**\
Part 622 - ECOLOGICAL AND INTERPRETATIVE GROUPS**

**CONTENTS**

**PART TITLE PAGE**

622.00 Definition 622-1

622.01 Policy and Responsibilities 622-1

622.02 Land Capability Classification 622-1

622.03 Farmland Classification 622-2

622.04 Prime Farmland Soils 622-3

622.05 Highly Erodible Land - Highly Erodible Soil Map Unit List 622-4

622.06 Hydric Soils 622-4

622.07 Ecological Sites 622-5

622.08 Windbreaks 622-5

622.09 Wildlife Habitat 622-6

622.10 Plant Name, Common 622-6

622.11 Plant Name, Scientific 622-6

622.12 Ecosystem ID 622-6

622-13 Ecosystem Name 622-7

622.14 Ecosystem Type 622-7

622.15 Earth Cover, Kind 622-7

Exhibit 622-1 Prime and Unique Farmlands 622-10

Exhibit 622-2 Land Capability Classification 622-16

**\
Part 622 - ECOLOGICAL AND INTERPRETATIVE GROUPS**

## 622.00 Definition.

Ecological and interpretative groups are specified land use and specific
management groupings that are assigned to soil areas because
combinations of soils have similar behavior for specified practices.
Most are based on soil properties and other factors that directly
influence the specific use of the soil. They allow users of soil surveys
to plan reasonable alternatives for the use and management of soils.

## 622.01 Policy and Responsibilities.

The soil criteria used to determine the rating is coordinated
nationally. Data elements, classes, or groups that are used in national
legislation have strict adherence to national procedures. Guides that
are developed locally or by states to rate soil survey land
classification and groups are reviewed according to the procedure
discussed in part 617.05. Prime farmland, hydrologic soil groups, and
other Interpretative groups important to many different users are
published in the soil survey report.

The state soil scientist is responsible for program specific and state
interpretative group assignments to soil map units. The state soil
scientist ensures that all nationally significant interpretative group
assignments to map units are included in the National Soil Information
System (NASIS).

## 622.02 Land Capability Classification.

**(a) Definition**. Land capability classification is a system of
grouping soils primarily on the basis of their capability to produce
common cultivated crops and pasture plants without deteriorating over a
long period of time.

**(b) Classes**. Land capability classification is subdivided into
capability class and capability subclass nationally. Some states also
use a capability unit.

**(c) Significance**. Land capability classification has value as a
grouping of soils. National Resource Inventory information, Farmland
Protection Policy Act, and many field office technical guides have been
assembled according to these classes. The system has been adopted in
many textbooks and has wide public acceptance. Some state legislation
has used the system for various applications. Users should reference
Agriculture Handbook No. 210 (Exhibit 622-2) for a listing of
assumptions and broad wording used to define the capability class and
capability subclass.

**(d) Application**.

All map unit components, including miscellaneous areas, are assigned a
capability class and subclass. Agriculture Handbook No. 210 (Exhibit
622-2) provides general guidance, and individual state guides provide
assignments of the class and subclass applicable to the state. Land
capability units can be used to differentiate subclasses at the
discretion of the state. Capability class and subclass are assigned to
map unit components in the National Soil Information System (NASIS).

**(e) Categories.**

**(1) Capability Class.**

**(i) Definition.** Capability class is the broadest category in the
land capability classification system. Class codes I (1), II (2), III
(3), IV (4), V (5), VI (6), VII (7), and VIII (8) are used to represent
both irrigated and nonirrigated land capability classes.

**(ii) Classes and definitions.**

*Class I (1)* soils have slight limitations that restrict their use.

*Class II (2)* soils have moderate limitations that reduce the choice of
plants or require moderate conservation practices.

*Class III (3)* soils have severe limitations that reduce the choice of
plants or require special conservation practices, or both.

*Class IV (4)* soils have very severe limitations that restrict the
choice of plants or require very careful management, or both.

*Class V (5)* soils have little or no hazard of erosion but have other
limitations, impractical to remove, that limit their use mainly to
pasture, range, forestland, or wildlife food and cover.

*Class VI (6)* soils have severe limitations that make them generally
unsuited to cultivation and that limit their use mainly to pasture,
range, forestland, or wildlife food and cover.

*Class VII (7)* soils have very severe limitations that make them
unsuited to cultivation and that restrict their use mainly to grazing,
forestland, or wildlife.

*Class VIII (8)* soils and miscellaneous areas have limitations that
preclude their use for commercial plant production and limit their use
to recreation, wildlife, or water supply or for esthetic purposes.

**(2) Capability Subclass.**

**(i) Definition.** Capability subclass is the second category in the
land capability classification system. Class codes e, w, s, and c are
used for land capability subclasses.

**(ii) Subclasses and definitions.**

*Subclass e* is made up of soils for which the susceptibility to erosion
is the dominant problem or hazard affecting their use. Erosion
susceptibility and past erosion damage are the major soil factors that
affect soils in this subclass.

*Subclass w* is made up of soils for which excess water is the dominant
hazard or limitation affecting their use. Poor soil drainage, wetness, a
high water table, and overflow are the factors that affect soils in this
subclass.

*Subclass s* is made up of soils that have soil limitations within the
rooting zone, such as shallowness of the rooting zone, stones, low
moisture-holding capacity, low fertility that is difficult to correct,
and salinity or sodium content.

*Subclass c* is made up of soils for which the climate (the temperature
or lack of moisture) is the major hazard or limitation affecting their
use.

**(iii) Application.** The subclass represents the dominant limitation
that determines the capability class. Within a capability class, where
the kinds of limitations are essentially equal, the subclasses have the
following priority: e, w, s, and c. Subclasses are not assigned to soils
in capability class I (1) and subclass "e" is not used in class V (5).

**(3) Capability Unit.**

**(i) Definition.** Capability unit is the first category listed in the
land capability classification system. It is a grouping of one or more
individual soil mapping units having similar potentials and continuing
limitations or hazards.

**(ii) Application.** Use of this category and definition of codes are
state options. Valid entries in NASIS are integers ranging from 1 to 99.

**(f) Entries.** Enter the appropriate capability class and subclass
code for each map unit component, including miscellaneous areas. Enter
the appropriate capability unit code, if one is to be used in the area.
Allowable entries for capability class are I (1), II (2), III (3), IV
(4), V (5), VI (6), VII (7), or VII (8). Allowable entries for subclass
are e, w, s, or c. Enter subclass for all classes except class I (1) and
subclass "e" is not used in class V (5). Valid entries for capability
unit are integers ranging from 1 to 99. Nonirrigated land capability
classes and subclasses should be entered for all map unit components,
including miscellaneous areas. Enter the irrigated land capability class
and subclass if the soil component is irrigated or potentially will be
irrigated.

## 622.03 Farmland Classification.

**(a) Definition**. The farmland classification identifies map units as
prime farmland, farmland of statewide importance, or farmland of local
importance.

**(b) Significance**. Farmland classification identifies the location
and extent of the most suitable land for producing food, feed, fiber,
forage, and oilseed crops. This identification is useful in the
management and maintenance of the resource base that supports the
productive capacity of American agriculture.

**(c) Measurement.** NRCS policy and procedures on prime and unique
farmlands are published in the Code of Federal Regulations 7CFR657..
This regulation is reproduced in Exhibit 622-1 for convenience. The web
site is: *http://www.access.gpo.gov/nara/cfr/waisidx_99/7cfr657_99.html*

**(d) Entries.** Enter the numerical code for the classification of each
map unit. Soils of unique, statewide, or local importance are
[not]{.underline} prime farmland. Allowable entries are numerical codes
as follows:

> 0 - Not prime farmland.
>
> 1 - All areas are prime farmland.
>
> 2 - Prime farmland if drained.
>
> 3 - Prime farmland if protected from flooding or not frequently
> flooded during the growing season.
>
> 4 - Prime farmland if irrigated.
>
> 5 - Prime farmland if drained and either protected from flooding or
> not frequently flooded during the growing season.
>
> 6 - Prime farmland if irrigated and drained.
>
> 7 - Prime farmland if irrigated and either protected from flooding or
> not frequently flooded during the growing season.
>
> 8 - Prime farmland if subsoiled, completely removed the root
> inhibiting soil layer.
>
> 9 - Prime farmland if irrigated and the product of I (soil
> erodibility) x C (climate factor) does not exceed 60.
>
> 10 - Prime farmland if irrigated and reclaimed from excess salts and
> sodium.
>
> 30 - Farmland of statewide importance.
>
> 50 - Farmland of local importance.
>
> 70 - Farmland of unique importance.

## 622.04 Prime Farmland Soils.

**(a) Definition**.

Prime farmland is land that has the best combination of physical and
chemical characteristics for producing food, feed, forage, fiber, and
oilseed crops and that is available for these uses. It has the
combination of soil properties, growing season, and moisture supply
needed to produce sustained high yields of crops in an economic manner
if it is treated and managed according to acceptable farming methods. In
general, prime farmland has an adequate and dependable water supply from
precipitation or irrigation, a favorable temperature and growing season,
an acceptable level of acidity or alkalinity, an acceptable content of
salt or sodium, and few or no rocks. Its soils are permeable to water
and air. Prime farmland is not excessively eroded or saturated with
water for long periods of time, and it either does not flood frequently
during the growing season or is protected from flooding. Users of the
lists of prime farmland map units should recognize that soil properties
are only one of several criteria that are necessary. Other
considerations include:

**(1)** Land use - Prime farmland is designated independently of current
land use, but it cannot be areas of water or urban or built-up land as
defined for the National Resource Inventories. Map units that are
complexes or associations containing components of urban land or
miscellaneous areas as part of the map unit name cannot be designated as
prime farmland. The soil survey memorandum of understanding determines
the scale of mapping and should reflect local land use interests in
designing of map units.

**(2)** Frequency of flooding - Some map units may include both prime
farmland and land not prime farmland because of variations in flooding
frequency.

**(3)** Irrigation - Some map units include areas that have a developed
irrigation water supply that is dependable and of adequate quality and
areas that do not have such a supply. In these units, only the irrigated
areas meet the prime farmland criteria.

**(4)** Water table - Some map units include both drained and undrained
areas. Only the drained areas meet the prime farmland criteria.

**(5)** Wind erodibility - The product of I (soil erodibility) x C
(climate factor) cannot exceed 60 to meet prime farmland criteria. A map
unit may be considered prime farmland in one part of a survey area but
not in another where the climate factor is different.

**(b) Purpose**.

The Natural Resources Conservation Service (NRCS) is committed to the
management and maintenance of the resource base that supports the
productive capacity of American agriculture. This management and
maintenance includes identifying of the location and extent of the most
suitable land for producing food, feed, fiber, forage, and oilseed
crops. Prime farmland information may be supplemented with separate
designations of soil map units that have state-wide, local, or unique
importance as farmland capable of producing these crops.

**(c) Code of Federal Regulations**.

NRCS policy and procedures on prime and unique farmlands are published
in the Code of Federal Regulations 7CFR657. The content is reproduced in
Exhibit 622-1 for convenience. The web site is:
*http://www.access.gpo.gov/nara/cfr/waisidx_99/7cfr657_99.html*

**(d) Policy**.

State soil scientists prepare and maintain an up-to-date list of soil
survey map units that meet the soil criteria for prime farmland. The
list given in field office technical guides for users concerned with
only a single area is a subset of the state list. The list of prime
farmland soils should be kept up-to-date. The state soil scientist
ensures that prime farmland soil interpretations are made for all soil
mapping units in that state. Mapping units continuing across state lines
should be coordinated with the adjoining state. Other policy guidance is
given in part 510 of the National Inventory and Monitoring Manual.

**(e) List of Prime Farmland Map Units**.

Soil survey map units that meet the soil requirements for prime farmland
are to be identified, coordinated, and listed. The list or its subset is
to be available to users of soil survey information.

