime and have a torric moisture regime

that borders on a xeric regime.

pithie Torriorthents are like Typic Torriorthents except for

Lithic Ustic Torriorthents are like Typic Torriorthents except
for b and d, They either (1) have a hyperthermic or an iso
soil temperature regime or (2) have a thermic or mesic soil
temperature regime and have a torric moisture regime that
borders on an ustic regime.

Lithic Xeric Torriorthents are like Typic Torriorthents ex-
cept for b and d. They have a thermic, mesic, or frigid soil
temperature regime and an aridic moisture regime that bor-
ders on a xeric regime.

Ustertic Torriorthents are like Typic Torriorthents except for
c, with or without d or e, or both. Unless irrigated, they
have cracks that remain open from 175 to 240 days, cumu-
lative, and are not closed for as many as 60 consecutive days
during the 120 days following the winter solstice in 3 or
more years out of 10 if the soil temperature regime is ther-
mic, mesic, or frigid.


219
Ustox

Key to great groups

CCA; Ustox that have a sombric horizon within 150 cm of
the soil surface.
Sombriustox, p. 224

CCB: Other Ustox that have both an apparent ECEC of less
than 1.50 cmol(+) kgTM clay and a pH value (1 M KCl) of 5
or more in some part of the oxic or kandic horizon within a
depth of 150 cm of the soil surface,

Acrustox, p. 219

CCC: Other Ustox that have more than 35 percent base sat-
uration (NH,OAc) in all parts within a depth of 125 cm of
the soil surface,

Eutrustox, p. 220

CCD: Other Ustox that have more than 40 percent clay in
the surface 18 cm after mixing, and the upper boundary of
a kandic horizon occurring within a depth of 150 cm of the
soil surface,

Kandlustox, p. 223

CCE: Other Ustox.
Haplustox, p. 222

Acrustox:
to ro)

CCBA. Acrustox that have mottles of 4 or more value moist
and 2 or less chroma within a depth of 125 cm of the soil
surface and a petroferric contact within 125 cm of the soil
surface.

Aquic Petroferric Actustox

CCBB. Other Acrustox that have a petroferric contact within
125 cm of the soil surface.
Petroferric Acrustox

CCBC. Other Acrustox that have mottles of 4 or more value
moist and 2 or Jess chroma within a depth of 125 cm of the
soil surface and a lithic contact within 125 cm of the soil
surface,

Aquic Lithic Acrustox

CCBD. Other Acrustox that have a lithic contact within a
depth of 125 cm of the soil surface,
Lithic Acrustox

CCBE. Other Acrustox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and have a delta pH (KCI pH - 1:1 water pH)
with a 0 or net positive charge in some layer 18 cm or more
thick within a depth of 125 cm of the soil surface.

Aquic Anionic Acrustox

CCBF. Other Acrustox that have a delta pH (KCI pH - 1:1
water pH) with a 0 or net positive charge in some layer 18


19
Other Diagnostic Soil Characteristics

Abrupt textural change

An abrupt textural change is a change from an ochric
epipedon or an albic horizon to an argillic horizon. There
is, in the zone of contact, a very appreciable increase in clay
content within a very short distance in depth. If the clay
content of the ochric epipedon or the albic horizon is <20
percent, the clay content should double within a distance in
depth of 7.5 cm or less. If the clay content exceeds 20
percent, the increase in clay content should be at least 20
percent of the fine-earth fraction, for example, from 22
percent to 42 percent, within a distance of 7.5 cm in depth,
and the clay content in some part of the argillic horizon
should be at least double that of the horizon above.

A transitional horizon normally is not present or is too thin
to be sampled. In some soils, however, there may be
tonguing or interfingering of albic materials, which are de-
fined later, in parts of the argillic horizon. The horizon
boundary in such a soil is irregular or even discontinuous.
The sampling of such a mixture as a single horizon might
create the impression of a relatively thick transitional hori-
zon, even though the thickness of the actual transition at the
contact may be only 1 mm or so,

Amorphous material dominant in the exchange complex

Amorphous material, as the term is used here, is colloidal
material that includes allophane and has all or most of the
Properties of allophane. The term is more inclusive, how-
ever, than allophane as it is defined by some workers.
Amorphous material, as used here, is generally amorphous
under X-ray analysis, but enough crystalline materials may
be present, especially in mixtures, to cause small and disor-
dered peaks. The amorphous material is associated with or-
ganic matter, but it contains aluminum, and it never has
more than traces of aluminum that can be extracted with
KCl. Consequently, if the base saturation is low, that is,
<35 percent, the amorphous, material has a permanent charge
of less than 10 cmol(+) kgTM*. It has high exchange capacity,
however, in a system buffered at pH 7, and very high ex-
change capacity at pH 8.2. The exchange capacity is clearly
pH induced. The amorphous material also has high anion-
exchange capacity. It has an enormous surface area and re-
tains much water against 1500 kPa tension, commonly 50 to
100 percent or more. It cannot be dispersed readily in
hexametaphosphate.

If amorphous material dominates an exchange complex, we
find that the following conditions are satisfied:

1. The exchange capacity of the clay at pH 8,2 is >150
lt, kg”" measured clay, and commonly is >500 cmol(+)

The high value is, in part, the result of the poor dis-
persion.

2. If there is enough clay to have a 1500 kPa water content
of 20 percent or more, the pH of a suspension of 1 g soil in
50 mi 1 M NaF is >9.4 after 2 minutes.



14

Seventh, an air-dry fragment about the size of a fist slakes
or fractures when placed in water.

Gypsic horizon

‘The gypsic horizon is a noncemented or weakly cemented
horizon of enrichment with secondary sulfates that is 15 cm
or more thick, has at least 5 percent more gypsum than the
C horizon or the underlying stratum, and in which the
product of the thickness in centimeters and the percentage
of gypsum is >150, Thus, a horizon 30 cm thick that has 5
percent gypsum qualifies if gypsum is absent in the under-
lying horizon. A layer 30 cm thick that has 6 percent gyp-
sum qualifies if the gypsum content of the underlying hori-
zon is not more than I percent, Cementation is weak
enough that a dry fragment slakes in water.

The percentage of gypsum can be calculated by multiplying
the milliequivalents of gypsum per 100 g soil by the mil-
liequivalent weight of gypsum, which is 0.086.

Kandic horizon
The kandic horizon:

1. Is a vertically continuous subsurface horizon and has,
starting at the point where the clay increase requirements
are met, a CEC of <16 cmol(+) kg”! flay (by 1M NH,OAc
pH 7) and an ECEC <12 cmol(+) kg”! clay (sum of bases
extracted with 1 M NH,OAc pH 7 plus | M KCl-extractable
Al) in at least the major part of the horizon,

2. Has a thickness of at least 30 cm, or if a lithic, par-
alithic, or petroferric contact occurs within 50 cm of the soil
surface, then the thickness of the kandic horizon is at least
60 percent of the vertical distance between 18 cm and the
contact but at least 15 cm thick.

3. Has a texture of loamy very fine sand or finer.

4. Underlies a coarser textured surface horizon. The mini-
mum thickness of the surface horizon is 18 cm after mixing,
or 5 cm if the textural transition to the kandic horizon is
abrupt and if there is no lithic, paralithic, or petroferric
contact within 50 cm,

5. Has more total clay than the overlying coarser textured
surface horizon and the increased clay content is reached
within a vertical distance of 15 cm or less as follows:
a, If the surface horizon as defined above has less than
20 percent total clay, the kandic horizon begins where
some subhorizon contains at least 4 percent more clay
absolute than the overlying horizon.
b. If the surface horizon as defined above has 20 to 40
percent total clay the kandic horizon begins where some
subhorizon has at least 1.2 times more clay than the
overlying horizon,
c. If the surface horizon as defined above has more than
40 percent total clay, the kandic horizon begins where
some subhorizon has at least 8 percent more clay absolute
than the overlying horizon.


3

organic materials that may meet the definition of a histic
epipedon (defined later). Otherwise one soil may contain
only one epipedon,

A recent alluvial or eolian deposit that retains fine stratifi-
cations or an Ap horizon that is directly underlain by mate-
rial that retains fine stratifications are not are not included.
in the concept of the epipedon because time has not been
sufficient for soil-forming processes to erase these transient
marks of deposition and for diagnostic and accessory prop-
erties to develop.

The epipedon is not a synonym for the A horizon because it
may include part or all of the illuvial B horizon if the
darkening by organic matter extends from the surface into
or through the B horizon. To avoid changes in classification
of a soil as the result of plowing, the properties of the
epipedon, except for structure, should be determined after
the surface soil to a depth of 18 cm has been mixed or, if
the depth to bedrock is <18 cm, after the whole soil down to
rock has been mixed.

Anthropic epipedon

In summary, the anthropic epipedon conforms to all the re-
quirements of the mollic epipedon except (1) the limits on
acid-soluble P,O,, with or without the base saturation, or
(2) the length of the period during which it has available
moisture. Additional data on anthropic epipedons from
several parts of the world may permit improvements in this
definition.

Histic epipedon (Gr. histos, tissue)

The histic epipedon normally is at the surface, although it
may be buried at a shallow depth. It normally is a thin
horizon of peat or muck if the soil has not been plowed. If
the soil has been plowed, the histic epipedon has the very
high content of organic matter that results from mixing peat
with some mineral material. Since peaty deposits occur in
wet places, the histic epipedon either is saturated with water
for 30 consecutive days or more during the year or has been
artificially drained.

The histic epipedon, therefore, can be defined as a layer
(one horizon or more) at or near the surface that is saturated
with water for 30 consecutive days or more at some time in
most years, or is artificially drained, and that meets one of
the following requirements:

1, The surface horizon consists of organic soil materials that
either
a, Is 75 percent or more, by volume, sphagnum fibers or
has a bulk density, when moist, <0.1 and is <60 cm (24
in.) but >20 cm thick; or
b, Is <40 cm but >20 cm thick and meets one of the fol-
lowing requirements with respect to organic-carbon con-
tent and thickness;
(1) Has 18 percent or more organic carbon if the
mineral fraction is 60 percent or more clay;


135

(2) Less than 12.5 cm of the subsurface and bottom tiers

occupied by sapric materials;
c. Do not have a layer of water within the control section
beneath the surface tier;
4. Do not have limnic layer(s) that are 5 cm or more thick
within the control section,
e. Do not have a lithic contact within the control section;
f, Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier;
g- Are never frozen within the control section about 2
months after the summer solstice or are never frozen below
a depth of 5 cm in most years;
h. Have a mean annual soil temperature higher than 0°C.
Cryic Sphagnofibrists are like Typic Sphagnofibrists except
for g and have a mean annual soil temperature lower than
8°C but higher than 0°C,
Fluvaquentic Sphagnofibrists are like Typic Sphagnofibrists
except for a, with or without 5,
Hemic Sphagnofibrists are like Typic Sphagnofibrists except
for B(1).
Hydric Sphagnofibrists are like Typic Sphagnofibrists except
for c,
Limnic Sphagnofibrists are like Typic Sphagnofibrists except
for d, with or without a or 6, or both.
Lithic Sphagnofibrists are like Typic Sphagnofibrists except
for e, with or without all or any of a, b, d, f, or A.
Pergelic Sphagnofibrists are like Typic Sphagnofibrists ex-
cept for A and g, with or without all or any of a, 5, d, e, or

f

Sapric Sphagnofibrists are like Typic Sphagnofibrists except
for b(2).

Terric Sphaguofibrists are like Typic Sphagnofibrists except
for f, with or without @ or d, or both.

‘Tropofibrists

Distinctions between Typic Tropofibrists and other sub-
groups

Typic Tropofibrists are the Tropofibrists that
a. Have
(1) Less than 25 cm of the thickness of the subsurface
and bottom tiers occupied by hemic materials, and
(2) Less than 12.5 cm of the thickness of the subsurface
and bottom tiers occupied by sapric materials;
b, Have less than three-fourths of their fibers, by volume,
derived from Sphagnum in the surface tier or in more of the
contro! section;
c. Do not have limnic layer(s) that are 5 cm or more thick
within the control section;
d. Do not have a lithic contact within the control section;
¢. Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier;
f, Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier; and
g. Do not have a layer of water within the control section
beneath the surface tier.

IS


112

percent to a depth of 1.25 m, and the mean annual soil
temperature is higher than 0°C. (Strata of sand or loamy
sand may have less organic carbon if finer sediments at a
depth of 1.25 m or below have 0.2 percent organic carbon or
more).

Fluvents, p. 117

JE. Other Entisols.
Orthents, p. 120

Aquents
Key to great groups

JAA. Aquents that have sulfidic materials within 50 cm of
the mineral soil surface,
Sulfaquents, p. 116

JAB. Other Aquents that have an n value of >0.7 and that
have at least 8 percent clay in all subhorizons between a
depth of 20 and 50 cm and that have a mean annual soil
temperature higher than 0°C.

Hydraquents, p, 115

JAC. Other Aquents that have a cryic but not a pergelic”
soil temperature regime.
Cryaquents, p. 113

JAD. Other Aquents that have an organic carbon content®
that decreases irregularly with depth or that remains above
0.2 percent to a depth of 1.25 m; and that have texture finer
than loamy fine sand in some or all subhorizons between the
Ap horizon or a depth of 25 cm, whichever is deeper, and 1
m or a lithic or paralithic contact, whichever is shallower.
Thin strata of sand may have less organic carbon if the finer
sediments at a depth of 1.25 m or below have 0.2 percent
organic carbon or more,

Fluvaquents, p. 113

JAE. Other Aquents that have a difference of <5°C between
the mean summer and mean winter soil temperatures at a
depth of 50 cm,

‘Tropaquents, p. 116

JAF. Other Aquents that have a sandy particle-size class in
all subhorizons between the Ap horizon or a depth of 25 cm,
whichever is deeper, and 1 m or a lithic or paralithic
contact, whichever is shallower, and that have mean summer
and mean winter soil temperatures at a depth of 50 cm that
differ by 5°C or more.

Psammaquents, p. 115

JAG. Other Aquents.
Haplaquents, p. 114

—__,
‘Soils that otherwise could be Aq
i

permafrost.
Scphe carbon should be of Holocene age. It is not the intent to include fossil

‘carbon from transported fragments of bedrock or from buried Pleistocene de~
posits, The mean residence time of the earbon should be <11,000 years B.P.

‘are grouped with Aquepts if there is



69
Plinthaqualfs

Plinthaqualfs are the Aqualfs that have plinthite that forms
a continuous phase or that constitutes half or more of the
matrix of some subhorizon of the argillic horizon within 150
cm of the soil surface.

Umbragualfs

Distinctions between Typic Umbraquaifs and other sub-
groups

Typic Umbraqualfs are the Umbraqualfs that
a, Do not have a layer above a depth of 75 cm that has a
texture finer than loamy fine sand, that is as much as 18 cm
thick, that has a bulk density (at 33 kPa water tension) of
0,95 g per cubic centimeter or less in the fine-earth frac-
tion, and that has either

(1) a ratio of measured clay to 1500 kPa water

(percentages) of 1.25 or less, or

(2) a ratio of CEC (at pH near 8) to 1500 kPa water of

>1.5 and more exchange acidity than the sum of bases

plus KCl-extractable aluminum; and
b, Do not have, in the umbric epipedon and in horizons
above the argillic horizon, soft discrete nodules 2.5 to 30 cm
in diameter that constitute >5 percent of the volume, that
are cemented by iron, and that lie above and in an irregular
or broken upper boundary of the argillic horizon.

The typic subgroup is the only one that has been recognized
in the United States to date. Item a of the definition of
Typic Umbraqualfs provides for an andeptic subgroup, and
item b has been suggested for a ferrudalfic subgroup.

The Umbraqualfs are not extensive in the United States.
Most of them formed in alluvium or in marine deposits and
are nearly level. The base saturation in the argillic horizon
generally is low enough that liming the surface layer does
not change the classification.

Boralfs
Key to great groups

HBA. Boralfs that have an argillic horizon with its upper
boundary deeper than 60 cm below the mineral surface®,
that have texture finer than loamy fine sand in some sub-
horizon above the argillic horizon, and that have albic ma-
terials tonguing or interfingering in the argillic horizon,
Paleboralfs, p. 72

HBB. Other Boralfs that have a fragipan.
Fragiboralfs, p. 71

HBC. Other Boralfs that have a natric horizon,
Natriboralfs, p. 72

———_
‘if there rm ntle that has > 60 percent vitrie volcanic ash, cinders,

or other vitric pyroclastic materials, the depth to the argillic horizon is mea-
ured from the base of this mantle rather then from the surface of the mineral
‘oil.