**(f) Quality Control of Prime Farmland Map Units**.

**(1)** Computer generation of prime farmland map units in each state is
based on guidelines provided by the National Soil Survey Center. The
guidelines provide checks to identify concerns in the classification of
prime farmland based on soil properties. The computer checks can be used
for guidance but do not suffice as the sole determinant for prime
farmland map units.

**(2)** Each prime farmland map unit must be documented, either by the
computer check or by a statement of reasons that explain the decision.

**(3)** Some soil survey map units may meet the soil criteria for prime
farmland, but additional investigation is needed before a final
determination is made. The measures needed to qualify the soil as prime
farmland are indicated by an appropriate footnote or in a parenthetic
statement of explanation that follows the map unit name on the list.

## 622.05 Highly Erodible Land - Highly Erodible Soil Map Unit List.

**(a) Definition**.

Highly erodible land is defined by the Sodbuster, Conservation Reserve,
and Conservation Compliance parts of the Food Security Act of 1985 and
the Food, Agriculture, Conservation, and Trade Act of 1990.
Determinations for highly erodible land are based on an erodibility
index as defined in the National Food Security Act Manual.

**(b) Policy**.

Lists of highly erodible and potential highly erodible map units are
maintained in the field office technical guide. Policy and procedures
for developing and maintaining the lists are given in part 511 of the
National Food Security Act Manual.

## 622.06 Hydric Soils.

**(a) Definition**.

A hydric soil is a soil that formed under conditions of saturation,
flooding, or ponding long enough during the growing season to develop
anaerobic conditions in the upper part. Hydric soils along with
hydrophytic vegetation and wetland hydrology are used to define
wetlands.

**(b) Policy**.

The current criteria for generating a list of hydric soils is in the
Federal Register, September 18, 2002, volume 67, number 181, page 58756
The reference for field identification of hydric soils is Field
Indicators of Hydric Soils of the United States, Version 5.01 2003.
(http://soils.usda.gov/use/hydric).

States maintain current lists of hydric soil map units in the field
office technical guide.

## 622.07 Ecological Sites.

**(a) Definition.**

An ecological site is a distinctive kind of land with specific physical
characteristics that differs from other kinds of land in its ability to
produce a distinctive kind and amount of vegetation. An ecological site
is recognized and described on the basis of the characteristics that
differentiate it from other sites in its ability to produce and support
a characteristic plant community.

Forestland ecological sites and rangeland ecological sites are separated
based on the historic climax plant community that existed at the time of
European immigration and settlement. A site type of "forestland" is
assigned and described where a 25% overstory canopy of trees, as
determined by crown perimeter-vertical projection, dominated this
historic vegetation. A site type of "rangeland" is assigned where
overstory tree production was not significant in the climax vegetation.
Refer to the National Forestry Manual
(<ftp://ftp-fc.sc.egov.usda.gov/NSSC/National_Forestry_Manual/2002_nfm_complete.pdf>)
and the National Range and Pasture Handbook
(<http://www.glti.nrcs.usda.gov/technical/publications/nrph.html>) for
details on developing ecological site descriptions.

**(b) Policy**

Soil-ecological site correlation establishes the relationship between
soil components and ecological sites. Ecological sites are correlated on
the basis of soils and the resulting differences in species composition,
proportion of species, and total production of the historic climax plant
community. Sometimes it is necessary to extrapolate data on the
composition and production of a plant community on one soil to describe
the plant community on a similar soil for which no data are available.
The separation of two distinct soil taxonomic units does not necessarily
delineate two ecological sites. Likewise, some soil taxonomic units
occur over broad environmental gradients and may support more than one
distinctive historic climax plant community. Changes may be brought
about by other influences, such as an increase or decrease in average
annual precipitation.

Ecological sites are to be correlated between states. Only one Site ID
should be given to a single site that occurs in adjacent states within
the same MLRA. Refer to the National Forestry Manual
(<ftp://ftp-fc.sc.egov.usda.gov/NSSC/National_Forestry_Manual/2002_nfm_complete.pdf>)
and the National Range and Pasture Handbook
(<http://www.glti.nrcs.usda.gov/technical/publications/nrph.html>) for
details on the policy for correlating ecological sites.

\(c\) Responsibilities.

Soil scientists and the responsible discipline specialists work together
to map soils and ecological sites. Essential activities include
development of soil survey memorandum of understanding (work plan),
determination of composition of soil mapping units, preparation of map
legends, determination of mapping intensity, and conducting necessary
field reviews. State discipline specialists have the final
responsibility for correlating ecological sites to the map unit
component to ensure coordination among states and land use areas.

## 622.08 Windbreaks.

**(a) Definition**.

A windbreak is a living barrier of trees or a combination of trees and
shrubs that is located adjacent to a farmstead, field, feedlot, or other
area. It is established to protect soil resources, reduce wind erosion,
conserve energy or moisture, control snow deposition, provide shelter
for livestock or wildlife, or increase the natural beauty of an area. It
is also called a field windbreak, feedlot windbreak, or farmstead
windbreak, depending upon its intended use. Field windbreaks, often
called shelterbelts, are long, narrow strips of trees and shrubs that
are planted in a variety of patterns to check the movement of wind.

**(b) Policy**.

Soil interpretations are made for all soils in all areas where
windbreaks are a present or potential practice. These interpretations
are to be included in field office technical guides, soil handbooks, and
published soil surveys.

Refer to the National Forestry Manual for forestland interpretations.
Conservation Tree/Shrub Group is a forestland interpretation useful for
windbreak planning.

Soil scientists work with foresters in preparing windbreak
interpretations.

## 622.09 Wildlife Habitat.

**(a) Definition**.

The habitat of a particular animal is defined as the place where the
animal lives. Each habitat is the entire environmental complex, both
living and nonliving, that is present at the place occupied by the
animal species. Soils are rated in their described condition and do not
consider existing vegetation, water sources, or the presence or absence
of wildlife in the area. These factors need to be considered during the
site evaluation and planning process in order to obtain total habitat
quality.

**(b) Policy**.

Soil interpretations can be developed for all soils that have the
potential to provide some form of habitat to locally adapted wildlife
species. Soil scientists and biologists work together to identify
specific wildlife habitat elements and to develop the categorical lists
for the local area. This information is based on the inherent
capabilities of the soil to produce certain kinds of vegetation for use
as wildlife habitat or as habitat that meets specific requirements of an
animal species. The National Biology Manual provides more information.

## 622.10 Plant Name, Common

**(a) Definition**. The common plant name is the common name, accepted
by the state or region, for the plant species or genera.

**(b) Entries**. None required. The common plant name used in that state
will be provided by the system from the PLANTS database
(<http://plants.usda.gov/>) to match the plant symbol entered elsewhere.
Adjustment or additions can be made.

## 622.11 Plant Name, Scientific.

**(a) Definition**. Scientific plant name is the full genus and species
name with author. Refer to \"PLANTS,\" Plant List of Accepted
Nomenclature, Taxonomy, and Symbols.

**(b) Significance**. This information is important for technology
transfer and interchange.

**(c) Entries**. None required. The system will provide the scientific
plant name to match the plant symbol entered elsewhere.

## 622.12 Ecosystem ID

**(a) Definition**. Ecosystem ID is an identifier that, in conjunction
with \"ecosystem type,\" uniquely identifies a particular ecosystem. For
example, for range sites, the combination of ecosystem type = rangeland
and ecosystem id = rangesite id uniquely identifies a particular
rangesite.

**(b) Entries**. Enter the unique ID for the ecosystem for each map unit
component where needed. Valid entries are combinations of numbers and/or
letters up to 10 characters in length.

## 622.13 Ecosystem Name.

**(a) Definition**. Ecosystem name is the descriptive name of a
particular ecosystem. For example, \"loamy upland\" is a name of a range
site.

**(b) Entries**. Enter the appropriate name of the ecosystem for each
map unit component where needed.

## 622.14 Ecosystem Type.

**(a) Definition**. Ecosystem type is the type of ecosystem.

**(b) Classes**.

[choice]{.underline}

grazeable forest

hayland

native pasture

pasture

rangesite

**(c) Entries**. Enter the class name for each map unit component where
needed.

## 622.15 Earth Cover, Kind

**(a) Definition**. Earth cover, kind, is the natural or artificial
material that is observed to cover a portion of the Earth\'s surface. It
is determined (at least conceptually) as a vertical projection downward.
There are two levels of categories.

**(b) Significance**. Earth cover, kind, is useful in assessing soils
for use and management and monitoring for soil health. Earth cover kind
is important in linking to National Resources Inventory (NRI) data.

Soil data ranges included in the map unit records in NASIS may be
narrowed by indicating the cover type present for each map unit
component.

Significant differences for interpretations between the major cover
types can be shown by splitting the map unit component into these cover
types.

Earth cover is divided into two levels \-- the second being a
subdivision of the first.

**(c) Earth Cover Level 1 Classes.** These correspond to the Level 1
categories used in the National Resources Inventory \"Instructions for
Collecting 1992 National Resources Inventory Sample Data.\" The
definitions have been slightly altered.

Crop Cover The full cropping cycle, including land preparation and
post-harvest residue cover of annual or perennial herbaceous plants that
are cultivated or harvested, or both, for the production of food, feed,
oil, and fiber other than wood, and excluding hay and pasture.

Grass/ (\>50% grass, grass-like, or forb\
Herbaceous cover) Non-woody vegetative\
Cover cover composed of annual or

> perennial grasses, grasslike plants (sedges/rushes), forbs (including
> alfalfa and clovers), mosses, lichens, and ferns.

Tree Cover (\>25% tree canopy cover) Vegetative cover recognized as
woody plants which usually have one perennial stem, a definitely formed
crown of foliage, and a mature height of at least 4 meters. This
category contains all trees, even those planted for the purpose of
producing food or ornamentals, including Christmas trees. It also
includes those lands which have been harvested of trees, even those that
have been clear cut, but will return to tree cover.

Shrub Cover (\>50% shrub canopy cover) Vegetative cover composed of
multi-stemmed, woody plants and single-stemmed species that attain less
than 4 meters in height at maturity. This category contains all shrubs
and woody vines, even those planted for the purpose of producing food.

Barren land Nonvegetative (\<5% vegetated cover) natural cover often
having a limited capacity to support vegetation, with a surface of sand,
rock, thin soil, or permanent ice or snow. This category also includes
bare soil resulting from construction activities and extractive
activities such as mining.

Artificial Nonvegetative cover either made

Cover or modified by human activity that prohibit or restrict vegetative
growth and water penetration. Examples include highways, rooftops, road
surfaces, paved and stone surface parking areas, sidewalks, and
driveways.

Water Earth covered by water in a fluid state. This category includes
seasonally frozen areas.

[CODE]{.underline} [CLASS]{.underline}

C Crop cover

G Grass/Herbaceous cover

T Tree cover

S Shrub cover

B Barren land

A Artificial cover

W Water cover

**(d) Earth Cover Level 2 classes.** These are subdivisions of Level 1
classes.

[Level 1]{.underline} [Level 2]{.underline}

Crop Cover Row crops (corn, soybeans, cotton, tomatoes and other

truck crops, and tulips)

Close-grown crops (wheat, rice, oats, and rye)

Grass/herbaceous Rangeland, grassland (\<10%

cover trees, \<20% shrubs). This subdivision includes rangeland used for
hayland, including bluestems, mixed midgrasses and shortgrasses.

Rangeland, savanna (10 to 25% tree cover)

Rangeland, shrubby ( 20 to 50% shrub cover)

Rangeland, tundra

Pastureland, tame (fescues, bromegrass, timothy, and lespedeza)

Hayland (fescues, bromegrass, timothy, and alfalfa)

Marshland (grasses and grass-like plants)

Other plants.

Tree cover Crop trees (apples, pecans, date palms, citrus, ornamental
nursery stock, and Christmas trees)

Conifers (spruce, pines, and Douglas fir)

Hardwoods (oak, hickory, elm, and aspen)

Intermixed conifers and hardwoods (oak-pine mix)

Tropical (mangrove and royal palms)

Swamp (trees and shrubs)

Other

Shrub cover Crop shrubs (filberts, blueberry, and ornamentals used as
nursery stock)

Crop vines (grapes, blackberries, and raspberries)

Native shrubs (creosote bush, shrub live oak, sagebrush, and mesquite,
includes rangeland with \>50% shrub cover)

Other

Barren Rock

Sand and gravel

Culturally induced (saline seeps, mines, quarries, and areas of
oil-waste)

Permanent snow and ice

Other (salt flats, slickspots, mud flats, and badlands)

Artificial cover Rural transportation (highways, and railroads.)

Urban and built-up (cities, towns, farmsteads, and industrial sites)

Water

**(e) Entries.** Enter the applicable Level 1 class for each map unit
component. Enter the applicable Level 2 class as appropriate.

## Exhibit 622-1 Prime and Unique Farmlands.

*The Code of Federal Regulations for title 7 part 657 are maintained in
the following web site. http://www.gpoaccess.gov/cfr/index.htmlThe
January 1, 1999 version was amended on September 25, 2000 with the
changes published in the Federal Register as follows:*