212

Eutrotorrox
Key to subgroups

CBBA. Eutrotorrox that have a petroferric contact within a
depth of 125 cm of the soil surface.
Petroferric Eutrotorrox

CBBB. Other Eutrotorrox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Eutrotorrox

CBBC. Other Eutrotorrox,
Typic Eutrotorrox

Haplotorrox

Key to subgroups

CBCA. Haplotorrox that have a petroferric contact within a
depth of 125 cm of the soil surface.
Petroferric Haplotorrox

CBCB. Other Haplotorrox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Haplotorrox

CBCC. Other Haplotorrox,
Typic Haplotorrox

Udox
Key to great groups

CEA: Udox that have a sombric horizon within a depth of
150 cm of the soil surface.
Sombriudox, p. 218

CEB; Other Udox that have both an apparent ECEC of less
than 1.50 cmol(+) kg" clay and a pH value (1 M KCl) of 5
‘or more in some part of the oxic or kandic horizon within a
depth of 150 cm of the soil surface.

Acrudox, p. 213

CEC: Other Udox that have more than 35 percent base sat-
uration (NH,OAc) in all parts within a depth of 125 cm of
the soil surface,

Eutrudox, p. 214

CED: Other Udox that have more than 40 percent clay in
the surface 18 cm after mixing, and the upper boundary of
a kandic horizon occurring within a depth of 150 cm of the
surface.

Kandiudox, p. 217

CEE; Other Udox,
Hapludox, p. 215


24

drying and rewetting. After a single drying, it will re-
moisten, and then it can be dispersed in large part by shak-
ing in water with a dispersing agent.

In a moist soil, plinthite is soft enough that it can be cut
with a spade. After irreversible hardening, it is no longer
considered plinthite but is called ironstone. Indurated iron-
stone materials can be broken or shattered with a spade but
cannot be dispersed by shaking in water with a dispersing
agent.

Potential linear extensibility

This characteristic is the sum of the products, for each
horizon, of the thickness of the horizon in centimeters and
the COLE of the horizon.

Sequum: number and kind

A sequence of an eluvial horizon and its subjacent B hori-
zon, if one is present, is called a sequum. An albic horizon
and a spodic horizon immediately underlying it, for exam-
ple, constitute a sequum. Similarly, a mollic epipedon over
a cambic horizon or an argillic horizon over a k horizon also
constitute a sequum. Two sequa may be present in vertical
sequence in a single soil, and that sequence is called a bise-
quum,

Slickensides

Slickensides are polished and grooved surfaces that are pro-
duced by one mass sliding past another. Some of them oc-
cur at the base of a slip surface where a mass of soil moves
downward on a relatively steep slope, Slickensides are very
common in swelling clays in which there are marked
changes in moisture content.

Soft powdery lime

Soft powdery lime is a phrase that is used in the definitions
of a number of taxa. It refers to translocated authigenic
lime, soft enough to be cut readily with a fingernail, that
was precipitated in place from the soil solution rather than
inherited from a soil parent material such as a calcareous
loess or till, It should be present in a significant enough
accumulation to constitute a k horizon.

To be identifiable, soft powdery lime must have some rela-
tion to the soil structure or fabric. It may disrupt the fabric
to form spheroidal aggregates, or white eyes, that are soft
and powdery when dry. Or the lime may be present as soft
coatings in pores or on structural faces. If present as coat-
ings, it covers a significant part of the surface. Commonly,
it coats the whole surface to a thickness of | to 5 mm or
more. But only part of a surface may be coated if little
lime is present in the soil. The coatings should be thick
enough to be visible when moist and should cover a contin-
uous area large enough to be more than filaments. The
pseudomycelia commonly seen in a dry calcareous horizon
do not come within the meaning of soft powdery lime.
Pseudomycelia are soft powdery filaments on structural


M7

Typic Cryandepts are Cryandepts that

a, Do not have mottles that have chroma of 2 or less within
1 m of the soil surface;

b. Are not thixotropic in half or more of the thickness of all
horizons between depths of 25 cm and | m, and the
weighted average 1500 kPa water retention’ is <20 percent
between depths of 25 cm and 1 m, or between 25 cm and a
lithic or paralithic contact if there is one between 50 cm and
Im;

c. Do not have a lithic contact within 50 cm of the soil
surface;

d. Have an epipedon that has the color and thickness of a
mollic epipedon or have a horizon that meets the color and
thickness requirements of 2 mollic epipedon and has its
upper boundary within 50 cm of the soil surface;

e. Have a mean annual soil temperature higher than 0°C;

f. Do not have a placie horizon:

g. Do not have a duripan that has its upper boundary within
1 m of the soil surface.

Dystric Cryandepts are like Typic Cryandepts except for b,
with or without d, and base saturation (by NH,OAc) is <50
Percent in all subhorizons between 25 and 75 cm.

Dystric Lithie Cryandepts are \ike Typic Cryandepts except
for b and c, and base saturation (by NH,OAc) is <50 percent
in all subhorizons between 25 and 75 cm.

Entic Cryandepts are like Typic Cryandepts except for d.
Lithic Cryandepts are like Typic Cryandepts except for c or
for ¢ and d.

Durandepts

Proposed distinctions between Typic Durandepts and other
subgroups:

Typic Durandepts are the Durandepts that

a. Have an ustic moisture regime;

b, Have an epipedon that meets the color and thickness
requirements of a mollic epipedon;

¢. Have a duripan that is continuous throughout each pedon
or, if fractured, the average lateral dimensions of the
fragments are >10 cm.

Entic Durandepts are like Typic Durandepts except for c.
Xeric Durandepts are like Typic Durandepts except for a,
and they have a xeric moisture regime.

Dystrandepts

Distinctions between Typic Dystrandepts and other
Subgroups

Typic Dystrandepts are the Dystrandepts that
a, Do not have mottles that have chroma of 2 or less within
1 m of the soil surface;

‘The amount of water retained mnsion of 1500 kPa may be reduced by
drying these soils. Since 1500 kPa water retention is used as a measure of ef-
fective clay content, it would be unrealistic to use the extremely high value
obtained on a field-moist Andept. That value reflects mostly the climatic
history rather than a badle soil property. The value for 1500 kPa water re-
tention that is referred to here, therefore, is that of a sample that has been
dried at 40°C,



245
Udults

Key to great groups

FCA. Udults that have plinthite that forms a continuous
phase or constitutes more than half the volume in some sub-
horizon within 150 cm of the soil surface.

Piisthudults, p. 251

FCB. Other Udults that have a fragipan in or below the
argillic or kandic horizon.
Fragindults, p. 246

FCC, Other Udults that

1, Have a CEC <16 cmol(+) kg? glay (by 1 M NH,OAc pH
7) and an ECEC <12 emol(+) kg” clay (sum of bases ex-
tracted with | M NHOAc pH 7 plus 1 M KCl-extractable
Al) in the major part of the argillic or kandic horizon or the
major part of the upper 100 cm of the argillic or kandic
horizon if these horizons are thicker than 100 cm;
2, Do not have a lithic, paralithic, or petroferric contact
within 150 cm of the soil surface: and
3. Have a clay distribution such that the percentage of clay
does not decrease from its maximum amount by as much as
20 percent within a depth of 150 cm from the soil surface
or the layer in which the clay percentage decreases by more
than 20 percent has at least 5 percent of the volume con-
sisting of skeletans on faces of peds and there is at least 3
percent (absolute) increase in clay below the layer.
Kandiudults, p. 247

FCD. Other Udults that have a CEC <16 cmol(+) kg? slay
(by 1 M NH,OAc pH 7) and an ECEC <12 cmol(+) kg” clay
(sum of baseS extracted with | M NH|OAc pH 7 plus 1 M
KCl-extractable AJ) in the major part of the argillic or
kandic horizon or the major part of the upper 100 cm of the
argillic or kandic horizon if these horizons are thicker than
100 cm.

Kanhapludults, p. 249

FCE. Other Udults that have a clay distribution such that
the percentage of clay does not decrease from its maximum
amount by more than 20 percent within 150 cm of the soil
surface or the layer in which the clay percentage decreases
by more than 20 percent has at least 5 percent of the vol-
ume consisting of skeletans on faces of peds and there is at
least 3 percent (absolute) increase in clay below the layer,
Paleudults, p, 250

FCF. Other Udults that have

1, An epipedon that has a color value, moist, less than 3.5 in

all parts; and

2. An argillic horizon that has a color value, dry, less than 5

and not more than | unit higher than the value, moist.
Rhodudalts, p, 251

FCG, Other Udults.
Hapludults, p. 246

ULT


10

thick should have a combined thickness of at least 15 cm.
If the argillic horizon is loamy or clayey, it should be at
least 7.5 cm thick.

3. In structureless soils, the argillic horizon has oriented clay
bridging the sand grains and also in some pores.

4, If peds are present, an argillic horizon should meet one of

the following requirements:
a. Have clay skins on some of both the vertical and hor-
izontal ped surfaces and in the fine pores or have ori-
ented clay in 1 percent or more of the cross section;
b. Meet requirements | and 2 and also have a broken or
irregular upper boundary and some clay skins in the
lowest part of the horizon;
¢. If the horizon is clayey, if the clay is kaolinitic, and if
the surface horizon has >40 percent clay, have some clay
skins on peds and in pores in the lower part of the hori-
zon that has blocky or prismatic structure; or
d. If the illuvial horizon is clayey with 2-to-1 lattice
clays, an argillic horizon does not need to have clay skins
if there are uncoated grains of sand or silt in the overly~
ing horizon and evidences of pressure caused by swelling
or if the ratio of fine to total clay in the horizon is
greater by at least one-third than the ratio in the overly~
ing or the underlying horizon or if it has >8 percent more
fine clay. The evidences of pressure may be occasional
slickensides or wavy horizon boundaries in the illuvial
horizon.

5. If a soil has a lithologic discontinuity between the eluvial
horizon and the argillic horizon or if only a plow layer
overlies the argillic horizon, the argillic horizon needs to
have clay skins in only some part, either in some fine pores
or, if peds exist, on some vertical and horizontal ped sur-
faces, Either thin sections should show that some part of
the horizon has about | percent or more of oriented clay
bodies or the ratio of fine clay to total clay should be
greater than in the overlying or the underlying horizon.

Calcic horizon and k horizon

The calcic horizon is a horizon of accumulation of calcium
carbonate or of calcium and magnesium carbonate. The
accumulation may be in the C horizon, but it may also be in
a variety of other horizons such as a mollic epipedon, an
argillic or a natric horizon, or a duripan.

The calcic horizon has two forms. In one, the underlying
materials have less carbonate than the calcic horizon. This
form of calcic horizon includes horizons of secondary car~
bonate enrichment that are 15 cm (6 in.) or more thick, have
a carbonate content equivalent to >15 percent CaCO,, and
have a CaCO, equivalent at least 5 percent greater than the
C horizon. In the other form, the calcic horizon is 15 cm or
more thick, has a CaCO, equivalent 215 percent, and con-
tains >5 percent, by volume, of identifiable secondary car-
bonates as pendants on pebbles, concretions, or soft powdery
forms. If this calcic horizon rests on limestone, marl, or
other very highly calcareous materials (240 percent CaCO,


145

Chapter 9
Inceptisols
Key To Suborders

TA. Inceptisols that
1. Have an aquic moisture regime or are artificially
drained and have one or more of the following:
a. A histic epipedon;
b. A sulfuric horizon that has its upper boundary
within 50 cm of the mineral soil surface;
¢. An umbric or mollic epipedon that is underlain
immediately or at a depth <50 cm below the soil
surface by a horizon that has dominant colors, moist,
‘on ped faces, or in the matrix if peds are absent, as
follows:
(A) IE there is mottling, chroma is 2 or less';
(2) If there is no mottling, chroma is 1 or less;
d. An ochric epipedon that is underlain at a depth <50
cm below the mineral soil surface by a cambic horizon
or a fragipan either or both of which has dominant
color, moist, on ped faces, or in the matrix if peds are
absent as follows:
(1) If there is mottling, chroma is 2 or less®;
(2) If there is no mottling, chroma is I or less;
2. Or have an SAR 213 (or sodium saturation that is 15
percent or more) in half or more of the soil to a depth of
50cm that decreases with depth below 50 cm and
ground water within | m of the surface at some time of
the year,
Aquepts, p. 149

IB, Other Inceptisols that have to a depth of 35 cm or more,
or to a lithic or paralithic contact if one is shallower than 35
cm, one or both of the following:
1, Bulk density (at 33 kPa water retention) of the fine-
earth fraction that is <0.85 g per cubic centimeter and an
exchange complex that is dominated by amorphous
materials; or
2, Sixty percent or more of the sail (by weight) is vitric®
volcanic ash, cinders or other pyroclastic materials.
Andepts, p. 146

IC. Other Inceptisols that have a plaggen epipedon.
Plaggepts, p. 163

ID. Other Inceptisols that have an isomesic or warmer iso
temperature regime.
‘Tropepts, p. 163

Tic che he ia redder thon 10¥R, of red parent materiale that remain
red after citrate-dithionite extraction, the requirement for low chroma is
waived.
ir the hue is redder than OYR because of red parent materials that remain
red after citrate-dithionite extraction, the requirement for low chroma is
waived.

included in the meaning of vitrie materials in this definition are crystalline
particles that are coated with glass and partially devitrifed glass as well as
lass.



188

GFF. Other Ustolls that have a mollic epipedon below any
Ap horizon that is 50 percent or more by volume wormholes
and wormeasts or filled animal burrows, and that either rests
on a lithic contact or has a transition to the underlying
horizon in which 25 percent or more of the material is
discrete wormcasts or animal burrows filled with material
from the mollic epipedon and the underlying horizon.
Vermustolls, p. 194

GFG. Other Ustolis.
Haplustolls, p. 191

Argiustolls
Distinctions between Typic Argiustolls and other subgroups

Typic Argiustolls are the Argiustolls that

a. Do not have mottles that have chroma of 2 or less within

1 m of the soil surface if artificially drained or, if

undrained, are not continuously saturated with water within

1 m of the soil surface for as long as 3 months in most

years;

b. Do not have a brittle horizon 15 cm or more thick within

1 m of the soil surface that contains some opal coatings or

some (<20 percent by volume) durinodes;

©. Do not have a lithic contact within 50 cm of the surface;

d. Do not have an albic horizon or other eluvial horizon

above the argillic horizon that has a color value too high for

a mollic epipedon and chroma too high for an albic horizon;

e. Have a mollic epipedon <50 cm thick, or the texture is

loamy fine sand or coarser if the mollic epipedon is >50 cm

thick;

f. When neither irrigated nor fallowed to store moisture:

(1) If the soil temperature regime is mesic or thermic,
are dry for more than four-tenths of the cumulative days
in some part of the moisture control section when the soil
temperature at a depth of 50 cm exceeds 5°C; or

(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days
during @ period when the soil temperature at a depth of
50 cm exceeds 8°C;

g. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part, and that extend upward to the surface
or to the base of an Ap horizon,

(2) A coefficient of linear extensibility (COLE) of 0.07
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.25 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.25 m, and

(3) More than 35 percent clay in horizons that total >50
cm in thickness;

h, When neither irrigated nor fallowed to store moisture,
(1) If the soil temperature regime is mesic or thermic,
are dry less than six-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) during a period when the soil
temperature at a depth of 50 cm is higher than 5°C, or



29

winter solstice in 6 or more years out of 10, The moisture
contro} section is moist in some part more than half the
time, cumulative, that the soil temperature at a depth of 50
cm is higher than S°C, or in 6 or more years out of 10 it is
moist in some part for at least 90 consecutive days when the
soil temperature at a depth of 50 cm is continuously higher
than 8°C. In addition, the mean annual soil temperature is
lower than 22°C, and mean summer and mean winter soil
temperatures differ by 5°C or more at a depth of 50 cm or
at a lithic or paralithic contact, whichever is shallower.

Soil temperature regimes

Classes of soi] temperature regimes

The following soil temperature regimes are used in defining
classes at various categoric levels in the taxonomy.

Pergelic (L. per, throughout in time and space, and L.
gelare, to freeze; connoting permanent frost),.--Soils with a
pergelic temperature regime have a mean annual temperature
lower than 0°C. These are soils that have permafrost if they
are moist, or dry frost if excess water is not present. It
seems likely that the moist and the dry pergelic regimes
should be defined separately, but at present we have only
fragmentary data on the dry soils of very high latitudes.

Cryie (Gr. kryas, coldness; connoting very cold soils).--In
this regime soils have a mean annual temperature higher
than 0°C (32°F) but lower than 8°C (47°F).

1, In mineral soils the mean summer soil temperature (June,
July, and August in the northern hemisphere and December,
January, and February in the southern hemisphere) at a
depth of 50 cm or at a lithic or paralithic contact, whichever
is shallower, is as follows:
a. If the soil is not saturated with water during some part
of the summer and
(1) There is no © horizon, lower than 15°C (59°F);
(2) There is an O horizon, lower than 8°C (47°F);
b. If the soil is saturated with water during some part of
the summer and
(1) There is no O horizon, lower than 13°C (55°F);
(2) There is an O horizon or a histic epipedon, lower
than 6°C (43°F),

2. In organic soils, either
a, The soil is frozen in some layer within the control
section in most years about 2 months after the summer
solstice; that is, the soil is very cold in winter but warms
up slightly in summer; or
b, The soil is not frozen in most years below a depth of 5
cm; that is, the soil is cold throughout the year but, be-
cause of marine influence, does not freeze in most years.