*\[Federal Register: September 25, 2000 (Volume 65, Number 186)\]*

*\[Rules and Regulations\]*

*\[Page 57537-57538\]*

*From the Federal Register Online via GPO Access
\[wais.access.gpo.gov\]*

*\[DOCID:fr25se00-2\]*

*\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--*

*DEPARTMENT OF AGRICULTURE*

*Natural Resources Conservation Service*

*7 CFR Part 657*

*Prime and Unique Farmlands\--Important Farmlands Inventory*

*AGENCY: Natural Resources Conservation Service, Agriculture.*

*ACTION: Final rule.*

*\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--*

*SUMMARY: The Natural Resources Conservation Service is amending its*

*regulations regarding responsibilities for conducting important*

*farmland inventories under the Federal Crop Insurance Reform and*

*Department of Agriculture Reorganization Act of 1994 (the 1994 Act).*

*The amendments reflect changes to individual and organizational titles*

*made since the regulations were originally drafted.*

*EFFECTIVE DATE: September 25, 2000.*

*FOR FURTHER INFORMATION CONTACT: Horace Smith, Division Director, Soil*

*Survey Division, Natural Resources Conservation Service, P.O. Box
2890,*

*Washington, D.C. 20013; 202-720-1820.*

*SUPPLEMENTARY INFORMATION: This final rule makes corrections to*

*nomenclature in the regulations for conducting important farmland*

*inventories (7 CFR*

*\[\[Page 57538\]\]*

*Part 657, Subpart A.) Since the implementing legislation was passed,*

*the names of the offices and titles of officials charged with*

*conducting important farmland inventories have changed. This amendment*

*reflects those changes. In addition, this rule amends the authority*

*citation to clarify the list of statutory authorities for the*

*inventories.*

*These rules are not expected to have significant economic impact*

*under the criteria of the Regulatory Flexibility Act. They will not*

*impose information collection requirements under the provisions of the*

*Paperwork Reduction Act of 1980, 44 U.S.C. Chapter 35.*

*List of Subjects in 7 CFR Part 657*

*Farmlands.*

*For the reasons set forth above, Subpart A, Part 657 of Chapter VI*

*of Title 7 of the Code of Federal Regulations is amended as follows:*

*PART 657\--PRIME AND UNIQUE FARMLAND*

*Subpart A\--Important Farmlands Inventory*

*1. The authority citation for Subpart A, Part 657 is revised to*

*read as follows:*

*Authority: 7 U.S.C. 1010a; 16 U.S.C. 590a-590f; 42 U.S.C. 3271-*

*3274.*

*Sec. 657.4 \[Amended\]*

*2. Section 657.4(a)(3)(iii) is amended by revising \`\`NRCS Technical*

*Service Centers (TSC\'s). (See 7 600.3, 600.6)\'\' to read \`\`National
Soil*

*Survey Center. (see 7 CFR 600.2(c), 600.6)\'\'.*

*3. Section 657.4(a)(4) is amended by revising the first sentence to*

*read as follows: \`\`Coordinate soil mapping units that qualify as
prime*

*farmlands with adjacent States, including Major Land Resource Area*

*Offices (see 7 CFR 600.4, 600.7) responsible for the soil series.\'\'*

*4. Section 657.4(a)(6) is amended by revising \`\`Administrator\'\' to*

*read \`\`Chief\'\'.*

*5. Section 657.4(b) is amended by revising the heading and the*

*first sentence to read as follows: \`\`National Soil Survey Center.
The*

*National Soil Survey Center is to provide requested technical*

*assistance to State Conservationists and Major Land Resource Area*

*Offices in inventorying prime and unique farmlands (see 7 CFR*

*600.2(c)(1), 600.4, 600.7).\'\'*

*6. Section 657.4(c) is amended by revising \`\`Assistant*

*Administrator for Field Services (See 7 CFR 600.2)\'\' to read
\`\`Deputy*

*Chief for Soil Survey and Resource Assessment (see 7 CFR*

*600.2(b)(3))\'\'.*

*Signed in Washington, D.C. on September 14, 2000.*

*Pearlie S. Reed,*

*Chief.*

*\[FR Doc. 00-24525 Filed 9-22-00; 8:45 am\]*

*BILLING CODE 3410-16-P*

*Title 7\--Agriculture*

*CHAPTER VI\--NATURAL RESOURCES CONSERVATION SERVICE,*

*DEPARTMENT OF AGRICULTURE*

*PART 657\--PRIME AND UNIQUE FARMLANDS*

*\[Code of Federal Regulations\]*

*\[Title 7, Volume 6, Parts 400 to 699\]*

*\[Revised as of January 1, 1999\](Amended September 25, 2000)*

*From the U.S. Government Printing Office via GPO Access*

*\[CITE: 7CFR657.1; 7CFR657.2; 7CFR657.3; 7CFR657.4; 7CFR657.5.\]*

*\[beginning Page 699\]*

*TITLE 7\--AGRICULTURE*

*DEPARTMENT OF AGRICULTURE*

*PART 657\--PRIME AND UNIQUE FARMLANDS\--Table of Contents*

*Subpart A\--Important Farmlands Inventory*

*Section 657.1 Purpose.*

*Section 657.2 Policy.*

*Section 657.3 Applicability.*

*Section 657.4 NRCS Responsibilities.*

*Section 657.5 Identification of important farmlands.*

*Sec. 657.1 Purpose.*

*NRCS is concerned about any action that tends to impair the*

*productive capacity of American agriculture. The Nation needs to know*

*the extent and location of the best land for producing food, feed,
fiber*

*forage, and oilseed crops. In addition to prime and unique farmlands,*

*farmlands that are of statewide and local importance for producing
these*

*crops also need to be identified.*

*Sec. 657.2 Policy.*

*It is NRCS policy to make and keep current an inventory of the prime*

*farmland and unique farmland of the Nation. This inventory is to be*

*carried out in cooperation with other interested agencies at the*

*National, State, and local levels of government. The objective of the*

*inventory is to identify the extent and location of important rural*

*lands needed to produce food, feed, fiber, forage, and oilseed crops.*

*Sec. 657.3 Applicability.*

*Inventories made under this memorandum do not constitute a*

*designation of any land area to a specific land use. Such designations*

*are the responsibility of appropriate local and State officials.*

***Sec. 657.4 NRCS responsibilities.***

***(a) State Conservationist. Each NRCS State Conservationist is to:***

***(1) Provide leadership for inventories of important farmlands for***

***the State, county, or other subdivision of the State. Each is to
work***

***with appropriate agencies of State government and others to
establish***

***priorities for making these inventories.***

***(2) Identify the soil mapping units within the State that qualify
as***

***prime. In doing this, State Conservationists, in consultation with
the***

***cooperators of the National Cooperative Soil Survey, have the***

***flexibility to make local deviation from the permeability criterion
or***

***to be more restrictive for other specific criteria in order to
assure***

***the most accurate identification of prime farmlands for a State. Each
is***

***to invite representatives of the Governor\'s office, agencies of
the***

***State government, and others to identify farmlands of statewide***

***importance and unique farmlands that are to be inventoried within
the***

***framework of this memorandum.***

***(3) Prepare a statewide list of:***

***(i) Soil mapping units that meet the criteria for prime farmland;***

***(ii) Soil mapping units that are farmlands of statewide importance***

***if the criteria used were based on soil information; and***

***(iii) Specific high-value food and fiber crops that are grown and,***

***when combined with other favorable factors, qualify lands to meet
the***

***criteria for unique farmlands. Copies are to be furnished to NRCS
Field***

***Offices and to** National Soil Survey Center. (see 7 CFR 600.2(c),
600.6)*

***(4)** Coordinate soil mapping units that qualify as prime*

*farmlands with adjacent States, including Major Land Resource Area*

*Offices (see 7 CFR 600.4, 600.7) responsible for the soil series.*

***Since farmlands of statewide importance and unique farmlands are***

***designated by others at the State level, the soil mapping units
and***

***areas identified need not be coordinated among States.***

***(5) Instruct NRCS District Conservationists to arrange local
review***

***of lands identified as prime, unique, and additional farmlands of***

***statewide importance by Conservation Districts and representatives
of***

***local agencies. This review is to determine if additional farmland***

***should be identified to meet local decision making needs.***

***(6) Make and publish each important farmland inventory on a base
map***

***of national map accuracy at an intermediate scale of 1:50,000 or***

***1:100,000. State Conservationists who need base maps of other scales
are***

***to submit their requests with justification to the** Chief **for ***

***consideration.***

***(b)** National Soil Survey Center. The National Soil Survey Center
is*

*to provide requested technical assistance to State Conservationists*

*and Major Land Resource Area Offices in inventorying prime and unique*

*farmlands (see 7 CFR 600.2(c)(1), 600.4, 600.7). **This includes
reviewing ***

***statewide lists of soil mapping units that meet the criteria for
prime***

***farmlands and resolving coordination problems that may occur among***

***States for specific soil series or soil mapping units.***

***(c) National Office. The** Deputy Chief for Soil Survey and Resource*

*Assessment (see 7 CFR 600.2(b)(3)) **is to provide national leadership
in ***

***preparing guidelines for inventorying prime farmlands and for
national***

***statistics and reports of prime farmlands.***

***Sec. 657.5 Identification of important farmlands.***

***(a) Prime farmlands\--(1) General. Prime farmland is land that has***

***the best combination of physical and chemical characteristics for***

***producing food, feed, forage, fiber, and oilseed crops, and is
also***

***available for these uses (the land could be cropland, pastureland,***

***rangeland, forest land, or other land, but not urban built-up land
or***

***water). It has the soil quality, growing season, and moisture
supply***

***needed to economically produce sustained high yields of crops when***

***treated and managed, including water management, according to
acceptable***

***farming methods. In general, prime farmlands have an adequate and***

***dependable water supply from precipitation or irrigation, a
favorable***

***temperature and growing season, acceptable acidity or alkalinity,***

***acceptable salt and sodium content, and few or no rocks. They are***

***permeable to water and air. Prime farmlands are not excessively
erodible***

***or saturated with water for a long period of time, and they either
do***

***not flood frequently or are protected from flooding. Examples of
soils***

***that qualify as prime farmland are Palouse silt loam, 0 to 7
percent***

***slopes; Brookston silty clay loam, drained; and Tama silty clay loam,
0***

***to 5 percent slopes.***

***(2) Specific criteria. Prime farmlands meet all the following***

***criteria: Terms used in this section are defined in USDA
publications:***

***\`\`Soil Taxonomy, Agriculture Handbook 436\'\'; \`\`Soil Survey
Manual,***

***Agriculture Handbook 18\'\'; \`\`Rainfall-erosion Losses From
Cropland,***

***Agriculture Handbook 282\'\'; \`\`Wind Erosion Forces in the United
States***

***and Their Use in Predicting Soil Loss, Agriculture Handbook 346\'\';
and***

***\`\`Saline and Alkali Soils, Agriculture Handbook 60.\'\'***

***(i) The soils have:***

***(A) Aquic, udic, ustic, or xeric moisture regimes and sufficient***

***available water capacity within a depth of 40 inches (1 meter), or
in***

***the root zone (root zone is the part of the soil that is penetrated
or***

***can be penetrated by plant roots) if the root zone is less than 40***

***inches deep, to produce the commonly grown cultivated crops
(cultivated***

***crops include, but are not limited to, grain, forage, fiber,
oilseed,***

***sugar beets, sugarcane, vegetables, tobacco, orchard, vineyard, and
bush***

***fruit crops) adapted to the region in 7 or more years out of 10;
or***

***(B) Xeric or ustic moisture regimes in which the available water***

***capacity is limited, but the area has a developed irrigation water***

***supply that is dependable (a dependable water supply is one in
which***

***enough water is available for irrigation in 8 out of 10 years for
the***

***crops commonly grown) and of adequate quality; or,***

***(C) Aridic or torric moisture regimes and the area has a developed***

***irrigation water supply that is dependable and of adequate quality;
and,***

***(ii) The soils have a temperature regime that is frigid, mesic,***

***thermic, or hyperthermic (pergelic and cryic regimes are
excluded).***

***These are soils that, at a depth of 20 inches (50 cm), have a mean***

***annual temperature higher than 32 deg. F (0 deg. C). In addition,
the***

***mean summer temperature at this depth in soils with an O horizon
is***

***higher than 47 deg. F (8 deg. C); in soils that have no O horizon,
the***

***mean summer temperature is higher than 59 deg. F (15 deg. C); and,***

***(iii) The soils have a pH between 4.5 and 8.4 in all horizons
within***

***a depth of 40 inches (1 meter) or in the root zone if the root zone
is***

***less than 40 inches deep; and,***

***(iv) The soils either have no water table or have a water table
that***

***is maintained at a sufficient depth during the cropping season to
allow***

***cultivated crops common to the area to be grown; and,***

***(v) The soils can be managed so that, in all horizons within a
depth***

***of 40 inches (1 meter) or in the root zone if the root zone is less
than***

***40 inches deep, during part of each year the conductivity of the***

***saturation extract is less than 4 mmhos/cm and the exchangeable
sodium***

***percentage (ESP) is less than 15; and,***

***(vi) The soils are not flooded frequently during the growing
season***

***(less often than once in 2 years); and,***

***(vii) The product of K (erodibility factor) x percent slope is
less***

***than 2.0, and the product of I (soils erodibility) x C (climatic***

***factor) does not exceed 60; and***

***(viii) The soils have a permeability rate of at least 0.06 inch***

***(0.15 cm) per hour in the upper 20 inches (50 cm) and the mean
annual***

***soil temperature at a depth of 20 inches (50 cm) is less than 59 deg.
F***

***(15 deg. C); the permeability rate is not a limiting factor if the
mean***

***annual soil temperature is 59 deg. F (15 deg. C) or higher; and,***

***(ix) Less than 10 percent of the surface layer (upper 6 inches) in***

***these soils consists of rock fragments coarser than 3 inches (7.6
cm).***

***(b) Unique farmland\--(1) General. Unique farmland is land other
than***

***prime farmland that is used for the production of specific high
value***

***food and fiber crops. It has the special combination of soil
quality,***

***location, growing season, and moisture supply needed to
economically***

***produce sustained high quality and/or high yields of a specific
crop***

***when treated and managed according to acceptable farming methods.***

***Examples of such crops are citrus, tree nuts, olives, cranberries,***

***fruit, and vegetables.***

***(2) Specific characteristics of unique farmland. (i) Is used for a***

***specific high-value food or fiber crop; (ii) Has a moisture supply
that***

***is adequate for the specific crop; the supply is from stored
moisture,***

***precipitation, or a developed-irrigation system; (iii) Combines***

***favorable factors of soil quality, growing season, temperature,***

***humidity, air drainage, elevation, aspect, or other conditions, such
a***

***nearness to market, that favor the growth of a specific food or
fiber***

***crop.***

***(c) Additional farmland of statewide importance. This is land, in***

***addition to prime and unique farmlands, that is of statewide
importance***

***for the production of food, feed, fiber, forage, and oil seed
crops.***

***Criteria for defining and delineating this land are to be determined
by***

***the appropriate State agency or agencies. Generally, additional***

***farmlands of statewide importance include those that are nearly
prime***

***farmland and that economically produce high yields of crops when
treated***

***and managed according to acceptable farming methods. Some may produce
as***

***high a yield as prime farmlands if conditions are favorable. In
some***

***States, additonal farmlands of statewide importance may include
tracts***

***of land that have been designated for agriculture by State law.***

***(d) Additional farmland of local importance. In some local areas***

***there is concern for certain additional farmlands for the production
of***

***food, feed, fiber, forage, and oilseed crops, even though these lands
are***

***not identified as having national or statewide importance. Where
appropriate,***

***these lands are to be identified by the local agency or agencies
concerned.***

***In places, additional farmlands of local importance may include
tracts***

***of land that have been designated for agriculture by local
ordinance.***

## Exhibit 622-2 Land Capability Classification (Agriculture Handbook 210)

**LAND-CAPABILITY**

**CLASSIFICATION**

Agriculture Handbook No. 210

SOIL CONSERVATION SERVICE

U.S. DEPARTMENT OF AGRICULTURE

**FOREWORD**

Since soil surveys are based on all of the characteristics of soils that
influence their use and management, interpretations are needed for each
of the many uses. Among these interpretations the grouping of soils into
capability units, subclasses, and classes is one of the most important.
This grouping serves as an introduction of the soil map to farmers and
other land users developing conservation plans.

As we have gained experience in this grouping, the definitions of the
categories have improved. It is the purpose of this publication to set
forth these definitions. In using the capability classification, the
reader must continually recall that it is an interpretation. Like other
interpretations, it depends on the probable interactions between the
kind of soil and the alternative systems of management. Our management
systems are continually changing. Economic conditions change. Our
knowledge grows. Land users are continually being offered new things,
such as new machines, chemicals, and plant varieties.

The new technology applies unevenly to the various kinds of soil. Thus
the grouping of any one kind of soil does not stay the same with changes
in technology. That is, new combinations of practices increase the
productivity of some soils more than others, so some are going up in the
scale whereas others are going down, relatively. Some of our most
productive soils of today were considered poorly suited to crops a few
years ago. On the other hand, some other soils that were once regarded
as good for cropping are now being used more productively for growing
pulpwood. These facts in no way suggest that we should not make
interpretations. In fact, they become increasingly important as
technology grows. But these facts do mean that soils need to be
reinterpreted and regrouped after significant changes in economic
conditions and technology.

Besides the capability classification explained in this publication,
other important interpretations are made of soil surveys. Examples
include groupings of soils according to crop-yield predictions, woodland
suitability, range potentiality, wildlife habitat, suitability for
special crops, and engineering behavior. Many other kinds of special
groupings are used to help meet local needs.

CHARLES E. KELLOGG

Assistant Administrator for Soil Survey

Soil Conservation Service

**CONTENTS**

Assumptions 3

Capability classes 6

Land suited to cultivation and other uses 6

Land limited in use \-- generally not suited to cultivation 9

Capability subclasses 11

Capability units 12

Other kinds of soil groupings 13

Criteria for placing soils in capability classes 14

Arid and semiarid stony, wet, saline-sodic, and overflow soils 15

Climatic limitations 16

Wetness limitations 16

Toxic salts 17

Slope and hazard of erosion 18

Soil depth 19

Previous erosion 19

Available moisture holding capacity 19

Glossary 20

**Issued September 1961**

**Approved for reprinting January 1973**

**LAND-CAPABILITY\
CLASSIFICATION**

By A.A. Klingebiel and P.H. Montgomery,

*Soil Scientists, Soil Conservation Service*

The standard soil-survey map shows the different kinds of soil that are
significant and their location in relation to other features of the
landscape. These maps are intended to meet the needs of users with
widely different problems and, therefore, contain considerable detail to
show important basic soil differences.

The information on the soil map must be explained in a way that has
meaning to the user. These explanations are called interpretations. Soil
maps can be interpreted by (1) the individual kinds of soil on the map,
and (2) the grouping of soils that behave similarly in responses to
management and treatment. Because there are many kinds of soil, there
are many individual soil interpretations. Such interpretations, however,
provide the user with all the information that can be obtained from a
soil map. Many users of soil maps want more general information than
that of the individual soil-mapping unit. Soils are grouped in different
ways according to the specific needs of the map user. The kinds of soil
grouped and the variation permitted within each group differ according
to the use to be made of the grouping.

The capability classification is one of a number of interpretive
groupings made primarily for agricultural purposes. As with all
interpretive groupings, the capability classification begins with the
individual soil-mapping units, which are building stones of the system
(table 1). In this classification, the arable soils are grouped
according to their potentialities and limitations for sustained
production of the common cultivated crops that do not require
specialized site conditioning or site treatment. Nonarable soils (soils
unsuitable for longtime sustained use for cultivated crops) are grouped
according to their potentialities and limitations for the production of
permanent vegetation and according to their risks of soil damage if
mismanaged.

The individual mapping units on soil maps show the location and extent
of the different kinds of soil. One can make the greatest number of
precise statements and predictions about the use and management of the
individual mapping units shown on the soil map. The capability grouping
of soils is designed (1) to help landowners and others use and interpret
the soil maps, (2) to introduce users to the detail of the soil map
itself, and (3) to make possible broad generalizations based on soil
potentialities, limitations in use, and management problems.

The capability classification provides three major categories of soil
groupings:\
(1) capability unit, (2) capability subclass, and (3) capability class.

**TABLE 1. Relationship of soil-mapping unit to capability
classification.**

+-----------------------------------+-----------------------------------+
| > **Soil-mapping unit**           | > **Capability unit**             |
| >                                 | >                                 |
| > A soil mapping unit is a        | > A capability unit is a grouping |
| > portion of the landscape that   | > of one or more individual soil  |
| > has similar characteristics and | > mapping units having similar    |
| > qualities and whose limits are  | > potentials and continuing       |
| > fixed by precise definitions.   | > limitations or hazards. The     |
| > Within the cartographic         | > soils in a capability unit are  |
| > limitations and considering the | > sufficiently uniform to (a)     |
| > purpose for which the map is    | > produce similar kinds of        |
| > made, the soil mapping unit is  | > cultivated crops and pasture    |
| > the unit about which the        | > plants with similar management  |
| > greatest number of precise      | > practices, (b) require similar  |
| > statements and predictions can  | > conservation treatment and      |
| > be made.                        | > management under the same kind  |
| >                                 | > and condition of vegetative     |
| > The soil mapping units provide  | > cover, (c) have comparable      |
| > the most detailed soils         | > potential productivity.         |
| > information. The basic mapping  | >                                 |
| > units are the basis for all     | > The capability unit condenses   |
| > interpretive groupings of       | > and simplifies soils            |
| > soils. They furnish the         | > information for planning        |
| > information needed for          | > individual tracts of land,      |
| > developing capability units,    | > field by field. Capability      |
| > forest site groupings, crop     | > units with the class and        |
| > suitability groupings, range    | > subclass furnish information    |
| > site groupings, engineering     | > about the degree of limitation, |
| > groupings, and other            | > kind of conservation problems   |
| > interpretive groupings. The     | > and the management practices    |
| > most specific management        | > needed.                         |
| > practices and estimated yields  |                                   |
| > are related to the individual   |                                   |
| > mapping unit.                   |                                   |
+-----------------------------------+-----------------------------------+
| > **Capability subclass**         | > **Capability class**            |
| >                                 | >                                 |
| > Subclasses are groups of        | > Capability classes are groups   |
| > capability units which have the | > of capability subclasses or     |
| > same major conservation         | > capability units that have the  |
| > problem, such as:               | > same relative degree of hazard  |
| >                                 | > or limitation. The risks of     |
| > e - Erosion and runoff          | > soil damage or limitation in    |
| >                                 | > use become progressively        |
| > w - Excess water                | > greater from class I to class   |
| >                                 | > VIII.                           |
| > s - Root-zone limitations       | >                                 |
| >                                 | > The capability classes are      |
| > c - Climatic limitations        | > useful as a means of            |
| >                                 | > introducing the map user to the |
| > The capability subclass         | > more detailed information on    |
| > provides information as to the  | > the soil map. The classes show  |
| > kind of conservation problem or | > the location, amount, and       |
| > limitations involved. The class | > general suitability of the      |
| > and subclass together provide   | > soils for agricultural use.     |
| > the map user information about  | > Only information concerning     |
| > both the degree of limitation   | > general agricultural            |
| > and kind of problem involved    | > limitations in soil use are     |
| > for broad program planning,     | > obtained at the capability      |
| > conservation need studies, and  | > class level.                    |
| > similar purposes.               |                                   |
+-----------------------------------+-----------------------------------+

The first category, capability unit, is a grouping of soils that have
about the same responses to systems of management of common cultivated
crops and pasture plants. Soils in any one capability unit are adapted
to the same kinds of common cultivated and pasture plants and require
similar alternative systems of management for these crops. Longtime
estimated yields of adapted crops for individual soils within the unit
under comparable management do not vary more than about 25 percent.[^1]

The second category, the subclass, is a grouping of capability units
having similar kinds of limitations and hazards. Four general kinds of
limitations or hazards are recognized: (1) erosion hazard, (2) wetness,
(3) rooting-zone limitations, and (4) climate.

The third and broadest category in the capability classification places
all the soils in eight capability classes. The risks of soil damage or
limitations in use become progressively greater from class I to class
VIII. Soils in the first four classes under good management are capable
of producing adapted plants, such as forest trees or range plants, and
the common cultivated field crops[^2] and pasture plants. Soils in
classes V, VI, and VII are suited to the use of adapted native plants.
Some soils in classes V and VI are also capable of producing specialized
crops, such as certain fruits and ornamentals, and even field and
vegetable crops under highly intensive management involving elaborate
practices for soil and water conservation.[^3] Soils in class VIII do
not return on-site benefits for inputs of management for crops, grasses,
or trees without major reclamation.

The grouping of soils into capability units, subclasses, and classes is
done primarily on the basis of their capability to produce common
cultivated crops and pasture plants without deterioration over a long
period of time. To express suitability of the soils for range and
woodland use, the soil-mapping units are grouped into range sites and
woodland-suitability groups.

**ASSUMPTIONS**

In assigning soils to the various capability groupings a number of
assumptions are made. Some understanding of these assumptions is
necessary if the soils are to be grouped consistently in the capability
classification and if the groupings are to be used properly. They are:

1.  A taxonomic (or natural) soil classification is based directly on
    soil characteristics. The capability classification (unit, subclass,
    and class) is an interpretive classification based on the effects of
    combinations of climate and permanent soil characteristics on risks
    of soil damage, limitations in use, productive capacity, type of
    clay minerals, and the many other similar features are considered
    permanent soil qualities and characteristics. Shrubs, trees, or
    stumps are not considered permanent characteristics.

2.  The soils within a capability class are similar only with respect to
    degree of limitations in soil use for agricultural purposes or
    hazard to the soil when it is so used. Each class includes many
    different kinds of soil, and many of the soils within any one class
    require unlike management and treatment. Valid generalizations about
    suitable kinds of crops or other management needs cannot be made at
    the class level.

3.  A favorable ratio of output to input[^4] is one of several criteria
    used for placing any soil in a class suitable for cultivated crop,
    grazing, or woodland use, but no further relation is assumed or
    implied between classes and output-input ratios. The capability
    classification is not a productivity rating for specific crops.
    Yield estimates are developed for specific kinds of soils and are
    included in soil handbooks and soil-survey reports.

4.  A moderately high level of management is assumed \-- one that is
    practical and within the ability of a majority of the farmers and
    ranchers. The level of management is that commonly used by the
    "reasonable" men of the community. The capability classification is
    not, however, a grouping of soils according to the most profitable
    use to be made of the land. For example, many soils in class III or
    IV, defined as suitable for several uses including cultivation, may
    be more profitably used for grasses or trees than for cultivated
    crops.

5.  Capability classes I through IV are distinguished from each other by
    a summation of the degree of limitations or risks of soil damage
    that affect their management requirements for longtime sustained use
    for cultivated crops. Nevertheless, differences in kinds of
    management or yields of perennial vegetation may be greater between
    some pairs of soils within one class than between some pairs of
    soils from different classes. The capability class is not determined
    by the kind of practices recommended. For example, class II, III, or
    IV may or may not require the same kind of practices when used for
    cultivated crops, and classes I through VII may or may not require
    the same kind of pasture, range, or woodland practices.

6.  Presence of water on the surface or excess water in the soil; lack
    of water for adequate crop production; presence of stones; presence
    of soluble salts or exchangeable sodium, or both; or hazard of
    overflow are not considered permanent limitations to use where the
    removal of these limitations is feasible.[^5]

7.  Soils considered feasible for improvement by draining, by
    irrigating, by removing stones, by removing salts or exchangeable
    sodium, or by protecting from overflow are classified according to
    their continuing limitations in use, or the risks of soil damage, or
    both, after the improvements have been installed. Differences in
    initial costs of the systems installed on individual tracts of land
    do not influence the classification. The fact that certain wet soils
    are in classes II, III, and IV does not imply that they should be
    drained. But it does indicate the degree of their continuing
    limitation in use or risk of soil damage, or both, if adequately
    drained. Where it is considered not feasible to improve soils by
    drainage, irrigation, stone removal, removal of excess salts or
    exchangeable sodium, or both, or to protect them from overflow, they
    are classified according to present limitations in use.

8.  Soils already drained or irrigated are grouped according to the
    continuing soil and climatic limitations and risks that affect their
    use under the present systems or feasible improvements in them.

9.  The capability classification of the soils in an area may be changed
    when major reclamation projects are installed that permanently
    change the limitations in use or reduce the hazards or risks of soil
    or crop damage for long periods of time. Examples include
    establishing major drainage facilities, building levees or
    flood-retarding structures, providing water for irrigation, removing
    stones, or large-scale grading of gullied land. (Minor dams,
    terraces, or field conservation measures subject to change in their
    effectiveness in a short time are not included.)

10. Capability groupings are subject to change as new information about
    the behavior and responses of the soils becomes available.

11. Distance to market, kinds of roads, size and shape of the soil
    areas, locations within fields, skill or resources of individual
    operators, and other characteristics of land-ownership patterns are
    not criteria for capability groupings.

12. Soils with such physical limitations that common field crops can be
    cultivated and harvested only by hand are not placed in classes I,
    II, III, and IV. Some of these soils need drainage or stone removal,
    or both, before some kinds of machinery can be used. This does not
    imply that mechanical equipment cannot be used on some soils in
    capability classes V, VI, and VII.

13. Soils suited to cultivation are also suited to other uses such as
    pasture, range, forest, and wildlife. Some not suited to cultivation
    are suited to pasture, range, forest, or wildlife; others are suited
    only to pasture or range and wildlife; others only to forest and
    wildlife; and a few suited only to wildlife, recreation, and
    water-yielding uses. Groupings of soils for pasture, range,
    wildlife, or woodland may include soils from more than one
    capability class. Thus, to interpret soils for these uses, a
    grouping different from the capability classification is often
    necessary.

14. Research data, recorded observations, and experience are used as the
    bases for placing soils in capability units, subclasses, and
    classes. In areas where data on response of soils to management are
    lacking, soils are placed in capability groups by interpretation of
    soil characteristics and qualities in accord with the general
    principles about use and managemcnt developed for similar soils
    elsewhere.

**CAPABILITY CLASSES**

**Land Suited to Cultivation and Other Uses**

**Class I \-- Soils in class I have few limitations that restrict their
use.**

Soils in this class are suited to a wide range of plants and may be used
safely for cultivated crops, pasture, range, woodland, and wildlife. The
soils are nearly level[^6] and erosion hazard (wind or water) is low.
They are deep, generally well drained, and easily worked. They hold
water well and are either fairly well supplied with plant nutrients or
highly responsive to inputs of fertilizer.

The soils in class I are not subject to damaging overflow. They are
productive and suited to intensive cropping. The local climate must be
favorable for growing many of the common field crops.

In irrigated areas, soils may be placed in class I if the limitation of
the arid climate has been removed by relatively permanent irrigation
works. Such irrigated soils (or soils potentially useful under
irrigation) are nearly level, have deep rooting zones, have favorable
permeability and water-holding capacity, and are easily maintained in
good tilth. Some of the soils may require initial conditioning including
leveling to the desired grade, leaching of a slight accumulation of
soluble salts, or lowering of the seasonal water table. Where
limitations due to salts, water table, overflow, or erosion are likely
to recur, the soils are regarded as subject to permanent natural
limitations and are not included in class I.

Soils that are wet and have slowly permeable subsoils are not placed in
class I. Some kinds of soil in class I may be drained as an improvement
measure for increased production and ease of operation.

Soils in class I that are used for crops need ordinary management
practices to maintain productivity \-- both soil fertility and soil
structure. Such practices may include the use of one or more of the
following: fertilizers and lime, cover and green-manure crops,
conservation of crop residues and animal manures, and sequences of
adapted crops.

Class II \-- Soils in class II have some limitations that reduce the
choice of plants or require moderate conservation practices.

Soils in class II require careful soil management, including
conservation practices, to prevent deterioration or to improve air and
water relations when the soils are cultivated. The limitations are few
and the practices are easy to apply. The soils may be used for
cultivated crops, pasture, range, woodland, or wildlife food and cover.

Limitations of soils in class II may include singly or in combination
the effects of\
(1) gentle slopes, (2) moderate susceptibility to wind or water erosion
or moderate adverse effects of past erosion, (3) less than ideal soil
depth, (4) somewhat unfavorable soil structure and workability, (5)
slight to moderate salinity or sodium easily corrected but likely to
recur, (6) occasional damaging overflow, (7) wetness correctable by
drainage but existing permanently as a moderate limitation, and (8)
slight climatic limitations on soil use and management.

The soils in this class provide the farm operator less latitude in the
choice of either crops or management practices than soils in class I.
They may also require special soil-conserving cropping systems, soil
conservation practices, water-control devices, or tillage methods when
used for cultivated crops. For example, deep soils of this class with
gentle slopes subject to moderate erosion when cultivated may need one
of the following practices or some combination of two or more:
terracing, stripcropping, contour tillage, crop rotations that include
grasses and legumes, vegetated water disposal areas, cover or
green-manure crops, stubble mulching, fertilizers, manure, and lime. The
exact combinations of practices vary from place to place, depending on
the characteristics of the soil, the local climate, and the farming
system.

Class III \-- Soils in class III have severe limitations that reduce the
choice of plants or require special conservation practices, or both.

Soils in class III have more restrictions than those in class II and,
when used for cultivated crops, the conservation practices are usually
more difficult to apply and to maintain. They may be used for cultivated
crops, pasture, woodland, range, or wildlife food and cover.