Cryic soils that have an aquic moisture regime commonly are
churned by frost.

Most isofrigid soils with a mean annual soil temperature
above 0°C have a cryic temperature regime. A few with or-
ganic materials in the upper part are exceptions. Through-


170

with water at some time of the year when its temperature is
>5°C or if there is artificial drainage;
b. Have an umbric or mollic epipedon that is <50 cm thick;
c. Have a cambic horizon;
d, Have a content of organic carbon that decreases regularly
with depth or have slopes >25 percent;
e. Do not have a lithic contact within 50 cm of the soil
surface; and
f. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has buik density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either
(1) a ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less or
(2) a ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum.
Andic Xerumbrepts are like Typic Xerumbrepts except for /.
Entic Xerumbrepts are like Typic Xerumbrepts except for c.
Fluventic Xerumbrepts are like Typic Xerumbrepts except
for d.
Lithie Xerumbrepts are like Typic Xerumbrepts except for e,
with or without c.
Pachic Xerumbrepts are like Typic Xerumbrepts except for
6, with or without a or c, or both.


280

zons in the overlying deposit. Some buried horizons, how~
ever, formed in material lithologically like that of the over-
lying deposit. A prefix is not used to distinguish material of
such buried horizons. If the material in which a horizon of
a buried soil formed is lithologically unlike that of the
overlying material, the discontinuity is designated by num~
ber prefixes and the symbol for a buried horizon is used as
well: Ap-Bti-Bt2-BC-C- 2Ab-2Btb1-2Btb2-2C.

In organic soils, discontinuities between different kinds

of layers are not identified. In most cases the differences
are shown by the letter suffix designations, if the different
layers are organic, or by the master symbol if the different
layers are mineral.

Use of the prime.--\dentical designations may be appropri~
ate for two or more horizons or layers separated by at least
one horizon or layer of a different kind in the same pedon.
The sequence A-E-Bt-E-Btx-C is an example: the soil has
two E horizons, To make communication easier, the prime
is used with the master horizon symbol of the lower of two
horizons having identical letter designations: A-E-Bt-E'-
Btx-C, The prime is applied to the capital letter designa-
tion, and any lower case symbols follow it: B’t. The prime
is not used unless all letters of the designations of two dif-
ferent layers are identical. Rarely, three layers have iden-
tical letter symbols; a double prime can be used: E".

The same principle applies in designating layers of or-
ganic soils. The prime is used only to distinguish two or
more horizons that have identical symbols: Oi-C-O'i-C’ or
Oi-C-Oe-C’. The prime is added to the lower C layer to
differentiate it from the upper.



190

g- Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
or to the base of an Ap horizon,

(2) A coefficient of linear extensibility (COLE) of 0.07
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1,25 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.25 m, and

(3) More than 35 percent clay in horizons that total >50
cm in thickness.

h, When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry for more than four-tenths of the cumulative days
in some part of the moisture control section when the soil
temperature at a depth of 50 cm exceeds 5°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days
during a period when the soil temperature at a depth of
50 cm exceeds 8°C;

Aquic Calciustolls are like Typic Calciustolls except for a or

for a and b.

Aridic Calciustolls are like Typic Calciustolls except for b.

Lithic Calciustolls are like Typic Calciustolls except for ¢ or

for b and ¢.

Lithie Petrocalcic Calciustolls are like Typic Calciustolls

except for c and ¢ or for c, ¢, or b.

Pachic Calciustolls are like Typic Calciustolls except for d,

with or without a.

Petrocalcic Calciustolls are like Typic Calciustolls except for

e or for b and e.

Torrertic Calciustolls are like Typic Calciustolls except for

g, with or without any or all of a, 6, and d, and the cracks

are open 180 days or more, cumulative, in most years.

Udertic Calciustolts are like Typic Calciustolls except for ¢

and A, with or without a or 6 or both, and cracks are open

Jess than 135 days in most years.

Udic Calciustolts are like Typic Calciustolls except for A.

Vertic Calciustolls are like Typic Calciustolls except for g,

with or without any or all of a, b, and d, and the cracks are

open between 135 and 180 days in most years.

Durustolls
Distinctions between Typic Durustolls and other subgroups.

Typic Durustolls are the Durustolls that:

a. Have an argillic horizon above the duripan;

b. Have a duripan that is massive and platy and that has

half or more of its upper boundary coated or indurated with

opal and silica with or without sesquioxides or that is in-
durated in some subhorizon below its upper boundary;

¢. Do not have a natric horizon above the duripan;

d, When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry less then six-tenths of the time in half or more
years in some part of the moisture control section (not


276

particles or may occur as discrete pellets. In some
horizons, coatings have coalesced, filled pores, and
cemented the horizon, The symbol “h” is also used
in combination with "s" as "Bhs" if the amount of
sesquioxide component is significant but value and
chroma of the horizon are 3 or less.

Slightly decomposed organic material

This symbol is used with "O" to indicate the least
decomposed of the organic materials. Rubbed fiber
content is more than about 2/5 of the volume,

Accumulation of carbonates

This symbol is used to indicate accumulation of al-
kaline earth carbonates, commonly calcium carbon-
ate.

Cementation or induration

This symbol! is used to indicate continuous or nearly
continuous cementation. Symbol is used only for
horizons that are more than 90 percent cemented,
though they may be fractured. Roots penetrate “m"
horizons only through cracks. The cement-

ing material is also symbolized. If 90 percent or
more of the horizon is cemented by carbonates,
"km" is used; by silica, "qm", by iron, "sm"; by
gypsum, "ym"; by both lime and silica, "kam"; by
salts more soluble than gypsum, "zm".

Accumulation of sodium

This symbol is used to indicate accumulation of
exchangeable sodium.

Residual accumulation of sesquioxides

This symbol is used to indicate residual accumula-
tion of sesquioxides.

Plowing or other disturbance

This symbol is used to indicate disturbance of the
surface layer by cultivation, pasturing, or similar
uses, A disturbed organic horizon is designated Op.
A disturbed mineral horizon, even though clearly
once a E, B, or C horizon, is designated Ap.

Accumulation of silica

This symbol is used to indicate accumulation of
secondary silica. If silica cements the layer and
cementation is continuous or nearly continuous,
“qm" is used.

Weathered or soft bedrock

This symbol is used with "C" to indicate layers of
soft bedrock or saprolite, such as weathered igneous


273

genetic horizon are layers of illuvial concentration of
carbonates, gypsum, or silica that are the result of pe-
dogenic processes (these layers may or may not

be cemented) and brittle layers that have other evi-
dence of alteration, such as prismatic structure or illu-
vial accumulation of clay.

Examples of layers that are not B horizons are layers
in which clay films coat rock fragments or are on
finely stratified unconsolidated sediments, whether the
films were formed in place or by illuviation, and lay-
ers into which carbonates have been illuviated unless
contiguous to an overlying genetic horizon.

C horizons or layers: Horizons or layers, excluding hard
bedrock, that are little affected by pedogenic processes and
lack properties of O, A, E, or B horizons. Most are mineral
layers, but limnic layers*, whether organic or inorganic, are
included. The material of C layers may be either like or un-
like that from which the solum presumably formed. A C
horizon may have been modified even if there is no evidence
of pedogenesis.

Included as C layers are sediments, saprolite, and
consolidated bedrock that when moist can be dug with
a spade. Some soils form in material that is already
highly weathered, and such material that does not
meet the requirements of A, E, or B horizons

is designated C. Changes not considered pedogenic
are those not related to overlying horizons. Layers
having accumulations of silica, carbonates, or gypsum
or more soluble salts are included in C horizons, even
if indurated, unless these layers are obviously affected
by pedogenic processes; then they are a B horizon.

R Layers: Hard Bedrock.

Granite, basalt, quartzite, and indurated limestone or
sandstone are examples of bedrock that are designated R.
The bedrock of an R layer is sufficiently coherent when
moist to make hand digging with a spade impractical, al-
though it may be chipped or scraped with a spade. Some
R layers can be ripped with heavy power equipment.
‘The bedrock may contain cracks, but these are

few enough and small enough that few roots can pene-
trate. The cracks may be coated or filled with clay or
other material,

Transitional horizons

There are two kinds of transitional horizon, In one,

the properties of an underlying or overlying horizon are su-
perimposed on properties of the other horizon throughout
the transition zone. In the other, parts that are characteris-
tic of an overlying or underlying horizon are enclosed by
parts that are characteristic of the other horizon, Special
conventions are used to designate these kinds of horizons.



99

Xerollic Haplargids are like Typic Haplargids except for e
with or without 4, have a mean annual soil temperature
lower than 22°C, and the mean summer and mean winter
soil temperatures at a depth of 50 cm differ by 5°C or more.
They have an ari moisture regime that borders on a xeric
regime.

Nadurargids
Distinctions between Typic Nadurargids and other subgroups

Typic Nadurargids are the Nadurargids that
a, Are not saturated with water in any horizon within a
depth of 1 m at any period or do not have either of the
following characteristics within the horizon or horizons that
are saturated:
(1) Dominant chroma of | or less throughout and hue as
yellow or yellower than 2.5Y in some part;
(2) Both a dominant chroma of 2 or less and mottles that
are not due to segregated lime;
b, Have a platy or massive duripan that is indurated in some
subhorizon; and
c. Have a duripan shallower than 18 cm; or have a weighted
average percentage of organic carbon in the upper soil to a
depth of 40 cm that is <0.6 if the weighted average ratio of
sand to clay to that depth is 1.0 or less, or that is less than
one-seventh percent if the ratio of sand to clay is 13 or
more, or have an intermediate amount of organic carbon if
the ratio of sand to clay is between 1,0 and 13; or have a
weighted average percentage of organic carbon in the
surface soil to a depth of 18 cm that is not one-fifth more
than the values just stated if there is a duripan that is
shallower than 40 cm but deeper than 18 cm.
Aquic Haplic Nadurargids are like Typic Nadurargids except
for a and , with or without c.
Haplic Nadurargids are like Typic Nadurargids except for b.
Haploxerollic Nadurargids are like Typic Nadurargids
except for b and c, They have an aridic moisture regime
that borders on a xeric regime.
Xerollic Nadurargids are like Typic Nadurargids except for
¢, They have a mean annual soil temperature lower than
22°C, and the mean summer and mean winter soil
temperatures at a depth of 50 cm differ by 5°C or more,
They have an aridic moisture regime that borders on a xeric
regime.

Natrargids
Distinctions between Typic Natrargids and other subgroups

Typic Natrargids are the Natrargids that
a, Either are not saturated with water in any horizon within
1 m of the surface at any time or do not have either of the
following characteristics in the horizon or horizons that are
saturated:
(1) Dominant chroma of | or less throughout and hue as
yellow or yellower than 2.5Y in some part; or
(2) Both a dominant chroma of 2 or less accompanied by
mottles that are not due to segregated lime;
b. Do not have a horizon within 1 m of surface that is more
than 15 cm thick and that either contains 20 percent or

rN


143

Terric Medisaprists are like Typic Medisaprists except for c,
with or without a or e, or both.

‘Troposaprists

Distinctions between Typic Troposaprists and other sub-
groups

Typic Troposaprists are the Troposaprists that
a. Do not have a mineral layer between 5 and 30 cm thick
within organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier;
b, Have
(1) Less than 12.5 cm of the subsurface and bottom tiers
consisting of fibric materials; and
(2) Less than 25 cm of the subsurface and bottom tiers
consisting of hemic materials;
¢. Do not have a mineral layer 30 cm or more thick that has
its upper boundary in the control section below the surface
tier;
d, Do not have a layer of water within the control section
beneath the surface tier;
e. Do not have limnic layer(s) that are 5 cm or more thick
within the control section; and
f. Do not have a lithic contact within the control section,
Fibric Troposaprists are like Typic Troposaprists except for
WI).
Fibrie Terrie Troposaprists are like Typic Troposaprists ex-
cept for 5(1) and c, with or without a or e, or both.
Fluvaquentic Troposaprists are like Typic Troposaprists ex-
cept for a, with or without 5.
Hemic Troposaprists are like Typic Troposaprists except for
2),
Hemic Terric Troposaprists are like Typic Troposaprists ex-
cept for (2) and c, with or without a or e, or both.
Limnic Troposaprists are like Typic Troposaprists except for
e, with or without a or b, or both.
Lithic Troposaprists are like Typic Troposaprists except for
J, with or without all or any of a, b, ¢, or e.
Terric Troposaprists are like Typic Troposaprists except for
¢, with or without @ or e, or both.


91

paralithic contact is deeper than 50 cm but shallower than
1.5 m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness;
h, Have an argillic horizon that is continuous vertically for
at least the upper 20 cm that is not composed entirely of
lamellae, and that has a texture finer than loamy fine sand;
1. Do not have a calcic horizon that has its upper boundary
within the upper 1 m of soil; and
j. Have an argillic horizon that is continuous horizontally
throughout the area of each pedon.
Aquic Haploxeralfs are like Typic Haploxeralfs except for a
or for a and b,
Aquultic Haploxeralfs are like Typic Haploxeralfs except for
a and f with or without b.
Calcic Haploxeralfs are like Typic Haploxeralfs except for i.
Lithic Haploxeralfs are like Typic Haploxeralfs except for c.
Lithic Mollic Haploxeralfs are like Typic Haploxeralfs ex-
cept for ¢ and b.
Lithic Ruptic-Xerochreptic Haploxeralfs are like Typic
Haploxeralf’s except for ¢ and j.
Mollie Haploxeralfs are like Typic Haploxeralfs except for

Matric Haploxeralfs are like Typic Haploxeralfs except for
d.

Psammentic Haploxeralfs are like Typic Haploxeralfs except
for h, with or without 4 or /, or both.

Ultic Haploxeralfs are like Typic Haploxeralfs except for f
or for f and

Vertic Haploxeralfs are like Typic Haploxeralfs except for g
or for b and g.

Natrixeralfs
Distinctions between Typic Natrixeralfs and other subgroups

Typic Natrixeralfs are the Natrixeralfs that

a, Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if there is ground water in the
mottled horizon at some time when the temperature of that
horizon is S°C or higher.

Aquic Natrixeralfs are like Typic Natrixeralfs except for a.

Palexeralfs
Distinctions between Typic Palexeralfs and other subgroups

The list of subgroups is incomplete for the world. A few
subgroups are defined that are not known to occur in the
United States, but a number of others that have not yet been
defined are known to exist.

Typic Palexeralfs are the Palexeralfs that

a. Do not have mottles that have chroma of 2 or less within
75 cm of the soil surface if the mottled horizon is saturated
with water at some time of the year when its temperature is
5°C or higher or there is artificial drainage;

b. Do not have a calcic horizon within 1.5 m of the soil
surface;

¢. Have an A horizon that, throughout its upper 10 cm, has
a color value, moist, of 3.5 or more or contains <0.7 percent


224

CCDD. Other Kandiustox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Kandiustox

CCDE. Other Kandiustox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface and mottles of 4 or more value moist and 2 or
less chroma within a depth of 125 cm of the soil surface.
Plinthaquic Kandiustox

CCDF. Other Kandiustox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Kandiustox

CCDG. Other Kandiustox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface.

Aquic Kandlustox

CCDH. Other Kandiustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface.

Humic Rhodic Kandiustox

CCDI. Other Kandiustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Kandiustox

CCDJ, Other Kandiustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humlc Kandiustox

CCDK. Other Kandiustox that have a color hue of 2.5 YR
or redder with moist values of less than 4 in most of the 25
to 125 cm depth from the soil surface.

Rhodic Kandiustox

CCDL. Other Kandiustox that have a color hue of 7.5 YR or
yellower with moist values of 6 or more in most of the 25 to
125 cm depth from the soil surface.

Xanthic Kandiustox

CCDM. Other Kandiustox.
Typic Kandiustox

Sombriustox
Kev to subgroups
CCAA. Sombriustox that have a petroferric contact within a

depth of 125 cm of the soil surface.
Petroferric Sombriustox


197

Calcic Pachic Argixerolls are like Typic Argixerolls except
for c and g, with or without a.

Durargidic Argixerolls are like Typic Argixerolls except for
dand f.

Durie Argixerolls are like Typic Argixerolls except for d,
with or without c.

Lithic Argixerolls are like Typic Argixerolls except for e,
with or without ¢ or f, or both,

Lithic Ultic Argixerolls are like Typic Argixerolls except for
eand h.

Pachic Argixerolls are like Typic Argixerolls except for g,
with or without a,

Pachic Ultic Argixerolls are like Typic Argixerolls except
for g and h, with or without a.