Limitations of soils in class III restrict the amount of clean
cultivation; timing of planting, tillage, and harvesting; choice of
crops; or some combination of these limitations. The limitations may
result from the effects of one or more of the following: (1) moderately
steep slopes; (2) high susceptibility to water or wind erosion or severe
adverse effects of past erosion; (3) frequent overflow accompanied by
some crop damage; (4) very slow permeability of the subsoil; (5) wetness
or some continuing waterlogging after drainage; (6) shallow depths to
bedrock, hardpan, fragipan, or claypan that limit the rooting zone and
the water storage; (7) low moisture-holding capacity; (8) low fertility
not easily corrected; (9) moderate salinity or sodium; or (10) moderate
climatic limitations.

When cultivated, many of the wet, slowly permeable but nearly level
soils in\
class III require drainage and a cropping system that maintains or
improves the structure and tilth of the soil. To prevent puddling and to
improve permeability, it is commonly necessary to supply organic
material to such soils and to avoid working them when they are wet. In
some irrigated areas, part of the soils in class III have limited use
because of high water table, slow permeability, and the hazard of salt
or sodic accumulation. Each distinctive kind of soil in class III has
one or more alternative combination of use and practices required for
safe use, but the number of practical alternatives for average farmers
is less than that for soils in class II.

Class IV \-- Soils in class IV have very severe limitations that
restrict the choice of plants, require very careful management, or both.

The restrictions in use for soils in class IV are greater than those in
class III and the choice of plants is more limited. When these soils are
cultivated, more careful management is required and conservation
practices are more difficult to apply and maintain. Soils in class IV
may be used for crops, pasture, woodland, range, or wildlife food and
cover.

Soils in class IV may be well suited to only two or three of the common
crops or the harvest produced may be low in relation to inputs over a
long period of time. Use for cultivated crops is limited as a result of
the effects of one or more permanent features such as (1) steep slopes,
(2) severe susceptibility to water or wind erosion, (3) severe effects
of past erosion, (4) shallow soils, (5) low moisture-holding capacity,
(6) frequent overflows accompanied by severe crop damage, (7) excessive
wetness with continuing hazard of waterlogging after drainage, (8)
severe salinity or sodium, or (9) moderately adverse climate.

Many sloping soils in class IV in humid areas are suited to occasional
but not regular cultivation. Some of the poorly drained, nearly level
soils placed in class IV are not subject to erosion but are poorly
suited to inter-tilled crops because of the time required for the soil
to dry out in the spring and because of low productivity for cultivated
crops. Some soils in class IV are well suited to one or more of the
special crops, such as fruits and ornamental trees and shrubs, but this
suitability itself is not sufficient to place a soil in class IV.

In subhumid and semiarid areas, soils in class IV may produce good
yields of adapted cultivated crops during years of above average
rainfall; low yields during years of average rainfall; and failures
during years of below average rainfall. During the low rainfall years
the soil must be protected even though there can be little or no
expectancy of a marketable crop. Special treatments and practices to
prevent soil blowing, conserve moisture, and maintain soil productivity
are required. Sometimes crops must be planted or emergency tillage used
for the primary purpose of maintaining the soil during years of low
rainfall. These treatments must be applied more frequently or more
intensively than on soils in class III.

**Land Limited in Use \-- Generally Not Suited to Cultivation**[^7]

Class V \-- Soils in class V have little or no erosion hazard but have
other limitations impractical to remove that limit their use largely to
pasture, range, woodland, or wildlife food and cover.

Soils in class V have limitations that restrict the kind of plants that
can be grown and that prevent normal tillage of cultivated crops. They
are nearly level but some are wet, are frequently overflowed by streams,
are stony, have climatic limitations, or have some combination of these
limitations. Examples of class V are: (1) soils of the bottom lands
subject to frequent overflow that prevents the normal production of
cultivated crops, (2) nearly level soils with a growing season that
prevents the normal production of cultivated crops, (3) level or nearly
level stony or rocky soils, and (4) ponded areas where drainage for
cultivated crops is not feasible but where soils are suitable for
grasses or trees. Because of these limitations, cultivation of the
common crops is not feasible but pastures can be improved and benefits
from proper management can be expected.

Class VI \-- Soils in class VI have severe limitations that make them
generally unsuited to cultivation and limit their use largely to pasture
or range, woodland, or wildlife food and cover.

Physical conditions of soils placed in class VI are such that it is
practical to apply range or pasture improvements, if needed, such as
seeding, liming, fertilizing, and water control with contour furrows,
drainage ditches, diversions, or water spreaders. Soils in class VI have
continuing limitations that cannot be corrected, such as (1) steep
slope, (2) severe erosion hazard, (3) effects of past erosion, (4)
stoniness, (5) shallow rooting zone, (6) excessive wetness or overflow,
(7) low moisture capacity, (8) salinity or sodium, or (9) severe
climate. Because of one or more of these limitations, these soils are
not generally suited to cultivated crops. But they may be used for
pasture, range, woodland, or wildlife cover or for some combination of
these.

Some soils in class VI can be safely used for the common crops provided
unusually intensive management is used. Some of the soils in this class
are also adapted to special crops such as sodded orchards, blueberries,
or the like, requiring soil conditions unlike those demanded by the
common crops. Depending upon soiI features and local climate, the soils
may be well or poorly suited to woodlands.

Class VII \-- Soils in class VII have very severe limitations that make
them unsuited to cultivation and that restrict their use largely to
grazing, woodland, or wildlife.

Physical conditions of soils in class VII are such that it is
impractical to apply such pasture or range improvements as seeding,
liming, fertilizing, and water control with contour furrows, ditches,
diversions, or water spreaders. Soil restrictions are more severe than
those in class VI because of one or more continuing limitations that
cannot be corrected, such as (1) very steep slopes, (2) erosion, (3)
shallow soil, (4) stones, (5) wet soil, (6) salts or sodium, (7)
unfavorable climate, or (8) other limitations that make them unsuited to
common cultivated crops. They can be used safely for grazing or woodland
or wildlife food and cover or for some combination of these under proper
management.

Depending upon the soil characteristics and local climate, soils in this
class may be well or poorly suited to woodland. They are not suited to
any of the common cultivated crops; in unusual instances, some soils in
this class may be used for special crops under unusual management
practices. Some areas of class VII may need seeding or planting to
protect the soil and to prevent damage to adjoining areas.

Class VIII \-\-- Soils and landforms in class VIII have limitations that
preclude their use for commercial plant production and restrict their
use to recreation, wildlife, or water supply or to esthetic purposes.

Soils and landforms in class VIII cannot be expected to return
significant on-site benefits from management for crops, grasses, or
trees, although benefits from wildlife use, watershed protection, or
recreation may be possible.

Limitations that cannot be corrected may result from the effects of one
or more of the following: (1) erosion or erosion hazard, (2) severe
climate, (3) wet soil, (4) stones, (5) low moisture capacity, and (6)
salinity or sodium.

Badlands, rock outcrop, sandy beaches, river wash, mine tailings, and
other nearly barren lands are included in class VIII. It may be
necessary to give protection and management for plant growth to soils
and landforms in class VIII in order to protect other more valuable
soils, to control water, or for wildlife or esthetic reasons.

**CAPABILITY SUBCLASSES**

Subclasses are groups of capability units within classes that have the
same kinds of dominant limitations for agricultural use as a result of
soil and climate. Some soils are subject to erosion if they are not
protected, while others are naturally wet and must be drained if crops
are to be grown. Some soils are shallow or droughty or have other soil
deficiencies. Still other soils occur in areas where climate limits
their use. The four kinds of limitations recognized at the subclass
level are: risks of erosion, designated by the symbol (e); wetness,
drainage, or overflow (w); rooting-zone limitations (s); and climatic
limitations (c). The subclass provides the map user information about
both the degree and kind of limitation. Capability class I has no
subclasses.

Subclass **(e) erosion** is made up of soils where the susceptibility to
erosion is the dominant problem or hazard in their use. Erosion
susceptibility and past erosion damage are the major soil factors for
placing soils in this subclass.

Subclass **(w) excess water** is made up of soils where excess water is
the dominant hazard or limitation in their use. Poor soil drainage,
wetness, high water table, and overflow are the criteria for determining
which soils belong in this subclass.

Subclass **(s) soil limitations within the rooting zone** includes, as
the name implies, soils that have such limitations as shallowness of
rooting zones, stones, low moisture-holding capacity, low fertility
difficult to correct, and salinity or sodium.

Subclass **(c) climatic limitation** is made up of soils where the
climate (temperature or lack of moisture) is the only major hazard or
limitation in their use.[^8]

Limitations imposed by erosion, excess water, shallow soils, stones, low
moisture-holding capacity, salinity, or sodium can be modified or
partially overcome and take precedence over climate in determining
subclasses. The dominant kind of limitation or hazard to the use of the
land determines the assignment of capability units to the (e), (w), and
(s) subclasses. Capability units that have no limitation other than
climate are assigned to the (c) subclass.

Where two kinds of limitations that can be modified or corrected are
essentially equal, the subclasses have the following priority: e, w, s.
For example, we need to group a few soils of humid areas that have both
an erosion hazard and an excess water hazard; with them the e takes
precedence over the w. In grouping soils having both an excess water
limitation and a rooting-zone limitation, the w takes precedence over
the s. In grouping soils of subhumid and semiarid areas that have both
an erosion hazard and a climatic limitation, the e takes precedence over
the c; and in grouping soils with both rooting-zone limitations and
climatic limitations, the s takes precedence over the c.

Where soils have two kinds of limitations, both can be indicated, if
needed, for local use; the dominant one is shown first. Where two kinds
of problems are shown for a soil group, the dominant one is used for
summarizing data by subclasses.

**CAPABILITY UNITS**

The capability units provide more specific and detailed information than
the subclass for application to specific fields on a farm or ranch. A
capability unit is a grouping of soils that are nearly alike in
suitability for plant growth and responses to the same kinds of soil
management. That is, a reasonably uniform set of alternatives can be
presented for the soil, water, and plant management of the soils in a
capability unit, not considering effects of past management that do not
have a more or less permanent effect on the soil. Where soils have been
so changed by management that permanent characteristics have been
altered, they are placed in different soil series. Soils grouped into
capability units respond in a similar way and require similar management
although they may have soil characteristics that put them in different
soil series.

Soils grouped into a capability unit should be sufficiently uniform in
the combinations of soil characteristics that influence their qualities
to have similar potentialities and continuing limitations or hazards.
Thus the soils in a capability unit should be sufficiently uniform to
(a) produce similar kinds of cultivated crops and pasture plants with
similar management practices, (b) require similar conservation treatment
and management under the same kind and condition of vegetative cover,
and (c) have comparable potential productivity. (Estimated average
yields under similar management systems should not vary more than about
25 percent among the kinds of soil included within the unit.)

**OTHER KINDS OF SOIL GROUPINGS**

Other kinds of interpretive soil groupings are necessary to meet
specific needs. Among these are groupings for range use, woodland use,
special crops, and engineering interpretation.

The range site is a grouping of soils with a potential for producing the
same kinds and amounts of native forage. The range site for rangeland is
comparable to the capability unit for cultivated land. The purpose of
such a grouping is to show the potential for range use and to provide
the basis for which the criteria for determining range condition can be
established. The soils grouped into a single range site may be expected
to produce similar longtime yields and respond similarly to alternative
systems of management and to such practices as seeding, pitting, and
water spreading.

Soils suitable for range but not for common cultivated crops may be
placed in capability classes V and VI if they are capable of returning
inputs from such management practices as seeding, fertilizing, or
irrigating; and in class VII if they are not. If these soils do not give
economic returns under any kind of management when used for cultivated
crops, pasture, woodland or range, they fall in class VIII.

Soil-woodland site index correlations are essential for interpreting the
potential wood production of the individual soil units that are mapped.
Woodland-site indices are commonly developed for individual kinds of
soils. Soil-mapping units can be placed in woodland groupings according
to site indices for adapted species and other responses and limitations
significant to woodland conservation. Such groupings do not necessarily
parallel those for capability units or range sites; however, in some
areas capability units may be grouped into range sites and
woodland-suitability groups.