Ultic Argixerolis are like Typic Argixerolls except for A.
Vertic Argixeralls ace like Typic Argixerolls except for i,
with or without all or any of a, c, or g.

Calcixerolls
Distinctions between Typic Calcixerolls and other subgroups

Typic Calcixerolls are the Calcixerolls that

a, Do not have mottles within 75 cm of the surface that are

due to segregation of iron or manganese if artificially

drained, and if undrained are not continuously saturated

with water within 1 m of the soil surface for as long as 90

days in most years;

b. Have a mollic epipedon that is <50 cm thick, or the tex~

ture is loamy fine sand or coarser if the mollic epipedon is >

50 cm thick;

c. Have a xeric moisture regime;

4. Do not have a lithic contact within 50 cm of the soil

surface;

e, Do not have a mollic epipedon that below any Ap horizon

has 50 percent or more by volume wormholes, wormcasts, or

filled animal burrows; and

f. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part, and that extend upward to the surface
or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1,5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m; and
(3) More than 35 percent clay in horizons that have a
total thickness of >50 cm.

Aquic Calcixerolls are like Typic Calcixerolls except for a.

Aridie Calcixerolls are like Typic Calcixerolls except for c

and have an aridic moisture regime that borders on xeric.

Lithic Calcixerolls are like Typic Calcixerolls except for d

or for c and d.

Pachic Calcixerolls are like Typic Calcixerolls except for b

or for a and 4, with or without c.

Vermic Calcixerolls are like Typic Calcixerolls except for e.

Vertic Calcixerolls are like Typic Calcixerolls except for f,

with or without a or b, or both,

MO


equivalent), the percentage of carbonates need not decrease
with depth.

If the particle-size class is sandy, sandy-skeletal, coarse-
loamy, or loamy-skeletal with less than 18 percent clay, the
15 percent requirement for CaCO, equivalent is waived.
But to qualify as a calcic horizon, Sthe horizon must have at
least 5 percent (by volume) more soft powdery secondary
CaCO, than an underlying horizon, and the calcic horizon
must be at least 15 cm thick.

If a horizon enriched with secondary carbonate is indurated
or cemented to the degree that dry fragments do not slake in
water, it is considered to be a petrocalcic horizon, which is
discussed later. Air-dry fragments of a calcic horizon
stake in water. Pendants below rocks and concretions nor-
mally do not slake, but these are not connected, and the soil
material between the concretions will slake.

Cambic horizon

In summary, the cambic horizon is an altered horizon that
does not have the dark color, organic-matter content, and
structure that are definitive of a histic, a mollic, or an um-
bric epipedon, and it has

1, Texture that is very fine sand, loamy very fine sand, or
finer in the fine-earth (<2 mm) fraction;

2, Soil structure or absence of rock structure in at least half
the volume;

3, Minerals that consist of (a) enough amorphous or 2:1 lat-
tice clay to give a cation-exchange capacity (by NH,OAc) of
more than 16 cmol(+) kg? clay or (b) >10 percent weather-
able minerals;

4, Evidence of alteration in one of the following forms:
a, Gray colors as defined for an aquic moisture regime,
defined later, or artificial drainage, and one or more of
the following properties:
(1) A regular decrease in the amount of organic car-
bon with depth and a content of <0.2 percent organic
carbon at a depth of 1.25 m below the surface or im-
mediately above a sandy-skeletal substratum that is at
a depth of <1,25 m;
(2) Cracks that open and close in most years and are 1
cm or more wide at a depth 50 cm below the surface;
(3) Permafrost at some depth;
(4) A histic epipedon consisting of mineral soil mate-
rials or a mollic or umbric epipedon;
b. Stronger chroma, redder hue, or higher clay content
than the underlying horizon;
ce. Evidences of removal of carbonates. Particularly, the
cambic horizon has less carbonate than the underlying
k horizon. If all coarse fragments in the k horizon are
completely coated with lime, some in the cambic horizon
are partly free of coatings. If coarse fragments in the k
horizon are coated only on the under side, those in the
cambic horizon should be free of coatings;



98

temperature regime and an aridic moisture regime that
borders on an ustic regime.

Borollic Vertic Haplargids are like Typic Haplargids except
for ¢ and g, with or without h. The mean annual soil
temperature is lower than 8°C, and the mean summer and
mean winter soil temperatures at a depth of 50 cm differ by
5°C or more. The cracks are not closed for as many as 60
consecutive days of the 120 days following the winter
solstice in 3 or more years out of 10.

Duric Haplargids are like Typic Baplargids except for c.
Durixerollic Haplargids are like Typic Haplargids except for
¢ and e, with or without 4. They have a mean annual soil
temperature lower than 22°C, and the mean summer and
mean winter soil temperatures at a depth of 50 cm differ by
5°C or more, The aridic moisture regime borders on a xeric
regime.

Lithic Haplargids are like Typic Haplargids except for d.
Lithic Ruptic-Entic Xerollic Haplargids are like Typic
Haplargids except for d, e, and /, with or without h, They
have a mean annual soil temperature lower than 22°C, and
the mean summer and mean winter soil temperatures at a
depth of 50 cm differ by 5°C or more. The aridic moisture
regime borders on a xeric regime.

Lithic Ustollic Haplargids are \ike Typic Haplargids except
for d and e, with or without 4, They have a mean annual
soil temperature of 8°C or higher and an aridic moisture
regime that borders on an ustic regime.

Lithie Xerollic Haplargids are like Typic Haplargids except
for d and e, with or without h. They have a mean annual
soil temperature that is lower than 22°C, and the mean
summer and mean winter soil temperatures at a depth of 50
em differ by 5°C or more. They have an aridic moisture
regime that borders on a xeric regime.

Ustalfic Haplargids are like Typic Haplargids except for h.
They have a mean annual soil temperature of 8°C or higher
and an aridic moisture regime that borders on an ustic
regime.

Ustertic Haplargids are like Typic Haplargids except for ¢,
with or without e or h, or both. They have cracks that
remain open from 175 to 240 days, cumulative, in most
years and that are not closed for as many as 60 consecutive
days during the 120 days following the winter solstice in 3
or more years out of 10 if the soil temperature regime is
thermic, mesic, or frigid. Other frigid soils are excluded.
Ustollic Haplargids are like Typic Haplargids except for e,
with or without h, They have a mean annual soil
temperature of 8°C or higher and an aridic moisture regime
that borders on an ustic regime.

Vertic Haplargids are like Typic Haplargids except for g or
for g and / and have cracks that remain open for 8 months
or more, cumulative, in most years.

Xeralfic Haplargids are like Typic Haplargids except for h.
They have a mean annual soil temperature lower than 22°C,
and the mean summer and mean winter soil temperatures at
a depth of 50 cm differ by 5°C or more, They have an
aridic moisture regime that borders on a xeric regime.
Xerertic Haplargids are like Typic Haplargids except for ¢
or ¢ and g and have a thermic, mesic, or frigid soil
temperature regime, and they have cracks that close for 60
consecutive days or more during the 120 days following the
winter solstice in more than 7 out of 10 years.


191

necessarily the same part) during a period when the soil
temperature at a depth of 50 cm exceeds 5°C, or
(2) If the soil temperature regime is hyperthermic or
isomesic, or warmer, are moist in some or all parts of the
moisture control section for 90 consecutive days or more
during a period when the soil temperature at a depth of
50 cm exceeds 8°C.
Aridic Durustolls are like Typic Durustolls except for d and
have an aridic moisture regime that border on ustic.
Orthidic Durustolls are like Typic Durustolls except for a
and d and have an aridic moisture regime that borders on
ustic,

Haplustolls
Distinctions between Typic Haplustolls and other subgroups

Typic Haplustolls are the Haplustolls that
a, Do not have mottles that have chroma of 2 or less within
1 m of the surface if artificially drained or, if undrained,
are not continuously saturated with water within 1 m of the
soil surface for 90 days or more in most years;
b. Have a mollic epipedon that is <50 cm thick, or the tex-
ture is loamy fine sand or coarser if the mollic epipedon is
250 cm thick;
¢. Do not have a brittle horizon 15 cm or more thick within
1 m of the surface that contains some opal coatings or some
durinodes (<20 percent by volume);
d. Have a cambic horizon, or the lower part of the mollic
epipedon meets the requirements of a cambic horizon except
for color and for organic-carbon content, and either the
cambic horizon or the lower part of the mollic epipedon is
free of carbonates in some part;
e. Have a regular decrease in organic-carbon content with
increasing depth to a level of 0.3 percent or less within 1.25
m of the surface unless a lithic or paralithic contact occurs
at a shallower depth or the slope is >25 percent;
f. Do not have a lithic contact within 50 cm of the surface;
8. Do not have a salic horizon that has its upper boundary
within 75 cm of the surface;
hh. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0.07
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.25 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.25 m; or
(3) More than 35 percent clay in horizons that total >50
cm in thickness;
i, When neither irrigated nor fallowed to store moisture:
(1) If the soil temperature regime is mesic or thermic,
are dry for more than four-tenths of the cumulative days
in some part of the moisture control section when the soil
temperature at a depth of 50 cm exceeds 5°C; or
(2) If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days

MOL


103

EBD, Other Orthids that have a gypsic or petrogypsic
horizon whose upper boundary is within ] m of the soil
surface.

Gypsiorthids, p. 107

EBE. Other Ort that have a calcic horizon whose upper
boundary is within 1 m of the surface and that are
calcareous in all parts above the calcic horizon after the
upper soil, to a depth of 18 cm, is mixed unless the texture
is as coarse or coarser than loamy fine sand.

Calciorthids, p. 103

EBF. Other Orthids (that have a cambic horizon).
Camborthids, p, 104

Calctorthids
Distinctions between Typic Calciorthids and other subgroups

Typic Calciorthids are the Calciorthids that
a. Are not saturated with water for 90 consecutive days or
more in most years within 1 m of the surface and do not
have any of the following characteristics within a depth of !
m below the surface if the soil above that depth is saturated
with water at some period in most years or the soil is
artificially drained:
(1) Dominant chroma of | or less throughout and hue as
yellow or yellower than 2.SY in some part;
(2) Dominant chroma of 2 or less and mottles that are
not due to segregated lime; or
(3) Both a dominant chroma of 2 or less and a greater
SAR (or percentage of exchangeable Na) in more than
half the thickness of the horizons between the surface
and 50 cm than in the saturated zone;
'b. Do not have a horizon within | m of the surface that is
>15 cm thick that either contains 20 percent or more
durinodes in a nonbrittle matrix or is brittle and has firm
consistence when moist;
¢. Do not have a lithic contact within 50 cm of the surface;
d, Have a weighted average content of organic carbon in the
upper soil to a depth of 40 cm that is <0.6 percent if the
weighted average ratio of sand to noncarbonate clay for this
depth is 1.0 or less, or is <0.15 percent if the ratio is 13 or
more, or is intermediate if the ratio of sand to clay is
between 1.0 and 13; or a weighted average percentage of
organic carbon in the surface soil to a depth of 18 cm that
is not one-fifth more than the values just stated if there is a
lithic or pasalithic contact that is shallower than 40 cm but
deeper than 18 cm;
e, Are dry in all parts of the moisture control section more
than three-fourths of the time (cumulative) that the soil
temperature is 5°C or higher at a depth of 50 cm; and
f. Do not have reddish peds below the calcic horizon that
are weakly calcareous or noncalcareous but that are thickly
coated with lime.
Aquic Caiciorthids are like Typic Calciorthids except for a,
with or without d or e, or both,
Aquic Durie Calciorthids are like Typic Calciorthids except
for a and 5, with or without d or e, or both.
Argic Calciorthids are like Typic Calciorthids except for /.



229

e. Do not have an intermittent upper black subhorizon of
the spodic horizon that has a ratio of free iron (elemental) to
carbon that is <0.2; or if plowed and the Ap horizon rests
directly on the spodic horizon, do not have tongues of such
a subhorizon;

f. Do not have an argillic or kandic horizon,

Alfic Fragiaquods are like Typic Fragiaquods except for /.
Cryic Fragiaquods are like Typic Fragiaquods except for a
or for a and b,

Haplaquods
Distinctions between Typic Haplaquods and other subgroups

Typic Haplaquods are the Haplaquods that
a. Have an umbric epipedon or one that would meet the re-
quirements for an umbric epipedon if it were plowed to a
depth of 25 to 30 cm;
b. Do not have an argillic or kandic horizon underlying the
spodic horizon;
c. Do not have a sandy epipedon (loamy fine sand or coarser
throughout) that is 75 cm or more thick;
d, Have a spodic horizon that has a weighted average of 0.6
percent or more organic carbon in the matrix of the upper
30 cm of the spodic horizon or have an upper subhorizon of
the spodic horizon that
(1) Has 2.3 percent or more organic carbon in the upper
2 cm; and
(2) Is continuous or is present in more than 90 percent of
each pedon;
e. Have <5 percent by volume of iron-cemented nodules 2,5
to 30 cm in diameter in any subhorizon of the spodic hori-
zon;
f. Do not have a lithic contact within 50 cm of the mineral
soil surface;
g. Do not have a surface horizon >30 cm thick that meets all
requirements of a plaggen epipedon except thickness;
h, Do not have a histic epipedon; and
i. Do not have a placic horizon in or below the spodic
horizon,
Aeric Haplaquods are like Typic Haplaquods except for a.
Alfic Haplaquods are like TYpic Haplaquods except for 6,
with or without a or d, or both, and have either base satu-
ration of 35 percent or more (by sum of cations) in some
part of the argillic or kandic horizon or have a mean annual
soil temperature lower than 8°C.
Alfic Arenic Haplaquods are like Typic Haplaquods except
for a, b, and ¢, with or without c, with or without d, and
have base saturation of 35 percent or more (by sum of
cations) in some part of the argillic horizon or kandic or
have a mean annual soil temperature lower than 8°C and the
upper boundary of the spodic horizon is between 75 cm and
1.25 m below the soil surface.
Arenic Haplaquods are like Typic Haplaquods except for a
and c, and the upper boundary of the spodic horizon is be-
tween 75 cm and 1.25 m below the soil surface.
Arenic Ultic Haplaquods are like Typic Haplaquods except
for a, 6, and c with or without d and have base saturation
(by sum of cations) of less than 35 percent throughout the
Argillic or kandic horizon and have a mean annual soil tem-
perature of 8°C or higher and the upper boundary of the



206

CDBC. Other Acroperox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface and a lithic contact within 125 cm of the
soil surface.

Aquic Lithic Acroperox

CDBD. Other Acroperox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Acroperox

DBE. Other Acroperox that have a delta pH (KCI pH - 1:)
water pH) with a 0 or net positive charge in some layer 18
cm or more thick within a depth of 125 cm of the soil sur-
face.

Anionic Acroperox

CDBF. Other Acroperox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Acroperox

CDBG. Other Acroperox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface.

Aquic Acroperox

CDBH. Other Acroperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and a color hue of 2.5 YR or redder with
moist values of less than 4 in most of the 25 to 125 cm
depth from the soil surface.

Humic Rhodic Acroperox

CDBI. Other Acroperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter and color hue of 7.5 YR or yellower with
moist values of 6 or more in most of the 25 to 125 cm depth
from the soil surface.

Humic Xanthic Acroperox

CDBJ. Other Acroperox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Acroperox

CDBK. Other Acroperox that have a color hue of 2.5 YR or
redder with moist values of less than 4 in most of the 25 to
125 cm depth from the soil surface.

Rhodic Acroperox

CDBL. Other Acroperox that havé a color hue of 7.5 YR or
yellower with moist values of 6 or more in most of the 25 to
125 cm depth from the soil surface.

Xanthic Acroperox

CDBM. Other Acroperox.
Typic Acroperox


196

GDE. Other Xerolls that have an argillic horizon,
Argixerolls, p. 196

GDF. Other Xerolls.
Haploxerolls, p. 198

Argixerolls
Distinctions between Typic Argixerolls and other subgroups

Typic Argixerolls are the Argixerolis that

a, Do not have mottles that have chroma of 2 or less within

75 cm of the surface if artificially drained or if undrained

are not continuously saturated with water within 1 m of the

soil surface for 90 days or more in most years;

'b. Do not have an albic horizon above the argillic horizon;

c. Do not have a calcic horizon or soft, powdery secondary

lime within a depth of 1.5 m if the weighted average parti-

cle-size class of the upper 50 cm of the argillic horizon is

sandy, 1.1 m if it is loamy, and 90 cm if it is clayey, or

above a lithic contact that is shallower than these depths;

d. Do not have a horizon within 1 m of the surface that is

>15 om thick that either contains at least 20 percent durin-

odes in a nonbrittle matrix or is brittle and has firm consis-

tence when moist;

e. Do not have a lithic contact within 50 cm of the soil

surface;

f. Have a xeric moisture regime;

g. Have a mollic epipedon that is <50 cm thick or the tex-

ture is loamy fine sand or coarser if the mollic epipedon is

250 cm thick;

h. Have base saturation (by sum of cations) of >75 percent

throughout the upper 75 cm or above a lithic or paralithic

contact, whichever is shallower; and

i. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the surface
‘or to the base of an Ap horizon, and
(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m, and
(3) More than 35 percent clay in horizons that have a
total thickness of >50 cm.

Aquic Argixerolls are like Typic Argixerolls except for a,

with or without c.

Aquultic Argixerolls are like Typic Argixerolls except for a

and h.

‘Aridic Argixerolls are like Typic Argixerolls except for f

and they have an aridic moisture regime that borders on

xeric.

Aridic Calcic Argixerolls are like Typic Argixerolls except

for ¢ and f, and they have an aridic moisture regime that

borders on xeric.

Boralfic Argixerolls are like Typic Argixerolls except for b,

with or without all or any of c, g, or h, and the mean an-

nual soil temperature is lower than 10°C.

Calcic Argixerolls are like Typic Argixerolls except for c.



120

a potential linear extensibility of 6 cm or more in the
upper 1.25 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.25 m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness,
¢, Have an Ap horizon that has a color value, moist, of 4 or
more or has a color value, dry, of 6 or more when crushed
and smoothed, or the A_ horizon is <15 cm thick if its color
value, moist, is less than 3.5
Aquic Ustifluvents ate like Typic Ustifluvents except for a
or for a and c,
Mollic Ustifluvents are like Typic Ustifluvents except for c.
Vertic Ustifluvents are like Typic Ustifluvents except for b
or for b and a.

Xerofluvents

Distinctions between Typic Xerofluvents and other sub-
groups

Typic Xerofluvents are the Xerofluvents that

a, Are not saturated with water within 1.5 m of the surface

during any period in most years;

b. Do not have a horizon within 1 m of the surface that is

>15 cm thick that either contains 20 percent or more durin-

odes in a nonbrittle matrix or that is brittle and has firm
consistence when moist;

c. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are } cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or to the base of an Ap horizon;

(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m; and

(3) More than 35 percent clay in horizons that total >50
cm in thickness; and

d. Have an Ap horizon that has a color value, moist, of 4 or

more or has a color value, dry, of 6 or more when crushed

and smoothed, or the A horizon is <15 cm thick if its color

value, moist, is less than 3.5.

Aquic Xerofluvents are like Typic Xerofluvents except for a

or for a and d.

Aquic Durorthidic Xerofluvents are like Typic Xerofluvents

except for @ and b with or without 4,

Mollic Xerofluvents are like Typic Xerofluvents except for

d.

Vertic Xerofluvents are like Typic Xerofluvents except for c

or for c and a,

Orthents
Key to great groups
JEA. Orthents that have a cryic or pergelic temperature

regime.
Cryorthents, p. 121


65

(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum,

¢. Do not have a horizon within a depth of 1 m from the

surface that is brittle, that is 15 cm or more thick, and that

contains some opal coatings or some (<20 percent) durinodes;

d. Either have an Ap horizon that has a color value, moist,

of 4 or more, or a color value, dry, of 6 or more after the

soil has been crushed and smoothed, or have, after the soil
to a depth of 18 cm has been mixed, an upper layer that has
these colors;

e. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm and at least 30 cm long in
some part and that extend upward to the surface or to
the base of an Ap or an albic horizon;

(2) A coefficient of linear extensibility (COLE) of 0.09
or more in a horizon or horizons at least 50 cm thick and
@ potential linear extensibility of 6 cm or more in the soil
to a depth of 1 m or in the whole soil if the depth to a
lithic or paralithic contact is >50 cm but <1 m;

(3) More than 35 percent clay in horizons that have a
total thickness of >50 cm;

f. Have texture that is very fine sand or finer in some sub-

horizon within a depth of 50 cm from the soil surface; and

g. Have a surface horizon that, after the soil to a depth of

18 cm has been mixed, has <30 percent clay and is continu-

ous throughout each pedon,

Aeric Albaqualfs are like Typic Albaqualfs except for a.

Arenic Albaqualfs are like Typic Albaqualfs except for /,

with or without a or d, or both.

Mollic Albaqualfs are like Typic Albaqualfs except for d.

Ruptic-Vertic Albaqualfs are like Typic Albaqualfs except

for e and g with or without a or d, or both,

Udollic Albaqualfs are like Typic Albaqualfs except for a

and d,

Vertic Albaqualfs are like Typic Albaqualfs except for e

with or without a or d, or both.

Duraqualfs

Duraqualfs are the Aqualfs that have a duripan below the
argillic horizon. They are not known to occur in the United
States, The group has been proposed for other countries,
but definitions of subgroups have not been suggested,

Fraginqualfs
Distinctions between Typic Fragiaqualf's and other subgroups

Typic Fragiaqualfs are the Fragiaqualfs that

a. Do not have a mottled horizon between the A or Ap
horizon and a fragipan that has dominant chroma more than
2 if the hue is 10YR or redder or more than 3 if the hue is
2.5Y or yellower;

b. Have <5 percent plinthite (by volume) in all subhorizons
within ].5 m (60 in.) of the surface;

c. Have an Ap horizon that has either a color value, moist,
of 4 or more or a color value, dry, of 6 or more after the
soil has been crushed and smoothed; or the upper soil to a
depth of 18 om, after mixing, has these color values;


248

2. Saturation with water in the mottled zone at some time
of year when the soil temperature in that zone is 5°C or
higher, or there is artificial drainage;
b. Do not have an epipedon that is $0 cm to 100 cm thick if
the particle-size class is sandy throughout;
¢. Do not have an epipedon that is >100 cm thick if the
particle-size class is sandy throughout;
d. Do not have a subhorizon within 150 cm of the soil sur-
face that has >5 percent plinthite by volume;
e. Have an argillic or kandic horizon that has a color hue of
SYR or yellower in some part, or has a value, moist, of 3.5
or more or has a value, dry, that is more than | unit higher
than the value, moist;
f. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either of the following:
1. A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
2. A ratio of CEC (pH 8.2) to 1500 kPa water of >1.5
and more exchange acidity than the sum of bases plus
KCl-extractable aluminum;
g. Have a hue redder than 10YR in all parts of the soil
above a depth of 75 cm that have color value, moist, of 4 or
more if there are mottles of high chroma within that depth
and if the hue becomes redder with depth within 100 cm of
the soil surface;
h. Have an ECEC (sum of bases plus 1 M KCl-extractable
Al) of more than 1.5 cmol(+) kg”? clay in all subhorizons to
a depth of 150 cm below the soil surface, and
i. Do not have a sombric horizon within 150 cm of the soil
surface.
Acric Kandiudults are like Typic Kandiudults except for h,
with or without f.
Acri¢ Plinthic Kandiudults are like Typic Kandiudults except
for d and h, with or without f.
Andaquic Kandiudults are like Typic Kandiudults except for
aand f.
‘Andic Kandiudults are like Typic Kandiudults except for f.
Aquic Kandiudults are like Typic Kandiudults except for a,
Aquic Arenic Kandiudults are like Typic Kandiudults except
for a and b,
Arenic Kandiudults are like Typic Kandiudults except for 6.
Arenic Plinthaquic Kandiudults are like Typic Kandiudults
except for a, b, and d.
Arenic Plinthic Kandiudults are like Typic Kandivdults ex-
cept for b and d.
Arenic Rhodic Kandiudults are like Typic Kandiudults ex~
cept for b and e,
Epiaquic Kandiudults are like Typic Kandiudults except for

&
Grossarenic Kandiudults are like Typic Kandiudults except
for ¢ or for a and c.

Grossarenic Plinthic Kandiudults are like Typic Kandiudults
except for c and d.

Plinthaquic Kandiudults are \ike Typic Kandiudults except
for a and d.

Plinthic Kandiudults are like Typic Kandiudults except for
4.

Rhodic Kandiudults are like Typic Kandiudults except for e.


W

(1) If its upper boundary is <50 cm below the soil sur-
face, does not have mottles that have chroma of 2 or less
in the upper 25 cm if it is saturated with water within
that depth at some time when the soil temperature is 5°C
or higher; or
(2) If the upper boundary of the argillic horizon is 50 cm
or more, does not have mottles that have chroma of 2 or
less within a depth of 75 cm below the soil surface;
b. Have a texture finer than loamy fine sand in some sub-
horizon within 50 cm of the surface;
c. Do not have tongues of albic materials in the argillic
horizon (interfingering is permitted);
d. Do not have a lithic contact within 50 cm of the surface;
e. Have an Ap horizon that has a color value, moist, of 4 or
more or a color value, dry, of 6 or more (crushed and
smoothed), or the soil to a depth of 18 cm, after mixing, has
these colors; and
f, Have an argillic horizon that has a texture finer than
loamy fine sand and is continuous vertically for at least the
upper 15 cm (not in lamellae).
Aquic Eutroboralfs are like Typic Eutroboralfs except for a,
with or without e or f or both,
Aquic Arenic Eutroboralfs are like Typic Eutraboralfs except
for a and b with or without ¢ or e or both.
Arenic Eutroboralfs are like Typic Eutroboralfs except for 6,
with or without c or e, or both.
Glossaquic Eutroboralfs are like Typic Eutroboralfs except
for a and c with or without e.
Glossic Eutroboralfs are like Typic Eutroboralfs except for
c.
Lithic Eutroboralfs are like Typic Eutroboralfs except for d,
with or without all or any of a, b, e, or f.
Mollic Eutroboraifs are like Typic Eutroboralfs except for ¢.
Psammentic Eutroboralfs are like Typic Eutroboralfs except
for f with or without all or any of 6, c, or e.

Fragiboralfs
Distinctions between Typic Fragiboralfs and other subgroups

Typic Fragiboralfs are the Fragiboralfs that

a. Do not have mottles that have chroma of 2 or less
(defined in ch. 1) in the upper 25 cm of the argillic horizon
(bleached coatings of silt or sand may be on peds beside or
below tongues of the albic horizon).

Aquic Fragiboraifs are like Typic Fragiboralfs except they
have mottles that have chroma of 2 or less within the upper
25 cm of the argillic horizon and are saturated with water at
some time within this depth.

Glossoboralfs

Distinctions between Typic Glossoboralfs and other sub-
groups

Typic Glossoboralfs are the Glossoboralfs that

a. Do not have mottles that have chroma of 2 or less in the
upper 25 cm of the argillic horizon if the mottled horizons
are Saturated with water at a time when the soil temperature
is 5°C or higher (bleached coatings of silt or sand may be on
peds beside or below tongues of the albic horizon);


205

CADD. Other Haplaquox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of the surface litter.

Humic Haplaquox

CADE, Other Haplaquox.
Typic Haplaquox

Plinthaquox
Key to subgroups

CABA. Plinthaquox that have mottles with chroma of more
than 2 in 50 percent or more of the horizon immediately
below the epipedon.

Aeric Plinthaquox

CABB, Other Plinthaquox.
Typic Plinthaquox

Perox
Key To Great Groups

CDA: Perox that have a sombric horizon within 150 cm of
the soil surface.
Sombriperox, p. 211

CDB: Other Perox that have both an apparent ECEC of less
than 1.50 cmol(+) kgTM clay and a pH value (1 M KCl) of 5
or more in some part of the oxic or kandic horizon within a
depth of 150 cm of the soil surface.

Acroperox, p. 205

CDC: Other Perox that have more than 35 percent base sat-
uration (NH,OAc) in all parts within a depth of 125 cm of
the soil surface.

Eutroperox, p. 207

CDD: Other Perox that have more than 40 percent clay in
the surface 18 cm, after mixing, and the upper boundary of
a kandic horizon occurring within a depth of 150 cm of the
soil surface.

Kandiperox, p. 209

CDE: Other Perox.
Haploperox, p. 208

Acroperox

Key to subgroups

CDBA. Acroperox that have mottles of 4 or more value
moist and 2 or less chroma within a depth of 125 cm of the
soil surface and a petroferric contact within 125 cm of the
soil surface.

Aquic Petroferric Acroperox

CDBB. Other Acroperox that have a petroferric contact
within 125 cm of the soil surface.
Petroferric Acroperox


16

contains < 20 percent clay; <8 percent absolute if the surface
contains 240 percent clay;

6. Does not have andic soil properties (see section on “andic
soil properties later in this chapter);

7. Has less than 5 percent by volume that shows rock struc-
ture unless the lithorelicts containing weatherable minerals
are coated with sesquioxides.

Petrocalcic horizon

The petrocalcic horizon is a continuous, cemented or in-
durated calcic horizon that is cemented by calcium carbonate
or in some places by calcium and some magnesium carbon-
ate. Accessory silica may be present. The petrocalcic hori-
zon is continuously cemented throughout the pedon to the
degree that dry fragments do not slake in water. It cannot
be penetrated by spade or auger when dry. It is massive or
platy, very hard or extremely hard when dry, and very firm
or extremely firm when moist. Noncapillary pores are
filled, and the petrocalcic horizon is a barrier to roots. Hy-
draulic conductivity is moderately slow to very slow. The
horizon is usually much more than 10 cm (4 in.) thick.

A laminar capping commonly is present but is not required.

If a laminar horizon rests on bedrock, it is considered a

petrocalcic horizon if it is 2.5 cm of more thick and the

product of the thickness in centimeters multiplied by the
percentage of CaCO, equivalent is 200 or more.

Petrogypste horizon

‘The petrogypsic horizon is a gypsic horizon that is strongly
enough cemented with gypsum that dry fragments do not
slake in water and that roots cannot enter, The gypsum
content commonly is far greater than the minimum require-
ments for the gypsic horizon and usually exceeds 60 percent.
Petrogypsic horizons are restricted to arid climates and to
parent materials that are rich in gypsum.

Placic horizon

The placic horizon (Gr. base of plas, flat stone; meaning a
thin cemented pan) is a thin, black to dark reddish pan ce-
mented by iron, by iron and manganese, or by an iron-or-
ganic matter complex. Its thickness ranges generally from 2
mm to 10 mm. Rarely, it is as thin as 1 mm or as thick as
20 to 40 mm in spots, It may be, but not necessarily, asso-
ciated with stratification in parent materials, It is in the
solum, roughly parallel to the soil surface, and is commonly
within the upper 50 cm of the mineral soil. It has a pro-
nounced wavy or even convolute form. It normally occurs
as a single pan, not as multiple sheets one underlying an-
other, but in places it may be bifurcated. It is a barrier to
water and roots,

An iron-cemented pan is strong brown to dark reddish
brown. A pan cemented by iron and manganese or by iron-
organic matter complexes is black or reddish black, A sin-


164

d, Have a content of organic carbon’ that decreases

regularly with depth and, unless a lithic or paralithic contact

is present at a shallower depth, reaches a level of 0.2 percent

or less within 1.25 m of the soil surface, or have slopes >25

percent;

e. Do not have a lithic or a petroferric contact within 50 cm

of the soil surface;

f. Have a CEC (by 1 M NH,OAc pH 7) of 24 or more

cmol(+) kg? clay" in the major part of the soil below a

depth of 25 cm but above 100 cm or a lithic or paralithic

contact if one is shallower than 100 cm.

g. Have a udic moisture regime; and

h. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are | cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0.09
or more if the soil moisture regime is udic, or 0.07 or
more if it is ustic, in a horizon or horizons at least 50 cm
thick, and a potential linear extensibility of 6 cm or more
in the upper 1 m or 1.25 m, respectively, of the soil or in
the whole soil if a lithic or paralithic contact is deeper
than 50 cm but shallower than 1 m or 1.25 m;
(3) More than 35 percent clay in horizons that total >50
cm in thickness.

Aquic Dystropepts are like Typic Dystropepts except for a.

Fluventic Dystropepts are like Typic Dystropepts except for

@.

Lithic Dystropepts are like Typic Dystropepts except for ¢
and have a lithic contact within a depth of 50 cm.

Oxie Dystropepts are like Typic Dystropepts except for /.
Ustie Dystropepts are like Typic Dystropepts except for g,
and they have an ustic moisture regime.

Ustoxie Dystropepts are like Typic Dystropepts except for f
and g, and they have an ustic moisture regime.

Vertic Dystropepts are like Typic Dystropepts except for h,
with or without any or all of a, c, d, and g.

Eutropepts
Distinctions between Typic Eutropepts and other subgroups

Typic Eutropepts are the Eutropepts that
a. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or

Tepe carbon should be of Holocene age. It ia not the intent to include fowl

carbon from bedrock.

M4 gome cambie horizons that have properties that approach those of an oxic

horizon do not disperse wall. If the ratio of the percentage of water retained

at tension of 1600 kPa to the percentage of measured clay is 0.6 or more, the

percentage of clay is determined by the higher value of (1) the measured per-
centage of clay or (2) 2.5 times the percentage of water retained at tencion of
1500 kPa,



238

FAC. Other Aquults that have an abrupt textural change
between the ochric epipedon or the albic horizon and the
argillic or kandic horizon and have slow hydraulic conduc-
tivity in the argillic or kandic horizon.