Rice has soil requirements unlike those of the common cultivated crops
requiring well-aerated soils. Some fruits and ornamentals do not require
clean cultivation. Therefore, these crops are not given weight in the
capability grouping. Instead, special groupings of the soils for each of
these crops are made in the areas where they are significant.

With a good basic table of yields and practices, the soils can be placed
in any number of suitability groups. Commonly, five groups \-- unsuited,
fairly suited, moderately suited, well suited, and very well suited \--
are sufficient.

Kinds of soil shown on the soil map are also grouped according to need
for applying engineering measures including drainage, irrigation, land
leveling, land grading; determining suitability as subgrade for roads;
and constructing ponds and small dams. Such groupings may be unlike
those made for other purposes.

**CRITERIA FOR PLACING SOILS IN CAPABILITY CLASSES**

Soil and climatic limitations in relation to the use, management, and
productivity of soils are the bases for differentiating capability
classes. Classes are based on both degree and number of limitations
affecting kind of use, risks of soil damage if mismanaged, needs for
soil management, and risks of crop failure. To assist in making
capability groupings, specific criteria for placing soils in units,
subclasses, and classes are presented here. Because the effects of soil
characteristics and qualities vary widely with climate, these criteria
must be for broad soil areas that have similar climate.

Capability groupings are based on specific information when available
information about the responses of the individual kinds of soil to
management and the combined effect of climate and soil on the crops
grown. It comes from research findings, field trials, and experiences of
farmers and other agricultural workers. Among the more common kinds of
information obtained are soil and water losses, kinds and amounts of
plants that can be grown, weather conditions as they affect plants, and
the effect of different kinds and levels of management on plant
response. This information is studied along with laboratory data on soil
profiles. Careful analysis of this information proves useful not only in
determining the capability of these individual kinds of soil but also in
making predictions about the use and management of related kinds of
soil.

Basic yield estimates of the adapted crops under alternative, defined
systems of management are assembled in a table. Where data are few, the
estimates should be reasonable when tested against available farm
records and studies of the combinations of soil properties.

Where information on response of soils to management is lacking, the
estimates of yields and the grouping of soils into capability units,
subclasses, and classes are based on an evaluation of combinations of
the following:

1.  Ability of the soil to give plant response to use and management as
    evidenced by organic-matter content, ease of maintaining a supply of
    plant nutrients, percentage base saturation, cation-exchange
    capacity, kind of clay mineral, kind of parent material, available
    water holding capacity, response to added plant nutrients, or other
    soil characteristics and qualities.

2.  Texture and structure of the soil to the depth that influences the
    environment of roots and the movement of air and water.

3.  Susceptibility to erosion as influenced by kind of soil (and slope)
    and the effect of erosion on use and management.

4.  Continuous or periodic waterlogging in the soil caused by slow
    permeability of the underlying material, a high water table, or
    flooding.

5.  Depth of soil material to layers inhibiting root penetration.

6.  Salts toxic to plant growth.

7.  Physical obstacles such as rocks, deep gullies, etc.

8.  Climate (temperature and effective moisture).

This list is not intended to be complete. Although the soils of any area
may differ from one another in only a few dozen characteristics, none
can be taken for granted. Extreme deficiencies or excesses of trace
elements, for example, can be vital. Commonly, the underlying geological
strata are significant to water infiltration, water yield, and erosion
hazard.

Any unfavorable fixed or recurring soil or landscape features may limit
the safe and productive use of the soil. One unfavorable feature in the
soil may so limit its use that extensive treatment would be required.
Several minor unfavorable features collectively may become a major
problem and thus limit the use of the soil. The combined effect of these
in relation to the use, management, and productivity of soils is the
criterion for different capability units.

Some of the criteria used to differentiate between capability classes
are discussed on the following pages. The criteria and ranges in
characteristics suggested assume that the effects of other soil
characteristics and qualities are favorable and are not limiting factors
in placing soils in capability classes.

**Arid and Semiarid, Stony, Wet, Saline-Sodic, and Overflow Soils**

The capability-class designations assigned to soils subject to flooding,
poorly or imperfectly drained soils, stony soils, dry soils needing
supplemental water, and soils having excess soluble salts or
exchangeable sodium are made on the basis of continuing limitations and
hazards after removal of excess water, stones, salts, and exchangeable
sodium.

When assessing the capability class of any soil the feasibility of any
necessary land improvements must be considered. Feasible as used here
means (1) that the characteristics and qualities of the soil are such
that it is possible to remove the limitation, and (2) that over broad
areas it is within the realm of economic possibility to remove the
limitation. The capability designation of these areas is determined by
those practices that are practical now and in the immediate future.

The following kinds of soil are classified on the basis of their present
continuing limitations and hazards: (1) dry soils (arid and semiarid
areas) now irrigated, (2) soils from which stones have been removed, (3)
wet soils that have been drained, (4) soils from which excess quantities
of soluble salts or exchangeable sodium have been removed, and (5) soils
that have been protected from overflow.

The following kinds of soil are classified on the basis of their
continuing limitations and hazards as if the correctable limitations had
been removed or reduced: (1) dry soils not now irrigated but for which
irrigation is feasible and water is available, (2) stony soils for which
stone removal is feasible, (3) wet soils not now drained but for which
drainage is feasible, (4) soils that contain excess quantities of
soluble salts or exchangeable sodium feasible to remove, and (5) soils
subject to overflow but for which protection from overflow is feasible.
Where desirable or helpful, the present limitation due to wetness,
stoniness, etc., may be indicated.

The following kinds of soil are classified on the basis of their present
continuing limitations and hazards if the limitations cannot feasibly be
corrected or removed:\
(1) dry soils, (2) stony soils, (3) soils with excess quantities of
saline and sodic salts, (4) wet soils, or (5) soils subject to overflow.

**Climatic Limitations**

Climatic limitations (temperature and moisture) affect capability.
Extremely low temperatures and short growing seasons are limitations,
especially in the very northern part of continental United States and at
high altitudes.

Limited natural moisture supply affects capability in subhumid,
semiarid, and arid climates. As the classification in any locality is
derived in part from observed performance of crop plants, the effects of
the interaction of climate with soil characteristics must be considered.
In a subhumid climate, for example, certain sandy soils may be
classified as class VI or class VII, whereas soils with similar
water-holding capacity in a more humid climate are classified as class
III or IV. The moisture factor must be directly considered in the
classification in most semiarid and arid climates. The capability of
comparable soils decreases as effective rainfall decreases.

In an arid climate, the moisture from rain and snow is not enough to
support crops. Arid land can be classed as suited to cultivation (class
I, II, III, or IV) only if the moisture limitation is removed by
irrigation. Wherever the moisture limitation is removed in this way, the
soil is classified according to the effects of other permanent features
and hazards that limit its use and permanence, without losing sight of
the practical requirements of irrigation farming.

**Wetness Limitations**

Water on the soil or excess water in the soil presents a hazard to or
limits its use. Such water may be a result of poor soil drainage, high
water table, overflow (includes stream overflow, ponding, and runoff
water from higher areas), and seepage. Usually soil needing drainage has
some permanent limitation that precludes placing it in class I even
after drainage.

Wet soils are classified according to their continuing soil limitations
and hazards after drainage. In determining the capability of wet areas,
emphasis is placed on practices considered practical now or in the
foreseeable future. The vast areas of marshland along the seacoast or
high-cost reclamation projects not now being planned or constructed are
not classified as class I, II, or III. If reclamation projects are
investigated and found to be feasible, the soils of the area are
reclassified based on the continuing limitations and hazards after
drainage. This places the classification of wet soils on a basis similar
to that of the classification of irrigated, stony, saline, or overflow
soils. Some large areas of bottomland subject to overflow are
reclassified when protected by dikes or other major reclamation work.
There are examples of these along streams where levees have been
constructed. Land already drained is classified according to the
continuing limitations and hazards that affect its use.

Needs for initial conditioning, such as for clearing of trees or swamp
vegetation, are not considered in the capability classification. They
may be of great importance, however, in making some of the
land-management decisions. Costs of drainage, likewise, are not
considered directly in the capability classification, although they are
important to the land manager.

**Toxic Salts**

Presence of soluble salts or exchangeable sodium in amounts toxic to
most plants can be a serious limiting factor in land use. Where toxic
salts are the limiting factor, the following ranges are general guides
until more specific criteria are available:

-   Class II \-- Crops slightly affected. In irrigated areas, even after
    salt removal, slight salinity or small amounts of sodium remains or
    is likely to recur.

-   Class III \-- Crops moderately affected. In irrigated areas, even
    after salt removal, moderate salinity or moderate amounts of sodium
    remains or is likely to recur.

-   Classes IV-VI \-- Crops seriously affected on cultivated land.
    Usually only salt-tolerant plants will grow on noncultivated land.
    In irrigated areas, even after leaching, severe salinity or large
    amounts of sodium remains or is likely to recur.

-   Class VII \-- Satisfactory growth of useful vegetation impossible,
    except possibly for some of the most salt-tolerant forms, such as
    some Atriplexes that have limited use for grazing.

**Slope and Hazard of Erosion**

Soil damage from erosion is significant in the use, management, and
response of soil for the following reasons:

1.  An adequate soil depth must be maintained for moderate to high crop
    production. Soil depth is critical on shallow soils over
    nonrenewable substrata such as hard rock. These soils tolerate less
    damage from erosion than soils of similar depth with a renewable
    substrata such as the raw loess or soft shale that can be improved
    through the use of special tillage, fertilizer, and beneficial
    cropping practices.

2.  Soil loss influences crop yields. The reduction in yield following
    the loss of each inch of surface soil varies widely for different
    kinds of soil. The reduction is least on soils having little
    difference in texture, consistence, and fertility between the
    various horizons of the soil. It is greatest where there is a marked
    difference between surface layers and subsoils, such as among soils
    with claypans. For example, corn yields on soils with dense, very
    slowly permeable subsoils may be reduced 3 to 4 bushels per acre per
    year for each inch of surface soil lost. Yield reduction is normally
    small on deep, moderately permeable soils having similar textured
    surface and subsurface layers and no great accumulation of organic
    matter in the surface soil.

3.  Nutrient loss through erosion on sloping soils is important not only
    because of its influence on crop yield but also because of cost of
    replacement to maintain crop yields. The loss of plant nutrients can
    be high, even with slight erosion.

4.  Loss of surface soil changes the physical condition of the plow
    layer in soils having finer textured layers below the surface soil.
    Infiltration rate is reduced; erosion and runoff rates are
    increased; tilth is difficult to maintain; and tillage operations
    and seedbed preparation are more difficult.

5.  Loss of surface soil by water erosion, soil blowing, or land
    leveling may expose highly calcareous lower strata that are
    difficult to make into suitable surface soil.

6.  Water-control structures are damaged by sediments due to erosion.
    Maintenance of open drains and ponds becomes a problem and their
    capacity is reduced as sediment accumulates.

7.  Gullies form as a result of soil loss. This kind of soil damage
    causes reduced yields, increased sediment damage, and physical
    difficulties in farming between the gullies.

The steepness of slope, length of slope, and shape of slope (convex or
concave) all directly influence the soil and water losses from a field.
Steepness of slope is recorded on soil maps. Length and shape of slopes
are not recorded on soil maps; however, they are often characteristic of
certain kinds of soil, and their effects on use and management can be
evaluated as a part of the mapping unit.

Where available, research data on tons of soil loss per acre per year
under given levels of management are used on sloping soils to
differentiate between capability classes.