Albaquults, p. 238

FAD. Other Aquults that

1, Have a CEC <16 cmol(+) kg" slay (by 1 M NHOAc pH
7) and an ECEC <2 cmol(+) kg”? clay (sum of bases ex-
tracted with 1 M NH,OAc pH 7 plus | M KCl-extractable
Al) in the major part‘of the argillic or kandic horizon or the
major part of the upper 100 cm of the argillic or kandic
horizon if these horizons are thicker than 100 cm;
2. Do not have a lithic, paralithic, or petroferric contact
within 150 cm of the soil surface; and
3. Have a clay distribution such that the percentage of clay
does not decrease from its maximum by as much as 20 per~
cent within a depth of 150 cm from the soil surface or the
layer in which the clay percentage decreases by more than
20 percent has at least 5 percent of the volume consisting of
skeletans on faces of peds and there is at least 3 percent
(absolute) increase in clay below the layer.

Kandiaquults, p. 239

FAE. Other Aquults that have a CEC <16 cmol(+) kg"! pay
(by 1 M NH,OAc pH 7) and an ECEC <12 cmol(+) kg” clay
(sum of bases extracted with 1 M NH,OAc pH 7 plus 1 M
KCl-extractable Al) in the major part’ of the argillic or
kandic horizon or the major part of the upper 100 cm of the
argillic or kandic horizon if these horizons are thicker than
100 cm.

Kanhaplaquults, p. 240

FAF, Other Aquults that have a clay distribution such that
the percentage of clay does not decrease from its maximum
amount by as much as 20 percent within a depth of 150 cm
from the soil surface and do not have a lithic or the layer in
which the clay percentage decreases by more than 20 per-
cent has at least 5 percent of the volume consisting of
skeletans on faces of peds and there is at least 3 percent
(absolute) increase in clay below the layer.

Paleaquults, p. 240

FAG. Other Aquults that have an ochric epipedon.
Ochraquults, p. 240

FAH, Other Aquults that have an umbric or a mollic
epipedon,

Umbraquults, p. 241
Albaquults
Description of subgroups

Only two subgroups of Albaquults have been proposed,
Typic Albaquults and Aeric Albaquults.

Typic Albaquults.--These are the Albaquults that have the
colors definitive for the suborder in 60 percent or more of
the matrix between the Ap horizon and a depth of 75 cm.


100

more durinodes in a nonbrittle matrix or is brittle and has
firm consistence when moist,

¢. Do not have more than 10 percent of the ped surfaces
deeper than 2.5 cm below the upper boundary of the natric
horizon covered by skeletans;

d. Do not have a lithic contact within 50 cm of the soil
surface;

¢. Have a weighted average percentage of organic carbon in
the upper soil to a depth of 40 cm that is <0.6 if the
weighted average of sand to clay in that depth is 1.0 or less,
or is not more than one-seventh percent if the ratio is 13 or
more, or has an intermediate percentage of organic carbon if
the ratio is between 1.0 and 13; or have a weighted average
percentage of organic carbon in the surface soil to a depth
of 18 cm that is not one-fifth more than the values just
stated if there is a lithic or paralithic contact that is
shallower than 40 cm but deeper than 18 cm; and

f. Have an SAR of >13 or have 15 percent or more
saturation with sodium throughout the major part of the
natric horizon.

Aquic Natrargids are like Typic Natrargids except for a or
for a and e.

Borollic Natrargids are like Typic Natrargids except for e or
for ¢ and f, The mean annual soil temperature is lower than
8°C, the mean summer and mean winter soil temperatures at
a depth of 50 cm differ by >5°C, and the moisture regime is
aridic bordering on ustic,

Borollic Glossie Natrargids are like Typic Natrargids except
for c and e, with or without f. The mean annual soil
temperature is lower than 8°C, the mean summer and mean
winter soil temperatures at a depth of 50 cm differ by >5°C,
and the moisture regime is aridic bordering on ustic.

Duric Natrargids are like Typic Natrargids except for b or
for b and f.

Durixerollic Natrargids are like Typic Natrargids except for
bande. They have a mean annual soil temperature lower
than 22°C. The mean summer and mean winter soil
temperatures at a depth of 50 cm differ by 5°C or more,
and the moisture regime is aridic bordering on xeric.

Glossic Ustollic Natrargids are like Typic Natrargids except
for c and e, with or without f. They have a mean annual
soil temperature of 8°C or higher and an aridic moisture
regime that borders on ustic.

Haplic Natrargids are like Typic Natrargids except for f.
Haploxerollic Natrargids are like Typic Natrargids except
for e and f. They have a mean annual soil temperature
lower than 22°C, and the mean summer and mean winter
soil temperatures at a depth of 50 cm differ by 5°C or more.
They have an aridic moisture regime that borders on a xeric
regime.

Haplustoltic Natrargids are like Typic Natrargids except for
eand f. They have a mean annual soil temperature of 8°C
or higher, and the moisture regime is aridic but borders on
ustic.

Lithic Natrargids are like Typic Natrargids except for d.
Lithic Xerollic Natrargids are like Typic Natrargids except
for d and e. They have a mean annual soil temperature
Jower than 22°C, and the mean summer and mean winter
soil temperatures at a depth of 50 om differ by 5°C or more.
They have an aridic moisture regime that borders on a xeric
regime,


21

water, but prolonged soaking can result in spalling of very
thin platelets and some slaking. The durinodes are firm or
very firm; they are brittle when wet, both before and after
treatment with acid; and they are disconnected and they
range upward in size from a diameter of about 1 cm. Most
durinodes are roughly concentric when viewed in cross sec-
tion, and concentric stringers of opal may be visible under a
hand lens.

Gilgai

Gilgai is the microrelief that is typical of clayey soils that
have a high coefficient of expansion with changes in mois-
ture content and that also have distinct seasonal changes in
moisture content. The microrelief consists of either a suc-
cession of enclosed microbasins and microknolls in nearly
level areas or of microvalleys and microridges that run up
and down the slope. The height of the microridges com-
monly ranges from a few centimeters to 1 m. Rarely does
the height approach 2 m.

Lithic contact

A lithic contact is a boundary between soil and coherent un-
derlying material. Except in Ruptic-Lithic subgroups the
underlying material must be continuous within the limits of
a pedon except for cracks produced in place without signif-
icant displacement of the pieces. Cracks should be few, and
their average horizontal spacing should be 10 cm or more.
The underlying material must be sufficiently coherent when
moist to make hand digging with a spade impractical, al-
though it may be chipped or scraped with a spade. If it is a
Single mineral, it must have a hardness by Mohs scale of 3
or more. If it is not a single mineral, chunks of gravel size
that can be broken out must not disperse during shaking for
15 hours in water or in sodium hexametaphosphate solution.
The underlying material considered here does not include
diagnostic soil horizons such as duripan or a petrocalcic
horizon,

A lithic contact is diagnostic at the subgroup level if it is
within 125 cm of the soil surface of Oxisols and within 50
cm of the soil surface of all other mineral soils,

Mottles that have chroma of 2 or less

It refers to colors in a horizon in which parts have chroma
of 2 or less, moist, and value, moist, of 4 or more, whether
or not that part is dominant in volume or whether or not it
is a continuous phase surrounding spots of higher chroma,
If either the minor or major part of a horizon has chroma of
1 to 2 and value, moist, or 4 or more and there are spots of
higher chroma, the part that has the lower chroma is in-
cluded in the meaning of "mottles that have chroma of 2 or
less." The part is excluded from the meaning if all the
horizon has chroma of 2 or less or if no part of the horizon
has chroma as low as 2.

The phrase also means that the horizon that has such mottles
is saturated with water at some period of the year or the soil
is artificially drained, It is also implicit in the meaning that


52

Uncoated. The moisture equivalent is <2 percent. The -
moisture retained at tension of 50 kPa may be substituted
for the moisture equivalent. Or, if moisture tension data are
not available, the silt plus clay is <5 percent.

The moisture equivalent for this distinction is the weighted
average for the control section, weighted for the thickness
of each horizon or layer.

Slope or shape of soil

Soils of aquic great groups normally have level or concave
surfaces. They are mainly in places where ground water
saturates the soil during some period of the year. A few,
however, are on the sides of slopes where water cannot
stand and are kept wet by more or less continuous precipi-
tation and by seepage of water from higher areas. In a very
few, the hydrostatic pressure keeps the soil wet. No consis-
tent internal morphologic clues have yet been found that
distinguish these sloping aquic soils if the dissolved oxygen
content is low, but their recognition in the field from the
position of the soil in the landscape is generally easy. In
aquic great groups, particularly in Aquolls, Aquox, and
Aquults, use the shape of the soil as a family differentia.
For Aquolls and Aquults use classes of level and sloping as
these classes are defined in the Soil Survey Manual. For
Aquox use sloping in the names of families if slope is >8
percent. It may be necessary to use slope classes as family
differentiae in other orders, but they should not be used in
families of Aquods or Albaqualfs, Level is assumed in fam-
ilies of aquic soils if no slope modifier is used in the family
name,

Classes of permanent cracks

Hydraquents consolidate® after drainage and become Flu-
vaquents. In the process, they form polyhedrons, roughly 12
to 50 cm in diameter, depending on the » value and particle
size. The polyhedrons are separated by cracks that range in
width from 2 mm to >1 cm. The polyhedrons may shrink
and swell with changes in moisture content of the soil, but
the cracks are permanent and can persist for some hundreds
of years even though the soils are cultivated. The cracks
permit rapid movement of water through the soil either ver-
tically or laterally. Yet the soils may have the same particle
size, mineralogy, and other family properties as soils that are
not cracked or that have cracks that open and close with the
seasons, The soils that have permanent cracks are so rare in
the United States that only a provisional definition of their
characteristics can be presented,

The modifier "cracked" is used only to designate families of
Fluvaquents. It means that there are continuous, permanent,
fateral and vertical cracks, at least 2 mm wide, spaced at
average lateral intervals of 50 cm or less. If this modifier is
not in the family name, permanent cracks are assumed to be
absent.

She process ie designated by a Dutch word that means "to ripen” because the
change resembles the change in coneistence of cheese as water is removed.


96

(3) Both a dominant chroma of 2 or Jess and a greater
SAR (or percentage of exchangeable sodium) in more
than half the thickness of the horizon between the
surface and 50 cm depth than in the saturated zone;
b. Have a platy or massive duripan that is indurated in some
subhorizon;
c. Have a duripan at a depth <18 cm; or the weighted
average percentage of organic carbon in the upper soil to a
depth of 40 cm is <0.6 if the weighted average ratio of sand
to clay in the upper soil to that depth is 1.0 or less, or is less
than one-seventh percent if the ratio is 13 or more, or is
intermediate between 0.6 percent and one-seventh percent if
the ratio of sand to clay in the upper soil is >1.0 but <13; or
the weighted average percentage of organic carbon in the
upper soil to a depth of 18 cm is not as much as one-fifth
more than the values just stated if a duripan is present at a
depth <40 cm but >18 cm;
d. Do not have an argillic horizon that has 35 percent or
more clay in some part and also has either
(1) An increase of 15 percent or more clay (absolute)
within a vertical distance of 2.5 cm at the upper
boundary of the argillic horizon; or
(2) An increase of 10 percent or more clay (absolute) if
cultivated and the lower boundary of the Ap horizon is
the upper boundary of the argillic horizon; and
e. Are dry in all parts of the moisture control section more
than three-fourths of the time (cumulative) that the soil
temperature at a depth of 50 cm is 5°C or higher.
Abruptic Durargids are like Typic Durargids except for d.
Abruptic Xerollic Durargids are like Typic Durargids except
for c, d, and e. They have a mean annual soil temperature
lower than 22°C, the mean summer and mean winter soil
temperatures at a depth of 50 cm differ by 5°C or more,
and they have an aridic moisture regime that borders on a
xeric regime,
Haplic Durargids are like Typic Durargids except for b.
Haploxerollic Durargids are like Typic Durargids except for
b and c, with or without e. They have a mean annual soil
temperature lower than 22°C, the mean summer and mean
winter soil temperatures at a depth of 50 cm differ by S°C
‘or more, and they have an aridic moisture regime that
borders on a xeric regime.
Yerollic Durargids are like Typic Durargids except for c,
with or without e. They have a mean annual soil
temperature lower than 22°C, the mean summer and mean
winter soil temperatures at a depth of 50 cm differ by $°C
or more, and they have an aridic moisture regime that
borders on a xeric regime.

Haplargids
Distinctions between Typic Haplargids and other subgroups

Typic Haplargids are the Haplargids that
a. Are not saturated with water for 90 consecutive days or
more within 1 m of the surface in most years and do not
have any of the following characteristics within a depth of 1
m below the surface if there is ground water within this
depth at some time in most years:
(1) Dominant chroma of | or less throughout and a hue
as yellow or yellower than 2.5Y in some part,



244

2. Saturation with water in the mottled zone at some time
of year when the soil temperature in that zone is 5°C or
higher or there is artificial drainage;
b. Do not have a lithic contact within 50 cm or the mineral
soil surface;
¢, Have an udic moisture regime;
d, Do not have a Jayer in the upper 75 cm that has texture
finer than loamy fine sand, that is as much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or less in the fine-earth fraction, and that
has either of the following:
1, A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or fess; or
2. A ratio of CEC (pH 8.2) to 1500 kPa water of >1.5
and more exchange acidity than the sum of bases plus
KCl-extractable aluminum;
e. Have a hue redder than 10YR in all parts of the soil
above a depth of 75 cm that have a color value, moist, of 4
or more if there are mottles of high chroma above that
depth and if the hue becomes redder with depth within 100
cm of the soil surface; and
f. Do not have an anthropic epipedon.
Andic Kanhaplohumults are like Typic Kanhaplohumults
except for d, with or without e¢ or f.
Andic Ustic Kanhaplohumults are like Typic Kanhaplohu-
mults except for ¢ and d, with or without ¢ or f, and they
have an ustic moisture regime.
Anthropic Kanhaplohumults are like Typic Kanhaplohumults
except for f.
Aquic Kanhaplohumults are like Typic Kanhaplohumults ex-
cept for a or for a and e.
Epiaquic Kanhaplohumults are like Typic Kanhaplohumults
except for e.
Lithic Kankaplohumults are like Typic Kanhaplohumults
except for 6 with or without any of a, c, d, e, or f.
Ustic Kanhaplohumults are like Typic Kanhaplohumults ex-
cept for c and they have an ustic moisture regime.

Plinthohumults

These are the Humults that have plinthite that forms a con-
tinuous phase or that constitutes more than half the volume
of some subhorizon within 1.25 m of the soil surface. They
are not known to occur in the United States, but the great
group has been proposed for other countries (Sys 1969).
Subgroups have not been developed,

Sombrihumults

These are the Humults that have a sombric horizon whose
upper boundary is within } m of the soil surface. They are
not known to occur in the United States, but the great group
is provided for use elsewhere, Humoxic and orthoxic sub-
groups have been proposed (Sys 1969) for the soils that have
low CEC, that is, <24 cmol(+) kgTM clay. The humoxic sub-
group is proposed for soils that have an isothermic or cooler
temperature regime and the orthoxic subgroup for soils that
have an isohyperthermic temperature regime,


33

2. Silt- and sand-size minerals (0.02 to 0.2 mm in diameter):
Feldspars, feldspathoids, ferromagnesian minerals, glass,
micas, zeolites, and apatite.

It should be noted that this is a restricted meaning of
weatherable minerals. Calcite, for example, is readily solu-
ble in a humid environment. If it is dissolved, it leaves no
trace or residue. Soils that have been intensely and deeply
weathered in a humid environment of the past are, in some
places, preserved today in an arid environment. Calcite
could reappear in one of these soils if it were brought in as
dust, The intent is to include, in the context of the meaning
of weatherable minerals for this purpose, only those minerals
that are unstable in a humid climate relative to other min-
erals, such as quartz and 1:! lattice clays, and that are more
resistant to weathering than calcite.

LITERATURE CITED

Brewer, R, 1964, Fabric and mineral analysis of soils. John
Wiley and Sons, Inc,, New York, London, Sydney. 470 p.

Pons, L.J. and IS, Zonneveld. 1965. Soil ripening and soil
classification, Initial soil formation in alluvial deposits and a
classification of the resulting soils. Int. Inst. Land Reclam.
and Impr. Pub. 13. Wageningen, The Netherlands. 128 p.

Cy


172

(a) Value of 4 and chroma of 2 and also some
mottles that have value of 4 or more and chroma
less than 2;
(b) Value of 5 or more and chroma of 2 or less
and also mottles that have higher chroma; or
(c) Value of 4 and chroma <2; or
4. A calcic or petrocalcic horizon that has its upper
boundary within 40 cm of the surface.
Aquolls, p. 173

GC. Other Mollisols that have all the following
characteristics:
1, Have a mollic epipedon that is not more than 50 cm
thick;
2. Do not have an argillic horizon;
3. Do not have a calcic horizon;
4. The soil materials in or immediately below any mollic
epipedon, including coarse fragments less than 7.5 cm in
diameter, have a CaCO, equivalent of 40 percent or
more; and
5. Have a udic moisture regime or a cryic temperature
regime;
Rendolls, p. 183

GD. Other Mollisols that have a xeric moisture regime or an
aridic moisture regime bordering on xeric but do not have a
cryic temperature regime.

Xerolls, p..195

GE. Other Mollisols that have a frigid, cryic, or pergelic
temperature regime,
Borolls, p, 176

GF, Other Mollisols that have an ustic or an aridic moisture
regime that borders on ustic.
Ustolis, p. 187

GG. Other Mollisols.
Udolis, p. 184

Albolis
Key to great groups

GAA. Albolls that have a natric horizon,
Natralbolls, p. 173

GAB. Other Albolls,
Argialbolls, p, 172

Argialbolls
Distinctions between Typic Argialbolls and other subgroups

Typic Argialbolls are the Argialbolls that

a. Do not have a layer in the upper 75 cm that has a texture
finer than Joamy fine sand, that is as much as 18 cm thick,
that has a bulk density (at 33 kPa water tension) of 0.95 g
per cubic centimeter or less in the fine~earth fraction, and
that has either


136

Fluvaquentic Tropofibrists are like Typic Tropofibrists ex-
cept for e, with or without a.

Hemic Tropofibrists are like Typic Tropofibrists except for
a(1).

Hemic Terric Tropofibrists are like Typic Tropofibrists ex-
cept for a(1) and f, with or without ¢ or e, or both.
Hydric Tropofibrists are like Typic Tropofibrists except for

&

Limnic Tropofibrists are like Typic Tropofibrists except for
c, with or without a or e, or both.

Lithic Tropofibrists are like Typic Tropofibrists except for

d, with or without all or’any of a, 5, c, e, or f.

Sapric Tropofibrists are like Typic Tropofibrists except for
(2

Sapric Terrie Tropofibrists are like Typic Tropofibrists ex-
cept for a(2) and f, with or without c or e, or both.

Terric Tropofibrists are like Typic Tropofibrists except for
f, with or without c or e, or both.

Folists
Key to great groups

AAA. Folists that have a cryic or colder temperature regime.
Cryofolists, p. 136

AAB. Other Folists that have an isomesic or warmer tem-
perature regime.
Tropofolists, p. 137

AAC. Other Folists that have a frigid temperature regime,
Borofolists, p. 136

Borofolists

Distinctions between Typic Borofolists and other subgroups
Typic Borofolists are the Borofolists that

a. Have fragmental materials with interstices filled with or-
ganic materials in half or more of each pedon; and

b. Do not have a lithic contact within | m of the surface,
Lithic Borofolists are like the Typic Borofolists except for 6
or for a and b,

Cryofolists
Distinctions between Typic Cryofolists and other subgroups —

Typic Cryofolists are the Cryofolists that

a. Have fragmental materials in which the interstices are
filled or partly filled with organic materials in half or more
of each pedon; and

b. Do not have a lithic contact within 1 m of the surface,
Lithic Cryofolists are like Typic Cryofolists except for 5 or
for a and b.


17

gle pan may contain two or more layers cemented by dif-
ferent agents. Iron-organic matter cements commonly are
Present in the upper part of the pan.

Identification is seldom difficult. The hard brittle pan dif-
fers so much from the material in which it occurs and is so
close to the surface of the mineral soil material that it is ob-
vious unless its thickness is minimal. A few analyses of
placic horizons show that organic carbon is present in
amounts ranging from 1 percent to 10 percent or more, The
presence of organic carbon as well as the shape and position
of the pan distinguish the placic horizon from the ironstone
Sheet that may form where water hangs or moves laterally at
a lithologic discontinuity.

Salic horizon

A salic horizon is a horizon 15 cm or more thick that con-
tains a secondary enrichment of salts more soluble in cold
water than gypsum. It contains at least 2 percent salt, and
the product of its thickness in centimeters and salt percent-
age by weight is 60 or more. Thus, a horizon 20 cm thick
would need to contain 3 percent salt to qualify as a salic
horizon and a horizon 30 cm thick would need 2 percent.

Sombric horizon

The sombric horizon is a subsurface horizon of mineral soils
formed under free drainage. It contains illuvial humus that
is neither associated with aluminum, as is the humus in the
spodic horizon, nor dispersed by sodium, as is common in
the natric horizon, Consequently, the sombric horizon does
not have the high cation-exchange capacity of a spodic
horizon relative to clay, and it does not have the high base
saturation of a natric horizon. The sombric horizon does not
underlie an albic horizon,

Sombric horizons are thought to be restricted to the cool
moist soils of the high plateaus and mountains in tropical or
subtropical regions, Because of the annual leaching, base
saturation is low, <50 percent by NH,OAc.

The sombric horizon has lower color value or chroma, or
both, than the overlying horizon and commonly, but not
necessarily, contains more organic matter than the overlying
horizon. It may have formed in an argillic, a cambic, or,
possibly, an oxic horizon. If peds are present, the dark col-
ors are most pronounced on ped surfaces,

A sombric horizon is easily confused in the field with a
buried A horizon. It can be distinguished from some buried
epipedons by lateral tracing. In thin sections, the organic
matter of a sombric horizon appears more concentrated on
peds and in pores than uniformly dispersed through the ma-
trix.

Spodic horizon
A. spodic horizon is normally a subsurface horizon that un-

derlies an O, A, Ap, or E horizon. It may, however, meet
the definition of an umbric epipedon, A spodic horizon has

wR


60

G. Other soils that
1. Have either of the following:
a. A mollic epipedon;
or
b, A surface horizon that, after the soil to a depth of
18 cm is mixed, meets all requirements of a mollic
epipedon except thickness, and, in addition, have an
upper subhorizon >7.5 cm thick that is in an argillic,
kandic or a natric horizon, that meets the requirements
of a mollic epipedon with respect to color, content of
organic carbon, base saturation, and structure but is
separated from the surface horizon by an albic hori-
zon;
and, in addition,
2. Have base saturation of 50 percent or more (by
NH,OAc) as follows:
either
a. If there is an argillic, kandic or natric horizon,
from its upper boundary to a depth of 1.25 m below
that boundary, or to a depth 1.8 m below the soil
surface or to a lithic or paralithic contact, whichever
is least;
or
b. If there is no argillic, kandic, or natric horizon, in
all subhorizons to a depth 1.8 m below the soil surface
or to a lithic or paralithic contact, whichever is least;
and, furthermore
3. If the exchange complex is dominated by amorphous
materials, have, in some subhorizon within a depth of 35
cm or to a lithic or paralithic contact shallower than 35
cm, a bulk density (at 33 kPa water tension) of the fine-
earth fraction of 0.85 or more and have <60 percent vit
ric volcanic ash?, cinders, or other pyroclastic material in
the silt, sand, and gravel fractions within this depth;
Mollisols, p. 171

H. Other soils that
either
1, Have an argillic, kandic or natric horizon but no
fragipan;
or
2, Have a fragipan that
a. Is in or underlies an argillic or kandic horizon;
or
b. Meets all requirements of an argillic or kandic
horizon; or
c. Has clay skins >1 mm thick in some part,
Alfisols, p. 63

—-—
Vitrie material, as used here, includes glass and also crystalline particles that
are coated with glass or with partly devitrified glass,


222

CCCM. Other Eutrustox that have 16 Kg or more organic
carbon per square meter to a depth of one meter, exclusive
of surface litter.

Humic Eutrustox

CCCN. Other Eutrustox that have a color hue of 2.5 YR or
redder with moist values of less than 4 in most of the 25 to
125 em depth from the soil surface.

Rhodic Eutrustox

CCCO, Other Eutrustox that have a color hue of 7.5 YR or
yellower with moist values of 6 or more in most of the 25 to
125 em depth from the soil surface.

Xanthic Eutrustox

CCCP. Other Eutrustox.
Typic Eutrastox

Haplustox
Kev to subgroups

CCEA, Haplustox that have mottles of 4 or more value moist
and 2 or less chroma within a depth of 125 cm of the soil
surface and a petroferric contact within 125 cm of the soil
surface.

Aquic Petroferric Haplustox

CCEB. Other Haplustox that have a petroferric contact
within 125 cm of the soil surface.
Petroferric Haplustox

CCEC. Other Haplustox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface and a lithic contact within 125 cm of the
soil surface,

Aquic Lithic Haplustox

CCED. Other Haplustox that have a lithic contact within a
depth of 125 cm of the soil surface.
Lithic Haplustox

CCEE. Other Haplustox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface and mottles of 4 or more value moist and 2 or
less chroma within a depth of 125 cm of the soil surface.
Plinthaquic Haplustox

CCEF. Other Haplustox that have more than 5 percent
plinthite in some horizon within a depth of 125 cm of the
soil surface.

Plinthic Haplustox

CCEG. Other Haplustox that have mottles of 4 or more
value moist and 2 or less chroma within a depth of 125 cm
of the soil surface and have the lower boundary of the oxic
horizon within a depth or 125 cm of the soil surface.
Aqueptic Haplustox


133

Hemic Borofibrists are like Typic Borofibrists except for
a(1).

Hemic Terric Borofibrists are like Typic Borofibrists except
for af1) and f, with or without c or e, or both.

Hydric Borofibrists are like Typic Borofibrists except for g.
Limnic Borofibrists are like Typic Borofibrists except for c,
with or without a or e, or both,

Lithie Borofibrists are like Typic Borofibrists except for d,
with or without all or any of a, b, c, e, or f.

Sapric Borofibrists are like Typic Borofibrists except for
a(2).

Sapric Terrie Borofibrists are like Typic Borofibrists except
for a(2) and f, with or without ¢ or e, or both.

Sohagnic Borofibrists are like Typic Borofibrists except for

Sphagnie Terrie Borofibrists are like Typic Borofibrists ex-
cept for b and f, with or without ¢ or e, or both.

Terrie Borofibrists are like Typic Borofibrists except for f,
with or without ¢ or e, or both.

Cryofibrists
Distinctions between Typic Cryofibrists and other subgroups

Typic Cryofibrists are the Cryofibrists that

a. Have less than three-fourths of their fiber volume de-
rived from Sphagnum spp. in the surface tier or more of the
control section;

b. Have a mean annual soil temperature higher than 0°C;

¢. Do not have a lithic contact within the control section;
d. Do not have a mineral layer between 5 and 30 cm thick
with organic materials or do not have two or more thin,
continuous mineral layers in the control section below the
surface tier;

e. Do not have a mineral layer 30 cm or more thick whose
upper boundary is below the surface tier in the control sec-
tion; and

f, Have organic materials that are continuous laterally
throughout each pedon in at least the surface tier.
Fluvaquentic Cryofibrists are like Typic Cryofibrists except
for d.

Lithic Cryofibrists are like Typic Cryofibrists except for c,
with or without a or both @ and 6.

Pergelic Cryofibrists are like Typic Cryofibrists except for
6, with or without any or all or a, d, or e,

Sphagnic Cryofibrists are like Typic Cryofibrists except for
a,

Terrie Cryofibrists are like Typic Cryofibrists except for ¢
or for d and e,

Luvifibrists

Luvifibrists are not known to occur in the United States, but
the great group is provided tentatively for use in other
countries if needed. These soils are the Fibrists that have a
horizon within the control section that is 2 cm or more thick
and is half or more humilluvic materials, Because these soils
cannot be studied in the United States, a precise definition
is not attempted here. It should be noted, however, that the
soils normally are acid and that they have been cultivated
for a long time. been cultivated for a long time.


116

the A horizon is less than 15 cm thick if its color value,
moist, is lower than 3.5; and

c. Do not have an albic horizon at the surface or
immediately under an A or Ap horizon that, in turn, is
underlain by another horizon that has a color value more
than one unit darker or that has chroma of 6 or more.
Humaqueptic Psammaquents are like Typic Psammaquents
except for b, and their base saturation (by NH,OAc) is <50
percent in more than half the thickness of the subhorizons
within the upper 1 m.

Lithic Psammaquents are like Typic Psammaquents except
for a,

Mollic Psammaquents are like Typic Psammaquents except
for 6, and their base saturation (by NH,OAc) is 50 percent
or more in more than half the thickness of the subhorizons
within the upper 1 m.

‘Spodic Psammaquents are like Typic Psammaquents except
for ¢.

Sulfaquents
Definition of Typic Sulfaquents

Typic Sulfaquents are the Sulfaquents that

a. Have sulfidic materials within 50 cm of the mineral soil
surface if the n value is >{ or within 30 cm if the n value is
<i,

‘Tropaquents

The definition of the great group of Tropaquents that
follows cannot be tested in the United States and is
provisional,

Tropaquents are the Aquents that

1. Have an isomesic or warmer iso temperature regime;

2. Have an n value of 0.7 or less or have <8 percent clay in
some subhorizon between 20 and 50 cm; and

3. Have an organic-carbon content® that decreases regularly
with depth below 25 cm and reaches a level of 0.2 percent
of less within a depth of 1.25 m,

‘Subgroups have not been defined.
Arents

The Arents form a unique suborder in that not only are no
great groups recognized, but also there is no typic subgroup.
Subgroups of Arents are intergrades to suborders or great
groups of Spodosols, Alfisols, or other orders, according to
the nature of the fragments that can be identified and ac-
cording to the soil moisture and soil temperature regimes of
the suborders, Thus, if fragments of an argillic horizon can
be identified by their clay content and clay skins, the soil
might be called an Udalfic Arent if the moisture regime is
udic or a Xeralfic Arent if the moisture regime is xeric, At

the carbon should be of Holocene age. It is not the intent to include fousll
carbon from transported fragments of bedrock or from buried Pleistocene de-
posite, The mean residence time of the carbon should be <11,000 years B.P.


Kandiaqualfs..
Kandiaquults..
Kandic horizon.
Kandihumults

Kandiperox 209
Kandiudalfs
Kandiudox. 217

Kandiudults 247
Kandiustalfs.......e0000 83
Kandiustox, 223
Kandiustults. +253

Kanhaplaquults.... 240
Kanhaplohumults.. 1243
Kanhapludalf s,s 78
Kanhapludult:

Kanhaplustalf'
Kanhaplustult
Key to mineralogy classes

Mineral soil,definition
Mineral soil material...
Mineralogy classes
Moisture regimes...
Mollic epipedon.
Mottles that have chroma
Of 2 OF LeSS sssse

n value
Nadurargids
Natralbolls........0
‘Natraqualfs

Natrixerolls.......
Natrudalfs..
Natrustalfs..


118

and smoothed, or the A horizon is <15 cm thick if its color
value, moist, is less than 3.5,

Andeptic Cryofluvents are like Typic Cryofluvents except for
a.

Aquic Cryofluvents are like Typic Cryofluvents except for b
or for b and c.

Mollic Cryofluvents are like Typic Cryofluvents except for c.