**Soil Depth**

Effective depth includes the total depth of the soil profile favorable
for root development. In some soils, this includes the C horizon; in a
few only the A horizon is included. Where the effect of depth is the
limiting factor, the following ranges are commonly used: class I, 36
inches or more; class II, 20-36 inches; class III, 10-20 inches; and
class IV, less than 10 inches. These ranges in soil depth between
classes vary from one section of the country to another depending on the
climate. In arid and semiarid areas, irrigated soils in class I are 60
or more inches in depth. Where other unfavorable factors occur in
combination with depth, the capability decreases.

**Previous Erosion**

On some kinds of soil previous erosion reduces crop yields and the
choice of crops materially; on others the effect is not great. The
effect of past erosion limits the use of soils (1) where subsoil
characteristics are unfavorable, or (2) where soil material favorable
for plant growth is shallow to bedrock or material similar to bedrock,
in some soils, therefore, the degree of erosion influences the
capability grouping.

**Available Moisture-Holding Capacity**

Water-holding capacity is an important quality of soil. Soils that have
limited moisture-holding capacity are likely to be droughty and have
limitations in kinds and amounts of crops that can be grown; they also
present fertility and other management problems. The ranges in
water-holding capacity for the soils in the capability classes vary to a
limited degree with the amount and distribution of effective
precipitation during the growing season. Within a capability class, the
range in available moisture-holding capacity varies from one climatic
region to another.

**GLOSSARY**

**Alluvial soils** \-- Soils developing from transported and relatively
recently deposited material (alluvium) with little or no modification of
the original materials by soil-forming processes. (Soils with
well-developed profiles that have formed from alluvium are grouped with
other soils having the same kind of profiles, not with the alluvial
soils.)

**Available nutrient in soils** \-- The part of the supply of a plant
nutrient in the soil that can be taken up by plants at rates and in
amounts significant to plant growth.

**Available water in soils** \-- The part of the water in the soil that
can be taken up by plants at rates significant to their growth; usable;
obtainable.

**Base saturation** \-- The relative degree to which soils have metallic
cations absorbed. The proportion of the cation-exchange capacity that is
saturated with metallic cations.

**Cation-exchange capacity** \-- A measure of the total amount of
exchangeable cations that can be held by the soil. It is expressed in
terms of milliequivalents per 100 grams of soil at neutrality (pH 7) or
at some other stated pH value. (Formerly called base-exchange capacity.)

**Clay mineral** \-- Naturally occurring inorganic crystalline material
in soils or other earthy deposits of clay size-particles less than 0.002
mm in diameter.

**Deep soil** \-- Generally, a soil deeper than 40 inches to rock or
other strongly contrasting material. Also, a soil with a deep black
surface layer; a soil deeper than about 40 inches to the parent material
or to other unconsolidated rock material not modified by soil-forming
processes; or a soil in which the total depth of unconsolidated
material, whether true soil or not, is 40 inches or more.

**Drainage, soil** \-- (1) The rapidity and extent of the removal of
water from the soil by runoff and flow through the soil to underground
spaces. (2) As a condition of the soil, soil drainage refers to the
frequency and duration of periods when the soil is free of saturation.
For example, in well-drained soils, the water is removed readily, but
not rapidly; in poorly drained soils, the root zone is waterlogged for
long periods and the roots of ordinary crop plants cannot get enough
oxygen; and in excessively drained soils, the water is removed so
completely that most crop plants suffer from lack of water.

**Drought** \-- A period of dryness, especially a long one. Usually
considered to be any period of soil-moisture deficiency within the plant
root zone. A period of dryness of sufficient length to deplete soil
moisture to the extent that plant growth is seriously retarded.

**Erosion** \-- The wearing away of the land surface by detachment and
transport of soil and rock materials through the action of moving water,
wind, or other geological agents.

**Fertility, soil** \-- The quality of a soil that enables it to provide
compounds, in adequate amounts and in proper balance, for the growth of
specified plants, when other growth factors such as light, moisture,
temperature, and the physical condition of the soil are favorable.

**Field capacity** \-- The amount of moisture remaining in a soil after
the free water has been allowed to drain away into drier soil material
beneath; usually expressed as a percentage of the ovendry weight of soil
or other convenient unit. It is the highest amount of moisture that the
soil will hold tinder conditions of free drainage after excess water has
drained away following a rain or irrigation that has wet the whole soil.
For permeable soils of medium texture, this is about 2 or 3 days after a
rain or thorough irrigation. Although generally similar for one kind of
soil, values vary with previous treatments of the soil.

**First bottom** \-- The normal flood plain of a stream, subject to
frequent or occasional flooding.

**Parent material** \-- The unconsolidated mass of rock material (or
peat) from which the soil profile develops.

**Permeability, soil** \-- The quality of a soil horizon that enables
water or air to move through it. It can be measured quantitatively in
terms of rate of flow of water through a unit cross section in unit time
under specified temperature and hydraulic conditions. Values for
saturated soils usually are called hydraulic conductivity. The
permeability of a soil may be limited by the presence of one nearly
impermeable horizon even though the others are permeable.

**Phase, soil** \-- The subdivision of a soil type or other
classificational soil unit having variations in characteristics not
significant to the classification of the soil in its natural landscape
but significant to the use and management of the soil. Examples of the
variations recognized by phases of soil types include differences in
slope, stoniness, and thickness because of accelerated erosion.

**Profile (soil)** \-- A vertical section of the soil through all its
horizons and extending into the parent material.

**Range (or rangeland)** \-- Land that produces primarily native forage
plants suitable for grazing by livestock, including land that has some
forest trees.

**Runoff** \-- The surface flow of water from an area; or the total
volume of surface flow during a specified time.

**Saline soil** \-- A soil containing enough soluble salts to impair its
productivity for plants but not containing an excess of exchangeable
sodium.

**Series, soil** \-- A group of soils that have soil horizons similar in
their differentiating characteristics and arrangement in the soil
profile, except for the texture of the surface soil, and are formed from
a particular type of parent material. Soil series is an important
category in detailed soil classification. Individual series are given
proper names from place names near the first recorded occurrence. Thus
names like Houston, Cecil, Barnes, and Miami are names of soil series
that appear on soil maps and each connotes a unique combination of many
soil characteristics.

**Sodic soil (alkali)** \-- Soil that contains sufficient sodium to
interfere with the growth of most crop plants; soils for which the
exchangeable-sodium-percentage is 15 or more.

**Soil** \-- (1) The natural medium for the growth of land plants. (2) A
dynamic natural body on the surface of the earth in which plants grow,
composed of mineral and organic materials and living forms. (3) The
collection of natural bodies occupying parts of the earth's surface that
support plants and that have properties due to the integrated effect of
climate and living matter acting upon parent material, as conditioned by
relief, over periods of time.

A soil is an individual three-dimensional body on the surface of the
earth unlike the adjoining bodies. (The area of individual soils ranges
from less than 1/2 acre to more than 300 acres.)

A kind of soil is the collection of soils that are alike in specified
combinations of characteristics. Kinds of soil are given names in the
system of soil classification. The terms "the soil" and "soil" are
collective terms used for all soils, equivalent to the word "vegetation"
for all plants.

**Soil characteristic** \-- A feature of a soil that can be seen and/or
measured in the field or in the laboratory on soil samples. Examples
include soil slope and stoniness as well as the texture, structure,
color, and chemical composition of soil horizons.

**Soil management** \-- The preparation, manipulation, and treatment of
soils for the production of plants, including crops, grasses, and trees.

**Soil quality** \-- An attribute of a soil that cannot be seen or
measured directly from the soil alone but which is inferred from soil
characteristics and soil behavior under defined conditions. Fertility,
productivity, and erodibility are examples of soil qualities (in
contrast to soil characteristics).

**Soil survey** \-- A general term for the systematic examination of
soils in the field and in the laboratories, their description and
classification, the map­ping of kinds of soil, and the interpretation of
soils according to their adaptability for various crops, grasses, and
trees, their behavior under use or treatment for plant production or for
other purposes, and their pro­ductivity under different nianagernew
systems.

**Structure, soil** \-- The arrangement of primary soil particles into
compound particles or clusters that are separated from adjoining
aggregates and have properties unlike those of an equal mass of
unaggregated primary soil particles. The principal forms of soil
structure are platy, prismatic, columnar (prisms with rounded tops),
blocky (angular or subangular), and granular. Structureless soils are
(1) single grain \-- each grain by itself, as in dune sand; or (2)
massive \-- the particles adhering together without any regular cleavage
as in many claypans and hardpans. ("Good" or "bad" tilth are terms for
the general structural condition of cultivated soils according to
particular plants or sequences of plants.)

**Subsoil** \-- The B horizons of soils with distinct profiles. In soils
with weak profile development, the subsoil can be defined as the soil
below the plowed soil (or its equivalent of surface soil), in which
roots normally grow. Although a common term, it cannot be defined
accurately. It has been carried over from early days when "soil" was
conceived only as the plowed soil and that under it as the "subsoil."

**Surface soil** \-- The soil ordinarily moved in tillage, or its
equivalent in uncultivated soil, about 5 to 8 inches in thickness.

**Texture, soil** \-- The relative proportions of the various size
groups of individual soil grains in a mass of soil. Specifically, it
refers to the proportions of sand, silt, and clay.

**Type, soil** \-- A subgroup or category under the soil series based on
the texture of the surface soil. A soil type is a group of soils having
horizons similar in differentiating characteristics and arrangement in
the soil profile and developed from a particular type of parent
material. The name of a soil type consists of the name of the soil
series plus the textural class name of the upper part of the soil
equivalent to the surface soil. Thus Miami silt loam is the name of a
soil type within the Miami series.

**Water table** \-- The upper limit of the part of the soil or
underlying rock material that is wholly saturated with water. In some
places an upper, or perched, water table may be separated from a lower
one by a dry zone.

**Water-holding capacity** \-- The capacity (or ability) of soil to hold
water against gravity (see **Field capacity**). The water-holding
capacity of sandy soils is usually considered to be low while that of
clayey soils is high. It is often expressed in inches of water per foot
depth of soil.

**Waterlogged** \-- A condition of soil in which both large and small
pore spaces are filled with water. (The soil may be intermittently
waterlogged because of a fluctuating water table or waterlogged for
short periods after rain.)

[^1]: Yields are significant at the capability-unit level and are one of
    the criteria used in establishing capability units within a
    capability class. Normally, yields are estimated under the common
    management that maintains the soil resource. The main periods for
    such yield estimates are 10 or more years in humid areas or under
    irrigation and 20 or more years in subhumid or semiarid areas. The
    25 percent allowable range is for economically feasible yields of
    adapted cultivated and pasture crops.

[^2]: As used here the common crops include: corn, cotton, tobacco,
    wheat, tame hay and pasture, oats, barley, grain sorghum, sugarcane,
    sugar beets, peanuts, soybeans, field-grown vegetables, potatoes,
    sweet potatoes, field peas and beans, flax, and most
    clean-cultivated fruit, nut, and ornamental plants. They do not
    include: rice, cranberries, blueberries, and those fruit, nut, and
    ornamental plants that require little or no cultivation.

[^3]: Soil and water conservation practices is a general expression for
    all practices including but not limited to those for erosion
    control.

[^4]: Based on longtime economic trends for average farms and farmers
    using moderately high level management. May not apply to specific
    farms and farmers but will apply to broad areas.

[^5]: Feasible as used in this context means (1) that the
    characteristics and qualities of the soil are such that it is
    possible to remove the limitation, and (2) that over broad areas it
    is within the realm of present-day economic possibility to remove
    the limitation.

[^6]: Some rapidly permeable soils in class I may have gentle slopes.

[^7]: Certain soils grouped into classes V, VI, VII, and VIII may be
    made fit for use for crops with major earthmoving or other costly
    reclamation.

[^8]: Especially among young soils such as alluvial soils, although not
    limited to them, climatic phases of soil series must be established
    for proper grouping into capability units and into other
    interpretive groupings. Since the effects result from interactions
    between soil and climate, such climatic phases are not defined the
    same in terms of precipitation, temperature, and so on, for
    contrasting kinds of soil.