Torrifluvents

Distinctions between Typic Torrifluvents and other sub-
groups

Typic Torrifluvents are the Torrifluvents that
a. Do not have a horizon within { m of the surface that is
>15 cm thick that either contains as much as 20 percent
durinodes in a nonbrittle matrix or is brittle and has firm
consistence when moist;
b. Do not have all three of the following characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
long in some part, and that extend upward to the soil
surface or to the base of an Ap horizon;
(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potentia) linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1,5 m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness within the upper 1 m;
c. Do not have an anthropic epipedon; and
d. Are dry in all parts of the moisture control section three-
fourths or more of the time (cumulative) that the soil tem-
perature at a depth of 50 cm is 5°C or more,
Anthropic Torrifluvents are like Typic Torriftuvents except
for c.
Durorthidic Torrifluvents are like Typic Torrifluvents except
for a.
Durorthidic Xeric Torrifluvents are like Typic Torrifluvents
except for aand d. They have a thermic, mesic, or frigid
soil temperature regime and a torric moisture regime that
borders on a xeric regime.
Ustertic Torriftuvents are like Typic Torrifluvents except for
6, with or without d. Unless the soils are irrigated, the
cracks remain open in most years from 175 to 240 days, cu-
mulative, and are not closed for as many as 60 consecutive
days during the 120 days following the winter solstice in 3
or more years out of 10 if the soil temperature regime is
thermic, mesic, or frigid.
Ustie Torrifluvents are like Typic Torriftuvents except for d,
and they have a torric moisture regime that borders on an
ustic regime.
Vertic Torrifluvents are like Typic Torrifluvents except for
4, with or without ¢ or d or both. Unless the soils are irri-
gated, the cracks remain open in most years for more than
240 days, cumulative, and are not closed for as many as 60
consecutive days at any season in most years.
Xeric Torrifluvents are like Typic Torrifluvents except for
d, and they have a thermic, mesic, or frigid soil temperature


254

1, A ratio of measured clay to 1500 kPa water
(percentages) of 1.25 or less; or
2. A ratio of CEC (pH 8.2) to 15-water of >1.5 and more
exchange acidity than the sum of bases plus KCl-ex-
tractable aluminum;
f. When neither irrigated nor fallowed to store moisture:
1. If the soil temperature regime is mesic or thermic, are
moist more than six-tenths of the time in half or more
years in some part of the moisture control section (not
necessarily the same part) when the soil temperature at a
depth of 50 cm exceeds 5°C; or
2. If the soil temperature regime is hyperthermic,
isomesic, or warmer, are moist in most years in some or
all parts of the moisture control section for 180 or more
days during a period when the soil temperature at a
depth of 50 cm exceeds 8°C; and
g. When neither irrigated nor fallowed to store moisture:
1. If the soil temperature regime is mesic or thermic, are
dry for more than 135 cumulative days in some part of
the moisture control section when the soil temperature at
a depth of 50 cm exceeds 5°C; or
2. If the soil temperature regime is hyperthermic,
isomesic, or warmer, the soils are dry in some or all parts
of the moisture control section for more than 90 days
during a period when the soil temperature at a depth of
50 cm exceeds 8°C; and
h. Have an ECEC (sum of bases plus KCl-extractable Al) of
more than 1.5 cmol(+) kgTM clay in all subhorizons to a depth
of 150 cm below the soil surface.
Aric Kandiustults are like Typic Kandiustults except for h
with or without a, 6, or d.
Andic Kandiustults are like Typic Kandiustults except for e,
with or without 6.
Andie Udie Kandiustults are like Typic Kandiustults except
for e and g.
Aquic Kandiustults are like Typic Kandivstults except for a.
Arenic Kandiustults are like Typic Kandiustults except for c.
Arenic Plinthic Kandiustults are like Typic Kandiustults ex-
cept for b and c,
Aridic Kandiustults are like Typic Kandiustults except for /.
Plinthic Kandiustults are like Typic Kandiustults except for
b
Rhodic Kandiustults are like Typic Kandivstults except for
a

Udic Kandiustults are like Typic Kandiustults except for g.
Kanhaplustults

Distinctions between Typic Kanhaplustults and other sub-
groups

Typic Kanhaplustults are the Kanhaplustults that
a. Do not have a lithic contact within 50 em of the mineral
soil surface;

b. Do not have the following combination of characteristics
in the upper 75 cm of the soil if the chroma throughout the
upper 75 cm is not controlled by uncoated sand grains; or if
the chroma throughout the upper 75 cm is controlled by
uncoated sand grains, do not have the following combination
of characteristics throughout the upper 12.5 cm of the
argillic or kandic horizon:


4

(2) Has 12 percent or more organic carbon if the
mineral fraction has no clay;

(3) Has an intermediate proportional content of or-
ganic carbon if part but less than 60 percent of the
mineral fraction is clay.

2. The plow layer is 25 cm or more thick and has 8 percent
or more organic carbon if it has no clay, or 16 percent or
more organic carbon if 60 percent or more of the mineral
fraction is clay, or an intermediate proportional content of
organic carbon if part but less than 60 percent of the min~
eral fraction is clay.

3. A layer of organic material that has enough organic car-
bon and is thick enough to satisfy one of the requirements
under item 1 Jies beneath a surface layer of mineral materi-
als that is <40 cm (16 in.) thick. In such a soil, the histic
epipedon has been buried but the mineral materials at the
surface are too thin to be considered diagnostic in the clas-
sification.

4. A surface layer of organic material <25 cm thick that has
enough organic carbon to satisfy the minimum requirements
under item 2 after the soil has been mixed to a depth of 25
cm.

Mollic epipedon (L. mollis, soft)

The mollic epipedon is defined in terms of its morphology
rather than its genesis. It consists of mineral soil material.
It is a surface horizon or horizons unless (a) it underlies a
recent deposit that is <S0 cm thick and that has fine strati-
fications if not plowed or (b) it underlies a thin layer of or-
ganic material in a wet soil (see histic epipedon). If the
layer of organic material is thick enough that the soil is or-
ganic, the mineral soil is considered to be buried.

The mollic epipedon has the following properties:

1, Soil structure is strong enough that the major part of the
horizon is not both massive and hard, or very hard when
dry. Very coarse prisms, >30 cm in diameter, are included
in the meaning of massive if there is no secondary structure
within the prisms.

2. Unless there is >40 percent finely divided lime, both bro-
ken and crushed samples have Munsell color value darker
than 3.5 when moist and 5.5 when dry, and chroma less than
3.5 when moist’; the color value normally is at least | Mun-
sell unit darker or the chroma is at least 2 units less (both
moist and dry) than that of the 1C horizon if an 1C horizon
is present. If only a 2C horizon or an R layer is present,
the comparison should be made with the horizon that over-
lies the 2C. Some parent materials such as loess, cinders,
alluvium, or carbonaceous shales also can have dark color

The chroma is permitted to range up to but not to include 4.0 soils that have
a hyperthermic or isohyperthermic temperature regime, The color when moist
is that of a specimen that is moist enough that an additional drop of water
produces no change in the color. The color when dry is that of a specimen dry
enough that continued drying produces no further change.


93
Rhodoxeralfs

Distinctions between Typic Rhodoxeralf's and other sub-
groups

The list of subgroups that follows is incomplete because the
soils are of such limited extent in the United States.

Typic Rhodoxeralfs are the Rhodoxeralfs that

‘a, Have an argillic horizon that is >15 cm thick and is con-
tinuous in each pedon;

b. Do not have a lithic contact within 50 cm of the soil
surface,

c. Do not have a petrocalcic horizon whose upper boundary
is within 1.5 m of the soil surface; and

d, Do not have a calcic horizon whose upper boundary is
within 1.5 m of the soil surface.

Gateic Rhodoxeralfs are tike Typic Rhodoxeralfs except for

Liane Rhodoxeralfs are like Typic Rhodoxeralfs except for
b

Petrocalcic Rhodoxeralfs are like Typic Rhodoxeralfs except
for c.


39

top 30 cm (12 in.) exclusive of loose surface litter or living
mosses,

A surface mineral layer <40 cm (16 in.) thick is present on
some organic soils as a result of flooding, additions by men
to increase soil strength or reduce frost hazard, volcanic
eruptions, or other causes, If present, it is considered a part
of the surface tier, even though it may be >30 cm thick, and
the depth then is measured from the top of the mineral
layer,

Subsurface tier

The subsurface tier is 60 cm (24 in.) thick unless the control
section ends at a lithic or paralithic contact or at water
within this depth or unless the soil is frozen at too shallow a
depth. In any of these situations the subsurface tier extends
from the base of the surface tier to the base of the control
section. It includes any unconsolidated mineral layers that
may be present within those depths.

Bottom tier

The bottom tier is 40 cm (16 in.) thick unless the control
section stops within the maximum span.


162

(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
a potential linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m; and
(3) More than 35 percent clay in horizons that total >50
cm in thickness; or
f. Do not have a calcic horizon or soft powdery lime within
a depth of 1.5 m if the weighted average particle-size class
from depths of 25 cm to 1 m is sandy or to a lithic or
paralithic contact if one is shallower than | m, or within a
depth of 1.1 m if the weighted average particle-size class is
loamy, or within a depth of 90 cm if it is clayey;
g. Do not have a layer in the upper 75 cm that has texture
finer than loamy fine sand, that is a much as 18 cm thick,
that has bulk density (at 33 kPa water tension) of 0.95 g per
cubic centimeter or fess in the fine-earth fraction, and that
has either of the following:
(1) A ratio of measured clay to 1500 kPa water
(percentages) of 1,25 or less; or
(2) A ratio of CEC (at pH near 8) to 1500 kPa water of
>1.5 and more exchange acidity than the sum of bases
plus KCl-extractable aluminum,
h. Do not have a petrocalcic horizon within a depth of 100
cm of the soil surface!
i. Do not have a gypsic horizon within a depth of 100 cm of
the soil surface’?
Andic Xerochrepts are like Typic Xerochrepts except for g
or for b and g.
Aquie Xerochrepts ate like Typic Xerochrepts except for a,
Aquic Dystric Xerochrepts are like Typic Xerochrepts except
for a and b,
Calcixerollic Xerochrepts are like Typic Xerochrepts except
for f.
Dystric Xerochrepts are like Typic Xerochrepts except for b.
Dystric Fluventic Xerochrepts are like Typic Xerochrepts
except for 5 and c.
Dystric Lithie Xerochrepts are like Typic Xerochrepts except
for b and d.
Fluventic Xerochrepts are like Typic Xerochrepts except for

6

Gypsie Xerochrepts are like Typic Xerochrepts except for i,
with or without f.

Lithic Xerochrepts are like Typic Xerochrepts except for d.
Lithic Ruptic-Xerorthentic Xerochrepts are like Typic
Xerochrepts except for d, and have an intermittent cambic
horizon.

Petrocalcie Xerochrepts are like Typic Xerochrepts except
for A, with or without f or i or both.

Ruptic-Lithic Xerochrepts are like Typic Xerochrepts except
for d and have a lithic contact in some part but less than
half of each pedon.

Vertic Xerochrepts are like Typic Xerochrepts except for e,
with or without a or c, or both.

Thpecousl communications with Di ‘
‘Personal communications with Dr. R. Tavernier and Ph.D. thesis by M.
Iaiwi, Univ. of Ghent.

1 Sc¢ footnote 11 above.


127

moisture regime and have enough clay to coat at least 75
percent of the surfaces of the sand grains.

Torripsamments

Distinctions between Typic Torripsamments and other sub-
groups

Typic Torripsamments are the Torripsamments that

a. Do not have a lithic contact within 50 cm of the soil
surface;

b. Do not have a horizon within 1 m of the surface that is
>15 cm thick and either contains 20 percent or more durin-
odes in a nonbrittle matrix or is brittle and has firm consis-
tence when moist; and

c. Are dry in all parts of the moisture control section three-
fourths or more of the time (cumulative) that the soil tem-
perature at a depth of 50 cm is 5°C or higher.

Durorthidic Xeric Torripsamments are like Typic Torrip-
samments except for 6 and c, and they have a thermic,
mesic, or frigid soil temperature regime and a torric mois-
ture regime that borders on xeric.

Lithic Torripsamments are like Typic Torripsamments except
for a or for a and ¢.

Ustic Torripsamments are like Typic Torripsamments except
for c, and they have a torric moisture regime that borders
‘on an ustic regime.

Xeric Torripsamments are like Typic Torripsamments except
for c, and they have a thermic, mesic, or frigid soil tem-
perature regime and a torric moisture regime that borders on
an xeric regime.

Tropopsamments

Distinctions between Typic Tropopsamments and other sub-
groups

Typic Tropopsamments are the Psamments that

a, Do not have a lithic contact within 50 cm of the soil
surface; and

b. Do not have mottles above a depth of | m that have
chroma of 2 or less, or if the color is due to uncoated sand
grains, have a ground-water table within 1 m of the soil
surface for less than 60 cumulative days in most years.
Aquic Tropopsamments are like Typic Tropopsamments ex-
cept for b.

Lithic Tropopsamments are like Typic Tropopsamments ex-
cept for a.

Udipsamments

Distinctions between Typic Udipsamments and other sub-
groups

Typic Udipsamments are the Udipsamments that
a, Do not have lamellae within 1.5 m of the soil surface that
meet all requirements for an argillic horizon except thick-
ness;

‘The clay content cannot be estimated with precision in lamellae that are
very thin, The lamellae in soils of alfic subgroups generally are about 0.5 to 1


101

Ustollic Natrargids are like Typic Natrargids except for e.
They have a mean annual soil temperature of 8°C or higher
and an aridic moisture regime that borders on an ustic
regime,

Xerollic Natrargids are like Typic Natrargids except for e.
They have a mean annual soil temperature lower than 22°C,
and the mean summer and mean winter soil temperatures at
a depth of 50 cm differ by 5°C or more. The moisture
regime is aridic, bordering on xeric.

Paleargids
Distinctions between Typic Paleargids and other subgroups

Typic Paleargids are the Paleargids that

a. Do not have a horizon within 1 m of the surface that is

>15 cm thick that either contains 20 percent or more

durinodes in a nonbrittle matrix or is brittle and has firm
consistence when moist;

b. Have a weighted average percentage of organic carbon in

the upper soil to a depth of 40 cm of <0.6 percent if the

weighted average ratio of sand to clay above this depth is

1.0 or less, or one-seventh percent if the ratio is 13 or more,

or an intermediate percentage of organic carbon if the ratio

of sand to clay is between 1.0 and 13; or a weighted average
percentage of organic carbon in the surface soil to a depth
of 18 cm that is not one-fifth more than the values just
stated if there is a petrocalcic horizon whose upper
boundary is shallower than 40 cm but deeper than 18 cm;

¢. Do not have a petrocalcic horizon whose upper boundary

is within 1 m of the soil surface;

d. Have either
(1) An increase of 15 percent or more clay (absolute)
within a vertical distance of 2.5 cm at the upper
boundary of the argillic horizon, or
(2) An increase of 10 percent or more clay (absolute) if
the soil is cultivated and the lower boundary of the Ap
horizon is the upper boundary of the argillic horizon;

e. Do not have the following combination of characteristics:
(1) Cracks at some period in most years that are 1 cm or
more wide at a depth of 50 cm, that are at least 30 cm
Jong in some part, and that extend upward to the soil
surface, to the base of an Ap horizon, or to the top of
the argillic horizon;

(2) A coefficient of linear extensibility (COLE) of 0.05
or more in a horizon or horizons at least 50 cm thick and
@ potential linear extensibility of 6 cm or more in the
upper 1.5 m of the soil or in the whole soil if a lithic or
paralithic contact is deeper than 50 cm but shallower than
1.5 m; and

(3) More than 35 percent clay in horizons that total >50
cm in thickness; and

f. Are dry in all parts of the moisture control section more

than three-fourths of the time (cumulative) that the soil

temperature at a depth of 50 cm is 5°C or higher,

Borollic Paleargids are like Typic Paleargids except for b or

for 6 and f. The mean annual soil temperature is lower than

8°C, and the mean summer and mean winter soil
temperatures at a depth of 50 cm differ by >5°C. They
have an aridic moisture regime that borders on an ustic
regime.



43

Clayey’.-- The fine earth contains 35 percent or more clay
by weight, and rock fragments are <35 percent by volume.
Fine. A clayey particle-size class that has 35 through 59
percent clay in the fine-earth fraction (30 through 50 per
cent in Vertisols).

Very-fine. A clayey particle-size class that has 60 percent
or more clay in the fine-earth fraction,

Modifiers that reolace names of particle-size classes

There are three situations in which particle-size class names
are not used. In one, the name is redundant. Psamments
and Psammaquents, by definition, are sandy, and no parti-
cle~size class name is needed or used in the family name.

In the second situation, particle size is a meaningless concept
because, presumably, the soil consists of a mixture of dis-
crete mineral particles and of gels. The concept of either
texture or particle size is not applicable to a gel, particularly
if the gel cannot be dispersed. Consequently, no particle-
size class names are used if the soil is mostly glass or if the
exchange complex is dominated by amorphous materials, as
is the situation with Andepts by definition. In families of
Andepts and Andaquepts, in most andic subgroups of In-
ceptisols and andaqueptic and andeptic subgroups of other
orders, and in families of Entisols and Aridisols with modi-
fiers listed below, particle-size class names, as such, are not
used for the part of the soil that does not disperse.

In the third situation, the content of organic matter is high
and particle size has only limited relation to the physical and
chemical properties of the soils. This seems to be normal in
soils that have both a cryic temperature regime and a spodic
horizon. Therefore, particle-size class names are not used
for the spodic horizons® or Cryaquods, Cryohumods, Cry-
orthods, or Cryic Placohumods.

The following terms are substituted for the particle-size
class names in the taxa that have been listed unless the par~
ticle-size modifier is redundant. They reflect a combination
of particle size and mineralogy, and they take the place of
both.

Cindery,--Sixty percent or more of the whole soil (by
weight)* volcanic ash, cinders, and pumice; 35 percent or
more (by volume) is cinders that have diameter of 2 mm or
more.

77 the ratio of 1500 KP. in 0.6 or more in half or more of the
control section, the percentage of clay is considered to be 2.6 times the per-
cantage of 1600 kPa water. Carbonates of clay sine are not considered to be
clay but are treated aa silt in all particle-ize classes.

SParticle-sise class names are applied to other spodic horisons but with reser~
vations. Somewhat different classes probably should be used for most families
of Spodosols, but data are too few to permit the testing of alternatives. Some
‘tories that would otherwise be reasonably homogeneous are aplit at the family
level by the particle-sine classes, These aoils have appreciable but not very
large amounts of organic matter in the spodie horizon.

‘Percentages by weight in these definitions are estimated from grain counts;
usually, a count of one or two dominant tite fractions of the conventional
mechanical analysis is enough for placemant of the soil